@article{sadala_2018,
title = {A new continuous sliding mode control approach with actuator saturation for control of 2-DOF helicopter system},
author = {Sadala, S.P.; Patre, B.M.},
journal = {ISA Transactions},
year = {2018},
institution = {Shri Guru Gobind Singhji Institute of Engineering and Technology, India},
abstract = {The 2-degree of freedom (DOF) helicopter system is a typical higher-order, multi-variable, nonlinear and strong coupled control system. The helicopter dynamics also includes parametric uncertainties and is subject to unknown external disturbances. Such complicated system requires designing a sophisticated control algorithm that can handle these difficulties. This paper presents a new robust control algorithm which is a combination of two continuous control techniques, composite nonlinear feedback (CNF) and super-twisting control (STC) methods. In the existing integral sliding mode (ISM) based CNF control law, the discontinuous term exhibits chattering which is not desirable for many practical applications. As the continuity of well known STC reduces chattering in the system, the proposed strategy is beneficial over the current ISM based CNF control law which has a discontinuous term. Two controllers with integral sliding surface are designed to control the position of the pitch and the yaw angles of the 2- DOF helicopter. The adequacy of this specific combination has been exhibited through general analysis, simulation and experimental results of 2-DOF helicopter setup. The acquired results demonstrate the good execution of the proposed controller regarding stabilization, following reference input without overshoot against actuator saturation and robustness concerning to the limited matched disturbances. },
keywords = {Composite nonlinear feedback (CNF) Actuator saturation 2-DOF helicopter Siding mode control (SMC) Integral sliding mode control (ISMC) Super-twisting control (STC)},
language = {English},
publisher = {Elsevier B.V.}
}

The 2-degree of freedom (DOF) helicopter system is a typical higher-order, multi-variable, nonlinear and strong coupled control system. The helicopter dynamics also includes parametric uncertainties and is subject to unknown external disturbances. Such complicated system requires designing a sophisticated control algorithm that can handle these difficulties. This paper presents a new robust control algorithm which is a combination of two continuous control techniques, composite nonlinear feedback (CNF) and super-twisting control (STC) methods. In the existing integral sliding mode (ISM) based CNF control law, the discontinuous term exhibits chattering which is not desirable for many practical applications. As the continuity of well known STC reduces chattering in the system, the proposed strategy is beneficial over the current ISM based CNF control law which has a discontinuous term. Two controllers with integral sliding surface are designed to control the position of the pitch and the yaw angles of the 2- DOF helicopter. The adequacy of this specific combination has been exhibited through general analysis, simulation and experimental results of 2-DOF helicopter setup. The acquired results demonstrate the good execution of the proposed controller regarding stabilization, following reference input without overshoot against actuator saturation and robustness concerning to the limited matched disturbances.

Interconnection and damping assignment passivity based control (IDA-PBC) is a method that has been developed to (asymptotically) stabilize nonlinear systems formulated in port-controlled Hamiltonian (PCH) structure. This method has gained increasing popularity and has been successfully applied to a wide range of dynamical systems. However, little is known about the robustness of this method in response to the effects of uncertainty which could result from disturbances, noises, and modeling errors. This paper explores the possibility of extending some energy shaping methods, taking into account the robustness aspects, with the aim of maintaining (asymptotic) stability of the system in the presence of perturbations which inevitably exist in any realistic applications. We propose constructive results on robust IDA-PBC controllers for underactuated mechanical systems that are quite commonly found in practice and have the most challenging control problems within this context. The proposed results extend some existing methods and provide a new framework that allows the implementation of integral and input-to-state stability controllers to underactuated mechanical system.

@article{bolat_2018,
title = {Active Control of a Small-Scale Wind Turbine Blade Containing Magnetorheological Fluid},
author = {Bolat, F.C.; Sivrioglu, S.},
journal = {Micromachines},
year = {2018},
volume = {9},
number = {2},
institution = {Bayburt University, Turkey; Gebze Technical University, Turkey},
abstract = {This research study proposes a new active control structure to suppress vibrations of a small-scale wind turbine blade filled with magnetorheological (MR) fluid and actuated by an electromagnet. The aluminum blade structure is manufactured using the SH3055 (Bergey Windpower Co. Inc., Norman, OK, USA) code numbered airfoil which is designed for use on small wind turbines. A dynamic interaction model between the MR fluid and the electromagnetic actuator is constructed to obtain a force relation. A detailed characterization study is presented for the proposed actuator to understand the nonlinear behavior of the electromagnetic force. A norm based multi-objective H2/H∞ controller is designed using the model of the elastic blade element. The H2/H∞ controller is experimentally implemented under the impact and steady state aerodynamic load conditions. The results of experiments show that the MR fluid- electromagnetic actuator is effective for suppressing vibrations of the blade structure. },
keywords = {active vibration control; elastic blade; magnetorheological fluid; robust control},
language = {English}
}

This research study proposes a new active control structure to suppress vibrations of a small-scale wind turbine blade filled with magnetorheological (MR) fluid and actuated by an electromagnet. The aluminum blade structure is manufactured using the SH3055 (Bergey Windpower Co. Inc., Norman, OK, USA) code numbered airfoil which is designed for use on small wind turbines. A dynamic interaction model between the MR fluid and the electromagnetic actuator is constructed to obtain a force relation. A detailed characterization study is presented for the proposed actuator to understand the nonlinear behavior of the electromagnetic force. A norm based multi-objective H2/H∞ controller is designed using the model of the elastic blade element. The H2/H∞ controller is experimentally implemented under the impact and steady state aerodynamic load conditions. The results of experiments show that the MR fluid- electromagnetic actuator is effective for suppressing vibrations of the blade structure.

@article{hernandez-perez_2018,
title = {An improvement on the PI controller for a class of high-order unstable delayed systems: Application to a thermal process},
author = {Hernandez-Perez, M.A.; del Muro-Cuellar, B.; Velasco-Villa, M.; Novella-Rodriguez, D.F.; Garrido-Moctezuma, R.A.; Garcia-Ramirez, P.J.},
journal = {Control Engineering and Applied Informatics},
year = {2018},
volume = {20},
number = {1},
institution = {Universidad Veracruzana, Mexico; Instituto Politécnico Nacional, Mexico; CINVESTAV-IPN, Mexico},
abstract = {This work addresses the stabilization and control problem of a class of input-output delayed unstable linear systems, i.e. n -order systems with one unstable pole and possibly one minimum phase zero. The problem is solved employing a modified version of the traditional PI, called the PIf controller, which incorporates a low-pass first order filter. This new scheme allows improving the existing results using the PI controller for high-order systems with time delay. The proposed control strategy is experimentally assessed through the temperature control of an unstable heat flow process. },
keywords = {Linear Systems, time–delay, modified PI control, unstable process, thermal process},
language = {English}
}

This work addresses the stabilization and control problem of a class of input-output delayed unstable linear systems, i.e. n -order systems with one unstable pole and possibly one minimum phase zero. The problem is solved employing a modified version of the traditional PI, called the PIf controller, which incorporates a low-pass first order filter. This new scheme allows improving the existing results using the PI controller for high-order systems with time delay. The proposed control strategy is experimentally assessed through the temperature control of an unstable heat flow process.

@article{alemaryeen_2018,
title = {Antenna Effects on Respiratory Rate Measurement using a UWB Radar System},
author = {Alemaryeen, A.; Noghanian, S.; Fazel-Rezai, R.},
journal = {IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology},
year = {2018},
institution = {Electrical Engineering, University of North Dakota, USA},
abstract = {State-of-the-art advances in the field of radar technology have made it possible to design non-invasive sensing devices of vital signs. This paper presents the effects of antenna characteristics on Ultra Wide Band (UWB) radar-based respiratory rate measurement system for tele-health-monitoring applications. The performance of three types of antenna for a UWB radar respiratory rate measurement system was studied in this work. In this context, the proposed system was comprehensively evaluated using two experimental sets. First, a mechanical setup was used to provide a series of controlled frequency and distance motions for measurement test. The error analysis for various parameters associated with pulmonary activities such as breathing frequency and chest displacement was performed. Results indicated that the proposed sensing system used effectively as a respiratory rate measurement is less affected and shows less error when an antenna with directive radiation pattern, low cross-polarization and stable phase center was used. Due to its good radiation characteristics and small form-factor this antenna was selected to study the respiratory rates of ten test subjects. The results were compared with a standard respiratory-rate measurement using respiration belt transducer. The measurement results using the proposed and the standard systems showed excellent agreement. The mean error value of the respiratory rate measurements was 0.03 Hz with a statistical standard deviation of 0.03 Hz. },
issn = {2469-7249},
keywords = {Antennas, respiratory rate detection, remote sensing, ultra-wide band (UWB) radar},
language = {English},
publisher = {IEEE}
}

State-of-the-art advances in the field of radar technology have made it possible to design non-invasive sensing devices of vital signs. This paper presents the effects of antenna characteristics on Ultra Wide Band (UWB) radar-based respiratory rate measurement system for tele-health-monitoring applications. The performance of three types of antenna for a UWB radar respiratory rate measurement system was studied in this work. In this context, the proposed system was comprehensively evaluated using two experimental sets. First, a mechanical setup was used to provide a series of controlled frequency and distance motions for measurement test. The error analysis for various parameters associated with pulmonary activities such as breathing frequency and chest displacement was performed. Results indicated that the proposed sensing system used effectively as a respiratory rate measurement is less affected and shows less error when an antenna with directive radiation pattern, low cross-polarization and stable phase center was used. Due to its good radiation characteristics and small form-factor this antenna was selected to study the respiratory rates of ten test subjects. The results were compared with a standard respiratory-rate measurement using respiration belt transducer. The measurement results using the proposed and the standard systems showed excellent agreement. The mean error value of the respiratory rate measurements was 0.03 Hz with a statistical standard deviation of 0.03 Hz.

@inbook{shakev_2018,
title = {Autonomous Flight Control and Precise Gestural Positioning of a Small Quadrotor},
author = {Shakev N.G., Ahmed S.A., Topalov A.V., Popov V.L., Shiev K.B.},
booktitle = { Learning Systems: From Theory to Practice},
year = {2018},
volume = {756},
institution = {Control Systems Department, TU–Sofia, Bulgaria},
abstract = {Precise gestural positioning interface of a small quadrotor, presented here, is an advance continuation (ending stage) of intelligent autonomous flight control strategy. It is based on gestures and visual computing techniques and ensures intuitive way of prepositioning (fine movements in flight’s end point proximity) in absence of GPS signal or when human interaction is crucial. Therefore, a human operator could control the implementation of various maneuvers during the flight of the rotorcraft via specific gestures and body postures. A Parrot AR. Drone quadrotor and a Microsoft Kinect sensor have been used to implement and evaluate the proposed autonomous and semi-autonomous flight control. },
language = {English},
series = {Studies in Computational Intelligence},
publisher = {Springer, Cham},
isbn = {978-3-319-75180-1},
pages = {179-197}
}

Precise gestural positioning interface of a small quadrotor, presented here, is an advance continuation (ending stage) of intelligent autonomous flight control strategy. It is based on gestures and visual computing techniques and ensures intuitive way of prepositioning (fine movements in flight’s end point proximity) in absence of GPS signal or when human interaction is crucial. Therefore, a human operator could control the implementation of various maneuvers during the flight of the rotorcraft via specific gestures and body postures. A Parrot AR. Drone quadrotor and a Microsoft Kinect sensor have been used to implement and evaluate the proposed autonomous and semi-autonomous flight control.

@article{brentari_2018,
title = {Benchmark model of Quanser’s 3 DOF Helicopter},
author = {Brentari, M.; Bosetti, P.; Queinnec, I.; Zaccarian, L.},
year = {2018},
institution = {University of Trento, Italy; Universite de Toulouse, CNRS, France},
abstract = {This paper proposes a software benchmark tool for the Quanser “3 DOF Helicopter” in the Mathworks Simscape environment, based on a multi-body model of the experimental setup. The proposed benchmark tool takes into account a number of implementation features of the experimental setup and aims at providing a tool for simulative validation and performance analysis of control strategies. Along with this software-in-the-loop tool, a novel reduced complexity non-linear model for theQuanser “3 DOF Helicopter” is derived from the Lagrangian description of the full multi-body model, with the scope of being used in the control synthesis phase. The identification of the models parameters is carried out following a “gray-box” type of paradigm in order to match the models with the experimental setup. A feedback linearizing control law is as well proposed, based on the reduced complexity model. Closed-loop experimental results both show the accuracy of the simulated response compared to the experimental response, and the effectiveness of the proposed control strategy in a set-point regulation task. },
language = {English}
}

This paper proposes a software benchmark tool for the Quanser “3 DOF Helicopter” in the Mathworks Simscape
environment, based on a multi-body model of the experimental setup. The proposed benchmark tool takes into account a number of implementation features of the experimental setup and aims at providing a tool for simulative validation and performance analysis of control strategies. Along with this software-in-the-loop tool, a novel reduced complexity non-linear model for theQuanser
“3 DOF Helicopter” is derived from the Lagrangian
description of the full multi-body model, with the scope of being used in the control synthesis phase. The identification of the models parameters is carried out following a “gray-box” type of paradigm in order to match the models with the experimental setup. A feedback linearizing control law is as well proposed, based on the reduced complexity model. Closed-loop experimental results both show the accuracy of the simulated response compared to the experimental response, and the effectiveness of the proposed control strategy in a set-point regulation task.

@article{keshavarz_2018,
title = {Comparing simulator sickness in younger and older adults during simulated driving under different multisensory conditions},
author = {Keshavarz, B.; Ramkhalawansingh, R.; Haycock, B.; Shahab, S.; Campos, J.L.},
journal = {Transportation Research Part F: Traffic Psychology and Behaviour},
year = {2018},
month = {04},
volume = {54},
institution = {University Health Network, Toronto Rehabilitation Institute, Canada; Ryerson University, Canada; University of Toronto, Canada; Centre for Addiction and Mental Health, Research Imaging Centre, Canada},
abstract = {Driving simulators are valuable tools for traffic safety research as they allow for systematic reproductions of challenging situations that cannot be easily tested during real-world driving. Unfortunately, simulator sickness (i.e., nausea, dizziness, etc.) is common in many driving simulators and may limit their utility. The experience of simulator sickness is thought to be related to the sensory feedback provided to the user and is also thought to be greater in older compared to younger users. Therefore, the present study investigated whether adding auditory and/or motion cues to visual inputs in a driving simulator affected simulator sickness in younger and older adults. Fifty-eight healthy younger adults (age 18–39) and 63 healthy older adults (age 65+) performed a series of simulated drives under one of four sensory conditions: (1) visual cues alone, (2) combined visual + auditory cues (engine, tire, wind sounds), (3) combined visual + motion cues (via hydraulic hexapod motion platform), or (4) a combination of all three sensory cues (visual, auditory, motion). Simulator sickness was continuously recorded while driving and up to 15 min after driving session termination. Results indicated that older adults experienced more simulator sickness than younger adults overall and that females were more likely to drop out and drove for less time compared to males. No differences between sensory conditions were observed. However, older adults needed significantly longer time to fully recover from the driving session than younger adults, particularly in the visual-only condition. Participants reported that driving in the simulator was least realistic in the visual-only condition compared to the other conditions. Our results indicate that adding auditory and/or motion cues to the visual stimulus does not guarantee a reduction of simulator sickness per se, but might accelerate the recovery process, particularly in older adults. },
keywords = {Motion sickness Driving Aging Multimodal cue combination Vection},
language = {English},
publisher = {Elsevier B.V.},
pages = {47-62}
}

Driving simulators are valuable tools for traffic safety research as they allow for systematic reproductions of challenging situations that cannot be easily tested during real-world driving. Unfortunately, simulator sickness (i.e., nausea, dizziness, etc.) is common in many driving simulators and may limit their utility. The experience of simulator sickness is thought to be related to the sensory feedback provided to the user and is also thought to be greater in older compared to younger users. Therefore, the present study investigated whether adding auditory and/or motion cues to visual inputs in a driving simulator affected simulator sickness in younger and older adults. Fifty-eight healthy younger adults (age 18–39) and 63 healthy older adults (age 65+) performed a series of simulated drives under one of four sensory conditions: (1) visual cues alone, (2) combined visual + auditory cues (engine, tire, wind sounds), (3) combined visual + motion cues (via hydraulic hexapod motion platform), or (4) a combination of all three sensory cues (visual, auditory, motion). Simulator sickness was continuously recorded while driving and up to 15 min after driving session termination. Results indicated that older adults experienced more simulator sickness than younger adults overall and that females were more likely to drop out and drove for less time compared to males. No differences between sensory conditions were observed. However, older adults needed significantly longer time to fully recover from the driving session than younger adults, particularly in the visual-only condition. Participants reported that driving in the simulator was least realistic in the visual-only condition compared to the other conditions. Our results indicate that adding auditory and/or motion cues to the visual stimulus does not guarantee a reduction of simulator sickness per se, but might accelerate the recovery process, particularly in older adults.

@article{saadatzi_2018,
title = {Comparison of Human-Robot Interaction Torque Estimation Methods in a Wrist Rehabilitation Exoskeleton},
author = {Saadatzi, M.; Long, D.C.; Celik, O.},
journal = {Journal of Intelligent & Robotic Systems},
year = {2018},
institution = {Colorado School of Mines, USA},
abstract = {In this paper, experimental implementation and comparative accuracy evaluation of five methods for estimation of human-robot interaction torques are presented. These methods vary from the simplest case of using solely commanded motor torques, to partial consideration of the robot dynamics, to advanced methods considering full robot dynamics such as inverse dynamics (ID) and nonlinear disturbance observer (NDO) based algorithms. Dynamic and friction models of the exoskeleton were developed and their parameters were identified using an evolutionary optimization algorithm to ensure high parameter accuracy. When used with accurate model parameters, ID method led to 20 to 22% average error, while NDO method generated 12 to 18% average error, as evaluated in experiments with a force sensor. These values compare to average error values of up to 132% for using motor torques only, and between 25 to 69% when partial dynamics were used. A sensitivity analysis of the ID and NDO methods to inaccuracies in model parameter estimations revealed considerable sensitivity of these advanced methods to model parameter variations. A summary is provided for the typical estimation accuracy levels that can be expected of these methods and discuss the limitations and considerations that should be taken into account for their use. },
issn = {0921-0296},
keywords = {Nonlinear disturbance observer, Force estimation, System identification, Sensitivity analysis, Friction modeling, Exoskeletons},
language = {English},
publisher = {Springer Netherlands}
}

In this paper, experimental implementation and comparative accuracy evaluation of five methods for estimation of human-robot interaction torques are presented. These methods vary from the simplest case of using solely commanded motor torques, to partial consideration of the robot dynamics, to advanced methods considering full robot dynamics such as inverse dynamics (ID) and nonlinear disturbance observer (NDO) based algorithms. Dynamic and friction models of the exoskeleton were developed and their parameters were identified using an evolutionary optimization algorithm to ensure high parameter accuracy. When used with accurate model parameters, ID method led to 20 to 22% average error, while NDO method generated 12 to 18% average error, as evaluated in experiments with a force sensor. These values compare to average error values of up to 132% for using motor torques only, and between 25 to 69% when partial dynamics were used. A sensitivity analysis of the ID and NDO methods to inaccuracies in model parameter estimations revealed considerable sensitivity of these advanced methods to model parameter variations. A summary is provided for the typical estimation accuracy levels that can be expected of these methods and discuss the limitations and considerations that should be taken into account for their use.

@conference{chiaradia_2018,
title = {Design and Embedded Control of a Soft Elbow Exosuit},
author = {Chiaradia, D.; Xiloyannis, M.; Antuvan, C.W.; Frisoli, A.; Masia, L.},
booktitle = {IEEE International Conference on Soft Robotics},
year = {2018},
institution = {Scuola Superiore Sant’Anna, Italy; Nanyang Technological University, Singapore},
abstract = {The use of soft materials to transmit power to the human body has numerous advantages, amongst which safety and kinematic transparency stand out. In previous work we showed that a tethered fabric-based exosuit for the elbow joint, driven by an electric motor through a Bowden cable transmission, reduces the muscular effort associated with flexion movements by working in parallel with its wearer's muscles. We herein propose a refined design of the suit and present an untethered control architecture for gravity compensation and motion-intention detection. The architecture comprises four interconnected modules for power management, low-level motor control and high-level signal processing and data streaming. The controller uses a silicone stretch sensor and a miniature load cell, integrated in the fabric frame, to estimate and minimise the torque that its user needs to exert to perform a movement. We show that the device relieves its wearer from an average of 77% of the total moment required to sustain and move a light weight, with a consequent average reduction in muscular effort of 64.5%. },
language = {English}
}

The use of soft materials to transmit power to the human body has numerous advantages, amongst which safety and kinematic transparency stand out. In previous work we showed that a tethered fabric-based exosuit for the elbow joint, driven by an electric motor through a Bowden cable transmission, reduces the muscular effort associated with flexion movements by working in parallel with its wearer's muscles. We herein propose a refined design of the suit and present an untethered control architecture for gravity compensation and motion-intention detection. The architecture comprises four interconnected modules for power management, low-level motor control and high-level signal processing and data streaming. The controller uses a silicone stretch sensor and a miniature load cell, integrated in the fabric frame, to estimate and minimise the torque that its user needs to exert to perform a movement. We show that the device relieves its wearer from an average of 77% of the total moment required to sustain and move a light weight, with a consequent average reduction in muscular effort of 64.5%.

@article{mu_2018,
title = {Distributed LQR Consensus Control for Heterogeneous Multi-Agent Systems: Theory and Experiments},
author = {Mu, B.; Shi, Y.},
journal = {IEEE/ASME Transactions on Mechatronics},
year = {2018},
institution = {University of Victoria, British Columbia Canada },
abstract = {Controlling heterogeneous multi-agent systems (MASs) to cooperatively accomplish tasks is currently an emerging topic in the application-oriented research of robotics. This paper investigates the consensus problem of an MAS consisting of quadrotors and two-wheeled mobile robots (2WMRs). Directed and switching interaction topologies over the network are considered. We propose a distributed linear quadratic regulation (LQR) consensus protocol for the quadrotors and design an LQR-based Rotate&Run Consensus Scheme for the 2WMRs to update the states. We use the algebraic graph theory and stochastic matrix analysis to conduct the convergence analysis of consensus. The underactuation characteristic of the 2WMR dynamics is considered in the controller design. The effectiveness of the control methods is verified by experiments. },
issn = {1941-014X },
keywords = {Consensus, multi-agent systems, two-wheeled mobile robot, quadrotor, distributed LQR},
language = {English},
publisher = {IEEE}
}

Controlling heterogeneous multi-agent systems (MASs) to cooperatively accomplish tasks is currently an emerging topic in the application-oriented research of robotics. This paper investigates the consensus problem of an MAS consisting of quadrotors and two-wheeled mobile robots (2WMRs). Directed and switching interaction topologies over the network are considered. We propose a distributed linear quadratic regulation (LQR) consensus protocol for the quadrotors and design an LQR-based Rotate&Run Consensus Scheme for the 2WMRs to update the states. We use the algebraic graph theory and stochastic matrix analysis to conduct the convergence analysis of consensus. The underactuation characteristic of the 2WMR dynamics is considered in the controller design. The effectiveness of the control methods is verified by experiments.

@article{chen_2018,
title = {Effects of different coherency models on utility tunnel through shaking table test},
author = {Chen, Z.; Liang, S.; He, C.},
journal = {Journal of Earthquake Engineering },
year = {2018},
institution = {Tongji University, China; Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, China},
abstract = {Since defining ground motions is crucial for reliable analysis of structural responses, it is vital to select coherency model when conducting seismic analyses of extended structures under non-uniform excitation. In the present paper, a series of shaking table tests are conducted to study the effect of coherency models on seismic performances of a utility tunnel. The test results show that there are significant differences in seismic performances of the utility tunnel for using different coherency models. Structural strain and acceleration responses are relative to the decaying of coherency models at low frequency and high frequency, respectively. },
keywords = {Non-Uniform Excitation; Coherency Models; Utility Tunnel; Shaking Table Test; Spatially Varying Ground Motion},
language = {English}
}

Since defining ground motions is crucial for reliable analysis of structural responses, it is vital to select coherency model when conducting seismic analyses of extended structures under non-uniform excitation. In the present paper, a series of shaking table tests are conducted to study the effect of coherency models on seismic performances of a utility tunnel. The test results show that there are significant differences in seismic performances of the utility tunnel for using different coherency models. Structural strain and acceleration responses are relative to the decaying of coherency models at low frequency and high frequency, respectively.

@article{ahmed_2018,
title = {Environmental monitoring using a robotized wireless sensor network},
author = {Ahmed, S.A.; Popov, V.L.; Topalov, A.V.; Shakev, N.G.},
journal = {AI & Society},
year = {2018},
institution = {Technical University of Sofia, branch Plovdiv, Bulgaria},
abstract = {Big cities and growing industrial areas bring high risk of different kinds of pollutions which would implicate to the quality of life of the society. Discovering and monitoring of polluted areas using autonomous mobile robots is nowadays a frequently considered solution concerning both environmental and human safety problems. Being part of a distributed control system, such robots can help to improve the efficiency of the existing conventional pollution prevention systems. On the other hand, during the last decade, wireless sensor networks (WSN) have provoked the interest of specialists from different areas by imposing a large number of theoretical and practical challenges related to their implementation. This paper attempts to deal with both issues by presenting a possible way for building robotized WSNs that can be suitable for solving different environmental monitoring tasks. The goal is to transform the WSN into an adaptive sensor system with intelligent behavior that can be used to discover and track spots or areas where given monitored environmental parameters violate defined thresholds. The inclusion of robotized agents into the WSN structure can provide additional flexibility with respect to the installation of the network sensors and allow reliable information gathering and transfer. The proposed algorithmic methods have been tested on a pre-built laboratory prototype of a robotized WSN. The robotized agents (mobile network nodes) have been built using iRobot Create mobile platforms that are additionally equipped with a single-chip computers Gumstix Verdex pro TM XL6P with various expansion modules. },
issn = {0951-5666},
keywords = {Mobile robots, Wireless sensor networks, Intelligent control, Collective robotics, Intelligent sensors, Multiagent systems},
language = {English},
publisher = {Springer, London}
}

Big cities and growing industrial areas bring high risk of different kinds of pollutions which would implicate to the quality of life of the society. Discovering and monitoring of polluted areas using autonomous mobile robots is nowadays a frequently considered solution concerning both environmental and human safety problems. Being part of a distributed control system, such robots can help to improve the efficiency of the existing conventional pollution prevention systems. On the other hand, during the last decade, wireless sensor networks (WSN) have provoked the interest of specialists from different areas by imposing a large number of theoretical and practical challenges related to their implementation. This paper attempts to deal with both issues by presenting a possible way for building robotized WSNs that can be suitable for solving different environmental monitoring tasks. The goal is to transform the WSN into an adaptive sensor system with intelligent behavior that can be used to discover and track spots or areas where given monitored environmental parameters violate defined thresholds. The inclusion of robotized agents into the WSN structure can provide additional flexibility with respect to the installation of the network sensors and allow reliable information gathering and transfer. The proposed algorithmic methods have been tested on a pre-built laboratory prototype of a robotized WSN. The robotized agents (mobile network nodes) have been built using iRobot Create mobile platforms that are additionally equipped with a single-chip computers Gumstix Verdex pro TM XL6P with various expansion modules.

@inproceedings{solowjow_2018,
title = {Event-triggered Learning for Resource-efficient Networked Control},
author = {Solowjow, F.; Baumann, D.; Garcke, J.; Trimpe, S.},
journal = {2018 American Control Conference},
year = {2018},
institution = {Max Planck Institute for Intelligent Systems, Germany; University of Bonn, Germany, Fraunhofer SCAI, Germany},
abstract = {Common event-triggered state estimation (ETSE) algorithms save communication in networked control systems by predicting agents' behavior, and transmitting updates only when the predictions deviate significantly. The effectiveness in reducing communication thus heavily depends on the quality of the dynamics models used to predict the agents' states or measurements. Event-triggered learning is proposed herein as a novel concept to further reduce communication: whenever poor communication performance is detected, an identification experiment is triggered and an improved prediction model learned from data. Effective learning triggers are obtained by comparing the actual communication rate with the one that is expected based on the current model. By analyzing statistical properties of the inter-communication times and leveraging powerful convergence results, the proposed trigger is proven to limit learning experiments to the necessary instants. Numerical and physical experiments demonstrate that event-triggered learning improves robustness toward changing environments and yields lower communication rates than common ETSE. }
}

Common event-triggered state estimation (ETSE) algorithms save communication in networked control systems by predicting agents' behavior, and transmitting updates only when the predictions deviate significantly. The effectiveness in reducing communication thus heavily depends on the quality of the dynamics models used to predict the agents' states or measurements. Event-triggered learning is proposed herein as a novel concept to further reduce communication: whenever poor communication performance is detected, an identification experiment is triggered and an improved prediction model learned from data. Effective learning triggers are obtained by comparing the actual communication rate with the one that is expected based on the current model. By analyzing statistical properties of the inter-communication times and leveraging powerful convergence results, the proposed trigger is proven to limit learning experiments to the necessary instants. Numerical and physical experiments demonstrate that event-triggered learning improves robustness toward changing environments and yields lower communication rates than common ETSE.

@article{prado_2018,
title = {Experimental evaluation of HJB optimal controllers for the attitude dynamics of a multirotor aerial vehicle},
author = {Acampora Prado I.A. , de Freitas Virgílio Pereira M., Ferreira de Castro M., dos Santos D.A., Balthazar J.M.},
journal = {ISA Transactions},
year = {2018},
institution = {Instituto Tecnologico de Aeronautica, Brazil},
abstract = {The present paper is concerned with the design and experimental evaluation of optimal control laws for the nonlinear attitude dynamics of a multirotor aerial vehicle. Three design methods based on Hamilton-Jacobi-Bellman equation are taken into account. The first one is a linear control with guarantee of stability for nonlinear systems. The second and third are a nonlinear suboptimal control techniques. These techniques are based on an optimal control design approach that takes into account the nonlinearities present in the vehicle dynamics. The stability Proof of the closed-loop system is presented. The performance of the control system designed is evaluated via simulations and also via an experimental scheme using the Quanser 3-DOF Hover. The experiments show the effectiveness of the linear control method over the nonlinear strategy. },
keywords = {Multirotor Aerial Vehicles; Hamilton-Jacobi-Bellman equation; Optimal control; Attitude control},
language = {English},
publisher = {Elsevier Ltd.}
}

The present paper is concerned with the design and experimental evaluation of optimal control laws for the nonlinear attitude dynamics of a multirotor aerial vehicle. Three design methods based on Hamilton-Jacobi-Bellman equation are taken into account. The first one is a linear control with guarantee of stability for nonlinear systems. The second and third are a nonlinear suboptimal control techniques. These techniques are based on an optimal control design approach that takes into account the nonlinearities present in the vehicle dynamics. The stability Proof of the closed-loop system is presented. The performance of the control system designed is evaluated via simulations and also via an experimental scheme using the Quanser 3-DOF Hover. The experiments show the effectiveness of the linear control method over the nonlinear strategy.

@article{yuan_2018,
title = {Force Reflecting Control for Bilateral Teleoperation System under Time-Varying Delays},
author = {Yuan Y., Wang Y., Guo L.},
journal = { IEEE Transactions on Industrial Informatics},
year = {2018},
institution = {Northwestern Polytechnical University, China; Beihang University, China},
abstract = {In this paper, the force reflection control problem is addressed for a bilateral teleoperation system with time-varying delays. A dynamic gain force observer is proposed to obtain the force information for the force reflection control scheme. In virtue of the adaptive law, the internal uncertainties can be estimated based on the prescribed performance functions. The corrective wave variable method is utilized such that the bilateral teleoperation system could achieve a satisfactory control performance. A number of practical experiments are implemented on the bilateral teleoperation system to demonstrate the validation of the proposed methodology. },
issn = {1551-3203},
keywords = {Bilateral teleoperation system, force reflecting control, force observer, adaptive law},
language = {English},
publisher = {IEEE}
}

In this paper, the force reflection control problem is addressed for a bilateral teleoperation system with time-varying delays. A dynamic gain force observer is proposed to obtain the force information for the force reflection control scheme. In virtue of the adaptive law, the internal uncertainties can be estimated based on the prescribed performance functions. The corrective wave variable method is utilized such that the bilateral teleoperation system could achieve a satisfactory control performance. A number of practical experiments are implemented on the bilateral teleoperation system to demonstrate the validation of the proposed methodology.

@article{sun_2018,
title = {Fuzzy Neural Network Control of a Flexible Robotic Manipulator Using Assumed Mode Method},
author = {Sun, C.; Gao, H.; He, W.; Yu, Y.},
journal = {IEEE Transactions on Neural Networks and Learning Systems},
year = {2018},
institution = {Southeast University, China; University of Science and Technology Beijing, China; },
abstract = {In this paper, in order to analyze the single-link flexible structure, the assumed mode method is employed to develop the dynamic model. Based on the discrete dynamic model, fuzzy neural network (NN) control is investigated to track the desired trajectory accurately and to suppress the flexible vibration maximally. To ensure the stability rigorously as the goal, the system is proved to be uniform ultimate boundedness by Lyapunov's stability method. Eventually, simulations verify that the proposed control strategy is effective, and the control performance is compared with the proportion derivative control. The experiments are implemented on the Quanser platform to further demonstrate the feasibility of the proposed fuzzy NN control. },
issn = {2162-2388 },
keywords = {Adaptive control, assumed mode method (AMM), dynamic modeling, flexible robotic manipulator, neural networks (NNs), vibration control},
language = {English},
publisher = {IEEE}
}

In this paper, in order to analyze the single-link flexible structure, the assumed mode method is employed to develop the dynamic model. Based on the discrete dynamic model, fuzzy neural network (NN) control is investigated to track the desired trajectory accurately and to suppress the flexible vibration maximally. To ensure the stability rigorously as the goal, the system is proved to be uniform ultimate boundedness by Lyapunov's stability method. Eventually, simulations verify that the proposed control strategy is effective, and the control performance is compared with the proportion derivative control. The experiments are implemented on the Quanser platform to further demonstrate the feasibility of the proposed fuzzy NN control.

@article{kumar_2018,
title = {H∞ tracking control for an inverted pendulum},
author = {Kumar, M.A.; Kanthalakshmi, S.},
journal = {Journal of Vibration and Control},
year = {2018},
institution = {PSG College of Technology, Coimbatore, India},
abstract = {The objective of this paper is to design an H∞ controller for an inverted pendulum system, synthesized using the H-infinity loop shaping technique. In the H∞ loop shaping technique, a linear plant model is augmented with certain weight functions, such as the sensitivity weight function and complementary sensitivity weight function, so that the closed loop transfer function of the plant will have the desired performance. In this work, the H-infinity controller is synthesized and the analysis on robustness and performance of the system is done by taking the singular value response and robustness indicator plots. },
keywords = {Uncertainty, perturbation model, loop shaping, H∞ norm, H∞ control, inverted pendulum, weighted sensitivity, linear fractional transformation},
language = {English},
publisher = {SAGE}
}

The objective of this paper is to design an H∞ controller for an inverted pendulum system, synthesized using the H-infinity loop shaping technique. In the H∞ loop shaping technique, a linear plant model is augmented with certain weight functions, such as the sensitivity weight function and complementary sensitivity weight function, so that the closed loop transfer function of the plant will have the desired performance. In this work, the H-infinity controller is synthesized and the analysis on robustness and performance of the system is done by taking the singular value response and robustness indicator plots.

@article{gonzalez_2018,
title = {Influence of Elbow Flexion and Stimulation Site on Neuromuscular Electrical Stimulation of the Biceps Brachii},
author = {Gonzalez, E.J.; Downey, R.J.; Rouse, C.A.; Dixon, W.E.},
journal = {IEEE Transactions on Neural Systems and Rehabilitation Engineering},
year = {2018},
institution = {University of Florida, USA; Stanford University, USA; Medical University of South Carolina, USA},
abstract = {Functional electrical stimulation (FES) can help individuals with physical disabilities by assisting limb movement; however, the change in muscle geometry associated with limb movement may affect the response to stimulation. The aim of this study was to quantify the effects of elbow flexion and stimulation site on muscle torque production. Contraction torque about the elbow was measured in 12 healthy individuals using a custom elbow flexion testbed and a transcutaneous electrode array. Stimulation was delivered to 6 distinct sites along the biceps brachii over 11 elbow flexion angles. Flexion angle was found to significantly influence the optimal (i.e., torque-maximizing) stimulation site (χ2(10, N=24) = 135.75, p = 3.12×10-24), with post hoc analysis indicating a proximal shift in optimal stimulation site with increased flexion. Similarly, the biceps stimulation site was found to significantly influence the flexion angle at which peak torque occurred (χ2(5, N=24) = 101.82, p = 2.18×10-20), with post hoc analysis indicating an increase in peak-torque flexion angle as stimulation site is moved proximally up the biceps. Since maximizing muscle force per unit stimulation is a common goal in rehabilitative FES, future efforts could examine methods which compensate for the shift in optimal stimulation site during FESinduced limb movement. },
issn = {1534-4320},
keywords = {Elbow Flexion, Electrode Array, Functional Electrical Stimulation (FES), Neuromuscular Electrical Stimulation (NMES)},
publisher = {IEEE}
}

Functional electrical stimulation (FES) can help individuals with physical disabilities by assisting limb movement; however, the change in muscle geometry associated with limb movement may affect the response to stimulation. The aim of this study was to quantify the effects of elbow flexion and stimulation site on muscle torque production. Contraction torque about the elbow was measured in 12 healthy individuals using a custom elbow flexion testbed and a transcutaneous electrode array. Stimulation was delivered to 6 distinct sites along the biceps brachii over 11 elbow flexion angles. Flexion angle was found to significantly influence the optimal (i.e., torque-maximizing) stimulation site (χ2(10, N=24) = 135.75, p = 3.12×10-24), with post hoc analysis indicating a proximal shift in optimal stimulation site with increased flexion. Similarly, the biceps stimulation site was found to significantly influence the flexion angle at which peak torque occurred (χ2(5, N=24) = 101.82, p = 2.18×10-20), with post hoc analysis indicating an increase in peak-torque flexion angle as stimulation site is moved proximally up the biceps. Since maximizing muscle force per unit stimulation is a common goal in rehabilitative FES, future efforts could examine methods which compensate for the shift in optimal stimulation site during FESinduced limb movement.

@article{ozdagli_2018,
title = {Low-cost, efficient wireless intelligent sensors (LEWIS) measuring real-time reference-free dynamic displacements},
author = {Ozdagli, A.I.; Liu, B.; Moreu, F.},
journal = {Mechanical Systems and Signal Processing},
year = {2018},
month = {07},
volume = {107},
institution = {University of New Mexico, USA; Institute of Disaster Prevention, Beijing, China},
abstract = {According to railroad managers, displacement of railroad bridges under service loads is an important parameter in the condition assessment and performance evaluation. However, measuring bridge responses in the field is often costly and labor-intensive. This paper proposes a low-cost, efficient wireless intelligent sensor (LEWIS) platform that can compute in real-time the dynamic transverse displacements of railroad bridges under service loads. This sensing platform drives on an open-source Arduino ecosystem and combines low-cost microcontrollers with affordable accelerometers and wireless transmission modules. The proposed LEWIS system is designed to reconstruct dynamic displacements from acceleration measurements onboard, eliminating the need for offline post-processing, and to transmit the data in real-time to a base station where the inspector at the bridge can see the displacements while the train is crossing, or to a remote office if so desired by internet. Researchers validated the effectiveness of the new LEWIS by conducting a series of laboratory experiments. A shake table setup simulated transverse bridge displacements measured on the field and excited the proposed platform, a commercially available wired expensive accelerometer, and reference LVDT displacement sensor. The responses obtained from the wireless system were compared to the displacements reconstructed from commercial accelerometer readings and the reference LVDT. The results of the laboratory experiments demonstrate that the proposed system is capable of reconstructing transverse displacements of railroad bridges under revenue service traffic accurately and transmitting the data in real-time wirelessly. In conclusion, the platform presented in this paper can be used in the performance assessment of railroad bridge network cost-effectively and accurately. Future work includes collecting real-time reference-free displacements of one railroad bridge in Colorado under train crossings to further prove LEWIS’ suitability for engineering applications. },
keywords = {Real-time monitoring, Low-cost sensing, Wireless sensing, Acceleration, Displacement, Intelligent sensor, Railroad bridges},
language = {English},
publisher = {Elsevier B.V.},
pages = {343-356}
}

According to railroad managers, displacement of railroad bridges under service loads is an important parameter in the condition assessment and performance evaluation. However, measuring bridge responses in the field is often costly and labor-intensive. This paper proposes a low-cost, efficient wireless intelligent sensor (LEWIS) platform that can compute in real-time the dynamic transverse displacements of railroad bridges under service loads. This sensing platform drives on an open-source Arduino ecosystem and combines low-cost microcontrollers with affordable accelerometers and wireless transmission modules. The proposed LEWIS system is designed to reconstruct dynamic displacements from acceleration measurements onboard, eliminating the need for offline post-processing, and to transmit the data in real-time to a base station where the inspector at the bridge can see the displacements while the train is crossing, or to a remote office if so desired by internet. Researchers validated the effectiveness of the new LEWIS by conducting a series of laboratory experiments. A shake table setup simulated transverse bridge displacements measured on the field and excited the proposed platform, a commercially available wired expensive accelerometer, and reference LVDT displacement sensor. The responses obtained from the wireless system were compared to the displacements reconstructed from commercial accelerometer readings and the reference LVDT. The results of the laboratory experiments demonstrate that the proposed system is capable of reconstructing transverse displacements of railroad bridges under revenue service traffic accurately and transmitting the data in real-time wirelessly. In conclusion, the platform presented in this paper can be used in the performance assessment of railroad bridge network cost-effectively and accurately. Future work includes collecting real-time reference-free displacements of one railroad bridge in Colorado under train crossings to further prove LEWIS’ suitability for engineering applications.

@article{arnal_2018,
title = {Magneto-optical nanoparticles for cyclic magnetomotive photoacoustic imaging},
author = {Arnal, B.; Yoon, S.J.; Li, J.; Gao, X.; O'Donnell, M.},
journal = {Physica C: Superconductivity and its Applications},
year = {2018},
month = {05},
volume = {548},
institution = {Department of Bioengineering, University of Washington, USA},
abstract = {Photoacoustic imaging is a highly promising tool to visualize molecular events with deep tissue penetration. Like most other modalities, however, image contrast under in vivo conditions is far from optimal due to background signals from tissue. Using iron oxide-gold core-shell nanoparticles, we previously demonstrated that magnetomotive photoacoustic (mmPA) imaging can dramatically reduce the influence of background signals and produce high-contrast molecular images. Here we report two significant advances toward clinical translation of this technology. First, we introduce a new class of compact, uniform, magneto-optically coupled core-shell nanoparticle, prepared through localized copolymerization of polypyrrole (PPy) on an iron oxide nanoparticle surface. The resulting iron oxide-PPy nanoparticles solve the photo-instability and small-scale synthesis problems previously encountered by the gold coating approach, and extend the large optical absorption coefficient of the particles beyond 1000 nm in wavelength. In parallel, we have developed a new generation of mmPA imaging featuring cyclic magnetic motion and ultrasound speckle tracking, with an image capture frame rate several hundred times faster than the photoacoustic speckle tracking method demonstrated previously. These advances enable robust artifact elimination caused by physiologic motion and first application of the mmPA technology in vivo for sensitive tumor imaging. },
keywords = {Magnetic nanoparticles (MNPs) Core-shell nanoparticles Polypyrrole},
language = {English},
publisher = {Elsevier B.V.},
pages = {90-92}
}

Photoacoustic imaging is a highly promising tool to visualize molecular events with deep tissue penetration. Like most other modalities, however, image contrast under in vivo conditions is far from optimal due to background signals from tissue. Using iron oxide-gold core-shell nanoparticles, we previously demonstrated that magnetomotive photoacoustic (mmPA) imaging can dramatically reduce the influence of background signals and produce high-contrast molecular images. Here we report two significant advances toward clinical translation of this technology. First, we introduce a new class of compact, uniform, magneto-optically coupled core-shell nanoparticle, prepared through localized copolymerization of polypyrrole (PPy) on an iron oxide nanoparticle surface. The resulting iron oxide-PPy nanoparticles solve the photo-instability and small-scale synthesis problems previously encountered by the gold coating approach, and extend the large optical absorption coefficient of the particles beyond 1000 nm in wavelength. In parallel, we have developed a new generation of mmPA imaging featuring cyclic magnetic motion and ultrasound speckle tracking, with an image capture frame rate several hundred times faster than the photoacoustic speckle tracking method demonstrated previously. These advances enable robust artifact elimination caused by physiologic motion and first application of the mmPA technology in vivo for sensitive tumor imaging.

@conference{torabi_2018,
title = {Manipulability of teleoperated surgical robots with application in design of master/slave manipulators},
author = {Torabi A., Khadem M., Zareinia K., Sutherland G.R., Tavakoli M.},
booktitle = {2018 International Symposium on Medical Robotics (ISMR)},
year = {2018},
institution = {University of Alberta, Canada; University of Calgary, Canada},
abstract = {Teleoperated surgical robots can significantly improve the performance of minimally invasive surgeries. The performance of a master-slave robotic system depends significantly on the capability of its master device to appropriately interface the user with the slave robot. However, master robots currently used in the clinic present several drawbacks such as the mismatch between the slave and master workspaces and the inability to intuitively transfer the slave robot's dexterity and joint limits to the user. In this paper, the "teleoperation manipulability index (TMI)" is introduced as a quantifiable measure of the combined master-slave system manipulability. We also demonstrate the application of the TMI in the design of master-slave robotic systems. By employing the proposed manipulability index, we are able to modify the design of a commercially available master robot that 1) enhances surgeon's control over force/velocity of a surgical robot, 2) minimizes the master robot's footprint, 3) optimizes the surgeons' control effort, and 4) avoids singularities and joint limits of the master and slave robots. A simulation study is performed to validate the performance of the modified master-slave robotic system. },
keywords = {Indexes, Ellipsoids, Jacobian matrices, Surgery, Master-slave, Medical robotics},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-2513-2 }
}

Teleoperated surgical robots can significantly improve the performance of minimally invasive surgeries. The performance of a master-slave robotic system depends significantly on the capability of its master device to appropriately interface the user with the slave robot. However, master robots currently used in the clinic present several drawbacks such as the mismatch between the slave and master workspaces and the inability to intuitively transfer the slave robot's dexterity and joint limits to the user. In this paper, the "teleoperation manipulability index (TMI)" is introduced as a quantifiable measure of the combined master-slave system manipulability. We also demonstrate the application of the TMI in the design of master-slave robotic systems. By employing the proposed manipulability index, we are able to modify the design of a commercially available master robot that 1) enhances surgeon's control over force/velocity of a surgical robot, 2) minimizes the master robot's footprint, 3) optimizes the surgeons' control effort, and 4) avoids singularities and joint limits of the master and slave robots. A simulation study is performed to validate the performance of the modified master-slave robotic system.

@article{okyay_2018,
title = {Mechatronic design, actuator optimization, and control of a long stroke linear nano-positioner},
author = {Okyay, A.; Erkorkmaz, K.; Khamesee, M.B.},
journal = {Precision Engineering},
year = {2018},
institution = {University of Waterloo, Canada},
abstract = {In this paper, mechatronic design, actuator optimization and controls of a long-stroke (20 mm) linear nano-positioner are presented. The mechatronic design is described in terms of the stage’s most prominent features regarding mechanical design, assembly, actuator configuration, and power supply. A novel air-bearing/bushing arrangement has been used in which the commonly employed double shaft arrangement is replaced with a single shaft supported by an air bearing from the bottom to constrain the roll motion. The assembly is greatly simplified by exploiting the self-aligning property of the air-bushings which are held in the housings by O-rings. Also, the footprint of the stage is reduced. Voice coil actuators (VCA) in moving magnet mode have been used in complementary double configuration for uniformity of force response. The performance objectives of previously optimized VCA’s as standalone actuators are re-evaluated in this configuration. It is observed that while the performance objectives decrease a bit, the desirability of the design point is still retained. Controller design has been made for the current control and position control loops. Heydemann’s method for the compensation of encoder quadrature detection errors is implemented. The positioning resolution of the stage as measured from the sensor output is experimentally determined to be +/−5 nm. Dynamic Error Budgeting (DEB) method has been used to analyze the contributing factors to the positioning error, and sensor broadband noise is determined to be the major contributor. The actual positioning accuracy of the stage is estimated by DEB to be 0.682 nm root-mean-square (RMS). The trajectory following accuracy is determined to be +/−15 nm. It is expected that trajectory following accuracy can substantially improve if more advanced compensation methods for encoder quadrature errors are implemented. },
keywords = {Voice coil actuator, Topology optimization, Dynamic Error Budgeting, Air bearing, Nano-positioning, Optical encoder, Encoder quadrature detection errors, Eddy currents},
language = {English},
publisher = {Elsevier B.V.}
}

In this paper, mechatronic design, actuator optimization and controls of a long-stroke (20 mm) linear nano-positioner are presented. The mechatronic design is described in terms of the stage’s most prominent features regarding mechanical design, assembly, actuator configuration, and power supply. A novel air-bearing/bushing arrangement has been used in which the commonly employed double shaft arrangement is replaced with a single shaft supported by an air bearing from the bottom to constrain the roll motion. The assembly is greatly simplified by exploiting the self-aligning property of the air-bushings which are held in the housings by O-rings. Also, the footprint of the stage is reduced. Voice coil actuators (VCA) in moving magnet mode have been used in complementary double configuration for uniformity of force response. The performance objectives of previously optimized VCA’s as standalone actuators are re-evaluated in this configuration. It is observed that while the performance objectives decrease a bit, the desirability of the design point is still retained. Controller design has been made for the current control and position control loops. Heydemann’s method for the compensation of encoder quadrature detection errors is implemented. The positioning resolution of the stage as measured from the sensor output is experimentally determined to be +/−5 nm. Dynamic Error Budgeting (DEB) method has been used to analyze the contributing factors to the positioning error, and sensor broadband noise is determined to be the major contributor. The actual positioning accuracy of the stage is estimated by DEB to be 0.682 nm root-mean-square (RMS). The trajectory following accuracy is determined to be +/−15 nm. It is expected that trajectory following accuracy can substantially improve if more advanced compensation methods for encoder quadrature errors are implemented.

@article{meller_2018,
title = {Model-based feedforward and cascade control of hydraulic McKibben muscles},
author = {Meller, M.; Kogan, B.; Bryant, M.; Garcia, E.},
journal = {Sensors and Actuators A: Physical},
year = {2018},
institution = {Cornell University, USA; North Carolina State University, USA},
abstract = {McKibben artificial muscle actuators are predominantly pneumatically powered. Recently, hydraulic operation has gained interest due to its higher rigidity and efficiency. While there has been extensive control system development for pneumatic artificial muscles, little has been conducted hydraulically. This paper investigates three different controllers developed for a loaded robotic arm actuated with oil-hydraulic McKibben muscles. The goal was to achieve good angular position tracking over a range of frequencies up to 1 Hz. The first scheme, serving as the baseline, is a proportional-integral controller. The second architecture adds a nonlinear model-based feedforward term to the baseline controller; the feedforward includes the expected flowrate demands based on the actuator kinematics as well as the valve flow gain. The last scheme adds an inner pressure feedback loop to the second architecture. All controllers were evaluated with frequency and step response experiments. The results show that a simple proportional-integral controller has significant phase lag and attenuation at the higher frequencies tested; including the feedforward term almost completely eliminates these. The cascaded loop improves rise and settling times. },
keywords = { McKibben muscle; Fluidic artificial muscle; hydraulic artificial muscle; fluid power control; hydraulic control; robotics},
language = {English},
publisher = {Elsevier B.V.}
}

McKibben artificial muscle actuators are predominantly pneumatically powered. Recently, hydraulic operation has gained interest due to its higher rigidity and efficiency. While there has been extensive control system development for pneumatic artificial muscles, little has been conducted hydraulically. This paper investigates three different controllers developed for a loaded robotic arm actuated with oil-hydraulic McKibben muscles. The goal was to achieve good angular position tracking over a range of frequencies up to 1 Hz. The first scheme, serving as the baseline, is a proportional-integral controller. The second architecture adds a nonlinear model-based feedforward term to the baseline controller; the feedforward includes the expected flowrate demands based on the actuator kinematics as well as the valve flow gain. The last scheme adds an inner pressure feedback loop to the second architecture. All controllers were evaluated with frequency and step response experiments. The results show that a simple proportional-integral controller has significant phase lag and attenuation at the higher frequencies tested; including the feedforward term almost completely eliminates these. The cascaded loop improves rise and settling times.

@conference{savoie_2018,
title = {Modelling and Compensation of Hysteresis in Polarization of Piezoelectric Actuators},
author = {Savoie, M.; Shan J.},
booktitle = {2018 AIAA/AHS Adaptive Structures Conference},
year = {2018},
institution = {York University, ON, Canada},
abstract = {This paper presents a domain wall modelling approach to linearise the polarization of a unipolar piezoelectric actuator. Polarization is measured through its impedance which is determined with a low amplitude overlaid sinusoidal signal. Linearisation is achieved through the inversion of the physical model and the physical significance of the parameters are retained. The controlled output showed a maximum error of 5% which could be reduced further by modifying the proposed model to account for minor hysteresis loops. },
language = {English},
publisher = {AIAA}
}

This paper presents a domain wall modelling approach to linearise the polarization of a unipolar piezoelectric actuator. Polarization is measured through its impedance which is determined with a low amplitude overlaid sinusoidal signal. Linearisation is achieved through the inversion of the physical model and the physical significance of the parameters are retained. The controlled output showed a maximum error of 5% which could be reduced further by modifying the proposed model to account for minor hysteresis loops.

@article{gao_2018,
title = {Neural Network Control of a Two-Link Flexible Robotic Manipulator Using Assumed Mode Method},
author = {Gao, H.; He, W.; Zhou, C.;Sun, C.},
journal = {IEEE Transactions on Industrial Informatics},
year = {2018},
institution = {University of Science and Technology Beijing, China; Southeast University, China},
abstract = {In this paper, the n-dimensional discretized model of the two-link flexible manipulator is developed by the assumed mode method (AMM). Subsequently, based on the discretized dynamic model, both full state feedback control and output feedback control are investigated to achieve the trajectory tracking and vibration suppression. In order to guarantee the stability strictly, uniform ultimate boundedness (UUB) of the closed-loop system is realized by the Lyapunov's stability. Furthermore, through appropriately choosing control parameters, the states of the system will converge to zero with a small neighborhood. Eventually, extensive simulations and experiments on the Quanser platform for a two-link robotic manipulator are carried out to demonstrate the feasibility of the proposed neural network (NN) controller. },
issn = {1551-3203},
keywords = {Neural Networks, Vibration Control, Assumed Mode Method, Dynamic Modeling, Flexible Robotic Manipulator, Two-Link, Flexible Structure},
language = {English},
publisher = {IEEE}
}

In this paper, the n-dimensional discretized model of the two-link flexible manipulator is developed by the assumed mode method (AMM). Subsequently, based on the discretized dynamic model, both full state feedback control and output feedback control are investigated to achieve the trajectory tracking and vibration suppression. In order to guarantee the stability strictly, uniform ultimate boundedness (UUB) of the closed-loop system is realized by the Lyapunov's stability. Furthermore, through appropriately choosing control parameters, the states of the system will converge to zero with a small neighborhood. Eventually, extensive simulations and experiments on the Quanser platform for a two-link robotic manipulator are carried out to demonstrate the feasibility of the proposed neural network (NN) controller.

@article{schindeler_2018,
title = {Online Identification of Environment Hunt–Crossley Models Using Polynomial Linearization},
author = {Schindeler, R.; Hashtrudi-Zaad, K.},
journal = { IEEE Transactions on Robotics},
year = {2018},
volume = {34},
number = {2},
institution = {Queen's University, Kingston, ON, Canada},
abstract = {Online environment dynamic estimates are often used for the control of robots, telerobots, and haptic systems. The nonlinear Hunt–Crossley (HC) model, which is physically consistent with the behavior of soft objects with limited deformation at a single point of contact, is being increasingly used in robotic control systems. The HC model can be identified online using a single-stage log linearization technique; however, the accuracy and applicability of the existing method is limited. We propose a two-stage polynomial identification method, which uses a quadratic approximation in the first stage to generate a linearly parameterized model of the HC dynamics (Quad-Poly). The coefficients of the Quad-Poly model are then used in the second stage to extract the HC parameters using a lookup table and recursive least squares parameter estimation. The proposed method is experimentally assessed against a previous natural logarithm linearization method, and further tested for time-varying environment dynamics and human-generated trajectories and for robustness against uncertainties in the measured data and system parameters. },
issn = {1552-3098},
keywords = {Hunt–Crossley (HC), Kelvin Voight (KV), online model identification, parameter estimation, polynomial linearization},
language = {English},
publisher = {IEEE},
pages = {447-458}
}

Online environment dynamic estimates are often used for the control of robots, telerobots, and haptic systems. The nonlinear Hunt–Crossley (HC) model, which is physically consistent with the behavior of soft objects with limited deformation at a single point of contact, is being increasingly used in robotic control systems. The HC model can be identified online using a single-stage log linearization technique; however, the accuracy and applicability of the existing method is limited. We propose a two-stage polynomial identification method, which uses a quadratic approximation in the first stage to generate a linearly parameterized model of the HC dynamics (Quad-Poly). The coefficients of the Quad-Poly model are then used in the second stage to extract the HC parameters using a lookup table and recursive least squares parameter estimation. The proposed method is experimentally assessed against a previous natural logarithm linearization method, and further tested for time-varying environment dynamics and human-generated trajectories and for robustness against uncertainties in the measured data and system parameters.

@article{sen_2018,
title = {Optimisation of a PID controller for a two-floor structure under earthquake excitation based on the bees algorithm},
author = {Sen, M.A.; Tinkir, M.; Kalyoncu, M.},
journal = {Journal of Low Noise, Vibration and Active Control},
year = {2018},
institution = {Selçuk University, Turkey; Necmettin Erbakan University, Turkey},
abstract = {The control of vibration and displacement in structures under seismic excitation is very challenging, and designing a structural control system against disturbances has drawn great attention. This paper concentrates on implementing the bees algorithm to tune gains of traditional PID controller for active vibration control of a building-like structure with two floors under Northridge Earthquake excitation. Bees algorithm is a diverse method to ensure an efficient solution for optimisation of a controller according to customary trial-error design methods. The main aim of this study is optimisation of KP, KI and KD gains with bees algorithm in order to obtain a more effective PID controller to suppress vibrations of the floors during the earthquake excitation. After definition of the system and bees algorithm, PID controller offline tuned with bees algorithm using mathematical model of system. Moreover, the aim is to compare the performances of the BA with an existing optimisation method, genetic algorithm (GA), implemented on the system. The paper presents the experimental results that were obtained from the structure system to show the efficiency of the tuned PID controller. As a result, the performance and effectiveness of the tuned PID controller are investigated and verified experimentally. The displacements and accelerations of the floors and the cart are decreased considerably. The experimental responses of the system are given in graphical form. },
issn = {1461-3484},
keywords = {Bees algorithm, two-floor structure, PID controller, active mass damping, Northridge earthquake},
language = {English},
publisher = {SAGE}
}

The control of vibration and displacement in structures under seismic excitation is very challenging, and designing a structural control system against disturbances has drawn great attention. This paper concentrates on implementing the bees algorithm to tune gains of traditional PID controller for active vibration control of a building-like structure with two floors under Northridge Earthquake excitation. Bees algorithm is a diverse method to ensure an efficient solution for optimisation of a controller according to customary trial-error design methods. The main aim of this study is optimisation of KP, KI and KD gains with bees algorithm in order to obtain a more effective PID controller to suppress vibrations of the floors during the earthquake excitation. After definition of the system and bees algorithm, PID controller offline tuned with bees algorithm using mathematical model of system. Moreover, the aim is to compare the performances of the BA with an existing optimisation method, genetic algorithm (GA), implemented on the system. The paper presents the experimental results that were obtained from the structure system to show the efficiency of the tuned PID controller. As a result, the performance and effectiveness of the tuned PID controller are investigated and verified experimentally. The displacements and accelerations of the floors and the cart are decreased considerably. The experimental responses of the system are given in graphical form.

@article{he_2018,
title = {PDE Model-Based Boundary Control Design for a Flexible Robotic Manipulator With Input Backlash},
author = {He, W.; He, X.; Zou, M.; Li, H.},
journal = {IEEE Transactions on Control Systems Technology},
year = {2018},
institution = {University of Science and Technology Beijing, China; University of Electronic Science and Technology of China, China; Bohai University, China},
abstract = {This brief considers the control design problem for a flexible robotic manipulator. Our control strategies are to: 1) move the manipulator to the certain desired angle; 2) suppress the vibration at the neighborhood of the desired angle; and 3) handle the backlash nonlinearity existing in the practical system. Based on the infinite-dimensional dynamic model, a boundary controller with input backlash is designed to achieve the control aims. An output feedback method is adopted to represent a controller to handle the feedback signals that are not able to be measured directly. The effectiveness of the designed controllers and the stability of the system are demonstrated by theoretical analysis, numerical simulations, and physical experiments. },
issn = {1558-0865 },
keywords = {Distributed parameter system, flexible robotic manipulator, input backlash, output feedback, vibration control},
language = {English},
publisher = {IEEE}
}

This brief considers the control design problem for a flexible robotic manipulator. Our control strategies are to: 1) move the manipulator to the certain desired angle; 2) suppress the vibration at the neighborhood of the desired angle; and 3) handle the backlash nonlinearity existing in the practical system. Based on the infinite-dimensional dynamic model, a boundary controller with input backlash is designed to achieve the control aims. An output feedback method is adopted to represent a controller to handle the feedback signals that are not able to be measured directly. The effectiveness of the designed controllers and the stability of the system are demonstrated by theoretical analysis, numerical simulations, and physical experiments.

@article{li_2018,
title = {Relative posture-based kinematic calibration of a 6-RSS parallel robot by optical coordinate measurement machine},
author = {Li, P.; Zeng2, R.; Xie, W.; Zhang, X.},
journal = { International Journal of Advanced Robotic Systems},
year = {2018},
volume = {15},
number = {2},
institution = {Concordia University, Canada; Beihang University, China},
abstract = {In this article, a relative posture-based algorithm is proposed to solve the kinematic calibration problem of a 6-RSS parallel robot using the optical coordinate measurement machine system. In the research, the relative posture of robot is estimated using the detected pose with respect to the sensor frame through several reflectors which are fixed on the robot end-effector. Based on the relative posture, a calibration algorithm is proposed to determine the optimal error parameters of the robot kinematic model and external parameters introduced by the optical sensor. This method considers both the position and orientation variations and does not need the accurate location information of the detection sensor. The simulation results validate the superiority of the algorithm by comparing with the classic implicit calibration method. And the experimental results demonstrate that the proposal relative posture-based algorithm using optical coordinate measurement machine is an implementable and effective method for the parallel robot calibration. },
keywords = {Parallel robot, calibration, optical sensor, kinematic analysis},
language = {English},
publisher = {SAGE}
}

In this article, a relative posture-based algorithm is proposed to solve the kinematic calibration problem of a 6-RSS parallel robot using the optical coordinate measurement machine system. In the research, the relative posture of robot is estimated using the detected pose with respect to the sensor frame through several reflectors which are fixed on the robot end-effector. Based on the relative posture, a calibration algorithm is proposed to determine the optimal error parameters of the robot kinematic model and external parameters introduced by the optical sensor. This method considers both the position and orientation variations and does not need the accurate location information of the detection sensor. The simulation results validate the superiority of the algorithm by comparing with the classic implicit calibration method. And the experimental results demonstrate that the proposal relative posture-based algorithm using optical coordinate measurement machine is an implementable and effective method for the parallel robot calibration.

@article{prakash_2018,
title = {Robust and novel two degree of freedom fractional controller based on two-loop topology for inverted pendulum},
author = {Dwivedi, P.; Pandey, S.; Junghare, A.S.},
journal = {ISA Transactions},
year = {2018},
institution = {National Institute of Technology, Uttarakhand, India; Visvesvaraya National Institute of Technology, Nagpur, India},
abstract = {A rotary single inverted pendulum (RSIP) typically represents a space booster rocket, Segway and similar systems with unstable equilibrium. This paper proposes a novel two degree of freedom (2-DOF) fractional control strategy based on 2-loop topology for RSIP system which can be extended to control the systems with unstable equilibrium. It comprises feedback and feed-forward paths. Primary controller relates the perturbation attenuation while the secondary controller is accountable for set point tracking. To tune the parameters of proposed fractional controller a simple graphical tuning method based on frequency response is used. The study will serve the outstanding experimental results for both, stabilization and trajectory tracking tasks. The study will also serve to present a comparison of the performance of the proposed controller with the 1-DOF FOPID controller and sliding mode controller (SMC) for the RSIP system. Further to confirm the usability of the proposed controller and to avoid the random perturbations sensitivity, robustness, and stability analysis through fractional root-locus and Bode-plot is investigated. },
keywords = {FOPID controller, 2-DOF PID controller, Inverted pendulum, Sliding mode controller, Iso-damping, Fractional root-locus},
language = {English},
publisher = {Elsevier Ltd.}
}

A rotary single inverted pendulum (RSIP) typically represents a space booster rocket, Segway and similar systems with unstable equilibrium. This paper proposes a novel two degree of freedom (2-DOF) fractional control strategy based on 2-loop topology for RSIP system which can be extended to control the systems with unstable equilibrium. It comprises feedback and feed-forward paths. Primary controller relates the perturbation attenuation while the secondary controller is accountable for set point tracking. To tune the parameters of proposed fractional controller a simple graphical tuning method based on frequency response is used. The study will serve the outstanding experimental results for both, stabilization and trajectory tracking tasks. The study will also serve to present a comparison of the performance of the proposed controller with the 1-DOF FOPID controller and sliding mode controller (SMC) for the RSIP system. Further to confirm the usability of the proposed controller and to avoid the random perturbations sensitivity, robustness, and stability analysis through fractional root-locus and Bode-plot is investigated.

@article{cheng_2018,
title = {Switched-Impedance Control of Surgical Robots in Teleoperated Beating-Heart Surgery},
author = {Cheng, L.; Tavakoli, M.},
journal = {Journal of Medical Robotics Research},
year = {2018},
institution = {University of Alberta, Canada},
abstract = {A novel switched-impedance control method is proposed and implemented for telerobotic beating-heart surgery. Differing from cardiopulmonary-bypass-based arrested-heart surgery, beating-heart surgery creates challenges for the human operator (surgeon) due to the heart's fast motions and, in the case of a teleoperated surgical robot, the oscillatory haptic feedback to the operator. This paper designs two switched reference impedance models for the master and slave robots to achieve both motion compensation and non-oscillatory force feedback during slave-heart interaction. By changing the parameters of the impedance models, different performances for both robots are obtained: (a) when the slave robot does not make contact with the beating heart, the slave robot closely follows the motion of the master robot as in a regular teleoperation system, (b) when contact occurs, the slave robot automatically compensates for the fast motions of the beating heart while the human operator perceives the non-oscillatory component of the slave-heart interaction forces, creating the feeling of making contact with an idle heart for the human operator. The proposed method is validated through simulations and experiments. },
keywords = {Beating-heart surgery; teleoperation; motion compensation; non-oscillatory haptic feedback},
language = {English},
publisher = {World Scientific Publishing Company}
}

A novel switched-impedance control method is proposed and implemented for telerobotic beating-heart surgery. Differing from cardiopulmonary-bypass-based arrested-heart surgery, beating-heart surgery creates challenges for the human operator (surgeon) due to the heart's fast motions and, in the case of a teleoperated surgical robot, the oscillatory haptic feedback to the operator. This paper designs two switched reference impedance models for the master and slave robots to achieve both motion compensation and non-oscillatory force feedback during slave-heart interaction. By changing the parameters of the impedance models, different performances for both robots are obtained: (a) when the
slave robot does not make contact with the beating heart, the slave robot closely follows the motion of the master robot as in a regular teleoperation system, (b) when contact occurs, the slave robot automatically compensates for the fast motions of the beating heart while the human operator perceives the non-oscillatory component of the slave-heart interaction forces, creating the feeling of making contact with an idle heart for the human operator. The proposed method is validated through simulations and experiments.

@conference{coronado_2017,
title = {A Comparison of Fuzzy Schemes for Trajectory Tracking on the Furuta Pendulum},
author = {Coronado, A.; Penaloza-Mejia, O.; Estrada-Manzo, V.; Bernal, M.},
booktitle = {National Congress on Automatic Control 2017},
year = {2017},
month = {10},
institution = {Sonora Institute of Technology, Mexico},
abstract = {This paper presents real-time implementation of trajectory tracking on a Furuta pendulum via two fuzzy output regulation schemes: the first one uses convex representations; the second one employs dynamic mappings. Additionally, the stabilizing part of the control law is computed by means of linear matrix inequalities, so speed convergence and input constraints can be directly considered. Simulation and real-time results are given to show the effectiveness of the approaches },
keywords = {Trajectory tracking; output regulation; fuzzy mappings; dynamic mapping; fuzzy modeling; Furuta pendulum},
language = {English},
pages = {499-503}
}

This paper presents real-time implementation of trajectory tracking on a Furuta pendulum via two fuzzy output regulation schemes: the first one uses convex representations; the second one employs dynamic mappings. Additionally, the stabilizing part of the control law is computed by means of linear matrix inequalities, so speed convergence and input constraints can be directly considered. Simulation and real-time results are given to show the effectiveness of the approaches

@conference{fauser_2017,
title = {A comparison of inertial-based navigation algorithms for a low-cost indoor mobile robot},
author = {Fauser, T.; Bruder, S.; El-Osery, A.},
booktitle = {2017 12th International Conference on Computer Science and Education (ICCSE)},
year = {2017},
institution = {Embry-Riddle Aeronautical University, AZ, USA; New Mexico Tech, NM, USA},
abstract = {Reliable navigation of a low-cost mobile robot in an indoor environment can prove to be challenging as position fixing sensors, such as a GNSS receiver, are typically unavailable. Subscribing to the premise of a baseline of odometry and inertial sensors, this paper compares three navigation strategies, namely, a full 6-DOF inertial measurement unit (IMU) with kinematic constraints, a partial IMU with gyro pseudo-measurements, and an IMU with a depth camera. In the third configuration, by embracing the reality that vertical and horizontal planes dominate the indoor environment, an infrared depth camera is employed to determine surface normals and thereby provide attitude aiding. The paper presents a theoretical basis of the aided inertial navigational problems, MATLAB/Simulink-based simulation results, and finally the performance realized from the implementation of the algorithms on a QUANSER QBot 2 mobile robot employing a VectorNav VN-200 IMU and Kinect IR depth camera. },
issn = {2473-9464 },
keywords = {Localization, inertial navigation, inertial measurement unit, odometry, mobile robot, depth camera, aided inertial navigation},
language = {English},
publisher = {IEEE},
isbn = {978-1-5090-2509-1}
}

Reliable navigation of a low-cost mobile robot in an indoor environment can prove to be challenging as position fixing sensors, such as a GNSS receiver, are typically unavailable. Subscribing to the premise of a baseline of odometry and inertial sensors, this paper compares three navigation strategies, namely, a full 6-DOF inertial measurement unit (IMU) with kinematic constraints, a partial IMU with gyro pseudo-measurements, and an IMU with a depth camera. In the third configuration, by embracing the reality that vertical and horizontal planes dominate the indoor environment, an infrared depth camera is employed to determine surface normals and thereby provide attitude aiding. The paper presents a theoretical basis of the aided inertial navigational problems, MATLAB/Simulink-based simulation results, and finally the performance realized from the implementation of the algorithms on a QUANSER QBot 2 mobile robot employing a VectorNav VN-200 IMU and Kinect IR depth camera.

@article{du_2017,
title = {A Control Performance Index for Multicopters Under Off-nominal Conditions},
author = {Du, G.-X.; Quan, Q.; Xi, Z.; Liu, Y.; Cai, K.-Y.},
year = {2017},
institution = {School of Automation Science and Electrical Engineering, Beihang University, China},
abstract = {In order to prevent loss of control (LOC) accidents, the real-time control performance monitoring (CPM) problem is studied for multicopters. Different from the existing literature, this paper does not try to monitor the performance of the controllers directly. Conversely, the unknown disturbances of the multicopter under off-nominal conditions are modeled and assessed. The monitoring results will tell the user whether a multicopter will be LOC or not. Firstly, a new degree of controllability (DoC) will be proposed for multicopters subject to control constrains and off-nominal conditions. Then a control performance index (CPI) will be defined based on the new DoC to reflect the control performance of the multicopters. Besides, the proposed CPI is applied to a new switching control framework to guide the control decision of multicopter under off-nominal conditions. Finally, simulation and experimental results will show the effectiveness of the CPI and the switching control framework proposed in this paper. },
keywords = {Multicopters, loss of control, control performance monitoring, degree of controllability},
language = {English}
}

In order to prevent loss of control (LOC) accidents, the real-time control performance monitoring (CPM) problem is studied for multicopters. Different from the existing literature, this paper does not try to monitor the performance of the controllers directly. Conversely, the unknown disturbances of the multicopter under off-nominal conditions are modeled and assessed. The monitoring results will tell the user whether a multicopter will be LOC or not. Firstly, a new degree of controllability (DoC) will be proposed for multicopters subject to control constrains and off-nominal conditions. Then a control performance index (CPI) will be defined based on the new DoC to reflect the control performance of the multicopters. Besides, the proposed CPI is applied to a new switching control framework to guide the control decision of multicopter under off-nominal conditions. Finally, simulation and experimental results will show the effectiveness of the CPI and the switching control framework proposed in this paper.

@article{sanz_2017,
title = {A generalized smith predictor for unstable time-delay SISO systems},
author = {Sanz, R.; Garcia, P.; Albertos, P.},
journal = {ISA Transactions},
year = {2017},
institution = {Universitat Politecnica de Valencia, Spain},
abstract = {In this work, a generalization of the Smith Predictor (SP) is proposed to control linear time-invariant (LTI) time-delay single-input single-output (SISO) systems. Similarly to the SP, the combination of any stabilizing output-feedback controller for the delay-free system with the proposed predictor leads to a stabilizing controller for the delayed system. Furthermore, the tracking performance and the steady-state disturbance rejection capabilities of the equivalent delay-free loop are preserved. In order to place this contribution in context, some modifications of the SP are revisited and recast under the same structure. The features of the proposed scheme are illustrated through simulations, showing a comparison with respect to the corresponding delay-free loop, which is here considered to be the ideal scenario. In order to emphasize the feasibility of this approach, a successful experimental implementation in a laboratory platform is also reported. },
keywords = {Smith Predictor, Time delay, External disturbances, Single-input single-output system},
language = {English},
publisher = {Elsevier Ltd.}
}

In this work, a generalization of the Smith Predictor (SP) is proposed to control linear time-invariant (LTI) time-delay single-input single-output (SISO) systems. Similarly to the SP, the combination of any stabilizing output-feedback controller for the delay-free system with the proposed predictor leads to a stabilizing controller for the delayed system. Furthermore, the tracking performance and the steady-state disturbance rejection capabilities of the equivalent delay-free loop are preserved. In order to place this contribution in context, some modifications of the SP are revisited and recast under the same structure. The features of the proposed scheme are illustrated through simulations, showing a comparison with respect to the corresponding delay-free loop, which is here considered to be the ideal scenario. In order to emphasize the feasibility of this approach, a successful experimental implementation in a laboratory platform is also reported.

@article{atashzar_2017_2,
title = {A grasp-based passivity signature for haptics-enabled human-robot interaction: Application to design of a new safety mechanism for robotic rehabilitation},
author = {Atashzar, S.F.; Shahbazi, M.; Tavakoli, M.; Patel, R.V.},
journal = {International Journal of Robotics Research},
year = {2017},
institution = {University of Western Ontario, Canada; University of Alberta, Canada},
abstract = {In this paper, the biomechanical capability of the human upper limb in absorbing physical interaction energy during human-robot interaction is analyzed. The outcome is a graphical map that can quantitatively correlate the extent of the grasp pressure and the geometry of interaction to the extent of hand passivity. For this purpose, a user study has been conducted for 11 healthy human subjects to characterize the energy absorption capability in their arm and wrist. The above correlation is statistically validated. The identified user-specific grasp-based passivity signature map can be used as a graphical tool to assess the biomechanical capabilities of the upper limb in absorbing interaction energy. In this paper, the proposed grasp-based passivity signature map is utilized in the design of a new stabilizer for haptic systems, that takes into account the variation in energy absorption during haptic task execution. The goal is to optimize the haptic system fidelity while guaranteeing human-robot interaction stability despite the potential existence of delays and a non-passive environment. The controller is termed grasp-based passivity signature map stabilizer. If the user provides minimum to no energy absorption during the interaction, the controller makes the force reflection gate tight to guarantee stability. However, when the user demonstrates high capability in absorbing interaction energy, the controller allows the forces to be reflected. The grasp-based passivity signature map stabilizer is an alternative for both conventional stabilizers of haptic/telerobotic systems and fixed conservative force limits in rehabilitation systems where patient-robot interaction safety is a crucial requirement. This provides the practical motivation for this work. Experimental results are presented. },
keywords = {Human-robot interaction, excess of passivity, haptics, non-passive environments, physical energy dissipation, safety and stability, rehabilitation robotics, telerobotic and haptic systems},
language = {English},
publisher = {SAGE}
}

In this paper, the biomechanical capability of the human upper limb in absorbing physical interaction energy during human-robot interaction is analyzed. The outcome is a graphical map that can quantitatively correlate the extent of the grasp pressure and the geometry of interaction to the extent of hand passivity. For this purpose, a user study has been conducted for 11 healthy human subjects to characterize the energy absorption capability in their arm and wrist. The above correlation is statistically validated. The identified user-specific grasp-based passivity signature map can be used as a graphical tool to assess the biomechanical capabilities of the upper limb in absorbing interaction energy. In this paper, the proposed grasp-based passivity signature map is utilized in the design of a new stabilizer for haptic systems, that takes into account the variation in energy absorption during haptic task execution. The goal is to optimize the haptic system fidelity while guaranteeing human-robot interaction stability despite the potential existence of delays and a non-passive environment. The controller is termed grasp-based passivity signature map stabilizer. If the user provides minimum to no energy absorption during the interaction, the controller makes the force reflection gate tight to guarantee stability. However, when the user demonstrates high capability in absorbing interaction energy, the controller allows the forces to be reflected. The grasp-based passivity signature map stabilizer is an alternative for both conventional stabilizers of haptic/telerobotic systems and fixed conservative force limits in rehabilitation systems where patient-robot interaction safety is a crucial requirement. This provides the practical motivation for this work. Experimental results are presented.

@article{paul_2017,
title = {A method for bidirectional active control of structures},
author = {Paul, S.; Yu, W.},
journal = {Journal of Vibration and Control},
year = {2017},
institution = {Departamento de Control Automatico, CINVESTAV-IPN (National Polytechnic Institute), Mexico City, Mexico},
abstract = {Proportional-derivative (PD) and proportional-integral-derivative (PID) controllers are popular control algorithms in industrial applications, especially in structural vibration control. In this paper, the designs of two dampers, namely the horizontal actuator and torsional actuator, are combined for the lateral and torsional vibrations of the structure. The standard PD and PID controllers are utilized for active vibration control. The sufficient conditions for asymptotic stability of these controllers are validated by utilizing the Lyapunov stability theorem. An active vibration control system with two floors equipped with a horizontal actuator and a torsional actuator is installed to carry out the experimental analysis. The experimental results show that bidirectional active control has been achieved. },
keywords = {PID control, bidirectional control, active vibration control, stability, building structure},
language = {English},
publisher = {SAGE}
}

Proportional-derivative (PD) and proportional-integral-derivative (PID) controllers are popular control algorithms in industrial applications, especially in structural vibration control. In this paper, the designs of two dampers, namely the horizontal actuator and torsional actuator, are combined for the lateral and torsional vibrations of the structure. The standard PD and PID controllers are utilized for active vibration control. The sufficient conditions for asymptotic stability of these controllers are validated by utilizing the Lyapunov stability theorem. An active vibration control system with two floors equipped with a horizontal actuator and a torsional actuator is installed to carry out the experimental analysis. The experimental results show that bidirectional active control has been achieved.

@article{alibeji3_2017,
title = {A Modified Dynamic Surface Controller for Delayed Neuromuscular Electrical Stimulation},
author = {Alibeji, N.; Kirsch, N.; Dicianno, B.; Sharma, N.},
journal = {IEEE/ASME Transactions on Mechatronics},
year = {2017},
institution = {Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA,USA},
abstract = {A widely accepted model of muscle force generation during neuromuscular electrical stimulation (NMES) is a second-order nonlinear musculoskeletal dynamics cascaded to a delayed first-order muscle activation dynamics. However, most nonlinear NMES control methods have either neglected the muscle activation dynamics or used ad hoc strategies to tackle the muscle activation dynamics, which may not guarantee control stability. We hypothesized that a nonlinear control design that includes muscle activation dynamics can improve the control performance. In this paper, a dynamic surface control (DSC) approach was used to design a PID-based NMES controller that compensates for EMD in the activation dynamics. Because the muscle activation is unmeasurable, a model based estimator was used to estimate the muscle activation in realtime. The Lyapunov stability analysis confirmed that the newly developed controller achieves uniformly ultimately bounded (SGUUB) tracking for the musculoskeletal system. Experiments were performed on two able-bodied subjects and one spinal cord injury subject using a modified leg extension machine. These experiments illustrate the performance of the new controller and compare it to a previous PID-DC controller that did not consider muscle activation dynamics in the control design. These experiments support our hypothesis that a control design that includes muscle activation improves the NMES control performance. },
issn = {1083-4435},
keywords = {Muscles, Dynamics, Delays, Control design, Stability analysis, Knee},
language = {English},
publisher = {IEEE}
}

A widely accepted model of muscle force generation during neuromuscular electrical stimulation (NMES) is a second-order nonlinear musculoskeletal dynamics cascaded to a delayed first-order muscle activation dynamics. However, most nonlinear NMES control methods have either neglected the muscle activation dynamics or used ad hoc strategies to tackle the muscle activation dynamics, which may not guarantee control stability. We hypothesized that a nonlinear control design that includes muscle activation dynamics can improve the control performance. In this paper, a dynamic surface control (DSC) approach was used to design a PID-based NMES controller that compensates for EMD in the activation dynamics. Because the muscle activation is unmeasurable, a model based estimator was used to estimate the muscle activation in realtime. The Lyapunov stability analysis confirmed that the newly developed controller achieves uniformly ultimately bounded (SGUUB) tracking for the musculoskeletal system. Experiments were performed on two able-bodied subjects and one spinal cord injury subject using a modified leg extension machine. These experiments illustrate the performance of the new controller and compare it to a previous PID-DC controller that did not consider muscle activation dynamics in the control design. These experiments support our hypothesis that a control design that includes muscle activation improves the NMES control performance.

@article{elumalai_2017,
title = {A new algebraic LQR weight selection algorithm for tracking control of 2 DoF torsion system},
author = {Elumalai V.K.; Subramanian, R.G.},
journal = {Archives of Electrical Engineering},
year = {2017},
volume = {66},
number = {1},
institution = {VIT University, India; Eindhoven University of Technology, The Netherlands},
abstract = {This paper proposes a novel linear quadratic regulator (LQR) weight selection algorithm by synthesizing the algebraic Riccati equation (ARE) with the Lagrange multiplier method for command following applications of a 2 degree of freedom (DoF) torsion system. The optimal performance of LQR greatly depends on the elements of weighting matrices Q and R. However, normally these weighting matrices are chosen by a trial and error approach which is not only time consuming but cumbersome. Hence, to address this issue, blending the design criteria in time domain with the ARE, we put forward an algebraic weight selection algorithm, which makes the LQR design both simple and modular. Moreover, to estimate the velocity of a servo angle, a high gain observer (HGO) is designed and integrated with the LQR control scheme. The efficacy of the proposed control scheme is tested on a benchmark 2 DoF torsion system for a trajectory tracking application. Both the steady state and dynamic characteristics of the proposed controller are assessed. The experimental results accentuate that the proposed HGO based LQR scheme can guarantee the system to attain the design requirements with minimal vibrations and tracking errors. },
keywords = {ARE, high gain observer, LQR, Q and R matrices, 2 DoF torsion system, trajectory tacking},
language = {English}
}

This paper proposes a novel linear quadratic regulator (LQR) weight selection algorithm by synthesizing the algebraic Riccati equation (ARE) with the Lagrange multiplier method for command following applications of a 2 degree of freedom (DoF) torsion system. The optimal performance of LQR greatly depends on the elements of weighting matrices Q and R. However, normally these weighting matrices are chosen by a trial and error approach which is not only time consuming but cumbersome. Hence, to address this issue, blending the design criteria in time domain with the ARE, we put forward an algebraic weight selection algorithm, which makes the LQR design both simple and modular. Moreover, to estimate the velocity of a servo angle, a high gain observer (HGO) is designed and integrated with the LQR control scheme. The efficacy of the proposed control scheme is tested on a benchmark 2 DoF torsion system for a trajectory tracking application. Both the steady state and dynamic characteristics of the proposed controller are assessed. The experimental results accentuate that the proposed HGO based LQR scheme can guarantee the system to attain the design requirements with minimal vibrations and tracking errors.

This paper studies the derivation of kinematic and dynamic models of a newly developed active ankle foot orthosis (AFO) that was designated for testing gait-assistive compliance control algorithms. The AFO is characterized with a closed-loop chain structure and powered by a linear ServoTube motor making it very fast and responsive. The paper first derives kinematic and dynamic models for the AFO. Then, a torque controller is developed based on the dynamic model of the AFO and it is shown that the AFO is able to track the position and velocity of the desired trajectory with a satisfactory accuracy.

@article{eris_2017,
title = {A New Delayed Resonator Design Approach for Extended Operable Frequency Range},
author = {Eris, O.; Alikoc, B.; Ergenc, A.F.},
journal = {Journal of Vibration and Acoustics},
year = {2017},
institution = {Istanbul Technical University, Turkey; Czech Technical University in Prague, Czech Republic},
abstract = {The operable frequency range of the Delayed Resonators (DR) is known to be narrow due to stability issues. This study presents a novel approach for DR design with a combined feedback strategy that consists of a delayed velocity and non-delayed position feedback to extend the operable frequency range of the DR method. The non-delayed position feedback is used to alter the natural frequency of the DR artificially while delayed velocity feedback is employed to tune the frequency of DR matching with the undesired vibrations. The proposed method also introduces an optimization parameter that provides freedom for the designer to obtain fast vibration suppression while improving the stability range of the DR. An optimization approach is also provided within the scope of this study. Theoretical findings are verified over an experiment utilizing the active suspension system of the Quanser© Company. },
keywords = {Design, Feedback, Stability, Optimization, Vibration, Vibration suppression, Suspension systems},
language = {English},
publisher = {ASME}
}

The operable frequency range of the Delayed Resonators (DR) is known to be narrow due to stability issues. This study presents a novel approach for DR design with a combined feedback strategy that consists of a delayed velocity and non-delayed position feedback to extend the operable frequency range of the DR method. The non-delayed position feedback is used to alter the natural frequency of the DR artificially while delayed velocity feedback is employed to tune the frequency of DR matching with the undesired vibrations. The proposed method also introduces an optimization parameter that provides freedom for the designer to obtain fast vibration suppression while improving the stability range of the DR. An optimization approach is also provided within the scope of this study. Theoretical findings are verified over an experiment utilizing the active suspension system of the Quanser© Company.

@conference{bucak_2017,
title = {A new design concept of magnetically levitated 4 pole hybrid mover driven by linear motor},
author = {Bucak, M.; Bozkurt, A.F.; Erkan, K.; Uvet, H.},
booktitle = {2017 IEEE International Conference on Robotics and Automation (ICRA)},
year = {2017},
institution = {Yıldız Technical University, Istanbul, Turkey},
abstract = {This paper reports a new design topology of 4 pole hybrid electromagnetic levitation system in conjunction with linear synchronous motor. The mover, 4 pole hybrid electromagnet, is levitated underneath of the linear motor with zero power control algorithm. Propulsion and one-dimensional planar motion of the hybrid electromagnet is provided by the vector controlled linear motor. The new design of 4 pole hybrid electromagnet has several improvements over older systems, such as weight reduction and less material usage. Diagonal drive integration of mover and linear motor is proposed and experimental results are presented. },
keywords = {Permanent magnet motors, Induction motors, Synchronous motors, Coils, Magnetic levitation, Magnetic cores},
language = {English},
publisher = {IEEE}
}

This paper reports a new design topology of 4 pole hybrid electromagnetic levitation system in conjunction with linear synchronous motor. The mover, 4 pole hybrid electromagnet, is levitated underneath of the linear motor with zero power control algorithm. Propulsion and one-dimensional planar motion of the hybrid electromagnet is provided by the vector controlled linear motor. The new design of 4 pole hybrid electromagnet has several improvements over older systems, such as weight reduction and less material usage. Diagonal drive integration of mover and linear motor is proposed and experimental results are presented.

@article{komisar_2017,
title = {A novel method for synchronizing motion capture with other data sources for millisecond-level precision},
author = {Komisar, V.; Novak, A.C.; Haycock, B.},
journal = {Gait & Posture},
year = {2017},
volume = {51},
institution = {Toronto Rehabilitation Institute, Canada; University of Toronto, Canada},
abstract = {Synchronization of multiple data collection systems is necessary for accurate temporal alignment of data, and is particularly important when considering rapid movements which occur in less than one second. This paper describes a novel method for synchronizing multiple data collection instruments including load cells and a motion capture system, using a common analog signal. An application of the synchronization method is demonstrated using biomechanical data collected during a rapid reach-to-grasp reaction, where data from motion capture and load cells are collected. Results are provided to validate and demonstrate the accuracy of the synchronization of motion capture with other data collection systems. During the reach-to-grasp trials, delays between the data collection systems ranged from 4 ms to 235 ms. The large range and variability in delay times between trials highlights the need for synchronization on a continual basis, rather than application of an average or constant value to correct for time delays between systems. },
keywords = {Motion capture, Data synchronization, Kinematics, Kinetics},
language = {English},
publisher = {Elsevier B.V.},
pages = {125-131}
}

Synchronization of multiple data collection systems is necessary for accurate temporal alignment of data, and is particularly important when considering rapid movements which occur in less than one second. This paper describes a novel method for synchronizing multiple data collection instruments including load cells and a motion capture system, using a common analog signal. An application of the synchronization method is demonstrated using biomechanical data collected during a rapid reach-to-grasp reaction, where data from motion capture and load cells are collected. Results are provided to validate and demonstrate the accuracy of the synchronization of motion capture with other data collection systems. During the reach-to-grasp trials, delays between the data collection systems ranged from 4 ms to 235 ms. The large range and variability in delay times between trials highlights the need for synchronization on a continual basis, rather than application of an average or constant value to correct for time delays between systems.

@inproceedings{zhang2_2017,
title = {A Novel Sliding Mode Control Algorithm for a Servo Gantry with Guaranteed Transient Performance},
author = {Zhang, Y.; Yan, P.},
booktitle = {Proceedings of the 36th Chinese Control Conference},
year = {2017},
institution = {Beihang University, China; Shandong University, Jinan, China},
abstract = {This paper investigates the tracking control problems of a voice coil motor (VCM) actuated servo gantry system. A novel sliding mode disturbance observer based control algorithm is proposed to accommodate both model uncertainties and various disturbances. In the proposed control architecture, the sliding mode observer is introduced to estimate the total disturbances such that the observer error can converge to zero in a finite time, and the fast terminal sliding mode (TSM) control technique is adopted to solve the tracking problem such that the tracking error can converge to zero in a finite time. Particularly, the singularity problem in the conventional TSM systems is avoided by switching the sliding mode function between two different terminal sliding structures. The finite-time stability of the whole closed-loop system is also proved. Finally, numerical simulations and real time experiments demonstrate excellent tracking performance of the proposed criteria. },
issn = {1934-1768 },
keywords = {Finite Time Control, Sliding Mode Control, Voice Coil Motor, Motion Control},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-2918-5 }
}

This paper investigates the tracking control problems of a voice coil motor (VCM) actuated servo gantry system. A novel sliding mode disturbance observer based control algorithm is proposed to accommodate both model uncertainties and various disturbances. In the proposed control architecture, the sliding mode observer is introduced to estimate the total disturbances such that the observer error can converge to zero in a finite time, and the fast terminal sliding mode (TSM) control technique is adopted to solve the tracking problem such that the tracking error can converge to zero in a finite time. Particularly, the singularity problem in the conventional TSM systems is avoided by switching the sliding mode function between two different terminal sliding structures. The finite-time stability of the whole closed-loop system is also proved. Finally, numerical simulations and real time experiments demonstrate excellent tracking performance of the proposed criteria.

@conference{castillo2_2017,
title = {A novel technique to enlarge the maximum allowable delay bound in sampled-data systems},
author = {Castillo, O.; Benitez Perez, H.},
booktitle = {National Congress on Automatic Control 2017},
year = {2017},
institution = {Instituto de Investigaciones en Matematicas Aplicadas y en Sistemas, UNAM, Mexico},
abstract = { is well known that in physical implementation of control systems delays are induced in the dynamic of the system. Specifically, time is consumed through communication between electronic devices. Therefore, control theory requires algorithms capable of maintaining the stability of the system even if delays in the feedback are significant. So, in this work, we show that by means of a pulse control signal, we can enlarge the classic Maximum Allowable Delay Bound (MADB) on sampled-data systems. Experimental results are presented to prove the effectiveness of our technique. },
keywords = {sampled-data systems, retarded systems, impulsive systems, networked control systems},
language = {English},
pages = {312-316}
}

is well known that in physical implementation of control systems delays are induced in the dynamic of the system. Specifically, time is consumed through communication between electronic devices. Therefore, control theory requires algorithms capable of maintaining the stability of the system even if delays in the feedback are significant. So, in this work, we show that by means of a pulse control signal, we can enlarge the classic Maximum Allowable Delay
Bound (MADB) on sampled-data systems. Experimental results are presented to prove the effectiveness of our technique.

@article{alibeji2_2017,
title = {A PID-Type Robust Input Delay Compensation Method for Uncertain Euler-Lagrange Systems},
author = {Alibeji, N.; Sharma, N.},
journal = {IEEE Transactions on Control Systems Technology},
year = {2017},
institution = {Department of Mechanical Engineering and Materials Science, University of Pittsburgh, USA},
abstract = {Robust delay compensation techniques for uncertain nonlinear systems with unknown input delays are, in general, lacking. The result in this brief extends a modified proportional-integral derivative (PID)-type controller that contains a distributed delay term to Euler-Lagrange systems with an unknown constant input delay. Additive disturbances and uncertainties in the nonlinear system were considered in the control development and stability analysis. The stability analysis also hinges upon Lyapunov-Krasovskii functionals that were designed to prove semiglobal uniformly ultimately bounded tracking. Experiments on a 3-degree of freedom robot were performed to depict the performance of the new controller. },
issn = {1063-6536},
keywords = {Delay compensation, Euler-Lagrange systems, robust control, unknown input delay},
language = {English},
publisher = {IEEE}
}

Robust delay compensation techniques for uncertain nonlinear systems with unknown input delays are, in general, lacking. The result in this brief extends a modified proportional-integral derivative (PID)-type controller that contains a distributed delay term to Euler-Lagrange systems with an unknown constant input delay. Additive disturbances and uncertainties in the nonlinear system were considered in the control development and stability analysis. The stability analysis also hinges upon Lyapunov-Krasovskii functionals that were designed to prove semiglobal uniformly ultimately bounded tracking. Experiments on a 3-degree of freedom robot were performed to depict the performance of the new controller.

@article{zhao_2017,
title = {A PIMR-type Repetitive Control for a Grid-tied Inverter: Structure, Analysis, and Design},
author = {Zhao, Q.; Ye, Y.},
journal = {IEEE Transactions on Power Electronics},
year = {2017},
institution = {Nanjing University of Aeronautics and Astronautics, China},
abstract = {This paper proposes a proportional integral (inertial) multi-resonant (PIMR) type repetitive control (PIMRtype RC) scheme for a grid-tied inverter. The proposed control scheme is composed of a repetitive controller in parallel with a proportional gain for the purpose of replacing lots of parameters of the conventional proportional multi-resonant controller, and therefore, only a few parameters need to be designed. The proportional gain not only improves the dynamic response, but also enables RC to accommodate a larger RC gain, and hence a faster convergence rate. Theoretical analysis and stability analysis of PIMR-type RC are given, and then a practical step-by-step design tutorial is also provided. The experimental results validate the feasibility and outstanding performance of the proposed control scheme. },
issn = {0885-8993},
keywords = {Proportional integral multi-resonant control, grid-tied inverter, repetitive control, convergence rate},
language = {English},
publisher = {IEEE}
}

This paper proposes a proportional integral (inertial) multi-resonant (PIMR) type repetitive control (PIMRtype RC) scheme for a grid-tied inverter. The proposed control scheme is composed of a repetitive controller in parallel with a proportional gain for the purpose of replacing lots of parameters of the conventional proportional multi-resonant controller, and therefore, only a few parameters need to be designed. The proportional gain not only improves the dynamic response, but also enables RC to accommodate a larger RC gain, and hence a faster convergence rate. Theoretical analysis and stability analysis of PIMR-type RC are given, and then a practical step-by-step design tutorial is also provided. The experimental results validate the feasibility and outstanding performance of the proposed control scheme.

@conference{pyrhonen_2017,
title = {A reduced-order two-degree-of-freedom composite nonlinear feedback control for a rotary DC servo motor},
author = {Pyrhonen, V.-P.; Koivisto, H.J.; Vilkko, M.K.},
booktitle = {2017 IEEE 56th Annual Conference on Decision and Control (CDC)},
year = {2017},
institution = {Tampere University of Technology, Finland},
abstract = {We study in this paper nonlinear control of a rotary DC servo motor application. To be more specific, we design a reduced-order two-degree-of-freedom (2DOF) composite nonlinear feedback (CNF) controller for a Quanser QUBE-Servo 2 unit with a disc attachment. We compare our results with a carefully tuned proportional-derivative (PD) controller with set point weighting. Our simulation and experimental results show that the closed-loop system using 2DOF CNF controller yields much better set point tracking performance compared with the system using conventional PD-controller in terms of settling time. },
keywords = {DC motors, Feedforward systems, Servomotors, Actuators, State feedback, PD control},
language = {English},
publisher = {IEEE},
isbn = {978-1-5090-2874-0}
}

We study in this paper nonlinear control of a rotary DC servo motor application. To be more specific, we design a reduced-order two-degree-of-freedom (2DOF) composite nonlinear feedback (CNF) controller for a Quanser QUBE-Servo 2 unit with a disc attachment. We compare our results with a carefully tuned proportional-derivative (PD) controller with set point weighting. Our simulation and experimental results show that the closed-loop system using 2DOF CNF controller yields much better set point tracking performance compared with the system using conventional PD-controller in terms of settling time.

@article{atashzar_2017,
title = {A Small-Gain Approach for Non-Passive Bilateral Telerobotic Rehabilitation: Stability Analysis and Controller Synthesis},
author = {Atashzar, S.F.; Polushin, I.G.; Patel, R.V.},
journal = {IEEE Transactions on Robotics},
year = {2017},
volume = {33},
number = {1},
institution = {Department of Electrical and Computer Engineering, Western University, London, ON, Canada},
abstract = {In this paper, the design of a novel bilateral telerobotic architecture for rehabilitation purposes is proposed and the related feasibility, stability, and control challenges are studied. The objective is to incorporate the supervision of a local/remote human physiotherapist into haptics-enabled rehabilitation systems and allow the therapist to provide nonpassive nonlinear assistive/resistive forces in response to the patient's movements. This can address a challenge of conventional software-based rehabilitation systems, i.e., limited capability in adjusting the therapy. To guarantee human–robot interaction safety, a new design framework and a stabilizing controller are developed based on the small-gain approach. System stability and transparency are analyzed in the presence of the nonpassive, nonlinear, and nonautonomous behavior of the terminals (the therapist and the patient) and time-varying delays for the case of remote and cloud-based therapy. Several practical considerations have been taken into account to match the clinical needs and minimize the implementation cost. Simulation studies, practical implementation, and experimental evaluations are presented. },
issn = {1552-3098},
keywords = {Haptics, physical human–robot interaction, rehabilitation robotics, stability, telerobotics},
language = {English},
publisher = {IEEE},
pages = {49-66}
}

In this paper, the design of a novel bilateral telerobotic architecture for rehabilitation purposes is proposed and the related feasibility, stability, and control challenges are studied. The objective is to incorporate the supervision of a local/remote human physiotherapist into haptics-enabled rehabilitation systems and allow the therapist to provide nonpassive nonlinear assistive/resistive forces in response to the patient's movements. This can address a challenge of conventional software-based rehabilitation systems, i.e., limited capability in adjusting the therapy. To guarantee human–robot interaction safety, a new design framework and a stabilizing controller are developed based on the small-gain approach. System stability and transparency are analyzed in the presence of the nonpassive, nonlinear, and nonautonomous behavior of the terminals (the therapist and the patient) and time-varying delays for the case of remote and cloud-based therapy. Several practical considerations have been taken into account to match the clinical needs and minimize the implementation cost. Simulation studies, practical implementation, and experimental evaluations are presented.