@article{abdelkader_2018,
title = {Robust H ∞ gain neuro-adaptive observer design for nonlinear uncertain systems},
author = {Abdelkader, K.; Krais, B.},
journal = {Transactions of the Institute of Measurement and Control},
year = {2108},
institution = {Higher Institute of Computer Science of Mahdia, Tunisia},
abstract = {To guarantee convergent state estimates and exact approximations, it is highly desirable that observers can independently dominate the effects of unmodelled dynamics. Based on adaptive nonlinear approximation, this paper presents a robust H∞ gain neuro-adaptive observer (RH∞GNAO) design methodology for a large class of uncertain nonlinear systems in the presence of time-varying unknown parameters with bounded external disturbances on the state vector and on the output of the original system. The proposed RH∞GNAO incorporates radial basis function neural networks (RBFNNs) to approximate the unknown nonlinearities in the uncertain system. The weight dynamics of every RBFNN are adjusted online by using an adaptive projection algorithm. The asymptotic convergence of the state and parameter estimation errors is achieved by using Lyapunov cogitation under a well-defined persistent excitation condition, and without recourse to the strictly positive real condition. The repercussions of unknown disturbances are reduced by integrating an H∞ gain performance criterion into the proposed estimation approach. The condition imposed by this proposed observer approach, such that all estimated signals are uniformly ultimately bounded, is expressed in the form of the linear matrix inequality problem and warrants the demanded performances. To evaluate the performance of the proposed observer, various simulations are presented. },
keywords = {Uncertain nonlinear systems, Lyapunov stability, disturbances, neural networks, adaptive observer, H-infinity, linear matrix inequality},
language = {English},
publisher = {SAGE}
}

To guarantee convergent state estimates and exact approximations, it is highly desirable that observers can independently dominate the effects of unmodelled dynamics. Based on adaptive nonlinear approximation, this paper presents a robust H∞ gain neuro-adaptive observer (RH∞GNAO) design methodology for a large class of uncertain nonlinear systems in the presence of time-varying unknown parameters with bounded external disturbances on the state vector and on the output of the original system. The proposed RH∞GNAO incorporates radial basis function neural networks (RBFNNs) to approximate the unknown nonlinearities in the uncertain system. The weight dynamics of every RBFNN are adjusted online by using an adaptive projection algorithm. The asymptotic convergence of the state and parameter estimation errors is achieved by using Lyapunov cogitation under a well-defined persistent excitation condition, and without recourse to the strictly positive real condition. The repercussions of unknown disturbances are reduced by integrating an H∞ gain performance criterion into the proposed estimation approach. The condition imposed by this proposed observer approach, such that all estimated signals are uniformly ultimately bounded, is expressed in the form of the linear matrix inequality problem and warrants the demanded performances. To evaluate the performance of the proposed observer, various simulations are presented.

@inproceedings{kasimzade_2019,
title = {Analytical and Experimental Modal Analysis of a Model Cold Formed Steel (CFS) Structures Using Microtremor Excitation},
author = {Kasimzade A.A.; Tuhta S.; Atmaca G.; Ozdemir S.},
booktitle = {Seismic Isolation, Structural Health Monitoring, and Performance Based Seismic Design in Earthquake Engineering},
year = {2019},
institution = {Ondokuz Mayis University, Turkey},
abstract = {In this study was investigated the possibility of using the recorded micro-tremor data on ground level as ambient vibration input excitation data for investigation and application Operational Modal Analysis (OMA) on the bench-scale earthquake simulator (The Quanser Shake Table) for model cold formed steel (cfs) structures. As known OMA methods (such as EFDD, SSI and so on) are supposed to deal with the ambient responses. For this purpose, analytical and experimental modal analysis of a model (cfs) structure for dynamic characteristics was evaluated. 3D Finite element model of the building was evaluated for the model (cfs) structure based on the design drawing. Ambient excitation was provided by shake table from the recorded micro tremor ambient vibration data on ground level. Enhanced Frequency Domain Decomposition is used for the output-only modal identification. From this study, best correlation is found between mode shapes. Natural frequencies and analytical frequencies in average (only) 2.99% are differences. },
keywords = {Experimental modal analysis, Modal parameter, EFDD, Shake table },
language = {English},
publisher = {Springer, Cham},
isbn = {978-3-319-93156-2},
pages = {217-231}
}

In this study was investigated the possibility of using the recorded micro-tremor data on ground level as ambient vibration input excitation data for investigation and application Operational Modal Analysis (OMA) on the bench-scale earthquake simulator (The Quanser Shake Table) for model cold formed steel (cfs) structures. As known OMA methods (such as EFDD, SSI and so on) are supposed to deal with the ambient responses. For this purpose, analytical and experimental modal analysis of a model (cfs) structure for dynamic characteristics was evaluated. 3D Finite element model of the building was evaluated for the model (cfs) structure based on the design drawing. Ambient excitation was provided by shake table from the recorded micro tremor ambient vibration data on ground level. Enhanced Frequency Domain Decomposition is used for the output-only modal identification. From this study, best correlation is found between mode shapes. Natural frequencies and analytical frequencies in average (only) 2.99% are differences.

@article{xin_2019,
title = {Input-output tracking control of a 2-DOF laboratory helicopter with improved algebraic differential estimation},
author = {Xin, Y.; Qin, Z.-C.; Sun, J.-Q.},
journal = {Mechanical Systems and Signal Processing},
year = {2019},
month = {02},
volume = {116},
institution = {Tianjin University, China; Shandong University of Technology, China; University of California, Merced, USA},
abstract = {This paper presents a study on input-output feedback linearization control (OFLC) of a laboratory twin rotor helicopter system based on an improved algebraic differential estimation approach. In the previous algebraic differential estimation studies, the reset time T(r) is always selected cautiously in a narrow range because the estimation accuracy is very sensitive to T(r). Too small or too large T(r) reset time will lead to an inaccurate estimation of signal derivatives. In this paper, we first propose a new resetting and overlapping strategy for improving the robustness of the estimation algorithm. Then it is used to estimate the velocities of pitch and yaw motions. The OFLC is designed and verified by letting the output signals track different periodic reference signals. Both simulation and experimental results show better control performance as compared with the LQR design. },
keywords = {Output feedback linearization control (OFLC), Algebraic differential estimation, Trajectory tracking 2-DOF helicopter},
language = {English},
publisher = {Elsevier Ltd.},
pages = {843-857}
}

This paper presents a study on input-output feedback linearization control (OFLC) of a laboratory twin rotor helicopter system based on an improved algebraic differential estimation approach. In the previous algebraic differential estimation studies, the reset time T(r) is always selected cautiously in a narrow range because the estimation accuracy is very sensitive to T(r). Too small or too large T(r) reset time will lead to an inaccurate estimation of signal derivatives. In this paper, we first propose a new resetting and overlapping strategy for improving the robustness of the estimation algorithm. Then it is used to estimate the velocities of pitch and yaw motions. The OFLC is designed and verified by letting the output signals track different periodic reference signals. Both simulation and experimental results show better control performance as compared with the LQR design.

@conference{lai_2018,
title = {},
author = {Lai, W.; Cao, L.; Xu, Z.},
booktitle = {2018 IEEE International Conference on Robotics and Automation (ICRA)},
year = {2018},
institution = {Nanyang Technological University, Singapore},
abstract = {Accurate haptic feedback is a critical challenge for surgical robots, especially for flexible endoscopic surgical robots whose transmission systems are Tendon-Sheath Mechanisms (TSMs) with highly nonlinear friction profiles and force hysteresis. For distal end haptic sensing of TSMs, this paper, for the first time, proposes to measure the compression force on the sheath at the distal end so that the tension force on the tendon, which equals the compression force on the sheath, can be obtained. A new force sensor, i.e., a nitinol tube attached with an optical Fiber Bragg Grating (FBG) fiber, is proposed to measure the compression force on the sheath. This sensor, with similar diameter and configuration (hollow) as the sheath, can be compactly integrated with TSMs and surgical end-effectors. In this paper, mechanics analysis and verification tests are presented to reveal the relationship between the tension force on the tendon and the compression force on the sheath. The proposed force sensor was calibrated in tests with a sensitivity of 24.28 pm/N and integrated with a tendon-sheath driven grasper to demonstrate the effectiveness of the proposed approach and sensor. The proposed approach and sensor can also be applied for a variety of TSMs-driven systems, such as robotic fingers/hands, wearable devices, and rehabilitation devices. },
issn = {2577-087X },
keywords = {Haptic Sensing, Fiber Bragg Gratings, Flexible Surgical Endoscopic Robot, Tendon-Sheath Mechanisms},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-3082-2 }
}

Accurate haptic feedback is a critical challenge for surgical robots, especially for flexible endoscopic surgical robots whose transmission systems are Tendon-Sheath Mechanisms (TSMs) with highly nonlinear friction profiles and force hysteresis. For distal end haptic sensing of TSMs, this paper, for the first time, proposes to measure the compression force on the sheath at the distal end so that the tension force on the tendon, which equals the compression force on the sheath, can be obtained. A new force sensor, i.e., a nitinol tube attached with an optical Fiber Bragg Grating (FBG) fiber, is proposed to measure the compression force on the sheath. This sensor, with similar diameter and configuration (hollow) as the sheath, can be compactly integrated with TSMs and surgical end-effectors. In this paper, mechanics analysis and verification tests are presented to reveal the relationship between the tension force on the tendon and the compression force on the sheath. The proposed force sensor was calibrated in tests with a sensitivity of 24.28 pm/N and integrated with a tendon-sheath driven grasper to demonstrate the effectiveness of the proposed approach and sensor. The proposed approach and sensor can also be applied for a variety of TSMs-driven systems, such as robotic fingers/hands, wearable devices, and rehabilitation devices.

@article{furtado2_2018,
title = {3-D UAV Path Planning in a Cluttered Environment using PSO},
author = {Furtado, J.S.; Liu, H.H.T.},
year = {2018},
institution = {University of Toronto Institute for Aerospace Studies, Canada},
abstract = {The use of Unmanned Aerial Vehicles (UAVs) in a wide variety of civilian and military applications such as surveillance, inspection, and precision agriculture has become increasingly popular over the last few years. The performance of the mission is based on the time taken to complete the mission. Path planning is therefore a key component in most UAV applications. The main objective of this work is to plan efficient three-dimensional (3-D) paths for a UAV to get from its start location to its goal location avoiding any collision with obstacles in the environment. Based on literature review, Swarm Intelligence (SI) based algorithm, Particle Swarm Optimisation (PSO) is utilised to generate collision free trajectories for a UAV in a cluttered environment. SI is an innovative distributed and intelligent paradigm used for solving optimization problems. It is inherently robust, scalable and stochastic, inspired by the collective behaviour seen in biological systems. The objective function being optimised is the length of the path to be own by the UAV subject to collision constraints. The algorithm generates discrete waypoints using which a smooth flyable path is generated by spline interpolation. Simulation as well as experimental results are shown to demonstrate the results of this work after testing in different scenarios. },
language = {English}
}

The use of Unmanned Aerial Vehicles (UAVs) in a wide variety of civilian and military applications such as surveillance, inspection, and precision agriculture has become increasingly popular over the last few years. The performance of the mission is based on the time taken to complete the mission. Path planning is therefore a key component in most UAV applications. The main objective of this work is to plan efficient three-dimensional (3-D) paths for a UAV to get from its start location to its goal location avoiding any collision with obstacles in the environment. Based on literature review, Swarm Intelligence (SI) based algorithm, Particle Swarm Optimisation (PSO) is utilised to generate collision free trajectories for a UAV in a cluttered environment. SI is an innovative distributed and intelligent paradigm used for solving optimization problems. It is inherently robust, scalable and stochastic, inspired by the collective behaviour seen in biological systems. The objective function being optimised is the length of the path to be own by the UAV subject to collision constraints. The algorithm generates discrete waypoints using which a smooth flyable path is generated by spline interpolation. Simulation as well as experimental results are shown to demonstrate the results of this work after testing in different scenarios.

@article{kammer_2018,
title = {A Data-Driven Fixed-Structure Control Design Method with Application to a 2-DOF Gyroscope},
author = {Kammer, C.; Karimi, A.},
year = {2018},
institution = {Laboratoire d’Automatique, Ecole Polytechnique Federale de Lausanne, Switzerland},
abstract = {This paper presents the practical aspects and application of a novel data-driven, fixed-structure, robust control design method. Only the frequency response data of the system is needed for the design, and no parametric model is required. The method can be used to design fully parametrized continuous- or discrete-time matrix transfer function controllers. The control performance is specified as constraints on the H-infinity or H2 norm of weighted sensitivity functions, and a convex formulation of the robust design problem is proposed. An application of the presented method is explored on an experimental setup, where a multivariable controller for a gyroscope is designed based only on the measured frequency response of the system. },
language = {English}
}

This paper presents the practical aspects and application of a novel data-driven, fixed-structure, robust control design method. Only the frequency response data of the system is needed for the design, and no parametric model is required. The method can be used to design fully parametrized continuous- or discrete-time matrix transfer function controllers. The control performance is specified as constraints on the H-infinity or H2 norm of weighted sensitivity functions, and a convex formulation of the robust design problem is proposed. An application of the presented method is explored on an experimental setup, where a multivariable controller for a gyroscope is designed based only on the measured frequency response of the system.

@conference{abdullah_2018,
title = {A Formal Sensitivity Analysis for Laguerre Based Predictive Functional Control},
author = {Abdullah, M.; Rossiter, J.A.},
booktitle = {Control 2018 - 12th UKACC International Conference on Control},
year = {2018},
institution = {University of Sheffield, UK},
abstract = {A Laguerre Predictive Functional Control (LPFC) is a simple input shaping method, which can improve the prediction consistency and closed-loop performance of the conventional approach (PFC). However, it is well-known that an input shaping method, in general, will affect the loop sensitivity of a system. Hence, this paper presents a formal sensitivity analysis of LPFC by considering the effect of noise, unmeasured disturbance and parameter uncertainty. Sensitivity plots from bode diagrams and closed-loop simulation are used to illustrate the controller robustness and indicate that although LPFC often provides a better closed-loop tracking response and disturbance rejection, this may involve some trade-off with the sensitivity to noise and parameter uncertainty. Finally, to validate the practicality of the results, the sensitivity of the LPFC control law is illustrated on real-time laboratory hardware. },
keywords = {Predictive Control, PFC, Sensitivity Analysis, Laguerre function, Parameter Uncertainty, Noise, Disturbance},
language = {English},
publisher = {IEEE}
}

A Laguerre Predictive Functional Control (LPFC) is a simple input shaping method, which can improve the prediction consistency and closed-loop performance of the conventional approach (PFC). However, it is well-known that an input shaping method, in general, will affect the loop sensitivity of a system. Hence, this paper presents a formal sensitivity analysis of LPFC by considering the effect of noise, unmeasured disturbance and parameter uncertainty. Sensitivity plots from bode diagrams and closed-loop simulation are used to illustrate the controller robustness and indicate that although LPFC often provides a better closed-loop tracking response and disturbance rejection, this may involve some trade-off with the sensitivity to noise and parameter uncertainty. Finally, to validate the practicality of the results, the sensitivity of the LPFC control law is illustrated on real-time laboratory hardware.

@article{zhao_2018,
title = {A Frequency Adaptive PIMR-Type Repetitive Control for a Grid-Tied Inverter},
author = {Zhao, Q.; Chen, S.; Wen, S.},
year = {2018},
institution = {Zhongyuan University of Technology, China},
abstract = { A proportional integral multiresonant-type repetitive control (PIMR-type RC) has not only a better harmonic suppressing performance but also a faster error convergence rate. However, the harmonics suppressing performance of PIMRtype RC will significantly decrease when the grid fundamental frequency fluctuates in a large range. In this paper, an improved frequency adaptive PIMR-type RC (FA-PIMR-type RC) is proposed to cope with the frequency fluctuation in a large range. The improved PIMR-type RC is based on fractional delay filter which can be approximately realized by finite impulse response (FIR) filter. The varying fractional delay filters ensure that the resonant frequencies can match the actual reference frequency and harmonic frequencies. The synthesis, stability analysis, and parameters design criteria of the proposed FA-PIMR-type RC are given in this paper. The simulation and experimental results show that the improved PIMR-type RC can track grid reference signal, suppress harmonic signals and have good error convergence rate under grid frequency fluctuation. },
issn = {2169-3536 },
keywords = {Grid-tied inverter, repetitive control (RC), FIR filter, frequency adaptive PIMR-type RC},
language = {English},
publisher = {IEEE}
}

A proportional integral multiresonant-type repetitive control (PIMR-type RC) has not only a better harmonic suppressing performance but also a faster error convergence rate. However, the harmonics suppressing performance of PIMRtype RC will significantly decrease when the grid fundamental frequency fluctuates in a large range. In this paper, an improved frequency adaptive PIMR-type RC (FA-PIMR-type RC) is proposed to cope with the frequency fluctuation in a large range. The improved PIMR-type RC is based on fractional delay filter which can be approximately realized by finite impulse response (FIR) filter. The varying fractional delay filters ensure that the resonant frequencies can match the actual reference frequency and harmonic frequencies. The synthesis, stability analysis, and parameters design criteria of the proposed FA-PIMR-type RC are given in this paper. The simulation and experimental results show that the improved PIMR-type RC can track grid reference signal, suppress harmonic signals and have good error convergence rate under grid frequency fluctuation.

@article{rose_2018,
title = {A Hybrid Rigid-Soft Hand Exoskeleton to Assist Functional Dexterity},
author = {Rose, C.; O'Malley, M.},
journal = {IEEE Robotics and Automation Letters},
year = {2018},
institution = {Rice University, TX, USA},
abstract = { A hybrid hand exoskeleton, leveraging rigid and soft elements, has been designed to serve as an assistive device to return the ability to perform activities of daily living (ADLs) and improve quality of life (QOL) for a broad population with hand impairment. This glove-like exoskeleton, the SeptaPose Assistive and Rehabilitative (SPAR) Glove, is underactuated, enabling seven hand poses which support most ADLs. The device resides on the spectrum between traditional rigid devices and the latest soft robotic designs. It includes novel ergonomic elements for power transmission and additional features to enable self-donning and doffing. Embedded sensors enable pose estimation and intent detection for intuitive control of the glove. In this paper, we summarize the overall design of the glove, and present details of the novel rigid palm bar and hyperextension prevention elements. We characterize the grasp force and range of motion (ROM) of the glove, and present initial feedback from an end-user. The SPAR Glove meets or exceeds the functional requirements of ADLs for both ROM and grasp force. Additionally, the glove exceeds the grasp force capabilities of comparable devices, while simultaneously offering the highest number of poses. In addition to its role as an assistive device, the SPAR Glove exoskeleton has the potential to provide "hands-in" rehabilitation centered on performing functional tasks. In the near term, the glove is a highly capable prototype for exploring hybrid assistive device design, intent detection, and user interface research. },
issn = {2377-3766 },
keywords = {Physically Assistive Devices, Wearable Robots, Rehabilitation Robotics, Prosthetics and Exoskeletons},
language = {English}
}

A hybrid hand exoskeleton, leveraging rigid and soft elements, has been designed to serve as an assistive device to return the ability to perform activities of daily living (ADLs) and improve quality of life (QOL) for a broad population with hand impairment. This glove-like exoskeleton, the SeptaPose Assistive and Rehabilitative (SPAR) Glove, is underactuated, enabling seven hand poses which support most ADLs. The device resides on the spectrum between traditional rigid devices and the latest soft robotic designs. It includes novel ergonomic elements for power transmission and additional features to enable self-donning and doffing. Embedded sensors enable pose estimation and intent detection for intuitive control of the glove. In this paper, we summarize the overall design of the glove, and present details of the novel rigid palm bar and hyperextension prevention elements. We characterize the grasp force and range of motion (ROM) of the glove, and present initial feedback from an end-user. The SPAR Glove meets or exceeds the functional requirements of ADLs for both ROM and grasp force. Additionally, the glove exceeds the grasp force capabilities of comparable devices, while simultaneously offering the highest number of poses. In addition to its role as an assistive device, the SPAR Glove exoskeleton has the potential to provide "hands-in" rehabilitation centered on performing functional tasks. In the near term, the glove is a highly capable prototype for exploring hybrid assistive device design, intent detection, and user interface research.

This article presents a model-based velocity controller able to induce a chaotic motion on n-degrees of freedom flexible joint robot manipulators. The proposed controller allows the velocity link vector of a robot manipulator to track an arbitrary, chaotic reference vector field. A rigorous theoretical analysis based on Lyapunov’s theory is used to prove the asymptotic stability of the tracking error signals when using the proposed controller, which implies that a chaotic motion is induced to the robotic system. Experimental results are provided using a flexible joint robot manipulator of two degrees of freedom. Finally, by using Poincaré maps and Lyapunov exponents, it is shown that the behavior exhibited by the robot joint positions is chaotic.

@article{ghannadi_2018,
title = {A modified homotopy optimization for parameter identification in dynamic systems with backlash discontinuity},
author = { Ghannadi, B.; Razavian, R.S.; McPhee, J.},
journal = {Nonlinear Dynamics},
year = {2018},
institution = {University of Waterloo, Canada},
abstract = {Model-based control considers system dynamics to solve challenging control problems; recently, the amount of activity in developing model-based controllers is growing, specifically in rehabilitation robotics. The performance of this controller depends on how accurate the system dynamics has been modeled. Dynamic parameter identification (DPI) of the systems is required for optimal performance of the model-based controller. Current DPI methods are more suitable for systems with continuous dynamics. If any type of discontinuity (e.g., backlash) is present in the system, the DPI may have numerical problems for convergence. In this work, we propose a modified homotopy optimization to identify parameters of a system with mechanical discontinuity (i.e., backlash). The performance of the proposed method was first evaluated through a computer simulation on a system with sandwiched backlash. Results of the DPI showed that the proposed homotopy optimization can identify the discontinuous system parameters with a good accuracy. It was found that ignoring the backlash in the system dynamics imposes large errors in the system DPI. After verifying the proposed method using computer simulations, the DPI was implemented to identify the parameters of a rehabilitation robot with actuator backlash. The proposed method provided a better estimate of the system parameters compared to the no-backlash DPI of the experimental robot. Despite the noise in velocity and acceleration due to the numerical differentiation of the sampled angle measurements, the forward dynamics results are quite accurate for all of the tested configurations with the discontinuous backlash model. },
issn = {0924-090X},
keywords = {Parameter identification, System dynamics, Sandwiched backlash, Homotopy optimization, Rehabilitation robot },
language = {English},
publisher = {Springer Netherlands}
}

Model-based control considers system dynamics to solve challenging control problems; recently, the amount of activity in developing model-based controllers is growing, specifically in rehabilitation robotics. The performance of this controller depends on how accurate the system dynamics has been modeled. Dynamic parameter identification (DPI) of the systems is required for optimal performance of the model-based controller. Current DPI methods are more suitable for systems with continuous dynamics. If any type of discontinuity (e.g., backlash) is present in the system, the DPI may have numerical problems for convergence. In this work, we propose a modified homotopy optimization to identify parameters of a system with mechanical discontinuity (i.e., backlash). The performance of the proposed method was first evaluated through a computer simulation on a system with sandwiched backlash. Results of the DPI showed that the proposed homotopy optimization can identify the discontinuous system parameters with a good accuracy. It was found that ignoring the backlash in the system dynamics imposes large errors in the system DPI. After verifying the proposed method using computer simulations, the DPI was implemented to identify the parameters of a rehabilitation robot with actuator backlash. The proposed method provided a better estimate of the system parameters compared to the no-backlash DPI of the experimental robot. Despite the noise in velocity and acceleration due to the numerical differentiation of the sampled angle measurements, the forward dynamics results are quite accurate for all of the tested configurations with the discontinuous backlash model.

@article{zhou_2018,
title = {A Multi-Time-Scale Finite Time Controller for the Quadrotor UAVs with Uncertainties},
author = {Zhou, Z.; Wang, H.; Hu, Z.; Wang, Y.; Wang, H.},
journal = {Journal of Intelligent & Robotic Systems},
year = {2018},
institution = {Yanshan University, China},
abstract = {A control method with a multi-time-scale structure is proposed to perform finite time motion control of the quadrotor unmanned aerial vehicles (UAVs) with uncertainties. In order to facilitate the controller-design, finite time extended state observer (ESO) in the first and second time scales is applied to estimate the system uncertainties; the attitude controllers and the height controller are designed for finite time stabilization of the equilibriums in the third time scale; and finally, the output feedback technique is utilized to design the horizontal auxiliary controllers, meanwhile the reference angles are settled for the attitude dynamics in the fourth and slowest time scale. It allows us to analyze the system dynamics in each time scale independently, and conclusions on finite time stabilization are achieved gradually with a large region of attraction. Simulation and experimental results on the Qball2 platform are given to verify the efficacy of the strategy and establish the feasibility of implementation. },
issn = {0921-0296},
keywords = {Finite time control, Extended state observer, Multi-time-scale, System uncertainties, Quadrotor UAVs},
language = {English},
publisher = {Springer Netherlands}
}

A control method with a multi-time-scale structure is proposed to perform finite time motion control of the quadrotor unmanned aerial vehicles (UAVs) with uncertainties. In order to facilitate the controller-design, finite time extended state observer (ESO) in the first and second time scales is applied to estimate the system uncertainties; the attitude controllers and the height controller are designed for finite time stabilization of the equilibriums in the third time scale; and finally, the output feedback technique is utilized to design the horizontal auxiliary controllers, meanwhile the reference angles are settled for the attitude dynamics in the fourth and slowest time scale. It allows us to analyze the system dynamics in each time scale independently, and conclusions on finite time stabilization are achieved gradually with a large region of attraction. Simulation and experimental results on the Qball2 platform are given to verify the efficacy of the strategy and establish the feasibility of implementation.

@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.

@conference{frazelle_2018,
title = {A Nonlinear Control Strategy for Extensible Continuum Robots},
author = {Frazelle, C.G.; Kapadia, A.D.; Walker, I.D.},
booktitle = {2018 IEEE International Conference on Robotics and Automation (ICRA)},
year = {2018},
institution = {Clemson University, USA},
abstract = {In this paper, we describe a novel nonlinear control strategy for the closed-loop control of extensible continuum robots. Previous attempts at controlling continuum robots have proved difficult due to the complexity of their system dynamics. Taking advantage of a previously developed dynamic model for a three-section, planar, continuum manipulator, we develop an adaptation-based control law. We present simulation results of a set-point tracking between a rigid-link control device and an extensible continuum manipulator. Experimental results of the controller implemented on a six degree-of-freedom continuum robot are also presented. },
issn = {2577-087X },
keywords = {closed loop systems, control system synthesis, manipulators, nonlinear control systems, PD control, variable structure systems},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-3082-2}
}

In this paper, we describe a novel nonlinear control strategy for the closed-loop control of extensible continuum robots. Previous attempts at controlling continuum robots have proved difficult due to the complexity of their system dynamics. Taking advantage of a previously developed dynamic model for a three-section, planar, continuum manipulator, we develop an adaptation-based control law. We present simulation results of a set-point tracking between a rigid-link control device and an extensible continuum manipulator. Experimental results of the controller implemented on a six degree-of-freedom continuum robot are also presented.

@conference{xie_2018,
title = {A position estimation and control system for the quadrotor in GPS-deny situation based on FAST detection and optical flow},
author = {Xie, N.; Li, X.; Yu, Y.},
booktitle = {2018 33rd Youth Academic Annual Conference of Chinese Association of Automation (YAC)},
year = {2018},
institution = {University of Science and Technology Beijing, China},
abstract = {Position estimation based on vision system is essential for a UAV in the GPS-deny situation to realize the position control. However, in the practice, the hardware and software are not ideal for the UAV to carry when flying. Thus, this study is aiming at the problem of position estimation and control for a quadrotor UAV based on vision. Firstly, a position estimation algorithm based on vision is proposed, in which optical flow is used combining with FAST corner detection to ensure the real-time performance of the estimation in condition with limited loader. Meanwhile, a robust controller with nonlinear compensating input has been designed in this paper to deal with the position control for the quadrotor. A simulation is presented in this paper to verify the performance of the controller. Moreover, an experiment is also utilized in this paper to show that the method is practical and with high performance. },
keywords = {quadrotor UAV, optical flow, FAST detection, sliding model control, position estimation and control},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-7256-3 }
}

Position estimation based on vision system is essential for a UAV in the GPS-deny situation to realize the position control. However, in the practice, the hardware and software are not ideal for the UAV to carry when flying. Thus, this study is aiming at the problem of position estimation and control for a quadrotor UAV based on vision. Firstly, a position estimation algorithm based on vision is proposed, in which optical flow is used combining with FAST corner detection to ensure the real-time performance of the estimation in condition with limited loader. Meanwhile, a robust controller with nonlinear compensating input has been designed in this paper to deal with the position control for the quadrotor. A simulation is presented in this paper to verify the performance of the controller. Moreover, an experiment is also utilized in this paper to show that the method is practical and with high performance.

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{jurado_2018,
title = {A wavelet neural control scheme for a quadrotor unmanned aerial vehicle},
author = {Jurado, F.; Lopez, S.},
journal = {Philosophical Transactions of the Royal Society of Mathematical, Physical and Engineering Sciences},
year = {2018},
volume = {376},
number = {2126},
institution = {Tecnológico Nacional de México, Mexico; Instituto Tecnológico de La Laguna, Mexico},
abstract = {Wavelets are designed to have compact support in both time and frequency, giving them the ability to represent a signal in the two-dimensional time–frequency plane. The Gaussian, the Mexican hat and the Morlet wavelets are crude wavelets that can be used only in continuous decomposition. The Morlet wavelet is complex-valued and suitable for feature extraction using the continuous wavelet transform. Continuous wavelets are favoured when high temporal and spectral resolution is required at all scales. In this paper, considering the properties from the Morlet wavelet and based on the structure of a recurrent high-order neural network model, a novel wavelet neural network structure, here called a recurrent Morlet wavelet neural network, is proposed in order to achieve a better identification of the behaviour of dynamic systems. The effectiveness of our proposal is explored through the design of a decentralized neural backstepping control scheme for a quadrotor unmanned aerial vehicle. The performance of the overall neural identification and control scheme is verified via simulation and real-time results. This article is part of the theme issue ‘Redundancy rules: the continuous wavelet transform comes of age’. },
keywords = {backstepping control, Morlet wavelet, quadrotor, recurrent wavelet neural network},
language = {English},
publisher = {The Royal Society Publishing}
}

Wavelets are designed to have compact support in both time and frequency, giving them the ability to represent a signal in the two-dimensional time–frequency plane. The Gaussian, the Mexican hat and the Morlet wavelets are crude wavelets that can be used only in continuous decomposition. The Morlet wavelet is complex-valued and suitable for feature extraction using the continuous wavelet transform. Continuous wavelets are favoured when high temporal and spectral resolution is required at all scales. In this paper, considering the properties from the Morlet wavelet and based on the structure of a recurrent high-order neural network model, a novel wavelet neural network structure, here called a recurrent Morlet wavelet neural network, is proposed in order to achieve a better identification of the behaviour of dynamic systems. The effectiveness of our proposal is explored through the design of a decentralized neural backstepping control scheme for a quadrotor unmanned aerial vehicle. The performance of the overall neural identification and control scheme is verified via simulation and real-time results.

This article is part of the theme issue ‘Redundancy rules: the continuous wavelet transform comes of age’.

@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{yan_2018,
title = {Adaptive Fault Detection and Isolation for Active Suspension Systems With Model Uncertainties},
author = {Yan, S.; Sun, W.; He, F.; Yao, J.},
journal = {IEEE Transactions on Reliability},
year = {2018},
institution = {Harbin Institute of Technology, China; Nanjing University of Science and Technology, China},
abstract = {Suspension operation reliability is one of the most significant performance indexes that concerns maneuvering stability and drive safety. In this paper, in order to guarantee good suspension reliability, an adaptive fault detection and isolation scheme is proposed for quarter-car active suspension systems with parametric and nonlinear uncertainties. To realize fault diagnosis for active suspensions, an adaptive fault detection estimator and several fault isolation estimators are designed to generate state residuals. Corresponding adaptive thresholds are developed to help judge the occurrence and type of possible faults. In the process of constructing state estimators, the uncertain parameter is updated online so that good sensitivity of fault detection can be achieved. Illustrative simulation is carried out to validate the effectiveness of the fault diagnosis scheme, and results indicate that the proposed method is sensible to sudden faults and maintain robustness to model uncertainties appearing in suspension systems. },
issn = {0018-9529 },
keywords = {Active suspension systems, fault detection, fault isolation, model uncertainties, parameter adaption},
language = {English},
publisher = {IEEE}
}

Suspension operation reliability is one of the most significant performance indexes that concerns maneuvering stability and drive safety. In this paper, in order to guarantee good suspension reliability, an adaptive fault detection and isolation scheme is proposed for quarter-car active suspension systems with parametric and nonlinear uncertainties. To realize fault diagnosis for active suspensions, an adaptive fault detection estimator and several fault isolation estimators are designed to generate state residuals. Corresponding adaptive thresholds are developed to help judge the occurrence and type of possible faults. In the process of constructing state estimators, the uncertain parameter is updated online so that good sensitivity of fault detection can be achieved. Illustrative simulation is carried out to validate the effectiveness of the fault diagnosis scheme, and results indicate that the proposed method is sensible to sudden faults and maintain robustness to model uncertainties appearing in suspension systems.

@article{das_2018,
title = {Adaptive Predator-Prey Optimization for Tuning of Infinite Horizon LQR applied to Vehicle Suspension System},
author = {Das, R.R.; Elumalai, V.K.; Subramanian, R.G.; Venkata, K.; Kumar, A.},
journal = {Applied Soft Computing},
year = {2018},
institution = {Eindhoven University of Technology, The Netherlands; VIT University, India; Larson and Toubro Limited, India},
abstract = {This paper puts forward an adaptive predator-prey optimization algorithm to solve the weight selection problem of linear quadratic control applied for vibration control of vehicle suspension system. The proposed technique addresses the two key issues of PSO, namely (a) the premature convergence of the particles, and (b) the imbalance between exploration and exploitation of the particles in finding the global optimum. The main principle behind this optimization algorithm is that the inertia weight is adaptively updated based on the success rate of the particles to increase the convergence, and the predator-prey strategy is reinforced to avoid the particles getting trapped in a local minimum thereby, guaranteeing convergence of the particles towards the global optimal solution. The convergence of the particles towards the global minimum is guaranteed on the basis of a passivity argument. Moreover, the strength of this new adaptive optimization technique to tune the gains of linear quadratic regulator is validated experimentally on a laboratory scale active vehicle suspension system for improved ride comfort and passenger safety. },
keywords = {LQR, Active Vehicle Suspension System, PSO, AIWF, Predator-Prey strategy},
language = {English},
publisher = {Elsevier B.V.}
}

This paper puts forward an adaptive predator-prey optimization algorithm to solve the weight selection problem of linear quadratic control applied for vibration control of vehicle suspension system. The proposed technique addresses the two key issues of PSO, namely (a) the premature convergence of the particles, and (b) the imbalance between exploration and exploitation of the particles in finding the global optimum. The main principle behind this optimization algorithm is that the inertia weight is adaptively updated based on the success rate of the particles to increase the convergence, and the predator-prey strategy is reinforced to avoid the particles getting trapped in a local minimum thereby, guaranteeing convergence of the particles towards the global optimal solution. The convergence of the particles towards the global minimum is guaranteed on the basis of a passivity argument. Moreover, the strength of this new adaptive optimization technique to tune the gains of linear quadratic regulator is validated experimentally on a laboratory scale active vehicle suspension system for improved ride comfort and passenger safety.

@article{riviere_2018,
title = {Agile Robotic Fliers: A Morphing-Based Approach},
author = {Riviere, V.; Manecy, A.; Viollet, S.},
journal = {Soft Robotics},
year = {2018},
institution = {Aix Marseille University, France; ONERA Midi-Pyrenees Toulouse Center, France},
abstract = {The aerial robot presented here for the first time was based on a quadrotor structure, which is capable of unique morphing performances based on an actuated elastic mechanism. Like birds, which are able to negotiate narrow apertures despite their relatively large wingspan, our Quad-Morphing robot was able to pass through a narrow gap at a high forward speed of 2.5 m.s−1 by swiftly folding up the structure supporting its propellers. A control strategy was developed to deal with the loss of controllability on the roll axis resulting from the folding process, while keeping the robot stable until it has crossed the gap. In addition, a complete recovery procedure was also implemented to stabilize the robot after the unfolding process. A new metric was also used to quantify the gain in terms of the gap-crossing ability in comparison with that observed with classical quadrotors with rigid bodies. The performances of these morphing robots are presented, and experiments performed with a real flying robot passing through a small aperture by reducing its wingspan by 48% are described and discussed. },
keywords = {morphing robot, quadrotors, obstacle avoidance, bioinspired, aerial robot, elastic folding mechanism},
language = {English},
publisher = {Mary Ann Liebert, Inc.}
}

The aerial robot presented here for the first time was based on a quadrotor structure, which is capable of unique morphing performances based on an actuated elastic mechanism. Like birds, which are able to negotiate narrow apertures despite their relatively large wingspan, our Quad-Morphing robot was able to pass through a narrow gap at a high forward speed of 2.5 m.s−1 by swiftly folding up the structure supporting its propellers. A control strategy was developed to deal with the loss of controllability on the roll axis resulting from the folding process, while keeping the robot stable until it has crossed the gap. In addition, a complete recovery procedure was also implemented to stabilize the robot after the unfolding process. A new metric was also used to quantify the gain in terms of the gap-crossing ability in comparison with that observed with classical quadrotors with rigid bodies. The performances of these morphing robots are presented, and experiments performed with a real flying robot passing through a small aperture by reducing its wingspan by 48% are described and discussed.

@article{oksuz_2018,
title = {Alternative Controller Design for Rotary Inverted Pendulum},
author = {Oksuz, M.; Onal, M.B.; Halicioglu, R.; Dulger, L.C.},
journal = {Tehnicki Glasnik},
year = {2018},
volume = {12},
number = {3},
institution = {Turkish Aeronautical Association University, Turkey; İzmir University of Economics, Turkey},
abstract = {The inverted pendulum has been considered a classical control problem. Two designs of inverted pendulum are planar and rotary with a nonlinear unstable system characteristic. Inverted pendulum systems are nonlinear. They can be used for testing and studying various observers and controllers. Control of a rotary inverted pendulum is studied here. This paper proposes stabilization of the rotary inverted pendulum at its upright position by using full-state controller. Full-state controllers are designed by using different damping ratios. MATLAB simulation results and the experimental results are taken for 10 degrees step for 5 seconds. The best controller is chosen for SRV02-Rotary inverted pendulum by looking at the simulation and experimental results. },
keywords = {controller design; full-state controller; linearization; pole placement; rotary inverted pendulum (RIP); stabilization},
language = {English},
pages = {139-145}
}

The inverted pendulum has been considered a classical control problem. Two designs of inverted pendulum are planar and rotary with a nonlinear unstable system characteristic. Inverted pendulum systems are nonlinear. They can be used for testing and studying various observers and controllers. Control of a rotary inverted pendulum is studied here. This paper proposes stabilization of the rotary inverted pendulum at its upright position by using full-state controller. Full-state controllers are designed by using different damping ratios. MATLAB simulation results and the experimental results are taken for 10 degrees step for 5 seconds. The best controller is chosen for SRV02-Rotary inverted pendulum by looking at the simulation and experimental results.

@conference{abdullah2_2018,
title = {Alternative Method for Predictive Functional Control to Handle an Integrating Process},
author = {Abdullah, M.; Rossiter, J.A.},
booktitle = {Control 2018 - 12th UKACC International Conference on Control},
year = {2018},
institution = {University of Sheffield, UK; International Islamic University Malaysia, Malaysia},
abstract = {This work proposes an improved method for Predictive Functional Control (PFC) to handle an integrating process. Instead of assuming a constant future input, the dynamic is shaped with a first-order Laguerre polynomial so that it converges to the expected steady state value. This modification provides simpler coding and tuning compared to the conventional method in the literature. Simulation results show that the proposed controller improves the consistency of the open-loop prediction of an integrating process and thus improves closed-loop performance and constraint handling properties. The practicality of this algorithm is also validated on laboratory hardware. },
keywords = {Predictive Control, PFC, Laguerre Function, Constraints, Integrating Process, Transparent Control, Servo System},
language = {English},
publisher = {IEEE}
}

This work proposes an improved method for Predictive Functional Control (PFC) to handle an integrating process. Instead of assuming a constant future input, the dynamic is shaped with a first-order Laguerre polynomial so that it converges to the expected steady state value. This modification provides simpler coding and tuning compared to the conventional method in the literature. Simulation results show that the proposed controller improves the consistency of the open-loop prediction of an integrating process and thus improves closed-loop performance and constraint handling properties. The practicality of this algorithm is also validated on laboratory
hardware.

@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.

Plant-wide control implies advanced supervisory algorithms to maintain desired performance in the involved coupled sub-systems. The dynamical interactions among these sub-systems can vary with the operating point, material properties and disturbances present in the process. Recirculating loops introduce additional phenomena in the dynamic response, further challenging the control tasks. Complex process dynamics may be linear parameter varying (LPV) and may be difficult, if not impossible, to identify properly. In this context, maintaining global performance is a challenge one must undertake with limited information at hand. This paper investigates the trade-off between the complexity of the implementation and achieved performance, using supervisory predictive control with limited information shared, applied on a test-bench representative for process control industry. The robustness of the proposed algorithms is tested against a nominal scenario in which the prediction model is fully identified, with complete information exchange. Experimental tests are performed on a test-bench process characterized by strong interactions, and the results illustrate the usefulness of this work.

@article{castillo_2018,
title = {An oil sloshing study: adaptive fixed-mesh ALE analysis and comparison with experiments},
author = {Castillo, E.; Cruchaga, M.A.; Baiges, J.; Flores, J.},
journal = {Computational Mechanics},
year = {2018},
institution = {Universidad de Santiago de Chile, Chile; Universitat Politècnica de Catalunya, Spain},
abstract = {We report in this work a numerical analysis of the sloshing of a squared tank partially filled with a domestic vegetable oil. The tank is subject to controlled motions with a shake table. The free-surface evolution is captured using ultrasonic sensors and an image capturing method. Only confirmed data within the error range is reported. Filling depth, imposed amplitude and frequency effects on the sloshing wave pattern are specifically evaluated. The experiments also reveal the nonlinear wave behavior. The numerical model is based on a stabilized finite element method of the variational multi-scale type. The free-surface is captured using a level set technique developed to be used with adaptive meshes in Arbitrary Lagrangian–Eulerian framework. The numerical results are compared with the experiments for different sloshing conditions near the first sloshing mode. The simulations satisfactorily match the experiments, providing a reliable tool for the analysis of this kind of problems. },
issn = {0178-7675},
keywords = {Sloshing, Experimental validation, Arbitrary Lagrangian–Eulerian (ALE), Stabilized finite element methods, Adaptive mesh },
language = {English},
publisher = {Springer Berlin Heidelberg}
}

We report in this work a numerical analysis of the sloshing of a squared tank partially filled with a domestic vegetable oil. The tank is subject to controlled motions with a shake table. The free-surface evolution is captured using ultrasonic sensors and an image capturing method. Only confirmed data within the error range is reported. Filling depth, imposed amplitude and frequency effects on the sloshing wave pattern are specifically evaluated. The experiments also reveal the nonlinear wave behavior. The numerical model is based on a stabilized finite element method of the variational multi-scale type. The free-surface is captured using a level set technique developed to be used with adaptive meshes in Arbitrary Lagrangian–Eulerian framework. The numerical results are compared with the experiments for different sloshing conditions near the first sloshing mode. The simulations satisfactorily match the experiments, providing a reliable tool for the analysis of this kind of problems.

@article{chang_2018,
title = {Analytical and experimental investigations of Modified Tuned Liquid Dampers (MTLDs)},
author = {Chang, Y.; Noormohamed, A.; Mercan, O.},
journal = {Journal of Sound and Vibration},
year = {2018},
volume = {428},
institution = {University of Toronto, Canada},
abstract = {Modified Tuned Liquid Dampers (MTLDs) are a variation of a traditional Tuned Liquid Damper (TLD) which utilize a rotational spring system at the base, and therefore experience combined horizontal and rotational motions as the structure sways. To date, there have been very few studies conducted on MTLDs with experimental validation. In this research study, an MTLD-structure system is investigated using Lu's analytical model. Using Real-Time Hybrid Simulation (RTHS), a state-of-the-art testing method, the capabilities of the analytical model are experimentally verified. Important MTLD parameters such as the dimensionless rotational stiffness parameter, frequency ratio, and damping ratio are studied in detail. RTHS is used to study the effectiveness of the MTLD in mitigating structural response under sinusoidal inputs, as well as a range of ground motion records. It is shown both analytically and experimentally that when properly designed, the MTLD can exhibit more efficiency than a traditional TLD in mitigating vibrations. },
keywords = {Earthquake response, Energy dissipation, Modified Tuned Liquid Damper, Passive control, Real time hybrid simulation, Vibration control},
language = {English},
publisher = {Elsevier B.V.},
pages = {179-194}
}

Modified Tuned Liquid Dampers (MTLDs) are a variation of a traditional Tuned Liquid Damper (TLD) which utilize a rotational spring system at the base, and therefore experience combined horizontal and rotational motions as the structure sways. To date, there have been very few studies conducted on MTLDs with experimental validation. In this research study, an MTLD-structure system is investigated using Lu's analytical model. Using Real-Time Hybrid Simulation (RTHS), a state-of-the-art testing method, the capabilities of the analytical model are experimentally verified. Important MTLD parameters such as the dimensionless rotational stiffness parameter, frequency ratio, and damping ratio are studied in detail. RTHS is used to study the effectiveness of the MTLD in mitigating structural response under sinusoidal inputs, as well as a range of ground motion records. It is shown both analytically and experimentally that when properly designed, the MTLD can exhibit more efficiency than a traditional TLD in mitigating vibrations.

@article{dede_2018,
title = {Analytical Dynamic Analysis of a Kinesthetic Haptic Device},
author = {Dede, M.I.C.; Maaroof, O.W.; Ceccarelli, M.},
journal = {Journal of Science and Engineering},
year = {2018},
month = {05},
volume = {20},
number = {59},
institution = {Izmit Institute of Technology, Turkey; University of Cassino, Italy},
abstract = {A hybrid-structured kinesthetic haptic device based on an R-CUBE mechanism and a serial spherical wrist mechanism is considered in this article. This device is designed to simulate point-type contacts on the user. Hence, only three-dimensional forces are simulated to the user through the R-CUBE mechanism. This paper presents the quasi-static force analysis, gravity compensation calculations and dynamic analysis of the R-CUBE mechanism to serve for better understanding the capabilities of the mechanism and to be used in haptics controller development in the future studies. Making use of the derived dynamic equations, torque requirements from the actuators are examined for use in the haptic application scenarios. },
keywords = {haptics, parallel mechanisms, dynamics},
language = {English},
pages = {492-508}
}

A hybrid-structured kinesthetic haptic device based on an R-CUBE mechanism and a serial spherical wrist mechanism is considered in this article. This device is designed to simulate point-type contacts on the user. Hence, only three-dimensional forces are simulated to the user through the R-CUBE mechanism. This paper presents the quasi-static force analysis, gravity compensation calculations and dynamic analysis of the R-CUBE mechanism to serve for better understanding the capabilities of the mechanism and to be used in haptics controller development in the future studies. Making use of the derived dynamic equations, torque requirements from the actuators are examined for use in the haptic application scenarios.

@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.

@conference{sun2_2018,
title = {Anti-Disturbance Study of Position Servo System Based on Disturbance Observer},
author = {Sun, J.; Wang, C.; Xin, R.},
booktitle = {3rd IFAC Conference on Advances in Proportional-Integral-Derivative Control PID 2018},
year = {2018},
institution = {Changchun University of Science and Technology, China},
abstract = {In this paper, the mechanism and method of using disturbance observer (DOB) to eliminate the disturbance are studied and applied to the control of position servo system. The DOB consists of an inverse model of the controlled object and a filter, and suppresses the external disturbance acting on the servo system. Based on the traditional proportional integral derivative (PID) controller, simulations on MATLAB/Simulink and tests on Quanser semi-physical experiment platform are performed for the PID controller with DOB and without DOB. Simulation and experimental results show that the introduction of DOB can effectively suppress the external disturbance and improve the dynamic response performance and stability of the servo system. },
keywords = {Proportional Integral Derivative Control, Disturbance Observer, Anti-Disturbance Position Servo System, Quanser Experiment Device.},
language = {English},
series = {IFAC-PapersOnLine},
publisher = {Elsevier Ltd.}
}

In this paper, the mechanism and method of using disturbance observer (DOB) to eliminate the disturbance are studied and applied to the control of position servo system. The DOB consists of an inverse model of the controlled object and a filter, and suppresses the external disturbance acting on the servo system. Based on the traditional proportional integral derivative (PID) controller, simulations on MATLAB/Simulink and tests on Quanser semi-physical experiment platform are performed for the PID controller with DOB and without DOB. Simulation and experimental results show that the introduction of DOB can effectively suppress the external disturbance and improve the dynamic response performance and stability of the servo system.

@conference{kogan_2018,
title = {Architecture for testing learning-based autonomous vehicle control design},
author = {Kogan, M.; Jardine, P.T.; Givigi, S.N.},
booktitle = {2018 Annual IEEE International Systems Conference (SysCon)},
year = {2018},
institution = {Royal Military College of Canada, Canada},
abstract = {This paper presents the architecture for the testing of autonomous vehicle controllers designed using machine learning. A localization system feeds measurement data into a ground station. The ground station processes this data and provides the position of the vehicle to the controller, which has been tuned offline via machine learning. Control inputs are then generated and provided to the vehicle in order to accomplish the desired mission. The performance of the learned controller is compared to a nominal case. During the offline tuning process, a vehicle model is used to simulate the actual vehicle. Once tuning is complete, the parameters are used to control a real vehicle in order to accomplish the desired mission. The proposed architecture was tested by tuning a model predictive controller to guide a differential drive robot to a series of waypoints using a Reinforced Learning technique known as Learning Automata. The controller was then tested online with a similar but different problem on a real differential drive robot. The results showed that after tuning, the vehicle performed significantly better. This demonstrated that offline learning techniques can be used to optimally select controller parameters. },
issn = {2472-9647},
keywords = {Computer architecture, Testing, Machine learning, Tuning, Mathematical model, Robot kinematics},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-3665-7}
}

This paper presents the architecture for the testing of autonomous vehicle controllers designed using machine learning. A localization system feeds measurement data into a ground station. The ground station processes this data and provides the position of the vehicle to the controller, which has been tuned offline via machine learning. Control inputs are then generated and provided to the vehicle in order to accomplish the desired mission. The performance of the learned controller is compared to a nominal case. During the offline tuning process, a vehicle model is used to simulate the actual vehicle. Once tuning is complete, the parameters are used to control a real vehicle in order to accomplish the desired mission. The proposed architecture was tested by tuning a model predictive controller to guide a differential drive robot to a series of waypoints using a Reinforced Learning technique known as Learning Automata. The controller was then tested online with a similar but different problem on a real differential drive robot. The results showed that after tuning, the vehicle performed significantly better. This demonstrated that offline learning techniques can be used to optimally select controller parameters.

@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{nandi_2018,
title = {Chance Constraint based Design of Open-Loop Controllers for Linear Uncertain Systems},
author = {Nandi, S.; Singh, T.},
journal = { IEEE/ASME Transactions on Mechatronics},
year = {2018},
institution = {University at Buffalo, USA},
abstract = {This paper considers the problem of state-to-state transition with state and control constraints, for a linear system with time invariant model parameter uncertainties. Polynomial chaos is used to transform the stochastic model to a deterministic surrogate model. This surrogate model is used to pose a chance constrained optimal control problem where the state constraints and the residual energy cost are represented in terms of the mean and variance of the stochastic states. The resulting convex optimization is illustrated on the problem of rest-to-rest maneuver of the benchmark floating oscillator and on an experimental two-tank setup. },
issn = {1083-4435 },
keywords = {Uncertain System, Vibration Control, Chance Constraint, Polynomial Chaos, Stochastic Optimal Control},
language = {English},
publisher = {IEEE}
}

This paper considers the problem of state-to-state transition with state and control constraints, for a linear system with time invariant model parameter uncertainties. Polynomial chaos is used to transform the stochastic model to a deterministic surrogate model. This surrogate model is used to pose a chance constrained optimal control problem where the state constraints and the residual energy cost are represented in terms of the mean and variance of the stochastic states. The resulting convex optimization is illustrated on the problem of rest-to-rest maneuver of the benchmark floating oscillator and on an experimental two-tank setup.

@conference{furtado_2018,
title = {Comparative Analysis of OptiTrack Motion Capture Systems},
author = {Furtado, J.S.; Liu, H.H.T.; Lai, G.; Lacheray, H.; Desouza-Coelho, J.},
booktitle = {CSME International Congress 2018},
year = {2018},
institution = {University of Toronto Institute for Aerospace Studies, Canada; Quanser, Canada},
abstract = {A comparative analysis of four different OptiTrack motion capture systems is provided in this paper. Tracking accuracy, workspace volume, marker size and camera range are the main criteria used for comparison. The tracking accuracy is tested using Quanser’s linear motion platform by comparing the measured position of the cart with the position obtained using the encoder. The workspace volume limits are obtained by flying a LiteHawk Neon drone in the circles of increasing radii at different heights until tracking fails. The relationship between marker size and camera range is obtained through theoretical calculations. The experimental as well as theoretical results are presented, illustrating the performance of these four systems. These will serve as a baseline to select the right motion capture system for any particular application. },
keywords = {Motion capture; OptiTrack; Optical-Passive},
language = {English},
publisher = {CSME}
}

A comparative analysis of four different OptiTrack motion capture systems is provided in this paper. Tracking accuracy, workspace volume, marker size and camera range are the main criteria used for comparison. The tracking accuracy is tested using Quanser’s linear motion platform by comparing the measured position of the cart with the position obtained using the encoder. The workspace volume limits are obtained by flying a LiteHawk Neon drone in the circles of increasing radii at different heights until tracking fails. The relationship between marker size and camera range is obtained through theoretical calculations. The experimental as well as theoretical results are presented, illustrating the performance of these four systems. These will serve as a baseline to select the right motion capture system for any particular application.

@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.

@conference{kloppelt_2018,
title = {Comparison of different Methods for Encoder Speed Signal Filtering exemplified by an Inverted Pendulum},
author = {Klöppelt, C.; Meyer, D.},
booktitle = { 2018 19th International Conference on Research and Education in Mechatronics (REM)},
year = {2018},
institution = {Ostfalia University of Applied Sciences, Germany},
abstract = {This paper deals with the problem of filtering speed signals captured by means of an encoder in conjunction with the frequency measurement method. Filtering is necessary to cope with the quantization noise, which has an extremely negative influence on a state space controller using these signals as input. A simple low pass filter and two model based filter approaches (a Kalman filter and an adaptive Kalman filter) are presented and their effect on the performance of the controller is compared through the example of a cart-pole system. },
keywords = {cart-pole system, speed measurement, encoder, model based filter, adaptive Kalman filter},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-5413-2 }
}

This paper deals with the problem of filtering speed signals captured by means of an encoder in conjunction with the frequency measurement method. Filtering is necessary to cope with the quantization noise, which has an extremely negative influence on a state space controller using these signals as input. A simple low pass filter and two model based filter approaches (a Kalman filter and an adaptive Kalman filter) are presented and their effect on the performance of the controller is compared through the example of a cart-pole system.

@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.

@article{rios_2018,
title = {Continuous Sliding-Modes Control Strategies for Quad-Rotor Robust Tracking: Real-Time Application},
author = {Rios, H.; Falcon, R.; Gonzalez, O.A.; Dzul, A.E.},
journal = {IEEE Transactions on Industrial Electronics},
year = {2018},
institution = {Instituto Tecnologico de La Laguna, Mexico},
abstract = {The design of robust tracking control for Quad-Rotors is an important and challenging problem nowadays. In this paper a robust tracking output-control strategy is proposed for a Quad-Rotor under the influence of external disturbances and uncertainties. Such a strategy is composed of a Finite-Time Sliding-Mode Observer (FTSMO) which estimates the full state from the measurable output and identifies some type of disturbances; and also of a combination between PID controllers and Continuous Sliding-Modes Controllers (Continuous-SMCs), that robustly track a desired time-varying trajectory with exponential convergence and despite the influence of external disturbances and uncertainties. The closed-loop stability is provided based on Input-to-State Stability (ISS) and Finite- Time ISS (FT-ISS) properties. Finally, experimental results in real-time show the performance of the proposed control strategy. },
issn = {0278-0046 },
keywords = {Robust Output-Control, Quad-Rotor, Continuous Sliding-Mode Control },
language = {English},
publisher = {IEEE}
}

The design of robust tracking control for Quad-Rotors is an important and challenging problem nowadays. In this paper a robust tracking output-control strategy is proposed for a Quad-Rotor under the influence of external disturbances and uncertainties. Such a strategy is composed of a Finite-Time Sliding-Mode Observer (FTSMO) which estimates the full state from the measurable output and identifies some type of disturbances; and also of a combination between PID controllers and Continuous Sliding-Modes Controllers (Continuous-SMCs), that robustly track a desired time-varying trajectory with exponential convergence and despite the influence of external disturbances and uncertainties. The closed-loop stability is provided based on Input-to-State Stability (ISS) and Finite- Time ISS (FT-ISS) properties. Finally, experimental results in real-time show the performance of the proposed control strategy.

@article{eisen_2018,
title = {Control Aware Radio Resource Allocation in Low Latency Wireless Control Systems},
author = {Eisen, M.; Rashid, M.M.; Gatsis, K.; Cavalcanti, D.; Himaya, N.; Ribeiro, A.},
year = {2018},
institution = {University of Pennsylvania, USA; Intel Corporation, USA},
abstract = {We consider the problem of allocating radio resources over wireless communication links to control a series of independent wireless control systems. Low-latency transmissions are necessary in enabling time-sensitive control systems to operate over wireless links with high reliability. Achieving fast data rates over wireless links thus comes at the cost of reliability in the form of high packet error rates compared to wired links due to channel noise and interference. However, the effect of the communication link errors on the control system performance depends dynamically on the control system state. We propose a novel control-communication co-design approach to the low-latency resource allocation problem. We incorporate control and channel state information to make scheduling decisions over time on frequency, bandwidth and data rates across the next-generation Wi-Fi based wireless communication links that close the control loops. Control systems that are closer to instability or further from a desired range in a given control cycle are given higher packet delivery rate targets to meet. Rather than a simple priority ranking, we derive precise packet error rate targets for each system needed to satisfy stability targets and make scheduling decisions to meet such targets while reducing total transmission time. The resulting Control-Aware Low Latency Scheduling (CALLS) method is tested in numerous simulation experiments that demonstrate its effectiveness in meeting control-based goals under tight latency constraints relative to control-agnostic scheduling. },
keywords = {wireless control, low-latency, codesign, IEEE 802.11ax},
language = {English}
}

We consider the problem of allocating radio resources over wireless communication links to control a series of independent wireless control systems. Low-latency transmissions are necessary in enabling time-sensitive control systems to operate over wireless links with high reliability. Achieving fast data rates over wireless links thus comes at the cost of reliability in the form of high packet error rates compared to wired links due to channel noise and interference. However, the effect of the communication link errors on the control system performance depends dynamically on the control system state. We propose a novel control-communication co-design approach to the low-latency resource allocation problem. We incorporate control and channel state information to make scheduling decisions over time on frequency, bandwidth and data rates across the next-generation Wi-Fi based wireless communication links that close the control loops. Control systems that are closer to instability or further from a desired range in a given control cycle are given higher packet delivery rate targets to meet. Rather than a simple priority ranking, we derive precise packet error rate targets for each system needed to satisfy stability targets and make scheduling decisions to meet such targets while reducing total transmission time. The resulting Control-Aware Low Latency Scheduling (CALLS) method is tested in numerous simulation experiments that demonstrate its effectiveness in meeting control-based goals under tight latency constraints relative to control-agnostic scheduling.

@article{maddalena_2018,
title = {Control with Sensor Fault Tolerance for an Underactuated Linear Positioning System Using the TFL/LTR Technique},
author = {Maddalena, E.T.; Kienitz, K.H.},
journal = {Journal of Control, Automation and Electrical Systems},
year = {2018},
month = {10},
volume = {29},
number = {5},
institution = {Insituto Tecnologico de Aeronautica Sao Jose dos Campos, Brazil},
abstract = {In this work, the applicability of a Lyapunov filter-based target feedback loop/loop transfer recovery controller to open-loop unstable plants is investigated on an underactuated linear positioning mechanism. Uncertainties in friction coefficients are taken into account. Lyapunov filter target loops yield robustly stable dynamics and tolerance to abrupt sensor faults, i.e., sensors affected by any attenuation in the interval [0, 1). Experimental results confirm the effectiveness of the proposed solution when compared to alternative control methods. },
issn = {2195-3880},
keywords = {Robust control, TFL/LTR controllers, Fault tolerance, Underactuated systems},
language = {English},
publisher = {Springer US}
}

In this work, the applicability of a Lyapunov filter-based target feedback loop/loop transfer recovery controller to open-loop unstable plants is investigated on an underactuated linear positioning mechanism. Uncertainties in friction coefficients are taken into account. Lyapunov filter target loops yield robustly stable dynamics and tolerance to abrupt sensor faults, i.e., sensors affected by any attenuation in the interval [0, 1). Experimental results confirm the effectiveness of the proposed solution when compared to alternative control methods.

@article{medina-dorantes_2018,
title = {Controller with time-delay to stabilize first-order processes with dead-time},
author = {Medina-Dorantes, F.; Villafuerte-Segura, R.; Aguirre-Hernandez, B.},
journal = {Journal of Control Engineering and Applied Informatics},
year = {2018},
volume = {20},
number = {2},
institution = {Universidad Autónoma Metropolitana-Iztapalapa, Mexico; Universidad Autónoma del Estado de Hidalgo, Mexico},
abstract = {This paper focuses on the stability analysis of analytic functions with two transcendental terms in order to obtain parameters that guarantee an exponential decay rate σ in the response of the linear time-invariant system associated with the analytic function. As a consequence of this stability analysis, analytic expressions to tune all of the gains of a controller with time-delay action called Proportional Integral Retarded (PIR) control law that σ -stabilizes a first-order process with dead-time are obtained. To illustrate the effectiveness of the theoretical results proposed, an application on a Quanser thermal platform is given. Furthermore, a comparison with a classical PID control law is made. },
keywords = {D-composition method, first-order system, time delay systems, stability analysis, stabilizing feedback},
language = {English},
pages = {42-50}
}

This paper focuses on the stability analysis of analytic functions with two transcendental terms in order to obtain parameters that guarantee an exponential decay rate σ in the response of the linear time-invariant system associated with the analytic function. As a consequence of this stability analysis, analytic expressions to tune all of the gains of a controller with time-delay action called Proportional Integral Retarded (PIR) control law that σ -stabilizes a first-order process with dead-time are obtained. To illustrate the effectiveness of the theoretical results proposed, an application on a Quanser thermal platform is given. Furthermore, a comparison with a classical PID control law is made.

@article{liang_2018,
title = {Design a software real-time operation platform for wave piercing catamarans motion control using linear quadratic regulator based genetic algorithm},
author = {Liang, L.; Yuan, J.; Zhang, S.; Zhao, P.},
journal = {Plos One},
year = {2018},
volume = {13},
number = {4},
institution = {Harbin Engineering University, China},
abstract = {This work presents optimal linear quadratic regulator (LQR) based on genetic algorithm (GA) to solve the two degrees of freedom (2 DoF) motion control problem in head seas for wave piercing catamarans (WPC). The proposed LQR based GA control strategy is to select optimal weighting matrices (Q and R). The seakeeping performance of WPC based on proposed algorithm is challenged because of multi-input multi-output (MIMO) system of uncertain coefficient problems. Besides the kinematical constraint problems of WPC, the external conditions must be considered, like the sea disturbance and the actuators (a T-foil and two flaps) control. Moreover, this paper describes the MATLAB and LabVIEW software plats to simulate the reduction effects of WPC. Finally, the real-time (RT) NI CompactRIO embedded controller is selected to test the effectiveness of the actuators based on proposed techniques. In conclusion, simulation and experimental results prove the correctness of the proposed algorithm. The percentage of heave and pitch reductions are more than 18% in different high speeds and bad sea conditions. And the results also verify the feasibility of NI CompactRIO embedded controller. },
language = {English}
}

This work presents optimal linear quadratic regulator (LQR) based on genetic algorithm (GA) to solve the two degrees of freedom (2 DoF) motion control problem in head seas for wave piercing catamarans (WPC). The proposed LQR based GA control strategy is to select optimal weighting matrices (Q and R). The seakeeping performance of WPC based on proposed algorithm is challenged because of multi-input multi-output (MIMO) system of uncertain coefficient problems. Besides the kinematical constraint problems of WPC, the external conditions must be considered, like the sea disturbance and the actuators (a T-foil and two flaps) control. Moreover, this paper describes the MATLAB and LabVIEW software plats to simulate the reduction effects of WPC. Finally, the real-time (RT) NI CompactRIO embedded controller is selected to test the effectiveness of the actuators based on proposed techniques. In conclusion, simulation and experimental results prove the correctness of the proposed algorithm. The percentage of heave and pitch reductions are more than 18% in different high speeds and bad sea conditions. And the results also verify the feasibility of NI CompactRIO embedded controller.

@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%.

@conference{wang_2018,
title = {Design and implementation of fractional PID controller for rotary inverted pendulum},
author = {Wang, C.; Liu, X.; Shi, H.; Xin, R.; Xu, X.},
booktitle = {2018 Chinese Control And Decision Conference (CCDC)},
year = {2018},
institution = {Changchun University of Science and Technology, China},
abstract = {As for the stability control problem for rotary inverted pendulum, the two closed-loop fractional order PID control scheme is used to control the pendulum. First, the mathematical model of rotary inverted pendulum is established according to the Euler-Lagrange equation. Then, a fractional order PID controller is designed based on the Bode ideal transfer function. Finally, the fractional order PID (FOPID) controller, fractional PD (FOPD) controller and integer order PD (IOPD) controller are applied to the rotary inverted pendulum system which based on the Quanser company loop simulation experiment platform. The results show that the FOPID controller is better than the FOPD and IOPD controller in stabilizing the system and the angle of the pendulum is closest to the stable equilibrium point. },
issn = {1948-9447 },
keywords = {rotary inverted pendulum; fractional PID controller; Bode ideal transfer function; stable control},
language = {English},
publisher = {IEEE}
}

As for the stability control problem for rotary inverted pendulum, the two closed-loop fractional order PID control scheme is used to control the pendulum. First, the mathematical model of rotary inverted pendulum is established according to the Euler-Lagrange equation. Then, a fractional order PID controller is designed based on the Bode ideal transfer function. Finally, the fractional order PID (FOPID) controller, fractional PD (FOPD) controller and integer order PD (IOPD) controller are applied to the rotary inverted pendulum system which based on the Quanser company loop simulation experiment platform. The results show that the FOPID controller is better than the FOPD and IOPD controller in stabilizing the system and the angle of the pendulum is closest to the stable equilibrium point.

@conference{wang4_2018,
title = {Design and Verification of Model-based Nonlinear Controller for Fluidic Soft Actuators},
author = {Wang, T.; Zhan, Y.; Chen, Z.},
booktitle = {2018 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM)},
year = {2018},
institution = {Zhejiang University, China},
abstract = {Soft actuators are of great interests in recent years due to inherent compliance and adaptability. However, most of current studies focus on the physical actuation phenomenon and their manufaction, few results can be found on the modeling and closed-loop control due to their complicated elastic deformation. This work studies physical modeling, parameter identification, and nonlinear robust backstepping control for fluidic soft bending actuators governed by high-speed on-off solenoid valves. A second-order transfer function is used to describe the dynamic behavior from driving pneumatic pressure to soft actuator bending angle, and the model parameters are identified by with different operating frequencies. The nonlinear dynamical model of pneumatic valves is also built and identified by using least square method. Based on the identified high-order model, a robust backstepping control algorithm is designed for soft actuator to deal with nonlinearities and parameter uncertainties. Experimental results show that the closed-loop stability is guaranteed and the good tracking performance is achieved by the proposed method. },
issn = {2159-6255},
keywords = {Soft actuators, fluidic power, system identification, backstepping design, dynamic control},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-1855-4 }
}

Soft actuators are of great interests in recent years due to inherent compliance and adaptability. However, most of current studies focus on the physical actuation phenomenon and their manufaction, few results can be found on the modeling and closed-loop control due to their complicated elastic deformation. This work studies physical modeling, parameter identification, and nonlinear robust backstepping control for fluidic soft bending actuators governed by high-speed on-off solenoid valves. A second-order transfer function is used to describe the dynamic behavior from driving pneumatic pressure to soft actuator bending angle, and the model parameters are identified by with different operating frequencies. The nonlinear dynamical model of pneumatic valves is also built and identified by using least square method. Based on the identified high-order model, a robust backstepping control algorithm is designed for soft actuator to deal with nonlinearities and parameter uncertainties. Experimental results show that the closed-loop stability is guaranteed and the good tracking performance is achieved by the proposed method.

@article{kim_2018,
title = {Design of a Portable Pneumatic Power Source with High Output Pressure for Wearable Robotic Applications},
author = { Kim, S.J.; Chang, H.; Park, .; Kim, J.},
journal = { IEEE Robotics and Automation Letters},
year = {2018},
institution = { KAIST, South Korea},
abstract = {Despite the rapid advances in soft robotic actuation technologies, the main energy source that empowers most wearable systems remains the conventional tethered stationary air compressor that greatly limits these systems' applicability. Several portable pneumatic energy sources have been introduced; however, the limited maximum output pressure and flow rate, size and weight, large operational noise, and potential safety hazards must still be resolved before being applied to current wearable applications. In this study, we propose the design of a portable double-piston crank microcompressor that can generate up to a maximum absolute output pressure of 986 kPa and a maximum flow rate of 9.78 LPM, while maintaining a simple structure, static mass of 1.5 kg and not generating any safety hazards. The design requirements in terms of maximum pressure and flow rate were optimized based on wearable robotic applications. The sound intensity level generated by the developed microcompressor was approximately 65 dB, which can be used for long-term usage, at maximum flow rate when measured from a 0.5 m distance. },
issn = {2377-3766},
keywords = {Assistive technology, exoskeleton, mechanical power transmission, pneumatic actuators, pneumatic systems},
language = {English},
publisher = {IEEE}
}

Despite the rapid advances in soft robotic actuation technologies, the main energy source that empowers most wearable systems remains the conventional tethered stationary air compressor that greatly limits these systems' applicability. Several portable pneumatic energy sources have been introduced; however, the limited maximum output pressure and flow rate, size and weight, large operational noise, and potential safety hazards must still be resolved before being applied to current wearable applications. In this study, we propose the design of a portable double-piston crank microcompressor that can generate up to a maximum absolute output pressure of 986 kPa and a maximum flow rate of 9.78 LPM, while maintaining a simple structure, static mass of 1.5 kg and not generating any safety hazards. The design requirements in terms of maximum pressure and flow rate were optimized based on wearable robotic applications. The sound intensity level generated by the developed microcompressor was approximately 65 dB, which can be used for long-term usage, at maximum flow rate when measured from a 0.5 m distance.

@conference{sun_2018,
title = {Design of fractional order proportional differentiation controller for second order position servo system},
author = {Sun, J.;Wang, C.; Xin, R.},
booktitle = {2018 Chinese Control And Decision Conference (CCDC)},
year = {2018},
institution = {Changchun University of Science and Technology, China},
abstract = {This paper considers a tuning method of factional order proportional derivative (FOPD) controller based on vector model for the second order position servo system. This method is designed to improve the closed-loop system's dynamic performance and robustness. Simulations in MATLAB/Simulink and tests on Quanser semi-physical experiment platform are performed after the design of controller for position servo system. The simulation and experimental results reveal that the designed factional order proportional derivative (FOPD) controller works more effectively than integer order proportional integral derivative (IOPID) controller, with the improved performance of faster response speed and stronger anti-jamming capability. },
issn = {1948-9447},
keywords = {Fractional order proportional differentiation controller, Vector model, Position servo system, Quanser experiment device, Robustness},
language = {English},
publisher = {IEEE}
}

This paper considers a tuning method of factional order proportional derivative (FOPD) controller based on vector model for the second order position servo system. This method is designed to improve the closed-loop system's dynamic performance and robustness. Simulations in MATLAB/Simulink and tests on Quanser semi-physical experiment platform are performed after the design of controller for position servo system. The simulation and experimental results reveal that the designed factional order proportional derivative (FOPD) controller works more effectively than integer order proportional integral derivative (IOPID) controller, with the improved performance of faster response speed and stronger anti-jamming capability.

@conference{fandel_2018,
title = {Development of Reinforcement Learning Algorithm for 2-DOF Helicopter Model},
author = {Fandel, A.; Birge, A.; Miah, S.},
booktitle = {2018 IEEE 27th International Symposium on Industrial Electronics (ISIE)},
year = {2018},
institution = {Bradley University, USA},
abstract = {This paper examines a reinforcement learning strategy for controlling a two degree-of-freedom (2-DOF) helicopter. The pitch and yaw angles are regulated to their corresponding reference angles by applying appropriate actuator commands (input voltages) to the main and tail rotors of a 2-DOF helicopter using the proposed reinforcement learning [herein called the approximate dynamic programming (ADP)] strategy. Furthermore, the proposed strategy has the ability to configure the 2-DOF helicopter to track time-varying reference angles. The proposed ADP technique is capable of dealing with coupling effects between the rigid body structure and propeller dynamics associated with the 2-DOF helicopter model considered in this work. A set of computer simulations is conducted to evaluate the performance of the proposed algorithm. The performance of the proposed algorithm is also compared to that of a conventional linear-quadratic regulator (LQR). },
issn = {2163-5145},
keywords = {2-DOF helicopter, approximate dynamic programming, feedback control, reinforcement learning, state-space modeling, regulation},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-3705-0}
}

This paper examines a reinforcement learning strategy for controlling a two degree-of-freedom (2-DOF) helicopter. The pitch and yaw angles are regulated to their corresponding reference angles by applying appropriate actuator commands (input voltages) to the main and tail rotors of a 2-DOF helicopter using the proposed reinforcement learning [herein called the approximate dynamic programming (ADP)] strategy. Furthermore, the proposed strategy has the ability to configure the 2-DOF helicopter to track time-varying reference angles. The proposed ADP technique is capable of dealing with coupling effects between the rigid body structure and propeller dynamics associated with the 2-DOF helicopter model considered in this work. A set of computer simulations is conducted to evaluate the performance of the proposed algorithm. The performance of the proposed algorithm is also compared to that of a conventional linear-quadratic regulator (LQR).

@inbook{max_2018,
title = {Development of Robust H-Infinity Steering Control System for Autonomous Vehicles},
author = {Max, G.; Vass, S.; Kiss, B.},
booktitle = {Vehicle and Automotive Engineering 2. VAE 2018},
year = {2018},
institution = {Budapest University of Technology and Economics, Hungary},
abstract = {Undoubtedly one of the most significant security systems for today’s autonomous ground vehicles is their steering system. A commonly used approach for control purposes in the automotive industry is the steering-by-wire concept. Despite its simplicity, this method is rather new and several concerns may arise regarding external loads arising from the tire-ground contact patch. This paper discusses the robust controller design of an electric steering-by-wire system taking into account multiple sources of uncertainty. In order to achieve robust performance, an H∞ controller was selected for the task. This allows excellent disturbance rejection while requiring low computational needs. The design is verified using simulations and the final verification phase includes testing on the RECAR autonomous vehicle by utilizing rapid prototyping and hardware-in-the-loop tools. },
keywords = {H-infinity controller, steer-by-wire, autonomous vehicle},
language = {English},
series = {Lecture Notes in Mechanical Engineering},
publisher = {Springer, Cham},
isbn = {978-3-319-75676-9},
pages = {393-402}
}

Undoubtedly one of the most significant security systems for today’s autonomous ground vehicles is their steering system. A commonly used approach for control purposes in the automotive industry is the steering-by-wire concept. Despite its simplicity, this method is rather new and several concerns may arise regarding external loads arising from the tire-ground contact patch. This paper discusses the robust controller design of an electric steering-by-wire system taking into account multiple sources of uncertainty. In order to achieve robust performance, an H∞ controller was selected for the task. This allows excellent disturbance rejection while requiring low computational needs. The design is verified using simulations and the final verification phase includes testing on the RECAR autonomous vehicle by utilizing rapid prototyping and hardware-in-the-loop tools.