Wen-Hong Zhu - Academia.edu (original) (raw)
Papers by Wen-Hong Zhu
The recent success of NASA’s Mars Exploration Rovers has demonstrated the important benefits that... more The recent success of NASA’s Mars Exploration Rovers has demonstrated the important benefits that mobility adds to landed planetary exploration missions. The Canadian Space Agency (CSA) has been conducting research in ground control and in autonomous robotics for several years already. One of the target applications is planetary exploration using mobile platforms. The emphasis of our research program is on reactive on-board autonomy software and long-range rover navigation. This paper describes recent activities of the CSA in this area. Key results are described in the areas of terrain modelling, path planning and rover guidance.
IFAC Proceedings Volumes, 2008
Use of flexible link robots is motivated by applications featuring lightweight or long arms. Howe... more Use of flexible link robots is motivated by applications featuring lightweight or long arms. However, the control problem faces strong technical challenges resulting from the complex dynamics. In this paper, the virtual decomposition control (VDC) approach is applied for the first time to address the technical challenges of this thorny problem mainly resulting from the dynamic coupling effects among flexible links. In view of the VDC approach, the control problem of a multiple-flexible-link robot is no more complex than the control problem of individual flexible links subject to kinematics constraints. A planar beam governed by Euler-Bernoulli equation is studied as an example for simplicity. A possible extension to robots with multiple flexible links is theoretically possible by creating appropriate virtual power flows at the two ends of each beam. The validity of the theoretical results is verified by simulations with respect to two typical space systems in planar motion.
This paper presents an adaptive control scheme for a mobile manipulator robot based on the virtua... more This paper presents an adaptive control scheme for a mobile manipulator robot based on the virtual decomposition control (VDC). The control strategy was tested on three degrees of freedom manipulator arm mounted on two degrees of freedom mobile platform to track a desired trajectory. The desired trajectory is obtained from the workspace trajectory using the inverse kinematics. Differently to the known decentralized control that divides the mobile manipulator into two subsystems, in this paper, the mobile manipulator has N degrees of freedom, divided virtually into N subsystems. The applicability of the proposed scheme is demonstrated in real time validation. The experimental results show the effectiveness of the VDC approach.
This paper presents an adaptive backstepping control scheme for a mobile manipulator robot based ... more This paper presents an adaptive backstepping control scheme for a mobile manipulator robot based on the virtual decomposition control (VDC). The control scheme was applied on a three degrees of freedom manipulator arm mounted on a two degrees of freedom mobile platform to track a desired workspace trajectory. The desired joint space trajectory is obtained by using the inverse kinematics. In this paper, the mobile manipulator has N degrees of freedom, divided virtually into N subsystems. The validation of the proposed scheme is proved in real time implementation. The experimental results show the effectiveness of the proposed control schemes based on VDC approach.
International Journal of Control Automation and Systems, Jun 27, 2017
This paper presents a nonlinear control scheme for multiple mobile manipulator robots (MMR) movin... more This paper presents a nonlinear control scheme for multiple mobile manipulator robots (MMR) moving a rigid object in coordination. The dynamic parameters of the handled object and the mobile manipulators are estimated online using the virtual decomposition approach. The control law is designed based on an appropriate choice of the Lyapunov function candidate. The proposed control design ensures that the position error in the workspace converges to zero, and the external force error is bounded. Numerical simulations and an experimental validation are carried out for two mobile manipulators transporting an object in order to show the effectiveness of the proposed controller.
the experimental results that were obtained through two seasons of test c a m p a i g n s. 1.
A four-channel control architecture has been suggested in the liter-ature to achieve transparency... more A four-channel control architecture has been suggested in the liter-ature to achieve transparency for master-slave teleoperator systems under position control. In this paper, the result is generalized to in-clude teleoperator systems that are under rate control or more gen-eral master-slave kinematic correspondence laws, such as a mixed-position/rate mode. A one-degree-of-freedom example is given to outline the design and analysis of such a system for transparency and stability. The validity of the theory has been verified through simulations and experiments. KEY WORDS—teleoperation, force feedback, rate control, transparency
This paper summarizes the major conclusions of twenty years of research in robot force control, p... more This paper summarizes the major conclusions of twenty years of research in robot force control, points out remaining problems, and introduces issues that need more attention. By looking at force control from a distance, a lot of common features among diierent control approaches are revealed; this allows us to put force control into a broader (e.g., diierential-geometric) context. The paper starts with the basics of force control at an introductory level, by focusing at one or two degrees of freedom. Then the problems associated with the extension to the multidimensional case are described in a diierential-geometric context. Finally, robustness and adaptive control are discussed.
A four-channel control architecture has been suggested in the literature to achieve transparency ... more A four-channel control architecture has been suggested in the literature to achieve transparency for master-slave teleoperator systems under position control. In this paper, the result is generalized to include teleoperator systems that are under rate control or more general master-slave kinematic correspondence laws, such as a mixedposition/rate mode. A one-degree-of-freedom example is given to outline the design and analysis of such a system for transparency and stability. The validity of the theory has been verified through simulations and experiments. KEY WORDS—teleoperation, force feedback, rate control, transparency 1.
Applied Bionics and Biomechanics, 2018
There are two main categories of force control schemes: hybrid position-force control and impedan... more There are two main categories of force control schemes: hybrid position-force control and impedance control. However, the former does not take into account the dynamic interaction between the robot’s end effector and the environment. In contrast, impedance control includes regulation and stabilization of robot motion by creating a mathematical relationship between the interaction forces and the reference trajectories. It involves an energetic pair of a flow and an effort, instead of controlling a single position or a force. A mass-spring-damper impedance filter is generally used for safe interaction purposes. Tuning the parameters of the impedance filter is important and, if an unsuitable strategy is used, this can lead to unstable contact. Humans, however, have exceptionally effective control systems with advanced biological actuators. An individual can manipulate muscle stiffness to comply with the interaction forces. Accordingly, the parameters of the impedance filter should be t...
The aim of this paper is to derive the equations of motion for biped robot during different walki... more The aim of this paper is to derive the equations of motion for biped robot during different walking phases using two well-known formulations: Euler-Lagrange (E-L) and Newton-Euler (N-E) equations. The modeling problems of biped robots lie in their varying configurations during locomotion; they could be fully actuated during the single support phase (SSP) and over-actuated during the double support phase (DSP). Therefore, first, the E-L equations of 6-link biped robot are described in some details for dynamic modeling during different walking phases with concentration on the DSP. Second, the detailed description of modified recursive Newton-Euler (N-E) formulation (which is very useful for modeling complex robotic system) is illustrated with a novel strategy for solution of the over-actuation/discontinuity problem. The derived equations of motion of the target biped for both formulations are suitable for control laws if the analyzer needs to deal with control problems. As expected, t...
This paper summarizes the major conclusions of twenty years of research in robot force control, p... more This paper summarizes the major conclusions of twenty years of research in robot force control, points out remaining problems, and introduces issues that need more attention. By looking at force control from a distance, a lot of common features among different control approaches are revealed; this allows us to put force control into a broader (e.g., differential-geometric) context. The paper starts with the basics of force control at an introductory level, by focusing at one or two degrees of freedom. Then the problems associated with the extension to the multidimensional case are described in a differential-geometric context. Finally, robustness and adaptive control are discussed. 1 Introduction The purpose of force control could be quite diverse, such as applying a controlled force needed for a manufacturing process (e.g., deburing or grinding), pushing an external object using a controlled force, or dealing with geometric uncertainty by establishing controlled contacts (e.g., in ...
This paper presents results from the 2006 and 2007 test campaigns of the Canadian Space Agency... more This paper presents results from the 2006 and 2007 test campaigns of the Canadian Space Agency's autonomous rover navigation research. In particular, results are provided in the area of terrain modelling, path planning and 3D odometry. Results are also provided for integrated system tests whereby the rover travelled autonomously and semi-autonomously beyond its sensing horizon. It provides a summary of the experimental results that were obtained through two seasons of test campaigns.
International Journal of Digital Signals and Smart Systems, 2017
This paper presents an adaptive coordinated control scheme for multiple mobile manipulator robots... more This paper presents an adaptive coordinated control scheme for multiple mobile manipulator robots (MMR) moving a rigid object in coordination. The dynamic parameters of the object handled and of the mobile manipulators are considered unknown but constant. The control law and the adaptation of uncertain parameters are designed using the virtual decomposition (VDC) approach. This control approach was originally applied to multiple manipulator robot systems. The proposed control design ensures that the position error in the workspace converges to zero, and that the external force error is bounded. The global stability of the system using VDC is proven through the virtual stability of each subsystem. Numerical simulations and an experimental validation are carried out for two mobile manipulators transporting an object, and are compared with the results obtained using the computed torque approach in order to show the effectiveness of the proposed controller.
Control Engineering Practice, 2019
Abstract In addition to high-precision closed-loop control performance, energy efficiency is anot... more Abstract In addition to high-precision closed-loop control performance, energy efficiency is another vital characteristic in field-robotic hydraulic systems as energy source(s) must be carried on board in limited space. This study proposes an energy-efficient and high-precision closed-loop controller for the highly nonlinear hydraulic robotic manipulators. The proposed method is twofold: 1) A possibility for energy consumption reduction is realized by using a separate meter-in separate meter-out (SMISMO) control set-up, enabling an independent metering (pressure control) of each chamber in hydraulic actuators. 2) A novel subsystem-dynamics-based and modular controller is designed for the system actuators, and it is integrated to the previously designed state-of-the-art controller for multiple degrees-of-freedom (n-DOF) manipulators. Stability of the overall controller is rigorously proven. The comparative experiments with a three-DOF redundant hydraulic robotic manipulator (with a payload of 475 kg) demonstrate that: 1) It is possible to design the triple objective of high-precision piston position, piston force and chamber pressure trackings for the hydraulic actuators. 2) In relation to the previous SMISMO-control methods, unprecedented motion and chamber pressure tracking performances are reported. 3) In comparison to the state-of-the-art motion tracking controller with a conventional energy-inefficient servovalve control, the actuators’ energy consumption is reduced by 45% without noticeable motion control (position-tracking) deterioration.
Springer Tracts in Advanced Robotics, 2010
This paper presents the approach for autonomous over-the-horizon rover navigation developed at th... more This paper presents the approach for autonomous over-the-horizon rover navigation developed at the Canadian Space Agency. The adopted sensing modality is the one of LIDAR range sensors due to their robustness in the harsh lighting conditions of space. Irregular triangular meshes (ITM) are used for representing the environment providing with an accurate yet compact spatial representation. The ITM is directly usable by path planning algorithms based on efficient graph search such as A*. Experimental results from the 2006 and 2007 extensive field-testing campaigns are provided.
This study designs a high-precision bilateral teleoperation control for a dissimilar master-slave... more This study designs a high-precision bilateral teleoperation control for a dissimilar master-slave system. The proposed nonlinear control design takes advantage of a novel subsystem-dynamics-based control method that allows designing of individual (decentralized) model-based controllers for the manipulators locally at the subsystem level. Very importantly, a dynamic model of the human operator is incorporated into the control of the master manipulator. The individual controllers for the dissimilar master and slave manipulators are connected in a specific communication channel for the bilateral teleoperation to function. Stability of the overall control design is rigorously guaranteed with arbitrary time delays. Novel features of this study include the completely force-sensor-less design for the teleoperation system with a solution for a uniquely introduced computational algebraic loop, a method of estimating the exogenous operating force of an operator, and the use of a commercial ha...
It is well known that flexibility of robotic links causes deformation and reduced positioning acc... more It is well known that flexibility of robotic links causes deformation and reduced positioning accuracy of the robot at the end-effector and this problem becomes more complicated when the links are made of new materials such as composite. Various approaches including strain gauges, fiber Bragg grating, computer vision and optoelectronics have been applied to solve the problem. This paper proposes an optoelectronic method with a reduced number of position sensing detectors and laser diodes to determine both bending and torsion deformations of a robotic link. The attachment of two optoelectronic sensors on the link and two laser dots produced on these sensors by lasers provide the data required for computations and the tip deflection values are obtained by trigonometric functions along with iterative computations. The method has been analysed to identify possible sources of error. Experiments were conducted to verify the proposed method and the results have demonstrated its efficiency.
The recent success of NASA’s Mars Exploration Rovers has demonstrated the important benefits that... more The recent success of NASA’s Mars Exploration Rovers has demonstrated the important benefits that mobility adds to landed planetary exploration missions. The Canadian Space Agency (CSA) has been conducting research in ground control and in autonomous robotics for several years already. One of the target applications is planetary exploration using mobile platforms. The emphasis of our research program is on reactive on-board autonomy software and long-range rover navigation. This paper describes recent activities of the CSA in this area. Key results are described in the areas of terrain modelling, path planning and rover guidance.
IFAC Proceedings Volumes, 2008
Use of flexible link robots is motivated by applications featuring lightweight or long arms. Howe... more Use of flexible link robots is motivated by applications featuring lightweight or long arms. However, the control problem faces strong technical challenges resulting from the complex dynamics. In this paper, the virtual decomposition control (VDC) approach is applied for the first time to address the technical challenges of this thorny problem mainly resulting from the dynamic coupling effects among flexible links. In view of the VDC approach, the control problem of a multiple-flexible-link robot is no more complex than the control problem of individual flexible links subject to kinematics constraints. A planar beam governed by Euler-Bernoulli equation is studied as an example for simplicity. A possible extension to robots with multiple flexible links is theoretically possible by creating appropriate virtual power flows at the two ends of each beam. The validity of the theoretical results is verified by simulations with respect to two typical space systems in planar motion.
This paper presents an adaptive control scheme for a mobile manipulator robot based on the virtua... more This paper presents an adaptive control scheme for a mobile manipulator robot based on the virtual decomposition control (VDC). The control strategy was tested on three degrees of freedom manipulator arm mounted on two degrees of freedom mobile platform to track a desired trajectory. The desired trajectory is obtained from the workspace trajectory using the inverse kinematics. Differently to the known decentralized control that divides the mobile manipulator into two subsystems, in this paper, the mobile manipulator has N degrees of freedom, divided virtually into N subsystems. The applicability of the proposed scheme is demonstrated in real time validation. The experimental results show the effectiveness of the VDC approach.
This paper presents an adaptive backstepping control scheme for a mobile manipulator robot based ... more This paper presents an adaptive backstepping control scheme for a mobile manipulator robot based on the virtual decomposition control (VDC). The control scheme was applied on a three degrees of freedom manipulator arm mounted on a two degrees of freedom mobile platform to track a desired workspace trajectory. The desired joint space trajectory is obtained by using the inverse kinematics. In this paper, the mobile manipulator has N degrees of freedom, divided virtually into N subsystems. The validation of the proposed scheme is proved in real time implementation. The experimental results show the effectiveness of the proposed control schemes based on VDC approach.
International Journal of Control Automation and Systems, Jun 27, 2017
This paper presents a nonlinear control scheme for multiple mobile manipulator robots (MMR) movin... more This paper presents a nonlinear control scheme for multiple mobile manipulator robots (MMR) moving a rigid object in coordination. The dynamic parameters of the handled object and the mobile manipulators are estimated online using the virtual decomposition approach. The control law is designed based on an appropriate choice of the Lyapunov function candidate. The proposed control design ensures that the position error in the workspace converges to zero, and the external force error is bounded. Numerical simulations and an experimental validation are carried out for two mobile manipulators transporting an object in order to show the effectiveness of the proposed controller.
the experimental results that were obtained through two seasons of test c a m p a i g n s. 1.
A four-channel control architecture has been suggested in the liter-ature to achieve transparency... more A four-channel control architecture has been suggested in the liter-ature to achieve transparency for master-slave teleoperator systems under position control. In this paper, the result is generalized to in-clude teleoperator systems that are under rate control or more gen-eral master-slave kinematic correspondence laws, such as a mixed-position/rate mode. A one-degree-of-freedom example is given to outline the design and analysis of such a system for transparency and stability. The validity of the theory has been verified through simulations and experiments. KEY WORDS—teleoperation, force feedback, rate control, transparency
This paper summarizes the major conclusions of twenty years of research in robot force control, p... more This paper summarizes the major conclusions of twenty years of research in robot force control, points out remaining problems, and introduces issues that need more attention. By looking at force control from a distance, a lot of common features among diierent control approaches are revealed; this allows us to put force control into a broader (e.g., diierential-geometric) context. The paper starts with the basics of force control at an introductory level, by focusing at one or two degrees of freedom. Then the problems associated with the extension to the multidimensional case are described in a diierential-geometric context. Finally, robustness and adaptive control are discussed.
A four-channel control architecture has been suggested in the literature to achieve transparency ... more A four-channel control architecture has been suggested in the literature to achieve transparency for master-slave teleoperator systems under position control. In this paper, the result is generalized to include teleoperator systems that are under rate control or more general master-slave kinematic correspondence laws, such as a mixedposition/rate mode. A one-degree-of-freedom example is given to outline the design and analysis of such a system for transparency and stability. The validity of the theory has been verified through simulations and experiments. KEY WORDS—teleoperation, force feedback, rate control, transparency 1.
Applied Bionics and Biomechanics, 2018
There are two main categories of force control schemes: hybrid position-force control and impedan... more There are two main categories of force control schemes: hybrid position-force control and impedance control. However, the former does not take into account the dynamic interaction between the robot’s end effector and the environment. In contrast, impedance control includes regulation and stabilization of robot motion by creating a mathematical relationship between the interaction forces and the reference trajectories. It involves an energetic pair of a flow and an effort, instead of controlling a single position or a force. A mass-spring-damper impedance filter is generally used for safe interaction purposes. Tuning the parameters of the impedance filter is important and, if an unsuitable strategy is used, this can lead to unstable contact. Humans, however, have exceptionally effective control systems with advanced biological actuators. An individual can manipulate muscle stiffness to comply with the interaction forces. Accordingly, the parameters of the impedance filter should be t...
The aim of this paper is to derive the equations of motion for biped robot during different walki... more The aim of this paper is to derive the equations of motion for biped robot during different walking phases using two well-known formulations: Euler-Lagrange (E-L) and Newton-Euler (N-E) equations. The modeling problems of biped robots lie in their varying configurations during locomotion; they could be fully actuated during the single support phase (SSP) and over-actuated during the double support phase (DSP). Therefore, first, the E-L equations of 6-link biped robot are described in some details for dynamic modeling during different walking phases with concentration on the DSP. Second, the detailed description of modified recursive Newton-Euler (N-E) formulation (which is very useful for modeling complex robotic system) is illustrated with a novel strategy for solution of the over-actuation/discontinuity problem. The derived equations of motion of the target biped for both formulations are suitable for control laws if the analyzer needs to deal with control problems. As expected, t...
This paper summarizes the major conclusions of twenty years of research in robot force control, p... more This paper summarizes the major conclusions of twenty years of research in robot force control, points out remaining problems, and introduces issues that need more attention. By looking at force control from a distance, a lot of common features among different control approaches are revealed; this allows us to put force control into a broader (e.g., differential-geometric) context. The paper starts with the basics of force control at an introductory level, by focusing at one or two degrees of freedom. Then the problems associated with the extension to the multidimensional case are described in a differential-geometric context. Finally, robustness and adaptive control are discussed. 1 Introduction The purpose of force control could be quite diverse, such as applying a controlled force needed for a manufacturing process (e.g., deburing or grinding), pushing an external object using a controlled force, or dealing with geometric uncertainty by establishing controlled contacts (e.g., in ...
This paper presents results from the 2006 and 2007 test campaigns of the Canadian Space Agency... more This paper presents results from the 2006 and 2007 test campaigns of the Canadian Space Agency's autonomous rover navigation research. In particular, results are provided in the area of terrain modelling, path planning and 3D odometry. Results are also provided for integrated system tests whereby the rover travelled autonomously and semi-autonomously beyond its sensing horizon. It provides a summary of the experimental results that were obtained through two seasons of test campaigns.
International Journal of Digital Signals and Smart Systems, 2017
This paper presents an adaptive coordinated control scheme for multiple mobile manipulator robots... more This paper presents an adaptive coordinated control scheme for multiple mobile manipulator robots (MMR) moving a rigid object in coordination. The dynamic parameters of the object handled and of the mobile manipulators are considered unknown but constant. The control law and the adaptation of uncertain parameters are designed using the virtual decomposition (VDC) approach. This control approach was originally applied to multiple manipulator robot systems. The proposed control design ensures that the position error in the workspace converges to zero, and that the external force error is bounded. The global stability of the system using VDC is proven through the virtual stability of each subsystem. Numerical simulations and an experimental validation are carried out for two mobile manipulators transporting an object, and are compared with the results obtained using the computed torque approach in order to show the effectiveness of the proposed controller.
Control Engineering Practice, 2019
Abstract In addition to high-precision closed-loop control performance, energy efficiency is anot... more Abstract In addition to high-precision closed-loop control performance, energy efficiency is another vital characteristic in field-robotic hydraulic systems as energy source(s) must be carried on board in limited space. This study proposes an energy-efficient and high-precision closed-loop controller for the highly nonlinear hydraulic robotic manipulators. The proposed method is twofold: 1) A possibility for energy consumption reduction is realized by using a separate meter-in separate meter-out (SMISMO) control set-up, enabling an independent metering (pressure control) of each chamber in hydraulic actuators. 2) A novel subsystem-dynamics-based and modular controller is designed for the system actuators, and it is integrated to the previously designed state-of-the-art controller for multiple degrees-of-freedom (n-DOF) manipulators. Stability of the overall controller is rigorously proven. The comparative experiments with a three-DOF redundant hydraulic robotic manipulator (with a payload of 475 kg) demonstrate that: 1) It is possible to design the triple objective of high-precision piston position, piston force and chamber pressure trackings for the hydraulic actuators. 2) In relation to the previous SMISMO-control methods, unprecedented motion and chamber pressure tracking performances are reported. 3) In comparison to the state-of-the-art motion tracking controller with a conventional energy-inefficient servovalve control, the actuators’ energy consumption is reduced by 45% without noticeable motion control (position-tracking) deterioration.
Springer Tracts in Advanced Robotics, 2010
This paper presents the approach for autonomous over-the-horizon rover navigation developed at th... more This paper presents the approach for autonomous over-the-horizon rover navigation developed at the Canadian Space Agency. The adopted sensing modality is the one of LIDAR range sensors due to their robustness in the harsh lighting conditions of space. Irregular triangular meshes (ITM) are used for representing the environment providing with an accurate yet compact spatial representation. The ITM is directly usable by path planning algorithms based on efficient graph search such as A*. Experimental results from the 2006 and 2007 extensive field-testing campaigns are provided.
This study designs a high-precision bilateral teleoperation control for a dissimilar master-slave... more This study designs a high-precision bilateral teleoperation control for a dissimilar master-slave system. The proposed nonlinear control design takes advantage of a novel subsystem-dynamics-based control method that allows designing of individual (decentralized) model-based controllers for the manipulators locally at the subsystem level. Very importantly, a dynamic model of the human operator is incorporated into the control of the master manipulator. The individual controllers for the dissimilar master and slave manipulators are connected in a specific communication channel for the bilateral teleoperation to function. Stability of the overall control design is rigorously guaranteed with arbitrary time delays. Novel features of this study include the completely force-sensor-less design for the teleoperation system with a solution for a uniquely introduced computational algebraic loop, a method of estimating the exogenous operating force of an operator, and the use of a commercial ha...
It is well known that flexibility of robotic links causes deformation and reduced positioning acc... more It is well known that flexibility of robotic links causes deformation and reduced positioning accuracy of the robot at the end-effector and this problem becomes more complicated when the links are made of new materials such as composite. Various approaches including strain gauges, fiber Bragg grating, computer vision and optoelectronics have been applied to solve the problem. This paper proposes an optoelectronic method with a reduced number of position sensing detectors and laser diodes to determine both bending and torsion deformations of a robotic link. The attachment of two optoelectronic sensors on the link and two laser dots produced on these sensors by lasers provide the data required for computations and the tip deflection values are obtained by trigonometric functions along with iterative computations. The method has been analysed to identify possible sources of error. Experiments were conducted to verify the proposed method and the results have demonstrated its efficiency.