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"Huang, An-chyau"
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Adaptive control of robot manipulators
This book introduces an unified function approximation approach to the control of uncertain robot manipulators containing general uncertainties. It works for free space tracking control as well as compliant motion control. It is applicable to the rigid robot and the flexible joint robot. Even with actuator dynamics, the unified approach is still feasible. All these features make the book stand out from other existing publications.
eBook
FAT-based Force Sensorless Adaptive Impedance Controller Design of Robot Manipulators Without Using Force Estimators
A function approximation technique (FAT) based force sensorless adaptive impedance controller is proposed in this paper for rigid robot manipulators without using force estimators. The basic idea is to rewrite the traditional impedance controller by replacing the contact force with the target impedance so that a force sensorless impedance controller is obtained. A lumped uncertainty can then be found by collecting all the uncertainties in the new controller. The FAT is employed to facilitate the design of the adaptive loop justified by the Lyapunov stability theory. In this new design, computation of tedious regressor matrix used in most traditional robot adaptive designs are avoided. Both the renowned singularity problem and the joint acceleration feedback problem are circumvented. The number of functions to be estimated is reduced to be linear to the number of robot joints which is a great simplification in real-time computation. Simulation results show that the proposed design can give good performance regardless of various uncertainties and unavailability of the contact force signals.
Journal Article
Adaptive control of rotary inverted pendulum system with time-varying uncertainties
In this paper, an adaptive controller is proposed to balance a rotary inverted pendulum with time-varying uncertainties. The goal of the control is to bring the pendulum close to the upright position regardless of the various uncertainties and disturbances. Its underactuated dynamics is first decoupled by Olfati’s transformation into a cascade form, and then an adaptive controller is designed to deal with the uncertainties in the new space. Based on the Lyapunov-like theory, the closed loop stability and boundedness of all internal signals can be proved. The simulation results show that the proposed scheme is capable of giving good performance, as desired.
Journal Article
Contact force cancelation in robot impedance control by target impedance modification
A force sensorless impedance controller is proposed in this paper for robot manipulators without using force estimators. From the observation of the impedance control law, the force feedback term can be canceled if the inertia matrix in the target impedance is the same as the robot inertia matrix. However, the inertia matrix in the target impedance is almost always a constant matrix, while the robot inertia matrix is a function of the robot configuration, and hence, they may not be identical in general. A modification of the coefficient matrix for the contact force term in the target impedance is suggested in this paper to enable cancelation of the force feedback term in the impedance control law so that a force sensorless impedance controller without using force estimators can be obtained. The tracking performance in the free space phase and the motion trajectory in the compliant motion phase of the new design are almost the same as those in the traditional impedance control. Modification of the inertia matrix in the target impedance will result in small variations of the contact force which is acceptable in practical applications. For robot manipulators containing uncertainties, an adaptive version of the new controller is also developed in this paper to give satisfactory performance without the need for force sensors. Rigorous mathematical justification in closed-loop stability is given in detail, and computer simulations are performed to verify the efficacy of the proposed design.
Journal Article
Vibration Suppression in the Underactuated Dynamics of ATMD Systems Under Earthquake Excitation
Purpose
The active tuned mass damper (ATMD) system is underactuated where the number of actuators is less than the number of system’s DOF. It is well known that the regulation of an underactuated system is challenging. Few reports can be found in the literature relating to the design of ATMD systems from the view point of their underactuated dynamics. In this paper, we firstly clarify the underactuated behavior of an ATMD system whose ill-conditioned controllability matrix largely limits the flexibility of controller design. Controllers are proposed to circumvent the underactuated dynamics to ensure vibration attenuation during the earthquake and rapid state convergence in the ATMD when the earthquake vanishes.
Methods
This paper proposes a redefined output function to destroy the underactuated dynamics so that a stabilizing controller can be designed to regulate the new output. A low pass filter is suggested in the control loop to give boundedness of primal and auxiliary systems simultaneously supported by BIBO stability.
Results
The simulation results show that the proposed ATMD design can give much better performance in both time and frequency responses compared with the traditional TMD design under the 1940 El Centro earthquake and 1985 Mexico City earthquake.
Conclusion
The proposed output redefinition design removes the underactuated dynamics in the ATMD system effectively, and the low-pass filter inclusion preserves system passivity so that convergence of the states can be obtained. These have been justified by mathematical proofs and simulation verifications.
Journal Article
Adaptive Impedance Control of Robot Manipulators based on Function Approximation Technique
This paper presents an adaptive impedance control scheme for an $n$-link constrained rigid robot manipulator without using the regressor. In addition, inversion of the estimated inertia matrix is also avoided and the new design is free from end-point acceleration measurements. The dynamics of the robot manipulator is assumed that all of the matrices in robot model are unavailable. Since these matrices are time-varying and their variation bounds are not given, traditional adaptive or robust designs do not apply. The function approximation technique is used here to represent uncertainties in some finite linear combinations of the orthogonal basis. The dynamics of the output tracking can thus be proved to be a stable first order filter driven by function approximation errors. Using the Lyapunov stability theory, a set of update laws is derived to give closed loop stability with proper tracking performance. A 2 DOF planar robot with environment constraint is used in the computer simulations to test the efficacy of the proposed scheme.
Journal Article
A regressor-free adaptive controller for robot manipulators without Slotine and Li's modification
Similar to the traditional adaptive strategies for robot manipulators, the regressor-free adaptive controller design also requires applying Slotine and Li's modification to avoid the feedback of joint accelerations. In this paper, a simple method is proposed to construct a regressor-free adaptive controller for robot manipulators without Slotine and Li's modification. In the new design, the joint acceleration vector is lumped into an unknown time-varying function and the function approximation technique is utilized to cover its effect; therefore, its implementation is free from joint acceleration feedback. The closed-loop stability and boundedness of internal signals are justified by the Lyapunov-like technique. Both simulation and experimental results for a two-link robot are presented to show the effectiveness of the proposed design.
Journal Article
Adaptive impedance controller design for flexible-joint electrically-driven robots without computation of the regressor matrix
To the best of our knowledge, this is the first paper focus on the adaptive impedance control of robot manipulators with consideration of joint flexibility and actuator dynamics. Controller design for this problem is difficult because each joint of the robot has to be described by a fifth-order cascade differential equation. In this paper, a backstepping-like procedure incorporating the model reference adaptive control strategy is employed to construct the impedance controller. The function approximation technique is applied to estimate time-varying uncertainties in the system dynamics. The proposed control law is free from the calculation of the tedious regressor matrix, which is a significant simplification in implementation. Closed-loop stability and boundedness of internal signals are proved by the Lyapunov-like analysis with consideration of the function approximation error. Computer simulation results are presented to demonstrate the usefulness of the proposed scheme.
Journal Article
A regressor-free adaptive impedance controller for robot manipulators without Slotine and Li's modification: theory and experiments
Slotine and Li's modification is a well-known, simple, and elegant approach for robot adaptive control to avoid the feedback of joint accelerations. This paper presents a simple strategy to implement a regressor-free adaptive impedance controller without using Slotine and Li's modification. In the new strategy, the joint acceleration vector and the dynamics of robot are assumed to be unavailable. Their effects are covered by using the function approximation technique so that there is no need for the joint acceleration feedback. The closed-loop stability and boundedness of internal signals are justified by the Lyapunov-like technique. Experimental results for a two-dimensional (2D) robot are presented to show the effectiveness of the proposed strategy.
Journal Article