K. Glass

Direct adaptive impedance control of robot manipulators

This article presents an adaptive scheme for controlling the end-effector impedance of robot manipulators. The proposed control system consists of three subsystems: a simple “filter” that characterizes the desired dynamic relationship between the end-effector position error and the end-effector/environment contact force, an adaptive controller that produces the Cartesian-space control input required to provide this desired dynamic relationship, and an algorithm for mapping the Cartesian-space control input to a physically realizable joint-space control torque. The controller does not require knowledge of either the structure or the parameter values of the robot dynamics and is implemented without calculation of the robot inverse kinematic transformation. As a result, the scheme represents a general and computationally efficient approach to controlling the impedance of both nonredundant and redundant manipulators. Furthermore, the method can be applied directly to trajectory tracking in free-space motion by removing the impedance filter. Computer simulation results are given for a planar four degree-of-freedom redundant robot under adaptive impedance control. These results demonstrate that accurate end-effector impedance control and effective redundancy utilization can be achieved simultaneously by using the proposed controller.

Real-time collision avoidance for redundant manipulators

This paper presents a simple and robust approach to achieving collision avoidance for kinematically redundant manipulators at the control-loop level. The proposed scheme represents the obstacle avoidance requirement as inequality constraints in the manipulator workspace, and ensures that these inequalities are satisfied while the end-effector tracks the desired trajectory. The control scheme is the damped-least-squares formulation of the configuration control approach implemented as a kinematic controller. Computer simulation and experimental results are given for a Robotics Research 7 DOF redundant arm and demonstrate the collision avoidance capability for reaching inside a truss structure. These results confirm that the proposed approach provides a simple and effective method for real-time collision avoidance. >

Global regulation of uncertain manipulators using bounded controls

This paper considers the position regulation problem for uncertain robot manipulators in the presence of constraints on the available actuator torques, and proposes two new controllers as solutions to this problem. The first controller is derived under the assumption that the manipulator state is measurable, while the second strategy is developed for those applications in which only position measurements are available. Each scheme consists of a nonadaptive component for gross position control and an adaptive component to ensure convergence to the desired position. The controllers are computationally simple, require very little information regarding the manipulator model or the payload, and ensure that the position error is globally convergent. The capabilities of the proposed control strategies are illustrated though both computer simulations and laboratory experiments with an IMI Zebra Zero manipulator.

Decentralized Adaptive Control of Manipulators

This article presents two new adaptive schemes for motion control of robot manipulators. The first controller possesses a partially decentralized structure in which the control input for each task variable is computed based on information concerning only that variable and on two “scaling factors” that depend on the other task variables. The need for these scaling factors is eliminated in the second controller by exploiting the underlying topology of the robot configuration space, and this refinement permits the development of a completely decentralized adaptive control strategy. The proposed controllers are computationally efficient, do not require knowledge of either the mathematical model or the parameter values of the robot dynamics, and are shown to be globally stable in the presence of bounded disturbances. Furthermore, the control strategies are general and can be implemented for either position regulation or trajectory tracking in joint-space or task-space. Computer simulation results are given for a PUMA 762 manipulator, and these demonstrate that accurate and robust trajectory tracking is achievable using the proposed controllers. Experimental results are presented for a PUMA 560 manipulator and confirm that the proposed schemes provide simple and effective real-time controllers for accomplishing high-performance trajectory tracking.

Adaptive control of nonholonomic mechanical systems

This paper considers the problem of controlling nonholonomic mechanical systems in the presence of incomplete information concerning the system model and state, and presents a class of adaptive controllers as a solution to this problem. The proposed control strategies provide simple and robust solutions to a number of important nonholonomic system control problems, including stabilization to an equilibrium manifold, stabilization to an equilibrium point, and trajectory tracking control. All of the schemes are computationally efficient, are implementable without system dynamic model or rate information, and ensure uniform boundedness of all signals and accurate motion control.

Cartesian control of redundant robots

A Cartesian-space position/force controller is presented for redundant robots. The proposed control structure partitions the control problem into a nonredundant position/force trajectory tracking problem and a redundant mapping problem between Cartesian control input F is a set member of the set R(sup m) and robot actuator torque T is a set member of the set R(sup n) (for redundant robots, m is less than n). The underdetermined nature of the F yields T map is exploited so that the robot redundancy is utilized to improve the dynamic response of the robot. This dynamically optimal F yields T map is implemented locally (in time) so that it is computationally efficient for on-line control; however, it is shown that the map possesses globally optimal characteristics. Additionally, it is demonstrated that the dynamically optimal F yields T map can be modified so that the robot redundancy is used to simultaneously improve the dynamic response and realize any specified kinematic performance objective (e.g., manipulability maximization or obstacle avoidance). Computer simulation results are given for a four degree of freedom planar redundant robot under Cartesian control, and demonstrate that position/force trajectory tracking and effective redundancy utilization can be achieved simultaneously with the proposed controller.

Robust adaptive control of redundant manipulators

This paper presents an adaptive scheme for the motion control of kinematically redundant manipulators. The proposed controller is very general and computationally efficient since it does not require knowledge of either the mathematical model or the parameter values of the robot dynamics, and is implemented without calculation of the robot inverse dynamics or inverse kinematic transformation. It is shown that the control strategy is globally stable in the presence of bounded disturbances, and that in the absence of disturbances the size of the residual tracking errors can be made arbitrarily small. The performance of the controller is illustrated through computer simulations with a nine degree-of-freedom (DOF) compound manipulator consisting of a relatively small, fast six-DOF manipulator mounted on a large three-DOF positioning device. These simulations demonstrate that the proposed scheme provides accurate and robust trajectory tracking and, moreover, permits the available redundancy to be utilized so that a high bandwidth response can be achieved over a large workspace.

Adaptive regulation of rigid-link electrically-driven manipulators

This paper considers the position regulation problem for uncertain rigid-link electrically-driven manipulators, and presents an adaptive control strategy as a solution to this problem. The proposed controller is computationally simple, requires virtually no a priori information concerning either the manipulator or actuator models, and ensures semiglobal stability and convergence of the manipulator position error to zero. Experimental results are presented for a Zebra Zero manipulator and demonstrate that the proposed scheme provides a simple and effective means of obtaining high performance position regulation. Additionally, the experiments indicate that accurate trajectory tracking can also be realized with this controller.

Adaptive output stabilization of manipulators

This paper considers the position regulation problem for rigid robots for the case in which only joint position measurements are available, and proposes two adaptive controllers as solutions to this problem. The first controller is developed by assuming that the structure of the vector of gravity torques is known, but that the inertial parameters for the manipulator and payload are unknown; it is shown that this scheme ensures semiglobal stability and convergence of the position error to zero. Alternatively, the second adaptive strategy is derived under the assumption that no information is available concerning the manipulator model, and in this case it is shown that the controller provides uniform boundedness of all signals and exponential convergence of the position error to a set which can be made arbitrarily small. Experimental results are presented for a Zebra Zero manipulator and demonstrate that the proposed approach provides a simple and effective means of obtaining high performance position regulation.<<ETX>>

A new class of adaptive controllers for robot trajectory tracking

This article presents a new class of adaptive schemes for the motion control of robot manipulators. The proposed controllers are very general and computationally efficient because they do not require knowledge of either the mathematical model or the parameter values of the manipulator dynamics, and are implemented without calculation of the robot inverse dynamics or inverse kinematic transformations. It is shown that the control strategies are globally uniformly bounded in the presence of bounded disturbances, and that in the absence of disturbances the ultimate bound on the size of the tracking errors can be made arbitrarily small. Computer simulation results are given for a PUMA 560 manipulator, and demonstrate that accurate and robust trajectory tracking can be achieved by using the proposed controllers.