Control Strategies for Robot Manipulators—A Review
TL;DR: In this article, a review of the basic problems involved and their existing control solutions is presented, and a broad-based classification of control strategies is given for industrial robot control strategies.
Abstract: Industrial robots are multilink, highly nonlinear and coupled dynamic systems, where control is a difficult and challenging task. This paper presents a review of the basic problems involved and their existing control solutions. This review also attempts to give a broadbased classification of control strategies.
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TL;DR: In this article, the authors present a technique which adopts the idea of "inverse problem" and extends the results of "resolved-motion-rate" controls, which deals directly with the position and orientation of the hand.
Abstract: Position control of a manipulator involves the practical problem of solving for the correct input torques to apply to the joints for a set of specified positions, velocities, and accelerations. Since the manipulator is a nonlinear system whose joints are highly coupled, it is very difficult to control. This paper presents a technique which adopts the idea of "inverse problem" and extends the results of "resolved-motion-rate" controls. The method deals directly with the position and orientation of the hand. It differs from others in that accelerations are specified and that all the feedback control is done at the hand level. The control algorithm is shown to be asymptotically convergent. A PDP 11/45 computer is used as part of a controller which computes the input torques/forces at each sampling period for the control system using the Newton-Euler formulation of equations of motion. The program is written in floating point assembly language, and has an average execution time of less than 11.5 ms for a Stanford manipulator. This makes a sampling frequency of 87 Hz possible. The controller is verified by an example which includes a simulated manipulator.
1,231 citations
01 Feb 1978
TL;DR: It is verified through hybrid simulation that trajectories which are close to ideal sliding modes exist when the controller is designed according to theory.
Abstract: A new control algorithm is developed for manipulators using the theory of variable structure systems. The control is designed so that a new type of state space trajectories called sliding mode exists. Due to delays, neglected small time constants, and other idealizations, ideal sliding modes as predicted by the theory do not exist. We have verified through hybrid simulation that trajectories which are close to ideal sliding modes exist when the controller is designed according to theory. To illustrate the design procedures, a two-joint manipulator is considered.
595 citations
TL;DR: In this paper, a model-referenced adaptive control law is developed for maintaining uniformly good performance over a wide range of motions and payloads, and a learning signal approach is designed to minimize initial transients arising from abrupt changes in the inertial payload.
Abstract: The achievement of quality dynamic performance in manipulator systems is difficult using conventional control methods because of both the inherent geometric nonlinearities of these systems and the dependence of the system dynamics on the characteristics of manipulated objects. A model-referenced adaptive control law is developed for maintaining uniformly good performance over a wide range of motions and payloads. The effectiveness of the approach is demonstrated in several simulations and the system stability as a function of input is investigated. Also developed is a 'learning signal' approach designed to minimize initial transients arising from abrupt changes in the inertial payload.
534 citations
482 citations
TL;DR: In this paper, three nonlinear methods are presented, two of which are direct design procedures for industrial robots, based on a suitable partition of the dynamic equation of the industrial robot and provide directly applicable, explicit control laws for each drive.
Abstract: Models of industrial robots are characterized by highly nonlinear equations with nonlinear couplings between the variables of motion. In this paper, three nonlinear methods are presented, two of which are direct design procedures for industrial robots. These direct nonlinear methods are based on a suitable partition of the dynamic equation of the industrial robot and provide directly applicable, explicit control laws for each drive. The design procedures presented greatly simplify the derivation of the algorithm for computer-controlled industrial robots. The methods are applied to two different types of industrial robots.
470 citations