June 14, 2009
June 14, 2009
June 17, 2009
14.161.1 - 14.161.6
Adaptive Robot Manipulators in Global Technology
Model-based feedback control algorithms for robot manipulators require the on-line evaluation of robot dynamics and are particularly sensitive to modeling inaccuracies. This paper presents an adaptive technique for practical implementation of model-based robot control strategies and introduces a novel adaptive algorithm which makes the design insensitive to modeling errors. The design incorporates an on-line identification technique to eliminate parameter errors and individual joint controllers to compensate for modeling inaccuracies. An illustrated example is given to demonstrate the development of the proposed algorithm through a simple two- dimensional manipulator. New applications for robot manipulators are continually being discovered with global impacts due to integration of computer controlled robots.
The continuously increasing demands for enhanced productivity and improved precision have imposed special requirements on the control of industrial robots and caused a shift of emphasis towards the dynamic behavior of manipulators. This shift has led to the development of model- based control algorithms which incorporate the dynamic model of the manipulator in the control law in order to decouple the robot joints. The underlying principle is to: (1) design a nonlinear feedback algorithm that will effectively linearize the dynamic behavior of the robot joints; and (2) synthesize linear controllers to specify the closed-loop response.
The critical assumption in model-based control is that the robot dynamics are modeled accurately based upon precise knowledge of the kinematic and dynamic parameters of the manipulator. Unfortunately, this assumption is not always practical. Inevitable modeling and parameter errors may degrade controller performance and even lead to instability. Modeling errors are introduced by unmodeled dynamics or simplified models that are designed to reduce the real-time computational requirements of the controller. Parameter errors arise from practical limitations in the specification of numerical values for the kinematic and dynamic robot parameters or from payload variations.
The objective of this paper is to introduce an adaptive design to improve the performance of robot manipulators. The proposed design augments the model-based robot controller with an adaptive identifier of robot dynamics to reduce parameter errors. The identifier estimates the dynamic parameters of the manipulator from measurements of the inputs and outputs (joint positions, velocities, and accelerations) and calibrates adaptively the model in the controller.
II. Problem Statement
The matrix-vector formulation of the closed-form dynamic model for a robot with N joint axes1 is: && & D(q, λ) q + h ( q, q, λ) = F(t) (1)
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