A New Approach to Control Single-Link Flexible Arms, Part III: Adaptive Control of the Tip Position with Payload Changes

Abstract

This third report describes a new method to control single-link lumped-mass flexible arms in the case of having friction in the joint and changes in the payload. Both linear and nonlinear friction components are overcome by using the very robust control scheme developed in the second report, which is based on two nested fecdback loops: an inner one that controls the motor position and an outer one that controls the tip position. In order to compensate for changes in the payload an adaptive control scheme is used. Two cases are considered when compensating for changes in the tip payload the arm is a minimum phase system or a non-minimum phase one. Different adaptive control schemes are proposed in each case. In them, compensation for changes in the load is achieved in two steps: first the tip payload is estimated from a very simple procedure proposed here, and then the feedfarward and feedback controllers are tuned according to this estimated value. It results in a quite simple control law that can be used for real-time control of flexible arms, and that needs minimal computing effort. Experimental results are shown.