A Multiple Rate Control Scheme of Robot Manipulators

Abstract

Due to modelling errors or environmental uncertainties, robot motion may present signijcant positioning errors using the conventional computed torque method. To impove tracking capability of robot manipulators, sliding mode control and nonlinear control algorithms have been introduced, but computation is costly, and thus a fast motion execution using simple computer sources is impossible. To solve this problem, we present a composite control algorithm to control robot motion combining a discrete feedforward component and a continuous feedback component. The discrete feedforward component provides a nominal torque computed using the robot dynamics and compensates for dynamic coupling between the links, This part can be updated in a large sampling time, and can generally be computed off-line; thus real-time computation is decreased. The continuous feedback con fro1 component uses a structure of the Variable Structure System and provides a robust control of disturbances during the sliding mode. This part can be digitally implemented using a short sampling time, and thus fast motion of a multi-degree freedom robot manipulator can be executed by using a simple computer, or even a single board computer with an 8-bit CPU. The stability of the proposed multiple-rate control scheme is proven in the paper and eficiency of the control scheme has been demonstrated by simulations of a three-link robot subject to parameter and payload uncertainties.