A novel variable structure control scheme for an industrial robot: theory and experiments

Dynamic behavior of a system in the sliding mode is entirely defined by the sliding surface. Customarily, the surface is selected as a hyperplane in the system state-space resulting in a PD type sliding surface. This is not the only possible structure, and other designs with more complex or time-varying surfaces may provide definite advantages. We present a new design procedure and stability analysis for robotic variable structure controllers with PID like sliding surface. Two versions of the controllers are presented: regular and adaptive. The former is very simple and can operate with an unknown robot dynamic model; the only information required is a bound on one parameter. The latter provides an online estimation for this bound. Both versions of the controllers are robust with respect to bounded external disturbances and some unmodeled dynamic effects. The control schemes are applied to an industrial robot without requiring the knowledge of the dynamic model and the parameter values of the robot. Experiments conducted with a Reis industrial robot have shown stable and accurate performance of the developed controller