AN ADAPTIVE CONTROLLER FOR A DIRECT-DRIVE SCARA ROBOT

This paper presents a direct adaptive controller for trajectory tracking of high-speed robots such as a direct-drive SCARA robot. In this robot, nonlinear effects due to centrifugal, Coriolis, and inertial forces are more important than friction and gravity forces, unlike most industrial robots. The control law of the adaptive scheme consists in a PD regulator plus feedforward compensation of full dynamics. The feedforward terms are adjusted by an adaptation law so that the steady-state position errors are zero. It should be noted that with this adaptive controller, the joint accelerations measurement is not required and no inversion of the estimated mass matrix is involved. The tracking performances of the controller applied to a 2-dof SCARA is illustrated by a real-time implementation based on a single-chip digital signal processor (DSP).