An adaptive controller for a direct-drive SCARA robot: Analysis and simulation

A direct adaptive controller for trajectory tracking of high-speed robots such as a direct-drive SCARA robot is presented. In this robot, nonlinear effects due to centrifugal, Coriolis, and gravity forces are more important than friction forces. The control law of the adaptive scheme consists in a PD regulator and feedforward compensation of full dynamics. The feedforward terms are adjusted by an adaptation law so that the steady-state position errors are zero. The regulator gain matrix can be fixed or time-varying; in the latter case, the adaptive scheme becomes similar to the computed torque scheme. However, with the adaptive controller, 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 4 d.o.f. SCARA robot are illustrated by a digital simulation