Repetitive Control of a Two Degree of Freedom SCARA Manipulator

In this paper we examine the application of repetitive control schemes for robot manipulators. The controllers consist of a fixed PD action and a repetitive action for feed-forward nonlinearity compensation. When the manipulator is required to track a periodic desired trajectory, better tracking performance can be obtained using repetitive control algorithms than using conventional linear controllers or computed torque techniques. The repetitive control input can be adjusted periodically, with comparatively simple algorithms, using the tracking error signal from current and previous trials, without requiring explicit knowledge of the manipulator dynamic model. Several repetitive control algorithms are examined and compared in this paper. The algorithms include those presented in [21, 18, 9, 14]. The performance of the control algorithms is evaluated in a computer simulation study, using the model of the Berkeley-NSK two axis manipulator developed by Kang et al. [11].