Sliding mode control for a robot SCARA

The variable structure systems (VSS) theory has been developed many years ago, and it has been proved that it's well suited for robotics arms where the robust performances are most important in spite of the presence of parametric variations and disturbances. A practical realization of a robust controller using VSS is described in this paper. The important issue in the design of VSS is to avoid the chattering caused by the switched input. This problem is solved by introducing the continuous control input instead of switched input. To this end, a PID corrector which can be tuned on line, is used. This paper shows the benefits of using such controller associated to VSS to eliminate the chartering. At the end, the robustness of the control against input disturbance and payload variations is demonstrated. In this study the controller design is obtained by combining classical transfer function techniques, sliding mode systems ideas and PID control. The interest of the overall controller is in its potential to combine the good transient performance and the steady stale properties of the VSS-PID control. The PID boundary layer provides adaptive tracking quality even under changing process parameters. The above mentioned techniques are applied to the regulation (point to point) control of a robot SCARA with the three degree of freedom. In this work, experimental results obtained by applying the VSS-PID control law to real manipulator are given. Copyright (C) 1998 IFAC.