Robust control design for flexible-link/flexible-joint robots

We present an output feedback sliding mode control (OFSMC) architecture for slewing flexible joint and link robot structures. A decoupled two-channel OFSMC is used to servo the flexible structure and suppress residual vibrations. A separate sliding surface is specified for each channel. The results of this study include the analytical dynamic and control system development with experimental verification. The control algorithm uses the output sensor data from the encoder and strain sensor along with filters to derive velocity information to compute the control effort for the motor and strain actuators. Near-minimum time maneuvers based on an equivalent rigid structure are used to slew the flexible active structure. The tip mass was varied to evaluate control system robustness. Experimental slewing studies were performed to compare the benefits of using active rather than passive structures. In addition, the OFSMC was compared against a conventional PID controller. For the active case the experimental results showed a reduction in residual vibration and settling time