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.

This paper describes two methods for controlling the surface of a liquid in an open container as it is being carried by a robot arm. Both methods make use of the fundamental mode of oscillation and damping of the liquid in the container as predicted from a boundary element model of the fluid. The first method uses an infinite impulse response filter to alter an acceleration profile so that the liquid remains level except for a single wave at the beginning and end of the motion. The motion of the liquid is similar to that of a simple pendulum. The second method removes the remaining two surface oscillations by tilting the container parallel to the beginning and ending wave. A double pendulum model is used to determine the trajectory for this motion. Experimental results of a FANUC S-800 robot moving a 230 mm diameter hemispherical container of water are presented.