Hydraulic Actuator Tuning in the Control of a Rotating Flexible Beam Mechanism

The end point position and vibration control of a rotating flexible beam mechanism driven by a hydraulic cylinder actuator are considered. An integrated nonlinear system model comprised of beam dynamics, hydraulic actuator, control valves, and control scheme is presented. Control based on simple position feedback, along with a hydraulic actuation system tuned to suppress beam vibration over a wide range of angular motion, is investigated. For positioning to small to moderate mechanism angles, a linear system model with the actuator tuned for good open-loop performance is developed. Actuator tuning is accomplished by varying the system hydraulic resistance according to a dimensionless parameter defining the interaction between actuator dynamics and the fundamental mode of the flexible beam. Simulation results for a closed-loop system indicate that this simple tuned control provides comparable performance and requires less control effort than an untuned system with a more complex state feedback optimal controller. To compensate for geometric nonlinearities that cause instability when positioning to large mechanism angles, an active actuator tuning scheme based on continuous variation of hydraulic resistance is proposed. The active variable resistance controller is combined with simple position feedback and designed to provide a constant dimensionless actuator-flexible beam interaction parameter throughout the motion. Simulation results are presented to show the stabilizing effect of this control strategy.