Design, Analysis, and Control of a Stiffness-Tunable 3-DOF Rubber-Bearing Positioning Stage

A 3-DOF θ x -Y- θ z rubber bearing stage with stiffness-adjustment capability is design, realized, and controlled in this work. The stiffness of rubbers can be adjusted easily by adding a preload from different directions. Base on elastomeric materials analysis, the stiffness of rubber and therefore dynamic characteristics of the stage can be changed with such a preload. In comparison with positioning stages designed by compliance mechanism approach, such characteristics could be an opportunity to improve the performance by replacing compliant bearing with rubber-bearing one. The dynamic testing results show that with a compression of 0.8mm on a 1.5mm thick rubber, the stiffness and natural frequency increased by 100% and 30% in Y -axis, 15% and 7% in θ x -axis, and even by 510% and 140% in θ z -axis, respectively. Associated PID and integral sliding mode controllers are then implemented for characterizing the position control performance. Currently, the rubber bearing stage can achieve a 79 Hz and 110 Hz controlling bandwidth by using PID and integral sliding mode controller, respectively in Y -axis motion. In the future, the effect of different pre-compression displacement on dynamics characteristics of the stage, such as stiffness, natural frequency, damping ratio, will be tested. Additional control design in multi-axis coupling will be addressed to evaluate the performance in precision motion related applications.