Development of friction free controller for electro-hydrostatic actuator using feedback modulator and disturbance observer

Hydraulic actuators have high power-to-weight ratios, making them suitable for high-power robotic applications such as in walking robots and construction machines. However, large frictional forces in hydraulic actuators, rotary hydraulic actuators in particular, degrade the control performance. To suppress frictional forces and increase robustness against modeling errors, this study considered the integration of feedback modulators (with minimum control inputs exceeding static frictional forces) with disturbance observers. In the proposed controller, nonlinear static frictional forces are suppressed by the feedback modulators and linear disturbances are suppressed by the disturbance observers. The validity was experimentally verified in this study.