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