Integration of disturbance observer and feedback modulator for dead zone compensation of hydraulic actuator

Hydraulic actuators are superior to electric motors in term of power/weight ratio. In addition, recent technical progress of electro-hydraulic valves provides fast tracking performance. However, there is a problem of steady state errors because hydraulic actuators have dead zones around zero outputs. Disturbance observers are powerful tools to eliminate disturbances on robot systems. However, if there is a dead zone, disturbance observers generate residual oscillation. Feedback modulators cancel Coulomb friction by quantizing inputs. However, viscous friction, gravitational force, modeling errors, and the other disturbances cannot be compensated by feedback modulators. Therefore, in this paper, the dead zone is compensated by integrating disturbance observers and feedback modulators. The validity of the proposed method is experimentally confirmed.