Force servo actuator with asymmetric nonlinear differential hydraulic force feedback

A hydraulic servo control system, comprising in combination:

• a force servo actuator of the type having an actuator piston mounted in a dual-chamber actuator cylinder for bi-directionally moving a load in oppositely directed strokes;
• a force servovalve operatively connected to the force servo actuator, the servovalve including a spool valve of the type wherein its position along its axis is controlled by volumes of fluid in first and second opposed control signal input ports, the spool valve having at least one inlet port for receiving a flow of pressurized fluid, at least one return port, and first and second outlet ports for delivering pressurized fluid to respective chambers of the dual-chamber actuator cylinder;
• and
• hydraulic means for controlling a force asymmetry acting upon the force servo actuator, characterized by:
• a first fluid passageway for providing negative nonlinear hydraulic force feedback communication between the first outlet port and the second control signal input port;
• a second fluid passageway for providing negative nonlinear hydraulic force feedback communication between the second outlet port and the first control signal input port;
• a first orifice in the first fluid passageway having a first preselected hydraulic force feedback impedance value;
• a second orifice in the second fluid passageway having a second preselected hydraulic force feedback impedance value;
• wherein the first and second preselected hydraulic force feedback impedance values are unequal and wherein the values are a function of the known or postulated force asymmetry acting upon the actuator.