Force servo actuator with asymmetric nonlinear differential hydraulic force feedback

DETAILED DESCRIPTION The hydraulic servo control system of this invention acts on an actuator piston which is subject to force asymmetries and which is mounted in a dual-chamber cylinder for bi-directionally moving a load in oppositely-directed strokes.
The servo control system includes a spool valve of the type wherein its position along its axis is controlled by volumes of fluid in two opposed control signal input ports.
The spool valve has at least one inlet port for receiving a flow of pressurized fluid, at least one return port, and at least one outlet port for delivering pressurized fluid to the actuator cylinder.
A manifold is operatively connected to a traditional hydraulic flow control servovalve, which controls what would typically have been a displacement servo or velocity servo actuator, so as to change it into a force servo actuator.
The servo control system further includes hydraulic means for compensating for any known or postulated force asymmetry related to the actuator.
The hydraulic means is characterized by fluid passageways for providing negative nonlinear hydraulic force feedback communication between the outlet ports and control signal input ports and orifices in the fluid passageways having preselected but unequal hydraulic force feedback impedances.
The impedance values are preselected as a function of the known or postulated force asymmetry.
In a preferred embodiment of the invention, the servovalve controls fluid flow to the dual-chamber force servo actuator cylinder, and includes a first and a second hydraulic control-signal input port to the final stage, a high pressure port and at least one return port.
The servovalve further includes first and second fluid outlet ports in fluid communication with the respective actuator cylinder chambers for applying hydraulic fluid under pressure to the opposite faces of the actuator piston during alternate cycles.
Still with respect to the preferred embodiment, the servo control system is provided with hydraulic means for compensating for known or postulated force asymmetries