Electrohydraulic valve system

A control system for controlling a double-acting hydraulic cylinder having retraction and extension chambers, the control system comprising:

• a first electrically controlled pressure-reducing valve having an inlet communicated with a pump and having an outlet communicated with the retraction chamber;
• a second electrically controlled pressure-reducing valve having an inlet communicated with the retraction chamber and having an outlet communicated with a reservoir;
• first check valve means for preventing fluid flow from the retraction chamber to the first valve;
• a third electrically controlled pressure-reducing valve having an inlet communicated with the extension chamber and having an outlet communicated with the reservoir;
• a fourth electrically controlled pressure-reducing valve having an inlet communicated with the pump and having an outlet communicated with the extension chamber;
• second check valve means for preventing fluid flow from the extension chamber to the fourth valve;
• operator-controlled means for generating a command signal representing a desired position of the piston relative to the cylinder;
• position-sensing means for generating a feedback signal representing an actual position of the piston relative to the cylinder;
• and
• a control circuit including means for generating error signals representing a difference between the feedback and command signals and means for applying the error signals to selected ones of the electrically controlled valves to control the position of the piston relative to the cylinder.

A control system for a hydraulic system including a pump, a reservoir, a double-acting cylinder having a piston moveable therein and four electrically and independently operable valves for controlling fluid communication between the cylinder, the pump and the reservoir, the control system comprising:

• position sensing means for generating a feedback signal indicative of a sensed position of the piston relative to the cylinder;
• operator-controllable command means for generating a command signal indicative of a desired position of the piston relative to the cylinder;
• first difference means for generating a first error signal representing a difference between the feedback and command signals;
• differentiating means for converting the feedback signal to a velocity signal indicative of the rate of change of the position of the piston relative to the cylinder;
• second difference means for generating a second error signal representing a difference between the first error signal and the velocity signal;
• inverting means for converting the second error signal to an inverted error signal;
• a first pair of driver circuits, each receiving the second error signal and coupled to a corresponding first pair of the four valves to operate the first pair of valves in response to the second error signal to control movement of the piston relative to the cylinder in a first direction;
• and
• a second pair of driver circuits, each receiving the inverted error signal and coupled to a second pair of the four valves to operate the second pair of valves in response to the inverted error signal to control movement of the piston relative to the cylinder in a second direction.