All-digital electrically powered servo

A completely digital, electrically powered, electrohydraulic servo, the hydraulic actuator of said servo controlled in accordance with a binary reference representing the command position, a binary error derived from the difference of said binary reference and a binary feedback representing the position of the actuator, said binary error limited and converted to a pulse train having a pulse repetition frequency which is proportional to the magnitude of the binary error, each pulse of said pulse train gated by the sign bit of the error binary number to one of two electrohydraulic incrementers through the set input of a corresponding set/reset flip flop, the initiation of the servo drive signal by the change from a low state to a high state of the output of the flip flop as the result of the set pulse, the termination of the servo drive signal by the change from a high state to a low state of said output as the result of a reset pulse, the servo drive signal formed by the set and reset pulses, said drive signal power amplified and applied to the corresponding solenoid of a solenoid driven piston pump, a pump position indicator set to issue the reset pulse at a point near the full extension of the piston pump;

• the injection of the displaced incremental volume of fluid through an injection check valve into the corresponding actuator control chamber by the extension of the piston pump, the ejection of said volume through an ejection check valve from the opposite actuator control chamber by the retraction of said piston pump;
• a volume adjuster connected to the actuator control chambers, said volume adjuster consisting of a free-floating, stepped piston, first and second areas separately connected to the first and second actuator control chambers, respectively, said first and second areas sized proportionally to the piston areas of the actuator facing the first and second control chambers, the opposite side of the volume adjuster charged with compressed gas which sets the operating common mode pressure of the actuator.