Electro-hydraulic proportional actuator

An electro-hydraulic proportional actuator comprising:

• an actuator assembly having a double-acting linearly movable piston contained in a cylinder having a chamber at each end;
• a pair of three-way solenoid valves each of which has an actuator port, an inlet port, and an outlet port;
• each end chamber of the actuator assembly cylinder being coupled to the actuator port of one of the valves;
• and each valve inlet port being coupled through a check valve to a fluid pressure source and the return ports being coupled to each other with the fluid flow therefrom being routed to a flow control valve;
• and an electronic control system for operating the solenoid valves to direct fluid flow into and out of the cylinder chambers, comprising;
• an operator controlled means for providing an input voltage V.sub.1 representing a desired actuator assembly piston position,
• a transducer means coupled to the actuator assembly to generate an output voltage Vv representing the actual position of the piston,
• the difference between the input V.sub.1 and output Vv voltages forming a difference signal Ve.sub.2 representing the difference or error between the desired and actual positions of the actuator piston,
• a sample-and-hold circuit having an input to which the Ve.sub.2 signal is coupled,
• a clock logic means including a clock means providing a sampling frequency coupled through first input of an "OR" gate having an output and two inputs to an input of the sample-and-hold circuit,
• the output of the "OR" gate comprising a sample-and-hold circuit,
• the output of the "OR" gate comprising a sample-and-hold circuit input control signal V.sub.sh,
• the sample-and-hold circuit passing the Ve.sub.2 signal when the V.sub.sh signal is in a logic "1" state and retaining the last value of Ve.sub.2 when the V.sub.sh returns to a logic "0" state,
• during a sampling instant, when the clock means sampling frequency pulse is high or in a logic "1" state, the control system operating to turn either solenoid valve on or off so as to move the piston in either direction or to hold the piston at a desired position until the next sampling instant.