Positioning apparatus and method utilizing PWM control of a double-acting hydraulic cylinder
AssigneeMartin Marietta Corporation
InventorRobert F. Larkin
Life of this patent
Estimating the term…
Abstract
A double-acting hydraulic cylinder is controlled by a pair of three-way solenoid valves respectively fluid connected to the two ends of the cylinder and energized in parallel with a continuous stream of pulse width modulated (PWM) pulses to create a mean effective fluid pressure balance at the cylinder ends that hold a desired position of a connected load and mean effective fluid pressure imbalances in the cylinder ends that produce variable rate load movement in either of two directions to a desired new position, all determined by the pulse duty cycle.
Claims9
A positioning apparatus comprising:
- a fluid actuator including a cylinder and a piston disposed in the cylinder to define first and second chambers;
- a first fluid valve having a quiescent valve position connecting the first chamber to a source of fluid pressure and an actuated valve position venting the first chamber;
- a second fluid valve having a quiescent valve position venting the second chamber and an actuated valve position connecting the second chamber to the source of fluid pressure;
- a module, connected to the first and second fluid valves and responsive to input commands, for periodically and simultaneously activating the first and second fluid valves to their respective actuated valve positions for time periods effective to create differential fluid pressures in the first and second chambers, thereby producing relative motion of the piston and the cylinder;
- and
- means for translating the relative motion into positioning movements of a load.
A method for positioning a load comprising the steps of:
- linking a fluid actuator to the load, the actuator including a piston disposed in a cylinder to define first and second chambers;
- providing a source of pressured fluid;
- providing a first fluid valve having a first valve position venting the first chamber and a second valve position connecting the first chamber to the pressurized fluid source;
- providing a second fluid valve having a first valve position connecting the second chamber to the pressurized fluid source and a second valve position venting the second chamber;
- periodically shifting the first and second fluid valves concurrently to their first valve positions for a succession of first time periods and concurrently to their second valve positions for a succession of second time periods, the first and second time periods occurring in alternation;
- equalizing the first and second time periods to balance fluid pressures in the first and second chambers, whereby to hold the load in a desired position;
- increasing the first time periods relative to the second time periods to unbalance the fluid pressures in the first and second chambers, whereby to move the load in a first direction;
- and
- decreasing the first time periods relative to the second time periods to unbalance the fluid pressures in the first and second chambers, whereby to move the load in a second direction.
Dependencies are inferred from the claim text.