Thermal contraction control apparatus for hydraulic cylinders
AssigneeGrove U.S. L.L.C.
InventorsStephen J. Schoonmaker, Jeffrey L. Addleman
Life of this patent
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Abstract
A method and apparatus for operating a load lifting device to move a load and hold the load steady is disclosed. In the conventional arts, a lifted or lowered suspended load had a tendency to move from its desired position, as hydraulic fluid in the lifting system cooled, e.g. a stick slip condition. The present invention monitors a fluid pressure in the lifting system and compensates the fluid pressure to accommodate any pressure drop due to fluid cooling. Thereby, the load can be effectively held steady at a desired position, and the stick slip condition can be avoided.
Claims20
A method of operating a load lifting device to move a load and hold the load steady, said method comprising the steps of:
- applying primary hydraulic fluid to one of two sides of a piston in a hydraulic cylinder, thereby moving the piston such that the load is moved to a desired position;
- monitoring a hydraulic pressure on one of the two side of the piston;
- and
- increasing hydraulic pressure on one of the two sides of the piston, if the monitored hydraulic pressure changes by a predetermined amount.
A method of operating a load lifting device to move a load and hold the load steady, said method comprising the steps of:
- sensing that the load lifting device has stopped moving a load;
- measuring a first initial hydraulic pressure in a first hydraulic cylinder;
- storing the first initial hydraulic pressure as a value in memory;
- monitoring the hydraulic pressure in the first hydraulic cylinder;
- and
- if the hydraulic pressure in the first hydraulic cylinder drops by a first predetermined value relative to the first initial hydraulic pressure, applying hydraulic fluid to the first hydraulic cylinder to raise the hydraulic pressure to a second predetermined value.
A lift control system for a load lifting apparatus comprising:
- a hydraulic cylinder having a piston moveably mounted therein;
- a primary pump for providing hydraulic fluid to one side of said piston in said hydraulic cylinder to cause said piston to move;
- a main control value to control the flow of hydraulic fluid from said primary pump to said hydraulic cylinder;
- a compensator pump for providing hydraulic fluid to one side of said piston in said hydraulic cylinder;
- a compensator control valve to control the flow of hydraulic fluid from said compensator pump to said hydraulic cylinder;
- a transducer connected to said hydraulic cylinder to measure a hydraulic pressure therein;
- and
- a controller communicatively connected to said compensator control valve and said transducer, wherein said controller causes compensatory hydraulic fluid to be supplied to said hydraulic cylinder to maintain an approximately constant hydraulic pressure in said hydraulic cylinder in order to prevent movement of a load when the load lifting apparatus has positioned the load at a desired height.
Dependencies are inferred from the claim text.