Velocity based method for controlling a hydraulic system

A method of operating a hydraulic system in which a hydraulic actuator is connected in a circuit branch between a supply line containing pressurized fluid and a return line connected to a tank, said method comprising:

• sensing pressure in the supply line to produce a supply pressure measurement;
• sensing pressure in the return line to produce a return pressure measurement;
• sensing a parameter which varies with changes of a force acting on the hydraulic actuator;
• deriving an equivalent flow coefficient which characterizes fluid flow through the hydraulic circuit and which is derived from the supply pressure measurement, the return pressure measurement, and the parameter;
• and
• controlling the fluid in the hydraulic system based on the equivalent flow coefficient.

In a hydraulic system having a circuit branch in which a first electrohydraulic proportional valve couples a first port of a hydraulic actuator to a supply line containing pressurized fluid and a second electrohydraulic proportional valve couples a second port of the hydraulic actuator to a return line connected to a tank, a method comprising:

• sensing pressure in the supply line;
• sensing pressure in the return line;
• sensing pressure at the first port;
• sensing pressure at the second port;
• deriving an equivalent flow coefficient, Keq, representing fluid conduction of the hydraulic circuit branch, wherein that deriving is based on the pressure in the supply line, the pressure in the return line, the pressure at the first port, and the pressure at the second port;
• and
• controlling operation of the circuit branch based on the equivalent flow coefficient.

In a hydraulic system having a circuit branch in which a first electrohydraulic proportional valve couples a first port of a hydraulic actuator to a supply line containing pressurized fluid, and a second electrohydraulic proportional valve couples a second port of the hydraulic actuator to the supply line, a third electrohydraulic proportional valve couples the first port to a return line connected to a tank, and a fourth electrohydraulic proportional valve couples the second port to the return line, a method comprising:

• selecting a direction in which the hydraulic actuator is to move;
• designating given ones of the first, second, third and fourth electrohydraulic proportional valves to be operated to produce movement of the hydraulic actuator in the direction that is selected;
• sensing pressure in the supply line to produce a supply pressure measurement, Ps;
• sensing pressure in the return line to produce a return pressure measurement, Pr;
• sensing pressure at the first port to produce a first port pressure measurement, Pa;
• sensing pressure at the second port to produce a second port pressure measurement, Pb;
• deriving an equivalent flow coefficient representing flow of the hydraulic circuit branch, wherein that deriving is selected from a group consisting of a conductance coefficient and a restriction coefficient and is based on the supply pressure measurement, the return pressure measurement, the first port pressure measurement and the second port pressure measurement;
• and
• activating the given ones of the first, second, third and fourth electrohydraulic proportional valves in response to the equivalent flow coefficient to move the hydraulic actuator in the direction that is selected.

A method of operating an electrohydraulic proportional valve which is connected in series with a hydraulic actuator in a hydraulic circuit branch between a supply line containing pressurized fluid and a return line connected to a tank, said method comprising:

• requesting a commanded velocity {dot over (x)} for the hydraulic actuator;
• sensing a force Fx acting on the hydraulic actuator;
• sensing pressure in at least one of the supply line and the return line to produce a pressure measurement;
• calculating an equivalent flow coefficient, representing fluid conductance of the hydraulic circuit branch, wherein the calculating employs the force, the pressure measurement, and a surface area on which hydraulic fluid acts in the hydraulic actuator;
• and
• activating the electrohydraulic proportional valve based on the equivalent flow coefficient to control the hydraulic actuator.

A method of operating a hydraulic system in which an electrohydraulic proportional valve is connected to a hydraulic actuator and to at least one of a supply line containing pressurized fluid and a return line connected to a tank, said method comprising:

• requesting a desired velocity for the hydraulic actuator;
• sensing a parameter which varies with changes of a force acting on the hydraulic actuator;
• sensing at least one of pressure in the supply line and pressure in the return line to produce a pressure measurement set;
• deriving an equivalent flow coefficient which characterizes fluid flow through the electrohydraulic proportional valve, wherein the equivalent flow coefficient is based on the desired velocity, the pressure measurement set, and the parameter;
• and
• controlling operation of the electrohydraulic proportional valve based on the equivalent flow coefficient.

A method of operating a hydraulic system in which a hydraulic actuator is connected in a circuit branch to a supply line containing pressurized fluid and a return line connected to a tank, said method comprising:

• requesting a desired motion for the hydraulic actuator;
• sensing a parameter which varies with changes of a force acting on the hydraulic actuator;
• deriving a control value which characterizes fluid flow through the hydraulic circuit and which is derived from the desired motion and the parameter;
• controlling pressure in at least one of the supply line and the return line in response to the parameter;
• and
• controlling the fluid in the hydraulic system based on the control value.