Electrohydraulic valve control circuit with magnetic hysteresis compensation

1. A method by which a controller operates an electrohydraulic valve, the method comprising:

determining how magnetic hysteresis affects electrohydraulic valve operation;

receiving a command designating a desired magnitude of electric current to be applied to the electrohydraulic valve;

in response to the determining, modifying the command to compensate for the magnetic hysteresis to produce a compensated command, wherein modifying the command comprises deriving an intermediate value denoting change of the command with time and multiplying the intermediate value by another value that characterizes how magnetic hysteresis affects electrohydraulic valve operation; and

applying electric current to the electrohydraulic valve in response to the compensated command, wherein a constant magnitude of electric current is applied to the electrohydraulic valve for as long as the command remains unchanged.

2. The method as recited in claim 1 wherein determining how magnetic hysteresis affects electrohydraulic valve operation comprises varying electric current applied to the electrohydraulic valve while sensing a parameter related to an amount that the electrohydraulic valve is open.

3. The method as recited in claim 1 wherein determining how magnetic hysteresis affects electrohydraulic valve operation comprises:

producing a first set of data indicating relationships between magnitudes of electric current applied to the electrohydraulic valve and positions of the electrohydraulic valve while opening;

producing a second set of data indicating relationships between magnitudes of electric current applied to the electrohydraulic valve and positions of the electrohydraulic valve while closing; and

analyzing the first and second sets of data.

4. The method as recited in claim 1 wherein modifying the command is performed during only one of while the electrohydraulic valve is opening and while the valve is closing.

5. The method as recited in claim 1 wherein a product of the multiplying is used to derive a compensation amount by adding the product to a previous value of the compensation amount to produce a new value for the compensation amount.

6. The method as recited in claim 1 wherein modifying the command comprises reducing the desired magnitude of electric current by a compensation amount.

7. The method as recited in claim 6 wherein:

deriving an intermediate value comprises determining a difference between the desired magnitude of electric current designated by the command and a magnitude of electric current designated by a previous command;

multiplying the intermediate value comprises multiplying the difference by a value that characterizes how magnetic hysteresis affects operation of the electrohydraulic valve, thereby producing a preliminary compensation factor; and

wherein modifying the command further comprises adding the preliminary compensation factor to a previous value of the compensation amount to produce a new value for the compensation amount.

8. The method as recited in claim 7 wherein modifying the command further comprises limiting the new value to a predefined range of values.

9. The method as recited in claim 1 further comprising:

receiving a signal from a user operated input device; and

producing the command in response to that signal.

10. A method by which a controller operates an electrohydraulic valve, the method comprising:

deriving a characterization value that represents how magnetic hysteresis affects operation of the electrohydraulic valve;

receiving a command designating a magnitude of electric current to be applied to the electrohydraulic valve;

determining a compensation value in response to the command, the characterization value, and a previous compensation value;

producing a compensated command in response to the compensation value, wherein producing a compensated command comprises deriving an intermediate value denoting change of the command with time and multiplying the intermediate value by another value that characterizes how magnetic hysteresis affects electrohydraulic valve operation; and

applying electric current to the electrohydraulic valve in response to the compensated command.

11. The method as recited in claim 10 further comprising:

receiving a signal from a user operated input device; and

producing the command in response to that signal.

12. The method as recited in claim 10 wherein deriving a characterization value comprises:

producing a first set of data indicating relationships between magnitudes of electric current applied to the electrohydraulic valve and positions of the electrohydraulic valve while opening;

producing a second set of data indicating relationships between magnitudes of electric current applied to the electrohydraulic valve and positions of the electrohydraulic valve while closing; and

determining the characterization value based how the first and second sets of data differ.

13. The method as recited in claim 10 wherein determining a compensation value comprises:

determining a difference between the command and a previous command that designated a desired magnitude of electric current;

producing a preliminary compensation factor by multiplying the difference and the characterization value; and

producing the compensation value by adding the preliminary compensation factor to a previous compensation value.

14. The method as recited in claim 13 wherein determining a compensation further comprises limiting the compensation value to a predefined range of values.

15. The method as recited in claim 10 wherein producing a compensated command comprises modifying the command in response to the compensation value.

16. A method by which a controller operates an electrohydraulic valve, the method comprising:

deriving a characterization value that indicates how magnetic hysteresis affects operation of the electrohydraulic valve;

receiving a command designating a desired magnitude of electric current to be applied to the electrohydraulic valve;

determining a difference between the magnitude of electric current designated by the command and a magnitude of electric current designated by a previous command;

producing a preliminary compensation factor by multiplying the difference and the characterization value;

producing a compensation value by adding the preliminary compensation factor to a previous compensation value;

producing a compensated command by arithmetically combining the command and the compensation value; and

applying electric current to the electrohydraulic valve in response to the compensated command.

17. The method as recited in claim 16 further comprising:

receiving a signal from a user operated input device; and

producing the command in response to that signal.

18. The method as recited in claim 16 wherein determining a compensation further comprises limiting the compensation value to a predefined range of values.

19. The method as recited in claim 16 wherein deriving a characterization value comprises:

producing a first set of data indicating relationships between magnitudes of electric current applied to the electrohydraulic valve and positions of the electrohydraulic valve while opening;

producing a second set of data indicating relationships between magnitudes of electric current applied to the electrohydraulic valve and positions of the electrohydraulic valve while closing; and

determining the characterization value based how the first and second sets of data differ.