System and method for servo control of nonlinear electromagnetic actuators

Claims

We claim:

1. A system for controlling an electromagnetic solenoid including an armature and one or more windings, the system comprising:

a. measurement means couplable to said solenoid for obtaining a position measurement of said armature;

b. means for setting a target flux associated with said solenoid as a function of said measurement; and

c. means for maintaining a solenoid magnetic flux associated with operation of said solenoid near said target, said means including a circuit arrangement which detects an oscillatory slope of a current supplied to the one or more windings, which develops a ratio based on the amount of current being supplied to the one or more windings and the oscillatory slope, and which controls the amount of current with respect to the ratio.

2. The system of claim 1, wherein said means for maintaining said solenoid magnetic flux includes amplifier means for controlling an electric current in at least one of said one or more windings.

3. The system of claim 2, wherein said means for obtaining said position measurement includes means for inferring an approximate ratio of said electric current to said solenoid magnetic flux.

4. The system of claim 3, wherein said approximate ratio is based on a sum of a constant plus a first linear term relating to said electric current plus a second linear term relating to said solenoid magnetic flux.

5. The system of claim 3, wherein said approximate ratio is based on a sum of a constant plus a first linear term relating to said electric current.

6. The system of claim 2 wherein said amplifier means includes a switching amplifier coupled to at least one of said one or more windings.

7. The system of claim 6, wherein said switching amplifier includes a voltage-switching output stage and a comparator input stage, said comparator input stage responding to an error difference between said solenoid magnetic flux and said target to produce an oscillation of variable duty cycle, said variable duty cycle causing said error difference to cross frequently through zero.

8. The system of claim 1, wherein said means for setting said target includes means for determining a magnetic force acting on said armature.

9. The system of claim 3, wherein said means for determining said magnetic force is part of servo means for controlling a position of said armature.

10. The system of claim 8, further comprising derivative control means, responsive to a rate of change in said position measurement, to generate a damping variation in said magnetic force.

11. The system of claim 8, further comprising integral control means, responsive to a persistent error in said position measurement, to generate an accumulating corrective variation in said magnetic force.

12. The system of claim 1, further comprising:

a. means for measuring from at least one of said one or more windings an induced voltage indicative of a time derivative of said solenoid magnetic flux;

b. means for measuring net variations in said solenoid magnetic flux by way of time integration of said induced voltage; and,

c. means for ensuring that said net variations in said solenoid magnetic flux substantially match said target.

13. The system of claim 12, further comprising:

a. means for determining time-integral measures of said current through said one or more windings;

b. means for determining sums of said time integral measures and said net variations; and

c. means for ensuring that said sums substantially match said target.

14. The system of claim 1, wherein said means for determining said measurement of said position includes a sensor separable from said solenoid.

15. The system of claim 14, wherein said sensor includes a hall-effect sensor.

16. The system of claim 1, wherein said means for maintaining said solenoid magnetic flux includes a hall-effect sensor.

17. A system for controlling an electromagnetic solenoid including an armature and one or more windings, the system comprising:

a. means for detecting an oscillatory slope of an electric current in at least one of said one or more windings; and

b. control means, responsive to said oscillatory slope and to a ratio of the current divided by the oscillatory slope, for controlling the electric current and for said ratio to vary as a function of the oscillatory slope.

18. The system of claim 17 wherein said control means comprises amplifier means for controlling the electric current in at least one of said one or more windings.

19. The system of claim 17, wherein said control means includes means responsive to a transfer function of said oscillatory slope, wherein the transfer function includes at least one of: a proportional term, a time-integral term, and a band-limited derivative term.

20. The system of claim 17, wherein said control means includes means for causing the square of said ratio to vary in proportion to a transfer function of said oscillatory slope.

21. The system of claim 17 further comprising:

a. means for generating a difference of weighted sums of logarithms of the current, the magnetic flux, the oscillatory slope, and a bias signal of said control means; and

b. means for controlling the current in response to the signal difference varying as a function of the weighted sums of the logarithms.

22. A solenoid having a core of a material which minimizes core loss at a predetermined frequency comprising:

a. a drive coil;

b. an armature capable of movement within said drive coil;

c. a yoke coupled to said drive coil, wherein said yoke is positioned in relation to said armature such that there is at least one air gap between said yoke and said armature; and

d. control means including a drive coil controller coupled to said drive coil, wherein said control means regulates movement of said armature within said drive coil based upon measurements of current and an oscillatory characteristic of the current from said drive coil.

23. The solenoid as claimed in claim 22, wherein said control means includes means for measuring a position of said armature and delivering to said drive coil controller said armature position measurement.

24. The solenoid as claimed in claim 22, wherein said control means includes means for measuring a magnetic flux of said drive coil and deriving from said magnetic flux a position measurement of said armature for delivery to said drive coil controller.

25. The solenoid as claimed in claim 22, further comprising a sense coil proximate to said drive coil, wherein said sense coil is used to independently determine said position measurement of said armature.

26. The solenoid as claimed in claim 25, wherein said control means includes a voltage-switching amplifier coupled to said drive coil for controlling movement of said armature.

27. The solenoid as claimed in claim 25, wherein said control means includes a first servo control loop means for determination of position of said armature, and a second servo control loop means related to a determination of force for regulating a drive pulse transmitted by said drive coil controller.

28. The solenoid as claimed in claim 25, wherein said first servo control loop means is coupled to said second servo control loop means.

29. A solenoid comprising:

a drive coil;

an armature capable of movement within said drive coil;

a yoke coupled to said drive coil, wherein said yoke is positioned in relation to said armature such that there is at least one air gap between said yoke and said armature;

control means including a drive coil controller coupled to said drive coil, wherein said control means regulates movement of said armature within said drive coil based upon electrical measurements from said drive coil; and

launch control means for computing and initiating drive coil signals for movement of said armature with minimal electrical power consumption.

30. The solenoid as claimed in claim 29, wherein said launch control means further includes a comparator designed to compare a position of said armature with a set of pre-defined armature positions so as to define a termination operation of said drive coil.

31. The solenoid as claimed in claim 30, including means for identifying a starting position of said armature and internal calibration means.

32. The solenoid as claimed in claim 31, wherein said solenoid is a pump actuator and wherein the solenoid is controlled by a circuit which identifies, based on the position of the armature, the content of the fluid being pumped by the pump.

33. The solenoid as claimed in claim 31 further comprising means for delivering a drive pulse to said drive coil sufficient to force near closure of said gap between said armature and said yoke.

34. The solenoid as claimed in claim 33, further comprising means for delivering a secondary drive pulse to said drive coil to force movement of said armature from near closure to complete closure.

35. The solenoid as claimed in claim 34, further comprising means for delivering a holding signal to said drive coil to maintain complete closure of said armature until delivery of a stop-holding signal.

36. The solenoid as claimed in claim 22, wherein said armature and said yoke have a design based on a pot core.

37. A method for controlling the duration of a drive pulse transmitted to a drive coil of a solenoid having an armature and a yoke so as to move said armature to a prescribed position, said method comprising the steps of:

a. supplying a drive pulse to said drive coil for movement of said armature in relation to said yoke;

b. determining a signal sensitive to movement of said armature;

c. defining as a function of time a threshold for said signal sensitive to said movement;

d. comparing said signal with said threshold; and

e. terminating said drive pulse either when said signal substantially corresponds with said threshold, or when a predefined time limit is reached.

38. The method as claimed in