System and method for servo control of nonlinear electromagnetic actuators

• US 20010043450A1
• Filed: 01/30/2001
• Published: 11/22/2001
• Est. Priority Date: 06/26/1997
• Status: Active Grant

• Current Assignee: Thistle Advisors, Inc.
• Original Assignee: Venture Scientifics LLC
• Inventors: Seale, Joseph B., Bergstrom, Gary E.
• Granted Patent: US 6,942,469 B2
• Time in Patent Office: Days
• US Class Current: 361/160
• CPC Class Codes: B60L 13/06 Means to sense or control vehicle position or attitude with respect to railway
• CPC Class Codes: F01L 2009/2105 comprising two or more coils
• CPC Class Codes: F01L 2009/4086 Soft landing, e.g. applying braking current; Levitation of armature close to core surface
• CPC Class Codes: F01L 9/20 by electric means
• CPC Class Codes: F02D 13/0253 Fully variable control of valve lift and timing using camless actuation systems such as hydraulic, pneumatic or electromagnetic actuators, e.g. solenoid valves
• CPC Class Codes: F02D 2041/001 for engines with variable valve actuation
• CPC Class Codes: F02D 2041/1419 the control loops being cascaded, i.e. being placed in series or nested
• CPC Class Codes: F02D 2041/2027 Control of the current by pulse width modulation or duty cycle control
• CPC Class Codes: F02D 2041/2055 with means for determining actual opening or closing time
• CPC Class Codes: F02D 2041/2058 using information of the actual current value
• CPC Class Codes: F02D 2041/2079 the circuit having several coils acting on the same anchor
• CPC Class Codes: F02D 41/1401 characterised by the control or regulation method F02D41/1473, F02D41/1477 take precedence
• CPC Class Codes: F02D 41/20 Output circuits, e.g. for controlling currents in command coils
• CPC Class Codes: H01F 2007/185 with armature position measurement
• CPC Class Codes: H01F 2007/1866 with regulation loop
• CPC Class Codes: H01F 2007/1894 minimizing impact energy on closure of magnetic circuit
• CPC Class Codes: H01F 7/1607 Armatures entering the winding
• CPC Class Codes: H01F 7/18 Circuit arrangements for obtaining desired operating characteristics, e.g. for slow operation, for sequential energisation of windings, for high-speed energisation of windings
• CPC Class Codes: H01F 7/1844 Monitoring or fail-safe circuits for relays H01H47/002
• CPC Class Codes: H01H 47/325 by switching regulator
• CPC Class Codes: H02K 41/03 : Synchronous motors; Motors moving step by step; Reluctance motors H02K41/035 takes precedence
• CPC Class Codes: H02N 15/00 : Holding or levitation devices using magnetic attraction or repulsion, not otherwise provided for electric or magnetic devices for holding work on machine tools B23Q3/15 ; monorail vehicle propulsion or suspension B60L13/00; sliding or levitation devices for railway systems B61B13/08; material handling devices associated with conveyors incorporating devices with electrostatic or magnetic grippers B65G47/92; separating thin or filamentary articles from piles using magnetic force B65H3/16; delivering thin or filamentary articles from magnetic holders by air blast or suction B65H29/24; bearings using magnetic or electric supporting means F16C32/04; relieving bearing loads using magnetic means F16C39/06; magnets H01F7/00; dynamo-electric clutches or brakes H02K49/00 ; electric furnaces with simultaneous levitation and heating H05B6/32
• CPC Class Codes: H02P 25/032 : Reciprocating, oscillating or vibrating motors
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies

Abstract

Servo control using ferromagnetic core material and electrical windings is based on monitoring of winding currents and voltages and inference of magnetic flux, a force indication; and magnetic gap, a position indication. Third order nonlinear servo control is split into nested control loops: a fast nonlinear first-order inner loop causing flux to track a target by varying a voltage output; and a slower almost linear second-order outer loop causing magnetic gap to track a target by controlling the flux target of the inner loop. The inner loop uses efficient switching regulation, preferably based on controlled feedback instabilities, to control voltage output. The outer loop achieves damping and accurate convergence using proportional, time-integral, and time-derivative gain terms. The time-integral feedback may be based on measured and target solenoid drive currents, adjusting the magnetic gap for force balance at the target current. Incorporation of permanent magnet material permits the target current to be zero, achieving levitation with low power, including for a monorail deriving propulsion from the levitation magnets. Linear magnetic approximations lead to the simplest controller, but nonlinear analog computation in the log domain yields a better controller with relatively few parts. When servo controlled solenoids provide a actuation of a pump piston and valves, electronic I.C resonance measurements determine liquid volume and gas bubble volume.

Claims

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 for magnetic 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.

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 1

, wherein said means for setting said target includes means for determining a magnetic force acting on said armature.

4. 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.

5. The system of

claim 3

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

6. The system of

claim 3

, further comprising integral control means, responsive to a persistent error in said position measurement, to generate an accumulating corrective variation in said magnetic force.

7. 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.

8. The system of

claim 7

, wherein said approximate ratio is based on a sub of a constant plus a first linear term relating to said electric current plus a second linear term relating to said solenoid magnetic flux.

9. The system of

claim 7

, wherein said approximate ratio is based on a sum of a constant plus a first linear tend relating to said electric current.

10. 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.

11. The system of

claim 10

, 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.

12. The system of

claim 2

wherein said amplifier means includes a switching amplifier coupled to at least one of said one or more windings.

13. The system of

claim 12

, 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.

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. switch control means, responsive to said oscillatory slope and to a ratio of said current divided by said oscillatory slope, causing said ratio to vary as a function of said oscillatory slope.

18. The system of

claim 17

further comprising amplifier means for controlling said electric current in at least one of said one or more windings.

19. The system of

claim 17

, wherein said responsiveness to said oscillatory slope includes response to a transfer function of said oscillatory slope, said transfer function including at least one selected from the group consisting of:

a proportional term, a time-integral term, and a band-limited derivative term.

20. The system of

claim 17

, comprising 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 said current, said magnetic flux, said oscillatory slope, and a bias signal of said solenoid control means; and

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

22. A solenoid 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 electrical measurements 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 control A 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 fist 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. The solenoid as claimed in

claim 22

, further comprising 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 piston pump, said solenoid further comprising means for identifying pre-loading of said a mature through actuation of said drive coil.

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

claim 37

further comprising the step of coupling a sense coil to said yoke for determining said signal.

39. The method as claimed in

claim 38

, wherein the step of determining said signal includes the step of measuring a magnetic flux of said solenoid.

40. The method as claimed in

claim 37

, wherein the step of determining said signal includes the step of measuring a current through said drive coil.

41. The method as claimed in

claim 38

further comprising the step of determining a minimum holding current to be supplied to said drive coil so as to maintain said armature in a fixed position.

42. The method as claimed in

claim 39

further comprising the step of determining an initial position of said armature prior to initiating said drive pulse by transmitting a probe pulse to said drive coil and sensing with said sense coil said magnetic flux of said solenoid.

43. The method as claimed in

claim 42

, wherein said initial position is determined from a ratio of a current through said drive coil and said magnetic flux measured by said sense coil.

44. The method as claimed in

claim 43

further comprising the step of introducing a plurality of pre-defined threshold drive pulses based upon measured characteristics of said solenoid so as to define variable armature travel conditions.

45. A system for levitation and propulsion of a structure, the system comprising:

a. a plurality of substantially abutting electromagnets for coupling to means capable of supporting said structure;

b. flux control means coupled to said electromagnets, for controlling magnetic fluxes associated with the operation of said electromagnets;

c. position indication means as part of said control means;

d. means for computing weighted sums of signals from said position indication means; and

e. servo control means, providing input to said flux control means, responsive to said weighted sums of signals for controlling said weighted sums.

46. The system as claimed in

claim 45

, wherein said electromagnets include permanent magnet components.

47. The system as claimed in

claim 45

, wherein:

a. said position indication means includes signals indicating electric currents associated with said controlling of said magnetic fluxes;

b. said weighted sums of signals includes weighted sums of said signals indicating said electric currents; and

c. said controlling of said weighted sums of said signals includes causing at least one of said weighted sums of said electric currents average a small value over time.

48. The system as claimed in

claim 45

, wherein:

a. said means capable of supporting said structure includes a track; and

b. said track includes a lower surface proximate to said plurality of electromagnets, said surface permitting ferromagnetic attraction of said plurality of electromagnets toward said lower surface for supporting said vehicle.

49. The system as claimed in

claim 48

, wherein:

a. said lower surface includes vertical ripples along the longitudinal direction thereof; and

b. operation of said flux control means causes variations of said magnetic fluxes to synchronize with said vertical ripples to produce longitudinal thrust.

50. The system as claimed in

claim 48

, wherein said lower surface has convex curvature in the lateral dimension thereof.

51. The system as claimed in

claim 48

, wherein the magnetic fields of said substantially abutting electromagnets cause the magnetic field strength induced in a given volume within said track, during the passage of said plurality of said electromagnets past said given volume, to undergo a single uni-polar magnetic cycle characterized by an increase from near-zero to a maximum field strength, a plateau near said maximum field strength with fractional variations of less than 50%, and a decrease back to near-zero field strength.