Rotary position sensor and transducer for use therein

• US 6,534,970 B1
• Filed: 11/15/2000
• Issued: 03/18/2003
• Est. Priority Date: 05/22/1998
• Status: Expired due to Term

• Current Assignee: Synaptics (UK) Ltd. (Synaptics Incorporated)
• Original Assignee: Synaptics (UK) Ltd. (Synaptics Incorporated)
• Inventors: Jones, Ross P., Ely, David T. E.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US09/700,418
• Time in Patent Office: 853 Days
• Field of Search: 324/207.17, 324/207.25, 324/232, 340/870.31, 318/653, 318/656, 318/658, 318/659, 318/660, 318/661, 360/68.13
• US Class Current: 324/207.17
• CPC Class Codes: G01D 5/2073 by movement of a single coil with respect to two or more coils
• CPC Class Codes: G01D 5/2086 by movement of two or more coils with respect to two or more other coils

Abstract

A rotary position detector includes first and second members, the first member generating a magnetic field which spatially varies around the axis of rotation in a cyclic manner and the second member sensing the generated magnetic field. In response to the generated magnetic field, first and second signals are generated by first and second sensors respectively, which signals vary with the relative angular position of the first and second members and the relative angular position of the first and second members is determined from the first and second signals.

Claims

1. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of predetermined ones of the harmonic components generated by said second magnetic field generator;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

whereby, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

means for determining the relative angular position of said first and second members from said first and second signals.

2. A detector according to claim 1, wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of the harmonic components generated by said second magnetic field generator which have an angular frequency of M±

1.

3. A detector according to claim 1, wherein the circumferential spacing between said loop portions is arranged so as to try to eliminate the harmonic components generated by said second magnetic field generator which have an angular frequency of M±

1.

4. A detector according to claim 1, wherein the circumferential spacing between said loop portions is arranged so as to try to eliminate the harmonic components generated by said second magnetic field generator which have an angular frequency of M±

2.

5. A detector according to claim 1, wherein said second magnetic field generator is operable to generate said magnetic field by passing a current through said winding.

6. A detector according to claim 5, wherein said second magnetic field generator further comprises a power source for generating said current.

7. A detector according to claim 1, wherein said first magnetic field generator comprises a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of M and some harmonic components thereof.

8. A detector according to claim 7, wherein said first magnetic field generator is operable to generate said magnetic field by passing a current through said winding.

9. A detector according to claim 8, wherein said first magnetic field generator further comprises a power source for generating said current.

10. A detector according to claim 7, wherein the ends of each winding are connected together through a respective capacitor, so that each magnetic field generator comprises a respective resonator.

11. A detector according to claim 10, wherein the resonant frequency the first magnetic field generator is different to the resonant frequency of the second magnetic field generator.

12. A detector according to claim 11, wherein the resonant frequency of said first magnetic field generator is lower than the resonant frequency of the second magnetic field generator.

13. A detector according to claim 7, wherein the winding of said first magnetic field generator is electrically connected to the winding of said second magnetic field generator.

14. A detector according to claim 13, wherein adjacent loops of said second magnetic field generator are electrically connected through the loops of the first magnetic field generator and vice versa.

15. A detector according to claim 13, wherein the ends of said windings are connected together through a capacitor, to form a resonator.

16. A detector according to claim 13, wherein the ends of said windings are connected together to form a short circuit coil.

17. A detector according to claim 15, further comprising means for energising said short circuit coil or said resonator to cause said current to flow through said winding.

18. A detector according to claim 17, wherein said second member comprises said energising means.

19. A detector according to claim 18, wherein said energising means comprises a winding which is circumferentially wound around said axis of rotation.

20. A detector according to claim 7, wherein said windings are located on but electrically separate from each other.

21. A detector according to claim 7, wherein said windings are formed from at least two layers of conductor tracks which are connected together at a plurality of vias which pass through an insulating layer disposed between said at least two layers of conductor tracks.

22. A detector according to claim 21, wherein said windings are formed from conductor tracks on at least two layers of a printed circuit board.

23. A detector according to claim 7, wherein said loop portions of said windings lie in one or more planes which are substantially parallel to said axis of rotation.

24. A detector according to claim 7, wherein said loop portions of said first magnetic field generator are symmetrically spaced around said axis of rotation.

25. A detector according to claim 24, wherein each of said loop portions of said first magnetic field generator comprises a multi turn spiral conductor.

26. A detector according to claim 24, wherein each of said loop portions of said first magnetic field generator have substantially the same form.

27. A detector according to claim 7, wherein the loop portions of said first magnetic field generator are wound in the same sense.

28. A detector according to any of claim 7, wherein said first magnetic field generator comprises M loop portions.

29. A detector according to claim 1, wherein said loop portions of said second magnetic field generator enclose different areas.

30. A detector according to claim 1, wherein each loop portion comprises at least two substantially radial portions.

31. A detector according to claim 17, wherein the spacings between the substantially radial portions of the loops of said second magnetic field generator are not the same.

32. A detector according to claim 1, wherein at least one loop portion of said second magnetic field generator is wound in the opposite sense to the other loop portions of said second magnetic field generator.

33. A detector according to claim 1, wherein said second magnetic field generator is operable to generate a harmonic component which spatially varies around said axis of rotation with an angular frequency of M.

34. A detector according to claim 1, wherein said second magnetic field generator comprises M loop portions.

35. A detector according to claim 1, wherein said first sensor comprises a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation so as to be sensitive to a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M.

36. A detector according to claim 35, wherein said first sensor further comprises a second winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation so as to be sensitive to a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M;

wherein the loop portions of the respective windings are circumferentially spaced apart;

wherein said first sensor is operable to generate two signals in response to said first magnetic field generator generating a magnetic field, one from each of said first sensor windings; and

wherein said determining means is operable to determine a fine position measurement from said two signals from said first sensor.

37. A detector according to claim 36, wherein the circumferential spacing between the two windings of said first sensor is π

/2M or an integer multiple thereof, so that said two signals are in phase quadrature.

38. A detector according to claim 36, wherein said determining means is operable to determine said fine position measurement using a trigonometric relationship between said two signals.

39. A detector according to claim 35, wherein the or each first sensor winding comprises 2M loop portions arranged in succession around said axis of rotation, each loop extending circumferentially around said axis of rotation and said loops being arranged so that EMFs induced in adjacent loops by a common alternating magnetic field oppose each other.

40. A detector according to claim 1, wherein said second sensor comprises a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation so as to be sensitive to a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of N.

41. A detector according to claim 40, wherein said second sensor further comprises a second winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation so as to be sensitive to a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of N;

wherein the loop portions of the respective windings are circumferentially spaced apart;

wherein said second sensor is operable to generate two signals in response to said second magnetic field generator generating a magnetic field, one from each of said first sensor windings; and

wherein said determining means is operable to determine a coarse position measurement from said two signals from said second sensor.

42. A detector according to claim 41, wherein the circumferential spacing between the two windings of said first sensor is π

/2N or an integer multiple thereof, so that said two signals are in phase quadrature.

43. A detector according to claim 41, wherein said determining means is operable to determine said fine position measurement using a trigonometric relationship between said two signals.

44. A detector according to claim 40, wherein the or each second sensor winding comprises 2N loop portions arranged in succession around said axis of rotation, each loop extending circumferentially around said axis of rotation and said loops being arranged so that EMFs induced in adjacent loops by a common alternating magnetic field oppose each other.

45. A detector according to claim 40, wherein said first sensor comprises a winding which is wound around said axis of rotation and which has a plurality of loop potions circumferentially spaced around said axis of rotation so as to be sensitive to a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M and wherein said sensor windings are formed on but electrically spaced from each other.

46. A detector according to claim 45, wherein said sensor windings are formed from at least two layers of conductor tracks which are connected together at a plurality of vias which pass through an insulating layer disposed between said at least two layers of conductor tracks.

47. A detector according to claim 46, wherein said windings are formed from conductor tracks on a multi-layer printed circuit board.

48. A detector according to claim 47, wherein said sensor windings lie in one or more planes which are substantially parallel to said axis of rotation.

49. A detector according to claim 47, wherein the conductor tracks for the windings of said first sensor are located in the layer which is closest to said magnetic field generators.

50. A detector according claim 1, wherein N equals one.

51. A detector according to claim 1, wherein M equals eight.

52. A detector according to claim 1, wherein said first and second magnetic field generators are passive and wherein said second member further comprises means for energising said magnetic field generators.

53. A detector according to claim 50, wherein said energising means is operable to apply a pule of driving signal during a first time interval and wherein said determining means is operable to process said sensor signals during a subsequent second time interval.

54. A detector according to claim 51, wherein said determining means comprises a synchronous detector for demodulating the signals received from said first and second sensors.

59. A transducer for use in a position detector according to claim 1, comprising the first and second magnetic field generators and the first and second sensors.

55. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to try to eliminate predetermined ones of said harmonic components generated by said second magnetic field generator;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

whereby, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

means for determining the relative angular position of said first and second members from said first and second signals.

56. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of some of the harmonic components generated by said second magnetic field generator, relative to the amount of said harmonic components which exist in a corresponding square wave signal;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

whereby, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

means for determining the relative angular position of said first and second members from said first and second signals.

57. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of the harmonic components generated by said second magnetic field generator which have an angular frequency of M±

1;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

whereby, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

means for determining the relative angular position of said first and second members from said first and second signals.

58. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to eliminate the harmonic components generated by said second magnetic field generator which have an angular frequency of M±

1;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

whereby, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

means for determining the relative angular position of said first and second members from said first and second signals.

60. A transducer for use in a rotary position detector, comprising:

(a) a first magnetic field generator for generating a magnetic field which spatially varies around an axis in a cyclic manner with an angular frequency of M;

(b) a second magnetic field generator comprising a winding which is wound around said axis and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of some of the harmonic components generated by said second magnetic field generator;

(c) a first sensor which is sensitive to magnetic fields which spatially vary around said axis in a cyclic manner and with an angular frequency of M; and

(d) a second sensor which is sensitive to magnetic fields which spatially vary around said axis in a cyclic manner and with an angular frequency of N.

61. A transducer for use in a rotary position detector, comprising:

a first circuit board comprising at least two layers of conductor tracks which are connected together at a plurality of vias to form;

(a) a first winding which, when energised, is operable for generating a magnetic field which spatially varies around an axis of the circuit board in a cyclic manner and with an angular frequency of M; and

(b) a second winding which is wound around said axis and which has a plurality of loop portions circumferentially spaced around said axis of rotation, which winding is operable, when energised, for generating a magnetic field which spatially varies around said axis in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of some of the harmonic components which are generated by said second winding when it is energised; and

a second circuit board comprising at least two layers of conductor tracks which are connected together at a plurality of vias to form;

(a) a first sensor winding which is wound around an axis of the second circuit board in a cyclic manner so as to have a sensitivity to magnetic fields which spatially vary around said axis with an angular frequency of M; and

(b) a second sensor winding which is wound around said axis in a cyclic manner so as to have a sensitivity to magnetic fields which spatially vary around said axis with an angular frequency of N.

62. A method of detecting the position of first and second members, at least one of which is rotatable relative to the other about an axis of rotation, the method comprising the steps of:

providing on the first member (a) a first magnetic field generator for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, for generating a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of predetermined ones of the harmonic components generated by said second magnetic field generator;

providing on said second member (a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

generating a magnetic field with said first and second magnetic field generators;

sensing the magnetic fields generated by said first and second magnetic field generators with said sensors, to generate first and second signals which vary with the relative angular position of the first and second members; and

determining the relative angular position of said first and second members from said first and second signals.

63. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of predetermined ones of the harmonic components generated by said second magnetic field generator;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of H; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

wherein, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

a position processor operable to process said first and second signals to determine the relative angular position of said first and second members.

64. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of N; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to try to eliminate predetermined ones of said harmonic components generated by said second magnetic field generator;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

wherein, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

a position processor operable to determine the relative angular position of said first and second members using said first and second signals.

65. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of b˜ and

some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of some of the harmonic components generated by said second magnetic field generator, relative to the amount of said harmonic components which exist in a corresponding square wave signal;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

wherein, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

a position processor operable to determine the relative angular position of said first and second members using said first and second signals.

66. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof, wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of the harmonic components generated by said second magnetic field generator which have an angular frequency of N±

1;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M;

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

wherein, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

a position processor operable to determine the relative angular position of said first and second members from said first and second signals.

67. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to eliminate the harmonic components generated by said second magnetic field generator which have an angular frequency of M±

1;

said second member comprising;

(a) a first sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second sensor which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

wherein, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second sensors respectively, which signals vary with the relative angular position of said first and second members; and

a position processor operable to determine the relative angular position of said first and second members from said first and second signals.

68. A transducer for use in a rotary position detector, comprising:

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around an axis in a cyclic manner with an angular frequency of

(b) a second magnetic field generator comprising a winding which is wound around said axis and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis n a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of some of the harmonic components generated by said second magnetic field generator;

c) a first sensor which is sensitive to magnetic fields which spatially vary around said axis in a cyclic manner and with an angular frequency of M; and

(d) a second sensor which is sensitive to magnetic fields which spatially vary around said axis in a cyclic manner and with an angular frequency of N.

69. A transducer for use in a rotary position detector, comprising:

a first circuit board comprising at least two layers of conductor tracks which are connected together at a plurality of vias to form;

(a) a first winding which, when energised, is operable to generate a magnetic field which spatially varies around an axis of the circuit board in a cyclic manner and with an angular frequency of M; and

(b) a second winding which is wound around said axis and which has a plurality of loop portions circumferentially spaced around said axis of rotation,

which second winding is operable, when energised, to generate a magnetic field which spatially varies around said axis in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of some of the harmonic components which are generated by said second winding when it is energised; and

a second circuit board comprising at least two layers of conductor tracks which are connected together at a plurality of vias to form;

(a) a third winding which is wound around an axis of the second circuit board in a cyclic manner so as to have a sensitivity to magnetic fields which spatially vary around said axis with an angular frequency of M; and

(b) a fourth winding which is wound around said axis in a cyclic manner so as to have a sensitivity to magnetic fields which spatially vary around said axis with an angular frequency of N.

70. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is arranged so as to reduce the amount of predetermined ones of the harmonic components generated by said second magnetic field generator;

said second member comprising;

(a) a first winding which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of M; and

(b) a second winding which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner and with an angular frequency of N;

wherein, in response to a magnetic field being generated by said first and second magnetic field generators, first and second signals are generated by said first and second windings respectively, which signals vary with the relative angular position of said first and second members; and

a position processor operable to process said first and second signals to determine the relative angular position of said first and second members.

71. A transducer for use in a rotary position detector, comprising:

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around an axis in a cyclic manner with an angular frequency of M; and

(b) a second magnetic field generator comprising a winding which is wound around said axis and which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis in a cyclic manner and which comprises a fundamental component with an angular frequency of N and some harmonic components thereof,

wherein N<

M, and wherein the circumferential spacing between said loop portions is non-uniform and is arranged so as to reduce the amount of some of the harmonic components generated by said second magnetic field generator, relative to the amount of said harmonic components which exist in a corresponding square wave signal.

72. A rotary position detector, comprising:

first and second members, at least one of which is rotatable relative to the other about an axis of rotation;

said first member comprising;

(a) a first magnetic field generator operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of H; and

(b) a second magnetic field generator comprising a winding which is wound around said axis of rotation and

which has a plurality of loop portions circumferentially spaced around said axis of rotation, and operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and which comprises a fundamental component with an angular frequency of N and harmonic components thereof,

wherein N<

M and wherein the circumferential spacing between said loop portions is non-uniform and arranged so as to reduce the amount of predetermined ones of the harmonic components generated by said second magnetic field generator relative to the amount of said harmonic components which exist in a corresponding square wave signal;

said second member comprising;

(a) a first excitation winding which is operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner and with an angular frequency of H for energising said first magnetic field generator;

(b) a second excitation winding which is operable to generate a magnetic field which spatially varies around said axis of rotation in a cyclic manner with an angular frequency of N, for energising said second magnetic field generator; and

(c) a sensor winding which is sensitive to magnetic fields which spatially vary around said axis of rotation in a cyclic manner with an angular frequency of N and M;

wherein upon excitation by said first and second excitation windings, first and second signals are generated by said sensor winding, which signals vary with the relative angular position of said first and second members; and

a position processor operable to process said first and second signals to determine the relative angular position of said first and second members.