Position detecting apparatus using a magnetic sensor and a closed magnetic circuit with non-uniform magnetic flux distribution

• US 4,810,965 A
• Filed: 09/11/1986
• Issued: 03/07/1989
• Est. Priority Date: 09/13/1985
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Endo, Michiko, Hirano, Akira, Komenou, Kazunari, Wakatsuki, Noboru, Kojima, Yuji, Fujiwara, Yoshiro
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US06/906,027
• Time in Patent Office: 908 Days
• Field of Search: 324/207, 324/208, 324/251, 324/252, 338/32 R, 338/32 H, 336/30, 336/45
• US Class Current: 324/207.22
• CPC Class Codes: G01D 5/20 by varying inductance, e.g. by a movable armature

Abstract

A position detector having a magnetic sensor for measuring linear or angular displacement, or detecting a position of a body without contact thereto. The detector has a closed circuit including magnets and yokes. The magnetic leakage flux which emanates from the inside surfaces of the yokes is utilized to detect the position of the body. The magnetic sensor is transferred along the inside surfaces of the yokes by a transferring circuit, which senses the magnetic field intensity of the leakage flux distributed thereon. This enables the detector to have a longer measuring range than that of a prior art detectors. An output signal is stable due to the shielding effect of the yokes. The magnetic closed circuit has many magnetic and mechanical configurations. For example, for the magnet, a permanent magnet and an electromagnet can be used. Further, improvements are proposed for enhancing the linearity of the output signal voltage with respect to the transferring distance of the sensing element and for compensating the offset drift of an amplifier or changing the coercive force of permanent magnets.

Claims

1. A position detecting apparatus comprising:

a closed magnetic circuit, including;

magnetic field generating means for generating a magnetic field;

yoke means, operatively connected to said magnetic field generating means and including a magnetic material and having an inside surface, for guiding at least a portion of said magnetic field therethrough and for emanating a magnetic leakage flux from said inside surface, said magnetic leakage flux having a non-uniform magnetic field intensity distribution between a first position on said yoke means and a second position on said yoke means;

magnetic sensing means, located along the inside surface of said yoke means, for sensing a magnetic field intensity of said magnetic leakage flux emanating from the inside surface of said yoke means and for outputting an output signal responsive to said sensing; and

transferring means for mounting said magnetic sensing means and for transferring said magnetic sensing means along the inside surface of said yoke means between said first and second positions.

2. A position detecting apparatus according to claim 1, wherein said magnetic sensing means is a magnetic sensor having a magnetoresistive sensing element.

3. A position detecting apparatus according to claim 2, wherein said magnetoresistive sensing element is a barber-pole type magnetic sensor.

4. A position detecting apparatus according to claim 1, wherein said magnetic field generating means is a permanent magnet.

5. A position detecting apparatus according to claim 4, wherein said yoke means is U-shaped having two straight branches in parallel with each other, and wherein said permanent magnet is positioned between said two straight branches and connected thereto such that the magnetic pole axis of said permanent magnet is substantially perpendicular to said two straight branches.

6. A position detecting apparatus according to claim 4, wherein said yoke means includes a pair of circular yokes in parallel with each other and having first and second ends, wherein a small gap is formed between said first and second ends, said pair of circular yokes connected to each other by a magnetic material located at the first ends of said circular yokes on a first side of said small gap, said permanent magnet being positioned between said circular yokes and connected thereto at the second ends of said circular yokes on a second side of said small gap, so that the magnetic pole axis of said permanent magnet is substantially perpendicular to said pair of circular yokes.

7. A position detecting apparatus according to claim 6, wherein said pair of circular yokes have the same dimension and have a washer-like shape, and wherein the surfaces of each of said pair of circular yokes are substantially parallel to the plane in which said pair of circular yokes lie.

8. A position detecting apparatus according to claim 6, wherein said pair of circular yokes includes a pair of co-axial short cylinders having a first diameter and a second diameter, respectively, the first diameter being larger than the second diameter, the surfaces of said pair of circular yokes being substantially perpendicular to the plane in which said pair of circular yokes lie.

9. A position detecting apparatus according to claim 1, wherein said yoke means includes two yoke plates arranged substantially in parallel to each other and having a distance therebetween, and wherein said yoke plates extend along a path of a predetermined shape.

10. A position detecting apparatus according to claim 9, wherein said two yoke plates extend in a circle.

11. A position detecting apparatus according to claim 9, wherein said two yoke plates extend in a straight line.

12. A position detecting apparatus according to claim 11, wherein said magnetic field generating means includes two permanent magnets positioned between said two yoke plates at both ends of said two yoke plates, respectively, the magnetic pole axes of said two permanent magnets being substantially perpendicular to said two yoke plates and the direction of polarity of the magnetic poles of said two permanent magnets being opposite each other.

13. A position detecting apparatus according to claim 1, wherein said yoke means is U-shaped having two straight branches substantially in parallel to each other, and wherein said permanent magnet is positioned between said two straight branches and is connected thereto, such that the magnetic pole axis of said permanent magnet is substantially perpendicular to said two straight branches.

14. A position detecting apparatus according to claim 1, wherein said yoke means includes two straight plate-like yokes substantially in parallel to each other, and wherein said magnetic field generating means includes two permanent magnets positioned between said two plate-like yokes at both ends of said two plate-like yokes, respectively, the magnetic pole axes of said two permanent magnets being substantially perpendicular to said two plate-like yokes and the direction of polarity of the magnetic poles of said two permanent magnets being opposite each other.

15. A position detecting apparatus according to claim 14, wherein said transferring means is a transferring rod of a non-magnetic material and each of said two permanent magnets has a hole therein, said transferring rod being capable of sliding in a longitudinal direction of said two plate-like yokes.

16. A position detecting apparatus according to claim 1, wherein said yoke means includes two straight plate-like yokes substantially in parallel to each other, and wherein said magnetic field generating means includes first, second and third permanent magnets connected between said two straight plate-like yokes, said first and second permanent magnets positioned at either end of said two straight plate-like yokes and said third permanent magnet positioned between said first and second permanent magnets, the magnetic pole axes of said first, second and third permanent magnets are substantially perpendicular to the plane of said two straight plate-like yokes, and the direction of polarity of said first, second and third magnetic poles are alternately opposite each other, thus forming a magnetic circuit including two closed magnetic sub-circuits connected in series.

17. A position detecting apparatus according to claim 16, wherein said magnetic sensing means includes a pair of magnetoresistive sensing elements arranged substantially in parallel to each other and separated from each other by a predetermined distance.

18. A position detecting apparatus according to claim 17, wherein said first and second permanent magnets each include a first sub-permanent magnet, a non-magnetic spacer block placed on said first sub-permanent magnet, and a second sub-permanent magnet placed on said non-magnetic spacer block, and wherein said their permanent magnet includes two sub-permanent magnets facing each other and having a space therebetween sufficient to allow the passage of said magnetic sensing means.

19. A position detecting apparatus according to claim 18, wherein said transferring means is a transferring rod of a non-magnetic material and said first and second permanent magnets located at each end of said two straight plate-like yokes have a hole in each of said non-magnetic spacer blocks so that said transferring means is capable of sliding in the longitudinal direction of said two straight plate-like yokes.

20. A position detecting apparatus according to claim 1, wherein said yoke means is a single circular yoke, wherein said magnetic field generating means is a tapered wedge-like permanent magnet, and wherein said tapered wedge-like permanent magnet being embedded in said single circular yoke and having a tapered edge oriented toward the inside of said single circular yoke.

21. A position detecting apparatus according to claim 1, wherein said yoke means includes a cylindrical yoke and a rod yoke which is co-axially surrounded by said cylindrical yoke.

22. A position detecting apparatus according to claim 21, further comprising a lid formed of a magnetic material closing one end of said cylindrical yoke and being magnetically connected to the entire cross-sectional area of said rod yoke.

23. A position detecting apparatus according to claim 22, wherein said transferring means comprises a transferring ring slidable along the axis of said rod yoke and having said magnetic sensing means attached thereto.

24. A position detecting apparatus according to claim 22, wherein said cylindrical yoke has an inside wall and said rod yoke has a surface, and wherein said magnetic field generating means is a permanent magnet ring having a co-axial hole therein, said permanent magnet ring positioned between said cylindrical yoke and said rod yoke at an end opposite said lid, said permanent magnet ring being connected to the inside wall of said cylindrical yoke and the surface of said rod yoke.

25. A position detecting apparatus according to claim 21, wherein said magnetic field generating means includes two permanent magnet rings magnetized in a radial direction and positioned between said cylindrical yoke and said rod yoke at both ends of said yokes, respectively, the directions of polarity of the magnetic poles of said two permanent magnet rings being opposite each other.

26. A position detecting apparatus according to claim 25, wherein said transferring means includes a transferring ring formed of a non-magnetic material and having an inner hole formed therein, said rod yoke fitted in said inner hole and said transferring ring being capable of sliding in the axial direction of said rod yoke.

27. A position detecting apparatus according to claim 26, further comprising a shielding means, formed of a magnetic material and enclosing the entire position detecting apparatus, for magnetically shielding said position detecting apparatus.

28. A position detecting apparatus according to claim 1, wherein said yoke means has a continuously varying cross-sectional area in the longitudinal direction.

29. A position detecting apparatus according to claim 28, wherein said yoke means includes two straight yokes having inner surfaces substantially parallel to each other and having concave outer surfaces, and wherein said magnetic field generating means includes two permanent magnets positioned between said two straight yokes at each end of said two straight yokes, respectively, the magnetic pole axes of said two permanent magnets being substantially perpendicular to said two straight yokes and the direction of polarity of the magnetic poles of said two permanent magnets being opposite each other.

30. A position detecting apparatus according to claim 29, wherein said concave surfaces are V-shaped.

31. A position detecting apparatus according to claim 29, wherein said concave surfaces are curved surfaces determined by a formula:

space="preserve" listing-type="equation">Y=kX.sup.3/2

wherein k is a constant, wherein X is the length along the longitudinal direction of said yoke member, and wherein Y is the thickness of said yoke member perpendicular to the longitudinal direction.

32. A position detecting apparatus according to claim 1, wherein said magnetic field generating means is an electromagnet.

33. A position detecting apparatus according to claim 32, wherein said electromagnet includes an exciting coil and a magnetic core formed of a magnetic material extending to form said yoke means.

34. A position detecting apparatus according to claim 32, further comprising an alternating current power supply having a predetermined frequency, wherein said electromagnet is excited by said alternating current power supply.

35. A position detecting apparatus according to claim 1, wherein said magnetic field generating means includes two electromagnets having exciting coils wound in mutually opposite directions, and wherein said yoke means includes a rectangular yoke formed of a magnetic material and having sides which correspond to cores of said two electromagnets.

36. A position detecting apparatus according to claim 35, further comprising an alternating current power supply having a predetermined frequency, wherein said electromagnets are excited by said alternating current power supply.

37. A position detecting apparatus according to claim 1, wherein said inside surface of said yoke means has a notched surface.

38. A position detecting apparatus according to claim 37, wherein said notched surface includes grooves having a specified depth, width and pitch.

39. A position detecting apparatus according to claim 1, further comprising a subsequent circuit, wherein said magnetic sensing means includes a pair of magnetic sensing elements having a compensating function for sensing a magnetic field, for outputting signal voltages of opposite polarities from said respective magnetic sensing elements, and for providing a sum of said output signal voltages as a position detecting signal to said subsequent circuit.

40. A position detecting apparatus according to claim 1, wherein said magnetic sensing means includes a pair of magnetic sensing elements arranged substantially in parallel and having a predetermined distance therebetween, said magnetic sensing means detecting the sensitivity of said magnetic sensing elements.

41. A position detecting apparatus according to claim 1, wherein said magnetic sensing means includes a magnetic sensing element and an enclosure formed of a magnetic material having a magnetic hysteresis characteristic, said magnetic sensing element being enclosed by said enclosure.

42. A position detecting apparatus according to claim 41, wherein said magnetic sensing element is a magnetoresistive sensing element having a magnetizing axis which coincides with the axis of magnetization of said enclosure.

43. A position detecting apparatus according to claim 41, wherein said magnetic material of said enclosure is a resin having a magnetizing property.

44. A position detecting apparatus according to claim 42, wherein said magnetic material of said enclosure is a resin having a magnetizing property.

45. A position detecting apparatus according to claim 41, wherein said enclosure is a cylindrical enclosure.

46. A position detecting apparatus according to claim 45, wherein said magnetic sensing element is a magnetoresistive sensing element having a magnetizing axis which coincides with the axis of magnetization of said enclosure.