Position transducer having position-dependent amplitude encoding applying first and second modulations

• US 6,335,618 B1
• Filed: 10/05/1999
• Issued: 01/01/2002
• Est. Priority Date: 10/05/1999
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Nahum, Michael
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US09/412,789
• Time in Patent Office: 819 Days
• Field of Search: 324/207.12, 324/1, 324/207.29, 324/207.24, 340/870.36, 340/870.35, 340/870.31, 340/870.32, 340/870.33, 336/45, 336/130-135, 336/136, 318/653-655, 318/657, 341/15
• US Class Current: 324/207.17
• CPC Class Codes: G01B 3/205 provided with a counter for digital indication of the measured dimension
• CPC Class Codes: G01D 5/2053 by a movable non-ferromagnetic conductive element

Abstract

A high-accuracy inductive absolute position transducer system has two members movable relative to each other and includes an amplitude modulating transducer including flux modulators of progressively varying properties. The amplitude modulating transducer includes a transmitter winding and at least one set of receiver windings. An amplitude modulating transducer has a plurality of flux modulator zones distributed along the measuring axis. Flux modulators are formed in at least some of the flux modulator zones. The properties of different flux modulators are varied so as to generate varied flux. A signal generating and processing circuit is connected to the transmitter winding. The flux modulators modulate the inductive coupling based on the relative position between the read head member and the scale member.

Claims

1. An inductive absolute position transducer, comprising:

a scale member;

a read head member, the read member and the scale member movable relative to each other along a measuring axis;

at least one transmitter winding formed on the read head member,

at least one set of receiver windings formed on the read head member, each set comprising at least two receiver windings, and

a signal generating and processing circuit electrically connectable to at least one transmitter winding and at least one set of receiver windings; and

a plurality of flux modulating elements formed on the scale member and spatially distributed along the measuring axis, the flux modulating elements arranged into at least one track, wherein;

for each track, the flux modulating elements of that track apply a first modulation to the inductive coupling between at least a first transmitter winding corresponding to that track and at least one set of receiver windings corresponding to that track based on the spatial distribution of the flux modulating elements of that track along the measuring axis and on a relative position between the read head member and the scale member along the measuring axis, and

for at least one track, the flux modulating elements of that track have at least one varying flux modulating property that varies between the flux modulating elements and along the measuring axis to apply a second modulation to the inductive coupling between the at least first transmitter winding and the at least one set of receiver windings corresponding to that track based on the at least one flux modulating property.

2. The inductive absolute position transducer of claim 1, wherein the signal generation and processing circuit determines an absolute position of the readhead member relative to the scale member to a first resolution based at least partly on a signal component arising from the flux modulating elements having the at least one varying flux modulating property.

3. The inductive absolute position transducer of claim 2, wherein the signal generating and processing circuit determines the absolute position of the read head member relative to the scale member to a second resolution that is finer than the first resolution based at least partly on a signal component arising from the spatial distribution of the flux modulating elements along the measuring axis.

4. The inductive absolute position transducer of claim 1, wherein the spatial distribution of the flux modulating elements in at least one track is a periodic function.

5. The inductive absolute position transducer of claim 1, wherein the further modulation of the inductive coupling between the at least first transmitter winding and the at least one set of receiver windings by the flux modulating elements is a linear function along the measuring axis.

6. The inductive absolute position transducer of claim 1, wherein the at least one track of flux modulating elements comprises a single track of flux modulating elements.

7. The inductive absolute position transducer of claim 1, wherein the at least one track of flux modulating elements comprises two tracks of flux modulating elements.

8. The inductive absolute position transducer of claim 7, wherein the signal generating and processing circuit processes signals generated by each of the two tracks to determine an absolute position of the read head member relative to the scale member, the determined absolute position being relatively insensitive to overall signal amplitude variations.

9. The inductive absolute position transducer of claim 1, wherein at least one of the flux modulating elements is a flux enhancing element.

10. The inductive absolute position transducer of claim 9, wherein the flux modulating property is magnetic permeabilities of the flux enhancing elements.

11. The inductive absolute position transducer of claim 1, wherein at least one of the flux modulating elements is a flux disrupting element.

12. The inductive absolute position transducer of claim 11, wherein the flux modulating property is conductivities of the flux disrupting elements.

13. The inductive absolute position transducer of claim 11, wherein the flux modulating property is thicknesses of the flux disrupting elements.

14. The inductive absolute position transducer of claim 1, wherein at least one of the flux modulating elements is a flux coupling loop.

15. The inductive absolute position transducer of claim 1, wherein the flux modulating property is a varying area of the flux modulating elements.

16. The inductive absolute position transducer of claim 15, wherein the varying area is varying widths across the measuring axis of the flux modulating elements.

17. The inductive absolute position transducer of claim 16, wherein the varying widths of the flux modulating elements vary linearly along the measuring axis.

18. The inductive absolute position transducer of claim 15, wherein the varying area is varying lengths along the measuring axis of the flux modulating elements.

19. The inductive absolute position transducer of claim 18, wherein the varying lengths of the flux modulating elements vary linearly along the measuring axis.

20. A method for operating an inductive absolute position transducer system, the inductive absolute position transducer system comprising:

a first member;

a second member movable relative to the first member along a measuring axis;

at least one first winding formed on a first one of the first and second members;

at least one set of second windings formed on the first one of the first and second member, each set of second windings having a constant spatial wavelength; and

a plurality of flux modulating elements formed on a second one of the first and second members and arranged along the measuring axis;

the method comprising;

generating a changing magnetic flux using one of the at least one first windings;

configuring the changing magnetic flux sensed by at least one set of second windings according to a first spatial modulation which is a spatially periodic function of the relative position of the second member relative to the first member along a measuring axis using at least some of the plurality of flux modulating elements;

configuring the changing magnetic flux sensed by at least one set of second windings according to a second predetermined spatial modulation which is a function of the relative position of the second member relative to the first member along the measuring axis using at least some of the plurality of flux modulating elements; and

sensing the spatially modulated changing magnetic flux using the at least one set of second windings to generate at least one spatially periodic sensed signal having an amplitude range that depends on the relative position between the first and second members.

21. The method of claim 20, wherein spatially modulating the changing magnetic flux comprises varying the flux modulators.

22. The method of claim 21, wherein varying the flux modulators comprises varying the flux enhancing properties of at least one of the flux modulating elements.

23. The method of claim 22, wherein the varying the flux enhancing properties comprises modulating the magnetic permeability of the flux enhancing elements.

24. The method of claim 21, wherein varying the flux modulators comprises varying the flux disrupting properties of at least one of the flux modulating elements.

25. The method of claim 24, wherein the varying the flux disrupting properties comprises varying the conductivities of the flux disrupting elements.

26. The method of claim 24, wherein the varying the flux disrupting properties comprises varying the thicknesses of the flux disrupting elements.

27. The method of claim 21, wherein varying the flux modulators comprises varying a dimension of a flux coupling loop.

28. The method of claim 21, wherein varying the flux modulators comprises varying an area of the flux modulating elements.

29. The method of claim 28, wherein varying the area comprises varying widths of the flux modulating elements across the measuring axis.

30. The method of claim 29, wherein varying the widths comprises varying the widths of the flux modulating elements linearly along the measuring axis.

31. The method of claim 28, wherein varying the area comprises varying lengths of the flux modulating elements along the measuring axis.

32. The method of claim 31, wherein varying the lengths comprises varying the lengths of the flux modulating elements vary linearly along the measuring axis.

33. The method of claim 28, wherein varying the area comprises varying areas of one or more holes in each of the flux modulating elements.

34. The method of claim 33, wherein varying areas comprises varying the areas linearly along the measuring axis.

35. A method for operating an inductive absolute position transducer system, the inductive absolute position transducer system comprising:

a first member;

a second member movable relative to the first member along a measuring axis;

at least one first winding formed on a first one of the first and second members;

at least one set of second windings formed on the first one of the first and second member, each set of second windings having a constant spatial wavelength; and

a plurality of flux modulating elements formed on a second one of the first and second members and arranged along the measuring axis;

the method comprising;

generating a changing magnetic flux using one of the at least one first windings;

positionally-dependently spatially modulating the changing magnetic flux sensed by the other of the at least one first winding and the at least one set of second windings using the plurality of flux modulating elements such that a degree of the spatial modulation is position dependent;

sensing the spatially modulated changing magnetic flux using the other of the at least one first winding and the at least one set of second windings to generate at least one spatially periodic sensed signal having an amplitude range that depends on the relative position between the first and second members.