Electronic caliper using a reduced offset induced current position transducer

• US 5,901,458 A
• Filed: 11/21/1997
• Issued: 05/11/1999
• Est. Priority Date: 11/21/1997
• Status: Expired due to Term

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Masreliez, Karl G., Andermo, Nils Ingvar
• Primary Examiner(s): BENNETT, GEORGE B
• Application Number:
  US08/975,651
• Time in Patent Office: 536 Days
• Field of Search: 33/706, 33/708, 33/783, 33/784, 33/810, 33/811, 33/812, 324/207.15, 324/207.17, 324/207.24, 324/244, 324/249, 324/259, 324/664
• US Class Current: 33/810
• CPC Class Codes: G01B 3/205 provided with a counter for digital indication of the measured dimension
• CPC Class Codes: G01D 5/2086 by movement of two or more coils with respect to two or more other coils

Abstract

An electronic caliper having a reduced offset position transducer that uses two sets of coupling loops on a scale to inductively couple a transmitter winding on a read head on a slide to one or more receiver windings on the read head. The transmitter winding generates a primary magnetic field. The transmitter winding is inductively coupled to first loop portions of first and second sets of coupling loops by a magnetic field. Second loop portions of the first and second sets of coupling loops are interleaved and generate secondary magnetic fields. A receiver winding is formed in a periodic pattern of alternating polarity loops and is inductively coupled to the second loop portions of the first and second sets of coupling loops by the secondary magnetic fields. Depending on the relative position between the read head and the scale, each polarity loop of the receiver winding is inductively coupled to a second loop portion of either the first or second set of coupling loops. The relative positions of the first and second loop portions of the first and second sets of coupling loops are periodic and dependent on the relative position of the coupling loops on the scale.

Claims

1. An electronic caliper comprising:

a slide;

an elongated beam having a measuring axis, the slide movable along the measuring axis;

at least one magnetic field generator, each magnetic field generator responsive to a drive signal to generate a first changing magnetic flux in a first flux region;

at least one flux coupling loop, a first portion of the at least one flux coupling loop positionable within the first flux region and responsive to the first changing magnetic flux when positioned within the first flux region to produce a second changing magnetic flux in a second portion of the flux coupling loop in a second flux region that is separated from the first flux region; and

at least one magnetic flux sensor;

wherein;

one of a) the at least one magnetic flux sensor or b) the at least one magnetic field generator includes an inductive area extending along the measuring axis, and the inductive area is spatially modulated along the measuring axis in a pattern including alternating increases and decreases in width,

each magnetic flux sensor is positioned outside the first flux region to sense the second changing magnetic flux in the second flux region portion of at least one flux coupling loop, and

each magnetic flux sensor is responsive to the second changing magnetic flux to generate an output signal which is a function of the relative position between the slide and the elongated beam.

2. The electronic caliper of claim 1, wherein the inductive area comprises a plurality of alternating polarity regions.

3. The electronic caliper of claim 2, wherein the pattern of alternating polarity regions comprises regions along a surface, the regions bounded by at least one conductor positioned on the surface in a prescribed pattern.

4. The electronic caliper of claim 1, wherein the one of a) the at least one magnetic field generator or b) the at least one magnetic flux sensor which has the inductive area spatially modulated along the measuring axis is positioned on one of the slide and the elongated beam, and the at least one flux coupling loop is positioned on the other one of the slide and the elongated beam.

5. The electronic caliper of claim 4, wherein the other of a) the at least one magnetic field generator and b) the at least one magnetic flux sensor is positioned on either the slide or the elongated beam.

6. The electronic caliper of claim 1, wherein in the absence of the at least one flux coupling loop, the output signal generated by each magnetic flux sensor is insensitive to the changing magnetic flux generated by each magnetic field generator.

7. The electronic caliper of claim 1, wherein the at least one magnetic field generator, the at least one flux coupling loops and the at least one magnetic flux sensor are fabricated by printed circuit board processing.

8. The electronic caliper of claim 1, further comprising:

an energy supply source that outputs a power supply;

a drive circuit that inputs the power supply and outputting a drive signal to the at least one magnetic field generator during each measurement cycle; and

an analyzing circuit that inputs the output signal from each at least one magnetic field sensor, determines the position of the slide relative to the elongated beam, and outputs a position signal indicative of the position of the slide relative to the elongated beam at a first level of resolution.

9. The electronic caliper of claim 8, wherein the drive circuit comprises a capacitor discharged through the at least one magnetic field generator.

10. The electronic caliper of claim 9, wherein the capacitor and the at least one magnetic field generator form a resonant circuit.

11. The electronic caliper of claim 8, wherein the analyzing circuit comprises a counter for counting fractions of cycles of the at least one output signal output from the at least one magnetic field sensor at a second level of resolution coarser than the first level of resolution in response to motion of the slide along the measuring axis.

12. The electronic caliper of claim 8, wherein each of a plurality of 3*N, where N is greater than or equal to 1, of magnetic flux sensors comprise identical inductive areas spatially modulated along the measuring axis with a periodic modulation having a wavelength W, and such inductive areas are offset from each other by a length O=W/3N along the measuring axis;

and

the analyzing circuit substantially eliminates the influence of signal components which are third harmonics of the wavelength W.

13. The electronic caliper of claim 1, wherein the changing magnetic flux generated by the at least one magnetic field generator changes at a rate equivalent to an oscillation frequency of at least 1 MHz.

14. The electronic caliper of claim 1, wherein the pattern including alternating increases and decreases in width comprises a periodic pattern having a selected wavelength.

15. The electronic caliper of claim 14, wherein the portion of each coupling loop adjacent the periodic pattern spans, at most, one-half wavelength along the measuring axis.

16. The electronic caliper of claim 14, wherein a first plurality of coupling loops of a first type are arranged along the measuring axis at a pitch equal to the wavelength.

17. The electronic caliper of claim 16, wherein a second plurality of coupling loops of a second type are arranged along the measuring axis offset by one-half wavelength from the first plurality of coupling loops and at a pitch equal to the wavelength, and the coupling loops of the first and second type alternate along the measuring axis in at least the region adjacent to the periodic pattern.

18. The electronic caliper of claim 17, wherein, in one of the first or second coupling loop types, the induced current produces the same polarity flux in the first flux region portion and the second flux region portion, and, in the other of the first or second coupling loop types, the induced current produces flux in the second flux region portion which is opposite in polarity to the flux induced in the first flux region portion.

19. The electronic caliper of claim 17, wherein the first and second coupling loop types couple to the same magnetic flux generator region and are configured so that coupling loops of the first type extend in a first direction perpendicular to the measuring axis to couple to a first magnetic flux sensor region and the coupling loops of the second type extend in an opposite direction perpendicular to the measuring axis to couple to a second magnetic flux sensor region.

20. The electronic caliper of claim 17, wherein the first and second coupling loop types couple to the same magnetic flux sensor region, but are configured so that coupling loops of the first type extend in a first direction perpendicular to the measuring axis to couple to a first magnetic flux generator region and the coupling loops of the second type extend in an opposite direction perpendicular to the measuring axis to couple to a second magnetic flux generator region.

21. The electronic caliper of claim 1, wherein a) the at least one magnetic flux generator or b) the at least one magnetic flux sensor comprises two similar portions arranged symmetrically on opposite sides of the other of the at least one magnetic flux generator and the at least one magnetic flux sensor, such that in absence of coupling loops, the net flux through the magnetic flux sensor is substantially zero as a result of the symmetric configuration.

22. The electronic caliper of claim 1, wherein the at least one flux coupling loop comprises a plurality of flux coupling loops arranged along the measuring axis and the measuring range of the sensor is determined by the extent of the plurality of coupling loops.

23. The electronic caliper of claim 1, wherein each of a plurality of the inductive areas which are spatially modulated along the measuring axis comprises an area outlined by a patterned conductor insulated from other patterned conductors, and a plurality of such inductive areas at least partially overlap.

24. The electronic caliper of claim 23, wherein each of a plurality of N inductive areas which are spatially modulated along the measuring axis is identical and is periodically modulated along the measuring axis with a selected wavelength W, and such inductive areas are offset from each other by a length O along the measuring axis, where O=W/2N for N equal to 2, and O=W/N for N greater than 2.

25. An electronic caliper comprising:

a slide;

an elongated beam having a measuring axis, the slide movable along the measuring axis;

a low power energy supply source on the slide capable of providing a power supply to a drive circuit on the slide;

the drive circuit connected to the power supply and responsive to a control signal to output an intermittent drive signal;

at least one magnetic field generator on the slide, each magnetic field generator responsive to the drive signal to generate a first changing magnetic flux in a first flux region;

at least one flux coupling loop on the elongated beam, a first portion of the at least one flux coupling loop positionable within the first flux region and responsive to the first changing magnetic flux when positioned within the first flux region to produce a second changing magnetic flux in a second flux region proximate to a second portion of the flux coupling loop outside the first flux region;

at least one magnetic flux sensor on the slide, each magnetic flux sensor positioned outside the first flux region for sensing the second changing magnetic flux in the second flux region portion of the at least one flux coupling loop, and each magnetic flux sensor responsive to the second changing magnetic flux to generate an output signal which is a function of the relative position between the magnetic flux sensor and the at least one flux coupling loop; and

an analyzing circuit on the slide responsive to the output signal from at least one magnetic flux sensor to output an output signal indicative of the position of the slide relative to the elongated beam at a first level of resolution.

26. The electronic caliper of claim 25, wherein the drive circuit comprises a capacitor that discharges through the magnetic field generator.

27. The electronic caliper of claim 26, wherein the capacitor and the magnetic field generator operate as a resonant circuit.

28. The electronic caliper of claim 26, wherein the first changing magnetic flux changes at a rate equivalent to an oscillation frequency of at least 1 MHz in response to the intermittent drive signal.

29. The electronic caliper of claim 26, wherein the intermittent drive signal comprises at least one pulse signal.

30. The electronic caliper of claim 29, wherein the analyzing circuit determines changes in the relative position at a coarse level of resolution during each pulse interval, and determines the relative position at a finer level of resolution once during a plurality of pulse intervals.

31. The electronic caliper of claim 29, wherein the analyzing circuit includes synchronous sampling means for sampling the output signal from at least one magnetic flux sensor synchronously with the pulse signal.

32. The electronic caliper of claim 31, wherein the synchronous sampling uses sample timing based on an expected time delay between the pulsed signal and a peak in a response to a resonant circuit formed by the pulse generator components and the magnetic field generator components.

33. The electronic caliper of claim 26, wherein:

at least one of a) the at least one magnetic flux sensor, and b) the at least one magnetic field generator includes an inductive area extending along the measuring axis, and the inductive area is spatially modulated along the measuring axis in a pattern including alternating increases and decreases in width;

the output signal from each magnetic flux sensor exhibits spatial cycles which are a function of a relative position between the magnetic flux sensor and the at least one flux coupling loop; and

the analyzing circuit comprises a counter for counting fractions of cycles of the output signal from the at least one magnetic flux sensor in response to motion of the slide along the elongated beam, at a second level of resolution coarser than the first level of resolution, the counter providing an approximate position of the slider assembly relative to the elongate beam.

34. The electronic caliper of claim 33, wherein the counter is responsive at spatial intervals of at most 1/4 cycle.

35. The electronic caliper of claim 33, wherein the inductive area comprises a plurality of alternating polarity regions.

36. The electronic caliper of claim 35, wherein the plurality of alternating polarity regions comprises regions of a surface bounded by at least one conductor positioned on the surface in a prescribed pattern.

37. A method for operating an electronic caliper, comprising:

supplying power from a self-contained energy supply source to a drive circuit of the electronic caliper;

outputting a drive signal from the drive circuit in response to a control signal;

inducing a current in at least one flux coupling loop in response to the drive signal, wherein the at least one flux coupling loop is positioned on one of a slide and an elongated beam of the electronic caliper, the elongated beam having a measuring axis, the slide being moveable along the measuring axis, and the at least one flux coupling loop being arranged along the measuring axis;

producing a spatially modulated time-varying magnetic field with the at least one flux coupling loop in response to the current, the spatially modulated time-varying magnetic field extending along the measuring axis;

sensing the spatially modulated time-varying magnetic field using at least one magnetic flux sensor on the other of the slide and the elongated beam;

generating a position signal based on the sensed field; and

analyzing the position signal to generate an output indicative of a relative position of the slide and the elongated beam.

38. The method of claim 37, wherein:

the spatially modulated time-varying magnetic field is generated and sensed in a sensing track positioned parallel to the measuring axis; and

the spatially modulated time-varying magnetic field predominates the total magnetic field within the sensing track.