Electronic caliper using a self-contained, low power inductive position transducer

• US 5,973,494 A
• Filed: 05/13/1996
• Issued: 10/26/1999
• Est. Priority Date: 05/13/1996
• Status: Expired due to Fees

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Atherton, Kim W., Masreliez, Karl G., Andermo, Nils Ingvar
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/645,483
• Time in Patent Office: 1,261 Days
• Field of Search: 324/207.22, 324/207.24, 324/207.25, 324/207.16, 324/207.17, 324/207.18, 324/207.19, 33/706, 33/708, 33/783, 33/784, 33/806, 33/819
• US Class Current: 324/207.24
• CPC Class Codes: G01B 3/205 provided with a counter for digital indication of the measured dimension
• CPC Class Codes: G01D 5/2046 by a movable ferromagnetic element, e.g. a core

Abstract

An electronic caliper using a low power induced current position transducer includes a slider assembly mounted on an elongated beam with first and second measuring jaws projecting from the main beam and slider assembly. The position of the slider assembly on the beam is indicative of the distance between the first and second jaws. A depth bar is also attached to, and projects from, the slider assembly. Relative movement between the measuring jaws is determined by an inductive read head mounted on the slider assembly that couples to flux modulators on the beam. The read head includes a transmitter winding and a pair of receiver windings carried by a common printed circuit board. The flux modulators, which can include both flux disrupters and flux enhancers, are carried by the beam and modulate the magnetic fields produced by the transmitter. Thus, the receiver windings produce output voltages corresponding to the overlap between the modulators and the receiver windings. Signal processing electronics are connected to the read head and determine the relative positions of the jaws by monitoring the output of the receiver windings. A digital display displays the determined position. In one embodiment, either flux enhancers or flux disrupters are used. In another embodiment, both flux disrupters and flux enhancers are used. The relatively insensitive nature of the low power induced current position transducer to industrial contaminants allows the caliper to function with improved reliability when operating in traditional shop environments.

Claims

1. An electronic caliper, comprising:

a slide member;

a beam member having a measuring axis, the slide member movably mounted on the beam member and movable along the measuring axis;

at least one magnetic field generator, each magnetic field generator generating a changing magnetic flux in a flux region in response to a drive signal;

a low-power energy supply source outputting a power supply;

a drive circuit inputting the power supply and outputting an intermittent drive signal to at least one of the at least one magnetic field generator; and

at least one flux modulator, each flux modulator positionable within the flux region and capable of altering the changing magnetic flux within a modulation region proximate to the flux modulator; and

at least one magnetic flux sensor, each magnetic flux sensor positioned within the flux region and sensing the changing magnetic flux in the flux region, each magnetic flux sensor generating an output signal indicative of a relative position between the magnetic flux sensor and the at least one flux modulator based on the sensed magnetic flux.

2. The electronic caliper of claim 1, wherein at least one of a) each magnetic flux sensor, and b) each magnetic field generator is formed in an alternating pattern of polarity regions.

3. The electronic caliper of claim 2, wherein the alternating pattern of polarity regions comprises sinusoidally shaped areas bounded by conductive elements.

4. The electronic caliper of claim 2, wherein the one of each magnetic field generator and each magnetic flux sensor which is formed in the alternating pattern of polarity regions is positioned on one of the slide member and the beam member, and the at least one flux modulator is positioned on the other one of the beam member and the slide member.

5. The electronic caliper of claim 4, wherein the other of each magnetic field generator and each magnetic flux sensor which is not formed in the alternating pattern of polarity regions is positioned on either of the slide member and the beam member.

6. The electronic caliper of claim 1, wherein in the absence of the at least one flux modulator, 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 each of the at least one flux modulator comprises one of a) a flux disrupter and b) a flux enhancer.

8. The electronic caliper of claim 1, wherein each magnetic field generator includes a field generating conductor and each magnetic flux sensor includes a sensing conductor, the field generating conductor of each magnetic field generator and the sensing conductor of each magnetic flux sensor positioned within a thin zone.

9. The electronic caliper of claim 1, further comprising an analyzing circuit inputting the output signal from each at least one magnetic field sensor and outputting a position signal indicative of the position of the slide member on the beam member at a first level of resolution.

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

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

12. The electronic caliper of claim 9, wherein the intermittent drive signal comprises at least one pulse signal.

13. The electronic caliper of claim 9, 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 member along the measuring axis.

14. 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.

42. The electronic caliper of claim 1, wherein each magnetic field generator and each magnetic flux sensor form a continuous spatially modulated inductive coupling.

15. An electronic inductive caliper comprising:

a slide;

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

a low-power energy supply source providing a power supply to a drive circuit;

the drive circuit inputting the power supply and outputting an intermittent drive signal;

an inductive transducer connected to the elongated beam and the slide, the inductive transducer inputting the intermittent drive signal and outputting at least one sensed signal responsive to a relative position of the slide on the elongated beam; and

an analyzing circuit inputting the at least one sensed signal and outputting an output signal indicative of the position of the slide on the elongated beam at a first level of resolution.

16. The electronic caliper of claim 15, wherein the drive circuit comprises a capacitor discharged through the inductive transducer.

17. The electronic caliper of claim 16, wherein the capacitor and the inductive transducer form a resonant circuit.

18. The electronic caliper of claim 15, wherein a magnetic field of the inductive transducer changes at a rate equivalent to an oscillation frequency of at least 1 MHz in response to the intermittent drive signal.

19. The electronic caliper of claim 18, wherein the intermittent drive signal comprises at least one pulse signal.

20. The electronic caliper of claim 15, wherein the analyzing circuit comprises a counter for counting fractions of cycles of the at least one sensed signal outputted from the inductive transducer 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 relative position of the slide on the elongated beam.

21. The electronic caliper of claim 20, wherein the counter is responsive at spatial intervals of at most 1/4 cycle.

22. The electronic caliper of claim 15, wherein the inductive transducer comprises:

at least one magnetic field generator, each magnetic field generator generating a changing magnetic flux in a flux region in response to the intermittent drive signal;

at least one flux modulator, each flux modulator positionable within the flux region and capable of altering a magnetic flux within a modulation region proximate to the flux modulator; and

at least one magnetic flux sensor, each magnetic flux sensor positioned within the flux region and sensing the magnetic flux in the flux region, each magnetic flux sensor generating one of the at least one sensed signals, each sensed signal indicative of a relative position between the magnetic flux sensor and the at least one flux modulator based on the sensed magnetic flux.

23. The electronic caliper of claim 22, wherein at least one of a) each magnetic flux sensor, and b) each magnetic field generator, is formed in an alternating pattern of polarity regions.

24. The electronic caliper of claim 23, wherein the alternating pattern of polarity regions comprises sinusoidally shaped areas bounded by conductive elements.

25. The electronic caliper of claim 22, wherein in the absence of the at least one flux modulator, the output signal generated by each magnetic flux sensor is insensitive to the changing magnetic flux generated by each magnetic field generator.

26. The electronic caliper of claim 22, wherein each of the at least one flux modulator comprises one of a) a flux disrupter and b) a flux enhancer.

27. The electronic caliper of claim 22, wherein each magnetic field generator includes a field generating conductor and each magnetic flux sensor includes a sensing conductor, the field generating conductor of each magnetic field generator and the sensing conductor of each magnetic flux sensor positioned within a thin zone.

28. The electronic caliper of claim 15, 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.

29. The electronic caliper of claim 15, wherein the electronic caliper draws at most an average current of 200 μ

A.

41. The electronic caliper of claim 15, wherein the energy supply source is a self-contained, low-power energy supply source.

43. The electronic caliper of claim 22, wherein each magnetic field generator and each magnetic flux sensor form a continuous spatially modulated inductive coupling.

46. The electronic caliper of claim 41, wherein the low-power energy supply source is at least one of a battery and a solar cell.

47. The electronic inductive caliper of claim 15, wherein energy is conserved by creating a resonant circuit between a capacitor and a magnetic field generator of the inductive transducer and disconnecting the capacitor in close proximity to a resonant peak of the resonant circuit.

48. The electronic inductive caliper of claim 15, wherein an average current of at most 75 μ

A is supplied from the power supply to the drive circuit.

49. The electronic caliper of claim 17, wherein the capacitor is disconnected from the inductive transducer in close proximity to a resonant peak of the resonant circuit.

30. A method for operating a caliper, the caliper comprising:

a beam member having a measurement axis;

a slide member mounted on the beam member and slidable along the measurement axis;

a magnetic flux sensor provided on one of the slide member and the beam member,

a flux modulator provided on the other of the beam member and the slide member,

a magnetic flux generator provided on one of the slide member and the beam member;

a low-power energy supply source; and

a drive circuit;

the method comprising;

providing a low-power supply signal from the low-power energy supply source to the drive circuit;

intermittently outputting a drive signal to the magnetic flux generator;

producing a changing magnetic flux with the magnetic flux generator in a flux region in response to the intermittent drive signal;

moving the slide member relative to the beam member to a measurement position which is relative to an established reference position, wherein the flux modulator modulates the inductive coupling between the magnetic flux sensor and the magnetic flux generator corresponding to a relative position between the slide member and the beam member;

sensing the modulated magnetic flux with the magnetic flux sensor to produce a sensed signal corresponding to the relative position between the slide member and the beam member;

monitoring the sensed signal produced by the magnetic flux sensor; and

determining, in response to the monitored sensed signal, a distance between the established reference position and the measurement position.

31. The method of claim 30, wherein the magnetic flux generator is a transmitter winding and the step of producing a changing magnetic flux comprises providing a driving signal to the transmitter winding, the driving signal causing a changing current to flow through the transmitter winding to induce the changing magnetic flux.

32. The method of claim 31, wherein the step of providing a driving signal to the transmitter winding comprises:

producing a series of pulses at a selected pulse interval with a pulse generator to produce a pulsed signal; and

supplying the pulsed signal to an input terminal of the transmitter winding.

33. The method of claim 32, wherein the step of monitoring the sensed signal produced by the magnetic flux sensor includes sampling the sensed signal synchronously with the pulsed signal.

34. The method of claim 33, wherein the step of sampling the sensed signal synchronously with the pulsed signal includes sampling the sensed signal based on an expected time delay between the pulsed signal and a peak in a response of a resonant circuit formed by the pulse generator and the transmitter winding.

35. The method of claim 32, wherein the determining step comprises:

determining changes in relative position at a coarse level of resolution during each pulse interval; and

determining the distance between the established reference position and the measurement position at a finer level of resolution once during a plurality of pulse intervals.

36. The method of claim 30, further comprising the step of operating the electronic caliper at at most an average current draw of 200 μ

A.

37. The method of claim 30, wherein the step of producing a changing magnetic flux with the magnetic flux generator includes supplying an average current at at most 75 μ

A to the magnetic flux generator.

44. The method for operating a caliper of claim 30, wherein:

each magnetic flux generator and each magnetic flux sensor form a spatially modulated inductive coupling; and

in the step of moving the slide member, the flux modulator further modulates the spatially modulated inductive coupling between the slide member and the beam member to provide a continuously changing output from the at least one magnetic flux sensor.

50. The method for operating the caliper of claim 30, wherein the energy supply source is a self-contained, low-power energy supply source.

51. The method for operating the caliper of claim 30, wherein the low-power energy supply source is at least one of a battery and a solar cell.

38. An electronic caliper, comprising:

a slide member;

a beam member having a measuring axis, the slide member movably mounted on the beam member and movable along the measuring axis;

at least one magnetic field generator, each magnetic field generator generating a changing magnetic flux in a flux region in response to a drive signal;

a low-power energy supply source outputting a power supply;

a drive circuit inputting the power supply and outputting an intermittent drive signal to at least one of the at least one magnetic field generator; and

at least one flux modulator, each flux modulator positionable within the flux region and capable of altering the changing magnetic flux within a modulation region proximate to the flux modulator; and

at least one magnetic flux sensor, each magnetic flux sensor positioned within the flux region and sensing the changing magnetic flux in the flux region, each magnetic flux generator generating an output signal indicative of a relative position between the magnetic flux sensor and the at least one flux modulator based on the sensed magnetic flux;

wherein each magnetic field generator and each magnetic flux sensor from a spatially modulated inductive coupling, and each output signal varies as a substantially linear function of a total overlapping area, the overlapping area defined by a cross-sectional area of each at least one flux modulator which overlaps both the flux region and an effective area of each at least one magnetic flux sensor when projected normal to an effective plane of the at least one flux sensor, where areas of opposite inductive coupling polarity are defined as areas of opposite sign.

39. The electronic caliper of claim 38, wherein the area of at least one of a) each magnetic field generator and b) each magnetic flux sensor is sinusoidally modulated at a chosen spatial frequency to define the spatially modulated inductive coupling.

40. The electronic caliper of claim 38, wherein the total overlapping area varies as a sinusoidal function at a chosen spatial frequency as a function of the relative position.

45. The electronic caliper of claim 38, wherein the spatially modulated inductive coupling is a continuous spatially modulated inductive coupling.