Capacitive sensing techniques

• US 20060071671A1
• Filed: 06/22/2005
• Published: 04/06/2006
• Est. Priority Date: 06/23/2004
• Status: Active Grant

• Current Assignee: Fe Technical Services, Inc.
• Original Assignee: Fe Technical Services, Inc.
• Inventors: Tola, Jeffry, Brown, Kenneth A.
• Granted Patent: US 7,138,807 B2
• Time in Patent Office: Days
• US Class Current: 324/662
• CPC Class Codes: G01D 5/2415 adapted for encoders
• CPC Class Codes: G01D 5/2497 Absolute encoders G01D5/2454 takes precedence
• CPC Class Codes: H03M 1/26 with weighted coding, i.e. the weight given to a digit depends on the position of the digit within the block or code word, e.g. there is a given radix and the weights are powers of this radix

Abstract

One embodiment of the present invention comprises a sensor with a face having several tracks spaced apart from one another. One of these tracks has a first electrode and a second electrode separated by an electrically nonconductive gap. Also included is a detection device extending across the tracks to receive signals by capacitive coupling. Sensor circuitry electrically coupled to the tracks and the detection device is structured to generate a first number of bits from a sequential signal pattern applied to the tracks in accordance with an established sequence. The circuitry is also structured to generate a second number of bits as a function of a first signal and a second signal. The first bits and second bits represent a position of the detection device along the tracks with the first bits being more numerically significant than the second bits.

Claims

1. A method, comprising:

providing a sensor with a first member including a first electrode and a second electrode separated from the first electrode by an electrically nonconductive gap, and a second member including a third electrode positioned opposite the first member;

sequentially applying a first voltage waveform to the first electrode and a second voltage waveform to the second electrode;

capacitively coupling the third electrode to the first member to provide a first signal in response to the application of the first waveform and a second signal in response to the application of the second waveform; and

evaluating the first signal and the second signal relative to one another to resolve position of the third electrode to one of four or more different positions corresponding to a range, the range being from a first point on the first electrode, and along the gap to a second point on the second electrode.

2. The method of claim 1, wherein the second waveform is an inverted form of the first waveform and said evaluating includes:

determining a sum from the first signal and the second signal;

determining a difference from the first signal and the second signal;

determining a ratio from the sum and the difference; and

determining the one of the positions as a function of the ratio.

3. The method of claim 1, which includes:

applying a third voltage waveform to the second electrode during the application of the first voltage waveform to the first electrode, the first signal corresponding to a response from the first electrode to the first waveform and the second electrode to the third waveform;

applying a fourth voltage waveform to the first electrode during application of the second voltage waveform to the second electrode, the second signal corresponding to a response from the first electrode to the fourth waveform and the second electrode to the second waveform;

determining a ratio from the first signal and the second signal, one of the first signal and the second signal corresponding to a sum and another of the first signal and the second signal corresponding to a difference; and

determining the one of the positions as a function of the ratio.

4. The method of claim 3, wherein the first waveform and the third waveform are approximately the same and the fourth waveform is approximately an inverse of the second waveform.

5. The method of claim 3, wherein the first waveform is approximately an inverse of the third waveform and the second waveform and the fourth waveform are approximately the same.

6. The method of claim 1, wherein the four or more positions number at least eight, said evaluating includes interpolating the one of the positions as function of a relationship between the first signal and the second signal, the first member includes a number of segmented tracks, the electrode and the second electrode being included in a selected one of the tracks, the second member extends across the tracks, and further comprising:

determining a first set of bits each corresponding to a different one of the tracks; and

determining a second set of bits in accordance with said evaluating, the second number of bits corresponding to the one of the positions along the range for the selected one of the tracks, the first set of bits being more numerically significant that the second set of bits.

7. The method of claim 6, wherein the third member includes an electrode with a first portion sized to span across all of the tracks, and a second portion sized and shaped to span across the selected one of the tracks and less than all of the tracks.

8. A method, comprising:

applying a voltage waveform sequence to a sensor track, the track including a first electrode and a second electrode separated by an electrically nonconductive gap, and a third electrode positioned opposite the track;

capacitively coupling the third electrode to the first electrode and the second electrode to provide a sequence of detection signals in response to the waveform sequence;

processing the sequence of detection signals to provide a comparison of a signal sum and a signal difference; and

interpolating position of the third electrode relative to a range along the first electrode, the gap, and the second electrode.

9. The method of claim 8, wherein said applying includes providing a first waveform to the first electrode and a second waveform to the second electrode at different times during the voltage waveform sequence, the second waveform being approximately an inversion of the first waveform.

10. The method of claim 8, wherein the sequence of detection signals includes a first signal from the first electrode and a second signal from the second electrode, and said processing includes determining the signal sum and the difference from the first signal and the second signal.

11. The method of claim 8, wherein said applying includes providing a first pair of voltage waveforms simultaneously to the first electrode and the second electrode during a first time period of the waveform sequence and a second pair of voltage waveforms simultaneously to the first electrode and the second electrode during a second time period of the waveform sequence, and further comprising:

determining the signal sum from one of the first pair and the second pair; and

determining the signal difference from another of the first pair and the second pair.

12. The method of claim 8, wherein said interpolating resolves the position to one of eight or more positions along the range, the sensor track is a selected one of a number of sensor tracks, and the third electrode extends across the tracks, and further comprising:

determining a first set of bits each corresponding to a different one of the tracks; and

determining a second set of bits from said interpolating, the first set of bits being more numerically significant that the second set of bits.

13. The method of claim 12, wherein the third member includes an electrode with a first portion sized to span across all of the tracks, and a second portion sized and positioned to span across only two of the tracks including the selected one of the tracks, and a third portion sized and positioned to span across only the selected one of the tracks.

14. Apparatus, comprising:

a sensor face including a track with a first electrode and a second electrode separated from one another by an electrically nonconductive gap;

a detection device spaced apart from the track to receive signals form the first electrode and the second electrode by capacitive coupling; and

sensor circuitry electrically coupled to the track and the detection device, the circuitry being structured to provide a voltage waveform sequence to the first electrode and the second electrode and process a sequence of detection signals from the detection device in response to the waveform sequence by comparing a signal sum and a signal difference to interpolate position of the detection device relative to a range of positions along the first electrode and the second electrode.

15. The apparatus of claim 14, wherein the sensor face is mounted to turn with a first shaft, the detection device is mounted to turn with a second shaft, and the apparatus is structured to provide an output corresponding to torque based on the position.

16. The apparatus of claim 15, wherein the sensor face and the detection device are operatively coupled to the sensor circuitry by capacitive coupling.

17. The apparatus of claim 14, wherein the sensor face includes a plurality of other tracks and the detection device extends across the other tracks.

18. The apparatus of claim 14, wherein the circuitry includes means for determining a ratio and interpolating the position as a function of the ratio with a resolution to any of eight or more possible positions.

19. The apparatus of claim 14, wherein the detection device includes an electrode with a first portion extending across the track and the other tracks, and a second portion extending across the track and less than all the other tracks.

20. The apparatus of claim 18, wherein the electrode includes a third portion sized and positioned to extend across only the track and the second portion is sized and positioned to extend across only the track and one of the other tracks.