Method of sensing absolute position of a structure using a capacitively coupled position encoder

• US 7,420,376 B2
• Filed: 08/29/2006
• Issued: 09/02/2008
• Est. Priority Date: 06/23/2004
• Status: Expired due to Fees

• Current Assignee: TT Electronics PLC
• Original Assignee: TT Electronics PLC
• Inventors: Tola, Jeffry, Brown, Kenneth A.
• Primary Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US11/511,925
• Publication Number:
  US 20060284622A1
• Time in Patent Office: 735 Days
• Field of Search: 324/662, 324/661, 324/660, 324/658, 324/686, 324/690, 33/1.PT, 33/1.N, 337/06, 337/07, 337/08, 340/870.37, 714/724, 341/11, 341/15
• US Class Current: 324/661
• 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

A method of sensing absolute position of a structure includes: generating a signal pattern to repetitively provide a changing voltage to each of two or more tracks of a sensor, capacitively coupling an electrode of the sensor to the tracks to determine a first electrode position along the tracks by detecting a first group of signals emitted in response to the signal pattern, moving at least one of the electrode and the tracks relative to another of the electrode and the tracks to result in a second electrode position along the tracks different from the first electrode position, and detecting a second group of signals emitted in response to the signal pattern with the electrode capacitively coupled to the tracks to determine the second electrode position.

Claims

1. A method, comprising:

generating a signal pattern to repetitively provide a changing voltage to each of two or more tracks of a sensor;

capacitively coupling an electrode of the sensor to the tracks to determine a first electrode position along the tracks by detecting a first group of signals emitted in response to the signal pattern, a first one of the tracks includes a first set of electrode segments each spaced apart from another by a corresponding one of a first set of electrically nonconductive gaps, a second one of the tracks includes a second set of electrode segments each spaced apart from another by a corresponding one of a second set of electrically nonconductive gaps, the first set of electrode segments includes a first electrode subset and a second electrode subset, and each member of the first electrode subset alternates with a member of the second electrode subset along the first one of the tracks;

moving at least one of the electrode and the tracks relative to another of the electrode and the tracks to result in a second electrode position along the tracks different from the first electrode position; and

detecting a second group of signals emitted in response to the signal pattern with the electrode capacitively coupled to the tracks to determine the second electrode position.

2. The method of claim 1, wherein said moving includes rotating at least one of the tracks and the electrode, and the tracks are each in a closed loop form.

3. The method of claim 1, wherein the generating includes:

providing a first voltage waveform to one of the electrode segments in the first subset to cause a first signal to be emitted there from that belongs to the first group;

providing a second voltage waveform to one of the electrode segments in the second subset to cause a second signal to be emitted there from that belongs to the first group;

while in the first electrode position, the electrode overlapping the one of the electrode segments in the first subset, the one of the electrode segments in the second subset, and an electrically nonconductive gap positioned therebetween; and

determining the first electrode position as a function of the first signal and the second signal.

4. The method of claim 3, wherein the first voltage waveform is provided to the one of the electrode segments of the first subset as the second voltage waveform is provided to the one of the electrode segments of the second subset, the second signal is approximately an inverted form of the first signal, and the electrode provides an output signal representative of a sum of the first signal and the second signal.

5. The method of claim 3, which includes:

applying the first voltage waveform and the second voltage waveform at different times in accordance with an established sequence;

providing an output signal from the electrode for each of the first signal and the second signal; and

interpolating the first electrode position as a function of the first signal and the second signal, the first one of the tracks having more electrode segments than the second one of the tracks.

6. The method of claim 1, wherein the electrodes of the second set each have a length along the second one of the tracks greater than each of the electrodes of the first set along the first one of the tracks.

7. A method, comprising:

generating a signal pattern to repetitively provide a changing voltage to each of two or more tracks of a sensor,

capacitively coupling an electrode of the sensor to the tracks to determine a first electrode position along the tracks by detecting a first group of signals emitted in response to the signal pattern, with a first one of the tracks including a first set of electrode segments having a first electrode subset and a second electrode subset wherein each member of the first electrode subset alternates with a member of the second electrode subset along the first one of the tracks;

moving at least one of the electrode and the tracks relative to another of the electrode and the tracks to result in a second electrode position along the tracks different from the first electrode position; and

detecting a second group of signals emitted in response to the signal pattern with the electrode capacitively coupled to the tracks to determine the second electrode position.

8. The method of claim 7, wherein said moving includes rotating at least one of the tracks and the electrode, and the tracks are each in a closed loop form.

9. The method of claim 7, wherein the generating includes:

providing a first voltage waveform to one of the electrode segments in the first subset to cause a first signal to be emitted there from that belongs to the first group;

providing a second voltage waveform to one of the electrode segments in the second subset to cause a second signal to be emitted there from that belongs to the first group;

while in the first electrode position, the electrode overlapping the one of the electrode segments in the first subset, the one of the electrode segments in the second subset, and an electrically nonconductive gap positioned therebetween; and

determining the first electrode position as a function of the first signal and the second signal.

10. The method of claim 9, wherein the first voltage waveform is provided to the one of the electrode segments of the first subset as the second voltage waveform is provided to the one of the electrode segments of the second subset, the second signal is approximately an inverted form of the first signal, and the electrode provides an output signal representative of a sum of the first signal and the second signal.

11. The method of claim 9, which includes:

applying the first voltage waveform and the second voltage waveform at different times in accordance with an established sequence;

providing an output signal from the electrode for each of the first signal and the second signal; and

interpolating the first electrode position as a function of the first signal and the second signal, the first one of the tracks having more electrode segments than the second one of the tracks.

12. The method of claim 8, wherein the electrodes of the second set each have a length along the second one of the tracks greater than each of the electrodes of the first set along the first one of the tracks.