Absolute digital position encoder

• US 5,880,683 A
• Filed: 07/23/1997
• Issued: 03/09/1999
• Est. Priority Date: 07/22/1993
• Status: Expired due to Fees

• Current Assignee: Bourns Incorporated
• Original Assignee: Bourns Incorporated
• Inventors: Brandestini, Marco
• Primary Examiner(s): Williams, Howard L.
• Application Number:
  US08/899,407
• Time in Patent Office: 594 Days
• Field of Search: 341/6, 341/7, 341/8, 341/9, 341/10, 341/11, 341/13, 341/17
• US Class Current: 341/10
• CPC Class Codes: G01D 5/2492 Pulse stream
• CPC Class Codes: H03M 1/285 of the unit Hamming distance type, e.g. Gray code

Abstract

A method and apparatus to convert absolute angular or linear position to digital information utilizes a ternary coding scheme. The code is arranged along a single track. Sensors placed at essentially equal intervals distinguish three states per position. The sensor outputs are converted from ternary to binary data by combinatorial logic. The sensors may be mechanical contacts, optical detectors, magnetic detectors, or capacitive detectors. Such an encoder may be used as a potentiometer, multiposition switch replacement, shaft encoder, or length measurement device.

Claims

1. A method of manufacturing an absolute Gray coded position encoder that has n sensors, each sensor having k states so that an output code of the encoder is of order k, the method comprising the steps of:

(a) generating all n-digit, k-order necklaces that do not have a sub-period;

(b) ordering a plurality of the necklaces generated in step (a) to obtain an ordered set of necklaces such that a Gray code condition is met between adjacent necklaces of said ordered set;

(c) encoding a track of said encoder using said ordered set of necklaces generated in step (b); and

(d) providing n sensors along said track, each sensor detecting one respective digit of the output code.

2. The method according to claim 1, wherein said ordered set of necklaces if formed such that (i) exactly one digit differs in adjacent necklaces of said ordered set, and (ii) exactly one digit differs between first and last necklaces of said ordered set.

3. The method according to claim 1, wherein step (b) comprises the sub-step of determining a number positions a first necklace must be rotated so that said first necklace differs in exactly one digit from a second necklace.

4. The method according to claim 1, wherein the ordered set generated in step (b) includes all of the n-digit, k-order necklaces.

5. The method according to claim 1, wherein n is greater than 5.

6. The method according to claim 1, wherein the track is generally circular, and step (d) comprises positioning the n sensors such that the sensors are equally spaced apart from one another over an angular range of 360 degrees.

7. A method of manufacturing an absolute Gray coded position encoder that has n sensors, each sensor having k states so that an output code of the encoder is of order k, the method comprising the steps of:

(a) identifying all n-digit, k-order bi-necklaces that do not repeat when rotated by less than 2n positions, each bi-necklace including, respectively, a necklace and a complement of the necklace;

(b) ordering a plurality of the bi-necklaces generated in step (a) to obtain an ordered set of bi-necklaces such that the respective necklaces of adjacent bi-necklaces of said plurality satisfy a Gray code condition;

(c) encoding a track of the encoder using said ordered set of bi-necklaces generated in step (b); and

(d) providing n sensors along said track, each sensor detecting one respective digit of the output code.

8. The method according to claim 7, wherein the ordered set generated in step (b) includes all of the bi-necklaces identified in step (a).

9. The method according to claim 7, wherein n is greater than 5.

10. The method according to claim 7, wherein k=2.

11. The method according to claim 7, wherein said ordered set of bi-necklaces is formed such that exactly one digit differs between the respective necklaces of the first and last bi-necklaces of said ordered set.

12. The method according to claim 7, wherein the track is generally circular, and step (d) comprises positioning the n sensors along the track over an angular range of no more that 180 degrees.

13. A quaternary, Gray-coded, absolute digital position encoder, comprising:

a first member having first and second circular tracks thereon, said first and second tracks positioned in concentric relation to one another, said first track having a first binary code formed thereon and said second track having a second binary code formed thereon, said first and second binary codes forming a quaternary code, and said first and second tracks forming a quaternary track; and

a second member movably mounted with respect to said first member, said second member having a plurality of quaternary sensors which sense said quaternary code, each quaternary sensor comprising, respectively, a first binary sensor which senses said first binary code and a second binary sensor which senses said second binary code, said first and second binary sensors being angularly aligned with one another, each quaternary sensor generating a respective quaternary digit of a code word;

wherein said quaternary sensors are positioned relative to said first and second tracks such that individual values of the code word correspond uniquely to respective relative positions of said first and second members, and such that only one quaternary digit of the code word can change at-a-time during relative movement of said first and second members.

14. The digital position encoder according to claim 13, wherein the number of said quaternary sensors is 4, and the number of unique values of the code word is 256.

15. The digital position encoder according to claim 13, wherein each quaternary sensor generates, respectively, two bits of the code word, and wherein said quaternary sensors are positioned relative to said first and second tracks such that only one bit of the code word can change at-a-time during relative movement of said first and second members.

16. The digital position encoder according to claim 13, wherein the quaternary sensors are spaced apart at equal angular intervals along said quaternary track.

17. The digital position encoder according to claim 13, wherein each quaternary sensor comprises a pair of angularly-aligned LEDs that are illuminated by a respective LED.

18. The digital position encoder according to claim 13, wherein each quaternary sensor comprises a pair of angularly-aligned binary light sensors that are illuminated by a respective light source.

19. A ternary, absolute digital position encoder, comprising:

a first member having thereon a single circular track with a plurality of ternary code elements extending therealong to form a ternary code; and

a second member supported for relative movement with respect to the first member, the second member having thereon a plurality of ternary sensors which are positioned adjacent to the track and configured to read the ternary code, each of the ternary sensors corresponding to a respective ternary digit of a code word;

wherein the ternary code and the sensors are arranged such that each value of the code word corresponds uniquely to a relative position of the first and second members.

20. The ternary position encoder according to claim 19, wherein the ternary code and the sensors are arranged such that the code word follows a Gray code sequence when the first and second members are moved relative to each other.

21. The ternary position encoder according to claim 20, wherein the ternary code and the sensors are arranged such that the code word follows a Gray code sequence over multiple revolutions of the first and second members.

22. The ternary position encoder according to claim 19, wherein the sensors are spaced at equal angular intervals along at least a portion of the track.

23. The ternary position encoder according to claim 19, wherein the ternary code elements comprise contact segments that are maintained at one of three possible voltage states, each voltage state representing a different ternary state.

24. The ternary position encoder according to claim 19, wherein each ternary code element comprises a segment which has one of three possible magnetic states, each magnetic state representing a different ternary state.

25. A quaternary, absolute digital position encoder, comprising:

a first member having thereon a circular track with a quaternary code extending therealong; and

a second member supported for relative movement with respect to the first member, the second member having thereon a plurality of quaternary sensors which are positioned adjacent to the track and configured to read the quaternary code, each of the quaternary sensors comprising a pair of angularly-aligned photodetectors that are illuminated by a common light source, each quaternary sensor corresponding to a respective quaternary digit of a code word;

wherein the quaternary code and the sensors are arranged such that each value of the code word corresponds uniquely to a relative position of the first and second members.

26. The quaternary position encoder according to claim 25, wherein the quaternary code and the sensors are arranged such that the code word follows a Gray code sequence when the first and second members are moved relative to each other.

27. The quaternary position encoder according to claim 26, wherein the quaternary code and the sensors are arranged such that the code word follows a Gray code sequence over multiple revolutions of the first and second members.

28. The quaternary position encoder according to claim 25, wherein the sensors are spaced at equal angular intervals along the track.

29. The digital position encoder according to claim 25, wherein the number of said quaternary sensors is 4, and the number of unique values of the code word is 256.