Chain code position detector

• US 6,327,791 B1
• Filed: 06/09/2000
• Issued: 12/11/2001
• Est. Priority Date: 06/09/1999
• Status: Expired due to Fees

• Current Assignee: Snorkel International Incorporated (Elwood Holdings LLC), The United States of America As Represented By The Secretary of Commerce
• Original Assignee: National Institute of Standards and Technology (Government of the United States of America), The United States of America As Represented By The Secretary of Agriculture
• Inventors: Norcross, Richard J., Bunch, W. Robert, Engvall, David P.
• Primary Examiner(s): Fulton, Christopher W.
• Application Number:
  US09/590,895
• Time in Patent Office: 550 Days
• Field of Search: 337/06, 337/07, 337/03, 337/05, 337/10, 33D/IG.3
• US Class Current: 33/706
• CPC Class Codes: F15B 15/2846 using detection of markings, e.g. markings on the piston rod
• CPC Class Codes: F15B 15/2876 using optical means, e.g. laser
• CPC Class Codes: G01D 5/2495 Pseudo-random code
• CPC Class Codes: G01D 5/34792 with only digital scales or both digital and incremental scales
• CPC Class Codes: H03M 1/282 of the pattern-shifting type, e.g. pseudo-random chain code

Abstract

A position detector for sensing the position of a movable member which moves along an axis relative to a stationary member. A nonrepeating N bit chain code embodied in a scale on the movable member runs along the axis. A detector fixed to the stationary member is positioned to sense a portion of the chain code. The detector has K elements (K>>N) generating a plurality of signals. A controller determines the position of the movable member relative to the stationary member as a function of the signals.

Claims

1. A device for sensing the position of a movable member which moves along an axis relative to a stationary member, comprising:

a scale including a nonrepeating code on the movable member aligned substantially along the axis;

a two-dimensional detector fixed to the stationary member and positioned to sense a portion of the scale within a view of the detector, said detector generating a plurality of signals, each signal indicative of the particular viewed portion of the scale sensed by the detector; and

a controller determining the position of the movable member relative to the stationary member as a function of the signals.

2. The device of claim 1 wherein the code comprises consecutive bits, where each bit is either a mark or a space, where N consecutive bits form a unique value as compared to any other N consecutive bits of the code.

3. The device of claim 2 wherein each mark has a length oriented substantially perpendicular to the axis and wherein the detector comprises an array forming L rows of elements and K columns of elements where L and K are integers and K is much greater than N, wherein each column of elements aligns substantially along the length of the marks, wherein the detector simultaneously views at least N consecutive bits of the code, and wherein each successive row or each successive column is read to generate the plurality of signals.

4. The device of claim 1 wherein the scale comprises an N-bit code where N is a sequential number of bits that form a unique value and where each bit is a mark or a space, each mark having a length oriented substantially perpendicular to the axis, and wherein the detector comprises an array forming L rows of elements aligned substantially along the length of each mark and forming K columns of elements aligned substantially along the axis of motion, the elements in each column read successively and adjacent columns being read successively to generate a plurality of signals.

5. The device of claim 4 wherein the portion of the scale being detected equals N+A bits, where A is greater than or equal to one, and wherein the portion of the scale being processed by the controller equals N bits within in the N+A bits being detected.

6. The device of claim 5 wherein two different sets of N bits within the N+A bits are processed by the controller.

7. The device of claim 4 wherein the code is a group of two repeating codes, where each repeating code has a different number of bits, where the number of bits do not have a common denominator, where when aligned with each other along the axis of motion the combination of N bits from each repeating code does not repeat for the length of the scale.

8. The device of claim 4 wherein the repeating codes are chain codes.

9. The device of claim 1 wherein the scale comprises evenly spaced bits of marks or spaces on the movable member and where the mark width is less than the bit spacing.

10. The device of claim 1 wherein the scale comprises evenly spaced marks, and wherein the length of the mark defines its bit value.

11. The device of claim 1 wherein the scale comprises unevenly spaced bits of marks or spaces on the movable member, and wherein the width of the mark or the width of the space defines the bit value.

12. The device of claim 1 wherein the scale comprises a code having N bits where each bit is a mark or a space, each mark having a length oriented substantially perpendicular to the axis, and wherein the detector comprises an array forming L rows of elements aligned substantially along the length of each mark and forming K columns of elements aligned substantially along a width of each mark, the elements in each row being read successively and adjacent rows being read successively to generate a plurality of signals.

13. The device of claim 12 wherein the portion of the scale being detected equals N+A bits, where A is greater than or equal to one, and wherein the portion of the scale being processed by the controller equals N bits within in the N+A bits being detected.

14. The device of claim 13 wherein two different sets of N marks within the N+A marks are processed by the controller.

15. The device of claim 1 wherein the scale comprises a chain code of bits represented by marks and spaces and having gaps therebetween, each mark having a width which is less than the spacing between marks and spaces.

16. The device of claim 1 wherein the detector comprises a housing supporting a substantially flat detector array for reading the scale, an optical conduit positioned between the array and the scale for transmitting an image of the scale onto the array, and an illumination source positioned to illuminate the scale.

17. The device of claim 1 wherein the detector comprises a housing supporting a substantially flat detector array for reading the scale, a lens positioned between the array and the scale for projecting an image of the scale onto the array, and an illumination source positioned to illuminate the scale.

18. The device of claim 1 wherein the code consists of a single linear code aligned substantially linearly along the axis.

19. A device for sensing the position of a cylinder rod driven along an axis relative to a linear motion cylinder, said device comprising:

a scale having a non-repeating code on the cylinder rod along the axis of motion;

a two-dimensional detector on the cylinder and positioned to sense a portion of the scale within a view of the detector which portion uniquely identifies position, said detector generating a plurality of signals, each signal indicative of the particular viewed portion of the scale sensed by the detector.

20. The device of claim 19 wherein the scale comprises a chain code having marks, each mark having a length oriented substantially perpendicular to the axis, and wherein the detector comprises an array forming L rows of elements along the length of each mark and forming K columns of elements along the axis of motion, the elements in each column being read successively and adjacent columns being read successively to generate a plurality of signals.

21. The device of claim 20 wherein the scale comprises a chain code having marks, each mark having a length oriented substantially perpendicular to the axis, and wherein the detector comprises an array forming L rows of elements along the length of each mark and forming K columns of elements along the axis of motion, the elements in each row being read successively and adjacent rows being read successively to generate a plurality of signals.

22. The device of claim 19 wherein the scale comprises a chain code having bits represented by marks and spaces having gaps therebetween.

23. The device of claim 19 wherein the detector comprises a housing supporting a substantially flat detector array for reading the scale, an optical conduit positioned between the array and the scale for transmitting an image of the scale onto the array, and an illumination source positioned to illuminate the scale.

24. The device of claim 19 wherein the detector comprises a housing supporting a substantially flat detector array for reading the scale, a lens positioned between the array and the scale for projecting an image of the scale onto the array, and an illumination source positioned to illuminate the scale.

25. The machine of claim 19 wherein the code consists of a single linear code aligned substantially linearly along the axis.

26. A machine comprising:

a base;

an extendible member supported by the base and having a movable section movable relative to a reference section;

a cylinder having a cylinder housing and having a cylinder rod movable along an axis of motion with either the cylinder housing or the cylinder rod connected to the movable section and the other of the cylinder housing or cylinder rod connected to the reference section such that movement of the cylinder rod along the axis of motion relative to the cylinder housing causes movement of the movable section relative to the reference section;

a controller controlling the position of the cylinder rod relative to the cylinder housing;

a scale having a nonrepeating code on the cylinder rod running along the axis;

a detector fixed to the cylinder housing and positioned to sense a portion of the code, said portion being sufficient to uniquely identify the position of the rod relative to the cylinder housing, said detector generating a plurality of signals, each indicative of the portion of the code; and

wherein the controller determines the position of the cylinder rod relative to the cylinder housing as a function of the signals.

27. The machine of claim 26 wherein the scale comprises a chain code having bits represented by marks or spaces, each mark having a length oriented substantially perpendicular to the axis, and wherein the detector comprises an array forming L rows of elements along the length of each mark and forming K columns of elements along the axis of motion, the elements in each column being read successively and adjacent columns being read successively to generate a plurality of signals.

28. The machine of claim 26 wherein the scale comprises a chain code having bits represented by marks and spaces, each mark having a length oriented substantially perpendicular to the axis, and wherein the detector comprises an array forming L rows of elements along the length of each mark and forming K columns of elements along the axis of motion, the elements in each row being read successively and adjacent rows being read successively to generate a plurality of signals.

29. The machine of claim 26 wherein the scale comprises a chain code have marks and spaces and having gaps therebetween.

30. The machine of claim 26 wherein the detector comprises a housing supporting a substantially flat detector array for reading the scale, an optical conduit positioned between the array and the scale for transmitting an image of the scale onto the array, and an illumination source positioned to illuminate the scale.

31. The machine of claim 30 wherein the detector comprises a housing supporting a substantially flat detector array for reading the scale, a lens positioned between the array and the scale for projecting an image of the scale onto the array, and an illumination source positioned to illuminate the scale.

32. The device of claim 26 wherein the code consists of a single linear code aligned substantially linearly along the axis.

33. A device for sensing the position of a movable member which moves along an axis relative to a stationary member, comprising:

a scale including a nonrepeating code of N bits on the movable member aligned substantially along the axis;

a detector fixed to the stationary member and positioned to sense a portion of the scale, said detector having K elements where K is an integer much greater than N, each of said elements generating a signal indicative of the code of the portion of the scale sensed by the detector; and

a controller determining the position of the movable member relative to the stationary member as a function of the signals.

34. A device for sensing the position of a cylinder rod driven along an axis relative to a linear motion cylinder, said device comprising:

a linear scale having a non-repeating code on the cylinder rod along the axis of motion;

a first plurality of detector elements on the cylinder and positioned to sense a portion of the scale which portion uniquely identifies position, said first plurality of detector elements generating a first signal indicative of the particular viewed portion of the scale;

a second plurality of detector elements on the cylinder and positioned to sense the portion of the scale, said second plurality of detector elements generating a second signal indicative of the particular viewed portion of the scale; and

a controller determining the position of the cylinder rod relative to the linear motion cylinder as a function of the first and second signals.

35. The device of claim 34 wherein the code consists of a single linear code aligned substantially linearly along the axis.