Precision electronic absolute and relative position sensing device and method of using same

• US 5,258,931 A
• Filed: 08/02/1991
• Issued: 11/02/1993
• Est. Priority Date: 07/08/1988
• Status: Expired due to Term

• Current Assignee: Parker Intangibles LLC (Parker-Hannifin Corporation)
• Original Assignee: Parker-Hannifin Corporation
• Inventors: Hassler, William L. Jr.
• Primary Examiner(s): Harvey, Jack B.
• Assistant Examiner(s): PIPALA, EDWARD J
• Application Number:
  US07/741,219
• Time in Patent Office: 823 Days
• Field of Search: 364/559, 364/560, 364/561, 364/562, 364/571.01, 364/571.03, 364/571.04, 364/571.07, 250/252.1, 250/237 G, 377/17, 377/18, 356/375, 356/383, 356/387, 356/399, 356/401, 341/13, 33/700, 33/701, 33/702, 33/706, 33/707, 33/DIG. 3, 33/DIG. 4
• US Class Current: 702/105
• CPC Class Codes: G01D 5/347 using displacement encoding scales
• CPC Class Codes: G01D 5/366 Particular pulse shapes

Abstract

A novel position sensing device and novel method for determining position use an electronic memory to retain a look up table for calibrated position indicia on a scale. The position indicia are preferably arranged along the scale so that at least two indicia are positioned at unique distances apart in each length segment of the scale. A reader electrically reads the at least two indicia of a segment and the electronic memory look up table allows the at least two indicia to determine the segment, position within segment, and the position relationship between the position within the segment and the reader. Preferably, the indicia are slits in a scale bar, and the reader is a light source and charge-coupled device. The position of the slits is preferably determined using more than one pixel of the charge-coupled device.

Claims

1. A precision electronic absolute position device comprising:

a scale disposed along a position line defined by a set of position segments;

said scale having machine readable indicia fixed thereon in an arrangement and a combination along the position line such that at least two indicia are disposed in each of said segments and the arrangement of said indicia is such that a line position relationship between the at least two indicia in each segment is unique to define the segment, and the combination of the line positions of the at least two indicia defines a precise position along the position line within each segment;

a machine reading means movable with respect to said scale along the position line such that said reading means extends adjacent said position line a length sufficient for reading the at least two indicia of each segment, for reading and converting to electrical signals the at least two indicia in the at least one segment of said scale such that said electrical signals indicate the line position relationship between the at least two indicia, the combination of the line positions of the at least two indicia and a relative line position of the machine reading means with respect to the indicia;

electronic memory means for retaining and electronically communicating for each segment a segment indication corresponding to the line position relationship between the at least two indicia of each segment, and an indication of precise position along the position line corresponding to the segment indication and the combination of line positions of the at least two indicia of said segment; and

position determining means electrically connected to said machine reading means and said memory means for receiving said electronic signals from said reading means, interpreting said signals by electrically communicating with said memory means to determine a segment indication corresponding to said signals and an indication of position along the position line corresponding to said signals, and determining therefrom an absolute position along said position line of said reading means with respect to said scale.

2. The device of claim 1 wherein said determining means comprises:

calculation means connected to said reading means and said memory means for calculating from information derived from said electrical signals from said reading means and from information derived from said memory means a precise position measurement along the position line corresponding to the segment adjacent the reading means and a relative position measurement of said reading means with respect to said precise position.

3. The device of claim 2 wherein said scale comprises a bar and wherein said indicia comprise slits extending through said bar oriented to extend across said position line to allow light to pass therethrough.

4. The device of claim 3 wherein said machine reading means comprises a charge-coupled device disposed on one side of said bar and extending along and adjacent said position line a sufficient distance to always be in position for reading the at least two slits of at least one segment.

5. The device of claim 4 which further comprises a light source disposed on an opposite side of said bar so as to direct light through said slits to said charge-coupled device.

6. The device of claim 5 wherein said light source is connected to said machine reading means to move with said machine reading means as it moves with respect to the position line of said scale.

7. The device of claim 6 wherein said light source approximates a lambertian light source and extends adjacent said position line of said scale a sufficient distance to always be in position for directing light through said at least two slits positioned for reading by said charge-coupled device.

8. The device of claim 7 wherein said calculation means comprises a means for calculating the center of the light intensity of light which is directed through said slits to said charge-coupled device.

9. The device of claim 8 wherein said light source is positioned less than 0.050 inches from said bar.

10. The device of claim 9 wherein said charge-coupled device is positioned less than 0.050 inches from said bar.

11. The device of claim 10 wherein said charge-coupled device has a resolution of at least 500 pixels per inch, a dynamic range of at least 500 to 1 and a read speed of less than 2 milliseconds.

12. The device of claim 2 wherein said memory means comprises a read only memory device and wherein said calculation means comprises a computer.

13. The device of claim 12 which further comprises a temperature sensor for sensing the temperature of said scale and converting the sensed temperature to an electrical signal indicating said temperature and wherein said calculation means compensates for a thermal expansion of said scale corresponding to said temperature by using said electrical signal indicating said temperature as it determines said absolute position along said position line of said reading means with respect to said scale.

14. The device of claim 12 wherein said read only memory comprises an erasable programmable read only memory device so that said memory indications can be reset to correct for changes in the positions represented by said memory indications.

15. The device of claim 1 wherein said scale has only two machine readable indicia fixed thereon for each of said segments.

16. The device of claim 15 wherein said scale comprises a metal member and said indicia comprise slits extending through said metal member.

17. The device of claim 16 wherein each of said segments is discrete and segments do not overlap.

18. The device of claim 17 wherein said slits each have a width in the range of about 0.005 inches to about 0.1 inches.

19. The device of claim 18 wherein said two slits of each of said segments are spaced apart from each other a unique distance in the range of about 0.05 inches to about 2.0 inches.

20. The device of claim 19 wherein said machine reading means comprises a charge-coupled device extending adjacent said position line a length sufficient for reading said two slits of at least one segment, and having a resolution of at least 500 pixels per inch, a dynamic range of at least 500 to 1, and a read speed of less than 2 milliseconds.

21. The device of claim 20 which further comprises a light source connected to move with said charge-coupled device and disposed to direct light through said slits to said charge-coupled device;

said light source approximating a lambertian light source extending along and adjacent said metal member a sufficient length to always direct such light for reading through said two slits of at least one segment.

22. A precision electronic position device comprising:

a scale disposed along a position line defined by a set of position segments;

said scale having machine readable indicia fixed thereon disposed along the position line;

a machine reading means movable with respect to said scale along the position line for reading and converting said indicia to electrical signals;

a memory means comprising a look up table for retaining and a electrically communicating for each indicia an indication of relative position of said indicia along said position line; and

position determining means for receiving said electrical signals from said reading means, interpreting said electrical signals using said memory means, and determining therefrom a relative position along said position line of said reading means with respect to said scale.

23. The device of claim 22 wherein said scale comprises a bar and wherein said indicia comprises slits extending through said bar oriented to extend across said position line to allow light to pass therethrough.

24. The device of claim 23 wherein said machine reading means comprises a charge-coupled device disposed on one side of said bar and extending along and adjacent said position line a sufficient distance to always be in position for reading the at least two slits of at least one segment.

25. A method of determining a position of a machine reader with respect to a scale having position indicia thereon comprising:

calibrating the scale by recording in an electronic memory determined positions of the indicia thereon as indicated by a position calibration machine so as to create a look up table in the electronic memory of calibrated positions with respect to the scale of each of the position indicia;

reading the position indicia of the scale with the machine reader; and

using the look up table of the electronic memory to determine the calibrated position of the machine reader with respect to the scale.

26. The method of claim 25 wherein the position indicia comprise slits in the scale, wherein said reader comprises a charge-coupled device.

27. A method of determining an absolute position of a machine reader with respect to a scale defined by a set of position segments, comprising:

forming position indicia on said scale such that at least two indicia are disposed in an arrangement and a combination in each position segment of said scale and the arrangement of the indicia is such that a position relationship between the at least two indicia in each segment is unique to define each segment and the combination of the positions of the at least two indicia in each segment defines a position within each segment,

calibrating the scale by recording in an electronic memory the position relationship between the at least two indicia and a position defined by the combination of the positions of the at least two indicia so as to form a look up table in the electronic memory for each segment of relationship and combination position information, all as indicated by a position calibration machine;

reading the at least two indicia of a segment of the scale with the machine reader; and

using the look up table of the electronic memory to determine the segment and combination position of the at least two indicia read so as to determine thereby the absolute position of the machine reader with respect to the scale.

28. The method of claim 27 wherein the position indicia comprise slits in the scale, wherein said reader comprises a charge-coupled device.