Single track absolute encoder

• US 4,947,166 A
• Filed: 05/11/1988
• Issued: 08/07/1990
• Est. Priority Date: 02/22/1988
• Status: Expired due to Term

• Current Assignee: GSI Lumonics Corporation (Novanta Inc.)
• Original Assignee: Dynamics Research Corporation (Science Applications International Corporation)
• Inventors: Wingate, Sidney A., Rust, Gregory J.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Hoff, Marc S.
• Application Number:
  US07/193,245
• Time in Patent Office: 818 Days
• Field of Search: 341/8, 341/9, 341/13, 341/15
• US Class Current: 341/13
• CPC Class Codes: G01D 5/2497 Absolute encoders G01D5/2454 takes precedence

Abstract

An absolute encoder providing a multi-bit output binary code indicative of the position of a rotary or linear scale. The encoder employs a code track, which contains a serial code, and a clock track. The encoder may be either rotary or linear, and may be implemented optically, magnetically, inductively, capacitatively or by any other binary sensing technique.

Claims

1. An absolute encoder providing a code of length N representative of absolute angular position comprising:

a disc mounted for rotation about an axis, said disc having a single circumferential serial code track having a plurality n of binary segments, whereby each combination of a predetermined number N-2 of adjacent segments creates a code unique to said code track, where n=2^N-2, each representative of a particular one of a plurality of angular sectors that subtend 2π

/2^N-2 radians;

said disc further having one circumferential clock code track having a plurality 2n of alternating binary segments defining a clock code;

means for reading said clock code track to produce a clock signal indicative of the transition of said clock code;

means for reading said serial code track in response to said clock signal to produce a plurality of first code signals of length N-2, each representative of a particular one of said plurality of angular sectors;

means responsive to said clock signal for providing a plurality of second code signals for each said first code signal, each representative of a partition of the corresponding one of said plurality of first code signals into a finer angular sector within each said angular sector; and

means coupled to said first and to said second code signals to provide said code of length N representative of the rotary position of said disc.

2. The absolute encoder of claim 1, wherein the adjacent segments are circumferentially arranged on said one serial code track.

3. The absolute encoder of claim 2, wherein the code defined by the segments of the code track is a shift register code.

4. The absolute encoder of claim 1, wherein said means to provide a code representative of position comprises a shift register means.

5. The absolute encoder of claim 1, wherein said binary segments of said serial code track are respectively light-transmitting or opaque.

6. The absolute encoder of claim 1, wherein said binary segments of said serial code track are respectively light-reflecting or non-reflective.

7. The absolute encoder of claim 1, wherein said binary segments of said serial code track are magnetic.

8. The absolute encoder of claim 1, wherein said binary segments of said serial code track are capacitive.

9. An absolute encoder comprising:

a disc mounted for rotation about an axis, said disc including a single circumferential serial code track having binary segments, wherein a predetermined number of adjacent segments defines a unique serial code for each segment of disc rotation, and a circumferential clock track having alternating binary segments;

first means for sensing the clock track and producing a clock signal representative of relative disc rotation and direction;

second means for sensing the serial code track in response to said clock signal and producing a serial code;

means for storing said serial code for readout as a parallel word; and

means for converting said parallel word to a signal representative of the relative angular position of said disc;

wherein the first means includes first reticle means for defining the positions at which the clock track is sensed; and

wherein the second means includes second reticle means for defining the positions at which the serial code track is sensed.

10. The apparatus of claim 9, wherein said means for storing includes a shift register and circuit means operative to transfer the serial code into a first input or a last input of the shift register in accordance with the relative phase of clock signals derived from said clock track.

11. The apparatus of claim 10, wherein the means for converting includes a memory means operative in response to an output code from the shift register to provide a code representative of the relative angular position of said disc.

12. The apparatus of claim 11, wherein the binary segments of the serial code track and of the clock track are respectively light-responsive and non-responsive;

wherein the first means comprises a light source operative to direct light through the first reticle means to the clock track, and first and second light sensors for receiving light from the clock track and operative to produce the clock signal; and

wherein the second means comprises a first and second light source operative to direct light through the second reticle means to the serial code track, and third and fourth light sensors for receiving light from the serial code track and operative to produce the serial code.

13. The apparatus of claim 9, further including circuit means for providing at least one bit of said serial code from the clock track.

14. The apparatus of claim 11, wherein the binary segments of the serial code track and of the clock track are respectively light-responsive and non-responsive;

wherein the first means comprises a light source operative to direct light through the first reticle means to the clock track, and first and second light sensors for receiving light from the clock track and operative to produce the clock signal; and

wherein the second means comprises a light source operative to direct light through the second reticle means to the serial code track, and a light sensor for receiving light from the serial code track and operative to produce the serial code.

15. An absolute encoder comprising:

a scale mounted for relative motion with respect to a reference and comprising a single serial code track having binary segments, wherein a predetermined number of adjacent segments defines a unique serial code for each segment of relative motion, and a clock track having alternating binary segments;

first means for sensing the clock track and producing a clock signal representative of relative movement and direction;

second means for sensing said single serial code track in response to said clock signal and producing a serial code;

a shift register having selectable left-right and right-left serial storability;

means responsive to the clock signal for storing said serial code in the shift register selectably left-right and right-left in dependence on relative movement and direction; and

means for converting said serial code to a signal representative of the relative position of said scale.

16. The absolute encoder of claim 15, wherein said first means for sensing the clock track and producing a clock signal representative of relative movement and direction comprises:

a light emitting diode;

first and second light sensing elements to sense the light from said light emitting diode;

first and second comparators providing signals in response to said first and second light sensing elements, respectively;

first and second means respectively coupled to said first and second comparators to invert the respective signals from said first and second comparators;

first digital gate means for ANDING said signal from said first comparator and said inverted signal from said second comparator;

second digital gate means for ANDING said inverted signal from said first comparator and said inverted signal from said second comparator; and

shift register means having a first input coupled to the outPut of said first digital gate means, and a second input coupled to the output of said second digital gate means.

17. The absolute encoder of claim 15, wherein said first means for sensing the clock track and producing a clock signal representative of relative movement and direction comprises:

a light emitting diode;

first and second light sensing elements to sense the light from said light emitting diode;

first and second comparators providing signals in response to said first and second light sensing elements, respectively;

first and second digital inverting means respectively coupled to said first and second comparators to invert said signals from said first and second comparators;

digital X-OR means having one input coupled to said first comparator and having a second input coupled to said first comparator by delay means to produce a short pulse during a delay period;

first digital AND means to AND the output of said X-OR means and the output of said second digital inverting means;

second digital AND means to AND the output of said first comparator and the output of said first digital AND means;

third digital AND means to AND the output of said first digital inverting means and said first digital AND means; and

shift register means having a first input coupled to the output of said second digital AND means and a second input coupled to the output of said third digital AND means.

18. The absolute encoder of claim 16 wherein said second means for sensing the serial code track in response to said clock signal and producing a serial code comprises:

second and third light emitting diodes;

third and fourth light sensing elements for sensing light from said second and third light emitting diodes, respectively;

third and fourth comparators having a first input coupled to said third and fourth light sensing elements, respectively, and having a second input coupled to a voltage reference source; and

said shift register means coupled to the outputs of said third and fourth comparators to receive a code signal therefrom.

19. The absolute encoder of claim 17 wherein said second means for sensing the serial code track in response to said clock signal and producing a serial code comprises:

a second light emitting diode;

third and fourth light sensing elements for sensing light from said second light emitting diode;

third and fourth comparators having a first input coupled to said third and fourth light sensing elements, respectively, and having a second input coupled to a voltage reference source;

fourth digital AND means coupled at one input to the output of said fourth comparator and coupled at the other input to the output of said third digital AND means;

fifth digital AND means coupled at one input to the output of said third comparator and coupled at the other input to the output of said second digital AND means; and

said shift register means coupled to the outputs of said fourth and fifth digital AND means to receive a code signal therefrom.

20. An absolute encoder comprising:

a disc mounted for rotation about an axis, said disc including a single circumferential serial code track having binary segments, wherein a predetermined number of adjacent segments defines a unique serial code for each segment of disc rotation, and a circumferential clock track having alternating binary segments;

first means for sensing the clock track and producing a clock signal representative of relative disc rotation and direction;

second means for sensing the serial code track in response to said clock signal and producing a serial code;

means for storing said serial code for readout as a parallel word;

means for converting said parallel word to a signal representative of the relative angular position of said disc;

wherein said means for storing includes a shift register and circuit means operative to transfer the serial code into a first input or a last input of the shift register in accordance with the relative phase of clock signals derived from said clock track.

21. An absolute encoder comprising:

a scale mounted for relative motion with respect to a reference and comprising a single serial code track having binary segments, wherein a predetermined number of adjacent segments defines a unique serial code for each segment of relative motion, and a clock track having alternating binary segments;

first means for sensing the clock track and producing a clock signal representative of relative movement and direction;

second means including first and second sensing elements that are spaced apart a distance that corresponds to a distance defined by said predetermined number of adjacent segments for sensing the serial code track in response to said clock signal and producing a serial code;

a shift register having selectable left-right and right-left serial storability; and

means responsive to the clock signal for storing said serial code in the shift register selectably left-right and right-left in dependence on relative movement and direction from a predetermined one of said first and second sensing elements for left-right storability and from the other one thereof for right-left storability.

22. An absolute encoder comprising:

a disc mounted for relative motion with respect to a reference and comprising a single serial code track having binary segments, wherein a predetermined number of adjacent segments defines a unique serial code for each segment of relative motion, and a clock track having alternating binary segments;

first means for sensing the clock track and producing a clock signal representative of relative movement and direction;

second means including first and second sensing elements that are spaced apart a distance that corresponds to a distance defined by said predetermined number of adjacent segments for sensing the serial code track in response to said clock signal and producing a serial code;

a shift register having selectable left-right and right-left serial storability; and

means responsive to the clock signal for storing said serial code in the shift register selectably left-right and right-left in dependence on relative movement and direction from a predetermined one of said first and second sensing elements for left-right storability and from the other one thereof for right-left storability.