Reflective shaft angle encoder

• US 4,952,799 A
• Filed: 03/10/1989
• Issued: 08/28/1990
• Est. Priority Date: 03/10/1989
• Status: Expired due to Term

• Current Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Loewen, Victor D.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): HSIA, SHERRIE Y
• Application Number:
  US07/321,994
• Time in Patent Office: 536 Days
• Field of Search: 250/231 SE, 250/237 G, 250/231.16, 341/13
• US Class Current: 250/231.16
• CPC Class Codes: H03M 1/301 Constructional details of parts relevant to the encoding mechanism, e.g. pattern carriers, pattern sensors

Abstract

An optical shaft angle encoder has a code wheel with alternating reflective and non-reflective areas in a circumferential path on one face of the wheel. A light emitting diode is spaced apart from the reflective areas on the wheel. Four photodetectors are also spaced apart from the same face of the wheel so that, as the wheel rotates, the photodetectors are alternately illuminated or not illuminated by light from the light emitting diode that is reflected from the reflective areas. Preferably the light emitting diode is relatively nearer the shaft axis than the photodetectors and is in a radial direction from the shaft axis which bisects the array of photodetectors.

Claims

1. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel;

a light emitting device elongated in a radial direction for illuminating the circumferential path;

a plurality of photodetectors having elongated detection areas extending in a radial direction arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is reflected from reflective areas on the code wheel; and

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation.

2. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel;

a light emitting device for directly illuminating the circumferential path;

a plurality of photodetectors arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is directly reflected from reflective areas on the code wheel;

wherein the photodetectors and light emitting device are in the same plane, which plane is parallel to the plane of the code wheel; and

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation.

3. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel;

a light emitting device for illuminating the circumferential path;

a plurality of photodetectors arrayed side by side on the same plane as the light emitting device, which plane is parallel to the plane of the code wheel, for receiving light from the light emitting device which is reflected from reflective areas on the code wheel, the width of each cycle of photodetectors being twice the width of each cycle of reflective and non-reflective areas; and

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation.

4. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel;

a light emitting device for illuminating the circumferential path;

a plurality of photodetectors arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is reflected from reflective areas on the code wheel, wherein the light emitting device is at one radial distance from the axis of the code wheel and the photodetectors are at a different radial distance from the axis of the code wheel; and

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation.

5. A shaft angle encoder as recited in claim 4 wherein the light emitting device is relatively nearer the axis and the photodetectors are relatively further from the axis.

6. A shaft angle encoder as recited in claim 4 wherein the light emitting device is in a radial direction bisecting the array of photodetectors.

7. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel, wherein the non-reflective areas comprise windows in the code wheel and a non-reflective region beyond the opposite face of the code wheel;

a light emitting device for illuminating the circumferential path;

a plurality of photodetectors arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is reflected from reflective areas on the code wheel; and

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation.

8. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the code wheel on one face of the code wheel;

a light emitting device for directly illuminating the circumferential path;

a plurality of photodetectors arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is directly reflected from reflective areas on the code wheel; and

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation.

9. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel;

a light emitting device for directly illuminating the circumferential path;

at least four photodetectors arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is directly reflected from reflective areas on the code wheel; and

comparator means for comparing signals from the four photodetectors to produce two output channels of information indicative of shaft position and code wheel rotation.

10. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around the wheel;

a light emitting device for illuminating the circumferential path;

a plurality of photodetectors arrayed side by side on the same side of the code wheel as the light emitting device for receiving light from the light emitting device which is reflected from reflective areas on the code wheel;

comparator means for comparing signals from the photodetectors and producing signals indicative of code wheel rotation; and

a plurality of detents on the opposite face of the wheel from the reflective areas for tangibly indicating wheel position.

11. A shaft angle encoder comprising:

a rotatable code wheel having a plurality of reflective areas arrayed in a circumferentially extending path around the wheel;

light emitting means for emitting light along a line transverse to the circumferential path for illuminating the reflective areas; and

a plurality of photodetector areas elongated in a radial direction and arranged for illumination by light from the line of light emitting means which is reflected from each of a plurality of the reflective areas, for producing a plurality of electrical signals indicative of a code wheel position.

12. A shaft angle encoder comprising:

a rotatable code wheel having a plurality of reflective areas arrayed in a circumferentially extending path around the wheel;

light emitting means for emitting light along a line transverse to the circumferential path for illuminating the reflective areas; and

a plurality of photodetector areas arranged for illumination by light from the light emitting means which is reflected from each of a plurality of the reflective areas, for producing a plurality of electrical signals indicative of a code wheel position; and

wherein

the light emitting means and the photodetector areas are equidistant from the code wheel and the width of each cycle of photodetector area is twice the width of each cycle of reflective and non-reflective areas.

13. A shaft angle encoder comprising:

a rotatable code wheel having a plurality of reflective areas arrayed in a circumferentially extending path around the wheel;

light emitting means for emitting light along a line transverse to the circumferential path for illuminating the reflective areas; and

a plurality of photodetector areas arranged for illumination by light from the light emitting means which is reflected from each of a plurality of the reflective areas, for producing a plurality of electrical signals indicative of a code wheel position, wherein the light emitting means is at a relatively smaller radial distance from the axis of the code wheel and the photodetectors are at a relatively larger radial distance from the axis of the code wheel.

14. A shaft angle encoder as recited in claim 13 wherein the light emitting device is in a radial direction bisecting the array of photodetectors.

15. A shaft angle encoder comprising:

a rotatable code wheel having a plurality of reflective areas arrayed in a circumferentially extending path around the wheel;

light emitting means for emitting light along a line transverse to the circumferential path for illuminating the reflective areas; and

a plurality of photodetector areas arranged for illumination by light from the light emitting means which is reflected from each of a plurality of the reflective areas, for producing a plurality of electrical signals indicative of a code wheel position, wherein the distance between adjacent photodetectors is the same as the width of the emission line.

16. A shaft angle encoder comprising:

a rotatable code wheel comprising a plurality of alternating reflective and non-reflective areas extending in a circumferential path around one face of the wheel;

an effective point source light emitting device for illuminating the circumferential path; and

at least one photodetector in the same plane as the light emitting device for producing electrical signals in response to light from the light emitting device which is reflected from reflective areas on the code wheel, wherein the light emitting device is at a relatively smaller radial distance from the axis of the code wheel and the photodetector is at a relatively larger radial distance from the axis of the code wheel.

17. A shaft angle encoder as recited in claim 16 wherein both the light emitting device and the photo-detector are elongated in a radial direction.

18. An optical shaft angle encoder comprising:

an opaque housing;

a rotatable shaft mounted in the housing;

a hub rotatable with the shaft and including a plurality of detent holes on a back face;

a detent ball and means for biasing the detent ball toward engagement with the detent holes for tangibly indicating wheel position;

a plurality of alternating reflective and non-reflective areas in a circumferential band on a front face of the hub;

a light emitting diode spaced apart from the reflective areas on the front face of the hub; and

a plurality of photodetectors spaced apart from the reflective areas on the front face of the hub the same distance as the light emitting diode, the photodetectors being spaced apart from the shaft axis a greater distance than the light emitting diode is spaced from the shaft axis for illumination by light from the light emitting diode that is reflected from the reflective areas, the array of photodetectors being bisected by a radial plane through the light emitting diode.

19. An optical shaft angle encoder as recited in claim 18 wherein the alternating reflective and non-reflective areas comprise a non-reflective groove in the front face of the hub and a reflective code wheel adjacent to the front face of the hub, and having a circumferentially extending band of windows through the code wheel.

20. An optical shaft angle encoder as recited in claim 18 wherein the light emitting diode is elongated in a radial direction and the photodetectors are elongated in a radial direction.