Light distribution system for optical encoders

• US 4,342,908 A
• Filed: 08/28/1980
• Issued: 08/03/1982
• Est. Priority Date: 08/28/1980
• Status: Expired due to Term

• Current Assignee: ABB Power T&D Limited (ABB Limited)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Henningsen, Tom, Moates, Roger D., Coyle, Forrest E.
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US06/182,300
• Time in Patent Office: 705 Days
• Field of Search: 250/227, 250/231 R, 250/231 SE, 250/231 GY, 250/229, 350/96.1, 350/96.15, 340/347 P
• US Class Current: 250/227.11
• CPC Class Codes: H03M 1/161 in pattern-reading type converters, e.g. with gearings
• CPC Class Codes: H03M 1/245 Constructional details of parts relevant to the encoding mechanism, e.g. pattern carriers, pattern sensors
• CPC Class Codes: H03M 1/282 of the pattern-shifting type, e.g. pseudo-random chain code

Abstract

A light distribution system for optical encoders includes a light guide plate and a light input coupler for distributing input incident radiations into the light guide plate as a flat distributed beam of beam segments intercepted by a pattern of discrete light output couplers reflecting narrow output beams for providing a uniform pattern of encoding illuminations.

Claims

1. A light distribution system for an optical encoder having an array of photosensitive sensors, comprising:

a transparent light guide plate having front and back parallel surfaces;

a light input coupler including an incident radiation distributing area formed within said light guide plate for receiving a predetermined beam of input incident radiations, said distributing area spreading the input incident radiations into a distributed beam having plural beam segments each being directed in said light guide plate substantially wholly parallel to a single predetermined radiation path and further being substantially parallel to said front and back surfaces; and

a predetermined pattern of plural discrete light output couplers each formed by an output reflecting surface recessed into one of said front and back surfaces, each of the output reflecting surfaces being in optical alignment with only a single one of said predetermined radiation paths to intercept a separate one of said beam segments, said reflecting surfaces having different surface areas corresponding to the different lengths of the predetermined radiation paths from said distributing area to produce output beams for uniformly illuminating each of said sensors of said array.

2. The light distribution system as claimed in claim 1 wherein said predetermined ones of said light output couplers are spaced closer and farther from said distributing area, and wherein the area of the output reflecting surfaces are smaller to intercept a narrower beam segment when closer to said distributing area and the surfaces are larger for farther ones of said output couplers.

3. The light distribution system as claimed in claim 2 wherein at least two of said predetermined ones of said light output couplers have the output reflecting surfaces thereof intercepting at least two partially overlapping beam segments and further wherein the closer one of said predetermined output couplers has a shorter recessed area and the farther one of said predetermined output couplers has a longer recessed area.

4. The light distribution system as claimed in claim 1 wherein each of said output couplers includes a flat output reflecting surface recessed into said light guide at angle in the order of forty-five degrees.

5. The light distribution system as claimed in claim 1 wherein said incident radiation distributing area includes a circularly extending reflector having a circularly extended parabolic reflecting surface recessed into one of said front and back surfaces and wherein said input coupler includes a light source positioned at the focal point of said parabolic reflecting surface.

6. The light distribution system as claimed in claim 5 wherein said light source is formed by a semiconductor light emitting device with the wafer element thereof positioned at said focal point.

7. The light distribution system as claimed in claim 6 wherein said light emitting device includes an optically transparent material encasing said wafer element and contiguous with one of said front and back surfaces of said light guide plate.

8. The light distribution system as claimed in claim 1 wherein said incident radiation distributing area includes a circularly extending reflector having a ninety degree conical reflecting surface and wherein said input coupler includes a light source for producing said input radiations along the center axis of said conical reflecting surface.

9. The light distribution system as claimed in claim 8 wherein said light source is formed by a semiconductor light emitting device having a collimating lens aligned with said center axis of said conical reflecting surface.

10. The light distribution system as claimed in claim 1 wherein said light guide plate includes predetermined intermediate reflecting surfaces for directing secondary reflections of redirected ones of said beam segments extending between said incident radiation distributing area and further predetermined ones of said light output couplers.

11. The light distribution system as claimed in claim 10 wherein at least one of said intermediate reflecting surfaces is formed along a common edge of said light guide plate.

12. The light distribution system as claimed in claim 11 wherein said intermediate reflecting surfaces are formed along at least two different edges of said light guide plate.

13. The light distribution system as claimed in claim 1 wherein said predetermined patterns of light output couplers are symmetrically disposed along a single straight axis and wherein the adjacently disposed beam segments have a substantial arcuate extent for directing the separate beam segments to each of said light output couplers.

14. The light distribution system as claimed in claim 10 wherein at least one of said intermediate and reflecting surfaces is formed with a concave reflecting surface.

15. The light distribution system as claimed in claim 1 wherein said light input coupler includes a light source mounted within said light guide plate and laterally adjacent said incident radiation distributing area.

16. The light distribution system as claimed in claim 15 wherein said incident radiation distributing area includes a circularly extending reflector having a parabolic reflecting surface.

17. A light distribution system for a meter dial register encoder having an array including groups of circularly disposed photoconductive sensors, wherein said light distribution system comprises:

a light source;

a flat transparent light guide plate having opposite front and back parallel surfaces terminated by edge surfaces defining an elongated horizontal configuration;

a light input coupler for mounting said light source at the light guide plate and said input coupler including an incident radiation distributing area arranged for receiving a predetermined beam of input incident radiations from said light source, said distributing area being formed by a recessed circularly arcuate reflecting surface in said light guide plate effective to produce a flat distributed beam uniformly spread out along individual radially extending beam segments extending substantially parallel to the opposite light guide plate surfaces;

a pattern of light output couplers symmetrically disposed with respect to said input coupler and optically aligned with said array of sensors, each of said light output couplers including an output reflecting surface extending at substantially the same angle into a common one of said opposite surfaces of said light guide plate so as to have a predetermined optical alignment for intercepting separate ones of said beam segments and for reflecting individual output beams in a substantially collimated manner to uniformly illuminate said array including groups of circularly disposed photoconductive sensors.

18. The light distribution system as claimed in claim 17 wherein said light guide plate further includes plural intermediate reflectors each positioned for redirecting predetermined ones of said beam segments from said light input coupler and to predetermined ones of said light output couplers so that the predetermined ones of said beam segments are directed in a bent and indirect manner to the predetermined ones of said light output couplers.

19. The light distribution system as claimed in claim 18 wherein said pattern of light output couplers includes plural groups of circularly disposed input couplers substantially evenly positioned on either side of a center vertical reference axis of said light guide plate extending through the center of said input coupler so that substantially equal numbers of the beam segments are spread out from said distributing area on either side of said vertical reference axis.

20. The light distribution system as claimed in claim 19 wherein said light guide plate includes a plurality of hole openings for receiving dial pointer shafts associated with each of separate register dials to be encoded and wherein each group in said pattern of light output couplers circumscribes each of said hole openings.

21. The light distribution system as claimed in claim 20 wherein said plural intermediate reflectors are formed by at least two peripheral edges of said light guide plate and wherein a further one of said plural intermediate reflectors is formed by an edge partially forming one of said hole openings in said light guide plate.

22. The light distribution system as claimed in claim 17 wherein said reflecting surface of said distributing area is formed with a parabolic reflecting surface configuration and wherein said light source is positioned at the focal point of the parabolic reflecting surface configuration.

23. The light distribution system as claimed in claim 17 wherein said reflecting surface of said distributing area has a recessed conical configuration.

24. The light distribution system as claimed in claim 17 wherein said output reflecting surface of each of said output couplers extends at an angle of forty-five degrees along a flat output reflecting surface.

25. The light distribution system as claimed in claim 24 wherein each flat output reflecting surface has a larger area when included in an output coupler farther from said light input coupler.

26. The light distribution system as claimed in claim 17 wherein each of the output reflecting surfaces is convave.

27. The light distribution system as claimed in claim 17 wherein said light source is integrally molded within said light guide plate.

28. The light distribution system as claimed in claim 27 wherein said reflecting surface of said distributing area has a parabolic surface configuration with said light source being integrally molded at the focal point of said parabolic surface configuration.

29. A light distribution system for an optical encoder having an array of photosensitive sensors, comprising:

a transparent light guide plate having front and back parallel surfaces;

a light input coupler including an incident radiation distributing area including a parabolic reflecting surface recessed into one of said parallel surfaces so as to be defined by a surface of revolution generated by revolving a segment of a parabola about an axis extending through the center of said distributing area and perpendicular to the parallel plate surfaces for receiving a predetermined beam of input incident radiations, said reflecting surface of said distributing area reflectively spreading the input incident radiations into a circularly arcuate distributed beam having plural beam segments, each of the beam segments being propagated in said light guide plate radially of said axis substantially parallel to a single predetermined radial radiation path and being further propagated substantially parallel to said front and back surfaces; and

a predetermined pattern of plural discrete light output couplers each formed by an output reflecting surface recessed into one of said front and back surfaces, each of the output reflecting surfaces being in optical alignment with only one of said predetermined radial radiation paths to intercept a separate one of said beam segments, and each of said reflecting surfaces producing an output beam for uniformly illuminating each of said sensors of said array.