Optical encoder of the reflective type

• US 3,983,391 A
• Filed: 05/21/1975
• Issued: 09/28/1976
• Est. Priority Date: 05/21/1975
• Status: Expired due to Term

• Current Assignee: Motion Systems LLC
• Original Assignee: Itek Corp (Northrop Grumman Corporation)
• Inventors: Clemons, Calvin
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US05/579,516
• Time in Patent Office: 496 Days
• Field of Search: 250/231 R, 250/231 SE, 250/237 R, 250/237 G, 356/169, 356/170, 324/175, 340/347 P
• US Class Current: 250/237.00G
• CPC Class Codes: G01D 5/34715 Scale reading or illumination devices
• CPC Class Codes: H03M 1/301 Constructional details of parts relevant to the encoding mechanism, e.g. pattern carriers, pattern sensors

Abstract

Reflective optical encoder for monitoring the movement of a machine tool component or the like. The encoder comprises a code disc having a code track thereon in the form of alternating radiation transmissive and radiation opaque areas. A source of radiation and at least two detectors are supported on one side of the code disc while a reflector is supported on the opposite side. Radiation from the source is directed through the code track to the reflector and is reflected off of the reflector back through the code track to the detectors such that the detectors will receive radiation modulated by the code track as a function of the movement of the code disc.

The reflector is preferably provided with an aspheric reflector surface, and most preferably, with a conical reflector surface which can be adjusted in orientation to enable radiation directed to one of the detectors to be retarded in phase by desired amounts relative to radiation directed to the other detector to permit maximizing of the system resolution and to determine direction of rotation.

The encoder system provided eliminates the need for the slit plate of conventional encoders and, in general, provides a low cost, medium resolution encoder having a minimum number of parts and reduced tolerance requirements.

Claims

1. Encoder apparatus comprising:

A. a code member, said code member having code track means thereon, said code track means comprising a pattern of alternating radiation transmissive and radiation opaque areas; and

,

B. monitoring means for monitoring relative movement of said code member, said monitoring means comprising;

a. source means supported on one side of said code member for directing radiation to said code track means;

b. detector means responsive to radiation from said source means, said detector means including at least first and second detector means for generating first and second signals, respectively, proportional to the radiation impinging thereon;

c. reflector means supported on the opposite side of said code member from said source means for receiving radiation passing through said code track means from said source means and for reflecting at least a portion of said received radiation back through said code track means to said first and second detector means whereby said first and second detector means will each be impinged by radiation modulated by said code track means as a function of the relative movement of said code member and will generate signals indicative of said relative movement of said code member, said reflector means including an aspheric reflecting surface for directing radiation to said first detector means out of phase with respect to radiation directed to said second detector means; and

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d. processing means coupled to said first and second detector means for processing said first and second signals.

2. Apparatus as recited in claim 1 wherein an adjacent radiation transmissive and radiation opaque area of said code track means comprises a code track cycle, and wherein said aspheric reflector surface includes means for directing radiation to said first detector means which is out-of-phase relative to a code track cycle with respect to radiation directed to said second detector means.

3. Apparatus as recited in claim 2 wherein said aspheric reflector surface includes means for directing radiation to said first detector means which is 90°

out-of-phase relative to a code track cycle with respect to radiation directed to said second detector means.

4. Apparatus as recited in claim 1 wherein said aspheric reflecting surface comprises a conical reflecting surface.

5. Apparatus as recited in claim 1 wherein said reflector means includes adjustment means for adjusting the orientation of said aspheric reflecting surface relative to said first and second detector means for adjusting the phase difference between radiation directed to said first and second detector means.

6. Apparatus as recited in claim 5 wherein said aspheric reflecting surface comprises a conical reflecting surface and wherein said adjustment means comprises means for pivoting said conical reflecting surface around an axis generally perpendicular to the axis of said conical surface.

7. Apparatus as recited in claim 4 wherein said code member comprises a code disc, said code track means comprises an annular code track having alternating radiation transmissive and radiation opaque areas which are tapered toward said disc center, and wherein said conical reflecting surface has a taper generally equal to the taper of said tapered areas on said code track means.

8. Encoder apparatus for monitoring the movement of a moveable element comprising:

A. a code member coupled to and moveable with said moveable element, said code member having code track means comprising a pattern of alternating radiation transmissive and radiation opaque areas; and

,

B. monitoring means for monitoring the movement of said code member and, hence, of said moveable element, said monitoring means comprising;

a. source means supported on one side of said code member for directing radiation to said code track means;

b. detector means responsive to radiation from said source means, said detector means including at least first and second detector means for generating first and second signals, respectively, proportional to the radiation impinging thereon;

c. reflector means having an aspheric reflecting surface supported on the opposite side of said code member from said source means for receiving radiation passing through said code track means from said source means and for reflecting at least a portion of said received radiation back through said code track means to said first and second detector means whereby said first and second detector means will each be impinged by radiation modulated by said code track means as a function of the movement of said code member and will generate signals indicative of said movement of said code member; and

,

d. processing means coupled to said first and second detector means for processing said first and second signals.

9. Apparatus as recited in claim 8 wherein said reflector means includes means for directing radiation to said first detector means out-of-phase with respect to radiation directed to said second detector means.

10. Apparatus as recited in claim 9 wherein an adjacent radiation transmissive and radiation opaque area of said code track means comprises a code track cycle, and wherein said reflector means includes means for directing radiation to said first detector means which is out-of-phase relative to a code track cycle with respect to radiation directed to said second detector means.

11. Apparatus as recited in claim 9 wherein said reflector means includes adjustment means for adjusting the orientation of said aspheric reflecting surface relative to said first and second detector means for adjusting the phase difference between radiation directed to said first and second detector means.

12. Apparatus as recited in claim 11 wherein said aspheric reflecting surface comprises a conical reflecting surface and wherein said adjustment means comprises means for pivoting said conical reflecting surface around an axis generally perpendicular to the axis of said conical surface.

13. Apparatus as recited in claim 12 wherein said code member comprises a code disc, said code track means comprises an annular code track having alternating radiation transmissive and radiation opaque areas which are tapered towards the center of said code disc, and wherein said conical reflecting surface has a taper generally equal to the taper of said tapered areas on said code track means.