LINEAR ENCODER IMMUNE TO SCALE BENDING ERROR

• US 3,628,026 A
• Filed: 09/05/1969
• Issued: 12/14/1971
• Est. Priority Date: 09/05/1969
• Status: Expired due to Term

• Current Assignee: David V. Cronin
• Original Assignee: David V. Cronin
• Inventors: Cronin, David V.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Leedom, C. M.
• Application Number:
  US04/855,546
• Time in Patent Office: 830 Days
• Field of Search: 250/231,237G,237,219D
• US Class Current: 250/214.1
• CPC Class Codes: G01D 5/38 by diffraction gratings

Abstract

A linear encoder in which scale bending error does not materially affect encoder performance. An elongated generally rectangular encoder scale is provided having a plurality of alternately light responsive and opaque segments on one surface thereof and a plurality of similar segments on an opposite surface thereof, the segments on one surface experiencing equal and opposite deformation to the segments on the opposite surface in the presence of bending stress. An interference pattern sensed from both pluralities of segments is not materially affected by such bending stress, with the result of markedly improved encoder performance under-bending error conditions.

Claims

1. An electro-optical encoder comprising:

an elongated scale member having first and second substantially parallel plane surfaces thereon, a first plurality of alternately light responsive and opaque segments formed in a parallel array along the longitudinal axis of one surface thereof, and a second like plurality of alternately light responsive and opaque segments formed in a parallel array along the longitudinal axis of the opposite surface thereof;

an optical assembly;

said scale member and said optical assembly being adapted for relative longitudinal movement therebetween;

said optical assembly including;

means for superimposing an image of the segments on one surface of said scale member onto the segments on the opposite surface of said scale member to provide an interference pattern; and

means operative to sense variations in light from said interference pattern representative of the extent of relative motion between said scale member and said optical assembly and to produce electrical signals representative of the extent of relative scale motion.

2. An encoder according to claim 1 wherein said light responsive segments are light transmissive, and said first and second pluralities of segments are disposed on respective opposite surfaces of said scale member in lateral spaced relation along an axis orthogonal to the length of said member.

3. An encoder according to claim 2 wherein said optical assembly includes:

means for illuminating the segments on one surface of said scale member; and

means for projecting an image of the segments on said one surface onto the segments on the opposite surface of said scale member to provide said interference pattern.

4. An encoder according to claim 1 wherein said light responsive segments are light reflective.

5. An encoder according to claim 1 wherein said light responsive segments are light reflective, and said first and second pluralities of segments are disposed on respective opposite surfaces of said scale member in parallel arrays along one end of said member.

6. An encoder according to claim 2 wherein said optical assembly includes:

an illumination source disposed adjacent one surface of said scale member and operative to illuminate a first portion of the segments formed on the opposite surface thereof;

optical means for projecting an image of the segments of said first portion onto the segments on said one surface of said scale member, said optical means including means for rotating said image 180* in the plane of said scale.

7. An encoder according to claim 6 wherein said optical means incLudes means for reflecting the image of said first portion in a direction parallel to said scale member;

and a pentaprism operative to reflect said image onto the segments on said one surface of said scale member and rotate said image 180* in the plane of said scale member.