PHOTOELECTRIC ENCODER ASSEMBLY

• US 3,815,125 A
• Filed: 09/01/1972
• Issued: 06/04/1974
• Est. Priority Date: 09/01/1972
• Status: Expired due to Term

• Current Assignee: Paul L. May, Richard J. Poe
• Original Assignee: Paul L. May, Richard J. Poe
• Inventors: May, Paul L., Poe, Richard J.
• Primary Examiner(s): Henon, Paul J.
• Assistant Examiner(s): Boudreau, Leo H.
• Application Number:
  US05/285,596
• Time in Patent Office: 641 Days
• Field of Search: 235/92MP,92GC,151.11 250/237 340/146.3H,347P 74/DIG.2,DIG.7,240,241 318/567
• US Class Current: 341/11
• CPC Class Codes: G01D 5/34753 Carriages; Driving or coupling means
• CPC Class Codes: H03M 1/30 incremental
• CPC Class Codes: Y10S 74/07 Indicators-sensors and meters

Abstract

A photoelectric encoder assembly including a housing, a U-shaped reader assembly positioned therein, and a scale located between the legs of the U. The reader assembly includes one leg supporting at least one light source and condensing lens on one side of the scale and another leg supporting at least one photocell on the other side of the scale. The scale is translatably secured to a moved element of a machine tool, and the reader is slidably and rotatably mounted on a rod extending parallel to the direction of motion of the moved element of the machine tool, such that relative motion of reader and scale occurs as the element moves, the reader being pivotable on the rod to automatically correct for inaccuracies of orientation of the scale in response to movements of a pair of adjustably positioned, low-friction bearing surfaces in the form of nylon screws threaded into the legs of the reader assembly and bearing on both sides of the scale, for precisely relatively positioning the photosensitive element and the scale for all translations of the scale by preventing changes of spacing between the scale and the lens and photo-cell reader for all relative locations of reader and scale.

Claims

1. An attachment for measuring distance travelled by a translatable object with respect to a stationary reference object, comprising a scale, said scale including a planar plate having digital markings thereon, the plane of said plate being subject to random inaccuracies of orientation, a readout for scanning said scale and counting said markings, said readout including a source of a beam of light located on one side of said scale and a photocell located on the other side of said scale in the path of said beam of light, said readout including substantially frictionless elements rigidly secured to said readout and engaging both sides of said scale simultaneously, and means pivotally mounting said readout to enable said readout to precisely follow the plane of said scale in response to movements of said substantially frictionless elements despite said inaccuracies of orientation.

2. A photoelectric encoder assembly comprising:

a. a housing, b. a planar scale element positioned in said housing, said scale element including transparent spaced markings, c. a reader of said scale, said reader including at least one directed light beam source and at least one photosensitive element, said light beam source being positioned on one side of said scale element and directing a beam of light toward said markings, said photosensitive element being positioned on the opposite side of said scale element for detecting transmissions of said light by said markings, and d. means for maintaining a predetermined spacing between said scale element and said photosensitive element for all relative positions of said scale element and reader, said last means including a plurality of low friction bearing surfaces fixed on said reader and in slidable contact with both sides simultaneously of said scale element for all relative positions of said scale element and reader and means mounting said reader rotatably with respect to an axis extending parallel to the plane of said scale element, said last means also allowing limited movement of the said photosensitive element at right angles to the plane of said scale.

3. A photoelectric encoder assembly as defined in claim 2, wherein said low friction bearing surfaces are adjustably positioned in said reader for movement transversely of the plane of said scale element.

4. A photoelectric encoder assembly as defined in claim 3, wherein said low friction bearing surfaces include threaded screw elements engageable with threaded holes in said reader.

5. A photoelectric encoder assembly as defined in claim 4, wherein said reader has a U-shaped portion including a pair of legs and a bight portion, each of said screw elements being positioned in one of said legs, said scale element extending between said legs and the plane of said scale element extending parallel to said legs.

6. A photoelectric encoder assembly as defined in claim 2, including a rod positioned in said housing and extending parallel to the plane of said scale element, and means including a ball bushing secured immovably to said reader, said rod extending slidably through said ball bushing and said ball bushing being rotatable on said rod.

7. The combination according to claim 2, wherein said last means includes a bracket having on one of its arms a rounded point set screw and on the other of its arms and in opposition to said rounded point set screw a spring loaded ball point rod, a pin located between said arms, said rounded point and said ball point contacting the ends of said rod so as to enable limited relative movement of the photosensitive element and scale element in a sense perpendicular of the scale element.

8. A digital system for measuring the distance travelled by a lineArly translatable object with respect to a stationary object, comprising a planar scale consisting of a transparent linearly extensive plate having uniform thickness along its length and having equally spaced markings along its length, means rigidly securing said scale to said movable object for longitudinal motion therewith, the plane of said plate being only approximately parallel to the translatory path of said translatable object, and a line perpendicular to the plane of said plate having a possible range of angular relations to said translatable object, a readout for scanning said scale and developing pulses in response to movement of said scale and its markings relative to said readout markings, means securing said readout for translation with said stationary object, said readout including a source of a beam of light directed toward said markings from one side of said scale and a photo-cell responsive to said beam of light located on the other side of said scale, and means for maintaining the relative spacings of said source, said scale and said photo-cell during motion of said scale with respect to said photo-cell, said last means including substantially frictionless bearing elements fixedly secured to said readout on opposite sides of said scale and spaced to equal the thickness of said scale and slidingly engaging said scale, said last means further including a rod extending parallel to said scale and a bushing immovably secured to said readout on said rod such that said readout can rotate to conform with movements of said frictionless bearing elements transversely of said longitudinal motion.