Method of optically detecting position of object and position detecting apparatus using the method

• US 5,129,725 A
• Filed: 09/17/1991
• Issued: 07/14/1992
• Est. Priority Date: 11/04/1986
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Satoh, Chikara, Ishii, Satoshi, Ishizuka, Koh, Nishimura, Tetsuharu, Tsukiji, Masaaki
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US07/759,950
• Time in Patent Office: 301 Days
• Field of Search: 356/373, 356/374, 250/231 SE, 250/237 G, 250/231.14, 33/706, 33/707
• US Class Current: 356/617
• CPC Class Codes: H03M 1/285 of the unit Hamming distance type, e.g. Gray code
• CPC Class Codes: H03M 1/308 with additional pattern means for determining the absolute position, e.g. reference marks

Abstract

A method of and apparatus for optically detecting the position or amount of movement of a movable object, in which a plurality of position data element arrays are provided on a scale attached to the object such that the arrays are arranged in the direction of movement of the object. A string of light beam such as a laser beam, which extends in the same direction as the position data element array, is made to illuminate one of the arrays, and the light reflected by or transmitted through the position data element array is received by a sensor array such as CCD sensor which produces a signal representing the pattern of arrangement of the data elements in the illuminated position data element array and indicating absolute position of the object, whereby the instant absolute position of the object is detected.

Claims

1. A displacement measuring device, comprising:

a movable scale for measuring displacement, said scale having a plurality of codes thereon, each code being formed by a plurality of bit patterns arranged in a predetermined direction, said scale also having thereon an incremental pattern having a plurality of diffraction grating patterns arranged with a smaller pitch than the arrangement of the codes, and a reference pattern corresponding to each of the plurality of codes;

reference signal detecting means including first and second light-receiving elements for detecting the reference pattern by comparing outputs of said first and second light-receiving elements, and generating a reference signal;

code detecting means for subsequently detecting the codes in response to the reference signal output from said reference signal detecting means;

incremental signal detecting means for detecting interference light formed by diffracted light from the diffraction grating patterns in response to the displacement of the scale to output an incremental signal;

counting means for counting the incremental signal output from said incremental signal detecting means, said counting means being reset in response to the reference signal; and

position detecting means for detecting an absolute position of said scale on the basis of detected codes and the counting of said counting means.

2. A device according to claim 1, further comprising illuminating means for illuminating the codes, and detecting means for detecting light from the codes.

3. A device according to claim 2, wherein said illuminating means illuminates bit patterns of the codes with a light beam having a longitudinal direction set to said predetermined direction of the bit patterns.

4. A device according to claim 3, wherein said illuminating means includes a laser and an anamorphic optical system for converting the laser light from said laser into the light beam.

5. A device according to claim 4, wherein said anamorphic optical system includes a cylindrical lens.

6. A device according to claim 2, wherein said detecting means includes a sensor array for receiving light from a plurality of bit patterns.

7. An encoder for reading out a plurality of codes on a scale, each code being formed by a plurality of bit patterns ranging from a least significant bit to a most significant bit and disposed in a predetermined direction on the scale and arranged such that a least significant bit is not adjacent to a second least significant bit, said encoder further comprising:

illuminating means for illuminating the codes; and

a sensor array to read the illuminated codes that comprises a plurality of sensors arranged in a predetermined direction, wherein said sensor array reads the plurality of bit patterns.

8. An encoder according to claim 7, wherein said illuminating means comprises a linear beam for illuminating the codes, having a longitudinal direction set to the predetermined direction of the bit patterns of the codes.

9. An encoder according to claim 8, wherein the least significant bit and the second least significant bit are arranged such that one comprises one bit pattern end portion of the codes and the other comprises another bit pattern end portion of the codes.

10. A method for reading out a plurality of codes formed on a scale along a moving direction of the scale, each of said codes comprising a plurality of bit patterns ranging from a least significant bit to a most significant bit and arranged in a predetermined direction, said method comprising the steps of:

arranging the bit patterns so that the least significant bit is not adjacent to a second least significant bit;

supplying a linear radiation beam;

adjusting the radiation beam by utilizing the least significant bit and the second least significant bit so that the longitudinal direction of the radiation beam is substantially coincident with the predetermined direction of the bit patterns; and

subsequently projecting the bit patterns of each of the codes on a sensor array in response to displacement of the scale with the radiation beam after completion of said adjusting step, thereby reading out each of the codes.

11. A method according to claim 10, wherein said arrange step further comprises arranging the least significant bit and the second least significant bit so that one forms a bit pattern end portion of each of the codes and the other forms another bit pattern end portion of each of the codes.