Encoder

• US 10,190,892 B2
• Filed: 12/20/2016
• Issued: 01/29/2019
• Est. Priority Date: 12/22/2015
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Kimura, Akihide
• Primary Examiner(s): LEE, JOHN R
• Application Number:
  US15/384,613
• Publication Number:
  US 20170176218A1
• Time in Patent Office: 770 Days
• CPC Class Codes: G01D 5/34746 Linear encoders
• CPC Class Codes: G01D 5/38 by diffraction gratings

Abstract

A scale is provided with a reference mark and an incremental pattern. A detection head is relatively movable in a measurement direction with respect to the scale, and detects a light intensity distribution of diffracted beams if beams radiated onto the scale are diffracted by the reference mark, and outputs the detection result. A signal processing unit detects a reference position based on a position in the light intensity distribution where light intensity is lower than a predetermined value. The reference position has a plurality of pattern areas having a plurality of patterns arranged with a predetermined pitch in the measurement direction. At least one pattern area of the plurality of pattern areas is disposed with an offset from a neighboring pattern area in the measurement direction.

Claims

1. An encoder comprising:

a scale having a reference mark and having an incremental pattern;

a detection head configured to be relatively movable in a measurement direction with respect to the scale, and to detect a light intensity distribution of diffracted beams, when beams radiated onto the scale are diffracted by the reference mark and to output a detection result, the detection head including a light receiver, the light receiver being positioned so as to be able to detect diffracted beams other than a zeroth-order diffracted beam of light that passed through the reference mark; and

a signal processor configured to detect a reference position based on a position in the light intensity distribution where light intensity is lower than a predetermined value,

wherein the reference mark comprises a plurality of pattern areas arranged sequentially in the measurement direction and having a plurality of patterns each having a predetermined equal pitch in the measurement direction, each of the patterns comprising spaced pattern elements with the spaces between the pattern elements being devoid of pattern elements and

at least one pattern area of the plurality of pattern areas is disposed with an offset, in the measurement direction, with respect to a neighboring pattern area.

2. The encoder according to claim 1, wherein:

the offset is half of the predetermined equal pitch of the plurality of patterns repeatedly disposed in the measurement direction.

3. The encoder according to claim 1, wherein:

the detection head detects the light intensity distribution of positive first-order diffracted beams and/or negative first-order diffracted beams diffracted by the reference mark.

4. The encoder according to claim 1, wherein:

the plurality of pattern areas is disposed such that a plurality of joint lines occurs due to an offset of one or both of two neighboring pattern areas.

5. The encoder according to claim 4, wherein:

the joint lines are disposed in a random manner or a pseudo-random manner.

6. The encoder according to claim 5, wherein:

the joint lines are disposed based on an M-sequence code.

7. The encoder according to claim 1, wherein the incremental pattern and the plurality of pattern areas of the reference mark have a same pitch.

8. The encoder according to claim 1, further comprising a joint line provided between each of the plurality of pattern areas.

9. The encoder according to claim 1, wherein a pitch of the incremental pattern in the measurement direction is equal to the predetermined pitch of the pattern areas of the reference mark.

10. The encoder according to claim 1, wherein the offset is equal to one half of the predetermined pitch of the reference mark, in the measurement direction.

11. The encoder according to claim 1, wherein the offset is larger than 180°

.