ENCODER

• US 20170176218A1
• Filed: 12/20/2016
• Published: 06/22/2017
• Est. Priority Date: 12/22/2015
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: KIMURA, Akihide
• Granted Patent: US 10,190,892 B2
• Time in Patent Office: 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 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 if beams radiated onto the scale are diffracted by the reference mark and to output a detection result; and

a signal processing unit 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 has a plurality of pattern areas having a plurality of patterns arranged with a predetermined pitch in the measurement direction, and

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.

2. The encoder according to claim 1, wherein:

the offset is half of the pitch 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.