Displacement encoder

Patent metadata

Field	Value
Publication number	US-10274344-B2
Application number	US-201816012064-A
Country	US
Kind code	B2
Filing date	Jun 19, 2018
Priority date	Dec 27, 2016
Publication date	Apr 30, 2019
Grant date	Apr 30, 2019

Abstract

A detection head movable relative to a scale detects diffracted light and outputs a detection result. The diffracted light is diffracted by an incremental pattern. A signal processing unit calculates a relative displacement between the scale and the detection head. The detection head includes: a light source emitting the light to the scale; and a detection unit including a light-receiving unit receiving the diffracted light through an optical element, in which the light-receiving elements outputting detection signals are periodically arranged with a predetermined period. The number of the plurality of light-receiving elements is an even number. The predetermined period is a value obtained by multiplying a fundamental period by an odd-number. The fundamental period is a period of interference fringes formed on the light-receiving unit by +1st and −1st order diffracted lights. A width of the light-receiving element is not equal to an integral multiple of the fundamental period.

First claim

What is claimed is:

1. A displacement encoder comprising:
a scale with an incremental pattern formed therein;
a detection head movable relative to the scale in a measurement direction, the detection head being configured to detect diffracted light and output a detection result, the diffracted light being obtained by diffraction of light emitted to the scale by the incremental pattern; and
a signal processing unit configured to calculate a relative displacement between the scale and the detection head based on the detection result obtained by the detection head, wherein
the detection head comprises:
a light source configured to emit the light to the scale;
a detection unit comprising a light-receiving unit comprising a plurality of light-receiving elements periodically arranged in the measurement direction with a predetermined period, the plurality of light-receiving elements being configured to output a detection signal of the diffracted light from the scale; and
an optical element configured to guide the diffracted light to the detection unit,

the number of the plurality of light-receiving elements arranged in the measurement direction is an even number,
the predetermined period is a value obtained by multiplying a fundamental period by an odd-number, the fundamental period being a period of interference fringes formed on the light-receiving unit by +1st order diffracted light and −1st order diffracted light of the diffracted light, and
a width of the light-receiving element in the measurement direction is not equal to an integral multiple of the fundamental period.

2. The displacement encoder according to claim 1 , wherein the +1st order diffracted light, −1st order diffracted light, and 0th order diffracted light from the scale are incident on the detection unit.

3. The displacement encoder according to claim 1 , wherein
the light-receiving unit comprises a plurality of detection areas arranged in the measurement direction,
each detection unit comprises the even number of the light-receiving elements arranged in the measurement direction; and
among the plurality of detection areas, two detection areas adjacent to each other are shifted from each other by a distance equivalent to a quarter of the fundamental period so as to be apart from each other in the measurement direction.

4. The displacement encoder according to claim 3 , wherein
first and second detection areas are arranged in this order in the measurement direction, and
the detection unit outputs a detection signal output from the first detection area to the signal processing unit as an A phase signal and outputs a detection signal output from the second detection area to the signal processing unit as a B phase signal.

5. The displacement encoder according to claim 3 , wherein
first, second, third and fourth detection areas are arranged in this order in the measurement direction, and
the detection unit outputs a differential A phase signal and a differential B phase signal to the signal processing unit, the differential A phase signal being a differential signal between an A phase signal and an A− phase signal, the differential B phase signal being a differential signal between a B phase signal and a B− phase signal, the A phase signal being a detection signal output from the first detection area, the A− phase signal being a detection signal output from the third detection area, the B phase signal being a detection signal output from the second detection area, and the B− phase signal being a detection signal output from the fourth detection area.

6. The displacement encoder according to claim 1 , wherein
the light-receiving unit comprises a plurality of detection areas arranged in the measurement direction,
each detection unit comprises the even number of the light-receiving elements arranged in the measurement direction; and
among the plurality of detection areas, two detection areas adjacent to each other are shifted from each other by a distance equivalent to one third of the fundamental period so as to be apart from each other in the measurement direction.

7. The displacement encoder according to claim 6 , wherein
first, second and third detection areas are arranged in this order in the measurement direction in the detection unit, and
the detection unit outputs a differential A phase signal and a differential B phase signal to the signal processing unit, the differential A phase signal and the differential B phase signal being generated by combining an A phase signal, a B phase signal, and a C phase signal, and having phases different from each other by 90°, the A phase signal being a detection signal output from the first detection area, the B phase signal being a detection signal output from the second detection area, and the C phase signal being a detection signal output from the third detection area.

8. The displacement encoder according to claim 1 , wherein
the optical element condenses the +1st order diffracted light and −1st order diffracted light to form the interference fringes on the detection unit.

9. The displacement encoder according to claim 8 , wherein
the optical element comprises one of a diffraction grating and an optical system comprising one or more lenses.

10. The displacement encoder according to claim 8 , wherein
the optical element comprises two mirrors,
one mirror reflects the +1st order diffracted light to the detection unit, and
the other mirror reflects the −1st order diffracted light to the detection unit.

11. The displacement encoder according to claim 2 , wherein
k is an integer equal to or more than two,
the fundamental period is P,
k detection areas arranged in a direction traverse to the measurement direction constitute a detection sequence,
the detection areas are shifted with respect to each other by a pitch of P/k.

12. The displacement encoder according to claim 11 , wherein
n is an integer equal to or more than one,
k detection sequences are periodically arranged in the measurement direction with a pitch of nP+P/k.

Assignees

• Mitutoyo Corp

Inventors

• Kimura Akihide
• Tobiason Joseph Daniel

Classifications

• G01D5/38

  by diffraction gratings · CPC title

• G01D5/34746 Primary

  Linear encoders · CPC title

• G01D5/347 Primary

  using displacement encoding scales · CPC title

• G01D5/34715

  Scale reading or illumination devices · CPC title