Measurement encoder

Patent metadata

Field	Value
Publication number	US-10823587-B2
Application number	US-201415024519-A
Country	US
Kind code	B2
Filing date	Sep 26, 2014
Priority date	Oct 1, 2013
Publication date	Nov 3, 2020
Grant date	Nov 3, 2020

Abstract

An encoder apparatus including a scale including a series of features defining at least one scale track and a readhead for reading the scale's features. The readhead includes at least one light source for illuminating the scale and at least one detector. The configuration of the at least one light source is such that there is a structure in the light projected toward the scale. The readhead is configured such that the structure is angled so that it is substantially misaligned with respect to the scale's features so as to reduce measurement error in the signal output by the readhead.

First claim

The invention claimed is:

1. An encoder apparatus comprising a scale comprising a series of incremental or absolute features defining at least one incremental or absolute scale track and a readhead for reading the scale's features, the readhead comprising at least one light source for illuminating the scale and at least one detector,
wherein the configuration of the at least one light source is such that the light source comprises at least one bond pad and/or current spreader at or near its emission surface and in its emission area, the at least one bond pad and/or current spreader imparting a structure in the light projected toward the scale, and wherein the readhead is configured such that the structure is angled so that it is substantially misaligned with respect to the incremental or absolute scale features so as to reduce measurement error in the signal output by the readhead.

2. An encoder apparatus as claimed claim 1 , in which any predominant elongate components of the structure in the light projected toward the scale are angled with respect to the scale's features.

3. An encoder apparatus as claimed in claim 1 , in which the configuration of the light source imparts periodicity in the structure of the light projected, in at least one direction, and in which the readhead is configured such that the direction of periodicity is angled so that it is substantially misaligned with respect to the periodicity of the scale's features.

4. An encoder apparatus as claimed in claim 1 , in which the at least one light source is configured such that the intensity distribution of light projected toward the scale, as measured in the encoder apparatus' measuring dimension has a modulation depth of no more than 0.5.

5. An encoder apparatus as claimed in claim 1 , in which the structure in the light comprises an array of features, and in which the readhead is configured such that the array of features are angled with respect to the scale's features.

6. An encoder apparatus as claimed in claim 1 , in which the at least one light source comprises a light emitting diode (LED).

7. An encoder apparatus as claimed in claim 1 , in which the detector comprises a photodetector, and in which light interacts with the scale and at least one diffraction grating within the readhead to produce a resultant field at the photodetector which changes with relative movement of the scale and readhead.

8. An encoder apparatus as claimed in claim 1 , in which the readhead comprises a diffraction grating, and in which the light from the at least one light source interacts first with the scale to produce a first set of diffraction orders which then interact with the readhead's diffraction grating to produce further diffraction orders which combine to produce an interference fringe at the detector which changes with relative movement of the scale and readhead.

9. An encoder apparatus as claimed in claim 1 , in which the detector comprises a photodetector array.

10. An encoder apparatus as claimed in claim 9 , in which the photodetector array comprises a plurality of sensing channels extending in an array.

11. An encoder apparatus as claimed in claim 10 , in which the direction of the array extends substantially parallel to the reading direction of the readhead.

12. An encoder apparatus as claimed in claim 11 , in which the readhead is configured such that the structure in the light as it is projected from the light source toward the scale is angled with respect to the plurality of sensing channels.

13. An encoder apparatus as claimed in claim 10 , in which the readhead is configured such that the structure in the light as it is projected from the light source toward the scale is angled with respect to the plurality of sensing channels.

14. An encoder apparatus as claimed in claim 1 , in which the detector comprises a photo-sensor array which comprises two or more sets of interdigitated photo-sensitive sensors, each set detecting a different phase of an interference fringe at the detector.

15. An encoder readhead for reading a scale to determine the relative position between them, the readhead comprising:
a light source for illuminating a scale, in which the configuration of the light source is such that the light source comprises at least one bond pad and/or current spreader at or near its emission surface and in its emission area, the at least one bond pad and/or current spreader imparting a structure into the light projected by the light source; and
an array of photodetectors defining a plurality of sensing channels, in which the direction the array extends is substantially parallel to the reading direction of the readhead;
wherein the readhead is configured such that the structure in the light as it is projected from the light source toward the scale is angled with respect to the plurality of sensing channels.

Assignees

• Renishaw Plc

Inventors

• Mcadam Simon Eliot

Classifications

• G01D5/366

  Particular pulse shapes · CPC title

• G01D5/2457

  Incremental encoders having reference marks · CPC title

• G01D5/38

  by diffraction gratings · CPC title

• G01D5/34715 Primary

  Scale reading or illumination devices · CPC title