Absolute position measurement method, absolute position measurement apparatus and scale

Patent metadata

Field	Value
Publication number	US-9651403-B2
Application number	US-201414540743-A
Country	US
Kind code	B2
Filing date	Nov 13, 2014
Priority date	May 15, 2012
Publication date	May 16, 2017
Grant date	May 16, 2017

Abstract

Provided are an absolute position measurement method, an absolute position measurement apparatus, and a scale. The scale includes a scale pattern formed by replacing repeatedly arranged pseudo-random-codes with a sequence of a linear feedback shift register of N stages using a first symbol with first width representing a first state and a second symbol with second width representing a second state. The first is divided into two or more first symbol areas of different structures, and the second symbol is divided into two or more second symbol areas of different structures. There is at least one overlap area in which the first symbol and the second symbol overlap each other to have the same structure.

First claim

What is claimed is:

1. An absolute position measuring method comprising:
forming a scale pattern by replacing repeatedly arranged pseudo-random-codes with a sequence of a linear feedback shift register of N stages using a first symbol with first width representing a first state and a second symbol with second width representing a second state, wherein the first symbol is divided into two or more first symbol areas of different structures and the second symbol is divided into two or more second symbol areas of different structures, and there is at least one overlap area in which the first symbol and the second symbol overlap each other to have the same structure; and
extracting at least one data relative to a minimum area among the overlap area, the first symbol areas, and the second symbol areas and extracting a sensing signal relative to measurement width equal to or greater than length of a codeword including the N stages.

2. The absolute position measurement method of claim 1 , wherein the first width is three or more times greater than width of the minimum area, the first symbol is divided at equidistant intervals as the minimum area, and the second symbol is divided at equidistant intervals as the minimum area, and
which further comprises at least one of:
summing the sensing signals measured at intervals of the first width within the range of the measurement width to extract summing signals;
specifying an overlap area of the first symbol and the second symbol using the summing signals;
analyzing the codeword on the basis of the overlap area to extract coarse absolute position information; and
extracting a phase using the sensing signal corresponding to the overlap area to extract fine absolute position information.

3. The absolute position measurement method of claim 2 , wherein the first symbol is divided into three sections at equidistant intervals as the minimum areas, and the second symbol is divided into three sections at equidistant intervals as the minimum area.

4. The absolute position measurement method of claim 2 , wherein the pseudo-random-code is a maximum length sequence.

5. The absolute position measurement method of claim 2 , wherein there are two or three sensing signals relative to the overlap area.

6. The absolute position measurement method of claim 2 , wherein the overlap area includes two overlap areas spaced apart from each other.

7. The absolute position measurement method of claim 2 , wherein the overlap area includes two overlap areas disposed successively.

8. The absolute position measurement method of claim 2 , wherein the sensing signal is an optical signal reflected from the scale.

9. The absolute position measurement method of claim 2 , wherein the sensing signal is an optical signal passing through the scale.

10. The absolute position measurement method of claim 2 , wherein the first width is between several micrometers and several millimeters.

11. A scale for measuring an absolute position, comprising:
a scale pattern formed by replacing repeatedly arranged pseudo-random-codes with a sequence of a linear feedback shift register of N stages using a first symbol with first width representing a first state and a second symbol with second width representing a second state,
wherein the first symbol is divided into two or more first symbol areas of different structures, the second symbol is divided into two or more second symbol areas of different structures, and there is at least one overlap area in which the first symbol and the second symbol overlap each other to have the same structure.

12. The scale of claim 11 , wherein the first symbol and the second symbol include at least one bar pattern.

13. The scale of claim 11 , wherein the pseudo-random-code is a maximum length sequence.

14. The scale of claim 11 , wherein the overlap area includes two overlap areas spaced apart from each other.

15. The scale of claim 11 , wherein the overlap area includes two overlap areas disposed successively.

16. An absolute position measurement apparatus comprising:
a scale including a scale pattern formed by replacing repeatedly arranged pseudo-random-codes with a sequence of a linear feedback shift register of N stages using a first symbol with first width representing a first state and a second symbol with second width representing a second state, wherein the first symbol is divided into two or more first symbol areas of different structures and the second symbol is divided into two or more second symbol areas of different structures, there is at least one overlap area in which the first symbol and the second symbol overlap each other to have the same structure, and at least one data is extracted relative to a minimum area among the overlap area, the first symbol areas, and the second symbol area;
a sensor array adapted to measure a sensing signal relative to measurement width equal to or greater than length of a codeword including the N stages, wherein the first width is three times greater than width of the minimum area, the first symbol is divided at equidistant intervals as the minimum areas, and the second symbol is divided at equidistant intervals as the minimum areas; and
a processing unit configured such that the sensing signals measured at intervals of the first width within the range of the measurement width are summed to provide summing signals.

17. The absolute position measurement apparatus of claim 16 , wherein the processing unit specifies the first symbol and the second symbol by using the summing signals, analyzes the codeword on the basis of the overlap area to extract coarse absolute position information, and extracts a phase by using the sensing signal corresponding to the overlap area to extract fine absolute position information.

18. An absolute position measurement method comprising:
providing a binary scale including an absolute position binary code, wherein a data cell representing one bit of the absolute position binary code includes a data section, a neutral section, and a clock section of a relatively fixed position, each of the sections includes at least one segment, and the data cell is sub-divided into the segments at equidistant intervals;
obtaining an image of the binary scale through an optical system and an optical sensor array; and
processing the image to calculate an absolute position,
wherein a magnification of the optical system is adjusted such that a width of an image corresponding to one segment is an integer multiple of a pixel width of the optical sensor array.

19. The absolute position measurement method of claim 18 , wherein the data section is shifted by one segment to represent a binary state in the data cell.

20. The absolute position measurement method of claim 18 , wherein processing the image to calculate an absolute position comprises at least one of:
finding a clock pixel most closely aligned with the clock section in a pixel subset corresponding to one data cell width;
assigning an order of the clock pixel to a clock pixel index in the pixel subset corresponding to one data cell width;
circularly shifting the clock pixel index in a direction of reducing the clock pixel index to obtain an absolute code pixel index;
deciding a binary state of a pixel subset using the intensities of absolute code pixels corresponding to the absolute code pixel index in each pixel subset;
converting a binary code of pixel subsets whose binary state is decided into an absolute position code through a lookup table;
finding a data pixel corresponding

Assignees

• Korea Res Inst Standards & Sci

Inventors

• Kim Jong-Ahn
• Kim Jae-Wan
• Eom Tae-Bong
• Kang Chu-Shik
• Jin Jong-Han

Classifications

• G01D5/34776

  Absolute encoders with analogue or digital scales · CPC title

• G01D5/34746

  Linear encoders · CPC title

• G01D5/34792 Primary

  with only digital scales or both digital and incremental scales · CPC title

• G01D5/2455

  with incremental and absolute tracks on the same encoder · CPC title

• G01D5/34707 Primary

  Scales; Discs, e.g. fixation, fabrication, compensation · CPC title