Absolute encoder setup indication

• US 8,505,210 B2
• Filed: 10/27/2009
• Issued: 08/13/2013
• Est. Priority Date: 10/28/2008
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: Gribble, Andrew Paul, Gordon-Ingram, Iain Robert
• Primary Examiner(s): Bennett, G. Bradley
• Application Number:
  US13/120,349
• Publication Number:
  US 20110173832A1
• Time in Patent Office: 1,386 Days
• Field of Search: 33/1.PT, 337/06, 337/07, 337/08, 337/01
• US Class Current: 33/701
• CPC Class Codes: G01D 5/24461 by redundancy or plausibility
• CPC Class Codes: G01D 5/2495 Pseudo-random code
• CPC Class Codes: G01D 5/34715 Scale reading or illumination devices
• CPC Class Codes: G01D 5/34776 Absolute encoders with analogue or digital scales
• CPC Class Codes: G01D 7/005 Indication of measured value by colour change

Abstract

This invention relates to a method of operating an absolute encoder apparatus comprising a scale having features defining absolute position information in at least one measuring dimension, and a readhead configured to read the features. The method comprises: obtaining at least one representation of at least some of the features defining absolute position information; analyzing the at least one representation to determine at least one parameter indicative of the quality of the representation; and providing an output indicative of the relative setup of the scale and readhead based at least in part on the at least one parameter.

Claims

1. A method of operating an absolute encoder apparatus, the encoder apparatus comprising a scale having features defining absolute position information in at least one measuring dimension, and a readhead configured to read the features, the method comprising:

obtaining at least one representation of at least some of the features defining absolute position information;

analysing the at least one representation to determine at least one parameter indicative of the quality of the representation; and

providing an output indicative of the relative setup of the scale and readhead based at least in part on the at least one parameter.

2. A method as claimed in claim 1, in which determining the at least one parameter is based solely on the at least one representation.

3. A method as claimed in claim 1, in which analysing the at least one representation comprises analysing the quality of at least some of the features in the representation.

4. A method as claimed in claim 1, in which analysing the at least one representation comprises analysing the strength of at least some of the features in the at least one representation.

5. A method as claimed in claim 4, in which analysing the at least one representation comprises analysing the amplitude of at least some of the features in the at least one representation.

6. A method as claimed in claim 1, in which the track comprises a first type of feature and at least a second type of feature, the quality of representation of the first type being more sensitive to the relative arrangement of the readhead and scale, and in which determining the at least one parameter comprises analysing features of the first type.

7. A method as claimed in claim 6 in which the features of the first type are smaller than the features of the second type at least in the at least one measuring dimension.

8. A method as claimed in claim 6, in which analysing the at least one representation comprises comparing features of the first type to the features of the second type.

9. A method as claimed in claim 1, in which analysing the at least one representation comprises Fourier Transforming at least part of the representation.

10. A method as claimed in claim 9, comprising performing one or more Fourier Transforms of at least part of representation at one or more frequencies related to the spatial frequency of the features of the first type.

11. A method as claimed in claim 9, in which the parameter indicative of the quality of the representation is based on the magnitude of at least one Fourier Transform.

12. A method as claimed in claim 1, in which analysing the at least one representation comprises analysing the orientation of at least some of features in the at least one representation.

13. A method as claimed in claim 1, in which the output is based solely on the at least one parameter.

14. A method as claimed in claim 1, in which the encoder apparatus is an optical encoder apparatus.

15. A method as claimed in claim 1, in which the scale comprises a single track only.

16. A method as claimed in claim 1, further comprising, analysing the at least one representation to determine the relative position of the readhead and scale in the at least one measuring dimension.

17. A method as claimed in claim 1, the readhead comprising circuitry which is configured to determine the at least one parameter.

18. A method as claimed in claim 1, the readhead comprising an output device, and in which the output based on the at least one parameter is output via the output device.

19. A method as claimed in claim 18, in which the output device comprises a visual indication device.

20. A method as claimed in claim 19, in which the output device comprises a Light Emitting Diode.

21. A method as claimed in claim 1, in which the output is at least partly based on the determination of whether the quality of the representation meets a threshold quality.

22. A method as claimed in claim 21, in which the output is indicative of the level of the quality of the representation.

23. A method as claimed in claim 21, in which the threshold quality is greater than the quality of representation required in order to extract reliable position information from the representation.

24. An absolute encoder apparatus comprising a scale having features defining absolute position information in at least one measuring dimension, and a readhead configured to read the features, in which the apparatus is configured to:

obtain, via the readhead, at least one representation of at least some of the features;

analyse the at least one representation to determine at least one parameter indicative of the quality of the representation; and

provide an output indicative of the relative setup of the scale and readhead based at least in part on the at least one parameter.

25. A readhead for an absolute encoder apparatus, comprising:

at least one sensor for obtaining at least one representation of at least some of the features;

circuitry configured to analyse the at least one representation to determine at least one parameter indicative of the quality of the representation; and

an output device for providing an output indicative of the relative setup of the scale and readhead based at least in part on the at least one parameter.