SURFACE SENSOR OFFSET

• US 20100132432A1
• Filed: 07/11/2008
• Published: 06/03/2010
• Est. Priority Date: 07/13/2007
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: Grzesiak, Jean-Louis, Wallace, David Sven
• Granted Patent: US 8,756,973 B2
• Time in Patent Office: Days
• US Class Current: 73/1.750
• CPC Class Codes: G01B 21/045 Correction of measurements G01B9/02055 takes precedence

Abstract

A method of operating a coordinate positioning apparatus having a surface sensor that is rotatable about at least a first axis. The method comprises obtaining a first measurement with the surface sensor at a first angular orientation and obtaining a at least a second measurement with the surface sensor at a second angular orientation. The first and second angular orientations are different to each other such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and second measurements. The method then compensates and/or establishes for the offset using the first and second measurements.

Claims

1. A method of operating a coordinate positioning apparatus having a surface sensor that is rotatable about at least a first axis, the method comprising:

obtaining a first measurement with the surface sensor at a first angular orientation;

obtaining at least a second measurement with the surface sensor at a second angular orientation, the first and second angular orientations being different to each other such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and second measurements; and

using the first and second measurements to compensate for or establish the offset.

2. A method as claimed in claim 1, in which the second angular orientation is different to the first angular orientation such that the affect on the second measurement of any offset of the surface sensor from an expected position is substantially equal and opposite to its affect on the first measurement.

3. A method as claimed in claim 2 in which the second angular orientation is substantially the inverse of the first angular orientation.

4. A method as claimed in claim 1, in which obtaining the first and second measurements comprise moving the surface sensor such that the surface sensor measures in a first dimension only relative to itself.

5. A method as claimed in claim 1, in which obtaining the first and second measurements comprise moving the surface sensor relative to the artefact such that the surface sensor measures in first and second dimensions relative to itself.

6. A method as claimed in claim 1 in which compensating for the offset comprises determining the offset of the surface sensor in at least a first dimension.

7. A method as claimed in claim 6 in which compensating for the offset comprises determining the offset of the surface sensor in at least a second dimension.

8. A method as claimed in claim 6, comprising determining at least first and second offset sources.

9. A method as claimed in claim 8, in which the first offset source comprises the difference between the actual and expected position of the at least first axis and the second offset source comprises the difference between the actual and expected position of the surface sensor relative to the first axis.

10. A method as claimed in claim 1 in which compensating for the offset comprises determining a resultant measurement from the first and second measurements.

11. A method as claimed in claim 1 in which the second measurement is a repeat of the first measurement with the surface sensor at a different angular orientation.

12. A method as claimed in claim 1 in which obtaining each of the first and second measurements comprises measuring a plurality of points of an artefact.

13. A method as claimed in claim 1 in which obtaining the first and second measurements comprise obtaining first and second measurements of a circular feature.

14. A method as claimed in claim 1 in which the surface sensor is rotatable about at least a second axis that is perpendicular to the first axis.

15. A method as claimed in claim 14, in which the first and second angular orientations are taken about the first axis and measured relative to the second axis.

16. A method as claimed in claim 14 which obtaining the first and second measurements comprise rotating the surface sensor about the second axis.

17. A method as claimed in claim 16, in which obtaining the first and second measurements comprises maintaining the linear position of the second axis.

18. A method as claimed in claim 14 in which second angular orientation is substantially equal and opposite the first angular orientation.

19. A method as claimed in claim 14, in which obtaining the first and second measurements comprises moving the linear position of the first and second axes and maintaining the rotational position of the surface sensor about the first and second axes.

20. A method as claimed in claim 1 in which the surface sensor is a contact tip of a contact probe.

26. A coordinate positioning apparatus having a surface sensor that is rotatable about at least a first axis and a controller which is configured to perform the method of claim 1.

27. A computer program code comprising instructions which when executed by a controller of a measurement system having a surface sensor that is rotatable about at least a first axis causes the measurement system to perform the method of claim 1.

28. A computer readable medium, bearing computer program code as claimed in claim 27.

21. A method of operating a coordinate positioning apparatus having a surface sensor that is rotatable about at least first and second perpendicular axes, the method comprising:

positioning the surface sensor at a first angle about the first axis relative to a line that extends through the first axis and parallel to the second axis and obtaining a first measurement;

positioning the surface sensor at a second angle about the first axis relative to a line that extends through the first axis and parallel to the second axis and obtaining a second measurement, the second angle being opposite in direction to the first angle relative to the first axis such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and second measurements; and

using the first and second measurements to compensate for or establish the offset.

22. A method as claimed in claim 21, in which obtaining the first and second measurements comprise rotating the surface sensor about the second axis.

23. A method as claimed in claim 21 in which the second angle is substantially equal and opposite to the first angle.

24. A method of operating a coordinate positioning apparatus having a surface sensor which is rotatable about at least a first axis, the method comprising:

positioning the surface sensor at a first angular orientation and obtaining a first measurement by translationally moving the surface sensor;

positioning the surface sensor at least at a second angular orientation and obtaining at least a second measurement by translationally moving the surface sensor, the second angular orientation being different to the first angular orientation such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and at least second measurements; and

using the first and at least second measurements to compensate for or establish the offset.

25. A method as claimed in claim 24 in which the angular orientation of the surface sensor is fixed during obtaining the first and at least second methods.