Method for scanning the surface of a workpiece

• US 20090307916A1
• Filed: 04/19/2006
• Published: 12/17/2009
• Est. Priority Date: 04/25/2005
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: McLean, Ian William, Somerville, Leo Christopher, Rees, Martin Simon, Weston, Nicholas John
• Granted Patent: US 7,908,759 B2
• Time in Patent Office: Days
• US Class Current: 33/503
• CPC Class Codes: G01B 21/04 by measuring coordinates of points
• CPC Class Codes: G05B 19/4207 in which a model is traced or scanned and corresponding data recorded
• CPC Class Codes: G05B 2219/37063 Controlled scanning, the head is moved along a given path

Abstract

A method for measuring a surface profile using a surface sensing device mounted on an articulating probe head in which the probe head is moved along a nominal path relative to the surface profile, an at least approximation of the surface normal of the surface profile, the surface profile is sensed with the surface sensing device and the distance or force of the surface sensing device relative to the surface profile substantially in the direction of the surface normal. The surface normal may be determined by approximating at least one section to a curved profile which can be mathematically parameterised.

Claims

1. A method for measuring a surface profile using a surface sensing device mounted on a probe head, the probe head including a drive for producing rotational movement of the surface sensing device about one or more axis, the method comprising the following steps, in any suitable order:

(a) moving the probe head along a nominal path relative to the surface profile;

(b) determining an at least approximation of the surface normal of the surface profile;

(c) sensing the surface profile with the surface sensing device;

(d) and adjusting the distance or force of the surface sensing device relative to the surface profile substantially in the direction of the surface normal.

2. A method according to claim 1 wherein the surface normal is determined in step (b) by use of a 3D probe.

3. A method according to claim 1 wherein the surface normal is determined in step (b) by use of historical data.

4. A method according to claim 1 wherein the surface normal is determined in step (b) from the defined geometry of the surface profile.

5. A method according to claim 1 wherein the surface normal is determined in step (b) by approximating at least one section of the surface profile to a curved profile which can be mathematically parameterised.

6. A method according to claim 1 wherein the surface sensing device comprises a deflectable stylus and wherein the step of sensing the surface with the surface sensing device in step (c) comprises transducing the deflection of the stylus.

7. A method according to claim 1 wherein the surface sensing device comprises a stylus, wherein the step of sensing the surface with the surface sensing device in step (c) comprises transducing the force at the stylus.

8. A method according to claim 1 wherein the surface sensing device comprises a non contact probe and wherein the step of sensing the surface with the surface sensing device in step (c) comprises transducing the distance of the surface from the non contact probe.

9. A method of according to claim 1, wherein the adjustment step (d) is obtained through producing rotational movement of the surface sensing device about one or more axis.

10. A method for measuring a surface profile using a surface sensing device mounted on a probe head, the probe head including a drive for producing rotational movement of the surface sensing device about one or more axis, the method comprising the following steps, in any suitable order:

(a) approximating at least one section of the surface profile to a curved profile which can be mathematically parameterised;

(b) determining the surface normal of the at least one section of the curved profile;

(c) measuring the surface of the at least one section of the surface profile with the surface sensing device and wherein the distance or force reported by the surface sensing device is controlled in substantially the direction of the normal of the curved profile.

11. A method according to claim 10 wherein the curved profile comprises a parameterised parabola.

12. A method according to claim 10 wherein the curved surface has defined height and width parameters.

13. A method according to claim 12 wherein the curved surface has different height and width parameters at the start and end of a section, the height and width parameters being merged together between the two ends.

14. A method according to claim 10 wherein a nominal scan path of the surface sensing device is created by superimposing a wave over the curved profile.

15. A method according to claim 10, wherein two or more sections of the surface profile are approximated to a corresponding number of curved profiles.

16. A method according to claim 15 wherein the two or more sections are selected so that each region curves in only one direction.

17. A method according to claim 15 wherein points of inflection of the surface profile are selected as the boundaries of the sections.

18. A method according to claim 10 wherein the parameters are adjusted so they better approximate the surface profile.

19. A method according to claim 15 wherein the measurement profiles of the two or more curved profiles are blended together.

20. A method for determining complex paths for an apparatus moving in multiple axes, the method comprising the steps of:

(a) dividing the complex path into at least two sections, the intersection of the two sections defining a way-point, the way-point having an associated radius;

(b) determining the velocity of each axis when a point of interest enters the radius of the way-point;

(c) determining the velocity of each axis when a point of interest exits the radius of the way-point;

(d) mathematically modelling the acceleration for a smooth transition from the velocity in step (b) to the velocity in step (c) in each axis.

21. A method according to claim 20 wherein the axes comprise physical axes.

22. A method according to claim 21 wherein the axes comprise time varying parameters.

23. A method according to claim 20 wherein the apparatus is mounted on a coordinate positioning apparatus, which enables the apparatus to move relative to a part of the coordinate positioning apparatus.

24. A method according to claim 20 wherein the apparatus includes a drive for producing rotational movement about one or more axes.

25. A method according to claim 20 wherein the point of interest is associated with a surface sensing device.

26. A method according to claim 25 wherein the surface sensing device comprises a measurement probe with a stylus and wherein the point of interest is the stylus tip.

27. A method according to claim 25 wherein the surface sensing device comprises a non contact probe and whereas the point of interest comprises the position of the measuring apparatus of the probe offset by a constant length vector whose position and orientation is fixed with respect to the probe.

28. A method according to claim 20 including the use of a polynomial equation in step (d).

29. A method according to claim 20, wherein the apparatus comprises an articulating probe head with a surface sensing device mounted thereon, which is mounted on a coordinate positioning machine.

30. A method according to claim 29 wherein the articulating probe head provided rotary motion about two axes and the coordinate positioning machine provides linear motion in three axes.

31. A method according to claim 29 wherein the apparatus is used to measure a boss, and the coordinate positioning machine moves the probe head in a square trajectory about the boss.

32. Apparatus for measuring a surface profile with a surface sensing device mounted on a probe head on a coordinate positioning apparatus, wherein the coordinate positioning apparatus may be operated to produce relative movement between the probe head and the surface profile and wherein the probe head includes a drive for producing rotational movement of the surface sensing probe about one or more axis, and the apparatus comprising a controller for carrying out the following steps, in any suitable order:

(a) moving the probe head along a nominal path relative to the surface profile;

(b) determining an at least approximation of the surface normal of the surface;

(c) sensing the surface with the surface sensing device;

(d) and adjusting the distance or force of the surface sensing device relative to the surface substantially in the direction of the surface normal.

33. Apparatus for measuring a surface profile using a surface sensing device mounted on a probe head on a coordinate positioning apparatus, wherein the coordinate positioning apparatus may be operated to produce relative movement between the probe head and the surface profile and wherein the probe head includes a drive for producing rotational movement of the surface sensing device about one or more axis, the apparatus comprising a controller for carrying out the following steps, in any suitable order:

(a) approximating at least one section of the surface profile to a curved profile which can be mathematically parameterised;

(b) determining the surface normal of the curved profile;

(c) measuring the surface of the at least one section of the surface profile with the measurement probe and wherein the distance or force reported by the surface sensing device is controlled in substantially the direction of the normal of the curved profile.

34. Apparatus for measuring a surface profile using a measurement probe with a surface sensing device mounted on a probe head on a coordinate positioning apparatus, wherein the coordinate positioning apparatus may be operated to produce relative movement between the probe head and the surface profile and wherein the probe head includes a drive for producing rotational movement of the surface sensing device about one or more axis, the apparatus comprising a controller for carrying out the following steps, in any suitable order:

(a) dividing the surface profile into at least two sections, the intersection of the two sections defining a way-point, the way-point having an associated radius;

(b) determining the velocity of each axis when a point of interest enters the radius of the way-point;

(c) determining the velocity of each axis when a point of interest exits the radius of the way-point;

(d) mathematically modelling the acceleration for a smooth transition from the velocity in step (b) to the velocity in step (c) in each axis.

35. A method for scanning a surface of an unknown part using a surface sensing device which is mounted on a probe head being mounted on a coordinate position apparatus, wherein the coordinate positioning apparatus may be operated to produce relative movement between the probe head and a surface profile and wherein the probe head includes one or more drives for producing rotational movement of the surface sensing device about one or more axes, the method comprising:

moving the motorized scanning head along a nominal path around the part and measuring the surface with the surface sensing device;

serving the probe head to keep the surface sensing device in range when the surface change from its nominal path has a rate of change within the bandwidth range of both the probe head and the coordinate positioning apparatus; and

serving the motion of the coordinate positioning apparatus when the surface change from its nominal path has a rate of change greater than bandwidth range of the probe head.

36. A method according to claim 35 wherein the surface sensing device is a probe and wherein for surface changes having a bandwidth greater than the bandwidth of the probe head, the probe deflection reacts to the surface change.