SURFACE MEASUREMENT APPARATUS AND METHOD

• US 20150025844A1
• Filed: 02/27/2013
• Published: 01/22/2015
• Est. Priority Date: 02/27/2012
• Status: Abandoned Application

• Current Assignee: Taylor Hobson Limited (Ametek Incorporated)
• Original Assignee: Taylor Hobson Limited (Ametek Incorporated)
• Inventors: Mansfield, Daniel Ian
• Application Number:
  US14/381,012
• Publication Number:
  US 20150025844A1
• Time in Patent Office: Days
• US Class Current: 702/167
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures
• CPC Class Codes: G01B 21/042 Calibration or calibration artifacts G01B3/30, G01B9/02072 take precedence
• CPC Class Codes: G01B 5/008 using coordinate measuring machines
• CPC Class Codes: G01B 5/20 for measuring contours or curvatures
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00

Abstract

A metrological apparatus has a workpiece support surface (16) and a mover (9) to carry out a measurement by effecting relative movement in a measurement direction, X, between the workpiece support surface and a stylus (11) such that the stylus is deflected as a stylus tip of the stylus follows surface variations. A transducer (39) provides a measurement data set in a measurement coordinate system representing the deflection, a, of the stylus at measurement points in the measurement direction, X. A rotation device (16) effects relative rotation of the workpiece support surface and the mover about a rotation axis. A data processor is provided to determine a location of intersection of a first measurement data set representing a measurement along a measurement path on a calibration component surface which is not symmetric about the rotation axis and a second measurement data set representing a measurement along a measurement path on the calibration component surface after rotation of 180 degrees about the rotation axis and to determine the frame of reference of the apparatus using the determined intersection.

Claims

1. A metrological apparatus for measuring a surface characteristic of a workpiece, the apparatus comprising:

a workpiece support surface defining a frame of reference having a first axis, x, extending parallel to the workpiece support surface and a second axis, z, normal to the workpiece support surface;

a mover to carry out a measurement by effecting relative movement in a measurement direction, X, between the workpiece support surface and a stylus such that the stylus is deflected as a stylus tip of the stylus follows surface variations along a measurement path on a surface of a workpiece supported on the workpiece support surface;

a transducer to provide a measurement data set in a measurement coordinate system representing the deflection, a, of the stylus at measurement points in the measurement direction, X, along the measurement path;

a rotation device to effect relative rotation of the workpiece support surface and the mover about a rotation axis; and

a data processor configured to;

to receive a first measurement data set representing a measurement along a measurement path on a calibration component surface which is not symmetric about the rotation axis;

to receive a second measurement data set representing a measurement along a measurement path on the calibration component surface after rotation of 180 degrees about the rotation axis;

to determine a location of intersection of the first and second measurement data sets; and

to determine the frame of reference of the apparatus on the basis of the determined intersection.

2. A metrological apparatus according to claim 1, wherein the calibration component surface is an inclined flank or plane.

3. A metrological apparatus according to any of the preceding claims, wherein the measurement direction is at an angle β

to the first axis, x.

4. A metrological apparatus according to any of the preceding claims, providing a pivotal mounting for the stylus such that an arm of the stylus pivots about a pivot axis as the stylus tip follows surface variations.

5. A metrological apparatus according to claim 1, wherein the calibration component surface is an inclined flank or plane, the measurement direction is at an angle β

to the first axis, x, a pivotal mounting is provided for the stylus such that an arm of the stylus pivots about a pivot axis as the stylus tip follows surface variations, and wherein a relationship between a location (x_s, z_s) of the stylus tip in the frame of reference and in the measurement coordinate system (G, X) is determined in accordance with

L cos(β

+α

₀)+X cos β

−

L cos α

=x_s

L sin(β

+α

₀)+X sin β

+Δ

Z_col−

L sin α

=z_s

where α

is the stylus deflection angle at a measurement point and is related to the measurement value G;

α

₀ is a pivot offset angle.

6. A metrological apparatus according to claim 5, wherein the data processor is configured to determine the tangent of the angle of the inclined plane as dz_s/dx_s, to define a perturbation Δ

β

of the measurement direction angle β

, to solve dz_s/dx_s for Δ

β and

_to modify the measurement direction angle in accordance with the determined perturbation Δ

β

.

7. A metrological apparatus according to claim 5, wherein the data processor is configured to add a perturbation Δ

β

to the measurement direction angle β

, to determine the tangent of the angle of the inclined plane;

8. A metrological apparatus according to claim 5, 6 or 7, wherein the data processor is configured to set the parameters X!, G! and corresponding stylus angle α

! representing the location of intersection of the first and second measurement data sets as equal to another parameter set X₂, G₂ and corresponding stylus angle α

₂ representing the location of intersection but for which the measurement data value is such that α

₂=β

+α

₀, so that;

x_s=L cos(β

+α

₀)+X! cos β

−

L cos α

!=L cos(β

+α

₀)+X₂ cos β

−

L cos(β

+α

₀)

z_s=L sin(β

+α

₀)+X! sin β

+Z₁−

L sin α

!=L sin(β

+α

₀)+X₂ sin β

+Z₂−

L sin(β

+α

₀)

and to solve for (X₂−

X!) and (Z₂−

Z₁);

(X₂−

X!)=L(cos(β

+α

₀)−

cos α

!)/cos β

(Z₂−

Z₁)=L(sin(β

+α

₀)−

sin α

!)−

(X₂−

X!)sin β

to provide as (X₂−

X!) and (Z₂−

Z₁) shifts to the measurement direction position and z position to place the stylus tip centre on the rotation axis with the transducer mid-range.

9. A metrological apparatus according to any of the preceding claims, comprising a traverse unit to move the stylus in the measurement direction.

10. A metrological apparatus according to claim 9, wherein the traverse unit is movable in the z direction.

11. A metrological apparatus according to any of the preceding claims, wherein the surface characteristic is a surface form of a surface of the workpiece.

12. A metrological apparatus according to any of the preceding claims, wherein the rotation device is a turntable which also provides the workpiece support surface.

36. A computer program product comprising program instructions to program a processor to carry out data processing of a method according to any of claims 13 to 24 and 35 or to program a processor to provide the data processor of any of claims 1 to 12 and 25 to 34.

13. A method for facilitating measurement of a surface characteristic of a workpiece using an apparatus comprising:

a workpiece support surface defining a frame of reference having a first axis, x, extending parallel to the workpiece support surface and a second axis, z, normal to the workpiece support surface;

a mover to carry out a measurement by effecting relative movement in a measurement direction, X, between the workpiece support surface and a stylus such that the stylus is deflected as a stylus tip of the stylus follows surface variations along a measurement path on a surface of a workpiece supported on the workpiece support surface;

a transducer to provide a measurement data set in a measurement coordinate system representing the deflection, a, of the stylus at measurement points in the measurement direction, X, along the measurement path; and

a rotation device to effect relative rotation of the workpiece support surface and the mover about a rotation axis, the method comprising;

determining a location of intersection of a first measurement data set representing a measurement along a measurement path on a calibration component surface which is not symmetric about the rotation axis and a second measurement data set representing a measurement along a measurement path on the calibration component surface after rotation of 180 degrees about the rotation axis; and

determining the frame of reference of the apparatus using the determined intersection.

14. A method according to claim 13, wherein the calibration component surface is an inclined flank or plane.

15. A method according to claim 13 or 14, wherein the measurement direction is at an angle β

to the first axis, x.

16. A method according to claim 13, 14 or 15, providing a pivotal mounting for the stylus such that an arm of the stylus pivots about a pivot axis as the stylus tip follows surface variations.

17. A method according to claim 13, wherein the calibration component surface is an inclined flank or plane, the measurement direction is at an angle β

to the first axis, x, a pivotal mounting is provided for the stylus such that an arm of the stylus pivots about a pivot axis as the stylus tip follows surface variations, and wherein a relationship between a location (x_s, z_s) of the stylus tip in the frame of reference and in the measurement coordinate system (G, X) is determined in accordance with

L cos(β

+α

₀)+X cos β

−

L cos α

=x_s

L sin(β

+α

₀)+X sin β

+Δ

Z_col−

L sin α

=z_s

where α

is the stylus deflection angle at a measurement point and is related to the measurement value G;

α

₀ is a pivot offset angle.

18. A method according to claim 17, comprising determining the tangent of the angle of the inclined plane as dz_s/dx_s, defining a perturbation Δ

β

of the measurement direction angle β

, to solve dz_s/dx_s for Δ

β and

_modifying the measurement direction angle in accordance with the determined perturbation Δ

β

.

19. A method according to claim 17, comprising adding a perturbation Δ

β

to the measurement direction angle β

, determining the tangent of the angle of the inclined plane;

20. A method according to claim 17, 18 or 19, comprising setting the parameters X!, G! and corresponding stylus angle α

! representing the location of intersection of the first and second measurement data sets as equal to another parameter set X₂, G₂ and corresponding stylus angle α

₂ representing the location of intersection but for which the measurement data value is such that α

₂=β

+α

₀, so that;

x_s=L cos(β

+α

₀)+X! cos β

−

L cos α

!=L cos(β

+α

₀)+X₂ cos β

−

L cos(β

+α

₀)

z_s=L sin(β

+α

₀)+X! sin β

+Z₁−

L sin α

!=L sin(β

+α

₀)+X₂ sin β

+Z₂−

L sin(β

+α

₀)

and solving for (X₂−

X!) and (Z₂−

Z₁);

(X₂−

X!)L(cos(β

+α

₀)−

cos α

!)/cos β

(Z₂−

Z₁)=L(sin(β

+α

₀)−

sin α

!)−

(X₂−

X!)sin β

to provide as (X₂−

X!) and (Z₂−

Z₁) shifts to the measurement direction position and z position to place the stylus tip centre on the rotation axis with the transducer mid-range.

21. A method according to any of claims 13 to 20, wherein a traverse unit moves the stylus in the measurement direction.

22. A method according to claim 21, wherein the traverse unit is movable in the z direction.

23. A method according to any of claims 13 to 22, wherein the surface characteristic is a surface form of a surface of the workpiece.

24. A method according to any of claims 13 to 23, wherein the rotation device is a turntable which also provides the workpiece support surface.

25. A data processor for a metrological apparatus for measuring a surface characteristic of a workpiece, the apparatus comprising:

a workpiece support surface defining a frame of reference having a first axis, x, extending parallel to the workpiece support surface and a second axis, z, normal to the workpiece support surface;

a mover to carry out a measurement by effecting relative movement in a measurement direction, X, between the workpiece support surface and a stylus such that the stylus is deflected as a stylus tip of the stylus follows surface variations along a measurement path on a surface of a workpiece supported on the workpiece support surface;

a transducer to provide a measurement data set in a measurement coordinate system representing the deflection, a, of the stylus at measurement points in the measurement direction, X, along the measurement path; and

a rotation device to effect relative rotation of the workpiece support surface and the mover about a rotation axis, the data processor being configured to;

to receive a first measurement data set representing a measurement along a measurement path on a calibration component surface which is not symmetric about the rotation axis;

to receive a second measurement data set representing a measurement along a measurement path on the calibration component surface after rotation of 180 degrees about the rotation axis;

to determine a location of intersection of the first and second measurement data sets; and

to determine the frame of reference of the apparatus on the basis of the determined intersection.

26. A data processor according to claim 25, wherein the calibration component surface is an inclined flank or plane.

27. A data processor according to claim 25 or 26, wherein the measurement direction is at an angle β

to the first axis, x.

28. A data processor according to any of claims 25 to 27, providing a pivotal mounting for the stylus such that an arm of the stylus pivots about a pivot axis as the stylus tip follows surface variations.

29. A data processor according to claim 25, wherein the calibration component surface is an inclined flank or plane, the measurement direction is at an angle β

to the first axis, x, a pivotal mounting is provided for the stylus such that an arm of the stylus pivots about a pivot axis as the stylus tip follows surface variations, and wherein a relationship between a location (x_s, z_s) of the stylus tip in the frame of reference and in the measurement coordinate system (G, X) is determined in accordance with

L cos(β

+α

₀)+X cos β

−

L cos α

=x_s

L sin(β

+α

₀)+X sin β

+Δ

Z_col−

L sin α

=z_s

where α

is the stylus deflection angle at a measurement point and is related to the measurement value G;

α

₀ is a pivot offset angle.

30. A data processor according to claim 29, wherein the data processor is configured to determine the tangent of the angle of the inclined plane as dz_s/dx_s, to define a perturbation Δ

β

of the measurement direction angle β

, to solve dz_s/dx_s for Δ

β and

_to modify the measurement direction angle in accordance with the determined perturbation Δ

β

.

31. A data processor according to claim 29, wherein the data processor is configured to add a perturbation Δ

β

to the measurement direction angle β

, to determine the tangent of the angle of the inclined plane;

32. A data processor according to claim 29, 30 or 31, wherein the data processor is configured to set the parameters X!, G! and corresponding stylus angle α

! representing the location of intersection of the first and second measurement data sets as equal to another parameter set X₂, G₂ and corresponding stylus angle α

₂ representing the location of intersection but for which the measurement data value is such that α

₂=β

+α

₀, so that;

x_s=L cos(β

+α

₀)+X! cos β

−

L cos α

!=L cos(β

+α

₀)+X₂ cos β

−

L cos(β

+α

₀)

z_s=L sin(β

+α

₀)+X! sin β

+Z₁−

L sin α

!=L sin(β

+α

₀)+X₂ sin β

+Z₂−

L sin(β

+α

₀)

and to solve for (X₂−

X!) and (Z₂−

Z₁);

(X₂−

X!)=L(cos(β

+α

₀)−

cos α

!)/cos β

(Z₂−

Z₁)=L(sin(β

+α

₀)−

sin α

!)−

(X₂−

X!)sin β

to provide as (X₂−

X!) and (Z₂−

Z₁) shifts to the measurement direction position and z position to place the stylus tip centre on the rotation axis with the transducer mid-range.

33. A metrological apparatus substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.

34. A data processor substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.

35. A method substantially as hereinbefore described with reference to and/or as illustrated in FIG. 4 of the accompanying drawings.