Method and measuring machine for determining dimensional properties of a measurement object

Patent metadata

Field	Value
Publication number	US-9826201-B2
Application number	US-201615221879-A
Country	US
Kind code	B2
Filing date	Jul 28, 2016
Priority date	Jul 31, 2015
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

Abstract

A method and a measuring machine for determining dimensional properties of a measurement object each use a workpiece table and a camera having an image sensor and an imaging optics. The imaging optics exhibits aberrations and is configured to be focused on a plurality of different working positions relative to the workpiece table. The aberrations are minimized by using first calibration values provided for a defined working position. A first working distance of the camera relative to a region of interest is determined. Subsequently, the imaging optics is focused, using the first working distance and using second calibration values that represent an image field curvature of the camera, such that the region of interest is substantially brought into a defined working position. Subsequently, the image recording and image evaluation take place to determine measurement values that represent the dimensional properties of the measurement object in the region of interest.

First claim

What is claimed is:

1. A method for determining dimensional properties of a measurement object, comprising the steps of:
providing an optical measuring machine comprising a workpiece table and a camera having an image sensor and an imaging optics, wherein the imaging optics exhibits aberrations and is configured to be focused on a plurality of different working positions relative to the workpiece table,
providing first calibration values that are selected such that the aberrations are minimized for a defined working position from the plurality of different working positions,
providing second calibration values that represent an image field curvature of the camera,
positioning the measurement object on the workpiece table,
defining a first region of interest on the measurement object,
determining a first working distance of the camera to the first region of interest,
focusing the imaging optics using the first working distance and the second calibration values such that the first region of interest is substantially brought into the defined working position,
recording an image of the first region of interest while it substantially is in the defined working position, and
determining measurement values that represent the dimensional properties of the measurement object in the first region of interest on the basis of the image and on the basis of the first calibration values,
wherein the first calibration values further comprise distance-dependent correction values for correcting at least one of telecentricity errors and coma, and wherein the measurement values are determined in dependence on the first working distance and the distance-dependent correction values.

2. The method of claim 1 , wherein the first calibration values effect a correction of distortion errors of the imaging optics at the defined working position.

3. The method of claim 1 , wherein the imaging optics is initially focused on the first region of interest in order to determine the first working distance.

4. The method of claim 1 , wherein a second region of interest on the measurement object is defined, which second region of interest is laterally spaced apart from the first region of interest, and wherein the imaging optics is focused using the second calibration values such that the first region of interest and the second region of interest each are brought as close as possible to the defined working position.

5. The method of claim 4 , wherein the imaging optics is focused onto the second region of interest in order to determine a second working distance, and wherein the imaging optics is focused, using the first working distance, the second working distance and the second calibration values, so as to bring the first region of interest and the second region of interest each as close as possible to the defined working position.

6. The method of claim 4 , wherein the first region of interest and the second region of interest form segments of a common region of interest.

7. The method of claim 1 , wherein a CAD data set is provided, which CAD data set represents nominal dimensional properties of the measurement object, and wherein at least one of the first working distance and the second working distance is determined on the basis of the CAD data set.

8. The method of claim 1 , wherein a further region of interest on the measurement object is defined, and wherein a further image of the measurement object is recorded, after the further region of interest has substantially been brought into the defined working position using the second calibration values.

9. The method of claim 1 , wherein an area centroid of the first region of interest is determined, and wherein the first working distance is determined relative to the area centroid.

10. The method of claim 1 , wherein a surface topography of the measurement object is determined in dependence on the second calibration values.

11. The method of claim 1 , wherein the second calibration values are provided in the form of a value table comprising values each representing a spatially dependent focus shift.

12. The method of claim 1 , wherein the second calibration values are provided in the form of coefficients of a spatially dependent polynomial.

13. The method of claim 12 , wherein the polynomial is a Zernike polynomial.

14. The method of claim 1 , wherein the second calibration values further comprise orientation-dependent contributions of the image field curvature that result from astigmatic aberrations.

15. A measuring machine for determining dimensional properties of a measurement object, comprising:
a workpiece table,
a camera having an image sensor and an imaging optics, wherein the imaging optics exhibits aberrations and is configured to be focused on a plurality of different working positions relative to the workpiece table,
a first memory for providing first calibration values that are selected such that the aberrations are minimized for a defined working position from the plurality of different working positions, wherein the first calibration values comprise distance-dependent correction values for correcting at least one of telecentricity errors and coma,
a second memory for providing second calibration values that represent an image field curvature of the camera, and
an evaluation and control unit having an interface for defining a first region of interest on the measurement object,
wherein the evaluation and control unit is configured for
a) determining a first working distance of the camera to the first region of interest,
b) focusing the imaging optics using the first working distance and using the second calibration values such that the first region of interest is brought into the defined working position,
c) recording an image of the first region of interest while it is on the defined working position using the camera, and
d) determining measurement values that represent the dimensional properties of the measurement object in the first region of interest on the basis of the image and on the basis of the first calibration values, wherein the measurement values are determined in dependence on the first working distance and the distance-dependent correction values.

Assignees

• Zeiss Carl Industrielle Messtechnik Gmbh

Inventors

• Goehnermeier Aksel
• Jester Philipp
• Widulle Frank

Classifications

• G01B11/24 Primary

  for measuring contours or curvatures · CPC title

• H04N7/183 Primary

  for receiving images from a single remote source · CPC title