Method for measuring the geometry of an object by means of a co-ordination measuring device

• US 20040264758A1
• Filed: 12/17/2002
• Published: 12/30/2004
• Est. Priority Date: 09/22/2000
• Status: Active Grant

• Current Assignee: Werth Messtechnik GmbH
• Original Assignee: Werth Messtechnik GmbH
• Inventors: Christoph, Ralf
• Granted Patent: US 7,064,845 B2
• Time in Patent Office: Days
• US Class Current: 382/141
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures
• CPC Class Codes: G05B 19/40937 concerning programming of machining or material parameters, pocket machining
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

Abstract

The invention relates to a method for measuring the geometry of an object (12), particularly a work piece or a tool, by means of a co-ordination measuring device (10). The geometry of an object (12) is recorded by an optical sensor (14), for example a camera, and is represented in the form of an image content (32). Geometric structures (60 70) in the image content adapted to the measurement of the object (12), such as geometric elements or contours, are selected and subsequently evaluated. The aim of the invention is to enable even non-experienced operators to carry out a measurement in a fast and fault-free manner. When the image content (32) is changed, it is automatically analysed in relation to the geometric structures (60-70) adapted to the object measurement (12), and the adapted structures are marked and prepared for subsequent evaluation.

Claims

1. Process for the measurement of an object geometry (12), especially a workpiece or tool geometry, by means of a coordinate measuring device (10), whereby the object geometry (12) is recorded by means of an optical sensor (14), such as a camera, and represented as an image content (32), and whereby, within the image content, geometric structures (60-70) suitable for the measurement of the object (12), such as geometric elements or contours, are selected and subsequently evaluated,

characterized in that

at the time of any modification of the image content (32), said image content is automatically searched for the geometric structures (60-70) suitable for the measurement of the object (12), and the suitable structures are marked and made available for further evaluation.

2. Process according to claim 1,

characterized in that

the modification of the image content (32) takes place when modification of the optical magnification and/or of the position of mechanical axes of the coordinate measuring device (10) and/or of the light intensity is implemented.

3. Process according to claim 1 or 2,

characterized in that

the modification of the image content (32) is represented by a signal.

4. Process according to at least one of the previous claims,

characterized in that

the signal representing the modification of the image content (32) is produced by a control unit (22) of a zoom lens of the coordinate measuring device (10) at the time of modification of the optical magnification.

5. Process according to at least one of the previous claims,

characterized in that

the signal representing the modification of the image content (32) is produced by a replacement unit (56), such as a revolving holder, when the modification of the optical magnification is produced by replacement of the objective.

6. Process according to at least one of the previous claims,

characterized in that

the signal representing the modification of the image content (32) is produced by an actuation control (18), such as CNC control, when the state of a counter on at least one axis of the coordinate measuring device (10) remains constant, following a position change, for longer than a predetermined interval of “

dead time”

.

7. Process according to at least one of the previous claims,

characterized in that

the signal representing the modification of the image content (32) is produced by a lighting control (24), when a nominal lighting value, following a modification of lighting, remains within a tolerance range for longer than a predetermined interval of “

dead time”

.

8. Process according to at least one of the previous claims,

characterized in that

the signal representing the modification of the image content (32) is produced by an additional optical sensor, when the constancy of the light ratios gives rise to an inference with regard to the modification of the image content.

9. Process according to at least one of the previous claims,

characterized in that

the signal representing the modification of the image content (32) is manually produced by an operator, preferably by pressing a button.

10. Process according to at least one of the previous claims,

characterized in that

the image content (32) is automatically searched for at least one regular geometric element, such as a circle and/or a straight line.

11. Process according to at least one of the previous claims,

characterized in that

the automatically proposed geometric structures such as contours and geometric elements (60-70) are manually selected by an operator, for example, through the control of a monitor by means of an input device such as a mouse, touchpad, touch screen and so forth.

12. Process according to at least one of the previous claims,

characterized in that

the automatically selected geometric structures can be automatically incorporated into a characteristic list at the time of a new modification of the image content (32).

13. Process according to at least one of the previous claims,

characterized in that

the automatically preselected elements (60-70) are manually deleted and modified by the operator, whereby, especially, an area of interest from the represented object geometry—

such as a contour—

can be defined by the operator him/herself.

14. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

for identification of the relevant geometric structures (60-70) suitable for the measurement of the object (12), a comparison of the recorded geometric structures of the object geometry with at least one regular geometric element, such as a circle and/or a straight line, is performed, and characterized in that the geometric structures of the object geometry which show the least deviation in shape, relative to the regular geometric element, are marked.

15. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

the marking of the geometric structure suitable for the measurement of the object takes place in a manner whereby an image processing window (72, 74, 76, 78) is automatically adjusted to the marked geometric structure, such as a geometric element or contour.

16. Process according to claim 15,

characterized in that

an optimized adjustment takes place by means of a predetermined part tolerance.

17. Process according to claim 15 and/or 16,

characterized in that

the automatic adjustment is performed with respect to the direction and proportion of the marked geometric structure (64, 66).

18. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

out of the quantity of preselected geometric structures (60-70, 82, 84), the structure located closest to the middle of a represented image section (88) is automatically selected.

19. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

as a function of an object class to be measured and/or the mode of operation of the coordinate measuring device (10), strategies for the marking of the geometric structures (60-70) suitable for the measurement of the object (12) are selected and/or determined.

20. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

the strategies for the marking of the geometric structures (60-70) suitable for the measurement of the object (12) are dependent upon the type of object material, such as metal, plastic and the like.

21. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

the strategies for the marking of the geometric structures (60-70) suitable for the measurement of the object (12) are dependent upon a property of reflection of the surface of the object (12), such as, for example, light, dark, or similar.

22. Process according to at least one of the previous claims,

characterized in that

as a strategy for contour and feature extraction, image filters and/or contour filters, such as, for example, erosion, dilation, Sobel filters or contrast amplifiers are used.

23. Process for the measurement of an object geometry preferably according to claim 1,

characterized in that

in the course of an automatic sweep of several objects (12) of the same type, both an image processing algorithm and the image processing window (74, 76, 78) are allocated to an average value of the respective geometric structures.

24. Process for the measurement of a geometric structure, especially according to claim 1,

characterized in that

as a function of the geometric structures suitable for the measurement of the object, various processes such as scanning or point-by-point measurement are accessed for the purpose of evaluation of a shape, such as a circle, a straight line or similar, or for the purpose of evaluation of a dimension, such as diameter, distance, angle or similar.

25. Process for the measurement of a geometric structure, especially according to claim 1,

characterized in that

for the selection of the geometric structures, such as contours and/or geometric elements, available nominal files are used for comparison.

26. Process for the measurement of workpiece geometries by means of coordinate measuring devices with image processing sensors, especially according to claim 1,

characterized in that

image processing contours (108) are provided, within a pixel raster (106), with additional information with regard to subpixel coordinates within the pixel.

27. Process according to claim 26,

characterized in that

the contours (108) are described by so-called Freeman Chains and that corresponding subpixel bytes (114) are added to each byte of the Freeman Chain.

28. Process according to claim 26 or 27,

characterized in that

in image processing operations both the Freeman code and the subpixel information are processed.

29. Process according to at least one of the previous claims,