WO2004003833A2

WO2004003833A2 - Method and device for examining the precision of the shape of objects

Info

Publication number: WO2004003833A2
Application number: PCT/DE2003/002148
Authority: WO
Inventors: Peter Müller
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-06-27
Filing date: 2003-06-27
Publication date: 2004-01-08
Also published as: WO2004003833A3; DE10228901A1

Abstract

The invention relates to a method for examining the precision of the shape of an object (1'), wherein the object (1') which is to be examined is compared to a reference element (2). Said method is characterised in that a scatter band (2) forming the reference element (2) is formed around the contour (1a, 1b) of a reference object (1), and the contour (1a, 1b) of the object (1) which is to be examined is compared to the scatter band. The invention also relates to a device for carrying out the above-mentioned method, comprising an image capture device (4) for detection of the contour (1a, 1b) of an object which is to be examined (1'). Said device is characterised in that a memory (5) is provided for storing a scatter band (2) surrounding the contour (1a, 1b), and a first comparison device (6) which examines the contour (1a, 1b) of the object (1') which is to be examined to see if it is located in the scatter band (2).

Description

description

Method and device for checking the shape accuracy of objects

The invention relates to a method according to the preamble of claim 1 for checking the shape accuracy of an object, in which the object to be checked is compared with a reference element. Furthermore, the invention relates to a device according to the preamble of claim 6, for carrying out the above-mentioned method, with an image recording device for detecting the contour of an object to be checked.

The optical search, position determination, classification and testing of objects, which are summarized below under the term checking the shape accuracy of an object, are frequently recurring tasks in automation technology, especially in industrial image evaluation. In this context, classification means making a decision as to whether or not an object recorded in an image section is a specific object.

This classification is usually carried out by comparing the object image data with the image data of a previously recorded reference object. When checking an object, for example, the dimensional accuracy or completeness of the object to be checked is determined in comparison to the reference object and monitored to ensure that maximum permissible deviations are not exceeded.

For the quantification of a deviation, for example, an area-wide error measure can be used, which, for example, has a value range between 0 and 1 as a normalized, scalar value, with 0 for no excess attunement and 1 stand for an ideal match between the object to be checked and the reference object.

As such an error measure, e.g. B. a correlation coefficient, which is calculated by a two-dimensional correlation of the object image data with the image data of the reference object, or serve the normalized pixel distance, which is obtained by direct comparison of the image data of corresponding pixels. The calculation of the pixel distance is often referred to as pattern matching. The normalized sum of the amounts of the differences between the data values of mutually corresponding pixels in the object and sample image is calculated.

The disadvantage of such an error measure calculated over the entire object area lies in its low informative value with regard to local errors. An error caused, for example, exclusively by signal noise, which is distributed over the entire object image, can hardly be distinguished from a smaller, local defect.

This disadvantage will be explained using an example: an object has a size of 100 x 100 pixels in the captured image, so it contains 10,000 pixels, also called pixels. Even if the sample object is resubmitted, signal noise and deviations due to the discrete-location scanning lead to an integral error of approximately 2 to 5% during image recording. This corresponds to 200 to 500 pixels, at which the values in the image data deviate completely from one another if one assumes that the values for the other pixels agree. The result of this is that a local error with an areal extension of up to approximately 200 pixels cannot be detected with certainty, since a corresponding error measure can already be achieved by the above-mentioned error sources. It is the object of the invention to design a method and a device mentioned at the outset such that small local deviations in the contour of an object to be checked from a reference object can be reliably determined.

The solution to this problem results from the features of the characterizing part of claim 1. Advantageous further developments of the invention result from the subclaims.

According to the invention, a method for checking the shape accuracy of an object, in which the object to be checked is compared with a reference element, is characterized in that a scattering area forming the reference element is formed around the contour of a reference object and the contour of the object to be checked is compared with the Spreading range is compared.

Furthermore, according to the invention, a device for carrying out a method according to one of the preceding claims, with an image recording device for detecting the contour of an object to be checked, characterized in that a memory is available for storing a scattering area surrounding the contour, and a first one Comparison device, by means of which the contour of the object to be checked is checked to determine whether it is in the scattering area.

Because a scattering area is formed around the contour of a reference object and the contour of the one to be checked

Object is compared with the scattering area, deviations of the contour of the object to be checked from the contour of the reference element can be detected in an advantageous manner, which are larger than the deviations defined by the scattering area. Deviations that occur within the

Scatter range are ignored, since the contour of the object to be checked is within the permissible tolerance ranzbereich located. It can thus be recognized for an object to be checked whether its contour is outside the permissible tolerance range, even if this exceeding occurs only in a small partial area of the overall contour.

For example, a single deviation can also be recognized, which is locally restricted but is outside the scattering range. If the remaining contour of the object to be checked has only very slight deviations from the contour of the reference object, such a deviation would not be recognized with the previous method, since the total deviation, i. H. the integral of all deviations, is within the allowable tolerance. However, such deviations can be reliably recognized by the method according to the invention, since they are determined independently of the sum of all deviations.

In a special embodiment of the invention it is provided that the scattering area is formed by the contour of a predetermined number of objects being detected. By detecting the contours of a predetermined number of objects, the deviations of the contours from one another form the scattering range. It goes without saying that the contours are only detected by objects that are within a permissible tolerance range, i. H. were found to be good in a quality inspection. The number of objects to be detected depends on the nature of the contour and the tolerances that occur. Experience has shown that it is usually sufficient to measure the contour of around ten to twenty objects.

In a further particular embodiment, it is provided that ascertained deviations are compared with a tolerance measure. This makes it possible to sum up the areas of the deviations lying outside the scatter range. and compare with a scalar value. Although the comparison is essentially the same as in the prior art, it cannot be overlooked that the value to be compared only relates to such deviations that lie outside the range. I.e. , Very high demands can be placed on the value to be compared, since this value does not contain permissible deviations.

It is particularly advantageous if the scattering area is divided into partial areas and the contour of the object to be checked is compared in partial areas. With such an embodiment it is possible to evaluate the deviations locally differently. In particular, it is possible to weight the deviations of the partial areas, as is provided for in a further special embodiment. For example, critical areas of the contour can be taken into account with a multiple of the weight, such as less critical areas.

As has already been mentioned, a device according to the invention is characterized in that there is a memory for storing a scattering area surrounding the contour, and a first comparison device, by means of which the contour of the object to be checked is checked to determine whether it is located in the scattering area ,

Because the device according to the invention has a memory for storing a scattering area surrounding the contour, the contours of objects to be checked can be checked in a simple manner by means of the first comparison device to determine whether they are located within the scattering area.

An embodiment of the invention is particularly advantageous in which there is a scattering area former in which the contours of a predetermined number of objects can be entered and which due to the tolerances of the contours Spreading area forms. It is hereby possible for the contours of a predetermined number of objects to be recorded in the same way as the contours of objects to be checked and for the corresponding data to be entered into the scattering area generator. The spreading area former then forms the spreading area from the deviations of the contours from one another. This means that it is not necessary to calculate the scattering range separately and to enter it in the memory, as this could also happen.

In a further special embodiment of the invention, it is provided that a second comparison device is provided, by means of which the sum of the elements located outside the scattering range is compared with a tolerance value. This makes it easy to distinguish between the objects to be checked in good and bad. The quality level can be changed easily by changing the tolerance value.

An embodiment of the invention is particularly advantageous in which there is a partial area former, by means of which the scattering area is divided into partial areas, and the first comparison device performs the contour of the object to be checked in partial areas. In this way, the contour of the object to be checked can be divided into critical and non-critical areas, for example. The deviations in the critical areas could then be subject to higher requirements than the deviations in the non-critical areas. In particular, it is possible that the partial areas are weighted differently, as is provided in a further special embodiment of the invention.

Further details, features and advantages of the present invention result from the following description of a particular exemplary embodiment with reference to the drawing. Show it:

FIG. 1 a reference object,

2 shows the reference object shown in FIG. 1 with a scattering area surrounding its contour, FIG. 3 shows the scattering area shown in FIG. 2 without a reference object, FIG. 4 shows the scattering area shown in FIG. 3 with the contour of an object to be checked, which is partially outside the scattering area 5 shows a schematic arrangement of a device according to the invention.

As can be seen in FIG. 1, a reference object 1 has an outer contour 1 a and an inner contour 1 b, the inner contour 1 b enclosing an opening. Due to manufacturing tolerances, the contours of actually manufactured objects deviate from the contours la, lb of the reference object 1. So far, these deviations have been summed up and compared with a threshold value. If the sum of the deviations exceeded the threshold, the objects were classified as bad; if the sum of the deviations was below the threshold, the objects were classified as good.

In the same way that objects with small deviations are produced, objects are also produced whose contours exactly match the contours la, lb of the reference object 1. If such objects locally show a deviation due to a manufacturing defect that is no longer tolerable, it may still be that the area of this deviation lies below the threshold value; because the object shows no further deviations apart from the local deviation. This would classify the property as good.

As can be seen in FIG. 2, a scattering region 2 is formed around the contours la, lb of the reference object 1 in accordance with the method according to the invention. The spreading area 2 is like this dimensioned such that all objects which have contours la, lb located within the scattering area 2 can be classified as good. Although the scattering area is also regularly designed such that the contours la, lb of the reference object 1 run in the middle of the scattering area 2, it may still be necessary for the scattering area 2 to be arranged at least partially asymmetrically to the contour, as shown in FIG top right corner of Figure 2 is shown.

As can be seen in FIG. 3, the scattering area 2 can be subdivided into partial areas 2a, 2b, 2c. A different weight can be assigned to the individual sub-areas 2a, 2b, 2c. In this way, deviations from the contour of the reference object, which lie outside the scattering area 2, can be assessed to different degrees in the partial areas 2a, 2b, 2c.

As can be seen in FIG. 4, the contour la ', lb' of an object 1 'to be checked is outside the partial area 2a of the scattering area 2, as a result of which the object 1' to be checked is to be classified as poor. The element 3 of the object 1 'to be checked, which is located outside the partial area 2a, is the only deviation which the object 1' to be checked has from the reference object 1. The sum of all deviations of the object 1 'to be checked from the reference object 1 is therefore relatively small and would, according to the conventional method, result in the object 1' to be checked being classified as good. By means of the method according to the invention, however, this deviation is reliably detected, as a result of which the object 1 'to be checked is classified as bad.

If the area of the contour 1 a 'of the object 1' to be checked, in which the element 3 located outside the scattering area 2 is located, is critical, the corresponding partial area 2a of the scattering area 2 can, for example, use the factor ten are weighted. As a result, deviations in this area are included in the overall assessment of the object 1 'to be checked ten times as strongly as deviations lying outside the partial area 2a.

As can be seen in FIG. 5, a device for carrying out the method according to the invention has an image recording device 4, by means of which the contours of objects 1, 1 'can be recorded. The image recording device 4 is constructed in a conventional manner and essentially consists of an objective and a CCD sensor, on which the objects 1, 1 'are imaged with the aid of the objective.

The image recording device 4 is connected to a controller 10, by means of which the CCD sensor delivers image signals corresponding to the recorded image to a scattering area generator 8. The contours of a predetermined number of objects having typical tolerances and well classified are compared with one another in the scattering region generator 8. The spreading area generator 8 forms the spreading area 2 from the area covered by the contours.

The data of the mask formed in this way in the scattering region generator 8 are input into a memory 5. The dates of the

However, the mask, ie the scattering area 2, can also be entered directly into the memory 5 by the controller 10. For this purpose, the contour 1 a, 1 b of a reference element 1 could be acquired via the image recording device 4 and a scattering area belonging to the contour could be calculated by the controller 10. Instead of detecting the contour 1a, 1b of a reference element 1, the contour data or the data of the scattering area 2 could also be entered in another way in the controller 10, which then forwards it to the memory 5. The memory 5 is connected to a partial area former 9, which divides the scattering area 2 into partial areas 2a, 2b, 2c. In the partial area generator 9, the partial areas 2a, 2b, 2c are weighted in accordance with weighting signals 9a, 9b, 9c applied to the partial area former 9.

The data of the weighted partial areas 2a, 2b, 2c are applied to a first comparison device 6, to which the control 10 also applies image data of objects 1 'to be checked, which are detected by means of the image recording device 4. In the comparison device 6, the image data of the object 1 'to be checked, which is created by the controller 10, is compared with the data of the weighted partial areas 2a, 2b, 2c.

The sum of the deviations resulting from the comparison is applied to a second comparison device 7. In the second comparison device 7, the sum of the deviations is compared with a tolerance value 7a. If the sum of the deviations is smaller than the tolerance value 7a, the second comparison device 7 emits a signal at its output 7b which classifies the object 1 'to be checked as good; If the sum of the deviations is greater than the tolerance signal 7a, the second comparison device 7 emits a signal at its output 7b which classifies the object 1 'to be checked as bad.

Claims

claims

1. A method for checking the shape accuracy of an object (1 '), in which the object (1') to be checked is compared with a reference element (2), characterized in that around the contour (la, lb) of a reference object (1) a scattering area (2) forming the reference element (2) is formed and the contour (la, lb) of the object (1 ') to be checked is compared with the scattering area (2).

2. The method according to claim 1, characterized in that the scattering area (2) is formed in that the contour (la, lb) of a predetermined number of objects (1; 1 ') is detected.

3. The method according to claim 1 or 2, characterized in that ascertained deviations are compared with a tolerance measure (7a).

4. The method according to any one of claims 1 to 3, characterized in that the scattering area (2) is divided into partial areas (2a, 2b, 2c) and the comparison of the contour (la, lb) of the object to be checked (1; 1 ' ) in some areas.

5. The method according to claim 4, characterized in that the deviations of the partial areas (2a, 2b, 2c) are weighted differently.

6. Device for carrying out a method according to one of the preceding claims, with an image recording device (4) for detecting the contour (la, lb) of an object to be checked (1; 1 '), characterized in that a memory (5) is present , for storing a scatter region (2) surrounding the contour (la, lb), and a first comparison device (6), by means of which the contour (la, lb) of the object to be checked (1; 1 ') is checked to see whether it is in the scattering area (2).

7. The device according to claim 6, characterized in that a scattering area former (8) is provided, in which the contours (la, lb) of a predetermined number of objects (1) can be entered and which due to the tolerances of the contours (la, lb) forms the scattering area (2).

8. The device according to claim 6 or 7, characterized in that a second comparison device (7) is present, by means of which the sum of the elements (3) located outside the scattering area (2) is compared with a tolerance value (7a).

9. Device according to one of claims 6 to 8, characterized in that a partial area former (9) is provided, by means of which the scattering area (2) is divided into partial areas (2a, 2b, 2c), and the first comparison device (6 ) performs the contour (la, lb) of the object to be checked (1; 1 ') in some areas.

10. The device according to claim 9, characterized in that the partial areas (2a, 2b, 2c) are weighted differently.