JP4418651B2 - Defect detection method and apparatus - Google Patents

Description

  The present invention relates to a defect detection method and apparatus for optically detecting a shape defect of a three-dimensional object to be measured such as a press-formed product.

  Conventionally, as disclosed in Patent Document 1, a lattice pattern is projected onto a measurement object, a lattice image deformed according to the height distribution of each part of the measurement object is photographed, and a moire method or a heterodyne method is used. There are known methods and apparatuses for optically measuring the three-dimensional shape of an object to be measured from this lattice image.

In the moire method, the height distribution is obtained by generating moire fringes that give contour lines of the height distribution of the object to be measured by superimposing a reference lattice on the deformed lattice image. In the heterodyne method, the reference grating is considered as an unmodulated spatial carrier frequency signal, the deformation grating image is regarded as a spatially phase-modulated carrier signal, and the amount of deformation is detected as the phase to detect the height distribution of the object to be measured. Looking for.
Japanese Patent Laid-Open No. 10-246612

  However, in these conventional methods and apparatuses, whether or not there is a defect in the object to be measured, for example, when the object to be measured is a press-molded product, foreign matter that has entered the surface between the mold and the material at the time of pressing. There is a problem that it cannot be easily determined from the measured values indicating the height distribution of each part of the object to be measured whether there is a defect such as a dent due to.

  An object of the present invention is to provide a defect detection method and apparatus capable of easily detecting a defect of an object to be measured.

In order to achieve this problem, the present invention has taken the following methods and means in order to solve the problem. That is,
A defect in the shape of the three-dimensional object to be measured is optically detected, and the object to be measured is a press-molded product, which is generated by a foreign matter that has entered between the mold and the material during press molding. In the defect detection method for detecting defects,
After projecting a lattice pattern on the object to be measured and photographing the lattice image, relatively moving the object to be measured, projecting the lattice pattern onto the object to be measured again, This is a defect detection method characterized in that the two lattice images are photographed and the two lattice images are overlapped to detect as a defect a location where the lattice appears thick due to a shift between the two lattice images.

In addition, optically detect the shape defect of the three-dimensional object to be measured, and the object to be measured is a press-molded product, which is caused by foreign matter that has entered between the mold and the material during press molding. In the defect detection apparatus for detecting the defect,
  Projecting means for projecting a lattice pattern onto the object to be measured;
  Photographing means for photographing a lattice image projected by the projection means;
  Moving means for relatively translating the object to be measured and the projecting means and the photographing means;
  Before and after the movement by the moving means, two lattice images obtained by photographing the lattice pattern projected by the projecting means are superimposed, and a place where the lattice appears thick due to the displacement of the two lattice images by the filtering process. Detection control means for detecting as a defect;
This is a defect detection apparatus characterized by comprising:

The moving means may be configured to move the object to be measured in parallel.

  As described above in detail, according to the defect detection method and apparatus of the present invention, it is possible to easily detect defects by relatively moving the object to be measured and superimposing the lattice images taken before and after the object. There is an effect.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
As shown in FIG. 1, reference numeral 1 denotes a defect detection device. The defect detection device 1 includes a light source 2, and light from the light source 2 is reflected by a mirror 4 and then irradiated to a lattice pattern 6. The lattice pattern 6 is projected onto the object to be measured 10 by the projection lens 8. In the present embodiment, the DUT 10 is a press-formed product formed by pressing, and is, for example, an automobile body.

  A lattice image of the lattice pattern 6 on the DUT 10 is imaged on the image sensor 14 by the imaging lens 12. Image data from the image sensor 14 is input to the image processing circuit 16. In the present embodiment, the imaging range by the image sensor 14 is 200 mm × 200 mm. The image processing circuit 16 optically measures the three-dimensional shape of the DUT 10 and has a resolution of about 10 μm in the optical axis direction connecting the imaging lens 12 and the image sensor 14.

  The DUT 10 is placed on the moving mechanism 18, and the moving mechanism 18 can move the DUT 10 in parallel. In the present embodiment, the optical axis connecting the imaging lens 12 and the image sensor 14 is arranged to be perpendicular to the object to be measured 10, and the moving mechanism 18 moves in a direction perpendicular to the optical axis. Is configured to do.

Next, the operation of the above-described defect detection apparatus of the present embodiment will be described with reference to the flowchart shown in FIG.
First, the grid pattern 6 is projected onto the object 10 via the projection lens 8 by the light from the light source 2 (step 100). The lattice pattern 6 becomes a lattice image deformed according to the three-dimensional shape of the DUT 10. This lattice image is taken by the image sensor 14 through the imaging lens 12 (step 110).

  As shown in FIG. 3A, a lattice image deformed according to the three-dimensional shape of the DUT 10 is obtained. When the object to be measured 10 is a defect, for example, when the object to be measured 10 is a press-molded product, a defect such as a dent due to a foreign substance that has entered between the mold and the material occurs during the pressing process. The lattice image is also deformed by this defect.

  After taking the lattice image, it is determined whether or not the image is taken for the second time (step 120). If it is not the second time, the DUT 10 is moved by the moving mechanism 18. The moving amount at this time may be about several mm, and may be determined according to the shape of the object to be measured 10, the size of the defect, etc.

  After moving the device under test 10, the processing in steps 100 to 120 is repeated again in the same manner as described above, and the image sensor 14 captures a lattice image in which the lattice pattern 6 projected onto the device under test 10 is deformed. As shown in FIG. 3B, the second lattice image is also deformed according to the defect, but the deformed position is the position corresponding to the amount of movement with respect to the first lattice image. Is off.

  Then, after photographing twice, a process of superimposing the first lattice image and the second lattice image described above is executed (step 140). As shown in FIG. 3C, the superimposed lattice image appears with the lattice shifted in a place where there is a defect. When this lattice image is filtered, as shown in FIG. 3 (d), the place with the defect becomes black, and it is easily understood that there is a defect.

  That is, when the object to be measured 10 has no defect, the first lattice image and the second lattice image almost overlap each other even if the measurement is performed by moving several millimeters. When the DUT 10 is an automobile body, the three-dimensional shape is a gently curved surface. When the moving amount of the device under test 10 is as small as several mm, even if the image is slightly shifted, the deformation of the lattice image is almost the same. When the first lattice image and the second lattice image are superimposed, overlap.

  On the other hand, when the object to be measured 10 has a defect, when a place where the object to be measured 10 is defective is photographed, the lattice image is deformed according to the defect. And if the to-be-measured object 10 is moved and it image | photographs again, the lattice image will also deform | transform according to a defect.

  When there is a defect such as a depression, the amount of deformation is larger than that of other gently curved surfaces, and a difference appears in the degree of lattice deformation between the first lattice image and the second lattice image. When the first lattice image and the second lattice image are superimposed, the lattice of the lattice image appears thick at a place where there is a defect. Thereby, it can be easily determined that the DUT 10 is defective.

In this way, it is possible to easily detect defects by superimposing lattice images taken before and after movement, and there is no need to prepare a master for measurement. Further, when the DUT 10 is a press-molded product, there is a difference due to variations in individual molded products, and defects cannot be easily detected even when compared with the master. As in the present embodiment, the defect can be easily detected by moving the DUT 10 and superimposing the lattice images taken before and after.

  In addition, when the area of the device under test 10 is large, the device under test 10 may be moved and detection may be performed at that location. Alternatively, a wide range may be detected using a plurality of defect detection devices. Further, when a defect is detected, a mark may be attached to the defective portion by an ink jet print head or the like.

  The present invention is not limited to such embodiments as described above, and can be implemented in various modes without departing from the gist of the present invention.

It is a schematic block diagram of the defect detection apparatus as one Embodiment of this invention. It is a flowchart which shows an example of the detection control process performed in the image processing circuit of this embodiment. It is explanatory drawing of the lattice image before and behind the movement of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Defect detection apparatus 2 ... Light source 4 ... Mirror 6 ... Lattice pattern 8 ... Projection lens 10 ... Object 12 ... Imaging lens 14 ... Image sensor 16 ... Image processing circuit 18 ... Moving mechanism

Claims (3)

A defect in the shape of the three-dimensional object to be measured is optically detected, and the object to be measured is a press-molded product, which is generated by a foreign matter that has entered between the mold and the material during press molding. In the defect detection method for detecting defects,
After projecting a lattice pattern on the object to be measured and photographing the lattice image, relatively moving the object to be measured, projecting the lattice pattern onto the object to be measured again, A defect detection method comprising: photographing, superimposing the two lattice images, and detecting as a defect a place where the lattice appears thick due to a shift between the two lattice images. A defect in the shape of the three-dimensional object to be measured is optically detected, and the object to be measured is a press-molded product, which is generated by a foreign matter that has entered between the mold and the material during press molding. In a defect detection device for detecting defects,
Projecting means for projecting a lattice pattern onto the object to be measured;
Photographing means for photographing a lattice image projected by the projection means;
Moving means for relatively translating the object to be measured and the projecting means and the photographing means;
Before and after the movement by the moving means, two lattice images obtained by photographing the lattice pattern projected by the projecting means are superimposed, and a place where the lattice appears thick due to the displacement of the two lattice images by the filtering process. Detection control means for detecting as a defect ;
A defect detection apparatus comprising: 3. The defect detection apparatus according to claim 2 , wherein the moving means moves the object to be measured in parallel.

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