Apparatus for surface inspection of a workpiece arranged in a capture region

Abstract

The invention relates to an apparatus for surface inspection of a drilled hole wall (12) of a drilled hole arranged in a workpiece (2), comprising an image capturing device (3), the optical path (6) of which is directed onto a capture portion (5) of a capture region (1) via a probe head (4) that can be displaced relative to the capture region (1), wherein the probe head (4) can be displaced along a feed axis (13) and pivoted about the feed axis (13) by means of a drive apparatus in order to inspect the surface of the drilled hole wall (12) of the drilled hole, and comprising a main illumination device (7) and a secondary illumination device (8a, 8b), which illuminate the capture portion (5) from different illumination directions. In order to allow reliable automated detection of defects without requiring a complex structure, it is proposed that the optical path (9) of the main illumination device (7) runs collinearly with respect to the optical path (6) of the image capturing device (3) in the capture portion (5).

Description

[0001] Device for surface inspection of a workpiece arranged in a detection area

[0002] Technical area

[0003] The invention relates to a device for surface testing of a borehole wall of a borehole arranged in a workpiece, comprising an image capture device whose optical path is directed to a detection section of the detection section via a probe head that is displaceable relative to a detection area, wherein the probe head for surface testing of the borehole wall of the borehole is displaceable along a feed axis via a drive device and pivotable about the feed axis, and comprising a main illumination device and a secondary illumination device that illuminate the detection section from different illumination directions.

[0004] State of the art

[0005] A device for surface inspection of a workpiece is known from US6327374B1. For this purpose, an image capture device is directed at a workpiece to be inspected in the detection section of a detection area, wherein a probe head of the image capture device can be displaced relative to the detection area. In order to image defects of different nature in the detection section, these are alternately illuminated from different illumination directions. For this purpose, illumination devices are provided whose beam paths, running along their optical paths, impinge on the detection section at different angles of incidence. The resulting different shadows cast by any defects located in the detection section enable the imaging of different structures of the defects and thus their automated classification and evaluation by a computing unit.The disadvantage, however, is that during automated surface testing, intentionally introduced surface structures or other discolorations and residues are often incorrectly assessed as defects.

[0006] US6837595B2 discloses a device for surface inspection of a printed circuit board arranged in a detection area, using an image capture device. The device comprises several illumination devices that illuminate the printed circuit board from different illumination directions. DE102006059190A1 discloses a similar device for surface inspection of a wafer, wherein the optical path of the image capture device is collinear with the optical path of an illumination device.

[0007] US9134232B1 shows a device for surface testing of a borehole wall of a borehole arranged in a workpiece with a laser that is directed onto the point to be tested.

[0008] Description of the invention

[0009] The invention is therefore based on the object of proposing a device for surface testing which allows reliable automated detection of defect locations without requiring a complex structure.

[0010] The invention achieves this objective by having the optical path of the main illumination device in the detection section collinear with the optical path of the image capture device. Due to the inventive features, the image capture device can generate two images with different characteristics when illuminated alternately by the secondary illumination device and the main illumination device. When the secondary illumination device is activated, shadows and thus strong differences in brightness arise in the area of ​​three-dimensional surface structures. The shadows captured when the main illumination device is activated are negligibly small when imaged by the image capture unit due to the collinearity of their optical paths, so that the remaining differences in brightness are attributable in particular to the surface discolorations.It has also been found that intentionally introduced surface structures are significantly easier to detect when the main illumination device is activated. Due to the inventive collinearity of the optical paths from the image capture device and the main illumination device, the imaged geometry of the surface structure can be captured largely independently of shadows and thus evaluated much more reliably. Thus, according to the invention, at least two images are generated, with significant differences in the images indicating intentionally introduced surface structures or surface discolorations.

[0011] The relative movement between the probe head, from which the optical path of the image capture device emerges, can be achieved by moving the detection area past the stationary probe head in the opposite direction to the inspection direction. However, to enable surface inspection independent of the surface, a drive device can be provided that displaces the probe head in the inspection direction. In particular, the image capture device, the main illumination device, and the secondary illumination device can also be displaced together with the probe head. The drive device can, for example, be a linear drive, on whose support the probe head and preferably the image capture device, the main illumination device, and the secondary illumination device are mounted.Within the scope of the invention, the optical path of the image capture device refers to the path of the light beam that reaches the capture section from the capture section. The optical path can be deflected by mirrors. Within the scope of the invention, the optical path of the main illumination device and secondary illumination device refers to the path of the light beam emanating from the respective illumination device and reaching the capture section. This optical path can also be deflected by mirrors. For the inventive effect, it is therefore sufficient that the collinearity of the optical paths of the main illumination device and the image capture device exists only in the capture section. The optical paths can thus be deflected upstream of the capture section via any mirrors, as long as they run collinearly in the capture section, which enables a particularly simple design of the device.Particularly precise detection of intentionally introduced surface structures or surface discolorations by images created using the main illumination device is achieved when the optical path of the image capture device in the capture section is orthogonal to the capture area. The main illumination device and the secondary illumination device can be of identical design or have a common light source.

[0012] In order to be able to inspect large areas on the one hand and to enable a variable resolution of these areas in the inspection direction on the other, it is proposed that the image capture device comprise a line scan camera. This results in the advantage that the optical distortion only needs to be taken into account in one dimension and the resolution in the inspection direction of the image can be determined by the speed of the relative movement between the probe head and the detection area. The probe head can be formed by the field of view exit section of the line scan camera or by the line scan camera itself. In the sense of the invention, a line scan camera is understood to be a camera with image sensors whose pixels extend in a main direction, while only one or a small number of pixels are provided in the transverse direction.

[0013] An advantageous possibility for creating collinearity between the optical paths of the main illumination device and the image capture device, while simultaneously achieving a compact design of the device, is achieved if the optical paths of the image capture device and the main illumination device are aligned collinearly via a semi-transparent mirror in the capture section. In this way, the main illumination device can be arranged next to the image capture device. For example, the optical path of the image capture device in the capture section can be directed orthogonally toward the capture area in a transmitting manner through the semi-transparent mirror, while the optical path of the main illumination device, which originates next to the optical path of the image capture device, is deflected into the optical path of the image capture device via the semi-transparent mirror.

[0014] To enable comprehensive imaging of particularly irregular defects or surface structures and, in particular, to obtain sufficiently accurate depth information about them, a second secondary illumination device can be provided whose illumination direction differs from both the illumination direction of the first secondary illumination device and the main illumination device. In this context, the illumination direction is understood to be the direction in which the optical path of the respective illumination device strikes a workpiece in the detection section. The different illumination devices can generate images with differing shadows, from which depth information can be derived in a manner known to those skilled in the art.

[0015] In order to reliably obtain depth information with minimal computational effort, regardless of the surface geometry, it is proposed that the illumination directions of the secondary lighting devices be opposite each other with respect to the illumination direction of the main lighting device. On the one hand, illumination from two different, opposite spatial directions ensures that sufficient image information is available to reconstruct the depth information. On the other hand, the simplified geometric relationships can be used to accelerate the calculation, particularly when the illumination directions of the secondary lighting devices are arranged symmetrically. The secondary lighting devices opposite each other with respect to the illumination direction of the main lighting device can form a first pair of secondary lighting devices.For a further improved representation of the depth information, two pairs of secondary illumination devices can be provided, wherein the illumination directions of the secondary illumination devices of one pair of secondary illumination devices are offset by an angle relative to the illumination directions of the secondary illumination devices of the other pair of secondary illumination devices around the optical path of the image capture device in the capture section. The angle can preferably be 45°-90°, more preferably 70°-90°, in particular 80°-90°.

[0016] In principle, different surfaces can be inspected using the device. If the device is to be used to inspect cavities such as holes, for example drill holes, it is proposed that the probe head for surface inspection of a drill hole arranged in a workpiece can be displaced along a feed axis via a drive device and pivoted about the feed axis. Since the optical path of the image capture device runs through the probe head and is thus predetermined by it, this optical path is also displaced by displacing the probe head along the feed axis for insertion into the drill hole and by pivoting it about the feed axis, so that a two-dimensional image of the curved three-dimensional drill hole wall can be created by pivoting. For pivoting, in particular for rotation, the probe head can be arranged on a motor carrier.The probe head can comprise a housing in which the image capture device, the main illumination device, and the secondary illumination device are arranged. Thus, if the housing is relocated, the image capture device, the main illumination device, and the secondary illumination device are also relocated, eliminating the need to constantly readjust the illumination conditions to the moving capture section and enabling rapid imaging under different lighting conditions.

[0017] To create a particularly narrow device that can also be used for boreholes with small diameters, the probe head can have a deflecting mirror that deflects the optical path of the image acquisition device away from the feed axis. The optical path of the image acquisition device can therefore initially leave the image acquisition device parallel to the feed axis and thus parallel to the borehole axis and be directed radially toward the borehole wall via a mirror. In this way, the image acquisition device can be aligned in the direction of the feed axis, creating advantageous space requirements.

[0018] Focusing and alignment of the illumination devices is necessary, especially if the device is to be used for various boreholes with significantly different diameters. In particular, the optical paths of the main illumination device, the secondary illumination devices, and the image acquisition device should meet in the acquisition section at the surface to be inspected and not intersect before reaching the surface. Therefore, to be able to shift the intersection point of the optical paths, it is proposed that the probe head be displaceable transversely to the feed axis. This shifts the probe head from the feed axis, which runs collinearly with the borehole axis, so that with secondary illumination devices permanently connected to the probe head, the intersection point is also shifted and can thus be placed on the borehole wall.The normal distance between this intersection point and the probe head therefore does not change. At the same time, a stationary arrangement of the image acquisition device with the probe head enables a constant distance from the borehole wall, resulting not only in consistent illumination conditions but also in consistent imaging conditions. For this purpose, the components of the device can be arranged in a housing of the probe head. A simple displacement of the probe head transverse to the feed axis is achieved if it is mounted on a linear drive mounted on a rotary motor. The rotary motor specifies the pivoting movement around the feed axis, allowing the linear drive and probe head to be pivoted. The linear drive enables displacement of the probe head transverse to the feed axis.

[0019] A particularly compact and lightweight device, which can be used for boreholes of different diameters, results when the secondary illumination devices comprise light sources that can be moved relative to the probe head. In this way, the entire probe head does not have to be moved to move the intersection point of the optical paths of the image capture device and the secondary illumination device and can therefore remain in the feed axis so that the pivot axis of the probe head is the same as the feed axis. To move the light sources, both translational and rotational movements can be performed on the light sources. The light sources can be moved using linear drives, stepper motors, or flexure joints driven by actuators such as piezo elements. Here, too, the components, in particular the components for displacement, can be arranged in a housing with the light sources.

[0020] The device according to the invention can be used in a method for surface inspection of a workpiece arranged in a detection zone, wherein the image capture device creates a first image of the detection section when illuminated by the main illumination device and a second image of the detection section when illuminated by the secondary illumination device. From the images, a test point mask is generated, based on which parameters are determined for each test point from the first and second images, on the basis of which parameters the test point is evaluated. According to the invention, a test point mask taking both images into account is thus generated from at least two images with different characteristics, namely from the image with the main illumination device activated and the image with the secondary illumination device activated, which causes a more pronounced shadow.Using the inspection point mask, parameters for evaluation, such as roundness, depth, flank pitch, extension, area, etc., are then determined from the first and second images of the captured section for each inspection point to be examined. Based on the recorded parameters and specified tolerance limits, the respective inspection point can be assessed as a defect location or not. With multiple secondary illumination devices, the method according to the invention can be carried out taking multiple images into account. Since, on the one hand, only the inspection points specified by the inspection point mask are examined, and after the examination only parameters and no image data are processed, a large number of images can be examined with low resource consumption.

[0021] The inspection point mask can be generated, for example, by calculating differences between the preferably normalized brightness values ​​of the two images, pixel by pixel. All connected pixel groups in the inspection point mask for which the difference between the original pixels in the images lies above a predetermined threshold can then be viewed as inspection points. In a preferred embodiment, for this purpose, binarization can be performed in advance based on the threshold and / or morphological operators can be applied to the inspection point mask. When generating the inspection point mask, the individual images can be weighted differently. If, for example, the workpiece to be inspected is an object with an expected high level of surface discoloration, the weighting can be applied to the image with activated secondary illumination in order to reduce the number of inspection points.

[0022] To enable a precise evaluation of test points with different defect origins, it is proposed that the test points be assigned to a test point class depending on their parameters for evaluation. In this way, the test point can be assessed as an acceptable or unacceptable defect depending on class-specific limit values. For example, blowholes can have significantly different limit values ​​in terms of admissibility than scratches in the surface, so that certain recorded parameters justify a permissible defect for a blowhole, while they represent an exclusion criterion for a scratch, i.e. an unacceptable defect in the workpiece. The classification can be carried out using a classification and regression method based on test points from images of real, previously classified test points; for example, a random forest method can be used.

[0023] For particularly irregular defects or surface structures, it may be advantageous for the device to have an additional secondary illumination device whose illumination direction is symmetrical to the illumination direction of the other secondary illumination device with respect to the illumination direction of the main illumination device. In this way, the image capture device can generate images upon activation of either a main illumination device or a secondary illumination device, and those images generated under the illumination conditions of the symmetrically arranged secondary illumination devices can be combined to form a differential image before this differential image is further processed with other images to form the inspection point mask. Particularly advantageous differential images are obtained when the images are brightness-normalized in advance.

[0024] Brief description of the invention

[0025] The drawing shows an example of the subject matter of the invention.

[0026] Fig. 1 is a schematic side view of a first embodiment of the surface testing device according to the invention,

[0027] Fig. 2 is a schematic side view of a second embodiment of the device according to the invention for testing the surface of a borehole wall. Fig. 3 is a schematic cross-section of the second embodiment according to Fig.

[0028] Fig. 2 on an enlarged scale, with the main and secondary illumination devices focused on the borehole wall, Fig. 4 shows a cross-section of the second embodiment corresponding to Fig. 3, with the main and secondary illumination devices not focused on the borehole wall,

[0029] Fig. 5 is a schematic side view of a third embodiment of the device according to the invention for testing the surface of a borehole wall and

[0030] Fig. 6 shows a schematic cross section of a fourth embodiment of the device according to the invention for surface testing of a borehole wall.

[0031] Ways to implement the invention

[0032] A device for surface inspection of a workpiece 2 arranged in a detection area 1 has an image capture device 3. The detection area 1 is that area of ​​the workpiece 2 which can be imaged by the image capture device 3 through relative movement between the workpiece 2 and the image capture device 3. The relative movement R can be achieved by guiding the workpiece 2 along the image capture device 3 and / or by guiding a probe head 4 of the image capture device 3 along the workpiece 2, for example by a motorized slide guide or a robot arm. The image capture device 3, for example a line scan camera, thus does not image the entire detection area 1 at once, but rather a detection section 5 of the detection area 1 that can be displaced as a result of the relative movement R.The detection section 5 is defined by the optical path 6 of the image capture device 3, which runs over the probe head 4. The probe head 4 can, for example, be a movable optic of an image capture device 3, but in a simple case, it can also be a field of view exit section of a camera, so that the probe head 4 can be part of the camera itself, for example, a line scan camera. To illuminate the detection section 5 from different illumination directions, a main illumination device 7 and at least one secondary illumination device 8a, 8b are provided, which selectively illuminate the detection section 5 from different illumination directions. According to the invention, the optical path 9 of the main illumination device 7 in the detection section 5 runs collinearly with the optical path 6 of the image capture device 3.

[0033] Fig. 1 shows that the optical path 9 of the main illumination device 7 can be aligned collinearly with the optical path 6 of the image capture device 3 via a semi-transparent mirror 10. According to the invention, it is sufficient that the collinearity of the optical paths 6, 9 of the illumination device 3 and the main illumination device 7 is present in the capture section 5. Accordingly, it is sufficient if the optical paths 6, 9 of the illumination device 3 and the main illumination device 7 enter the capture section 5 at the same angle. The optical paths 11a, 11b of the secondary illumination devices 8a, 8b, on the other hand, are antiparallel to the optical paths 6, 9 of the illumination device 3 and the main illumination device 7, respectively. Preferably, the optical paths 6, 9 of the illumination device 3 and the main illumination device 7 are aligned orthogonally to the surface of the workpiece 2 to be inspected.

[0034] The secondary illumination device 8a, 8b can illuminate any test points in the detection section 5 from the side to obtain depth information. To obtain direction-independent depth information from test points, multiple secondary illumination devices 8a, 8b can be provided, illuminating the detection section from different illumination directions. For example, a second secondary illumination device 8b can be provided, the illumination direction of which differs from both the illumination direction of the first secondary illumination device 8a and the main illumination device 7. The illumination directions of the secondary illumination devices 8a, 8b are preferably opposite one another with respect to the illumination direction of the main illumination device in the detection section 5, since this allows sufficiently accurate depth information from inhomogeneous defect locations to be obtained.In an advantageous embodiment, the illumination directions of the secondary illumination devices 8a, 8b can be symmetrical with respect to the illumination directions of the main illumination device 7. The illumination directions of the illumination devices 7, 8a, 8b are determined by their optical paths 9, 11a, 11b.

[0035] For example, it can be seen from Figs. 2, 3 and 4 that for the surface inspection of a borehole wall 12, the image capture device 3, the secondary illumination devices 8a, 8b, the semi-transparent mirror 10 and the main illumination device 7 can be arranged in a probe head 4, which can thus form a housing. For this purpose, the probe head 4 can be displaced along a feed axis 13 via a drive device not shown in detail in Fig. 2 and can be pivoted or rotated about this feed axis 13. To manipulate the optical path 6 of the image capture device 3, the probe head 4 can have a deflection mirror 14, which deflects the optical path 6 from the feed axis 13 in the direction of the borehole wall 12.

[0036] By pivoting the probe head 4 around the feed axis 13, the curved borehole wall can be imaged two-dimensionally.

[0037] While the main and secondary illumination devices 7, 8a, 8b in Fig. 3 are focused on the borehole wall 12 and thus enable a high-quality image of the detection section 5, the focal point in Fig. 4 is no longer on the borehole wall 12 due to the larger diameter of the borehole.

[0038] There are several options for focusing. On the one hand, as indicated in Fig. 5, the probe head 4 can be displaced transversely to the feed axis 13, so that the focal point is displaced together with the probe head 4 relative to the borehole wall 12. This can be achieved by a drive device 15 comprising a motor 16 on which a linear drive 17 for the probe head 4 is arranged. The motor 16 pivots the linear drive 17 together with the probe head 4 about the feed axis 13, which is arranged collinearly with the borehole axis. The linear drive 17 displaces the probe head 4 transversely to the feed axis 13 via the linear drive 17.

[0039] On the other hand, as indicated in Fig. 6, the focusing can be achieved by the secondary illumination devices 8a, 8b light sources

[0040] 18a, 18b, which are displaceable relative to the probe head 4. In this way, the focus can be shifted from a smaller borehole (indicated by dash-dotted lines) to a larger borehole. For this purpose, the light sources 18a, 18b can be arranged displaceably, for example, on a linear drive 19. Alternatively or additionally, the direction of the optical paths 11a, 11b of the light sources 18a, 18b can be changed via rotary encoders.

Claims

Patent claims 1. Device for surface testing of a borehole wall (12) of a borehole arranged in a workpiece (2), with an image capturing device (3), the optical path (6) of which is directed to a Detection section (5) of the detection area (1 ), wherein the probe head (4) for surface testing of the borehole wall (12) of the borehole is displaceable along a feed axis (13) via a drive device and pivotable about the feed axis (13), and with a main illumination device (7) and a secondary illumination device (8a, 8b), which illuminate the detection section (5) from different Illuminate illumination directions, characterized in that the optical path (9) of the main illumination device (7) in the detection section (5) runs collinearly with the optical path (6) of the image detection device (3).

2. Device according to claim 1, characterized in that the image capture device (3) comprises a line scan camera.

3. Device according to claim 1 or 2, characterized in that the optical paths (6, 9) of the image capture device (3) and the main illumination device (7) are aligned collinearly via a semi-transparent mirror (10) in the capture section (5).

4. Device according to one of claims 1 to 3, characterized in that a second secondary lighting device (8b) is provided, the direction of illumination of which deviates from both the direction of illumination of the first secondary lighting device (8a) and the main lighting device (7).

5. Device according to claim 4, characterized in that the illumination directions of the secondary illumination devices (8a, 8b) are opposite one another with respect to the illumination direction of the main illumination device (7).

6. Device according to claim 1, characterized in that the probe head (4) has a deflecting mirror (14) which deflects the optical path (6) of the image capture device (3) from the feed axis (13).

7. Device according to claim 1 or 6, characterized in that the probe head is displaceable transversely to the feed axis (13).

8. Device according to claim 1, 6 or 7, characterized in that the secondary illumination devices comprise light sources which are displaceable relative to the probe head.

9. Method for surface testing of a workpiece (2) arranged in a detection area with a device according to one of claims 1 to 8, characterized in that the image detection device (3) makes a first image of the detection section (5) when illuminated by the main illumination device (7) and a second image of the detection section (5) when illuminated by the secondary illumination device (8a, 8b) and from the images a test point mask is generated, on the basis of which parameters are determined for each test point from the first and the second image, on the basis of which parameters the test point is evaluated.

Images