OPTICAL TESTING DEVICE

Description

[0001] The invention relates to an optical testing device for testing flat test objects.

[0002] When inspecting flat test objects, the object is often only scanned and measured from one side using an optical inspection device. Profile projectors, for example, can be used to capture the object's bilateral shape and position. Twists caused by the manufacturing process are of minor importance in this case.

[0003] If the test object has a precise and tightly toleranced surface topography that is to be captured using a 3D measuring system, twisting of the test object plays a significant role. Magnetic or vacuum-assisted fixtures can be used to hold the test object in a measurement plane during the test. After capturing or measuring one side of the test object, it must be repositioned to capture or measure the other side. This is time-consuming and leads to a significant decrease in measurement accuracy.

[0004] DE 10 2015 205 461 A1 discloses a correction device for an optical measuring instrument in which a light-transmitting scale is arranged in the measuring beam path.

[0005] Further testing and measuring devices are known from US 2015 / 192404 A1, US 2018 / 364028 A1, JP 4 132736 B2, US 2014 / 193064 A1, WO 2013 / 182960 A1 and DE 10 2017 124978 A1.

[0006] The invention is based on the objective of providing an optical testing device for testing flat test objects, which enables fast and reliable testing with high measurement accuracy.

[0007] This problem is solved by the features of the independent claim. The dependent claims contain advantageous embodiments of the invention.

[0008] The invention provides an optical testing device for inspecting flat test objects, which includes a holder for the test object. According to the invention, the testing device has two optical sensors for detecting the three-dimensional surface topography of the test object. According to the invention, the holder is designed, at least partially, as a test standard and is arranged relative to the sensors such that the sensors probe the test object from opposite sides and, when detecting the test object, also detect the holder as a test standard, at least partially.

[0009] The basic idea of ​​the invention is to geometrically capture the front and back surfaces of a flat test object in a single measurement process and to design the holder, at least in sections, as a test standard that is also captured when the surfaces of the component are measured. The geometry of the test standard is precisely defined or previously known, so that the geometry of the test standard captured during the measurement serves as a reference for the measurement.

[0010] The reference provided by the test standard allows, on the one hand, the sensor readings representing opposite sides of the test object to be compared to each other. On the other hand, alignment errors of the sensors relative to each other can be compensated for.

[0011] For example, and in particular, the holder can be frame-like with a window-like recess and have a support structure, for example in the form of tabs spaced apart from each other along the circumference of the recess, onto which the test object is placed.

[0012] During the test, the three-dimensional topography of the test object's surface is captured by optical sensors probing both sides of the object. According to the invention, the surface of the holder, which serves as the test standard, is also captured, at least partially, so that the test object's position in three-dimensional space is unambiguously determined. Prior mechanical or computational alignment of the test object is therefore unnecessary.

[0013] In this way, the testing of corresponding test objects is simplified and the measurement accuracy in determining the three-dimensional topography of the surface of the test object is increased.

[0014] A particular advantage of the invention is that both sides of the test object are simultaneously measured and the position of the test object is not changed during the testing process. This significantly increases the testing speed and avoids measurement inaccuracies that can occur when the position of the test object has to be changed during the test, for example by repositioning it.

[0015] By designing and using the existing holder for the test object as a test standard, the invention results in a relatively simple design of the test device.

[0016] An advantageous embodiment of the invention provides that the holder is designed as a frame. The test object held in the frame is optically accessible from both sides and can thus be probed by the sensors.

[0017] Depending on the specific requirements and circumstances, the design of the frame can be selected within broad limits. One advantageous embodiment provides for a circumferentially closed frame with a window-like recess. In this embodiment, the circumferentially closed frame ensures high mechanical stability of the mount, while the recess allows optical access to both surfaces of the test object, enabling them to be probed by the sensors.

[0018] Another advantageous embodiment of the invention provides that the frame has a support structure onto which the test object can be loosely placed. In this embodiment, the test object is placed loosely onto the support structure of the holder in a particularly simple manner.

[0019] The support structure can be designed in a variety of ways, depending on the specific requirements and circumstances, and can, for example, consist of a transparent material. The support structure can also be thread-like and span the recess in the holder.

[0020] A further development of the invention provides that the support structure has spaced-apart lugs in the circumferential direction of the frame. It is sufficient and desirable for the sake of static determinacy if three lugs spaced apart in the circumferential direction of the frame or the recess in the frame are provided.

[0021] Depending on the specific requirements and circumstances, the holder can be designed in a variety of ways. For a particularly simple design, an advantageous refinement involves the holder being configured as a plane-parallel plate. The plate's thickness and the size of the recess are adapted to the specific test object or family of test objects. The plate material can be selected according to the application, for example, aluminum for measurement tasks requiring relatively low accuracy and Zerodur for measurement tasks requiring high accuracy.

[0022] Another advantageous embodiment of the invention provides that the holder is coated, at least in sections. The coating allows for the creation of a desired or required surface finish in surface areas of the holder that serve as test normal surfaces for the test standard, in accordance with the requirements of the optical sensors used. However, this can also be achieved through mechanical processing methods.

[0023] Depending on the specific requirements and circumstances, different optical sensors can be used, with the sensor selection depending, for example, on the surface properties of the test object, its aspect ratio, the required cycle time, and the tolerances of the object being measured. Regarding the sensor design, an advantageous embodiment of the invention provides that at least one optical sensor is designed and configured for the area-wide detection of the test object. Due to the area-wide detection of the test object, relative movement between the holder and the sensors is not required during the testing process. For example, area-wide white light sensors or holographic sensors can be used for area-wide detection of the test object.

[0024] Another advantageous embodiment of the invention, with regard to the selection of sensors, provides that at least one optical sensor is designed and configured for line-wise detection of the test object, wherein a feed device is provided for relative movement of the holder relative to the sensors, such that the test object is scanned by the sensor during the feed. Suitable sensors can include, for example, laser triangulation sensors or photogrammetric sensors.

[0025] Moreover, suitable optical sensors are generally known to experts and are therefore not explained in more detail here.

[0026] According to the invention, two sensors are generally sufficient for the simultaneous detection of both sides of the test object during testing, each of which is assigned to one side of the test object. However, depending on the specific requirements and circumstances, two or more sensors can also be assigned to each side of the test object.

[0027] Provided that both sides of the test object have the same or similar surface properties and, accordingly, the measurement task for the sensors is the same or similar, the sensors of the test device according to the invention can be identical in construction. However, for test objects with different surface properties on the two sides, different sensors can also be used.

[0028] The invention provides that the holder comprises two preferably plate-like components, each with a window-like recess for receiving the test object in a reference plane. The surfaces facing each other are designed as test standard surfaces. The components are connected to one another in the reference plane in such a way that the test standard surfaces of one component can be detected or are detected by one of the sensors through the recess in the other component. In this embodiment, it is sufficient to machine only the contact surfaces of the components of the holder to a very flat finish. At the same time, the measurement accuracy is increased by reducing the influence of deviations in the geometry of the test standard on the measurement result.

[0029] Another advantageous embodiment of the testing device according to the invention provides that the holder is equipped on at least one test surface with surface features detectable by at least one sensor. The corresponding surface features can, for example, form a scale by which the feed movement of a feed device can be precisely measured. Such a scale can also be used to detect imperfections in the sensors used and to take these into account when evaluating the test result.

[0030] Claim 11 specifies a method according to the invention for testing flat test objects, in which a test device according to the invention is used.

[0031] The test object can in particular be a bipolar plate of a fuel cell or a battery foil, as provided for in advantageous further developments of the method according to the invention.

[0032] The invention is explained in more detail below with reference to the accompanying, highly schematic drawing and exemplary embodiments. It is evident to those skilled in the art that each individual feature of an exemplary embodiment further develops that embodiment independently of the other features. The subject matter and disclosure of this application also include combinations of features of the apparatus claims with features of the method claims. Furthermore, the subject matter and disclosure of this application include combinations of features of one exemplary embodiment with features of another. Likewise, the subject matter and disclosure of this application include subcombinations of the claims in which at least one feature of a claim is omitted or replaced by another feature.

[0033] It shows: Fig. 1 shows a highly schematic and perspective view of a first embodiment of an optical testing device according to the invention, Fig. 2 shows a schematic side view of the testing device according to the invention. Fig. 1 during a test procedure, Fig. 3 shows a schematic side view of a holder of a second embodiment of a test device according to the invention, and Fig. 4 shows the holder according to Fig. 3 in a top view.

[0034] The following will refer to Fig. 1 bis Fig. 4 Exemplary embodiments of a test device according to the invention are explained in more detail.

[0035] In Fig. 1 Figure 1 shows a first embodiment of an optical testing device 2 according to the invention for testing flat test objects, which has a holder 4 for a test object 6, which in this embodiment is formed by a bipolar plate of a fuel cell.

[0036] According to the invention, the test device 2 has two optical sensors 8, 10 for detecting the three-dimensional surface topography of the test object 6. The sensors 8, 10 are arranged facing each other with respect to their measuring direction, so that they probe the test object 6 from its two opposite sides.

[0037] According to the invention, the holder 4 is designed at least partially as a test standard and is arranged relative to the sensors 8, 10 in such a way that the sensors 8, 10 probe the test object 6 from opposite sides and the holder 4 is also detected as a test standard when the test object 6 is detected.

[0038] In the illustrated embodiment, the bracket 4 consists of a plane-parallel plate and is designed as a frame 12. As shown Fig. 1 As can be seen, in the illustrated embodiment, the frame is designed as a circumferentially closed frame with a central window-like recess 14. The frame 14 has a support structure at its recess, onto which the test object 6 is loosely placed. The support structure can, for example, have spaced-apart lugs around the circumference of the frame.

[0039] As from Fig. 1 As can be seen, the arrangement of the holder 4 and the sensors 8, 10 relative to each other is such that when the test object 6 is detected by the sensors 8, 10, the frame 12 is also detected, at least partially. By including the frame as a test standard, the position of the test object 6 in space is uniquely defined, so that the measured values ​​of the sensors 8, 10 can be related to each other without the need for prior mechanical or computational alignment of the test object.

[0040] In the illustrated embodiment, sensors 8 and 10 are identical in design and configured for line-wise detection of the test object. To scan the test object 6, the holder 4 is moved in the X-direction by a feed mechanism. The design of such a feed mechanism is generally known to those skilled in the art and is therefore not explained in detail here. For the sake of simplicity, the feed mechanism is also not shown in the drawing.

[0041] Suitable sensors are generally known to experts and are therefore not explained in detail here.

[0042] The holder 4 is finely machined at least in the areas that are also captured during the capture of the surface of the test object 6 and thus form test standard surfaces, so that the geometry of the holder is precisely determined and known at least in these areas, so that the holder 4 functions as a test standard or measurement standard according to the invention.

[0043] The measured values ​​obtained during the scanning of the test object 6 by the sensors 8, 10 are evaluated by an evaluation device that is in data transmission connection with the sensors 8, 10, so that at the end of the test process the actual geometry of the test object 6 is available as the test result or measurement result.

[0044] Because, according to the invention, a geometric inspection of the test object is possible without prior mechanical or computational alignment, the inspection of test objects is quick and easy.

[0045] Since it is not necessary to change the position of the test object 6 to test both sides of the test object 6, measurement uncertainties are avoided and the measurement accuracy is improved.

[0046] Fig. 2 shows in a side view the embodiment according to Fig. 1 , wherein the measuring or probing direction of the sensors 8, 10 is ideally perpendicular to a measuring plane in which the test object 6 is held on the holder 4. In Fig. 1 The exaggerated reading indicates an alignment error of sensor 8 due to tilting relative to the measuring plane.

[0047] The alignment error can be corrected after measurement as follows: Sensor 8 acquires measured values ​​of the surface of the top of the test object 6 in a first sensor coordinate system SKS1. From the measured values ​​of the top of the holder 4 as the test standard, a plane is calculated in the evaluation unit, and a coordinate transformation of the measured values ​​of the surface of the test object 6 is performed using the normal vector of this plane. By evaluating previously selected features of the top, for example, an edge, the plane in the first sensor coordinate system SKS1 is rotated around the normal vector VN1 into the coordinate system of the test object 6 (workpiece coordinate system WKS). Thus, the measured values ​​of the top of the test object 6 are available in the workpiece coordinate system.

[0048] In a corresponding manner, sensor 10 acquires measured values ​​from the surface of the underside of the holder 4. From these values, a plane is calculated, and a coordinate transformation of the measured values ​​of the surface of the test object 6 is performed using the normal vector of this plane. Similarly, for sensor 8, a plane is calculated by selecting previously chosen features of the underside, for example, an edge. The plane of the sensor coordinate system SKS2 is then rotated into the workpiece coordinate system WKS around the normal vector of this plane. Subsequently, the measured values ​​can be transformed into the workpiece coordinate system.

[0049] As a result, the top and bottom surfaces of the test object 6 are recorded in a common coordinate system and can therefore be subjected to further evaluation.

[0050] Alternatively, a correction can be performed during the measurement in the Y / Z plane. In this case, a direct reference to the reference plane is established for each measurement line xi, thus compensating for path inaccuracies in the Z direction during movement in the X direction. A deviation of the path in the Y direction can be detected by evaluating, for example, an edge of the support 4 and compensated accordingly.

[0051] If necessary or desired, the data obtained by sensors 8, 10 can be processed as images to perform image processing, for example to carry out artifact detection in a grayscale image.

[0052] In Fig. 3 A second embodiment of a test device 2 according to the invention is shown, which differs from the first embodiment in the design of the holder 4.

[0053] In the second embodiment, the holder 4 comprises two plate-like, rectangular components 4', 4" designed as identical parts, each with a window-like rectangular recess 14, 14" for receiving the test object 6 in a reference plane. The surfaces facing each other are designed as test normal surfaces. The components 4', 4" are connected to each other in the reference plane in such a way that the test normal surfaces of one component 4' or 4" can be detected or are detected by one of the sensors 8, 10 through the recess 14" or 14' in the other component 4" or 4'.

[0054] As from Fig. 4As can be seen, the offset of the individual parts 14', 14" and the design of the contact surfaces between them create two test normal surfaces. These surfaces are visible from both sides (top and bottom) and can be detected by the sensors 8, 10. Both surfaces lie in the same plane, thus defining a zero plane, so that measurement errors due to parallelism tolerances and thickness variations of the holder 4 are avoided. This reliably prevents deviations of the geometry of the holder 4, which serves as the test normal, from the specified or desired geometry from influencing the measurement result.

Claims

1. Optical testing device (2) for testing flat test objects (6), having a holder (4) for the test object (6), having at least two optical sensors (8, 10) for detecting the three-dimensional surface topography of the test object (6), wherein the holder (4) is formed at least in sections as a test standard and is arranged relative to the sensors (8, 10) in such a way that the sensors (8, 10) touch the test object (6) from opposite sides and, when the test object (6) is detected, also detect the holder (4) as a test standard at least in sections, and having an evaluation device which is connected to the sensors (8, 10) and evaluates the actual geometry of the test object (6), wherein the geometry of the test standard is known in advance and wherein, by means of the reference provided as a test standard, the measured values of the sensors (8, 10) which represent the opposite sides of the test object (6) are related to one another; characterized in that: the holder (4) has two preferably plate-like individual parts (4', 4") with in each case one window-like cutout (14', 14") for receiving the test object (6) in a reference plane, which individual parts are formed on their mutually facing surfaces as test standard surfaces, wherein the individual parts (4', 4") are connected to one another in a manner offset relative to one another in the reference plane in such a way that in each case test standard surfaces of one individual part (4' or 4") can be touched or are touched by one of the sensors (8, 10) through the cutout (14" or 14') in the other individual part (14", 14').

2. Testing device according to Claim 1, wherein the holder (4) is formed as a frame (12).

3. Testing device according to Claim 2, wherein the frame (12) is formed as a frame which is closed in the circumferential direction and has a window-like cutout.

4. Testing device according to Claim 2 or 3, wherein the frame (12) has a supporting structure on which the test object (6) can be loosely placed.

5. Testing device according to Claim 4, wherein the supporting structure has lugs which are spaced apart from one another in the circumferential direction of the frame (12).

6. Testing device according to one of the preceding claims, wherein the holder (4) is formed as a plane-parallel plate.

7. Testing device according to one of the preceding claims, wherein the holder (4) is coated at least in sections.

8. Testing device according to one of the preceding claims, wherein at least one optical sensor (8, 10) is formed and set up for areally detecting the test object (6).

9. Testing device according to one of Claims 1 to 7, wherein at least one optical sensor (8, 10) is formed and set up for linearly detecting the test object (6), wherein a feed device is provided for moving the holder (4) relative to the sensors (8, 10) in such a way that, during the feed, the test object (6) is scanned by the sensor.

10. Testing device according to one of the preceding claims, wherein the holder (6) is provided, on at least one test normal surface, with surface features which can be detected by at least one sensor (8, 10).

11. Method for testing flat test objects, wherein a testing device according to one of the preceding claims is used.

12. Method according to Claim 11, wherein the test object is a bipolar plate of a fuel cell.

13. Method according to Claim 11, wherein the test object is a battery foil.