Method for optically inspecting object and corresponding inspection device

Abstract

The invention relates to a cost-effective method for optical inspection of an object and a corresponding inspection device, the inspection device comprising an illumination unit and a matrix camera, the object and the inspection device being moved relative to each other in a feed direction at a predetermined movement speed, wherein the illumination unit continuously illuminates the object with a respective illumination pattern, the illumination pattern comprising N1 (N1 > = 2) light and dark stripes spaced apart in the feeding direction by a gap length LAB, each light and dark stripe having a length LST in the feeding direction, and comprising a plurality of identical light and dark structures arranged side by side in the lateral direction, each light and shade structure forms a period B1 in the transverse direction, each pair of light and shade stripes adjacent in the feed direction has a phase shift B1 / N1 in the transverse direction, and wherein the matrix camera generates a plurality of image captures in an image capture sequence of the illuminated region of the object, the matrix camera is configured such that each image capture simultaneously records all N1 light and dark stripes over a predetermined width in the lateral direction, and wherein the matrix camera provides image capture data to the computing unit via the corresponding interface for inspecting the object.

Description

[0001] The present invention relates to a method for optically inspecting an object and a corresponding inspection device.

[0002] Optically inspecting an object that performs relative movement with respect to an inspection device is a frequently and advantageously employed procedure in production, because it allows for a non-contact assessment of the quality of the object. The object can in particular consist of a transparent material such as glass or structured glass (e.g., a glass plate or a glass ribbon), but can also be made of an opaque material, for example a material having at least partially reflective surfaces that are painted or otherwise applied. The inspection focuses on surface defects such as scratches, and / or for transparent materials, inclusions within the transparent material, such as air bubbles or dust. Deposits on the surface (such as dust particles) also fall within the scope of inspection. Inspections can also be carried out to determine the dimensions and / or optical parameters of the object.

[0003] When using a camera as an optical capture device to optically inspect an object consisting of a transparent or reflective material (such as glass or structured glass), both bright-field illumination and dark-field illumination must be used simultaneously in order to contrast various types of defects, because some defects can only be distinguished under one illumination or the other. Absorptive defects such as inclusions can be detected under bright-field illumination, where the transparent material is illuminated by an illumination unit and the camera is arranged on the opposite side of the transparent material. In contrast, scattering or deflection defects such as scratches are detected by dark-field illumination. In dark-field illumination, the area of the illumination unit that is next to the capture area of the camera is illuminated, such that in the absence of surface defects, the camera ideally sees a dark field. However, if a defect or deposit is located on the surface, it reflects light into the camera's image, and thus the defect can be detected. This is also referred to as dark-field illumination.

[0004] Therefore, for transparent materials, a transmitted-light arrangement is usually used, and sometimes an incident-light arrangement is used for reasons of accessibility. For non-transparent materials, an incident-light arrangement must always be employed. The present invention relates to incident-light arrangements and transmitted-light arrangements.

[0005] A device and a method for optically inspecting an object are known from DE 10 2010 021 853 A1, in which a line camera and an illumination unit are provided, the illumination unit having a plurality of individually switchable illumination elements, such as light-emitting diodes (LEDs) or jointly switchable groups of LEDs. A computing unit is further provided and configured to control the individual illumination elements in different ways, namely, to turn them on and off, for a plurality of captures in a given resolution area. This allows for various illumination configurations such that, due to the flexibly switchable illumination unit, multiple captures with desired different illumination and capture conditions in a single resolution area can be achieved through this configuration. In particular, the illumination elements of the illumination unit are arranged exactly in one illumination row oriented transversely to the transport direction, and the computing unit is configured to activate the illumination elements in this row with different illumination configurations according to a predefined (i.e., adjustable) illumination cycle. Preferably, the number of activations in the illumination cycle exactly corresponds to the number of captures in the expected resolution area, i.e., the illumination cycle is selected such that it is completed once the object has been transported in the feed direction with the desired resolution. For three, four, five, or six captures in the resolution area, the illumination row is activated three, four, five, or six times in the illumination cycle and switched according to the desired illumination configuration. In this known method and device, the illumination switches rapidly back and forth between the individual configurations, synchronized with the line camera. This rapid switching of the illumination requires a considerable complexity in the control electronics for the individual illumination elements, which is also expensive. A method for optically inspecting a surface is known from DE 10 2020 109 945 A1, in which, during an image capture sequence, a time-periodic pattern with different illumination patterns is generated on the surface and recorded by the inspection device.

[0006] An image capture system is known from US 2016 / 0048969 A1, which is used to record at least one image of a sample surface using a projector and a camera to determine the height profile of the sample surface, where the sample, the camera, and the projector are moved relative to each other. The projector projects a pattern onto the sample, which may include sub-patterns in the form of four rectangular fields. The detection area of the camera may correspond to these fields, whereby information about the height profile of the sample is obtained from the images captured by the camera. No inspection in the sense of the present invention is carried out here.

[0007] Accordingly, it is an object of the present invention to provide an inspection device that is more cost-effective and less complex in structure. Another object is to specify a corresponding inspection method.

[0008] The above object is achieved by a method for optical inspection having the features of claim 1 and an inspection device having the features of claim 8.

[0009] In particular, this object is achieved by a method for optically inspecting an object by means of an inspection device comprising at least one illumination unit and at least one matrix camera, wherein the object and the inspection device perform a relative movement with respect to each other at a predetermined movement speed in a feed direction. The at least one illumination unit continuously illuminates the object with a single illumination pattern, wherein the illumination pattern comprises at least N1 (N1 ≥ 2) light and dark stripes that are spaced apart from each other by a gap length L in the feed direction AB , the light and dark stripes having a length of L ST , and having a plurality of identical light and dark structures arranged directly adjacent to each other in the transverse direction, wherein each light and dark structure forms a period B1 in the transverse direction, for example, forms a bright field and an adjacent dark field in the transverse direction, and wherein a phase shift with a width of B1 / N1 in the transverse direction is present between each pair of adjacent light and dark stripes in the feed direction. The object is continuously illuminated by the illumination unit with this illumination pattern. Furthermore, the at least one matrix camera generates a plurality of image captures of the area of the object illuminated by the illumination unit in an image capture sequence such that each capture of the sequence simultaneously records all N1 light and dark stripes of the illumination pattern over a predetermined width in the transverse direction, wherein the capture sequence of the matrix camera is synchronized with the movement speed in the feed direction with respect to the illumination pattern such that the relative movement between the object and the inspection device between two successive captures in the feed direction is at most L = L AB + L ST . The matrix camera makes the image capture data available to a computing unit via a corresponding interface such that the computing unit can perform an inspection of the object based on the image data of the illumination pattern

[0010] The at least one illumination unit continuously illuminates the object in a predetermined area with a corresponding illumination pattern, that is, the illumination unit provides incident light to the object with a constant light intensity and does not turn off or switch during the inspection. The illumination pattern is generated by the light-emitting part of the illumination unit itself or by irradiating through a grating that generates the pattern. The illumination is in the visible light wavelength range. The pattern is projected onto the object surface as incoherent light. The matrix camera records an image sequence of the illuminated area of the object, that is, it captures the illumination pattern in a manner relative to the reflection (incident light arrangement) or transmission (transmitted light arrangement) of the object. The digitized image data generated by the matrix camera is transmitted by the camera to a computing unit (computer, processor, etc.) via a suitable interface. Then, the computing unit performs the desired inspection of the object based on this data, that is, it detects defects or deposits in / on the object and / or determines object parameters, such as the refractive index, height profile, or dimensions of the object, from the image data. Defects can include inclusions and surface damage, such as scratches, inside the object or on its surface

[0011] A matrix camera, also known as a "line scan camera", records a large area of an object. For example, it can be implemented as a CCD camera. The matrix camera captures the light intensity of multiple matrix elements (pixels) arranged in rows and columns (in a matrix). For each pixel, the camera has a photosensitive element (e.g., a CCD sensor). The area captured by each such element determines the resolution of the camera. As described below, if the area captured by the matrix camera is spatially synchronized with the area of the object, a volume element and / or a surface element of the object can be assigned to each pixel. In addition, the matrix camera is arranged to observe the object vertically so that it clearly images the entire predetermined object area. Multiple matrix cameras can be arranged side by side in the lateral direction to inspect particularly wide objects.

[0012] As described above, the object and the inspection device perform relative movement with respect to each other in the feed direction at a predetermined movement speed. The lateral direction extends transversely (preferably perpendicular to the feed direction). For example, the object can be conveyed at a predetermined speed on a conveyor belt past a stationary inspection device while the inspection device itself remains stationary. Alternatively, only the inspection device moves, or both the inspection device and the object move. If the relative movement between the object and the inspection device is a uniform motion, i.e., a motion at a constant speed, this is advantageous for image data processing because it simplifies the processing of the image data for object inspection.

[0013] The pattern generated by the illumination unit includes N1 (N1 ≥ 2) bright and dark stripes that are spaced apart by a gap length L in the feed direction AB, where a phase shift with a width of B1 / N1 in the transverse direction is presented between each pair of adjacent bright and dark stripes in the feeding direction. B1 is the period of the bright and dark structure forming the bright and dark stripes (i.e., the width of a single bright and dark structure in the transverse direction). In one embodiment, the period B1 of the bright and dark structure is greater than or equal to 100 µm (B1≥100 µm), for example, greater than or equal to 200 µm (B1≥200 µm). In another example, the illumination pattern has N1 = 6 bright and dark stripes and a period B1 = 0.25 mm, such that two adjacent bright and dark stripes have an offset (phase shift) with a width of 0.25 mm / 6 = 41.7 µm in the transverse direction. Each bright and dark stripe consists of a plurality of identical bright and dark structures arranged side by side in the transverse direction. All bright and dark stripes use the same bright and dark structure (i.e., the same sequence of at least one bright field and at least one dark field). Therefore, each bright and dark stripe has a periodic intensity distribution with a period of B1 in the transverse direction, and each period contains at least one bright field (high light intensity) and one dark field (low light intensity). For example, the bright and dark structure can consist of one bright field and one adjacent dark field. In this example, each bright and dark stripe includes a sequence of alternating identical bright and dark fields (bright field - dark field - bright field - dark field, etc.). The intensity distribution in the transverse direction can be, for example, sinusoidal or rectangular. In one embodiment, the widths of the bright and dark fields in the transverse direction and the lengths in the feeding direction are equal, but other configurations can be used. For example, the bright field can be wider than the dark field or vice versa, or longer in the feeding direction or vice versa. All N1 bright and dark stripes are formed equally (all bright and dark stripes consist of the same bright and dark structure), but are offset by B1 / N1 in the transverse direction relative to their respective adjacent stripes. Each bright and dark stripe has a total length L in the feeding direction ST . Two adjacent bright and dark stripes are separated by a constant bright stripe or dark stripe (separation stripe) extending across the entire transverse width of the illumination pattern, where the distance from the end of the first bright and dark stripe to the start of the adjacent second bright and dark stripe (in the feeding direction) is L AB . Therefore, the separation stripe has a length L in the feeding direction AB . This similarly applies to the distance from the third bright and dark stripe to the second bright and dark stripe (in the feeding direction), and so on. In one embodiment, the length L ST is at least three times the period B1. The separation stripe creates a clear boundary between the light intensities of adjacent bright and dark stripes in the captured image, minimizing interference

[0014] The matrix camera is oriented and configured such that in a single image capture of an image capture sequence, it captures the light generated by a constant illumination pattern that spans all N1 bright and dark stripes simultaneously over a predetermined width (e.g., the width of the object). In subsequent captures of the sequence, due to the relative movement and the synchronization of the image capture (i.e., matrix camera readout) of the matrix camera, a relative movement with a maximum length of L = L AB + L ST occurs in the feed direction. In a relative movement with a length of L = L AB + L ST in a predetermined section of the object, in the next capture of all N1 bright and dark stripes, adjacent bright stripes that are offset by B1 / N1 in the lateral direction appear in this predetermined section. Thus, each object area / section is captured in at least N1 images of the matrix camera, and once the data of at least N1 images has been digitized and transmitted to the computing unit, all of these at least N1 images are used for inspection. The matrix camera can be configured such that at least one photosensitive element captures the light of a single field of the illumination pattern (i.e., one bright field or one dark field of the bright and dark structure). In one embodiment, two or more photosensitive elements of the matrix camera can capture the light of a field. Along the feed direction, the matrix camera can likewise be configured such that along a field at least one photosensitive element (e.g., two or more photosensitive elements) captures the light of this one field.

[0015] On the one hand, the method of the present invention achieves a long exposure time for each object position because at least N1 captures (captures of N1 bright and dark stripes for each position) are performed for each position. This results in an improved signal-to-noise ratio, or allows a reduction in the illumination intensity with the same signal-to-noise ratio compared to conventionally captured images. This leads to a reduction in the energy consumption and cooling requirements of the illumination unit. On the other hand, using a constant illumination of the object by the illumination unit without any switching during the inspection of the object reduces the system complexity and the number of devices. No control electronics for the individual elements (LEDs) of the illumination unit that are used for rapid switching during the inspection are required. This makes the inspection less complex and more cost-effective.

[0016] In one embodiment, for each of the N1 bright and dark fringes, the coincidence image capture region (with respect to position) of the matrix camera is assigned to each real position of the object. This means that the computing unit knows exactly from which real position (object point) of the object the light captured by each photosensitive element of the matrix camera originates. Thus, the illumination unit and the object are spatially synchronized with respect to the image captures generated by the matrix camera at different points in time. The assignment of the real positions and image points of the N1 different image captures can be determined by the computing unit, for example, by transformation and by the uniform relative movement of the known object and the inspection device (at a relative speed, for example, by means of the predefined or measured feed speed of the object), and is assigned to the image points of the corresponding image captures of the matrix camera. In other words, in this embodiment, the capture intensity values of each pixel or each pixel group of the matrix camera for different image captures are assigned to each other (synchronized) and are assigned to the real positions of the object. The assignment is performed in such a way that the N1 light intensity values recorded at different times with respect to the N1 different bright and dark fringes are assigned to each real object position. Furthermore, the assignment is characterized in that, when recording the pixel or pixel group assigned to it, the specific real object position is located in the relevant region of the corresponding bright and dark fringe. This means that the light intensity values of the pixels captured at different times are assigned to each other and to the real positions of the object. Each bright and dark fringe represents a specific type of illumination.

[0017] Due to the illumination unit setup and the design of the matrix camera described below, in one embodiment, an image of the object can be taken simultaneously with bright-field illumination and dark-field illumination, which are recorded for the same object position but at different points in time. The pixels of the matrix camera image that capture the light generated by the bright-field illumination using the bright and dark structure can be used for the bright-field image, and the pixels of the matrix camera image that capture the light generated in the dark field of the bright and dark structure can be used for the dark-field image. Here, if necessary, the images of the capture device generated by the capture region are separated and combined to form the desired image, such as a bright-field image, a dark-field image, a reflection image, or a transmission image. For example, a bright-field transmission image, a dark-field transmission image, a reflection image, and data regarding two different deflections (see below) can be generated. Thus, as part of the object inspection in this embodiment, defect detection can be performed based on the data (dark-field image) from the image capture from the dark field originating from the bright and dark structure, and / or defect detection can be performed based on the data (bright-field image) from the image capture from the bright field originating from the bright and dark structure.

[0018] Regarding the above-mentioned transmission image and reflection image, at least two illumination units can be set in the inspection device, and each illumination unit has an associated illumination pattern, where the first illumination unit is for the transmission image and the second illumination unit is for the reflection image. The first illumination unit is located on the side of the object opposite to the matrix camera, that is, the object is arranged between the first illumination unit and the matrix camera. The light emitted by the first illumination unit irradiates through the (at least partially transparent) object and is captured after passing through the matrix camera, where the matrix camera observes the first illumination unit along its axis. In contrast, the second illumination unit and the matrix camera are on the same side of the object. The light from the second illumination unit reaches the matrix camera after being reflected from the surface of the object. In one embodiment, the first illumination unit and the second illumination unit are arranged relative to the matrix camera such that the image captures of the transmission image and the reflection image are arranged adjacent to each other horizontally on the matrix camera, so that they can be distinguished by their positions on the screen of the matrix camera. In this case, the matrix camera simultaneously captures a sequence of reflection images and a sequence of transmission images as described above, synchronized with the relative movement of the object and the inspection device, and focuses on the object in both cases. Therefore, in this embodiment, the matrix camera captures the illumination pattern reflected on the surface of the object and / or the illumination pattern transmitted through the object, where the image is captured in the illumination area. Alternatively or additionally, when the matrix camera observes at a small angle deviating from the axis of the first illumination unit, an off-axis transmission image sequence can be similarly captured by the matrix camera.

[0019] Therefore, in one embodiment, the computing unit is configured to synthesize at least two images of the object based on multiple records made in the illumination area of the object, and evaluate them individually or in combination for the presence of defects or with respect to the optical parameters of the object. The at least two images consist of corresponding records of a part or the entire area of the illumination area of the object. For example, a bright-field image and a dark-field image of the object or a reflection image and a transmission image of the object are combined. Then these images can be evaluated individually or in combination by the computing unit to determine the location and extent of the defect and / or to determine the type of the defect. For example, a combined evaluation of the reflection image and the transmission image can be used to distinguish between open bubbles and closed bubbles in glass. In particular, the matrix camera observes the illumination area in bright-field illumination and also directly observes the illumination unit through the transparent material in the transmission-light arrangement. Defects appear as contrast regions in bright field. In the case of dark-field illumination, the matrix camera observes the darkness next to the illumination without error, so nothing can be seen. If a defect / deposit occurs, the defect / deposit is detected by the computing unit due to the light reflection in the dark environment.

[0020] The regions of the object covered by the image capture can be completely separated from each other or configured to overlap each other.

[0021] The inspection of an object performed by a computing unit based on data captured by an image can be implemented as a computer-implemented method, i.e., a method performed using a computing unit (computer). For example, based on image capture, a defect detection method is used to determine a defect as a local deviation from an image capture signal generated by a defect-free object.

[0022] In one embodiment, the illumination pattern further includes at least N2 (N2≥2) lateral line structures positioned adjacent to each other in the feed direction, where each lateral line structure includes a bright line and a dark line extending across the entire width of the illumination pattern, and where the length (period) ML of each lateral line structure in the feed direction has a maximum value LMAX, which is calculated as the product of the relative speed between the inspection device and the object (e.g., the feed speed of the object) (e.g., the feed speed of the object in the case of a fixed inspection device) and 4 times the time required for the matrix camera to generate an image capture (= the reciprocal value of the capture frequency). The resolution of the matrix camera is also configured to capture the light of the area of the object illuminated by N2 lateral line structures such that the measurement lines on the dark lines, the measurement lines at the first transition between the dark line and the bright line, the measurement lines on the bright line, and the measurement lines at the second transition between the bright line and the next dark line are captured. For example, the course of the light intensity in the feed direction of the lateral line structure may include a sine or rectangular profile. Local synchronization is also performed for these four measurement lines, i.e., the computing device knows at which position of the object each pixel of the corresponding measurement line is recorded. The image captures of the four measurement lines generated at four different time points are respectively assigned to the corresponding positions of the object. The assignment may require a transformation different from the transformation of the above-mentioned bright and dark stripes. The measurement lines provide measurement information for each position, which is out of phase by 90° with the information from the bright and dark stripe image. Thus, the known Dynamic Moiré Algorithm can be used to determine the phase or the deflection angle. Four different independent optical values can thus be calculated, where the lateral direction represents the x direction and the feed direction represents the y direction: dAx / dx, dAy / dy, dAx / dy, dAy / dx, where dAx and dAy represent the deflection (distortion) in the x direction or the y direction, and dx and dy are the associated path differences. Thus, the refractive power in the x direction and / or the y direction can be determined in a known manner. Therefore, in this embodiment, based on the N1 continuously created image captures of the bright and dark stripes and at least (N2 - 1)×4 created image captures of the lateral line structures, the phase and the deflection angle in the lateral direction and / or the feed direction can be determined from multiple positions on the object surface, and for example, the refractive power in the lateral direction and / or the feed direction can be determined therefrom. That is, if N2 = 2, at least 4 image captures are required.

[0023] For example, this is derived from determining four intensity values related to the illumination period, with the deflection angle Φ≈arctan Φ = (I1 - I3) / (I2 - I4), where I1, I2, I3, and I4 represent the intensity values determined in this order at corresponding positions by the matrix camera during the illumination period. This can be used to determine the refractive power proportional to the phase shift ΔΦ = Φ2 - Φ1.

[0024] In one embodiment, the period length ML of the lateral line structure in the feed direction is equal to the period length B1 of the bright and dark stripes in the lateral direction. This ensures that the deflections in the feed direction and the lateral direction can be measured with the same measurement accuracy.

[0025] The illumination unit may include several individually switchable illumination elements, such as light-emitting diodes (LEDs) or groups of jointly switchable light-emitting diodes (LEDs). In this case, the illumination pattern is generated by the overall combination of the illumination elements themselves. Thus, the individually switchable illumination elements may consist of illuminants (such as LEDs) or of several illuminants (such as groups of several LEDs) combined together and switchable together. In such a configuration of the illumination unit, the computing unit is preferably configured to control the individual illumination elements differently, i.e., to turn them on and off, where the control does not occur during the inspection of the object, but before or after the inspection. The bright field / lines are generated by the turned-on LEDs, and the dark field / lines are generated by the turned-off LEDs. This allows for a flexible illumination configuration, for example, from the same side of the object, from different sides of the object, at different angles to the object, and / or using light of different wavelengths.

[0026] Alternatively or additionally, the illumination unit may include a lamp (such as a fluorescent tube) that fully illuminates the area to be illuminated. A grating is arranged between the light and the object, which generates the desired illumination pattern. The bright field / lines are generated by the corresponding slots in the grating, and the dark field / lines are generated by the corresponding webs.

[0027] The illumination unit can provide different illumination patterns. This allows for the targeted implementation of additional illumination channels on the matrix camera, in particular as bright field or dark field illumination, as illumination of different sides of the object, and / or as illumination with light of different wavelengths.

[0028] However, since the dark field illumination does not occur immediately at the transition from the illuminated element to the non-illuminated element, according to the present invention, it may be advantageous to combine several turned-off (i.e., dark) illumination elements adjacent to each other.

[0029] The geometry of the optical image, together with the dimensions of the photosensitive elements (pixels, image points) of the matrix camera, determines the length of the path of the object imaged onto the lines of the camera. Since most matrix cameras have square pixels and the optics image radially symmetrically with respect to the optical axis, the resolution in the feed direction is usually equal to the resolution transverse to the path. Different ratios can also be achieved by selecting suitable asymmetric optics or non-square pixels, but this is expensive and thus not commonly used due to the need for special components. Such adjustment is also possible only within a narrow range.

[0030] The resolution of the object in the feed direction is determined by the speed at which the individual rows and columns of the matrix camera are captured. In principle, the higher the readout speed that can be selected, the finer the resolution.

[0031] The inspection device according to the invention can be used both for transparent materials, in particular structured glass strips, and for opaque materials, such as painted vehicle body surfaces, and can be implemented in an incident light illumination arrangement and a transmitted light illumination arrangement.

[0032] To adapt the light to a specific inspection purpose, an optical light shaping unit can be arranged between the illumination unit and the object and / or between the object and the matrix camera. The light shaping unit is particularly composed of lenses, diffusers, and / or microlenses. Such a light shaping unit is particularly suitable for inspecting objects made of structured glass, in particular structured glass strips, in a transmitted light arrangement. In bright-field illumination for structured glass, the light can be incident on the structured glass as uniformly as possible from the front, back, right, and left (i.e., from all directions), so that the existing structural pattern is as faint as possible, and the defects to be searched for can be detected in a transmitted light arrangement with high contrast. On the other hand, dark-field illumination requires more directional illumination perpendicular to the transmission direction, so that the boundary between the bright LED group and the dark LED group is as clear as possible.

[0033] A particularly advantageous light shaping unit for this purpose is a cylindrical Fresnel lens arranged between the illumination unit and the object, preferably in combination with a diffuser arranged between the Fresnel lens and the illumination unit. The cylindrical Fresnel lens distributes the light particularly in the transmission direction and then focuses the illumination unit onto the object to be inspected. Thus, the illumination unit (such as an LED) is reduced in size by the cylindrical Fresnel lens and projected onto the material of the object, in particular structured glass. The diffuser can be used to slightly homogenize the intensity in the transverse direction. The diffuser should preferably have weak scattering optical properties, otherwise the boundaries between the individual bright fields or dark fields or lines become blurred, and the quality of dark-field detection is impaired.

[0034] In one embodiment, the inspection device includes several independent lighting units, which are arranged on different sides of the object and / or at different angles with respect to the object. When using lighting units arranged at different angles with respect to the object, the texture on the surface can be suppressed, for example, in order to distinguish them from topological defects. Alternatively or additionally, the lighting units can be arranged such that the corresponding lighting patterns are generated adjacent to each other in the transverse direction on the object, in order to inspect very wide objects.

[0035] In another embodiment, the lighting unit alternatively or additionally includes a plurality of lighting elements that emit light in different wavelength ranges. By using light of different wavelengths, it is possible to accurately distinguish the light reflected or transmitted by the object and captured by the matrix camera according to which lighting element it originated from. This requires that the matrix camera be able to distinguish incident light from different wavelength ranges.

[0036] The above object is achieved in particular by an inspection device for optically inspecting an object using a lighting unit and at least one matrix camera, wherein the inspection device is configured such that: The object and the inspection device perform a relative movement with respect to each other at a predetermined moving speed in the feed direction, The lighting unit continuously irradiates the object with a lighting pattern, where the lighting pattern includes at least N1 (N1≥2) light and dark stripes, which are spaced apart by a gap length L in the feed direction AB The light and dark stripes have a length L in the feed direction ST and have a plurality of light and dark structures arranged adjacent to each other in the transverse direction, where each light and dark structure forms a period B1 in the transverse direction and is composed of, for example, a bright field and a dark field arranged adjacent to each other in the transverse direction, and a phase shift with a width of B1 / N1 in the transverse direction is presented between each pair of adjacent light and dark stripes in the feed direction, At least one matrix camera generates a plurality of image captures of the area of the object irradiated by the lighting unit in an image capture sequence, such that in each image capture of the image capture sequence, all N1 light and dark stripes of the lighting pattern are simultaneously captured over a predetermined width in the transverse direction, The image capture sequence of the matrix camera is synchronized with the moving speed in the feed direction with respect to the lighting pattern, such that the relative movement between the object and the inspection device between two consecutive image captures in the feed direction is at most L = L AB +L ST and The matrix camera makes the image capture data available at the interface of the matrix camera for a computing unit connected to the matrix camera, such that an object can be inspected with the aid of the computing unit based on the image capture data of the illumination pattern. The advantages of the inspection device have been explained above in connection with the method according to the invention, which inspection device together with the computing unit is configured as an inspection system. Reference is also made to the embodiments of the inspection device described below.

[0037] In one embodiment, the inspection device is further configured such that each true position of the object is assigned to a coincidence image capture region of the matrix camera for each of the N1 light and dark fringes. In particular, each pixel of each image capture is assigned to a volume element and / or a surface element of the object.

[0038] In one embodiment, the inspection device is further configured such that during the inspection of the object, defect detection is performed based on the image capture data from the dark field originating from the light and dark structure and / or the bright field originating from the light and dark structure.

[0039] In one embodiment, the inspection device is additionally configured such that the illumination pattern additionally includes a section having at least N2 (N2≥2) transverse line structures, which transverse line structures are directly (immediately) adjacent to each other in the feed direction, wherein each transverse line structure includes a bright line and a dark line extending over the entire width of the illumination pattern, and wherein the length of each transverse line structure in the feed direction is at most L / N2. The section having the transverse line structures is arranged at a distance from the N1 light and dark fringes in the feed direction.

[0040] In one embodiment, the inspection device is additionally configured such that the computing unit determines the phase and the deflection angle in the transverse direction and / or the feed direction, and thereby determines, for example, the refractive power in the transverse direction and / or the feed direction, from the image captures of the N1 light and dark fringes continuously generated from a plurality of positions on the object surface based on the N1 image captures of the transverse line structures and at least (N2 - 1)×4 image captures.

[0041] In one embodiment, the inspection device is additionally configured such that the matrix camera captures the illumination pattern reflected at the surface of the object and / or the illumination pattern transmitted through the object, wherein the image is captured in the illumination area.

[0042] In one embodiment, the inspection device is additionally configured such that at least two of the plurality of images generated in the illumination area are combined and evaluated individually or in combination to determine the presence of a defect.

[0043] In one embodiment, the inspection device provides an illumination unit having a plurality of individually switchable lighting elements arranged in a matrix and / or having an illuminator and a grating arranged between the illuminator and the object, the illumination unit generating light and dark stripes and, if applicable, also generating a lateral line structure, thereby generating an illumination pattern.

[0044] The invention is particularly useful for inspecting objects in the form of flat glass strips or structured glass.

[0045] The other advantages, features and possible applications of the present invention will be described below with reference to the embodiments and the drawings. All features described and / or shown constitute the object of the present invention, even if they are not outlined in the claims and their references.

[0046] It is schematically shown that: Figure 1 is an embodiment of an inspection device according to the present invention, wherein the object is in a side view, Figure 2 is according to Figure 1 a top view of a first embodiment of the grating of the illumination unit of the inspection device, Figure 3 is by according to Figure 2 a section of an enlarged top view of the illumination pattern generated by the grating, Figure 4 is according to Figure 1 a top view of a second embodiment of the grating of the illumination unit of the inspection device, Figure 5 is by according to Figure 4 a section of an enlarged top view of the illumination pattern generated by the grating, Figure 6 is a partial synchronization of image capture.

[0047] Figure 1 An embodiment of an inspection device is shown that inspects possible defects and deposits on an object on a surface (e.g., a flat glass strip 1). When the flat glass strip 1 moves past the fixed inspection device at a predetermined constant speed in the feeding direction (see arrow 11), the flat glass strip 1 is indicated by the arrow. The inspection device has a first illumination unit 31, a second illumination unit 32 and a matrix camera 5, wherein the first illumination unit 31 is arranged on the same side as the matrix camera 5, and the second illumination unit 32 is arranged on the side of the flat glass strip 1 opposite to the matrix camera 5.

[0048] Each illumination unit 31, 32 includes, for example, an LED matrix or a fluorescent tube as a light source and as Figure 2 and Figure 3The gratings 33 shown generate illumination patterns on the surface of the flat glass strip (for the first illumination unit 31) and in / on the opposite surface of the flat glass strip (for the second illumination unit 32). The matrix camera 5 observes the object and thus the respective illumination patterns of the two illumination units 31, 32. The illumination of the flat glass strip 1 takes place during the inspection with a constant intensity and without interruption, i.e., without a switching-on or switching-off process. The line of sight from the matrix camera 5 to the first illumination unit 31 is shown by the arrow 51, while the line of sight from the matrix camera 5 to the second illumination unit 32 is shown by the arrow 52. It can be clearly seen from the lines of sight (arrow 51, arrow 52) that the matrix camera 5 observes the first illumination unit 31 in a reflection manner and the second illumination unit 32 in a transmission manner with respect to the flat glass strip 1. The matrix camera 5 (e.g., a CCD camera) includes a screen 53, and the screen 53 contains photosensitive elements (e.g., CCD sensors) that capture the intensity of the light arriving there with a spatial resolution. The photosensitive elements are arranged in a matrix. The matrix camera 5 observes the surface of the flat glass strip 1 vertically such that, in image capture, the predetermined width of the flat glass strip (i.e., perpendicular to the feed direction) captures the surface of the flat glass strip 1 in clear focus. Figure 1 It is also shown that the light of the first illumination unit 31 is incident laterally onto the screen 53 beside the light of the second illumination unit 32. Thus, the reflected signal and the transmitted signal can be captured separately from each other, where the CCD camera can read both channels simultaneously.

[0049] Figure 2 The first embodiment of the grating 33 shown generates a corresponding illumination pattern 43 in the region of the flat glass strip 1. The grating 33 has four slit bars 33a, 33b, 33c, 33d, which are arranged adjacent to each other in the feed direction (see arrow 11) and generate a corresponding number (N1 = 4) of light and dark fringes 43a, 43b, 43c, 43d with bright and dark fields. The adjacent slit bars 33a, 33b, 33c, 33d are separated from each other by bars 33p, 33q, 33r extending across the entire width of the grating 33. In each case, the dark field is arranged beside the bright field, and the bright and dark fields have the same size. One bright field and one dark field together form a light and dark structure, where a plurality of light and dark structures adjacent to each other in the lateral direction form the light and dark fringes 43a, 43b, 43c, 43d. Adjacent light and dark fringes, such as the light and dark fringes 43a and 43b or 43b and 43c, are each shifted by B1 / 4 in the lateral direction (see arrow 12, B1 is the period of each light and dark fringe). The illumination pattern observed in reflection or transmission also has a gap length L AB which is the gap length L AB between the adjacent light and dark fringes 43a, 43b, 43c, 43d, and this gap length L ABFor example, it is 1.5 mm, while the lengths L of the bright and dark stripes 43a, 43b, 43c, 43d ST are 3.5 mm. At this gap length L AB the illumination pattern has constant dark stripes 43p, 43q, 43r (separation stripes), i.e., each separation stripe 43p, 43q, 43r has a length L AB in the feed direction (arrow 11) (e.g., L AB = 1.5 mm). The widths of the individual separation stripes 43p, 43q, 43r in the transverse direction (arrow 12) correspond to the widths of the bright and dark stripes 43a, 43b, 43c, 43d or the width of the pattern 43. Alternatively, the separation stripes can also be configured as constant bright stripes.

[0050] The flat glass strip 1 is continuously illuminated by two illumination units 31, 32 with the illumination pattern shown in the middle part Figure 3 . The matrix camera 5 generates image captures of the two illumination patterns at predetermined time intervals t1, t2, t3, t4, and specifically generates image captures over the entire width in the transverse direction (arrow 12) of the respective illumination pattern (also see Figure 6 , which is intended to show the capture of a defect 60 in the flat glass strip 1, where for better illustration each capture is shown shifted to the right relative to the previous capture). The matrix camera also captures all four bright and dark stripes 43a, 43b, 43c, 43d of the illumination pattern simultaneously with one image capture. The images can be distinguished by the arrangement on the screen 53 of the matrix camera 5. The moving speed of the flat glass strip 1 in the feed direction (arrow 11) is known or continuously measured. The feed speed is used to assign the four image capture regions of the matrix camera 5 to positions x1, x2, x3 or x4 of the flat glass strip 1 such that a time interval (e.g., t2 - t1) is maintained between every two consecutively created image captures, and this time interval corresponds to the path L = L AB + L ST in the feed direction that the flat glass covers during this time. With this type of local synchronization, the four image captures are assigned to the respective positions of the flat glass strip 1, i.e., there is one image capture for each of the four bright and dark stripes 43a, 43b, 43c, 43d taken at times t1, t2, t3, t4. This assignment is made in Figure 6is shown by the dashed arrows. These image captures of the intensity values of each photosensitive element (pixel) of the screen 53 containing the matrix camera are transmitted in digital form via the interface 54 of the matrix camera to the computing unit 7 connected to the matrix camera by means of a data line, which performs an inspection of the flat glass ribbon 1 based on the image capture of the illumination pattern and the above-described method. The data of the image capture is associated with position information such that each intensity value (pixel) of the image capture can be assigned to a volume element / surface element of the flat glass ribbon 1. Each volume element is configured as a surface element on the surface of the flat glass ribbon, which reflects the light emitted by the first illumination unit and is observed by the matrix camera 5 by means of the line of sight 51.

[0051] Figure 4 is shown by means of Figure 1 a second embodiment of a grating for inspection by means of the inspection device shown, the grating comprising Figure 2 the grating 33 shown and three transversely and parallel to each other extending recesses on one side of the grating in the feed direction, which recesses produce the respective bright lines a, c, e of the illumination pattern (see Figure 5 ). Between the bright lines a, c, e of the illumination pattern section 44, there are provided dark lines b, d extending transversely and parallel to each other. In total, the bright and dark lines a, b, c, d, e form two horizontal line structures, each horizontal line structure consisting of a bright line and a dark line and an additional bright line. Further dark lines delimit the illumination pattern section 44 in the feed direction. The matrix camera 5 is designed in such a way that it simultaneously captures in the image capture Figure 5 the four measuring lines ML shown by the dashed lines in, one measuring line extending on the bright horizontal line of the illumination pattern, two measuring lines extending between the bright and dark horizontal lines (with different sequences of bright and dark lines), and one measuring line extending on the dark horizontal line. As Figure 4 is shown in reference to the gratings 33, 34 and Figure 3 , the length by which the flat glass ribbon 1 moves between two image captures approximately corresponds to the distance in the feed direction between two adjacent ones of the four measuring lines ML, such that in the next image capture, different positions of the flat glass ribbon are illuminated by the measuring lines of the section 44 of the entire illumination pattern 43, 44 and recorded by the matrix camera 5. Furthermore, with respect to the illumination pattern section 44, the computing unit 7 can assign volume and surface area elements of the flat glass ribbon 1 to each intensity value of each image capture, similar to the above-described procedure.

[0052] The program has the following advantages: Defect detection during inspection is based on multiple image data generated from positions of the flat glass strip 1, which is illuminated by illumination patterns 43, 44 including alternating bright and dark regions in the transverse direction and illumination patterns 43, 44 alternating bright and dark regions in the feed direction. This image data can also be forwarded from the matrix camera to the computing unit 7, where it can be used to inspect the flat glass strip 1.

[0053] In particular, data generated from image recordings of a capture sequence with modulation of the light source in the transverse direction and in the feed direction as described above can determine the longitudinal deflection and transverse deflection of each line element in the longitudinal and transverse directions, and thus detect linear refractive power defects in the longitudinal and transverse directions.

[0054] The grating with structures 33, 34 can include, for example, a dimension Q1 of 250 mm in the transverse direction and a length L of 40 mm in the feed direction G . These parameters are as Figure 4 shown. In the case of light and dark stripes, the vertical slits are approximately 1 mm wide, and the stripes extending between them are also 1 mm wide in each case (in each case, in the transverse direction).

[0055] The above method or inspection device can achieve a good signal-to-noise ratio at a relatively low illumination intensity, because each position of the flat glass strip receives four or five times the exposure time compared to single image capture in conventional methods (depending on which grating is used for illumination). This can reduce energy consumption. Additionally, there is no need to switch the lighting unit during inspection. This makes the inspection device more cost-effective and less complex.

[0056] The method can also be used very variably, because it can generate a dark-field image of the flat glass strip 1 from the image data of the dark field or dark lines of the illumination pattern, and generate a bright-field image from the image data of the bright field or bright lines of the illumination pattern and use them for corresponding defect detection. Additionally, the method can work in transmission or reflection mode. An additional lighting unit for generating an off-axis dark field can also be provided. This lighting unit can also be illuminated with an analog grating 33, 34 and a continuous illumination light source similar to the above lighting units 31, 32, such that the corresponding illumination patterns 43, 44 can be achieved in the region of the flat glass strip 1 and observed by the matrix camera 5.

Claims

1. A method for optically inspecting an object (1) by means of an inspection device, wherein, The inspection device includes at least one illumination unit (31, 32) and at least one matrix camera (5), wherein the object and the inspection device perform a relative movement with respect to each other in a feed direction at a predetermined movement speed, wherein the at least one illumination unit continuously irradiates the object by means of respective illumination patterns (43, 44), wherein the at least one illumination unit is configured such that the illumination pattern includes N1 (N1≥2) light and dark stripes (43a, 43b, 43c, 43d), and the light and dark stripes are spaced apart from each other in the feed direction by a gap length L AB and have a length L in the feed direction ST and have a plurality of identical light and dark structures arranged adjacent to each other in the transverse direction, wherein each light and dark structure is configured to form a period B1 in the transverse direction and, for example, consists of a bright field and a dark field arranged adjacent to each other in the transverse direction, wherein between each pair of adjacent light and dark stripes in the feed direction, a phase shift with a width of B1 / N1 in the transverse direction is presented, wherein the at least one matrix camera generates a plurality of image captures of the area of the object respectively irradiated by the illumination units in an image capture sequence, such that in each image capture of the image capture sequence, all N1 light and dark stripes of the illumination pattern are simultaneously captured over a predetermined width in the transverse direction, and wherein the image capture sequence of the matrix camera is synchronized with the movement speed in the feed direction with respect to the illumination pattern, such that the relative movement between the object and the inspection device between two successive image captures in the feed direction is at most L = L AB + L ST , and wherein the matrix camera enables the data of the image captures to be available at a corresponding interface (54) for a computing unit (7), such that the computing unit can perform an inspection of the object based on the data of the image captures of the illumination pattern.

2. The method according to claim 1, wherein For each of the N1 bright and dark fringes, the coincidence image capture region of the matrix camera is assigned to each true position of the object.

3. The method according to any one of the preceding claims, characterized in that, As part of the object inspection, defect detection is performed based on the data of the image capture of the dark field derived from the bright and dark structure and / or defect detection is performed based on the data of the image capture of the bright field derived from the bright and dark structure.

4. The method according to any one of the preceding claims, characterized in that, The illumination pattern further includes a section (44) having at least N2 (N2≥2) lateral line structures (a, b, c, d, e) positioned adjacent to each other in the feed direction, wherein each lateral line structure includes a bright line and a dark line extending over the entire width of the illumination pattern, and wherein the length ML of each lateral line structure in the feed direction is at most LMAX.

5. The method according to claim 4, characterized in that, Based on the N1 consecutively generated image captures of the bright and dark fringes and at least (N2 - 1)×4 generated image captures of the lateral line structures, the phase and the deflection angle in the lateral direction and / or in the feed direction are determined from a plurality of positions on the surface of the object, and thereby, for example, the refractive power in the lateral direction and / or in the feed direction is determined.

6. The method according to any one of the preceding claims, characterized in that The matrix camera captures, by means of the image capture in the illumination region, the illumination pattern reflected at the surface of the object and / or the illumination pattern transmitted through the object.

7. The method according to any one of the preceding claims, characterized in that, At least two of the plurality of image captures generated in the illumination region are combined and evaluated individually or in combination to determine the presence of a defect.

8. An inspection device for optically inspecting an object (1) using illumination units (31, 32) and at least one matrix camera (5), wherein, The inspection device is configured such that: The object and the inspection device perform a relative movement with respect to each other at a predetermined movement speed in the feed direction. The illumination pattern (43, 44) for the illumination unit continuously irradiates the object, where the illumination pattern has at least N1 (N1≥2) light and dark stripes (43a, 43b, 43c, 43d), and the light and dark stripes are spaced apart by a gap length L in the feeding direction AB , and has a length L in the feeding direction ST , and has a plurality of laterally adjacent identical light and dark structures, where each light and dark structure forms a period B1 in the lateral direction and is composed of, for example, a bright field and a dark field adjacent to each other in the lateral direction, and a phase shift with a width of B1 / N1 in the lateral direction is presented between each pair of adjacent light and dark stripes in the feeding direction The at least one matrix camera generates a plurality of image captures of the region of the object illuminated by the illumination unit in an image capture sequence such that in each image capture of the image capture sequence, all N1 bright and dark fringes of the illumination pattern are captured simultaneously over a predetermined width in the lateral direction. The image capture sequence of the matrix camera is synchronized with the speed of movement in the feed direction relative to the illumination pattern such that the relative movement between the object and the inspection device during two successive image captures in the feed direction is at most L = L AB + L ST and The matrix camera makes the data of the image capture available at the interface (54) of the matrix camera for a computing unit (7) connected to the matrix camera such that the computing unit can perform the inspection of the object based on the data of the image capture of the illumination pattern.

9. The inspection device according to claim 8, further configured to: for each of the N1 bright and dark fringes, assign the coincidence image capture region of the matrix camera to each true position of the object.

10. The inspection device according to any one of claims 8 to 9, further configured to perform defect detection by the computing unit based on the data of the image capture of the dark field derived from the bright and dark structure and / or the bright field derived from the bright and dark structure during the object inspection.

11. The inspection device according to any one of claims 8 to 10 is further configured such that the illumination pattern additionally includes a section (44) having at least N2 (N2≥2) lateral line structures (a, b, c, d, e) positioned adjacent to each other in the feed direction, wherein each lateral line structure includes a bright line and a dark line extending over the entire width of the illumination pattern, and wherein the length ML of each lateral line structure in the feed direction is at most LMAX.

12. The inspection device according to claim 11 is further configured for the calculation unit to determine the phase and the deflection angle in the lateral direction and / or the feed direction from a plurality of positions on the surface of the object based on the N1 successively captured images of the bright and dark fringes and at least (N2-1)×4 created images of the lateral line structures, and thereby determine, for example, the refractive power in the lateral direction and / or the feed direction.

13. The inspection device according to any one of claims 8 to 12 is further configured to capture, by means of the image capture in the illumination area, the illumination pattern reflected at the surface of the object and / or the illumination pattern transmitted through the object.

14. The inspection device according to any one of claims 8 to 13 is further configured to combine at least two of the plurality of image captures generated in the illumination area, and to evaluate the at least two image captures individually or in combination to determine the presence of a defect.

15. The inspection device according to any one of claims 8 to 14, wherein, To generate the illumination pattern, an illumination unit is provided, which has a plurality of individually switchable illumination elements arranged in a matrix form and / or has an illuminator and a grating arranged between the illuminator and the object for generating the bright and dark fringes and, if applicable, for generating the lateral line structures.

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