Inspection device for a converting machine

Abstract

The present invention relates to an inspection device (42) for checking at least one coating position on a blank (1) transported through a converting machine (10). The inspection device comprises a camera (49) configured to capture an image of a portion of the blank (1) bearing a reference mark (30) with at least one coating, the optical axis (A) of the camera (49) being arranged at a first angle with respect to a vertical axis (V) defined by a normal vector (N) to the surface of the blank (1). An illumination system (50) is configured to emit incident light rays toward a measurement point (Pm) on the blank 1. The incident light rays emitted by the illumination system (50) are directed to the reference mark (30), while the specularly reflected light rays of the reference mark (30) are captured by the camera (49).

Description

Invention Field

[0001] This invention relates to a conversion machine for producing packaging containers, such as flat-pack or folding boxes. In particular, this invention relates to an inspection system for detecting printing colors and coating positions and alignment. Background of the Invention

[0003] The conversion machine can be configured to create packaging containers, such as flat-packs or folding boxes, from printed, cut, and creasing paper substrates to form blanks. These blanks can then be folded and assembled into three-dimensional boxes. These boxes are designed to be folded manually or automatically in a folding and gluing machine.

[0004] When packaging containers or boxes have printed patterns containing multiple colors and different coatings, each color or coating must be correctly positioned on the blank, and the colors and coatings must be aligned with each other.

[0005] Color calibration, often referred to as printing registration setting, is typically accomplished by printing reference marks along the edges of the blank and capturing images of these marks using a camera system. The displacement of different elements within the reference marks can then be determined. Based on this information, the printing unit in the converter can be adjusted manually or automatically. However, existing systems face difficulties in detecting transparent coatings such as varnishes. Summary of the Invention

[0006] In view of the above problems, the objective of the present invention is to provide an inspection device capable of high-precision detection of coatings, and also advantageously to provide an inspection device capable of high-precision detection of different colors.

[0007] This objective is achieved by the inspection device of claim 1.

[0008] According to a first aspect of the invention, an inspection apparatus is provided for inspecting the location of at least one coating on a blank transported via a converter. The inspection apparatus includes a camera configured to capture images of a portion of the blank bearing a reference mark with at least one coating. The optical axis of the camera forms a first angle with a vertical axis defined by a normal vector of the blank surface, and the inspection apparatus includes an illumination system comprising a first illumination module having at least one illumination unit.

[0009] The illumination unit is configured to emit incident light rays toward a measurement point on the surface of the blank, the emitted light rays forming a second angle with the vertical axis, and the first and second angles are selected such that the incident light rays from the illumination unit point toward the reference mark, and the specularly reflected light rays from the reference mark are captured by the camera.

[0010] This invention is based on the understanding that a reflective coating can be detected by a camera through the mirror effect produced by the coating. The angle of the optical axis enables the camera to capture specularly reflected light, thereby detecting the reflective coating.

[0011] The mirrored light rays are captured by the camera because they are guided into the entrance pupil of the camera lens.

[0012] The entrance pupil is the optical aperture from the blank. In other words, the entrance pupil can be defined as the optical opening of the camera through which light can enter.

[0013] The surface of the blank can be horizontal. Therefore, the vertical axis may be aligned with the direction of gravity. The measurement point is located on the surface of the blank with printed reference marks.

[0014] In the context of this application, the "coating" is transparent, i.e., colorless. It is precisely this transparency that makes it invisible to conventional camera systems. The reference mark can be a composite reference mark consisting of multiple individual reference marks. Therefore, the reference mark includes at least one individual reference mark printed with the coating. Each individual reference mark can be printed by a separate flexographic printing cylinder.

[0015] The first illumination module can be configured to illuminate a reference mark that produces a specular reflection. The reference mark that produces a specular reflection may include varnish.

[0016] In one embodiment, the first lighting unit of the first lighting module includes a diffusion layer. The first lighting unit may further include light sources arranged in a zigzag pattern on a circuit board, and these light sources are covered by the diffusion layer.

[0017] In an advantageous embodiment, the reference marker includes at least a first separate reference marker and a second separate reference marker, and the inspection device includes a second illumination module configured to illuminate the separate reference markers configured to produce diffuse reflection of light. The second illumination module includes at least one illumination unit arranged at a third angle to the vertical axis, the third angle being selected such that incident light from the at least one illumination unit is directed toward the reference marker, and specularly reflected light from the reference marker is directed outside the entrance pupil of the camera lens.

[0018] The second separate reference mark is printed with color. The color is printed with opaque ink containing at least one colorant (such as a dye or pigment). These colors typically produce diffuse reflection of light.

[0019] The second illumination module may include at least two illumination units, wherein the first and second illumination units are respectively arranged opposite to the optical axis of the camera.

[0020] The first and second lighting units are preferably elongated and include multiple light sources arranged in a straight line. The longitudinal extension of the lighting units is perpendicular to the transport direction of the blank.

[0021] The first and second illumination units can be positioned at a large angle relative to the field of view of the blank. This allows light from both sides to be received outside the entrance pupil of the camera lens, thereby achieving uniform illumination.

[0022] In one embodiment, the first and second illumination units include only light sources located at both ends of their length extension. Thus, the illumination units are arranged within a square around the optical axis of the camera. This allows for a uniform distribution of the illumination units around the camera, thereby providing uniform illumination within the camera's field of view.

[0023] The light intensities of the first and second illumination modules can be varied. By changing the light intensity, the balance between reflections and strong illumination of the reference marker can be optimized to obtain an accurately captured image of the reference marker.

[0024] In one embodiment, the first lighting module can be deactivated. This is advantageous if the reference marker does not include a reflective coating.

[0025] In another embodiment, the second lighting module can be deactivated. If the blank contains colored markings with low contrast to the blank background color, but the markings exhibit different reflective properties than the background, it is advantageous to illuminate it using only the first lighting module.

[0026] In a preferred embodiment, the inspection device is mounted within a housing. The inspection device may further include a laterally extending slide rail perpendicular to the transport path of the blank, and the inspection device is configured to move along the slide rail. The slide rail extends perpendicularly above or below the transport path of the blank.

[0027] In one embodiment, the camera is triggered by a time signal emitted by a control unit. This signal is emitted when the optical sensor detects the leading edge of the blank, and the time signal corresponds to the time when the reference marker arrives in the reflective illumination area of ​​the camera's field of view. The reflective illumination area may be provided by the first illumination module. Attached Figure Description

[0028] The present invention will now be described by way of embodiments shown in the examples and drawings, wherein the same reference numerals are used for similar elements, and wherein:

[0029] Figure 1a This is a plan view of the box blank;

[0030] Figure 1b This is a detailed view of the first type of reference mark located at the edge of the blank;

[0031] Figure 1c This is a detailed view of the second type of reference marker;

[0032] Figure 2 This is a 3D schematic diagram of the converter, which is configured as a rotary die-cutting machine;

[0033] Figure 3 This is a schematic diagram of a flexographic printing module and inspection device according to an embodiment of the present invention;

[0034] Figure 4 This is a perspective view of an inspection device according to an embodiment of the present invention;

[0035] Figure 5 yes Figure 4 Exploded view of the inspection device in the diagram;

[0036] Figure 6 This is a cross-sectional schematic diagram illustrating the installation of the camera inside the inspection device;

[0037] Figure 7a This is a cross-sectional schematic diagram showing the light emitted by the first illumination module for the blank;

[0038] Figure 7b This is a cross-sectional schematic diagram showing the light emitted by the second illumination module for the blank;

[0039] Figure 8 This is a cross-sectional schematic diagram illustrating the installation of the inspection device inside the converter; and

[0040] Figure 9a and 9b These are images taken with and without the first illumination module, respectively. Detailed Implementation

[0041] Figure 1a An example of blank 1 for use in flat packaging or folding boxes is shown. Blank 1 may be made of cardboard, hardboard, plastic or similar materials.

[0042] Blank 1 can be produced in converter 10, such as Figure 2As shown. The converter 10 is configured as a rotary die-cutting machine 10. At the inlet position of the converter 10, the paper substrate 1 is placed in the feeding module 14 and transported along the transport direction T through the converter 10 for a series of operations that print, cut, and creasing the paper substrate 1 to form a blank 1. Therefore, in the context of this application, the term "blank" applies to the paper substrate 1 that has already been provided with a printed pattern by at least one printing unit. The transport direction T is defined from the inlet to the outlet of the converter 10. The blank 1 is transported along the transport path P, which can be defined as the trajectory of the blank 1 through the converter 10.

[0043] Downstream from the inlet of the converter 10 along the transport direction T, the converter 10 may include a pre-feeder 12, a feeding module 14, a printing module 15, a die-cutting module 18, a bundling and stacking module 20, and a palletized sorter 22. Optionally, a drying module 13 may be provided after the flexographic printing module 15, configured to dry the ink before the blank 1 enters the die-cutting module 18. A main operating interface 11 may also be provided near the converter 10.

[0044] like Figure 3 As shown, the printing module 15 includes multiple flexographic printing units 16a to 16e. Each flexographic printing unit 16 includes a flexographic printing assembly comprising a flexographic printing cylinder and is configured to print individual patterns on the paper substrate 1 in a separate color or coating. The individual patterns collectively form the final pattern 2 on the blank 1. Generally, at least four flexographic printing units 16a to 16d are provided to enable printing in different colors according to a large color swatch.

[0045] like Figure 1b and 1c As shown, the reference mark 30 is printed together with the pattern 2 by the flexographic printing unit 16. Each flexographic printing unit 16 is configured to print an individual reference mark 30' while the individual pattern is printed onto the paper substrate 1. In this way, a composite reference mark 30 is formed by different flexographic printing units 16. The reference mark 30 is preferably located on the leading edge 4 of the blank 1.

[0046] Optionally, an additional second reference mark 34 may be provided on the tail edge 6 of the blank 1. The reference mark 30 on the leading edge 4 and the second reference mark 34 on the tail edge 6 of the blank 1 help to determine the rotational displacement offset of the blank 1 in the flexographic printing module 15.

[0047] like Figure 1bAs shown, the reference mark 30 may include a grid 36 and a plurality of individual dot-shaped reference marks 30' arranged in the grid 36. The grid 36 is typically printed by the first flexographic printing unit 16a together with the first color of the individual dot-shaped reference marks 30'. The grid 36 has a predetermined height H and length L.

[0048] As the paper substrate 1 passes through the flexographic printing module 15, each flexographic printing unit 16 prints dot-shaped reference marks 30' in the grid 36. If the color and coating are aligned, i.e., perfectly registered, each dot-shaped reference mark 30' is located at a predetermined position in the grid 36, for example, at the center of the grid 36.

[0049] Or, such as Figure 1c As shown, grid 36 can be omitted, with only dotted reference marks 30' printed in each flexographic printing unit 16. These reference marks 30 indicate the position and alignment of different colors and coatings in two dimensions through their mutual distances in the X and Y coordinates.

[0050] like Figure 3 As shown, the converter 10 includes a print quality control system 40, which is configured to detect the position of individual patterns transferred from each flexographic printing unit 16 onto the paper substrate 1 and the alignment between different individual patterns. The print quality control system 40 includes an inspection device 42, a control unit 44, and a memory 46.

[0051] The printing quality control system 40 is configured to detect and measure the longitudinal and lateral displacements between different colors and coatings in the reference mark 30. The longitudinal displacement is in the transport direction T, and the lateral displacement is in a direction perpendicular to the transport direction T. In this way, printing registration, i.e., the position and alignment between different colors and coatings, can be determined. If the printing units 16 are not properly registered with each other, the final pattern 2 will show misalignment of the individual patterns printed in different colors.

[0052] The print quality control system 40 is configured to calculate longitudinal and lateral displacements and send correction information to the central control system 48 of the converter 10. The correction information includes the necessary adjustments to the angle and lateral position of the printing cylinder of the printing module 15. The converter 10 can be configured to automatically adjust the angle and lateral position of the printing cylinder. Alternatively, the print quality control system 40 can display the correction information required for manual adjustment of the printing module 15 on the machine interface 11.

[0053] If the printing quality control system 40 detects a defective blank 1 with misaligned colors and coatings, the central control system 48 can send a message to the waste removal module 17 to discard the blank 1.

[0054] like Figure 4 , 6As shown in 7a and 7b, the inspection apparatus 42 includes an imaging system 49 and an illumination system 50. The imaging system 49 may be a camera 49 with an active pixel sensor (e.g., a CMOS sensor) whose interface protocol is configured to transmit images to the control unit 44. The camera 49 is configured to receive light from the blank 1 within its field of view 51.

[0055] like Figure 8 As shown, the inspection device 42 can be mounted on the slide rail system 45, also referred to as the "slide rail system 45". The slide rail system 45 includes a longitudinal slide rail 47 extending perpendicularly to the transport direction T.

[0056] Reference Figure 3 An optical sensor 52 can be placed upstream and close to the camera 49, and is configured to detect the arrival of the leading edge 4 of the blank 1. When the optical sensor 52 detects the leading edge 4 of the blank 1, the camera 49 is triggered by a time signal from the control unit 44.

[0057] The inspection device 42 is installed downstream of the flexographic printing module 15. For example... Figure 3 As shown, the inspection device 42 is located below the transport path P of the blank 1. However, the inspection device 42 can also be positioned above the upper transport path P of the blank 1. Therefore, the position of the inspection device 42 ensures that the field of view 51 of the lighting system 50 and the camera 49 faces the printing surface of the blank 1. If the converter 10 is equipped with a drying module 13, the inspection device 42 can be located after the flexographic printing module 15 and the drying module 13. Alternatively, the inspection device can be located between the flexographic printing module 15 and the drying module 13.

[0058] like Figure 6 , 7a As shown in Figure 7b, camera 49 has an optical axis A, which is a straight line passing through the geometric center of lens 53 of camera 49. Optical axis A forms a first angle with the direction defined by the normal vector N to the surface of the printing paper of blank 1. arrangement.

[0059] like Figure 4 As shown, the lighting system 50 includes a first lighting module 56, which includes at least one lighting unit 57. (As...) Figure 7a As clearly shown, the light emitted from the first illumination unit 57 to the measuring point Pm of the blank 1 forms a second angle -α, which is a negative angle with the vertical axis V defined by the normal vector N of the paper surface of the blank 1. The second angle -α is a negative angle. The measuring point Pm is preferably located within the reference mark 30.

[0060] The absolute value of the second angle -α and the first angle They can be equal. However, the first angle of optical axis A... It is a positive angle.

[0061] In the context of this application, a positive angle is the result of rotating counterclockwise from the vertical axis V. Correspondingly, a negative angle is the result of rotating clockwise from the vertical axis V.

[0062] like Figure 7a As shown, the blank 1 with a reflective surface is illuminated by the first illumination unit 57. The second angle -α of the first illumination unit 57 is selected to direct the incident light from the first illumination unit 57 toward the reference mark 30 and guide the specularly reflected light from the reference mark 30 into the entrance pupil 55 of the camera lens 53.

[0063] Paints such as varnishes are highly reflective, making them difficult to detect without creating a "mirror reflection" effect as they enter the camera lens 53 through the entrance pupil 55. These types of paints produce a specular reflection when illuminated.

[0064] The first illumination unit 57 is configured to emit diffused light rays directed from multiple directions toward the reference mark 30. This ensures that a portion of the reflected specular light rays are received through the entrance pupil 55 of the camera lens 53. The first illumination unit 57 includes at least one light source 58 and a diffusion layer 59. The diffusion layer 59 is located above the at least one light source 58. The diffusion layer 59 is configured to scatter the transmitted light rays from the light source 58 and provide a uniform diffused light radiation surface. The diffusion layer 59 may be made of an optically diffusing material, such as polymethyl methacrylate.

[0065] In the illustrated embodiment, the first illumination unit 57 is configured such that only a portion of the light reflected from the field of view 51 on the blank 1 is received through the entrance pupil 55 of the camera lens 53. This portion is referred to as the reflected illumination region Ria. Therefore, the surface area of ​​the reflected illumination region Ria on the blank 1 is smaller than the area of ​​the field of view 51 on the blank 1. Thus, when the camera 49 captures an image of the reflective reference mark 30, the reference mark 30 needs to be placed within the reflected illumination region Ria of the field of view 51 on the blank 1.

[0066] When the optical sensor 52 detects the leading edge 4 of the blank 1, the control unit 44 sends a time signal to trigger the camera 49. This signal can be set to correspond to the time when the reference mark 30 arrives at the field of view 51 of the reflective illumination area Ria.

[0067] In one embodiment, the first lighting unit 57 may be elongated and have multiple light sources 58 arranged in a row. The longitudinal extension of the lighting unit 57 is perpendicular to the transport direction T. The longitudinal direction of the light sources is also perpendicular to the transport direction T and coincides with the longitudinal extension of the reference mark 30 on the blank 1.

[0068] The light sources 58 can be arranged in one or more rows. The light sources 58 can be mounted on a printed circuit board (PCB). The distance between the light sources is selected to obtain uniform illumination of the diffusion layer 59.

[0069] When the inspection device 42 is installed in the converter 10, the camera axis A is at a first angle. Arranged relative to the vertical axis V. The horizontal axis is defined by the printing surface on blank 1, and the vertical axis V is perpendicular to it. First angle This enables camera 49 to capture the specular light reflected at the angle of reference mark 30. First angle. It can be between 1° and 15°, preferably about 5°.

[0070] In a preferred embodiment, a second illumination module 60 is also provided. The second illumination module 60 is configured to illuminate printed colors that produce diffuse reflection under specular illumination. These types of colors include, for example, water-based or solvent-based inks. Due to the diffuse reflection of light from the reference mark 30, the camera 49 will receive reflected light entering the entrance pupil 55 of the camera lens 53. The second illumination module 60 is configured to uniformly illuminate the reference mark 30 on the blank 1.

[0071] like Figure 4 and 7b As shown, the blank 1 with a reflective surface is illuminated by a second illumination module 60. The second illumination module 60 includes at least one illumination unit 62, 63, 65, configured to emit light rays along a vertical axis V defined by a third angle β relative to the normal vector N of the surface of the blank 1. The third angle β is selected to direct the incident light rays from the second illumination module 60, from at least one illumination unit 62, 63, 65, towards the reference mark 30, and to guide the specularly reflected light rays from the reference mark 30 beyond the entrance pupil 55 of the camera lens 53. This allows the camera 49 to capture a clear image of the reference mark 30 without glare. Therefore, when the illumination has a reflective surface, specularly reflected light rays are not received into the entrance pupil 55 of the camera lens 53. The entire field of view 51 of the second illumination module can be illuminated on the blank 1.

[0072] At least one lighting unit 62, 63, 65 may be elongated and may include a plurality of light sources 64 arranged in a straight line. The longitudinal extension of at least one lighting unit 62, 63, 65 is perpendicular to the transport direction T of the blank 1.

[0073] The second lighting module 60, comprising at least one lighting unit 62, 63, 65, may include a continuous line of light sources 64 arranged at constant intervals between each other. Alternatively, at least one lighting unit 62, 63, 65 may include only the light sources 64 located at both ends of the line. In this way, the light sources 64 are arranged in a square around the camera 49.

[0074] In one embodiment, an additional second illumination unit 63 is disposed on the opposite side of the optical axis A of the camera 49, relative to the first illumination unit 62. This allows for further improvement and uniform illumination of the field of view 51 on the blank 1. In one embodiment, a third illumination unit 65 may also be provided on at least one side of the camera 49. Each illumination unit 62, 63, 65 may be configured to emit light toward the blank 1 at a different third angle β. Therefore, in Figure 7b In the example shown, there are three illumination units 62, 63, and 65, whose emitted light rays are respectively referred to as β1, β2, and β3. These angles are chosen so that the specular reflection of the light rays is directed outside the entrance pupil 55 of the camera 49. The angles β1, β2, and β3 can be different as long as the reflected light rays are not received into the entrance pupil 55.

[0075] The first illumination module 56 and the second illumination module 60 can operate simultaneously, during which time the camera 49 captures an image of the reference marker 30. Alternatively, either the first illumination module 56 or the second illumination module 60 can be operated, and the camera 49 can capture an image. In another embodiment, only one of the plurality of illumination units 62, 63, 65 is operated.

[0076] For inks that produce diffuse reflection under illumination, the first illumination module 56 can be disabled. Depending on the color and reflective properties of the coating, only the reference mark 30 needs to be illuminated using the second illumination module 60. This avoids reflection from reflective surfaces on the blank 1. Figure 9b As shown, when illuminated by the first illumination module 56, the blank 1 reflects light from a smooth area that was unintentionally brushed against by friction in the converter 10. Figure 9a In the middle, blank 1 is illuminated only by the second illumination module 60 and shows less reflection.

[0077] The light intensity of the first illumination module 56 and the second illumination module 60 can be varied. This allows the illumination settings to be adjusted based on the characteristics of a reference mark. In particular, for reflective coatings (inks or varnishes), the illumination can be calibrated to obtain detectable reflections.

[0078] like Figure 5 and 6 As shown, camera 49 is mounted inside an outer housing 70 of inspection device 42. A cover 72 is provided on the top of housing 70. The cover has a transparent surface 73, such as a glass surface 73. The outer housing 70 is designed to provide a sealed enclosure surrounding and enclosing camera 49. The sealing rating may be, for example, IP64.

[0079] The outer housing 70 may include walls 74 of varying thicknesses. Walls of varying thicknesses can provide greater penetration for the fasteners 71, increasing the rigidity of the walls 74. The walls 74 of the housing 70 may also include an inclined portion 75 that forms a first angle with the longitudinal extension of the outer housing 70. This causes the optical axis A of camera 49 to form a first angle with the vertical axis V. The vertical axis V is aligned with the longitudinal direction of the outer housing 70, and the camera 49 faces through the opening 76 on the cover 72 located between the lighting modules 56 and 60.

[0080] A thermoelectric element 78 is disposed between the camera 49 and the outer housing 70. The thermoelectric element 78 may be a Peltier element 78. The camera 49 includes an optical module 49a and an electronic processing module 49b. The electronic processing module 49b includes sensitive electronic components, and the camera 49 is preferably configured such that the electronic components are close to the thermoelectric element 78. In this way, the electronic processing module 49b is thermally connected to the thermoelectric element 78.

[0081] An insulating inner housing 80 is disposed inside the outer housing 70 and configured to surround the camera 49. The inner housing 80 may include a first housing portion 80a surrounding the electronic processing module 49b of the camera 49 and a second housing portion 80b surrounding the optical module 49a. The second housing portion 80b may be tubular.

[0082] The first housing portion 80a may include a recess 82, within which the second housing portion 80b is partially received. This allows for modular design and access to the optical module 49a of the camera 49 without disassembling the first housing portion 80a.

[0083] like Figure 5 As shown, the first housing portion 80a includes an insulating portion 83 and a heat-conducting portion 84. The heat-conducting portion 84 includes a heat-conducting plate 84, such as a metal plate. For example, the heat-conducting plate 84 may be made of aluminum or silver. A thermoelectric element 78 is located between the heat-conducting plate 84 and the outer housing cover 70. The heat-conducting plate 84 distributes and propagates the cold generated by the thermoelectric element 78 to the electronic processing module 49b of the camera 49. The camera is secured to the outer housing cover 70 by at least one fastener 71. In the illustrated embodiment, multiple fasteners 71, such as four fasteners 71, connect the inner housing 80 of the camera 49 to the outer housing cover 70.

[0084] When current is applied to both sides of the thermoelectric element 78, the thermoelectric element 78 generates a hot side and a cold side. Therefore, the cold side of the thermoelectric element 78 is in contact with the heat-conducting plate 84, and the hot side is in contact with the outer housing cover 70. In this way, the electronic processing module 49b of the camera 49 is cooled, while the outer housing cover 70 can be used to transfer heat away from the thermoelectric element 78.

[0085] like Figure 3 As shown, the inspection device 42 can be positioned below the vacuum transfer 9 of the flexographic printing module 15. Alternatively, the vacuum transfer can be located below the inspection device 42. The vacuum suction generated by the vacuum transfer 9 induces airflow through the outer housing 70, which provides heat transfer to the surrounding air.

[0086] A drying module 13 can be installed after the flexographic printing module 15 to ensure that the ink is dried before the blank 1 is moved to a subsequent module (such as a die-cutting or folding module). The drying module 13 operates by blowing hot air onto the printing surface of the blank 1.

[0087] By integrating the thermoelectric element 78 into the current inspection device 42 as described above, a cooling effect can be achieved to reduce the heat radiation from the dryer to the camera 49. Furthermore, a dust-free environment can be provided for the camera 49.

Claims

1. An inspection apparatus (42) for inspecting the position of at least one coating on a blank (1) transported via a converter (10), the inspection apparatus comprising: A camera (49) configured to capture images of the blank (1) portion bearing at least one coating reference mark (30); The optical axis (A) of the camera (49) forms a first angle (φ) with the vertical axis (V) defined by the normal vector (N) of the surface of the blank (1), and the inspection device (42) includes an illumination system (50) comprising a first illumination module (56) having at least one first illumination unit (57); wherein the first illumination unit (57) is configured to emit incident light toward a measurement point (Pm) on the surface of the blank (1), the emitted light forming a second angle (-α) with the vertical axis (V), and the first and second angles (φ, -α) are selected such that the incident light from the first illumination unit (57) is directed toward the reference mark (30), and the camera (49) captures specularly reflected light from the reference mark (30).

2. The inspection apparatus according to claim 1, wherein the reference mark (30) comprises a plurality of individual reference marks (30'), each of the individual reference marks (30') being printed by a separate flexographic printing cylinder.

3. The inspection apparatus according to claim 1 or 2, wherein the first illumination module (56) is configured to illuminate the reference mark (30) that produces a specular reflection.

4. The inspection device according to claim 3, wherein the reference mark (30) comprises varnish.

5. The inspection apparatus according to claim 1 or 2, wherein the first illumination unit (57) includes a diffusion layer (59).

6. The inspection apparatus according to claim 5, wherein the first lighting unit (57) of the first lighting module (56) includes a plurality of light sources (58) arranged side by side on a circuit board, and the light sources are covered by the diffusion layer (59).

7. The inspection apparatus of claim 2, wherein the reference mark (30) comprises at least a first individual reference mark (30') and a second individual reference mark (30'), wherein the inspection apparatus comprises a second illumination module (60) configured to illuminate the individual reference marks (30') and generate diffuse light reflection, the second illumination module (60) comprising at least one second illumination unit (62, 63, 65) arranged at a third angle (β) with respect to the vertical axis (V), the third angle (β) being selected such that incident light from the at least one second illumination unit (62, 63, 65) is directed toward the reference mark (30), and specularly reflected light from the reference mark (30) is directed outside the entrance pupil (55) of the camera lens (53).

8. The inspection device according to claim 7, wherein the second illumination module (60) comprises at least two second illumination units (62, 63, 65), wherein the at least two second illumination units (62, 63, 65) are arranged on opposite sides of the optical axis (A) of the camera.

9. The inspection apparatus according to claim 8, wherein the at least two second illumination units (62, 63, 65) are elongated and comprise a plurality of light sources arranged in a straight line.

10. The inspection apparatus according to claim 9, wherein the at least two second illumination units (62, 63, 65) are arranged at an angle opposite to the vertical axis (V).

11. The inspection apparatus of claim 10, wherein the at least two second illumination units (62, 63, 65) comprise only light sources located at both ends of their elongated extensions.

12. The inspection apparatus of claim 7, wherein the light intensity from the first and second illumination modules (56, 60) is variable.

13. The inspection device according to claim 1 or 2, wherein the first lighting module (56) can be deactivated.

14. The inspection device according to claim 7, wherein the second lighting module (60) can be deactivated.

15. The inspection device according to claim 1 or 2, wherein the inspection device (42) is installed inside the housing (70).

16. The inspection device according to claim 1 or 2, further comprising a slide rail (47) that is opposite to and extends laterally to the transport path (P) of the blank (1), and the inspection device being configured to move along the slide rail (47).

17. The inspection device according to claim 1 or 2, wherein, When the optical sensor (52) detects the leading edge (4) of the blank, the control unit (44) sends a time signal, the camera (49) is triggered by the time signal, and the time signal corresponds to the time when the reference mark (30) arrives in the reflected illumination area (Ria) of the field of view (51) of the camera (49), the reflected illumination area being provided by the first illumination module (56).

Images