Test method and reading device for a security marking

Description

[0001] The application concerns a reading unit and a testing procedure for reading and testing security markings, in particular security markings on packaging, such as those used in a deposit return system.

[0002] Security markings are used in a variety of ways to make counterfeiting more difficult and to offer the best possible assurance of the authenticity of a document, product, banknote, or the like. Security markings are used on deposit-bearing products because the deposit value is typically higher than the value of the packaging itself.

[0003] It is known to apply a security marking to an outer packaging covering, label, or band, which may be made of, for example, plastic, metal, or cardboard. This security marking may consist of several adjacent fields with different reflective properties. One of these fields is, for example, a contrast field with a comparatively high reflectivity across a broad wavelength range, including, for example, visible and infrared light. A second field is a dark field with a low reflectivity across the same broad wavelength range compared to the contrast field. A third field is a security field that exhibits different reflective properties in at least one known wavelength range than in another. For example, the security field may have low reflectivity in a first, e.g., visible wavelength range of light.In a second, different, visible or invisible wavelength range of light, the safety field, however, has a higher reflectivity - or vice versa.

[0004] The reflectivity of each field for a given wavelength depends on the ink used to print that field onto a given background. Typically, the ink used to print the contrast field(s) is a broadband reflector, while the ink used to print the dark field(s) is a broadband absorber. The contrast field can also be formed by the background itself if it is broadband reflector.

[0005] The ink used to print the safety field(s) has higher absorption in the first wavelength range than in the second. Accordingly, the ink used to print the safety field(s) has higher reflectivity, higher transparency, or both in the second wavelength range. If the ink used to print the safety field(s) has higher reflectivity in the second wavelength range than in the first, the intensity of the reflected light in the second wavelength range is always greater than the intensity of the reflected light in the first wavelength range.If the ink used to print the safety field(s) has higher transparency in the second wavelength range than in the first, the intensity of the reflected light in the second wavelength range will be greater than the intensity of the reflected light in the first wavelength range, provided the substrate beneath the ink has sufficiently high reflectivity in this second wavelength range. If the ink used to print the safety field(s) already has high reflectivity in the second wavelength range, the reflectivity of the substrate beneath the ink is less important or even irrelevant.

[0006] One way to test a security marking of the type described is to illuminate the security marking first with light in the first wavelength range and second with light in the second wavelength range.

[0007] In DE 10 2006 011 143, DE 102 47 252 and DE 43 19 555, a safety field is described that is printed with an ink that strongly absorbs visible light and is transparent to infrared light, such that the reflectivity of the safety field in the infrared wavelength range is determined by the substrate beneath the ink. The substrate of the safety field is white, so that under infrared light the safety field also appears as white as the substrate and the surrounding area, because the ink used to print the safety field is transparent to infrared light and therefore invisible, so that under infrared light the substrate beneath the ink is visible.

[0008] Another testing method focuses on determining the degree to which the safety field reflects more strongly in the second wavelength range than in the first. This method has the advantage that the testing of the safety field does not need to reference the surroundings of the safety field or any reference field that has the same color as the background on which the color for the safety field is printed.

[0009] The other testing method has the disadvantage that the intensity of the light reflected by the safety field depends on the intensity of the illumination – hereinafter also referred to as illuminance. The illuminance, in turn, depends not only on the intensity of a light source, but also, for example, on the distance between the safety field being tested and the light source, or on the angle at which the light from the light source strikes the safety field.

[0010] EP 1 821 096 A2 discloses a security marking and the testing of such a marking.

[0011] The security marking comprises a contrast field with high reflectivity in a first and a second wavelength range, and a security field that exhibits different reflection properties in the first wavelength range than in the second. Furthermore, EP 1 821 096 A2 discloses a test method and a corresponding test apparatus for the security marking. In this method, the contrast between the contrast field and the security field is determined at the two wavelengths and compared with corresponding threshold values.

[0012] The invention is based on the objective of improving a testing method in the manner of another testing method or of providing means for an improved testing method.

[0013] According to the invention, this problem is solved by a test method according to claim 1, in which the intensity of the light reflected by the contrast field when illuminated with light in the first wavelength range (in which the safety field strongly absorbs) is used to correct a difference value derived from the difference between the two different intensities of the light reflected by the safety field in the two different wavelength ranges. Thus, according to this method, the intensities of the light reflected by the safety field and the contrast field in two different wavelength ranges are detected and evaluated. A difference value is derived from the two different intensities of the light reflected by the safety field in the two different wavelength ranges.A correction value is derived from the intensity of the light reflected by the contrast field when illuminated with light in the first wavelength range, which is used to correct the difference value determined from the intensities of the light reflected by the safety field.

[0014] The testing procedure is preferably carried out by a selection unit that is trained to perform the testing procedure.

[0015] The invention includes the finding that the intensity of the light reflected from the contrast field when illuminated with light in the first wavelength range, in the case of a light source whose intensity is essentially constant, depends primarily on the distance and angle that the safety marking has to the light source.

[0016] Preferably, the difference value is calculated such that it also depends on the intensities of the light reflected by at least one dark field. For example, a difference between the intensities of the light reflected by the safety field and the dark field can first be calculated for each wavelength range. This can be done by calculating a first gray value si for each wavelength range, representing the intensity of the light reflected by the dark field in that wavelength range. This first gray value si can be subtracted from a second gray value di, which represents the intensity of the light reflected by the safety field in the same wavelength range. In this way, a contrast value can be calculated for each of the two wavelength ranges. Subsequently, the difference between the two contrast values ​​calculated in this way can be determined.The difference between a gray value di of the safety field and a gray value si of the dark field for a given wavelength range i can be understood as the contrast value (di - si), which represents the contrast between the safety field and the dark field. The contrast value is greater the more strongly the safety field reflects light in the first or second wavelength range, i.e., the greater the difference in brightness between the dark field and the safety field when illuminated in the respective wavelength range. Since the safety field reflects less light in the first wavelength range than in the second, the contrast value for the second wavelength range is greater than for the first.If the difference value is formed as the difference ((d 1 - s 1 ) - (d 2 - s 2 )) between two contrast values, the difference value is a measure of how much greater the reflectivity of the safety field in the second wavelength range is compared to the reflectivity in the first wavelength range.

[0017] Preferably, each contrast value is normalized using a maximum contrast value that represents the difference between a gray value wi of the contrast field and a gray value di of the dark field for a given wavelength range. Normalization can be achieved by dividing the respective contrast value by the corresponding maximum contrast value, resulting in a normalized contrast value for each of the two wavelength ranges.

[0018] In this case, the difference value is preferably the difference between the normalized contrast values. The product of the correction factor k and the gray value w1 of the contrast field for light in the first wavelength range constitutes the aforementioned correction value.

[0019] In the simplest case, the gray value w 1 of the contrast field in the first wavelength range can also be used as a correction value.

[0020] In this case we will calculate the difference in contrast values ​​( d 2 - s 2) - ( d 1 - s 1 ) thus normalized with a value - namely the grey value w 1 of the contrast field - which depends on the distance of the safety marking to the respective light source.

[0021] The correction factor k is preferably a constant that has been determined in advance for a particular readout unit or readout unit type and is stored in the respective readout unit.

[0022] According to further variations of the testing procedure, the security marking and, in particular, the security field are tested not only in two different wavelength ranges, but in several different wavelength ranges, so that the spectral properties of the security marking fields – especially the spectral properties of the security field and the color or colors with which it is printed – can be tested even more precisely, making counterfeiting even more difficult.

[0023] The inventive concept is further embodied by a reading unit according to claim 7 for a security marking on packaging of the type described above. According to the invention, the reading unit is designed to detect the intensity of the light reflected by the security field of the security marking in at least two different wavelength ranges, a first wavelength range being one in which the security field strongly absorbs, while the second wavelength range is one in which the security field reflects comparatively more strongly.

[0024] The readout unit preferably comprises an image acquisition module with an area sensor having light-sensitive sensor elements, which are preferably arranged in a matrix. The image acquisition module with area sensor serves to capture an image projected onto the sensor in two dimensions.

[0025] For this purpose, an optical system is usually attached in front of the area sensor, which projects the image of a respective safety marking as sharply as possible onto the area sensor.

[0026] The light-sensitive sensor elements are sensitive to both wavelengths of light and the second wavelength range, and are therefore able to capture images of the security marking, and in particular the security field, when illuminated by light in the first wavelength range as well as when illuminated by light in the second wavelength range. In this design variant, whether the image of the security marking is captured by light in the first wavelength range or by light in the second wavelength range depends on the type of light illuminating the packaging with the security marking.

[0027] Accordingly, in a preferred embodiment, the readout unit includes an illumination module designed and arranged to illuminate a viewing area of ​​the image acquisition module simultaneously or alternately with light in the first wavelength range and with light in the second wavelength range. The viewing area of ​​the image acquisition module here refers to the space in which the security marking of a package is located when its image is sharply projected onto the area sensor.

[0028] Alternatively, a lighting module can be provided that illuminates the field of view of the image acquisition module simultaneously with light in the first wavelength range and with light in the second wavelength range – for example, broadband. In this case, light filters can be alternately switched in front of the image acquisition module, one of which is transparent to light in the first wavelength range and the other to light in the second wavelength range, blocking the other wavelength range. Two lighting modules can also be provided, one for light in the first wavelength range and one for light in the second wavelength range, which are switched on alternately.Similarly, two image acquisition units can be provided which, due to the properties of their area sensor or due to appropriate filters, only capture images with light in the first wavelength range on the one hand and only capture images with light in the second wavelength range on the other.

[0029] Finally, it is also possible to provide an illumination module that simultaneously emits light in both the first and second wavelength ranges, and an image capture module that is sensitive to light in both wavelength ranges without requiring additional filters. With this variant, the resulting image of the safety marking would be dark in the dark areas, as these areas absorb light in both wavelength ranges. The contrast area would be bright, as it exhibits high reflectivity for light in both wavelength ranges.The safety field, on the other hand, would have a medium gray value, since while it absorbs light in the first wavelength range, it has a relatively high reflectivity for light in the second wavelength range, which is always higher than the reflectivity of the dark fields for light in the second wavelength range. Even if the safety field had the same high reflectivity for light in the second wavelength range as the contrast field, in the latter configuration, where the safety marking is illuminated with light in both the first and second wavelength ranges and the reflected light is captured broadband, the safety field will not appear completely bright, but rather gray, since it absorbs light in the first wavelength range in any case.

[0030] In all variants, the lighting module preferably has narrowband light sources, such that the spectral bandwidth (from half-value of the maximum to half-value of the maximum (FWHM: full with at half maximum)) is less than 60 nm. The mean wavelength between these two half-value wavelengths is referred to in this description as the central wavelength of the respective wavelength range.

[0031] The lighting module is preferably designed to emit light in the visible wavelength range in two partial wavelength ranges, the central wavelengths of which are preferably more than 200 nm apart.

[0032] The intensity of the shorter wavelength range is preferably between 25 and 40% of the total intensity of the visible light emitted in both partial wavelength ranges. Light-emitting diodes (LEDs) are particularly suitable light sources. These have short response times and narrow bandwidths.

[0033] The lighting module is preferably designed such that the viewing area of ​​the detection module, in which an evaluative package is located, is illuminated so uniformly that the intensity difference across the viewing area is at most 25%.

[0034] Furthermore, the lighting module is preferably arranged such that the illumination angle relative to a surface normal of the safety marking to be illuminated is between 20° and 45°.

[0035] The image acquisition module with associated optics for imaging a safety marking to be evaluated on the area sensor is preferably designed such that 1 mm 2< of the safety marking is detected by at least four whole sensor elements (pixels).

[0036] The readout unit preferably comprises an evaluation unit connected to the image acquisition module, configured to detect average gray values ​​for at least one contrast field, at least one dark field, and the security field, preferably separately for light in the first wavelength range and for light in the second wavelength range. Finally, an evaluation unit connected to the evaluation unit is configured to perform an evaluation of the detected security marking based on the gray values ​​of the security field detected for the two different wavelength ranges.If the evaluation of the gray values ​​by the evaluation unit reveals that, in particular, the gray values ​​in the area of ​​the security field image deviate by a predetermined amount from the gray values ​​when illuminated with light in the second wavelength range, the security marking is evaluated as OK. Otherwise, it is evaluated as not OK. In the intended use in a reverse vending machine, the latter would mean that the packaging is not accepted but returned. In this case, the deposit is not refunded. However, if a detected security marking is evaluated as OK, the corresponding packaging is accepted by a reverse vending machine with the reading unit according to the invention, and the deposit is refunded.

[0037] The invention will now be explained in more detail using an exemplary embodiment with reference to the figures: Figure 1: shows an example of packaging with a security marking according to the invention; Figure 2: shows an embodiment of a simplest variant of a security marking for packaging according to the invention; Figure 3: shows an extended embodiment of the security marking from Figure 2; Figure 4: shows the security marking from Figure 3 in its form for a different substrate; Figure 5: shows an alternative embodiment of a security marking; Figure 6: shows a schematic representation of a reading unit according to the invention.

[0038] Figure 1 Shows an example of packaging 10 in the form of a can with a safety marking 12.

[0039] The security mark 12 serves to identify the packaging 10 as packaging for which a deposit is payable by the consumer upon purchase, and which the consumer receives back upon return of the packaging. The security mark is designed in such a way that it is not easily possible to equip packaging for which no deposit has been paid with the security mark. Since the deposit value is greater than the value of the packaging, the party accepting the returned packaging and refunding the deposit would incur a loss in the case of packaging with a counterfeit security mark.

[0040] Figure 2Figure 12 shows the essential features of the security marking 12, namely a comparatively highly reflective contrast field 14 that encloses a security field 16 and a signal field 18. The contrast field 14 is highly reflective over a broad wavelength range, particularly in the visible wavelength range of light and in the transition to the infrared wavelength range.

[0041] The safety field 16 has the property that it is weakly reflective in a first, preferably visible wavelength range of light, i.e. strongly absorbing and therefore appears dark.

[0042] In a second, preferably also visible, wavelength range of light, the security field 16 is highly reflective, for example, as highly reflective as the contrast field 14. The security field 16 acquires this property of different reflectivity at different wavelengths because the ink with which the security field 16 is printed has lower absorption in the second wavelength range than in the first wavelength range.

[0043] This means that when viewing the packaging 10 in the first wavelength range, e.g. in normal daylight, the security field 16 is clearly visible as a dark field against a light background, while when viewing in the second wavelength range, e.g. with the help of a suitable camera, the security field 16 is less visible, since the security field 16 has a higher reflectivity in the second wavelength range, which is similar to that of the contrast field 14.

[0044] The reflectivity of each field for a given wavelength—and thus the intensity with which light in a given wavelength range is reflected—depends on the ink used to print the field onto the background. Typically, the ink used to print contrast field 14, or contrast fields, is a broadband reflector, while the ink used to print dark fields 20 and 22 is a broadband absorber. Contrast field 14 can also be formed by the background itself if it is broadband reflector, meaning that contrast field 14 does not necessarily have to be printed.

[0045] The ink used to print security field 16 has higher absorption in the first wavelength range than in the second. Accordingly, the ink used to print security field 16 has higher reflectivity or higher transparency, or both, in the second wavelength range than in the first. If the ink used to print security field 16 has higher reflectivity in the second wavelength range than in the first, the intensity of the reflected light in the second wavelength range is always greater than the intensity of the reflected light in the first wavelength range.If the ink used to print security field 16 has higher transparency in the second wavelength range than in the first, the intensity of the reflected light in the second wavelength range will be greater than the intensity of the reflected light in the first wavelength range, provided the substrate beneath the ink used to print security field 16 has sufficiently high reflectivity in this second wavelength range. If the ink used to print security field 16 already has high reflectivity in the second wavelength range, the reflectivity of the substrate beneath the ink used to print security field 16 becomes less important or even irrelevant.

[0046] For security reasons, however, it is advantageous if the substrate beneath the ink used to print the security field 16 has a reflectivity that differs from that of the contrast field 14. This means that the security field 16 can be printed with two colors: first, with a color having reflective properties that differ from those of the contrast field 14, and then with a second color, such that the second color covers the first. The second color used to print the security field 16 is then the color that, as described above, has a higher reflectivity and / or transparency in the second wavelength range than in the first.

[0047] The security field 16 has an asymmetrical shape, so that its orientation in relation to the rest of the security marking is clearly recognizable.

[0048] Another component of the security marking 12 is a signal field 18 which, depending on the type of packaging, is either strongly absorbing (as in Figure 2 (shown) or is highly reflective. In the latter case – highly reflective signal field 18 – the signal field 18 has the same color as the background 14 and is therefore practically non-existent, but is determined solely by the abstract definition of its intended location. In the embodiment according to Figure 2 The signal field 18 is shown in a strongly absorbing color, i.e. weakly reflective and therefore dark.

[0049] Signal field 18 serves to signal to a device for reading the security marking whether and, if so, which stored parameters must be taken into account when checking the security marking. Parameters can be, for example, stored correction factors.

[0050] To locate the security marker 12' (see Figure 3 ) on a packaging 10 and to facilitate the finding of the signal field 18 within the security marking 12', the security marking 12' preferably has further fields, namely dark fields firstly in the form of corner markings 20 and secondly in the form of orientation markings 22.

[0051] The dark fields 20 and 22 have the property of being strongly absorbing, and therefore weakly reflecting, in both the first wavelength range and the second wavelength range, and thus appear dark.

[0052] Alternatively or additionally, one or more of the dark fields – similar to the security field – can be printed with two colors: first with a color that has reflective properties different from those of contrast field 14, and then with a second color that covers the first. The second color has a higher reflectivity and / or transparency in the second wavelength range than in the first. This further increases counterfeit protection. With this design variant, it is also helpful if at least one dark field is broadband absorbing and appears dark in both the first and second wavelength ranges.

[0053] The corner markings 20 are in the form of right-angled, isosceles triangles. This shape is particularly suitable because such shapes practically do not occur in the rest of the packaging printing. The legs of each isosceles triangle 20 run parallel to the edges of the security marking 12'. The hypotenuses of the corner markings 20 are therefore directed inwards with respect to the security marking 12'.

[0054] The orientation markings 22 act firstly as corner markings for locating two further corners of the overall rectangular safety marking 12'. Secondly, they enclose the signal field 18 between them, so that it is easy to locate even if it has the same color as the background 14, as is shown in the example in Figure 3 is shown.

[0055] Both the corner markings 20 and the orientation markings 22 can have shapes other than those shown in the exemplary embodiment and can, for example, be composed of several sub-areas, so that information can be encoded with the corner markings 20 and / or orientation markings 22, similar to how this is done with the help of the signal field 18.

[0056] Figure 4 It basically shows the same 12" safety marking as Figure 3 The only difference between the 12" safety marking and the 12" marking is... Figure 4 opposite the safety marking 12' out Figure 3 consists of the fact that the safety field 18 at the safety mark 12" is made of Figure 4 weakly reflective, i.e., dark, and thus has the same color as the orientation markings 22 and the corner markings 20, while the safety field 18' of the safety marking 12' is made of Figure 3is highly reflective and therefore has the same color as contrast field 14.

[0057] Figure 5Figure 12 shows a variant of a security marking 12‴ with a signal field 18‴, which is subdivided into a total of 8 sub-signal fields, which are either highly or weakly reflective. The eight sub-fields can thus represent an 8-bit (1 byte) code. Depending on the value of the respective bit – 0 or 1 – the corresponding sub-field is highly or weakly reflective. In the exemplary embodiment, the signal field 18‴ represents the byte 10100110 or 01011001, depending on whether a high or low reflectivity is assigned to the bit value 1. With such a subdivided signal field 18‴, it is possible not only to represent binary information (directionally reflective or diffusely reflective), but in the exemplary embodiment, 256-valued information, such as a multitude of different correction factors for, for example, various packaging.

[0058] Based on the in Figure 6The schematic, sketch-like representation of a reading device 30 for reading security markings 12 on packaging such as the packaging 10 shown will now be used to describe its essential components and its function.

[0059] The reading device 30, which can, for example, be part of a reverse vending machine for beverage packaging, has, firstly, a transport device 32 with which a package 10' can be positioned in front of a reading unit 34 so that it is within the field of view of the image acquisition unit 36 ​​of the reading unit 34. The field of view is in Figure 5 indicated by dashed diagonal lines.

[0060] A lighting module comprising two lighting units 38.1 and 38.2 is provided to illuminate the viewing area. The direction of illumination, and thus the angle at which the illumination falls on a package 10 to be read, is indicated by dotted arrows. The illumination angle should be between 20° and 45° with respect to the surface normal of the package 10. The lighting units 38.1 and 38.2 of the lighting module are arranged and aligned accordingly.

[0061] Lighting units 38.1 and 38.2 each have a number of light-emitting diodes (LEDs) as light sources. Lighting unit 38.1 is designed to illuminate packaging 10 with light intensity of the reflected light in the second wavelength range, while lighting unit 38.2 illuminates packaging 10 with light intensity of the reflected light in the first wavelength range. Lighting unit 38.2 has two types of LEDs: one type emitting blue visible light and one type emitting red visible light. The visible light emitted by lighting unit 38.2 thus consists of two wavelength ranges, each with a central wavelength in the blue region of the visible spectrum and a central wavelength in the red region. The half-power bandwidth of the two LEDs emitted by lighting unit 38.The wavelength range of the two partial wavelength ranges emitted for visible light is each less than 50 nm.

[0062] The lighting module and its lighting units 38.1 and 38.2 allow for the setting of specific lighting scenarios. In normal operation, lighting units 38.1 and 38.2 are operated alternately, so that the packaging 10 is illuminated either only with light in the second wavelength range from lighting unit 38.1 or with light in the first wavelength range from lighting unit 38.2. As explained at the beginning, however, it is also possible to illuminate the packaging 10 continuously with both lighting units 38.1 and 38.2.

[0063] The light reflected from the surface of the packaging 10 is captured by the image acquisition module 36. For this purpose, the image acquisition module 36 has an area sensor 40 and optics 42, which project a sharp image of the surface of the packaging 10 onto a surface of the area sensor 40. The surface of the area sensor 40 is formed by a plurality of light-sensitive sensor elements. These are preferably arranged in a matrix. The sensor elements of the area sensor 40 and the optics 42 are designed such that one square millimeter of the surface of the packaging 10 is projected onto a partial surface of the area sensor 40 such that the partial surface contains at least four complete sensor elements.Thus, the image scale with which the optics 42 projects an image of the surface of the packaging 10 onto the surface of the area sensor 40 depends on the size of the sensor elements on the surface of the area sensor 40 and the distance between the sensor elements. It goes without saying that the optics 42 are designed to project a sharp image of the surface of the packaging 10 onto the area sensor 40 within the depth of field required by varying packaging diameters.

[0064] The sensor elements of the area sensor 40 are broadband light-sensitive, meaning they are sensitive at least in the partial wavelength ranges of light emitted simultaneously or alternately by the illumination units 38.1 and 38.2. The output value supplied by each individual sensor element of the area sensor 40 – also referred to here as the gray value – corresponds to the total intensity of all light in the various wavelength ranges detected by the respective sensor element.

[0065] The output value supplied by each sensor element of the area sensor 40, also referred to here as the gray value, is greater the greater the total intensity of the light striking that particular sensor element. The total intensity of the light striking that particular sensor element is composed of the partial intensities of the light in the various wavelength ranges that make up the light incident on that particular sensor element.

[0066] This total intensity is the intensity of the light detected by the sensor element in the second wavelength range when the packaging is illuminated exclusively by the lighting unit 38.1 with light in the second wavelength range. Similarly, the output value of each sensor element corresponds to the respective intensity in the first wavelength range of the light when the packaging surface is illuminated exclusively by the lighting unit 38.2 with light in the first wavelength range.

[0067] If, on the other hand, the surface of the packaging 10 is illuminated simultaneously by both the lighting unit 38.1 and the lighting unit 38.2 with light in the second wavelength range as well as with light in the first wavelength range, the light intensity detected by a respective sensor element - and thus the output gray value - depends on the sum of the intensity with which a respective surface element assigned to the sensor element via the image reflects light in the first wavelength range and in the second wavelength range.

[0068] This means that sensor elements that detect, for example, part of the contrast field 14 of the safety marking 12 will always detect a high brightness value and thus deliver a high output value – and therefore a high gray value wi. In contrast, sensor elements that detect part of an orientation marking 22 or a corner marking 20 will always detect a low brightness value and thus also deliver a low output value and gray value si, regardless of whether the illumination is provided by light in the first wavelength range or with light in the second wavelength range. The gray value di that a sensor element provides when part of the safety field 16 is mapped onto it, however, depends on the type of illumination.

[0069] When the packaging is illuminated with light in the first wavelength range, the intensity reflected by the security field 16 is low, so a sensor element detecting part of the security field 16 delivers only a low gray value d1. However, if the packaging is illuminated with light in the second wavelength range, the intensity of the light reflected by the security field is significantly higher – depending on the background – and can, for example, correspond to the intensity reflected by the contrast field 14. Accordingly, a sensor element on which part of the security field is mapped delivers a high gray value d2 when the packaging 10 is illuminated with light in the second wavelength range. If, on the other hand, the packaging 10 is illuminated simultaneously with light in the first and second wavelength ranges, the gray value delivered by a sensor element detecting the security field is a medium gray value.

[0070] Within the image acquisition module 36, the gray values ​​supplied by the area sensor 40 are preprocessed in a preprocessing unit 44. The processed gray values ​​(output values ​​of the sensor elements of the area sensor 40) are fed to an evaluation unit 46, in which the various areas of the safety marking are detected using pattern recognition methods known per se.

[0071] This image capture of the security marking also serves to determine the location of signal field 18 in order to read its intensity. Depending on the intensity of the light reflected by signal field 18, the evaluation unit 46 activates a different reference threshold for assessing the intensity of the light reflected by security field 16 in the second wavelength range.

[0072] Secondly, the intensity values ​​supplied by the various fields of the security marking are compared with respective reference thresholds to evaluate the respective security marking. This evaluation is carried out by an evaluation unit, which is part of the evaluation unit 46 and therefore in Fig. 5 not shown in detail. Of particular importance for the evaluation is the reference threshold for the intensity values ​​recorded when the safety marking was illuminated with light in the second wavelength range in the area of ​​safety field 16.

[0073] The evaluation of the intensity values ​​represented by corresponding gray values ​​d2, which are to be assigned to security field 16 when illuminated with light in the second wavelength range, is carried out with reference to the gray values ​​d1 – and thus the intensity values ​​– which are to be assigned to security field 16 when illuminated with light in the first wavelength range. Depending on how much the intensity of the reflected light in the second wavelength range deviates from the intensity of the reflected light in the first wavelength range, a package is accepted and the deposit refund is processed or not.

[0074] The evaluation unit 46 performs the test according to the following procedure: First, the intensities of the light reflected by the safety field in two different wavelength ranges are recorded as grayscale values ​​d1 and d2. Additionally, the intensities of the light reflected by the contrast field in the first wavelength range are recorded as a grayscale value w1, which may be averaged. A difference value is derived from the two grayscale values ​​d1 and d2, which represent the different intensities of the light reflected by the safety field in the two different wavelength ranges. A correction value is derived from the grayscale value w1, which represents the intensity of the light reflected by the contrast field when illuminated with light in the first wavelength range. This correction value is then used to correct the difference value determined from the intensities of the light reflected by the safety field.

[0075] For example, the difference value is calculated so that it also depends on the intensities of the light reflected from the dark field. For instance, a difference between the intensities of the light reflected from the safety field and the dark field can first be calculated for each wavelength range. This can be done by calculating a first gray value si for each wavelength range, representing the intensity of the light reflected from the dark field in that specific wavelength range. This first gray value si can then be subtracted from a second gray value di, which represents the intensity of the light reflected from the safety field in the same wavelength range. In this way, a contrast value can be calculated for each of the two wavelength ranges. The difference between these two contrast values ​​can then be determined.The difference between a gray value di of the safety field and a gray value si of the dark field for a given wavelength range i can be understood as the contrast value (di - si), which represents the contrast between the safety field and the dark field. The contrast value is greater the more strongly the safety field reflects light in the first or second wavelength range, i.e., the greater the difference in brightness between the dark field and the safety field when illuminated in the respective wavelength range. Since the safety field reflects less light in the first wavelength range than in the second, the contrast value for the second wavelength range is greater than for the first.If the difference value is formed as the difference ((d 1 - s 1 ) - (d 2 - s 2 )) between two contrast values, the difference value is a measure of how much greater the reflectivity of the safety field in the second wavelength range is compared to the reflectivity in the first wavelength range.

[0076] Preferably, each contrast value is normalized using a maximum contrast value that represents the difference between a gray value wi of the contrast field and a gray value si of the dark field for a respective wavelength range. Normalization can be achieved by dividing the respective contrast value by the corresponding maximum contrast value, thus generating a normalized contrast value for each of the two wavelength ranges.

[0077] In this case, the difference value is preferably the difference between the normalized contrast values. The product of the correction factor k and the gray value w1 of the contrast field for light in the first wavelength range constitutes the aforementioned correction value.

[0078] In the simplest case, the gray value w 1 of the contrast field in the first wavelength range can also be used as a correction value.

[0079] In this case we will calculate the difference in contrast values ​​( d 2 - s 2) - ( d 1 - s 1 ) thus normalized with a value - namely the grey value w 1 of the contrast field - which depends on the distance of the safety marking to the respective light source.

[0080] The correction factor k is preferably a constant that has been determined in advance for a particular readout unit or readout unit type and is stored in the respective readout unit.

[0081] The evaluation unit 46 is also connected to a control unit 48, which, for example, controls the lighting units 38.1 and 38.2 and also controls the transport device 32, for example, to rotate the packaging 10 by means of the transport device 32 so that the security marking on the surface of the packaging 10 is within the field of view of the readout unit 34. Image recognition by the evaluation unit 46 is also used for this purpose.

[0082] The control unit also manages deposit refunds and the return of packaging.

Claims

1. Inspection method for a security marking (12) comprising at least one contrast field (14) having a comparatively high reflectivity in a first and a second wavelength range and a security field (16) having different reflectivity properties in the first wavelength range than in the second wavelength range, the test method comprising the following steps: - capturing of the intensities of the light reflected by the safety field (16) in the two different wavelength ranges, whereby the intensities of the light reflected by the safety field in two different wavelength ranges are captured in the form of grey values, - forming a difference value on the basis of the two different intensities of the light reflected by the security field (16) at the two different wavelength ranges, the difference value representing the extent to which the grey values in the region of the image of the security field deviate when illuminated with light in the second wavelength range from the grey values when illuminated with light in the first wavelength range, - capturing the intensity of the light reflected by the contrast field (14) in the first wavelength range - forming a correction value based on the intensity of the light reflected by the contrast field (14) when illuminated with light in the first wavelength range, and - correcting the difference value using the correction value - assessing the safety marking (12) on the basis of the recorded grey values - wherein, in the event that the corrected difference value corresponds to a predetermined reference, the assessment of the safety marking as being in order and - otherwise an assessment is made as being not in order.

2. Inspection method according to claim 1 for a security marking (12) which additionally has at least one dark field (20, 22) with a comparatively low reflectivity in a first and a second wavelength range, characterised in that the difference value is formed as the difference between two contrast values, of which a first contrast value reflects a difference in the intensities produced by the security field (16) and the dark field (20, 22) in the first wavelength range and a second contrast value reflects a difference in the intensities produced by the security field (16) and the dark field (20, 22) in the second wavelength range.

3. Inspection method according to claim 2, characterised in that the contrast values are normalized taking into account the correction value.

4. Inspection method according to at least one of claims 1 to 3, characterised in that the inspection of the security marking (12) and in particular the inspection of the security field (16) is carried out in more than two different wavelength ranges of the light.

5. Security marking (12) comprising at least one contrast field (14) with a comparatively high reflectivity in a first and a second wavelength range and a security field (16) which has different reflective properties in the first wavelength range than in the second wavelength range, characterised in that the security field (16) is printed with two inks, namely firstly with a first ink with reflective properties which differ from those of the contrast field (14) and then with a second ink so that the second ink covers the first ink, namely initially with a first ink with reflective properties which differ from those of the contrast field (14), and subsequently with a second ink, so that the second ink covers the first ink, the second ink having a higher reflectivity and / or transparency in the second wavelength range than in the first wavelength range.

6. Security marking (12) according to claim 5, which additionally comprises at least one dark field (20, 22) with a comparatively low reflectivity in a first and a second wavelength range, wherein the dark field (20; 22) is printed with two inks, namely initially with a first ink with reflective properties which differ from those of the contrast field (14), and subsequently with a second ink, so that the second ink covers the first ink, the second ink having a higher reflectivity and / or transparency in the second wavelength range than in the first wavelength range.

7. Readout unit (34) for a security marking (12), which comprises at least one contrast field (14) with a comparatively high reflectivity in a first and a second wavelength range and a security field (16) which has different reflection properties in the first wavelength range than in the second wavelength range, characterised in that the readout unit (34) is configured, - to capture in at least two different wavelength ranges an intensity of light reflected by the security field (16) of the security marking (12) in the form of grey values, one wavelength range being a wavelength range in which the security field (16) has a high reflectivity, while the other wavelength range is a wavelength range in which the security field (16) has a low reflectivity (high absorption), - to form a difference value on the basis of the two different intensities of the light reflected by the security field (16) at the two different wavelength ranges, the difference value representing the extent to which the grey values in the region of the image of the security field deviate when illuminated with light in the second wavelength range from the grey values when illuminated with light in the first wavelength range, - to capture an intensity of the light reflected by the contrast field (14) in the first wavelength range, - to form a correction value based on the intensity of the light reflected by the contrast field (14) when illuminated with light in the first wavelength range - correct the difference value using the correction value - assessing the safety marking (12) on the basis of the recorded grey values in such a way that if the corrected difference value corresponds to a predetermined reference, the safety marking is assessed as being in order and otherwise it is evaluated as not being in order.

8. Readout unit (34) according to claim 7, characterised in that the readout unit has an image detection module (36) with an area sensor (40) with light-sensitive sensor elements, preferably arranged in a matrix-like manner, for detecting an image imaged on the sensor in two dimensions, said light-sensitive sensor elements being light-sensitive both in the first wavelength range of the light and in the second wavelength range.

9. Readout unit (34) according to claim 8, characterised in that the readout unit (34) has an illumination module (38.1, 38.2) which is designed and arranged to illuminate a viewing area of the image acquisition module (36) simultaneously or alternately with light in the first wavelength range and in the second wavelength range.

10. Readout unit (34) according to claim 9, characterised in that the illumination module (38.1, 38.2) emits light in the visible wavelength range with two main wavelengths during operation of the readout unit (34), one of the two main wavelengths corresponds to red light and the other main wavelength corresponds to blue light.

11. Readout unit (34) according to claim 9 or 10, characterised in that the illumination module (38.1, 38.2) has light-emitting diodes as light sources.

12. Readout unit (34) according to claim 11, characterised in that the illumination module (38.1, 38.2) has different light-emitting diodes, of which a first number of light-emitting diodes emits light in a second wavelength range during operation of the readout unit (34), the wavelength of which is matched to the ink of the security field (16) in such a way that the emitted wavelength is at most 100 nm above a wavelength at which the absorption of the ink is less than 40% of the absorption of the ink in the first wavelength range.