Brand Sensor

Abstract

The invention relates to a sensor for determining marks, in particular contrast marks and / or color marks, comprising a light source for emitting transmitted light, wherein the light source is associated with optics for focusing the transmitted light onto a detectable area, and a light receiver for receiving reflected and / or remitted transmitted light from the detectable area, preferably in the spectral ranges red, green and / or blue. The object of the invention described here is to provide a sensor that overcomes the disadvantages of the prior art, in particular that there is no angular dependence of the light incident on the light receiver, no readjustment of the scanning range is required and the sensor has a simple, cost-effective and durable design. This problem is solved according to the invention by providing the light receiver with a diffusing disk for scattering the reflected and / or remitted transmitted light to be received.

Description

[0001] The invention relates to a sensor for determining marks, in particular contrast marks and / or color marks, comprising a light source for emitting transmitted light, wherein the light source is associated with an optical system for focusing the transmitted light on an area to be recognized, and a light receiver for receiving reflected and / or remitted transmitted light from the area to be recognized, preferably in the spectral ranges red, green and / or blue.

[0002] Sensors for marks, especially contrast sensors or print mark sensors, are used to detect print marks on sheets of paper, for example. They also position labels before applying them to bottles or other packaging materials, as well as detecting a mark on a surface to trigger a further production process, for example.

[0003] Such a sensor should reliably detect any contrast differences, or if possible, color differences, between the target mark and the background. It should also be possible to identify a specific color mark on an irregular background.

[0004] In the first sensors of this type, a light-emitting diode projected a small, sharply defined light spot, also called a scanning area, ideally in a rectangular shape, onto a print mark to be identified. A photodiode measured the amount of reflected light. If the mark was detected, a switching process was triggered.

[0005] These types of sensors, which used only one light color, particularly red, had the problem that a print mark of the same color, for example, a red print mark on white paper, did not produce any contrast difference, and therefore the mark could not be detected by the sensor. This is because the sensor's red transmitted light is reflected and / or remitted by the red mark in the same way as the red transmitted light is reflected by the white background, and the sensor therefore cannot distinguish between light from the background and light from the mark.

[0006] Further development saw the addition of print mark sensors with switchable LEDs. These, in particular, allowed switching between red and green emitted light. However, the user had to specify in advance which color should be used, or rather, which color of emitted light should be used to scan the area to be detected by the sensor. The disadvantage of this is that when switching the color, the scanning area, which is often point-shaped or rectangular, usually shifts, so that readjustment of the sensor's scanning field is often necessary after changing the emitted light.

[0007] Print mark sensors with a white LED have also been used. These have the advantage of being sensitive to all colors. However, they lack the sensitivity of a sensor that scans a detection area with a complementary color. Another advantage of using a white LED is that switching between different emitted light sources is not necessary, allowing the sensor's usually point-shaped or rectangular scanning area to remain in the same location.

[0008] For this reason, RGB illumination has become the standard for print mark sensors. These typically comprise three LEDs arranged closely together and sequentially illuminate the area to be scanned, particularly a print mark. The sensor measures the contrast difference between the mark and the background with each color and then selects the light color with the greatest contrast difference. This type of sensor is therefore capable of reliably detecting, for example, the minimal brightness difference of a yellow mark on white paper at maximum switching frequency. One such method, which involves selecting the correct scanning emitted light color for such a sensor, is described, for example, in DE 198 46 002 A1.

[0009] However, the image of the three light-emitting diodes, especially LEDs, on the print mark does not result in a homogeneous scanning area. In learning mode, when all three LEDs successively scan the area to be detected in pulses, the result is a shapeless scanning area in which the three colors used predominate next to each other, with mixed colors in the transition area. After selecting the light color with the greatest contrast, the scanning area is monochromatic and shifted in the scanning location, which makes precise adjustment of the sensor's scanning area to a fine print mark difficult. Furthermore, such a diffuse, multi-colored scanning area does not meet today's aesthetic standards.

[0010] To solve this problem, German patent DE 10 2015 115 016 B4 describes a light contrast sensor with RGB illumination. A complex-shaped mixed light guide is located above the RGB illumination, mixing the light components of the three individual LEDs in such a way that a single, homogeneous light spot is visible on the print mark. This design has the disadvantage of requiring a lot of space in the optics and causing a significant loss of light output, which ultimately reduces the sensor's sensitivity.

[0011] The same principle with the same disadvantages, only in this case with a straight mixed light guide, is described in patent EP 1 715 313 ​​B1.

[0012] Special RGB photodiodes with three areas, each with a color filter connected upstream, are also known from color measurement technology. A print mark reader or scanner, which features powerful white LED illumination and a precise scanning area on a print mark, as well as an RGB photodiode as a receiver, is functionally equivalent to print mark readers with pure RGB illumination. With this type of sensor, the print mark is illuminated in rapid succession with white light pulses, and the intensity of the reflected RGB color components is determined in parallel. For maximum print mark detection speed, equivalently, as already described in the above-mentioned DE 198 46 002 A1, only the color channel with the highest contrast is evaluated in the subsequent measurement.

[0013] Since the RGB color components can be determined in parallel, complete color recognition can still be carried out at a relatively high speed, making it possible to recognize a colored print mark on a busy, high-contrast background.

[0014] By using a powerful white LED, an intensive scanning area is created on the print mark, resulting in a high, evaluable RGB color value with low noise. The resulting challenge, however, is the correct selection of the RGB photodiode. The optical path in a sensor's optics causes the light reflected or emitted by the mark to fall onto the RGB photodiode at different angles. Therefore, it is important that the RGB photodiodes incorporate classic color filters that are not angle-dependent, as with this type of filter, the filtering effect remains independent of the angle of incidence of the received light. Commercially available RGB photodiodes with interference filters for the RGB photodiodes exhibit a strong angle dependence. Such RGB photodiodes with classic color filters have, by design, three photodiodes arranged parallel to one another or in a 120° segment arrangement.Other versions with fine pixels or honeycomb structure for good mixing of the RGB color values ​​are sometimes realized with interference filters, but these are not suitable due to the angular sensitivity and are also comparatively expensive and often contain disruptive additional electronics, such as preamplifiers and / or signal converters.

[0015] The problem with the RGB photodiodes with the RGB single diodes arranged next to each other, as in Fig. 2, is the inhomogeneity of the RGB intensity measurement. If, for example, the print mark moves sideways into the scanning area, the received light on the RGB photodiode will also fall on the individual RGB diodes one after the other. The RGB color ratio changes so significantly when the print mark is passed through that color recognition is hardly possible and pure contrast analysis is only possible when all three diodes are connected together, which prevents the effect of increasing contrast through the correct color selection. Varying the distance of the print mark also leads to different illumination levels because the image of the scanning area on the RGB photodiodes varies in diameter and therefore primarily the center of the diode is illuminated with maximum intensity, which often results in the red photodiode receiving the largest proportion of the light intensity.

[0016] Based on this prior art, the invention described here has set itself the task of providing a sensor for determining marks, in particular contrast and / or color marks, which overcomes the aforementioned disadvantages of the prior art.

[0017] This object is achieved by means of a sensor according to the features of the applicable claim 1. Furthermore, this is achieved by a method according to the independent method claim 15. Further advantageous embodiments can be found in the dependent claims.

[0018] According to a first aspect of the invention, a sensor for detecting marks, in particular contrast and / or color marks, is provided. The sensor comprises a light source for emitting transmitted light, wherein the light source is associated with an optical system for focusing the transmitted light on a region to be detected, as well as a light receiver for receiving reflected and / or remitted transmitted light from the region to be detected, preferably in the red, green, and / or blue spectral ranges.

[0019] The invention is characterized in that a diffusing disk is assigned to the light receiver to scatter the reflected and / or remitted transmitted light to be received. This has the particular advantage that incident inhomogeneous light is mixed in such a way that the light receiver is evenly illuminated. This, in particular, prevents the previously described technical disadvantage of the prior art, namely variable or inhomogeneous illumination of the light receiver.

[0020] Instead of a diffuser with, for example, a simple, inexpensive RGB photodiode, it is also conceivable to use an RGB photodiode with fine pixels or a honeycomb structure. However, such a photodiode usually has interference filters with strong angular dependence of the filter edges and is no longer offered as a pure photodiode without additional electronics. This would require expensive optical measures to ensure that the light falls onto the photodiode in as parallel a beam as possible. This can only be achieved with large optical losses and considerably higher expenditure for the lens optics. In addition, there is the problem that such diodes without additional electronics are no longer available on the market, and therefore a very expensive special component would have to be introduced. All of these disadvantages are overcome by using a diffuser according to the sensor according to the invention.

[0021] Preferably, the diffusing disc has a scattering angle of 10° to 90°, particularly preferably 30°, relative to the light receiver. Furthermore, in an advantageous embodiment, the diffusing disc is arranged in front of the light receiver, preferably at a distance of 0.5 mm to 5 mm, particularly preferably at a distance of 1.5 mm.

[0022] The advantageous use of a white LED to illuminate the area to be detected results in a sharply imaged scanning area that does not change its color or structure once the sensor has made its color selection. Therefore, readjustment of the sensor is no longer necessary.

[0023] Furthermore, in an advantageous embodiment, the sensor comprises a collimator, in particular a collimator lens, in the optics associated with the light source. This allows the transmitted light to be emitted onto the area to be detected with an approximately parallel beam path. Particularly advantageously, the sensor according to the invention comprises an aperture, particularly preferably with a rectangular cross-section, in order to allow the transmitted light to be incident on the area to be detected in a desired shape, for example, point-shaped or rectangular. Furthermore, in an advantageous embodiment, the optics can comprise a beam splitter. The beam splitter makes it possible, in particular, to achieve a compact design of the sensor.

[0024] The diffuser in front of the RGB photodiode for mixing the received light allows the use of simple, cost-effective photodiodes with a coarse structure. Therefore, the invention preferably provides for the sensor to have a light receiver comprising at least one color channel, particularly in the red, green, or blue spectral range. Particularly advantageously, the light receiver is an RGB photodiode with at least three photosensitive regions, with the preferably photosensitive regions being in the red, green, or blue spectral range.

[0025] In order to realize parallel evaluation of the RGB color values ​​and thus high-speed color recognition, and to ensure reliable detection even with colored print marks on a busy background, the invention provides, in an advantageous embodiment, for the sensor in which the photosensitive areas, in particular RGB photodiodes, are arranged next to one another, preferably in a 120° segment arrangement. This function is not available in prior art print mark readers with pure RGB illumination, or is only possible at a significantly reduced speed, since the three LEDs must be pulsed one after the other.

[0026] Particularly advantageously, at least one color filter is assigned to at least one photosensitive area of ​​the RGB photodiode. This ensures that only the light to be analyzed from the photosensitive area, for example, red light, falls on the photodiode and that no interference occurs with light of other frequencies.

[0027] Finally, in an advantageous embodiment, the sensor has an evaluation unit that generates a signal, in particular an object detection signal, depending on the transmitted light received from the light receiver. Based on such a signal, various action instructions can then be issued, for example, a new process step can be initiated.

[0028] A second aspect of the invention relates to a method for detecting marks, in particular contrast marks and / or color marks, using a sensor according to the invention. First, a transmitted light is sent from a light source to an area to be detected, and reflected and / or remitted transmitted light from the area to be detected is received by a light receiver, preferably light in the red, green, and / or blue spectral range. However, by means of a diffusion screen arranged in front of the light receiver, the reflected and / or remitted transmitted light to be received is mixed before entering the light receiver.

[0029] This has the particular advantage that incident inhomogeneous light is mixed in such a way that the light receiver is evenly illuminated. This prevents the previously described technical disadvantage of the prior art, namely variable or inhomogeneous illumination.

[0030] In a first advantageous embodiment of the method, an area to be detected is first scanned with transmitted light, and a color selection is made based on the highest contrast with the scanned area for detecting another area to be detected. This so-called "learning phase" ensures that recurring contrast marks are reliably detected by the sensor.

[0031] A similar advantage is achieved with color marks in that an area to be recognized is first scanned and, based on the scanned area and on the at least three color channels red, green and blue, a further area to be recognized is recognized.

[0032] The invention is explained in more detail below using an exemplary embodiment.

[0033] It shows: Fig. 1 schematic representation of a sensor according to the invention for detecting marks. Fig. 2 an RGB photodiode with photosensitive areas arranged in series, and Fig. 3 an RGB photodiode with photosensitive areas in a 120° segment arrangement.

[0034] Fig. 1 shows a schematic representation of a sensor 1 according to the invention for detecting brands. The sensor 1 comprises a light source 2, a light receiver 8, here in the form of an RGB photodiode, and an optical system. The term light source is understood to mean any suitable light source, in particular LEDs. The optical system consists of a collimator 5, a beam splitter 6, and a converging lens 7. A diffusing screen 9 is arranged in front of the light receiver 8. From the light source 2, transmitted light 3 is sent via the optical system, i.e. through the collimator 5, the beam splitter 6, and the converging lens 7, onto an area 4 to be detected. Reflected and / or remitted light 10 from the area 4 to be detected is sent back through the beam splitter 6 towards the diffusing screen 9 and thus ultimately to the light receiver 8. The light incident on the diffusing screen 9 is homogenized or dispersed by the diffusing screen 9 before entering the light receiver.mixed, so that ultimately a homogeneous light falls on all photosensitive areas 12 of the light receiver 8, here an RGB photodiode 11.

[0035] Fig. 2 and Fig. 3 show two different types of RGB photodiodes 11. In Fig. 2 shows an RGB photodiode 11 in which the photosensitive areas 12, here a red, green and blue photodiode, are arranged next to each other. Fig. 3, the photosensitive areas 12, also here a red, green and blue photodiode, are arranged in a 120° segment arrangement.

[0036] Thus, a sensor for detecting marks, in particular contrast and / or color marks, is disclosed above, in which there is no angle dependence of the light incident on the light receiver, no readjustment of the scanning range is required and which has a simple, cost-effective and durable design. LIST OF REFERENCE SYMBOLS 1 sensor 2 light source 3 Transmitting light 4 area to be recognized 5 Collimator 6 beam splitters 7 Converging lens 8 light receivers 9 Diffuser 10 reflected or remitted transmitted light 11 RGB photodiode 12 photosensitive area QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 198 46 002 A1 [0008, 0012] DE 10 2015 115 016 B4

[0010] EP 1 715 313 ​​B1

[0011]

Claims

[1] Sensor (1) for determining marks, in particular contrast marks and / or colour marks, comprising: a light source (2) for emitting transmitted light (3), wherein the light source (2) is associated with an optical system for focusing the transmitted light (3) on an area (4) to be detected, a light receiver (8) for receiving reflected and / or remitted transmitted light (10) from the area to be detected (4), preferably in the spectral ranges red, green and / or blue, characterized by that the light receiver (8) is assigned a diffusing disc (9) for scattering the reflected and / or remitted transmitted light (10) to be received. [2] Sensor according to claim 1, characterized by that the diffusing disc (9) has a scattering angle of 10° to 90°, preferably 30°, relative to the light receiver (8). [3] Sensor according to claim 1 or 2, characterized bythat the diffusing disc (9) is arranged in front of the light receiver (8), preferably at a distance of 0.5 mm to 5 mm, particularly preferably at a distance of 1.5 mm. [4] Sensor according to at least one of claims 1 to 3, characterized by that the light source (2) is a white light-emitting diode, preferably with a broad spectral light distribution, comprising a red, green and blue spectral range. [5] Sensor according to at least one of the preceding claims, characterized by that the optics associated with the light source (2) comprises a collimator (5). [6] Sensor according to at least one of the preceding claims, characterized by that the optics associated with the light source (2) comprises a diaphragm, preferably with a rectangular cross-section. [7] Sensor according to at least one of the preceding claims, characterized by that the optics associated with the light source (2) have a beam splitter (6). [8] Sensor according to at least one of the preceding claims, characterized by that the light receiver (8) comprises at least one color channel, in particular in the red, green or blue spectral range. [9] Sensor according to at least one of the preceding claims, characterized by that the light receiver (8) is an RGB photodiode (11) with at least three photosensitive areas (12). [10] Sensor according to claim 9, characterized by that the photosensitive areas of the RGB photodiode (11) are arranged next to each other. [11] Sensor according to claim 9 or 10, characterized by that at least one color filter is assigned to at least one photosensitive area (12) of the RGB photodiode (11). [12] Sensor according to claim 11, characterized by that at least one color filter is angle-independent. [13] Sensor according to at least one of the preceding claims 9 to 12, characterized bythat the photosensitive areas (12) are arranged in a 120° arrangement. [14] Sensor according to at least one of the preceding claims, characterized by that it comprises an evaluation unit which generates a signal, in particular an object detection signal, as a function of the received transmitted light (3) of the light receiver (8). [15] Method for the recognition of marks, in particular contrast marks and / or colour marks, by means of a sensor (1) according to one of the preceding claims 1 to 14, wherein a transmitted light (3) is sent from a light source (2) to an area (4) to be recognised and reflected and / or remitted transmitted light (10) from the area (4) to be recognised is received by a light receiver (8), preferably in the red, green and / or blue spectral range, wherein the reflected and / or remitted transmitted light (10) to be received is mixed by means of a diffusing screen (9) arranged in front of the light receiver (8). [16] Method according to claim 15, characterized by that an area to be recognized (4) is scanned and a color selection is made based on the highest contrast with the scanned area (4) for the detection of another area to be detected. [17] Method according to claim 15 or 16, characterized by that an area to be recognized (4) is scanned and, based on the scanned area (4) and the at least three color channels red, green and blue, a further area to be recognized is recognized.

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