Optoelectronic sensor for detecting object edges

0001The present invention relates to an optoelectronic sensor for detecting object edges of objects moved relative to the sensor in accordance with the features of the preamble of independent claim 1. Such an optoelectronic sensor is from the document <patcit id="pcit0001" dnum="US5841540A"><text>US 5,841,540</text></patcit>, <patcit id="pcit0002" dnum="US4217491A"><text>US 4,217,491</text></patcit>, <patcit id="pcit0003" dnum="JP58223004A"><text>JP 58-223004 A</text></patcit> or <patcit id="pcit0004" dnum="US5280171A"><text>US 5,280,171</text></patcit> known.

0002Optoelectronic sensors are often used to detect packaging, for example beverage cartons, transported along a conveyor belt for subsequent further processing, for example an application of a straw. As a rule, however, the packages are not isolated, but follow each other so closely that when the packages are passed the sensor, the transition from one package to the next package with a conventional triangulation button with a location-resolving light receiver, whose basic mode of operation is well known and therefore not here is explained in more detail, is difficult to recognize, as shown below <figref idref="f0001">Fig. 1</figref> is made clear.

0003<figref idref="f0001">Fig. 1a</figref> shows a plan view of a plurality of beverage cartons 11 arranged one behind the other, which move past a triangulation button on a conveyor belt, and a diagram of the associated desired course of the switching signal of the triangulation button. <figref idref="f0001">Fig. 1b</figref> shows a section of a side view of the beverage cartons 11 <figref idref="f0001">Fig. 1a</figref> and a scanning track 13 of a light spot generated by the transmitted light beam of the triangulation button on the beverage cartons 11. <figref idref="f0001">Fig. 1c</figref> shows the recorded course of a position signal X and the corresponding course of an intensity signal I of the button.

0004There is a large gap between the first and the second beverage carton (from the left), which can be detected sufficiently well via the two signals X and I. However, if there is a small gap, as is the case between the second and the third beverage carton, the associated transition can no longer be clearly identified on the basis of the courses X and I, as is shown at 15. In addition, there are other sources of error which make it difficult to generate the desired switching signal from the signal profiles X and I, in particular by means of one or more threshold value comparisons. For example, the scanning track 13 leads over a text printed in black on the beverage cartons, ie ultimately via an inhomogeneous texture, so that the center of gravity of an image of the light spot recorded by the light receiver and thus the position signal X fluctuates accordingly, as shown at 17. In addition, a glossy area through which the light is at least partially reflected in a directed manner, or an offset of a beverage carton perpendicular to the conveying direction can disturb the intensity signal I, as shown at 19 or 21. These sources of error can consequently produce a higher signal swing than a transition between two successive beverage cartons, so that the edges of the beverage cartons cannot be detected robustly.

0005It is known from the prior art to specifically accelerate the packaging at an interface between a slower and a faster conveyor belt in order to generate large and thus easily detectable gaps. However, such arrangements take up a lot of space and are very cost-intensive in comparison to an optoelectronic sensor alone.

0006It is therefore an object of the invention to provide an inexpensive optoelectronic sensor of the type mentioned at the outset with robust edge detection.

0007This object is achieved by an optoelectronic sensor with the features of claim 1.

0008In this way, the transition between two successive objects can be recognized in particular on the basis of the rear object edge of the front object in the direction of movement and / or the front edge of the rear object. The two light receivers are preferably arranged in a receiver plane, in particular formed by the light emitting device and the two light receivers, and in particular running horizontally, which extends transversely, in particular perpendicularly, to the alignment of the object edges.

0009If, for example, the respective transmitted light beam is oriented at least substantially parallel to a normal of a flat side of the object facing the sensor, at least approximately the same amount of light falls on the two light receivers, ie the two light receivers detect at least approximately the same reception intensity (balanced state). If the transmitted light beam hits the rear edge, more light falls on the rear light receiver in the direction of movement and less light on the front light receiver than in the balanced state. For the leading edge, this is exactly the opposite. The two light receivers thus represent a kind of energetic balance, which can deflect in different directions depending on whether it is a rear or front object edge.

0010By comparing, in particular forming the difference, the received intensities recorded by the two light receivers, which change when the transmitted light beam strikes an object in the region of an edge with simultaneous movement of the object and therefore have a large signal swing relative to one another, an assessment can then be made whether there is a gap or object edge or not. Such a comparison, which is based on the energetic evaluation of two reception intensities, can also identify edges of objects lying very close to one another or small gaps.

0011An evaluation of the result of a respective comparison includes, according to the invention, that the result of the respective comparison is evaluated together with one or more results from one or more other comparisons. If the evaluation is based on a single result, for example a difference between the two reception intensities, the evaluation can consist, for example, in a comparison of the difference with a threshold value.

0012Such a sensor can achieve a considerable cost advantage over the implementations known from the prior art. Such a sensor enables high switching frequencies with at the same time relatively low power consumption, and can be built in a relatively small size.

0013The evaluation unit is designed to jointly evaluate the results of the comparisons of at least two recordings, the joint evaluation preferably being carried out continuously or continuously over time.

0014A recording is to be understood as a recording of the two images of the light spot of the transmitted light beam of a light transmitter recorded by the two light receivers.

0015If the conveying speed of the objects is known, then it is also known, with a known gap width to be recognized, with what time offset after the detection of a potential rear edge a front edge should be detected, so that the robustness of the edge detection can be increased with just one light transmitter . In particular, it is therefore preferred if the at least two recordings follow one another in time or at least two different times. The time interval between the at least two recordings can be within a predetermined time interval.

0016Alternatively and / or additionally, it can also be provided that the at least two recordings are made by the at least two light transmitters. Again, two recordings are evaluated together, but in this case they are not assigned to a single light transmitter from whose light spot at least two recordings are taken in succession, but at least two light transmitters, by means of which the at least two recordings can be taken at least substantially simultaneously, where "essentially" refers in particular to alternately controlled light transmitters. A potential front edge (by one light transmitter) and a potential rear edge (by the other light transmitter) can be detected at least substantially simultaneously by the at least two light transmitters. The conveying speed of the objects does not have to be known. In this case in particular, it is preferred if the two light receivers and the light transmitter (s) are provided in a line arrangement or arranged in a row and / or arranged in the aforementioned receiver level.

0017For example, a difference can be formed from the optionally weighted two individual differences (the received intensities recorded by the two light receivers) obtained at least two different times and / or by the at least two light transmitters, and this difference can be compared with a threshold value. Basically, instead of this difference formation, an algorithm can also be used in general, by means of which the two individual differences can be compared with one another and evaluated together.

0018In particular, the sensor can be designed to adapt the time interval between the at least two recordings and / or the distance between the at least two light transmitters to a predetermined expected distance between two adjacent objects or a predetermined width of a gap formed between two adjacent objects. As a result, the sensor can be set to different gap widths, in particular the desired gap width to be detected.

0019The at least two light receivers are preferably purely energetic receivers, ie receivers that have no spatial resolution. Such receivers offer a cost advantage over spatially resolving light receivers. In this case in particular, it is preferred if the sensor is designed to drive the at least two light transmitters alternately, so that it is possible to differentiate between the recordings of different light transmitters. If light receivers with spatial resolution are provided, preferably only the reception intensities and no distance information are evaluated by the evaluation unit.

0020An even number of light receivers is preferably provided, at least four light receivers being provided, two light receivers each forming a pair of light receivers, and the two light receivers of a respective pair being arranged on the two opposite sides of the light transmitter device, preferably the evaluation unit therefor is trained, to use only one or more selected pairs for the detection of object edges, the number of selected pairs being in particular less than the number of existing pairs. The pair or pairs of light receivers that are best suited for edge detection can therefore be selected. If several pairs are selected, it is preferred if the results of the several pairs are offset against one another and evaluated together or be rated. In particular, the pairs are arranged in receiver planes running parallel to one another or one above the other.

0021For example, it can happen that an object is tilted backwards with respect to an axis running in the conveying direction, so that a lot of light is then reflected back onto a pair arranged in an upper receiver plane due to a gloss effect associated with the tilting of the object, as a result of which this pair is dazzled and the recording of this couple is disturbed. This upper pair is therefore not taken into account in the edge detection. Additionally and / or alternatively, it can also happen that a pair arranged in a lower receiver level then receives too little light, so that the recording of this pair is also not taken into account in the edge detection. In particular, it can therefore be preferred if the selection is dependent on at least one of the reception intensities of the two images recorded by the two light receivers of the respective pair, wherein a pair is preferably not selected if the at least one of the reception intensities exceeds a predetermined upper threshold value and / or falls below a predetermined lower threshold.

0022According to an embodiment of the invention, at least one further, in particular at least two further, spatially resolving light receivers are / are provided. As a result, the other sources of error mentioned at the beginning can be eliminated. In particular, the two further light receivers can be arranged on the other two opposite sides of the light emitting device.

0023The evaluation unit is preferably designed to offset the two distances determined by means of triangulation from the positions of the two images of the respective light spot recorded by the two further light receivers and to evaluate the result of the respective offset, preferably a particularly weighted one for the respective offset Average is formed from the two distances. In this way, disadvantageous effects such as those caused by an inhomogeneous texture can be avoided, since a shift in the center of gravity in one of the two further light receivers can be compensated for by an opposite shift in the center of gravity of the same amount in the other of the two further light receivers.

0024The weighting preferably depends on the two reception intensities of the two images of the respective light spot recorded by the two further light receivers, the relative weighting of the distance determined from the position of the respective image being preferably smaller, the greater the relative reception intensity of the respective image. As a result, gloss effects or Reflection caused errors in edge detection can be largely suppressed, since a shiny area normally only interferes with the distance determination of one of the two other light receivers. The "disturbed" light receiver then has an increased reception intensity compared to the other further light receiver, so that - if an increased reception intensity is determined - the corresponding distance can be weighted less when averaging.

0025This aspect of the present invention and developments thereof are also claimed independently of the at least two light receivers, ie The invention also relates to an optoelectronic sensor for detecting object edges of objects moved relative to the sensor, with a light emitting device with at least one light transmitter, in particular at least two light transmitters, for generating a respective collimated or focused transmission light beam, with at least two light receivers for receiving a through the light beam generated on a respective object, wherein the two light receivers are arranged on two opposite sides of the light emitting device, and with an evaluation unit which is designed to offset the two distances determined by triangulation from the positions of the two images of the respective light spot recorded by the two light receivers and the result evaluate the respective allocation in order to recognize an object edge, wherein a weighted mean value is formed from the two distances in the respective calculation, and the weighting depends on the two reception intensities of the two images of the respective light spot recorded by the two further light receivers.

0026In addition, it can be provided that the evaluation unit is designed to jointly evaluate the results of the calculations for the at least two light transmitters. This makes it possible, in particular, to avoid a disturbance in the edge detection by an object which is offset perpendicular to the conveying direction relative to the other objects, since this makes it possible to recognize when the light spots assigned to the at least two light transmitters fall on different objects. In this case in particular, it is again preferred if the sensor is designed to alternately control the at least two light transmitters, so that it is possible to differentiate between the reception intensities and the determined distances between different light transmitters.

0027According to another embodiment of the invention, the light emitting device and the at least two light receivers and / or at least two further light receivers each comprise a polarization filter, wherein preferably all polarization filters of the sensor are either linear polarization filters or circular polarization filters and / or wherein preferably the polarization direction of the polarization filter of the respective light receiver and / or respective further light receiver is at least substantially opposite or corresponds to the polarization direction of the polarization filter of the light emitting device. If the sensor is designed with linear polarization filters, the respective transmitted light beam is linearly polarized. The reflection of an object retains the polarization of the light, and the reflection is lost when it is reflected. By oppositely aligned, ie Reflected light, which causes errors in the distance determination, can be at least largely masked out by at least essentially 90 ° linear polarization filters. If the sensor is designed with circular polarization filters, the respective transmitted light beam is circularly polarized in one of two directions of rotation, left or right. When reflecting on an object, the direction of rotation of the polarization of light is reversed or rotated, the polarization is lost during a remission. Reflected light can in turn be blocked out at least for the most part by polarizing filters having the same direction, ie having the same direction of rotation.

0028The present invention further relates to a method according to claim 12.

0029Preferred embodiments of the method according to the invention result in an analog manner from the preferred configurations of the image sensor according to the invention.

0030Non-limiting exemplary embodiments of the invention are shown in the drawing and are described below.<dl id="dl0001"><dt>Fig. 1</dt><dd>beverage cartons arranged in a row and the signals determined for this by a conventional triangulation button,</dd><dt>Fig. 2</dt><dd>an optoelectronic sensor according to an embodiment of the invention in a plan view, and</dd><dt>Fig. 3</dt><dd>an optoelectronic sensor according to another embodiment of the invention in a rear view.</dd></dl>

0031The in <figref idref="f0002">Fig. 2</figref> The sensor shown comprises a light transmitter device with a light transmitter 23 and two light receivers 25 arranged at least substantially symmetrically on both sides in a receiver plane, ie to the left and right of the light transmitter 23. The light transmitter 23, which comprises a light source 27 and a transmission lens 29, transmits a collimated one or focused transmission light beam 31 which falls on beverage cartons 11 which are moved past the sensor in the conveying direction 33. The transmitted light beam 31 generates a light spot there. The transmitted light beam 31 is at least substantially perpendicular to the sides of the beverage cartons 11 facing the sensor.

0032The light remitted at the location of the light spot with Lambert characteristics returns to the sensor as receiving light beams 35 and is detected in the light receivers 25 via receiving lenses 37. The light receivers 25 are purely energetic receivers without spatial resolution, so that only the reception intensities of the images of the light spot recorded by the light receivers 25 are recorded there. In addition, a control and evaluation unit 39 connected to the light transmitter 23 and the light receivers 25 is provided in order to control the light transmitter 23 and to evaluate the aforementioned reception intensities.

0033If the transmitted light beam 31 strikes a beverage carton 11 outside an edge 41 (left image), the reception intensity detected by the front light receiver 25 in the conveying direction 33 corresponds at least approximately to the reception intensity detected by the rear light receiver 25 in the conveying direction 33, since at least approximately the same a lot of light falls on the two light receivers 25. An edge 41 is therefore not present. If, on the other hand, the transmitted light beam 31 strikes the beverage carton 11 in the area of ​​the edge 41 (right image), due to the rounding of the edge 41, significantly more light falls on the light receiver 25 at the rear in the conveying direction 33, so that the reception intensities of the two light receivers 25 differ significantly from one another .

0034The difference between the two reception intensities can therefore be used as a criterion for the presence of an edge 41. In particular, the criterion is met if the difference exceeds a predetermined threshold value. As a result, beverage cartons 11 or small gaps between beverage cartons 11 can be detected very close together.

0035On the rear edge 41 of a beverage carton 11, the front edge 41 of the next beverage carton 11 follows with a certain time interval, the limits of which result from the conveying speed of the beverage cartons 11 and the potential distances between the beverage cartons 11, the difference for the two Edges 41 has opposite signs. The robustness of the gap or edge detection can be further increased by the evaluation criterion as to whether a front edge 41 follows a rear edge 41 within a predetermined time interval. In particular, the difference between the difference for the rear edge 41 and the difference for the front edge 41 can be formed and compared with a threshold value, the criterion for the existence of a gap or a front and rear edge 41 is satisfied. However, the sign of this superordinate difference depends on the conveying direction 33.

0036At the in <figref idref="f0002">Fig. 3</figref> Simplified sensor is a further development of the in <figref idref="f0002">Fig. 2</figref> shown sensor. Notwithstanding that in<figref idref="f0002">Fig. 2</figref> shown sensor includes the sensor according to <figref idref="f0002">Fig. 3</figref> not just one, but two light transmitters 23, which are actuated alternately and which are arranged together with the two light receivers 25 in a horizontal row, and additionally two further, spatially resolving light receivers 43 with receiving lenses 45. The two light transmitters 23 comprise two light sources 27 and one common transmission lens 29.

0037In principle, however, two transmitting lenses can also be provided, or only one light source, from whose light beams two transmitting light beams are subsequently generated. The light transmitters 23 are preferably lasers or LEDs. The two light receivers 25 only provide reception intensities, and the two further light receivers 43 each additionally provide position or distance information. In principle, however, the two light receivers 25 can also be designed as spatially resolving light receivers and / or can provide position or distance information.

0038The two further light receivers 43 are arranged at least substantially symmetrically above and below the light transmitter device or in a further receiver plane which is perpendicular to the receiver plane formed by the light transmitters 23 and the light receivers 25. In the rear view shown, the light receivers 25 and the further light receivers 43 are circular, each offset by 90 ° from one another, distributed around the light transmission device. The further light receivers 43 can be, for example, single-line image sensors or image sensors with a pixel matrix, or PIN diodes.

0039A rear edge 41 and a front edge 41 can be detected essentially simultaneously by the two light transmitters 23 for a difference formation analogous to the aforementioned difference formation. The two light receivers 25 have a sufficiently large reception area in order to be able to record the images of both the light spot of the transmitted light beam 31 of the first light transmitter 23 and the light spot of the transmitted light beam 31 of the second light transmitter 23.

0040The corresponding criterion for the existence of an object is: <maths id="math0001" num="(1)"><math display="block"><mfrac><mrow><msub><mi>E</mi><mrow><mi>L</mi><mn>1</mn></mrow></msub><mo>−</mo><msub><mi>E</mi><mrow><mi>R</mi><mn>1</mn></mrow></msub></mrow><mrow><msub><mi>E</mi><mrow><mi>L</mi><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>R</mi><mn>1</mn></mrow></msub><mo>+</mo><mi>M</mi></mrow></mfrac><mo>−</mo><mfrac><mrow><msub><mi>E</mi><mrow><mi>L</mi><mn>2</mn></mrow></msub><mo>−</mo><msub><mi>E</mi><mrow><mi>R</mi><mn>2</mn></mrow></msub></mrow><mrow><msub><mi>E</mi><mrow><mi>L</mi><mn>2</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>R</mi><mn>2</mn></mrow></msub><mo>+</mo><mi>M</mi></mrow></mfrac><mo>&lt;</mo><mi>limit </mi><mn>1,</mn></math><img file="EP2390620B2_D0001.tif" /></maths> where E_L1 the reception intensity of the left light receiver for the first light transmitter, E_R1 the reception intensity of the right light receiver for the first light transmitter, E_L2 the reception intensity of the left light receiver for the second light transmitter and E_R2 is the reception intensity of the right light receiver for the second light transmitter, and where M ≠ 0, which is intended to prevent division by 0 at reception intensities of 0.

0041With simultaneous detection of the two edges 41, this difference takes on a maximum value which corresponds to the sum of the amount of the difference for the front edge 41 and the amount of the difference for the rear edge 41 and which exceeds the limit value 1, so that the criterion for the presence of a gap 41 is fulfilled. The sign of this difference is independent of the conveying direction 33.

0042Two triangulation buttons are implemented by the first or second light transmitter 23 and the two further light receivers 43, by means of which the distance of a beverage carton 11 from the sensor can be calculated. Since the further light receivers 43 are arranged symmetrically around the light transmitter 23, a disturbance in the two calculated distances caused by an inhomogeneous texture on the respective beverage carton 11 can be compensated for. For this purpose, an average value is formed from the two calculated distances, since with the associated addition the errors caused by the disturbance in the two calculated distances cancel each other out at least to a large extent.

0043The two calculated distances can be weighted when averaging. The weighting of the respective calculated distance is greater, the smaller the relative reception intensity on the respective further light receiver 43. This is particularly advantageous because it means that a calculated distance, which is incorrect due to a gloss effect, is weighted less. In this way, the object distance can be determined with particular accuracy and a particularly robust background suppression can be achieved.

0044The corresponding criterion for the existence of an object is then: <maths id="math0002" num="(2)"><math display="block"><mfrac><mn>1</mn><mn>2</mn></mfrac><mfenced><mrow><msub><mi>X</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mfrac><msub><mi>E</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub><mrow><msub><mi>E</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub></mrow></mfrac><mo>+</mo><msub><mi>X</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub><mfrac><msub><mi>E</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mrow><msub><mi>E</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub></mrow></mfrac></mrow></mfenced><mo>&lt;</mo><mi>limit </mi><mn>2,</mn></math><img file="EP2390620B2_D0002.tif" /></maths> where E_U1 the reception intensity of the lower light receiver for the first light transmitter, E_O1 the reception intensity of the upper light receiver for the first light transmitter, X_O1 the determined distance of the upper light receiver for the first light transmitter and X_U1 is the determined distance of the lower light receiver for the first light transmitter.

0045Since there are two light transmitters 23, a mutual offset of two successive beverage cartons 11 perpendicular to the conveying direction 33 can be recognized (that is, there is an edge) when the transmission light beam 31 from one of the two light transmitters 23 onto the one beverage carton 11 and the transmission light beam 31 of the other light transmitter 23 falls on the other beverage carton 11.

0046In this case, the corresponding criterion for the existence of an object is: <maths id="math0003" num="(3)"><math display="block"><mfenced><mrow><msub><mi>X</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mfrac><msub><mi>E</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub><mrow><msub><mi>E</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub></mrow></mfrac><mo>+</mo><msub><mi>X</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub><mfrac><msub><mi>E</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mrow><msub><mi>E</mi><mrow><mi>O</mi><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>U</mi><mn>1</mn></mrow></msub></mrow></mfrac></mrow></mfenced><mo>−</mo><mfenced><mrow><msub><mi>X</mi><mrow><mi>O</mi><mn>2</mn></mrow></msub><mfrac><msub><mi>E</mi><mrow><mi>U</mi><mn>2</mn></mrow></msub><mrow><msub><mi>E</mi><mrow><mi>O</mi><mn>2</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>U</mi><mn>2</mn></mrow></msub></mrow></mfrac><mo>+</mo><msub><mi>X</mi><mrow><mi>U</mi><mn>2</mn></mrow></msub><mfrac><msub><mi>E</mi><mrow><mi>O</mi><mn>2</mn></mrow></msub><mrow><msub><mi>E</mi><mrow><mi>O</mi><mn>2</mn></mrow></msub><mo>+</mo><msub><mi>E</mi><mrow><mi>U</mi><mn>2</mn></mrow></msub></mrow></mfrac></mrow></mfenced><mo>&lt;</mo><mi>limit </mi><mn>3,</mn></math><img file="EP2390620B2_D0003.tif" /></maths> where, E_U2 the reception intensity of the lower light receiver for the second light transmitter, E_O2 the reception intensity of the upper light receiver for the second light transmitter, X_O2 the determined distance of the upper light receiver for the second light transmitter and X_U2 is the determined distance of the lower light receiver for the second light transmitter.

0047In addition, it is preferred if, in the sense of background suppression, a criterion for the presence of an object is set which is based on the total energy received by the two further light receivers 43: <maths id="math0004" num="(4)"><math display="block"><msub><mi>E</mi><mi>U</mi></msub><mo>+</mo><msub><mi>E</mi><mi>O</mi></msub><mo>></mo><mi>limit </mi><mn>4,</mn></math><img file="EP2390620B2_D0004.tif" /></maths> where Eu is the reception intensity of the lower light receiver for the first and / or second light transmitter and Eo is the reception intensity of the upper light receiver for the first and / or second light transmitter.

0048The sensor according to <figref idref="f0002">Fig. 3</figref> is preferably designed in such a way that an object detection signal is output, ie that the presence of a beverage carton 11 is recognized when conditions (1) to (4) are met. If at least one of the conditions mentioned is not met, there is a transition between two successive beverage cartons 11 or an edge 41 is recognized.

0049A particularly robust edge detection can be achieved with the present invention.

Reference list

0050<dl id="dl0002" compact="compact"><dt>11</dt><dd>Beverage carton</dd><dt>13</dt><dd>Tracing track</dd><dt>15</dt><dd>little gap</dd><dt>17</dt><dd>inhomogeneous texture</dd><dt>19</dt><dd>shiny area</dd><dt>21</dt><dd>Offset</dd><dt>23</dt><dd>Light transmitter</dd><dt>25</dt><dd>Light receiver</dd><dt>27</dt><dd>Light source</dd><dt>29</dt><dd>Transmission lens</dd><dt>31</dt><dd>Transmitted light beam</dd><dt>33</dt><dd>Direction of conveyance</dd><dt>35</dt><dd>Received light beam</dd><dt>37</dt><dd>Receiving lens</dd><dt>39</dt><dd>Control and evaluation unit</dd><dt>41</dt><dd>Edge</dd><dt>43</dt><dd>further light receiver</dd><dt>45</dt><dd>Receiving lens</dd></dl>