Equipment for determining the speed and / or length of a product

Abstract

The present invention relates to a device for determining the speed and / or length of a product, in particular a strand, moving in a conveying direction. The device comprises a laser for irradiating the surface of the product and a detector arrangement for detecting laser radiation backscattered by the surface of the product. The detector arrangement comprises a first sensor, in particular a photodiode, with a first transmission grating arranged upstream of the first sensor, and a second sensor formed by an image sensor. Furthermore, a first beam splitter is provided, which splits the laser radiation backscattered by the product into laser radiation directed to the first sensor, on the one hand, and to the image sensor, on the other hand. An evaluation device is configured to determine the speed and / or length of the product based on an intensity modulation detected by the first sensor during product movement and / or based on a shift of a speckle pattern formed on the image sensor and detected by the image sensor during product movement.

Description

Technical Field

[0001] The invention relates to a device for determining the speed and / or length of a product, preferably a strand, moving in a conveying direction, comprising a laser for irradiating the surface of the product and detector means for detecting laser radiation backscattered by the surface of the product. Background Art

[0002] For example, when producing tubes in extrusion systems, the length of the produced strands needs to be measured. Accurately detecting the product length offers the potential for creating additional value. Contactless optical measurement methods are known from the prior art. These offer the advantage of being non-invasive and, therefore, largely wear-free. Avoiding slip also results in higher measurement accuracy and allows measurement of a wide range of products. The most common optical length measurement methods share the indirect length measurement through continuous speed measurement of the product.

[0003] Optical spatial filter measurement devices are known, in which a sensor detects an optical pattern generated by irradiating the product surface via a transmission grating. The sensor detects the movement of the product and the resulting movement of the optical pattern, in the simplest case as a simple intensity modulation. While this measurement method is characterized by its great structural and measurement simplicity, it has not been widely accepted in practice, particularly because it does not always provide reliable results at low speeds, (sudden) standstills, or under high positive or negative accelerations. It also cannot distinguish the direction of product movement.

[0004] In other optical length measuring devices, for example, a light-emitting diode is used to illuminate the product surface, and an objective lens is used to image the illuminated surface onto an imaging sensor, such as a CCD sensor. In this case, the surface structure of the product itself is used as the optical pattern. In the data recording, the individual pixels can be weighted in such a way as to simulate the effect of a transmission grating. The advantage of this measuring device is that, for example, multiple signals can be generated simultaneously from the original image by different grating weightings in the analysis. In this way, for example, directional sensitivity can be achieved. However, these measuring devices are not widely accepted in practice. This is particularly due to the limited bandwidth and spatial resolution of the imaging sensor and the resulting limitations on measurement accuracy and the measurable speed range. The use of imaging optical devices also makes the system inflexible and susceptible to spacing changes, thereby limiting the depth of field. The orientation of the measuring system is significantly expensive, and because the surface structure of the product is used as the optical pattern, problems arise when the product surface is very smooth.

[0005] In practice, laser Doppler measuring devices are particularly popular. Using the Doppler effect, laser light scattered back by a moving surface is analyzed. Two collimated laser beams, for example, can be incident on a product at a specific angle and superimposed on its surface. This superposition produces an interference pattern, whereby the intensity of the laser light scattered back by the surface modulates when the product moves. Even with such measuring devices, it is impossible to detect a product's stationary state or changes in direction without further precautions. Therefore, it has been proposed to use so-called Bragg cells to generate a frequency shift between the two laser measuring beams. This causes the interference pattern to move over the illuminated surface area of ​​the product and can identify the product's direction of movement or stationary state. However, Bragg cells are very expensive. Another disadvantage of laser Doppler devices is that the calibration of the measuring device's components depends on the angle of the two laser measuring beams and on the laser wavelength. This makes the measurement device complex to set up. Summary of the Invention

[0006] Therefore, starting from the described prior art, the object of the present invention is to provide a device of the type mentioned at the beginning, with which the speed and / or length of the product can be reliably measured at any time, and the direction change or standstill of the product can also be detected in a reliable, simple and cost-effective manner.

[0007] The present invention achieves this object by means of a device according to the invention for determining the speed and / or length of a product moving in a conveying direction. Advantageous embodiments are given in the description and the drawings.

[0008] The invention achieves this object in a device of the type mentioned at the outset in that the detector arrangement comprises a first sensor with a first transmission grating arranged upstream of the first sensor and a second sensor formed by an image sensor, further comprising a first beam splitter which divides the laser radiation backscattered by the product into laser radiation which is directed to the first sensor on the one hand and to the image sensor on the other hand, and an evaluation device which is designed to determine the speed and / or length of the product from an intensity modulation detected by the first sensor during product movement and / or from a shift of a speckle pattern detected by the image sensor during product movement and formed on the image sensor.

[0009] The product may be, in particular, a strand. The strand may be a tubular strand. In particular, the strand is conveyed by the device along its longitudinal axis. However, the product may also be, for example, a foil, a plate, or another profile. To convey the product through the device, the device may include a corresponding conveying device. The product may be made, for example, of plastic, metal, or glass. The product may, for example, come from an extrusion device in which the product is produced by extrusion. The device may also include the extrusion device.

[0010] In the apparatus according to the present invention, the surface of a product is irradiated with laser light, and the laser radiation is scattered by the product. A first sensor is provided, and a first transmission grating is arranged upstream of the first sensor in the beam path of the laser radiation. Radiation scattered back by the product accordingly strikes the first transmission grating, forming a speckle pattern on the first transmission grating. The speckle pattern is formed by the interference of sufficiently coherent radiation (here, laser radiation), which is scattered by locations at different heights on the product surface and has corresponding optical path differences that produce an interference pattern (speckle pattern). Radiation passes through the first transmission grating and is detected by the first sensor, corresponding to the speckle pattern formed on the first transmission grating. Movement of the product in the conveying direction causes corresponding movement of the speckle pattern on the transmission grating. This results in a corresponding modulation of the radiation intensity received by the first sensor. The frequency of the intensity modulation can be used to infer the speed of the product and, in turn, the length of the product between different measurement times, in a manner known per se. The modulation frequency is, in particular, proportional to the speed of the product. In particular, with a collimated laser beam, the laser beam is unaffected by movement of the product in directions other than the conveying direction. Therefore, collimated laser radiation can preferably be used. The path traveled by the product and the speckle pattern on the transmission grating are then identical, regardless of any movement of the product in directions other than the transport direction. However, the use of collimated laser radiation is not mandatory. Rather, it is also possible to not use collimated laser radiation or to use it only partially.

[0011] An example of a laser is an infrared laser. The speckle pattern is a true speckle pattern, i.e., a speckle pattern formed solely by the propagation of radiation scattered on a sufficiently rough surface and propagating in space. Because the speckle pattern is initially formed on the first transmission grating, it is always focused on this first transmission grating. Therefore, no imaging optics are required. Therefore, in the device according to the present invention, in particular, no imaging optics can be provided between the product and the first sensor. This makes the structure and configuration of the device according to the present invention simple and cost-effective. Furthermore, different working distances relative to the product can be achieved, and fluctuations in the distance can be tolerated during the measurement or between different measurements. The use of the speckle pattern ensures high contrast even for very smooth surfaces with roughness on the order of the laser wavelength, thereby ensuring high signal quality. Even very smooth surfaces can be reliably measured. Due to its significantly higher bandwidth, especially compared to imaging sensors such as CCD sensors, the first sensor can be used to perform measurements within the same velocity range as laser Doppler measurement devices using spatial filter methods.

[0012] However, as explained at the outset, spatial filter methods are fundamentally problematic at very slow product speeds, particularly when the product is stationary. As previously mentioned, it has been previously impossible to use spatial filter methods for directional detection without compromising measurement accuracy and speed range. To achieve directional sensitivity and measurement capabilities in a simple and cost-effective manner even at very low conveyor speeds down to a standstill, the device according to the present invention combines the described spatial filter method with image acquisition of the speckle pattern generated by irradiating the product surface with laser light. To this end, the device includes a second sensor in the form of an image sensor, i.e., a sensor surface with two-dimensional resolution. A speckle pattern is also formed on the sensor surface of the image sensor. Using a beam splitter, both sensors observe the same area of ​​the product surface or the laser radiation scattered by the same area of ​​the product surface. Consequently, both sensors detect the same speckle pattern. A first transmission grating can be positioned between the first beam splitter and the first sensor. The analysis device analyzes the measurement results of the second sensor (image sensor) using the so-called optical flow tracking method, which is also used in optical computer mice, for example. The speckle pattern formed on the image sensor is moved across the sensor surface in accordance with the conveying motion of the product. This shift in the speckle pattern allows, on the one hand, for measuring the speed and, therefore, the length of the product, even at very low conveyor speeds, down to a standstill. On the other hand, it also provides directional sensitivity, allowing, in particular, the measurement of movements transverse to the conveyor direction. Because the data analysis is based on correlation analysis, image sensors can measure slow conveyor speeds significantly more efficiently than with spatial filter measurement systems designed with optical gratings for a very wide speed range.

[0013] The device according to the present invention thus combines spatial filter measurement with imaging measurement using the optical flow tracking method. Due to the arrangement with the beam splitter, both sensors observe the same speckle pattern. This allows reliable, structurally simple, and cost-effective measurement of product speed and length, while also identifying the direction, over a wide speed range down to standstill. The first sensor can serve as the primary sensor, measuring the product's speed and / or length during normal operation when it reaches its operating speed. When the product's conveying speed is low, down to standstill, and / or for direction identification, the second sensor (an image sensor) can serve as an auxiliary sensor. Even very large acceleration values ​​are not a problem for reliable measurement. Furthermore, a very small distance between the detector device and the product, for example less than 10 cm, is possible, which allows for better analysis, especially with very small, particularly thin, or very smooth products. Furthermore, any protective housing that may be required can be made more compact, further reducing the complexity and cost of the device. Dust or other interfering factors in the beam path have little effect. Conventional laser Doppler devices require expensive additional protective components for this purpose. Furthermore, in the device according to the invention, the angle between the laser beam and the product has no relevant influence on the measurement result. This allows for simple calibration.

[0014] According to one embodiment, a first lens can be provided between the first transmission grating and the first sensor to focus the laser radiation directed to the first sensor onto the first sensor. The focusing lens ensures that all radiation that passes through the transmission grating and reaches the first sensor is conveyed to the first sensor and is thus available for analysis.

[0015] In a particularly practical manner, the first sensor may be a photodiode. A key advantage of a photodiode over an image sensor is its higher bandwidth. For example, a silicon photodiode may be used. Silicon photodiodes have a high sensitivity to, for example, commonly used infrared lasers.

[0016] According to another embodiment, a second lens can be provided between the first beam splitter and the image sensor to focus the laser radiation directed to the image sensor. While the speckle pattern is formed on the first transmission grating in the beam path of the first sensor, as described above, a speckle pattern is formed on the sensor surface in the beam path of the image sensor (second sensor). The focusing lens can focus the laser radiation onto the measurement aperture of the image sensor, enabling analysis of the entire laser radiation. This can further improve the analysis of the measurement signal. The focusing lens can be provided directly before the image sensor and / or, for example, directly after the first beam splitter to collect more radiation, for example, when there is a large distance or a small product.

[0017] According to another particularly practical embodiment, the image sensor can be a CCD sensor or a CMOS sensor.

[0018] According to another embodiment, the detector arrangement may further include a third sensor, and a second beam splitter is disposed between the first beam splitter and the image sensor. The second beam splitter splits the laser radiation from the first beam splitter into laser radiation directed to the image sensor and to the third sensor. According to another embodiment, the detector arrangement may further include a third sensor, and a second beam splitter is disposed between the first beam splitter and the first transmission grating. The second beam splitter splits the laser radiation from the first beam splitter into laser radiation directed to the first sensor and to the third sensor. According to another embodiment for determining the speed and / or length of a product, the analysis device may form a difference between the measurement signals of the first and third sensors. The measurement signal received by the first sensor contains a so-called DC component as an offset. This embodiment allows this DC component to be eliminated by subtracting the measurement signal of the third sensor from the measurement signal of the first sensor. The resulting difference signal no longer contains a DC component, thereby significantly improving the signal-to-noise ratio and, therefore, the detectability of the signal. If, for example, the product vibrates or has a periodic surface structure, periodic intensity fluctuations may occur, which in turn lead to interference frequencies in the signal. Naturally, such interference frequencies cannot always be distinguished from the actual modulation frequency of the useful signal. In the design described here, only the signal from the first sensor contains the useful signal, so that frequencies detected in the first and third sensors can be clearly identified as interference. This further improves the analysis of the measurement signal.

[0019] According to another design, a second transmission grating can be placed upstream of the third sensor, phase-shifted by 180° relative to the first transmission grating. This design not only eliminates the DC component but also, due to the 180° phase shift of the transmission grating, achieves maximum amplification of the intensity-modulated signal, in particular the corresponding signal oscillations. However, this requires precise positioning of the two transmission gratings, which may be prohibitively complex depending on the application. It is also possible to omit the transmission grating upstream of the third sensor, thus avoiding the problem of precise positioning. Thus, while the oscillating signal is not amplified, the DC component is still eliminated. Depending on the application, this solution may be sufficient or preferred.

[0020] The third sensor may also be a photodiode. The third sensor may again be, for example, a silicon photodiode, which has a particularly high sensitivity to common infrared lasers.

[0021] According to another embodiment, the evaluation device can be configured to determine a movement of the speckle pattern detected by the image sensor in a direction transverse to the product's conveying direction. Furthermore, an adjustment device can be provided for adjusting the impact position of the laser radiation on the product, at least transverse to the product's conveying direction, and the evaluation device can be configured to actuate the adjustment device based on the determined movement of the speckle pattern detected by the image sensor in a direction transverse to the product's conveying direction, so as to adjust the impact position of the laser radiation on the product, at least transverse to the product's conveying direction. In conventional measuring devices, particularly with thin products such as thin stranded products, there is the problem that potentially undetected lateral movement of the product can lead to imperfect illumination or measurement of the product with laser radiation. In this case, the lateral tolerance (i.e., transverse to the product's conveying direction) for the size of the laser spot on the surface is typically only a few millimeters. Because the device according to the present invention, which includes an image sensor, also detects lateral movement of the product, i.e., transverse to the conveying direction, this can be used to laterally adjust the laser by the evaluation device. The adjustment device can, for example, include a mirror with a galvanometer drive or the like. By controlling the adjustment device with the aid of the evaluation device, the direction of the laser can be adjusted transversely to the conveying direction in such a way that the product can always be optimally illuminated and measured. This allows significantly greater tolerances transverse to the conveying direction than in the prior art, for example, in the order of up to 100 mm for an optical system with dimensions of approximately 25 mm at a working distance of up to 500 mm.

[0022] According to another design solution, a distance adjustment device can also be provided, by which the distance between the laser and / or detector device and the product surface can be adjusted. The distance adjustment device can also be controlled by the analysis device. Such distance adjustment is advantageous because in this way the device, in particular the detector device and, if necessary, the laser, can be adjusted closer to the product. As already explained above, a small distance from the product provides various advantages, in particular in terms of particularly thin and smooth products, in particular stranded products, and also in terms of protective measures against and the influence of interfering particles. The device according to the present invention can also include a device for tilting the laser, so that even in the case of different distances between the laser and the product surface, the light spot irradiated by the laser on the product surface can always be kept, for example, vertically below the detector device.

[0023] According to another embodiment, a laser beam splitter can also be provided, which directs the laser radiation emitted by the laser perpendicularly onto the product surface. The laser radiation can be coupled directly into the beam path of the detector arrangement, in particular the first and second sensors, via the laser beam splitter. In particular, laser radiation scattered perpendicularly back from the product surface can be centrally directed onto the first beam splitter and, if necessary, the first and / or second sensors. In this embodiment, the laser's angle of attack does not need to be adjusted for different working distances. This, in turn, allows for a greater depth of field, since the laser spot does not shift to the left or right as the product moves back and forth. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following is a detailed description of an embodiment of the present invention with reference to the accompanying drawings.

[0025] Figure 1 A device according to a first embodiment of the invention is shown,

[0026] Figure 2 A device according to a second embodiment of the invention is shown,

[0027] Figure 3 Shows an illustration of the adjustability of the laser,

[0028] Figure 4 Three partial views are shown to illustrate the adjustment device for adjusting the impact position of the laser radiation, and

[0029] Figure 5 A device according to the invention is shown according to a third exemplary embodiment. DETAILED DESCRIPTION

[0030] Unless otherwise indicated, the same reference numerals in the figures denote the same objects.

[0031] exist Figure 1A tubular strand 10 is partially shown in the figure. It is conveyed along a conveying direction, as indicated by arrow 12, by means of a conveying device (not shown in detail). The conveying direction extends along the longitudinal axis of strand 10. Laser radiation is directed onto the surface of strand 10 by means of a laser 14. The laser radiation scattered by the surface is split into two radiation components by means of a first beam splitter 16. The first radiation component impinges on a first transmission grating 18. The laser radiation that passes through first transmission grating 18 is focused by a first lens 20 onto a first sensor 22, which may be, for example, a photodiode. The second radiation component reaches a second sensor 24, which may be an image sensor, such as a CCD or CMOS sensor. A focusing second lens 26 may be provided immediately upstream of image sensor 24. Alternatively or additionally, a focusing second lens 28 may also be provided immediately downstream of first beam splitter 16. Second lenses 26 and / or 28 focus the radiation from first beam splitter 16 onto the measuring aperture of image sensor 24.

[0032] By using coherent laser light, a speckle pattern is formed on the first transmission grating 18, on the one hand, and on the sensor surface of the image sensor 24, on the other hand. This speckle pattern is characterized by the surface structure of the strand 10 and, accordingly, by the movement of the strand 10. Thus, the first sensor 22 detects an intensity modulation having a modulation frequency that characterizes the movement of the strand 10. On the other hand, the speckle pattern moves on the sensor surface of the image sensor 24, and the image sensor 24 detects this movement. The measurement signals of the first sensor 22 and the image sensor 24 are supplied to an analysis device 30. The analysis device 30 determines the velocity and / or length of the strand between different measurement times based on the intensity modulation detected by the first sensor 22 and / or the movement of the speckle pattern detected by the image sensor 24.

[0033] Figure 2 Most of the equipment in Figure 1 Devices in. Figure 1 The difference between the devices in Figure 2 In the device of FIG. 1 , a second beam splitter 32 is arranged between the first beam splitter 16 and the image sensor 24, which splits the laser radiation from the first beam splitter 16 into laser radiation which is directed to the image sensor 24 on the one hand and to a third sensor 34 on the other hand. The third sensor 34 can also be formed by a photodiode. Figure 2In the exemplary embodiment, in addition to the measurement signals of the first sensor 22 and the image sensor 24, the measurement signal of the third sensor 34 is also fed to the evaluation device 30. The evaluation device 30 forms the difference between the measurement values ​​of the first sensor 22 and the third sensor 34 in order to eliminate the DC component in the measurement signal. This improves the signal-to-noise ratio and increases the measurement accuracy. It is possible to arrange a second transmission grating upstream of the third sensor 34, in particular between the second beam splitter 32 and the third sensor 34, which is phase-shifted by 180° relative to the first transmission grating 18. This additionally results in maximum amplification of the measured modulation signal when forming the difference between the sensor signals of the first sensor 22 and the third sensor 34.

[0034] exist Figure 3 China-Israel Figure 1 The device shown in the example shows how different distances between the surface of the strand 10 and the device, in particular the sensors 22, 24 or the beam splitter 16, can be adjusted by tilting the laser 14. Two different strand surfaces spaced apart from the device and correspondingly two different positions of the laser 14 are shown. By tilting the laser 14, it is ensured that the laser radiation always strikes the strand surface vertically below the beam splitter 16. This, of course, applies in the same way. Figure 2 Due to the fact that in the device according to the invention shown there is no need for imaging optics between the strand 10 and the sensors 22, 24 and, if appropriate, 34, and due to the fact that the speckle pattern formed on the first transmission grating 18 or the image sensor 24 is always sharp, additional calibration measures are particularly simple to implement even when the laser 14 is tilted.

[0035] exist Figure 4 , an adjustment device integrated in the laser 14 is shown very schematically, which serves to adjust the impact position of the laser radiation on the strand 10 in a direction transverse to the conveying direction of the strand 10. This can be applied in each of the illustrated embodiments. Figure 4 Three different partial views are shown in FIG, which show different states. Figure 4 In all three partial views, the conveying direction of the strand 10 extends perpendicularly into the plane of the drawing. Figure 4 The left partial view of FIG shows a state where the laser radiation from the laser 14 strikes the surface of the strand 10 vertically downwards and centrally. This central impact is the desired state. Figure 4The middle partial view shows a state in which the strand 10 moves transversely to the conveying direction, approximately to the left in this partial view. As a result, the impact position of the laser radiation that continues to be emitted vertically downward from the laser 14 is no longer centrally located on the strand surface. This leads to non-optimal illumination of the strand surface and, in the case of a correspondingly stronger lateral movement of the strand 10, may even lead to the strand 10 completely leaving the area of ​​the laser radiation. The lateral movement of the strand 10 can be identified by means of an analysis of the measurement signal of the image sensor 24, in particular by an analysis of the corresponding movement of the speckle pattern on the sensor surface of the image sensor 24 via the analysis device 30. The analysis device 30 can then control the regulating device in order to adapt the impact position of the laser radiation on the strand surface in such a way that the impact position is again centrally located on the strand 10, as in Figure 4 The adjustment device can, for example, comprise an adjustable mirror that directs the laser radiation onto the strand surface in a particularly simple manner. The mirror can be adjusted, for example, by means of a galvanometer drive.

[0036] exist Figure 5 A further embodiment of the device according to the invention is shown, which largely corresponds to the embodiment according to Figure 1 embodiment. In addition, a laser beam splitter 36 is provided here, which directs the laser radiation emitted by the laser 14 perpendicularly onto the surface of the strand 10. The laser radiation is here directly input-coupled into the beam path of the detector device, in particular the first and second sensors (22, 24) via the laser beam splitter 36. In particular, the laser radiation scattered back perpendicularly by the strand surface strikes the first beam splitter 16 centrally and strikes the first and second sensors 24, 26. The laser radiation scattered back perpendicularly by the strand surface also passes centrally through the first and second lenses 20, 28. A beam dump 38 is provided on the side of the laser beam splitter 36 opposite the laser 14 to prevent the laser radiation from passing through the laser beam splitter 36 directly onto the sensors 24, 26. The portion of the laser radiation that is directly transmitted by the laser beam splitter 36 is absorbed by the beam dump 38. Of course, according to Figure 5 The design scheme can also be combined with the Figure 2 The embodiments are combined.

[0037] Reference Signs List

[0038] 10-strand wire

[0039] 12 conveying device

[0040] 14 lasers

[0041] 16 First beam splitter

[0042] 18 First transmission grating

[0043] 20First lens

[0044] 22 First Sensor

[0045] 24 Second sensor (image sensor)

[0046] 26 Second lens

[0047] 28 Second lens

[0048] 30Analysis device

[0049] 32 Second beam splitter

[0050] 34 Third sensor

[0051] 36 laser beam splitters

[0052] 38 beam dump

Claims

1. A device for determining the speed and / or length of a product (10) moving in a conveying direction (12), comprising a laser (14) for irradiating the surface of the product (10) and a detector device for detecting laser radiation scattered back by the surface of the product (10), the detector device comprising a first sensor (22) together with a first transmission grating (18) arranged upstream of the first sensor (22) and a second sensor formed by an image sensor (24), further comprising a first beam splitter (16) which divides the laser radiation scattered back by the product (10) into laser radiation which is directed to the first sensor (22) on the one hand and to the image sensor (24) on the other hand, characterized in that An analysis device (30) is provided, which is designed to determine the speed and / or length of the product (10) based on the intensity modulation detected by the first sensor (22) when the product (10) moves and based on the movement of the speckle pattern detected by the image sensor (24) when the product (10) moves, and formed on the image sensor (24), the detector device also includes a third sensor (34), and a second beam splitter (32) is arranged between the first beam splitter (16) and the image sensor (24), the second beam splitter being designed so that it splits the laser radiation from the first beam splitter (16) into two beams directed to the image sensor (24) on the one hand and to the image sensor (24) on the other hand. and on the other hand directed to the laser radiation of the third sensor (34), or a second beam splitter (32) is provided between the first beam splitter (16) and the first transmission grating (18), the second beam splitter being designed so that the second beam splitter divides the laser radiation from the first beam splitter (16) into laser radiation directed to the first sensor (22) on the one hand and to the third sensor (34) on the other hand, and the analysis device (30) is designed to form a difference between the measurement signals of the first sensor (22) and the third sensor (34) for determining the speed and / or length of the product (10), thereby eliminating the DC component of the measurement signal received by the first sensor (22).

2. The device according to claim 1, characterized in that A first lens (20) is arranged between the first transmission grating (18) and the first sensor (22) for focusing the laser radiation directed to the first sensor (22) onto the first sensor (22).

3. The device according to claim 1 or 2, characterized in that The first sensor (22) is a photodiode.

4. The device according to claim 1 or 2, characterized in that A second lens (26, 28) is arranged between the first beam splitter (16) and the image sensor (24) for focusing the laser radiation directed to the image sensor (24).

5. The device according to claim 1 or 2, characterized in that The image sensor (24) is a CCD sensor or a CMOS sensor.

6. The device according to claim 1 or 2, characterized in that A second transmission grating is arranged upstream of the third sensor (34), and is phase-shifted by 180° relative to the first transmission grating (18).

7. The device according to claim 1 or 2, characterized in that The third sensor (34) is a photodiode.

8. The device according to claim 1 or 2, characterized in that The evaluation device (30) is designed to determine a shift of the speckle pattern detected by the image sensor (24) in a direction transverse to the conveying direction (12) of the product (10).

9. The device according to claim 8, characterized in that In addition, an adjusting device is provided for adjusting the impact position of the laser radiation on the product (10) at least in a direction transverse to the conveying direction (12) of the product (10), and the analyzing device (30) is designed to control the adjusting device based on a movement of the speckle pattern detected by the image sensor (24) in a direction transverse to the conveying direction (12) of the product (10) in order to adjust the impact position of the laser radiation on the product (10) at least in a direction transverse to the conveying direction (12) of the product (10).

10. The device according to claim 1 or 2, characterized in that Furthermore, a distance adjustment device is provided, by means of which the distance between the laser (14) and / or the detector device and the surface of the product (10) can be adjusted.

11. The device according to claim 1 or 2, characterized in that Furthermore, a laser beam splitter (36) is provided, which directs the laser radiation emitted by the laser (14) perpendicularly onto the surface of the product (10).

12. The device according to claim 1 or 2, characterized in that The product (10) is a strand.

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