Optical measuring arrangement and method for the presence detection of small objects in a beam path

Abstract

Optical measuring arrangement (1) for detecting the presence of small objects (3) in a beam path (5) for measuring light (7), with at least one receiving-side beam-shaping device (9) arranged in the beam path (5), by means of which the measuring light (7) transmitted through a sample volume (19) in the beam path (5) can be focused to an image width (25) in a first direction (17) oriented perpendicular to the beam path (5), and with at least one detection device (29) arranged in the beam path (5) for detecting the measuring light (7) transmitted by the receiving-side beam-shaping device (9), characterized in that the at least one detection device (29) is arranged at a working distance (37) from the receiving-side beam-forming device (9) which is smaller than the image distance (25), the optical measuring arrangement (1) comprises at least one light source (39) for emitting the measuring light (7), at least one transmitter-side beam-shaping device (41) is provided in the beam path (5), by means of which the measuring light (7) generated by the light source (39) can be focused into the sample volume (19) at least in the first direction (17), and the transmitter-side beam-forming device (41) has a double cylindrical lens effect which focuses the measuring light (7) generated by the light source (39) exactly into the sample volume (19) in the first direction (17) and collimates it in the second direction.

Description

[0001] The invention relates to an optical measuring arrangement for detecting the presence of small objects in a beam path for measuring light, comprising at least one receiving-side beam-shaping device arranged in the beam path, by means of which the measuring light transmitted through a sample volume in the beam path can be focused to an image width in a first direction oriented perpendicular to the beam path, and comprising at least one detection device arranged in the beam path for detecting the measuring light transmitted by the receiving-side beam-shaping device. The invention further relates to a method for optically detecting the presence, preferably also for measuring the height, of an object in a sample volume, in which measuring light is focused along a beam path in a first direction oriented perpendicular to the beam path in a sample volume, and the measuring light transmitted through the sample volume is collected.

[0002] Optical measuring systems for the presence detection of small objects, in particular, are well known. They are used, for example, in light barriers. Forked light barriers are just one example. Presence detection and position determination can be necessary or desirable for various applications.

[0003] For example, when automatically placing objects, it may be necessary to detect the presence of the object in a predetermined space, called the sample volume, and possibly also to determine the dimensions and position of the object, at least in one spatial direction. Knowing the immersion depth or penetration depth of the object when immersed in the sample volume can also be advantageous. By rotating the object around the immersion axis, the dimensions in all three spatial directions can even be determined.

[0004] From the document DE 102 97 222 T5, a method and a device for controlling light reflections from a position sensor are known. The method involves directing light onto a component, blocking it by the component, creating shadows of the component's outline. Part of the light is mirrored or reflected by the component, creating highlights or reflections. The light is then passed through a filter that blocks the highlights. The filter blocking is controlled by rotating the filter about an axis in the plane of the component. A detector is arranged behind the filter to detect the shadows.

[0005] A method and device for detecting thin, thread-like objects is known from German patent document DE 196 26 187 A1. In this method, a light trap is arranged upstream of the receiving device to prevent a light beam from directly impinging on a transducer, so that the transducer can only be exposed to radiation diffracted in various directions by an object.

[0006] US Pat. No. 5,897,611 A discloses a control system that precisely aligns electrical components, such as pick-and-place machines for surface-mounted components. The precision of a laser beam is utilized for this purpose. A slit aperture generates a precise light band that extends beyond the component and is detected by a sensor array.

[0007] From the document DE 20 2012 010 432 U1, an optical sensor is known with a transmitter for emitting electromagnetic radiation, with a receiver for detecting this radiation, and with optics for autocollimating the transmitted radiation, wherein the optical axis of the transmitter is offset parallel to the optical axis of the receiver, so that the transmitter and receiver are located perpendicular to the optical axes on the same circuit board, wherein the transmitted radiation can be directed in the direction of the optical axis of the receiver by means of two reflective, in particular totally reflecting surfaces, which each deflect the transmitted radiation essentially by 90 degrees. The transmitter and receiver optics consist of a single plastic part. Another example application is the application of liquid, weakly or highly viscous substances, for example adhesive, from nozzles onto substrates.Here it may be necessary to determine whether or not a drop of the substance is attached to the nozzle, how large the drop is, or whether there is a foreign object attached to the nozzle that could impair the function of the nozzle.

[0008] When detecting the presence and position of objects, it is usually necessary to precisely adjust the detection device in order to still detect any shadowing caused by the object to be detected. This is particularly important when the object is small, for example with a size in the sub-millimeter range. In this case, the shadowing is minimal and precise measurement is essential. The measuring arrangement should also be insensitive to small adjustment errors or disturbances and, if possible, also to influences from dust or similar. Furthermore, it is desirable for the optical measuring arrangement, particularly as part of a light barrier, to be suitable for the precise detection of even the smallest parts. Ultimately, the position height or immersion depth of an object or the time at which an object moving perpendicular to the barrier exactly breaks through a defined measuring line should also be detected or measured with sufficient precision for the intended application.can be measured.

[0009] Optical measuring arrangements in light barriers are known for detecting objects with a minimum size of, for example, 1 to 50 mm. So-called laser light barriers are also known, which use highly parallel light and can reliably detect even significantly smaller objects.

[0010] Simple light barriers can also be miniaturized. In the simplest case, an LED chip—which can even be an LED without a lens-like exit surface, with a chip size of, for example, 0.4 x 0.4 mm—radiates light through a front window on the transmitter side without optics. The light is interrupted somewhere in the beam path by an object to be detected. In the simplest case, the light is captured by a simple photodiode with a size of, for example, 1 x 1 mm. This allows the presence of an object typically measuring around 0.5 mm to be detected.

[0011] Laser light barriers, on the other hand, are constructed with a laser module consisting of a laser diode in a laser diode housing, a lens suitable for focusing and / or collimating lasers, and a stable mount for the laser diode and the lens to ensure that the focus is not significantly altered by vibrations or temperature changes, even during use. The housing is generally not compact enough to meet certain miniaturization requirements. On the receiving side, a simple photodiode behind a focusing lens or a line receiver behind a focusing cylindrical lens can be used. The transmitter, as well as the receiver structure, require space and are not easy to miniaturize. If the light barrier itself is small and the objects to be detected are very small, the optics become so small that dust resistance becomes very important.

[0012] It is therefore the object of the invention to provide an optical measuring arrangement and a method for presence detection that completely or partially resolves the above-mentioned problems. The optical measuring arrangement should be particularly suitable for a light barrier. The invention should make it possible to realize a miniaturized light barrier, preferably a light barrier whose total width in the direction of light propagation is less than 25 mm.

[0013] For the optical measuring arrangement mentioned at the outset, the object is achieved in that the at least one detection device is arranged at a working distance from the receiving-side beam-forming device which is smaller than the image distance.

[0014] For the method mentioned at the outset, the object is achieved by focusing the measuring light by at least one receiving-side beam-shaping device in the first direction, in particular to an image width, and by detecting the measuring light at a working distance from the beam-shaping device which is smaller than an image width of the receiving-side beam-shaping device.

[0015] The inventive solution, according to which the measuring light is detected between the receiving-side beam-shaping device and the image distance, eliminates the need for precise adjustment of the detection device at the level of the image distance, i.e., at the focus of the beam path. Since the measuring light generally has a larger diameter in the area in front of the image distance, the area in which the detection device can be positioned while still receiving measuring light is also larger. This increases the tolerance during adjustment.

[0016] The optical measuring arrangement according to the invention is ideally suitable for building a miniaturized light barrier that can detect the smallest objects in the sub-millimeter range, typically 0.1 mm, and can measure their position height in a first direction transverse to the direction of light propagation in a narrow measuring field or sample volume with an accuracy of approximately 10 µm.

[0017] The aforementioned image distance is determined by the at least one beam-shaping device. It can be calculated, for example, based on the properties of the beam-shaping device, such as focal length, etc. The image distance is the distance behind the receiving-side beam-shaping device at which the measurement light is focused by the receiving-side beam-shaping device.

[0018] Each beam-shaping device preferably comprises at least one refractive element, in particular a lens.

[0019] The solution according to the invention can be further improved by various embodiments, each of which is advantageous in itself and can be combined with one another as desired. These embodiments and their associated advantages are discussed below.

[0020] According to a first advantageous embodiment, the working distance is 20%-90% of the image width, preferably 40%-70%, i.e. about half to about two thirds of the image width.

[0021] The optical measuring arrangement comprises at least one light source for emitting measuring light along the beam path.

[0022] According to a further advantageous embodiment, the optical measuring arrangement preferably comprises at least one transmitter-side beam-shaping device arranged in the beam path, by means of which the measuring light can be focused in the sample volume at least in the first direction oriented perpendicular to the beam path. Preferably, the measuring light can be focused by the transmitter-side beam-shaping device only in the first direction, although technically induced deviations in the direction due to lens or alignment errors are possible.

[0023] According to the invention, the transmitter-side beam-shaping device of the optical measuring arrangement has a double cylindrical lens effect, which focuses the measuring light generated by the light source exactly into the sample volume in the first direction and collimates it in the second direction.

[0024] Alternatively, the transmitter-side beam-shaping device of the optical measuring arrangement can focus the measuring light generated by the light source in the first direction exactly into the sample volume and in the second direction into an intermediate focus between the sample volume and the receiver-side beam-shaping device.

[0025] Each beam-shaping device preferably comprises at least one refraction element, particularly preferably at least two refraction elements, namely one refraction element on a light entry side and one on a light exit side of the respective beam-shaping device.

[0026] In an embodiment with a focus in the first direction on the object detection area, i.e., on the sample volume, the image width corresponds to the distance at which this transmission focus is imaged in the first direction again by the receiving lens (receiving-side beam-forming device) and behind it. Thus, it also corresponds to the distance at which the object detection area is imaged. An object whose presence is to be detected can preferably be introduced into the sample volume. In other words, the sample volume is preferably accessible to an object, in particular accessible from outside the measuring arrangement.

[0027] The sample volume is preferably flat; in other words, the sample volume is preferably less extensive in the first direction than in the direction of the beam path and in a second direction that runs perpendicular to the beam path and perpendicular to the first direction. The sample volume, or measuring area, is preferably 2 x 2 mm in size, ± 1 mm in the direction of light propagation of the beam path and perpendicular to it in the second direction, in order to be able to detect even the smallest objects in a somewhat extended measuring area.

[0028] In order to keep the optical measuring arrangement compact, in particular to enable use in a forked light barrier, at least one receiving-side deflection element is preferably arranged between the sample volume and the detection device, by means of which the measuring light can be deflected on the beam path.

[0029] If a transmitter-side beam-shaping device is also provided, at least one transmitter-side deflection element is preferably arranged between a light source or the intended position of the light source in the beam path and the sample volume.

[0030] According to a particularly preferred, but not necessary, embodiment, a transmitter-side beam-forming device is provided and each of the two beam-forming devices is assigned a deflection element.

[0031] In particular, by using both a transmitter-side deflection element and a receiver-side deflection element, the optical measuring system can measure the smallest parts and their position height or immersion depth in a narrow sample volume with an accuracy of approximately 10 µm. It typically requires only a fraction of the space required by a laser light barrier optimized for small parts.

[0032] A simple deflection element can be obtained, for example, by a prism, in particular a 90° prism.

[0033] In order to obtain a simple structure, the at least one deflection element is part of the respective at least one beam-forming device.

[0034] Particularly preferably, the at least one deflection element is formed monolithically with at least one refractive element, in particular a lens, of the at least one beam-shaping device. This allows for a compact, easy-to-manufacture, and misalignment-resistant structure.

[0035] The at least one beam-shaping device can, in particular, be a plastic injection-molded part, especially in the case where at least one beam-shaping device comprises at least one refraction element and at least one deflection element. In this case, the beam-shaping device, including these parts, is preferably formed monolithically as a plastic injection-molded part.

[0036] The at least one detection device preferably comprises at least one line detector with a row of detection cells, wherein the row extends along a second direction perpendicular to the beam path and the first direction. This allows a shadow cast by an object in the sample volume to be imaged onto the various detection cells, or pixels. This not only increases the sensitivity compared to a single, large cell (photodiode) because the shadow is distributed across multiple cells, but also provides the possibility of at least roughly determining the extent of an object in the sample volume. The at least one detection device can in particular comprise a photodiode array, a CMOS line, a CCD line, and / or another suitable device. Detection by a digital camera is also possible.

[0037] According to a further advantageous embodiment, the optical measuring arrangement further comprises at least one light source. The light source is preferably a point light source, in particular a laser diode or a pinpoint LED with the smallest possible dimensions.

[0038] A compact optical measuring arrangement within the meaning of the invention for constructing a miniaturized light barrier can also be achieved by using a VCSEL (Vertical Cavity Surface Emitting Laser) as the light source. The VCSEL typically has an exit diameter between 5 and 20 µm. The light source is usually placed behind a front window, i.e., the transmitter-side beam-forming device. On the receiver side, a somewhat larger photodiode, for example, 4 x 1 mm in size, can be arranged behind a receiver window, i.e., the receiver-side beam-forming device. A disadvantage of this solution, however, can be undesirable dust sensitivity at the transmitter window. By projecting an almost point-shaped transmitter light source onto the small object to be detected, dust particles on the transmitter front window are perceived as magnified by a distance factor within the object detection range.The distance factor can be calculated as the ratio of the distance of the emitter light source behind the window to the distance of the emitter light source to the object to be detected. The magnification can be a factor of 5 to 10, meaning that even dust particles in the range of 2 x 10 µm can interfere with or even completely prevent the detection of small objects (0.1 mm) with high precision (10 µm).

[0039] To make the optical measuring arrangement, or a miniaturized light barrier equipped with it, less sensitive to dust, the effective light exit area on the transmitter front window, which in this case is the projection area on the front window in the line from the light source to the object, should be significantly enlarged. This can preferably be achieved by placing the transmitted light source at a distance behind the front window that is similar to or greater than the distance between the front window and the object. This means that only dust particles or windscreen contamination, bubbles in the glass, or breakouts on the glass surface measuring approximately 5 x 50 µm in size will cause interference. Furthermore, this can be further improved by using lenses to refocus the light into the object detection area.A cylindrical lens is preferably used to focus the light in the first direction, where high-precision measurements are required, onto the detection area. However, since an extended measurement range is desired in the transverse direction (second direction), the light in this direction should not be fully focused onto the detection area. Focusing can be omitted in this second direction, but preferably the light in this direction is only focused so far that it emerges approximately collimated. This can further reduce dust sensitivity.

[0040] The transmitter-side beam-shaping device, in particular the transmitter lens, has the further advantage that much more light (typically 10 to 50x) from the light source reaches the detection area, i.e., the sample volume, and then also the receiver-side beam-shaping device, or receiver lens. This also allows the use of pinpoint LEDs, whose exit surface, with a diameter of 40 to 150 µm or a rectangular area of approximately this dimension, is significantly larger than that of the VCSEL. The light from the pinpoint LED is emitted at a wide angle like a Lambertian radiator, thus resulting in much more light being lost than with the narrow-angle VCSEL. By using the transmitter lens, it can be ensured that enough light reaches the receiver to make the measurement fast, which is a further requirement for accurately measuring a moving object at speeds of 0.1 to 4 m / s.Depending on the maximum speed requirements, the receiver can be exposed and read at clock rates of 10 µs or faster. This requires the reception of a sufficient amount of light; otherwise, noise from the receiver, its amplifier, or its analog-to-digital converter will impair the required measurement accuracy.

[0041] There may still be two problems with the transmitter-side beam-forming device or the transmitter lens, which can, however, be solved by further advantageous embodiments of the invention a) If the focusing of the light in the first direction and the collimation in the second direction are achieved with a doubly curved cylindrical lens surface, then excessive lens aberrations can occur outside the lens axis, i.e. in the extended measuring range (typically 2 mm) in the second direction. While focusing in the first direction can be easily achieved in the center of this measuring range, i.e. on the optical axis, with aspherical (non-circular), doubly curved cylindrical lens surfaces, focusing may be poorer at the edges. For this reason, focusing in the two directions is preferably carried out separately. One focus in the first direction can preferably be achieved on the lens entrance side, and that in the second direction on the lens exit side. Furthermore, the focal length should not be too small to prevent lens aberrations from becoming too large.For an example object distance from the transmitter window of 10 mm and a preferred image scale of approximately 1:1, the focal length should be half as large, i.e. approximately 5 mm. b) The transmitter lens and in particular the required distance between the transmitter light source and the transmitter lens, which in the example just mentioned is approximately 10 mm, require space. However, this is difficult to achieve in a miniaturized light barrier. If the available space outside the free path between the transmitter and receiver windows is only a few millimeters, then this type of optic cannot be used. However, miniaturization is possible by deflecting the beam path by 90° in a direction where more space is available, for example, in the first direction mentioned. Due to space constraints, the assembly of individual components such as cylindrical lenses and deflection prisms is only possible where there is sufficient space. However, the solution of a monolithic optical part in the form of a precision injection-molded optical part that performs deflection and dual beam focusing in a single part enables the required miniaturization.The beam is preferably focused on the object area in the first direction on the beam entrance side, followed by prismatic deflection, and finally focusing on the exit side to collimate the beams in the second direction. In a slightly different embodiment, the deflection surface of the prism can also be used for focusing. Furthermore, the cylindrical focuses can be distributed to a certain extent across the two sides (inlet and exit). For example, 15% of the curvature for focusing in the first direction can occur at the exit surface and the remainder at the entrance surface. Conversely, this can also apply to focusing / collimation in the second direction. This then results in doubly curved cylindrical lenses on both sides, which are curved to different degrees in the first and second directions.

[0042] The optical measuring arrangement preferably further comprises at least one, in particular automatically, movable, preferably mobile, slide, through which at least one object to be measured can be moved into the sample volume. Particularly preferably, the at least one slide is movable parallel to the first direction. Alternatively, the slide can be stationary and the rest of the arrangement movable. The slide can be used to specifically control the immersion depth of the object into the sample volume. However, the measuring arrangement according to the invention and the method according to the invention are also expressly suitable for detecting objects that are not arranged on a slide, so to speak "free-flying" objects.

[0043] Measurements can be taken at different times while the slide is being inserted into the sample volume. This allows for both temporal and spatial measurement resolution. The spatial resolution is achieved automatically by the movement of the slide while simultaneously performing a time-synchronized measurement. The spatial resolution relates to the direction in which the slide is moved, preferably the first direction.

[0044] In some circumstances, a time-locked measurement may also be necessary because certain components that are considered part of the detection device, such as CCD sensors, must be read out regularly to enable a new measurement.

[0045] During the movements of the slide described above, it can either be loaded with an object or enter the sample volume without an object. One or more measurements without an object can serve as a reference measurement for the actual presence detection of an object. In the latter case, an object is then arranged on the slide. The measurement with an object can then be referenced by a reference measurement, for example by subtraction. If the measurement signal is above a predetermined threshold, the detection of an object can be confirmed. Referencing can be done for individual pixels or for curves formed from the series of pixels. In the case of curves, these are preferably linearly interpolated to obtain continuous curves.This is particularly helpful when the number of pixels is small, for example in the single or low double digit range, or when the number of measurements in a curve is significantly smaller than would be needed for the required measurement accuracy.

[0046] The method according to the invention can also be improved by automatically inserting an object arranged on a slide into the sample volume at different immersion depths and by detecting the measuring light at these different immersion depths.

[0047] Furthermore, based on the shadowing by the object, the position of the object, in particular the immersion depth into the sample volume, can be automatically determined, particularly in the first direction. It can also be provided to compare at least one measurement with at least one previous measurement. In other words, a previously learned position of an object can be recognized. Finally, the difference between a learned position and a measured position can also be detected.

[0048] The invention is explained in more detail below by way of example using advantageous embodiments with reference to the drawings. The combinations of features illustrated by way of example in the embodiment can be supplemented by further features in accordance with the above explanations, depending on the properties of the optical measuring arrangement according to the invention required for a specific application. Individual features can also be omitted from the described embodiments, also in accordance with the above explanations, if the effect of this feature is not important in a specific application. In the drawings, the same reference numerals are always used for elements with the same function and / or the same structure.

[0049] They show: Fig. 1 schematically shows the beam path of a first advantageous measuring arrangement according to the invention in a profile view; Fig. 2 the beam path Fig. 1 in a supervision; Fig. 3 a perspective view of a beam path with a slide, wherein the beam path corresponds at least in sections to that of the Fig. 1 and Fig. 2 corresponds; Fig. 4 schematically shows the beam path of a measuring arrangement not according to the invention in a profile view; Fig. 5 the beam path Fig. 4 in a supervision; Fig. 6 a perspective view of a beam path with a slide, wherein the beam path corresponds at least in sections to that of the Fig. 4 and Fig. 5 corresponds; Fig. 7 schematically shows the beam path of a further advantageous measuring arrangement according to the invention in a profile view; Fig. 8 schematically shows the beam path of a further advantageous measuring arrangement with deflection elements according to the invention in a profile view; Fig. 9 the beam path Fig. 8 in a supervision; Fig. 10 Line signals of a detection device during a measurement according to the invention; Fig. 11 the signal curve for different detection cells or pixels of the measurement Fig. 10; Fig. 12 the signal curve for different detection cells or pixels of a measurement without an object on the slide; and Fig. 13 the signal curve for measurements from Fig. 11 and Fig. 12 for a selected detection cell or pixel.

[0050] For better comparability, the Fig. 1 to 10 are each provided with a Cartesian coordinate system with the directions X, Y and Z.

[0051] In the following, the invention is explained using the beam path of a first embodiment with reference to the Fig. 1 to 3.

[0052] The optical measuring arrangement 1, hereinafter referred to as “measuring arrangement” 1, is used to detect the presence of small objects 3 in a beam path 5 for measuring light 7. An object 3 is in the Fig. 1 to 3 is only indicated by its position. The term "measuring light" refers to electromagnetic radiation that is specifically used for measuring and is suitable for passing through beam path 5.

[0053] The measuring arrangement 1 is intended to detect the presence of a small object 3 in the beam path 5. For this purpose, the measuring arrangement 1 has at least one receiving-side beam-shaping device 9 arranged in the beam path 5.

[0054] The beam-shaping device 9 preferably comprises at least one refraction element 11, in particular a lens 13. In the exemplary embodiment, the beam path 5 propagates along a propagation direction 14 which runs parallel to the Z-direction.

[0055] The receiving-side beam-forming device 9 may also consist of only one refraction element 11, in particular a lens 13. However, the beam-forming device 9 may also comprise further elements. This will be discussed later with reference to Fig. 8 and Fig. 9 received.

[0056] The beam-shaping device 9 can comprise a cylindrical lens 15, which preferably focuses light in a first direction 17, which in the exemplary embodiment runs parallel to the Y-direction. The first direction 17 is also oriented substantially perpendicular to the propagation direction 14 of the beam path 5.

[0057] The measuring light 7 has passed through a sample volume 19 on its way along the beam path 5. The sample volume 19 is the volume intended for the introduction of an object 3. This sample volume is an imaginary volume and is normally not limited by walls of any kind. The object 3 in the sample volume 19 usually attenuates the measuring light 7 at least somewhat, or the object 3 creates a shadow 21 that spreads along the beam path 5. The shadow 21 is in the Fig. 1 to 3 are shown for a rather large object and can also be significantly smaller.

[0058] The measuring light 7 is focused by the receiving-side beam-shaping device 9 to a focus 23, which is located at an image distance 25 from the receiving-side beam-shaping device 9. The image distance 25 depends on the properties of the beam-shaping device 9 and other objects located in the beam path 5, if present.

[0059] In the exemplary embodiment shown, the measuring light 7 is focused only in the first direction 17 due to the cylindrical lens 15. In a second direction 27 running perpendicular thereto, however, the measuring light 7 is not focused by the first beam-shaping device 9. The second direction 27 runs not only perpendicular to the first direction 17, but also to the propagation direction 14 and, in the illustrations, runs parallel to the X-direction.

[0060] The measuring light 7 is detected in a detection device 29 arranged in the beam path 5 along the propagation direction 14 behind the receiving-side beam shaping device 9.

[0061] The detection device 29 is preferably a line detector 31 with a row 33 of detection cells 35. This is in Fig. 2. The row 33 of detection cells 35 preferably extends along the second direction 27. The line detector 31 is preferably a photodiode array, a CMOS line, or a CCD line. Each detection cell 35 corresponds to a pixel of the detection device 29.

[0062] The shadow 21, which extends spatially along the second direction 27, can be imaged onto the detection device 29, so that the detection cells 35, which lie in the region of the shadow 21, receive less light than the detection cells 35, which lie outside the shadow 21.

[0063] The detection device 29 is arranged at a working distance 37 from the receiving-side beam-forming device 9. In other words, the detection device 29 is arranged at a working distance 37 behind the receiving-side beam-forming device 9 in the beam path 5, as viewed in the propagation direction 14. According to the invention, the working distance 37 is smaller than the image distance 25. In the illustrated embodiment, the working distance 37 is approximately 2 / 3 of the image distance 25.

[0064] The measuring arrangement 1 preferably also includes at least one light source 39 for generating or emitting the measuring light 7. The light source 39 is preferably a quasi-point light source, in particular a "pinpoint" LED. The term "quasi-point light source" is intended to illustrate that although it is a small, approximately point-shaped light source, it is not a point light source in the mathematical sense due to its actual spatial extent.

[0065] The measuring light 7 emitted by the light source 39 is preferably shaped by a transmitter-side beam-shaping device 41 arranged between the sample volume 19 and the light source 39, or focused in the first direction 17 onto the sample volume 19. In the first exemplary embodiment, the measuring light 7 is focused into the sample volume 19 in this first direction 17 by the transmitter-side beam-shaping device 41.

[0066] In the second direction 27, the measuring light 7 is preferably collimated, i.e. the light runs parallel in this plane, spanned by the second direction 27 and the light propagation direction 14. This is, for example, Fig. 2. These two focuses (or in other words, focusing and collimation) require two different cylindrical lens effects in the first and second directions 17 and 27.

[0067] Since the light source 39 is not an ideal point light source, there is no sharp focus in the sample volume 19, but rather an extended light disk 43 which has a thickness 45 that is at least partially constant in the first direction 17. The thickness 45 is smaller than the extent of the light disk in the directions 14 and 27. Preferably, a larger part of the light disk 43 is used as the sample volume 19. The sample volume 19 is therefore essentially flat. The spatial extent of the light disk 43 provides a tolerance with regard to the position of the object 3 in the directions 14 and 27. Because the light disk 43 is larger than the sample volume 19 in the second direction 27, a further tolerance with regard to position tolerances of the transmitted light source 39 and its optics is achieved.

[0068] The measuring arrangement 1 can further comprise a movable specimen slide 47, on which an object 3 can be arranged and with which an object 3 can be moved into the sample volume 19. Preferably, the specimen slide 47 is movable parallel to the first direction 17, preferably automatically. For example, the specimen slide 47 can be electrically movable. By moving the specimen slide 47, a penetration depth or immersion depth 65 of an object 3 into the sample volume 19 can be controlled.

[0069] The measuring arrangement 1 according to the invention increases the tolerance to adjustment errors or assembly errors. At least compared to an arrangement in which the detection device 29 were arranged at the focus 23, i.e., at a distance of the image width 25 from the receiving-side beam-forming device 9. If, for example, the light source were shifted in the first direction 17, the shift would affect the beam path 5, so that the measuring light 7 in the first direction 17 at the focus 23 would not lie on the optical axis 51 (i.e., the connecting line between the transmitter and receiver optics), but would be offset in the first direction 17. A detection device 29 arranged in the first direction 17 at the level of the focus 23 and on the optical axis 51 would then be outside the measuring light 7 and would not receive a signal. Detecting the presence of the object 3 would therefore be impossible.

[0070] Due to the arrangement of the detection device 29 at a working distance 37 which is smaller than the image distance 25, the image of the object 3 on the detection device 29 is indeed blurred compared to an arrangement in focus 23. However, it is ensured that at least in the event of a slight misalignment, measuring light 7, which also contains information about the shadow 21, still hits the detection device 29 and can be detected.

[0071] In the following, an embodiment known from the prior art is described with reference to the Fig. 4 to 6. For the sake of brevity, only the differences to the one with reference to the Fig. The embodiment described in 1 to 3 has been discussed.

[0072] In contrast to the previously described embodiment with a transmitter-side beam-shaping device 41, which focuses the measurement light 7 in the first direction 17 and collimates it in the second direction 27, the light in this embodiment is more strongly focused in the second direction 27, so that a focus is also created in the second direction 27. An intermediate focus 49 located behind the object 3 is thereby created for focusing in the second direction 27.

[0073] As in the first embodiment, the measuring light 7 then passes through the receiving-side beam-shaping device 9 and is focused by it at least in the first direction 17 to an image width 25, with the detection device 29, as before, being arranged in front of the focus 23. The working distance 37 in the second embodiment is approximately the same as in the first embodiment.

[0074] In the second direction 27, the receiving-side beam-forming device generates a substantially parallel beam in order to accurately image the shadow 21 onto the detection device 29.

[0075] In the following, a third advantageous embodiment of the measuring arrangement according to the invention is described with reference to the Fig. 7. As before, only the differences to the previously described embodiments are discussed here.

[0076] In the third advantageous embodiment, the detection device 29 is arranged at a working distance 37 from the receiving-side beam-forming device 9, which corresponds approximately to half the image width 25. The working distance is preferably 30 to 70%, particularly preferably 40 to 60%, of the image width 25. Otherwise, the structure of the measuring arrangement 1 can correspond to that of the first or second embodiment, depending on how the focusing in the second direction 27 is carried out.

[0077] The advantage of this embodiment is described below, although the principle can also be applied to the previously described embodiments. To illustrate the advantage of the embodiment, the measuring arrangement is shown with a slight misalignment of the light source 39: The light source 39 is shifted in the first direction 17. In Fig. 7, the light source 39 is shifted upward in the first direction 17. This shift appears in the area of the object 3 as a downward shift, each viewed with respect to an ideal optical axis 51.

[0078] Behind the object 3, the measuring light 7 hits the receiving-side beam-shaping device 9 rather in the lower area, with some rays of the measuring light 7 passing the beam-shaping device 9.

[0079] After the receiving-side beam-forming device 9, the measuring light 7 is shifted upwards again, so that in the area of the focus 23 an image of the object 3 would be above the optical axis 51.

[0080] If a detection device 29 were arranged at the level of the optical axis 51, it could be that the image of the object 3 would lie completely outside the detection device 29.

[0081] By arranging the detection device 29 at a working distance 37, which corresponds approximately to half the image distance 25, less measuring light is generally received because the received measuring light 7 is still insufficiently focused. However, the received measuring light 7 strikes the detection device 29 in a virtually similar manner, regardless of the displacement of the light source 39. The amount of light received changes only insignificantly as a result of this displacement, even though the receiving-side beam-shaping device 9 is not fully illuminated. Furthermore, the deliberately non-ideal focusing also achieves a tolerance to displacements of the detection device 29. This does not have to lie exactly on the optical axis 51.

[0082] In general, the detection device 29 can preferably be arranged between 25% and 80% of the image distance 25. The greater the insensitivity to displacements of the light source 39 or the detection device 29 is desired, the further the detector device 29 should be from the focus 23. If, however, a high signal strength is desired, the detection device 29 should be located closer to the focus 23.

[0083] Ideally, the detection device 29 is located at a working distance 37 at which the beams of the measuring light 7 intersect the optical axis behind the beam shaping device 9. This is Fig. 7 at a distance of 37: a similar number of rays hit the detection device 29 below as above the optical axis.

[0084] In the following, a fourth advantageous embodiment of the measuring arrangement 1 is described with reference to the Fig. 8 and Fig. 9. Here, too, only the differences to the previously mentioned embodiments are discussed. Fig. 9, dust grains 52 are shown on the refractive elements 59 and 11 for illustrative purposes only. The dust grains 52 are shown exaggeratedly large.

[0085] The measuring arrangement 1 of the fourth embodiment differs from the previous embodiments by the presence of deflection elements 53, 55, 57 in the beam path 5. Without the deflection elements 53, 55, 57, the beam path 5 would correspond to that of the second embodiment, which was described above with reference to the Fig. 4 to 6.

[0086] The deflection elements 53, 55, 57 allow the measuring arrangement 1 to be formed compactly. In particular, it can be used as part of a forked light barrier 60 (indicated by dashed lines in Fig. 8) be educated.

[0087] A first, transmitter-side deflection element 53 is arranged between the light source 39 and the sample chamber 19. The transmitter-side deflection element 53 is preferably a prism that deflects the measuring light 7 at a 90° angle. The transmitter-side deflection element 53 is preferably part of the transmitter-side beam-shaping device 41.

[0088] Particularly preferably, the transmitter-side beam-shaping device 41 is a single, monolithic component, comprising the transmitter-side deflection element 53 and a transmitter-side refraction element 58, in particular a cylindrical lens surface on the light entry side, and / or another transmitter-side refraction element 59, in particular a cylindrical lens surface on the light exit side. The two transmitter-side refraction elements 58 and 59 each act primarily in a different direction, one primarily in the first direction 17, the second primarily in the second direction 27.

[0089] Particularly preferably, the transmitter-side beam-shaping device 41 with the transmitter-side refraction elements 58 and 59 and the transmitter-side deflection element 53 is formed as a monolithic plastic injection-molded part. Alternatively, it can also be formed as a monolithic component made of another material, for example, glass.

[0090] Two receiving-side deflection elements 55 and 57 are arranged between the sample volume 19 and the detection device 29. A first receiving-side deflection element 55 is arranged behind the receiving-side refraction element 11 and in front of the receiving-side refraction element 12 and, together with the latter, forms part of the receiving-side beam-shaping device 9.

[0091] The first receiving-side deflection element 55 and the two receiving-side refraction elements 11 and 12 are preferably part of a monolithically formed receiving-side beam-shaping device 9. Like the transmitter-side beam-shaping device 41, the receiving-side beam-shaping device 9 is also preferably a plastic injection-molded part.

[0092] The first receiving-side deflection element 55 is preferably also a prism, which deflects the measuring light 7 at a 90° angle.

[0093] Preferably, a second receiving-side deflection element 57 is arranged between the receiving-side beam-forming device 9 and the detection device 29, which in turn deflects the measuring light 7 at a 90° angle onto the detection device 29.

[0094] In a further embodiment (not shown), the deflecting elements 55 and 57 as well as the receiving-side refraction element 11 are combined into a single monolithic part. The beam-refracting surface 12 can then be omitted, and the beam path, which in the embodiment described above runs between the surface 12 and the deflecting element 57, then runs entirely within this monolithic part. This has the advantage of lower costs, at least in the case of detecting extremely small parts with a highly miniaturized device, since the manufacture and assembly of an additional part can then be omitted, as well as the advantage of greater stability, since the beam deflection is only affected by the angular errors within the part and no longer by the angular errors in the assembly of the two parts. The influence of the assembly angular error of the double prism is then even completely eliminated.

[0095] Furthermore, the focusing of the light can be shifted from the refracting entrance and exit surfaces to the reflective deflection surface at both the transmitter and the receiver. This deflection surface(s) is preferably provided with a cylindrical curvature, which takes care of beam focusing or bundling.

[0096] The following is an example of the presence detection of an object 3 in the beam path 5 with reference to the Fig. 10 to 13. The presence detection described below can in principle be carried out with any of the previously described embodiments of the measuring arrangement 1 according to the invention.

[0097] It is assumed that an object 3 on a slide 47 is moved from an area outside the sample volume 19 or the light disc 43 into the sample volume 19, wherein measurements are taken with the detection device 29 at different times and thus at different immersion depths 65.

[0098] For example only, measurements are taken here at seven different immersion depths 65a to 65g. Immersion depth 65a refers to an immersion depth where the object is still located outside the beam path 5 or the sample volume 19.

[0099] In Fig. 10, the detection cells 35, or pixels 35, are plotted on the abscissa axis (X-axis). The received signal strength 67 of the individual cells 35 is plotted on the ordinate axis (Y-axis). The signal strength 67 is plotted as a relative signal strength 67, i.e., in relation to the full illumination of the cells 35, which is 100 on the Y-axis.

[0100] A measuring range 69 is also shown, which marks the cells 35 actually used for the measurement.

[0101] The greater the immersion depth 65, the stronger the shadow 21 is visible or detected by the cells 35. Likewise, at greater immersion depths 65, more cells 35 receive the shadow 21. However, the strong broadening of the shadow in the upper part at immersion depths 65f and 65g originates from the specimen slide, which in this example is wider than the specimen itself. At the greatest immersion depth 65g, the relative signal strength 67 of some cells 35 is almost zero. Therefore, the cells 35 located in the center of the shadow 21 are strongly shadowed.

[0102] The Fig. Figure 11 shows the signal strength 67 for selected cells 35 or pixels as a function of the immersion depth 65, here in micrometers. Fig. Figure 12 shows a similar image but for a slide 47 without object 3.

[0103] In Fig. 13 are the signal curves from the Fig. 11 and Fig. 12 for the pixel, or cell with the number 14. The dashed line shows the measurement with only the slide 47, and the solid line shows a measurement for the slide 47 with an object 3 arranged on it.

[0104] In Fig. Figure 13 shows the signals as a function of the immersion depth. The device or method presented here can only record the signals as a function of the immersion depth if the current position of the immersion depth is transmitted by a controller of the immersion mechanism (robot arm or a mechanical movement axis). In reality, this will rarely be the case; instead, the controller will initiate immersion at a fairly constant speed. Thus, although the device does not know the immersion depth, it can determine the point in time when an object is sufficiently immersed. In this case, the horizontal axis can be Fig. 12 and Fig. 13 could be replaced by a time axis. The curve would look exactly the same, only the numbers on the abscissa would be different. The time of undershoot during immersion or overshoot during re-emergence from measuring range 19 can be easily measured by the device. The immersion depth or immersion time can also be transmitted to the control system via digital data transmission.

[0105] In another version, the measured time of an object entering or emerging from the measuring area 19 can also be output with a switching pulse, even with a precisely defined measurement delay. However, if the measurement delay is as short as possible and the switching pulse is to be output as quickly as possible, the best possible accuracy is not achieved. Interpolation between different measurement points before and after the switching threshold cannot be performed in this case.

[0106] In Fig. 13 clearly shows that the continuous line leads to a decrease in signal strength 67, i.e., to shadowing, even at a lower immersion depth 65. A threshold 71 can be defined, which Fig. 13 is at an exemplary 50 percent signal strength. The threshold 71 can be used to determine the immersion depth of object 3, or of the object carrier 47 with or without object 3. As mentioned in the previous paragraph, in most applications, the point in time is determined when object 3 is immersed so far that the switching threshold is exceeded or fallen below. Taking into account the two measurements, once with and once without the object, then enables the clear detection of the presence of object 3.

[0107] In order to automate the evaluation, the first step can be to use the signals as they are in Fig. 10, first a minimum is sought to find the pixel 35 with the strongest shading.

[0108] In this case, the signals at different immersion depths 65 can also be compared. For example, if it is determined that a pixel 35 exhibits strong, particularly permanent, shadowing or signal attenuation regardless of the immersion depth 65, this may indicate contamination of cell 35. The signal of this cell 35 could then be divided by the attenuation factor, which could compensate for the permanent attenuation, for example, due to contamination of a front surface or a malfunction of the pixel (cell 35), or this cell 35 could even be ignored.

[0109] The accuracy of the method can be further improved if the signal strengths 67 for individual cells 35, as shown in Fig. 13, a linear interpolation is performed between the individual measurements. This is shown in Fig. 13 also indicated by the solid line or dashed line.

[0110] The accuracy of the method can be further improved by linear interpolation between three or more measurements, preferably for all measurements that lie in the medium, linear range, i.e., approximately between 20 and 80% of the maximum values, or close to the switching threshold 71. This allows the required high measurement accuracy of the immersion time to be calculated at a high immersion speed. Preferably, this is achieved by the measuring arrangement 1 or the light barrier 60, which preferably includes data processing, for example, in the form of a microprocessor.

[0111] The accuracy of the method is further improved if the measurement points can be measured and taken into account well before immersion, as well as after immersion, when object 3 with slide 47 is completely immersed in the measuring area 19. This allows each cell 35 being evaluated here to be individually scaled or calibrated to full signal (no immersion) and empty signal (complete immersion). This can be done anew for each immersion process, which also allows compensation for slowly changing conditions such as any disruptive ambient light or minimal mechanical stress that could lead to signal changes. For this purpose, the empty signal can be set as the zero point of the signal strength and the full signal as 100%.

Claims

[1] Optical measuring arrangement (1) for detecting the presence of small objects (3) in a beam path (5) for measuring light (7), with at least one receiving-side beam-shaping device (9) arranged in the beam path (5), by means of which the measuring light (7) transmitted through a sample volume (19) in the beam path (5) can be focused to an image width (25) in a first direction (17) oriented perpendicular to the beam path (5), and with at least one detection device (29) arranged in the beam path (5) for detecting the measuring light (7) transmitted by the receiving-side beam-shaping device (9), characterized by , that the at least one detection device (29) is arranged at a working distance (37) from the receiving-side beam-forming device (9) which is smaller than the image distance (25), the optical measuring arrangement (1) comprises at least one light source (39) for emitting the measuring light (7), at least one transmitter-side beam-shaping device (41) is provided in the beam path (5), by means of which the measuring light (7) generated by the light source (39) can be focused into the sample volume (19) at least in the first direction (17), and the transmitter-side beam-forming device (41) has a double cylindrical lens effect which focuses the measuring light (7) generated by the light source (39) exactly into the sample volume (19) in the first direction (17) and collimates it in the second direction. [2] Optical measuring arrangement (1) according to claim 1, characterized by that at least one deflection element (53, 55, 57) is arranged between the sample volume (19) and the light source (39), by means of which the measuring light (7) can be deflected on the beam path (5). [3] Optical measuring arrangement (1) according to claim 2, characterized by that the at least one deflection element (53, 55, 57) is part of at least one beam-shaping device (9, 41). [4] Optical measuring arrangement (1) according to one of the preceding claims, characterized by that between the sample volume (19) and the detection device (29) at least one deflection element (53, 55, 57) is arranged, by means of which the measuring light (7) can be deflected on the beam path (5). [5] Optical measuring arrangement (1) according to one of claims 2 to 4, characterized by that the at least one deflection element (53, 55, 57) is formed monolithically with at least one refraction element (11, 59) of at least one beam-shaping device (9, 41). [6] Optical measuring arrangement (1) according to one of the preceding claims, characterized by that the at least one beam-forming device (9, 41) is a plastic injection-molded part. [7] Optical measuring arrangement (1) according to one of the preceding claims, characterized byin that the at least one detection device (29) comprises a line detector (31) with a row (33) of detection cells (35), wherein the row (33) extends along a second direction (27) running perpendicular to the beam path (5) and to the first direction (17). [8] Optical measuring arrangement (1) according to one of the preceding claims, characterized by that the optical measuring arrangement (1) further comprises at least one movable object carrier (47) through which at least one object (3) to be measured can be moved into the sample volume (19). [9] Method for optically detecting the presence of an object (3) in a sample volume (19), comprising the following method steps: - Emitting a measuring light (7) from a light source (39) - focusing the measuring light (7) along a beam path (5) in a first direction (17) oriented perpendicular to the beam path (5) in a sample volume (19) and collimating the measuring light (7) in a second direction by a transmitter-side beam shaping device (41) with a double cylindrical lens effect; - collecting the measuring light (7) transmitted through the sample volume (19), - focusing the measuring light (7) by at least one receiving-side beam-shaping device (9) in the first direction (17) and - Detecting the measuring light (7) at a working distance (37) from the beam-forming device (9) which is smaller than an image distance (25) of the receiving-side beam-forming device (9). [10] Method according to claim 9, characterized bythe automatic introduction of an object (3) arranged on a slide (47) into the sample volume (19) at different immersion depths (65) and by detecting the measuring light (7) at different immersion depths (65). [11] Method according to one of claims 9 or 10, characterized by the automatic determination of the position, in particular the immersion depth (65) of an object (3) in the sample volume, in particular in the first direction (17).

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