Device and method for characterizing a particle

Abstract

The invention relates to a device (1) for characterizing a particle, comprising a light source (2) for projecting a light beam (4) along a beam axis (5) and comprising a beam-shaping optical unit (3) which is arranged along the beam axis (5) and is designed to adjust a location-dependent intensity distribution of the light beam (4) in a measurement volume (6) which extends partly along the beam axis (5). When a particle (7) is located in the measurement volume (6), a detector (10) is designed to detect a measurement beam (8) reflected and / or scattered by the particle (7) and output an intensity signal to an analysis unit. The analysis unit is designed to determine a particle characteristic within the measurement volume on the basis of the intensity signal. The beam-shaping optical unit (3) is designed to shape the intensity distribution on a projection plane (x-y), which extends transversely to the beam axis (5), such that the intensity of the light beam is minimal along the outer contour (15) of an oval (11) and maximal at at least one point within (14) the oval (11).

Description

[0001] Device and method for characterizing a particle

[0002] Description

[0003] The invention relates to a device according to the preamble of claim 1 and a method according to the preamble of claim 12.

[0004] A device and a method of the types mentioned above are generally known and are used in various applications to determine particle characteristics, such as particle position, particle velocity, or particle size. This can be used, for example, to monitor or control industrial manufacturing and processing processes.

[0005] A device for determining particle characteristics is known, for example, from DE 10 2019209213 A1 and comprises a light source by means of which a light beam is projected along a beam axis. Beam-shaping optics are arranged along the beam axis. The beam-shaping optics are designed to adjust a location-dependent intensity distribution of the light beam in a measurement volume, which extends partially along the beam axis. A particle to be characterized, which is located in the measurement volume, reflects or scatters the light beam at least partially as a measurement beam. This measurement beam is detected by a detector, which outputs an intensity signal to an evaluation unit. The evaluation unit serves to determine the particle characteristics within the measurement volume depending on the intensity signal.

[0006] Fundamentally, it is desirable to be able to characterize the particles within the measurement volume with high accuracy. Compared to the previously known device, an increase in accuracy is possible, for example, by increasing the power of the light source used, but this is typically associated with high costs. The invention is therefore based on the object of proposing a device and a method that offer a good balance between the achievable accuracy in particle characterization and the costs involved.

[0007] The object is achieved by a device having the features according to claim 1 and by a method having the features according to claim 12. Advantageous further developments are the subject matter of the respective dependent subclaims.

[0008] The device according to the invention comprises, in a manner known per se, a light source for projecting at least one light beam along a beam axis. Beam-shaping optics are arranged along the beam axis and designed to adjust a location-dependent intensity distribution of the light beam in a measurement volume, which extends in sections along the beam axis. A detector serves to detect a measurement beam reflected and / or scattered by a particle located in the measurement volume and to output at least one intensity signal to an evaluation unit. The evaluation unit is designed to determine a particle characteristic within the measurement volume depending on the intensity signal.

[0009] The device according to the invention differs from previously known devices in that the beam-shaping optics are designed to form the location-dependent intensity distribution in a projection plane, which extends within the measuring volume transversely to the beam axis, in such a way that an intensity of the light beam is minimal along an outer contour of an oval and is maximal at at least one point within the oval.

[0010] The invention is based on the discovery that adjusting the location-dependent intensity distribution, in which the light beam has a basic oval shape in the projection plane, results in increased accuracy in determining particle characteristics over a larger spatial area. Compared to a radially symmetric intensity distribution, in which the intensity of the light beam is minimal, for example, along a circular contour, the intensity distribution extends over a greater length along the vertical axis of the oval and over a shorter length along the width axis of the oval. Furthermore, the light beam can be more strongly focused along the vertical axis than along the width axis. Compared to previously known devices, the light beam can therefore have an overall higher power per unit area for the same light source power in the projection plane.This allows the light beam to be reflected and / or scattered with a correspondingly higher intensity by a particle located within the measurement volume. It is possible to characterize a particle with high spatial resolution over a large spatial area, particularly along the vertical axis of the oval.

[0011] Advantageously, the intensity of the light beam is maximum at least at a center of the oval, whereby, in particular, a Gaussian intensity distribution can be present. The intensity decreases continuously from the center of the oval toward the outer contour of the oval. The oval has, in particular, a vertical axis and a latitudinal axis, with respect to each of which the oval is symmetrical and has a larger dimension along the vertical axis than along the latitudinal axis. The oval is preferably an ellipse and, in particular, not a circle.

[0012] The particle characteristic can, for example, be a particle dimension or, preferably, a particle position along the vertical axis of the oval in the projection plane. In particular, the device is designed such that the particle position along the vertical axis can be determined with a spatial resolution of 1 micrometer. The detector preferably has a spatial resolution of 5 micrometers to 0.1 micrometers within the measurement volume, particularly preferably 3 micrometers to 1 micrometer, most preferably 1 micrometer.

[0013] The particle can be a solid in a gas, a vacuum, or a liquid. Furthermore, it can be an oil droplet in a water bath, or conversely, a water droplet in an oil bath. Likewise, it can be a liquid droplet in a gas or vacuum, or, in particular, a liquid droplet emerging from a nozzle, especially a spray nozzle.

[0014] The invention is not limited to a specific configuration of the light source. In a simple configuration, the light source comprises at least one laser with a laser diode, a superluminescent diode, a halogen lamp, or a comparable optical radiation source.

[0015] It is within the scope of the invention that at least the light source and the detector can be arranged in a transmission arrangement or a reflection arrangement. In the transmission arrangement, the light source and the detector are arranged on different sides of the projection plane. The light beam is scattered by the particle to be characterized, so that the measurement beam is present as a transmission beam. In the reflection arrangement, the light source and the detector are arranged on the same side with respect to the projection plane. The light beam is reflected by the particle to be characterized, so that the measurement beam is present as a reflection beam.It is further within the scope of the invention that at least two detectors are provided, wherein a first detector and the light source are arranged on different sides of the projection plane and wherein a second detector and the light source are arranged on one side of the projection plane. In such an embodiment, a combination of a reflection arrangement and a transmission arrangement is present between the light source and the detector. The beam-shaping optics can comprise a cylindrical lens in which a lens surface is curved in one axis and by means of which the intensity distribution of the light beam according to the invention can be adjusted. The detector can comprise a collector lens by means of which the measuring beam is bundled and directed onto at least one sensor element of the detector.In particular, the sensor element is a photodiode which outputs an electrical signal to the evaluation unit upon detection of the measuring beam and whose amplitude preferably depends on the intensity of the measuring beam.

[0016] Preferably, at least the light source and the beam-shaping optics are arranged stationary along the beam axis and, in particular, in a defined alignment with one another. At least in a reflection arrangement, the detector is preferably arranged with a measuring axis, along which the measuring beam can be detected, at an angle to the beam axis of the light beam.

[0017] The evaluation unit can be designed as an electronic processing unit, by means of which the particle characteristics can be determined. A mathematical model describing an analytically or empirically determined relationship between the intensity of the measuring beam and the particle characteristics can be implemented in the evaluation unit. By measuring the intensity of the measuring beam, the intensity signal output by the detector can be assigned to the particle characteristics to be determined using the mathematical model.

[0018] Additionally or alternatively, discrete table values ​​can be stored on the evaluation unit, by means of which a measured intensity value of the measuring beam can be compared with a stored intensity value and can be assigned to the corresponding particle characteristic.

[0019] Additionally or alternatively, at least one characteristic curve can be stored in the evaluation unit, indicating an intensity profile depending on the characteristics of a particle characteristic. Using the characteristic curve, a measured intensity of the measuring beam can be assigned to the particle characteristic to be determined. In particular, the characteristic curve describes a profile of the intensity of the measuring beam depending on a particle position along an axis in the projection plane, in particular the vertical axis of the oval.

[0020] In an advantageous development, the beam-shaping optics are configured to set a location-dependent polarization distribution in the projection plane in addition to the location-dependent intensity distribution, with a first polarization and a second polarization with different polarization directions present along the vertical axis of the oval. The detector is configured to determine at least two intensities of the measuring beam, which has the first polarization and / or the second polarization, and to output two polarization-dependent intensity signals to the evaluation unit. The evaluation unit is configured to determine the particle characteristics based on the two polarization-dependent intensity signals.

[0021] The above-described development is based on the applicant's recognition that the intensity of the measuring beam can depend simultaneously on multiple particle characteristics, such as particle position and particle size. This makes it difficult to clearly determine just one of these particle characteristics, since, for example, a varying particle size between different particles to be characterized can lead to different measurable intensities at the same particle position. By designing the beam-shaping optics, by means of which a location-dependent intensity distribution and a location-dependent polarization distribution can be set in the projection plane, another light property of the light beam can be set and taken into account.This makes it possible to consider not only the intensity of the measuring beam, but also the polarization, in order to determine a unique particle characteristic, in particular a particle position. Such a configuration of the intensity distribution and the polarization distribution results in the measuring beam reflected and / or scattered by the particle being able to exhibit at least two intensity components of different polarization.

[0022] For a better understanding, reference is made to the following example of determining the position of three particles: If a first particle is located in the measurement volume and scatters or reflects the light beam with a first intensity and a first polarization, the first intensity and the first polarization can be assigned to a first particle position. If a second particle is located in the measurement volume and scatters or reflects the light beam with a second intensity that is higher than the first intensity and a second polarization, it can be concluded that the second particle is located in a second position.If a third particle is located in the measuring volume and scatters or reflects the light beam with the second intensity and the first polarization, it can be concluded that the third position of the third particle corresponds to the first position of the first particle and that the second intensity is due to a larger particle dimension.

[0023] In a simple embodiment, the beam-shaping optics can comprise a so-called retardation plate, which generates the desired spatially dependent polarization distribution with the first and second polarization directions. Such a retardation plate is an optical component that can change the polarization and phase of passing light waves as needed. The retardation plate is preferably designed as a so-called spatial polarization converter, which is known, for example, from EP 2705393 B1 and can be manufactured according to the method known from US 20200408953 A1. Alternatively, the spatially dependent polarization distribution can also be generated using a so-called spatial light modulator or a so-called vortex plate.

[0024] The detector can, for example, comprise two photodiodes, each with a polarization filter for polarization-sensitive triggering. A first photodiode can be configured to output a first electrical signal depending on the intensity of the measuring beam with the first polarization. A second photodiode can be configured to output a second electrical signal depending on the intensity of the measuring beam with a second polarization.

[0025] In a simple embodiment, a mathematical model can be implemented in the evaluation unit, as already described, which assigns a plurality of intensity values ​​of different polarizations to a corresponding number of particle characteristics, in particular particle positions. In particular, the evaluation unit can have a stored evaluation routine by means of which at least two intensity values ​​of different polarizations are related to one another, and this relationship is assigned to a particle position based on a mathematical model and / or a table and / or a characteristic curve. Instead of the aforementioned relationship, a characteristic number corresponding to the relationship can also be determined.

[0026] In an advantageous development, the beam-shaping optics are designed to generate the location-dependent polarization distribution such that an angle of 180 degrees exists between the polarization directions of the first polarization and the second polarization. At least a third polarization exists along the vertical axis of the oval, preferably in the region of the point within the oval where the intensity is maximum. An angle of 90 degrees exists between the polarization directions of the first polarization and the third polarization and / or between the polarization directions of the second polarization and the third polarization.

[0027] The above-described refinement enables a further increase in the accuracy of determining particle characteristics. The beam-shaping optics are configured to adjust the third polarization. Furthermore, the detector is configured to detect the intensity of the measurement beam with the third polarization. The evaluation unit is further configured to determine the particle characteristics based on three intensity signals for the first, second, and third polarizations.

[0028] In a further advantageous development, the beam-shaping optics are designed to generate the location-dependent polarization distribution such that a fourth polarization is present along the vertical axis of the oval and between the first polarization and the third polarization and / or between the second polarization and the third polarization, wherein an angle of 45 degrees is present between the polarization directions of the fourth polarization and the third polarization.

[0029] The above-described refinement enables a further increase in the accuracy of determining the particle characteristics. The beam-shaping optics are configured to adjust the fourth polarization. Furthermore, the detector is configured to detect the intensity of the measurement beam with the fourth polarization. The evaluation unit is further configured to determine the particle characteristics based on four intensity signals at the first, second, third, and fourth polarizations.

[0030] In an advantageous further development, the detector is designed such that the polarization-dependent intensity components of the measuring beam can be determined in at least two of the following polarizations: 0 degrees, 45 degrees, 90 degrees, 135 degrees.

[0031] The above-described development is advantageous because the polarization directions mentioned can be easily adjusted using conventional beam-shaping optics. The detector can comprise a plurality of photodiodes with at least two polarization filters arranged relative to one another in such a way that light from the photodiodes is detected only in the polarization directions of the polarization filters.

[0032] Preferably, there is no phase difference or a phase difference of 180° between the portions of the light beam that have different polarization directions. This allows for a simple adjustment of linear polarization. However, investigations by the applicant have also shown that adjusting circular or elliptical polarization is also advantageous for clearly determining a particle characteristic, in particular a particle position.In an advantageous development, the light source and / or the beam-shaping optics are therefore designed to generate at least two light beams with a phase difference, wherein the phase difference is 90 degrees, in order to set a circular polarization at least in some regions in the projection plane, or wherein the phase difference is between 0 degrees and 90 degrees or between 90 degrees and 180 degrees in order to set an elliptical polarization at least in some regions in the projection plane. In a further advantageous development, the light source and / or the beam-shaping optics are designed to form the location-dependent intensity distribution in the projection plane such that the intensity of the light beam is minimal along two outer contours of two ovals whose vertical axes are arranged in a V-shape relative to one another, and that the intensity distribution is maximum in the regions of the vertical axes of the two ovals.The detector is designed to detect the intensities of two measuring beams with a time delay. The evaluation unit is used to determine a particle position within the measurement volume based on a time interval between the measured intensities of the two measuring beams.

[0033] The above-described development is based on the applicant's finding that the configuration of the location-dependent intensity distribution of the light radiation, in which the intensity is minimal along the outer contour of an oval, can be multiplied in the projection plane in order to reliably determine a particle characteristic, in particular a particle position. When a particle traverses the measurement volume in the projection plane and crosses the vertical axes of the two ovals, two measurement beams are reflected and / or scattered at a time offset from one another and detected by the detector with a corresponding time offset. With a known angle between the vertical axes arranged in a V-shape and a known particle velocity, the particle position can be deduced by taking into account the time interval between the two intensity signals.This further development is particularly advantageous when the particle velocities of several particles to be characterized do not differ and are known.

[0034] Alternatively, the device can be designed such that the intensity of the light beam is minimal along three outer contours of three ovals whose vertical axes are arranged in an N-shape relative to each other, and such that the intensity distribution is maximal in the regions of the vertical axes of the three ovals. The detector is designed to detect the intensities of three measuring beams with a time offset. The evaluation unit serves to determine a particle position within the measuring volume depending on at least two time intervals between the measured intensities of the three measuring beams.

[0035] An advantage of the above-described refinement is that the particle position within the measurement volume can be determined independently of the particle velocity. In particular, the particle position can be determined as a function of a ratio between the two time intervals. The applicant has discovered that determining such a ratio between the two time intervals enables a reliable determination of the particle position even with varying and unknown particle velocities.

[0036] In a further advantageous development, the light source and / or the beam-shaping optics are configured to project two light beams with different wavelengths, each along a beam axis, which overlap in the projection plane and thereby exhibit the location-dependent intensity distribution and a location-dependent wavelength distribution. The detector is configured to detect at least one wavelength-dependent intensity of the measuring beam. The evaluation unit is configured to determine a particle position within the measurement volume depending on the wavelength-dependent intensities of the measuring beam.

[0037] With the location-dependent wavelength distribution, in addition to the intensity of the measurement beam, another light property can be taken into account to clearly determine a particle characteristic. The location-dependent wavelength distribution can be used in addition to or as an alternative to a location-dependent polarization distribution to clearly determine a particle position within the measurement volume. The location-dependent intensity distribution can be symmetrical with respect to the vertical and horizontal axes of the oval. The location-dependent wavelength distribution can, for example, be different at two spaced-apart positions along the vertical axis.Such a configuration of the intensity distribution and the wavelength distribution results in the light beam reflected by the particle in the form of the measuring beam being able to have at least two wavelength components, the consideration of which enables a clear determination of the position of the particle within the projection plane.

[0038] The detector can have multiple photodiodes that are wavelength-sensitive, so that a detected measuring beam with different wavelength components results in different signal amplitudes from the corresponding photodiodes. The wavelength-dependent signals can be evaluated using a mathematical model, a table, or a characteristic curve to determine the particle characteristics, especially the particle position.

[0039] In an advantageous further development, the measuring volume along the beam axis has a length which corresponds to twice the Rayleigh length of the light beam.

[0040] The Rayleigh length describes, in a well-known manner, the distance along the beam axis between the focal plane and a position where its cross-sectional area doubles that of the focal plane. Therefore, the dimensions and / or position of the measurement volume relative to the beam axis can be adjusted depending on the properties of the light beam, particularly its focal plane.

[0041] Preferably, the beam-shaping optics and / or the detector are designed to form the measurement volume in an application-dependent manner and with adjustable dimensions. Preferably, the oval in the projection plane has a height between 10 micrometers and 1000 micrometers and / or a width between 100 micrometers and 5 centimeters.

[0042] A particular advantage of determining the particle position based on a plurality of polarization-dependent intensity values ​​is that a camera system is not required. Instead, the particle position can be determined based on discrete values, whereby both the detector and the evaluation unit can be designed simply. Investigations by the applicant have shown that the evaluation unit can be designed to determine a plurality of particle positions at a frequency above 10 MHz.

[0043] In an advantageous development, the light source and / or the beam-shaping optics and / or the detector are arranged spatially fixed relative to one another in order to form a stationary measurement volume and to detect a moving particle in the measurement volume. Alternatively, the light source and / or the beam-shaping optics and / or the detector are arranged movably in order to displace the measurement volume by means of a scanning movement and to detect a stationary particle in the measurement volume. Preferably, the light source and / or the beam-shaping optics and / or the detector are arranged immovably relative to one another during the scanning movement.

[0044] The scanning movement can be implemented using a conventional kinematic system, such as an articulated-arm robot or a similar device. With such a device embodiment, surfaces, in particular, can be examined to determine whether they are contaminated with one or more particles.

[0045] As mentioned above, the object is also achieved by a method according to claim 12.

[0046] In the method according to the invention for characterizing a particle, a light beam is projected along a beam axis, wherein the light beam has a location-dependent intensity distribution in a measurement volume that extends sectionally along the beam axis. A particle to be characterized reflects or scatters the light beam in the measurement volume at least partially as a measurement beam. A particle characteristic is determined within the measurement volume as a function of at least one intensity of the measurement beam. It is essential for the method that the location-dependent intensity distribution is minimal in a projection plane that extends within the measurement volume transversely to the beam axis, along an outer contour of an oval, and is maximum at at least one point within the oval, in particular a center point of the oval.

[0047] Preferably, the method can be carried out using the device according to the invention or an advantageous development thereof. Accordingly, the same statements made above with regard to the device according to the invention and the advantageous developments apply to the achievable advantages.

[0048] In an advantageous further development, the light beam is generated with a location-dependent polarization distribution and the particle characteristics are determined as a function of a polarization-dependent intensity of the measuring beam.

[0049] In another advantageous development, the light beam is generated with different wavelengths which overlap in the measuring volume, wherein the overlapping light beams in the projection plane have the location-dependent intensity distribution and a location-dependent wavelength distribution and wherein the particle to be characterized is determined within the measuring volume depending on a wavelength-dependent intensity of the measuring beam.

[0050] In a further advantageous development, the location-dependent intensity distribution in the projection plane is generated such that the intensity of the light beam is minimal along an outer contour of two ovals whose vertical axes are arranged in a V shape and maximal in the regions of the vertical axes of the two ovals. The particle to be characterized reflects or scatters the light beam at least partially in the measurement volume as two measurement beams. The intensities of the two measurement beams are recorded with a time offset. The particle characteristic, in particular a particle position, is determined within the measurement volume as a function of a time interval between two measured intensities of the measurement beams.

[0051] Alternatively, the location-dependent intensity distribution in the projection plane is generated such that the intensity of the light beam is minimal along an outer contour of three ovals whose vertical axes are arranged in an N-shape and maximal in the regions of the vertical axes of the three ovals. The intensities of the three measuring beams are recorded with a time offset. The particle characteristics are determined within the measurement volume as a function of two time intervals between the measured intensities of the measuring beams and preferably independently of the particle velocity. Further advantages of the invention are explained below using an exemplary embodiment and the figures.

[0052] It shows

[0053] Figure 1 is a schematic representation of a device according to the invention for characterizing a particle;

[0054] Figure 2 shows a first embodiment of a location-dependent

[0055] Intensity distribution with a location-dependent polarization distribution;

[0056] Figure 3 shows a diagram with a plurality of polarization-dependent

[0057] Intensity curves to determine a particle position;

[0058] Figure 4 shows a second embodiment of a location-dependent

[0059] intensity distribution;

[0060] Figure 5 shows a third embodiment of a location-dependent

[0061] intensity distribution;

[0062] Figure 6 shows a fourth embodiment of a location-dependent

[0063] Intensity distribution.

[0064] Figure 1 shows a device 1 for optically determining a particle position. For this purpose, the device 1 comprises a laser 2 and a beam-shaping optic 3, which includes a vortex plate and a cylindrical lens (not shown here).

[0065] The laser 2 is used to generate a light beam 4 extending along a beam axis 5. A section of the light beam 4 along the beam axis 5 serves as the measurement volume 6, which is traversed by a moving particle 7. According to Figure 1, the particle 7 is shown in two positions during a rectilinear movement.

[0066] As will be explained in detail with reference to Figures 2 and 3, the beam-shaping optics 3 with the cylindrical lens and the vortex plate serves to set a location-dependent intensity distribution and a location-dependent polarization distribution of the light beam 4 in a projection plane which extends perpendicular to the beam axis 5.

[0067] The particle 7 located in the measuring volume 6 at least partially reflects the light beam 4 in the form of a measuring beam 8, which is collected by the collector lens 9 and directed to a detector 10. The measuring beam 8 has a plurality of polarization-dependent intensities that can be determined by the detector 10. An evaluation unit, which in the embodiment shown here is integrated into the detector 10, serves to determine the desired particle position within the measuring volume 6 depending on at least one polarization-dependent intensity of the measuring beam 8.

[0068] As shown in Figure 2, the light beam in the projection plane essentially has the shape of an oval 11 with two axes of symmetry, i.e., an ellipse. Along a vertical vertical axis H, the oval has a height dimension 12 that is greater than a width dimension 13 along a horizontal width axis. The intensity of the light beam is distributed such that it is maximum at the center point 14 of the oval 11 and minimum along an outer contour 15. Within the oval 11, a two-dimensional Gaussian intensity distribution exists in a plane that runs perpendicular to the projection plane. In other words, the intensity is continuous in a region between the center point 14 and the surrounding outer contour 15, with the intensity decreasing from the center point 14 in the radial direction toward the outer contour 15.

[0069] Such an intensity distribution means that the light beam can be reflected with different intensities along the vertical axis H of the oval. By measuring the intensity of the measuring beam, a particle characteristic can be determined with high accuracy. If the particle characteristic to be determined is a particle position, it is advantageous to take into account that the intensity of the measurement signal can also vary depending on the particle size. Therefore, the embodiment of the intensity distribution shown in Figure 2 provides that the beam-shaping optics generates a location-dependent polarization distribution, which is indicated in Figure 2 by the arrows 16, 17, 18, 19 and 20. Here, a first polarization 16 and a second polarization 17 are present along the vertical axis H, which are spaced from one another along the vertical axis H of the oval 11 and whose polarization directions are at an angle of 180 degrees to one another.In the area of ​​the center point 14, a third polarization 18 is present, the polarization direction of which has a polarization angle of 90 degrees to the polarization directions of the first and second polarizations. Between the first polarization 16 and the third polarization 18, there is a fourth polarization 19, the polarization direction of which has an angle of 45 degrees to the polarization direction of the third polarization 18. Between the second polarization 17 and the third polarization 18, there is a fifth polarization 20, which also has an angular difference of 45 degrees to the third polarization 18. Contrary to the illustration shown, the location-dependent polarization distribution runs continuously along the vertical axis H and includes the discretely shown polarizations 16, 17, 18, 19, and 20.If particle 7 is located in the projection plane and in the region of the vertical axis H of the oval 11, the light beam is reflected in such a way that the measurement beam exhibits a plurality of intensity components of different polarizations. Taking these polarization-dependent intensity components into account allows the determination of a unique position of the particle within the projection plane.

[0070] Figure 3 shows a diagram with the location-dependent intensity curves 21, 22, 23, and 24. These intensity curves each describe the polarization-dependent intensity of the light beam along the vertical axis of the oval in its projection plane. The first intensity curve 21 corresponds to the location-dependent intensity of the light beam with the first polarization 18 according to Figure 2. The second intensity curve 22 corresponds to the location-dependent intensity of the light beam with the second polarization 16 and the third polarization 17 according to Figure 2. The polarization directions of the polarizations 16 and 17 are at an angle of 180 degrees, so that a polarization filter is permeable to light with both polarizations 16, 17. The third intensity curve 23 corresponds to the location-dependent intensity of the light beam with the fourth polarization 19 according to Figure 2.The fourth intensity curve 24 corresponds to the location-dependent intensity of the light beam with the fifth polarization 20 according to Figure 2.

[0071] If a particle is located in the projection plane of the light beam, which corresponds to the image plane of Figure 2, the reflected measuring beam has a plurality of polarization-dependent intensities which, depending on the y-position of the particle, correspond to the intensity curves 21, 22, 23 and 24 according to Figure 3. If the particle is located, for example, at a height of 0 pm along the y-axis, the measuring beam has a dominant intensity component which corresponds to the first intensity curve 21 and has the corresponding first polarization 18. At the same time, the measuring beam in this example has less pronounced intensity components which correspond to the intensity curves 23 and 24 and have the corresponding fourth polarization 19 and fifth polarization 20.In other words, at the y-position of 0 pm, polarization 18 according to Figure 2 predominates, which, however, can be represented by linear superposition of equal parts of polarizations 19 and 20 according to Figure 2.

[0072] By measuring the polarization-dependent intensities using the detector 10, these can be assigned to a unique position of the particle along the y-axis, for example using a mathematical model or a table. The asymmetrical course of the intensity curves 23, 24 allows, in particular, a clear distinction between two particle positions along the y-axis. In the embodiment of the device 1 shown in Figure 1, the light is split into two beams using a so-called 50:50 beam splitter, independent of polarization. Two photodiodes are arranged along the optical path behind this beam splitter and are designed to detect different polarization components. A first photodiode is designed to detect the polarizations 18, 16 and 17 according to Figure 2. The second photodiode is designed to detect the polarizations 19 and 20. Measuring beam.When the split measuring beam is detected, the photodiodes each emit an electrical signal corresponding to the intensity of the measured light component of one of the polarizations mentioned. The signals are evaluated in the evaluation unit, for example, using the mathematical model mentioned above.

[0073] Figure 4 shows an alternative embodiment of the intensity distribution in the projection plane, which can be generated by means of a device that essentially corresponds to the device 1 according to Figure 1. In contrast to the embodiment shown in Figure 1, the light source is designed to generate the location-dependent intensity distribution in the projection plane such that the intensity along an outer contour of two ovals 11, 11', whose vertical axes H, H' are arranged in a V-shape, is minimal and that the intensity is maximum in the regions of the vertical axes H, H', in this case in the surface centers 14, 14' of the two ovals 11 and 11', respectively. The detector is designed to detect the intensities of two measuring beams with a time offset. The evaluation unit is designed to determine a particle position within the measuring volume as a function of a time interval between the measured intensities of the two measuring beams.

[0074] The intensity distribution shown in Figure 4 extends along the x-axis over a range of approximately 1 mm. In an alternative embodiment, the extension along the x-axis can be up to 3 mm. When a particle moves through the measurement volume parallel to the x-axis and traverses the projection plane xy and crosses the vertical axes H, H' of the two connected ovals 11, 1T, two measuring beams are reflected at a time offset from one another and detected by the detector with a corresponding time offset. If the angle between the vertical axes H, H' arranged in a V-shape to one another and a known particle velocity is known, a particle position can be deduced in particular by taking into account the measured intensities. The application of this further development is particularly advantageous when the particle velocities of several particles to be characterized are known and do not differ.In this case, it is possible to directly deduce a particle position from the measured time interval. Figure 5 shows an alternative embodiment of the intensity distribution in the projection plane, which can be generated by means of a device that essentially corresponds to the device 1 according to Figure 1. In contrast to the device shown in Figure 1, the light source is designed to form the location-dependent intensity distribution in the projection plane in such a way that the intensity along an outer contour of three ovals 11, 11T, 11", whose vertical axes H, H', H" are arranged in an N-shape, is minimal, and that the intensity in the regions of the vertical axes H, H', H", in this case in the surface centers 14, 14' and 14", three ovals 11 and 11' respectively.11" is maximum, wherein the detector is designed to detect the intensities of three measuring beams with a time delay and wherein the evaluation unit is designed to determine a particle position within the measuring volume as a function of two time intervals between the two measured intensities of the measuring beams and in particular independently of one.

[0075] Particle velocity. The intensity distribution shown in Figure 5 extends along the x-axis over a range of approximately 1 mm. In an alternative embodiment, the extension along the x-axis can be up to 3 mm.

[0076] An advantage of the intensity distribution shown in Figure 5 is that the particle position within the measurement volume can be determined independently of particle velocity.

[0077] Figure 6 shows a further embodiment of the device, in which the light source 2 is designed to project two light beams with different wavelengths Ai, Ä2 along a respective beam axis, which overlap in the projection plane xy and thereby have the location-dependent intensity distribution and a location-dependent wavelength distribution, and wherein the detector is designed to detect at least one wavelength-dependent intensity of the measuring beam and to output a wavelength-dependent intensity signal to the evaluation unit, wherein the evaluation unit is designed to determine a particle position within the measuring volume as a function of the wavelength-dependent intensity signal.

[0078] With the location-dependent wavelength distribution, in addition to the intensity of the measuring beam, another light property can be taken into account to clearly determine a particle characteristic. The location-dependent wavelength distribution can be used, in particular, in addition to or alternatively to a location-dependent polarization distribution to clearly determine a particle position within the measurement volume. The configuration of the intensity distribution and the wavelength distribution shown in Figure 6 means that the light beam reflected or scattered by the particle, in the form of the measuring beam, can have at least two wavelength components, the consideration of which enables a clear determination of the particle's position within the projection plane.

[0079] The detector can have multiple photodiodes that are wavelength-sensitive, so that a detected reflection beam with different wavelength components results in different signal amplitudes from the corresponding photodiodes. The wavelength-dependent signals can be evaluated using a mathematical model, a table, or a characteristic curve to determine the particle characteristics, especially the particle position.

Claims

Claims Device (1) for characterizing a particle, with a light source (2), in particular a laser, for projecting at least one light beam (4) along a beam axis (5) and with beam-shaping optics (3), which are arranged along the beam axis (5) and are designed to set a location-dependent intensity distribution of the light beam (4) in a measuring volume (6) which extends in sections along the beam axis (5), and with at least one detector (10) which is designed to detect at least one measuring beam (8) reflected and / or scattered by a particle (7) located in the measuring volume (6) and to output at least one intensity signal to an evaluation unit, wherein the evaluation unit is designed to determine a particle characteristic within the measuring volume as a function of the intensity signal, characterized in thatin that the beam-shaping optics (3) are designed to form the location-dependent intensity distribution in a projection plane (xy), which extends within the measuring volume transversely to the beam axis (5), in such a way that an intensity of the light beam is minimal along an outer contour (15) of an oval (11) and is maximal in at least one point within (14) of the oval (11), in particular at least in a center point of the oval (11). Device (1) according to claim 1, wherein the beam-shaping optics (3) are designed to set a location-dependent polarization distribution in the projection plane (xy), wherein along a vertical axis (H) of the oval (11) at least one first polarization (16) and one second polarization (17) with different polarization directions are present, and the detector (10) is designed to at least two intensities of the measuring beam (8) which has the first polarization (16) and / or the second polarization (17),and output two polarization-dependent intensity signals to the evaluation unit, and, wherein the evaluation unit is designed to determine the particle characteristic, in particular a particle position, as a function of the at least two polarization-dependent intensity signals. Device (1) according to claim 2, wherein the beam-shaping optics (3) are designed to generate the location-dependent polarization distribution such that an angle of 180 degrees exists between the polarization directions of the first polarization (16) and the second polarization (17), and at least one third polarization (18) exists along the vertical axis (H) of the oval (11), preferably in the region of the point of the oval (11) at which the intensity is maximum, wherein an angle of 90 degrees exists in each case between the polarization directions of the first polarization (16) and the third polarization and / or between the polarization directions of the second polarization (17) and the third polarization.Device (1) according to claim 3, wherein the beam-shaping optics (3) are designed to generate the location-dependent polarization distribution such that a fourth polarization (19, 20) is present along the vertical axis (H) of the oval (11) and between the first polarization (16) and the third polarization (18) and / or between the second polarization (17) and the third polarization (18), wherein an angle of 45 degrees exists between the polarization directions of the fourth polarization (19, 20) and the third polarization (18). Device (1) according to claim 4, wherein the detector is designed to determine the polarization-dependent intensity components of the measuring beam (8) in at least two of the following polarizations: 0 degrees, 45 degrees, 90 degrees, 135 degrees. Device (1) at least according to claim 2, in which the light source and / or the beam-shaping optics are designed to generate at least two light beams with a phase difference, wherein the phase difference is 90 degrees in order to set a circular polarization at least in some areas in the projection plane (xy) or wherein the phase difference is between 0 degrees and 90 degrees or between 90 degrees and 180 degrees in order to set an elliptical polarization at least in some areas in the projection plane (xy).Device (1) according to one of the preceding claims, in which the light source (2), in particular the laser (2), and / or the beam-shaping optics (3) are designed to form the location-dependent intensity distribution in the projection plane (xy) in such a way that the intensity along two outer contours of two ovals (11, 11'), whose vertical axes (H, H') are arranged in a V-shape, is minimal and that the intensity in the regions of the vertical axes (H; H') of the two ovals (11, 11') is maximal, wherein the detector (10) is designed to detect the intensities of two measuring beams (8) with a time offset and wherein the evaluation unit is designed to determine a particle position within the measuring volume (6) at least as a function of a time interval between the measured intensities of the two measuring beams (8).Device (1) according to one of the preceding claims, in which the light source (2), in particular the laser (2), and / or the beam-shaping optics (3) are designed to form the location-dependent intensity distribution in the projection plane in such a way that the intensity along three outer contours of three ovals (11, 11', 11"), whose vertical axes (H, H', H") are arranged in an N-shape, is minimal and that the intensity in the regions of the vertical axes (H, H', H") of the three ovals (11, 11', 11") is maximal, wherein the detector (10) is designed to detect the intensities of three measuring beams (8) with a time offset, and wherein. the evaluation unit is designed to determine a particle position within the measuring volume (6) as a function of two time intervals between the measured intensities of the three measuring beams (8) and in particular independently of a particle speed.Device (1) according to one of the preceding claims, in which the light source (2), in particular the laser (2), and / or the beam-shaping optics (3) are designed to project two light beams (4) with different wavelengths (Ai, A2) along a respective beam axis (5), which overlap in the projection plane (xy) and thereby have the location-dependent intensity distribution and a location-dependent wavelength distribution, and wherein the detector (10) is designed to detect at least one wavelength-dependent intensity of the measuring beam (8) and output a wavelength-dependent intensity signal to the evaluation unit, wherein the evaluation unit is designed to determine a particle position within the measuring volume as a function of the wavelength-dependent intensity signal. Device (1) according to one of the preceding claims, in which the detector (10) has a spatial resolution of 5 micrometers to 0.1 micrometer, preferably from 3 micrometers to 1 micrometer, most preferably 1 micrometer. Device (1) according to one of the preceding claims, in which at least the light source (2), in particular the laser (2), and / or the beam-shaping optics (3) are arranged immovably in order to form the measuring volume (6) in a stationary manner, or in which the light source (2), in particular the laser (2), and / or the beam-shaping optics (3) and / or the detector (10) are arranged movably in order to displace the measuring volume (6) by means of at least one scanning movement. Method for characterizing a particle (7), in which a light beam (4) is projected along a beam axis (5), wherein the light beam (4) has a location-dependent intensity distribution in a measuring volume (6) which extends sectionally along the beam axis, and wherein a particle (7) to be characterized at least partially reflects or scatters the light beam (4) in the measuring volume (6) as a measuring beam (8), and a particle characteristic within the measuring volume (6) is determined as a function of at least one intensity of the measuring beam (8), characterized in that the location-dependent intensity distribution in a projection plane (xy), which extends within the measuring volume preferably transversely to the beam axis (5), has an intensity which is minimal along an outer contour (15) of an oval (11) and is maximum at at least one point (14) within the oval (11).Method according to claim 12, wherein the light beam (4) has a location-dependent polarization distribution, and the particle characteristics are determined as a function of a polarization-dependent intensity of the measuring beam (8). Method according to claim 12 or 13, wherein two light beams (4) with different wavelengths are generated and overlap in the measurement volume, wherein the overlapping light beams have the location-dependent intensity distribution and a location-dependent wavelength distribution in the projection plane (xy), and wherein the particle characteristics within the measurement volume are determined as a function of a wavelength-dependent intensity of the measuring beam (8). Method according to one of claims 12 to 14, in which the location-dependent intensity distribution in the projection plane (xy) is generated such that the intensity of the light beam (4) is minimal along an outer contour of three ovals (11), whose vertical axes (H, H', H") are arranged in an N-shape, and is maximal in the regions of the vertical axes (H, H', H") of the three ovals (11), and wherein the particle (7) to be characterized reflects or scatters the light beam (4) in the measuring volume (6) at least partially as three measuring beams (8), wherein the intensities of the three measuring beams are detected with a time offset and the particle characteristic, in particular a particle position, within the measuring volume (6) is determined as a function of two time intervals between the measured intensities of the measuring beams (8) and preferably independently of a particle speed.

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