Device and method for characterizing particles

Abstract

The present invention relates to a device (1) for characterizing particles, comprising a light source (2) for projecting a light beam (4) along a beam axis (5) and a beam shape measurement optical unit (3) arranged along the beam axis (5) and configured to adjust a position-dependent intensity distribution of the light beam (4) within a measurement volume (6) partially extending along the beam axis (5). When a particle (7) is located within the measurement volume (6), a detector (10) is configured 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 configured to determine particle characteristics within the measurement volume based on the intensity signal. The beam shape measurement optical unit (3) is configured to shape the intensity distribution on a projection plane (xy) extending transversely to the beam axis (5) such that the intensity of the light beam is minimum along an outer contour (15) of the oval (11) and maximum at at least one point (14) within the oval (11).

Description

[Technical Field]

[0001] The present invention relates to a device according to the preamble of claim 1 and to a method according to the preamble of claim 12.

[0002] Devices and methods of the type mentioned at the outset are known per se and are used in a variety of applications to determine particle position, particle velocity or particle properties such as particle size, etc. This information can be used, for example, to monitor or control industrial manufacturing and machining processes.

[0003] A device for determining particle characteristics is known, for example, from DE 10 2019 209 213 A1, and includes a light source that projects a light beam along a beam axis. A beam shape measurement optical unit is arranged along the beam axis. The beam shape measurement optical unit is configured to adjust the position-dependent intensity distribution of the light beam within a measurement volume that partially extends along the beam axis. Particles to be characterized located within the measurement volume at least partially reflect or scatter the light beam as a measurement beam. This measurement beam is detected by a detector, which outputs an intensity signal to an analysis unit. The analysis unit is used to determine particle characteristics within the measurement volume based on the intensity signal. [Background technology]

[0004] In principle, it is desirable to be able to characterize particles in a measurement volume with high accuracy. An increase in accuracy compared to previously known devices is possible, for example, by increasing the power of the light source used, but this is typically associated with high costs. The present invention is therefore based on the object of proposing a device and a method that are associated with a good ratio between the achievable accuracy for characterizing particles and the resulting costs.

[0005] Summary of the Invention This object is achieved by a device having the features of claim 1 and by a method having the features of claim 12. Advantageous further developments are the subject matter of the respective dependent claims.

[0006] As is known per se, the device according to the present invention comprises a light source for projecting at least one light beam along a beam axis. A beam shape measurement optical unit is arranged along the beam axis and configured to adjust the position-dependent intensity distribution of the light beam in a measurement volume partially extending along the beam axis. A detector is used to detect the measurement beam reflected and / or scattered by particles in the measurement volume and output at least one intensity signal to an analysis unit. The analysis unit is configured to determine particle characteristics in the measurement volume based on the intensity signal.

[0007] The device according to the invention differs from previously known devices in that the beam shape measurement optical unit is configured to shape the position-dependent intensity distribution in a projection plane extending transversely to the beam axis within the measurement volume so that the intensity of the light beam is minimum along the outer contour of the oval and maximum at at least one point within the oval.

[0008] The present invention is based on the finding that tailoring a position-dependent intensity distribution of a light beam to have a basic oval shape in the projection plane is associated with improved accuracy in determining particle characteristics over a larger spatial region. Compared to a radially symmetric intensity distribution, in which the intensity of the light beam is at a minimum along a circular contour, for example, the intensity distribution extends over a longer length along the vertical axis of the oval and a shorter length along the horizontal axis of the oval. Additionally, the light beam can be more focused along the vertical axis than along the horizontal axis. Therefore, compared to previously known devices, the light beam can have an overall higher power per unit area for the same source power in the projection plane. This means that the light beam can be reflected and / or scattered by particles within the measurement volume with a correspondingly higher intensity. It is possible to characterize particles over a larger spatial region with high spatial resolution, particularly along the vertical axis of the oval.

[0009] Advantageously, the intensity of the light beam is greatest at least at the surface center of the oval, and in particular there may be a Gaussian intensity distribution. The intensity continuously decreases from the surface center towards the outer contour of the oval. In particular, the oval has a longitudinal axis and a transverse axis, with which the oval is symmetrically configured and has a greater dimension along the longitudinal axis than along the transverse axis. Preferably, the oval is an ellipse, in particular not a circle.

[0010] The particle property can be, for example, the particle size or, preferably, the particle position along the vertical axis of the oval in the projection plane. In particular, the device is configured so that the particle position along the vertical axis can be determined with a spatial resolution of 1 micrometer. Preferably, the detector has a spatial resolution of 5 micrometers to 0.1 micrometers within the measurement volume, particularly preferably 3 micrometers to 1 micrometer, and most preferably 1 micrometer.

[0011] The particles can be solids in a gas, vacuum, or liquid. They can also be oil droplets in a water bath, or conversely, water droplets in an oil bath. They can also be liquid droplets in a gas or vacuum, or liquid droplets emerging from a nozzle, especially a spray nozzle.

[0012] The invention is not limited to a particular embodiment of the light source. In a simple embodiment, the light source comprises at least one laser with a laser diode, a superluminescent diode, a halogen illuminator or an equivalent light beam source.

[0013] It is within the scope of the present invention that at least the light source and the detector may be in a transmission or reflection configuration. In a transmission configuration, the light source and the detector are arranged on different sides of the projection plane. Here, the light beam is scattered by the characterized particles so that the measurement beam is present as a transmission beam. In a reflection configuration, the light source and the detector are arranged on the same side of the projection plane. The light beam is reflected by the characterized particles so that the measurement beam is present as a reflection beam. It is further within the scope of the present invention that at least two detectors are provided, with a first detector and light source arranged on different sides of the projection plane and a second detector and light source arranged on one side of the projection plane. In such an embodiment, a combination of a reflection configuration and a transmission configuration is provided between the light source and the detector.

[0014] The beam shape measuring optical unit may comprise a cylindrical lens whose lens surface is curved in one axis, allowing the intensity distribution of the light beam according to the invention to be adjusted. The detector may comprise a collector lens which focuses the measurement beam onto at least one sensor element of the detector. In particular, the sensor element is a photodiode which emits an electrical signal to the analysis unit when the measurement beam is detected, the amplitude of which preferably depends on the intensity of the measurement beam.

[0015] Preferably, at least the light source and the beam shape measurement optical unit are arranged at a fixed position along the beam axis, in particular in a defined alignment with respect to each other. At least in a reflective arrangement, the detector is preferably arranged with a measurement axis, along which the measurement beam can be detected, at an angle to the beam axis of the light beam.

[0016] The analysis unit can be configured as an electronic computing unit capable of determining particle properties. A mathematical model describing an analytically or empirically determined relationship between the intensity of the measurement beam and the particle properties can be implemented on the analysis unit. By measuring the intensity of the measurement beam, the intensity signal output by the detector can be assigned to the particle properties determined using the mathematical model.

[0017] Additionally or alternatively, discrete table values ​​can be stored in the analysis unit, whereby measured intensity values ​​of the measurement beam can be compared with the stored intensity values ​​and assigned to associated particle properties.

[0018] Additionally or alternatively, at least one characteristic curve showing an intensity profile based on the degree of the particle characteristic can be stored in the analysis unit. The characteristic curve can be used to assign the measured intensity of the measurement beam to the determined particle characteristic. In particular, the characteristic curve describes the profile of the intensity of the measurement beam based on the particle position along an axis in the projection plane, in particular along the vertical axis of the oval.

[0019] In an advantageous further development, the beam shape measuring optical unit is configured to adjust a position-dependent polarization distribution in the projection plane in addition to the position-dependent intensity distribution, so that a first polarization and a second polarization with different polarization directions lie along a vertical axis of the oval. The detector is configured to determine at least two intensities of the measurement beam with the first polarization and / or the second polarization and output two polarization-dependent intensity signals to an analysis unit. The analysis unit is configured to determine particle properties based on the two polarization-dependent intensity signals.

[0020] The above-mentioned further development is based on the applicant's discovery that the intensity of the measurement beam can simultaneously depend on multiple particle characteristics, such as particle position and particle size. This makes it difficult to unambiguously determine only one of these particle characteristics, since, for example, varying particle sizes between different particles characterized at the same particle position can result in different measurable intensities. Due to the design of the beam shape measurement optical unit, which allows the position-dependent intensity distribution and position-dependent polarization distribution to be adjusted in the projection plane, further optical characteristics of the light beam can be adjusted and taken into account. This makes it possible to take into account not only the intensity but also the polarization of the measurement beam in order to be able to determine unique particle characteristics, in particular the particle position. Such embodiments of the intensity and polarization distributions mean that the measurement beam reflected and / or scattered by the particle can have at least two intensity components with different polarizations.

[0021] For better understanding, see the following example of determining the positions of three particles. If a first particle is located within the measurement volume and scatters or reflects a light beam with a first intensity and a first polarization, the first intensity and first polarization can be assigned to the first particle position. If a second particle is located within the measurement volume and scatters or reflects a light beam with a second intensity and a second polarization that is higher than the first intensity, it can be concluded that the second particle is at a second position. If a third particle is located within the measurement volume and scatters or reflects a light beam with a second intensity and a first polarization, it can be concluded that the third position of the third particle corresponds to the first position of the first particle, and the second intensity is due to the larger particle size.

[0022] In a simple embodiment, the beam shape measurement optical unit can include a so-called retardation plate that generates the desired position-dependent polarization distribution with the first and second polarization directions. Such a retardation plate is an optical component that can change the polarization and / or phase of the light waves passing through it as required. Preferably, the retardation plate is configured 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 position-dependent polarization distribution can be generated using a so-called spatial light modulator or a so-called vortex plate.

[0023] The detector can include, for example, two photodiodes, each with a polarizing filter to enable polarization-sensitive triggering. The first photodiode can be configured to output a first electrical signal based on the intensity of the measurement beam having a first polarization. The second photodiode can be configured to output a second electrical signal based on the intensity of the measurement beam having a second polarization.

[0024] In a simple embodiment, as already explained, the analysis unit can be implemented with a mathematical model that assigns a number of intensity values ​​of different polarizations to a corresponding number of particle characteristics, in particular particle positions. In particular, the analysis unit can have a stored analysis routine in which at least two intensity values ​​of different polarizations are set relative to one another and this ratio is assigned to a particle position using a mathematical model and / or a table and / or a characteristic curve. Instead of the above-mentioned ratio, a metric corresponding to the ratio can also be determined.

[0025] In an advantageous further development, the beam shape measurement optical unit is configured to generate a position-dependent polarization distribution such that there is an angle of 180 degrees between the polarization directions of the first and second polarizations. At least one third polarization is present along the vertical axis of the oval, preferably in the region of a point in the oval where the intensity is maximum. There is an angle of 90 degrees in each case between the polarization directions of the first and third polarizations and / or between the polarization directions of the second and third polarizations.

[0026] The above-mentioned further developments allow for a further improvement in accuracy when determining particle characteristics. In this regard, the beam shape measurement optical unit is configured to adjust the third polarization. Furthermore, the detector is configured to detect the intensity of the measurement beam having the third polarization. The analysis unit is further configured to determine particle characteristics based on three intensity signals at the first, second, and third polarizations.

[0027] In a further advantageous further development, the beam shape measurement optical unit is configured to generate a position-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, and an angle of 45 degrees exists between the polarization direction of the fourth polarization and the polarization direction of the third polarization.

[0028] The above-mentioned further developments allow for a further improvement in accuracy when determining particle properties. In this regard, the beam shape measurement optical unit is configured to adjust the fourth polarization. Furthermore, the detector is configured to detect the intensity of the measurement beam having the fourth polarization. The analysis unit is further configured to determine particle properties based on four intensity signals at the first, second, third and fourth polarizations.

[0029] In an advantageous further development, the detector is configured such that the polarization-dependent intensity component of the measurement beam can be determined in at least two of the following polarizations: 0°, 45°, 90°, 135°.

[0030] The above-mentioned further development is advantageous because the above-mentioned polarization directions can be easily adjusted using a common beam shape measurement optical unit. The detector can have a plurality of photodiodes with at least two polarization filters, which are arranged relative to one another in such a way that light from the photodiodes is detected only in the polarization direction of the polarization filters.

[0031] Preferably, there is no phase difference or a phase difference of 180° between the portions of the light beam having different polarization directions. This facilitates the adjustment of the linear polarization. However, research by the applicant has also shown that it is advantageous to adjust the circular or elliptical polarization in order to be able to unambiguously determine the particle properties, in particular the particle position. Therefore, in an advantageous further development, the light source and / or the beam shape measurement optical unit is configured to generate at least two light beams with a phase difference, the phase difference being 90° in order to adjust the circular polarization in the projection plane in at least a region, or the phase difference being between 0° and 90° or between 90° and 180° in order to adjust the elliptical polarization in the projection plane in at least a region.

[0032] In yet another advantageous further development, the light source and / or the beam shape measuring optical unit are configured to shape the position-dependent intensity distribution in the projection plane so that the intensity of the light beam along the two outer contours of the two ovals whose vertical axes are arranged in a V-shape relative to one another is minimum, and the intensity distribution in the region of the vertical axes of the two ovals is maximum. The detector is configured to detect the intensities of the two measurement beams in a time-shifted manner. The analysis unit is used to determine the particle position in the measurement volume based on the time interval between the measured intensities of the two measurement beams.

[0033] The above-mentioned further development is based on the applicant's discovery that an embodiment of the position-dependent intensity distribution of the light beam, in which the intensity along the outer contour of the oval is minimal, can be multiplied in the projection plane to enable reliable determination of particle characteristics, particularly particle position. When a particle crosses the measurement volume in the projection plane and intersects the perpendicular axes of the two ovals, the two measurement beams are reflected and / or scattered in a time-shifted manner relative to each other and detected by the detector with a corresponding time shift. If the angle between the perpendicular axes arranged in a V-shape relative to each other is known and the particle velocity is known, the particle position can be determined by considering the time interval between the two intensity signals. This further development is particularly advantageous when the particle velocities of the particles to be characterized are not different and are known.

[0034] Alternatively, the device may be configured such that the intensity of the light beam along the three outer contours of the three ovals, whose vertical axes are arranged in an N-shape relative to one another, is minimum, and the intensity distribution in the region of the vertical axes of the three ovals is maximum. The detector is configured to detect the intensities of the three measurement beams in a time-shifted manner. The analysis unit is used to determine the particle position within the measurement volume based on at least two time intervals between the measured intensities of the three measurement beams.

[0035] One advantage of the above-mentioned further development 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 based on the ratio of two time intervals. It has been discovered by the applicant that determining such a ratio of two time intervals allows for a reliable determination of the particle position even with a varying and unknown particle velocity.

[0036] In a further advantageous further development, the light source and / or the beam shape measurement optical unit are configured to project two light beams having different wavelengths along respective beam axes, which light beams overlap in the projection plane and thereby have a position-dependent intensity distribution and a position-dependent wavelength distribution. The detector is configured to detect at least one wavelength-dependent intensity of the measurement beams. The analysis unit is configured to determine the particle position within the measurement volume based on the wavelength-dependent intensities of the measurement beams.

[0037] The position-dependent wavelength distribution allows further light properties to be taken into account in addition to the intensity of the measurement beam, so that particle properties can be unambiguously determined. In particular, a position-dependent wavelength distribution can be used in addition to or instead of a position-dependent polarization distribution to enable the particle position in the measurement volume to be unambiguously determined. The position-dependent intensity distribution can be formed symmetrically with respect to the longitudinal and transverse axes of the oval. The position-dependent wavelength distribution can, for example, differ along the vertical axis at two spaced positions. Such embodiments of the intensity distribution and wavelength distribution mean that the light beam reflected by the particle in the form of the measurement beam can have at least two wavelength components, the consideration of which allows the particle position in the projection plane to be unambiguously determined.

[0038] The detector can have multiple photodiodes configured to be wavelength sensitive, such that detected measurement beams with different wavelength components result in different signal amplitudes at corresponding photodiodes. Mathematical models, tables, or characteristic curves can be used to evaluate the wavelength-dependent signals in order to determine particle properties, in particular particle position.

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

[0040] The Rayleigh length, as known per se, represents the distance along the beam axis between the focal plane and the point where its cross-sectional area doubles relative to the focal plane. The size and / or position of the measurement volume relative to the beam axis can therefore be adjusted based on the properties of the light beam, in particular its focal plane.

[0041] Preferably, the beam shape measurement optical unit and / or the detector are configured to form a measurement volume with adjustable dimensions depending on the application. Preferably, the oval in the projection plane has a height of 10 micrometers to 1000 micrometers and / or a width of 100 micrometers to 5 centimeters.

[0042] One advantage of determining particle positions based on multiple polarization-dependent intensity values ​​is that a camera system is not required. Instead, particle positions can be determined based on discrete values, and both the detector and the analysis unit can be simple. Applicant's research has shown that the analysis unit can be configured to determine multiple particle positions at frequencies exceeding 10 MHz.

[0043] In an advantageous further development, the light source and / or the beam shape measuring optical unit and / or the detector are arranged at a fixed position relative to one another to stationarily form the measurement volume and detect moving particles in the measurement volume. Alternatively, the light source and / or the beam shape measuring optical unit and / or the detector are arranged movably to displace the measurement volume by a scanning movement and detect stationary particles in the measurement volume. Preferably, the light source and / or the beam shape measuring optical unit and / or the detector are arranged stationary relative to one another during the scanning movement.

[0044] The scanning movement can be implemented by kinematics known per se, for example by an articulated arm robot or an equivalent device. Such an embodiment of the device can in particular inspect surfaces to determine whether they are contaminated with one or more particles.

[0045] As mentioned above, this object is also achieved by a method as defined in claim 12.

[0046] In a method for characterizing particles according to the present invention, a light beam is projected along a beam axis, the light beam having a position-dependent intensity distribution in a measurement volume partially extending along the beam axis. The particles to be characterized at least partially reflect or scatter the light beam in the measurement volume as a measurement beam. A particle property in the measurement volume is determined based on at least one intensity of the measurement beam.

[0047] What is important for this method is that the position-dependent intensity distribution in the projection plane extending transversely to the beam axis within the measurement volume is minimum along the outer contour of the oval and maximum at at least one point within the oval, in particular at the surface center point of the oval.

[0048] Preferably, this method can be carried out by the device according to the invention or advantageous further developments thereof, so the same comments already provided above regarding the device according to the invention and advantageous further developments apply with regard to the advantages that can be achieved here.

[0049] In an advantageous further development, the light beam is generated with a position-dependent polarization distribution and the particle properties are determined on the basis of the polarization-dependent intensity of the measurement beam.

[0050] In another advantageous further development, light beams with different wavelengths that overlap in the measurement volume are generated, the overlapping light beams having a position-dependent intensity distribution and a position-dependent wavelength distribution in the projection plane, and the characterized particle in the measurement volume is determined based on the wavelength-dependent intensity of the measurement beam.

[0051] In a further advantageous further development, the position-dependent intensity distribution in the projection plane is generated such that the intensity of the light beam is minimum along the outer contours of two ovals whose vertical axes are arranged in a V-shape and maximum in the region of the vertical axes of the two ovals. The particle to be characterized at least partially reflects or scatters the light beam in the measurement volume as two measurement beams. The intensities of the two measurement beams are detected in a time-shifted manner. The particle characteristics, in particular the particle position, are determined in the measurement volume based on the time interval between the two measured intensities of the measurement beams.

[0052] Alternatively, a position-dependent intensity distribution in the projection plane is generated such that the intensity of the light beam is minimum along the outer contours of three ovals whose vertical axes are arranged in an N-shape and is maximum in the region of the vertical axes of the three ovals. The intensities of the three measurement beams are detected in a time-shifted manner. The particle characteristics in the measurement volume are determined based on two time intervals between the measured intensities of the measurement beams, preferably independently of the particle velocity.

[0053] Further advantages of the invention are explained below with reference to exemplary embodiments and drawings. [Brief explanation of the drawings]

[0054] [Figure 1] 1 shows a schematic diagram of a device according to the invention for characterizing particles; [Figure 2] 1 illustrates a first exemplary embodiment of a position-dependent intensity distribution having a position-dependent polarization distribution. [Figure 3] FIG. 10 shows multiple polarization dependent intensity profiles for determining particle position. [Figure 4] FIG. 10 illustrates a second exemplary embodiment of a position-dependent intensity distribution. [Figure 5] FIG. 10 illustrates a third exemplary embodiment of a position-dependent intensity distribution. [Figure 6] FIG. 10 illustrates a fourth exemplary embodiment of a position-dependent intensity distribution.

[0055] 1 shows a device 1 that can optically determine particle positions. For this purpose, the device 1 comprises a laser 2 and a beam shape measurement optical unit 3, which in a manner not shown here comprises a vortex plate and a cylindrical lens.

[0056] A laser 2 is used to generate a light beam 4 extending along a beam axis 5. The cross section of the light beam 4 along the beam axis 5 serves in this case as a measurement volume 6 through which a moving particle 7 passes. According to Figure 1, the particle 7 is shown in two positions during its linear motion.

[0057] As shown in detail in Figures 2 and 3, a beam shape measurement optical unit 3 comprising a cylindrical lens and a vortex plate is used to adjust the position-dependent intensity distribution and the position-dependent polarization distribution of the light beam 4 in a projection plane extending perpendicular to the beam axis 5.

[0058] A particle 7 located within the measurement volume 6 at least partially reflects the light beam 4 in the form of a measurement beam 8, which is collected by a collecting lens 9 and directed towards a detector 10. The measurement beam 8 has a plurality of polarization-dependent intensities that can be determined by the detector 10.

[0059] In the exemplary embodiment shown here, an analysis unit integrated into the detector 10 is used to determine the desired particle position within the measurement volume 6 based on the polarization-dependent intensity of at least one of the measurement beams 8.

[0060] As shown in FIG. 2, the light beam on the projection plane has substantially the shape of an oval 11, i.e., an ellipse, with two axes of symmetry. Along a vertical axis H, extending vertically, the oval has a height dimension 12 that is greater than a width dimension 13 along a horizontal axis extending horizontally. The intensity of the light beam is distributed such that it is greatest at the surface center point 14 of the oval 11 and is lowest along the outer contour 15. Within the oval 11, a two-dimensional Gaussian intensity distribution exists in a plane perpendicular to the projection plane. In other words, the intensity extends continuously in the region between the surface center point 14 and the circumferential outer contour 15, and the intensity decreases radially from the surface center point 14 toward the outer contour 15.

[0061] 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 measurement beam, particle characteristics can be determined with high precision. When the particle characteristic to be determined is particle position, it is advantageous to consider that the intensity of the measurement signal can also vary based on particle size. Thus, the embodiment of the intensity distribution shown in FIG. 2 enables the beam shape measurement optical unit to generate a position-dependent polarization distribution, indicated by arrows 16, 17, 18, 19, and 20 in FIG. 2. Here, first and second polarizations 16 and 17 exist along the vertical axis H, are spaced apart from each other along the vertical axis H of the oval 11, and their polarization directions form a 180-degree angle with each other. A third polarization 18 exists in the region of the surface center point 14, and its polarization direction has a 90-degree polarization angle with respect 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, whose polarization direction is at a 45-degree angle with respect 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 compared to the third polarization 18. Unlike the illustrated example, the position-dependent polarization distribution is continuous along the vertical axis H and includes discretely depicted polarizations 16, 17, 18, 19, and 20.

[0062] If a particle 7 is located in the region of the projection plane and the normal axis H of the oval 11, the light beam is reflected in such a way that the measurement beam has several intensity components of different polarizations. By taking these polarization-dependent intensity components into account, it is possible to determine the unambiguous position of the particle in the projection plane.

[0063] FIG. 3 shows a diagram with position-dependent intensity profiles 21, 22, 23, and 24. Each of these intensity profiles describes the polarization-dependent intensity of a light beam along the vertical axis of the oval in its projection plane. Here, the first intensity profile 21 corresponds to the position-dependent intensity of a light beam with the first polarization 18 according to FIG. 2. The second intensity profile 22 corresponds to the position-dependent intensity of a light beam with the second polarization 16 and the third polarization 17 according to FIG. 2. The polarization directions of the polarizations 16 and 17 are at an angle of 180 degrees so that the polarizing filter transmits light of both polarizations 16 and 17. The third intensity profile 23 corresponds to the position-dependent intensity of a light beam with the fourth polarization 19 according to FIG. 2. The fourth intensity profile 24 corresponds to the position-dependent intensity of a light beam with the fifth polarization 20 according to FIG. 2.

[0064] When a particle is located in the projection plane of the light beam, which corresponds to the image plane in FIG. 2, the reflected measurement beam has multiple polarization-dependent intensities corresponding to the intensity progressions 21, 22, 23, and 24 described in FIG. 3, depending on the y-position of the particle. For example, when the particle is located at a height of 0 μm along the y-axis, the measurement beam has a dominant intensity component corresponding to the first intensity progression 21 and a corresponding first polarization 18. At the same time, the measurement beam in this example has less prominent intensity components corresponding to the intensity progressions 23 and 24 and a corresponding fourth polarization 19 and fifth polarization 20. In other words, at a y-position of 0 μm, polarization 18 according to FIG. 2 dominates, which can be represented by a linear superposition of equal parts of polarizations 19 and 20 according to FIG. 2.

[0065] By measuring the polarization-dependent intensities using detector 10, these can be assigned to distinct positions of the particles along the y-axis, for example using a mathematical model or a table, where the asymmetric progression of the intensity progressions 23, 24 allows in particular a clear distinction between two particle positions along the y-axis.

[0066] In the exemplary embodiment of the device 1 shown in FIG. 1, the light is split into two beams, regardless of polarization, using a so-called 50:50 beam splitter. Two photodiodes configured to detect different polarization components are arranged along the optical path after this beam splitter. In this regard, the first photodiode is configured to detect polarizations 18, 16, and 17 according to FIG. 2. The second photodiode is configured to detect polarizations 19 and 20. The split measurement beams are then detected. Each photodiode outputs an electrical signal corresponding to the intensity of the corresponding measurement light component of one of the aforementioned polarizations. The signals are evaluated in an analysis unit, for example, using the mathematical model described above.

[0067] FIG. 4 shows an alternative embodiment of an intensity distribution in the projection plane that can be shaped using a device substantially corresponding to the device 1 described in FIG. 1. In contrast to the embodiment shown in FIG. 1, the light source is configured to shape the position-dependent intensity distribution in the projection plane so that the intensity is minimum along the outer contours of two ovals 11, 11' arranged in a V-shape with respect to their vertical axes H, H', and maximum in the region of the vertical axes H, H', in this case at the surface center points 14, 14' of the two ovals 11 or 11'. The detector is configured to detect the intensities of the two measurement beams in a time-shifted manner. The analysis unit is configured to determine the particle position in the measurement volume based on the time interval between the measured intensities of the two measurement beams.

[0068] The intensity distribution shown in FIG. 4 extends along the x-axis by approximately 1 mm. In an alternative embodiment, the extension along the x-axis can be up to 3 mm. When a particle moving through the measurement volume parallel to the x-axis crosses the projection plane xy and the vertical axes H, H' of two adjacent ovals 11, 11', the two measurement beams are reflected from each other in a time-shifted manner and detected by the detector with a corresponding time shift. If the angle between the V-shaped vertical axes H, H' and the particle velocity are known, the particle position can be determined by taking the measured intensity into account. This further development is particularly advantageous when the particle velocities of the particles to be characterized are known and do not differ. In this regard, it is possible to directly estimate the particle position based on the measured time intervals.

[0069] FIG. 5 shows an alternative embodiment of an intensity distribution in the projection plane that can be shaped using a device substantially corresponding to the device 1 described in FIG. 1. In contrast to the device shown in FIG. 1, the light source is configured to shape the position-dependent intensity distribution in the projection plane so that the intensity is minimum along the outer contours of three ovals 11, 11', 11'' arranged in an N-shape with respect to their vertical axes H, H', H'' and maximum in the region of the vertical axes H, H', H''—in this case, at the surface center points 14, 14', 14'' of each of the three ovals 11, 11', 11''. The detector is configured to detect the intensities of the three measurement beams in a time-shifted manner. The analysis unit is configured to determine the particle position within the measurement volume based on two time intervals between two measured intensities of the measurement beams, and in particular independently of the particle velocity. The intensity distribution shown in FIG. 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.

[0070] One advantage of the intensity distribution shown in Figure 5 is that the particle position within the measurement volume can be determined independently of the particle velocity.

[0071] Figure 6 shows a further embodiment of the device, in which the light source 2 is configured to project two light beams having different wavelengths λ1, λ2 along respective beam axes, which light beams overlap in the projection plane xy and thereby have a position-dependent intensity distribution and a position-dependent wavelength distribution, the detector is configured to detect the wavelength-dependent intensity of at least one of the measurement beams and output a wavelength-dependent intensity signal to an analysis unit, and the analysis unit is configured to determine the particle position within the measurement volume based on the wavelength-dependent intensity signal.

[0072] In addition to the intensity of the measurement beam, further optical properties can be taken into account in order to unambiguously determine particle properties due to the position-dependent wavelength distribution. In particular, a position-dependent wavelength distribution can be used in addition to or as an alternative to a position-dependent polarization distribution to enable the unambiguous determination of the particle position in the measurement volume. The embodiment of the intensity and wavelength distribution shown in Figure 6 means that the light beam reflected or scattered by the particle in the form of the measurement beam can have at least two wavelength components, which, when taken into account, allows the unambiguous determination of the particle position in the projection plane.

[0073] The detector may comprise multiple photodiodes configured to be wavelength sensitive, such that detected reflected beams having different wavelength components result in different signal amplitudes at corresponding photodiodes. Mathematical models, tables, or characteristic curves may be used to evaluate the wavelength-dependent signals to determine particle characteristics, particularly particle position.

Claims

1. A device (1) for characterizing particles, comprising: a light source (2), in particular a laser, for projecting at least one light beam (4) along a beam axis (5), a beam shape measurement optical unit (3) arranged along the beam axis (5) and configured to adjust a position-dependent intensity distribution of the light beam (4) within a measurement volume (6) extending partially along the beam axis (5), at least one detector (10) configured to detect at least one measurement beam (8) reflected and / or scattered by a particle (7) when the particle (7) is located within the measurement volume (6) and to output at least one intensity signal to an analysis unit, A device (1), wherein the analysis unit is configured to determine particle characteristics in the measurement volume based on the intensity signal, 1. A device (1), characterized in that the beam shape measurement optical unit (3) is configured to shape measure the position-dependent intensity distribution in a projection plane (x-y) extending transversely to the beam axis (5) within the measurement volume so that the intensity of the light beam is minimum along the outer contour (15) of an oval (11) and maximum at at least one point (14) within the oval (11), in particular at least at the surface center point of the oval (11).

2. the beam shape measurement optical unit (3) is configured to adjust a position-dependent polarization distribution in the projection plane (xy), and at least a first polarization (16) and a second polarization (17) having different polarization directions are present along a vertical axis (H) of the oval (11); and the detector (10) is configured to determine at least two intensities of the measurement beam (8) having the first polarization (16) and / or the second polarization (17) and to output two polarization-dependent intensity signals to the analysis unit, The device (1) according to claim 1, wherein the analysis unit is configured to determine the particle properties, in particular particle positions, based on at least two polarization dependent intensity signals.

3. the beam shape measurement optical unit (3) is configured to generate the position-dependent polarization distribution such that there is an angle of 180 degrees between the polarization direction of the first polarization (16) and the polarization direction of the second polarization (17); 3. The device (1) according to claim 2, wherein at least one third polarization (18) is present along the vertical axis (H) of the oval (11), preferably in the region of the point of the oval (11) where the intensity is maximum, and wherein an angle of 90 degrees exists in each case between the polarization direction of the first polarization (16) and the polarization direction of the third polarization and / or between the polarization direction of the second polarization (17) and the polarization direction of the third polarization.

4. 4. The device (1) of claim 3, wherein the beam shape measurement optical unit (3) is configured to generate the position-dependent polarization distribution such that a fourth polarization (19, 20) is located 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), and wherein an angle of 45 degrees exists between the polarization direction of the fourth polarization (19, 20) and the polarization direction of the third polarization (18).

5. 5. The device (1) according to claim 4, wherein the detector is configured to determine polarization-dependent intensity components of the measurement beam (8) in at least two of the following polarizations: 0 degrees, 45 degrees, 90 degrees, and 135 degrees.

6. the light source and / or the beam shape measurement optical unit are configured to generate at least two light beams having a phase difference; the phase difference is 90 degrees to adjust the circular polarization in the projection plane (xy) at least in the region; Or the device (1) according to at least claim 2, wherein said phase difference is between 0 degrees and 90 degrees or between 90 degrees and 180 degrees in order to adjust the elliptical polarization in said projection plane (xy) at least in the region.

7. the light source (2), in particular the laser (2), and / or the beam shape measurement optical unit (3) are configured to shape the position-dependent intensity distribution in the projection plane (x-y) in such a way that the intensity along the two outer contours of two ovals (11, 11') whose vertical axes (H, H') are arranged in a V-shape is minimum, and the intensity in the region of the vertical axes (H; H') of the two ovals (11, 11') is maximum, the detector (10) is configured to detect the intensities of the two measurement beams (8) in a time-shifted manner; and The device (1) according to any one of claims 1 to 6, wherein the analysis unit is configured to determine a particle position within the measurement volume (6) based on a time interval between measured intensities of at least the two measurement beams (8).

8. the light source (2), in particular the laser (2) and / or the beam shape measurement optical unit (3) are configured to shape the position-dependent intensity distribution on the projection plane in such a way that the intensity along the three outer contours of three ovals (11, 11', 11'') arranged in an N-shaped arrangement with their vertical axes (H, H', H'') is minimum, and the intensity in the region of the vertical axes (H, H', H'') of the three ovals (11, 11', 11'') is maximum, the detector (10) is configured to detect the intensities of the three measurement beams (8) in a time-shifted manner; 8. The device (1) according to any one of claims 1 to 7, wherein the analysis unit is configured to determine a particle position within the measurement volume (6) based on two time intervals between the measured intensities of the three measurement beams (8), and in particular independently of the particle velocity.

9. The light source (2), in particular the laser (2), and / or the beam shape measurement optical unit (3) emits light of different wavelengths (λ １ , λ ２ ) along respective beam axes (5), such that the two light beams (4) overlap in the projection plane (x-y) and thereby have the position-dependent intensity distribution and position-dependent wavelength distribution, the detector (10) is configured to detect at least one wavelength-dependent intensity of the measurement beam (8) and output a wavelength-dependent intensity signal to the analysis unit; The device (1) according to any one of the preceding claims, wherein the analysis unit is configured to determine a particle position within the measurement volume based on the wavelength-dependent intensity signal.

10. 10. The device (1) according to any one of the preceding claims, wherein the detector (10) has a spatial resolution in the measurement volume of between 5 micrometers and 0.1 micrometers, preferably between 3 micrometers and 1 micrometer, most preferably 1 micrometer.

11. at least the light source (2), in particular the laser (2) and / or the beam shape measurement optical unit (3) are arranged stationary to form the measurement volume (6) in a stationary manner, or The device (1) according to any one of claims 1 to 10, wherein the light source (2), in particular the laser (2), and / or the beam shape measurement optical unit (3), and / or the detector (10) are movably arranged to displace the measurement volume (6) by at least one scanning movement.

12. A method for characterizing particles (7), comprising: A light beam (4) is projected along a beam axis (5). the light beam (4) has a position-dependent intensity distribution within a measurement volume (6) extending partially along the beam axis, and the particle (7) to be characterized at least partially reflects or scatters the light beam (4) in the measurement volume (6) as a measurement beam (8); and 1. A method for determining particle properties in the measurement volume (6) based on the intensity of at least one of the measurement beams (8), comprising:

1. A method according to claim 1, wherein said position-dependent intensity distribution in a projection plane (x-y), preferably extending transversely to said beam axis (5) within said measurement volume, has an intensity minimum along an outer contour (15) of an oval (11) and a maximum at at least one point (14) within said oval (11).

13. 13. The method of claim 12, wherein the light beam (4) has a position-dependent polarization distribution and the particle properties are determined based on the polarization-dependent intensity of the measurement beam (8).

14. two light beams (4) having different wavelengths are generated and overlap in the measurement volume, the overlapping light beams having the position-dependent intensity distribution and position-dependent wavelength distribution in the projection plane (x-y); 14. The method according to claim 12 or 13, wherein the particle properties in the measurement volume are determined based on the wavelength-dependent intensity of the measurement beam (8).

15. the position-dependent intensity distribution in the projection plane (x-y) is generated in such a way that the intensity of the light beam (4) is minimum along the outer contour of three ovals (11) arranged in an N-shape with their vertical axes (H, H', H'') and is maximum in the region of the three ovals (11) with their vertical axes (H, H', H''); the particle (7) to be characterized reflects or scatters the light beam (4) in the measurement volume (6) at least partially as three measurement beams (8), the intensities of which are detected in a time-shifted manner; and 15. The method according to any one of claims 12 to 14, wherein the particle properties, in particular particle positions, within the measurement volume (6) are determined based on two time intervals between measured intensities of the measurement beam (8), and preferably independently of particle velocity.

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