Abstract:
The invention relates to a system for characterizing grinding material, especially milled grain, in a roll mill comprising a roll passage formed by a pair of rolls. The system comprises an extraction device which is analyzed downstream of the roller passages and used to extract a grinding material sample from the flow of grinding material leaving the roll passage; a presentation section for conveying and presenting the grinding material sample; a recording device for recording the grinding material sample conveyed through the presentation section; and an analysis device for analyzing the recorded grinding material sample.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority of International Application No. PCT/CH2005/000242, filed May 2, 2005 and German Application No. 10 2004 031 052.1, filed Jun. 25, 2004, the complete disclosures of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     a) Field of the Invention  
         [0003]     The invention relates to a system and a method for characterizing grinding stock in a cylinder mill with a roll passage formed by a roll pair.  
         [0004]     b) Description of the Related Art  
         [0005]     While milling grainy material, e.g., wheat, in a cylinder roll, the grainy material is comminuted between the roll pair rolls. In order to obtain flour with a specific fineness, the grinding stock must usually be passed through such a passage several times, during which air separators and screens are used for purposes of classification.  
         [0006]     The milling effect of a passage depends primarily on the nip gap between the two rolls of a roll pair. However, there are also other cylinder roll operating parameters that influence the milling effect of a passage. Therefore, it is desirable to characterize the grinding stock that exits after a specific passage. If the grinding stock is here found to deviate from a grinding stock setpoint characteristic, this deviation can be used as the basis for correcting the nip gap or, if necessary, another cylinder mill operating parameter, so as to compensate for the deviation again as quickly as possible.  
         [0007]     EP 0 433 498 A1 describes a cylinder mill in which a portion of the grinding stock is branched and passed by a measuring unit, with which the particle size of the grinding stock particles is determined.  
         [0008]     WO 01/03841 A1 describes a control system for milling processes. Grinding stock particles are here also passed by a measuring unit, with which the size of the grinding stock particles is determined.  
         [0009]     EP 0 487 356 A2 describes a method and a device for determining the degree of milling in a milling system, in which the grinding stock grains are passed between a coherent light source and a light receiver, in order to determine the particle sizes, and hence the milling degree of the grinding stock.  
         [0010]     None of the cited documents refer to a deagglomeration of the grinding stock particles.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0011]     The primary object of the invention is to provide a system and a method that enable a deagglomeration and characterization of the grinding stock exiting a milling passage in a cylinder mill.  
         [0012]     This object is achieved by means of a system in accordance with the invention for characterizing grinding stock, in particular of milled grain, in a cylinder mill with a roll passage formed by a roll pair. The system consists of removal means after the roll passage for removing a grinding stock sample from the grinding stock stream exiting the roll passage, a supply section for conveying through and supplying the removed grinding stock sample, acquisition means for acquiring the grinding stock sample conveyed through the supply section and analyzing means for analyzing the acquired grinding stock sample. The supply section has two opposing walls, between which a nip is formed. A pneumatic line empties in an outlet area in the nip formed between the opposing walls. The flow path changes direction by between 80° and 90° in the outlet area.  
         [0013]     Also in accordance with the invention, a method for characterizing grinding stock, in particular of milled grain, in a cylinder mill with a roll passage formed by a roll pair, in particular with the use of a system described above comprising the steps of removing a grinding stock sample from the grinding stock streams exiting the roll passage, conveying and supplying the removed grinding stock sample conveyed through the supply section and analyzing the acquired grinding stock sample.  
         [0014]     The system according to the invention encompasses a removal means after the roll passage for removing a grinding stock sample from grinding stock stream exiting the roll passage; a supply section for conveying and supplying the removed grinding stock sample; a detector for acquiring the grinding stock sample passing through the supply section; and an analyzer for analyzing the acquired grinding stock sample.  
         [0015]     According to the invention, the supply section has two opposing walls, between which a nip is formed, wherein the two opposing walls are preferably flat surfaces arranged parallel relative to each other.  
         [0016]     According to the invention, the pneumatic line mentioned further above empties in an outlet area in the nip formed between the opposing walls, wherein the flow path changes direction in the outlet area. This causes the grinding stock entrained in the conveying gas of the pneumatic line to collide against the line wall, helping to deagglomerate potential agglomerates. The change in direction of the flow path measures between 80° and 90° in the invention. This yields especially high pulse changes in the entrained grinding stock particles as they are deflected upon impact, and hence to an especially pronounced collision effect.  
         [0017]     The method according to the invention involves the following steps: Removing a grinding stock sample from the grinding stock stream exiting the roll passage; conveying and supplying the removed grinding stock sample in a supply section; acquiring the grinding stock sample conveyed through the supply section; and analyzing the acquired grinding stock sample.  
         [0018]     According to the invention, the grinding stock sample is conveyed through a pneumatic line and the supply section along a flow path, wherein the flow path is made to undergo a directional change in the outlet area that measures between 80° and 90°.  
         [0019]     In this way, the grinding stock exiting a milling passage can be deagglomerated and characterized.  
         [0020]     A deagglomeration section for deagglomerating grinding stock agglomerates in the grinding stock sample is preferably provided downstream from the removal means and upstream from or in the supply section. This prevents agglomerates of several grinding stock particles from mistakenly being acquired and identified as large grinding stock particles.  
         [0021]     The removal means can be connected by a pneumatic line with the supply section in such a way that the grinding stock can be conveyed through the pneumatic line and supply section along a flow path. In this way, the system according to the invention can also be linked to a location within a mill remote from the cylinder mill, thereby increasing the level of artistic freedom while designing a milling system.  
         [0022]     The acquisition means preferably has a camera for acquiring electromagnetic radiation or electromagnetic frequencies, in particular optical frequencies, wherein the camera is preferably aimed into or at the gap.  
         [0023]     In a first variant, the opposing walls of the supply section are permeable to electromagnetic radiation that can be detected by the camera, in particular optical frequencies. As a result, the camera can be situated on any side of the nip desired behind one of the walls.  
         [0024]     In this first configuration, the camera is arranged on the one side of the nip, away from the nip on one of the two permeable walls, and an electromagnetic radiation source, in particular a light source, for the electromagnetic radiation that can be detected by the camera, is located on the other side of the nip, away from the nip on the other of the two permeable walls. As a result, the grinding stock of the grinding stock sample conveyed through the nip can be irradiated by the electromagnetic radiation, and the shadow or projection of particles form the grinding stock sample gets into the visual field of the camera.  
         [0025]     In a second variant, the first wall of the two opposing walls of the supply section is permeable to the electromagnetic radiation that can be detected by the camera, in particular to optical frequencies, while the second wall is impermeable to electromagnetic frequencies detectable by the camera, in particular optical frequencies, and more absorbent than the grinding stock particles.  
         [0026]     In this second arrangement, the camera is situated downstream on the one side of the gap on the permeable wall, and a source for electromagnetic radiation, in particular a light source, for the electromagnetic radiation detectable by the camera is situated downstream on the same side of the gap on the permeable wall. In this way, the grinding stock of the grinding stock sample passed through the gap can be irradiated, and the scattered light or reflection of particles in the grinding stock sample gets into the visual field of the camera.  
         [0027]     It is here advantageous if the gap-side surface of the second wall absorbs the electromagnetic radiation emitted by the source more strongly than the surfaces of the grinding stock particles. This ensures that there is sufficient contrast between the reflecting grinding stock particles that move from the gap-side surfaces and the light reflected by the wall, thereby allowing for the effortless detection of imaged grinding stock particles and greatly facilitating subsequent image processing. This saves on expensive and time-consuming filtering processes during image processing.  
         [0028]     In an advantageous further development, a cleaning device is allocated to each of the two opposing walls, and can be used to remove grinding stock particles adhering to the two opposing walls. This ensures that not too many resting grinding stock particles, i.e., those adhering to one or the other wall, become imaged in the camera. The particle size distribution of the grinding stock particles adhering to the walls is generally different than that of the grinding stock particles entrained in the grinding stock stream. If the object is to forgo a distinction between resting and moving grinding stock particles when detecting and processing the grinding stock stream image information, the walls should therefore be routinely cleaned to “shake off” the particles adhering to the walls.  
         [0029]     The cleaning device can be a vibration source, in particular an ultrasound source, which is rigidly connected with the two respective opposing walls, so that it can impart vibration to the two walls. We also refer to this version as the “structure-borne noise version” of the cleaning device.  
         [0030]     As an alternative, the cleaning device can also be a vibration source, in particular an ultrasound source, with which the gaseous medium can be made to vibrate between the two opposing walls. We also refer to this version as the “airborne noise version” of the cleaning device.  
         [0031]     The deagglomeration section is preferably an impact surface in the inlet area of the presentation section. In addition to producing the deagglomeration effect via impact and pulse transmission to agglomerates, the airborne noise version of the wall cleaning device can also help deagglomerate grinding stock particles entrained in the air, wherein work takes place either sequentially or simultaneously with various ultrasound frequencies, as required.  
         [0032]     The directional change of the streaming path is preferably localized in the inlet area of the presentation section. As a result, impact takes place shortly before the optical detection of the grinding stock stream, so that the grinding stock particles are practically completely deagglomerated.  
         [0033]     It must be mentioned in this conjunction that it is also particularly advantageous to provide openings in the pneumatic line upstream just before the presentation openings to take in ambient air (“secondary air”) into the pneumatic line operated under a slight vacuum. This inwardly transferred, if necessary in pulses, secondary air also helps to clean the walls and deagglomerate.  
         [0034]     The presentation section or “window” is best larger than the viewing field of the camera, wherein the camera then only acquires a partial area of the presentation section. This makes it possible to place the camera inside the presentation area at a location on the wall or window, where minimal segregation of the grinding stock particles is to be expected within the grinding stock stream.  
         [0035]     If the presentation section or window is larger than the viewing field of the camera, several cameras can also each acquire a partial area of the presentation section. This makes it possible to average various grinding stock images from different locations within the presentation section. If the grinding stock stream is segregated at the different partial areas, averaging enables a homogenizing action, making it possible to at least partially balance out such mixtures, so that the entirety of information averaged from the respective grinding stock images is representative for the particle size distribution in the entire grinding stock stream.  
         [0036]     In a special embodiment, the several cameras are each selectively actuatable, so that selective sections of the grinding stock image on the image sensor can be used, and can be averaged.  
         [0037]     As an alternative, the presentation section can essentially correspond to the entire viewing field of the camera, wherein the image sensor of the camera can then be selective actuated, so that selective sections of the grinding stock image on the image sensor can be used. Such a selective actuation preferably takes place in a purely random manner, in particular via actuation using a random-check generator.  
         [0038]     In another advantageous further development, the system according to the invention consists of removal means after the roller passage situated along the axial direction of the roller passage, wherein a first removal means is advantageously arranged in the area of the first axial end of the roller passage, and a second removal means in the area of the second axial end of the roller passage. This makes it possible to obtain information about the degree of milling as a function of the axial position along the roller pair. Given non-symmetrical grinding stock characteristics along the roller pair, or in particular between the left and right end area of the roller passage, it can be concluded that the roller of the roller pair are misaligned, and corrective measures can be introduced.  
         [0039]     The light source and camera are best connected with a controller, which can synchronously turn the light source and camera on and off, producing a series of stroboscope pictures. Several light sources or stroboscope flash devices can also be provided, which are operated simultaneously, but differently, specifically with respect to flash duration and intensity.  
         [0040]     The analysis means preferably has an image processing system.  
         [0041]     This image processing system preferably has means for distinguishing between moving grinding stock particles and grinding stock particles adhering to the walls in the case of grinding stock particles imaged and acquired by the camera in the projection mode or reflection mode. Resting grinding stock particles adhering to the wall can then be left out of account in the evaluation during image processing, meaning that only the moving grinding stock particles are used for the evaluation. Similarly to what was described above, this prevents a distortion of grinding stock particle size distribution.  
         [0042]     During implementation of the method according to the invention, the grinding stock sample is preferably removed from the grinding stock stream exiting the roller passage at various locations, so that information about the relative roller alignment of the roller pair of the passage can be obtained, as described further above.  
         [0043]     The grinding stock sample obtained in this way is then preferably passed through the presentation section in a radial stream. In such a radial stream, the radial rate of flow in a radial direction decreases from the inside out. The loading of transport fluid (e.g., pneumatic air) is largely constant from the inside out, i.e., the number of grinding stock particles per volume unit is essentially also constant to the outside, so that the probability of particle overlaps while imaging the projection pattern or reflection pattern remains essentially constant over the radial area. By radially shifting the camera during the radial positioning of a partial acquisition area, an optimal assessment can then be made between a loading of the grinding stock stream dense enough to achieve a representative image on the one hand, and a dilution of the grinding stock stream sufficient to minimize the overlap of particle images in the camera (no “optical agglomerates”).  
         [0044]     Allowing secondary air to stream into the radially inward lying part of the detection area makes it possible to vary transport fluid loading.  
         [0045]     In order to cut down on computing time during image processing, it very much makes sense to acquire the grinding stock sample passed through the presentation section in partial areas only. At least one change then advantageously takes place during the entire acquisition process, e.g., between a first partial area where a first part of the acquisition process takes place initially, to at least one additional partial area, in which another part of the acquisition process takes place subsequently. The evaluation results for the various acquisition partial areas can then be averaged to obtain as representative a characterization of the entire grinding stock stream as possible. The respectively acquired partial areas of the presentation section are preferably selected randomly.  
         [0046]     As already mentioned, it is particularly advantageous if a continuous deagglomeration of grinding stock agglomerates takes place in the grinding stock sample before and/or while the grinding stock sample is conveyed through the presentation segment. Deagglomeration can here take place before the before the grinding stock sample is passed through the presentation section, primarily via deflection and impact. On the other hand, deagglomeration can take place as the grinding stock sample is passed through the presentation section, primarily via turbulence in the pneumatic grinding stock stream.  
         [0047]     The removed grinding stock samples are best pneumatically conveyed from removal to presentation, wherein removal, presentation, acquisition and analysis of the grinding stock samples preferably take place continuously. This yields a seamless monitoring of the milling process and quality.  
         [0048]     This can be used in an especially advantageous way to control the milling process, in particular to set the milling gap.  
         [0049]     The continuous grinding stock sample stream is best determined stroboscopically in a series of stroboscopic flashes.  
         [0050]     The following abbreviations are used in the following: 
    v=average rate of flow of the pneumatic medium;     D=average particle dimensions or average particle size of the grinding stock particles;     Dmin=minimum particle dimensions of a grinding stock particle;     Dmax=maximum particle dimensions of a grinding stock particle.    
 
         [0055]     Acquisition preferably takes place via a series of stroboscopic flashes, which have a first partial series of freeze-frame stroboscopic flashes with a first activation time T 1  and a first light intensity L 1  and a second partial series of trajectory stroboscopic flashes with a second activation time T 2  and a second light intensity L 2 , wherein the following correlation is satisfied: T 2 ≧2 T 1 .  
         [0056]     As a rule, it can be assumed for a grinding stock that Dmax≦2 Dmin. If the activation time T 2  of the trajectory stroboscopic flashes is roughly twice as long as the activation time T 1  of the freeze-frame stroboscopic flashes, a trajectory stroboscopic image of a particle always differs from a freeze-frame stroboscopic image of an extremely oblong particle, for which Dmax=2 Dmin. This makes it possible to prevent such an image of the shortest possible trajectory from being confused with an image of a resting, oblong particle during evaluation.  
         [0057]     A deactivation time T 3  between a freeze-frame stroboscopic flash and a trajectory stroboscopic flash preferably satisfies the correlation 2D&lt;v T 3 .  
         [0058]     This ensures that the images of a grinding stock particle will not overlap each other owing to two consecutive freeze-frame stroboscopic flashes.  
         [0059]     This is advantageous in some image sensors, e.g., charge-coupled devices (CCD).  
         [0060]     The deactivation time T 3  between the freeze-frame stroboscopic flash and the trajectory stroboscopic flash preferably satisfies the correlation 2 D&lt;v T 3 &lt;10 D, and in particular the correlation 2 D&lt;vT 3 &lt;7 D.  
         [0061]     As a result, the, distance between the respective freeze frame and respective trajectory for the moving grinding stock particles imaged once as a freeze frame and once as a trajectory will not be too great, thereby enabling a clear allocation between the respective freeze frame and respectively accompanying trajectory of a moving grinding stock particle.  
         [0062]     In order to obtain sufficiently sharp, i.e., virtually “unblurred” or “unsmudged” freeze frame images of the moving grinding stock particles, the activation time T 1  for the freeze-frame stroboscopic flashes should satisfy the correlation v T 1 &lt;&lt;D, and in particular the correlation v T 1 &lt;D/10.  
         [0063]     In order to obtain clear trajectory images that cannot be confused with freeze frames of extremely oblong grinding stock particles, the activation time T 2  of the trajectory stroboscopic flashes should satisfy the correlation v T 2 &gt;D, and in particular the correlation v T 2 ≧5 D.  
         [0064]     Independently of the features mentioned above, it is advantageous for the light intensity L 1  of the freeze-frame stroboscopic flashes and light intensity L 2  of the trajectory stroboscopic flashes to be different from each other. This can also be used for distinguishing the resultant freeze frames and trajectory images.  
         [0065]     A particle trajectory can be allocated to the particle freeze frames, which can be stored in a first freeze frame memory, so that the respective particle freeze frame information is stored in a freeze frame memory for each completed freeze-frame stroboscopic flash and trajectory stroboscopic flash.  
         [0066]     The particle freeze-frame information from consecutive freeze frames can then be statistically evaluated to determine in particular the average grinding stock particle size D, its standard deviation, and its statistical distribution. This information can be represented via a distribution function (differentiated) or histogram (integrate).  
         [0067]     The grinding stock characterization system according to the invention is preferably used in a mill, and is there allocated to a respective cylindrical mill.  
         [0068]     It is best that this cylindrical mill additionally have allocated to it:  
         [0069]     A comparator for comparing an acquired grinding stock characteristic with a desired grinding stock characteristics; and  
         [0070]     An adjuster for setting the gap distance or, if necessary, another cylindrical mill operating parameter as a function of a deviation between the acquired grinding stock characteristic and desired grinding stock characteristic.  
         [0071]     This makes it possible to control and regulate in particular the roll nip of the cylindrical mills in a mill.  
         [0072]     Additional advantages, features and potential applications of the invention may be gleaned from the following description of embodiments based on the drawing, which are not to be regarded as limiting. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0073]     In the drawings:  
         [0074]      FIG. 1  is a diagrammatic side view through a portion of a system according to the invention in order to illustrate the progression of the grinding stock stream;  
         [0075]      FIG. 2  is a block diagram of another portion of the system according to the invention in order to illustrate its means for acquiring and processing grinding stock information;  
         [0076]      FIG. 3  is an illustration of part of the acquisition and processing of grinding stock information; and  
         [0077]      FIG. 4  is a special aspect of the acquisition and processing of grinding stock information. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0078]      FIG. 1  shows a diagrammatic sectional view through a portion of a system according to the invention, with the aim of illustrating the progression of the grinding stock stream. A roller pair  2 ,  4  forms a milling passage  6  of a cylindrical mill. The grinding stock  1  diagrammatically denoted by solid dots, which consist of rye flour with particle sizes in the several 100 μm range, for example, gets into a funnel  8  that opens into a pneumatic line  18  after milled in the milling passage  6 . The grinding stock  1  is transported via this pneumatic line  18  to a gap  10  extending between a first wall  20  and a second wall  22 , which are parallel to each other. The grinding stock  1  enters into the gap  10  in an outlet area  19 , and then moves radially outward from this outlet area  19 , so as to arrive at a transition area  28  through which it is pneumatically and gravitationally conveyed downward, and gets into another pneumatic line  30 .  
         [0079]     In a first version (projection version), a camera  12  oriented toward the gap  10  is located above the light-permeable wall  20 . Situated below the light-permeable wall  22  is a light source  24  that penetrates the gap  10  through both walls  20 ,  22 . The camera  12  acquires the shadows projected by the grinding stock particles  1  on its image sensor.  
         [0080]     In a second version (reflection version, not shown), the light source  24  can alternatively be situated above the light-permeable wall  20  next to the camera  12 . In this case, the lower wall  22  is impervious to light, and has a dark surface on the side of the gap  10 . The camera  12  acquires the light reflected or scattered by the grinding stock particles  1  on its image sensor.  
         [0081]     The light source  24  is operated as a stroboscope. As a result, the shadows cast by the grinding stock particles (first version) or the images of the grinding stock particles (second version) are imaged on the image sensor of the camera  12  as freeze frames. These grinding stock stream freeze frames represent instantaneous snapshots of the grinding stock stream in the gap  10 . This image information is relayed to an image processing system  14  downstream from the camera  12 , in which the grinding stock stream freeze frames are processed so that statistical conclusions can be drawn about the size distribution of the grinding stock particles.  
         [0082]     The outlet area  19  has a deagglomeration section  16  in the form of a baffle plate. The grinding stock particles  1  transported in via the pneumatic line  18  hit this baffle plate  16 , after which the conveying air changes their direction by about 90° until they get between the two parallel walls  20 ,  22  in the gap  10 . The agglomerates in the grinding stock particles are then efficiently dissolved, and deagglomerated grinding stock particles get into the gap  10 . This prevents the agglomerates in the grinding stock from distorting the grinding stock characterization.  
         [0083]     The outlet area  19  also has an opening  38 , which extends annuarly around the pneumatic line  18 . Ambient air or “secondary air” gets into the gap through this opening  38 , since the pneumatic lines  18 ,  28  and  30  are operated under a slight vacuum. The secondary air entering through this secondary air opening  38  cleans the insides of the walls  20 ,  22 , thereby precluding occlusion of the gap  10 .  
         [0084]     The pneumatic line  30  again empties into the line leading away from the cylindrical mill (not shown). As a result, the removed grinding stock sample  1  is again relayed to the mill via a suction port (not shown), so that it can be further milled, screened or separated by air. This “vacuuming” back into the mill circulation by means of a vacuum cleaner  38  is diagrammatically indicated on  FIG. 1 .  
         [0085]     The pneumatic line  30  also accommodates a branch  32 , which forms a bypass line to the vacuum cleaner  36 . This branch line  32  contains a butterfly valve  34 , with which the flow resistance of the branch line  32  can be adjusted. This makes it possible to adjust the overall flow resistance of the parallel circuit formed by the vacuum cleaner  36  and the branch line  32 , and hence the flow velocity in the pneumatic lines  18 ,  28  and  30 . In other words, the butterfly valve  34  of the branch line  32  can modulate the suction power of the mill (or the “vacuum cleaner”  36 ). This enables a fine adjustment of the suction power.  
         [0086]     To achieve optimal operation of the system according to the invention for grinding stock characterization, the grinding stock density must not be excessively great on the one hand. On the other hand, the grinding stock velocity, flash duration and flash intensity of the stroboscopic lamp  24  along with the sensitivity of the optical resolution of the camera  12  must be harmonized to obtain sufficiently bright and sharp shadows and images of the grinding stock particles.  
         [0087]     Since the grinding stock in the gap  10  between the plates  20 ,  22  streams radially from the inside out, the grinding stock density and radial rate of flow taper off radially from the inside out. Therefore, the camera position and lamp position can be shifted in a radial direction via the light permeable wall  20  at prescribed flow conditions in the pneumatic lines  18 ,  28 ,  32  to enable an optimal particle density and particle velocity for acquiring and analyzing the image information.  
         [0088]     Independently of the radial camera and lamp position, the particle density can also be set by positioning the funnel below the roller passage  6  and/or via the size of the funnel opening.  
         [0089]     Both the particle density and particle velocity can also be set in the gap  10  by adjusting the gap distance, i.e., by adjusting the distance between the walls  20 ,  22 .  
         [0090]     Therefore, the system according to the invention offers a high level of freedom while setting the particle density and particle velocity, the coarse adjustment of which primarily takes place via the position of the funnel  8 , the wall distance in the gap  10 , and the quantity of secondary air supplied via the opening  38 , while fine adjustment primarily takes place via the butterfly valve  34  in the branch line  32 .  
         [0091]     In addition to coarsely cleaning the walls  20 ,  22  with the secondary air supply, the walls can also be finely cleaned through vibration, in particular via ultrasound, wherein the walls  20 ,  22  can be vibrated directly and/or indirectly via the air in the gap  10  (structure-borne or airborne noise). Continuously cleaning the wall surfaces, or more succinctly, continuously maintaining their cleanliness, is important, so that the camera does not acquire too many resting grinding stock particles in addition to the moving grinding stock particles in the form of freeze frames. This might cause distortions in the grinding stock characterization on the one hand, since the size distribution of the particles adhering to the wall is generally not identical to the particle size distribution of the transported grinding stock. On the other hand, too many grinding stock particles adhering to the walls lead to a very high particle density in the visual field of the camera, and hence to numerous overlaps of shadows or images of the grinding stock particles.  
         [0092]      FIG. 2  shows a block diagram of another portion of the system according to the invention, in order to illustrate its means for acquiring and processing grinding stock information. The light source  24  is located to the right of the gap  10 , and the camera  12  to the left of it (projection version). The light-permeable walls  20 ,  22  (see  FIG. 1 ) are not imaged here. The light source  24  is synchronized with the camera  12  by way of a timing generator  26 , thereby yielding a stroboscope  24 ,  26  and a camera with an activation time synchronous with the stroboscope. Therefore, the camera  12  takes freeze frames of the shadows cast by the grinding stock particles. The signal output of the camera  12  is connected with a computer  14 , on which the images are processed and the grinding stock freeze frames are statistically evaluated (see  FIG. 3 ). The timing generator or clock generator  26  can be used to freely select the flash duration of the stroboscopic lamp  24  and the activation time of the camera  12  (see  FIG. 4 ).  
         [0093]      FIG. 3  shows a portion of the acquisition and processing of grinding stock image information. The images acquired in the camera  12  can be more or less perfect, i.e., sharp, freeze frames. After the camera has been focused on the particles in the gap  10 , the sharpness of a particle image or particle shadow also depends on the particle velocity. Since no laminar flow is generally present in the gap  10 , and also not necessarily intended (turbulence can have a deagglomerating effect), the various grinding stock particles in the presentation section or visual field of the camera  12  sometimes exhibit rather disparate velocities. For example, it might happen that some of the particle images are sharp, and others blurred or smeared in the direction of the particle velocity.  
         [0094]     For acquisition purposes, it is initially important to illuminate the gap in the visual field of the camera  12  as uniformly as possible. This is especially important for the reflection version, since there might otherwise be too little of a contrast between the light reflected by the particles and the light reflected from the light-impermeable wall  22  (not shown).  
         [0095]     In addition to illuminating the gap  10  as homogeneously as possible and focusing as sharply as possible on the gap as mentioned above, attention should also be paid to sufficient depth of field, so that a sharp enough image is obtained even given a greater gap distance of more than one centimeter over the entire gap width.  
         [0096]     It can also be advantageous to set an especially low depth of field measuring about 0.2 to 2 mm. As a result, only a partial area (plane of the sharp image) of the acquisition area in which the particles are entrained in the fluid stream is acquired for the evaluation. This “optical filtering” makes it possible to reduce the overall number of particles moving in the acquisition area down to a statistically relevant number. For example, this is important largely preclude overlaps of particle images or shadow images.  
         [0097]     Once all of these measures have been taken, the raw images of the image sensor of the camera  12  obtained in this way can be processed even further.  
         [0098]     As shown on  FIG. 3 , the raw images of the camera are digitally processed for this purpose (pixel filters). An inhomogeneous illumination or brightness is here first corrected in the particle images and in the image background or in the particle shadows.  
         [0099]     Sharp particles or particle images are then selected, and then relayed to further processing. As a rule, it can be assumed that this selection is representative for the entirety of all particle images. Should this not be the case, several cameras  12  can be employed in various partial areas of the gap  10 , and the raw images or sharp particle images or particle shadows selected from them can be averaged.  
         [0100]     The particles or particle images or particle shadow are then measured, and a volume approximation is performed. As a rule, the assumption for a typical grain milled product (e.g., wheat, barley, rye) will here be that the maximum dimension Dmax for a grinding stock particle and the minimal dimension Dmin for a grinding stock particle hardly differ by more than a factor of two, so that Dmax&lt;Dmin. For example, the minimal dimension a and maximum dimension b of a particle image or particle shadow can be drawn upon, and used to derive the average value M=(a+b)/2, which in turn is multiplied by a geometric factor or form factor k that fits the conventional grinding stock particle form, thereby yielding V=function(a,b)=k m 3 =k [(a+b)/2] 3  as the volume approximation. As an alternative, the volume can also be approximated via the function V=V=k a 2 b. Since in this case the particles to be examined have a plate-like structure, it is also possible to replace the volume with the projection surface of the particles, i.e., the third dimension (thickness) is constant, and is incorporated into the geometric constant k.  
         [0101]     The average particle dimensions m or volume approximations V obtained in this way from the processed particle images or particle shadows are then statistically evaluated and charted on a histogram.  
         [0102]      FIG. 4  shows a special aspect of the invention and the processing of optical grinding stock information. The vertical axis shows the flash light intensity L. The horizontal axis shows time t. The chronological flash light progression shows a short, intensive freeze-frame stroboscopic flash followed somewhat later by a change in the flight path stroboscopic flash. Since this time interval between two consecutive freeze frame stroboscopic flashes can be more than 100 times, or even more than 1000 times the activation time of a stroboscopic flash, the time axis is shown intermittently.  
         [0103]     The particle images or particle shadows can be acquired using a series of stroboscopic flashes, which have a first partial series of freeze-frame stroboscopic flashes with a first activation time T 1  and a first light intensity L 1  and a second partial series of trajectory stroboscopic flashes with a second activation time T 2 ≧2 T 1  and a second light intensity L 2 &lt;L 1 .  
         [0104]     The deactivation time T 3  between the freeze-frame stroboscopic flash and the trajectory stroboscopic flash satisfies the correlation 2D&lt;v T 3 &lt;10 D, and in particular the correlation 2 D&lt;v T 3 &lt;7 D.  
         [0105]     In order to obtain sufficiently sharp, i.e., virtually “unblurred” or “unsmudged” freeze frame images of the moving grinding stock particles, the activation time T 1  for the freeze-frame stroboscopic flashes should satisfy the correlation v T 1 &lt;&lt;D, and in particular the correlation v T 1 &lt;D/10.  
         [0106]     In order to obtain clear trajectory images that cannot be confused with freeze frames of extremely oblong grinding stock particles, the activation time T 2  of the trajectory stroboscopic flashes should satisfy the correlation v T 2 &gt;D, and in particular the correlation v T 2 ≧5 D.  
         [0107]     Independently of the features mentioned above, it is advantageous for the light intensity L 1  of the freeze-frame stroboscopic flashes and light intensity L 2  of the trajectory stroboscopic flashes to be different from each other. This can also be used for distinguishing the resultant freeze frames and trajectory images.  
         [0108]     The particle freeze frames can be allocated to a particle trajectory, and stored in a first freeze frame memory, so that the respective particle freeze frame information is stored in a freeze frame memory for each freeze frame stroboscopic flash and trajectory stroboscopic flash that occurred.  
         [0109]     While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art that various changes may be made therein without departing from the true spirit and scope of the present invention.  
         [0000]     Reference List  
         [0000]    
       
           1  Grinding stock sample  
           2  Roller  
           4  Roller  
           6  Roller passage  
           8  Removal means, funnel  
           10  Presentation section, gap  
           12  Acquisition means for electromagnetic radiation, camera  
           14  Analysis means, image progressing system  
           16  Deagglomeration section, impact surface  
           18  Pneumatic line  
           19  Outlet area  
           20  First wall  
           22  Second wall  
           24  Electromagnetic radiation source, light source  
           26  Controller, timing generator  
           28  Transition area  
           30  Pneumatic line  
           32  Bypass line, branch line  
           34  Butterfly valve  
           36  Suction port, vacuum cleaner (return line to mill)  
           38  Secondary air opening  
          L 1  First intensity  
          L 2  Second intensity  
          T 1  First activation time  
          T 2  Second activation time  
          T 3  Deactivation time  
          D Average particle size of grinding stock particles  
          Dmin Minimal particle size of a grinding stock particle  
          Dmax Maximum particle size of a grinding stock particle