Abstract:
An apparatus for processing a sample including fibers and trash, having a cylinder rotating in a first direction for receiving the sample. The cylinder has a surface with rigid pins. The pins engage and retain the fibers of the sample. A collection surface receives the trash that falls from the cylinder. A counter-flow of air moves in a separation region between the cylinder and the collection surface in a direction that is substantially perpendicular to and towards the underside of the cylinder. The counter-flow of air has at each position within the separation region an air-flow velocity that is sufficient for the counter-flow of air to blow the fibers that are not originally retained by the pins up toward the cylinder and thereby engaging the fibers with the cylinder, and yet insufficient to prevent gravity from pulling the trash downward through the counter-flow of air.

Description:
[0001]    This application claims rights and priority on prior pending U.S. patent application Ser. No. 13/523,219 filed 2012 Jun. 14. This invention relates to the field of fiber quality measurement. More particularly, this invention relates to separating non-fiber entities (such as trash) from fibers (such as cotton). 
     
    
     BACKGROUND 
     Field 
       [0002]    Natural and man-made fibers are routinely assessed for a variety of different properties, so as to grade the fiber samples. These properties include things such as fiber length, strength, color, moisture content, crimp, fineness, and non-fiber content. For example, measuring the properties of cotton fiber so as to provide a grade for the quality of the cotton is an important step in determining the value of the fibers. 
         [0003]    Natural fibers such as cotton can be contaminated by non-primary-fiber material, which is often generally referred to as trash. Such trash may be, for instance, husks, seed, twigs, bark, leaves, dirt, or rocks. Measuring the non-fiber content of a fiber sample is accomplished by separating the fibers in a fiber sample from as much of the non-fiber content in the fiber sample as possible, and weighing or otherwise quantifying at least two of: (1) the original fiber sample, (2) the fibers that were separated from the original fiber sample, and (3) the trash that was separated from the original fiber sample. Typically, anything that is not the desired fibers themselves is considered non-fiber content, and designated as trash. 
         [0004]    Unfortunately, prior art separators typically allow significant quantities of fibers to remain mixed in with the separated trash, thus making it difficult to determine the total trash content of the original fiber sample, and also tend to take up a large amount of space. 
         [0005]    What is needed, therefore, is a system that reduces problems such as those described above, at least in part. 
       SUMMARY 
       [0006]    The above and other needs are met by the separation apparatus according to a first independent claim and the method according to a second independent claim. Various embodiments are defined in the dependent claims. 
         [0007]    The embodiments of the invention provide below a separation cylinder a counter-flow of air moving vertically upward towards the underside surface of the separation cylinder. The counter-flow of air has a velocity sufficient to blow upward fibers not retained by the surface of the separation cylinder, yet insufficient to prevent gravity from pulling trash downward. Thus, the trash falls through the counter-flow of air onto a collection surface, where it can be weighed on a scale. 
         [0008]    The separation apparatus for processing a fiber sample that includes both fibers and trash has a fiber-feeding device. It further includes a separation cylinder rotating in a first direction and receiving the fiber sample from the fiber-feeding device. The separation cylinder has a cylindrical surface with a length extending along a longitudinal axis. Rigid protrusions having distal ends extend from the cylindrical surface. The protrusions selectively engage and retain the fibers of the fiber sample. The trash is thereby separated from the fiber sample along a substantially downward direction. A collection surface receives the trash that falls downward from the separation cylinder. The separation apparatus further includes means for providing in a separation region between the separation cylinder and the collection surface a counter-flow of air moving in a direction that is substantially perpendicular to and towards the underside of the separation cylinder. In one embodiment, the counter-flow of air has at each position within the separation region an air-flow velocity sufficient for the counter-flow of air to blow the fibers that are not originally retained by the protrusions up toward the bottom of the separation cylinder, and yet insufficient to prevent gravity from pulling the trash downward through the counter-flow of air. 
         [0009]    The separation region is a region, such as a funnel-like region, in which the air-flow velocity substantially fulfills the above conditions. The air-flow velocity need not be locally uniform within the separation region, but may rather vary in all three directions in space. In an embodiment where the means for providing the counter-flow of air includes a counter-flow chamber laterally confined by a wall, a region adjacent to the wall might not be part of the separation region, since the air-flow velocity tends to zero in direct vicinity to the wall and generally increases in a radial direction with increasing distance from the wall. The separation region starts where the air-flow velocity is sufficient to blow the fibers up; it is located in a central region, such as an axial region of the counter-flow chamber. The counter-flow of air according to the invention can be consistent, meaning the flow rate is independent of time, and laminar, such as without turbulences. 
         [0010]    In one embodiment, the means for providing a counter-flow of air include a counter-flow chamber disposed below the separation cylinder, being laterally confined and open in a direction that is substantially perpendicular to and towards the underside surface of the separation cylinder, such that the counter-flow of air and the trash are able to pass through the counter-flow chamber. 
         [0011]    The means for providing a counter-flow of air may include a vacuum source disposed adjacent the separation cylinder. Additionally or alternatively, the means for providing a counter-flow of air may include an excess-pressure source such as an air fan. 
         [0012]    The means for providing a counter-flow of air can be such that an average air-flow velocity within the separation region is between about 10 m/min (0.17 m/s) and about 60 m/min (1.0 m/s). In one embodiment the average value is about 25 m/min (0.42 m/s). An optimum average air-flow velocity can be theoretically or experimentally determined. The determination of the air-flow velocity can be influenced by the type of fibers or trash to be separated, and by the kinetic energy and momentum given to the fiber and trash particles by the separation cylinder. 
         [0013]    In one embodiment, the separation apparatus includes a scale for measuring the weight of the trash and any fibers admixed to the trash that are received by the collection surface. A correction module may be provided for visually detecting fibers on the collection surface and subtracting an estimated weight of the detected fibers from the weight of the mixture of trash and fibers. 
         [0014]    The fiber-feeding device can include a feed roller disposed adjacent the separation cylinder, the feed roller for rotating in the rotational direction of the separation cylinder and presenting the fiber sample to the separation cylinder at a position where a feed roller tangential direction of motion is substantially opposite to a separation cylinder tangential direction of motion. 
         [0015]    The separation apparatus may further include a vacuum source disposed adjacent the separation cylinder, the vacuum source for drawing an air flow away from the cylindrical surface of the separation cylinder and removing the fibers from the protrusions. The vacuum source may be identical to the vacuum source for providing a counter-flow of air mentioned above. The separation apparatus may still further include a lint deflector made of bent and parallel tines disposed along the separation cylinder in the direction of rotation to prevent clumps of the fiber sample from falling to the collection surface and to guide clumps along the tines and back to the separation cylinder and vacuum source. Such clumps will pass a second time around the separation cylinder, thus being opened, or will be removed by the vacuum source. 
         [0016]    In one embodiment, the separation cylinder has a length of between about 25 cm and about 80 cm, and a diameter of between about 10 cm and about 30 cm. The separation cylinder is, for instance, rotatable at a rotational speed of between about 1000 rpm (16.7 s −1 ) and about 2000 rpm (33.3 s −1 ). 
         [0017]    The protrusions may extend from the cylindrical surface of the separation cylinder at an angle that is inclined toward the rotational direction. The protrusions can include at least one of saw teeth and pins. 
         [0018]    The separation apparatus may further include a knife edge extending parallel to the longitudinal axis and along substantially the entire length of an underside of the separation cylinder, and disposed adjacent the distal ends of the protrusions, for selectively removing from the fiber sample the trash that is not retained by the protrusions. 
         [0019]    The separation apparatus can include a stilling chamber disposed below the separation region, the stilling chamber having air that is substantially stagnant, in that there is no forced air flow in any direction within the stilling chamber. 
         [0020]    According to another aspect of the invention, there is described a method for processing a fiber sample that includes both fibers and trash. The fiber sample is fed onto a surface of a separation cylinder, the separation cylinder rotating in a rotational direction and having a cylindrical surface with a length extending along a longitudinal axis, and rigid protrusions having distal ends extending from the cylindrical surface. Fibers of the fiber sample are selectively engaged and retained with the separation cylinder. Trash that is not retained by the pins is selectively removed from the fiber sample in a substantially downward direction. The trash that has fallen downward from the separation cylinder is collected on a collection surface. The fibers and trash are contacted in a separation region between the separation cylinder and the collection surface with a counter-flow of air moving in a direction that is substantially perpendicular to and towards the underside of the separation cylinder. In one embodiment, the counter-flow of air has at each position within the separation region an air-flow velocity sufficient for the counter-flow of air to blow the fibers that are not originally retained by the protrusions up toward the bottom of the separation cylinder and thereby engaging the fibers with the separation cylinder, and yet insufficient to prevent gravity from pulling the trash downward through the counter-flow of air. 
         [0021]    An average air-flow velocity within the separation region can be between about 10 m/min (0.17 m/s) and about 60 m/min (1.0 m/s), and in one embodiment is about 25 m/min (0.42 m/s). 
         [0022]    The weight of the trash and any fibers admixed to the trash, collected on the collection surface can be measured. 
         [0023]    In one embodiment, fibers on the collection surface are visually detected with a correction module, and an estimated weight of the fibers is subtracted from the weight of the mixture of trash and fibers. 
         [0024]    The fiber sample may be presented to the separation cylinder with a feed roller that is disposed adjacent the separation cylinder, the feed roller rotating in the rotational direction of the separation cylinder and at a position where a feed roller tangential direction of motion is substantially opposite to a separation cylinder tangential direction of motion. 
         [0025]    In one embodiment an air flow is drawn away from the cylindrical surface of the separation cylinder and removes the fibers from the protrusions with a vacuum source disposed adjacent the separation cylinder. 
         [0026]    The separation cylinder can rotate at a rotational speed of between about 1000 rpm (16.7 s −1 ) and about 2000 rpm (33.3 s −1 ). 
         [0027]    Expressions such as “upwards,” “downwards,” “below,” “above,” “horizontal,” “vertical,” “height,” and so forth refer in the present document to the gravitational field of the earth, in which the apparatus according to the invention is deemed to stand. 
         [0028]    In some embodiments, the trash that falls onto the collection surface is at atmospheric pressure. Thus, it can easily be collected and weighed on the scale. This enables a relatively low-cost instrument for measuring trash gravimetrically. 
         [0029]    In the vertical separation region according to one embodiment, air drag and gravity exert a force on the particles. The two forces are opposite to each other. They can be balanced with respect to each other by adjusting the velocity of the vertical air-flow. With an appropriate air-flow velocity, trash particles would never be returned to the separation cylinder, independent of the height of the separation region. 
         [0030]    One single separation cylinder is sufficient in some embodiments of the present invention. This reduces the space requirements and the costs of the apparatus according to the invention. Nevertheless, the use of more than one separation cylinder is not excluded from other embodiments. 
     
    
     
       DRAWINGS 
         [0031]    Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
           [0032]      FIG. 1  depicts a trash separation apparatus from an end view of a separation cylinder according to an embodiment of the present invention. 
           [0033]      FIG. 2  is a front view of a separation cylinder according to an embodiment of the present invention. 
           [0034]      FIG. 3  is a side view of a separation cylinder and protrusions according to an embodiment of the present invention. 
       
    
    
     DESCRIPTION 
       [0035]    With reference now to the figures, there are described various embodiments of a trash separator  100 , which is operable for separating trash particles  104  from fibers  106  in a fiber sample  102 . The fiber sample  102  may take various forms. In one embodiment, the fiber sample  102  is cotton, but in other embodiments the fiber sample  102  is formed of other natural or man-made fibers, or combinations thereof. The fiber sample  102  includes both individual fibers  106  and trash particles  104 . 
         [0036]    In the embodiment depicted in  FIG. 1 , the fiber sample  102  is presented to the trash separator  100  by feeding it between a feed roller  108  and a feed surface, or feed plate,  110 . The feed roller  108  rotates in a first direction (such as indicated in  FIG. 1 ) at a rotational rate of from about one rotation per minute (0.017 s −1 ) to about four rotations per minute (0.067 s −1 ), such that the fiber sample  102  is pulled between the feed roller  108  and the feed surface  110 . In the embodiment as depicted, the feed roller  108  rotates in a clockwise direction, pulling the fiber sample  102  toward a separation cylinder  112 , which also rotates in the first direction (clockwise, as indicated in this embodiment as depicted) and at a rotational rate of from about one thousand rotations per minute (16.7 s −1 ) to about two thousand rotations per minute (33.3 s −1 ). 
         [0037]    In some embodiments the feed roller  108  is formed of a smooth-surfaced soft-matter coating (such as rubber) on a steel shaft, which adjusts to the varying thickness of the fiber sample  102  and retains the fiber sample  102  along the feed roller  108  axis, to prevent premature release of the fiber sample  102 . The feed roller  108  is adjustable to make the gap between the feed roller  108  and the feed surface  110  larger or smaller, such as according to the varying thickness of the fiber sample  102 . Therefore, the feed roller  108  holds the fiber sample  102  firmly while being combed by the separation cylinder  112 , effectively reducing the generation of unopened fiber clumps that might be pulled out and thrown down. 
         [0038]      FIG. 2  depicts a front view of the separation cylinder  112 . In some embodiments the separation cylinder  112  has a length L (in the axial direction) of from about 250 mm to about 800 mm, and a diameter D of from about 100 mm to about 300 mm. In some embodiments the feed roller  108  has a length that is substantially equal to that of the separation cylinder  112 , and a diameter of from about 35 mm to about 75 mm. 
         [0039]    Returning to  FIG. 1 , the feed roller  108  and the separation cylinder  112  are disposed adjacent one another at a first position, at which the tangential direction of motion of the feed roller  108  and the tangential direction of motion of the separation cylinder  112  are substantially opposite one another. The tangential direction of motion is defined as the direction of travel of a point on a surface of a rotating body. The feed surface  110  keeps the fiber sample  102  engaged by the feed roller  108  until the fiber sample  102  is disposed at substantially the first position (as opposed to releasing it much earlier), at which position the fiber sample  102  is contacted by the separation cylinder  112 , which is moving in the opposite tangential direction. These opposing directions of motion between the feed roller  108  and the separation cylinder  112  produce a severe shearing force on the fiber sample  102  that pulls it apart. This results in an aggressive opening action and a better separation of the trash from the fibers. 
         [0040]    As the fiber sample  102  separates, the fibers  106  tend to be predominantly engaged and retained by protrusions  114  of the separation cylinder  112 , while the trash particles  104  of the fiber sample  102  tend to remain predominantly unengaged by the protrusions  114 . Some of the trash  104  is separated from the fibers  106  at this point, as the protrusions  114  tend to bat the trash  104  in a downward direction and away from the fibers  106  that are engaged by the protrusions  114 . In some embodiments the protrusions  114  are saw-tooth structures, and in other embodiment the protrusions  114  are pins. In some embodiments, a combination of saw teeth and pins comprise the protrusions  114 . 
         [0041]    In some embodiments, and as depicted in more detail in  FIG. 3 , the protrusions  114  protrude from the cylindrical surface  116  of the separation cylinder  112  at an angle α in relation to the surface  116  of the separation cylinder  112 . The angle α is from about fifty degrees to about ninety degrees, and leans into the direction of rotation of the separation cylinder  112 . The length b of the protrusions  114  is from about 2 mm to about 4 mm. 
         [0042]    In some embodiments the protrusions  114  are evenly spaced-apart across the surface  116  of the separation cylinder  112 . In some embodiments the spacing of the protrusions  114  across the surface  116  depends upon the type of fiber sample  102  being tested. For example, for one type of fiber sample  102  it may be desirable to place the protrusions  114  relatively further apart, while with another fiber sample  102  it may be desirable to place the protrusions  114  relatively closer together. 
         [0043]    Returning again to  FIG. 1 , a knife  118  is disposed adjacent the separation cylinder  112 , such that the knife  118  extends parallel to the longitudinal axis and along substantially the entire length of the separation cylinder  112 . The knife  118  is positioned such that any trash  104  that is not entrained within the protrusions  114  is predominantly removed from the fibers  106  that are entrained within the protrusions  114 , and is deflected in a downward direction towards a counter-flow chamber  120 . In some embodiments, the edge of the knife  118  is disposed very close to the ends of the protrusions  114 . In some embodiments the edge of the knife  118  is straight and does not interdigitate the protrusions  114 . 
         [0044]    Some embodiments include a lint deflector  134 , such as made of parallel and bent metal tines disposed along the direction of rotation of the separation cylinder  112 , which help prevent large clumps of material from falling. The lint deflector  134  works as a filter or screen to help prevent clumps of fibers  106  from dropping to a trash collection surface  126 , but let the trash  104  to pass through. The tines of the lint deflector  134  in one embodiment are parallel to each other and bent along the direction of the air flow. The tines in one embodiment deflect the fiber clumps with a size larger than about six millimeters without catching individual fibers  106 . The ends of the wires of the lint deflector  134  are open near a vacuum source  124  so that material that is caught by the lint deflector  134  is not retained by the lint deflector  134 , but instead will be drawn off by the vacuum source  124 . 
         [0045]    The counter-flow chamber  120  provides an upward-directed counter-flow of air  122  that enters the counter-flow chamber  120  at the bottom of the counter-flow chamber  120  (as indicated in  FIG. 1 ), such that the air flow  122  is in an upward direction and substantially opposite to the direction of travel of the falling trash particles  104  and the few fibers  106  that were not originally engaged by the protrusions  114 . The purpose of the air flow  122 , which in some embodiments is generated by the vacuum source  124  and airflow from the rotating separation cylinder  112 , is to blow such non-engaged fibers  106  back up toward the bottom of the separation cylinder  112 , such that they engage with the protrusions  114 , or are carried by the air flow from the rotating separation cylinder  112  to the vacuum source  124 , and do not continue down through the counter-flow chamber  120 . The upwardly directed air flow  122  changes the trajectory of the falling fibers  106  by about 180 degrees, whereas an air flow in any other direction, such as a horizontal cross-flow of air, would only change the fiber  106  trajectory by no more than about ninety degrees. 
         [0046]    To accomplish this, the air flow  122  has, in some embodiments, at least in a separation region within the counter-flow chamber  120 , at each position an air-flow velocity such that any fibers  106  that attain the separation region are generally lofted upwards by the air flow  122  toward the separation cylinder  112 . However, the velocity of the air flow  122  is generally insufficient to prevent gravity and possibly other influences such as momentum from drawing the trash particles  104  downward through the counter-flow chamber  120 . The separation region is a central part of the counter-flow chamber  120 , extending like a funnel from the bottom of the counter-flow chamber  120  to its top. Regions in the vicinity of the walls of the counter-flow chamber  120  might not belong to the separation region, since the air-flow velocities in such regions might be too low to loft the fibers  106  upwards. 
         [0047]    An appropriate choice of the air-flow velocities within the separation region can enhance the separation of the trash from the fibers. One method for estimating the air-flow velocity is next described. Other methods may also be used. 
         [0048]    We consider a particle—fiber or trash—consisting of a uniform material and having a certain shape and certain dimensions, in a stationary, laminar, homogeneous and isotropic air flow directed upwards. The air flow exerts on the particle a force directed upwards, the flow resistance, which depends on the air-flow velocity. We calculate the air-flow velocity v necessary for compensating the gravitational force on the particle. In an air flow with this “threshold velocity” v, the particle would float at the same level; below the threshold velocity v the particle would fall down, above the threshold velocity v it would be lofted up. The threshold velocity v according to this model is: 
         [0000]    
       
         
           
             
               v 
               = 
               
                 
                   k 
                    
                   
                     ρ 
                     
                       ρ 
                       A 
                     
                   
                    
                   g 
                    
                   
                       
                   
                    
                   h 
                 
               
             
             , 
           
         
       
     
       Where: 
       [0000]    
       
         
           
             k is a shape factor depending on the geometric shape of the particle, 
             ρ is the mass density of the particle, 
             ρ A  is the mass density of air (ρ A =1.2 kg/m 3 ), 
             g is the gravitational acceleration (g=9.81 m/s 2 ), and 
             h is a characteristic height of the particle, i.e., a particle dimension in line with the air-flow direction. 
           
         
       
     
         [0054]    In a first example, let us consider a cylindrical cotton fiber floating with its axis in the horizontal direction in the air flow. The following values apply for this example:
       k=1.3,   ρ=1510 kg/m 3 , and   h=diameter of the cylinder=20 μm.
 
We get a threshold velocity of v=0.57 m/s=34 m/min. The threshold velocity v is apparently independent of the fiber length.
       
 
         [0058]    In a second example, we may consider a spherical ball of soil with:
       k=3.0,   ρ=1400 kg/m 3 , and   h=diameter of the sphere=0.2 mm.
 
We get a threshold velocity of v=2.6 m/s=156 m/min.
       
 
         [0062]    It follows from the two above examples that cotton fibers with a diameter of 20 μm and balls of soil with a diameter of 0.2 mm will be separated in a vertical counter-flow with air-flow velocities within the range between 34 m/min and 156 m/min. 
         [0063]    Whereas the model presented above is useful for theoretically estimating the required air-flow velocities, an experimental fine tuning of the apparatus  100  according to the invention with regard to the air-flow velocities is recommended. Experiments have shown that an average velocity of the air flow  122  through the counter-flow chamber  120  should be adjustable from about 10 m/min (0.17 m/s) to about 60 m/min (1.0 m/s), depending upon the type of fiber sample  102  being tested and the trash  104  to be separated. For example, when a heavier fiber  106  is being tested, then the air flow  122  may flow through the counter-flow chamber  120  at a relatively faster rate, to reduce the occurrence of the heavier fibers  106  falling through the counter-flow chamber  120 . On the other hand, when a lighter fiber  104  is being tested, the air flow  122  may flow through the counter-flow chamber  120  at a relatively slower rate, to reduce the occurrence of lighter trash particles  104  being drawn upwards toward the separation cylinder  112  and the vacuum source  124 . The kinetic energy and momentum given to the fiber and trash particles  106 ,  104  by the rotating separation cylinder  112  can also be allowed for in the determination of an optimum average air-flow velocity. A high rotational rate and/or a large diameter D of the separation cylinder  112  will, in most cases, require a higher air-flow velocity, to reduce the occurrence of fibers  106  dashing through the counter-flow chamber  120 . In one embodiment the average air-flow velocity for cotton fibers is 25 m/min (0.42 m/s). 
         [0064]    In some embodiments, a vacuum source  124  is disposed adjacent the separation cylinder  112 . In some embodiments, the vacuum source  124  is controlled to maintain a stable air flow  122  in the counter-flow chamber  120 . The vacuum source  124  draws an air flow away from the separation cylinder  112 , and removes the fibers  106  that were engaged by the protrusions  114  from the separation cylinder  112 . The vacuum source  124  is disposed after the knife  118 , relative to the direction of rotation of the separation cylinder  112 , as depicted in  FIG. 1 . In some embodiments the vacuum source  124  creates the air flow  122 . Thus, one and the same vacuum source  124  can be used for removing the fibers  106  from the separation cylinder  112  and for generating the air flow  122 . 
         [0065]    In the embodiment as depicted, the trash particles  104  that fall down through the counter-flow chamber  120  then fall through a stilling chamber  132  in which the air is substantially stagnant, in that there is no forced air flow in any direction. The trash particles  104  fall down through the chamber  132  and onto a collection surface  126 , such as a tray of a scale  128 . Because of the counter-flow of air  122 , few or no fibers  106  attain the collection surface  126 . Thus, the apparatus  100  achieves a highly successful separation of the fibers  106  and the trash  104  of the fiber sample  102 . Some embodiments include a trash vacuum wiper bar  138  to remove trash  104  (and fibers  106 , as needed) from the tray  126 . The stilling chamber  132  tends to ensure that the trash  104  that falls onto the collection surface  126  is at atmospheric pressure. Thus, it can more easily be collected and weighed on the scale  128 . 
         [0066]    The counter-flow chamber  120  and the stilling chamber  132  have an opening between them that allows air to enter the counter-flow chamber  120  and flow upward to the vacuum source  124 . The counter-flow of air  122  works as a filter for the freely flying loose fibers  106  to prevent them from dropping to the trash collection surface  126 . An excess-pressure source (not drawn) such as an air fan could be provided at the opening between the counter-flow chamber  120  and the stilling chamber  132  as an alternative or additional means for providing a counter-flow of air. 
         [0067]    In some embodiments, the trash content of the fiber sample  102  is determined by measuring the mass of the fiber sample  102  before it is processed through the trash separator  100 , and then measuring the mass of the trash particles  104 , such as by weighing the collection surface  126  and the trash  104  disposed thereon by means of the scale  128 . As desired, the trash  104  content as a percentage of the total weight of the fiber sample  102  can be calculated. In some embodiments, the mass of the fibers  106  that are eventually drawn off by the vacuum source  124  can also be measured and used in similar calculations. In some embodiments, an air curtain plate  136  is disposed between the counter-flow chamber  120  and the stilling chamber  132  or between the stilling chamber  132  and the collection surface  126 , and is used to seal off the collection surface  126  to minimize air currents  122  when the trash  104  is being weighed. 
         [0068]    Some fibers  106  still might attain the collection surface  126 . In some embodiments, these fibers  106  are manually removed before weighing the collection surface  126 . In other embodiments, the weight of the fibers  106  on the collection surface is determined with a correction module  130  that visually detects the fibers  106  on the collection surface  126 , estimates the weight of the detected fibers  106 , and subtracts that estimated weight from the weight of the mixture of trash  104  and fibers  106  on the collection surface  126 , thus yielding the weight of the trash particles  104 . 
         [0069]    The foregoing description of embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.