Abstract:
A method and apparatus for sorting a gas-driven stream of generally flat and light-weight articles of varying dimensions execute a, preferably optical, inspection and upon so finding a non-conforming article remove the latter from the stream. In particular, the inspection and the sorting are executed during a substantially straight movement of the articles. The removing is executed through gas driving in a direction substantially transverse to the straight movement. Advantageously, the inspection is preceded by orienting the articles through a centrifugal force that orients said articles against an inclined wall in a transition to the vertical movement. Also airflow means ( 83,84 ) can be used to confine the articles in a thin layer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a method for sorting a gas-driven stream of generally flat and light-weight articles of varying dimensions through executing a, preferably optical, inspection and upon so finding a non-conforming article removing the latter from the stream. Such articles may result from production processes that are agriculture-based, or from other sources and a prime example for the products to be sorted are tobacco products such as leaves or parts cut therefrom or stems. Such products once packaged are transported, and then the products are handled for separating them again. Typical sizes for conforming particles of the product under consideration are without limitation lengths and widths in a range from 1 to 500 millimeters. Tobacco is relatively quite expensive and the separated products may be accompanied by various matters of non-conforming tobacco character, as well as by various categories of non-tobacco origin, such as the successive stages of the production may introduce. It is noted here that “optical” means “radiative” and thus including the use of radiation that is not visible for the eye. Moreover, inspection by means of other techniques like by acoustic waves might be feasible.  
         [0002]     Prior art has realized the technical and economic usefulness of automatic sorting, but the present inventor has recognized that an optimized set-up would need at least some, but not necessarily all of the following features: 
        inspection with one or more relatively straightforward line-scan camera(s) arranged across the direction of motion of the articles;     orienting non-conforming articles in such manner that the detection device(s) will find the largest area of the article in question, whilst using only few or no moving parts for introducing and maintaining such orientation;     article motion and gas speed being adjustable and relatively uniform, in that relatively low speed will allow easy data processing, whereas higher speed will increase throughput, and requiring only few moving parts for attaining a low noise level;     a possibility for designing the apparatus through a substantially closed channel, also for keeping environmental dust level at low values; especially for a product like tobacco this is of great benefit;     removing the non-conforming matter through an underpressure facility that connects to the channel;     executing inspection and separation during substantially straight, in particular vertical, motion, inasmuch as such would tend to maintain particle orientation; a     free fall would be most advantageous, as such would tend to produce uniform particle speeds, especially in combination with gas-suction for particle removal;     and keeping the risk for jamming of the overall apparatus at an acceptably low value.        
 
         [0011]     Now in particular, U.S. Pat. No. 5,862,919 to Eason discloses the sorting of particles through feeding thereof by a horizontal conveyor belt, while separating both conforming and non-conforming articles through selectively activating a gas ejector during a falling trajectory of the particles, which trajectory will always deviate appreciably from a straight line. The present inventor has found that a straight line motion during both the inspection phase and the transmittal phase of the conforming articles is better for accurate detection and accurate removal of the particles. Furthermore, free motion of the particles allows for double-sided visual inspection. Moreover, such could be combined with better orienting the particles before inspection, which should give superior results.  
       SUMMARY TO THE INVENTION  
       [0012]     In consequence, amongst other things, it is an object of the present invention to provide a reliable method both on the level of the sorting proper and also on the level of overall operation.  
         [0013]     Now therefore, according to one of its aspects, a method according to the invention is characterized according to the characterizing part of Claim 1. Preferably the method is specifically dimensioned for sorting tobacco products such as leaves or parts thereof or stems. Preferably the inspection used is an optical inspection.  
         [0014]     The invention also relates to an apparatus being arranged for implementing the method as claimed in Claim  1 , and in particular as claimed in Claim 5. Further advantageous aspects of the invention are recited in dependent Claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]     These and further features, aspects and advantages of the invention will be discussed more in detail hereinafter with reference to the disclosure of preferred embodiments of the invention, and in particular with reference to the appended Figures that illustrate:  
         [0016]      FIG. 1 , an overall set-up of a sorting system according to the invention;  
         [0017]      FIG. 2 , an enlarged view of a part of a sorting facility proper, according to the invention;  
         [0018]      FIG. 3 , an article carrying channel wall with extensions to keep the articles from moving along the channel wall;  
         [0019]      FIG. 4 , an overall set-up of another sorting system according to the invention;  
         [0020]      FIG. 5 , an enlarged view of a part of the system of  FIG. 4 ;  
         [0021]      FIG. 6 , two cross-sections of the part of  FIG. 5  at different heights. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]      FIG. 1  illustrates in principle an overall set-up of a sorting apparatus according to the invention. It is to be noted that the installation configuration of the individual components of this set-up may be altered depending on the requirements (product, space, etc.), for instance when using the “open channel” organization (see further below). As shown, in this configuration the overall length of the machine is about 17 meters. Item  20  is a feeding conveyor belt that feeds the articles. The providing of the articles proper as resulting from splitting, etcetera, of the tobacco has not been shown for clarity. At indication  22 , the articles fall from the conveyor belt and into the transport system that in this embodiment centers on a substantially closed air-carrying duct arrangement. To this effect, a feeding chute  21  opens towards the conveyor belt side, and particles will fall through this chute. The transporting air circulates through various openings in an inclined plate  23 , although in principle, another gas or gas mixture could be used. The size and distribution of the openings and of other inlets, not shown in detail, would give an appropriate feeding speed for letting the articles or product travel independently from each other through the apparatus channel. Moreover, the net air exchange through chute  21  should be kept low to maintain both dust loss and also maintain air intake at low levels. One way to effect this is keeping the local internal air pressure of the system approximately equal to ambient air pressure.  
         [0023]     At indication  24  a rising duct will carry the particle stream to an appropriate height, in this case some 5 meters; thereafter, the rising duct proceeds as a generally horizontal tube. At indication  26 , the air duct is divided through an inclined and slowly slanting downwardly separation plate  33  that carries an air transmission pattern of holes. In this manner, part of the air stream can be diverted to bypass duct  28 , while the particles of interest cannot pass through the holes. On the other hand, small and generally uninteresting particles such as dust can pass through these holes. This feature allows for adjusting the air speed below the separating plate. Air speed before the separating plate is in a range of 20-30 meters/second, while it is in the range of e.g. 10-20 meters/second in the area where the inspection takes place. Through a certain centrifugal force, the particles of interest are driven to the descending and subsequently, nearly vertical wall at indication  30 , and generally tend to turn their broad area in a more or less horizontal direction to the right side in the Figure.  
         [0024]     Both the centrifugal force and the air outletting through the plate can contribute to orient conforming particles. The result should be a monolayer of well-oriented “good” particles, so that a large fraction thereof will be accepted. On the other hand, the effect on “bad” particles need not be considered, inasmuch as the optical survey discussed hereinafter would be able to pick them out as being non-conforming. The inventor has found that the above manner of orienting the particles is inexpensive, uncomplicated, and has a high success rate.  
         [0025]     Below indication  30 , the separation of unwanted particles is effected during the substantially vertical motion of the particles, through optical inspection and then removal to the right (or alternatively, to the left, or in other directions) in an inspection/separation duct  40 , which operation will be more clearly illustrated in  FIG. 2 . Although preferred to be vertical, the duct orientation, and therefore, the particle motion may have some deviation from vertical: it is contemplated that +/−15° would often be acceptable, and in any way, +/−5° would give a good solution. More or less similar deviations from a straight-line motion could apply. At indication  32 , the stream with particles retained and the bypass stream  28  of air merge again. Downstream from indication  32 , the useful particles are removed from the system in an air-operated product separator arrangement  34  for further processing not considered here. The air output of air-product separator  34  goes through further ducts and main driving air pump arrangement  36 . Finally, the overall duct is attached at indication  38  to the particle feeding position discussed earlier. Generally, there is little loss of air, and therefore also little air suppletion will be necessary, so that the process as a whole takes place in a substantially closed system: the air will cycle several times before being exhausted with the useful particles at air-product separator  34  or via the air bleed-off pipe which is connected to the circuit as a standard going to an exhaust air treatment device. This lowers overall noise levels, and also lowers the risk of high dust concentrations outside the system.  
         [0026]     Now, although the preferred embodiment as shown has the sorting during a falling motion of the particles, in principle other straight-line arrangements could operate in a satisfying manner. If the primary motion is horizontal, the removal of non-conforming particle could be effected in a substantially horizontal, in a substantially vertical manner, or according to still other orientations. If the primary motion is ascending or descending, various geometrical arrangements can be designed, also depending on the gas velocity, the size of the channel, the nature of the conforming and/or non-conforming particles, etcetera.  
         [0027]      FIG. 2  illustrates an enlarged view of a part of sorting facility proper according to the invention, showing in particular items  28 ,  30  and  40  of  FIG. 1 . In particular, note the downwardly inclined course at separation plate  50  (indicated with numeral  33  in  FIG. 1 ), which lets the particles more or less “approach” the wall  30  at reduced air velocities in a range of  10  to  20  meters/second. Whereas the downward inclination of plate  50  shown in the figures is plane, said inclination preferably is cylindrically towards wall  30 . The air flow through separation  50  would assist such “approach”. The transition between the part at  50  and the selection facility proper should be short to maintain the particle orientation; in the embodiment it is about 10% of the total system height, or some 35 centimeters. The vertical part of the duct  40  has a more or less square or rectangular cross-section.  
         [0028]     Now, the selecting proper is effected with double-sided background illumination sources such as lighting  56 , double sided narrow beam particle lighting  54 , double mirrors  53  and double-sided line cameras  52 . In this way the particles can be made well distinguishable, in that the nature of the background can be made to stand out relatively distinctly from properties of the particle such as intensity and color. The output signals from the horizontal line of optical detection units such as cameras are processed in a processing facility not shown, which facility can measure particle shapes in appropriate manner, through correlating successive scans, measuring total exposed particle area, and rejecting such particles as considered non-conforming to the standard range of particle shapes. Through the relatively low air speed, the available data processing time interval can be kept sufficiently long for a moderate-power computer.  
         [0029]     If the particle shape, and possibly color or other properties, are good, the particle proceeds downward in a vertical direction. If the particle is considered bad however, at indication  58  the particle will be removed by suction to the right. Through the suction by underpressure, no additional superfluous air motion and no unwanted turbulence will be introduced into the falling duct. The removal operation proper can be further effected or supported by a gas nozzle  66  that is momentarily activated for ejecting the particle through the opening at indication  58 ; this lets the non-conforming particle escape in a horizontal direction that is substantially across the primary motion of the particles before separation.  
         [0030]     Like the vertical orientation of the inspection/separation duct  40 , the removal can have some tolerance from horizontal, such as +/−15°. Anyway, right after the removal operation proper through output  58 , gravity and/or principal air movement will make the rejected particle fall downward. In fact, at indication  60 , a perforated plate separates the reject duct that goes to reject bin  64 , whereas the bulk of the air stream through underpressure by pump  70  will at indication  62  be led to another part of the closed system or elsewhere. In an alternative embodiment said air stream might near indication  62  reenter bypass duct  28 , and therefore remain as well in the overall system. At indication  68 , the two principal streams  28 , 72  of air merge again. This merging can alternatively occur behind air-product separator facility  34 , as in  FIG. 1 . For clarity, no extensive discussion of air-product separator facility  34  is given, inasmuch as the removing of particles by air-product separator activity is well-known to persons skilled in the art of air-driving particles in an industrial environment.  
         [0031]      FIG. 3  shows an article carrying channel wall  41  of duct  40  with extensions  42  to keep the articles from moving along the channel wall. It has been found that such will keep particle speed more uniform, so that the arrival of a particular particle at the position of nozzle  66  can be predicted more accurately. Indeed, the particles will not be delayed by extensive friction along the wall. The extensions will influence the boundary layer of the flowing gas and may look like fish scales. Their height (perpendicular to the wall) is in a range of 0.5 to 2.5 millimeters, whereas their area (along the duct&#39;s wall) is a few millimeters square. Mechanical working of the wall will allow easy manufacture thereof.  
         [0032]      FIG. 4  shows an overall set-up of another sorting system according to the invention. As in the example of  FIG. 1  the a figure shows a side view and the b figure shows a top view. The feeding conveyer  20  feeds the articles to a vibrating plate  46  that forms a uniform layer of the articles and the latter feeds the articles to a speedy tape transporter  47  that reduces the thickness of the layer of articles. The articles then are fed into the feeding chute  21  where below indication  30  the articles enter an inspection/separation duct  40  that is positioned within housing  86 . Again duct  40  forms a part of a quasi-closed system comprising tubes  41 , 42  that connect the duct  40  to air-operated product separator arrangement  34  which is connected to air pump arrangement  36 . In this case the articles are sucked into the duct  40  by an under-pressure that is created in tube  42 .  
         [0033]      FIG. 5  illustrates an enlarged view of a part of the system of  FIG. 4  comprising duct  40  below point  30  and chute  21 . The upper part of the duct  40  is here over a length of about 1 meter laterally bordered by a cover tube  84  which feeds though a throttle-valve  83  a leakage air flow into duct  40  at location  85 , below which the inspection and separation of impurities and unwanted articles takes place in a further part of duct  40  having a length of e.g. about 0.5 meter. The effect of said leakage airflow is illustrated in  FIG. 6 .  
         [0034]      FIG. 6  shows two cross-sections of the part shown in  FIG. 5  at different heights. The a and b  FIG. 6  are taken respectively above point  85  and below point  85  in  FIG. 5 . In the upper part of duct  40  (see  FIG. 6   a ) the particles  99  are present all over the cross-section of duct  40 , their main orientation being parallel to wall  41  of duct  40 . Below level  85  the leakage air flow is introduced into the duct  40 , flows along the walls thereof and forms a compartment  49  in duct  40  with a smaller width, into which compartment the articles  99  are confined. This has several advantages. Firstly, the walls of duct  40  which contain transparent parts below level  85  are kept free from impurities that may hamper the inspection. Secondly the layer of particles  99  is provided with a more uniform velocity distribution, which is important to enable an accurate timing between the observance of a bad particle and the moment of its separation. Thirdly, the focusing into the particles  99  has become easier since the layer thickness of the stream of particles  99 , which corresponds with the width of compartment  49  in  FIG. 6   b , is decreased.  
         [0035]     Below level  85  (see  FIG. 5  once more) the inspection and separation of particles is performed in housing  86 . The inspection takes place through two optical detection systems, in this example two camera&#39;s  52  that observe the reflected light from a particle in duct  40 . Two radiation sources, here lamps  80  are used for each camera  52  that throw angled radiation, here light, beams on the particle stream in order to reduce a possible shadow effect, if any. Radiating units  81  comprising LEDs (=Light Emitting Diodes) emitting radiation, in this example white light, provide a reference radiation beam for the optical detection systems such as camera&#39;s  52  in this example. After inspection, the removal of unwanted particles is accomplished by gas nozzle  66  by which such particles are ejected into a side-chamber  91  of the duct  40  which is through tube  93  connected to a reject enclosure and a separate air pump, the latter both not shown in the drawing. Anti back-flow arrangement  92 , which here involves a so-called snail-shell construction of underpressure facility  62 , prevents ejected particles from re-entering duct  40 . In addition chamber  91  can be advantageously provided with an over pressure valve—also not shown in the drawing—which contributes to the prevention of re-entrance of ejected particles to duct  40  in case of pressure fluctuations. The over pressure valve can be provided with a particle filter and can be used together with a pump connected to tube  93  or in stead of such a pump. In stead of an over pressure valve a ventilator may be connected to chamber  91 .  
         [0036]     Now, the present invention has hereabove been disclosed with reference to preferred embodiments thereof. Persons skilled in the art will recognize that numerous modifications and changes may be made thereto without exceeding the scope of the appended Claims. For example, the optical inspection and subsequent selection could be effected in a substantially vertical rising air stream.  
         [0037]     Still further, the overall apparatus could be based on an open channel organization. This will obviate the need for various gas input/output balancing configurations. In that case, conveyor belt  20  ( FIG. 1 ) could immediately feed duct  30  in  FIG. 2 . Where in the embodiments lamps are used for the optical inspection, the use of one or more lasers is feasible as well. Furthermore, the arrangement could need only a gas suction facility at the downstream end of the inspection/sorting channel prior to indication  68  in  FIG. 2 . Obviously, this would produce a low-cost arrangement as compared with the embodiment of  FIG. 2 . In consequence, the embodiments should be considered as being illustrative, and no restriction should be construed from those embodiments, other than as have been recited in the Claims.  
         [0038]     Finally, it is noted that elements of the various embodiments could be combined. The unit of  FIG. 5  could e.g. be used in the system of  FIG. 1 , the bypass of  FIG. 2  could be used in system of  FIG. 4  and details of the unit of  FIG. 2  could be used in the unit of  FIG. 5  and vice versa.