FIELD OF THE INVENTION  
         [0001]    This invention relates to handling and processing systems for mixed mail and related articles, and more particularly to a singulation mechanism for use in such systems which facilitate the handling of articles having significant variation in size, thickness and weight.  
         BACKGROUND OF THE INVENTION  
         [0002]    Mixed mail received at a post office or other location must be sorted and/or otherwise processed so as to be directable to a desired location. To accomplish this function, random items of incoming mail are typically stacked, either manually or otherwise, for feeding to a first mechanism which singulates the mail so that only a single piece of such mail, which is properly oriented and spaced, is passed on to the sorting or other processing mechanism of a mail handling system.  
           [0003]    While many mechanisms currently on the market do an adequate job of singulating certain types of mail, increasing demands are being placed on such systems, both as to the ranges in size, thickness and weight of the mail pieces to be handled and as to the speed at which such systems are to operate, while still maintaining high controllability on the outputted mail pieces, a low jam rate, low damage rate and substantial elimination of doubles passing into the sorting mechanism. For example, a specification for mail pieces to be handled in such a high performance system might include pieces ranging in thickness from 0.007″ to 1.25″, pieces ranging in weight from 0.03 oz to 6.0 lbs., and pieces ranging in size from 3.5″×5.0″ or 4.0″×4.0″ to 15″×15″.  
           [0004]    These variations in thickness, weight and size must be handled without sacrificing throughput, which may be up to approximately 14,500 mail pieces per hour, although this maximum rate may vary somewhat with the size of the pieces being processed, and preferably with an ability to control this rate. Further while the requirements discussed above are particularly applicable to mail handling systems, they can also arise in handling systems for packages and/or other generally flat articles.  
           [0005]    A singulation mechanism designed to meet these specifications is taught in co-pending application Ser. No. 09/411,961, filed Oct. 4, 1999, entitled “Singulation Mechanism” and assigned to the assignee of this application. The subject matter of this co-pending application is incorporated herein by reference. The system of the prior application, which is shown in attached FIG. 1A, includes a singulation station  14  which receives a stack of mail or other appropriate flat articles  62 , which articles contact a guide wall  32  on their leading edge side, and feeds such articles, one at a time, to a takeaway mechanism  16 . Singulation station  14  includes a head against which articles  62  are pressed with a controlled pressure by mechanisms not shown in the Figure. The singulation head includes a selectively perforated belt  34  driven by rollers  50 A- 50 E so as to pass in direction  38  over a pair of vacuum chambers V 1 , V 2 , chamber V 1  being under a trailing side of each article  62 , and chamber V 2  being under a leading side of each article. A first sensor FL 1  detects articles as they leave singulation station  14 , and a second sensor FL 2  senses articles as they reach a pinch roller mechanism  52  of takeaway mechanism  16 .  
           [0006]    In operation, vacuum chamber V 1  is first operated, as shown in FIG. 1B, to pull a trailing side of the article  16  in contact with belt  34  against the portion of belt  34  over the V 1  chamber. Since belt  34  has a very low friction surface, only the portion of the belt over the V 1  chamber engages a leading article  62  of the stack and causes the article to move with belt  34  in direction  38 . The distance between the leading edge of chamber V 1  and sensor FL 1  is such that the leading edge of even the smallest article  62  will reach FL 1  before the trailing edge of the article is no longer over chamber V 1 . When the leading edge of the article is detected by sensor FL 1 , suitable controls are operative to turn off chamber V 1  and to at the same time apply vacuum pressure to chamber V 2 . The turning off of vacuum pressure from chamber V 1  prevents chamber V 1  from feeding the next article in the stack, thus preventing the feeding of doubles, and the energization of chamber V 2  causes belt  34  to engage the trailing portion of the article being fed and to advance this article to takeaway station  16 . There is a slight deceleration of the article as chamber V 1  stops driving it and chamber V 2  is not fully operational. This deceleration, followed by a rapid acceleration as chamber V 2  kicks in, tends to shake loose any double adhering to the article being fed. Again, the distance between the leading end of chamber V 2  and sensor FL 2 /pinch roller  52  is less than the length of the shortest article being fed, this assuring that chamber V 2  can feed all articles  62  to be fed to pinch roller  52  where they are detected by detector FL 2 . When the article reaches roller  52 , its motion in direction  38  can be taken over by takeaway mechanism  16 , and chamber V 2  is therefore turned off as shown in FIG. 1B.  
           [0007]    While the singulation mechanism of FIGS. 1A and 1B provides far superior performance in meeting the specifications indicated above than any prior singulation mechanism, in practice, the large variations in size, thickness and weight for the articles being fed has made it difficult to provide sufficient vacuum to feed heavier articles to be fed, for example articles weighing 4-6 pounds, while not having so much vacuum that it bleeds through thinner articles, resulting in doubles being fed. It has therefore been very difficult to select the vacuum pressures for both chambers so as to be able to feed all articles, and in particular all mail items, within the above specification without also causing the feeding of an unacceptably high number of doubles.  
           [0008]    A second problem with the device shown in FIG. 1A has been that, once vacuum is removed from chamber V 1 , the chamber in practice does not quickly return to atmospheric pressure as shown in FIG. 1B, but continues to have some vacuum pressure even after chamber V 2  has been activated. This extended vacuum pressure in chamber V 1  can result in some lighter articles being pulled against belt  34  and held sufficiently so as to be fed by the belt while chamber V 2  is clearing the leading article, this also resulting in the potential feeding of a double.  
           [0009]    Another potential problem is that, in the system of FIG. 1A, operator skill is the only assurance that all articles  62  are aligned against wall or fence  32 . This results in some articles not being properly aligned, leading to potential feeding errors. The system of FIG. 1A also has potential problems in feeding shorter articles.  
           [0010]    A need therefore exists for an improved singulation mechanism which overcomes the problems indicated above, and which otherwise optimizes the singulation operation, particularly in high performance applications.  
         SUMMARY OF THE INVENTION  
         [0011]    In accordance with the above, this invention provides a singulation head for use in a singulation mechanism for flat articles of varying size and weight, which mechanism includes a takeaway mechanism for articles exiting the head, detectors for selectively detecting article position for an article being singulated, and controls for the singulation mechanism. The singulation head includes a selectively perforated belt driven across the head at a selected rate, at least two vacuum chambers positioned behind the belt so as to apply vacuum thereto when energized, the chambers being successively positioned along the belt, with the controls energizing the chambers in a predetermined sequence in response to outputs from the detectors, and a feedback mechanism selectively controlling pressure and/or flow for at least one of the chambers to facilitate the feeding by the head to the takeaway mechanism of heavier articles to be singulated, while inhibiting bleedthrough doubles for lighter articles to be singulated.  
           [0012]    The feed mechanism may include a metering plate between the chambers and the belt, the metering plate having openings therein over each chamber which permits sufficient pressure/flow to feed at least most of the articles with substantially no bleedthrough doubles. A mechanism may be provided for altering the metering plate for heavier articles to increase pressure/flow for at least one of the chambers sufficiently to feed such articles. The mechanism for altering may include second plate having larger openings formed therein over at least one of the chambers, the mechanism involving removing and replacing the metering plate, or the portion thereof over at least one of the chambers, using a second plate to cover or expose more or less of openings in the metering plate or other techniques.  
           [0013]    The feed mechanism may include a portion of the controls operating in response to an indication from at least one of the detectors that an article has not been fed by the head for increasing the pressure and/or flow for at least one of the chambers to facilitate feeding of such article. For some embodiments, there is a chamber V 1  adjacent a selected portion of each article at the beginning of a feed operation and a chamber V 2  downstream from chamber V 1 , the portion of the controls increasing pressure and/or flow for at least chamber V 1 . For one embodiment, chamber V 1  is divided into a chamber V 1   a  and a chamber V 1   b,  chamber V 1   a  being between chambers V 1   b  and V 2 . For this embodiment, chamber V 1   a,  but not chamber V 1   b,  is normally operated to feed articles, and a portion of the controls operates at least chamber V 1   b  to facilitate feeding of an unfed article detected by said detectors. A portion of the controls may operate both chambers V 1   a  and V 1   b  at substantially the same time to feed the heavier article or may operate only chamber V 1   b  for this purpose. Particularly in the latter situation, chamber V 1   b  provides a greater pressure/flow than chamber V 1   a.    
           [0014]    For various ones of the embodiments, a mechanism is included which provides a puff of air to a chamber, for example chamber V 1   a  where there is such a chamber, or chamber V 1 , at the end of each operation thereof. The puff of air may be sufficient to momentarily positively pressurize the chamber to which it is applied. The puff of air may be controlled by a puffer valve, with the same signal preferably triggering both chamber V 2  and the puffer valve.  
           [0015]    The invention may also include a fence against which a leading edge of each article is to abut, one of the vacuum chambers, V 2 , being the leading-most one of the vacuum chambers, and the fence terminating at a distance from the belt slightly greater than the thickest article to be fed and at a point on the belt over a portion of chamber V 2  between a mid-region thereof and a trailing edge thereof. A metering plate may be provided over chamber V 2 , the metering plate having openings formed therein over substantially only the portion of chamber V 2  on the leading end side of the fence. The detectors may include a first detector located past a leading side of chamber V 2 , a second detector between the singulation head and the take-away mechanism and a third detector at the take-away mechanism. For some embodiments, the fence bends in the leading direction at a selected point behind the end thereof.  
           [0016]    The invention also includes a singulation head for use in a singulation mechanism for flat articles of varying size and weight, which mechanism includes a takeaway mechanism for articles exiting the head, detectors for selectively detecting article position for articles being singulated and controls for the singulation mechanism, the singulation head including a selectively perforated belt driven across the head at a selected rate, at least two vacuum chambers positioned behind the belt so as to apply vacuum thereto when energized, the chambers being successively positioned along the belt, and the controls energizing the chambers in a predetermined sequence in response to outputs from the detectors, and a mechanism which provides a puff of air to at least one of the chambers at the end of each operation thereof. Such puff of air is preferably sufficient to momentarily positively pressurize the at least one chamber to which it is applied. As indicated above, the puff of air is preferably applied to chamber V 1  or to chamber V 1   a  where one of such chambers exists, and preferably controlled by a puffer valve triggered by the same trigger signal as chamber V 2 . The fence as described above may also be provided.  
           [0017]    Finally, the invention may also include a singulation head for use in a singulation mechanism for flat articles of varying size and weight, which mechanism includes a take-away mechanism for articles exiting the head, detectors for selectively detecting article position for articles being singulated and controls for the singulation mechanism, the singulation head including a selectively perforated belt driven across the head at a selected rate, at least two vacuum chambers positioned behind the belt so as to apply vacuum thereto when energized, the chambers being successively positioned along the belt, and the controls energizing the chambers in a predetermined sequence in response to outputs from the detectors, and a fence against which a leading edge of each article is to abut, one of the vacuum chambers, V 2 , being the leading-most one of the vacuum chambers, the fence terminating at a distance from the belt slightly greater than a thickest article to be fed and at a point on the belt over a portion of chamber V 2  between a mid-region thereof and a trailing end thereof. This aspect of the invention may include the metering plate over V 2  having openings as described above, the three detectors described above and/or the fence bending in the leading direction at a selected point beyond the end thereof.  
           [0018]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings, the same reference numerals being used for common elements in the various drawings. 
       
    
    
     IN THE DRAWINGS  
       [0019]    [0019]FIG. 1A is a graphic top view representation of a prior art singulation head and takeaway mechanism;  
         [0020]    [0020]FIG. 1B is a diagram illustrating a timing/distance profile for mail under the influence of vacuum chambers V 1 , V 2  for the prior art singulation head shown in FIG. 1A;  
         [0021]    [0021]FIG. 2A is a graphic top view representation of an improved singulation head in accordance with at least one aspect of this invention and of the corresponding takeaway mechanism.  
         [0022]    [0022]FIG. 2B is a diagram illustrating a timing/distance profile for mail for the head of FIG. 2A.  
         [0023]    [0023]FIG. 2C is a front view of a meter or face plate for vacuum chambers V 1 , V 2  of FIG. 2A.  
         [0024]    [0024]FIG. 3A is a graphic top view of the singulation head portion of the system shown in FIG. 2A as modified in accordance with one embodiment of the invention;  
         [0025]    [0025]FIGS. 3B and 3C are diagrams illustrating the pressure profile for chamber V 1  for the embodiments of FIG. 3A without use of a puffer valve and with use of the valve, respectively;  
         [0026]    [0026]FIG. 4A is a front perspective view of a pair of vacuum chambers suitable for use in practicing the embodiment of FIG. 2A;  
         [0027]    [0027]FIG. 4B is a front perspective view of a meter plate which may be placed over the front of the vacuum chambers of FIG. 4A, particularly to move heavy articles;  
         [0028]    [0028]FIG. 4C is a front perspective view of a meter plate which may be placed over the vacuum chambers of FIG. 4A to move lighter articles.  
         [0029]    [0029]FIG. 4D is a front perspective view of a plate which may be slid over the meter plate of FIG. 4B when lighter articles are to be fed and selectively removed for the feeding of heavier articles;  
         [0030]    [0030]FIG. 5 is a graphic top view representation of the singulation portion of the mechanism of FIG. 2A for an alternative embodiment of the invention; and  
         [0031]    FIGS.  6 A and FIG. 6B are front perspective views of the vacuum chamber head of FIG. 5 with the metering plate removed and with an illustrative metering plate in place, respectively. 
     
    
     DETAILED DESCRIPTION  
       [0032]    [0032]FIG. 2A illustrates an embodiment of the invention which differs from the embodiment of FIG. 1A in that alignment wall  32  has been replaced by an alignment wall  32 ′ which is further back on singulation head  14  and is bent from a position which is substantially the same as that for the wall  32  to the position shown when adjacent to the singulation head with the end of the wall spaced from the head by a distance slightly greater than the thickest article  62  to be fed and over a point near the middle of chamber V 2 . FIG. 2C shows a metering plate  66  which may be placed over vacuum chambers V 1  and V 2 , with the openings  67  in the plate over vacuum chamber V 1  being toward the leading side of this vacuum chamber and the openings  68  over the vacuum chamber V 2  being located over the portion of chamber V 2  which is on the forward or leading side of this vacuum chamber and is over the portion of the chamber beyond wall  32 ′. This embodiment of the invention also has an additional detector FL 5  which is located at the leading edge side of chamber V 2 , and thus generates an output when the leading end of the article being fed is fully over openings  68 . While for the embodiment shown in FIG. 2A, wall  32 ′ is roughly half way or a little over half way back on chamber V 2 , depending on application, the wall may, for this embodiment of the invention, be positioned anywhere from over a mid-region of chamber V 2  to the junction between the two chambers.  
         [0033]    The embodiment of FIG. 2A offers at least two advantages. First, articles  62  are typically manually aligned against wall  32 . While a skilled operator can normally do a good job of aligning the articles against this wall, inevitably, some articles, particularly smaller articles, will not be in registration against this wall. Smaller articles not being initially against the wall may prevent such articles from being properly fed and/or may result in vacuum also being applied to the article behind the forward most article, causing a double to be fed. The bent wall  32 ′ moves articles  62  to in the rear or trailing direction as they advance to the singulation head, thus facilitating the alignment of all or substantially all of the articles against wall  32 ′.  
         [0034]    Moving wall  32 ′ back and providing an additional sensor FL 5  also facilitates the feeding of smaller, shorter articles, assuring that these articles reach and are picked up by vacuum chamber V 2  and fed by this chamber to take-away mechanism  16 . Openings  68  being beyond wall  32 ′ and vacuum chamber V 1  being on for a shorter duration, as can be seen from FIG. 2B, also reduces bleed through of vacuum for such smaller articles, thereby reducing doubles generation.  
         [0035]    [0035]FIG. 3A illustrates an embodiment of the invention which may be used with either the embodiment of FIG. 1A or the embodiment of FIG. 2A, and FIGS.  4 A- 4 C illustrate variations on this embodiment. In FIG. 3A, it is seen that the embodiment of FIGS. 1A, 2A has been modified by adding a puffer valve  70  which is connected between a line  72  leading to a positive pressure air source and a line  74  leading to the back of chamber V 1 . Referring to FIG. 3B, without puffer valve  70 , there is a time delay between article  62  being detected by detector FL 5  and the time vacuum pressure to chamber V 1  is cut off and, once vacuum is cut off, there is a further significant time delay before the chamber returns to atmospheric pressure. For an illustrative embodiment, this time is 29 ms. Puffer valve  70  is enabled in response to the same output from FL 5  which turns off vacuum to chamber V 1  and turns on vacuum to chamber V 2 , and is enabled for the same time interval as chamber V 2 . As shown in FIG. 3C, while the pressure in chamber V 1  initially goes negative, when the article being fed reaches sensor FL 5 , vacuum pressure to chamber V 1  is cut off after some time delay and, at the same time, puffer valve  70  is activated causing a puff or burst of pressurized air to be applied to chamber V 1 . This reduces the time required for chamber V 1  to return to atmospheric pressure, for example by about 50% to 15 ms for an illustrative embodiment. The duration of this puff is sufficient so that, as seen in FIG. 3C, chamber V 1  becomes slightly positively pressurized for a duration until the article reaches FL 2 . The more rapid removal of vacuum pressure from chamber V 1  as a result of the application of the air puff or burst thereto ensures that vacuum pressure is not applied to a trailing document, thus reducing the likelihood of a doubles being fed. To the extent some vacuum pressure had previously been applied to a trailing document to pull it against belt  34 , the positive pressurization of the V 1  chamber pushes the mail item or other article away from the belt, assuring that it does not move therewith, and further reducing the possibility of a doubles occurring, particularly for smaller articles. Puffer valve  70  thus eliminates one of the problems with the prior art system of FIG. 1A which has been discussed previously.  
         [0036]    Referring to FIGS.  4 A- 4 D, a first metering plate  78  is shown which may be screwed over the front of vacuum chambers V 1  and V 2 , which plate has relatively large openings  80  and  82  formed therein over chambers V 1  and V 2 , respectively. Since plate  78  permits substantial pressure and flow from the vacuum chambers to be applied to the openings in belt  34 , and thus to the articles in contact therewith. Plate  78  is thus useful for feeding heavier articles. However, the flow with plate  78  can be sufficient that vacuum pressure bleeds through thinner articles being singulated by the head, permitting vacuum to be applied to the article in the stack behind the article being fed. If this second article is also a relatively small and light article which can be fed by the vacuum pressure applied thereto, this can result in a double being fed. Therefore, it is preferable when lighter and thinner documents are being fed that metering plate  84  be screwed to the face of chambers V 1  and V 2 , this plate having relatively small openings  86  over the leading end of the V 1  chamber and larger openings  88  over the leading edge of chamber V 2 ; however, the openings  88  are still substantially smaller than the openings  82  of plate  78 . The smaller openings of plate  84  restrict air flow, and thus restrict the vacuum applied to the article  62  adjacent belt  34 . The combination of the applied pressure and the openings  86  and  88  are selected to provide sufficient flow so that the head can feed most articles  62  which it is designed to feed; however, the flow through plate  84  is not sufficient to feed heavier articles. This means that an operator of the machine in which a head having plate  84  is being utilized must presort the mail or other articles to eliminate the heavier articles therefrom when head  84  is in place and must periodically unscrew and replace metering plate  84  with, for example, metering plate  78  to do one or more runs of the heavier articles.  
         [0037]    While the entire plate  78 ,  84  is replaced for the embodiment shown in FIGS.  4 A- 4 C, this is not a limitation on the invention, and it may, for example, be necessary only to replace the rear portion of the metering plate over chamber V 1  rather than the entire plate in order to feed heavier articles. Further, to speed up the exchange operation, rather than screwing the metering plates  78 ,  84  to the face of the vacuum chambers, it may be possible to snap or slide the plates into position to facilitate the exchanging thereof. Further, rather than fully replacing plate  78 , it may be possible to slide a plate  90  or pivot a plate  90  in place over plate  78  so that, for example, plate  90  covers half or two-thirds of the openings  82  to leave effective openings of the general size of openings  88  and openings  80  are covered to permit flow only through the much smaller openings  92 . With such an arrangement, it might be possible for plate  90 , for example, to normally be in place, permitting perhaps 80 percent or more of articles to be fed, and for plate  90  to be slid out of the way, wholly or partially, either by the operator or under automatic control, when the head is unable to feed an article applied thereto.  
         [0038]    While the techniques described above overcome the problem of being able to feed both relatively heavy articles and relatively light and thin articles with the same system without an unacceptably high level of doubles, it can also result in a significant reduction in the throughput of the system and, for at least some of the techniques indicated above, requires greater operator involvement, which can further reduce throughput and/or increase costs of operation. Operating in this way is therefore not preferred, particularly in applications where a significant number of heavier articles are likely to be encountered.  
         [0039]    [0039]FIG. 5 shows an alternative embodiment of the invention which facilitates automatic operation, thus permitting a wider range of article weights to be handled without an increase in the instance of doubles, and without a significant reduction in throughput. For this embodiment of the invention, instead of having two vacuum chambers V 1  and V 2 , three vacuum chambers V 1   a,  V 1   b  and V 2  are provided, with chamber V 1   a  being between chambers V 1   b  and V 2  and with chamber V 1   a  being smaller, and therefore providing less flow, than the other two chambers. As shown in FIG. 6B, the holes  95  in metering plate  94  over the vacuum chambers are also relatively small for chamber V 1   a,  further reducing flow for this chamber. Puffer valve  70  is provided for chamber V 1   a.  Each of the vacuum chambers is connected to a vacuum line  97  through a corresponding vacuum valve  96   1a - 96   2  and a corresponding vacuum line  98   1a - 98   2  to the corresponding vacuum chamber. Vacuum valves  96  are individually controlled from a suitable processor. Metering plate  94  has openings  100  in front of vacuum chamber V 1   b  which are slightly smaller than the openings  80  in metering plate  78  and has openings  88  in front of vacuum chamber V 2  which are substantially the same as openings  88  in metering plate  84 .  
         [0040]    In operation, vacuum pressure followed by air pressure from puffer valve  70  is normally applied to valve V 1   a,  the pressure profile for this vacuum chamber being substantially the same as that for chamber V 1  in FIG. 3C. At the same time that puffer valve  70  is operated, valve  96   1a  is closed and valve  96   2  is opened, causing vacuum to be applied to chamber V 2  to complete the feeding of the article. With the arrangement shown in FIGS. 5 and 6, and with valves V 1   a  and V 2  being operated as indicated, sufficient flow should be applied to feed most of a normal mixed mail input, perhaps 80% or more depending on the mix. When a heavier article is received at head  14 ″, for which activation as shown of chambers V 1   a  and V 2  does not provide sufficient pressure and flow to feed, at the end of a selected maximum time period for activation of chamber V 1   a,  sensor FL 5  will indicate that the leading edge of the article has not advanced to this point. When this occurs, chamber V 1   b  is activated, either alone or in conjunction with chamber V 1   a.  Because of the larger size and capacity of chamber V 1   b  and the larger openings  100  in metering plate  94  in front of chamber V 1   b,  chamber V 1   b  provides sufficient flow to move the heaviest article which the system is designed to handle, particularly when operated in conjunction with chamber V 1   a.  When the article has advanced to FL 1 , chamber V 1   b (and V 1   a  if still operated) is cut off and chamber V 2  energized to move the article to takeaway mechanism  16  in the manner previously described. While chamber V 1   a  could be operated in conjunction with chamber V 1   b,  the added flow provided by chamber V 1   a  may not be required for some applications. Further, while a puffer valve could be provided for chamber V 1   b,  since this chamber is operated only for larger heavier articles, any residual vacuum in this chamber is normally not a problem. However, in a truly mixed mail environment, where the mail item following a heavy item may be a small thin item, a puffer valve for chamber V 1   b,  while generally not required, may be included. Once the heavy article has been fed, the system returns to operating only with chambers V 1   a  and V 2  for the feeding of subsequent articles until the singulation mechanism  14 ″ is again unable to feed the article pressed against belt  34 .  
         [0041]    A system has thus been provided which permits optimum flow to be provided for each article being fed so that all articles within a relatively wide size and weight range may be successfully fed by the head, while maintaining the level of doubles passing from singulation head  14 - 14 ″ at an acceptably low level. While the invention has been particularly shown and described above with reference to several illustrative embodiments, and variations on these embodiments have been discussed, it is apparent that these various embodiments and modifications are being presented for purposes of illustration only and that further modifications may be made in the invention by one skilled in the art while still remaining within the spirit and scope of the invention, which is to be defined only by the appended claims.
An improved singulation mechanism is provided for flat articles having significant variations in size, thickness and weight, which mechanism utilizes at least two vacuum chambers positioned behind a moving perforated to feed the articles and selectively controls at least one of pressure and flow for at least one of the chambers to facilitate the feeding of heavier articles, while inhibiting bleed through doubles for lighter articles. A mechanism may be provided which provides a puff of air to at least one of the chambers at the end of the operation thereof to reduce the feeding of doubles and a bent fence may be suitably positioned to both facilitate feeding of shorter articles and to facilitate proper initial alignment of the articles.