Abstract:
A singulation mechanism is provided for use in a handling system for mail or other substantially flat articles, the mechanism having a singulation head with a drive mechanism which, in accordance with a first aspect of the invention, initially moves an article pressed thereagainst with high acceleration, interrupts the drive to the article for a brief instant and then moves the article again at high acceleration, a take-away mechanism removing the article exiting the head. In accordance with a second aspect of the invention, movement at a high acceleration is imparted to the article pressed against the singulation head only when the head is energized and substantially no movement in imparted when the head is not energized. More specifically, the singulation head may include a belt driven over a pair of vacuum chambers, with the trailing vacuum chamber being initially energized to draw the article against the bell and move the article with high acceleration to a position detected by a first detector, at which time the trailing vacuum chamber is turned off and the leading vacuum chamber turned on to again grab the article and move it to the take-away mechanism with high acceleration. This two-step acceleration process is effective for shaking free doubles from the article being singulated. The belt has a substantially friction-free surface in contact with the article to assure that movement is imparted to the article only when a vacuum chamber is turned on. The mechanism includes additional features, including a doubles resolver head, for preventing the passage of doubles to the take mechanism.

Description:
FIELD OF THE INVENTION 
     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 
     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. 
     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″. 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. A system capable of reliably achieving this level of performance without jams and other problems does not currently exist. 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. 
     SUMMARY OF THE INVENTION 
     In accordance with the above, this invention provides a singulation mechanism for use in a handling system for mail or other substantially flat articles. Mail/articles are fed, for example by a suitable feed mechanism, from a stack to a singulation head, the first piece of mail/article being preferably pressed from the stack against the head. In the broader sense and in accordance with a first aspect of the inventions, the singulation head includes a drive mechanism which initially moves a piece of mail or other article pressed thereagainst with high acceleration, interrupts the drive to the piece mail/article for a brief instant, and then moves the piece of mail/article again at high acceleration, a take-away mechanism removing mail/articles exiting the head. At least one position detector may be provided for articles moved by the head, drive interrupt and restart at the head being in response to a selected position detection by such detector. The drive mechanism may include a plurality of drive components, including at least a first rear component and a second forward component, the first component being initially energized to move the article, then de-energized to interrupt drive and the second component then being energized to move the article again. The drive mechanism may include a drive belt moving at a selected rate across the head, and the first and second components may be components selectively applying vacuum pressure through an adjacent portion of the belt. Where a doubled piece of mail may be hung up between the singulation head and the take-away mechanism, a detector may be provided which detects the presence of a piece of mail in between the head and take-away mechanism, and a control may be provided which is operative in response to an output from the detector, after detection that a piece of mail being singulated has reached a predetermined position in the take-away mechanism, for energizing the second component to move the doubled piece to the take-away mechanism. 
     More specifically, the singulation head to which a stack of mail/articles is fed may include a belt having a predetermined pattern of openings formed therein, which belt is driven across the head at a selected rate, and first and second vacuum chambers positioned behind the belt so as to apply vacuum therethrough when energized, the first vacuum chamber V 1  trailing the second vacuum chamber V 2 , the belt therefore passing over V 1  before V 2 . An article fed to the head is pressed against a surface of the belt opposite that passing over V 1  and V 2 . A first detector is provided for detecting when an article being singulated by the head reaches a selected first point near a leading edge of the head. A take-away mechanism is provided for articles exiting the head and a second detector is provided for detecting the articles reaching a selected second point of the take-away mechanism. Controls are also provided for selectively energizing V 1 , for de-energizing V 1  and energizing V 2  in response to an output from the first detector and for de-energizing V 2  in response to an output from the second detector. 
     The vacuum chambers when energized are preferably at a vacuum pressure of approximately 10 Hg to 25 Hg. For applications such as mail handling, the vacuum pressure depends at least in part on the selected weight range for the articles. Where the articles have a maximum weight of approximately 6 lbs., the vacuum pressure range is approximately 15 Hg to 24 Hg. The vacuum flow for the vacuum chamber is preferably in a range of approximately 14 cfm to 17 cfm. For an alternative embodiment, the controls also momentarily stop and restart the belt in response to an output from the first detector. The surface of the belt against which articles are pressed preferably has a low coefficient of friction, being substantially friction free, whereby, absent vacuum applied through the belt from a vacuum chamber, the belt does not impart substantial movement to an article pressed against it. The head preferably has at least one pressure sensor to detect the pressure at which articles are pressed against the surface of the belt, there preferably being a pressure sensor below the belt and at least one pressure sensor above the belt. There is also preferably at least one low pressure vacuum chamber trailing the belt to apply drag force to doubles and at least one low pressure vacuum chamber above and below the belt to stabilize articles and to further apply drag forces to doubles. A doubles resolver head may also be provided between the singulation head and the take-away mechanism to further assure against doubles reaching the take-away mechanism. For singulation of mail, the belt for the singulation head preferably operates at 78 to 85 in/sec and the take-away mechanism preferably operates at approximately 100 to 102 in/sec. 
     In accordance with a second aspect of the invention, the singulation head includes a drive mechanism which, when energized, moves a first article in a stack to be singulated at high acceleration and, when not energized, imparts substantially no movement to the article and a control for energizing the mechanism only when the first article is to be moved. For a preferred embodiment, the head includes a belt having a predetermined pattern of openings formed therein, which belt is driven across the head at a selected rate. The belt has a first side with a substantially friction-free surface against which the articles are pressed and a second side which is opposite the first side. A source selectively applies low pressure to the second side of the belt when an article is to be moved by the belt, the belt being substantially ineffective to move an article pressed against the friction-free surface thereof when low pressure is not applied to the belt. For preferred embodiments, the low pressure is a vacuum pressure and at least the friction-free surface of the belt is of a substantially friction-free material. Where the head is being used to singulate mixed mail, the belt is preferable approximately 3″ wide and continuously perforated. 
     The invention also includes a belt for use in a singulation head of a substantially flat article handling system, which belt includes a first side having a substantially friction-free surface against which the article is pressed and a second side opposite the first side to which the head selectively applies at least substantial vacuum pressure. A pattern of openings is formed in the belt between its first and second sides. Where the belt is being used for the singulation of mixed mail, the belt may for example be approximately 3″ wide and continuously perforated. 
     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. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a perspective view of a mixed mail feeder machine of a type suitable for use in practicing the teachings of this invention; 
     FIG. 2 is an enlarged perspective view of the front face of the singulation head for the machine shown in FIG. 1, this singulation head being a currently preferred embodiment of the invention; 
     FIG. 3 is a perspective view similar to that of FIG. 2, showing the head with the belts and covers removed; 
     FIG. 4 is a graphic top view representation of a singulation head, doubles resolver head and take-away mechanism suitable for use in practicing the teachings of this invention; and 
     FIG. 5 is a diagram illustrating an acceleration/deceleration profile for mail under the influence of vacuum chambers V 1 , V 2  of FIG. 4 for an exemplary implementation of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a mixed mail feeding machine  10  which consists of a mail feed section  12 , a singulation head  14 , a take-away mechanism  16 , and a control computer  18 . While computer  18  for the illustrative embodiment is shown at machine  10  and as having a keyboard and a monitor, the control computer need not be located at machine  10 ; for example several machines  10  could be controlled by a single separately located computer, or only a slave control could be located at the machine without input or output devices, the slave interfacing with a master computer. Feeding mechanism  12  may be any of a variety of mechanisms suitable for delivering a stack of mixed mail under controlled pressure to singulation head  14 . The illustrative mechanism shown in FIG. 1 includes a stacking table  20  having a rotating belt  22  mounted thereon, belt  22  being driven in direction  24  by a suitable drive mechanism (not shown). The drive mechanism for belt  22  could for example include a roller at each end of the belt, at least one of which rollers is driven by a servo motor under control of computer  18 . A pair of paddles or plates  26 A,  26 B extend upward substantially perpendicular to belt  22  and are each attached to a corresponding arm  28 A,  28 B fixed to the housing of feed mechanism  12  in a manner so that they may be pivoted away from belt  22 . A separate drive mechanisms  30 , which may for example, be driven by a worm gears rotated by a servo motor operating under control of computer  18 , controls the movement of plates  26 , and in particular the pressure applied by the plates to mail stacked between the plates and singulation head  14 . The movements of belt  22  and of plates  26  are independent, but are coordinated by processor  18 . In some applications, the surface of table  20  may be of a low friction material, and belt  22  not used. However, the configuration shown is preferable. An indexing wall  32  is provided on the leading edge side of table  20 . 
     FIG. 2 is an enlarged and more detailed view of singulation head  14  for a currently-preferred embodiment. The head includes a belt  34  of at least a low coefficient of friction material and preferably a nearly friction-free material (or at least having a low coefficient of friction/substantially friction-free outer, mail-contacting surface) having perforations  36  formed therein, the belt being moved in the direction of arrow  38 . Belt  34  may for example have an outer layer or coating with a lacquered urethane finish. While the inner layer may be of a variety of materials, it is preferable, for reasons discussed later, that this layer also be of a low or non-friction material, for example a fine napped polyester belt, and the entire belt  34  may be formed in one piece of such material The entire belt or outer layer may also be a commercially available Teflon™ synthetic resin polymer impregnated belt. For a mixed mail application, the belt may for example be 3″ wide. Singulation head  14  also has a pair of vacuum heads  40  on the rear or trailing side of belt  34 , a vacuum head  42  above belt  34  and two vacuum chambers  44 A,  44 B below the belt. Head  14  also has a top pressure sensor  46 T and a bottom pressure sensor  46 B which determine the pressure at which a mail stack is pressed against belt  34 . In particular, lower sensor  46 B determines stack pressure, while upper or top sensor  46 T provides an indication as to whether the mail is in the correct vertical plane (i.e., substantially parallel to belt  34 ) or whether uneven pressure is being applied across the mail in the vertical direction (normally greater pressure at the bottom and less pressure at the top) so that the lead mail piece may be slightly angled away from the belt in the vertical direction. If this condition is detected, control computer  18  can control either the drive for belt  22  or the drive  30  for the plate  26  being utilized so as to correct the problem, for example slowing or stopping belt  22  to reduce pressure at the bottom of the stack and/or applying greater force to the forward plate  26 B. Finally, plate  47  above the singulation head is ridged or waffled so as to have less surface area in contact with mail pieces passing thereacross, and thus less friction with the mall pieces. This results in less potential damage to the mail and in easier and more efficient pick-off of mail from the head. 
     Referring to FIG. 3, it is seen that for a preferred embodiment a pair of vacuum chambers V 1  and V 2  are positioned behind belt  34 . These chambers provide high flow, medium pressure vacuum to engage mail pieces through perforations or holes  36  in belt  34 . The medium volume vacuum needs to be strong enough so as to be able to move the maximum weight of mail for which the machine  10  is designed, but not so strong as to damage mail or to aggravate a doubles problem where the piece of mail being moved is relatively thin and potentially porous. Where the maximum weight of mail being handled is approximately 6 pounds, a vacuum pressure of approximately 15 to 24 Hg (inches of mercury) was found suitable for chambers V 1  and V 2  for an illustrative embodiment, a pressure range of 10 to 25 Hg covering most intended applications of the invention for mail handling. High air flow is required in order to rapidly acquire a piece of mail, for example in a quarter of a second or less, to achieve the desired rapid acceleration. However, high air flow can also cause a doubles problem through thin and relatively porous mail. For the weights, thicknesses and size of mail previously discussed, an air flow for vacuum chambers V 1  and V 2  of approximately 14 cfm to 17 cfm has been found suitable for an illustrative embodiment. 
     FIG. 3 also shows two of the rollers  50 A,  50 B over which belt  34  passes. FIG. 4 shows all 
     FIG. 3 also shows two of the rollers  50 A,  50 B over which belt  34  passes. FIG. 4 shows all five rollers  50 A- 50 E used for belt  34 , one of the rollers, roller  50 D for a preferred embodiment, being the drive roller which is driven by, for example, a servo motor under control of processor  18 . Roller  50 D is preferred as the drive roller since it pulls the belt across singulation head  14 , it being preferable to pull rather then push the belt. FIG. 4 also shows three detectors FL 1 , FL 2  and FL 3 , which are preferably photodetectors and which detect a mail piece at the leading end of singulation head  14  under a doubles resolver head  54 , at a trailing-end pressure roller  52  of take-away mechanism  16  and at the leading end of take-away mechanism  16 , respectively. Vacuum doubles resolver head  54  is also shown positioned over mail pieces as they leave singulation head  14 . This head, which has ½ to ⅓ the vacuum pressure of chambers V 1  and V 2 , is utilized to retard any doubles piece of mail still attached to a piece of mail being fed at this point, thereby stripping such double from the piece of mail being fed so that only a single piece of mail reaches take-away mechanism  16 . Takeaway mechanism  16 , which is described in detail in co-pending application Ser. No. 09/410,940 filed concurrent herewith, includes a belt (or belts)  56 , which is preferably a timing belt having a high coefficient of friction surface in contact with the mail pieces. Belt(s)  56  is driven by three rollers  58 A- 58 C, one of which, for example roller  58 A, is driven by a servo motor under control of processor  18 . In addition to pinch rollers  52  near the trailing side of take-away mechanism  16 , a plurality, for example two, fingers  60  are provided which are independently biased into contact with mail pieces passing over belts  56 . 
     In operation, a person normally places a stack of mail between the forward one of plates  26 , plate  26 B, and singulation head  14 , with the leading edge of the mail pieces  62  aligned against wall  32  as shown for example in FIG.  4 . An additional stack of mail may be placed between plates  26 A and  26 B. In a mixed mail application, the pieces of mail in a given stack will be of random size, thickness and weight. To the extent the stack includes magazines or similar mail bound on one side and open on the other, such mail should be stacked bound-side down to enhance handling during singulation and minimize damage. Once the mail is stacked, belt  22  is operated to move the stack or stacks of mail against singulation head  14  and drive (or drives)  30  is similarly activated to move plates  26  in direction  22 . These movements are controlled by processor  18  so as to deliver the mail stack to singulation head  14  under a predetermined pressure, which pressure is substantially uniform over the face of the singulation head. Any variation in pressure between the top and bottom of the singulation head, which variation is detected by detectors  46 T and  46 B, is compensated for by the drives for belt  22  and plates  26  under control of processor  18  in the manner previously described. 
     Since the surface of belt  34  is of a substantially friction-free material, mail  62  pressed thereagainst is not moved by the belt until vacuum is applied to either one or both of vacuum chambers V 1 , V 2 . The rear of belt  34  also being of a substantially friction-free material for preferred embodiments facilitates movement of the belt over the vacuum, chambers, reducing friction and thus heating at the head and belt wear, and also reducing the energy required to drive the belt. As shown in FIG. 5, when pressure detectors  46  determine that mail is in position at singulation head  14 , processor  18  initially energizes vacuum chamber V 1 , causing apiece of mail  62  adjacent belt  34  to be grabbed by the belt and rapidly accelerated with ajerking action in direction  38 . This jerking action at high acceleration tends to shear the piece of mail being moved from the next piece in the stack, minimizing doubles movement. As may be seen in FIG. 4, wall  32  is also spaced from belt  34  by a distance slightly greater than the maximum thickness of a piece of mail to be handled. This further reduces the likelihood of doubles passing to the take-away mechanism; however, since most mail is substantially thinner than the maximum allowed width, wall  32  alone is not sufficient to resolve the doubles problem. 
     Once the piece of mail in contact with belt  34  has been advanced to detector FL 1 , a distance of approximately 2 inches for an illustrative embodiment, the output signal from FL 1  resulting from the detection of the leading edge of the piece of mail causes processor  18  to turn off the vacuum for chamber V 1 , which results in a momentary deceleration of the piece of mail. As shown in FIG. 5, as vacuum chamber V 1  is deactivated, vacuum chamber V 2  is activated to grab the piece of mail closer to its leading edge and again rapidly accelerate it toward take-away mechanism  16 . This cycle of rapid acceleration, deceleration, and then rapid acceleration again, has been found to be effective for shaking free any doubles which might adhere to a piece of mail being fed, significantly reducing the incidence of such doubles. Vacuum chamber V 2  remains on until the piece of mail reaches detector FL 2 , meaning that the piece of mail has now been grabbed by the take-away mechanism. An output signal from FL 2 , indicating that the leading edge of the piece of mail has reached pinch roller  52  of take-away mechanism  16 , results in processor  18  turning off vacuum chamber V 2  so that the chamber does not feed the next piece of mail. For an embodiment where the length of the smallest piece of mail being handled is 5 inches, the space between the leading edge of chamber V 2 , (i.e., wall  32 ) and the center of pinch rollers  52  is roughly 4 ⅓ inches. This assures that a piece of mail is powered from singulation head  14  to take-away mechanism  16  and does not get hung up therebetween. 
     To this point, two mechanisms have been discussed for eliminating undesired doubles which can cause jamming of the machine, these mechanisms being the acceleration profile of FIG. 5, which tends to shake any doubles free from the piece of mail being fed, and wall  32  which is effective to remove a double where either one or both of the pieces of mail are relatively thick. However, the system shown in the Figures has several additional mechanisms for resolving doubles. First, vacuum resolver head  54  will retard any double which reaches that point in the machine. The vacuum pressure on resolver head  54  is a fraction of the pressure for chamber V 1  and V 2 , for example ⅓ to ½ the vacuum pressure for V 1 /V 2 , so that this head does not interfere or retard the passage of the desired piece of mail through the system. 
     However, since vacuum chamber V 2  turns off once the piece of mail being passed through the system reaches FL 2 , any double resolved by resolver head  54  can get caught up in the space between singulation head  14  and take-away mechanism  16 . This can cause a jam when the next piece of mail is fed. To eliminate this problem, when detector FL 3  detects that a piece of mail has left take-away mechanism  16 , it checks to see if there is still a piece of mail under detector FL 1 . If there is still a piece of mail under detector FL 1  at this time, it means that a resolved double is stuck in this region. However, since as previously indicated, the spacing between the end of vacuum chamber V 2  and take-away roller  52  is less than the length of the shortest piece of mail being processed, this also means that at least part of this resolved double is still over vacuum chamber V 2 . Processor  18  therefore turns off vacuum on resolver head  54  and turns on chamber V 2  until the leading edge of this resolved piece of mail is detected at detector FL 2  where it may be taken away by take-away mechanism  16 . Vacuum chamber V 2  is then turned off. For a preferred embodiment, vacuum from resolver head  54 , instead of being turned off, is diverted to chamber  44   b , this further retarding any additional double, particularly when the original double being cleared is a small piece of mail. Since belt  56  is moved at a higher speed than belt  34 , for example 15% to 20% faster, take-away mechanism  16  can clear the double without substantially slowing down the singulation heads operation. For one illustrative embodiment, the ratio of belt  56  to belt  34  is 102 in/sec to 78.54 in/sec; however, near optimum results in terms of doubles resolving, damage control, etc. in a mail application were found to be approximately 100 in/sec for belt  56  and approximately 85 in/sec for belt  34 . Vacuum chamber V 1  may be turned on again once processor  18  receives an indication that the trailing edge of the doubled piece of mail has cleared detector FL 1 . 
     Heads  40  also hold onto the trailing side of the next piece of mail in the stack behind the piece being fed to retard this piece of mail from being doubled and vacuum heads  42  and  44  perform a similar function on the next piece of mail to be fed as they are uncovered during movement of the piece of mail being fed. Vacuum heads  42  and  44  also hold the piece of mail being fed in alignment, preventing skewing thereof as it is being fed, so that the piece of mail reaches take-away mechanism  16  in proper alignment. 
     For magazine or similar mail bound on one side, which as indicated earlier is the bottom side of such mail as stacked, both singulation head  14  and take-away mechanism  16  are dimensioned and to engage tie lower, more robust portion of such mail, thereby enhancing handling and reducing damage thereof. Such engagement may, for example, be only on the lower 3″ of such mail for an illustrative embodiment. 
     While the invention has been described above with reference to a preferred embodiment, what is important in accordance with a first aspect of the invention is that the acceleration profile of FIG. 5 be imparted to the piece of mail being fed, namely an initial high acceleration movement followed by a short interval of no acceleration and ending with a second high acceleration movement to shake free any doubles. While the specific mechanism involving vacuum chambers V 1  and V 2  operated as indicated above is the currently preferred mechanism for achieving this profile, other ways for achieving the profile are also within the contemplation of the invention. For example, belt  34  may be started initially, stopped momentarily when the leading edge of the piece of mail being fed reaches FL 1  and then rapidly restarted, this being done either instead of having two separate vacuum chambers V 1 , V 2  operated as indicated, or in addition to having the two vacuum chambers operated as indicated. However, this technique does not seem to provide as good a result as using the two vacuum chambers alone. Using a single vacuum chamber which is turned on and turned off rather than two separate vacuum chambers as shown is another option which, while operationally simpler, is considered less effective since it tends to also move the next piece of mail in the stack as well as the piece of mail being fed. 
     In accordance with another expect of the invention, what is important is that mail or other article being moved be moved at high acceleration to shear it from doubles when movement is desired and that there be substantially no movement of the article when movement is not desired. This is accomplished for preferred embodiments by belt  34  being of a substantially frictionless material, or at least that the surface thereof incontact with the mail be of such a material. One problem with prior art singulation devices using a belt is that any time a mail piece comes in contact with the belt, it gets picked off. This is major cause of undesirable doubles. A second major problem is that movement of mail pieces in uncontrollable and somewhat unpredictable in that, since the motion is caused by friction, some motion can occur any time there is contact of mail piece with the belt, even when such motion is not desired. This lack of control also makes it vary difficult to achieve the high acceleration discussed earlier which provides a sheering effect between the piece of mail being delivered and the next following piece, even in the absence of the FIG. 5 double profile. Thus, even which a single vacuum chamber is being used, greater control is provided with a substantially friction-free belt so that feed can be made on demand, the rate at which mail pieces are fed can be controlled, the pitch and gap of the mail stream can be better controlled and the pressure of the mail stacked against the singulation head can be better controlled without worrying about doubles due to friction feed, thereby enhancing the ability to singulate from the stack. Therefore, the acceleration profiled of FIG.  5  and the controlled movement of mail/articles provided for example by the substantially friction-free mail-contacting surface of belt  34  are two important aspects of the invention, each of which individually provides enhanced singulation performance Together, these two features provide substantially enhanced performance of the singulator. 
     Other variations are also possible, and are within the contemplations of the invention, but are currently believed to be either less effective, more complicated, or both. Further, mechanisms can be used to detect pressure at the singulation head other than the projections  46 T,  46 B and the various supplemental vacuum heads  40 ,  42  and  44 , while desirable, are not essential to the practicing of the invention. Finally, while a continuously perforated belt is considered preferable for optimum singulation and throughput, various pitched or other hole patterns are possible for belt  34 , and may be useful in some applications. The belt hole pattern should generally correspond to any hole or slot pattern for the vacuum chambers. Thus, while the invention has been particularly shown and described above with reference to a preferred embodiment, the foregoing and other changes in form and detail may be made therein by one skilled in the art without departing from the spirit and scope of the invention which is to be defined only by the appended claims.