Abstract:
A method and apparatus for resolving doubles on singulated flat articles being passed in a downstream direction to a takeaway mechanism by use of a doubles resolver mechanism ahead of the takeaway mechanism. The doubles resolver mechanism includes a doubles resolver head through which negative pressure may be applied to articles passing thereunder, and a mount for the head which positions the head against such articles with a substantially constant force regardless of the thickness of the article. Negative pressure is applied to the head except when the head is detected as having resolved a double, at which time such pressure is momentarily removed to permit the double to be cleared.

Description:
FIELD OF THE INVENTION 
     This invention relates to methods and apparatus for handling flat articles, such as mixed mail, and more particularly to a mechanism for resolving doubles at the output from a singulation mechanism of such a system and to a method for the use of such mechanism. 
     BACKGROUND OF THE INVENTION 
     In systems for handling mixed mail or other flat articles, which may or may not be of a uniform size, the articles are frequently stacked on edge and passed through a singulation mechanism at the beginning of the operation. However, particularly where there are significant variations in the size, thickness and weight for the articles being singulated, the singulator will it from time to time pass two or more pieces of mail or other articles simultaneously, a smaller article for example piggy-backing on a larger article being singulated. This problem, which is commonly referred to as doubles or multiple feeds, if left unresolved, can possibly lead to missorts, damage to the articles, rejects or jams in downstream parts of the system. While many techniques have been employed in the past to resolve such doubles, particularly in mail handling systems, the variations in size, weight and thickness of mixed mail make doubles very difficult to resolve. For example, one specification for a mixed mail handling system requires handling mail vary in size from 4″×4″ or 3.5″×5.0″ to 15″×15″, weights from a 0.03 ounces to six pounds and thickness from 0.007″ up to 1.25 inches. Further, some of the larger pieces may be soft covered magazines, catalogs, telephone books or the like which are bound on only one edge, further complicating the singulation and doubles resolving process. Mechanisms for successfully resolving doubles at the output of a singulator in a system handling articles of mixed size, thickness and weight with variations on the order of those indicated above do not currently exist. 
     SUMMARY OF THE INVENTION 
     In accordance with the above, this invention provides a method and apparatus for resolving doubles exiting a singulation mechanism which takes advantage of the fact that the doubled piece will typically be a thinner, lighter piece. The invention thus provides, in a system for passing a singulated flat article in a downstream direction from a singulation mechanism to a takeaway mechanism, a doubles resolver mechanism which includes a doubles resolver head having negative pressure selectively applied to an operative surface thereof, and a mount for the head which mount positions the operative surface of the head against a side of each article which is opposite the side against which drive is applied by the singulation and takeaway mechanisms, the mount pressing the head against each article, as the article passes between the singulation mechanism and the takeaway mechanism, with a force which is substantially constant regardless of the thickness of the article. The mount preferably includes a gas spring operating on the head to apply the constant force thereto. For preferred embodiments, the gas spring is a pneumatic cylinder, a controlled positive pneumatic pressure source applying gas pressure to the cylinder to control the constant force being applied thereby. The mount may also include a stop which limits movement of the head against the force being applied by the gas spring. The head may also be attached to at least one shaft mounted in a bearing, the shaft moving in the bearing to facilitate movement of the head parallel to the direction of the force applied to the article. For at least one embodiment of the invention, the operative surface of the head is at a slight angle to the downstream direction. For another embodiment, the head is mounted to rotate from a position with its operative surface substantially parallel to the direction of article movement, or at a slight angle thereto, to a position at a greater angle to such direction as each article passes under the head. For this embodiment, a passive valve may be provided which reduces the negative pressure applied to the operative surface of the head as the angle for the operative surface increases, the valve substantially cutting off the negative pressure when the operative surface is an at a selected maximum angle for an illustrative embodiment. The head separates and holds a doubled article piggybacking on an article passing from the singulation to the takeaway mechanism, negative pressure normally being applied to the operative surface, but being cut off when a doubled article is detected as being held by the head. For preferred embodiments, the articles on which the doubles resolver mechanism is used are mixed mail. 
     The invention also includes a method for resolving doubles in a system of the type previously indicated, which method includes mounting a doubles resolver head having negative pressure applied to an operative surface thereof between the singulation mechanism and the takeaway mechanism, with the side of each article opposite that to which drive is applied by the singulation and takeaway mechanisms in contact with the operative surface of the head as each article passes thereunder; and pressing the head against each article with a force which is substantially constant regardless of the thickness of the article. The mounting step may mount the head with the operative surface angled slightly away from the direction of article movement or the head may be mounted to rotate from a position with its operative surface substantially parallel to the direction of article movement to a position at a slight angle to such direction as each article passes under the head. In the latter case, the negative pressure applied to the operative surface of the head may be reduced as the angle for such operative surface increases, and may be substantially cut off when the operative surface is at a selected maximum angle to the direction of article movement. The head preferably separates and holds a doubled article, negative pressure normally being applied to the operative surface and being cutoff when a doubled article is detected as being held by the head. When the negative pressure is cut off, the doubled article is preferably adjacent to the drive for at least one of the singulation or the takeaway mechanism and such drive is then operated to clear the doubled article. Finally, the invention includes a doubles resolver head having negative pressure normally applied to an operative surface of the head, and a mount for the head which mount positions an operative surface of the head against the non-driven side of each article as the article passes between the singulation and takeaway mechanisms, the head separating and holding a doubled article, and the negative pressure being cut off when a doubled article is detected as being held by the head. 
     The foregoing and other objects, features and advantages of the invention will be apparently 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 
     FIG. 1 is a semi-diagrammatic view illustrating a mixed mail handling system in which the teachings of this invention may be utilized. 
     FIGS. 2A and 2B are a rear bottom, left-side perspective view and a rear, bottom, right-side perspective view, respectively of a doubles resolver mechanism in accordance with one embodiment of the invention. 
     FIGS. 3A and 3B are partial side views of a doubles resolver head mechanism for a second embodiment of the invention shown in a normal position with vacuum on and a deflected position with vacuum off, respectively. 
     FIGS. 4A and 4B are diagrammatic side views illustrating articles of different thickness passing under the doubles resolver head for the embodiment of FIGS. 2A and 2B. 
     FIG. 5 is a diagrammatic side view illustrating the resolving of a double for the embodiment of the invention shown in FIGS. 2A and 2B. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a system  10  for processing a stack of articles  12  which, for the illustrative embodiment will be assumed to be mixed mail. The system includes a singulation mechanism  14 , a take away mechanism  16 , and a doubles resolver head  18  of this invention positioned between the singulation and take away mechanisms. The system shown in FIG. 1 is described in some detail in co-pending applications Ser. Nos. 09/411,961 and 09/410,940, both of which were filed on Oct. 4, 1999, and both of which are assigned to the Assignee of this application. While the system is generally described in both of the co-pending applications, singulation mechanism  14  is particularly described in the Ser. No. 09/411,961 application and take away mechanism  16  is particularly described in the Ser. No. 09/410,940 application. The descriptions of these mechanisms contained in the co-pending applications are incorporated herein by reference, and these mechanisms will therefore only be discussed briefly in this application, it being understood that the specific singulation mechanism  14  and take away mechanism  16  are being provided for purposes of illustration only, and that any mechanisms capable of performing the disclosed singulation and take away functions could be used in their place. 
     In particular, singulation mechanism  14  includes a drive belt  20  which moves in direction  22  across face  24  of a singulation head. Belt  20  passes over a series of rollers  26 A- 26 E, one of which, for example roller  26 D, is driven to move the belt. The surface of the belt against which articles  12  are pressed is preferably of a substantially friction free material so that articles  12  pressed against the belt are normally not moved in the direction  22  thereby unless vacuum is applied to the article through openings formed in the belt, vacuum being applied to either vacuum chamber V 1  or V 2 . As discussed in greater detail in the beforementioned co-pending applications, vacuum is applied first to vacuum chamber V 1  to cause an initial movement of the article in contact with the belt at high acceleration. This vacuum is then released and vacuum applied to vacuum chamber V 2  to cause a second acceleration of the article in direction  22 , this action being intended to shake or shear off any double attempting to piggy back on the article being fed. 
     An article (or where there is a double, articles) leaving singulation mechanism  14  pass under the doubles resolver mechanism of this invention, which will be described shortly, to take away mechanism  16 . Take away mechanism  16  includes a belt  28  passing over three rollers  30 A- 30 C, one of which, for example roller  30 A, is driven. Belt  28  preferably has a tacky outer surface, and for preferred embodiments is at least two spaced adjacent belts. A pair of rollers  32  and a pair of fingers  34  operate to hold an article in good contact with belt  28  to effect take away of the article. For the illustrative embodiment, belt  28  moves at a higher speed than belt  20  for reasons discussed in the co-pending applications, including clearing doubles and preventing jams. Detectors or sensors F 1 , F 2 , and F 3  are provided at various points in the travel path of the article, these sensors operating in conjunction with a processor (not shown) to control the operation of the system. 
     While the shearing action of vacuum chambers V 1  and V 2  minimizes doubles exiting singulation mechanism  14 , and wall  36  on the leading side of singulation mechanism  14 , which is spaced from belt  20  by a distance just larger than the thickness of the thickest article to be singulated, removes any relatively thick double which might try to pass, it is possible that the system shown in FIG. 1 will still pass, and the system in fact does sometimes pass, relatively thin doubles to the take away mechanism. The doubles resolver mechanism of this invention is intended to prevent any such double from reaching the take away mechanism. 
     FIGS. 2A and 2B illustrate a doubles resolver mechanism  18  for a first illustrative embodiment of the invention. This mechanism consists of a doubles resolver head  40  having an operative surface  42  with openings formed therein through which vacuum may be applied to articles  12  coming in contact with, or otherwise passing under the head, and a port  44  through which vacuum pressure may be applied to the head from a vacuum or other negative pressure source through a suitable hose  46  (see FIG.  1 ). For an illustrative mixed mail application, a vacuum of approximately 8″ to 10″ of mercury is pulled through the holes in surface  42 . Vacuum line  46  may be connected to a valve (not shown) that can be operated, preferably under processor control, to turn the vacuum on and off, as required. 
     Head  40  is connected by a pair of metal shafts  48  to a back plate  50 , shafts  48  passing through a linear pillow, bearing containing block  52  positioned between head  40  and plate  50 . A stop bolt  54  is also connected to back plate  50  and may bear against a block bracket  58  to limit the forward motion of head  40  so that it may get close enough to belt  20  to contact the thinnest article/mail passing through the system, while not actually contacting the belt. Backplate  50  both supports shafts  48  at their rear end and maintains their spacing equal to that at the linear bearings  52  to assure free movement of the shafts in the bearings. Plate  54  also has the end of a piston rod of pneumatic or air cylinder  56  attached thereto, the body of the cylinder  56  being mounted to bracket  58 , which bracket also supports pillow box or bearings  52 . Bracket  58  is secured by suitable brackets  60  and  62  to the housing of system  10 . Referring to FIG. 2B, pneumatic cylinder  56  has an air input port  64  connected through a suitable hose  66  to an air pressure regulator  68  having a gauge  70  and a control input  72 . Regulator  68  is connected to a source of positive air pressure  74 . Control  72  may either be manually adjusted or may be adjusted in response to control inputs from a processor to determine the air pressure applied to cylinder  56 , and thus the pressure or force at which operative surface  42  of head  40  is pressed against articles  12  passing thereunder. Air cylinder  56  acts as a constant force “air spring” to head  40 , the force being adjusted by controlling input  72  to regulator  68 . 
     As indicated earlier, doubles resolver head  18  is positioned in what may be considered an “idle zone” between the drives for singulation mechanism  14  and take away mechanism  16 . This permits resolver mechanism  18  to resolve any double exiting singulation mechanism  12  before such double reaches the take away mechanism. 
     As shown in FIG. 4A, operative surface  42  of resolver head  40  is at a slight angle θ to the direction  22  in which articles  12  move thereunder. The angle θ may for example be approximately 1.5°. This slight angle permits the leading edge of each article to act on operative face  42  to raise head  40  against the air spring action of pneumatic cylinder  56  so as to permit the article to pass under head  40  while maintaining surface  42  of the head in contact with the article with a substantially constant force. FIGS. 4A and 4B illustrate how head  40  moves to permit articles  12  of varying thickness to pass thereunder. When each article passes head  40 , the constant pressure of cylinder  56  returns head  40  to its fully extended position as determined by stop  54 . The stroke length of cylinder  54  is selected to allow articles/mail pieces within the full range of thicknesses for which the system is designed to pass under head  40 . Because of the constant force of air spring cylinder  56 , head  40  does not get bounced out of the way by incoming articles/mail  12 , but maintains a substantially constant pressure/force on the articles. The constant force is particularly advantageous when passing thicker articles, as for example shown in FIG. 4B, in that it applies the same amount of force to the article no matter how far the head is deflected. This differs from a standard extension spring which applies a greater amount of force as it is extended. A greater force applied to thicker articles could cause stalling of the article under the doubles resolver head, resulting in jams and possible damage to the articles being fed. 
     In operation, because of the relatively low vacuum pressure on head  40 , and because of the angle of surface  42 , single pieces of mail or other flat articles are able to pass under head  40 . Further, because of their momentum leaving singulation mechanism  14 , and because the spacing between wall  36  and roller  32  is less than the length of the shortest article being singulated, articles being singulated thus being driven during their entire passage past doubles resolver mechanism  18 , articles normally pass the doubles resolver without getting significantly slowed down or stopped. However, as may be seen in FIG. 5, when a double is passed under head  40 , the outside piece  12 ′ is not touching either of the drive belts  20 ,  28 , and is therefore contacted only by the vacuum double resolvers head  40 , which is therefore effective to grab and hold such doubled article. Because wall  36  will prevent a relatively large double from being passed, it can be assumed that any double to be resolved by mechanism  18  is significantly less than maximum in both thickness and weight so that the relatively low vacuum applied to surface  42  of head  40  is more than adequate for holding such doubles. The assumption of relatively thinner and lighter doubled articles is further supported by the fact that the inertia of a heavy article would prevent it from being doubled. Conversely, the inner article  12  does not touch resolver head  40  in a situation where there is a double, and therefore continues to be passed by a drive belt to the take away mechanism without being engaged or impeded by resolver head  40 . 
     A photocell or other suitable sensor F 1  senses when an article is in the space thereunder between the singulation and take away mechanisms and is not moving. Appropriate software in it a processor controlling the operation, by checking for example photocells F 1 , F 2  and F 3 , assesses the situation and determines that there is a resolved double being held by head  40 . In response to this determination, a valve (not shown) connecting vacuum line  46  to port  44  is turned off, momentarily removing vacuum from head  40 . When this occurs, the doubled article  12 ′ is forced back toward at least one of belts  20  and  28  by the action of air spring cylinder  56 . At the same time, vacuum chamber V 2  may be energized to provide drive to the article so that it may reach take away mechanism  16 , and in particular pinch rollers  32  thereof. This permits the doubled article  12 ′ to be cleared. 
     One problem in feeding articles such as mixed mail is that some of the mail articles are soft-covered catalogs, magazines and the like which are bound on only one side. To permit handling of such articles, the system is designed to have such articles fed bound-edge down. To permit resolving of doubles on such articles, head  40  is positioned approximately midway on the height of the smallest articles to be fed, for example 2″ from the bottom of the article where the smallest article is 4″×4″. At this height, the vacuum deals with the strongest portion of the article, the portion near the bound edge, thereby minimizing damage over the larger volume. 
     FIGS. 3A and 3B illustrate an alternative embodiment of the invention which utilizes the same shafts  48 , bearing pillow block  52  and pneumatic air cylinder  56  as for the prior embodiment, but utilizes a different head mechanism  40 ′. In particular, instead of having a fixed angular position for operative surface  42  relative to the direction of article movement as for the embodiment of FIGS. 2A and 2B, this embodiment of the invention mounts head  40 ′ so as to be rotatable about a hollow shaft  80 . Thus, in addition to an article causing head  40  to be raised against the force applied by air cylinder  56  as shown in FIGS. 4A and 4B, the head preferable being normally at a slight angle, for example 1.5°, as for the prior embodiment, to facilitate this action, an article passing under the head also causes the head to rotate from the normal position shown in FIG. 3A to the rotated position shown in FIG. 3B against the force applied to head  40 ′ by a spring-loaded pin  82 . Hollow shaft  80  has vacuum on vacuum line  46  applied thereto. There are two slots  84  in the wall of shaft  80  which, when the head is in the position shown in FIG. 3A, align with corresponding openings  86  in a fixed ring  88  surrounding the shaft to permit vacuum to be applied through the head to the openings of operative surface  42 . However, when the shaft is rotated as shown in FIG. 3B, openings  84  and  86  do not align, cutting off vacuum to the vacuum head. Shaft  80  and ring  88  thus form a passive valve for cutting off vacuum when head  40 ′ is substantially fully rotated. The small amount of rotation described above causes a peeling action on any double engaged by the resolver head to assure separation of the doubled article from the article  12  thereunder which is being fed. The movement of head  40  against the pressure of air spring cylinder  56  deals with thicker and heavier articles, providing increased movement and greater peeling action. The passive valve discussed above automatically releases the doubled article as the article  12  being singulated passes, permitting the doubled article to be cleared either automatically as a result of the slight forward momentum which the article still has as a result of the rotating action, or by for example reenergizing vacuum chamber V 2  as discussed above. 
     Thus, a doubles resolver mechanism has been provided which is capable of resolving doubles in mixed mail or other applications where articles of substantially different size, thickness and weight are being handled. While cylinder  56  is shown as an air cylinder for preferred embodiments, and air pressure is preferred because of its ready availability in most facilities where such a machine would be utilized, in a suitable application, a hydraulic cylinder might be utilized or some other constant pressure “spring” mechanism might be employed. Other details in design of mechanism  18  may also be varied with application. Thus, while the invention has been particularly shown and described above with reference to preferred embodiments, the foregoing and other changes in form and detail may be made therein by one skilled it the art while still remaining within the spirit and scope of the invention which is to be defined only by the appended claims.