Abstract:
A multi-stage, serpentine-shaped buffer has an entry area for receiving documents, a first level comprising a first plurality of document stages, a first turn-around for substantially reversing the direction of document travel following said first plurality of stages, a second level vertically adjacent to said first level, said second level comprising a second plurality of document stages, a second turn-around for substantially reversing the direction of document travel, and a third level vertically adjacent to said second level, said third level comprising a third plurality of document stages.

Description:
This Application is a continuation of U.S. application Ser. No. 08/544,811, filed Oct. 18, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This Application is related to U.S. application Ser. No. 08/544,811 entitled &#34;HIGH THROUGHPUT DOCUMENT-PROCESSING MACHINE HAVING DYNAMIC SPEED CONTROL,&#34; filed on Oct. 18, 1995, now abandoned on behalf of David Nyffenneger, et al. The entire disclosure of that application is incorporated herein by reference. 
     1. Field of the Invention 
     The invention relates in general to machines for automated processing of mailpieces, and in particular to a serpentine multi-stage buffer for queueing a plurality of documents or document sets. 
     2. Related Art 
     Computer-controlled insertion machines have been known for providing high-speed, automated insertion of documents into envelopes. Such insertion machines typically include a form feeder, or &#34;roll unwind,&#34; for supplying a web of attached sheets (or a sheet feeder for supplying individual sheets), with several adjacent sheets being associated together as a set; a burster or cutter for separating the web into individual sheets, those sheets including for each set a master document having an optical mark thereon for providing insertion instructions and other information about the set; a reader for reading the optical mark and providing the information therein to a central computer; an accumulator for accumulating individual sheets fed seriatim thereto into stacked sets; a folder for folding the sets; a series of insert hoppers for selectively feeding inserts onto the folded sets as the sets travel past the hoppers on an insert track/conveyor; an insert station for inserting each set and its associated inserts into an envelope; a sealer for sealing and closing the flap on the envelopes; and, a postage meter for applying postage to the completed mail piece. 
     Sheet-retarding devices have been used in document-processing machines of the prior art for temporarily slowing and/or stopping a mailpiece or other document as it travels along a conveyor. Such devices are typically provided for purposes of registering a document and/or ensuring that the same predetermined distance exists between each successive document. Sheet-retarding devices of the prior art typically include a gate which is selectively actuated by a rotary solenoid such that the gate drops down to momentarily restrict movement of a document along the conveyor. Once registration and/or delay of the mailpiece is complete, the gate is retracted by the solenoid and the document continues along the conveyor. 
     While sheet-retarding devices of the prior art have been provided for purposes of ensuring a uniform distance between documents output therefrom, such devices have failed to provide a means for adequately reducing a document throughput rate when that rate becomes higher than the rate at which a downstream device (such as a downstream inserter) can receive documents. The devices of the prior art typically have only one or two staging areas, e.g., areas where documents are slowed or halted, and therefore lack the mechanical staging capacity to provide adequate throughput rate compensation. Further, such devices lack the control logic and timing required to compensate for variations in the distance between documents fed thereto. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an improved document-staging device. 
     It is a further object of the invention to provide a document staging device with increased staging capacity. 
     It is a further object of the invention to provide a document-staging device which can compensate for large variations in the rate at which documents are delivered thereto. 
     It is a further object of the invention to provide a multi-stage document-staging device having a small footprint. 
     In a preferred embodiment, the invention provides a multi-stage, serpentine-shaped buffer having an entry area for receiving documents, a first-level comprising a first plurality of document stages, a first turn-around for substantially reversing the direction of document travel following said first plurality of stages, a second level vertically adjacent to said first level, said second level comprising a second plurality of document stages, a second turn-around for substantially reversing the direction of document travel, and a third level vertically adjacent to said second level, said third level comprising a third plurality of document stages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings, in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention. 
     FIG. 1 illustrates a partial left side elevational view of a multi-stage buffer of the invention. 
     FIG. 2 illustrates a partial right side elevational view of a multi-stage buffer of the invention. 
     FIG. 3 illustrates a left-side perspective view of a lower frame assembly of the buffer device of the invention. 
     FIG. 4 illustrates a right-side perspective view of an upper frame assembly of the buffer device of the invention. 
     FIG. 5 illustrates a partial view of the lower frame assembly with certain parts removed to show the stop gate assemblies. 
     FIG. 6 illustrates a right side elevational view of a belt transport system of the invention. 
     FIG. 7 illustrates a perspective view of a stop gate assembly of the invention according to a preferred embodiment. 
     FIG. 8 illustrates a side elevational view of a stop gate assembly of the invention according to a preferred embodiment. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 illustrate partial left and right side views, respectively, of a multi-stage buffer of the invention according to a first embodiment. The buffer of the invention is used, e.g., between an asynchronous upstream device (such as an accumulator) and a downstream synchronous device (such as an insertion section of an insertion machine). The buffer of the invention may be used to compensate for temporary document throughput speed changes at the accumulator such that documents are delivered to the downstream insertion section at a constant, optimized rate. 
     The buffer comprises a generally C-shaped upper frame assembly 40 and a generally C-shaped lower frame assembly 41. The assemblies 40 and 41 are interlocked as shown in FIGS. 1 and 2 to define an S-shaped path therebetween. Document sets enter the buffer and proceed along the S-shaped path past a series of eight stages. In the preferred embodiment, three stages are provided in the lower level of the S-shaped path, two stages are provided in the middle level, and three stages are provided in the upper level. 
     At each stage is a stop gate controlled by an associated rotary solenoid S1 through S8. If it is desired that a set be stopped at a particular stage, the solenoid at that stage is actuated and its associated stop gate is thereby caused to obstruct the document path and stop the set at that stage. When the set is to be released, the solenoid is reversely actuated, causing the gate to retract, thereby permitting the document to continue along the S-shaped path. 
     A multitude of product sensors C1 through C12 are located along the S-shaped path to track individual sets through the device and to monitor proper transport and detect any jams. The sensors C1 through C12 are positioned at the entry, exit, each loop turn-around and one in each of the eight buffer stages. The sensors in each of the eight buffer stages are used, e.g., to permit a dynamic speed control system to determine the number of buffer stages which are filled and to increase or decrease the speed of devices upstream from the buffer accordingly. 
     FIGS. 3 and 4 illustrate a left-side perspective view of the lower frame assembly 41 and a right-side perspective view of the upper frame assembly 40, respectively. Each solenoid S1 through S8 has associated with it a stop gate G1l through G8. The stop gates are illustrated and discussed in more detail below with reference to FIG. 5. The lower frame assembly 41 is attached to a first support frame 39 and the upper frame assembly 40 is attached to a second support frame 38. When the upper and lower frame assemblies are interlocked (as shown in FIG. 1), these support frames are at opposite ends of the interlocked assemblies. 
     FIG. 5 illustrates a partial view of the lower frame assembly with certain parts removed to show the stop gate assemblies. It should be noted that the a stop gate assembly 54 is attached to the shaft of its associated rotary solenoid via press pins 27 and solenoid levers 25 such that actuation of the solenoid causes the stop gate to rotate about its axis 57. The stop gate assembly 54 includes two gate fingers 55 which rotate into and out of the document path when the solenoid is actuated and reversely actuated, respectively. A spring 20 biases the solenoid levers 25 such that the stop gate assembly 54 remains in a &#34;closed&#34; position (i.e., it is positioned such that its gate fingers 55 obstruct the document path) when the associated solenoid is not active. 
     FIG. 6 illustrates a schematic side elevational view of a belt system for transporting sets along the S-shaped document path. The system generally comprises two belts 61 and 63 which engage a series of rollers, with at least one of the rollers being driven by a motor (FIG. 1) at a substantially constant speed. While FIG. 6 illustrates a right side view, it should be understood that a second, similar belt system would be seen from a left side view. FIG. 6 also illustrates the stop gate assemblies G1 through G8 at each of the stages. Stop gate assembly G8 is shown in the &#34;closed&#34; position, and the remaining gate assemblies are shown in the &#34;open&#34; position. 
     A document set enters the buffer at the nip between a pair of rollers R1 and R2 and is then engaged on its top and bottom broad sides by belts 61 and 63, respectively. The set proceeds between the belts along the lower level and ultimately reaches the roller R3, where reverses direction by being transported around the roller R3. The set then proceeds between the belts along the middle level and ultimately reaches the roller R4, where it reverses direction once again by being transported around the roller R4. The set then travels between the belts along the upper level until it reaches the nip between roller R5 and R6, whereupon it is released from the buffer. 
     A document in the eighth stage, i.e., the final stage, is released upon request by the host inserter for a new document. The first, second, fourth, sixth, and seventh stages, which are the stages that do not directly preceed a turn around, are released when either the next stage is empty or a set in the next stage clears the sensor in the next stage. The third and fifth stages, which directly preceed the turn-arounds, are released when either the next associated stage is empty or the next associated stage is released. The third and fifth stages will also be released when a set entering the next associated stage will be released immediately and that set reaches the lead edge sensor in the turn around. In each stage, the gate solenoid associated with that stage is de-energized when the set clears the sensor in the stage. The solenoids are all normally de-enegerized. 
     A first document set in a series is delivered to the buffer by the upstream accumulator (or other asynchronous upstream device) and enters the S-shaped path of the buffer. The first document set travels past the first seven stages of the buffer without stopping, and stops at the eighth stage. Assuming that the downstream insertion section is ready to receive the first document set, the set is released from the buffer and proceeds to the insertion section in synchronicity with the insertion section&#39;s machine cycle. 
     If subsequent document sets are then delivered to the buffer at a constant throughput speed which is approximately equal to the rate at which the insertion section can receive them, then they too will travel unobstructed past the first seven stages, pause briefly at the eighth stage, and be delivered to the insertion section. 
     However, if the accumulator then begins to output documents to the buffer at a higher speed such that a document set would arrive at the eighth stage before the preceding set has been released to the insertion section, then the solenoid S7 at the seventh stage will be actuated and cause that set to pause at the seventh stage while the eigth stage is occupied. At this point, the eighth and seventh stages of the buffer are said to be &#34;filled.&#34; 
     In this respect, it will be understood by those skilled in the art that subsequent throughput speed increases at the accumulator will result in more buffer stages being filled at a given time, and subsequent throughput speed decreases will result in fewer buffer stages being filled. 
     FIG. 7 illustrates a stop gate assembly 54 of the invention according to a preferred embodiment. In addition to the gate fingers 55, the stop gate assembly 54 after includes a document-deceleration tire, or &#34;ramp&#34; 101. The document-deceleration ramp 101 imparts a deceleration to a document approaching the gate fingers 55, and preferably comprises a polymer material with a suitable coefficient of friction for performing that function. Such materials include, e.g., acetal resin materials such as highly-crystalline polyformaldehyde homopolymers. These materials are marketed by E.I. Dupont De Nemours and Company under the name &#34;DELRIN. &#34; The document-deceleration ramp 101 is fastenened to the body of the gate assembly 54 via conventional means. 
     FIG. 8 illustrates a side elevational view from the perspective &#34;A--A&#34; of the stop gate assembly illustrated in FIG. 7. An anti-bounce-back plug 105 is inserted into a hole drilled in the lower surface of the document-deceleration ramp 101, and is held therein via a friction-fit. The anti-bounce back plug 105 is of a material which has a higher co-efficient of friction than the material of the document-deceleration ramp 101, and serves to further decelerate an approaching document 103 prior to the document&#39;s impact at the gate fingers 55 but subsequent to initial deceleration by the document-deceleration ramp 101. The combination of the anti-bounce-back plug and the document-deceleration ramp provides improved resistance to document bounce-back, while avoiding curling and other forms of paper jams. The anti-bounce-back plug 105 preferably comprises a suitable high-coefficient-of-friction polymer material, such as copolymers and terpolymers of vinylideneflouride hexaflouropropylene and tetraflouroethylene (commercially-available from the E.I. Dupont De Nemours and Company under the name &#34;VITON&#34;), or neoprene. The anti-bounce-back plug 105 is preferably removable for replacement due to wear. Plugs of different materials having various coefficients of friction can be used interchangeably to match the particular document material. 
     While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, while an S-shaped buffer having three levels has been described herein, a buffer within the scope of the invention may comprise additional levels if, e.g., more than eight stages are desired.