Method and device for improving stacker conveyor speed in a mail stacker

A method and device for stacking a plurality of vertically oriented mailpieces into a stack, wherein mailpieces are sequentially received into the back end of the stack. A paddle is used to support the front end of the stack in order to prevent the top mailpieces from falling forward. A conveyor belt is used to move the mailpieces in the stack and relieve the pack pressure so as to allow new mailpieces to join the stack. Information indicative of the mailpiece thickness is provided to a movement control module so that the conveyor belt is moved according to the thickness of the mailpieces received into the stack. As such, the pressure in the stack can be properly adjusted. The thickness information can be obtained from an upstream collator, for example.

TECHNICAL FIELD

The present invention relates generally to a mail stacking machine and, more particularly, to a vertical, or on-edge, stacker using a roller to move an input mailpiece into the back end of a mail stack.

BACKGROUND OF THE INVENTION

A mass mailing system generally comprises a mail inserting machine and a mail stacking machine. The mail inserting machine includes an envelope feeder and an enclosure document supply section. The envelope feeder is used to feed envelopes, one at a time, to an envelope insertion station. In the enclosure document supply section, a plurality of enclosure feeders is used to release enclosure documents to a chassis. The released documents are then gathered, collated and pushed by a plurality of pusher fingers to the envelope insertion station for insertion. Mail inserting machines are known in the art. For example, Roetter et al. (U.S. Pat. No. 4,169,341) discloses a mail inserting machine wherein documents are released onto a continuous conveyor mechanism to be collected and collated in a continuous process. If necessary, the collation can be folded such that each document is folded into two or more panels. Folding machines are known in the art. For example, Beck et al. (U.S. Pat. No. 4,701,233) discloses a method of folding a sheet by bulging a portion of the sheet and then folding the bulged portion through a roller nip. Marzullo (U.S. Pat. No. 4,875,965) discloses a folding apparatus wherein a buckle chute is used for stopping a sheet, causing the sheet to enter a roller nip for folding. After the enclosure documents are inserted into the envelopes, the filled envelopes are typically transported to another piece of equipment that seals the envelopes and affixes postage or prints a postage indicium on each envelope.

The filled envelopes are typically collected and loaded by an operator into mail trays or other forms of storage. This step in the mass mailing process has been found to be a “bottleneck”. One way to assist the operator in eliminating the bottleneck is to use an envelope stacking machine to automatically collect the filled envelopes into a stack so that the operator can remove the filled envelopes in stacks. One of the commonly used envelope stackers is an on-edge stacking apparatus. For example, Keane et al. (U.S. Pat. No. 6,388,204) discloses a mail stacking machine where a belt turn-up unit is used to turn the filled envelope from a horizontally facing direction to a vertical or “on-edge” position. The vertically oriented envelope is driven by a segmented roller into the back end of a vertical stack.

A typical mass mailing system is shown inFIG. 1. The mass mailing system1comprises a document collating station10, a folding device20, a mail inserting station30, a mail input device40and a mail stacker100. As shown inFIG. 2, a plurality of documents12, which are released by a plurality of document feeders in the collation station10, are collated into a stack or collation14as the documents are moved toward the mail inserting station30. If necessary, the stack14is folded into a folded stack22prior to the documents being inserted into an envelope32. After the stuffed envelope is scaled, it is referred to as a mailpiece50. The mailpiece50is turned from a horizontally facing position to a vertical position by the mail input device40. The vertically oriented mailpiece50is driven into the back end64of a vertical mail stack60in the mail stacker100. The mailing system1also has a central control module70, which is operatively connected to all of the sub-systems10,20,30,40and100in order to coordinate the operation in the sub-systems. For example, if one of the sub-systems is non-functional, it may be necessary to stop all other sub-systems to avoid a jam. Furthermore, the central control module70is also used to control the document feeders in the collation station10so that only a predetermined number of documents are released to form a stack for mail insertion.

A typical stacking machine100, as shown inFIG. 3, has an incoming mailpiece moving device110to move a mailpiece50released from the mailpiece input device40into a stacking deck120along a moving direction250. The mailpiece50is further driven into the back end64of the mail stack60. The stacking deck120has an upstream end202and a downstream end204. As more mailpieces50are added to the back end of the mail stack60, the stack60expands or grows toward the downstream end204of the stacking deck120. As the stack expands, the pressure on the incoming mailpiece increases. In order to relieve the stack pressure, a conveyor belt130moving along a direction230is used to space out the stacked mailpieces, thereby making room for the next incoming mailpiece50to join the stack60. At the same time, a paddle140is used to support the front end62of the stack, preventing the top mailpieces in the stack from falling toward the downstream end. The paddle140is movably disposed on a linear rod144for movement. The linear rod, which is substantially parallel to the moving direction230, is fixedly mounted on rod mounts146.

In order to achieve optimal operational efficiency, the rate at which the mailpiece input device feeding the mailpieces into the mail stacker is substantially equal to the rate at which the document stack is inserted into the envelope32in the mail inserting station. Furthermore, the insertion rate should also be equal to the rate at which the documents are released by each document feeder.

At the same time, the conveyor belt130is adapted to move at a certain speed in order to relieve the pressure in the mail stack. If the conveyor belt moves too slowly, the mailpieces will be packed too tightly. After a short time, a new mailpiece will not be able to squeeze into the stack and it will jam. If the conveyor belt moves too fast, the pack pressure will be too light and the mailpieces will move around as they settle down. In that situation, if an incoming mailpiece hits one of the mailpieces in the stack that is out of position, a jam may occur. Moreover, if the pack pressure is too light, the operator has to clear the stack more frequently. This makes the stacker less effective.

It is possible to set the speed of the conveyor belt130according to the feeding rate of the mailpiece input device40. For example, the speed of the conveyor belt can be set in proportion to the feeding rate. Alternatively, the speed of the conveyor belt130can be manually adjusted by an operator so as to adjust the pack pressure. However, the pack pressure is not only affected by the feeding rate but by other factors as well. For example, when the mail stacker is first turned on, the motor that drives the conveyor belt is cold. The motor runs faster than when it has warmed up. This requires the operator to adjust the speed at the start up time and again after a few minutes as the machine starts to warm up. Manual adjustment, however, is not always consistent. It relies heavily on the experience of the operator.

One of the major pressure-related problems is caused by the variation of the thickness of the mailpieces. The stack pressure increases as the thickness of the mailpieces increases. If the speed of the conveyor belt is set for thin mailpieces, then this speed will not work well for thick mailpieces, because the stack pressure will rapidly increase, thus quickly causing a full jam. Even if a full jam does not occur, the late arriving mailpieces may not be stacked properly. As such, the edge of the mail stack will not form a straight line, causing a problem for the operator when the mail stack has one or more zip-code breaks. In a typical mail stacker, when the control system is designed to indicate to an operator a zip-code break, a mail stop is moved in front of a registration wall so that the incoming mailpieces stop at the mail stop instead of the registration wall. The thickness of the mail stop is usually about ¾″, and the edge of the newly-arriving mailpieces is supposed to shift about the same amount. The shift at the edge serves as an indication to the operator that this is an important point in the stack. When the stack pressure is too high, however, the mailpieces may not be properly stacked to indicate the zip-code break.

It is advantageous and desirable to provide a method and system to control the movement of the conveyor belt so that the pressure in a mail stack can be properly maintained.

SUMMARY OF THE INVENTION

It is a primary objective of the present invention to control the movement of the conveyor belt in a mail stacker so as to maintain a proper pressure in the mail stack. This objective can be achieved by adjusting movement or displacement of the conveyor belt according to the thickness of the mailpieces based on the thickness information provided by the central control module of a mass mailing system.

Thus, according to the first aspect of the present invention, a method of adjusting mail stack pressure in a mail stacking device, wherein the mail stacking device is adapted to stack a plurality of mailpieces into a stack, each mailpiece having a thickness. The stacking device comprises:a stacking deck having an upstream end and a downstream end;a moving mechanism disposed on the stacking deck for supporting the stack, the stack having a first end and a second end;a supporting means positioned relative to the moving mechanism for supporting the second end of the stack;a mailpiece receiving mechanism, disposed at the upstream end of the stacking deck, for sequentially receiving mailpieces into the first end of the mail stack, wherein for each received mailpiece, the moving mechanism is adapted to move in a moving direction from the upstream end toward the downstream end so as to adjust the pressure in the stack due to receipt of said mailpiece in the stack, said method comprising the steps of:obtaining information indicative of the thickness of the received mailpiece in the stack, andadjusting the movement of the moving mechanism in the moving direction based on the thickness of the received mailpiece.

Preferably, when each mailpiece includes one or more sheets of enclosure materials, the information is partially based on the number of sheets of the enclosure materials.

Preferably, when the enclosure materials are folded, the information is partially based on the number of panels each sheet of the enclosure materials is folded into, the information is partially based on the total number of panels.

Preferably, when each mailpiece includes enclosure in an envelope, the information is partially based on the thickness of the envelope.

Preferably, the movement of the moving mechanism is effected by a plurality of displacement steps, and the displacement is adjusted based on the thickness of the received mailpiece.

Alternatively, the moving mechanism has a moving speed to effect the movement, and the moving speed is adjusted based on the thickness of the received mailpiece.

Advantageously, the stacker further comprises a sensing means for sensing the pressure in the stack, and the movement of the moving mechanism is also adjusted according to the sensed pressure.

According to the second aspect of the present invention, a mail stacking device for stacking a plurality of mailpieces into a stack, each mailpiece having a thickness. The stacking device comprises:

a stacking deck having an upstream end and a downstream end;

a moving mechanism disposed on the stacking deck for supporting the stack, the stack having a first end and a second end;

a supporting means positioned relative to the moving mechanism so as to support the second end of the stack;

a mailpiece receiving mechanism, disposed at the upstream end of the stacking deck, for sequentially receiving mailpieces into the first end of the mail stack, and

a control mechanism, operatively connected to the moving mechanism, for controlling the moving mechanism, wherein for each received mailpiece the moving mechanism is adapted to move in a moving direction from the upstream end toward the downstream end so as to adjust pressure in the stack due to receipt of said mailpiece in the stack, and the control mechanism is adapted to receiving information indicative of the thickness of the received mailpiece so as to adjust the movement of the moving mechanism in the moving direction based on the thickness of the received mailpiece.

Preferably, the movement of the moving mechanism is effected by a plurality of displacement steps, and the displacement is adjusted based on the thickness of the received mailpiece.

Preferably, the stacking device further comprises a driving mechanism for causing the displacement of the moving mechanism, and the control mechanism comprises an encoder operatively connected to the driving mechanism for adjusting the displacement.

Alternatively, the moving mechanism has a moving speed to effect the movement, and the moving speed is adjusted based on the thickness of the received mailpiece.

According to the third aspect of the present invention, a mailing system comprising:

a mail inserter for inserting enclosure materials into envelopes for providing mailpieces, anda mail stacking device, operatively connected to the mail inserter for sequentially receiving the mailpieces for stacking the received mailpieces into a stack, each mailpiece having a thickness. The stacking device comprises:

a stacking deck having an upstream end and a downstream end;

a moving mechanism disposed on the stacking deck for supporting the stack, the stack having a first end and a second end;

a supporting means positioned relative to the moving mechanism so as to support the second end of the stack;

a mailpiece receiving mechanism, disposed at the upstream end of the stacking deck, for inserting the sequentially received mailpieces into the first end of the mail stack, and

a control mechanism, operatively connected to the moving mechanism, for controlling the moving mechanism, wherein for each received mailpiece the moving mechanism is adapted to move in a direction from the upstream end toward the downstream end so as to adjust pressure in the stack due to receipt of said mailpiece in the stack, and the control mechanism is adapted to receiving information indicative of the thickness of the received mailpiece so as to adjust the movement of the moving mechanism in the moving direction according to the thickness of the received mailpiece.

The present invention will become apparent upon reading the description taken in conjunction withFIGS. 4 to 5.

BEST MODE TO CARRY OUT THE INVENTION

The method of adjusting the pack pressure in the mail stacker, according to present invention, is substantially based on the thickness of the incoming mailpieces50that are received into the stack60. When the thickness is known, the displacement of the conveyor belt130along the moving direction230can be adjusted accordingly. It should be noted that the movement of the conveyor belts130along the moving direction230can be intermittent or continuous. Preferably, the movement is intermittent in that it is effected by a plurality of discrete steps, and each of the steps has a displacement distance. When the thickness is known, the displacement distance can be adjusted accordingly. Preferably, the information indicative of the thickness of the mailpiece50is obtained from the central control module70, which monitors and controls the collation as it enters the chassis of the collation station10(FIG. 3). The collation is usually made up of a variable number of sheets of enclosure materials. These sheets of enclosure materials may be folded once or twice. For example, the central control module70should be able to indicate to the mail stacker100that the collation consists of four pages with two folds, for example. Because two folds make three panels, four folded pages are equal to 12 panels. Thus, the enclosure thickness is substantially equal to the thickness of 12 sheets. Knowing the thickness of the paper gives a direct value of the total thickness of the panels. This direct value can be used to adjust the displacement of the conveyor belt130along the moving direction230. Furthermore, the thickness of the envelope32(FIG. 2) should also be taken into consideration. For example, the thickness of the envelope can be manually entered into the central control module70every time a new batch of envelopes is used for mailing. Alternatively, thickness information of different types of envelopes can be stored in the central control module70.

To facilitate the speed or movement adjustment, a motor control module174, as shown inFIG. 4, is operatively connected to the central control module70in order to obtain the thickness information270from the control module70. As shown inFIG. 4, the conveyor belt130is looped around two rollers150and driven by a motor170. The control module70can control the distance the motor moves, and this distance translates into the distance the conveyor belt moves. The conveyor belt130can be moved in small steps, but it can also be moved in a constant speed. Advantageously, an encoder172of a certain resolution is operatively connected to the motor170to monitor the moving distance of the motor170and, thus, the displacement of the conveyor belt130. The encoder172is also operatively connected to the motor control module for providing thereto information272indicative of the moving distance of the motor170. Based on the information270and272, the motor control module determines the distance the conveyor belt needs to move. In particular, the encoder172is mounted on the shaft of the motor170. For example, the encoder172comprises a disk having five evenly spaced holes and a stationary photosensor aligned with the holes in order to read the transition in light intensity as the photosensor is blocked and unblocked when the holes pass by the photosensor. Five holes produce ten transitions, or counts, for position detection. Furthermore, a motor170is engaged with a gearbox having a gear ratio of 180 to 1. This is equal to 1800 counts per revolution of the gearbox. Furthermore, the pulley linking the roller150to the output of the gearbox is designed such that the conveyor belt130is displaced by 166.5 mm per revolution of the gearbox. Accordingly, the encoder172can measure the displacement of the conveyor belt130to a precision of 92.5 microns. With such precision, the motor control174is more than adequate to adjust the movement of the conveyor belt130according to the thickness of the incoming mailpiece50. With the encoder172in place, the motor control module174obtains the resolution (precision) when it starts and uses the resolution whenever the conveyor belt130needs to move a certain distance. In a distance-based approach, the motor170is turned on when a new mailpiece50arrives and turned off when the conveyor belt130has moved a desired distance. As such, whether the motor170is cold or warmed-up does not affect the pressure in the mail stack60. In this approach, the conveyor belt130makes a large number of small steps as it moves in the moving direction230. However, the speed of the conveyor belt130in this intermittent movement should be high enough to move an incoming mailpiece of any anticipated thickness and to provide ample time to accommodate the next mailpiece.

In a time-based approach, the speed of the conveyor belt130is increased to a level high enough to move mail of any thickness. But when the displacement of the conveyor belt130has reached a desired distance, the speed of the motor170is adjusted according to the thickness of the incoming mailpiece50. As such, the conveyor belt130appears to move in a continuous fashion as the mailpieces continue to enter into the stack60.

Advantageously, a sensor is provided in the mail stacker to monitor the pack pressure, as shown inFIG. 5. As shown inFIG. 5, the pack pressure sensor180is disposed behind the back end64of the stack60. The pack sensor is also operatively connected to the motor control module174. When a new mailpiece50is received into the stacking deck120, the pack pressure is examined by the pack sensor180. If the sensor indicates high pack pressure, then the motor control module174causes the conveyor belt130to move by a distance substantially equal to the thickness of the received mailpiece. If the pack sensor is still indicating a high pressure on the next mailpiece arrival, then the moving distance of the conveyor belt should be increased. Preferably, the increased amount is also based on the thickness of the received mailpiece. The moving distance is progressively increased until the pack sensor does not indicate a high pack pressure. The pack sensor180comprises a mechanical switch that can be activated by a spring lever when the lever is pressed by the back end of the stack60, for example.

It should be noted that the moving speed adjustment method, according to the present invention, can be made independently of the rate at which the mailpieces are received into the stack. Every time a mail piece is received, the conveyor belt can be caused to move a distance substantially equal to the thickness of the received mailpiece. Preferably, the motor control can be informed by the central control module when a new mailpiece arrives at the mail stacker, so that the conveyor belt is moved accordingly. Alternatively, a sensing device190can be used to monitor the arrival of a new mailpiece. However, it is also possible to adjust the moving speed of the conveyor belt according to the rate at which the mailpieces are received into the stack as well as the thickness of the mailpiece.

Although the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.