Method and system for transporting mailpieces in a printing station

The present invention describes a double belt transport system for moving a mailpiece into a printing area of a digital printer. The transport system includes an upper belt and a lower belt. The upper belt has a straight section to form a nip with the lower belt to ingest the mailpiece. The straight section also defines a registration plane to register the upper surface of the mailpiece with respect to the print head of the printer. In order to make sure the registration is consistent regardless of the thickness of the mailpiece, an up-lifting mechanism is used to push the bottom of the mailpiece in an upward direction against a shield plate, which is positioned substantially on the registration plane. A velocity measurement device, such as an optical encoder, is used to measure the moving speed of the belts so that the printing speed of the digital printer matches the moving speed of the mailpiece in the print area.

TECHNICAL FIELD

The present invention relates generally to a transport system that uses driving belts to move mailpieces and, more particularly, a transport system to move a mailpiece into a printing station to be printed with an indicia, address, advertisement slogan, or other image.

BACKGROUND OF THE INVENTION

Mailing machines utilizing an inkjet printer to print an indicia on a mailpiece are well known. Typically, an inkjet printer uses a print head consisting of one or more rows of nozzles to apply ink droplets over a printed area on the mailpiece surface. Because the printing must be completed over a period of time while the mailpiece moves past the nozzles, the printed image on the mailpiece could be distorted if the mailpiece is not moved in accordance with a specified speed or along a specified direction. Furthermore, the distance between the mailpiece surface to be printed and the nozzles must be appropriately spaced so as to avoid contact by the mailpiece surface with the nozzles.

For imaging, printers typically use rollers to move a substrate into the printing area while also limiting the gap to maintain image quality. These printers do not provide a mechanism to maintain the correct distance between the substrate surface and the print head for a wide range of substrate thickness. While those printers can be used to make print on regular paper stocks or postcards, they are not designed for printing mailpieces the thickness of which can vary considerably. Furthermore, in a printer that uses belt and rollers to ingest the mailpiece, the hard nip formed by the driven belt and rollers could cause the mailpiece to slow down relative to the transport belt when the mailpiece hits the hard nip. Moreover, if the mailpiece is guided by one or more nips formed by the driven belt and rollers, the motion of the mailpiece could be skewed such that the mailpiece may not travel along a specified direction through the printing area of the printer. The skewed motion of the mailpiece may distort a printed image printed by an inkjet printer or the like.

It is advantageous and desirable to provide a transport system to mailpieces in a printer for digital printing, wherein the aforementioned disadvantages can be eliminated.

SUMMARY OF THE INVENTION

The first aspect of the present invention is a double-belt transport system having an upstream end and a downstream end for moving a mailpiece from the upstream end into a printing area of a printer, wherein the mailpiece has a lower surface and an opposing upper surface to be printed by a print head located in the printing area. The transport system comprises:

an upper belt looping around an input pulley and an exit pulley to form a straight section covering the printing area and defining a registration plane of the print head;

a lower belt having an intake section running from the upstream end towards the downstream end, wherein the input pulley and the intake section form an ingest nip for providing a friction force to move the mailpiece from the upstream end into the printing area for printing.

Preferably, the double belt transport system further includes a shield plate having a reference surface facing the direction of the inkjet drop trajectory and located substantially in the registration plane in the printing area so as to allow the upper surface of the mailpiece to press against the reference surface of the shield plate for registration.

Preferably, the double belt transport system also includes a lifting mechanism located below the lower surface of the mailpiece for urging the mailpiece to register against the shield plate so that the upper surface of the mailpiece is kept in contact with the straight section while the mailpiece moves through the printing area.

Preferably, the double belt transport system also comprises a deck having an upstream section and a downstream section, wherein the upstream section is located adjacent to the ingest nip for supporting the mailpiece when the mailpiece moves towards the ingest nip.

Preferably, the double belt transport system further comprises a driving mechanism to drive both the upper looping belt and the lower looping belt in order to reduce shearing on the mailpiece.

Preferably, the double belt transport system also comprises a velocity measurement mechanism, such as an optical encoder, operatively connected to at least one of the looping belts to ensure that the printing speed of the print head is consistent with the moving speed of the mailpiece in the printing area.

The second aspect of the present invention is a method of moving a mailpiece from a downstream end towards an upstream end into a printing area having a length, wherein the mailpiece has a lower surface and an opposing upper surface to be printed by a print head in the printing area. The method comprises the steps of:

providing an upper belt having a straight section located between an input pulley and an exit pulley running the length of the printing area for defining a registration plane of the print head; and

providing a lower belt having an intake section running from the upstream end towards the downstream end, wherein the intake section and the input pulley form an ingest nip to provide a friction force to move the mailpiece into the printing area for printing.

Preferably, the method also comprises the step of urging the mailpiece to move towards the upper belt so that the mailpiece surface is kept in contact with the straight section of the upper belt.

Preferably, the method further comprises the step of providing a shield plate having a reference surface facing the direction of the inkjet drop trajectory and located substantially on the registration plane in the printing area so as to allow the upper surface of the mailpiece to press against the reference surface of the shield plate for registration.

The third aspect of the present invention is a printer having an upstream end and a downstream end for printing on the upper surface of a mailpiece. The printer comprises a print head located above a printing area; and a double belt transport system for moving the mailpiece from the upstream end into the printing area, wherein the mailpiece has a lower surface opposing the upper surface, and wherein the double belt transport system comprises an upper looping belt having a straight section covering the printing area, wherein the straight section defines a registration plane regarding the print head; and a lower looping belt having a mailpiece intake section running from the upstream end towards the downstream end, wherein the mailpiece intake section and the straight section form an ingest nip for providing a friction force to move the mailpiece into the printing area for printing.

The present invention will become apparent upon reading the description taken in conjunction withFIGS. 1 to 5d.

DETAILED DESCRIPTION

FIG. 1illustrates the double belt transport system10of the present invention. Preferably, the transport system10is used to move a mailpiece1in a digital printer which uses a print head102, such as an inkjet print head or the like, to print text, graphics or an image on the mailpiece1. As shown, the transport system10comprises an upper belt12and a lower belt14for transporting the mailpiece1from the upstream end along an input direction202to the downstream end along an exit direction212. A deck16is used to support the mailpiece as the mailpiece enters and exits the transport system10. A lifting mechanism70located below the print head102is used to urge the mailpiece1to move upwards toward the print head102, while a shield plate80, the lower surface of which defines a registration plane110(FIG. 3), allows the upper surface of the mailpiece1to press against the lower surface of the shield plate80for registering the mailpiece1relative to the print head102. The registration plane110is separated from the print head102substantially by a fixed distance. For example, if the print head102includes one or more rows of inkjet nozzles to provide a plurality of ink droplets for printing, then the distance should be kept minimal to attain the best possible spatial resolution of the print head. However, the distance should also be kept far enough from the print head to avoid smearing of the ink droplets. This distance is seen as a gap between the print head102and the lower surface of the shield plate80. This lower surface substantially coincides with the interface between the upper belt12and the lower belt14, when the mailpiece1is not present at the interface, as shown inFIG. 2.

As shown inFIG. 2, the mailpiece1has an upper surface4to be printed by the print head102and an opposing lower surface6supported by the deck16. The upper belt12loops around idler pulleys22,26,28and a drive pulley30. The tension of the upper belt12is maintained by a tensioning idler32. The lower belt14loops around idler pulleys42,44and a drive pulley50. The tension of the lower belt14is maintained by a tensioning idler46. The upper belt12and the lower belt14form an ingest nip40to move the mailpiece1into the printing area112for printing. The upper belt12has a straight section24between the pulleys26and28running the length of the printing area112for holding the mailpiece1on both the upper surface4and the lower surface6in order to minimize skew of the mailpiece1as the mailpiece1moves through the printing area112. The ingest nip40is in fact a soft nip, which is formed gradually by the wedge-shaped gap between the upper belt12and the lower belt14at the upstream end. The ingest nip40prevents the mailpiece1from slowing down as it would if the ingest nip were a hard nip. The plane joining the tangent of pulley26and the tangent of pulley28is substantially parallel to the print plane or the registration plane110(FIG. 3). Both the upper belt12and the lower belt14are driven by drive pulleys30and50, respectively, in order to minimize shearing on the mailpiece1. The motor60and the driving belt62that drive the drive pulleys30and50are illustrated inFIG. 3.

When the mailpiece1is ingested into the printing area112by the ingest nip40, it has the tendency to bend downward. For a thin mailpiece, the straight section24of the upper belt12and the same section of the lower belt14can pinch the mailpiece tightly to keep it from moving away from print head102and the registration plane110. However, if the mailpiece is thick, puffy or flexible, the straight section24of the upper belt12and the lower belt14may not be able to keep the upper surface4of the mailpiece1from moving downward and away from the registration plane110. Thus, it is preferable to have a lifting mechanism70located below the registration plane110and underneath the printing area112, as shown inFIG. 3, to push the mailpiece1towards the print head102. Furthermore, a shield plate80having a lower surface82located substantially on the registration plane110is used to register the upper surface4of the mailpiece1precisely with respect to the print head102. It is preferred that the lifting mechanism70has an opening (not shown) right under the print head102so that the print head102will not accidentally print on the lifting mechanism70when the mailpiece1is not present in the printing area112. As shown inFIG. 3, a tensioning idler52can be used to form an input nip56with the input pulley42of the lower belt14in order to reduce skew when the mailpiece1is moved to the belts12,14from the upstream end. The tensioning idler52may slow down the mailpiece1slightly when the mailpiece1hits the input nip56. However, when the mailpiece1is engaged with the upper belt12and the lower belt14, it moves along with the belts12,14. Furthermore, in order to ensure that the printing is in synchronism with the mailpiece1in that the drop ejection frequency of the print head102is matched to the movement of the mailpiece1, it is possible to install an encoder90to be operatively engaged with the belts12,14to measure their moving speed.

As shown inFIG. 4, the encoder90is connected to an encoder wheel92, which is positioned between pulley26and pulley28of the upper belt12such that the encoder wheel92is rotated by the motion of the straight section24of the lower belt12(FIG. 2). The belts12,14are not shown inFIG. 4.

In summary, double belts minimize skew of the mailpiece because both the upper and lower surfaces of the mailpiece are held by the belts when it moves through the printing area. Accurate registration of the upper surface of the mailpiece is achieved by the straight section of the upper belt, the shield plate and the lifting mechanism. The lifting mechanism can be loaded upward with springs. A velocity measurement mechanism, such as an optical encoder, is used to measure the speed of the upper belt and, therefore, the speed of the mailpiece in the printing area. The measured speed can be used to coordinate with the activation of the inkjet nozzles of the print head. It is also possible to install one or more encoders to make contact with the mailpiece itself in order to measure the moving speed of the mailpiece.

The printer as described in conjunction withFIGS. 1 to 4is oriented in such a way that the registration plane110is substantially located on a horizontal plane. However, it should be understood by those skilled in the art that the registration plane can be located on an oblique plane or a vertical plane. Furthermore, the various pulleys in the double-belt transport system, according to present invention, can be substituted by rollers or other cylindrical elements capable of supporting the belts.

Furthermore, the width and the location of the lower belt14, in relation to the upper belt12, can be changed based on the width of the mailpiece1(FIG. 1). It is preferable to have the inner edge of the lower belt14be positioned as close to the print area112under the print head102as possible, as shown inFIG. 5a. This position can help bias a narrow mailpiece against the shield plate80. As shown inFIG. 5a, the lower belt14is slight wider than the upper belt12. However, the lower belt14can be narrower than the upper belt12, or both the lower belt14and the upper belt12are of the same width, as shown inFIG. 5b. Moreover, it is possible to extend the inner edge of the lower belt14to the other side of the print head102, as shown inFIG. 5c. Alternatively, in addition to the lower belt14, a second lower belt14′ can be used to advance the mail. However, the second lower belt14′ must be driven in synchronism with the lower belt14so as not to cause skew and lateral shift in the mail.

Thus, 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 spirit and scope of this invention.