GB2238759A

GB2238759A - Vacuum assisted document transport in selective printers

Info

Publication number: GB2238759A
Application number: GB9023449A
Authority: GB
Inventors: A Justine Worley; Harold R Berrey
Original assignee: Ricoh Printing Systems America Inc
Current assignee: Ricoh Printing Systems America Inc
Priority date: 1989-11-09
Filing date: 1990-10-29
Publication date: 1991-06-12
Anticipated expiration: 2010-10-29
Also published as: JPH03224767A; GB9023449D0; DE4035357C2; DE4035357A1; GB2238759B; JP3195792B2; BR9005551A

Abstract

A media transport mechanism including a high accuracy vacuum belt used in conjunction with a pinch roller assembly. The media transport mechanism includes a vacuum belt supportably wrapped around two sprocket assemblies and disposed in facing relation to a print head. The vacuum belt has two pinch roller assemblies disposed in spaced-apart relation across the front surface of the vacuum belt, with each pinch roller assembly including two pinch rollers which, in conjunction with the vacuum belt, grip and advance a sheet of media across the front surface of the vacuum belt during printing. The vacuum belt provides a vacuum hold-down force for holding the media flat against the front surface of the vacuum belt.

Description

0 b a is 2,-> --3 el -7 E.) C3 HIGH ACCURACY VACUUM BELT AND PINCH ROLLER

MEDIA TRANSPORT MECHMUSM BACKGitOUND

1. Field of the invention

The present invention relates to a media transport mechanism in a printer and in particular to a high accuracy vacuum belt used in conjunction with pinch roller assemblies for precise media handling.

2. Description of the Prior Art

The prior art devices will be discussed in terms of printers, although the concepts may be equally applicable to other devices having vacuum belts in conjunction with pinch roller assemblies.

There has been a continuing need for precise media handling in a printer, and especially at the region of the media where the printing takes place. The prior art devices adopted one of many ways of transporting media through the printing area; however, each of them suffer from some inherent drawbacks which reduce. the accuracy of the printing.

In one type of prior art device, friction drive rollers alone are used. Typically, two sets of friction drive rollers are provided on two separate drive shafts. llowever, the use of friction drive rollers introduces printing inaccuracies due to some deficiencies. First, it is difficult to synchronize two drive shafts. A usual technique to overcome this problem is to slightly over-drive the exit rollers to ensure that the media is tensioned adequately. llowever, during the entrance and exit of the media, there are times when the media is held down by only one set of rollers. Inaccuracies may be introduced during the transition from one set of rollers to the other set. Second, inaccuracies may occur because the rollers may become deformed. Third, the leading and trailing edges of the media are not well controlled by the two 1 1 sets of drive rollers.

in a second type of prior art device, a rotary platen is used to advance media through the printing area. However, since the printing surface is curved, the resulting print gap will vary, which will cause inaccuraciesin printing..

In a third type of prior art device, a tractor feed device is used to transport continuous sheets of media across a printing area. flowever, the paper positioning accuracy is severely affected by the accuracy of the holes in the media. Furthermore, tractor feed is inappropriate for transportincj individual cut sheets.

SUMMARY OP THE IftVENTION

Accordingly, it is an object of this invention to provide a media transport mechanism which allows continuous and cut sheets of media to be transported through the printing area of a printer more precisely so as to reduce inaccuracies in printing.

It is another object of this Invention to provide a media transport mechanism which accurately controls media linear velocity and displacement.

It is another object of this invention to provide a media transport mechanism which presents a flat printing surface adjac-ent the print head to maintain a constant print gap.

It is another object of this invention to provide a media transport mechanism which prevents the print head from contacting the media.

It is another object of this Invention to provide a media transport mechanism which maintains control of the leading and trailing edges of the media at all times.

It is another object of this invention to provide a media transport mechanism which prevents media skew.

A media transport mechanism according to this invention comprises a vacuum belt supportably wrapped around two sprocket 2 assemblies and disposed in facinq relation to a print head, the vacuum belt having two pinch roller assemblies disposed in spacedapart relation across the front surface of the vacuum belt, with each pinch roller assembly including two pinch rollers which, in conjunction with the vacuum belt, grip and advance a sheet of media across the front surface of the vacuum belt during printing, with the vacuum belt providing a vacuum hold-down force for holding tile media flat against the front surface of the vacuum belt.

BRIEF DESCRIPTION OF THE DPAWINGS

The invention will be described In connection with ene embodiment thereof with reference to the accompanying drawings:

FIG. 1 is a perspective view of the vacuum belt and pinch roller assembly; FIG. 2 is a perspective view of tile vacuum belt and piy,.:.-11 roller assembly with detailed broken-down views of each of 't!ie parts; FIG. 3 is a righthand side view of the right wall of vacuum belt and pinch roller assembly; and FIG. 4 is a magnified view of a portion of the vacuum bel ie DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the vacuum belt and pinch rol er assembly will be described with reference to FIGS. 1-4.

FIGS. 1 and 2 show the vacuum belt and pinch roller assen,:ly to be used in a printer, which may be, for example, an ink jet or impact printer. A vacuum belt 2 is wrapped around two sets of sprockets, a pair of upper sprockets comprising an upper l-ft sprocket 20 and an upper right sprocket 22, and a pair of lc er sprockets comprising a lower left sprocket 24 and a lower ri--iit sprocket 26. The upper left sprocket 20 and the upper ri,-;it sprocket 22 are mounted oil opposite ends of an upper idler SI, ft 3 vacuum belt sprocket 26 lower idler idler shaft 34. The upper idler shaft 34 also mounEs the axle of a pulley 16, which operates to drive the upper idler shaft 34 and thus, the vacuum belt 2. Both the upper left sprocket 20 and the upper right sprocket 22 have sprocket pins 28 that are adapted to be fitted into sprocket holes 30 on opposite edges of the vacuum belt 2 for driving the vacuum belt 2. The vacuum belt 2 is guided and driven by the upper sprockets. Unlike the upper sprockets, the lower left sprocket 24 and the lower right sprocket 26 do not have sprocket pins. Thus, the lower sprockets only guide but do not drive the 2. The lower left sprocket 24 and the lower right are also mounted on opposite ends of a corresponding shaft 38. Unlike the upper idler shaft 34, the lower 38 is not connected to a pulley and is not driven.

The left ends of a plurality of elongated upper idler support is rollers 36 are attached to the inside of the upper left sprocket 20, and tile right ends of the plurality of elongated tipper idler support rollers 36 are attached to the inside of the upper right sprocket 22. The upper idler support rollers 36 provide support to hold the vacuum belt 2 flat and to prevent the vacuum belt 2 from collapsing in the middleportion. lliere is also a plurality of lower idler support rollers 40 having left ends attached to the lower left sprocket 24 and right ends attached to the lower right sprocket 26. The lower idler support rollers 40 perform the same function as the upper idler support rollers 36, that is, to provide support to hold the vacuum belt 2 flat and to prevent the vacuum belt 2 from collapsing in the middle portion.

As shown in FIGS. 1, 2 and 4, the vacuum belt 2 is formed with a plurality of perforated vacuum holes 32 spaced one-eighth of an inch apart from each other. The vacuum holes 32 should be substantially small to provide enough impedance to the air flow when a shpet of media 14 is riot covering the holes 32. The sheet of media 14 may be any type of printable sheet medium, such as 4 1 1 paper, transparencies or film. The vacuum holes 32 should also be in close proximity to each other so that the whole surface of the vacuum belt 2 beneath the media 14 forms a vacuum. As shown in FIG. 1, the vacuum holes 32 extend over a width of the vacuum belt 2 which is greater than the width of the s.heet of media 14. The vacuum belt 2 is also formed of a plurality of sprocket holes 30 which are aligned along both edges of the vacuum belt 2 and have a diameter which is wider than that of the vacuum holes 32. The sprocket holes aligned along the left edge of the vacuum belt 2 are adapted to receive the sprocket pins 28 of the upper left sprocket 20 while tile sprocket holes aligned along the right edge of the vacuum belt 2 are adapted to receive tile sprocket pins 28 of the upper right sprocket 22. The vacuum belt 2 is made from an elastic material, such as polyester, so that the inaccuracy due to btlt. stretching is minimal.

Referring to FIGS. 1 and 2, the vacuum belt and pinch roller assembly further comprises twd sets of pinch rollers, an upper set and a lower set. The upper set comprises a pair of upper ptncii rollers 8 which are adapted oil the outside surface of the ulper portion of the vacuum belt 2. The upper pinch rollers 8 are mounted on an upper roller shaft 4, which has its left end filted to an upper left arm 52 and its right end fitted to an upper right arm 50. The upper roller shaft 4 is an idler shaft and is not driven at all. The upper right arm 50 is mounted on the frame of a right wall 42 and the upper left arm 52 is mounted on the frame of a corresponding left wall 41. The upper pinch rollers 8 are spring loaded idlers that rotate only in response to the motion of the vacuum belt 2. The lower set of pinch rollers is identicai to the upper set. The lower set comprises a pair of lower p4 nch rollers 10 adapted oil the outside surtace of the lower portion of the vacuum belt 2, and mounted on a lower roller shatt 6 supportably held at opposite ends by a lower right arm 54 and a lower left arm 56. The lower right arm 54 and the lower left arm 56 are mounted on the frames of the right wall 42 and the left,all 41, respectively.

The vacuum belt 2 forms a vacuum chamber or plenum wiii,!i is enclosed on opposite ends by the left wal.1 41 and the right wall 42. The left wall 41 is air-tight so that no air can escape from the left wall 41. AS shown in FIGS. 1-3, the right wall 42 h...S an opening 44 which is connected to a vacuum blower 48 by a tul-e or duct 46. The vacuum blower is capable of generating a vacu-,-i at 0.2 - 0.4 inches of water at the flow rate of 10-100 cfm. A -gid platen (not shown) is disposed on the inside surface of the v -.uum belt 2, and provides support to the cioss-sectional area o_ the vacuum belt 2 between the two sprocket assemblies. The igid platen is formed with a plurality of vacuum slots so that the generated vacuum can be effectively felt by the plurality of v:uum holes 32 while the vacuum belt 2 is being advanced.

The pulley 16 is belt-driven by a belt 18. A stepper:..:,tor (riot shown) drives the pulley 16 so as to rotate the upper _'.Aler shaft 34, the upper left sprocket 20 and the upper right spr -.ket 22 in the clockwise direction (see FIGS. 2 and 3). Becaus- tile upper sprockets rotate, the sprocket pins 28 fitted In the spr, jket holes 30 on the vacuum belt 2 will also rotatably advancc- the vacuum belt 2.

The operation of the vacuum belt and pinch roller ass-.:ibly will now be described with reference to FIGS. 1 and 3. A she.tt of media 14 is initially picked from a media source, such as a t-ray or cassette, and the media's leading edge delivered to the ')wer portion of the front surface of the vacuum belt 2. The l e:,i rig edge of the media 14 is gripped by the lower pinch rollers 1 and the vacuum belt 2. As the vacuum belt 2 advances, the lower, nch rollers 10 also rotate and help to advance the media 14 alon the front surface of the vacuum belt 2. The vacuum plenum locatt. oil 6 1 1 the inside of the vacuum belt 2 produces a vacuum hold-down force which ensures that the media 14 is held flat against the front surface of the vacuum belt as the media is advanced through a printing area. The printing area is defined as the area of Elie vacuum belt 2 between the upper pinch rolle.rs 8 and the lower pinch rollers 10. The arrows 58 in FIG. 3 indicate the direction in which the media 14 is pulled towards the vacuum belt 2 by the vacuum hold-down force.

As the media 14 is advanced through the printing area, a reciprocating print head 12 held out of contact with the media 14 prints the desired pattern or text onto the media 14 (see FIG. 1). As the media 14 is advanced across the front surface of the vacuum belt 2, the upper pinch rollers a engage the leading edge of the media 14 and operate in unison with the vacuum belt 2 and the lower pinch rollers 10. As the trailing edge of the media 14 disengages the lower pinch rollers 10, the upper pinch rollers 8 assume control of the media 14 together with he vacuum belt 2 until the trailing edge of the media 14 is disengaged from the upper' pinch rollers 8 and delivered to an output tray (not shown).

The vacuum belt and pinch roller assembly described above accurately controls the transportation of continuous and cut sheets of media 14 through the printing area and ensures accurate linear velocity and displacement of the media. The use of the pinch rollers in conjunction with the vacuum bel_ allows conrol of the leading and trailing edges of the media 14 at all times while the media 14 is within the printing area. The vacuum belt and pinch roller assembly also prevents the print head 12 from touching the media 14, and the' effective vacuum hold-down force and the flat surface of the vacuum belt ensure that the gap between the media 14 and the print head 12 is conEant, thereby improving print quality.

7

Claims

What is claimed Is: 1. A printer comprising: a print head; two sprocket

assemblies, each sprocket assembly includinj two sprockets disposed on opposite ends of a drive shaft an-1 on opposite ends of a plurality of support rollers; a vacuum belt supportably wrapped around the support ro'lers of the two sprocket assemblies and disposed in facing relati-n to the print head; two pinch roller assemblies disposed in spaced-apart rel: tion across the surface of the vacuum belt, each pinch roller ass,mbly Including a plurality of pinch rollers mounted on an idle reller shaft; a printing area located on an area of the vacuum belt dirt-ctly facing the print head and in the space between the two pinch r. ller assemblies; the vacuum belt providing a vacuum hold-down force for ho.ding a sheet of media flat against the front surface of the vacuum!.-elt; and the vacuum belt being driven by at least one of the spr.cket assemblies to advance the sheet of media through the printing. rea, the media being gripped by the vacuum beLt and the pinch rollers of at least one pinch roller assembly.
2. A printer as recited in c laim. i, wherein the vacuum hold-down force is supplied by a vacuum blower.
3. A printer as recited in claim 1, wherein each sprocket is comprised of a plurality of sprocket pins, and wherein the vacuum belt comprises vacuum holes and sprocket holes, the sprocket holes being adapted to fit the sprocket pins.
4. A printer as recited in claim 1, wherein a stepper rotor rotatably drives the sprockets and the vacuum belt.

9 1 9
5. A method of advancing a sheet of media through a printing area in a printer, comprising the steps of: a first pinch roller assembly and a driven vacuum belt gripping the leading edge of the media; the vacuum belt imparting a hold-down force onto the media to hold the media flat against the front surface of the vacuum belt; advancing the media upwards along Elie front surface of the vacuum belt until the desired printing location of the media is disposed opposite a print head,printing a desired pattern or text onto the media; a second pinch roller assembly and the vacuum belt gripping the leading edge of the media; advancing the media upwards along the front surface of the vacuum belt until the trailing edge of the media becomes disengaged from the first pinch roller assembly, while printing is still taking place; and advancing the media upwards along the surface of the vacuum belt until. the trailing edge of the media becomes disengaged from the second pinch roller assembly.

Published 1991 atTbc Patent Office. State House. 66/71 High Holborn, LondonWCIR47?. Further copies -Y be obtained from Sales Branch, Unit
6. Nine Mile Point Cwmielinfach. Cross Kevs. Newport. NPI 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent.