This invention relates to a media feed system for an inkjet printer. It has been developed primarily for reducing media buckling in wideformat printers having a fixed printhead assembly.
The following applications have been filed by the Applicant simultaneously with the present application:
The disclosures of these co-pending applications are incorporated herein by reference. The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
Inkjet printing is well suited to the SOHO (small office, home office) printer market. Increasingly, inkjet printing is expanding into other markets, such as label and wideformat printing. Wideformat inkjet printing is attractive for printing onto a variety of media substrates, ranging from corrugated cartons and pizza boxes to display posters.
As used herein, the term “wideformat printer” refers to any printer capable of printing onto media widths greater than A4 size i.e. greater than 210 mm (8.3 inches). Usually, wideformat printers are configured for printing onto media widths of up to 36 inches (914 mm), up to 54 inches (1372 mm) or greater.
Conventional wideformat inkjet printers are characterized by their slow print speeds. In a conventional wideformat inkjet printer, the printhead traverses back and forth across the width of the media in swathes to produce a printed image. To some extent, the slow speeds and cost of printing has limited the uptake of wideformat inkjet printers.
The Assignee's Memjet® pagewide printing technology has revolutionized the inkjet printing market. Pagewidth printers employ one or more fixed printhead(s) while the print medium is fed continuously past the printhead(s). This arrangement vastly increases print speeds. Hence, wideformat printers manufactured using the Assignee's pagewide printing technology are gaining increasing traction in the wideformat market.
US2011/0025748, the contents of which are herein incorporated by reference, describes a wideformat printer based on the Assignee's pagewidth printing technology. This printer employs a plurality of fixed printheads staggered across the page and a media feed mechanism configured for aligning print media with the printheads as the print media are fed continuously past the printheads in a single pass.
One of the challenges of high-speed wideformat printing, where print media are fed past the fixed printhead assembly at speeds of 6 inches per second or greater, is maintaining accurate registration of the print medium with the printhead assembly. In particular, the print medium should be uniformly flat and travelling at a known velocity as it passes through the print zone. Any variation in flatness or velocity potentially causes a deterioration in print quality.
The known media feed system described in US2011/0025748 comprises a drive (“grit”) roller upstream of the print zone, a fixed vacuum platen in the print zone opposite the fixed printhead assembly, and a vacuum belt assembly downstream of the print zone. The vacuum belt assembly and the drive roller are coordinated via a print engine controller to maintain accurate registration of the print medium with the printhead assembly as it passes through the print zone.
One of the problems of pagewidth printing, which is particularly exacerbated in wideformat printing, is media buckling or ‘tenting’. Media buckling is a term used to describe a print medium which is not uniformly flat; in other words, a print medium having ripples which result in a varying height of the media surface relative to the printhead(s). Media buckling generally causes a loss of print quality. In a worst case scenario, media buckling causes the print medium to buckle into contact with the printhead(s) and cause a severe loss of print quality.
In the printer described in US2011/0025748, a relatively small degree of skew in the downstream vacuum belt assembly can generate buckling in print media and, as a consequence, produce visible artifacts in the printed image. In practice, it is difficult to manufacture a vacuum belt assembly having perfect parallel of alignment of the vacuum belt(s) with the media feed direction. For example, microscopic eccentricities in the shafts or pulleys supporting the vacuum belts can produce small deviations in the travel direction of the belts. These deviations are transferred to the print medium engaged with the belts and tend to amplify over the duration of a print, thereby causing media buckling and loss of print quality.
It would be desirable to provide a printer having a media feed mechanism, which minimizes the extent of media buckling and provides improved print quality. It would be particularly desirable to improve the media feed mechanism described in US2011/0025748 so as to minimize media buckling.
In a first aspect, there is provided a printer comprising a vacuum belt assembly for moving print media in a media feed direction along a media path, the vacuum belt assembly comprising:
a plurality of endless belts tensioned between first and second pulleys, the first and second pulleys having respective first and second axes of rotation perpendicular to the media feed direction; and
a vacuum chamber for drawing print media onto an upper surface of the belts, wherein each belt is independently laterally slidable along at least one of the first and second axes.
The printer according to the first aspect provides excellent control of media movement across the vacuum belt assembly with minimal media buckling due to the independent lateral movement of the individual belts.
Preferably, the second pulley is downstream of the first pulley with respect to the media feed direction.
Preferably, the second pulley is configured to allow a predetermined degree of lateral sliding along the second axis.
Preferably, the first pulley is configured to prevent any lateral movement of the belt along the first axis.
Preferably, the second pulley is a drive pulley operatively connected to a motor.
Preferably, the first pulley is an idler pulley.
Preferably, each belt is toothed and intermeshes with complementary grooves in at least one of the first and second pulleys.
Preferably, one first pulley and one second pulley together support a set of individual belts.
Preferably, the vacuum belt assembly comprises a plurality of first and second pulleys, each first and second pulley together supporting a respective set of individual belts.
Preferably, the second pulley comprises a plurality of circumferential ribs, each belt in the set being mounted between a respective pair of ribs, wherein a spacing between the pair of ribs is greater than a width of the belt.
Preferably, the ribs are positioned such that the belts in the set are spaced apart from each other.
Preferably, the vacuum chamber communicates with an elongate interstitial gap defined between each pair of adjacent belts.
Preferably, the belts are non-apertured belts.
Preferably, one or more vacuum antechambers are positioned in the interstitial gap defined between each adjacent pair of belts, each vacuum antechamber having a perimeter opening for suction engagement with print media, and each vacuum antechamber communicating with the vacuum chamber via a respective aperture defined in each antechamber.
Preferably, a plurality of elongate vacuum antechambers are positioned in each gap, a length dimension of each perimeter opening extending longitudinally in the media feed direction.
Preferably, a first perimeter opening of a first vacuum antechamber positioned towards an upstream side of the vacuum belt assembly is shorter than a second perimeter opening of a second vacuum antechamber positioned towards a downstream side of the vacuum belt assembly, the upstream and downstream sides being defined with respect to the media feed direction.
Preferably, the first vacuum antechamber has a first aperture defined therein and the second vacuum antechamber has a second aperture defined therein, the first and second apertures communicating with the vacuum chamber, wherein the first aperture has a larger diameter than the second aperture.
Preferably, the printer further comprises a fixed printhead assembly defining a print zone. Preferably, the fixed printhead assembly comprises a plurality of stationary printhead modules mounted in a staggered array across the media width.
Preferably, the vacuum belt assembly is positioned downstream of the fixed printhead assembly.
Preferably, the printer further comprises a fixed vacuum assembly positioned in the print zone opposite the fixed printhead assembly.
Preferably, the printer further comprises a drive roller engaged with a pinch roller, the drive roller being positioned upstream of the print zone.
Preferably, the print medium is engaged more strongly between the drive roller and pinch roller than the vacuum engaged between the print medium and the vacuum belt assembly.
Preferably, in use, the belts moves faster (e.g. about 0.5% to 2% faster) than the drive roller. Preferably, in use, the print medium slips relative to the belts by virtue of the faster movement of the belts relative to the drive roller.
In a second aspect, there is provided a printer comprising a moving vacuum belt assembly for moving print media in a media feed direction along a media path, the vacuum belt assembly comprising:
a plurality of spaced apart endless belts tensioned between first and second pulleys;
a vacuum chamber for drawing print media onto an upper surface of the belts; and
a plurality of vacuum antechambers communicating with the vacuum chamber, each vacuum antechamber having a perimeter opening for suction engagement with print media, a length dimension of each perimeter opening extending longitudinally in the media feed direction,
wherein a first perimeter opening of a first vacuum antechamber positioned towards an upstream side of the vacuum belt assembly is shorter than a second perimeter opening of a second vacuum antechamber positioned towards a downstream side of the vacuum belt assembly, the upstream and downstream sides being defined with respect to the media feed direction.
The printer according to the second aspect provides excellent control of suction force experienced by print media traversing across the vacuum belt assembly. The arrangement of perimeter openings of the vacuum antechambers assists, firstly, in initially grabbing print media and, secondly, in reducing media buckling by providing a lower suction force towards the downstream side of the vacuum belt assembly.
Preferably, the first vacuum antechamber has a smaller volume than the second vacuum antechamber.
Preferably, each vacuum antechamber communicates with the vacuum chamber via a respective aperture defined in each antechamber.
Preferably, the first vacuum antechamber has a first aperture defined therein and the second vacuum antechamber has a second aperture defined therein, the first and second apertures communicating with the vacuum chamber, wherein the first aperture has a larger diameter than the second aperture.
Preferably, the vacuum antechambers are positioned in an interstitial gap defined between each adjacent pair of belts,
Preferably, each perimeter opening has a width which is narrower than the interstitial gap between adjacent belts.
Preferably, the vacuum chamber is a common vacuum chamber communicating with each vacuum antechamber in the vacuum belt assembly, the common vacuum chamber being connected to a vacuum source in the printer.
Preferably, the vacuum belt assembly is a modular assembly comprised of a plurality of moving belt modules and a plurality of static platen modules.
Preferably, the moving belt modules and static platen modules are interconnected in an alternating arrangement to define the vacuum belt assembly.
Preferably, the vacuum chamber extends through a body of each of the interconnected moving belt modules and static platen modules.
Preferably, each moving belt module comprises a respective set of the spaced apart endless belts, each set of the belts being tensioned between one first pulley and one second pulley.
In a third aspect, there is provided a printer comprising a vacuum belt assembly for moving print media in a media feed direction along a media path, the vacuum belt assembly comprising a plurality of moving belt modules, each moving belt module comprising:
a body having an internal chamber defining at least part of a vacuum chamber;
a first pulley positioned at a first end of the body;
a second pulley positioned at a second end of the body; and
a set of spaced apart endless belts tensioned between the first and second pulleys, wherein the belts are non-apertured and the vacuum chamber communicates with an interstitial gap defined between each adjacent pair of belts in the set so as to draw print media onto an upper surface of the moving belt module.
The printer according to the third aspect provides improved stability of the suction force applied to print media as it traverses across the vacuum belt assembly. By avoiding apertured vacuum belts, the suction force is non-moving as the print media enters the vacuum belt assembly and, moreover, can be accurately controlled without relying on customized belts having apertures defined therein.
Preferably, a static platen module is positioned between each pair of moving belt modules.
Preferably, the moving belt modules and the static platen modules are interconnected in an alternating arrangement along a length of the vacuum belt assembly, the length of the vacuum belt assembly being coextensive with a width of the media path.
Preferably, each of the static and moving belt modules have complementary lateral datum features in interlocking engagement.
Preferably, each second pulley is a drive pulley and each first pulley is an idler pulley, the drive pulley being positioned downstream of the idler pulley.
Preferably, each drive pulley is mounted on a common drive shaft extending across the length of the vacuum belt assembly.
Preferably, each static platen module comprises a bearing for receiving the drive shaft.
Preferably, each set comprises three or more belts.
Preferably, each static platen module comprises a body having an internal chamber defining at least part of the vacuum chamber.
Preferably, the internal chambers of the static and moving belt modules communicate via sidewall openings to define a common vacuum chamber for the vacuum belt assembly.
Preferably, at least one of the static platen modules comprises an embedded encoder wheel for monitoring a velocity of print media moving over an upper platen surface thereof
Preferably, each static platen module has an upper surface configured for minimizing frictional engagement with the print media.
Preferably, each static platen module has a plurality of grooves defined in the upper surface, the grooves extending longitudinally in the media feed direction for minimizing frictional engagement with the print media.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
The printer of the present invention is similar in construction to the printer described in US2011/0025748. For the sake of completeness, an overview of the salient features of the print engine described in US2011/0025748 now follows.
Referring to
After exiting the cutter 62, the separated media sheet 54 feeds through the nip of a grit-coated drive roller 16 engaged with a pinch roller 16a. Referring now to
A fixed printhead assembly 56 comprises five printhead modules 42, 44, 46, 48 and 50 which span the width of a media path to define the print zone 14. The printhead modules are not positioned end-to-end, but rather are staggered in an overlapping arrangement with two of the printhead modules 44, 48 positioned upstream of the printhead modules 42, 46 and 50.
A known vacuum belt assembly 20, as described in US2011/0025748, is positioned immediately downstream of the print zone 14 and fixed vacuum platen 26. The known vacuum belt assembly 20 comprises a plurality of apertured vacuum belts 202, which cooperate with the drive roller 16 to feed the media sheet 54 at a predetermined velocity through the print zone 14. The known vacuum belt assembly 20 functions as a movable platen that engages the non-printed side of the media sheet 54 and pulls it out of the print zone 14 once the trailing edge of the media sheet 54 disengages from the nip of the input drive roller 16 and pinch roller 16a.
Still referring to
Still referring to
Significantly, the known vacuum belt assembly 20 has a belt speed marginally higher than the media feed speed provided by the input drive roller 16. In practice, the belt speed of the known vacuum belt assembly 20 is about 0.5 to 2% faster (typically about 1% faster) than the media feed speed provided by the drive roller 16. However, the engagement between the input drive roller 16 and the media is stronger than the engagement between the media and the vacuum belts 202. Consequently, there is a degree of slippage between the media sheet 54 and the belts 202 of the known vacuum belt assembly 20 until the trailing edge of the media disengages from the input drive roller 16.
A more detailed explanation of an exemplary ink delivery system, including the ink tanks 60 and accumulator reservoirs 88, can be found in US2011/0025748.
The ink inlet and outlet sockets (144 and 146) each have five ink spouts 142—one spout for each available ink channel. For example, the printer may have five channels; CMYKK (cyan, magenta, yellow, black and black).
The ink spouts 142 are arranged in a circle for engagement with complementary fluid couplings (not shown) in the print engine 72 during installation of the printhead module. Likewise, a row of electrical contacts 140 are configured for engagement with complementary contacts (not shown) in the print engine 72 during installation of the printhead module. The upper molding 134 also has a grip flange 136 at either end for manipulating the module during installation and removal.
From the foregoing, and with particular reference to
In practice, several problems exist with the known vacuum belt assembly 20 described above and described in greater detail in US2011/0025748 (see
In view of some of the problems associated with the known vacuum belt assembly 20 described in
Referring initially to
Each moving belt module 210 comprises a set of spaced apart belts 216 tensioned between a drive pulley 220 and an idler pulley 222 (see
A drive shaft 218 is rotatably mounted on the support chassis 214 for rotating each of the drive pulleys 220 and, hence, each of the belts 216 synchronously. The drive shaft 218 extends along the extent of the vacuum belt assembly 200. As shown most clearly in
The drive shaft 218 and drive pulleys 220 are positioned at a downstream side of the vacuum belt assembly 200, while the idler pulleys are positioned at an upstream side of the vacuum belt assembly. Hence, as viewed in
Referring to
Still referring to
Referring now to
Each belt 216 is a non-apertured belt having a relatively narrow width compared to both the length of the pulleys on which they are mounted and the media width. For example, the ratio of the drive pulley length to the belt width may be at least 4:1, at least 8:1 or at least 20:1. Moreover, the ratio of the media width to the belt width may be at least 100:1, at least 150:1 or at least 200:1. The vacuum belt assembly 200 may comprise at least 20, at least 30 or at least 40 individual belts.
Referring briefly to
More particularly, and returning now to
The vacuum antechambers 244 (and respective perimeter openings 252) are generally elongate and have a length dimension which extends longitudinally in the media feed direction. Typically, each vacuum antechamber 244 (and respective perimeter opening 252) has a width which is substantially the same or less than the width of the interstitial gap 217 in which the vacuum antechamber 244 is disposed.
As shown most clearly in
The relative lengths of the vacuum antechambers 244 (and corresponding perimeter openings 252) is an important feature of the vacuum belt assembly 200. At the upstream side of the vacuum belt assembly 200, a leading edge portion of the print medium must be grabbed quickly and pulled taught onto the belts 216 by the suction force. By having a relatively short vacuum antechamber 244A at the upstream side, a “vacuum cup” is quickly established with the leading edge portion of the print medium, which minimizes any initial lateral movement of the print medium relative to the belts. If the vacuum antechamber 244A were to have a longer perimeter opening, then the vacuum seal would take longer to establish and provide more opportunity for lateral movement of the print medium as it enters the vacuum belt assembly 200. (For the avoidance of doubt, the right-hand side of the moving belt module 210 shown in
Commensurate with the relative lengths (and chamber volumes) of the vacuum antechambers 244, the vacuum apertures 250 also vary in size so as to provide greater suction force at the upstream side of the vacuum belt assembly 200 compared to the downstream side. Accordingly, the vacuum aperture 250A defined in the upstream vacuum antechamber 244A has a larger diameter than the vacuum aperture 250D defined in the downstream antechamber 244D. The relatively larger diameter of vacuum aperture 250A combined with the relatively smaller volume of vacuum antechamber 244A means that the upstream side of the vacuum belt assembly 200 develops a stronger suction force than the downstream side. A relatively weaker vacuum force towards the downstream side of the vacuum belt assembly, by virtue of the relatively smaller diameter vacuum apertures 250C and 250D and relatively larger volume vacuum antechambers 244C and 244D, is optimal for minimizing media buckling as will be explained in more detail below.
Referring now to
A series of circumferential ribs 264 extend radially outwardly from the drive pulley 220 and are spaced apart along the longitudinal axis of the drive pulley to provide two important functional aspects of the vacuum belt assembly 200. The ribs 264 are positioned, firstly, to maintain a predetermined interstitial spacing between the belts 216 mounted about the drive pulley 220. As shown in
At the upstream side of the vacuum belt assembly 200, and referring now to
By allowing each individual belt 216 to move laterally and independently along the longitudinal axis of the downstream drive pulley 220, the steering of each set of belts becomes self-correcting over the duration of printing. In this way, media buckling is minimized. Moreover, the decreased vacuum force towards the downstream side of the vacuum belt assembly 200, by virtue of the relative volumes of the vacuum antechambers 244 and vacuum apertures 250 as described above, encourages a degree of lateral movement of the belts 216 along the drive pulley axis and helps to maintain the self-correcting characteristics of belt steering.
Turning now to
As described above in connection with
At the opposite upstream end of the static platen module 212, each mounting slot 271 defines a mounting for one end of an idler pulley 222 from a neighboring moving belt module 210. The engagement between the idler pulley 222 of a moving belt module 210 and the mounting slot 271 of a neighboring static platen module 212 is shown in
In addition, the first and second static platen modules 212A and 212B have the common feature of an upper platen surface 272 having a plurality of grooves 274 defined therein. The upper platen surface 272 supports print media between the moving belt modules 210, while the grooves 274 extending longitudinally in the media feed direction minimize frictional engagement between the print media and the upper platen surface 272. The grooves 274 are merely for reducing friction and are not apertured through to the internal chamber of the static platen module. In other words, the static platen modules 212 do not exert any suction on the print media via the upper platen surface 272. All the vacuum force experienced by the print media is finely controlled via the vacuum antechambers 244 described above.
Referring to
It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.
Number | Date | Country | |
---|---|---|---|
61769026 | Feb 2013 | US |