Patent Publication Number: US-6655679-B2

Title: Input converger for hardcopy devices

Description:
TECHNICAL FIELD 
     This invention relates to hardcopy devices, and more particularly to an input converger for accurate control of media movement therethrough. 
     BACKGROUND OF THE INVENTION 
     Hard copy devices process images on media, typically taking the form of scanners, printers, plotters (employing inkjet or electron photography imaging technology), facsimile machines, laminating devices, and various combinations thereof, to name a few. These hardcopy devices typically transport media in a sheet form from a supply of cut sheets or a roll, to an interaction zone where scanning, printing, or post-print processing, such as laminating, overcoating or folding occurs. Often different types of media are supplied from different supply sources, such as those containing plain paper, letterhead, transparencies, pre-printed media, etc. 
     The relative position of the paper and the operative structures in the interaction zone is precisely maintained to effect high-quality media processing in the interaction zone. For example, in the case of an inkjet printer, printing occurs in the interaction zone and the position of an ink cartridge as it reciprocates in a back and forth motion across the media, and the positioning and control of paper as it advances past the printheads in the ink cartridge are controlled to produce high quality images. The media advancement through the hardcopy devices, and the positioning of the operators in the interaction zone are typically separately controlled, although their operation is coordinated with a hardcopy controller. 
     Hardcopy apparatus typically include media advancement mechanisms that serve to advance the recording media from one or more media sources through a media feed path and through the interaction zone. Again in the case of an inkjet printer, the interaction zone is typically a “printzone” where ink is applied to the paper. The media advance mechanisms move the paper through the interaction zone the desired distance, often in incremental steps, at the desired rate, and in a manner such that the media is oriented correctly relative to the devices found in the interaction zone. Achieving high quality media processing is often impeded by media feed errors such as overfeeding and underfeeding, and misalignment errors such as skewing. 
     SUMMARY 
     The illustrated embodiment relates to apparatus for advancing media through a hardcopy device. A cylindrical guide wheel having a first radius is mounted on a shaft having an axis transverse to a media feed path axis. A guide surface is spaced apart from the guide wheel to define a media feed path therebetween. A drive wheel having an extended portion that is concentric with the guide wheel, and which has a greater radius than the first radius is fixed to the shaft. A pinch roller communicates with the media feed path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a semi-schematic perspective view of selected portions of a hardcopy device, here for the purposes of illustration shown as an inkjet printer illustrating an input converger assembly according to one embodiment the present invention housed in a printer chassis. 
     FIG. 2 is a semi-schematic perspective view of the input converger of FIG. 1, with major portions of the chassis and associated structure removed to illustrate the input converger more clearly. 
     FIG. 3 is a perspective view of the roller assembly utilized with the input converger of FIG.  2 . 
     FIG. 4 is a side elevation view of the roller assembly taken along the line  5 — 5  of FIG. 2, shown in isolation without other parts of the printer shown in FIG.  2 . 
     FIGS. 5 through 7 are a sequential series of cross sectional views taken along the line  5 — 5  of FIG.  2  and illustrating a sheet of media in various positions as it is advanced through the input converger and printer and along a media feed path, with: 
     FIG. 5 showing a sheet of media as it is first engaged by the roller assembly; 
     FIG. 6 showing the next sequential step from FIG. 5, illustrating the media forming a buckle as a media leading edge enters a pinch between the linefeed roller and an associated linefeed wheel; and 
     FIG. 7 showing the next sequential step from FIG. 6, where the roller assembly is in a home position and the media is advancing through the printer. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Most inkjet printers include a carriage that holds one or more ink-filled print cartridges. The carriage reciprocates in a back and forth motion across the printing surface, positioning the ink cartridge or cartridges adjacent the media, such as paper, for printing. During the printing operation the carriage is shuttled across the paper and minute ink droplets are ejected out of the cartridge onto the paper in a controlled manner to form a swath of an image each time the carriage is scanned across the page. Between carriage scans, the paper is advanced with a media feed assembly so that the next swath of the image may be printed. Sometimes, more than one swath is printed before the paper is advanced. In some printers, a stationary printhead or array of printheads may be provided as a page-wide-array (“PWA”) printhead or print bar, extending across the entire width of the paper that moves through the printer. 
     The relative position of the print cartridge(s) and paper is precisely maintained to effect high-resolution, high-quality printing. The position of the print cartridge as it reciprocates in a back and forth motion across the media, and the positioning and control of paper advancement past the printhead are usually separately controlled, although their operation is coordinated with a printer controller. 
     Paper advancement assemblies typically include friction rollers or tractor feed mechanisms that advance the recording media from one or more media trays through a “printzone” where ink is applied to the paper. With an inkjet printer, in the course of advancing the print media between swaths, an encoder, typically a disk encoder, and associated servo systems are one of the methods often employed for controlling the precise incremental advance of the media. This incremental advance is commonly called “linefeed.” Precise control of the amount of the advance, the linefeed distance, contributes to high print quality. As such, the structures that are used to advance the media are designed to minimize linefeed errors such as overfeeding and underfeeding, and misalignment errors such as skewing. 
     The paper advance mechanisms must move the paper through the printzone the desired distance with each incremental advance, at the desired rate, and so that the paper is oriented correctly relative to the printheads. There are several common printer problems that result from the failure to control these factors. As noted, these include linefeed errors and paper alignment errors. Overfeeding occurs when the linefeed roller incrementally advances the media too far relative to the printhead. On the other hand, underfeeding occurs when the paper has not advanced far enough. The result in either case is that ink is deposited in the wrong place on the paper, decreasing print quality. Skewing problems are caused by relative misalignment between the paper and the printheads. Ideally, the axis of media advancement should be perpendicular to the axis along which the printheads reciprocate. Stated in another way, the entire leading edge of a sheet of paper should enter the linefeed at the same time rather than being angled with respect to it. When the paper advances through the printzone in any orientation other than the ideal, the paper is skewed and the quality of the print job decreases. 
     Likewise, the position of the carriage as it reciprocates in a direction transverse to the direction that the paper is fed through the printer is also precisely controlled. Typically, the carriage assembly includes an optical sensor or encoder carried on the carriage positioned to view or read an encoder strip that extends laterally across the printer. A servo system is used in concert with the encoder and encoder strip to precisely control the position of the carriage relative to the media—typically by moving the carriage along a carriage shaft with a continuous drive belt. 
     The printer microprocessor controls and synchronizes both the reciprocating movement of the carriage, and the linefeed so that ink is deposited in a desired manner on the media. 
     The semi-diagrammatic illustration of FIG. 1 shows pertinent portions of a hardcopy device, illustrated for purposes herein as a representative inkjet printer  10  in which an illustrated embodiment of an input converger assembly according to the present invention may be used. For purposes of clarity and to illustrate the invention more clearly, many features of the printer structure and chassis are omitted from the figures. Although the invention is illustrated with respect to its embodiment in one specific type of printer, the invention may be embodied in numerous different types of printers and recorders. 
     Referring to FIGS. 1 and 2, inkjet printer  10  includes an input converger assembly, identified generally with reference number  12 , mounted in a chassis  14  in an operative position to receive recording media, such as individual sheets of paper in the illustrated embodiment from a lower paper tray  16 . As noted, many structural features in the printer are omitted from the drawings to clearly illustrate the invention. For example, printer  10  includes an inkjet cartridge(s) (not shown) and associated hardware mounted on a shaft for reciprocating movement past the media and along an axis that extends transverse to the media feed axis, which is defined as the axis of media travel as the media is fed through a printzone  18  (see FIG.  5 ). The media feed axis is perpendicular to the shaft axis. The inkjet cartridges are typically mounted to the chassis by conventional means such as a carriage assembly. The particular chassis  14  shown in the figures is used for illustration only, and is exemplary of the many different types of chassis assemblies that are used in printers of the type with which the present invention may be used. The chassis would of course be mounted in a printer housing and numerous other parts would be included in the complete printer. 
     The carriage assembly supports the inkjet cartridges above print media, such as a sheet of paper  20  (FIG.  6 ). A media interaction head, here, such as a conventional printhead (also not shown) may be attached to the inkjet printer on the underside of the cartridge. The printhead may be conventional, and typically is a planar member having an array of nozzles through which ink droplets are ejected. The cartridge is supported by and movable on a shaft so that the printhead is precisely maintained at a desired spacing from the paper  20  at the printzone  18 . 
     The carriage assembly may be driven in a conventional manner with a servo motor and drive belt, neither of which are shown, but which are under the control of the printer controller. The position of the carriage assembly relative to print media  20  is determined by way of an encoder strip that is mounted to the printer chassis in a conventional manner and extends laterally across the media, parallel to the shaft on which the inkjet carriage may be mounted. The encoder strip extends past and in close proximity to an encoder or optical sensor carried on the carriage assembly to thereby signal to the printer controller the position of the carriage assembly relative to the encoder strip. In most instances, the optical encoder carried on the carriage assembly encircles the encoder strip. 
     For other hardcopy devices, such as scanners and facsimile machines and the like, the printer cartridge may be replaced with another type of media interaction head, such as a scan head, which reads images previously recorded on media. Other interaction heads may, for example, apply overcoats or laminations to the media. 
     As described in greater detail below, input converger assembly  12  is supported by a chassis  14  and is configured to receive print media from a selected one of several sources, each of which supplies media to the assembly from a different direction. Among other functions, the converger assembly receives the media from these various sources and presents the media to a single media feed path through the printzone. For each media source that is included in printer  10  there is a separate media guide path defined from the media source to the input converger. Referring to FIG. 1, the media sources illustrated herein include lower paper tray  16 , which defines a first guide path labeled with arrow A (and referred to herein as media path A). 
     Referring briefly to FIG. 5, although the illustrated embodiment will be detailed with reference specifically to media  20  accepted from lower paper tray  16 , it will nonetheless be understood that assembly  12  also may accept media from other input sources, such as a duplexer, which defines a guide path labeled with arrow B, an optional paper tray that defines a guide path labeled with arrow C, and a multi-purpose tray or manual media feed slot that defines a guide path labeled with arrow D. Each of these guide paths defines a path along which media is fed from the respective media source, into the input converger assembly  12 . In the input converger assembly the various media guide paths A-D merge into a common guide path that leads to and through the printzone  18 . A given printer that embodies the input converger of the present invention may utilize any one or more of the media guide paths A-D described herein. 
     As illustrated in FIG. 1, lower paper tray  16  is mounted in chassis  14  with appropriate mounts such that paper  20  contained in the tray may be fed to guide path A. Individual sheets of paper  20  are stacked in tray  16  and are picked from the tray in a conventional manner, for example with a driven first pick roller  22  and second pick roller  24 , which also is driven. The printer is equipped with appropriate guides  34  to define a clear and unobstructed guide path entrance to path A through the printer. 
     Converger assembly  12  is illustrated separated from the rest of the printer and in greater detail in FIG.  2 . The assembly includes a plurality of guide wheels  26  mounted adjacent a like plurality of drive wheels  28 . All of the wheels  26  and  28  are mounted on a shaft  30  that has a central axis  31  (see FIG. 4) that extends transverse to the media feed axis as defined above. The opposite outer ends of shaft  30  are rotatably mounted to chassis  14  and a servomotor that is under the control of the printer controller drives the shaft in a conventional manner, such as with a drive belt or gears. The number of guide wheels illustrated herein is exemplary only, and the converger assembly may be fabricated with a greater or lesser number of wheels. Moreover, the input converger assembly may have different numbers of guide wheels and drive wheels. Further, the structure and function of the guide wheels and drive wheels may be accomplished with a single wheel that combines the structural features of both types of wheels, in which case, however, the combined wheel would likely be fixed to the mounting shaft. 
     Referring to FIGS. 2-4, guide wheels  26  are preferably mounted on shaft  30  so that the wheels freely rotate on the shaft with minimal drag. On the other hand, drive wheels  28  are fixedly mounted to shaft  30  so that these wheels rotate directly with the shaft. Guide wheels  26  are typically fabricated from plastic and the surface  36  that defines the outer circumference of the wheels  26  is preferably smooth to minimize, in combination with the manner in which the wheels are mounted for rotation on shaft  30 , the frictional drag on paper as it passes over the wheels. Alternately, guide wheels  26  may be fixed to the shaft so that they rotate with it, or cylindrical guides that are not mounted to the shaft and which are independent from it may be used for form the guide wheels. Optionally, the guide wheel surface  36  may be coated with a friction-decreasing material, such as Teflon®. 
     Drive wheels  28  are friction-type drive wheels that cooperate with pinch rollers (discussed below) to actively advance the media through the converger assembly feed paths A-D and to exit to the printzone  18  via a linefeed roller, as detailed below. As such, the outer, paper-contacting surface of the drive wheels is preferably coated with a friction-enhancing material such as rubber layer  32 , or with a grit-coated surface that aids in advancing the media through the input converger. 
     With reference to FIGS. 3 and 4, guide wheels  26  are preferably circular in outer circumference and define a circle having a radius R 1 . All of the guide wheels are of the same radial size and the guide wheels define a media guide surface that is separated from axis  31  by the length of RI. Drive wheels  28  are roughly D-shaped and define an extended portion identified with reference number  38  that defines an arc section  40  having a radius R 2  that is greater than R 1  and which is concentric with the circular outer circumference of guide wheels  26 . The length of arc section  40  is defined as arc length L. Arc length L defines an arc that is less than 360°. The specific shape of drive wheel  28  inwardly of extended portion  38  is not important, but in all instances the drive wheel is either smaller in size than guide wheels  26 , as illustrated in FIG. 4, or the same circumferential size as wheels  26 , except at extended portion  38 . As an alternate structure, the drive wheels themselves may be modified such that they function both as the guide wheel and the drive wheel. The combined-function wheel in this case would have one arc section that has a greater radius than the remainder of the wheel, and the remainder of the wheel would function as the guide portion of the wheel. 
     Shaft  30  and thus drive wheels  28  rotate in the clockwise direction in FIG. 4 (arrow E). Accordingly, the extended portion  38  defines a leading edge  41  and a trailing edge  43  as shaft  30  rotates. 
     Turning now to FIGS. 5 through 7, the operation of input converger  12  will be detailed by explaining the sequential operation of the converger as media is delivered to the converger along guide path A from lower paper tray  16 . As illustrated, media paths B, C and D each intersect a portion of the longest feed path A, so for the purposes of brevity, only path A will be described in detail. 
     Media  20 , which typically is a single sheet of paper, is picked from lower paper tray  16  in a conventional manner (as for example with pick rollers  22  and  24 ) and is directed into guide path A with the assistance of media guides  34 . Pick roller  24  is driven and thus actively advances media  20  in guide path A toward input converger assembly  12 . The input converger assembly  12  includes a circumferential media guide surface  42  that is generally concentric with guide wheels  26  and which is spaced apart from the outer surface  36  of the guide wheels to define a common media path  58  therebetween. Associated with each media path (paths A, B, C and D in the embodiment described herein) is an entry point that is defined generally as the position in the media path where media delivered from one of the media sources enters the input converger assembly and the common media path  58 , from those portions of the media path that are “upstream” of the entrance to path A, defined by media guides  34 . As used herein, “upstream” is used relative to the direction in which media is advancing through the printer. Thus, for example, printzone  18  is downstream from guide surface  42  because media advances through the printer in the direction from guide surface  42  toward printzone  18 . For media path A the entry point into the common media path is labeled with reference number  44 . For media path B the entry point is labeled with reference number  46 . The media path C entry point  48  is the same as the entry point for media path A, even though those two media paths are common for a short distance downstream of point  44 ,  48 . And finally, the entry point for media path D is labeled with reference number  50 . 
     Immediately downstream of each entry point  44 - 50  just described there are a series of spring loaded pinch rollers that extend along an axis parallel to shaft  30  and which communicate with the common media guide path  58  such that the outer surface of the pinch rollers contacts the extended portion  38  of the drive wheels to thereby form a pinch contact point with the extended portion of the drive wheels  28  when the drive wheels are rotationally oriented relative to the pinch rollers such that the extended portion  38  faces the pinch rollers. Stated another way, radius R 2  is slightly greater than the distance between the center of shaft  30  (defined by axis  31 ) and the outer surface of the pinch rollers, whereas radius R 1  is shorter than the same distance. Thus, the pinch rollers and guide wheel surfaces never contact, and instead define therebetween a portion of a media feed path extending from the supply sources of paths A-D to the printzone  18 . The pinch rollers associated with media path A and entry point  44  are shown in FIG. 5 as labeled with reference number  52 . Pinch rollers  52  are also associated with media path C and its associated entry point  48 . Although in the sectional view of FIG. 5 only one pinch roller  52  is shown, it will be appreciated that there is a pinch roller associated with each drive wheel  28 . The pinch rollers associated with media path B and entry point  46  are labeled with reference number  54 , and the pinch rollers for media path D and entry point  50  are labeled with reference number  56 . 
     The specific sequential series of steps involved in the operation of input converger  12  will now be described beginning with FIG. 5. A sheet of media  20  is picked from paper tray  16  and is advanced with the pick rollers such as roller  24  into media path A. Shaft  30  is rotated in the clockwise direction (arrow E) until leading edge  41  of extended section  38  touches pinch roller  52 , at which point shaft rotation is stopped. This results in a stationary pinch formed at the contact point between the leading edge of the extended sections and the pinch rollers. Media  20  is advanced through media path A and through entry point  44  into common media path  58  by pick roller  24 . When a leading edge  60  of media  20  enters the pinch between drive wheels  28  and pinch roller  52 , shaft  30  begins rotation to capture the leading edge  60  in the pinch. Once the drive wheels have accepted the media, the pick rollers decouple from the media so that advancement of media  20  is accomplished with drive wheels  28 . 
     It should be noted that media  20  is deskewed as the pick rollers decouple from active engagement with the media and media advancement is taken over by the drive wheels. 
     Turning now to FIG. 6, shaft  30  has continued its rotation about axis  31  in the direction of arrow E. The arc length L of extended section  40  is greater than the length of the arcuate path between the contact point on pinch roller  52  and the contact point on the next sequential pinch roller  56  in common media path  58 . Accordingly, as drive wheel  28  rotates with shaft  30 , media  20  is continuously pinched between the outer surface of drive wheel  28  in extended section  38  and pinch wheel  52 , until such time as the trailing edge  43  of the extended section rotates past pinch wheel  52 . Because the arc length L is greater than the arc distance between the contact point on pinch wheel  52  and the next pinch wheel  56 , media  20  continues to be advanced through the input converger after trailing edge  43  passes pinch wheel  52 , by the pinching pressure exerted on media  20  as it is captured between extended section  38  and pinch wheel  56 . The rubber coating  32  on extended section  38  aids in maintaining good driving contact between drive wheel  28  and the media. 
     Just downstream of pinch wheel  56  the common media guide path  58  is diverted over a guide member  64 . The leading edge  60  of media  20  is advanced over guide  64 , as illustrated in FIG. 6, and toward a linefeed pinch  68  defined between a linefeed pinch wheel  70  and a driven linefeed roller  72 . Immediately upstream of linefeed pinch  68 , a ceiling portion of chassis  14  defines an upwardly extending guide  74  that defines an upwardly extending buckle space  66 . The linefeed roller  72  remains stationary until the media leading edge  60  is advanced into linefeed pinch  68  across entire width of the media  20 . The arc length L of extended section  38  is long enough so that as the media leading edge  60  is entering the stationary pinch, media immediately upstream of the pinch is urged upwardly in buckle space  66  to form a buckle  76 . Thus, as the leading edge  60  of media  20  enters pinch  68  and before roller  72  begins rotation to pinch media  20  in pinch  68 , shaft  30  continues its clockwise rotation (arrow E), causing the formation of buckle  76 . Once the leading edge has entered the stationary pinch across the entire width of the media, linefeed roller  72  begins to rotate to capture the leading edge in the linefeed pinch. Trailing edge  43  of arc section  40  then passes pinch roller  56  and the driving engagement between drive wheel  28  and media  20  is disengaged or decoupled. Linefeed roller  72  continues its rotational movement in the clockwise direction in the figures (arrow F), and takes over the job of advancing media  20  through printzone  18 . The arc length L is thus set so that drive wheel  28  hands off media  20  to linefeed roller  72  after buckle  76  is formed in buckle space  66 , and media  20  has been accepted into linefeed pinch  68 . 
     If there are any media alignment errors prior to the media being accepted into the linefeed pinch, for instance, if the paper is skewed, those errors are corrected when the drive wheel decouples from pinch roller  56 . The linefeed roller does not begin to rotate until the entire leading edge has entered the linefeed pinch (which is parallel to the axis of print carriage movement and perpendicular to the media feed axis). As such, if there is any misalignment in the media, for instance, if the media is oriented so that the leading edge is not perpendicular with the drive axis, then the paper is twisted somewhat when the buckle is formed. After the leading edge has been accepted into the linefeed pinch, the drive wheel decouples from the pinch roller. When this happens the paper is untwisted—that is, deskewed. 
     Drive wheel  28  continues to rotate in the direction of arrow E so that the drive wheel is in a “home” or “neutral” position, which is defined as the position in which the extended portion  38  is not in contact with any of the pinch wheels, as shown in FIG.  7 . In this position the portions of media  20  that are upstream of linefeed roller  72  are dragged over guide wheels  26 . As noted earlier, the guide wheels  26  rotate freely on shaft  30  to minimize any frictional forces on media  20  during advancement through printzone  18 . Linefeed roller  72  thus is able to pull media  20  and advance it through printzone  18  with very little resistive force. 
     Linefeed errors, which are those printing errors attributable to media misfeed through printzone  18  as described above, are minimized because the media is being advanced only by the linefeed roller. The deskewing function of buckle  76  as described above minimizes media alignment problems. It will be appreciated that the same sequence of steps occurs regardless of which media guide path (i.e. A, B, C or D) is being used to accept the media into the input converger. 
     In addition to minimizing or eliminating linefeed errors, the illustrated embodiment of input converger  12  allows tailgating to be used to increase media throughput (which may be defined as the number of sheets of media that can be advanced through the printer over a given period of time, for instance, as a rating expressed in pages per minute). Because drive wheels  28  form a pinch with each set of pinch wheels  52 ,  54 ,  56  in a sequence, the leading edge  60  of a second sheet of media may follow the trailing edge  62  of the previous sheet as soon at the trailing edge  62  of the previous sheet leaves an open pinch. Thus, as soon as trailing edge  62  of media  20  passes pinch wheel  52 , the leading edge  60  of the next sequential sheet  20  in a print job may enter the pinch between drive wheel  28  and pinch wheel  52 . 
     In addition, by using passive, spring loaded pinch rollers  52 ,  54  and  56 , there is no need to incorporate an active disengaging mechanism such as a transmission-type release. Finally, media jam resolution is simplified by use of passive spring loaded pinch wheels  52 ,  54 ,  56  mounted in the converger assembly. When the pinch wheels are mounted directly in the paper guide structures as described herein, removal of the paper guides to provide access to a jammed sheet of paper is much easier, than, for example, in a converger assembly that utilizes a mechanical disengage mechanism. 
     Although preferred and alternative embodiments of the present invention have been described, it will be appreciated by one of ordinary skill in this art that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.