Patent Publication Number: US-6341777-B1

Title: Multiple-position idler roller

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to the art of paper sheet handling, and more particularly concerns a multiple position bidirectional idler roller for use in a sheet inverter system. 
     The invention is especially suited for use in the paper handling and inverter system of an electrophotographic printing machine and will be described with reference thereto; however, as will become apparent, the invention could be used in many types of paper sheet handling systems in a variety of different machines. 
     Although a sheet inverter is referred to in the copier/printer art as an “inverter”, its function is not necessarily to immediately turn the sheet over (i.e., exchange one face for the other). Its function is to effectively reverse the sheet orientation in its direction of motion. That is, to reverse the lead and trail edge orientation of the sheet. Typically, in inverters as disclosed here, the sheet is driven or fed by feed rollers or other suitable sheet driving mechanisms into a sheet reversing chute. By then reversing the motion of the sheet within the chute and feeding it back out from the chute, the desired reversal of the leading and trailing edges of the sheet in the sheet path is accomplished. Depending on the location and orientation of the inverter in a particular sheet path, this may, or may not, also accomplish the inversion (turning over) of the sheet. In some applications, for example, where the “inverter” is located at the comer of a 90° to 180° inherent bend in the copy sheet path, the inverter may be used to actually prevent inverting of a sheet at that point, i.e., to maintain the same side of the sheet face-up before and after this bend in the sheet path. On the other hand, if the entering and departing path of the sheet, to and from the inverter, is in substantially the same plane, the sheet will be inverted by the inverter. Thus, inverters have numerous applications in the handling of either original documents or copy sheets to either maintain, or change, the sheet orientation. 
     In the field of reprographic machines, it is often necessary to feed a copy sheet leaving the processor of the machine along one of two alternate paths, particularly when the machine can selectively produce simplex (one-sided) and duplex (two-sided) sheets. Simplex sheets may be fed directly to an output tray, whereas duplex sheets may pass to a sheet feeder, which automatically reverses the direction of movement of a simplex sheet and feeds it back into the processor, but inverted, so that the appropriate data can be applied to the second side of the sheet. 
     Many inverters, particularly those utilizing only spring action or gravity, have reliability problems in the positive output or return of the sheet at a consistent time after the sheet is released from the inverter. Furthermore, inverter reliability problems are aggravated by variations in the condition or size of the sheet. For example, a pre-set curl in the sheet can interfere with feed-out and even cause the sheet to assume an undesirable configuration when it is released. 
     Paper curl is defined as any deviation from its flat state. In the xerographic process, fusing drives moisture out. When regaining moisture, paper experiences curl due to differential hygroexpansivity and thermoexpansivity between the paper and toner, and dimensional instability of paper due to its moisture history. The paper expands due to moisture reabsorption, but the toner does not expand, thus developing curl. Paper curl is one of the primary causes for paper handling problems in copying machines. In an inverter, problems such as stubbing result from copy sheet curl These problems are more severe for color copies than black and white due to differences in their toner mass area, substrates, and fuser characteristics. 
     The use of a curved chute within an inverter, i.e., curved sheet guides or baffles to define the reversing chamber for the sheet, will not necessarily insure the proper orientation of the trail edge of the sheet relative to the exit nip, or the leading edge of the sheet relative to the inverter nip. Also, different weights or thickness of paper will have different beam strengths, i.e. different self-straightening forces. 
     It is desirable to develop a new and improved sheet inverter apparatus which overcomes the above noted problems and others encountered in the prior art. The present invention meets these needs and others and provides a bi-directional inverter nip which is simple and not likely to damage the documents handled therein. 
     The following disclosures may relate to various aspects of the present invention: 
     U.S. Pat. No. 5,720,478 to Carter et al., teaches a gateless sheet inverter in which a curved portion of the sheet path branch intersects a second portion of the sheet path to form a curved inverter throat. As the sheet is driven from the curved branch portion of the path into the throat portion, the beam strength of the sheet causes the trail edge of the sheet to flip toward a second nip leading to the second sheet path. A pair of reversing rollers captures the lead edge of the sheet to be inverted and then reverses to drive the sheets out of the second nip formed by the tri-roller arrangement. 
     U.S. Pat. No. 5,382,013 to Walsh, discloses a paper inverter system having a clutch-driven inverter nip for maintaining a positive bidirectional contact with the sheet. A pair of opposing rollers defines a nip, with a shaft connected to one of the pair of opposing rollers. The clutch couples one end of the shaft to a drive system while the other end of the shaft is connected to a spring, which resists rotation of the shaft. The drive system rotates the shaft in a first rotational direction against the spring force. The clutch then decouples the shaft from the drive system for rotation in the opposing direction with the spring force. 
     U.S. Pat. No. 5,374,049 to Bares et al., discloses an inverter comprised of a reversible roller onto which a sheet is scrolled and subsequently unscrolled, thereby reversing the lead and trail edges of the sheet. 
     U.S. Pat. No. 5,317,377 to Rubscha et al., discloses a tri-roller inverter in which a passive deflector gate is deflected by a sheet driven by the input nip. The gate is deflected to an open position, which allows the sheet to enter the inversion chute. After the sheet is past the gate, the gate returns to a closed position, thus allowing the sheet to be driven past it in reverse by a reversing roller. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided an inverter for reversing the direction of a sheet moving along a paper path. The inverter includes a drive roller and an idler roller in circumferential contact in at least two positions. A nip is defined in each position. 
     In accordance with another aspect of the invention, there is provided a method of operating an inverter for reversing the orientation of a moving paper sheet. The method comprises receiving a lead edge of a moving sheet into a continuously driven first nip, which includes a continuously driven main drive roller and a first idler roller. A bi-directionally driven nip, which includes a forward/reverse driven roller and a multiple position idler roller, is then driven in a first direction to receive the lead edge of the sheet into the bidirectional nip. The forward/reverse driven roller then reverses to a second direction, thereby moving the trailing edge of the moving paper sheet into a second continuously driven nip having a continuously driven main drive roller and a second idler roller to expel the sheet from the inverter. 
     Pursuant to yet another aspect of the present invention, there is provided an electrophotographic printing machine having a device for inverting a sheet along a paper path. The inverting device includes a drive roller and an idler roller in circumferential contact in at least two positions. A nip is defined in each position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the instant invention will be apparent and easily understood from a further reading of the specification, claims and by reference to the accompanying drawings in which: 
     FIG. 1 is a side schematic elevational view depicting an illustrative electrophotographic printing machine incorporating a sheet inverting device of the present invention; 
     FIG. 2 is a detailed side elevational view of a prior art inverter; 
     FIG. 3 is a detailed side elevational view of a first embodiment of a sheet inverter according to the invention herein; 
     FIG. 4 is a detailed side elevational view of a portion of the inverter of FIG. 3, with added detail illustrating an embodiment of the invention herein; and 
     FIGS. 5 and 6 are detailed side elevational views illustrating the operation of the invention herein. 
     All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teaching additional or alternative details, features, and/or technical background. 
    
    
     While the present invention will be described hereinafter in connection with a preferred embodiment thereof, it should be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. FIG. 1 schematically depicts an electrophotographic printing machine incorporating the features of the present invention therein. It will become evident from the following discussion that the inverter device of the present invention may be employed in a wide variety of machines and is not specifically limited in its application to the particular embodiment depicted herein. 
     Referring to FIG. 1 of the drawings, the electrophotographic printing machine employs a photoconductive belt  10 . Preferably, the photoconductive belt  10  is made from a photoconductive material coated on a ground layer, which, in turn, is coated on an anti-curl backing layer. The photoconductive material is made from a transport layer coated on a selenium generator layer. The transport layer transports positive charges from the generator layer. The generator layer is coated on an interface layer. The interface layer is coated on the ground layer made from a titanium coated Mylar®. The interface layer aids in the transfer of electrons to the ground layer. The ground layer is very thin and allows light to pass therethrough. Other suitable photoconductive materials, ground layers, and anti-curl backing layers may also be employed. Belt  10  moves in the direction of arrow  12  to advance successive portions sequentially through the various processing stations disposed about the path of movement thereof. Belt  10  is entrained about stripping roller  14 , tensioning roller  16 , idler rollers  18  and drive roller  20 . Stripping roller  14  and idler roller  18  are mounted rotatably so as to rotate with belt  10 . Tensioning roller  16  is resiliently urged against belt  10  to maintain belt  10  under the desired tension. Drive roller  20  is rotated by a motor coupled thereto by suitable means, such as a belt drive. As roller  20  rotates, it advances belt  10  in the direction of arrow  12 . 
     Initially, a portion of the photoconductive surface passes through charging station A. At charging station A, two corona generating devices indicated generally by the reference numerals  22  and  24  charge the photoconductive belt  10  to a relatively high, substantially uniform potential. Corona generating device  22  places all of the required charge on photoconductive belt  10 . Corona generating device  24  acts as a leveling device, and fills in any areas missed by corona generating device  22 . Next, the charged portion of the photoconductive surface is advanced through imaging station B. 
     At imaging station B, a raster output scanner (ROS), indicated generally by the reference numeral  26 , discharges selectively those portions of the charge corresponding to the image portions of the document to be reproduced. In this way, an electrostatic latent image is recorded on the photoconductive surface. An electronic subsystem (ESS), indicated generally by the reference numerals  28 , controls ROS  26 . ESS  28  is adapted to receive signals from a computer and transpose these signals into suitable signals for controlling ROS  26  so as to record an electrostatic latent image corresponding to the document to be reproduced by the printing machine. ROS  26  may include a laser with a rotating polygon mirror block. The ROS  26  illuminates the charged portion of the photoconductive surface. In this way, a raster electrostatic latent image is recorded on the photoconductive surface, which corresponds to the desired information to be printed on the sheet. Other types of imaging systems may also be used employing, for example, a pivoting or shiftable LED write bar or projection LCD (liquid crystal display) or other electro-optic display as the “write” source. 
     Thereafter, belt  10  advances the electrostatic latent image recorded thereon to development station C. Development station C has three magnetic brush developer rollers indicated generally by the reference numerals  34 ,  36  and  38 . A paddle wheel picks up developer material and delivers it to the developer rollers. When the developer material reaches rollers  34  and  36 , it is magnetically split between the rollers with half of the developer material being delivered to each roller. Photoconductive belt  10  partially wraps about rollers  34  and  36  to form extended development zones. Developer roller  38  is a clean-up roller. A magnetic roller, positioned after developer roller  38  in the direction of arrow  12 , is a carrier granule removal device adapted to remove any carrier granules adhering to belt  10 . Thus, rollers  34  and  36  advance developer material into contact with the electrostatic latent image. The latent image attracts toner particles from the carrier granules of the developer material to form a toner powder image on the photoconductive surface of belt  10 . Belt  10  then advances the toner powder image to transfer station D. 
     At transfer station D, a copy sheet is moved into contact with the toner powder image. First, photoconductive belt  10  is exposed to a pre-transfer light from a lamp (not shown) to reduce the attraction between photoconductive belt  10  and the toner powder image. Next, a corona generating device  40  charges the copy sheet to the proper magnitude and polarity so that the copy sheet is tacked to photoconductive belt  10  and the toner powder image attracted from the photoconductive belt to the copy sheet. After transfer, corona generator  42  charges the copy sheet to the opposite polarity to detack the copy sheet from belt  10 . Conveyor  44  advances the copy sheet to fusing station E. 
     Fusing station E includes a fuser assembly indicated generally by the reference numeral  46  which permanently affixes the transferred toner powder image to the copy sheet. Preferably, fuser assembly  46  includes a heated fuser roller  48  and a pressure roller  50  with the powder image on the copy sheet contacting fuser roller  48 . The pressure roller is cammed against the fuser roller to provide the necessary pressure to fix the toner powder image to the copy sheet. The fuser roller is internally heated by a quartz lamp. Release agent, stored in a reservoir, is pumped to a metering roller. A trim blade trims off the excess release agent. The release agent transfers to a donor roller and then to the fuser roller. 
     After fusing, the copy sheets are fed through a decurler  52 . Decurler  52  bends the copy sheet in one direction to put a known curl in the copy sheet and then bends it in the opposite direction to remove that curl. Forwarding rollers  54  then advance the sheet to duplex gate  100 . Duplex solenoid gate  100  guides the sheet to the finishing station F, or to inverter  102 . At finishing station F, copy sheets are stacked in a compiler tray and attached to one another to form sets. The sheets can be attached to one another by either a binder or a stapler. In either case, a plurality of sets of documents is formed in finishing station F. 
     When duplex solenoid gate  100  diverts the sheet into duplex path  101  the sheet is directed to the inverter  102  of the invention which will be described in detail below. The sheet is then directed back to transfer station D via conveyor  64  and rollers  66  for transfer of the toner powder image to the opposite side of the copy sheet. The duplex sheet may then be inverted again by being fed through the same path as the simplex sheet and directed by gate  120  into an output inverter  102  to be advanced to finishing station F. 
     Copy sheets are fed to transfer station D from the secondary tray  68 . The secondary tray  68  includes an elevator driven by a bi-directional AC motor. Its controller has the ability to drive the tray up or down. When the tray is in the down position, stacks of copy sheets are loaded thereon or unloaded therefrom. In the up position, successive copy sheets may be fed therefrom by sheet feeder  70 . Sheet feeder  70  is a friction retard feeder utilizing a feed belt and take-away rollers to advance successive copy sheets to transport  64  which advances the sheets to rollers  66  which feed the sheets to transfer station D. 
     Copy sheets may also be fed to transfer station D from the auxiliary tray  72 . The auxiliary tray  72  includes an elevator driven by a directional AC motor. Its controller has the ability to drive the tray up or down. When the tray is in the down position, stacks of copy sheets are loaded thereon or unloaded therefrom. In the up position, successive copy sheets may be fed therefrom by sheet feeder  74 . Sheet feeder  74  is a friction retard feeder utilizing a feed belt and take-away rollers to advance successive copy sheets to transport  64  which advances the sheets to rollers  66  to transfer station D. 
     Secondary tray  68  and auxiliary tray  72  are secondary sources of copy sheets. The high capacity sheet feeder, indicated generally by the reference numeral  76 , is the primary source of copy sheets. Feed belt  81  feeds successive uppermost sheets from the stack to a take-away drive roller  82  and idler rollers  84 . The drive roller and idler rollers guide the sheet onto transport  86 . Transport  86  advances the sheet to rollers  66  which, in turn, move the to transfer station D. 
     Invariably, after the copy sheet is separated from the photoconductive belt  10 , some residual particles remain adhering thereto. After transfer, photoconductive belt  10  passes beneath corona generating device  94 , which charges the residual toner particles to the proper polarity. Thereafter, the pre-charge erase lamp (not shown), located inside photoconductive belt  10 , discharges the photoconductive belt in preparation for the next charging cycle. Residual particles are removed from the photoconductive surface at cleaning station G. Cleaning station G includes an electrically-biased cleaner brush  88  and two de-toning rollers. The reclaim roller is electrically biased negatively relative to the cleaner roller so as to remove toner particles therefrom. The waste roller is electrically biased positively relative to the reclaim roller so as to remove paper debris and wrong sign toner particles. The toner particles on the reclaim roll are scraped off and deposited in a reclaim auger (not shown), where it is transported out of the rear of cleaning station G. 
     The controller  29  regulates the various machine functions. The controller  29  is preferably a programmable microprocessor, which controls all of the machine functions hereinbefore described. The controller provides a comparison count of the copy sheets, the number of documents being recirculated, the number of copy sheets selected by the operator, time delays, jam corrections, etc. The control of all of the exemplary systems heretofore described may be accomplished by conventional control switch inputs from the printing machine consoles selected by the operator. Conventional sheet path sensors or switches may be utilized to keep track of the position of the document and the copy sheets. In addition, the controller regulates the various positions of the gates depending upon the mode of operation selected. 
     The invention herein has been illustrated in a high-speed black and white printing machine. It is also very suitable for use in a high-speed full color or highlight color printing machine. 
     By way of background a prior art inverter system is illustrated in FIG. 2 of the drawings. Broadly, as illustrated in FIG. 2, earlier inverter systems generally comprise guide means  141  and  143  which define a predetermined course of paper movement or path indicated generally by the lines P and P 1 . In use, sheets are directed to a first pair of rollers  144  and  146 . The rollers  144  and  146  are positioned in opposed relationship to define a first drive nip  145 . Most commonly, only one of the rollers  144  or  146  is positively driven in the direction marked. Commonly, roller  146  is driven, whereas roller  144  is merely an idler roller. 
     Similar to the first input nip  145 , a pair of rollers  146  and  148  are positioned in opposed relationship to define a second drive nip  147 . Like the roller  144  the roller  148  is merely an idler roller. 
     An inverting station  102  includes a spaced pair of curved baffles between nips  151  and  147  and a pair of rollers  150  and  152  positioned in opposed relationship to define an inverter nip  151 . Roller  150  is positively driven while roller  152  is an idler roller. 
     In use, a sheet is received into the first drive nip  145  and fed along the path P by the roller  146  whereupon the sheet leading edge contacts rollers  150  and  152  of inverter nip  151 . As the trail end of the sheet passes through nip  145 , the beam strength of the sheet causes the trail edge to flip to the lower baffle toward nip  147 . The reversing nip  151  then drives the sheets out of the inverter toward nip  147  and the sheet is then driven by nip  147  along path P 1 . At that point the sheet is then expelled from the inverter system through the second drive nip  147  by the rotational motion of the driven roller  146 . 
     Because the geometry of the inverter throat is fixed, as is the position of the forward/reverse nip idler, there is little latitude for paper curl. This results in an inverter that has optimum position for paper curl latitude on output and paper stubbing (wear and damage to the edge of the original) on sheet input, when the leading edge of the sheet contacts one of the rollers in the inverter nip. This problem could be alleviated if the idler were not fixed, but instead could have multiple positions. 
     For a general understanding of the features of the instant invention having just discussed a popular prior inverter system, the preferred embodiment is best shown in FIGS. 3 through 6 of the drawings. In the drawings to follow, like reference numerals have been used throughout to designate identical or equivalent elements in the various embodiments. Also, the drawings are intended to illustrate the features of the present invention and are therefore not necessarily to scale. The system shown in the figures is specifically intended for use in an electrophotographic printing machine; however, the apparatus and system could clearly be used in a variety of other types of equipment incorporating sheet handling and transport systems. 
     FIG. 3 illustrates a detailed side elevation of the inverter system having a multiple position idler roller of the present invention. The inverter with a multiple-position idler includes a series of guide means  101  and  103  which define a predetermined course of paper movement or path indicated generally by the lines P and P 1 . In the preferred embodiment, guide means  101  direct sheets to a first pair of rollers  104  and  106  which are positioned in opposed relationship to each other to define an input nip  105 , which directs incoming sheets into the inverter. Roller  106  is driven in direction  114  while roller  104  is an idler roller. 
     An output nip  107  is defined by a pair of exit rollers  106  and  108  positioned in opposing relationship as illustrated in the figure. As with roller  104 , the roller  108  is an idler and rotates with driven roller  106 . Exit guide means  103  direct the inverted sheets to subsequent downstream electrophotographic operations along path P1 An assist to directing the trail edge of the sheet to exit nip  107  can be achieved by adding a fixed diverter  109  to direct the trail edge of the sheet into nip  107 . The geometry of the diverter  109  is such that the throat leading to nip  107  is much wider than the throat from nip  105  thereby increasing the likelihood that the sheet will be directed to nip  107 . 
     The inverter also includes a drive roller  110  and multiple position idler roller  112 , which form inverter nip  111 . Between nips  111  and  107  extends a curved baffle  103 . 
     Referring now to FIG. 4, torsion spring  115  supports and stabilizes idler roller shaft  116  and thereby holds idler roller  112  in pressing engagement with drive roller  110 . Other suitable means for supporting the idler roller in pressing engagement with the drive roller may be employed, such as a garter spring or nip spring. Lateral movement of idler shaft  116  is constrained by guide stop  118  and idler bracket guide  113 . The turning of the drive roller  110  causes the idler to be driven to each end of guide stop  118 , depending on the direction of rotation of drive roller  110 . As the drive roller rotates counterclockwise as a sheet enters the inverter, the passive idler roller  112  moves to a first position due to friction between the two rollers. As the drive roller rotates clockwise as a sheet leaves the inverter, the passive idler roller moves to a second position, through an angle θ. In the preferred embodiment this movement of the multiple position idler from a first position to a second position through angle θ is within the range of about 5° to about 15°. This movement permits improved sheet curl latitude in the inverter, as illustrated in FIGS. 5 and 6. 
     FIG. 5 illustrates the inverter of the present invention with the multiple position idler  112  in a first position, which would occur when the drive roller  110  is rotated counterclockwise and a sheet is entering the inverter. In this position idler  112  has rotated through angle θ, placing the idler and drive roller in a configuration such that a line drawn through their axes is perpendicular to the sheet path P, for less chance of stubbing. 
     FIG. 6 illustrates the inverter of the present invention with the idler  112  in a second position, which occurs when the drive roller  110  is rotated clockwise and a sheet is leaving the inverter. In this position, idler  112  has moved in the reverse direction back through angle θ, thereby increasing the curl radius that can be accommodated by the inverter. For example, if the idler  112  is moved clockwise by 10 degrees from a first position at 19° from vertical to a second position at 9° from vertical, the curl radius that can be accommodated goes from 170 mm to 120 mm, a significant improvement in curl latitude, for paper having a thickness of 0.4064 mm. 
     In recapitulation, there is provided a device for inverting a sheet along a path in an electric photographic printing machine. A sheet inverter is provided including a bidirectional nip having a forward/reverse drive roller and a multiple position idler roller in opposition to each other. The multiple position idler roller moves about the forward/reverse drive roller to accommodate an improved range of paper curl. 
     It is, therefore, apparent that there has been provided in accordance with the present invention, a bidirectional nip apparatus that fully satisfies the aims and advantages hereinbefore set forth. While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.