Abstract:
A reprographic marking device has two rolls, e.g., a pressure roll and a fuser roll, forming a nip. A drive motor moves the rolls in a continuous back and forth lateral motion to change the position of the rolls relative to a paper sheet passing through the nip.

Description:
BACKGROUND 
     The invention relates generally to a reprographic fusing device for fixing a toner image to a substrate. More specifically, the invention relates to a fusing device that is continuously movable relative to the print medium during printing. 
     In electrostatic printing, a dry marking material, such as toner, is fused to a substrate, such as a paper sheet. Fusing occurs when the substrate is subjected to pressure and/or heat to permanently affix the marking material to the substrate. Most common electrostatic printers use a fuser roll and a pressure roll that form a nip for the substrate to pass through. In many such printers, a variety of different size sheets may be passed through the nip of the rollers. 
     All conformable rolls suffer from surface wear, especially where the edges of the sheets contact the roll surface.  FIG. 1  shows how the edges and body of 11″ and 14″ sheets of paper are distributed along the surface of a fuser roll in the axial direction in printers without a registration distribution system. In such printers, the sheet edges produce a stress concentration as they pass through the fuser nip under pressure, causing the thin surface coating on the roll, as well as the elastomeric layer under the surface, to degrade. The degradation of the roll is often manifested as a narrow area of lower gloss from a lead edge to a trail edge across the print fused to the substrate. In the context of mixed paper sizes, a 14″ print often shows a differential gloss streak 11″ in from the outboard (registered) edge. Such artifacts become visible to the customer after only a few thousand prints have passed through the fuser, far short of the target life of the roll. 
     One proposed solution to such problems is to change fuser rolls to accommodate different size papers. However, this method is not always practical or in keeping with existing program goals. For example, if only one paper size is run for a given roll set, the edge wear exists, but is outside the normal visible area of the print and goes unnoticed. 
     Another proposed solution is provided in U.S. Pat. No. 5,323,216 which discloses a lateral moving fuser station. The lateral moving fusing station is an intelligent system in which detection of incoming paper size is utilized to reposition the roll in an axial direction based on usage demographics, such that the location of edge wear is spread over a larger area. 
     The station includes a pressure roller and a heated fusing roller that are in pressure contact with each other to form a fusing nip. The fusing station is mounted on a base plate and is moved by a stepping-type drive motor controlled by a control and logic circuit. The control and logic circuit either activates the stepping motor prior to the start of a copy cycle for a set time period to move the fuser station laterally a pre-set distance, or activates the motor after a pre-set volume of copies have been fused. This way, if most of the paper run is 11 inches wide, a discrete or specific location within the 3 inches of roll from the 11 inch position to the 14 inch position can be made available for edge redistribution. However, by restricting lateral movement of the fusing station as described, productivity may be slowed due to the necessity to move to the fusing station during a print operation, such as when the pre-set volume of copies have been fused. Furthermore, banding may also result from the use of such discrete stepping systems. 
     These and other known methods have drawbacks which severely limit any performance benefits from existing registration distribution systems. For example, by moving the fusing station only between copy runs or interframes a pre-set distance, the fuser roller will suffer unnecessary wear at the point where the edges of the sheets contact the roll surface. The wear will continue to manifest itself as a narrow area of lower gloss from lead to trail edge across the print. 
     SUMMARY 
     To address the problem of edge wear on fuser rolls, a registration distribution system is disclosed in which no prior knowledge of paper size is required and the axial motion of the rolls is continuous. By continuously moving the fuser assembly, differential gloss artifacts due to repetitive stress concentrations are spread out over a greater area thereby maximizing roll life with no dependence on paper size. Furthermore, continuously moving the fuser assembly eliminates the potential for banding caused by a stepping-type registration distribution system. 
     In an exemplary embodiment of the invention, the length of a fuser roll may be increased to allow even the largest paper size to have full travel across the roll area. In another exemplary embodiment, edge effects due to lead screw backlash are reduced by a mechanical system, such as a spring. In yet another exemplary embodiment of the invention, an edge smoothing algorithm is also employed in the invention to further reduce the perception of edge wear. 
     Although the following exemplary embodiments are described with reference to conformable fuser rolls, the systems and methods described herein pertain to any rolls having a conformable surface. 
     These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments of the systems and methods according to this invention will be described in detail, with reference to the following figures, wherein: 
         FIG. 1  shows conformable fuser roll wear distribution along the roll surface in the axial direction in printers without a registration distribution system; 
         FIG. 2  is a graph showing conformable fuser roll edge wear in a print system without a registration distribution system; 
         FIG. 3  is a graph showing the relationship between total number of sheets processed and measured conformable fuser roll differential gloss levels; 
         FIG. 4  shows an automated printing system; 
         FIG. 5  shows a perspective view of a print engine removed from the automated printing system; 
         FIG. 6  shows a schematic view of a partial fuser assembly according to an exemplary embodiment of the invention; 
         FIG. 7   a  shows a partial fuser assembly of the embodiment of  FIG. 6  in a maximum travel position in a first direction; 
         FIG. 7   b  shows a partial fuser assembly of the embodiment of  FIG. 6  in a maximum travel position in a second direction; 
         FIG. 8  shows a perspective view of a fuser assembly within a print engine; 
         FIG. 9  shows a partial fuser assembly within the print engine disconnected from a roll drawer; 
         FIG. 10  is a graph showing the effects of backlash on the conformable fuser roll wear distribution of edge wear over the total travel range of a fuser assembly according to an exemplary embodiment of the invention; 
         FIG. 11  shows a schematic view of an edge smoothing system according to an exemplary embodiment of the invention; and 
         FIG. 12  is a graph showing a conformable fuser roll wear distribution comparison resulting from an exemplary embodiment of the invention using 2 mm smoothing compared with a non-smoothed case with equivalent backlash and failure levels. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 2  is a graph of experimental results showing the relationship between the total number of sheets processed and measured differential gloss levels representing conformable fuser roll wear in a printing system without a registration distribution system. The graph represents onset of edge wear in a printing system without a registration distribution system and the determination of perceivable (differential) gloss. As sheets pass through a nip formed between a conformable fuser roll surface and a non-conformable pressure roll surface near the registration location  10 , the sheets are normally distributed according to the accuracy of the paper registration system upstream of the fuser. 
     Over a period of time, the distribution of conformable fuser roll wear grows to look like the diagram in  FIG. 2 , wherein the area under the curve  9  represents the total number of sheets passed through the nip. An example of a way in which edge wear is perceived is at the peak  11  when a certain differential gloss level has been reached. At the peak  11 , the results of edge wear are manifested as differential gloss and will be easily seen by an observer. Worn areas will have relatively lower gloss than will un-worn areas. 
     It was also determined that there is a direct correlation between peak edges per mm and differential gloss, as measured in Gardner Gloss Units (ggu) by a gloss meter. For example, below a certain threshold level (about 5 ggu), differential gloss is not readily perceived by the un-aided eye. Thus, in an exemplary embodiment of the invention, a design specification of about 5.0 ggu was determined to be an acceptable target range of differential gloss on fused sheets. 
     Differential gloss may be perceived by an observer at the transition point between worn and non-worn areas of the roll. For example, the slope  12  of the distribution shown in  FIG. 2  was determined to be important because a sharp transition, as represented by the slope  12 , from worn and non-worn areas is perceived more readily than smooth transitions. 
       FIG. 3  is a graph showing the relationship between total number of sheets processed and measured differential gloss levels. The results shown in  FIG. 3  were derived using a registration distribution system incorporating 4 mm of roll length to concentrate the effects of the registration distribution system over a known usable surface area to limit total roll life. From this and other experiments, the total amount of registration distribution system travel required to satisfy a desired roll life was determined. For example, it was determined that 12,600 edges per mm produces the targeted 5.0 ggu differential gloss level. Thus, in an exemplary embodiment of this invention, a target roll life of 425,000 prints, using approximately 34 mm of travel over the surface of the roll will result in an acceptance level of 5.0 ggu. In this embodiment, the 425,000 print are assumed to be uniform distributed, or zero fuser roll backlash, and does not take into account any edge smoothing at the ends of travel. Reduction in fuser roll backlash and edge smoothing will be discussed later. 
       FIG. 4  shows an automated marking system  100  for imparting marked images onto a substrate, such as a paper sheet. The automated marking system  100  includes a marking engine  105  disposed within the marking system  100 . In an exemplary embodiment of the invention, the marking engine  105  includes those components found in traditional electrostatic marking devices, such as a raster image scanner, photoconductive belt, charging station, corona generator, exposure station, development station, and the like (not shown). As a sheet passes through the marking engine  105  the sheet is passed through a nip between a fuser roll and a pressure roll and a toner image is fixed to the sheet. 
       FIG. 5  shows a perspective view of the marking engine  105  removed from the automated marking system  100 . As shown in  FIG. 5 , a removable roll drawer  150  is disposed in the marking engine  105 . The roll drawer  150  holds a pressure roll  140  and a fuser roll  145 . The roll drawer  150  is removable from the marking engine  105  to allow for roll replacement and servicing of the marking engine  105 . A nip is formed between the pressure roll  140  and the fuser roll  145  to affix a toner image to a sheet. The roll drawer  150  is attachable to a Registration Distribution Sensor (RDS) plate assembly  110  via the latch  155 . When the roll drawer  150  is attached to the RDS plate assembly  110  via a latch  155 , the roll drawer  150  is laterally moveable. When the roll drawer  150  containing the rollers  140 ,  145  is connected to the fuser translation block  125  via the latch  155 , the entire movable assembly is referred to as a fuser assembly  160 . 
       FIG. 6  shows a schematic view of the RDS plate assembly  110 . As shown in the exemplary embodiment of  FIG. 6 , the RDS plate assembly  110  is attachable to the marking engine  105  by screws (not shown) through screw holes  111 . The RDS plate assembly  110  provides a mounting point for an RDS home sensor  115  and an RDS position sensor  120 . The RDS sensors  115  and  120  monitor the movement of the fuser assembly  160  (described below). The sensors  115  and  120  are positioned on the RDS plate assembly  110  to detect positions of maximum travel of the fuser assembly  160 . The fuser translation block  125  includes the latch  155  attached at one side and extending in a direction parallel to the direction of movement of the fuser assembly  160 . 
     In an exemplary embodiment of the invention, when the roll drawer  150  is inserted into the marking engine  105 , the latch  155  latches to the roll drawer  150  thereby connecting the roll drawer  150  to the fuser translation block  125 . A reversible RDS drive motor  130  drives the fuser translation block  125  via a lead screw  112  through a slip clutch coupling  113  back and forth in a lateral direction, indicated by the direction of the arrow in  FIG. 6 . When either sensor  115 ,  120  is blocked by a flag  135  attached to the fuser translation block  125 , the drive motor  130  is stopped, thereby halting travel of the fuser translation block  125 , and therefore the fuser assembly  160 , in that direction. Motion is then reversed by inverting the polarity in the drive motor  130  and the drive motor  130  drives the fuser translation block  125  in the opposite direction until the other of the sensors  115 ,  120  is blocked by the flag  135 . 
     As shown in  FIG. 6 , the drive motor  130  rotates the lead screw  112  through the slip clutch coupling  113  to produce smooth linear motion of the fuser translation block  125  relative to the latch  155 , moving the entire fuser assembly  160  back and forth very slowly. In an exemplary embodiment of the invention, the fuser assembly  160  travels approximately 0.0011 mm per sheet fused. 
     In an exemplary embodiment of the invention, each of the sensors  115 ,  120  communicate with a smart controller  170  ( FIG. 4 ) that controls the amount movement of the fuser assembly  160 . For example, when the latch  155  reaches either determined first or second maximum travel position (see  FIGS. 7   a  and  7   b ), movement of the fuser assembly  160  is stopped, the polarity of the drive motor  130  is inverted, and fuser assembly  160  travel begins in the opposite direction. In the event a determined time has lapsed and the fuser assembly  160  has not reached a determined maximum travel position, then the smart controller  170  sets a fault alert to notify an operator of a potential problem. 
     In one exemplary embodiment of the invention, the fuser assembly  160  travels about 1.133 mm/min or 0.00074 in/sec. At this speed, the motion of the fuser assembly  160  is so slow that the sheet is transported continuously through the nip without stopping lateral movement of the fuser assembly  160 . 
       FIG. 7   a  shows the fuser assembly  160  without the roll drawer  150  attached to the RDS plate assembly  110  to better illustrate the position of the latch  155  and the fuser translation block  125 . In a maximum travel position in a first direction, indicated by the line marked X, the RDS position sensor  120  would be blocked by the flag  135  signifying the end of fuser assembly  160  travel in that direction. When the RDS position sensor  120  is tripped by the flag  135  to indicate end of travel fuser assembly travel is stopped, the polarity of the drive motor  130  is inverted, movement is reversed and fuser assembly  160  travel begins in the opposite direction. 
       FIG. 7   b  shows the fuser assembly  160  without the roll drawer  150  attached to the RDS plate assembly  110  to better illustrate the position of the latch  155  and the fuser translation block  125 . In a maximum travel position in a second direction, indicated by the line marked Y, the RDS position sensor  120  would be blocked by the flag  135  signifying the end of fuser assembly  160  travel in that direction. Because the RDS position sensor  120  is tripped by the flag  135  to indicate end of travel, travel stops, the polarity of the drive motor  130  is inverted, movement is reversed and fuser assembly  160  travel begins in the opposite direction. 
     In one exemplary embodiment of the invention, the registration distribution system changes the position of the fuser roll  145  by moving the entire fuser assembly  160  over an approximately 34 mm length, represented by the distance between line X and line Y in  FIGS. 7   a ,  7   b . Such movement increases the life expectancy of the fuser roll  145  by distributing wear over a greater surface area on the roll  145 . 
       FIG. 8  shows the RDS plate assembly  110  and the rolls  140 ,  145  disposed within the marking engine  105 . When the rolls  140 ,  145  are disposed in the roll drawer  150  and the roll drawer  150  is connected to the RDS plate assembly  110  via the latch  155 , the fuser assembly  160  is driven by the drive motor  130 . 
       FIG. 9  shows an exemplary embodiment of the invention. In the embodiment, the roll drawer  150 , including the rolls  140 ,  145 , is installed in the marking engine  105 . As shown in  FIG. 9 , the RDS plate assembly  110  is not connected to the drawer to better illustrate the position of the latch  155  and the fuser translation block  125 . In an exemplary embodiment of the invention, the registration distribution system changes the position of the fuser roll  145  by moving the entire fuser assembly  160  over an approximately 34 mm length, shown by the distance between lines X and Y. 
     Although the exemplary embodiment is described using a 34 mm distance to move the fuser assembly  160 , other distances are contemplated by this invention. Additionally, the distance a fuser assembly may travel for a given registration distribution system may change according to roll length, substrate width, and the like. 
     As described above, when the fuser assembly  160  reaches a maximum travel position, i.e., either the first or the second maximum travel direction, the drive motor  130  stops and reverses direction. During the stopping and reversing, an amount of backlash is possible. Backlash in the drive system and latch assembly results in loss of motion of the fuser assembly  160  at the ends of travel, thereby allowing extra sheets to pass over the same section of roll surface before motion in the opposite direction is resumed. 
       FIG. 10  shows how backlash of lead screw  112  (shown in  FIG. 6 ) may effect the distribution of edges over the total travel range of the fuser assembly  160 . As shown in  FIG. 10 , ends of fuser assembly travel  13  reach the determined 5.0 ggu failure threshold of 12.6 k edges/mm long before the normal wear portion of the travel ( 14 ). For example, on a 34 mm travel system with 1.0 mm of backlash reaches the 5.0 ggu failure threshold in 142 k prints rather than 407 k prints for the same system with only 0.1 mm of backlash. 
     To reduce edge effects due to the stopping and reversing of the drive motor  130  and the fuser assembly  160 , a system of backlash reduction is provided in the invention. To reduce the demonstrated affects of backlash the fuser assembly  160  is tensioned by a backlash spring  114  ( FIG. 6 ) to reduce potential slop in the lead screw  112  and accompanying follower mechanisms. Total fuser assembly travel is set at 34 mm, an amount determined to yield the desired roll life of 425 k prints. The backlash spring  114  is attached to a bracket  165  that is mounted to the fuser translation block  125 . The fuser translation block  125  is secured to the RDS plate assembly  110  thereby providing a fixed position at one end of the backlash spring  114 . The other end of the backlash spring  114  is attached to the moveable fuser translation block  125  to tension the fuser translation block  125  against one side of the lead screw  112  threads, thereby reducing most or all of the play or slop in the lead screw  112  and reducing backlash. 
     To further reduce the impact of edge effects, it was determined that if the edge between a moderately worn area and a non-worn area is masked, the difference in gloss in the two adjacent areas is not readily noticeable. Thus, if the transition between edge accumulation areas and non-edge accumulation areas is smoothed, the gloss reduction in the worn area will go unnoticed longer, extending the effective life of the fuser roll  145  in the sense that conformable fuser roll wear will not be as readily apparent to a marking engine fuser. 
     In one exemplary embodiment of the invention, to smooth the transition from the worn area within the 34 mm zone to the unworn area outside the zone, an edge smoothing system  500  is employed ( FIG. 11 ). In the edge smoothing system  500  a smoothing algorithm is employed at the end of fuser assembly travel. Essentially, when either travel sensor  115  or  120  is actuated by the flag  135 , the drive motor  130  continues to drive the fuser assembly  160  for a variable period of time, equating to a determined distance, before reversing direction, such that a desired edge distribution profile is achieved. 
     As shown in  FIG. 11 , a data source  300  is connected over a link to an input/output interface  510 . A data sink  400  is also connected to the input/output interface  510  through a link. 
     Each of the links can be implemented using any known or later developed device or system for connecting the data source  300  and the data sink  400 , respectively, to the edge smoothing system  500 , including a direct cable connection, a connection over a wide area network or a local area network, a connection over an intranet, a connection over the Internet, or a connection over any other distributed processing network or system. In general, each of the links can be any known or later developed connection system or structure usable to connect the data source  300  and the data sink  400 , respectively, to the edge smoothing system  500 . 
     Although the exemplary embodiment is described using a separate data source  300  and data sink  400 , it should be appreciated that the data source and data sink may be implemented in a single unit, such as the automated printing system  100 . 
     The input/output interface  510  inputs data from the data source  300  and outputs data to the data sink  400  via the link. The input/output interface  510  also provides the received data to one or more of a controller  170 , the memory  540 , and a smoothing algorithm or look-up table  530 . The input/output interface  510  receives data from one or more of the controller  170 , the memory  540 , and/or the smoothing algorithm or look-up table  530 . 
     The smoothing algorithm or look-up table  530  provides instructions to the controller  170  based on data, such as shown in  FIG. 11 , that smoothes the wear profile of a conformable roller. The controller  170  controls the drive motor  130  to continue movement of the fuser assembly  160  a determined distance beyond the detected position of maximum travel according to the instruction sent to the controller  170  by the smoothing algorithm or look-up table  530 . 
     The smoothing algorithm or look-up table  530  may be implemented as a circuit or routine of a suitably programmed general purpose computer. Such circuits or routines may also be implemented as physically distinct hardware circuits within an ASIC, or using a FPGA, a PDL, a PLA or a PAL, or using discrete logic elements or discrete circuit elements. The particular form each such circuit or routine will take is a design choice and will be obvious and predicable to those skilled in the art. 
     The memory  540  stores data received from the smoothing algorithm or look-up table  530 , the controller  170 , and/or the input/output interface  510 . The memory  540  can also store one or more control routines used by the controller  170  to operate the drive motor  130  to move the fuser assembly  160  a determined amount according to the smoothing algorithm or look-up table  530  upon receipt of a signal from the sensors  115 ,  120 . 
     The memory  540  can be implemented using any appropriate combination of alterable, volatile or non-volatile memory or non-alterable, or fixed, memory. The alterable memory, whether volatile or non-volatile, can be implemented using any one or more of static or dynamic RAM, a floppy disk and disk drive, a writable or re-writeable optical disk and disk drive, a hard drive, flash memory or the like. Similarly, the non-alterable or fixed memory can be implemented using any one or more of ROM, PROM, EPROM, EEPROM, an optical ROM disk, such as a CD-ROM or DVD-ROM disk, and disk drive or the like. 
     In one exemplary embodiment of the edge smoothing system  500  according to the invention, a sensor  115 ,  120  is placed approximately 2 mm from each travel limit position. Each time a sensor  115 ,  120  is tripped by the flag  135 , a signal is sent to the input/output interface  510 . The signal is also sent to the memory  540  and the smoothing algorithm or look-up table  530  via the bus  550 . The instructions for moving the fuser assembly  160  a determined amount are sent from the smoothing algorithm or look-up table  530  to the motor  130 . The motor  130  would continue to drive the fuser assembly  160  for a determined time period, i.e., distance. Different delay times may be derived through the smoothing algorithm or look-up table  530  so that the distribution desired was attained. 
     Although this exemplary embodiment is described with sensors  115 ,  120 , it should be appreciated that other means of tripping the flag  135  may be used. For example, a mechanical limit switch is contemplated. 
       FIG. 12  shows an exemplary case using 2 mm smoothing compared with a non-smoothed case with equivalent backlash and failure levels. The non-smoothed distribution, shown by the dashed line, shows a sharp wear transition  16  and a small backlash effect  15 . By starting a smoothing profile, shown by the solid line, 2 mm inside of the travel limit  17 , a more gradual wear transition can be attained  18 . 
     Although this exemplary embodiment is described using a 2 mm smoothing, other smoothing distances, such as 4 mm and 6 mm, for example, are contemplated by this invention. 
     While the invention has been described in conjunction with exemplary embodiments, these embodiments should be viewed as illustrative, not limiting. Various modifications, substitutes, or the like are possible within the spirit and scope of the invention.