Abstract:
A system and method for registering a sheet includes a lateral motion motor coupled to a nip and idler roller assembly that provides lateral alignment of the sheet. A de-skew assembly pivots the lateral motion motor and the nip and idler roller assembly about a pivot axis that is proximate to the lateral motion motor to de-skew the sheet.

Description:
TECHNICAL FIELD 
     The technical field relates to a sheet registration apparatus such as may be used in printing systems and more specifically to an active registration system. 
     BACKGROUND 
     Sheet registration systems deliver sheets of all kinds to a specified position and angle for a subsequent function within a printer, copier and other devices. The subsequent functions could include transferring an image to a sheet, stacking the sheet, slitting the sheet, etc. Conventional registration systems correct for skew and lateral offset. “Skew” is the angle of the leading edge of a sheet being transferred with respect to the direction of transfer. Lateral offset is the cross-process misalignment of the sheet being transferred with respect to the transfer path. 
     Skew contributors include the angle at which a sheet is supplied into the sheet drive apparatus, skew induced when the sheet is acquired by the feeder, and drive roller velocity differences between drive rollers on opposite ends of a common drive shaft. Lateral offset may be due to sheet supply location and sheet drive direction error. Sheet drive direction error is caused by the sheet drive shafts not being perpendicular to the intended sheet drive direction. This is a result of tolerances and excess clearance between drive shafts and frames, sheet transport mounting features and machine frames and machine module to module mounting. 
     In present day high speed copiers and printers, active registration systems are used to register the sheets accurately. In an active registration system, a sheet is passed over sensor arrays from which the sheet skew and lateral or cross process offset is calculated. In some registration systems, the sheet is then steered into the proper position by rotating drive rollers on opposite ends of a common drive axis at different velocities. This function must be performed within a specific time and distance, i.e. before the sheet passes out of the nip rollers. As the sheet is moved more rapidly to increase overall productivity, the time to register the sheet to correct for skew and lateral offset decreases. As the allotted time decreases, the speed and acceleration of the nip rollers increases. The increased speed and acceleration may result in a need for a larger motor to provide additional power. The increased speed and acceleration of the nip rollers may further result in early failure of the registration system. 
     Other known devices use a loop registration process. In accordance with a loop registration process, the leading edge of a sheet is brought into abutment against a non-moving nip and idler roller pair causing the sheet to bend. The leading edge of the sheet is thus aligned with the nip and idler roller pair by the elasticity of the sheet to correct skew. Thereafter, the nip and idler roller pair is rotated at a predetermined timing by a process or forward motion motor to move the sheet through the machine. 
     In such devices, a loop space for forming a loop is required which results in an increase in the size of the apparatus. In addition, when the skew of a sheet is too large for the space provided, a paper jam may occur due to the buckling of the sheet. Moreover, the skew correction ability is dependent upon the rigidity of the sheet. Specifically, a thick paper with high rigidity may actually thrust through the nip and idler roller pair as the sheet is forced against the nip and idler roller pair. While this problem may be avoided, such avoidance generally takes the form of additional equipment incorporated into the machine thereby increasing the cost and complexity of the machine. 
     Other automatic registration systems avoid the above problems by pivoting and translating the entire nip and idler roller assembly. In some of these devices, the skew of a sheet is first detected. Then, the nip and idler roller assembly is pivoted by a de-skew motor to match the detected skew condition prior to grasping the sheet with the nip and idler roller assembly. Once the paper is grasped by the nip and idler roller assembly, the nip and idler roller assembly are pivoted by the de-skew motor into a de-skewed position. The nip and idler roller assembly and the de-skewed sheet are then translated by a lateral motion motor to provide lateral alignment of the sheet. 
     In other systems, the sheet may be grasped by a nip and idler roller assembly while the nip and idler roller assembly is in a home position. Accordingly, the sheet is grasped in a skewed and laterally offset position with respect to the nip and idler roller assembly. The sheet and nip and idler roller assembly are then rotated and translated for de-skewing and lateral alignment of the sheet. This results in the nip and idler roller assembly being moved to a skewed position while the sheet is properly aligned. Then, after the sheet has left the nip and idler roller assembly, the nip and idler roller assembly is returned to the home position. In these systems, the skew sensors may be located before or after the nip and idler roller assembly. 
     The above discussed automatic registration systems are very effective in correcting skew and lateral offset. Nonetheless, there are some drawbacks associated with the above systems. For example, the motors used to effect the process motion and the translation (i.e. the process motor and the lateral motion motor) must be pivoted along with the nip and idler roller assembly. The pivoting of the extra mass necessitates a larger motor to provide the pivoting movement in the allotted time. 
     The problem of pivoting the additional mass is compounded by any distance between the mass and the pivot axis. Specifically, the pivot for the registration system is generally located underneath and toward the middle of the transfer path. Thus, the pivot axis is toward the middle of the transfer path. The motors, however, are located at the side of the transfer path. This separation creates a mechanical disadvantage both when starting the rotation and when stopping the rotation. The additional momentum that thus results necessitates more power from the motor used to provide the pivoting movement. 
     Of course, in view of the speed of many modern machines, even a slight increase in the mass being moved may necessitate a significant increase in the power, and therefore the size of the de-skew motor, to achieve the necessary movement within a very short time span. 
     SUMMARY 
     A sheet registration system and method that addresses limitations of previously known systems includes a lateral motion assembly that is located close to the axis of rotation of a nip and idler roller assembly. In one embodiment, a sheet transport system includes a lateral motion motor coupled to a nip and idler roller assembly to provide lateral alignment of a sheet being transported along a sheet transport path by the nip and idler roller assembly. A de-skew assembly coupled to the nip and idler roller assembly pivots the lateral motion motor and the nip and idler roller assembly about a pivot axis located proximate to the lateral motion motor to de-skew the sheet. 
     In one embodiment, a sheet is registered in a device by moving a nip and idler roller assembly along an axis substantially crosswise to the transport path with a lateral motion motor to provide lateral alignment of the sheet. The lateral motion motor and the nip and idler roller assembly are pivoted about a pivot axis proximate to the lateral motion motor to de-skew the sheet. 
     In a further embodiment, a sheet registration system includes a nip and idler assembly used to move a sheet along a transport path. A lateral motion motor is coupled to an end portion of the nip and idler roller assembly to move the nip and idler roller assembly along an axis substantially crosswise to the sheet transport path to provide lateral alignment of the sheet. A de-skew assembly coupled to the nip and idler roller assembly pivots the lateral motion motor and the nip and idler roller assembly about a pivot axis proximate to the lateral motion motor to de-skew the sheet. 
     The above-described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic front view of an exemplary sheet transport system in an electro-photographic machine incorporating an automatic registration system; 
         FIG. 2  shows a top view of the automatic registration system of  FIG. 1  wherein the process motor and the lateral motor are mounted to a pivot mount; 
         FIG. 3  shows a side view of the automatic registration system of  FIG. 1 ; 
         FIG. 4  shows a schematic diagram of the automatic registration system of  FIG. 1 ; 
         FIGS. 5A-5D  show schematic top views of the automatic registration system of  FIG. 1  correcting skew and lateral offset of a sheet; 
         FIG. 6  shows a side view of an automatic registration system wherein the pivot axis is located substantially coaxially with the process motor to minimize the inertia of the process motor and the lateral motor; and 
         FIG. 7  shows an alternative automatic registration system wherein the process motor is fixedly mounted. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  a schematic front view showing an exemplary electro-photographic printing machine  100  incorporating a registration system wherein sheets such as sheet  102  (image substrates) to be printed are fed along a sheet transfer path  104 . The transfer path  104  includes an input  106 , a duplexing return path  108 , and a sheet output path  110 . An image transfer station  112  and an image fuser  114  are also located along the transfer path  104 . The image transfer station  112  which transfers developed toner images from a photoreceptor  116  to the sheet  102  is immediately downstream from a sheet registration system  118 . The image fuser  114  fuses the transferred image on the sheet  102 . 
     As shown in  FIG. 2 , the registration system  118  includes a de-skew assembly  200 , a lateral motion assembly  202 , a process assembly  204  and a nip and idler roller assembly  206 . Also shown in  FIG. 2  is a pivot mount  208 , a lateral position sensor  210  and two skew sensors  212  and  214 . 
     The de-skew assembly  200  includes a de-skew motor  216  that drives a pinion  218 . The pinion  218  is engaged with a rack  220  that is attached to the nip and idler roller assembly  206 . The de-skew assembly  200  is used to pivot the nip and idler roller assembly  206  to de-skew a sheet as discussed more fully below. The rack  220  in this embodiment is made of plastic and is slightly curved about an arc centered on the axis of rotation defined by the pivot pin  226 . 
     The lateral motion assembly  202  includes a lateral motion motor  228  that drives a pinion  230  located on the shaft  232  of the lateral motion motor  228 . The pinion  230  is engaged with a rack  234  that is attached to the nip and idler roller assembly  206 . The lateral motion assembly  204  is used to move the nip and idler roller assembly  206  along an axis that is substantially crosswise to the transfer path  104 . In this embodiment, the rack  234  is hollow and rotatably attached to the nip and idler roller assembly  206  such that the nip and idler roller assembly  206  is allowed to rotate within the rack  234 . 
     The transfer path  104  is the path taken by a sheet as it moves through the nip and idler roller assembly  206 . The sheet  236  moves through the nip and idler roller assembly  206  generally in the direction of the arrow  238 . Accordingly, the lateral motion assembly  202  is used to move the nip and idler roller assembly  206  back and forth cross-wise to the direction of the sheet transfer path  104  substantially in the directions indicated by the double arrow  240 . In one embodiment, the lateral motion assembly  202  may be used at the same time as a sheet is being de-skewed as discussed below. Accordingly, the actual movement of the nip and idler roller assembly  206  may not be exactly parallel to the double arrow  240  depending on the orientation of the nip and idler roller assembly  206  as controlled by the de-skew assembly  200 . 
     The process assembly  204  includes a process motor  242  which drives a gear  244 . The gear  244  is engaged with a gear  246  on the nip and idler roller assembly  206 . The nip and idler roller assembly  206  includes a drive axle  248  to which the gear  246  is fixedly attached. A plurality of nip rollers  250  are mounted on the drive axle  248  as shown in  FIG. 3 . The nip and idler roller assembly further includes a plurality of idler rollers  252  mounted on an idler shaft  254  which is located beneath the drive shaft  248 . Alternatively, a single, wide roll and idler could be used. 
     The operation of the registration system  118  is controlled by a microprocessor  256  shown in  FIG. 4 . The microprocessor  256  receives input from a skew detector  258  and a lateral offset detector  260 . Based upon these inputs, the microprocessor  256  controls the de-skew motor  216  and the lateral motion motor  228  to correct the skew and lateral offset of a sheet within the nip and idler roller assembly  206 . The microprocessor further controls the process motor  242  so as to deliver the sheet in a coordinated manner to the image transfer station  112 . 
     In operation, the sheet  236  of  FIG. 2  is advanced along the sheet transfer path  104  toward the registration system  118 . The microprocessor  256  activates the process motor  242  thereby rotating the gear  244 . The gear  244  in turn causes the gear  246 , and thus the drive shaft  248 , to rotate. Accordingly, when the sheet  236  contacts the nip and idler roller assembly  206 , the leading edge of the sheet  236  is grasped by the opposing nip rollers  250  and idler rollers  252  and advanced along the transfer path  104  by the registration system  118  as shown in  FIG. 5A . 
     In this example, the sheet  236  is skewed and laterally offset. Therefore, as the registration system  118  advances the sheet  236  along the transfer path  104  in the direction of the arrow  262 , the leading edge of the sheet  236  is sensed by the skew sensors  212  and  214 . The skew detector  258  receives a signal from each of the skew sensors  212  and  214  indicating the detection of the sheet  236  and transmits a signal indicative of the skew of the sheet  236  to the microprocessor  256 . 
     The microprocessor  256  controls rotation of the de-skew motor  216  based upon the amount of skew in the sheet and the speed of the process motor  242 . In this example, the right side of the sheet  236  as shown in  FIG. 5A  is ahead of the left side of the sheet  236  along the transfer path  104 . Accordingly, the effective transfer path of the right side of the sheet  236  must be increased, or the relative speed of the left side of the sheet  236  increased, so that the left side of the sheet  236  “catches up” to the right side. Therefore, the microprocessor  256  determines the amount of pivoting of the nip and idler roller assembly  206  that is needed to de-skew the sheet  236  and activates the de-skew motor  216  so as to achieve de-skewing of the sheet  236 . 
     As the de-skew motor  216  rotates in the direction of the arrow  222 , the pinion  218  rotates in the same direction, causing the rack  220  to be forced in the direction of the arrow  224 . The nip and idler roller assembly  206 , however, is attached to the pivot mount  208  which is pivotably mounted on the pivot pin  226 . Accordingly, the nip and idler roller assembly  206  is pivoted about the pivot axis  227  (see  FIG. 3 ). 
     The pivot axis  227  extends perpendicular to and outside of the sheet transport path  104  which passes generally underneath the nip rollers  250 . Thus, the nip and idler roller assembly  206  is pivoted in the direction of the arrow  264  to the position shown in  FIG. 5B . As can be seen by reference to the location of the skew sensors  212  and  214  with respect to the leading edge of the sheet  236 , the rotation of the nip and idler roller assembly  206  has eliminated the skew of the sheet  236  as the sheet  236  continues to be advanced along the sheet transfer path  104  by the nip and idler roller assembly  206 . 
     In this embodiment, the lateral motion assembly  202  and the process assembly  204  are attached to the pivot mount  208 . Accordingly, they are also rotated when the nip and idler roller assembly  206  is rotated. The inertia that must be overcome both to begin rotation of the nip and idler roller assembly  206  and to stop the rotation is minimized, however, because the lateral motion assembly  202  and the process assembly  204  are located proximate to the pivot axis  227 . Moreover, the de-skew motor  216  is located alongside of the transfer path  104  at the side opposite to the location of the pivot pin  226 . Accordingly, a significant mechanical advantage is realized by the de-skew motor  216 . 
     Continuing with the operation of the registration system  118 , the microprocessor determines when the sheet  236  should be sensed by the lateral position sensor  210  based upon the speed at which the sheet  236  is being advanced along the sheet transfer path  104  if the sheet  236  is translationally positioned so as to be sensed by the lateral position sensor  210 . In the present example, however, while the sheet  236  is no longer skewed, the sheet is laterally offset from the desired final registration position for the sheet  236 , the nominal boundaries of which are indicated in  FIG. 5B  by the dashed lines  266  and  268 . Thus, as the sheet  236  continues to be advanced along the sheet transfer path  104  by the nip and idler roller assembly  206  to the position shown in  FIG. 5C , the sheet  236  is not sensed by the lateral position sensor  210  at the time expected by the microprocessor  256 . 
     Because the sheet  236  was not detected, the microprocessor  256  causes the lateral motion motor  228  to rotate in the direction of the arrow  270  which causes the pinion  230  to rotate in the same direction. As the pinion  230  rotates, the rack  234  is forced in the direction of the arrow  272 . Because the rack is attached to the nip and idler roller assembly  206 , the nip and idler roller assembly  206  and the sheet  236  which is grasped by the nip and idler roller assembly  206  also move in the direction of the arrow  272 . As shown in  FIG. 5C , the cross-wise movement of the nip and idler roller assembly  206  is not parallel to the double arrow  240  because a skew adjustment has been made. 
     The microprocessor  256  causes continued rotation of the lateral motion motor  228 , and thus translation of the sheet  236 , as the sheet  236  is advanced along the sheet transfer path  104  by the nip and idler roller assembly  206  until the sheet  236  is in the location shown in  FIG. 5D . As shown in  FIG. 5D , the sheet  236  has been translated until the outer edge of the sheet  236  is sensed by the lateral position sensor  210  which causes the lateral offset detector  260  to signal the microprocessor  256  that the sheet  236  has been sensed. Once the sheet  236  is sensed by the lateral position sensor  210 , the microprocessor  256  reverses the rotation of the lateral motion motor  228  thereby reversing the translation of the sheet  236  as described above until the edge of the sheet  236  is no longer sensed which correlates with the desired final registration location. Of course, in the event that the sheet  236  is initially sensed by the sensor  210 , the microprocessor simply translates the sheet  236  in a manner similar to that set forth above until the sheet  236  is no longer sensed. 
     In either event, the sheet  236  is properly aligned for the transfer of an image at the image transfer station  112 . The sheet  236  is still grasped, however, by the nip and idler roller assembly  206  which is not perpendicular to the sheet transfer path  104 . Thus, merely continuing to advance the sheet  236  with the nip and idler roller assembly  206  will result in lateral misalignment of the sheet  236 . Accordingly, the microprocessor  256  determines the necessary lateral adjustment and causes the lateral motion motor  228  to translate the nip and idler roller assembly  206  so as to maintain the sheet  236  in the desired registration position. The correction may be completed before the sheet  236  is released by the nip and idler roller assembly  206  or simultaneously with the release of the sheet  236 . 
     While the present invention has been described with reference to an embodiment wherein the registration system is integrated into a printing device, those of ordinary skill in the art will appreciate that the present invention may be incorporated into a variety of different devices wherein registration of a sheet is desired. Such devices include printers that utilize many different image marking processes including xerography, solid ink, thermal ink jet and others. 
     Moreover, the present invention may be used with a number of alternative detection or control schemes. By way of example, the skew of the sheet may be determined upstream of the nip and idler roller assembly. In such an embodiment, once the skew is determined and prior to grasping the sheet with the nip and idler roller assembly, the nip and idler roller assembly is pivoted to the same skew angle as the sheet. It may be further desired to translate the nip and idler roller assembly as the nip and idler roller assembly is being pivoted. This allows the nip and idler roller assembly to be optimally positioned with respect to the sheet transfer path even when the nip and idler roller assembly is at an angle to the sheet transport path. Once the sheet is grasped, the nip and idler roller assembly is pivoted to de-skew both the sheet and nip and idler roller assembly. Lateral correction can then be done and the sheet transported to the next nip or an image transfer station. 
     In yet a further embodiment, nip releases are used on the paper path drive nips located upstream of the registration system so that sheets would be free to rotate or move in a lateral direction. Such nip releases are commonly used with known paper registration devices. Additionally, lateral position sensors may be located prior to the nip and idler roller assembly. This allows the precise orientation of the sheet to be determined so that skew and lateral translation may be corrected at the same time. 
     Moreover, the weight of the lateral transfer motor and the process motor may vary from one device to another device. Accordingly, the location of the pivot may be varied so as to provide the desired weight distribution. By way of example,  FIG. 6  shows a registration device  300  that includes a nip and idler roller assembly  302 , a de-skew assembly  304 , a lateral motion assembly  306 , a process assembly  308  and a pivot pin  310 . The crosswise location of the pivot pin  310  is at the middle portion of the housing  312  of the process motor  308 . This is in contrast to the crosswise location of the pivot pin  226  shown in  FIG. 1  is inboard of the process motor  242 . 
     The power required to pivot a nip and idler roller assembly may be further reduced by allowing relative motion between the nip and idler roller assembly and the process motor. By way of example,  FIG. 7  shows a registration device  320  that includes a nip and idler roller assembly  322 , a de-skew assembly  324 , a lateral motion assembly  326  a process assembly  328  and a pivot  330 . 
     The process assembly  328  includes a process motor  332  that is used to a rotate a pulley  334 . The process motor  332  is fixedly mounted to the frame  336  of the registration device  320 . The process assembly further includes a pulley  338  that is in a fixed relationship with a gear  340 . The pulley  334  is connected to the pulley  338  by a belt  344 . Thus, when the pulley  334  rotates, the pulley  338  and the gear  340  will also rotate. The gear  340  is engaged with the gear  342  of the nip and idler roller assembly  322 . Thus, when the gear  340  rotates the nip and idler roller assembly  322  rotates. 
     The pulley  338  is mounted to the pivot mount  346 . Accordingly, when the de-skew assembly  324  causes the nip and idler roller assembly  322  to pivot, the pulley  338  will pivot. The process motor  332  remains stationary, however, because it is mounted to the frame  336 . Rather, the belt  344  twists, allowing for relative motion between the nip and idler roller assembly  322  and the process motor  332 , while allowing the process motor to continue to rotate the nip and idler roller assembly  322 . Accordingly, in the embodiment of  FIG. 7 , it is not necessary to pivot the process motor  332 . 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.