Patent Publication Number: US-10329109-B1

Title: Vacuum shuttle with stitch and roll capabilities

Description:
BACKGROUND 
     The exemplary embodiment relates to registration of sheet media and in particular to a registration system which includes a vacuum shuttle head configured for realignment of the sheets. 
     Transport systems are widely used for transporting sheet media between and within modules of a printing system, such as between a sheet feeder and a marking module, or on a return path through the marking module to enable duplex (double-sided) printing. The transport system may include a combination of rollers, conveyor belts, vacuum-assisted transport units, and the like. In order to ensure that each sheet arrives at a printer component with no more than an acceptable level of skew and lateral errors, registration subsystems are used to steer the sheets to achieve correct alignment. 
     There are demands for new printer designs that are able to increase the size of the sheet (e.g., to about 66 cm, or longer, in the process-direction) or to increase the printer speed from what is conventionally achievable. For the registration subsystem, steering long sheets and steering sheets at high speeds are challenging. In high speed printers, the amount of time available to perform the registration correction is reduced, which can increase stresses on the sheets. This means that sheets may not be correctly registered if their input error is too large. Registration correction algorithms are used to attempt to steer these sheets to the machine registration targets. However, the large corrections may result in sheet trailing edges being driven into the sidewalls of the transport (resulting in sheet damage or jams) or cause sheets to slip, breaking free of the drive nips, resulting in poor registration. 
     In one type of registration subsystem, skew and lateral errors are corrected in one motion. This correction induces more skew to move the sheet laterally, creating a ‘tail-wag’ motion of the sheet. This motion of the sheet is stressful, and the tangential forces on the sheet may exceed the threshold of slip with larger sheets. Another type of registration subsystem uses independent drive rolls for correcting skew while lateral correction is effected by a translating (cross process) carriage. This has an advantage of decoupling the lateral and skew correction. However, the use of the translating carriage limits the maximum speed of the printer system due to the limit on the carriage return time that can be achieved, given the mass of the carriage (including motors, rollers and other drive elements). 
     One method used to enable registering large sheets is to manually adjust the positions of preceding modules to try to keep the input error low. For example, the sheet feeder may undergo an alignment procedure to reduce the errors in the sheet entering the marking module, or a duplex path alignment procedure may be performed. However, such module alignment procedures impact only the mean input error and are unable to address sheet-to-sheet variations. Thus, even though the average input error may be within acceptable bounds, sheet-to-sheet variations can result in mis-registration of some of the sheets. 
     There remains a need for a system and method for media registration which address these deficiencies and enable improvements in the capability of a printing system to handle faster sheet speeds, larger sheet sizes, and/or larger weight sheets. 
     INCORPORATION BY REFERENCE 
     The following references, the disclosures of which are incorporated herein in their entireties are mentioned: 
     U.S. Pat. No. 5,090,683, issued Feb. 25, 1992, entitled ELECTRONIC SHEET ROTATOR WITH DESKEW, USING SINGLE VARIABLE SPEED ROLLER, by Kamath, et al., describes a device for selectively turning documents which includes separately-driven drive rollers that are aligned transverse to a process direction, enabling the documents to be turned. Sensors adjacent the drive rollers are used to measure the skew of the document prior to being rotated. 
     U.S. Pat. No. 5,301,892, issued Apr. 12, 1994, entitled APPARATUS AND METHOD FOR WINDING A STRIP OF WEB MATERIAL ONTO A SPOOL, by Merz, et al., describes a vacuum shuttle head for holding a cut end of a web. 
     U.S. Pat. No. 6,488,275, issued Dec. 3, 2002, entitled ACTIVE PRE-REGISTRATION SYSTEM USING LONG SHEET TRANSPORTS, by Schlageter, describes a pre-registration system, which decreases the lateral offset of sheets before they reach an active registration system, by pivoting a long transport with a stepper motor in conjunction with sensing a lateral edge of the sheets. 
     U.S. Pub. No. 20020140157, published Oct. 3, 2002, entitled VACUUM CORRUGATION SHUTTLE FEED DEVICE FOR HIGH CAPACITY FEEDER, by Moore, et al., describes a paper feeder which acquires individual sheets of paper using positive and negative air pressures from the top of a stack and transports them forward. By using information input by the operator (paper weight and coating configuration) and information from sensors (indicating curl direction and magnitude), blower speeds can be adjusted to achieve the best possible performance for the given paper conditions. 
     U.S. Pub. No. 20060255525, published Nov. 16, 2006, entitled SHEET FEEDER VACUUM FEED HEAD WITH VARIABLE CORRUGATION, by DiNatale, et al., describes a sheet separating and feeding system with a vacuum feed head for separating a top sheet from a stack of sheets for sheet feeding. 
     U.S. Pub. No. 20100061786, published Mar. 11, 2010, entitled APPARATUS AND METHOD FOR DETECTING THE TRAVEL DIRECTION OF MEDIA IN A MEDIA PATH IN AN IMAGE MARKING AND FUSING SYSTEM by Van Bortel, et al., describes controlling the rotational angle of a fusing module in response to sensed information on an unfused marked media travel direction. 
     U.S. Pub. No. 20100225691, published Sep. 9, 2010, entitled SYSTEM AND METHOD FOR CORRECTING STITCH AND ROLL ERROR IN A STAGGERED FULL WIDTH ARRAY PRINTHEAD ASSEMBLY, by Wright, et al., describes a method for evaluating and correcting printhead position in a staggered full width array (SFWA) inkjet printhead assembly. Positional correction data for roll and stitch displacements is obtained printhead actuators are operated when a predetermined threshold in a displacement range is exceeded. 
     U.S. Pub. No. 20110139586, published Jun. 16, 2011, entitled VACUUM TRANSPORT BELTS, by Liang-Bih Lin, et al., describes media vacuum transport systems including media vacuum transport members. 
     BRIEF DESCRIPTION 
     In accordance with one aspect of the exemplary embodiment, a vacuum-assisted sheet registration system includes a transport member on which an associated sheet is conveyed in a process direction. A vacuum shuttle includes a vacuum head, which applies suction to the sheet, and actuators for rotating the vacuum head and for translating the vacuum head in a cross-process direction, relative to the transport member. A feedback system generates feedback instructions. The translation and rotation occurs while the vacuum is applied to the sheet, in response to the feedback instructions, to register the sheet. 
     In accordance with another aspect of the exemplary embodiment, a printer includes a marking engine. A sheet transport system conveys associated sheets on a paper path in a process direction to the marking engine. A vacuum shuttle, positioned in the paper path upstream of the marking engine, is provided for reducing skew and lateral offset of at least some of the sheets. The vacuum shuttle includes a vacuum head for applying suction to the conveyed sheets, a first actuator for translating the vacuum head in a cross-process direction, during the applying of suction, and a second actuator for rotating the vacuum head, during the applying of suction. A control system controls the first and second actuators. 
     In accordance with another aspect of the exemplary embodiment, a vacuum-assisted sheet registration method includes conveying a sheet on a paper path in a process direction, providing for detecting skew and lateral offset of the sheet, applying suction to the sheet with a vacuum head, and while the vacuum is applied to the sheet, translating the vacuum head in a cross-process direction to reduce the detected lateral offset, and rotating the vacuum head to reduce the detected skew. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side sectional view of a printing system including a registration system in accordance with one aspect of the exemplary embodiment; 
         FIG. 2  is a top plan view of the vacuum shuttle of  FIG. 1  in a first position; 
         FIG. 3  is a top plan view of the vacuum shuttle of  FIG. 1  in a second position; 
         FIG. 4  is an enlarged schematic side sectional view of the registration system of  FIG. 1 ; 
         FIG. 5  is a control diagram for a vacuum shuttle in accordance with one embodiment; 
         FIG. 6  is a control diagram for a vacuum shuttle in accordance with another embodiment; 
         FIG. 7  illustrates a method of printing; 
         FIG. 8  is a plot illustrating a registration simulation showing tangential force on a paper sheet in the case of relatively high skew and lateral offset; and 
         FIG. 9  is a plot illustrating a registration simulation showing tangential force on a paper sheet in the case of relatively low skew and lateral offset. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the exemplary embodiment relate to a sheet registration system incorporating a vacuum feed shuttle (or simply, a vacuum shuttle) which is controllable for lateral translation and angular rotation and to a method for registering sheet media with the registration system. The vacuum shuttle is positioned to acquire a sheet in the registration path and pull the sheet towards a marking device transport. 
     As used herein, a “printer,” or a “printing system” refers to one or more devices used to generate printed media by forming images on print media, using a marking material, such inks or toner particles. The printer may be a digital copier, bookmaking machine, facsimile machine, multi-function machine, or the like, which performs a print outputting function. The print media may be sheets of paper, card, transparencies, parchment, film, fabric, plastic, photo-finishing papers, or other coated or non-coated flexible substrates suitable for printing. 
     The printer includes a print module which may incorporate one or more xerographic marking devices in which toner particles are transferred from an electrically charged surface to the print media and then fused to the sheet. Alternatively, the printer may be inkjet printer which incorporates an inkjet marking device including inkjet heads which jet droplets of ink onto the print media, which are then cured, e.g., with ultraviolet radiation. Other marking devices are also contemplated. The printer may be configured for monochrome (single color) and/or color (more than one color) printing. 
     The “leading edge” of a sheet of print media refers to an edge of the sheet that is furthest downstream in the process direction. The “process direction” refers to the direction in which a sheet travels along a paper path during the printing process. 
     While some components of the printer are described herein as modules, this is not intended to imply that they are separately housed from each other and in some embodiments, may be otherwise separated into different housings or contained in a single printer housing. 
       FIG. 1  is a schematic illustration of a printer  10 . The printer is configured for forming images on sheets  12  of print media, such as paper, using a marking material, such as inks or toners. The printer  10  may be a xerographic machine, inkjet printer, combination thereof, or the like. A sheet transport system  14  conveys sheets to be printed from a sheet media supply unit  16  along a paper path  18  to a print module  20  in the downstream (process) direction, illustrated by arrow A. From the print module, the sheet transport system  14  conveys the printed sheets to a printed sheet output  22 , such as an output tray of a sheet stacker module  24 , optionally via one or more additional printer components, such as the illustrated finisher module  26 , which performs post-processing operations, such as stapling, collating, binding, and the like. The paper path  18  may include one or more return loop(s), such as the illustrated return loop  28 , for returning sheet media from a downstream printer component to an upstream one, e.g., for duplex printing. 
     The transport system  14  may include various mechanisms for conveying the sheets, such as rollers, drive nips, belts, air/vacuum assisted transport mechanisms, and the like. In particular, a sheet feeder  30  draws sheets singly from a stack  32  in the supply unit  16  and sends them in single file along the paper path  18 . A registration system  34 , located in a registration module  36 , intermediate the sheet feeder  30  and the print module  20 , repositions each sheet, as needed, to reduce skew (angular rotation with respect to the process direction) and/or lateral offset (in the cross-process direction). 
     While the components  16 ,  20 ,  24 ,  26 ,  30 ,  34  of the printer are often described as modules, this is not intended to imply that they are separately housed from each other and in some embodiments, may be contained in a single printer housing. 
     The illustrated registration system  34  includes a vacuum shuttle  40 , positioned above the paper path  18 , which has stitch/roll capabilities. Specifically, the vacuum shuttle  40  is configured for addressing both skew and lateral offset of each sheet  12  traveling along the paper path  18 . The registration system  34  may further include one or more additional sheet registration devices for reducing skew and/or lateral offset, such as the illustrated pre-registration unit  42 , which is positioned upstream of the vacuum shuttle  40 , and/or a further registration device(s), downstream of the vacuum shuttle  40  (not shown). The sheet  12  may be supported on and/or translated by one or more transport member, such as roller, nips, belts, etc., as it passes through the registration module  36 . In the illustrated embodiment, the sheet is transported in the process direction A by a registration transport member  44 , such as a belt which is driven by one or more drive members  46 , such as rollers. The top part of the belt  44  may be supported, from below, by a planar backing member  48 . Other suitable transport members  44  include nip rollers. 
     Optionally, the printer  10  includes a feedback system  50  which detects at least one of skew and lateral offset of the sheets and provides feedback to components of the printer for assisting in correction of the detected registration errors. The feedback system can also be used for learning repetitive registration errors, allowing the registration system to anticipate the likely corrections which will be needed. The illustrated feedback system  50  includes one or more sensors  52 ,  54 ,  56 ,  57 , positioned along the paper path  18 , to collect registration (e.g., sensor) data  58  for the conveyed sheets, such as sheet position and/or motion data related to skew and/or lateral offset. Suitable sensors include charge-coupled devices (CCD), contact image sensors (CIS), and similar sensor arrays. The sensors  52 ,  54 ,  56 ,  57  may detect motion and/or position of some or all of the conveyed sheets, or acquire other information from which lateral offset and skew of the respective sheet can be determined. 
     The registration data  58 , acquired by the sensors, is fed to a control system  60 , such as a computing device or microprocessor. The control system  60  includes hardware, such as memory  62  a processor  64 , and one or more inputs/outputs  66 ,  68 , which may all be connected by a data/control bus  70 . The memory  62  stores instructions, such as the illustrated registration control module  71 , for receiving information  58  from the sensors and for determining adjustments to the registration system  34  (and optionally other components of the printer) to address (reduce or eliminate) registration errors, such as skew and/or lateral offset. The processor  64  executes the instructions and outputs control signals  72  to the registration module  36 , or components thereof, and/or to other components of the printer, such as the sheet feeder  30 , for making appropriate adjustments. 
     The print module  20  can be configured for simplex (single sided) and/or duplex (double-sided) printing. In the illustrated embodiment, the print module  20  is a xerographic (laser) printing module and includes one or more marking devices  80  and one or more fixing devices, such as fuser  82 . In the marking module, marking media in the form of toner particles is attracted from a photoconductor surface to the charged sheet  12  to form an image, which is fused to the sheet by the fuser  82  using heat and/or pressure. Image data  84  for forming the image to be printed, is received, by the print module  20 , from the control system  50 , or a separate control system. The sheets are conveyed from the registration module  36  to the marking engine  80  by a marking transport  86 , such as a conveyor belt. A diverter  88 , downstream of the marking engine  80 , may be used to divert the sheets into the return loop  28 , when needed, for duplex printing. 
     In other embodiments, the print module may be an inkjet print module which includes a printhead as the marking device  80 , the printhead including an array of inkjet nozzles that apply droplets of ink to the sheet in a predefined pattern to form the image. The images may be cured with heat and/or UV radiation applied by an appropriate fixing device  82 . 
     Independent of the type of print module(s)  20  employed, registration errors, such as skew and/or lateral offset in the sheet  12  as it enters the print module can result in incorrect positioning of the image on the sheet. The exemplary registration system  34  with vacuum shuttle  40  assists in reducing registration errors in a manner which places less stress on the sheets than a conventional registration system, can accommodate print media of larger sizes and/or weights, and is able to compensate for errors in each sheet individually. 
       FIGS. 2 and 3  schematically illustrate the operation of the vacuum shuttle  40  in registering of a sheet  12  as view from above. The axis of the desired registration of the sheet, in the process direction, is indicated by dashed line  90 , which may lie along the midpoint of the belt  44  or other suitable location. Skew s is the degree to which the sheet is angled from the line  90  and is typically measured in a measure or rotation, such as milliradians (mrad). Lateral offset l may be defined as the lateral distance, from the registration axis  90 , of the midpoint  92  of the leading edge  94  (or trailing edge  96 , or somewhere between the two) of the sheet  12  and may be measured in mm. Lateral offset can be particularly problematic for large sheets since, when combined with skew, can lead to large variations from one end of the sheet to the other. Accordingly, lateral tolerances are generally tighter for larger sheets. For example, for standard sheets (less than 20.5″ (52.07 cm) in length) in a conventional high-speed printer, the lateral specification for l may be ±11 mm, which may be decreased to ±4 mm for large sheets (20.5″ (52.07 cm) −22.5″ (57.15 cm) in length and ±2 mm for extra-large sheets above 22.5″ and ±1 mm for the largest sheets that can be processed (e.g., 35″ (about 90 cm)). Skew tolerance may be independent of the size of the sheet, such as ±20 mrad for s. With the present registration system, these tolerances may be increased 
     When the leading edge  94 , or other part of the sheet reaches a known target point (detected by a point sensor), the sheet lateral position and skew can be calculated. These values can then be used by the control system  60  to determine appropriate skew and lateral corrections to steer the sheet to its target, which in the embodiment illustrated in  FIG. 1 , is the marking engine  80 . 
     The illustrated vacuum feed shuttle  40  includes a vacuum head  98  which applies suction to the sheet  12  as the sheet moves in the process direction A. The vacuum head  98  is movable laterally, in the cross-process direction B, and rotatable, in a plane parallel to that of the sheet  12 , in order to implement the lateral and skew corrections determined by the control system  60 . The vacuum feed shuttle  40  thus serves to hold the forward end of the sheet, then translate and/or rotate it, before delivering the sheet to the marker transport. 
     As illustrated in  FIG. 2 , the vacuum head  98  has first, second, third, and fourth sides  100 ,  101 ,  102 ,  103 , which together define an upwardly-extending side wall of the vacuum head. The fourth side  103  defines a leading edge of the vacuum head. The first and third sides  100 ,  102  of the head  98  are the sides most closely aligned with the process direction and the second and fourth sides  101 ,  103  of the head  98  are the sides most closely aligned with the cross-process direction and are perpendicular (or substantially perpendicular) to the first and third sides  100 ,  102 . By “substantially perpendicular,” it is meant no more than 90°±10° or 90°±5°. The head  98  may have a length L, along the transverse axis T of the head, i.e., between sides  100 ,  102 , of at least one third or at least a half of the maximum width (in the cross process direction) of the sheets to be processed by the printer, and/or no greater than a minimum width of the sheets to be processed, e.g., L is at least 10 cm or at least 15 cm and may be up to 20 cm. The length L may be greater than the width, in the process direction, of the head  98 . 
     The vacuum shuttle  40  includes a first (stitch) actuator  104 , which is positioned adjacent the first side  100  (and/or third side  102 ) of the vacuum head  98  to implement lateral movement of the vacuum head. In particular, the actuator  104  is generally aligned with the transverse axis T of the vacuum head  98 . A second (roll) actuator  106  is positioned adjacent the second side  101  of the vacuum head  98 , to implement rotational movement of the head  98 , in a plane parallel to the sheet  12  and belt  44 . The actuator  106  is offset from the center of the second side  101 , i.e., closer to the third side  102  of the head than to the first side  100 . 
     As illustrated in  FIGS. 2 and 3 , each of the actuators  104 ,  106  may include a respective drive mechanism  108 ,  110 , such as a micro-stepper motor, servomotor, a solenoid, or other linear actuator. The drive mechanism  108 ,  110  drives an extensible member  112 ,  114  in a direction perpendicular or substantially perpendicular to the respective adjacent wall  100 ,  101  of the vacuum head  98 . 
     In one embodiment, the drive mechanisms  108 ,  110  each remain in a fixed position, with respect to the process and cross-process directions, although rotational movement may be permitted. The vacuum head  98  may be mounted on the extensible members, and/or otherwise supported for angular and lateral movement in a plane parallel to the sheet. In another embodiment, not illustrated, the drive mechanisms  108 ,  110  are attached to the respective side  100 ,  101  of the vacuum head and drive the extensible member  112 ,  114  in an opposite direction, away from the respective wall, against a respective bearing surface mounted in a fixed position adjacent to the actuator. The extensible member  112 ,  114  may be a post or screw, which is extended away from, or towards, the actuator motor, to push/pull the vacuum head  98  away from/towards the respective actuator. Depending on the amount of lateral or skew correction needed, the actuators  104 ,  106  may be driven at faster or slower speeds in order to complete the correction in the time available. In some embodiments, the transport  46  may be halted or slowed, temporarily, to increase the time available for correction. In general, correction can be achieved in about 100-200 ms. 
     The vacuum shuttle  40  can be adjusted with the stitch actuator  104  to compensate for lateral offset and any skew from the paper guides can be reduced with the roll actuator  106 , delivering a better pre-registered sheet to the downstream component(s) ahead of it. As shown in  FIG. 3 , which illustrates the sheet  12  after registration correction, the actuators  104 ,  106  on the vacuum shuttle have been operated to “stitch and roll” the vacuum head  98  to reduce the skew and fix the lateral position of the sheet before marking. As a result, angle s (the skew of the sheet) is reduced to closer to 0 mradians and the lateral offset l of the sheet is reduced to closer to 0 mm, as the vacuum head translates and rotates. 
     The vacuum head  98  applies suction to the sheet  12  during the translation and rotation of the vacuum head, e.g., through a two-dimensional array of suction ports  116 , as shown schematically in  FIG. 3 . The vacuum head  98  is controlled such that it applies suction only to a forward end  118  of the sheet (less than half of the sheet). As a result, the leading edge  94  of the sheet moves substantially in tandem with the movement of the shuttle  98 . The trailing edge  96  of the sheet, which is not tightly held by nips, responds to the movement of the leading edge and is thus also registered. When the stitch and roll motion is complete, the vacuum is released and the forward end  118  of the sheet drops onto a transport member below, such as the marker transport  86 . 
     Optionally, a constraint mechanism  120  serves to reduce upward shift of the portion of the sheet adjacent to the trailing edge  96  by providing a downward force on the sheet  12  and/or limiting its upward movement, without unduly limiting the ability of the trailing edge to move in the plane of the transport  44 . With reference also to  FIG. 4 , the exemplary constraint mechanism  120  includes a generally planar structure  122 , such as baffle plate or movable belt, positioned above the transport  44 , to hold the sheet between the structure  122  and the transport. The illustrated structure  122  supports an array of rotatable idler members  124 , such as balls, rollers, omnidirectional wheels, or the like. The rotatable members  124  do not significantly restrict freedom of movement of the sheet  12  in the plane of the sheet, but urge the sheet into contact with the transport member  44  below the sheet. The illustrated rotatable members  124  are spherical balls, which are spaced from each other in the process and cross process directions. The balls are each held within a respective bearing cavity  126  with an opening  128  in a lower surface  130  of the plate  122 . The cavity is slightly larger than the diameter of the ball, while the opening  128  is slightly smaller than the diameter of the ball, thus retaining the ball within the cavity, while allowing the ball to protrude through the opening  128  and contact the sheet. The balls  124  may be formed of rubber, metal, e.g., steel, or plastic. As the sheet  12  moves, the balls rotate. The balls are not driven and are independently free to move in any direction, allowing the sheet to undergo registration corrections as it passes under the constraint mechanism  120 . 
     Other constraint mechanisms  120  positioned above the sheet are also contemplated, such as a simple baffle, an air-assisted baffle through which air is pumped through perforations onto the sheet, a vibrating baffle, or the like, or a combination of constraint mechanisms. 
     The vacuum head  98  includes a horizontal plate  140  forming a base of the vacuum head. The array of suction ports  116  may be defined by openings in the plate  140 . For example, the openings may be distributed over the plate in rows and columns, as illustrated schematically in  FIG. 3 . There may be at least five rows of suction ports  116  in the cross process direction and at least three columns of suction ports in the process direction, or at least 15, or at least 20, or at least 30 suction ports in total. The suction ports  116  are in fluid communication with a plenum  144 , which in turn is connected to a suction source  146 , such as a vacuum pump. The suction source  146  may be located in the head  98 , as illustrated in  FIG. 4 , or located elsewhere in the printing system and fluidly connected with the plenum by suitable tubing. In other embodiments, the suction ports may be connected to separate vacuum tubes. The vacuum pump  146  may be controlled to apply suction to the sheet  12  prior to and during the lateral and/or rotational movement of the vacuum head  98 , e.g., by opening and closing a valve  148  in a conduit connecting the pump to the plenum  144 . The leading edge of the sheet is held by the suction from the suction heads and is registered as the vacuum shuttle moves laterally and/or rotates. The trailing edge  96  is drawn into the desired alignment by the movement of the leading edge  94 . The vacuum shuttle is not limited to the design shown in  FIG. 4 , other types of vacuum head  98  are also contemplated. 
     In addition to providing lateral and rotational movement of the leading edge of the sheet, the vacuum shuttle  40  may be used to convey the sheet in a downstream direction. For example, the vacuum shuttle  40  may apply pressurized air to the sheet (e.g., through ports  116  or separate ports) after the vacuum is released, in a direction to urge the sheet in the process direction. 
     As will be appreciated, a vacuum shuttle configured as for vacuum shuttle  40  can be used elsewhere in the printing system. A vacuum shuttle intermediate the sheet feeder  30  and the preregistration device  42 , e.g., at position P 1  and or P 2 , may be used to provide a more accurate input to the preregistration device  42 , compensating for variance in the feeder drawer latch system and operator error induced by poor paper loading. 
     The preregistration device  42 , where used, may be any suitable device for assisting in registration of the sheets  12 . As an example, the preregistration device  42  may be a Translation Electronic Registration (TELER) type of registration device or an agile nip registration device. A TELER system often includes three optical sensors, a pair of coaxial independently driven drive rolls, a carriage with a linear drive on which paper drive rolls are mounted, and a microprocessor controller. The carriage moves the rollers in the transverse direction and then is returned to its original position for the next sheet. In an agile system, a pair of independently driven selectively actuable nips are used to drive a sheet transverse to a paper path direction until the edge of a sheet is registered laterally and without skew. The transverse nips are then deactivated and a drive nip moves the sheet in a process direction along the paper path. U.S. Pub. Nos. 20030146567, 20060208416, and 20080240820, and U.S. Pat. Nos. 4,971,304, 5,169,140, 5,219,159, 5,278,624, 5,697,608, 5,794,176, 6,137,989, 6,168,153 and 6,533,268, incorporated by reference, provide descriptions of such registration systems, which may be used herein as a pre-registration device  42 . Alternatively or additionally, a registration device (not shown) as described for pre-registration device  42  may be positioned downstream of the vacuum shuttle, to provide a fine-tuned registration of the at least partially registered sheet  12 , after it leaves the vacuum shuttle  40  and before it enters the downstream printer component, such as the marking engine  80 . 
     The control system  60  controls the first and second actuators  104 ,  106  in order to reduce skew and/or lateral offset of the sheet. In particular, the information from the position sensor  54  may be used to control the first and second actuators  104 ,  106  to provide the appropriate movement of the vacuum head  98 , during suction, and may also be used to adjust the amount of suction applied by the vacuum head and/or the length of time over which the suction is applied to the sheet. The sensor  54  may acquire the sensor data  58  before the sheet has reached the vacuum shuttle. Additionally or alternatively, the sensor data may be acquired later. For example the sensor  54  may acquire the sensor data  58  when the vacuum shuttle has applied suction to the forward end  118  of the sheet. 
     Additional sensor(s)  56  ( FIG. 1 ), positioned to acquire sheet position data downstream of the vacuum head  98 , may be used to assess whether the registration correction was effective, and to fine tune the control of the actuators  104 ,  106  for registering subsequent sheets. Alternatively or additionally, the sensors  56  may be used to adjust downstream printer components, such as the marking device  80  and/or fixing device  82  to enable them to cope with any remaining mis-registered sheet. In the case of duplex printing, a sensor  57 , positioned downstream of the marking engine  80  may be used to ensure that the image on the second side of the sheet is closely aligned with that on the first side of the sheet. In this case, registration errors detected for the first side of the sheet may be retained for the second side and/or used to reposition the image on the second side. 
     In one embodiment, a feedback loop is used to learn the correction needed and position the vacuum shuttle  40  appropriately to receive the next sheet. In this embodiment, the sensor array  54  may be used to measure the position of the sheet when it is acquired by the vacuum shuttle  40 . A feedback loop then begins to adjust the shuttle head for the subsequent sheet. This approach may be useful to compensate for gradual shifts in the stack  32 , however, in order to be able to address outliers, the vacuum shuttle  40  is adjusted independently for each sheet. The various registration devices  40 ,  42 , etc. in the printing system can all be controlled by the same control system  60 , allowing them to operate in concert to reduce registration errors. Feedback instructions  72  may be provided to each of the registration devices, based on the received sensor information  58 . In the case of the vacuum shuttle, the feedback instructions may include some or all of start and stop times for the vacuum pump  146 /suction to commence and stop; lateral displacement of the feed head during suction (and/or other instructions for actuator  104 , such as speed of the actuator motor  108 ); angle of rotation of the vacuum feed shuttle during suction (and/or other instructions for actuator  106 , such as speed of the respective actuator motor  110 ). In some embodiments, the feedback instructions may include instructions suitable for returning the vacuum shuttle head  98  into a suitable position for receiving the next sheet. 
       FIGS. 5 and 6  illustrate example control diagrams.  FIG. 5  shows a control diagram for the case of a vacuum shuttle  40  forming a part of the registration system  34 . Input registration data  150  may be collected using a pair of CCD sensors  54  or similar sensing device, to read the skew and lateral offset of the forward edge  94  of the sheet ( FIG. 3 ). Output registration data  152  may be collected in a similar fashion, e.g., by sensor  56  ( FIG. 4 ), or it may be collected downstream of marking, where the sheet could be scanned, e.g., by sensor  57 , and corrections to image-on-paper (IOP) registration could be made on-the-fly. 
       FIG. 6  shows a control diagram for the case of a vacuum shuttle (analogous to vacuum shuttle  40 ) which forms a part of the sheet feeder  30 , e.g., at position P 1 . In this embodiment, nonvolatile memory (NVM) values may be stored values from previous runs, or zeroes (no correction) for the first run of a given media and tray. Output registration data  152  may be acquired by sensor  52  or the input registration data acquired by sensor  54 . 
     With reference to  FIG. 7 , a sheet registration method which may be performed with the registration system of  FIGS. 1-4  is shown. The method begins at S 100 . 
     At S 102 , first sensor data  58  is acquired from a first sensor array  54  positioned upstream of a vacuum shuttle  40  of a registration system to acquire sheet position and or motion information, e.g., as a leading edge  96  of a current sheet  12  is conveyed beneath the sensor array  54 . 
     At S 104 , the first sensor data is processed by the control system  60  to compute first feedback instructions  72  for the vacuum shuttle  40  which, when implemented, are predicted to reduce registration errors in the sheet to within acceptable tolerance limits on the errors. 
     At S 106 , in response to the first feedback instructions  72  (and/or second feedback instructions, described below), the vacuum shuttle  40  may be moved into a first position, by operating actuator  104  and/or  106 , if the vacuum shuttle is not already in a suitable position for receiving the sheet. 
     At S 108 , a vacuum is applied to the suction ports  116  of the vacuum head  98 , when the leading edge of the sheet has reached the vacuum shuttle, to apply suction to hold the forward end  118  of the sheet in a fixed position, relative to the vacuum head  98 . 
     At S 110 , the vacuum shuttle is moved from the first position ( FIG. 2 ) into a second position ( FIG. 3 ), by operating actuator  104  and/or  106  in accordance with the feedback instructions  72 , while maintaining the suction on the current sheet. The forward end  118  of the sheet is held by the suction, allowing the sheet to be registered. As will be appreciated, only one of, or neither of, the actuators may be needed for sheets which are within the predefined tolerances. 
     At S 112 , the registered sheet  12  is released by lowering the applied vacuum, and the sheet is conveyed downstream by a suitably positioned sheet transport  44  and/or  86 , and conveyed to a processing component, such as the marking engine. 
     Optionally, at S 114 , second sensor data  58  may be acquired from a second and/or third sensor array  56 ,  57  positioned downstream of the vacuum shuttle  40  to acquire sheet position and or motion information, e.g., as a leading edge  96  of the same sheet is conveyed beneath the sensor array  56 ,  57 . 
     At S 116 , the second sensor data acquired at S 114  may be processed by the control system  60  to compute feedback instructions  72  for the vacuum shuttle  40  which, when implemented, are predicted to assist in reducing registration errors in a subsequent sheet(s). The second feedback instructions may be provided to the vacuum shuttle  40  to assist in registering the subsequent sheet when the method returns to S 106 . 
     In some embodiments, preregistration of the current sheet is performed at S 118  and/or post registration of the current sheet is performed at S 120 . 
     If at S 122 , there are no more sheets to be registered, the methods proceeds to S 124 , otherwise returns to S 102  or S 118 , where the subsequent sheet serves as the current sheet. 
     The method ends at S 124 . 
     Advantages of the exemplary vacuum feed shuttle  40  may include the following: 
     1. Nips do not need to be opened and closed to perform separate corrections. Vacuum suction reduces the time necessary to perform steering. Also, this allows for a simpler method of closed loop correction, since small corrections to skew and lateral position of the sheet can occur on-the-fly without having to cycle nips through opened and closed positions and losing time to do corrections from those wait periods. 
     2. Corrections to lateral offset and skew can occur simultaneously, thus reducing the registration time significantly. This is advantageous for faster throughput. 
     3. Forces on the registration transport are reduced, with sheets being less out of specification. 
     4. Avoids/reduces the need for manual adjustment of printer components  80 ,  82 , etc., to compensate for lateral offset and/or skew. 
     The registration system  34  is able to correct or significantly reduce registration errors to within predefined tolerances on skew and lateral offset, such as the specifications noted above or narrower, not only in terms of the average sheet, but for individual sheets also.  FIGS. 8 and 9  illustrate registration simulations showing tangential force on the paper sheet in the cases of relatively high skew and lateral offset (Example 1 in Table 1) and relatively low skew and lateral offset (Example 2 in Table 1): 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Registration of sheet with high skew and lateral offset 
               
            
           
           
               
               
               
               
               
            
               
                 Paper Properties 
                 Learned offsets 
                 Input error data 
                 Ex. 1 
                 Ex. 2 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Process  
                 26 
                 Lateral  
                 0 
                 Leading edge 
                 2 
                 0.5 
               
               
                 length 
                   
                 offset 
                   
                 lateral shift  
                   
                   
               
               
                 (inches) 
                   
                 (mm) 
                   
                 (mm) 
                   
                   
               
               
                 X-process 
                 14.33 
                 Skew offset 
                 0 
                 Trailing edge 
                 −20 
                 −5 
               
               
                 width  
                   
                 (mrad) 
                   
                 lateral shift  
                   
                   
               
               
                 (inches 
                   
                   
                   
                 (mm) 
                   
                   
               
               
                 Sheet  
                 350 
                 Process dir. 
                 0 
                 Process time 
                 135 
                 135 
               
               
                 weight 
                   
                 offset  
                   
                 (ms) 
                   
                   
               
               
                 (gsm) 
                   
                 (mm) 
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     As can be seen from  FIGS. 8 and 9 , the tangential force on the input is corrected with the stitch and roll of the vacuum head. 
     It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. 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.