Abstract:
A sheet feeder is provided comprising at least two drives that drive a sheet of material along a paper path and at least two sensors that detect a lateral side of the sheet of material. A controller is connected to the two sensors and at least one of the drives. The controller varies the drive velocity of at least one of the drives to shift the lateral position of the sheet of material in a predetermined direction until one of the sensors detects the lateral side and then varies the velocity difference of the two drives to eliminate the skew of the sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet feeding system and, more particularly, to a sheet feeding system adapted to offset sheets of material for a sheet stacker. 
     2. Prior Art 
     Many different feeding devices are known in the sheet feeding art. For example, U.S. Pat. No. 5,639,080 discloses a system for handling purged sheets in the output of a printer which offsets print job sets relative to one another and also offsets purge sheets from regular job sheets with a laterally movable stacking tray. The mechanism associated with driving the laterally movable tray adds both cost and complexity to the sheet stacking device in order to provide offsetting capability. U.S. Pat. No. 5,887,996 discloses an apparatus and method for sheet registration using a single sensor that determines the position and skew of a sheet in a paper path. A pair of independently driven nips forward the sheet to a registration position in skew and at the proper time based on the output from the single sensor. Both U.S. Pat. Nos. 5,639,080 and 5,887,996 are herein incorporated by reference in their entirety. There is a desire to provide a sheet feeding system that provides capability to both deskew and offset sheets of material without the cost and complexity associated with a laterally movable tray being required in a sheet stacker. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a sheet feeder is provided comprising at least two drives that drive a sheet of material along a paper path and at least two sensors that detect a lateral side of the sheet of material. A controller is connected to the two sensors and at least one of the drives. The controller varies the drive velocity of at least one of the drives to shift the lateral position of the sheet of material in a predetermined direction until one of the sensors detects the lateral side. 
     In accordance with one method of the present invention, a sheet feeder is provided comprising a drive that drives a sheet of material along a paper path and at least three sensors proximate the drive. Two of the sensors detect a skew of the sheet of material, and at least one of the sensors detects the lateral offset of the sheet of material from the paper path. A controller is connected to the sensors and the drive. 
     In accordance with another embodiment of the present invention, a method of feeding sheets of material is provided comprising the steps of changing the skew of the sheet of material to a predetermined value and then detecting a lateral side of the sheet of material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
     FIG. 1 is a schematic view of a document creating apparatus; 
     FIG. 2 is a schematic elevation section view of a xerographic processing or printing section or engine; 
     FIG. 3 is a schematic plan view of the sheet feeder according to the present invention; 
     FIG. 4A is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the initial skew angle of the sheet has been determined; 
     FIG. 4B is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the skew angle of the sheet has been adjusted for right stacking; 
     FIG. 4C is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the edge of the sheet has been detected for right stacking; 
     FIG. 4D is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the sheet has been deskewed and offset for right stacking; 
     FIG. 5A is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the initial skew angle of the sheet has been determined; 
     FIG. 5B is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the skew angle of the sheet has been adjusted for left stacking; 
     FIG. 5C is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the edge of the sheet has been detected for left stacking; and 
     FIG. 5D is a schematic plan view showing a sheet of material being driven by the sheet feeder according to the present invention after the sheet has been deskewed and offset for left stacking. 
     FIG. 6 is a schematic plan view showing the second and third sensor placement. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown, in schematic form, a view of a document creating apparatus  2  for creating documents in accordance with teachings of the present invention. Although the present invention will be described with reference to the single embodiment shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms or embodiments. In addition, any suitable size, shape or type of elements or materials could be used. A copying or printing system of the type shown is preferably adapted to provide duplex or simplex stacked document sets from duplex or simplex collated document or print sets which result from either duplex or simplex original documents or output document computer files for print. 
     Document creating apparatus  2 , in the embodiment shown, is a copier. However, in an alternate embodiment, the apparatus could be a printer or any other suitable type of document creating apparatus. Document creating apparatus  2  generally comprises a xerographic processing or printing section  3 , a finishing section  6  and an output section  9 . Printing section  3  can be an electrostatographic printing system such as made by Xerox Corporation or alternately other xerographic or other type of printing apparatus. Printing section  3  incorporates an image transfer system and a transport system for transporting sheets of material. Finishing section  6  may typically incorporate a hole punch, a stacker, a stapler, or any other suitable type of feature known in the art. Output section  9  incorporates a tray  11  or a bin sorter that accepts and stacks documents or document sets output from finishing section  6  at output zone  12 . Documents are printed or copied in printing section  3  and output from printing section  3  to finishing section  6 . Documents can be sorted, stacked and bound at finishing section  6 . Document sets can be output from finishing section  6  at output zone  12 . 
     Referring now also to FIG. 2, there is shown is a schematic elevation view of one embodiment of the xerographic processing or printing section  3 . The printing section  3  has a photoconductive belt  14  that advances in the direction of arrow  16 . Photoconductive belt  14  passes through charging station  18  and exposure station  20  which is typically a raster output scanner that transmits a latent image from controller  22  onto the photoconductive surface of photoconductive belt  14 . Controller  22  gets the image from raster input scanner  24  that typically incorporates a CCD and scans an image from document handler  26 . Alternately, controller  22  gets the image from a separate computer  28  when printing section  3  operates as a printing device. Photoconductive belt  14  then advances to development station  30  where toner is electrostatically attracted to the latent image. Photoconductive belt  14  then advances to image transfer station  32 . A sheet of material  34  is advanced from sheet stack  38  or sheet stack  40  by a sheet transport system  36  that includes registration system  42  that registers sheet  34  and then advances sheet  34  past image transfer station  32  in a timed fashion. The toner deposited on the latent image of photoconductive belt  14  is transferred to sheet  34  due to sheet  34  becoming charged at image transfer station  32  and due to sheet  34  being registered or timed relative to the latent image. Sheet  34  is then advanced to fusing station  44  by belt  46  where the toner image is permanently affixed to sheet  34 , typically by heating, thus creating a document sheet. Sheet  34  will either be output to a finisher or a stacker by sheet feeder  50  or inverted at inverter  48  and recirculated through the printing section to have a second image deposited on its opposite side. Although the section  3  of the apparatus  2  has been described in detail above, features of the present invention could be used with other types of xerographic processing or printing sections having any suitably blank paper or sheet supply, created document output, image transfer system or paper path. The description above is merely intended to be exemplary. More or less features could also be provided. Although sheet feeder  50  is shown at a fixed position within the copying or printing apparatus, this position is intended to be exemplary and various alternative locations and modifications can be devised by those skilled in the art without departing from the invention. Such an alternative, for example, would be incorporating sheet feeder  50  at any point in the paper path of a copying or printing apparatus where the paper path is either upstream or downstream of the printing or copying operation. Such an alternative, for example, would be incorporating sheet feeder  50  in a finishing section or output section of a printing apparatus. An additional alternative, for example, would be incorporating belts instead of rollers within sheet feeder  50 . 
     Referring now also to FIG. 3, there is shown a schematic plan view of the sheet feeder  50  incorporating features of the present invention. Sheet feeder  50  includes the first drive  52  and the second drive  54 . First drive  52  and second drive  54  are shown on a common centerline but may alternately have offset centerlines from each other. First drive  52  has a first drive roll  56  and a first idler roll  58  located below drive roll  56 . Second drive  54  has a second drive roll  60  and a second idler roll  62  located below drive roll  60 . In each instance, the idler and drive rolls are urged against each other to allow sheets to be moved by frictional engagement between them. First drive roll  56  is driven by first motor  64 . Second drive roll  60  is driven by second motor  66 . Controller  68  is connected to first motor  64  and second motor  66 . Controller  68  is shown as a single controller, but may alternately be individual controllers, or logic circuits or part of an overall machine controller. First motor  64  may be directly connected to first drive roll  56  with shaft  70  or may be connected to additional drives or drive rolls in addition to first drive roll  56 . Through first motor  64 , controller  68  can vary first drive velocity  74  imparted to sheet of material A by first drive roller  56  either by varying the velocity of first motor  64 , by mechanical speed reduction as with gearing, belt or a clutch, or otherwise. Second motor  66  may be directly connected to second drive roll  60  with shaft  72  or may be connected to additional drives or drive rolls in addition to second drive roll  60 . Through second motor  66 , controller  68  can vary second drive velocity  76  imparted to sheet of material A by second drive roller  60  either by varying the velocity of second motor  66 , by mechanical speed reduction as with gearing, belt or a clutch, or otherwise. Sheet feeder  50  further comprises a first sheet sensor  78 , second sheet sensor  80  and third sheet sensor  82 . First sheet sensor  78 , second sheet sensor  80  and third sheet sensor  82  are connected to controller  68 . The sensors  78 ,  80  and  82  could be any type of suitable sensor, such as an optical sensor for example. The sensors  78 ,  80  and  82  are shown offset from shafts  70  and  72 , but may alternately be on the same centerline or further upstream or downstream of shafts  70  and  72 . The sensors  78 ,  80  and  82  are shown in line with each other, but may alternately be on the different centerlines further upstream or downstream. Sensors  78 ,  80  and  82  detect when an edge of sheet of material A passes and sends a signal to controller  72 . As the sheet of material A enters the sheet feeder, it is contacted by the two rolls  56 ,  58  of the first drive  52  and by the two rolls  60 ,  62  of the second drive  54 . Sheet of material A is advanced by the first drive  52  and the second drive  54  in a direction nominally parallel to the paper path  86  which is perpendicular to shafts  70  and  72 . Sheet of material A will continue to be advanced in a direction nominally parallel to the paper path  86  if first drive velocity  74  and second drive velocity  76  remain equal. 
     In the embodiment shown, first sensor  78  and second sensor  80  are positioned to determine the skew angle of sheet of material A when it passes through first drive  52  and second drive  54 . As sheet of material A enters first drive  52  and second drive  54  as shown in phantom as position A′, it is moving along the paper path  86  with a skew angle C measured from its leading edge  90  to a line perpendicular to paper path  86 . Phantom position A′ shows skew angle C to be initially in the clockwise direction, but it could be in a counterclockwise direction or straight (i.e.: C has zero degree angle). Controller  68  determines the skew angle C as a function of the velocity of sheet of material A and the time difference between when sheet of material A passes over first sensor  78  and second sensor  80 . Knowing the initial value of skew angle C, controller  68  can vary first drive velocity  74  and second drive velocity  76  to adjust skew angle C of leading edge  90  of sheet of material A to a desired value. Once a desired value for skew angle C is obtained, controller  68  can vary first drive velocity  74  and second drive velocity  76  such that they are equal and sheet of material A will then continue to be advanced in a direction nominally parallel to the paper path  86 . In the embodiment shown, second sensor  80  and third sensor  82  are positioned on opposite sides of the nominal location of the lateral side  92  of a sheet of material moving along paper path  86 . As a result, there is provided a sheet feeding system that provides capability to both deskew and offset sheets of material without the cost and complexity associated with a laterally movable tray being required in a sheet stacker. 
     Referring now to FIGS. 4A through 4D, there is shown a sheet feeding sequence where sheet of material A is offset a nominally fixed distance to the right of paper path  86 . FIG. 4A is a schematic plan view showing sheet of material A being driven by first drive roll  56  and second drive roll  60  after the initial skew angle C of lead edge  90  of sheet of material A has been determined from first sensor  78  and second sensor  80  as described above. FIG. 4B is a schematic plan view showing sheet of material A being driven by first drive roll  56  and second drive roll  60  after the skew angle of the sheet has been adjusted to skew angle C′ that is counterclockwise relative to paper path  86 . In the instance shown, where sheet of material A needed to rotate counterclockwise, this is accomplished with controller  68  varying first drive velocity  74  and second drive velocity  76  for a period of time such that first drive velocity  74  is greater relative to second drive velocity  76  until the desired skew angle C′ is being approached or is obtained. Once the desired skew angle C′ is being approached or is obtained, controller  68  can vary first drive velocity  74  and second drive velocity  76  such that they are equal and sheet of material A will then continue to be advanced in a direction nominally parallel to the paper path  86 . FIG. 4C is a schematic plan view showing a sheet of material A being driven by the first drive roll  56  and second drive roll  60  just after the lateral side  92  of sheet of material A has been detected by second sensor  80  and just before the deskewing maneuver. FIG. 4D is a schematic plan view showing sheet of material A being driven by the sheet feeder according to the present invention after the sheet has been deskewed and offset for right stacking. Sheet of material A is shown being driven by first drive roll  56  and second drive roll  60  after the skew angle of the lead edge  90  of sheet of material A has been adjusted to be perpendicular relative to paper path  86 . This is accomplished with controller  68  varying first drive velocity  74  and second drive velocity  76  for a period of time such that second drive velocity  76  is greater relative to first drive velocity  74  until the desired skew angle perpendicular to paper path  86  is being approached or is obtained. Once the desired skew angle is being approached or is obtained, controller  68  can vary first drive velocity  74  and second drive velocity  76  such that they are equal and sheet of material A will then continue to be advanced in a direction nominally parallel to the paper path  86  where lead edge  90  of sheet of material A is perpendicular relative to paper path  86 . In this manner, sheet of material A has been deskewed such that leading edge  90  is perpendicular to paper path  86  and lateral side  92  is offset to the right a nominally fixed distance relative to paper path  86  before sheet of material A completes contact with first drive roll  56  and second drive roll  60 . 
     Referring now to FIGS. 5A through 5D, there is shown a sheet feeding sequence where sheet of material A is offset a nominally fixed distance to the left of paper path  86 . FIG. 5A is a schematic plan view showing sheet of material A being driven by first drive roll  56  and second drive roll  60  after the initial skew angle C of lead edge  90  of sheet of material A has been determined from first sensor  78  and second sensor  80  as described above. FIG. 5B is a schematic plan view showing sheet of material A being driven by first drive roll  56  and second drive roll  60  after the skew angle of the sheet has been adjusted to skew angle C′ that is clockwise relative to paper path  86 . In the instance shown where sheet of material A needed to rotate clockwise, this is accomplished with controller  68  varying first drive velocity  74  and second drive velocity  76  for a period of time such that second drive velocity  76  is greater relative to first drive velocity  74  until the desired skew angle C′ is being approached or is obtained. Once the desired skew angle C′ is being approached or is obtained, controller  68  can vary first drive velocity  74  and second drive velocity  76  such that they are equal and sheet of material A will then continue to be advanced in a direction nominally parallel to the paper path  86 . FIG. 5C is a schematic plan view showing a sheet of material A being driven by the first drive roll  56  and second drive roll  60  just after the lateral side  92  of sheet of material A has been detected by third sensor  82  and just before the deskewing maneuver. Note that, as shown in FIG. 5C, first sensor  78  can similarly be used to detect lateral side  114  to trigger the deskewing maneuver for sheets that have the same width, thus eliminating the need for third sensor  82  in machines that are adapted to process sheets of material with a single width. FIG. 5D is a schematic plan view showing sheet of material A being driven by the sheet feeder according to the present invention after the sheet has been deskewed and offset for left stacking. Sheet of material A is shown being driven by first drive roll  56  and second drive roll  60  after the skew angle of the lead edge  90  of sheet of material A has been adjusted to be perpendicular relative to paper path  86 . This is accomplished with controller  68  varying first drive velocity  74  and second drive velocity  76  for a period of time such that first drive velocity  74  is greater relative to second drive velocity  76  until the desired skew angle perpendicular to paper path  86  is being approached or is obtained. Once the desired skew angle is being approached or is obtained, controller  68  can vary first drive velocity  74  and second drive velocity  76  such that they are equal and sheet of material A will then continue to be advanced in a direction nominally parallel to the paper path  86  where lead edge  90  of sheet of material A is perpendicular relative to paper path  86 . In this manner, sheet of material has been deskewed such that leading edge  90  is perpendicular to paper path  86  and lateral side  92  is offset to the left a nominally fixed distance relative to paper path  86  before sheet of material A completes contact with first drive roll  56  and second drive roll  60 . As a result, there is provided a sheet feeding system that provides capability to both deskew and offset sheets of material without the cost and complexity associated with a laterally movable tray being required in a sheet stacker. 
     Referring now also to FIG. 6, there is shown a schematic plan view showing the second sensor  80  and third sensor  82  placement for sheet feeder  50  incorporating features of the present invention. Sheet feeder  50  includes second drive  54  as herein described. Second drive  54  can vary second drive velocity  76 . Sheet feeder  50  further comprises second sheet sensor  80  and third sheet sensor  82  as herein described. Sensors  80  and  82  detect when the edge of sheet of material A passes. In the embodiment shown, second sensor  80  and third sensor  82  are positioned on opposite sides of the nominal edge position  126  of the lateral side of sheets of material moving along paper path  86 . Sensor  80  is located a distance  120  from nominal edge position  126  and a distance  124  from the centerline of second drive  54 . Distance  124  may be 3 millimeters. Distance  120  may be 5.5 mm. In and alternate embodiment, distances  120  and  124  may be greater or smaller or otherwise different. Sensor  82  is located a distance  122  from nominal edge position  126  and a distance  124  from the centerline of second drive  54 . Distance  124  may be 3 millimeters. Distance  122  may be 5.5 mm. In and alternate embodiment, distances  122  and  124  may be more or less or otherwise different. The system may offset and deskew sheets of material that are driven with an incoming lateral edge position range  128 . Incoming lateral edge position range  128  may be 6 millimeters (+/−3 millimeters). In alternate embodiments, incoming lateral edge position range  128  may be greater or smaller. The system may offset and deskew sheets of material with an output left edge position  136  located distance  140  from nominal edge position  126 . Distance  140  may be 8.5 millimeters. In an alternate embodiment, distance  140  may be greater or smaller. The system may offset and deskew sheets of material with an output left edge position range  138 . Output left edge position range  138  may be 3 millimeters (+/−1.5 millimeters). In an alternate embodiment, output left edge position range  138  may be more or less. The system may offset and deskew sheets of material with an output right edge position  130  located distance  132  from nominal edge position  126 . Distance  132  may be 8.5 millimeters. In an alternate embodiment, distance  132  may be greater or smaller. The system may offset and deskew sheets of material with an output right edge position range  134 . Output right edge position range  134  may be 3 millimeters (+/−1.5 millimeters). In an alternate embodiment, output right edge position range  134  may be more or less. In this manner, documents may be offset either left or right and easily identified by the user. 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.