Abstract:
A method measures the location of a sheet and then moves the sheet to a registered position. By measuring the actual location of the sheet and then moving the sheet to the registered position, the invention saves a substantial amount of time. An elongated array of LED sensors  130  stretches over several inches and is aligned with a collimated light source  110.  Each sensor in the array is spaced from its adjacent sensor by a known amount. This amount can be as small as a few tens of thousandths of an inch. The edge of a sheet covers the sensors. The sheet edge is measured and the registration device moves the edge of the sheet to the registered position for receiving the developed image.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of the priority filing date of U.S. provisional patent application Ser. No. 60/434,859 filed Dec. 19, 2002. 

   FIELD OF THE INVENTION 
   This invention relates in general to electrographic print engines, and in particular, to a method and apparatus for registering copy sheets with a developed image. 
   BACKGROUND 
   Printers and copiers that transfer a toner developed image to a copy sheet have a common problem. All such machines need to accurately register the copy sheet with the image. This can be difficult because the copy sheet and the image may be traveling at different speeds and along different paths. Some have attempted to solve this problem by driving a copy sheet to a fixed gate, but such a technique is generally slow. In modern, high-speed electrographic machines, copy sheets are often registered using opto-electronic systems. Such systems provide added speed and certainty of position. 
   As a copy sheet approaches its registration position, a suitable registering mechanism straightens the sheet and moves it to its registered position. In order to do this, it is often necessary to axially align the sheet by removing any angular rotation that the sheet may have with respect to the developed image. Once the sheet is axially aligned or otherwise taken out of skew, the sheet must then be jogged into its desired position. A mechanism for removing the skew and for jogging the sheet to its registered position is shown and described in U.S. Pat. No. 5,322,273, whose entire disclosure is herein incorporated by reference. 
   While the mechanism described above is capable of handling the sheet, the problem remains of how to determine the proper position for the sheet. In at least one prior art system, the problem is solved by using multiple pairs of light emitting diodes and photodetectors. The LEDs and photodiodes are positioned transverse to the sheet&#39;s path. The opto-electrical components are mounted on circuit boards that are fixed with respect to the registration mechanism. Multiple pairs of discrete LEDs and photodiodes are used in order to derive edge sensors for different size sheets, such as type letter, legal size, A4 and other sizes. In operation, the registering mechanism first removes the skew from the sheet before the photodiodes and LEDs are operated. The sheet is stopped by the registration mechanism and is moved in one direction and then in the opposite direction until the edge of the sheet just covers or reduces the light received by the photodiode that senses the edge of the sheet. In order words, the sheet is entirely removed from the path of the photodiode and then is incrementally moved back toward the photodiode corresponding to the known sheet length until the edge of the sheet is detected. 
   Such prior art systems have the advantage of providing certainty of location and are highly reliable. By systematically driving the sheet away from the photodiode and then back towards it until its light is initially attenuated, one can very accurately detect the edge of the sheet. Once the edge of the sheet is detected, the sheet can be jogged to a final reference position. Thereafter, the sheet is released from the registration mechanism and is fed into a transfer station where the toned image is transferred to the suitable registered copy sheet. 
   Although such registration systems are reliable, they still have a number of drawbacks. They are inherently slow because they must always move the sheet once the sheet is in the registering mechanism. This requires stopping the sheet and jogging the sheet in opposite directions. As productivity demands for electrographic machines increase almost to the level of small printing presses, the time it takes to stop and jog a sheet to register the copy sheet is no longer acceptable. In addition, such systems cannot, without modification, register arbitrary size paper. They depend upon standard size papers for operating a pair of sensors that corresponds to the anticipated size of the paper. If a paper with a non-standard size is used as a copy sheet, the machine cannot accurately register the paper. To do that, the registration system has to be altered to include a further set of sensors designed to register the non-standard paper. However, another non-standard paper size will require still another modification to the machine and another pair of sensors. Therefore, the problem of providing a reliable and fast apparatus for registering copy sheets and for providing a system that can register any size copy sheet remains unsolved. 
   SUMMARY 
   The invention solves the problem of the prior art by dispensing with the technique of moving the sheet to a predetermined register location. Instead, the invention actively measures the unskewed position of the sheet and then moves the sheet to the desired registered position. By measuring the actual location of the sheet and then moving the sheet to the registered position, the invention saves a substantial amount of time. No longer does the machine have to stop the sheet, move it in one direction and then the other and thereby incur acceleration and deceleration losses. Instead, the invention keeps the copy sheet in near continuous motion so that the time spent by the sheet in the registration station is substantially reduced. By using this technique of measuring the sheet rather than mere edge detection, the invention registers sheets of known size as well as sheets of arbitrary length. 
   In one embodiment of the invention, an elongated array of LED sensors stretches over several inches and is aligned with a collimated light source. Each sensor is spaced from its adjacent sensor by a known amount. This amount can be as small as a few tens of thousandths of an inch. By knowing where the edge of the sheet is relative to such a linear array, cross-tracking motors in the registration device can readily move the edge of the sheet to its proper registered position for receiving the developed image. 
   It is also be possible to use a single light source without collimating it together with one or more arrays of light sensors. One problem with using a single light source for multiple sensors is parallax. In addition, the light source might have to be made so intense that the light might even penetrate edges of the sheet and give a false reading. 
   Still another embodiment of the invention, it provides multiple pairs of light sources and arrays. The arrays are exposed on opposite sides of a path of the copy sheet. There is one light source per array. The parallax problem is solved by simple trigonometry and its solution is stored in the memory of a computer that normally operates the machine. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of the sheet registration mechanism, according to this invention, partly in cross-section, and with portions removed to facilitate viewing; 
       FIG. 2  is a view, in perspective, of the sheet registration mechanism of  FIG. 1 , with portions removed or broken away to facilitate viewing; 
       FIG. 3  is a top plan view of the sheet registration mechanism of  FIG. 1 , with portions removed or broken away to facilitate viewing; 
       FIG. 4  is a top schematic illustration of the sheet transport path showing the actions of the sheet registration mechanism according to this invention on an individual sheet as it is transported along such transport path; 
       FIG. 5  is a schematic view of one light source opposite one array; 
       FIG. 6  is a plan view of a portion of a registration board with multiple arrays; 
       FIG. 7  is an end view of the portion of the registration board shown in  FIG. 6 . 
   

   DETAILED DESCRIPTION 
   Referring now to the accompanying drawings, FIGS. 1–3 best show the sheet registration mechanism, designated generally by the numeral  10 . It is located in association with a substantially planar sheet transport path P of any well known device where sheets are transported seriatim from a supply (not shown) to a station where an operation is performed on the respective sheets. For example, the device may be a reproduction apparatus, such as a copier or printer or the like, where marking particle developed images of original information, are placed on receiver sheets. Marking particle developed images (e.g., image I) are transferred at a transfer station T from a movable web or drum (e.g., web W) to a sheet of receiver material (e.g., a cut sheet S of plain paper or transparency material) moving along the path P. 
   In reproduction apparatus of the above type, it is desired that the sheet S be properly registered with respect to a marking particle developed image in order for the image to be placed on the sheet in an orientation to form a suitable reproduction for user acceptability. Accordingly, the sheet registration mechanism  10  provides for alignment of the receiver sheet in a plurality of orthogonal directions. That is, the sheet is aligned, with the marking particle developed image, by the sheet registration mechanism by removing any skew in the sheet (angular deviation relative to the image), and moving the sheet in a cross-track direction so that the centerline of the sheet in the direction of sheet travel and the centerline of the marking particle image are coincident. Further, the sheet registration mechanism  10  times the advancement of the sheet along the path P such that the sheet and the marking particle image are aligned in the in-track direction as the sheet travels through the transfer station T. 
   In order to accomplish skew correction and cross-track and in-track alignment of the sheet, for example with respect to a marking particle developed image on the moving web W, the sheet registration apparatus  10  includes first and second independently driven roller assemblies  12 ,  14 , and a third roller assembly  16 . The first roller assembly  12  includes a first shaft  20  supported adjacent its ends in bearings  22   a ,  22   b  mounted on a frame  22 . Support for the first shaft  20  is selected such that the first shaft is located with its longitudinal axis lying in a plane parallel to the plane through the sheet transport path P and substantially perpendicular to the direction of a sheet traveling along the transport path in the direction of arrows R ( FIG. 1 ). 
   A first urging roller  24  is mounted on the first shaft  20  for rotation therewith. The urging roller  24  has an arcuate peripheral segment  24   a  extending about 180 degrees around such roller. The peripheral segment  24   a  has a radius to its surface measured from the longitudinal axis of the first shaft  20  substantially equal to the minimum distance of such longitudinal axis from the plane of the transport path P. A first stepper motor M 1 , mounted on the frame  22 , is operatively coupled to the first shaft  20  through a gear train  26  to rotate the first shaft when the motor is activated. The gear  26   a  of the gear train  26  incorporates indicia  28  detectable by a suitable sensor mechanism  30 . The sensor mechanism  30  can be either optical or mechanical depending upon the selected indicia. Location of the sensor mechanism  30  is selected such that when the indicia  28  is detected, the first shaft  20  will be angularly oriented to position the first urging roller  24  in a home position. The home position of the first urging roller is that angular orientation where the surface of the arcuate peripheral segment  24   a  of the roller  24 , upon further rotation of the shaft  20 , will contact a sheet in the transport path P. 
   The second roller assembly  14  includes a second shaft  32  supported adjacent its ends in bearings  22   c ,  22   d  mounted on the frame  22 . Support of the second shaft  32  is selected such that the second shaft is located with its longitudinal axis lying in a plane parallel to the plane through the sheet transport path P and substantially perpendicular to the direction of a sheet traveling along the transport path. Further, the longitudinal axis of the second shaft  32  is substantially coaxial with the longitudinal axis of the first shaft  20 . 
   A second urging roller  34  is mounted on the second shaft  32  for rotation therewith. The urging roller  34  has an arcuate peripheral segment  34   a  extending about 180 degree around such roller. The peripheral segment  34   a  has a radius to its surface measured from the longitudinal axis of the first shaft  20  substantially equal to the minimum distance of such longitudinal axis from the plane of the transport path P. The arcuate peripheral segment  34   a  is angularly coincident with the arcuate peripheral segment  24   a  of the urging roller  24 . A second independent stepper motor M 2 , mounted on the frame  22 , is operatively coupled to the second shaft  32  through a gear train  36  to rotate the second shaft when the motor is activated. The gear  36   a  of the gear train  36  incorporates indicia  38  detectable by a suitable sensor mechanism  40 . The sensor mechanism  40 , adjustably mounted on the frame  22 , can be either optical or mechanical depending upon the selected indicia. Location of the sensor mechanism  40  is selected such that when the indicia  38  is detected, the second shaft  32  will be angularly oriented to position the second urging roller  34  in a home position. The home position of the second urging roller is that angular orientation where the surface of the arcuate peripheral segment  34   a  of the roller  34 , upon further rotation of the shaft  32 , will contact a sheet in the transport path P. 
   The third roller assembly  16  includes a tube  42  surrounding the first shaft  20  and capable of movement relative to the first shaft in the direction of the longitudinal axis thereof. A pair of third urging rollers  48  are mounted on the first shaft  20 , supporting the tube  42  for relative rotation with respect to the third urging rollers. The third urging rollers  48  respectively have an arcuate peripheral segment  48   a  extending about 180 degree around each roller. The peripheral segments  48   a  each have a radius to its respective surface measured from the longitudinal axis of the first shaft  20  substantially equal to the minimum distance of such longitudinal axis from the plane of the transport path P. The arcuate peripheral segments  48   a  are angularly offset with respect to the arcuate peripheral segments  24   a ,  34   a  of the first and second urging rollers. The pair of third urging rollers  48  is coupled to the first shaft  20  by a key or pin  44  engaging a slot  46  in the respective rollers. Accordingly, the third urging rollers  48  will be rotated by drive shaft  20  when the first shaft is rotated by the first stepper motor M 1 , and are movable in the direction along the longitudinal axis of the first shaft with the tube  42 . For the purpose to be more fully explained below, the angular orientation of the third urging rollers  48  is such that the arcuate peripheral segments  48   a  thereof are offset relative to the arcuate peripheral segments  24   a  and  34   a.    
   A third independent stepper motor M 3 , mounted on the frame  22 , is operatively coupled to the tube  42  of the third roller assembly  16  to selectively move the third roller assembly in either direction along the longitudinal axis of the first shaft  20  when the motor is activated. The operative coupling between the third stepper motor M 3  and the tube  42  is accomplished through a pulley and belt arrangement  50 . The pulley and belt arrangement  50  includes a pair of pulleys  50   a ,  50   b , mounted for rotation and in fixed spatial relation, for example, to a portion of the frame  22 . A drive belt  50   c  entrained about the pulleys is connected to a bracket  52  which is in turn connected to the tube  42 . A drive shaft  54  of the third stepper motor M 3  is drivingly engaged with a gear  56  coaxially coupled to the pulley  50   a . When the stepper motor M 3  is activated, the gear  56  rotates the pulley  50   a  to move the belt  50   c  about its closed loop path. Depending upon the direction of rotation of the drive shaft  54 , the bracket  52  (and thus the third roller assembly  16 ) is selectively moved in either direction along the longitudinal axis of the first shaft  20 . 
   A plate  60  connected to the frame  22  incorporates an indicia  63  detectable by a suitable sensor mechanism  62 . The sensor mechanism  62 , adjustably mounted on the bracket  52 , can be either optical or mechanical depending upon the selected indicia. Location of the sensor mechanism  62  is selected such that when the indicia  63  are detected, the third roller assembly  16  is located in a home position. The home position of the third roller assembly  16  is selected such that the third roller assembly is substantially centrally located relative to the cross-track direction of a sheet in the transport path P. 
   The frame  22  of the sheet registration mechanism  10  also supports a shaft  64  located generally below the plane of the sheet transport path P. Pairs of idler rollers  66  and  68  are mounted on the shaft  64  for free rotation. The rollers of the idler pair  66  are respectively aligned with the first urging roller  24  and the second urging roller  34 . The rollers of the idler roller pair  68  are aligned with the respective third urging rollers  48 , and extend in a longitudinal direction for a distance sufficient to accommodate for maintaining such alignment over the range of longitudinal movement of the third roller assembly  16 . The spacing of the shaft  64  from the plane of the sheet transport path P and the diameter of the respective rollers of the idler roller pairs  66  and  68  are selected such that the rollers will respectively form a nip relation with the arcuate peripheral segments  24   a ,  34   a , and  48   a  of the urging rollers. For example, the shaft  64  may be spring loaded in a direction urging such shaft toward the shafts  20 ,  32 , where the idler roller pair  66  will engage spacer roller bearings  24   b ,  34   b.    
   With the above described construction for the sheet registration mechanism  10  according to this invention, sheets traveling seriatim along the sheet transport path P are aligned by removing any skew (angular deviation) in the sheet to square the sheet up with respect to the path, and moving the sheet in a cross-track direction so that the centerline of the sheet in the direction of sheet travel and the centerline CL of the transport path P are coincident. Of course, the centerline CL is arranged to be coincident with the centerline of the downstream operation station (in the illustrated embodiment, the centerline of a marking particle image on the web W). The sheet registration mechanism  10  times the advancement of the sheet along the transport path P for alignment in the in-track direction (again referring to the illustrated embodiment, in register with the lead edge of a marking particle image on the web W). 
   In order to effect the desired skew removal, and cross-track and in-track sheet alignment, the mechanical elements of the sheet registration mechanism  10  according to this invention are operatively associated with a logic and control unit  70  (see  FIG. 6 ). The control unit  70  is, for example, a microprocessor base controller receiving input signals from a plurality of sensors associated with the sheet registration mechanism and the downstream operation station. Based on such signals and a program resident in the microprocessor, the control unit  70  produces appropriate signals to control the independent stepper motors M 1 , M 2 , and M 3  of the sheet registration mechanism. The production of a program for a number of commercially available microprocessors is a conventional skill well understood in the art. The particular details of any such program would, of course, depend on the architecture of the designated microprocessor. 
   With reference to  FIG. 4 , there is shown an exemplary operating registration system provided with at least one light source  110  and one light sensor array  130 . Typical light source  110  is a light emitting diode provided by Optek and identified by its part number OP232W. It outputs visible and infrared light. The optical sensor array  130  is provided by Taos and its part number is TSL1402. It includes a linear array of 256 photodiodes  119 . A Wratten filter 87C  118  covers the photodiode array. The Wratten filter passes infrared radiation and excludes other radiation including invisible light. The filter is covered by a clear plastic lens  116 . Light and infrared radiation from the source  110  travel toward the sensor array  130 . The light diverges at an angle of about 20° from the center. Those skilled in the art will appreciate that this can create parallax between the edge of the paper  154  and the sensors  130 . In other words, due to the angle of the impinging light, the edge of the paper  154  will accurately correspond to photodiode only when the paper is at the exact center of the array  130  as shown in  FIG. 4 . However, when the paper is near one end of the array, then the angle of light will cast a shadow of the paper on a photodiode that does not correspond to the exact length of the paper  150 . Such problems are solved by trigonometry. See  FIG. 4B . The angle of the light is known and the distance (d) between the paper and the photodiode is known. The distance between the last shadowed pixel PL and the pixel corresponding to the edge of the paper PE is distance. The distance times the difference between the shadowed pixel PL and the edge pixel PE, is equal to d tan θ. 
   With reference to  FIG. 5 , there is shown a registration board  124 . The board  124  is fixed with respect to the registration mechanism  10 . The registration board has a number of LED sensor arrays  130 . 1 – 130 . 5 . A copy sheet  150  is partially shown over the registration board  24 . The sensors  130  are shown transverse to the path P that the sheet travels toward its registered position. The sheet sizes are shown on the edge  126  of the board. It is, in effect, an optical ruler that measures sheet length between about 10 inches and 14 inches with the sensor arrays  130 . 
   The optical ruler system  200  is schematically illustrated in  FIG. 6 . The LEDs  110 . 1 – 110 . 5  a are disposed above and the aligned with the center of their corresponding photodiode array detectors  130 . 1 – 130 . 5 . The multiple pairs of photodiodes and arrays are used to measure different sized sheets. For example, the pair  110 . 2  and  130 . 2  measure ordinary letter or 8.5″×11″ size sheets. In operation, the size sheet is selected by the operator so that the machine in the system  200  knows that an 8.5″×11″ sheet is expected. As such, the system will turn on photodiode  110 . 02 . As the sheet  150  passes along its registration path, its leading edge  154  will interrupt the light falling upon the array  130 . 2 . The registration machine will jog the machine  150  using the cross-tracking rollers until the edge of the sheet  154  covers the center pixel at the 11 inch position. The optical ruler  120  is generally housed in a light-tight environment. However, the Wratten filter is suitable for passing only one form of radiation, in particular, infrared. As such, even if some ambient visible light should inadvertently enter the system, the components will ignore the light because the Wratten filter will remove it. 
   The registration mechanism has suitable sensors, not shown, located on opposite sides of the mechanism for detecting the edges and confirming the edges are in alignment. A controller, not shown, receives data signals from the sensors and operates the motors M 1 , M 2 , and M 3 . The controller also receives data signals from the registration board and operates the cross-tracking stepper motor M 2  to align the paper. The controller receives a signal from the user to indicate the size of the paper. If the paper is a non-standard size, the user may select input the actual size of the paper into the controller through a suitable touch screen or keyboard or combination of them. The controller then selects the light source  110  and array  130  that is closest in size to the non-standard size paper. The controller will adjust the output of the cross-tracing motor M 2  to align the paper with the centerline of the non-standard paper. 
   In operation, a user selects a standard size sheet or inputs at least one dimension of a non-standard size sheet. The controller selects a light source  110  and diode array  120  that corresponds to the selected size sheet. The light source is turned on. As each successive copy sheet enters the registration station, its leading edge interrupts the light from source  110 . The leading edge casts a shadow on the diode array  130  and the last shadowed diode represents the length of the sheet. Parallax errors are corrected by a trigonometric program that is stored in and performed by the controller. By measuring the edge position and correcting for parallax, the machine knows whether or not to move the sheet forward or backward to the registered position for the particular sheet size. In this respect, the photodiodes are approximately 0.0025 inches on center. The stepper M 2  operates the cross-tracking mechanism. It receives a signal from the controller that corresponds to the distance the sheet must be moved to register its centerline along the path P. The motor M 2  is accurate enough to register the sheet with the toner image. It moves the sheet a distance that corresponds to the difference between the edge of the sheet and the centerline of the path. Then the sheet is released along the path to receive a toner image. 
   Having described an exemplary embodiment of the invention, those skilled in the art will appreciate that the embodiment may be modified by the addition of deletion of one or more of the components described above and by the substitution of equivalent components without departing from the spirit and scope of the a appended claims.