Abstract:
A variable interlacing system for use in xerographic imaging. Variable interlacing provides automatic reconfiguration of imaging parameters in an electrostatic printing machine. Print speed, format and resolution of the printed material may be traded-off against each other dynamically and on demand without changing any of the hardware, including the Raster Output Scanner (ROS). The system and the method of use of the system involve multi-beam irradiative sources in the ROS.

Description:
BACKGROUND  
       [0001]     Disclosed is a variable interlacing system for use in xerographic imaging. Variable interlacing provides automatic reconfiguration of imaging parameters in a printing machine. Print speed, format and resolution of the printed material may be traded-off against each other dynamically and on demand without changing any of the hardware, including the Raster Output Scanner (ROS).  
         [0002]     Xerography is an electrostatic printing process where a latent image is formed on a specially coated charged surface, sometimes referred to as a photoreceptor, by the action of light, and the latent image is developed with powders that adhere only to electrically charged areas. One xerographic imaging process involves an array of laser sources irradiating an array of micromechanical mirrors to image a series of spots onto a moving photoreceptor. Spots form the basis of an image on the photoreceptor, and interlacing involves the sequence of forming of a series of spots on the photoreceptor.  
         [0003]     Lasers or light emitting diodes (LEDs) may be used to expose spots on the photoreceptor. The photoreceptor has the property of holding an electrical charge in the absence of light. Illumination of a spot on the photoreceptor by a laser or LED causes the loss of charge at the exposed spot. In a typical xerographic system, charge left on the photoreceptor attracts toner that is then transferred to paper which has a greater charge than the photoreceptor. Single spot raster output scanning (ROS) print engines are known in the art.  
         [0004]      FIG. 1  shows a typical single spot polygon ROS printer  10 . The printer generally comprises a laser light source  20 , a modulator  30 , a polygonal scanning beam deflector mirror  40 , pre-scan optics  37 , post-scan optics  47 , a flying spot scanner  50 , xerographic printing engine  60  and the electronics  15  to control the printer operation. In operation, spot scanner  50  scans data modulated light beam  55  over a xerographic photoreceptor  65  as shown in  FIG. 1  in accordance with a predetermined raster scanning pattern.  
         [0005]     A motor (not shown) rotates the polygon mirror about its central axis  41 , as indicated by the arrow  43 , at a substantially constant angular velocity. Polygon mirror  40  is optically aligned between laser  20  and photoreceptor  65  so that its rotation causes the laser beam  25  to be intercepted by and reflected from one after another of the mirror facets  45 . As a result, beam  25  is cyclically swept across the photoreceptor  65  in a fastscan direction. Photoreceptor  65 , on the other hand, is advanced (by means not shown) simultaneously in an orthogonal, process direction at a substantially constant linear velocity, as indicated by arrow  63  so that the laser beam  55  scans the photoreceptor  65  in accordance with a raster scan pattern. As shown, the photoreceptor  65  is coated on a rotating drum  60 , though it will be apparent that it also could be carried by a belt or any other suitable substrate. Pre-scan and post-scan optics,  37  and  47 , respectively, of ROS systems are well known in the art for providing any optical correction that may be needed to compensate for scanner wobble and other optical irregularities, and as they are not significant to the invention, they are not described in detail here in order not to unnecessarily obscure the present disclosure.  
         [0006]     A flying spot scanner is described by Curry in U.S. Pat. No. 5,382,967. The scanner provides printing capability with a continuously tunable ROS. In another U.S. Pat. No. 5,638,107, Curry discloses a system for performing interlace scanning and formatting with plural light beams. However, it will be known to those skilled in the art of ROS systems that in order to maintain a particular resolution of an image on a photoreceptor of a certain speed, the rotation of the polygon mirror must also be maintained at a relatively constant rotational speed commensurate with the unvarying interlacing scheme of the present state of the art. It is desirable to be able to vary the resolution of the output image independent of the other parameters of the ROS system, such as the thruput of writing on the photoreceptor and the format of the printed material.  
       SUMMARY  
       [0007]     Aspects disclosed herein include  
         [0008]     an apparatus comprising an electrostatic imaging station having a Raster Output Scanner (ROS); a data processing apparatus associated with said ROS; a photoreceptor configured to interact with said imaging station; one or more image data files in said electronic data modules to instruct a set of interlacing factors to said ROS; and one or more arrays of irradiative sources to execute said interlacing factors.  
         [0009]     an apparatus comprising a Multi-Beam Raster Output Scanner (MBROS); a photoreceptor configured to interact with said MBROS; an electronic data module capable of interfacing with said MBROS; one or more image data files in said electronic data module to instruct a set of variable interlacing factors to said MBROS; and one or more beams to execute said interlacing instructions.  
         [0010]     a method comprising creating an image file; assigning portions of said image file into buffers; mapping said image files into interlacing factors; directing said interlacing factors to a ROS; forming images on a photoreceptor corresponding to said interlacing factors; and printing images with different resolutions at different photoreceptor and ROS speeds, and any combinations thereof. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]      FIG. 1  is a schematic drawing of a single beam Raster Output Scanner (ROS) showing the xerographic imaging of a single spot on a photoreceptor.  
         [0012]      FIG. 2  is a schematic drawing of an embodiment of a xerographic printing machine showing the various electronic modules that direct the ROS system of the machine to print materials at different speeds and different resolutions based on variable interlacing factors that are commanded by the electronic modules.  
         [0013]      FIG. 3  is a schematic drawing of an embodiment of an interlace scheme showing the printing pattern corresponding to an interlace factor I( 1 ) with a print resolution of 1200 dots per inch.  
         [0014]      FIG. 4  is a schematic drawing of an embodiment of an interlace scheme showing the printing pattern corresponding to an interlace factor I( 2 ) with a print resolution of 2400 dots per inch.  
         [0015]      FIG. 5  is a schematic drawing of an embodiment of an interlace scheme showing the printing pattern corresponding to an interlace factor I( 3 ) with a print resolution of 3600 dots per inch.  
         [0016]      FIG. 6  is a schematic drawing of an embodiment of a Multi-Beam Raster Output Scanner (MBROS) showing the xerographic imaging of one or more optic spots on a photoreceptor as illuminated by an array of Vertical Cavity surface Emitting Laser (VCSEL) beams. 
     
    
     DETAILED DESCRIPTION  
       [0017]     In embodiments there is illustrated:  
         [0018]     a system for enabling multiple print speeds and resolutions by changing the interlace factor without any change to the ROS hardware. The system involves a multiple VCSEL (vertical cavity surface emitting laser) source array with which resolution and print speed can be traded off against each other in ROS printers by changing the interlace addressing schemes on-the-fly. The interlace scheme can be dynamically changed while keeping the same optical magnification through electronic data manipulations. To accommodate different slow scan addressability schemes, either the xerographic process speed or the ROS motor speed can be changed.  
         [0019]      FIG. 2  depicts an input-output-terminal (IOT)  200  of an electrophotographic printing machine such as the Xerox iGen3®, which is incorporated here in its entirety as described in U.S. Pat. No. 6,788,904. An embodiment of the present disclosure as shown in  FIG. 2  utilizes ROS systems  215 ,  225 ,  235  and  245  comprising, but not limited to, an array of multiple VCSEL beams which makes possible to vary printing speed and resolution by varying interlacing dynamically, as described further in  FIGS. 3-5 . It will be understood that other irradiative beams, such as from side-light-emitting diodes (LEDs) or electron beams may be used to constitute multi-beam ROS (MBROS).  
         [0020]     The printing machine architecture shown in  FIG. 2  includes, but not limited to four processing stations and a photoconductive belt, or photoreceptor  205  that interacts with a ROS at each station. Photoreceptor  225  is arranged in a vertical orientation with vertical axis  207 . Photoreceptor  225  advances in the direction of arrow  201  to move successive portions of the external surface of photoreceptor  225  sequentially beneath the various processing stations  210 ,  220 ,  230  and  240  disposed about the path of movement thereof. Although processing stations  210 ,  220 ,  230  and  240  are shown to one side of the vertical axis  207 , it will be understood that similar stations could be positioned on the opposing side adjacent the photoreceptor  205 .  
         [0021]     Each of the four processing stations  210 ,  220 ,  230  and  240  shown in  FIG. 2  comprises, in addition to a representative VCSEL ROS shown in  FIG. 6 , a charging unit and a developer unit, which are well known in the art and, therefore, are not shown here in order not to unnecessarily obscure the  FIG. 2 . Suffice to say that initially, photoreceptor passes through first station  210  where the charging unit charges the exterior surface of the photoreceptor  205  to a uniform potential. Afterwards, the charged portion thereof advances to exposure ROS device  215  (shown in more detail in  FIG. 6 ), which illuminates the charged portion of the exterior surface of photoreceptor  205  to record first electrostatic latent image thereon. This first electrostatic latent image is developed by a developer unit (not shown). Developer unit deposits toner particles of a selected color, in this instance, magenta color, on the first electrostatic latent image. After the toner image has been developed on the exterior surface of photoreceptor  205 , the photoreceptor continues to advance counterclockwise in the direction of arrow  201  to the second station  220 .  
         [0022]     The process described above is repeated at the subsequent stations  220 ,  230  and  240  where the second, third and fourth electrostatic latent images are recorded, then exposed by respective VCSEL ROSs  225 ,  235  and  245  followed by depositing and developing toner particles in yellow, cyan and black, respectively. The black toner particles form a black toner powder image which may be partially or totally in superimposed registration with the previously formed cyan, yellow and magenta toner powder images. In this manner, a multi-color toner powder image is formed on the exterior surface of photoreceptor  205 . Thereafter, photoreceptor  205  advances the multi-color toner powder image to a transfer station, indicated generally by the reference numeral  250 . A receiving medium  260 , e.g., paper, is advanced by sheet feeders (not shown) and guided to transfer station  250 , where a corona generating device (not shown) sprays ions onto the back side of the paper. This attracts the developed multi-color toner image from the exterior surface of photoreceptor  205  to the sheet of paper. The photoreceptor  205  is then stripped away from the paper  260  having the toner image. A vacuum transport moves the sheet of paper  260  in the direction of arrow  203  to a fusing station (not shown). In the fusing operation, the toner particles coalesce with one another and bond to the sheet in image configuration, forming a multi-color image thereon. After fusing, the finished sheet is discharged to be collected by the printing machine operator.  
         [0023]     The latent images that are recorded on photoreceptor  205  through exposure of the photoreceptor  205  by VCSEL ROSs  215 ,  225 ,  235  and  245  at their respective process stations  210 ,  220 ,  230  and  240  are governed by digital data provided at their respective ROS control modules (RCM)  217 ,  227 ,  237  and  247  shown in  FIG. 2 . RCM serves the function of an interface between the electronics that operate the printing machine and ROS, which performs electronic image printing on the photoreceptor. Accordingly, each RCM drives, or modulates its laser beam or beams to form a latent image on the photoreceptor  205  resulting in a the final output multi-color toner image as a composite of the magenta, yellow, cyan and black toner images that were recorded by their respective VCSEL ROS.  
         [0024]     Using ROS control module  247  as exemplary of the other RCMs  237   227  and  217 , RCM  247 , like the others, receives pixel data from raster image module (RIM)  270 , which in turn, receives a binary image (pixel) file from a contone rendering module (CRM)  280 . (As is known in the art, contone rendering involves a combination of dithering-creating the illusion of new colors and shades by varying the pattern of dots- and printing at different levels of intensity to produce different colors and different shades of lightness and darkness). CRM  280  maps a binary image (pixels) file from the gray scale level for halftones, as interpreted by a digital front end (DFE)  290  of the electronics that controls the operation of the printer. DFE  290  interprets the various electronic files that command the processing of an image by the printer. The image data can be grayscale converted to multiple bits per pixel, or may be provided in binary format (i.e., one bit per pixel).  
         [0025]     DFE  290  interprets the type of document (file type). The interpreted information includes whether or not the image is in color or black/white, the resolution of the image and whether the image is text or picture. This process is sometimes referred to as tagging an image. DFE also converts the information to a uniform file type that CRM  280  can understand. The information may then be used to set the parameters of the printing machine on demand and “on-the-fly”, as described more in detail later.  
         [0026]     Interlacing involves exposing adjacent lines of dots of a particular color during sequential scans by a ROS. For example, odd numbered lines  1 ,  3 ,  5 , etc., may be exposed during first scan, and even numbered lines  2 ,  4 ,  6 , etc., during the next scan. In an embodiment,  FIG. 3  shows Interlace I( 1 ) scheme  300  where a given image file is processed as is. That is, each image line is exposed one after another in a sequential manner (scans  0 ,  1 ,  2 ,  3 ,  4 ) as shown in  FIG. 3 .  FIG. 4  shows Interlace II( 2 ) scheme  310  where the image file is split between odd and even lines into separate buffers say, A and B. The odd and even files are adjusted for location differences. With a ROS having an array of “n” number of VCSELS, for example, the even file prints its first beam “n” line locations below the first line. With Interlace III( 3 ) scheme  320  shown in  FIG. 5 , the image file is split into 3 parts (buffers A, B and C). Following the same process as in the Interlace II scheme before, every 3 rd  line goes to its respective buffer and the image in buffer B occurs “n” number of lines below those of buffer A. Similarly, the pattern corresponding to the image data in buffer C will be “n” lines below buffer B. As an exemplary, for n=31, and with beam to beam spacing “a” of 21.17 microns (μm), Interlace I in  FIG. 3  yields a resolution of 1200 lines per inch (Ipi), while Interlace II in  FIG. 4  yields a resolution of 2400 Ipi, and Interlace III in  FIG. 5 , 3600 Ipi with the corresponding line to line spacing “b” of about 21.17, 10.58 and 7.055 μm, respectively.  
         [0027]     A ROS capable of executing a reconfigured set of instructions received from the DFE of  FIG. 2  is shown in  FIG. 6 .  FIG. 6  shows an embodiment of an arrangement of an array of multi-beams in a multi-beam ROS (MBROS) or a multispot ROS system. The array shown comprises, but not limited to, an 8×4 array of VCSEL beams. It will be understood from  FIG. 6  that the light source for the multiple ROS system can range from a dual spot laser  330  to quad spot laser  340  to a VCSEL array  350  having 32 to 36 spots, or larger arrays. The multiple numbers of beams  360  emanating from the array  350  of VCSELs are deflected  360 ′ by polygon mirror  380  as shown in  FIG. 6 . A motor (not shown) rotates the polygon as indicated by arrow  383 , at a substantially constant angular velocity. Polygon mirror  380  is optically aligned between VCSEL array  350  and photoreceptor  430  so that its rotation causes one or more laser beams  360  to be intercepted by and reflected from one after another of the mirror facets  385 . As a result, beams  360 ′ are cyclically swept across the photoreceptor  430  in a fastscan direction. Photoreceptor  430 , on the other hand, is advanced (by means not shown) simultaneously in an orthogonal, process direction at a substantially constant linear velocity, as indicated by arrow  440  so that band of laser beams  410  scans the photoreceptor  430  in accordance with a raster scan pattern issued by ROS control module (RCM)  247  of  FIG. 2 . Pre-scan and post-scan optics,  370  and  390 , respectively, of ROS systems are used to compensate for scanner wobble and other optical irregularities, as stated earlier. It will be noted in  FIG. 6  that reference numeral  410  shows a multiplicity of beams representing one or more optic spots rather than a single spot beam.  
         [0028]     Returning to  FIG. 2 , an embodiment involves one or more digital image files that traverse a path  295  from the electronics to the photoreceptor  205  of the printing machine schematically shown in the same Figure. As an exemplary, if the file information at the digital front end (DFE)  290  is tagged as low resolution at 1200, 600 or 300 dots per inch (dpi), and it is in black/white, then the system can be set to print at a higher page rate. The trade off between speed and resolution can be governed by changing the interlacing factor of the ROSs  215 ,  225 ,  235  and  245  at the process stations  210 ,  220 ,  230  and  240  of  FIG. 2 . For text files, the 600 dpi may be rendered with 2×2 pixels per dot. The 300 dpi may be rendered with 4×4 pixels per dot.  
         [0029]     Along the same digital path  295 , at the contone rendering module (CRM)  280  in  FIG. 2 , if the contone resolution is 106 lines per inch, and the ROS resolution is 1200×1200 dpi, the number of ROS lines to create each grid of contone cells becomes 16. The number of ROS pixels is 136 per contone cell. The contone to pixels conversion is as follows:  
                                                                                 Contone (lpi)   ROS (dpi)   Lines   Pixels                                        106   1200   16   1336           106   2400   32   528           212   1200   8   36           212   2400   16   136                      
 
         [0030]     It will be noted that the conversion given above is based on a 45-degree contone screen angle. As is known in the art, for other color stations other angles must be used in order for the repetitive frequency patterns not to have Moiré (beating patterns) with each other. At different contone and resolutions, different number of grey levels are attained.  
         [0031]     Following the digital path  295 , the ROS interface module (RIM)  270  receives the binary files from CRM  280 . RIM codifies the interlace factors which are dependent upon the desired print resolution and comprise the following resolution elements:  
                                                                                                   Interlace Factor (I)                    1   2   3   4                            Print Resolution (dpi)   1200   2400   3600   4800                      
 
         [0032]     In an aspect of an embodiment described earlier, with 31 VCSEL beams shown in  FIG. 6  and interlace factor 2 (2400 dpi), the even file prints its first beam  31  line locations below the odd file. With the same number of beams and interlace factor 3 (3600 dpi), the file is split into 3 parts, namely, buffers A, B and C. Buffer B wires (exposes) 31 lines below buffer A and buffer C writes 31 lines below buffer B. Interlace  4  follows the same pattern where the file is split into 4 parts. It will be noted that no further processing is needed for interlace  1  at the ROS interface nodule (RIM)  270 . This is because, interlace factor of 1 produces simple sequential printing pattern with one buffer which outputs 31 lines at a time.  
         [0033]     The raster output scanners (ROSs)  215 ,  225 ,  235 ,  245  in  FIG. 2  and as described representatively in  FIG. 6 , prints (i.e., expose the photoreceptor  205 ) at a rate dictated by the video data stream (pixels) that come from the RIM  270  in each of the 31 channels corresponding to the 8×4 VCSEL array in  FIG. 6 , where the remaining one VCSEL is used to detect the start of scanning. Each channel creates 1 line of pixels in the scan direction.  
         [0034]     Hence, it will be apparent now that there are one or more different ways to enable multiple print speeds and resolutions by changing the interlace factor dynamically “on-the-fly”. In one embodiment, one may:  
         [0035]     1. adjust the photoreceptor speed;  
         [0036]     2. adjust the polygon mirror speed; or  
         [0037]     3. adjust both polygon and photoreceptor speed.  
         [0038]     In another embodiment, the ROS hardware can be made modular so that different characteristics of print speed, resolution for the same printing machine, may be obtained simply by exchanging one ROS for another and/or reprogramming the image files to affect the desired characteristics by making changes to the software. It will be understood that the photoreceptor may move at different speed to change line spacing. The data rates coming from the RIM  270  in  FIG. 6  may be changed to affect the scan direction pixel size.  
         [0039]     It will be appreciated that variations of the above-disclosed embodiments and other features and functions, or alternatives thereof, may be desirably combined into many other different devices or applications. For example, the embodiments may be practiced with other radiation sources such as the electron beam. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.