Patent Publication Number: US-8116658-B2

Title: Marking engine viewing system

Description:
BACKGROUND 
     The exemplary embodiment relates to printing systems. It finds particular application in connection with a viewing system which enables viewing of a print job in progress, and will be described with particular reference thereto. 
     Electronic printing systems typically employ an input terminal which receives images in digital form and conversion electronics for converting the image to image signals or pixels. The printing system may include a scanner for scanning image-bearing documents or be connected to a computer network which supplies the digital images. The signals are stored and are read out successively to a marking engine for formation of the images and transfer of the images to a print medium, such as sheets of paper. In a typical xerographic (electrostatographic) marking engine, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to the print medium. The fusing of the toner onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a complementary color. Each toner is associated with a separate developer station and applied to the photoreceptor in sequence. The single color toner images are successively transferred to the copy paper to create a multi-layered toner image on the paper. The multi-layered toner image is then permanently affixed to the copy paper in the fusing process. 
     For large scale printers, the sheets which constitute a print job may travel along a lengthy paper path, passing through one or more marking engines as well as other components, such as paper feeders, inverters, stackers, bookbinders, and the like, before being finally output. Many pages of the print job may thus be in progress in the printing system before the first pages of a job or assembled document copy are output. If there is an error in the print job, such as incorrect image content, incorrect sheet orientation, or even an incorrect document selected for the print job, the operator may not be aware of the error until the first few copies of the job are output. 
     The operator has no ready way of viewing a print job in progress to determine if such visible errors are occurring. The marking engine is enclosed within a housing cabinet which is designed to shield the photoreceptor from all light, other than the light used in exposure of the images. Typically the system is configured such that, if a door to the cabinet is opened, the current print job in progress is stopped. Since the opening of the door can allow light to enter and have a deleterious effect on the pages being printed, some or all of the pages may need to be reprinted once the door is closed and the system returned to an operational state. Thus, an operator avoids opening the door to view the job in progress. 
     INCORPORATION BY REFERENCE 
     The following references, the disclosures of each being totally incorporated herein by reference, relate generally to what have been variously called “tandem engine” printers, “parallel” printers, or “cluster printing” (in which an electronic print job may be split up for distributed higher productivity printing by different printers, such as separate printing of the color and monochrome pages): U.S. Pat. Nos. 5,568,246, 5,570,172, 5,596,416, 5,995,721, 6,973,286, and 7,188,929; and U.S. Publication Nos. 2006/0033771, 2006/0067756, and 2006/0114497. 
     BRIEF DESCRIPTION 
     In accordance with one aspect of the exemplary embodiment, a printing system includes a housing and a marking engine, within the housing, for marking print media conveyed on a paper path through the housing. A viewing system is positioned so as to enable an observer outside the housing to view a print job that is in progress within the housing. 
     In accordance with another aspect of the exemplary embodiment, a method includes printing a print job, including conveying print media on a paper path through a marking module, applying a marking material to the print media within the marking module to form marked media, and providing a viewing window whereby an observer is able to view a print job in progress. 
     In accordance with another aspect of the exemplary embodiment, a viewing system in a printing system which includes a paper path defined by a plurality of modules is provided. The plurality of modules includes at least one marking module, each of the plurality of modules including a housing. The at least one marking module includes a light sensitive photoreceptor, within its housing, for applying a toner to print media conveyed on the paper path. The viewing system includes a light source, within the at least one marking module housing, which illuminates print media having a toner image formed thereon. A window in the housing is positioned to enable an observer to view print media that has been marked by the marking engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a printing system in accordance with one aspect of the exemplary embodiment; 
         FIG. 2  is a side view of a portion of one of the marking modules of the printing system of  FIG. 1 , illustrating a window formed in the housing and a light source illuminating marked media within the housing; and 
         FIG. 3  is a schematic cross sectional view of one of the marking modules of the printing system of  FIG. 1 ; and 
         FIG. 4  is a schematic cross sectional view of an alternative embodiment of a marking module to be used in the system of claim  1 . 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the exemplary embodiment relate to a marking module with a viewing system and to a printing system including such a viewing system. The viewing system allows a print job in progress to be viewed, upstream of the output, so that visible errors in the printing can be detected. In one embodiment, the viewing system includes a viewing window formed in a housing of the marking module. In another embodiment, the viewing system includes an image capture device, such as a video camera, high speed still camera, or the like. 
     As used herein, a printing system can include any device for rendering an image on print media, such as a copier, laser printer, bookmaking machine, facsimile machine, or a multifunction machine. “Print media” can be a physical sheet of paper, plastic, or other suitable physical print media substrate for images. A “print job” or “document” is normally a set of related sheets, usually one or more collated copy sets copied from a set of original print job sheets or electronic document page images, from a particular user, or otherwise related. An image generally may include information in electronic form which is to be rendered on the print media by the image forming device and may include text, graphics, pictures, and the like. A “marking module” generally includes at least one marking engine for marking print media during the course of a print job. A “finisher” can be any post-printing accessory device, such as a tray or trays, sorter, mailbox, inserter, interposer, folder, stapler, stacker, hole puncher, bookbinder, collater, stitcher, binder, envelope stuffer, postage machine, or the like. The operation of applying images to print media, for example, graphics, text, photographs, etc., is generally referred to herein as printing or marking. A “document” is used herein to mean an electronic (e.g., digital) or physical (e.g., paper) recording of information. In its electronic form, a document may include image data, audio data, or video data. Image data may include text, graphics, or bitmaps. 
     With reference to  FIG. 1 , one embodiment of a modular printing system  10  is shown. The printing system  10  may be a printer, copier, or a multifunction device having printing and/or copying functions, optionally along with other capabilities such as faxing, emailing, bookbinding, and the like. The exemplary printing system  10  includes various modules  12 ,  14 ,  16 ,  18 ,  20 ,  22 , each including a respective outer housing  24 ,  26 ,  28 ,  30 ,  32 ,  34 , such as a cabinet having walls on all sides. Print media, such as paper, travels along a paper path  36  (illustrated in phantom) through the modules, generally in a downstream direction, as shown. Upstream paths (not shown) may additionally be provided. The print media may be in the form of sheets or a continuous web. Each module  12 ,  14 ,  16 ,  18 ,  20 ,  22  includes a portion of the paper path  36 . 
     The modules  12 ,  14 ,  16 ,  18 ,  20 ,  22  can be of any type normally associated with an electrostatographic printing system, such as one or more paper feeder modules  12 , one or more marking modules  14 ,  18  one or more interface modules  16 ,  20 , and one or more finisher modules  22 . The interface module(s)  16 ,  20  may include an inverter. The finisher module  22  or modules can include, for example, a stacker module, bookbinder module, stapler module, or combinations or multiples thereof, or the like, one or more of which can serve as output modules for a print job. Additionally, while the system  10  is shown as including individual modules for each of the components, each with a respective housing, it is also contemplated that two or more of the modules  12 ,  14 ,  16 ,  18 ,  20 ,  22  may be combined and share a housing. 
     The printing system  10  is used for printing, in which print media is fed from the feeder module  12  to one or more marking modules  14 ,  18 , where it is marked with a marking material, such as toner, fused, and then output at the finisher module  22 . A conveyor system (not shown) comprising drive rollers, air jets, or the like, conveys the print media through the printing system  10 , from the feeder module  12  to the finisher module  22 . The modules  12 ,  14 ,  16 ,  18 ,  20 ,  22  may all be under the control of a common control system  38 , which receives an incoming print job and schedules printing of the job by the one or more marking modules. The control system  38  may be what is commonly known as the digital front end (DFE) of the printing system and include the software and hardware for identifying pages of the print job, converting them to a suitable format for printing by the marking modules, then distributing the pages appropriately among the marking modules. 
     The marking module  14  includes a viewing window  40  which is arranged for viewing a print job in progress. Where two or more marking engine modules  14 ,  18  are present in the system  10 , each may be similarly configured with a respective window  40 ,  42 . The exemplary window  40 ,  42  is positioned in a respective front panel  44 ,  46  of the housing  26 ,  30 , so that an operator of the printing system  10  can look through the window  40  and see a portion of the paper path  36  and marking engine within the outer housing  26 . In the following description, only one of the marking modules  14  will be described in further detail, with the understanding that other marking module(s)  20  may be similarly configured. 
     As shown in  FIG. 2 , the window  40  may be formed from a layer or plate  48  of optically transmissive material which allows sufficient light  50  in the visible range of the spectrum to pass through to enable the operator  52  to view the print job through the window. For example, the window  40  or plate  48  may be formed from plastic (e.g., Plexiglass™), glass, or the like. In the illustrated embodiment, light from a light source  54  reflects off the printed media  56  and passes through the window  40 . The window  40  may be wavelength selective, e.g., by incorporating a filter  58  for filtering out wavelengths in one or more regions of the electromagnetic spectrum. While the window of  FIG. 2  is shown as including separate layers  48 ,  58 , it is to be appreciated that a filtering medium may alternatively be incorporated into the layer  48 . The filter  58  or filtering medium can reduce transmission of light into the housing  26 , which could interfere with proper functioning of the marking engine. The window may polarize light, for example, by incorporating a polarizing filter (as for layer  58 ) to avoid light entering the housing  26  from outside. 
     In the exemplary embodiment, the light source  54  is located within the housing  26 , although in other embodiments, the light source  54  may be located outside the housing  26  but positioned to illuminate the interior through a suitably positioned window, which may be the same as window  40  or a separate window. 
     The window  40  may be small in size, relative to the size of the outer housing  26 , such as about 5-15 cm in height and 10-30 cm in width, e.g., about 10×20 cm. 
     The front panel  44 ,  46  may be in the form of a door which allows access to the interior of the respective housing  26 ,  30 . Apart from the window  40 ,  42 , the front panel may be formed of a substantially non-transmissive material (i.e., does not permit viewing of the housing interior), such as an opaque plastic, metal, or the like. 
     With reference to  FIG. 3 , marking module  14  includes an electrostatographic marking engine  60  for applying images to print media  56  as the print media passes through the marking module along the paper path  36 . The marking engine  60  includes a charge retentive surface or imaging surface  62 , such as a surface of a photoreceptor  64 . The photoreceptor may be in the form of a continuous belt or drum. The exemplary photoreceptor  64  is in the form of a belt supported on rollers, and is driven in a counter clockwise direction as illustrated by arrow A. It is formed of a flexible material and may be at least partially permeable to light. At least one charging station is disposed adjacent the photoreceptor belt for charging the surface  62  of the photoreceptor  64 . The charging station may include a corotron or dicorotron corona generating device. For a single color imaging device, a single charging station is used. In the exemplary embodiment, which is suited to process color imaging of four color separations, magenta, yellow, cyan, and black, each color has its own charging station  70 ,  72 ,  74 ,  76  respectively arranged at spaced locations around the belt. 
     Each color separation has a respective latent image forming unit  80 ,  82 ,  84 ,  86 , which forms a latent image on the surface  62  of the photoreceptor belt. In the exemplary embodiment, the image forming units are laser raster output scanner (ROS) devices, which emit light in a narrow wavelength band, such as about 760 nm. A developing station  90 ,  92 ,  94 ,  96  is associated with each charging station for developing the latent image formed on the surface of the photoreceptor belt  64  by applying a toner to obtain a toner image. The toner is generally in the form of particles, although liquid toners are also contemplated. A transferring unit  100  transfers the toner image thus formed to the surface of a sheet of print media  56  passing along the paper path  36 . The sheet is carried by a prefuser transport unit  102 , located downstream of the image transfer point  104 , to a fuser  106 , which fuses the toner particles  108  (shown greatly enlarged for clarity) to the print media  56 . A cleaning station  110 , is positioned to clean residual toner from the photoreceptor  64  before the process is repeated. 
     The light source  54  may be a source of white light (emitting light in substantially all wavelengths in the visible range), such as a fluorescent lamp, incandescent lamp, light emitting diode (LED), metal halide lamp, or combinations or multiples thereof. Alternatively, the light source  54  is selected to emit light in a visible wavelength range which is outside the wavelength range emitted by the ROS  80 ,  82 ,  84 ,  86  and/or to which the photoreceptor  64  is particularly sensitive. For example if the photoreceptor  64  is most sensitive to light in the wavelength range of about 650-770 nm, the light source  54  emits light in a range of about 400-600 nm, e.g., below about 550 nm. In one embodiment, a filter  112  may be provided on or around the light source  54  to selectively filter out light in the range to which the photoreceptor is particularly sensitive. Filter  112  may be in the form of a coating or film, e.g., on an exterior surface of the lamp bulb. 
     The light source  54  may be mounted to part of the housing  26  and emits light when energized by an appropriate power source (not shown). In the exemplary embodiment, the light source  54  may remain on during printing of the job, or may be switched off once the operator has confirmed the job is proceeding satisfactorily. The light source  54 , unlike the laser  80 ,  82 ,  84 ,  86  or other light source used in the exposure of the photoreceptor  64 , thus remains continuously on (lit) and its light illuminates the same portion of the paper path for a relatively long period, e.g., at least for a plurality of revolutions of the photoreceptor  64 , while several sheets of printed media  56  pass by. The light source  54  may also have a lower intensity than the laser  80 ,  82 ,  84 ,  86  and emit in a broader range of wavelengths. 
     In one embodiment, the light source has selectable modes of operation, such as two or more of: a) on all the time the marking engine is powered, b) on only when photoreceptor is rotating, c) on only when requested by the observer, Keeping the light off when not being used for observations may help to protect the photoreceptor from light leaks. The light source may be controllable from the main control or a separate control device 
     As shown in  FIG. 3 , the light source  54  is positioned to illuminate a toner side  120  of the marked sheet  56 . In the exemplary embodiment, the light source is located proximate the paper path  36 , to illuminate the print media at a location which is downstream of the image transfer point  104 , e.g., intermediate the image transfer point  104  and the fuser  106 . The exemplary light source  54  is mounted above the paper path  36  to illuminate the imaged side of the sheet, e.g., it may be positioned intermediate an upwardly traveling portion  122  of photoreceptor belt and the sheet. The light source  54  may be mounted to a portion of the housing  28 . 
     A shield  124 , formed of an opaque material such as plastic or metal, is positioned to shield at least a portion  126  of the photoreceptor belt  64  from light emitted by the light source  54 . In the exemplary embodiment, the shield  124  is located within the housing  26  and is interposed between the light source  54  and at least that the portion  126  of the belt which has been charged and/or carries undeveloped images thereon (i.e., exposed but not developed with toner), i.e. shields that portion  126  of the photoreceptor  64  which extends between the first charging station  70  and the last developer station  96 . Since the exposure stations and developer stations are all located on the upstream side of the photoreceptor belt  64  in the exemplary embodiment, the light source  54  is conveniently positioned on the downstream side of the photoreceptor belt, with the shield  124  located in a cavity  128  interior of the belt  64 , such that the shield is surrounded by the photoreceptor belt, although other locations are contemplated. This allows a portion  122  of the photoreceptor  64  to be illuminated by the light source  54 , i.e., the portion  122  is located intermediate the light source  54  and the shield  124 . The exemplary shield  124  is fixed in position, while the photoreceptor belt  64  moves around it. The exemplary shield is L-shaped, although other configurations such as a flat plate, or curved shape are also contemplated. In one embodiment, parts of the photoreceptor belt  64  may be already shielded by components of the marking engine  60  and thus additional shielding may be limited to a plate  124  positioned adjacent lower end of the belt, and extending generally vertically. In this embodiment, the horizontal top part of component  124  may be eliminated as its function is provided by marking engine components which may be spaced from the vertical plate. In other embodiments, the shield may be attached to the belt  64 , e.g., as an inner layer of the belt. In the case of a photoreceptor  64  which is not light transmissive, such as a drum photoreceptor, formed from aluminum or the like, the photoreceptor itself may serve as the shield  124 . 
     The window  40 , shown in phantom in  FIG. 3 , is positioned to allow the viewer  52  ( FIG. 2 ) to see the top  120  of the sheet  56  with the toner particles  108  thereon. Although the toner particles  108  are not fixed and may be still in toner layers on the sheet  56 , the viewer can readily detect macro-errors in the printing of the print job in progress, such as incorrect image content, incorrect image orientation (e.g., an image which is oriented 180° to its desired orientation and thus may be upside down when the page is assembled as a book), or an incorrect document. 
     Additionally, the window  40  is positioned such that the adjacent portion  122  of the photoreceptor surface  62  is visible to the observer  52 , through the window. In one embodiment, test patches  130  are imaged onto the photoreceptor belt  64  intermediate the toner images to be transferred to the print media. These imaged test patches  130 , formed in a similar way to the toner images which are to be applied to the print media, remain on the belt  64  after it has passed the transfer point. A sensor  132  may be positioned to check the density or other properties of the test patches  130  as they pass by the sensor. An observer, looking through the window  40 , can check that the test patches have been formed and are still on the belt as they reach the sensor  132 . The window  40  is thus positioned to allow the observer to view a portion of the photoreceptor surface  62  that is located intermediate the transfer point  104  and the sensor  132 . 
     As previously noted, the filter  58 , where present in the window  40 , filters out ambient light (light from outside the housing) which is in a wavelength range to which the photoreceptor  64  is sensitive. 
     As will be appreciated, the window  40  is not intended to serve as a substitute for calorimetric sensors, densitometers, image registration sensors, or the like which are capable of detecting errors on a micro-scale which may not be detected simply by human observation of the moving sheets  56  or moving color patches  130  through the window. The exemplary viewing system comprising the window and light source, however, provides a valuable tool for detecting macro-scale errors and, in cases where the marking engine operation is virtually silent, an indicator that the printing device is actually printing. 
     In a printing system with two marking modules  14 ,  18 , one of which is used for marking a first side of the sheet and the other marking the other side, a viewing window  40 ,  42  can be provided in both housings  26 ,  30  so that the operator can check the toner images being formed on both sides of the sheet  56 . 
     If an error is detected by the operator, e.g., in the printed pages  56  of the print job or test patches  130 , the operator can take appropriate corrective action. For example, the operator may employ a user interface  134  ( FIG. 1 ) located on or close to the printing system  10  to communicate the problem to the control system  38 , so that the print job can be halted in a safe manner. The control system  38  controls the operation of the various modules  12 ,  14 ,  16 ,  18 ,  20 ,  22  during printing the print job. The user interface  134  can include one or more of a screen  136 , and a user input device  138 , such as a keyboard, keypad, cursor control device, touch screen, or the like. 
     With reference now to  FIG. 4  another embodiment of a marking module  14 ′ and visualization system is shown, where similar elements are accorded the same numbers and new elements are accorded new numbers. Marking module  14 ′ may be analogous to a marking module  14 , except as otherwise noted. In this embodiment, the visualization system includes an image capture device  140 , such as a video camera, digital camera, or the like, which captures images of the sheet  56  and/or patches  130  during the progress of the print job. Window  40  can therefore be omitted. The images captured by the image capture device  140  can be displayed in contemporaneously, i.e., substantially in real time, to the observer  52 , e.g., on the screen  136  of the user interface  134  or on a separate display device. The light source  54 , in this embodiment, may be positioned to illuminate the sheet  56  and/or patches  130  from a suitable angle for reflected light to be captured by the image capture device  140 . The image capture device  140  may be positioned within the housing  26 , as shown, or located outside the housing adjacent a suitably positioned window analogous to window  40 . 
     In various embodiments, the video camera may additionally be used for one or more of: local or remote diagnostics; job integrity monitoring by comparing captured images to scheduled images; and automated detection of gross errors in prints, such as significant deletions, smudges, belt hole defects, and the like. 
     Additional windows or video cameras may also be provided in other modules  12 ,  16 ,  20 ,  22 . 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.