Patent Publication Number: US-7720404-B2

Title: Methods of operating a multi-color image forming device in a mono-color mode

Description:
BACKGROUND 
   The present application is directed to methods of forming a toner image and particularly to methods of forming a mono-color toner image within a multi-color image forming device. 
   Color image forming devices such as but not limited to printers, facsimile machines, copiers, and combination machines form images with two or more different colors of toner. Each color of toner may be stored within an imaging station and transferred to an intermediate member as a toner image during the image formation process. For multi-color images, two or more different colors of toner are transferred to the intermediate member and combined to form the final image. For mono-color images, a single color of toner forms the final image. 
   Each imaging station includes at least one photoconductive member. During the image formation process, the imaging stations are activated and the photoconductive member is rotated. Further, the toner is moved within the image forming station. The life of the photoconductive member is largely determined by the total number of revolutions. Further, the toner within the imaging stations is churned during the image forming process which also decreases its effective life. Prior art image forming devices have addressed extending the lives of the photoconductive members and toner in a variety of different manners. 
   Many standard image forming device do not treat a multi-color image differently than a mono-color image. The imaging stations for the non-used toner continue to rotate the photoconductive member and churn the toner even though no toner is transferred from that specific station. Other image forming devices use a mechanism that retracts the intermediate member away from the photoconductive member. This may increase the life of the photoconductive member, but adds complexity and cost to the image forming device. 
   SUMMARY 
   The present application is directed to methods of operating a multi-color image forming device in a mono-color mode. One method may include determining whether an initial maximum number of mono-color pages have been printed. When the initial maximum number of mono-color pages has not been printed, the mono-color page may be printed with a first imaging station while the remainder of the imaging stations are in a non-operational mode. When the initial maximum number of mono-color pages has been printed, the non-operational imaging stations may be rotated a limited first amount and the mono-color page may be printed with the first imaging station. When an overall number of mono-color pages have been printed, the non-operational imaging stations may be reset by rotating the non-operational imaging stations a greater amount than the first amount. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of an image forming device according to one embodiment. 
       FIG. 2  is a process diagram of a partial method of forming a toner image according to one embodiment. 
       FIG. 3  is a process diagram of a partial method of forming a toner image according to one embodiment. 
       FIG. 4  is a schematic section view of an imaging station positioned at an intermediate transfer member according to one embodiment. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates one embodiment of an image forming device  100 . The device  100  includes a first toner transfer area  160  with one or more imaging stations  150  that are aligned horizontally extending from the front  110  to the back  111  of the body  101 . The imaging stations  150  are aligned along an intermediate transfer member (ITM)  129 . Each of the imaging stations  150  holds a different toner color. The imaging stations  150  are aligned in order relative to the direction of the ITM  129  with the yellow (Y) imaging station  150  being first and followed by cyan (C), magenta (M), and black (K). 
   Each imaging station  150  includes a toner reservoir  154  to contain the toner. One or more agitating members may further be positioned within the reservoir  154  to move the toner. A toner adder roller  155  is positioned in the reservoir  154  to move the toner to a developer roller  156 . The imaging stations  150  also include a photoconductive member  153  that receives toner from the developer roller  156 . A charging member  152  is positioned to charge the photoconductive (PC) member  153 . In one embodiment, each of the imaging stations  150  is substantially the same except for the color of toner. For purposes of clarity in  FIG. 1 , the elements are labeled on only the black K imaging station  150 . 
   During image formation, the surface of the PC member  153  is charged to a specified voltage such as −800 volts, for example. A laser beam from a printhead  191  is directed to the surface of the PC drum  153  and discharges those areas it contacts to form a latent image. In one embodiment, areas on the PC drum  153  illuminated by the laser beam are discharged to approximately −100 volts. The developer roller  156  then transfers toner to the PC drum  153  to form a toner image. The toner is attracted to the areas of the PC drum  153  surface discharged by the laser beam from the printhead  191 . 
   The ITM  129  is disposed adjacent to each of the imaging stations  150 . In this embodiment, the ITM  129  is formed as an endless belt trained about drive roller  131 , tension roller  132  and back-up roller  133 . During image forming operations, the ITM  129  moves past the imaging stations  150  in a clockwise direction as viewed in  FIG. 1 . One or more of the PC drums  153  apply toner images in their respective colors to the ITM  129 . For mono-color images, a toner image is applied from a single imaging station  150 . For multi-color images, toner images are applied from two or more imaging stations  150 . In one embodiment, a positive voltage field formed by transfer rollers  165  attracts the toner image from the PC drums  153  to the surface of the moving ITM  129 . 
   The ITM  129  rotates and collects the one or more toner images from the one or more imaging stations  150  and then conveys the toner images to a media sheet at a second transfer area. The second transfer area includes a second transfer nip  140  formed between the back-up roller  133  and a second transfer roller  141 . 
   A media path  144  extends through the device  100  for moving the media sheets through the imaging process. Media sheets are initially stored in an input tray  130  or introduced into the body  101  through a manual feed  148 . The media sheet receives the toner image from the ITM  129  as it moves through the second transfer nip  140 . The media sheets with toner images are then moved along the media path  144  and into a fuser area  180 . Fuser area  180  includes fusing rollers or belts  181  that form a nip to apply heat and pressure to fix the toner image to the media sheet. The fused media sheets then pass through exit rollers  145  that are located downstream from the fuser area  180 . Exit rollers  145  may be rotated in either forward or reverse directions. In a forward direction, the exit rollers  145  move the media sheet from the media path  144  to an output area  147  along the top portion  114  of body  101 . In a reverse direction, the exit rollers  145  move the media sheet into a duplex path  146  for image formation on a second side of the media sheet. 
   During formation of a multi-color image, toner images from two or more of the imaging stations  150  are transferred to the ITM  129 . In one embodiment, multi-color images require the image forming device  100  to operate in a multi-color mode with each of the imaging stations  150  being operational, even if a particular color is not included in the toner image. The image forming device  100  may also operate in a mono-color mode to form a mono-color image with a single color of toner. One example of a mono-color mode is referred to as black-only that forms images with just black toner. Specific examples of black-only printing include text and black-and-white images. 
   During the mono-color mode, a toner image is formed at the last imaging station  150  in the process direction and transferred to the ITM  129 . The operational imaging station  150  should be after the non-operational imaging stations  150  in the process so the toner image is not disturbed while traveling under a stationary PC member  153 . The present application includes methods to deactivate the other non-operational imaging stations  150  to prevent wear to their various elements and their toner. 
   A controller  190  is included within the image forming device  100  to control the overall printing process including creation and timing of the toner images, and movement of the media sheets. Controller  190  may include a microprocessor with associated memory. In one embodiment, controller  190  includes a microprocessor, random access memory, read only memory, and an input/output interface. Controller  190  receives print requests and forms a queue of each of the pages in the requests. The queue may include the pages from a single print request. or may include pages from two or more different print requests. Controller  190  further includes a raster image processor that turns vector digital information received in the print requests into a high-resolution raster image. The controller  190  is then able to determine whether each of the pages require a multi-color mode due to two or more colors of toner being necessary to form the image, or a mono-color mode when a single color of toner is necessary to form the image. 
   In one embodiment, the controller  190  may normally operate in the multi-color mode. The multi-color mode includes the operation of each of the imaging stations  150  including rotation of at least the developer roller  156 , PC member  153 , and charging roller  152 , and movement of the toner. A drawback to print a mono-color page while operating in the multi-color mode is wear on the elements of the imaging station  150  and churning of the toner. The present application includes methods of determining when the controller  190  can operate in the mono-color mode such that only one imaging station  150  is operational and the other imaging stations  150  are non-operational. The elements of the non-operational imaging stations  150  are stationary to prevent the wear and churn of the toner. 
   The methods of the present application include steps to maintain the image forming device  100  operating in the mono-color mode. The first loop includes continuous mono-color printing to an initial preset maximum number of mono-color pages. The second loop occurs when the number of printed mono-color pages exceeds the initial preset maximum. The second loop includes rotating the non-operational imaging stations  150 . A third loop occurs when the number of rotations in loop  2  exceeds a maximum number. The third loop includes resetting the non-operational image forming stations  150  to allow for continuing operation in the mono-color mode. 
   In the method described below and illustrated in  FIGS. 2 and 3 , the mono-color mode is a black-only mode. Only the K imaging station  150  is operational with the Y, C, and M imaging stations  150  being non-operational. Further, this example includes a single operational imaging station  150  and three non-operational imaging stations  150 . In other embodiments, two or more adjacent imaging stations  150  that are last in the process may be operational with one or more non-operational imaging stations  150 . 
   As illustrated in  FIG. 2 , an initial step is determining if the controller  190  should switch from the multi-color mode to the black-only mode (step  200 ). Although the black-only mode includes advantages of preventing wear and toner churn to the non-operational imaging stations  150 , too much switching between the modes causes extra wear to the non-operational imaging stations  150  because of the frequent starting and stopping. This extra wear is more detrimental than the advantages of operating in the black-only mode. Therefore, switching modes to black-only should only occur at certain occasions. 
   One occasion to switch includes when the image forming device  100  is idle and only one black-only page is in the print queue. Another occasion for switching includes when the next three pages in the print queue are black-only pages. Switching may also occur when the print queue is less than three pages and at least two consecutive pages are black-only pages. These are a few occasions of when switching modes is beneficial. Other occasions may also be used depending upon the context of use. If switching should not occur, then the image forming device  100  is set to the multi-color mode (step  201 ). 
   If a switch should occur, then only the black imaging station K is run-in and placed in the operational mode (step  202 ). The CMY non-operational imaging stations  150  are placed in the non-operational mode, and the corresponding transfer roller  165  for each is set to zero volts. Further, a rotate count is set to zero (step  203 ), and a count of printed black pages (K pages) is set to zero (step  204 ). 
   The next step is to print the black-only page which is the start of Loop  1  (step  205 ), and increment the count of printed black pages (K pages)(step  206 ). Controller  190  than determines whether the print queue is empty (step  207 ). If the queue is empty, it is then determined if the non-operational imaging stations  150  have a rotate count of zero (step  208 ). The rotate count indicates whether the PC members  153  of these imaging units  150  have been rotated to prevent a wear mark caused by contact with the moving ITM  129 . If the rotate count is zero, the non-operational imaging stations  150  are rotated (step  209 ). The rotation moves new sections of the PC members  153  into contact with the ITM  129 . Rotation may also move sections of the PC members  153  that may be exposed by the printhead  191 . In one embodiment, the PC members  153  are moved about 5 mm. The black K imaging station  150  is run out and the black-only mode is completed (step  211 ). 
   If the print queue is not empty (step  207 ), it is then determined whether the next page is black-only (step  213 ). If the next page is multi-color, the controller  190  transitions each of the imaging stations  150  to the multi-color mode (step  214 ). If the next page is black-only, it is then determined whether the number of printed black pages Kpages is greater than an initial predetermined maximum (step  215 ). The initial predetermined maximum is set as the maximum amount of pages that can be printed before causing a wear mark on the non-operational PC members  153 . If the initial predetermined maximum number is not exceeded, than the process stays in Loop  1  and loops back and prints the black-only page. If the maximum number of black-only pages is exceeded, the process moves to Loop  2  as described in the steps illustrated in  FIG. 3 . 
   The initial predetermined maximum number of black pages is predetermined to prevent leaving a wear mark on the stationary non-operating PC members  153  due to rubbing against the moving ITM  129 . This maximum may also prevent damage to other elements within the non-operational imaging stations  150  such as the developer rollers  156  and the charger roller  152 . To prevent wear marks, the non-operating imaging stations  150  are rotated to move a new section of the PC members  153  against the ITM  129 . Rotation also moves the other elements in the imaging stations  150 . Prior to rotating the PC members  153 , it is determined whether the rotate count exceeds a maximum amount of rotation (step  301 ). The maximum amount of rotation is determined as a function of a length of the rotations and a distance between a contact point of the developer roller  156  and the PC member  153  and the first transfer point between PC member  153  and the ITM  129 . 
     FIG. 4  illustrates a section view of an imaging station  150  with the developer roller  156  contacting against the PC member  153 , and the first transfer point between the PC member  153  and the ITM  129 . An angle α is formed between the contact point and the first transfer point. The length of the surface of the PC member  153  measured within the angle α is referred to as a toner free area and is the amount of available space for rotation. The maximum amount of rotation is determined by the angle α divided by the length of each rotation measured in degrees. The amount of rotation is determined by how accurate the controller  190  can control the degrees of rotation. In one embodiment, angle α is about 133 degrees, and the controlled rotation is about 22 degrees. Therefore, the maximum number of rotations is 6 (i.e., 133/6). In some embodiments, the amount of rotation could be different based on the diameter of the PC member  153 , the relative locations of the developer roller  156  and the first transfer area  140 , and the ability of the controller  190  to control the motor rotation. 
   Returning to the flowchart of  FIG. 3 , if the number of rotations does not exceed the maximum, than the non-operational imaging stations  150  are rotated (step  302 ). Further, the rotate count is incremented by one (step  304 ), and the number of black-only pages Kpages is set equal to zero (step  305 ). Printing of the black-only page may occur simultaneously with, before, or after steps  302 ,  304 , and  305  with the rotation occurring during the interpage gap. 
   The maximum number of black-only jobs that can be printed before conditioning the non-operating PC members  153  and other elements is a function of number of black-only pages that can be printed for each rotate location and the maximum rotate count. If the maximum number of black-only pages is 20 for each location on the PC members  153  and the maximum rotate count is 5, than 100 black-only pages may be printed before conditioning the non-operational PC members  153 . In another example, a maximum black-only pages of 40 and a maximum rotate count of 6 allows for 240 black-only pages to be printed before conditioning the non-operational PC members  153  and the other elements. 
   If the rotate count does exceed the maximum (step  301 ), then it is necessary in Loop  3  to reset the non-operational imaging stations  150 . This occurs when the toner free area formed on the surface of the non-operational PC members  153  has been used. As a result, the controller  190  will re-establish an initial condition on the non-operational PC members  153  to create new toner free areas. Further, the controller  190  will move other elements within the imaging stations  150  to prevent damage to these elements. Returning to  FIG. 3 , the non-operational imaging stations  150  are activated for a predetermined amount of time or movement of the imaging stations  150  (step  306 ). In one embodiment, the activation causes the PC members  153  to rotate about two revolutions. Further, an interpage gap between media sheets is set to a predetermined amount (step  307 ). In one embodiment, the interpage gap is about 205 mm. The black-only sheet is printed either at the same time, before, or after the non-operating imaging stations  150  are activated. After the non-operational imaging stations  150  are reset, then both the rotate count (step  308 ) and the black-only pages Kpages (step  309 ) are set equal to zero. 
   Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
   As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
   The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.