Patent Publication Number: US-7583905-B2

Title: Image forming apparatus and image forming method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-197328, filed Jul. 19, 2006, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus having a plurality of image forming sections, in particular, an image forming apparatus in which a plurality of image forming sections are detachably formed, and an image forming method used for the same. 
   2. Description of the Related Art 
   In prior art, electrophotography and inkjet printing are known as main image forming systems used for image forming apparatuses. 
   In image forming apparatuses using electrophotography, an electrostatic latent image is formed by irradiating a charged photosensitive drum with laser light corresponding to an image signal, and an image formed on the photosensitive drum is printed on paper by processes such as development, transfer, and stripping. 
   In image forming apparatuses using inkjet printing, an image signal is resolved to obtain intensity of each color, ink is discharged from nozzles in accordance with the respective intensities of the colors, and an image is printed on printing paper. 
   When these image forming systems are compared with each other, they have respective advantages and drawbacks. 
   For example, electrophotography is generally expensive, although it achieves printing at higher speed than that of inkjet printing. Inkjet printing generally has low printing speed, although it is more inexpensive than eletrophotography. 
   An image forming apparatus obtained by combining electrophotography and inkjet printing is disclosed (Jpn. Pat. Appln. KOKOKU Pub. No. 5-22232). 
   BRIEF SUMMARY OF THE INVENTION 
   An image forming apparatus according to a first aspect of the present invention is installed in a digital multifunction peripheral (MFP) having a copying function of recording images continuously and a function of transmitting and receiving information to and from an external apparatus, and comprises: a first storing section which stores recording media before recording; a plurality of image forming sections which form images and record the images on the recording media; and a second storing section which stores the recording media after recording, wherein the image forming sections are configured to selectively perform an operation of recording images on the recording media by individually performing an image forming operation in parallel, and an operation of recording images on one recording medium by performing the image forming operation by turns. 
   An image forming method according to a second aspect of the present invention is used for an image forming apparatus installed in a digital multifunction peripheral (MFP) having a copying function of recording images continuously and a function of transmitting and receiving information to and from an external apparatus, and comprises: storing recording media before recording; selectively controlling a plurality of image forming sections which form images and record the images on the recording media, and causing the image forming sections to perform an operation of recording images on the recording media by individually performing an image forming operation in parallel, and an operation of recording images on one recording medium by performing the image forming operation by turns; and storing the recording media after recording. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
       FIG. 1  is a diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. 
       FIG. 2  is a diagram illustrating a placement of a photosensitive drum and a process unit. 
       FIG. 3  is a diagram illustrating a basic concept of a multiengine image forming apparatus. 
       FIG. 4  is a diagram illustrating a laser system in contrast with an LED array system. 
       FIG. 5  is a diagram illustrating configuration examples obtained by combining image forming sections. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the present invention is explained, in which the present invention is applied to a digital MFP (multifunction peripheral) having a copying function of printing images continuously and information transmitting/receiving function with external apparatuses. 
     FIG. 1  is a diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. 
   An image forming apparatus  10  comprises a paper feed unit  11 , an image forming unit  12 , and a paper delivery unit  13 . 
   The paper feed unit  11  stores paper being recording media, and feeds the paper to the image forming unit  12 . The image forming unit  12  forms images, and prints the images on the fed paper. The paper delivery unit  13  accumulates and stores the printed paper. 
   The image forming unit  12  has two image forming sections, that is, a first engine module  20  and a second engine module  30 . 
   The first engine module  20  adopts quadruple tandem image forming system. The first engine module  20  is provided with photosensitive drums  21   a  to  21   d , process units  22   a  to  22   d , a transfer belt  23 , a drive roller  24 , a transfer roller  25 , a paper feed roller  26 , and a delivery roller  27 . 
     FIG. 2  is a diagram illustrating a placement of the photosensitive drum  21   a  and the process unit  22   a . The positional relationship between the photosensitive drums  21   b  to  21   d  and the respective process unit  22   b  and  22   d  is the same as this placement. 
   The photosensitive drum  21   a  is formed of a transparent glass tube, and a transparent conductive layer and a photosensitive layer are formed on the outer surface of the photosensitive drum. The photosensitive drum  21   a  rotates in a circumferential direction of the photosensitive drum  21 . An LED array  50   a  which does not rotate is provided inside the photosensitive drum  21   a.    
   Further, a charging device  51   a , a developer device  52   a , a cleaner  53   a , and a static eliminating device  54   a  which are provided on the process unit  22   a  are arranged around the photosensitive drum  21   a.    
   The charging device  51   a  uniformly charges the surface of the photosensitive drum  21   a . The LED array  50   a  emits and turns out light in response to image signals. Specifically, the LED array  50  performs back exposure. The LED array  50  has a structure in which a plurality of light-emitting elements are arranged in a main-scanning direction (in the direction in which the rotation axis of the photosensitive drum  21   a  extends). Therefore, the LED array  50  does not need a scanning mechanism such as a polygon mirror. 
   Light emitted from the LED array  50   a  is applied onto the photosensitive drum  21   a . When light is applied to the charged photosensitive drum  21   a , the potential of portions of the drum to which the light has been applied lowers, and an electrostatic latent image is formed. The developer device  52   a  applies a developer to the photosensitive drum  21   a , and thereby forms a toner image on the photosensitive drum  21   a . The formed toner image is transferred to paper. After transfer, the cleaner  53   a  removes toner remaining on the photosensitive drum  21   a . Thereafter, the static eliminating device  54   a  uniformly eliminates static electricity from the surface of the photosensitive drum  21   a . Thereby, the photosensitive drum  21   a  returns to the initial state, and comes into a state of waiting for next image formation. 
   The second engine module  30  adopts a quadruple tandem image forming system. The second engine module  30  is provided with photosensitive drums  31   a  to  31   d , process units  32   a  to  32   d , a transfer belt  33 , a drive roller  34 , a transfer roller  35 , a paper feed roller  36 , and a delivery roller  37 . 
   Operations of the photosensitive drums  31   a  to  31   d  and the process units  32   a  to  32   d  of the second engine module  30  are the same as the above operations, and detailed explanation thereof is omitted. 
   [First Operation] 
   Next, a first operation of the image forming apparatus  10  is explained with reference to  FIGS. 1 and 2 . In the first operation, the first engine module  20  and the second engine module  30  print color images independently of each other. 
   The transfer belt  23  of the first engine module  20  runs at fixed speed by the drive roller  24  rotated by a motor (not shown). 
   First, the charging device  51   a  in the process unit  22   a  uniformly charges the photosensitive drum  21   a . The charged photosensitive drum  21   a  is subjected to exposure by the LED array  50   a  in conformity with image information, and thereby an electrostatic latent image is formed on the photosensitive drum  21   a.    
   The developer device  52   a  containing a developer (toner) of yellow (Y) is disposed downstream from the exposure by the LED array  50   a . The electrostatic latent image on the photosensitive drum  21   a  is subjected to reverse development with the yellow toner, and a toner image is formed on the photosensitive drum  21   a.    
   A transfer roller (not shown) is disposed downstream from the developer device  52   a . A bias (+) having a polarity opposite to the charging polarity of the toner is applied to the transfer roller. As a result, the toner image on the photosensitive drum  21   a  is transferred onto the transfer belt  23 , as primary transfer, by a transfer electric field formed between the photosensitive drum  21   a  and the transfer roller. 
   The photosensitive drums  21   b  to  21   d  and the process units  22   b  to  22   d  perform the same processes, simultaneously with the timing of formation of a toner image by the photosensitive drum  21   a  and the process unit  22   a . As a result, toner images of magenta (M), cyan (C), and black (K) formed on the photosensitive drums  21   b ,  21   c  and  21   d , respectively, are transferred onto the transfer belt  23 , as primary transfer. 
   Paper being a transfer material is fed from the paper feed unit  11  into the first engine module  20  through the paper feed roller  26 . 
   The transfer roller  25  is disposed on the upper end portion of the transfer belt  23 . A bias (+) having a polarity opposite to the charging polarity of the toner is applied to the transfer roller  25 . As a result, the toner images on the transfer belt  23  are transferred onto the paper by a transfer electric field formed between the transfer belt  23  and the transfer roller  25 . 
   After the images transferred onto the paper are fixed by a fixing device (not shown), the paper is sent to the paper delivery unit  13  through the delivery roller  27  and stored therein. 
   Also in the second engine module  30 , images are printed on paper by the same operation as that of the first engine module  20 . After the images transferred onto the paper are fixed by a fixing device (not shown), the paper is sent to the paper delivery unit  13  through the delivery roller  37  and stored therein. 
   In the first operation, two image forming operations are performed in parallel in one image forming apparatus  10 . Therefore, the printing speed is increased twice the normal speed. 
   [Second Operation] 
   In the second operation, the first engine module  20  and the second engine module  30  successively operate, and print color images on the front and back sides of a sheet of paper. 
   The first engine module  20  performs the same operation as the operation explained above, and a sheet of paper onto which an image has been fixed is ejected from the first engine module  20  by the delivery roller  27 . However, the paper is not conveyed to the delivery unit  13 , but to the second engine module  30 . 
   In the second engine module  30 , toner images are transferred as primary transfer onto the transfer belt  33  as described above. However, paper is not fed from the paper feed unit  11 . The toner images on the transfer belt  33  are transferred onto the paper sent from the first engine module  20 , by a transfer electric field formed between the transfer belt  33  and the transfer roller  35 . Then, after the images transferred onto the paper are fixed by the fixing device (not shown), the paper is sent to the paper delivery unit  13  through the delivery roller  37  and stored therein. 
   In the second operation, part of two image formation operations are performed in parallel in one image forming apparatus  10 , and double-sided printing is performed. Therefore, the double-sided printing speed is increased. 
   It is also possible to print images only on one side of paper in a superposed manner, by providing a paper reverse mechanism (not shown) on the eject side of the first engine module  20 , and feeding paper to the second engine module  30  thereby. 
   As described above, the image forming apparatus according to the present invention has a plurality of image forming sections. Such an image forming apparatus is referred to as “multiengine image forming apparatus” hereinafter, to distinguish it from conventional apparatuses. Since the image forming sections are formed as modules, a multiengine image forming apparatus can be formed by combining a plurality of various image forming sections. 
     FIG. 3  is a diagram illustrating a basic concept of a multiengine image forming apparatus. ( 1 ) to ( 5 ) of  FIG. 3  illustrate structures of the image forming sections, and ( 6 ) of  FIG. 3  illustrates a state where a plurality of image forming sections are used in combination. 
     FIG. 3  ( 1 ) illustrates a color module. The color module is an electrophotographic module which prints color images at a speed of 30 to 45 PPM (pages per minute).  FIG. 3  ( 2 ) illustrates a monochrome module. The monochrome module is an electrophotographic module which prints monochrome images at a speed of 30 to 45 PPM.  FIG. 3  ( 3 ) illustrates an inkjet module. The inkjet module is a module which prints color images by the inkjet system. 
     FIG. 3  ( 4 ) illustrates a double-sided concurrent monochrome module. The double-sided concurrent monochrome module is an electrophotographic module which prints monochrome images on both sides of paper at a speed of 30 to 45 PPM.  FIG. 3  ( 5 ) illustrates a hybrid module. The hybrid module is a module which prints black color by electrophotography, and print other colors by the inkjet system. 
   Further, these image forming sections formed as modules can be used in combination as desired, as illustrated in  FIG. 3  ( 6 ). 
   However, various challenges must be solved to realize the above basic concept. The first challenge is to make the size of each module more compact such that a plurality of modules are contained in one housing of the multiengine image forming apparatus. The second challenge is to avoid generating a large difference in printing speed between the modules. 
   Methods of solving these challenges are explained below. 
   (1) It is indispensable to downsize image forming sections in a multiengine image forming apparatus having a plurality of image forming sections. 
   In this embodiment, as illustrated in  FIGS. 1 and 2 , an LED array is used as exposure means instead of a conventional laser optical system. 
   The LED array system uses a photosensitive drum, in which a transparent member such as glass is used as a cylindrical board holding a photosensitive member, and a transparent conductive layer, an electric charge injection blocking layer, a photosensitive layer, and a protective layer is formed on the board. Further, an LED array is disposed inside the drum, and back exposure in which exposure is performed from the inside of the drum is adopted. Since the exposure means is disposed in a dead space inside the drum and flexibility in arrangement of other devices such as developer devices is increased, the size of image forming sections is greatly reduced. 
     FIG. 4  is a diagram illustrating the laser system in contrast with the LED array system. Since the LED array system does not need a laser optical system which scans laser light, space saving is achieved. 
   Further, although LED arrays have a problem of being vulnerable to contamination such as toner and the like, this problem is solved by disposing the LED array inside the drum. 
   Further, if the quadruple color unit is changed to the monochrome unit in the laser optical system, it is inevitable to continue to use the 4-beam structure for color images as it is, and thus the running cost is increased. On the other hand, in the LED system, LED arrays other than that for monochrome images can be eliminated, as illustrated in  FIG. 3  ( 1 ) and ( 2 ). 
   (2) In a multiengine image forming apparatus having a plurality of image forming sections, it is indispensable to level out the speed of the image forming sections. 
   In this embodiment, when the inkjet system is used for a module, it is necessary to increase the printing speed thereof. 
   Therefore, a line-head type inkjet system is adopted as the inkjet system. In the line-head type inkjet system, it is possible to perform high-speed drive, and perform printing at the same speed as that of electrophotography. Consequently, adopting the line-head type inkjet system enables various combinations of electrophotography and inkjet system. 
     FIG. 5  is a diagram illustrating configuration examples of combinations of the image forming sections.  FIG. 5  illustrates functions and effects obtained in the cases where the first engine module and the second engine module are operated in parallel and in series. In the configuration examples, parallel operation indicates that the engine modules are operated individually or alone, and operation in series indicates that printing operation is performed by the first engine module and thereafter performed by the second engine module. 
   In Combination Case  1  of  FIG. 5 , the first engine module is an electrophotographic color module, and the second engine module is also an electrophotographic color module. In this combination, the printing speed is increased by operating the modules in parallel, and double-sided printing is performed at high speed by operating the modules in series. 
   In Combination Case  2 , the first engine module is an electrophotographic color module, and the second engine module is an electrophotographic monochrome module. This combination reduces the printing cost by operating the modules individually in accordance with the type (color/monochrome) of the document. 
   In Combination Case  3 , the first engine module is an electrophotographic monochrome module, and the second engine module is also an electrophotographic monochrome module. In this combination, the printing speed is increased by operating the modules in parallel, and double-sided printing is performed at high speed by operating the modules in series. 
   In Combination Case  4 , the first engine module is an electrophotographic monochrome module, and the second engine module is an inkjet module. In this combination, high-definition images are printed by operating the modules in series, and reduction of costs is achieved. 
   In Combination Case  5 , the first engine module is an inkjet module, and the second engine module is also an inkjet module. In this combination, the printing speed is increased by operating the modules in parallel, and double-sided printing is performed at high speed by operating the modules in series. 
   Although paper is used for image recording in the above embodiment, recording medium is not limited to paper, but recording medium such as OHP paper and fax paper can be used. 
   [Effects of the Embodiment] 
   As described above, the image forming method of the above embodiment produces various effects as follows. 
   Since modules can be made compact, it is possible to restructure the modules in conformity with change of customer needs. 
   For example, the cost in installation is reduced by using inexpensive engines of 30 to 45 sheets, and more modules are added in accordance with change of circumstances. Thereby, it is possible to achieve productivity as high as that of high-speed machines. 
   Further, ease of maintenance is improved by forming the image forming sections as modules, and downtime is reduced by making the system dual-redundant. 
   Specifically, since the image forming sections are formed as modules, failures can be dealt with by only changing the failed image forming section to new one as a rule, and thus the time necessary for maintenance is shortened. Further, since the system is made redundant, it is possible to avoid stopping the whole apparatus even when one module suffers a failure. 
   Specifically, the embodiment of the present invention produces the following effects. 
   (1) Increase in Speed: Since a plurality of image forming sections are operated in parallel, high-speed printing is achieved. 
   (2) Reduction in CPC (cost per copy): Since monochrome electrophotographic system and color inkjet system are operated in series, reduction in cost is achieved. 
   (3) Improvement in Image Quality: Since monochrome electrophotographic system and color inkjet system are operated in series, high-definition printing is achieved. 
   (4) High Reliability: Since a plurality of image forming sections are operated in parallel, even if one image forming section suffers a failure, other sections can output images. 
   (5) Upgradability: The apparatus can be upgraded as desired from a configuration having one monochrome picture system module to a configuration having n number of color picture system modules, in accordance with frequency of actual use thereof and user demands. Further, conversely, the apparatus can be downgraded as desired. 
   The functions explained in the above embodiment can be configured by using hardware, or may be realized by using software to read programs describing the functions into the computer. Further, the functions may be configured by selecting one of software and hardware according to necessity. 
   Furthermore, the functions can be realized by reading programs stored in recording media (not shown) into the computer. The recording media used in the above embodiment may adopt any recording format, as long as they are recording media which can record programs and from which the computer can read the programs. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.