Abstract:
An image forming apparatus including a plurality of process stations vertically arranged each of which includes an image bearing member on which a latent image is to be formed and a developing device for developing the latent image, image bearing member driving devices, for driving the image bearing members, development driving devices, for driving the developing devices, and a transfer material bearing and conveying device for bearing and conveying the transfer material, wherein, while the transfer member is vertically conveyed through transfer nips that are formed by the transfer material bearing and conveying device and the image bearing members of all of the plurality of process stations, images formed by the plurality of pocess stations are sequentially transferred to the transfer material to form an image, and wherein process stations to be used for image forming can be selected, and the image bearing member driving devices and the development driving devices are controlled, so that, during an image forming process, the image bearing members of the process stations that are not used for image forming are driven, while the developing devices thereof are halted.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an image forming apparatus, such as a printer or a copier, of an electrophotographic system or an electrostatic recording system, and relates in particular to a color image forming apparatus wherein a plurality of image forming means are arranged vertically.  
           [0003]    2. Related Background Art  
           [0004]    Recently, speed, function and color recording has been developed for image forming apparatuses of an electrophotographic system, and various types of printers and copiers are available on the market.  
           [0005]    Above all, image forming apparatuses of an in-line system, in which image forming means for plural colors are disposed in series and toner images are sequentially multi-layer transferred, can form color images at high speed, and it is anticipated that in the future color printers incorporating such in-line type image forming apparatuses will be the primary color printers.  
           [0006]    An in-line type image forming apparatus employs a method whereby a recording medium (transfer material) is borne on the surface of belt-shaped conveying means, for transporting the recording medium, while toner images are sequentially transferred to the recording medium to form a multi-layer color image. According to this method, the configurations of the apparatuses can be roughly sorted into two types, depending on the direction in which the recording media are conveyed.  
           [0007]    In one configuration, as is shown in FIG. 9, process stations  8 M,  8 C,  8 Y and  8 K, which are first, second, third and fourth image forming means for different colors, are arranged substantially horizontally along a transferring and conveying belt  7  as an endless conveying means for conveying a recording medium, and a recording medium  1  is borne on and conveyed horizontally by the transferring and conveying belt  7  while an image is formed. In another configuration, as shown in FIG. 10, the first to fourth process stations  8 M,  8 C,  8 Y and  8 K are arranged vertically (substantially in the gravitational direction) along the transferring and conveying belt  7 , so that a recording medium  1  is conveyed vertically while an image is formed.  
           [0008]    For the thus constructed color image forming apparatuses to output full color images, as shown in FIGS. 9 and 10 the four color process stations  8 M,  8 C,  8 Y and  8 K, or more specifically, photosensitive drums  9 M,  9 C,  9 Y and  9 K, which are image bearing members, are brought into close contact with the conveying belt  7 . Then, to form an image, a recording medium  1  is attracted by an attracting roller  18  to the surface of the transferring and conveying belt  7  so that the recording medium  1  is conveyed. Finally, to obtain a full color image, the respective color toner images are sequentially transferred to the recording medium  1 .  
           [0009]    On the contrary, when, for example, only a black image is to be formed by using only the fourth process station  8 K, which is located downstream-most in the direction in which the transferring and conveying belt  7  moves, the first to the third, upstream process stations  8 M,  8 C and  8 Y are not required, i.e., are not used for an image formation. As shown in FIGS. 11 and 12, the first to the third process stations  8 M,  8 C, and  8 Y are halted and a separation roller  19  separates the transferring and conveying belt  7  from the first to the third process station. With this arrangement, since developing devices  12 M,  12 C and  12 Y, of the first to the third process stations  8 M,  8 C and  8 Y perform no unnecessary operations, the service lives of these components can be extended.  
           [0010]    However, in the arrangement shown in FIG. 12, a recording medium  1  is conveyed substantially vertically (substantially in the gravitational direction). When only the black color image is developted, the recording medium  1  must arrive at the downstream-most, fourth process station  8 K, while closely attracted to the transferring and conveying belt  7 . Thus, a high voltage must be applied to the attracting roller  18  to attract the recording medium  1  to the transferring and conveying belt  7 , and the cost for the power supply required by the attracting roller  18  is increased.  
           [0011]    Further, when a recording medium  1  is rather damp or is bent, or when a recording medium  1  is formed with double sheets of paper such as an envelope, the force of attraction is deteriorated, so that the recording medium  1  tends to fall off due to its own weight to cause a paper jam.  
           [0012]    In the above normal arrangement, the image forming procedures for which only black and for which full color is used can easily be distinguished, one from the other. However, this is not so for the case shown in FIG. 13, where the first and the third process stations  8 M and  8 Y output images, while the second and fourth process stations  8 C and  8 K do not output images. In this case, the second and the fourth process stations  8 C and  8 K which are not required to form images must be driven. Therefore, the developing devices  9 C and  9 K in the second and the fourth process stations  8 C and  8 K are ealy deteriorated.  
         SUMMARY OF THE INVENTION  
         [0013]    It is an object of the present invention to provide an image forming apparatus that forms an image while conveying a transfer material vertically, and wherein the service life of developing means is extended.  
           [0014]    It is another object of the present invention to provide an image forming apparatus that forms an image while conveying a transfer material vertically, and wherein the conveyance of a transfer material is ensured without an increase in cost.  
           [0015]    To achiever the above objects, according to the present invention, an image forming apparatus comprises: a plurality of image forming means vertically arranged each of which includes an image bearing member on which a latent image is to be formed and developing means for developing the latent image; image bearing member driving means for driving the image bearing members, respectively; development driving means for driving the developing means, respectively; transfer material bearing and conveying means for bearing and conveying the transfer material; and control means for selecting image forming means to be used for image forming from among the plurality of image forming means, and for controlling the image bearing member driving means and the development driving means, so that, during an image forming process, image bearing members of image forming means that are not used for image forming among the plurality of image forming means are driven, while developing means of the image forming means that are not used for image forming are halted,  
           [0016]    wherein, while the transfer material is vertically conveyed through transfer nips that are formed by the transfer material bearing and conveying means and all the image bearing members of the plurality of image forming means, images formed by the plurality of image forming means are sequentially transferred to the transfer material to form an image.  
           [0017]    With this arrangement, when the developing means is not being used for image forming, the developing means is halted so that unnecessary deterioration of the developing means can be prevented, thereby ensuring that the service life of the developing means is extended.  
           [0018]    Further, since the image bearing member that is not being used for image forming can be driven and a transfer material can be conveyed while sandwiched between the transfer material bearing and conveying means and the image bearing members, the conveyance of the transfer material is ensured without an increase in cost being required. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention;  
         [0020]    [0020]FIG. 2 is a diagram showing a state wherein only the fourth process station of the image forming apparatus in FIG. 1 is driven;  
         [0021]    [0021]FIG. 3 is a diagram showing a state wherein the first and the third process stations of the image forming apparatus in FIG. 1 are driven;  
         [0022]    [0022]FIG. 4 is a diagram showing the configuration of an image forming apparatus according to another embodiment of the invention;  
         [0023]    [0023]FIG. 5 is a diagram showing a development sleeve separating mechanism;  
         [0024]    [0024]FIG. 6 is a block diagram showing a driving system;  
         [0025]    [0025]FIG. 7 is a diagram showing a state wherein the first and the third process stations of the image forming apparatus in FIG. 4 are driven;  
         [0026]    [0026]FIG. 8 is a diagram showing the configuration of an image forming apparatus according to still another embodiment of the invention;  
         [0027]    [0027]FIG. 9 is a schematic diagram showing an example arrangement of a conventional image forming apparatus;  
         [0028]    [0028]FIG. 10 is a schematic diagram showing another example arrangement of a conventional image forming apparatus;  
         [0029]    [0029]FIG. 11 is a diagram showing a state wherein only the fourth process station of the image forming apparatus in FIG. 9 is driven;  
         [0030]    [0030]FIG. 12 is a diagram showing a state wherein only the fourth process station of the image forming apparatus in FIG. 10 is driven; and  
         [0031]    [0031]FIG. 13 is a diagram showing a state wherein the first and the third process stations of the image forming apparatus in FIG. 10 are driven. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    An image forming apparatus according to the present invention will now be described in detail while referring to the accompanying drawings. The same reference numerals are used throughout to denote components that correspond to or are identical to the above described members.  
         [0033]    (First Embodiment)  
         [0034]    A first embodiment of the invention will now be described while referring to FIGS.  1  to  3 .  
         [0035]    As is shown in FIG. 1, a full color image forming apparatus in this embodiment has a configuration in which process stations  8 M,  8 C,  8 Y and  8 K as the first, second, third and fourth image forming means are stacked substantially vertically (substantially in the gravitational direction). The process stations  8 M to  8 K respectively form magenta, cyan, yellow and black images.  
         [0036]    The design that is used for all the process stations  8 M to  8 K is the same. The process stations  8 M to  8 K include photosensitive drums  9 M,  9 C,  9 Y and  9 K as image bearing members, chargers  10 M,  10 C,  10 Y and  10 K as charging means, developing devices  12 M,  12 C,  12 Y and  12 K as developing means containing developers (toners) of respective colors, cleaners  14 M,  14 C,  14 Y and  14 K, and exposing devices  11 M,  11 C,  11 Y and  11 K, respectively.  
         [0037]    The developing devices  12 M,  12 C,  12 Y and  12 K employ a non-contact developing method, and development sleeves  12 M 1 ,  12 C 1 ,  12 Y 1  and  12 K 1 , which are developer bearing members of the developing devices  12 M to  12 K, are separated by a gap of about 300 μm from their opposite photosensitive drums  9 M to  9 K. During developing, a development bias obtained by superimposing a rectangular alternate-current voltage on a direct-current voltage is applied to between the photosensitive drums  9 M to  9 K and the development sleeves  12 M 1  to  12 K 1 .  
         [0038]    Further, a transferring and conveying belt  7 , which serves as transfer material bearing and conveying means for bearing and conveying a transfer material  1 , is extended along the process stations  8 M to  8 K and around a drive roller  5 , a driven roller  6  and a belt tensioning roller  20 , which serve as belt drive means, and is moved in the direction indicated by an arrow A.  
         [0039]    Full color image forming process will now be explained while referring to FIG. 1.  
         [0040]    In the first process station  8 M, after the photosensitive drum  9 M has been uniformly charged by the charger  10 M, a laser beam corresponding to magenta image information, is emitted to form an electrostatic latent image on the drum  9 M. Then, to develop the electrostatic latent image, magenta toner, supplied by the developing device  12 M, is transferred by the application of the development bias, and a magenta toner image is formed on the photosensitive drum  9 M.  
         [0041]    Recording sheets  1  as the transfer material are picked up one by one from a paper feed portion  2  by a pickup roller  16 , and are fed along a paper feeding path  4  to the transferring and conveying belt  7 . Then, the recording sheet  1  is attracted to and borne on the transferring and conveying belt  7  by an attracting roller  18  as the attracting means. Thence, in registry with the magenta toner image on the photosensitive drum  9 M, the recording sheet  1  is conveyed to a transfer position T where the magenta toner image is transferred onto the recording sheet  1  by a transfer device  13 M.  
         [0042]    At the second, third and fourth process stations  8 C,  8 Y and  8 K, in the same manner as the process performed at the first process station  8 M, a cyan toner image, a yellow toner image and a black toner image are formed on the respective photosensitive drums  9 C,  9 Y and  9 K, and as the recording sheet  1  is conveyed by the transferring and conveying belt  7  to transfer positions T 2 , T 3  and T 4  of the second, third and fourth process stations  8 C,  8 Y and  8 K, transfer devices  13 C,  13 Y and  13 K transfer and superimpose the respective color toner images on the recording sheet  1 .  
         [0043]    The recording sheet  1  onto which the four color toner images are transferred is conveyed from the fourth, downstream-most process station  8 K to a fixing device  15 . The fixing device  15  fixes the toner images to the recording sheet  1  and discharges the recording sheet  1  to a discharge portion  3 .  
         [0044]    The cleaners  14 M to  14 K remove residual toners from the photosensitive drums  9 M to  9 K, from which the images have been transferred, to prepare the photosensitive drums  9 M to  9 K for the next image forming sequence.  
         [0045]    An explanation will now be given, while referring to FIG. 2, for the image output process, i.e., the image forming process, wherein only the fourth, downstream-most process station  8 K is used.  
         [0046]    During the image output process for which only the fourth, downstream-most process station  8 K is used, the developing devices  12 M,  12 C and  12 Y of the first, second and third, upstream process stations  8 M,  8 C and  8 Y, are halted. Since the developing devices  12 M to  12 K of this embodiment employ the non-contact developing method described above, the development sleeves  12 M 1  to  12 K 1  are not rubbed with the photosensitive drums  9 M to  9 K, regardless of whether an image is being output or not.  
         [0047]    At this time, the photosensitive drums  9 M to  9 Y of the first to third process stations  8 M to  8 Y, which are not being used for image output, are driven in contact with the transferring and conveying belt  7 , and serve as feeding rollers to advance the recording sheet  1  to the fourth process station  8 K, which is being used for the image output.  
         [0048]    The image output process using the first and third process stations  8 M and  8 Y will now be described while referring to FIG. 3.  
         [0049]    During this process, the developing devices  12 C and  12 K of the second and fourth process stations  8 C and  8 K, which are not being used for image output, are halted.  
         [0050]    Furthermore, the photosensitive drums  9 C and  9 K of the second and fourth process stations  8 C and  8 K, which are not being used for image output, closely contact the transferring and conveying belt  7 , and serve as feed rollers for conveying the recording sheet  1 .  
         [0051]    As is described above, according to the embodiment, as the developing device that are not used for image output are halted, unnecessary deterioration of the developing devices can be prevented, and their service lives can be extended. Further, since the photosensitive drums that are not being used for image output serve as feed rollers for the recording sheet, even a damp or bent recording sheet, or one, such as an envelope, that is formed of folded paper, can be precisely conveyed, with no increase in apparatus cost, and defects, such as paper jamming, resulting from falling recording sheets can be prevented.  
         [0052]    In this embodiment, the non-contact developing method, whereby a gap is maintained between a development sleeve and a photosensitive drum, has been employed. However, the contact developing method, whereby a development sleeve and a photosensitive drum contact each other, may also be employed and the same effects obtained.  
         [0053]    (Second Embodiment)  
         [0054]    A second embodiment of this invention will now be described while referring to FIGS.  4  to  7 . A full color image forming apparatus in the second embodiment has substantially the same configuration as in the first embodiment, except that development sleeves  12 K 1  to  12 M 1  of developing devices  12 M to  12 K of first to fourth process stations  8 M to  8 K can be brought into contact with and be separated from opposite photosensitive drums  9 M to  9 K.  
         [0055]    An image output process using only the fourth, downstream-most process station  8 K will now be described while referring to FIG. 4.  
         [0056]    During the image output process for which only the fourth, downstream-most process station  8 K is used, the developing devices  12 M,  12 C  12 Y, or more specifically, development sleeves  12 M 1 ,  12 C 1  and  12 Y 1 , of the first, second and third, upstream process stations  8 M,  8 C and  8 Y, are separated from the corresponding photosensitive drums  9 M,  9 C and  9 Y and halted.  
         [0057]    The photosensitive drums  9 M to  9 Y of the first to third process stations  8 M to  8 Y, which are not being used for image forming, are driven in close contact with the transferring and conveying belt  7 , and serve as feed rollers for advancing a recording sheet  1  to the fourth process station  8 K, which is being used for image output.  
         [0058]    [0058]FIG. 5 is a diagram showing a contact-separation mechanism for a development sleeve DS in a process station. In FIG. 5, the developing device  12  is mounted to be rotatable about a fulcrum  31 . With this arrangement, the development sleeve DS is contactable to and separable from the photosensitive drum  9 . A spring  30  as urging means that is located between the cleaner  14  and the developing device  12  applies an urging force by which the developing device  12  is urget to be in contact with the photosensitive drum  9 . As a developing device contact-separation motor  33  is driven, a developing device contact-separation lever  32  impelled by the contact-separation motor  33  pushes the bottom of the developing device  12  against the urging force of the spring  30  to rotate the developing device  12  about the fulcrum  31  and to separate the development sleeve DS from the photosensitive drum  9 . Conversely, when the developing device contact-separation motor  33  is rotated in reverse, the developing device contact-separation lever  32  is lowered, and as a result, the development sleeve DS approaches the photosensitive drum  9 .  
         [0059]    [0059]FIG. 6 is a block diagram showing a driving unit of the second embodiment. A drive motor  34  is drive means for driving the photosensitive drum  9  and the developing device  12 . The photosensitive drum  9  is driven via a drive gear  35 , and the developing device  12  is driven by a clutch  36 , which enables the release of the drive transmission to the developing device  12 . The developing device  12  is separated from and brought into contact with the photosensitive drum  9 , via the contact-separation lever  32 , by the contact-separation motor  33 . The drive motor  34 , the clutch  36  and the contact-separation motor  33  are controlled by a controlling portion  37  as the control means.  
         [0060]    In FIG. 6, the portion that includes the controlling portion  37 , the clutch  36  and the drive motor  34  has the same structure as in the first embodiment.  
         [0061]    An image output process for which only the first and third process stations  8 M and  8 Y are used will now be described while referring to FIG. 7.  
         [0062]    In this case, the developing devices  12 C and  12 K, or more specifically, the development sleeves  12 C 1  and  12 K 1 , of the second and fourth process stations  8 C and  8 K, which are not used for image output, are separated from their opposite photosensitive drums  9 C and  9 K and halted.  
         [0063]    The photosensitive drums  9 C and  9 K of the second and fourth process stations, which are not used for image output, are driven in close contact with the transferring and conveying belt  7 , and serve as feed rollers for conveying the recording sheet  1 .  
         [0064]    As is described above, according to the contact developing method in this embodiment, since the developing devices that are not used for image output are halted and separated from their opposite photosensitive drums, unwanted friction can be prevented between the photosensitive drums and the development sleeves, so that the service life of each of the developing devices can be extended. According to this embodiment, even if a developing device uses a non-contact developing method, its service life can also be extended.  
         [0065]    Furthermore, since the photosensitive drums that are not used for the image output serve as feed rollers for the recording sheet, even a damp or bent recording sheet, or one, such as an envelope, that is formed of folded paper, can be precisely conveyed, with no increase in apparatus cost, and defects, such as paper jamming, resulting from falling recording sheets  1  can be prevented.  
         [0066]    (Third Embodiment)  
         [0067]    A third embodiment of the invention will now be described while referring to FIG. 8. A full color image forming apparatus for this embodiment has basically the same configuration as in the second embodiment.  
         [0068]    As is described above, in an image output process for which only the fourth, downstream-most process station  8 K is used, developing devices  12 M,  12 C and  12 Y, or more specifically, development sleeves  12 M 1 ,  12 C 1  and  12 Y 1  of the first to third, upstream process stations  8 M,  8 C and  8 Y are separated from their opposite photosensitive drums  9 M,  9 C and  9 Y and halted.  
         [0069]    At this time, the photosensitive drums  9 M to  9 Y of the first to third process stations  8 M to  8 Y, which are not used for image output are driven and in contact with a transferring and conveying belt  7 , and serve as feed rollers for conveying a recording sheet  1  to the fourth process station  8 K, which is used for image forming.  
         [0070]    At the same time, a conveying bias of, for example, −1 kV, which has a polarity that is the opposite of the polarity of the transfer bias applied during the transfer process, is applied to transfer devices  13 M to  13 Y of the first to third process stations  8 M to  8 Y that are not being used for image forming. As a result, the recording sheet  1  is strongly attracted to the transferring and conveying belt  7 , and is more precisely conveyed.  
         [0071]    Further, since a charge is applied that has a polarity opposite to the polarity of the charge applied during transfer process, the image transfer at the fourth process station  8 K is easily performed. For example, since the transfer bias that generally requires 1.5 kV can be reduced to 1 kV, image failures can be prevented. So long as the conveying bias has no affect on an image, +1 kV may be employed as the conveying bias.  
         [0072]    In this embodiment, the development sleeve of the developing device that is not used for image forming is separated from the photosensitive drum. However, the arrangement in the first embodiment may be employed instead of the arrangement in this embodiment.  
         [0073]    As is described above, according to the embodiment, the recording sheet can be more accurately conveyed. Since the polarity of the conveying bias is taken into account, the transfer function can be improved, and a preferable image can be obtained.  
         [0074]    (Fourth Embodiment)  
         [0075]    A fourth embodiment will now be described. The feature of this embodiment is that only in the image forming process for which predetermined image forming means is used, developing means of the other image forming means that is not used for the image forming is halted. The arrangement of the second embodiment is employed for the other arrangement.  
         [0076]    An explanation will now be given for a case wherein only the fourth, downstream-most process station  8 K (black color) is designated as the predetermined image forming means, i.e., a case of the process for forming only a black image.  
         [0077]    In the image output process using only the fourth, downstream-most process station  8 K, developing devices  12 M,  12 C and  12 Y, or more specifically, development sleeves  12 M 1 ,  12 C 1  and  12 Y 1  of the first, second and third process stations  8 M,  8 C and  8 Y are separated form the corresponding photosensitive drums  9 M,  9 C and  9 Y and halted.  
         [0078]    The photosensitive drums  9 M to  9 Y of the first to third process stations  8 M to  8 Y, which are not used for image forming, are driven and in contact with a transferring and conveying belt  7 , and serve as feed rollers for conveying a recording sheet  1  to the fourth process station  8 K, which is used to output the image.  
         [0079]    During the image forming process using other image forming means than the predetemined image forming means, in all the first to fourth process stations, all the photosensitive drums and all the developing devices are driven, and the development sleeves are not separated from the photosensitive drums. It should be noted that an image forming process using other image forming means than the predetermined image forming means is other color image forming process than the black image forming process, that uses any of the first to third process stations.  
         [0080]    According to the present embodiment, only when a predetermined color (for example, black) image formation is frequently performed depending on a user&#39;s usage, the developing devices of any process stations which are not used for forming images can be halted and their development sleeves can be separated. Therefor, the control of the apparatus can be facilitated without any reductions in actual effectiveness.  
         [0081]    In this embodiment, the image formation using only black has been explained. However, depending on the application required by a user, image forming means for another color may be designated as the predetermined image forming means.  
         [0082]    Further, the arrangement for the second embodiment has been employed for this embodiment; however, the same effects can be obtained by using the arrangement of the first or third embodiment.