Abstract:
There is provided a development cartridge capable of switching development colors in a plurality of development cartridges without using development rack. A development cartridge of the present invention has a part of a drive member for switching development colors.

Description:
RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2005-197417 filed in Japan on Jul. 6, 2005, the content of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a development cartridge, a development device and an image formation apparatus. 
   As one of electrophotography-type image formation apparatuses, a four-cycle color image formation apparatus has conventionally been known. The color image formation apparatus of this type forms color images by forming four color toner images on a photoreceptor by four development cartridges corresponding to four color toners: yellow; magenta; cyan; and black, and sequentially superimposing these four color toner images on an intermediate transfer belt. 
   In the conventional four-cycle color image formation apparatus, as disclosed in JP 2001-83800 A shown below, the four development cartridges are generally loaded side by side in circumferential direction in a rotatable development rack. Normally, as shown in  FIGS. 7 and 8 , a development rack  60  is structured such that its peripheral region is divided into four sections by four blade-like members  64  provided radially around a rotation shaft  62  in a standing posture, and four development cartridges  66  are loaded in respective divided regions. Moreover, in both end portions, of the development rack  60  with each development cartridge  66  loaded therein, disc-shaped retention members  68 ,  70  for retaining each development cartridge are secured. The retention member  70  has an all-around gear formed in its peripheral portion, and the all-around gear is engaged with a drive gear  72 . Consequently, the drive gear  72  transmits drive force to the retention member  70 , by which the development rack  60  is rotationally driven. 
   However, the development rack  60  is heavy as four development cartridges  66  filled with toners of respective colors are loaded therein, and this incurs a possibility that torsion is generated due to transmission of rotational drive force from one end portion. Such torsion may cause parallelism between a development roller of a development cartridge at a development position and a photoreceptor off-balanced. Accordingly, in order to prevent the torsion from being generated, the development rack  60  requires properly high rigidity, and this has prevented reduction in size and weight of the development rack  60 . 
   Moreover, on the lateral surface of the retention member  70 , four plate-like development position detection pieces  74  are provided in a standing posture at 90 degrees intervals in circumferential direction. By detecting the plate-like development position detection pieces  74  by a sensor such as photointerrupters mounted on the image formation apparatus itself, each development cartridge can be stopped at a development position (referring hereinbelow to the position where the development roller is in contact with the photoreceptor). However, since the retention member  70  is a large member made of resin, it is difficult to secure component accuracy, and even when the development rack  60  is stopped at the position where the plate-like development position detection pieces  74  are detected, sometimes the position accuracy between the photoreceptor and the development roller cannot be secured. Accordingly, in order to secure the position accuracy, the loading positions of the development cartridges  66  need fine adjustment performed in the state that the development cartridges  66 , the development rack  60  and the retention members  68 ,  70  are assembled, and this operation is time-consuming. 
   Further, in the case of doing maintenance of a certain component around the development rack in the image formation apparatus, the development rack  60  still remains in the apparatus after all the development cartridges  66  are unloaded, making the maintenance operation difficult to perform. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a development cartridge, a development device and a color image formation apparatus using the same, which can achieve reduction in number of components, size and cost by removing development rack and retention members from a four-cycle color image formation apparatus. 
   In order to accomplish the object, a development cartridge of the present invention has a part of a drive, member for switching development colors. 
   According to the structure, drive force is transmitted through a part of the drive member to the development cartridge, so that the development cartridge can be moved to a development position. This makes it possible to eliminate the use of conventional development rack and retention members also including function as the members for rotationally driving the development rack, thereby achieving reduction in number of components, size and cost of the image formation apparatus. Moreover, the absence of the development rack in the image formation apparatus enhances the maintenance inside the apparatus. 
   The development cartridge of the present invention may further includes a development position detection section. 
   According to this structure, by detecting the development position detection section by a sensor such as photointerrupters, it can be accurately detected that the development cartridge reaches the development position. 
   The development cartridge of the present invention may further include a connection section for establishing direction connection to other development cartridges. 
   According to this structure, the development device can be constituted of the development cartridges which are connected to each other without special members interposed therebetween, which eliminates the use of the conventional development rack and retention members. 
   The development cartridge of the present invention may further include a part of a rotation spindle. 
   According to this structure, when the development device is constituted by connecting a plurality of development cartridges, a part of the rotation spindles are combined to constitute a column-shaped rotation spindle, which eliminates the necessity of additional provision of a rotation spindle for the development device. 
   In the development cartridge of the present invention, a part of the drive member may be integrated with the development cartridge. 
   According to this structure, forming a part of the drive member with the development cartridge by, for example, the integral molding can save the trouble of assembly and facilitates manufacturing. 
   In the development cartridge of the present invention, a part of the drive member may be provided respectively on both end sides in longitudinal direction of the development cartridge. 
   According to this structure, drive force is transmitted to the development cartridge in a balanced manner through a part of the drive members on both the ends, which prevents torsion to be generated in the development cartridge by the drive force. 
   Further in the development cartridge of the present invention, the drive member may be a series of gears. 
   According to this structure, a gear provided on the development cartridge is engaged with a drive gear to transmit drive force, so that the development cartridge can be moved. 
   There is provided in the present invention a color image formation apparatus including a development cartridge having a part of a drive member for switching development colors, wherein the development cartridge at a development position where a development roller is in contact with a photoreceptor is driven through a part of the drive member. 
   According to this structure, drive force is transmitted to a development cartridge at a development position through a part of the drive member to drive the development cartridge, so that the development cartridge can be moved to the development position at high accuracy. This makes it possible to eliminate the use of conventional development rack and retention members also including function as the members for rotationally driving the development rack, thereby achieving reduction in number of components, size and cost of the image formation apparatus. Moreover, the absence of the development rack in the image formation apparatus enhances the maintenance inside the apparatus. 
   In the color image formation apparatus of the present invention, the development cartridge may further include a development position detection section, and it may be detected by the development position detection section of the development cartridge at a development position that the development cartridge is at the development position where a development roller is in contact with a photoreceptor. 
   According to this structure, by detecting the development position detection section by a sensor such as photointerrupters, it can be accurately detected that the development cartridge reaches the development position. 
   In the color image formation apparatus of the present invention, the development cartridge may further include a part of a rotation spindle, and a position of the development position detection section may be detected on a straight line connecting a rotation center of the photoreceptor and a center of the rotation spindle. 
   According to this structure, the position detection of the development cartridge is performed on the straight line connecting the rotation center of the photoreceptor and the center of the rotation spindle, which allows the development cartridge to be aligned with the photoreceptor at high accuracy. 
   In the color image formation apparatus of the present invention, the development cartridge may further include a connection section for establishing direct connection with other development cartridges, and a plurality of development cartridges may be connected through the connection sections so that the a part of the drive members are combined to constitute a series of gears. 
   According to this structure, the development device can be constituted of the development cartridges which are directly connected to each other without special members interposed therebetween, which eliminates the use of the conventional development rack and retention members. Moreover, a part of the drive members are combined to constitute a series of gears so that a series of the gears is engaged with a drive gear to transmit drive force, and therefore a plurality of the development cartridges connected to each other can be moved. 
   Further, in the color image formation apparatus of the present invention, the development cartridge may further include a part of a rotation spindle, and a plurality of the development cartridges may be connected through the connection sections so that a part of the rotation spindles are combined to form a column shape. 
   According to this structure, when the development device is constituted by connecting a plurality of development cartridges, a part of the rotation spindles are combined to constitute a column-shaped rotation spindle, which eliminates the necessity of additional provision of a rotation spindle for the development device. 
   There is also provided in the present invention a development device including a plurality of development cartridges each having a connection section, the development cartridges being integrated by direction connection through the connection sections. 
   According to this structure, the development device is constituted by integrating a plurality of development cartridges through direct connection via the connection sections, which eliminates the use of conventional development rack for loading a plurality of development cartridges. This makes it possible to reduce number of components, size and cost of the image formation apparatus. 
   In the development device of the present invention, a plurality of the development cartridges integrated by direction connection through the connection sections may form an almost column shape. 
   According to this structure, the development device constituted by integrating a plurality of development cartridges through direct connection via the connection sections forms an almost column shape, so that rotational drive of the development device can move a specified development cartridge to a development position. 
   In the development device of the present invention, a plurality of the development cartridges may each include a part of a drive member for switching development colors, and a plurality of the development cartridges may be integrated by direct connection through the connection sections so that a part of the drive members are combined to constitute a series of gears. 
   According to this structure, the development device can be constituted of the development cartridges which are connected to each other without special members interposed therebetween, which eliminates the use of the conventional development rack and retention members. Moreover, a part of the drive members are combined to constitute a series of gears so that a series of the gears is engaged with a drive gear to transmit drive force, and therefore a plurality of the development cartridges connected to each other can be moved. 
   In the development device of the present invention, a series of the gears that is the drive member may be disposed respectively on both ends in longitudinal direction of the development device. 
   According to this structure, drive force is transmitted to the development cartridge in a balanced manner through a series of the gears on both the ends, which prevents torsion to be generated in the development cartridge by the drive force. 
   The development device of the present invention may be driven via a part of the drive member of the development cartridge positioned at a development position facing a photoreceptor. 
   According to this structure, even when the development device constituted by connecting a plurality of the development cartridges has loose linkage parts, driving the development device through a part of the drive member of the development cartridge at the development position facing the photoreceptor allows a specified development cartridge to be moved to the development position at high accuracy without being affected by the loose linkage parts. 
   In the development device of the present invention, the development cartridge may further include a part of a rotational spindle, and a plurality of the development cartridges may be connected and integrated so that a part of the rotation spindles are combined to form a column shape. 
   According to the structure, in the development device constituted by connecting a plurality of development cartridges, a part of the rotation spindles are combined to constitute a column-shaped rotation spindle, which eliminates the necessity of additional provision of a rotation spindle for the development device. 
   In the development device of the present invention, a plurality of the development cartridges may each have a development position detection section, and it may be detected by the development position detection section of the development cartridge at a development position that a specified development cartridge is at the development position facing a photoreceptor. 
   According to this structure, by detecting the development position detection section by a sensor such as photointerrupters, it can be accurately detected that a specified development cartridge reaches the development position. 
   As described above, according to the development cartridge, the development device and the image formation apparatus in the present invention, drive force is transmitted through a part of the drive member provided on the development cartridge so as to allow the development cartridge to be moved for switching development colors, which makes it possible to eliminate the use of conventional development rack and retention members also including function as the members for rotationally driving the development rack, thereby achieving reduction in number of components, size and cost of the image formation apparatus. Moreover, the absence of the development rack in the image formation apparatus enhances the maintenance inside the apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be further described with reference to the accompanying drawings wherein like reference numerals refer to like parts in the several views, and wherein: 
       FIG. 1  is an overall structural view showing a color image formation apparatus; 
       FIG. 2  is an enlarged view showing a development cartridge at a development position; 
       FIG. 3  is a view showing four development cartridges before being connected; 
       FIG. 4  is a view showing an all-around gear disposed on both ends of a development device; 
       FIG. 5  is a view showing a development device including an enlarged development cartridge for black toner; 
       FIG. 6  is a view showing a modified example of a development device constituted of four development cartridges which are connected in the state of being stacked in one direction; 
       FIG. 7  is a view showing a development rack and a retention member for use in a conventional color image formation apparatus; and 
       FIG. 8  is a view showing the state before four development cartridges are loaded in the development rack. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an outlined structure of a color image formation apparatus  10  in one embodiment of the present invention. The color image formation apparatus  10  has, for example, a dram-type photoreceptor  12  rotationally driven in an arrow A direction. The surface of the photoreceptor  12  is uniformly charged by an electrifier  14  and then the uniformly charged surface is exposed to laser light by an exposure unit  16  so as to form an electrostatic latent image. 
   An almost column-shaped development device  18  is disposed adjacent to the photoreceptor  12 . The development device  18  is supported rotatably around a column-shaped rotation spindle  19  disposed in a protruding manner from both end faces in longitudinal direction (i.e., vertical to the surface of the drawing sheet). The development device  18  is constituted of four development cartridges  20  respectively containing four color toners: yellow (Y); magenta (M); cyan (C); and black (K). Each development cartridge  20  has a development roller  22 . The development roller  22  is for transporting the toner contained in the development cartridge  20  by rotational drive so as to feed the toner for development of an electrostatic latent image on the surface of the photoreceptor  12 . 
   On a peripheral section in a longitudinal direction end section of the development device  18 , a series of gears (drive member)  24  is provided all around its periphery. The gears  24  are engaged with a drive gear  26 . Consequently, with the drive gear  26  being rotationally driven in an arrow B direction, the development device  18  is rotated in an arrow D direction. 
   An intermediate transfer belt  30  is in tight contact with the photoreceptor  12  by a primary transfer roller  28 . The intermediate transfer belt  30 , which forms an endless sheet made of, for example, a resin film, is supported in the state of being pulled from the inside by a specified tension by a drive roller  32 , a driven roller  34  and the primary transfer roller  28  and is rotationally driven by the drive roller  32  in an arrow E direction. 
   A portion of the intermediate transfer belt  30  supported by the drive roller  32  is in tight contact with a secondary transfer roller  42 . A contact portion between the intermediate transfer belt  30  and the secondary transfer roller  42  constitutes a secondary transfer section  44 . Above the secondary transfer section  44 , a fixation unit  46  made of a pair of rollers is provided. 
   In a lower portion of the color image formation apparatus  10 , a paper feed section  36  is provided. Paper sheets piled and stored in the paper feed section  36  are sent out one by one from the uppermost paper sheet to a paper transportation line  40  by a paper feed roller  38 . The paper transportation line  40  extends from the paper feed roller  38  through a pair of transportation rollers  48 , a pair of timing rollers  50 , the secondary transfer section  44  and the fixation unit  46  to a paper discharge roller  52 . 
   In the thus-structured color image formation apparatus  10 , upon input of a print signal containing image data from the outside, the photoreceptor  12  is rotationally driven so that the surface of the rotating photoreceptor  12  is uniformly charged by the electrifier  14 . The surface of the uniformly charged photoreceptor  12  is exposed to laser light corresponding to the image data by the exposure unit  16  so as to form an electrostatic latent image. The electrostatic latent image is developed by, for example, a yellow (Y) development cartridge  20  which is positioned at a development position (i.e., at the position of the development cartridge  20  whose development roller  22  is in contact with the photoreceptor  12 ) to make a yellow toner image. The yellow toner image is moved with rotation of the photoreceptor  12 , and is primary-transferred onto the intermediate transfer belt  30  by electrostatic force of the primary transfer roller  28  to which transfer bias is applied. 
   Then, rotational drive of the drive gear  26  in the arrow B direction rotates the development device  18  in the arrow D direction, and when a magenta (M) development cartridge  20  is moved to the development position, the rotation of the development device  18  is stopped. It is to be noted that a method for detecting that a specified development cartridge  20  reaches the development position will be described later. 
   At this point, a magenta electrostatic latent image is formed on the surface of the photoreceptor  12 , and the electrostatic latent image is developed by the magenta (M) development cartridge  20  which has reached the development position to make a magenta toner image. By electrostatic force of the primary transfer roller  28 , the magenta toner image is primary-transferred on top of the yellow toner image on the intermediate transfer belt  30  which has rotated one time. It is to be noted that when the intermediate transfer belt  30  rotates one time while carrying a toner image, the secondary transfer roller  42  is held in the state of being away from the intermediate transfer belt  30 . 
   Hereinafter in the same process, a cyan toner image and a black toner image are seriatim primary-transferred on top of the former two color toner images on the intermediate transfer belt  30 . The resultant four color toner images formed in the state of being superimposed on the intermediate transfer belt  30  are moved to the secondary transfer section  44  with the rotation of the intermediate transfer belt  30 . At this point, the secondary transfer roller  42  is returned to the state of being in tight contact with the intermediate transfer belt  30 , and by electrostatic force of the secondary transfer roller  42  to which transfer bias is applied, the four color toner images are secondary-transferred collectively from the intermediate transfer belt  30  onto a paper sheet which is sent away from the paper feed section  36  and is led into the secondary transfer section  44  by the pair of timing rollers  50 . 
   After the toner images on the paper sheet are fixed by heating when the paper sheet passes through the fixation unit  46 , the paper sheet is discharged out of the apparatus by the paper discharge roller  52 . 
   Now, the development device  18  is described in detail. 
   As described before, the development device  18  is constituted of four development cartridges  20 , and since all development cartridges  20  of respective color toners have the same structure, description is herein given of the yellow toner development cartridge  20  as an example. 
     FIG. 2  shows the yellow toner development cartridge  20  at the development position. The development cartridge  20  has a housing  21  made of, for example, resin for housing the toner. The housing  21  is formed from both end faces  21   a  in longitudinal direction (i.e., vertical direction to the surface of the drawing sheet) each in a fan shape having a 90-degree vertex angle, two plane lateral faces  21   b  extending in longitudinal direction so as to form the vertex angle, and a face  21   c  extending in longitudinal direction so as to connect the top end portions of two lateral faces  21   b  and curved in a circular arc shape. 
   On the peripheral face  21   c  of the housing  21 , an elongated rectangular aperture extending along the longitudinal direction is formed, and the development roller  22  is disposed in the state of being exposed to the aperture so as to slightly protrude outward from the aperture. In the case where the development cartridge  20  is positioned at the development position, its development roller  22  protruding from the aperture comes into contact with the photoreceptor  12 . 
   On the peripheral face  21   c  in the vicinity of one end face  21   a , a segment gear  24   a , which constitutes a series of gears  24  when four development cartridges  20  are connected and combined, is formed integrally with the peripheral face  21   c , and the segment gear  24   a  is engaged with the drive gear  26 . 
   On one lateral face  21   b  of the housing  21 , a connection protruding section (connection section)  23   a  having a trapezoid lateral face expanding toward the top end is provided. On the other lateral face  21   b  of the housing  21 , a connection recess section (connection section)  23   b  having a trapezoid lateral face expanding toward the inside so as to tight fit with the connection protruding section  23   a  is formed. The connection protruding section  23   a  and the connection recess section  23   b  can fit with each other by sliding two development cartridges  20  along each other in longitudinal direction, and once these sections fit, the two development cartridges  20  are not detached in circumferential direction. 
   On the vertex angle portions on the both end faces  21   a  of the housing  21 , part  19   a  of the rotation spindle  19 , which constitutes a column-shaped rotation spindle  19  when four development cartridges  20  are connected and combined, is provided in a protruding manner. On one end face  21   a  of the housing  21 , a plate-like development position detection piece (development position detection section)  25  is provided in a standing posture. A sensor S such as photointerrupters is mounted on the main body of the color image formation apparatus  10  so that the development position detection piece  25  is detected on a straight line L connecting the rotation center of the photoreceptor  12  and the center  19   b  of the rotation spindle  19  when the development device  18  is rotated around the rotation spindle  19 . Thus, by detecting the development position detection piece  25  by a sensor S on the straight line L connecting the rotation center of the photoreceptor  12  and the center  19   b  of the rotation spindle  19 , it can be accurately detected that the development cartridge  20  reaches the development position. 
   The thus-structured four development cartridges  20  are directly connected by fitting the connection protruding section  23   a  with the connection recess section  23   b  as shown in  FIG. 3 , by which the almost column-like development device  18  is constituted. Therefore, the development device  18  can be constituted by connecting the development cartridges  20  with each other without special members interposed therebetween, which eliminates the use of conventional development rack and retention members. 
   Moreover, in the development device  18 , the segment gears  24   a  provided on the respective development cartridges  20  are linked to constitute a series of all around gears  24 , and part  19   a  of the rotation spindle  19  provided on the respective development cartridges  20  are combined to constitute a column-shaped rotation spindle  19 . This eliminate the necessity of additional provision of a gear for driving the development device and a rotation spindle for supporting rotation of the development device. 
   Moreover, in the development device  18 , rotational drive force is transmitted to the development device  18  by engaging the segment gear  24   a  of the development cartridge  20  at the development position with the drive gear  26 , and therefore even when the development device  18  constituted by connecting the four development cartridges  20  has loose linkage parts, it becomes possible to move a specified development cartridge to the development position at high accuracy without being affected by the loose linkage parts. 
   Thus, according to the development cartridge  20  and the development device  18  in the color image formation apparatus  10  of the present embodiment, drive force is transmitted to a development cartridge  20  through the segment gear  24   a  to move the development cartridge  20 , so that the development cartridge  20  can be moved to the development position. This makes it possible to eliminate the use of conventional development rack and retention members also including function as the drive members, thereby achieving reduction in number of components, size and cost of the image formation apparatus. Moreover, the absence of the development rack in the image formation apparatus enhances the maintenance inside the apparatus. 
   It is to be understood that the present invention is not limited to the above-stated embodiment, and various modifications are acceptable. 
   For example, in the development device  18 , a series of the all around gears  24  is provided on one end section in the longitudinal direction. However, as shown in  FIG. 4 , a series of the all around gears  24  may be provided on both the end sections in longitudinal direction of the development device  18  so that the respective gears  24  are engaged with the drive gear  26 . In this case, drive force is transmitted to the development device  18  in a balanced manner through a series of the all around gears  24  on both the ends, which prevents torsion to be generated in the development cartridge  20  by the drive force. 
   Further, although in the above-stated embodiment, the development device is constituted of four development cartridges  20  corresponding to four color toners, the development device may be constituted by connecting two or three development cartridges corresponding to two color or three color toners, or the development device may be constituted by connecting five or more development cartridges corresponding to five or more color toners. 
   Even when the development device  18  is constituted of four development cartridges  20  corresponding to four color toners, it is not necessarily necessary to divide the development device  18  exactly into four sections to form the development cartridges  20  as in the above-stated embodiment. As shown in  FIG. 5 , a half of a column-shaped development device  18  in circumferential direction may be occupied by a black toner development cartridge  20 K, and the remaining half may be divided into three sections, each of which is occupied by a yellow toner development cartridge  20 Y, a magenta toner development cartridge  20 M and a cyan development cartridge  20 C. Thus, increasing the size of the black toner development cartridge  20 K larger than other cartridges makes it possible to support a large amount of black-and-white prints. 
   Further, in the above-stated embodiment, the development device  18  constituted by connecting four development cartridges  20  is rotated to switch development colors. However, as shown in  FIG. 6 , the development device  18  may be constituted by connecting four development cartridges  20  corresponding to four color toners in the state of being stacked in one direction, and in order to change development colors, the development device  18  is reciprocally moved in an arrow F direction by a drive gear  26  which is engaged with a series of gears  24  linked in a straight line by combining the four development cartridge  20 . 
   It is to be understood that the present invention is applicable to any of copying machines, printing machines, facsimiles and their complex machines as long as they are four-cycle color image formation apparatuses. 
   Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.