Patent Publication Number: US-6708011-B2

Title: System for forming color images

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a system for forming color images, and more particularly to a tandem type color image formation system wherein a plurality of photosensitive members are designed in a single cartridge unit form for detachment/attachment purposes, thereby improving the integrity of maintenance. 
     Generally, toner image formation means for electro-photography comprises a photosensitive member acting as an image carrier having a photosensitive layer on its outer surface, charger means for uniformly charging the outer surface of the photosensitive member, exposure means for subjecting the outer surface of that member uniformly charged by the charger means to selective exposure to form an electrostatic latent image and developing means for imparting toner that is a developing agent to the electrostatic latent image formed by the exposure means to make a visible (toner) image. 
     The tandem system for forming color images known in the art are broken down into two types, one called the intermediate transfer belt type wherein a plurality of (e.g., four) such toner image formation means as mentioned above are provided with respect to an intermediate transfer belt (that is one example of the transfer belt) and toner images formed by these monochromatic toner image formation means on photosensitive members are successively transferred on the intermediate transfer belt so that the toner images of different colors (e.g., yellow, cyan, magenta and black) are superposed on the intermediate transfer belt, thereby obtaining a full-color image thereon, and another called the delivery belt type wherein a recording medium (e.g., a recording sheet) is carried and delivered onto a recording medium carrier belt (that is another example of the transfer belt) and toner images formed by a plurality of different monochromatic image formation means are successively transferred on the recording medium, so that the toner images of different colors are superposed on the recording medium, thereby obtaining a full-color image thereon. 
     For instance, one such conventional tandem image formation system is disclosed in JP-A 62-141574. This system is constructed of a plurality of joinable units, each comprising a plurality of developing and other processing means, so that the joined units are attachable to or detachable from the system proper. The system is economically advantageous because the units are individually designed as being attachable or detachable, so that a dead cartridge(s) alone can be replaced by new one. 
     JP-A 03-238467 describes an image formation system wherein a plurality of process units, each comprising developing means and an image carrier, are supported on one single support plate. All the process units are removed from the system at a time, and so the integrity of maintenance of the system is improved. 
     JP-A 09-160471 shows that process units except one for black are integrated together for easy replacement, so that the frequency of replacement of a process portion can be reduced, making control of consumable parts easy. 
     JP-A 09-304994 shows that a plurality of image carriers are integrally supported. In the examples, such image carriers inclusive of developing means are integrated together, so that the precision of positions of the image carriers in the system proper can be improved, resulting in elimination of color misalignments, improvements in the integrity of maintenance, and no risk of anything wrong upon insertion of the image cartridges. 
     JP-A 11-174772 shows that a support member is provided to locate both ends of each image formation member at a given position, thereby minimizing position misalignments of each image formation member. 
     In general image formation systems wherein toner is imparted from developing means to electrostatic latent images on image carriers to render the latent images visible, the service life of the image carriers differs largely from that of the developing means. Especially in the case of an image formation system using a mono-component developing agent, it is necessary to engage a control blade with a developing roller under high loads, thereby controlling the thickness of a developing agent thin layer on the developing roller. Then, the developing roller and control blade wear away due to friction between both, inevitably resulting in their service life becoming shorter than that of the image carriers. Thus, a problem with a conventional system wherein image carriers and developing means are replaced at the same time is that running costs increase because the service life of the system is governed by the developing means and so there is a need of replacing the image carriers even when they are still of avail. In particular, recently developed image carriers are being shifted to the “cleaner-less” type wherein the service life of image carriers is increased because of the absence of any material that wears off the image carriers. There is thus an especially large difference in service life between the image carriers and developing means, leading to growing demands for replacement of only the developing means. 
     In the tandem type comprising a plurality of image carriers, the precision of color matching is largely depending on the position and shape of the image carriers. When the image carriers are replaced, color matching operation is needed after replacement, because it is difficult to keep the position and shape of the image carriers in perfect alignment between before and after replacement. Referring here to the aforesaid prior art wherein the image carriers are replaced along with the developing means, frequent color matching operations are needed, resulting in a problem that the efficiency of operation becomes low. 
     In a tandem system for the formation of images, the precision of color matching is largely dependent on the positions of the image carriers on which latent images are to be written. In the aforesaid prior art, write means are mounted on the system proper, and when the image carriers are replaced, there are displacements of latent images written on the image carriers, which give rise to color misalignments and cause image quality to deteriorate. 
     Furthermore in the tandem for forming images, the precision of color matching is considerably dependent on the precision of transfer positions on the image carriers. In the aforesaid prior art, when the image carriers are replaced, there are displacements of toner images transferred from the image carriers onto a transfer member (an intermediate transfer belt or recording medium), resulting in color misalignments and deterioration of image quality. 
     SUMMARY OF THE INVENTION 
     In view of such problems with the prior art as mentioned above, an object of the present invention is to provide a tandem system for the formation of color images wherein a plurality of image carriers are integrated into a single cartridge and developing means for each image carrier is designed to be detachable from or attachable to the cartridge, thereby improving the integrity of maintenance and cutting back on running costs. 
     Another object of the present invention is to provide a tandem system for the formation of color images wherein a plurality of image carriers and write means are integrated into a single cartridge and developing means for each image carrier is designed to be detachable from or attachable to the cartridge, thereby improving the integrity of maintenance, cutting back on running costs, and reducing color misalignments. 
     Yet another object of the present invention is to provide a tandem system for the formation of color images wherein a plurality of image carriers and an intermediate transfer belt are integrated into a single cartridge and developing means for each image carrier is designed to be detachable from or attachable to the cartridge, thereby improving the integrity of maintenance, cutting back on running costs, and improving the precision of transfer positions to reduce color misalignments. 
     A further object of the present invention is to provide a tandem system for the formation of color images wherein a plurality of image carriers and a recording medium carrier belt are integrated into a single cartridge and developing means for each image carrier is designed to be detachable from or attachable to the cartridge, thereby improving the integrity of maintenance, cutting back on running costs, and improving the precision of transfer positions to reduce color misalignments. 
     According to the first aspect of the present invention, the aforesaid objects are achievable by the provision of a tandem system for forming color images comprising at least two image formation stations, each comprising an image carrier, and charging means, developing means and transfer means disposed around said image carrier, wherein a color image is formed by passing a transfer medium through each station, characterized in that: 
     a plurality of image carrier are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and 
     developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. 
     The color image formation system according to the first aspect of the invention is suitable for the case where a developing agent in the developing means comprises a mono-component developing agent. 
     Thus, a plurality of image carriers are integrally mounted on the image carrier cartridge while they are mutually positioned. In this case, a plurality of developing cartridges, each forming developing means for each of the plurality of image carriers, may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner. Alternatively, a developing cartridge, wherein all developing means for the plurality of image carriers may be integrated into one piece, may be disposed with respect to the image carrier cartridge in a detachable/attachable manner. Still alternatively, two developing cartridges may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner, wherein in one of said two developing cartridges there is developing means for one specific image carrier in the plurality of image carriers, and in another of said two developing cartridges all developing means for the remaining image carriers are integrated together. 
     Preferably in this aspect of the invention, the driving forces for the plurality of image carriers and the developing means for each of the plurality of image carriers are received at one site on the system proper and the driving force for the plurality of image carriers is divided in the image carrier cartridge and then transmitted to the developing means. 
     In this case, the mutual transmission of driving force between the plurality of image carriers takes place via a gear train, a belt or a chain. 
     Alternatively, the driving force for the plurality of image carriers may be received from one driving source of the system proper and the driving force for developing means for each of the plurality of image carriers may be received from another driving source of the system proper. 
     Preferably, the color image formation system according to the first aspect of the invention comprises a mechanism for adjusting color misalignments by regulating the position of at least one image carrier in the image carrier cartridge relative to other image carriers therein. 
     It is acceptable that around each image carrier in the image carrier cartridge there is no cleaning means for collecting the remnants of the developing agent in an independent manner. 
     According to the second aspect of the present invention, there is provided a tandem system for forming color images comprising at least two image formation stations, each comprising an image carrier, and charging means, write means, developing means and transfer means disposed around said image carrier, wherein a color image is formed by passing a transfer medium through each station, characterized in that: 
     a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, 
     developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge, and 
     write means is located and mounted at a position corresponding to each of said plurality of image carriers in said image carrier cartridge. 
     The color image formation system according to the second aspect of the invention is suitable for the case where the developing agent in the developing means comprises a mono-component developing agent. 
     Thus, a plurality of image carriers are integrally mounted on the image carrier cartridge while they are mutually positioned. In this case, a plurality of developing cartridges, each forming developing means for each of the plurality of image carriers, may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner. Alternatively, a developing cartridge, wherein all developing means for the plurality of image carriers are integrated into one piece, may be disposed with respect to the image carrier cartridge in a detachable/attachable manner. Yet alternatively, two developing cartridges may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner, wherein in one of the two developing cartridges there is developing means for one specific image carrier in the plurality of image carriers, and in another of the two developing cartridges all developing means for the remaining image carriers are integrated together. 
     Preferably in the second aspect of the invention, the driving forces for the plurality of image carriers and the developing means for each of the plurality of image carriers are received at one site on the system proper and the driving force for the plurality of image carrier is divided in the image carrier cartridge and then transmitted to the developing means. 
     In that case, the mutual transmission of driving force between the plurality of image carriers takes place via a gear train, a belt or a chain. 
     In accordance with the second aspect of the invention, it is acceptable that the driving force for the plurality of image carriers is received from one driving source of the system proper and the driving force for developing means for each of the plurality of image carriers is received from another driving source of the system proper. 
     Preferably, the color image formation system according to the second aspect of the invention comprises a mechanism for adjusting the position of at least one image carrier in the image carrier cartridge relative to other image carriers therein, thereby adjusting color misalignments. 
     It is preferable that the write means is constructed as a line head for performing line writing on each of the image carriers. 
     It is also acceptable that around each image carrier in the image carrier cartridge there is no cleaning means for collecting the remnants of the developing agent in an independent manner. 
     According to the third aspect of the present invention, there is provided a tandem system for forming color images comprising at least two image formation stations, each comprising an image carrier, and charging means, developing means and transfer means disposed around said image carrier, wherein a color image is formed by passing a transfer medium through each station, characterized in that: 
     a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and an intermediate transfer belt is provided contiguously to said plurality of image carriers, and 
     developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. 
     The color image formation system according to this aspect of the invention is suitable for the case where the developing agent in the developing means comprises a mono-component developing agent. 
     Thus, a plurality of image carriers are integrally mounted on the image carrier cartridge while they are mutually positioned. In this case, a plurality of developing cartridges, each forming developing means for each of the plurality of image carriers, may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner. Alternatively, a developing cartridge, wherein all developing means for said plurality of image carriers are integrated into one piece, may be disposed with respect to the image carrier cartridge in a detachable/attachable manner. Yet alternatively, two developing cartridges may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner, wherein in one of the two developing cartridges there is developing means for one specific image carrier in the plurality of image carriers, and in another of the two developing cartridges all developing means for the remaining image carriers are integrated together. 
     Preferably in the third aspect of the invention, the driving forces for the plurality of image carriers, the developing means for each of the plurality of image carriers and the intermediate transfer belt are received at one site on the system proper and the driving force for the plurality of image carriers is divided in the image carrier cartridge and then transmitted to the developing means. 
     Preferably in that case, the mutual transmission of driving force between the plurality of image carriers takes place via a gear train, a belt or a chain. 
     It is acceptable that the driving forces for the plurality of image carriers and the intermediate transfer belt are received from one driving source of the system proper and the driving force for developing means for each of the plurality of image carriers is received from another driving source of the system proper. 
     Preferably in the third aspect of the invention, there is a speed difference between the peripheral speed of the plurality of image carriers and the delivery speed of the intermediate transfer belt. 
     Preferably in that case, the color image formation system comprises a mechanism for adjusting the transfer position at which the intermediate transfer belt comes into contact with the plurality of image carriers, thereby adjusting color misalignments. 
     The color image formation system according to the third aspect of the invention may also comprise a mechanism for adjusting the position of at least one image carrier in the image carrier cartridge relative to other image carriers therein, thereby adjusting color misalignments. 
     It is also acceptable that the write means is located and mounted at the position corresponding to each of the plurality of image carriers in the image carrier cartridge. 
     Preferably, the color image formation system of the third aspect comprises a mechanism for adjusting the position of at least one write means mounted on the image carrier cartridge, thereby adjusting color misalignments. 
     It is also preferable that the write means is constructed as a line head for performing line writing on each of the image carriers. 
     It is also acceptable that around each image carrier in said image carrier cartridge there is no cleaning means for collecting the remnants of the developing agent in an independent manner. 
     According to the fourth aspect of the present invention, there is provided a tandem system for forming color images comprising at least two image formation stations, each comprising an image carrier, and charging means, developing means and transfer means disposed around said image carrier, wherein a color image is formed by passing a transfer medium through each station, characterized in that: 
     a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and a recording medium carrier belt is provided contiguously to said plurality of image carriers, and 
     developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. 
     The color image formation system according to the fourth aspect of the invention is suitable for the case where the developing agent in said developing means comprises a mono-component developing agent. 
     Thus, a plurality of image carriers are integrally mounted on the image carrier cartridge while they are mutually positioned. In this case, a plurality of developing cartridges, each forming developing means for each of the plurality of image carriers, may be disposed with respect to the image carrier cartridge in a separately detachable/attachable manner. Alternatively, a developing cartridge, wherein all developing means for the plurality of image carriers are integrated into one piece, may be disposed with respect to the said image carrier cartridge in a detachable/attachable manner. 
     Yet alternatively, two developing cartridges may be disposed with respect to said image carrier cartridge in a separately detachable/attachable manner, wherein in one of the two developing cartridges there is developing means for one specific image carrier in the plurality of image carriers, and in another of the two developing cartridges all developing means for the remaining image carriers are integrated together. 
     Preferably in the third aspect of the invention, the driving forces for the plurality of image carriers, the developing means for each of said plurality of image carriers and the recording medium carrier belt are received at one site on the system proper and the driving force for the plurality of image carriers is divided in the image carrier cartridge and then transmitted to the developing means. 
     Preferably in that case, the mutual transmission of driving force between the plurality of image carriers takes place via a gear train, a belt or a chain. 
     It is acceptable that the driving forces for the plurality of image carriers and the recording medium carrier belt are received from one driving source of the system proper and the driving force for developing means for each of the plurality of image carriers is received from another driving source of the system proper. 
     Preferably in the fourth aspect of the invention, there is a speed difference between the peripheral speed of the plurality of image carriers and the delivery speed of the recording medium carrier belt. 
     Preferably in that case, there is provided a mechanism for adjusting the transfer position at which the recording medium carrier belt comes into contact with the plurality of image carriers, thereby adjusting color misalignments. 
     Preferably, there is also provided a mechanism for adjusting the position of at least one image carrier in the image carrier cartridge relative to other image carriers therein, thereby adjusting color misalignments. 
     It is acceptable that the write means is located and mounted at a position corresponding to each of the plurality of image carriers in the image carrier cartridge. 
     Preferably in that case, there is provided a mechanism for adjusting the position of at least one write means mounted on the image carrier cartridge, thereby adjusting color misalignments. 
     It is also preferable that the write means is constructed as a line head for performing line writing on each of the image carriers. 
     It is also acceptable that around each image carrier in the image carrier cartridge there is no cleaning means for collecting the remnants of the developing agent in an independent manner. 
     As described above, the first aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. Thus, the precision of relative positions of the image carriers is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means are replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     The second aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge, and write means are located and mounted at positions of said image carrier cartridge corresponding to a plurality of image carriers. Thus, the precision of relative positions of the image carriers and write means is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers and write means can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means are replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     The third aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper, an intermediate transfer belt is mounted contiguously to said plurality of image carriers, and developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. Thus, the precision of relative positions of the image carriers, and the precision of transfer positions is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers and transfer position misalignments can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means are replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     The fourth aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. Thus, the precision of relative positions of the image carriers is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means are replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     Still other objects and advantages of the invention will in part be obvious and will in part be apparent form the specification. 
     The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims] 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front schematic illustrative of the whole construction of one example of the color image formation system to which the invention is applied. 
     FIG. 2 is illustrative of the construction of FIG. 1 wherein photosensitive member cartridges are withdrawn out of the system proper. 
     FIG. 3 is a perspective view of the photosensitive cartridge  40  from which the developing devices are removed. 
     FIG. 4 is a perspective view illustrative of how one of a plurality of developing devices is detached from or attached to the photosensitive member cartridge with the rest remaining mounted thereon. 
     FIG. 5 is a perspective view illustrative of the attachment/detachment mechanism for one embodiment where all developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 6 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention, wherein the black developing device is constructed in the form of a single developing cartridge and the remaining developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 7 is illustrative of one embodiment of the mechanism for rotating the photosensitive members in the photosensitive member cartridge in synchronism with one another. 
     FIG. 8 is illustrative of one modification to the embodiment of FIG.  7 . 
     FIG. 9 is a schematic of the rotation transmission portion of FIG. 8 as viewed from above. 
     FIG. 10 is illustrative of the construction of the mechanism for synchronized rotation of the photosensitive members in an embodiment of the invention, wherein the photosensitive member cartridge  40  is mounted on the system proper, and the photosensitive members and developing devices are driven by means of separate driving sources. 
     FIG. 11 is illustrative of the construction of the mechanism for rotating the developing devices in the embodiment of FIG.  10 . 
     FIG. 12 is illustrative of one embodiment of the mechanism for adjusting the photosensitive member cartridge for color misalignments. 
     FIG. 13 is a front schematic illustrative of the whole construction of an embodiment of the color image formation system using a “cleaner-less” mode. 
     FIG. 14 is a front schematic illustrative of the whole construction of an embodiment of the color image formation system using a recording medium carrier belt instead of the intermediate transfer belt. 
     FIG. 15 is a front schematic illustrative of the whole construction of another color image formation system to which the invention is applied. 
     FIG. 16 is illustrative of the system proper, from which the photosensitive member cartridge has been withdrawn. 
     FIG. 17 is a perspective view of the photosensitive cartridge from which the developing devices are removed. 
     FIG. 18 is a perspective view illustrative of how one of a plurality of developing devices is detached from or attached to the photosensitive member cartridge with the rest remaining mounted thereon. 
     FIG. 19 is a perspective view illustrative of the attachment/detachment mechanism for one embodiment where all developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 20 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention, wherein the black developing device is constructed in the form of a single developing cartridge and the remaining developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 21 is illustrative of one embodiment of how exposure devices are attached to the frame of the photosensitive member cartridge. 
     FIG. 22 is a perspective schematic illustrative of how the exposure devices are each constructed in the form of an LED line head comprising an LED array. 
     FIG. 23 is illustrative of an embodiment of regulating color misalignments for the photosensitive member cartridge. 
     FIG. 24 is a front schematic illustrative of the whole construction of an embodiment of the color image formation system making use of a “cleaner-less” mode. 
     FIG. 25 is a front schematic illustrative of the whole construction of an embodiment of the color image system using a recording medium carrier belt in place of the intermediate transfer belt. 
     FIG. 26 is a front schematic illustrative of the whole construction of an embodiment of the color image formation system using a charge injection electrode line head as write means. 
     FIG. 27 is a perspective schematic illustrative of how the charge injection electrode line head of FIG. 26 is positioned and constructed with respect to the photosensitive member. 
     FIG. 28 is a front schematic illustrative of the whole construction of yet another color image formation system to which the invention is applied. 
     FIG. 29 is illustrative of the system of FIG. 28, from which the photosensitive member cartridge is withdrawn. 
     FIG. 30 is a perspective view of the photosensitive member cartridge from which the developing devices are removed. 
     FIG. 31 a perspective view illustrative of how one of a plurality of developing devices is detached from or attached to the photosensitive member cartridge with the rest remaining mounted thereon. 
     FIG. 32 is a perspective view illustrative of the attachment/detachment mechanism for one embodiment where all developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 33 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention, wherein the black developing device is constructed in the form of a single developing cartridge and the remaining developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 34 is illustrative of the construction of one embodiment wherein the photosensitive members and intermediate transfer belts in the photosensitive member cartridge are rotated in synchronism with each other. 
     FIG. 35 is illustrative of the construction of one modification to FIG.  34 . 
     FIG. 36 is illustrative of the construction of the mechanism for synchronized rotation of the photosensitive members in an embodiment of the invention, wherein the photosensitive member cartridge is mounted on the system proper, and the photosensitive members and developing devices are driven by means of separate driving sources. 
     FIG. 37 is illustrative of the construction of the mechanism for rotating the developing devices in the embodiment of FIG.  36 . 
     FIG. 38 is illustrative of one embodiment of the mechanism for adjusting the photosensitive member cartridge for color misalignments. 
     FIG. 39 is a front schematic illustrative of the whole construction of an embodiment of the color image formation system using a “cleaner-less” mode. 
     FIG. 40 is similar to FIG. 28, showing an embodiment of the invention wherein the exposure devices are integrated with the photosensitive member cartridge. 
     FIG. 41 is similar to FIG. 29, showing an embodiment of the invention wherein the exposure devices are integrated with the photosensitive member cartridge. 
     FIG. 42 is a partially enlarged perspective view of one embodiment of how the exposure devices are attached to the frame of the photosensitive member cartridge. 
     FIG. 43 is illustrative of another embodiment of the mechanism for adjusting the photosensitive member cartridge for color misalignments. 
     FIG. 44 is a front schematic illustrative of the whole construction of a further color image formation system to which the invention is applied. 
     FIG. 45 is illustrative of the system of FIG. 44, from which the photosensitive member cartridge is withdrawn. 
     FIG. 46 is a perspective view of the photosensitive member cartridge from which the developing devices are removed. 
     FIG. 47 is a perspective view illustrative of how one of a plurality of developing devices is detached from or attached to the photosensitive member cartridge with the rest remaining mounted thereon. 
     FIG. 48 is a perspective view illustrative of the attachment/detachment mechanism for one embodiment where all developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 49 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention, wherein the black developing device is constructed in the form of a single developing cartridge and the remaining developing devices are constructed in the form of an integral developing cartridge. 
     FIG. 50 is illustrative of the construction of one embodiment wherein the photosensitive members in the photosensitive member cartridge are rotated in synchronism with each other. 
     FIG. 51 is illustrative of the construction of one modification to FIG.  50 . 
     FIG. 52 is illustrative of the construction of the mechanism for synchronized rotation of the photosensitive members in an embodiment of the invention, wherein the photosensitive member cartridge is mounted on the system proper, and the photosensitive members and developing devices are driven by means of separate driving sources. 
     FIG. 53 is illustrative of the construction of the mechanism for rotating the developing devices in the embodiment of FIG.  52 . 
     FIG. 54 is illustrative of one embodiment of the mechanism for adjusting the photosensitive member cartridge for color misalignments. 
     FIG. 55 is a front schematic illustrative of the whole construction of an embodiment of the color image formation system using a “cleaner-less” mode. 
     FIG. 56 is similar to FIG. 44, showing an embodiment of the invention wherein the exposure devices are integrated with the photosensitive member cartridge. 
     FIG. 57 is illustrative of another embodiment of the mechanism for adjusting the photosensitive member cartridge for color misalignments. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The color image formation system according to the first aspect of the present invention is now explained with reference to its embodiments. 
     FIG. 1 is a front schematic illustrative of the whole construction of one embodiment of the color image formation system to which the invention is applied. As shown in FIG. 1, this image formation system comprises an intermediate transfer belt  30  that is spanned in place with tensions applied thereon by a driving roller  10 , a follower roller  20  and a tension roller  21 , and driven endlessly in the (counterclockwise) direction shown by an arrow. Four photosensitive members (drums)  41 K,  41 C,  41 M and  41 Y having photosensitive layers on their outer surfaces, i.e., image carriers, are arranged at a given interval with respect to the intermediate transfer belt  30 . The capital letters K, C, M and Y added to the numeral reference mean black, cyan, magenta and yellow, indicating the photosensitive members for black, cyan, magenta and yellow, respectively. The same holds true for other members. The photosensitive members  41 K,  41 C,  41 M and  41 Y are rotationally driven in synchronism with the intermediate transfer belt  30  in the (clockwise) direction indicated by an arrow. Around each photosensitive member  41  (K, C, M, Y), there is located a corona charger  42  (K, C, M, Y) comprising Scorotron acting as means for uniformly charging the outer surface of the photosensitive member  41  (K, C, M, Y), an exposure site  43  (K, C, M, Y) for selectively exposing the outer surface of the member  41  (K, C, M, Y) uniformly charged by the corona charger  42  (K, C, M, Y) to exposure light from an exposure unit  43  for each color, thereby forming an electrostatic latent image, a developing device  44  (K, C, M, Y) for imparting a developing agent that is a toner to the electrostatic latent image formed at this exposure site  43  (K, C, M, Y) to make a visible (toner) image, a primary transfer roller  45  (K, C, M, Y) for successively transferring toner images developed at this developing device  44  (K, C, M, Y) onto the intermediate transfer belt  30  for primary transfer purposes, and a cleaning device  46  (K, C, M, Y) working as cleaning means for removing the remnants of toner on the surface of the photosensitive member  41  (K, C, M, Y) after transfer. 
     Typically using a non-magnetic mono-component toner as the developing agent, the developing device  44  (K, C, M, Y) is constructed in the form of a developing cartridge  47  (K, C, M, Y) (see FIG.  4 ). Such a mono-component toner stored in the cartridge  47  is delivered to a developing roller  49  (K, C, M, Y) by way of a feed roller  48  (K, C, M, Y). The thickness of a developing agent film deposited onto the surface of the developing roller  49  (K, C, M, Y) is controlled by a control blade  50  (K, C, M, Y). Then, the developing roller  49  (K, C, M, Y) is brought into contact or engagement with the photosensitive member  41  (K, C, M, Y) so that the developing agent is deposited onto the photosensitive member  41  (K, C, M, Y) depending on the potential level of the photosensitive member, thereby developing the latent image in the form of a toner image. 
     The black, cyan, magenta and yellow toner images formed at four such monochromatic toner image-formation stations are successively primary transferred onto the intermediate transfer belt  30  by primary transfer biases applied on the primary transfer rollers  45  (K, C, M, Y), so that they are superposed successively one upon another on the intermediate transfer belt  30 , yielding a full-color toner image. Then, the full-color toner image is secondary transferred onto a recording medium P such as a recording sheet at a secondary transfer roller  66 , passing between a pair of fixing rollers  61  that are fixing means so that the toner image is fixed on the recording medium P. Finally, the recording medium is ejected by way of a pair of ejecting rollers  62  on an output tray  68  mounted on the top of the system. 
     In FIG. 1, it is noted that reference numeral  63  is a sheet feed cassette for storing a multiplicity of recording media P in a superposed fashion,  64  a pickup roller for feeding recording media P from the sheet feed cassette  63  one by one,  65  is a pair of gate rollers for controlling the timing of when the recording medium P is to be fed to the secondary transfer site of the secondary transfer roller  66 ,  66  the secondary transfer roller behaving as secondary transfer means for defining the secondary transfer site between it and the intermediate transfer belt  30 , and  67  a cleaning blade working as cleaning means for removal of the remnants of toner on the surface of the intermediate transfer belt  30  after secondary transfer. 
     It is here noted that the reasons why the black developing device  44 K is located on the uppermost stream side of the intermediate transfer belt  30  in its endless direction and the yellow developing device  44 Y is positioned on the lowermost stream side are that when the toner image is transferred onto the recording medium P, black causes the most noticeable fogging whereas yellow causes the least noticeable fogging. In the case of reversal development or the like, fogging is caused by toner particles that are allowed to bear charges of polarity opposite to normal polarity at the developing device. However, black toner particles showing the most noticeable fogging are first transferred onto the intermediate transfer belt  30  as the lowermost layer. Of the black toner particles, fogging-prone toner particles remain firmly deposited onto the intermediate transfer belt  30  by means of image force or the like, so that they are less likely to be transferred onto the recording medium P at the secondary transfer site. On the other hand, toner particles that cause the least noticeable yellow fogging are deposited onto the intermediate transfer belt  30  as the uppermost layer. Although they are easily passed onto the recording medium P, yet they are less noticeable. Such an arrangement as explained above ensures that fogging is generally less noticeable because the black toner particles leading to the most noticeable fogging are relatively less likely to be passed onto the recording medium P whereas the yellow toner particles leading to the least noticeable fogging are passed onto the recording medium P with relative ease. 
     Since a mono-component developing agent such as a non-magnetic mono-component toner is used, there is no need of using a carrier such as a two-component developing agent. Accordingly, it is possible to reduce the volume of each developing device  44  (K, C, M, Y) and so achieve a color image formation system of small size. 
     In such a color image formation system as constructed as explained above according to the present invention, the four photosensitive members  41 K,  41 C,  41 M and  41 Y, each provided therearound with the corona charger  42  (K, C, M, Y) and the cleaning device  46  (K, C, M, Y), are constructed in the form of an integral photosensitive member cartridge  40  that can be detached from or attached to the system proper, as shown in FIGS. 1 and 2. In this case, the developing devices  44 K,  44 C,  44 M and  44 Y that are appendixes to the photosensitive members  41 K,  41 C,  41 M and  41 Y are detachable from and attachable to the photosensitive member cartridge  40 . 
     Referring to FIG. 2, the photosensitive member cartridge  40  is provided on its frame  70  with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and their appendixes, i.e., the corona chargers  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) while they are relatively positioned. To withdraw this cartridge from the system proper, it is first lifted up as shown by a double-arrow and then slid. To this end, a pair of fixing rollers  61  and a pair of ejecting rollers  62  are mounted on a side plate  69  that can turn concentrically with respect to the center of rotation of the follower roller  20 . The pair of fixing rollers  61  and the pair of ejecting rollers  62  are retracted, thereby defining an opening through which the photosensitive member cartridge  40  is withdrawn out of the system. In the state where the photosensitive member cartridge  40  has been withdrawn out of the system, the photosensitive members  41  (K, C, M, Y) are spaced away from the intermediate transfer belt  30  so that the photosensitive member cartridge  40  can be detached from the system and replaced by a new photosensitive member cartridge  40 . 
     FIG. 3 is a perspective view of the photosensitive cartridge  40  from which the developing devices  44 K,  44 C,  44 M and  44 Y are removed, and FIG. 4 is a perspective view illustrative of how the developing device  44 Y is detached from or attached to the photosensitive member cartridge  40  with the developing devices  44 K,  44 C and  44 M remaining mounted thereon. The frame  70  is in a rectangular box form, between both sides plates of which there are four photosensitive members  41 K,  41 C,  41 M and  41 Y that are positioned at a given interval and parallel with one another for rotation on their shafts  71 K,  71 C,  71 M and  71 Y. The shaft  71  (K, C, M, Y) of each photosensitive member  41  (K, C, M, Y) is provided at its one end with a gear  72  (K, C, M, Y). By way of the gear train to be referred to later, the photosensitive members  41  (K, C, M, Y) are rotatable in the (clockwise) direction indicated by the arrow in FIG. 1 at the same speed and in synchronism with one another. 
     Between the same two side plates of the frame  70 , the corona chargers  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) (which, in FIG. 3, are invisible because of being concealed by the photosensitive members  41  (K, C, M, Y) and frame  70 ), all appendixes to the photosensitive members  41  (K, C, M, Y), are mounted at given positions. On one side of the side plate of the frame  70  there are provided electrodes  75  (K, C, M, Y) for applying high voltages on the discharge wires of the corona chargers or Scorotrons  42  (K, C, M, Y) and electrodes  76  (K, C, M, Y) for applying high voltages on the grits of the Scorotrons. On the same one side of the side plate of the frame  70  there are also provided electrodes  77  (K, C, M, Y) for applying developing bias voltages on the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) in the state where the developing devices  44  (K, C, M, Y) are mounted on the photosensitive member cartridge  40  and electrodes  78  (K, C, M, Y) for applying developing feed bias voltages on the feed rollers  48  (K, C, M, Y) in the same state. On the same side plate, there is further provided an IC  110  as memory means for storing information about the fabrication and use of the photosensitive member cartridge  40 , color misalignments, etc. Upon the photosensitive member cartridge  40  mounted on the system proper, the electrodes  75  (K, C, M, Y), electrodes  76  (K, C, M, Y), electrodes  77  (K, C, M, Y), electrodes  78  (K, C, M, Y) and IC  110  are automatically connected to the power source circuit and control circuit of the system proper. In this state, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are also automatically connected to ground for earth purposes. 
     At the inner upper sides of the same two side plates of the frame  70 , there are provided guide grooves  73  (K, C, M, Y) for receiving the developing devices  44  (K, C, M, Y) at constant positions corresponding to the photosensitive members  41  (K, C, M, Y). To fix the developing devices  44  (K, C, M, Y) received along the guide grooves  73  (K, C, M, Y), fixing levers  74  (K, C, M, Y) are pivotally provided. On both sides of the developing cartridge  47  (K, C, M, Y) of each developing device  44  (K, C, M, Y), there are guide ridges  79  (K, C, M, Y) that are to be inserted in the associated guide grooves  73  (K, C, M, Y) from the upper open ends thereof (see FIG. 4 where only one guide ridge  79 Y of the developing cartridge  47 Y is visible). To mount the developing devices  44  (K, C, M, Y) on the associated photosensitive members  41  (K, C, M, Y), the guide ridges  79  (K, C, M, Y) are inserted from above into the associated guide grooves  73  (K, C, M, Y) and the fixing levers  74  (K, C, M, Y) are then pivoted to fix the developing devices in place. To remove the developing cartridges  47  (K, C, M, Y) for replacement or other purposes, the fixing levers  74  (K, C, M, Y) are pivoted back to guide the developing cartridges  47  (K, C, M, Y) upward along the guide grooves  73  (K, C, M, Y). 
     According to the embodiment of FIG. 4, the developing cartridges  47  (K, C, M, Y) forming part of the individual developing devices  44  (K, C, M, Y) can separately be attached to or detached from the associated photosensitive members  41  (K, C, M, Y); of the developing devices  44  (K, C, M, Y), only an exhausted or dead developing device(s) can be replaced with no wasteful replacement of the rest, so that running cost reductions are achievable. 
     FIG. 5 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention wherein four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are constructed in the form of an integral development cartridge  47  for such a photosensitive member cartridge  40  as described above. In this embodiment, only one pair of guide grooves  73  are provided at the inner upper sites of both side plates of the frame  70  of the photosensitive member cartridge  40 , spanning between both side plates. Accordingly, only one pair of pivotal fixing levers  74  are provided. On the other hand, the four developing devices  44  (K, C, M, Y) are constructed in the form of an integrated single developing cartridge  47 . On each side of the developing cartridge  47  there is mounted a guide ridge  79  that is to be inserted into the associated guide groove  73  from the upper open end thereof (in FIG. 5, one guide ridge  79  alone is visible). To mount the developing cartridge  47  on the photosensitive member cartridge  40 , the guide ridges  79  are inserted from above into the guide grooves  73  and the fixing levers  74  are then pivoted to fix the developing cartridge in place. To remove the developing cartridge  47  for replacement or other purposes, the fixing levers  74  are pivoted back so that the developing cartridge  47  can be guided upward along the guide grooves  73 . 
     The embodiment of FIG. 5, wherein the four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are designed as the integral developing cartridge  47 , has the merit of reducing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. 
     FIG. 6 is a perspective view illustrative of the attachment/detachment mechanism for such a photosensitive member cartridge  40  as described above, wherein a black developing device  44 K is constructed in the form of one single developing cartridge  47 K that is detachable from or attachable to a black photosensitive member  41 K as is the case with FIG. 3 or FIG. 4, and three or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of an integral developing cartridge  47 YMC. At the inner upper sites of both side plates of a frame  70  of the photosensitive member cartridge  40  there are provided guide grooves  73 K for receiving the developing cartridge  47 K between both side plates and guide grooves  73 YMC for receiving the developing cartridge  47 YMC, and there are provided pivotal fixing levers  74 K and  74 YMC, accordingly. On the other hand, the black photosensitive member cartridge  40  is provided on both its sides with guide ridges  79 K and the three-color developing cartridge  47 YMC is provided on both its sides with guide ridges  79 YMC (in FIG. 6, only one guide ridge  79 YMC is visible on the developing cartridge  47 YMC). To mount the developing cartridge  47 K or  47 YMC on the photosensitive member cartridge  40 , the guide ridges  79 K or  79 YMC are inserted from above into the guide grooves  73 K or  73 YMC, whereupon the fixing levers  74 K or  74 YMC are pivoted to fix the developing cartridge in place. To remove the developing cartridge  47 K or  47 YMC for replacement or other purposes, the fixing levers  74 K or  74 YMC are pivoted back so that the developing cartridge  47 K or  47 YMC can be guided upward along the guide grooves  73 K or  73 YMC. 
     The embodiment of FIG. 6, wherein the three-color or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of the integral developing cartridge  47 YMC, has the merit of removing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. This embodiment has another merit of preventing the three-color or cyan, magenta and Y developing devices  44  (C, M, Y) from going to waste, because the black developing device  44 K most frequently used in general can be replaced in the form of the independent developing cartridge  47 K. 
     Next, an account is given of the mechanism of, upon the photosensitive member cartridge  40  mounted on the system proper, rotating the photosensitive members  41 K,  41 C,  41 M and  41 Y in the cartridge  40  in synchronism with one another, thereby preventing any color misalignments. FIG. 7 is illustrative of one construction for achieving this. As already mentioned, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are mounted at their one ends with gears  72 K,  72 C,  72 M and  72 Y, respectively, which are molded using the same mold. Three idle gears for transmission of rotational force are provided; an idle gear  81  is interposed between the gears  71 K and  72 C, an idle gear  82  between the gears  72 C and  72 M, and an idle gear  83  between the gears  72 M and  72 Y, forming a gear train. A driving gear  91  in mesh with one gear in this gear train, for instance, gear  72 Y, is disposed at a driving source  90  on the side of the system proper, so that upon the photosensitive cartridge  40  mounted at a given position, the driving gear  91  meshes with the gear  72 Y. 
     On the other hand, the shaft of the developing roller  49  (K, C, M, Y) of the developing device  44  (K, C, M, Y) is fixedly provided at its one end with a developing roller gear  84  (K, C, M, Y), and the shaft of the feed roller  48  (K, C, M, Y) is fixedly provided at its one end with a feed roller gear  85  (K, C, M, Y). An idle roller  86  (K, C, M, Y) is interposed between the developing roller gear  84  (K, C, M, Y) and the feed roller gear  85  (K, C, M, Y). The developing roller gear  84  (K, C, M, Y) meshes with the gear  72  (K, C, M, Y) of the photosensitive member  41  (K, C, M, Y), so that the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y), too, can be rotationally driven in synchronism with the photosensitive member  41  (K, C, M, Y). 
     By rotating the driving gear  91  of the driving source at one site on the side of the system proper according to this arrangement, it is possible to rotationally drive the four photosensitive members  41  (K, C, M, Y) and the appendixes thereto, i.e., the developing rollers  49  (K, C, M, Y) and feed rollers  48  (K, C, M, Y) of the developing devices  44  (K, C, M, Y), all in synchronism with one another. 
     This embodiment ensures the operating efficiency of attachment/detachment of the photosensitive member cartridge  40  is improved because the point of meshing of the gears for transmission of driving force upon attachment/detachment of the photosensitive member cartridge  40  is limited to one. Since the positioning criterion for the photosensitive member cartridge  40  is defined by this driving force transmission gear  91 , it is also possible to improve the precision of meshing and, hence, provide a system for forming high-quality images that are substantially free from any color misalignment or any banding (variations in densities, etc. at right angles with the feed direction). 
     It is understood that the mechanism for synchronized transmission of rotational force for the photosensitive members  41 K,  41 C,  41 M and  41 Y is not limited to such a gear train as shown, and so may be constructed using a belt or chain, for instance. 
     FIG. 9 is illustrative of one modification to the embodiment of FIG.  8 . FIG. 9 is a schematic of the rotation transmission portion comprising the gear  91 , gear  92 , clutch  93  and gears  94  to  96  of FIG. 8 as viewed from above. In this modification, the driving gear  91  of the driving source (FIG. 7) on the side of the system proper is designed to mesh with the gear  72 K via the gear  92 , with the omission of the idle gear  81  interposed between the gears  72 K and  72 C. Instead, a rotation transmission mechanism comprising the gear  92 , clutch  93  and gears  94  to  96  as shown in FIG. 9 is interposed between the gear  72 K and  72 C. As the clutch  93  is put on, the rotational force of the gear  92  is transmitted to the gear  94  and then to gear  95  in mesh with that gear  94 , so that rotation in the same direction as is the case with the gear  72 K is transmitted to the gear  72 C via the gear  96  interposed between that gear  95  and the gear  72 C. The rotation of the gears  72 M and  72 Y is transmitted as is the case with FIG.  7 . It is here noted that since the gears  92 ,  94  and  96  are molded using the same mold, the four photosensitive members are rotationally driven in synchronism and at the same speed. 
     In this modification, as the clutch  93  is put off, the rotation of the driving gear  91  is transmitted to only the black developing device  44 K, so that other developing devices  44  (C, M, Y) remain inoperative. When only a black image is formed, therefore, there is only the need of putting the black photosensitive member  41 K and the associated developing device  44 K in effective operation; other photosensitive members  41  (C, M, Y) and the associated developing devices  44  (C, M, Y), which are not required to be placed in operation, are rendered inoperative. It is thus possible to prevent unnecessary consumption of the developing devices  44  (C, M, Y), thereby extending their service lives. 
     FIGS. 10 and 11 are illustrative of an embodiment of the invention, wherein the photosensitive member cartridge  40  is mounted on the system proper and the photosensitive members  41  (K, C, M, Y) and developing devices  44  (K, C, M, Y) of the photosensitive member cartridge  40  are driven by means of separate driving sources. FIG. 10 is similar to FIG.  7 . In this embodiment, the developing roller gears  84  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) are not in mesh with the gears  72  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) or separated therefrom, as can be seen from FIG.  10 . The embodiment of FIG. 10 is different from that of FIG. 7 only in terms of the gear train of the photosensitive member cartridge  40 . By rotating the driving gear  91  of the driving source  90  on the side of the system proper, the four photosensitive members  41  (K, C, M, Y) can thus be rotationally driven in synchronism, as can be see from FIG.  10 . Although depending on the driving force of that driving source  90 , however, the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y) are kept from rotation. In this embodiment, there is another driving source  100  at another site on the side of the system proper, as shown in FIG.  11 . When the photosensitive member cartridge  40  is mounted at a given position of the system proper, four gears  101  (K, C, M, Y) of the separate driving source  100 , designed to rotate in synchronism and in the same direction, are positioned in such a way that they mesh with the developing roller gears  84  (K, C, M, Y) fixed at one ends of the shafts of the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) mounted on the photosensitive member cartridge  40 . Thus, the developing devices  44  (K, C, M, Y) are rotationally driven by the driving source  100  that is separate from that for the photosensitive members  41  (K, C, M, Y). 
     In such an arrangement as shown in FIG. 1, color misalignments and image banding are largely dependent on the precision of rotation of the image carriers; however, they are less dependent on the precision of rotation of the developing rollers. Therefore, if the driving source  90  for the photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40  is made separate from the driving source  100  for the developing devices  44  (K, C, M, Y) as shown in FIGS. 10 and 11, it is then possible to prevent rotation variations caused as by fluctuations in the torque of developing means from having influences on the rotation of the image carriers and, hence, provide a system for forming high-quality images with neither color misalignments nor image banding. 
     FIG. 12 is illustrative of one embodiment of the mechanism for adjusting color misalignments occurring due to position misalignments between the photosensitive members  41 K,  41 C,  41 M and  41 Y, especially skews in parallelism, when four different monochromatic toner images are transferred onto the intermediate transfer belt  30  in a superposed fashion. As shown in FIG. 12, while the shaft  71  (K, C, M, Y) of each photosensitive member  41  (K, C, M, Y) extending from one side plate of the frame  70  is sandwiched between an adjustment screw  105  and the leading end of an extensible spring  106 , the other end of the extensible spring  106  is fixed to the side plate  70 . In this state, if the leading end of the adjustment screw  105  is adjustable in the direction opposite to the direction of extension of the extensible spring  106  to adjust the position of one end of the shaft  71  (K, C, M, Y), it is then possible to adjust skews in parallelism between the photosensitive members  41 K,  41 C,  41 M and  41 Y. It is not always required to provide all the four photosensitive members  41 K,  41 C,  41 M and  41 Y with such color misalignment adjustment mechanisms. It is noted that it is acceptable to provide the opposite ends of the shafts  71  (K, C, M, Y) with such color misalignment adjustment mechanisms. However, this is not always necessary because misalignments can be electrically eliminated by controlling the timing of when color latent images formed on the photosensitive members  41  (K, C, M, Y) are to be written, as long as given parallelism is maintained between the photosensitive members  41  (K, C, M, Y). 
     By providing the photosensitive member cartridge  40  with the position alignment mechanism for the photosensitive members  41  (K, C, M, Y) in this way, it is possible to make fine adjustments of the positions of the photosensitive members  41  (K, C, M, Y) onto which latent images are to be written and transferred, thereby reducing color misalignments. It is here noted that the color misalignment adjustment by this color (position) misalignment adjustment mechanism may be made upon shipment of the photosensitive member cartridge  40  or anytime after its attachment to the system proper. 
     Referring now to an electrographic system wherein latent images formed on image carriers are toner developed and the resulting toner images are transferred onto transfer media, there is a so-called “cleaner-less” mode wherein the remnants of toner not transferred onto the image carriers are recovered at developing devices without recourse to such cleaning devices as shown in FIG. 1 (for instance, see JP-B 06-77166). This “cleaner-less” mode is embodied as shown in FIG. 13, dispensing with the cleaning devices  46  (K, C, M, Y). The embodiment of FIG. 13 is the same in construction as that of FIG. 1 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); any detailed account of its construction and action is not given. The construction of the photosensitive member cartridge  40  in this embodiment, too, is the same as that of FIGS. 1 and 2 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); four photosensitive members  41 K,  41 C,  41 M and  41 Y are integrated with corona chargers  42  (K, C, M, Y) disposed around them. 
     By use of the mode that dispenses with any cleaning device, it is possible to reduce the size of the photosensitive member cartridge  40  and the system proper. In addition, it is possible to diminish reaction force that may otherwise act on the photosensitive members  41  (K, C, M, Y) through the blades, etc. of cleaning devices, resulting in prevention of color misalignments. This is because the frame  70  is kept from deformation so that any position misalignment between the photosensitive members  41  (K, C, M, Y) can be avoided. 
     The present invention has been explained with reference to some embodiments applied to the tandem type system for forming color images using the intermediate transfer belt  30  (FIG.  1 ), wherein four photosensitive members  41  (K, C, M, Y) are integrated into the photosensitive member cartridge  40  according to the present invention. It is here noted that instead of the intermediate transfer belt, it is acceptable to use a recording medium carrier belt. In this case, the recording medium carrier belt is used to carry and deliver recording media such as recording sheets. A plurality of monochromatic toner images are successively transferred directly onto a recording sheet, followed by the fixation of toner images of different colors which are superposed one upon another on the recording medium. A typical example of this is shown in FIG.  14 . The embodiment of FIG. 14 is the same as that of FIG. 1 with the exception of the following points. Instead of the intermediate transfer belt  30  of FIG. 1, a recording medium carrier belt  30 ′ is used to carry and deliver a recording medium (sheet) P. The recording sheets from a sheet feed cassette  63  are picked up by a pickup roller  64  on a one-by-one basis, and the feed timing of the recording sheet is controlled by a pair of gate rollers  65  in such a way that it is in synchronism with electrostatic latent images formed on the photosensitive members  41  (K, C, M, Y). Toner images formed on the photosensitive members  41  (K, C, M, Y) are successively transferred and superposed onto the recording medium P being delivered under the action of primary transfer rollers  45  (K, C, M, Y). Then, the recording medium P bearing the resulting full-color image thereon is released from the recording medium carrier belt  30 ′ by a release roller  107 , and passes between a pair of fixing rollers  61  defining a fixing portion, where the full-color toner image is fixed onto the recording medium P. Finally, the recording medium is ejected via a pair of ejecting rollers  62  onto an output tray  68  mounted on the upper portion of the system. The construction of the photosensitive member cartridge  40  in particular is the same as that of FIG. 1 or the like. To those skilled in the art, it would be apparent that any one of the aforesaid embodiments can be applied to the tandem type of color image formation system where recording media are carried and delivered by such a recording medium carrier belt, not by the intermediate transfer belt, and toner images are transferred onto the recording media. 
     In accordance with the inventive color image formation system wherein, as explained above, a plurality of photosensitive members  41  (K, C, M, Y) are mutually positioned and mounted on a photosensitive member cartridge  40  detachable from and attachable to the system proper and developing devices  44  (K, C, M, Y) are disposed in such a way as to be detachable from and attachable to the photosensitive members  41  (K, C, M, Y) mounted on the photosensitive member cartridge  40 , the precision of relative positions between the photosensitive members is so improved that color misalignments ascribable to misalignments between the photosensitive members and skews thereof can be prevented. 
     Gears can be associated with the photosensitive members in such phase relations as to reduce speed fluctuations due to the gears that drive the photosensitive member, so that the cartridge  40  can be constructed in an integral form. In addition, color misalignments due to the photosensitive member-driving gears can be considerably reduced (FIG.  7  and so on). Where the photosensitive members are individually mounted on the system proper, it is impossible to make phase adjustments of such gears because the photosensitive members rotate by themselves. 
     Further, the photosensitive member cartridge  40  can be finished up using photosensitive members of uniform performance singled out at the time of shipping, so that color changes due to variations in the photosensitive members&#39; properties of different colors can be prevented. In addition, the integrity of maintenance can be improved because a plurality of photosensitive members can be replaced at the same time. 
     Furthermore, the arrangement wherein the developing devices  44  (K, C, M, Y) are designed as detachable from and attachable to the photosensitive member cartridge  40  ensures that the developing devices  44  (K, C, M, Y) can be replaced independently of the photosensitive member cartridge  40 . Therefore, even when the developing devices  44  (K, C, M, Y) are exhausted or used up and so must be replaced with new ones, there is no need of making a replacement for the photosensitive members  41  (K, C, M, Y), so that running cost reductions are achievable. 
     What is necessary when the developing devices  44  (K, C, M, Y) are used up is only their replacement. There is no need of any color matching operation depending on the positions and configuration of the photosensitive members  41  (K, C, M, Y). It is thus possible to provide an image formation system having improved operating efficiency. 
     For replacement of the developing devices  44  (K, C, M, Y), only the withdrawal of the photosensitive member cartridge  40  is needed. Then, new developing devices are attached to the photosensitive member cartridge  40 . Thus, the operation for replacement of the developing devices  44  (K, C, M, Y) is so facilitated that the integrity of maintenance can be improved. 
     It is also acceptable to construct a plurality of photosensitive members  41  (K, C, M, Y) in the form of one single replacement and the developing devices  44  (K, C, M, Y) in the form of one single replacement  47  (FIG.  19 ), so that the integrity of maintenance can be much more improved. 
     The color image formation system according to the second aspect of the present invention is now explained with reference to some embodiments. 
     FIG. 15 is a front schematic illustrative of the whole construction of another color image formation system to which the invention is applied. As shown in FIG. 15, this image formation system comprises an intermediate transfer belt  30  that is spanned in place with tensions applied thereon by a driving roller  10 , a follower roller  20  and a tension roller  21 , and driven endlessly in the (counterclockwise) direction indicated by an arrow. Four photosensitive members (drums)  41 K,  41 C,  41 M and  41 Y having photosensitive layers on their outer surfaces, i.e., image carriers, are arranged at a given interval with respect to the intermediate transfer belt  30 . The capital letters K, C, M and Y annexed to the numeral reference mean black, cyan, magenta and yellow, indicating the photosensitive members for black, cyan, magenta and yellow, respectively. The same holds true for other members. The photosensitive members  41 K,  41 C,  41 M and  41 Y are rotationally driven in synchronism with the intermediate transfer belt  30  in the (clockwise) direction indicated by an arrow. Around each photosensitive member  41  (K, C, M, Y), there is located a corona charger  42  (K, C, M, Y) comprising Scorotron acting as means for uniformly charging the outer surface of the photosensitive member  41  (K, C, M, Y), an exposure device  43 ′ (K, C, M, Y) for selectively exposing the outer surface of the member  41  uniformly charged by the corona charger  42  (K, C, M, Y) to exposure light for each color, thereby forming an electrostatic latent image, a developing device  44  (K, C, M, Y) for imparting a developing agent that is a toner to the electrostatic latent image formed at this exposure device  43 ′ (K, C, M, Y) to make a visible (toner) image, a primary transfer roller  45  (K, C, M, Y) for successively transferring toner images developed at this developing device  44  (K, C, M, Y) onto the intermediate transfer belt  30  for primary transfer purposes, and a cleaning device  46  (K, C, M, Y) working as cleaning means for removing the remnants of toner on the surface of the photosensitive member  41  (K, C, M, Y) after transfer. 
     Typically using a non-magnetic mono-component toner as the developing agent, the developing device  44  (K, C, M, Y) is constructed in the form of a developing cartridge  47  (K, C, M, Y) (see FIG.  18 ). Such a mono-component toner stored in the cartridge  47  is delivered to a developing roller  49  (K, C, M, Y) by way of a feed roller  48  (K, C, M, Y). The thickness of a developing agent film deposited onto the surface of the developing roller  49  (K, C, M, Y) is controlled by a control blade  50  (K, C, M, Y). Then, the developing roller  49  (K, C, M, Y) is brought into contact or engagement with the photosensitive member  41  (K, C, M, Y) so that the developing agent is deposited onto the photosensitive member  41  (K, C, M, Y) depending on the potential level of the photosensitive member, thereby developing the latent image in the form of a toner image. 
     The black, cyan, magenta and yellow toner images formed at four different such monochromatic toner image-formation stations are successively primary transferred onto the intermediate transfer belt  30  by primary transfer biases applied on the primary transfer roller  45  (K, C, M, Y), so that they are superposed successively one upon another on the intermediate transfer belt  30 , yielding a full-color toner image. Then, the full-color toner image is secondary transferred onto a recording medium P such as a recording sheet at a secondary transfer roller  66 , passing between a pair of fixing rollers  61  that are fixing means so that the toner image is fixed on the recording medium P. Finally, the recording medium is ejected by way of a pair of ejecting rollers  62  on an output tray  68  mounted on the top of the system. 
     In FIG. 15, it is noted that reference numeral  63  is a sheet feed cassette for storing a multiplicity of recording media P in a superposed fashion,  64  is a pickup roller for feeding recording media P from the sheet feed cassette  63  one by one,  65  is a pair of gate rollers for controlling the timing of when the recording medium P is to be fed to the secondary transfer site of the secondary transfer roller  66 . The secondary transfer roller  66  behaves as secondary transfer means for defining the secondary transfer site between it and the intermediate transfer belt  30 , and  67  is a cleaning blade working as cleaning means for removal of the remnants of toner on the surface of the intermediate transfer belt  30  after secondary transfer. 
     It is here noted that the reasons why the black developing device  44 K is located on the uppermost stream side of the intermediate transfer belt  30  in its endless direction and the yellow developing device  44 Y is positioned on the lowermost stream side are that when the toner image is transferred onto the recording medium P, black causes the most noticeable fogging whereas yellow causes the least noticeable fogging. In the case of reversal development or the like, fogging is caused by toner particles that are allowed to bear charges of polarity opposite to normal polarity at the developing device. However, black toner particles showing the most noticeable fogging are first transferred onto the intermediate transfer belt  30  as the lowermost layer. Of the black toner particles, fogging-prone toner particles remain firmly deposited onto the intermediate transfer belt  30  by means of image force or the like, so that they are less likely to be transferred onto the recording medium P at the secondary transfer site. On the other hand, toner particles that cause the least noticeable yellow fogging are deposited onto the intermediate transfer belt  30  as the uppermost layer. Although they are easily passed onto the recording medium P, yet they are less noticeable. Such an arrangement as explained above ensures that fogging is generally less noticeable because the black toner particles leading to the most noticeable fogging are relatively less likely to be passed onto the recording medium P whereas the yellow toner particles leading to the least noticeable fogging are passed onto the recording medium P with relative ease. 
     Since a mono-component developing agent such as a non-magnetic mono-component toner is used, there is no need of using a carrier such as a two-component developing agent. Accordingly, it is possible to reduce the volume of each developing device  44  (K, C, M, Y) and so achieve a color image formation system of small size. 
     In such a color image formation system as constructed as explained above according to the present invention, the four photosensitive members  41 K,  41 C,  41 M and  41 Y, each provided therearound with the corona charger  42  (K, C, M, Y), exposure device  43 ′ (K, C, M, Y) and the cleaning device  46  (K, C, M, Y), are constructed in the form of an integral cartridge  40  that can be detached from or attached to the system proper, as shown in FIGS. 15 and 16. In this case, the developing devices  44 K,  44 C,  44 M and  44 Y that are appendixes to the photosensitive members  41 K,  41 C,  41 M and  41 Y are detachable from and attachable to the photosensitive member cartridge  40 . 
     Referring to FIG. 16, the photosensitive member cartridge  40  is provided on its frame  70  with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and their appendixes, i.e., the corona chargers  42  (K, C, M, Y), exposure devices  43 ′ (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) while they are relatively. To withdraw this cartridge from the system proper, it is lifted up as shown by a double-arrow. To this end, the output tray  68  is mounted at its one end on the system proper in such a way that it can turn upwardly. The output tray  68  is retracted, thereby defining an opening through which the photosensitive cartridge  40  is withdrawn out of the system. In the state where the photosensitive member cartridge  40  has been withdrawn out of the system, the photosensitive members  41  (K, C, M, Y) are spaced away from the intermediate transfer belt  30  so that the photosensitive member cartridge  40  can be detached from the system and replaced by a new photosensitive member cartridge  40 . 
     FIG. 17 is a perspective view of the photosensitive cartridge  40  from which the developing devices  44 K,  44 C,  44 M and  44 Y are removed, and FIG. 18 is a perspective view illustrative of how the developing device  44 Y is detached from or attached to the photosensitive member cartridge  40  with the developing devices  44 K,  44 C and  44 M remaining mounted thereon. The frame  70  is in a rectangular box form, between both sides plates of which there are four photosensitive members  41 K,  41 C,  41 M and  41 Y that are positioned at a given interval and parallel with one another for rotation on their shafts  71 K,  71 C,  71 M and  71 Y. The shaft  71  (K, C, M, Y) of each photosensitive member  41  (K, C, M, Y) is provided at its one end with a gear  72  (K, C, M, Y). By way of the gear train to be referred to later, the photosensitive members  41  (K, C, M, Y) are rotatable in the (clockwise) direction indicated by the arrow in FIG. 15 at the same speed and in synchronism with one another. 
     Between the same two side plates of the frame  70 , the corona chargers  42  (K, C, M, Y), exposure devices  43 ′ (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) (which, in FIG. 17, are invisible because of being concealed by the photosensitive members  41  (K, C, M, Y) and frame  70 ), all appendixes to the photosensitive members  41  (K, C, M, Y), are mounted at given positions. On one side of the side plate of the frame  70  there are provided electrodes  75  (K, C, M, Y) for applying high voltages on the discharge wires of the corona chargers or Scorotrons  42  (K, C, M, Y) and electrodes  76  (K, C, M, Y) for applying high voltages on the grits of the Scorotrons. On the same one side of the side plate of the frame  70  there are also provided electrodes  169  (K, C, M, Y) for applying light emission control signals on the LED line heads of the exposure devices  43 ′ (K, C, M, Y) as well as electrodes  77  (K, C, M, Y) for applying developing bias voltages on the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) in the state where the developing devices  44  (K, C, M, Y) mounted on the photosensitive member cartridge  40  and electrodes  78  (K, C, M, Y) for applying developing feed bias voltages on the feed rollers  48  (K, C, M, Y) in the same state. On the same side plate, there is further provided an IC  110  as memory means for storing information about the fabrication and use of the photosensitive member cartridge  40 , color misalignments, etc. Upon the photosensitive member cartridge  40  mounted on the system proper, the electrodes  75  (K, C, M, Y), electrodes  76  (K, C, M, Y), electrodes  169  (K, C, Y, M), electrodes  77  (K, C, M, Y), electrodes  78  (K, C, M, Y) and IC  110  are automatically connected to the power source circuit and control circuit of the system proper. In this state, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are also automatically connected to ground for earth purposes. 
     At the inner upper sides of the same two side plates of the frame  70 , there are provided guide grooves  73  (K, C, M, Y) for receiving the developing devices  44  (K, C, M, Y) at constant positions corresponding to the photosensitive members  41  (K, C, M, Y). To fix the developing devices  44  (K, C, M, Y) received along the guide grooves  73  (K, C, M, Y), fixing levers  74  (K, C, M, Y) are pivotally provided. On both sides of the developing cartridge  47  (K, C, M, Y) of each developing device  44  (K, C, M, Y), there are guide ridges  79  (K, C, M, Y) that are to be inserted in the associated guide grooves  73  (K, C, M, Y) from the upper open ends thereof (see FIG. 18 where only one guide ridge  79 Y of the developing cartridge  47 Y is visible). To mount the developing devices  44  (K, C, M, Y) on the associated photosensitive members  41  (K, C, M, Y), the guide ridges  79  (K, C, M, Y) are inserted from above into the associated guide grooves  73  (K, C, M, Y) and the fixing levers  74  (K, C, M, Y) are then pivoted to fix the developing devices in place. To remove the developing cartridges  47  (K, C, M, Y) for replacement or other purposes, the fixing levers  74  (K, C, M, Y) are pivoted back to guide the developing cartridges  47  (K, C, M, Y) upward along the guide grooves  73  (K, C, M, Y). 
     According to the embodiment of FIG. 18, the developing cartridges  47  (K, C, M, Y) forming part of the individual developing devices  44  (K, C, M, Y) can separately be attached to or detached from the associated photosensitive members  41  (K, C, M, Y); of the developing devices  44  (K, C, M, Y), only an exhausted or dead developing device(s) can be replaced with no wasteful replacement of the rest, so that running cost reductions are achievable. 
     FIG. 19 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention wherein four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are constructed in the form of an integral development cartridge  47  for such a photosensitive member cartridge  40  as described above. In this embodiment, only one pair of guide grooves  73  are provided at the inner upper sites of both side plates of the frame  70  of the photosensitive member cartridge  40 , spanning between both side plates. Accordingly, only one pair of pivotal fixing levers  74  are provided. On the other hand, the four developing devices  44  (K, C, M, Y) are constructed in the form of an integrated single developing cartridge  47 . On each side of the developing cartridge  47  there is mounted a guide ridge  79  that is to be inserted into the associated guide groove  73  from the upper open end thereof (in FIG. 19, one guide ridge  79  alone is visible). To mount the developing cartridge  47  on the photosensitive member cartridge  40 , the guide ridges  79  are inserted from above into the guide grooves  73  and the fixing levers  74  are then pivoted to fix the developing cartridge in place. To remove the developing cartridge  47  for replacement or other purposes, the fixing levers  74  are pivoted back so that the developing cartridge  47  can be guided upward along the guide grooves  73 . 
     The embodiment of FIG. 19, wherein the four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are designed as the integral developing cartridge  47 , has the merit of reducing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. 
     FIG. 20 is a perspective view illustrative of the attachment/detachment mechanism for such a photosensitive member cartridge  40  as described above, wherein a black developing device  44 K is constructed in the form of one single developing cartridge  47 K that is detachable from or attachable to a black photosensitive member  41 K as is the case with FIG. 17 or FIG. 18, and three or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of an integral developing cartridge  47 YMC. At the inner upper sites of both side plates of a frame  70  of the photosensitive member cartridge  40  there are provided guide grooves  73 K for receiving the developing cartridge  47 K between both side plates and guide grooves  73 YMC for receiving the developing cartridge  47 YMC, and there are provided pivotal fixing levers  74 K and  74 YMC, accordingly. On the other hand, the black photosensitive member cartridge  40  is provided on both its sides with guide ridges  79 K and the three-color developing cartridge  47 YMC is provided on both its sides with guide ridges  79 YMC (in FIG. 20, only one guide ridge  79 YMC is visible on the developing cartridge  47 YMC). To mount the developing cartridge  47 K or  47 YMC on the photosensitive member cartridge  40 , the guide ridges  79 K or  79 YMC are inserted from above into the guide grooves  73 K or  73 YMC, whereupon the fixing levers  74 K or  74 YMC are pivoted to fix the developing cartridge in place. To remove the developing cartridge  47 K or  47 YMC for replacement or other purposes, the fixing levers  74 K or  74 YMC are pivoted back so that the developing cartridge  47 K or  47 YMC can be guided upward along the guide grooves  73 K or  73 YMC. 
     The embodiment of FIG. 20, wherein the three-color or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of the integral developing cartridge  47 YMC, has the merit of removing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. This embodiment has another merit of preventing the three-color or cyan, magenta and yellow developing devices  44  (C, M, Y) from going to waste, because the black developing device  44 K most frequently used in general can be replaced in the form of the independent developing cartridge  47 K. 
     In the second aspect of the invention as explained above, the frame  70  of the photosensitive member cartridge  40  is provided with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and the appendixes thereto, i.e., the corona chargers  42  (K, C, M, Y), exposure devices  43 ′ (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) while they are relatively positioned, as shown in FIG.  17 . FIG. 21 is illustrative of one embodiment of how the exposure devices  43 ′ (K, C, M, Y) are attached to the frame  70  of the photosensitive member cartridge  40 . To be specific, FIG. 21 is a partly enlarged perspective view of only one end portions of the photosensitive members  41 Y and  41 M in the photosensitive member cartridge  40 . To mount the exposure devices  43 ′ (K, C, M, Y) at precisely located positions on the associated photosensitive members  41  (K, C, M, Y) and parallel therewith, mounting struts  111  (K, C, M, Y) are provided, extending from the inside surfaces of both side plates of the frame  70  and opposing to each other. Each strut  111  (K, C, Y, M) is provided with locating holes for receiving locating pins and threaded holes, both holes not shown. Locating pins  115  provided at both ends of a long-length substrate  113  (FIG. 22) of each exposure device  43 ′ (K, C, M, Y) are inserted into the locating holes in the associated mounting strut  111  (K, C, M, Y) while fixing screws  112  (K, C, M, Y) are fixedly screwed into the threaded holes in the mounting strut  111  (K, C, M, Y) through screw-insertion holes in both ends of the long-length substrate  113  (FIG.  22 ), so that the each exposure device  43 ′ (K, C, M, Y) is fixed in place. 
     FIG. 22 is a perspective schematic of each exposure device  43 ′ (K, C, M, Y) constructed in the form of an LED line head comprising an LED array  116 . As mentioned above, each exposure device  43 ′ (K, C, M, Y) is mounted on the long-length substrate  113 , spanning between both side plates of the frame  70 . The LED array  116  for forming a line image on the photosensitive member  41  (K, C, M, Y) and parallel with its axis is mounted on the long-length substrate  113 , with each LED connected to a driver IC  117  for controlling light emission. The long-length substrate  113  is provided at each end with a locating pin  115  for the determination of a mounting position and a hole  114  for the insertion of a mounting screw. Thus, each exposure device is fixed at a precise position for the associated photosensitive member  41  (K, C, M, Y). In front of the LED array  116  there is integrally fixed a gradient index type rod lens array  118  having an image-formation action, by which a train of light emission points defined by the LED array  116  are allowed to form an image on the photosensitive surface of the associated photosensitive member  41  (K, C, M, Y). 
     Next, an account is given of the mechanism of, upon the photosensitive member cartridge  40  mounted on the system proper, rotating the photosensitive members  41 K,  41 C,  41 M and  41 Y in the cartridge  40  in synchronism with one another, thereby preventing any color misalignment. FIG. 7 is illustrative of one construction for achieving this. As already mentioned, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are mounted at their one ends with gears  72 K,  72 C,  72 M and  72 Y, respectively, which are molded using the same mold. Three idles gears for transmission of rotational force are provided; an idle gear  81  is interposed between the gears  71 K and  72 C, an idle gear  82  between the gears  72 C and  72 M, and an idle gear  83  between the gears  72 M and  72 Y, forming a gear train. A driving gear  91  in mesh with one gear in this gear train, for instance, gear  72 Y, is disposed at a driving source  90  on the side of the system proper, so that upon the photosensitive cartridge  40  mounted at a given position, the driving gear  91  meshes with the gear  72 Y. 
     On the other hand, the shaft of the developing roller  49  (K, C, M, Y) of the developing device  44  (K, C, M, Y) is fixedly provided at its one end with a developing roller gear  84  (K, C, M, Y), and the shaft of the feed roller  48  (K, C, M, Y) is fixedly provided at its one end with a feed roller gear  85  (K, C, M, Y). An idle roller  86  (K, C, M, Y) is interposed between the developing roller gear  84  (K, C, M, Y) and the feed roller gear  85  (K, C, M, Y). The developing roller gear  84  (K, C, M, Y) meshes with the gear  72  (K, C, M, Y) of the photosensitive member  41  (K, C, M, Y), so that the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y), too, can be rotationally driven in synchronism with the photosensitive member  41  (K, C, M, Y). 
     By rotating the driving gear  91  of the driving source at one site on the side of the system proper according to this arrangement, it is possible to rotationally drive the four photosensitive members  41  (K, C, M, Y) and the appendixes thereto, i.e., the developing rollers  49  (K, C, M, Y) and feed rollers  48  (K, C, M, Y) of the developing devices  44  (K, C, M, Y), all in synchronism with one another. 
     This embodiment ensures that the operating efficiency of attachment/detachment of the photosensitive member cartridge  40  is improved because the point of meshing of the gears for transmission of driving force upon attachment/detachment of the photosensitive member cartridge  40  is limited to one. Since the positioning criterion for the photosensitive member cartridge  40  is defined by this driving force transmission gear  91 , it is also possible to improve the precision of meshing and, hence, provide a system for forming high-quality images that are substantially free from any color misalignment or any banding (variations in densities, etc. at right angles with the feed direction). 
     It is understood that the mechanism for synchronized transmission of rotational force for the photosensitive members  41 K,  41 C,  41 M and  41 Y is not limited to such a gear train as shown, and so may be constructed using a belt or chain, for instance. 
     FIG. 9 is illustrative of one modification to the embodiment of FIG.  8 . FIG. 9 is a schematic of the rotation transmission portion comprising the gear  91 , gear  92 , clutch  93  and gears  94  to  96  of FIG. 8 as viewed from above. In this modification, the driving gear  91  of the driving source (FIG. 7) on the side of the system proper is designed to mesh with the gear  72 K via the gear  92 , with the omission of the idle gear  81  interposed between the gears  72 K and  72 C. Instead, a rotation transmission mechanism comprising the gear  92 , clutch  93  and gears  94  to  96  as shown in FIG. 9 is interposed between the gear  72 K and  72 C. As the clutch  93  is put on, the rotational force of the gear  92  is transmitted to the gear  94  and then to gear  95  in mesh with that gear  94 , so that rotation in the same direction as is the case with the gear  72 K is transmitted to the gear  72 C via the gear  96  interposed between that gear  95  and the gear  72 C. The rotation of the gears  72 M and  72 Y is transmitted as is the case with FIG.  7 . It is here noted that since the gears  92 ,  94  and  96  are molded using the same mold, the four photosensitive members are rotationally driven in synchronism and at the same speed. 
     In this modification, as the clutch  93  is put off, the rotation of the driving gear  91  is transmitted to only the black developing device  44 K, so that other developing devices  44  (C, M, Y) remain inoperative. When only a black image is formed, therefore, there is only the need of putting the black photosensitive member  41 K and the associated developing device  44 K in effective operation; other photosensitive members  41  (C, M, Y) and the associated developing devices  44  (C, M, Y), which are not required to be placed in operation, are rendered inoperative. It is thus possible to prevent unnecessary consumption of the developing devices  44  (C, M, Y), thereby extending their service lives. 
     FIGS. 10 and 11 are illustrative of an embodiment of the invention, wherein the photosensitive member cartridge  40  is mounted on the system proper and the photosensitive members  41  (K, C, M, Y) and developing devices  44  (K, C, M, Y) of the photosensitive member cartridge  40  are driven by means of separate driving sources. FIG. 10 is similar to FIG.  7 . In this embodiment, the developing roller gears  84  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) are not in mesh with the gears  72  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) or separated therefrom, as can be seen from FIG.  10 . The embodiment of FIG. 10 is different from that of FIG. 7 only in terms of the gear train of the photosensitive member cartridge  40 . By rotating the driving gear  91  of the driving source  90  on the side of the system proper, the four photosensitive members  41  (K, C, M, Y) can thus be rotationally driven in synchronism, as can be see from FIG.  10 . Although depending on the driving force of that driving source  90 , however, the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y) are kept from rotation. In this embodiment, there is another driving source  100  at another site on the side of the system proper, as shown in FIG.  11 . When the photosensitive member cartridge  40  is mounted at a given position of the system proper, four gears  101  (K, C, M, Y) of the separate driving source  100 , designed to rotate in synchronism and in the same direction, are positioned in such a way that they mesh with the developing roller gears  84  (K, C, M, Y) fixed at one ends of the shafts of the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) mounted on the photosensitive member cartridge  40 . Thus, the developing devices  44  (K, C, M, Y) are rotationally driven by the driving source  100  that is separate from that for the photosensitive members  41  (K, C, M, Y). 
     In such an arrangement as shown in FIG. 15, color misalignments and image banding are largely dependent on the precision of rotation of the image carriers; however, they are less dependent on the precision of rotation of the developing rollers. Therefore, if the driving source  90  for the photosensitive member cartridges  41  (K, C, M, Y) of the photosensitive member cartridge  40  is made separate from the driving source  100  for the developing devices  44  (K, C, M, Y) as shown in FIGS. 10 and 11, it is then possible to prevent rotation variations caused as by fluctuations in the torque of developing means from having influences on the rotation of the image carriers and, hence, provide a system for forming high-quality images with neither color misalignments nor image banding. 
     FIG. 23 is illustrative of one embodiment of the mechanism for adjusting color misalignments occurring due to relative position misalignments between the exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y positioned and mounted on the photosensitive members  41  (K, C, M, Y), especially skews in parallelism, when four different monochromatic toner images are transferred onto the intermediate transfer belt  30  in a superposed fashion. As shown in FIG. 23, while the mounting ridge  111  (K, C, M, Y) of each exposure device  43 ′ (K, C, M, Y) extending from one side plate of the frame  70  or a long-length substrate  113  is sandwiched between an adjustment screw  105  and the leading end of an extensible spring  106 , the other end of the extensible spring  106  is fixed to the side plate  70 . In this state, if the leading end of the adjustment screw  105  is adjustable in the direction opposite to the direction of extension of the extensible spring  106  to adjust the position of one end of the exposure device  43 ′ (K, C, M, Y), it is then possible to adjust skews in parallelism between the exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y. It is not always required to provide all the four exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y with such color misalignment adjustment mechanisms. It is noted that it is acceptable to provide the opposite ends of the exposure devices  43 ′ (K, C, M, Y) with such color misalignment adjustment mechanisms. However, this is not always necessary because misalignments can be electrically eliminated by controlling the timing of when color latent images formed at the exposure devices  43 ′ (K, C, M, Y) are to be written, as long as given parallelism is maintained between the exposure devices  43 ′ (K, C, M, Y). 
     By providing the photosensitive member cartridge  40  with the position alignment mechanism for the exposure devices  43 ′ (K, C, M, Y) in this way, it is possible to make fine adjustments of the positions of the photosensitive members  41  (K, C, M, Y) onto which latent images are to be written and transferred, thereby reducing color misalignments. It is here noted that the color misalignment adjustment by this color (position) misalignment adjustment mechanism may be made upon shipment of the photosensitive member cartridge  40  or anytime after its attachment to the system proper. 
     Referring now to an electrographic system wherein latent images formed on image carriers are toner developed and the resulting toner images are transferred onto transfer media, there is a so-called “cleaner-less” mode wherein the remnants of toner not transferred onto the image carriers are recovered at developing devices without recourse to such cleaning devices as shown in FIG. 15 (for instance, see JP-B 06-77166). This “cleaner-less” mode is embodied as shown in FIG. 24, dispensing with the cleaning devices  46  (K, C, M, Y). The embodiment of FIG. 24 is the same in construction as that of FIG. 15 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); any detailed account of its construction and action is not given. The construction of the photosensitive member cartridge  40  in this embodiment, too, is the same as that of FIGS. 15 and 16 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); four photosensitive members  41 K,  41 C,  41 M and  41 Y are integrated with corona chargers  42  (K, C, M, Y) disposed around them and exposure devices  43 ′ (K, C, M, Y). 
     By use of the mode that dispenses with any cleaning device, it is possible to reduce the size of the photosensitive member cartridge  40  and the system proper. In addition, it is possible to diminish reaction force that may otherwise act on the photosensitive members  41  (K, C, M, Y) through the blades, etc. of cleaning devices, resulting in prevention of color misalignments. This is because the frame  70  is kept from deformation so that any position misalignment between the photosensitive members  41  (K, C, M, Y) can be avoided. 
     The present invention has been explained with reference to some embodiments applied to the tandem system for forming color images using the intermediate transfer belt  30  (FIG.  15 ), wherein four photosensitive members  41  (K, C, M, Y) are integrated into the photosensitive member cartridge  40  according to the present invention. It is here noted that instead of the intermediate transfer belt, it is acceptable to use a recording medium carrier belt. In this case, the recording medium carrier belt is used to carry and deliver recording media such as recording sheets. A plurality of monochromatic toner images are successively transferred directly onto a recording sheet, followed by the fixation of toner images of different colors which are superposed one upon another on the recording medium. A typical example of this is shown in FIG.  25 . The embodiment of FIG. 25 is the same as that of FIG. 15 with the exception of the following points. Instead of the intermediate transfer belt  30  of FIG. 1, a recording medium carrier belt  30 ′ is used to carry and deliver a recording medium (sheet) P. The recording sheets from a sheet feed cassette  63  are picked up by a pickup roller  64  on a one-by-one basis, and the feed timing of the recording sheet is controlled by a pair of gate rollers  65  in such a way that it is in synchronism with electrostatic latent images formed on the photosensitive members  41  (K, C, M, Y). Toner images formed on the photosensitive members  41  (K, C, M, Y) are successively transferred and superposed onto the recording medium P being delivered under the action of primary transfer rollers  45  (K, C, M, Y). Then, the recording medium P bearing the resulting full-color image thereon is released from the recording medium carrier belt  30 ′ by a release roller  107 , and passes between a pair of fixing rollers  61  defining a fixing portion, where the full-color toner image is fixed onto the recording medium P. Finally, the recording medium is ejected via a pair of ejecting rollers  62  onto an output tray  68  mounted on the upper portion of the system. The construction of the photosensitive member cartridge  40  in particular is the same as that of FIG. 1 or the like. To those skilled in the art, it would be apparent that any one of the aforesaid embodiments can be applied to the tandem type of color image formation system where recording media are carried and delivered by such a recording medium carrier belt, not by the intermediate transfer belt, and toner images are transferred onto the recording media. 
     In the aforesaid embodiments, the LED line head comprising such an LED array as shown in FIG. 22 is used for the exposure device  43 ′ (K, C, M, Y) that are integrally mounted together with the photosensitive member  41  (K, C, M, Y) on the photosensitive member cartridge  40 . However, it is acceptable to make use of an organic EL line head comprising an organic EL array such as one proposed by the applicant in Japanese Patent Application No. 2001-208076 or the like or a liquid crystal line head comprising a liquid crystal shutter array. 
     The write means that are integrally mounted together with the photosensitive members  41  (K, C, M, Y) on the photosensitive member cartridge  40  are not necessarily limited to optical write means. For instance, it is acceptable to make use of write means having recourse to charge transfer such as injection or elimination of charges, for instance, those proposed by the applicant in Japanese Patent Application Nos. 2000-298925 and 2000-298927, etc. FIG. 26 is a front schematic illustrative of the whole construction of a color image formation system wherein charge injection electrode line heads  3  (K, C, M, Y) are used as write means, and FIG. 18 is a perspective schematic illustrative of how the charge injection line heads  3  (K, C, M, Y) are arranged and constructed with respect to photosensitive members  41  (K, C, M, Y). When writing is carried out by the injection of charges, it is not always necessary to use the chargers  42  (K, C, M, Y) of FIG.  15 . Accordingly, a photosensitive cartridge  40  of FIG. 26 is constructed without recourse to any charger. Alternatively, instead of the exposure devices  43 ′ (K, C, M, Y), such charge injection electrode line heads  3  (K, C, M, Y) as shown in FIG. 18 are disposed. The charge injection electrode line head  3  (K, C, M, Y) comprises an array of electrodes  3   b  that come in contact with the associated photosensitive member  41  (K, C, M, Y) to create a potential profile therein and so form a latent image. Charges injected into each electrode  3   b  are controlled by a driver IC  119 . The construction of FIG. 26 is otherwise the same as that of FIG. 15, and so is not explained. 
     In accordance with the inventive color image formation system wherein, as explained above, a plurality of photosensitive members  41  (K, C, M, Y) and a plurality of write means  43 ′ (K, C, M, Y) or  3  (K, C, M, Y) are mutually positioned and mounted on a photosensitive member cartridge  40  detachable from and attachable to the system proper and developing devices  44  (K, C, M, Y) are disposed in such a way as to be detachable from and attachable to the photosensitive members  41  (K, C, M, Y) mounted on the photosensitive member cartridge  40 , the precision of relative positions between the photosensitive members and the write means is so improved that color misalignments ascribable to misalignments between the photosensitive members or write means and skews thereof can be prevented. 
     Gears can be associated with the photosensitive members in such phase relations as to reduce speed fluctuations due to the gears that drive the photosensitive member, so that the cartridge  40  can be constructed in an integral form. In addition, color misalignments due to the photosensitive member-driving gears can be considerably reduced (FIG.  7  and so on). Where the photosensitive members are individually mounted on the system proper, it is impossible to make phase adjustments of such gears because the photosensitive members rotate by themselves. 
     Further, the photosensitive member cartridge  40  can be finished up using photosensitive members of uniform performance singled out at the time of shipping, so that color changes due to variations in the properties of the photosensitive members of different colors can be prevented. In addition, the integrity of maintenance can be improved because a plurality of photosensitive members can be replaced at the same time. 
     Furthermore, the arrangement wherein the developing devices  44  (K, C, M, Y) are designed as detachable from and attachable to the photosensitive member cartridge  40  ensures that the developing devices  44  (K, C, M, Y) can be replaced independently of the photosensitive member cartridge  40 . Therefore, even when the developing devices  44  (K, C, M, Y) are exhausted or used up and so must be replaced with new ones, there is no need of making a replacement for the photosensitive members  41  (K, C, M, Y), so that running cost reductions are achievable. 
     What is necessary when the developing devices  44  (K, C, M, Y) are used up is only their replacement. There is no need of any color matching operation depending on the positions and configuration of the photosensitive members  41  (K, C, M, Y) and write means  43 ′ (K, C, M, Y) or  3  (K, C, M, Y). It is thus possible to provide an image formation system having improved operating efficiency. 
     For replacement of the developing devices  44  (K, C, M, Y), only the withdrawal of the photosensitive member cartridge  40  is needed. Then, new developing devices are attached to the photosensitive member cartridge  40 . Thus, the operation for replacement of the developing devices  44  (K, C, M, Y) is so facilitated that the integrity of maintenance can be improved. 
     It is also acceptable to construct a plurality of photosensitive members  41  (K, C, M, Y) in the form of one single replacement and the developing devices  44  (K, C, M, Y) in the form of one single replacement  47  (FIG.  19 ), so that the integrity of maintenance can be much more improved. 
     The color image formation system according to the third aspect of the present invention is now explained with reference to some embodiments. 
     FIG. 28 is a front schematic illustrative of the whole construction of yet another color image formation system to which the invention is applied. As shown in FIG. 28, this image formation system comprises an intermediate transfer belt  30  that is spanned in place with tensions applied thereon by a driving roller  10 , a follower roller  20  and a tension roller  21 , and driven endlessly in the (counterclockwise) direction shown by an arrow. Four photosensitive members (drums)  41 K,  41 C,  41 M and  41 Y having photosensitive layers on their outer surfaces, i.e., image carriers, are arranged at a given interval with respect to the intermediate transfer belt  30 . The capital letters K, C, M and Y added to the numeral reference mean black, cyan, magenta and yellow, indicating the photosensitive members for black, cyan, magenta and yellow, respectively. The same holds true for other members. The photosensitive members  41 K,  41 C,  41 M and  41 Y are rotationally driven in synchronism with the intermediate transfer belt  30  in the (clockwise) direction indicated by an arrow. Around each photosensitive member  41  (K, C, M, Y), there is located a corona charger  42  (K, C, M, Y) comprising Scorotron acting as means for uniformly charging the outer surface of the photosensitive member  41  (K, C, M, Y), an exposure site  43  (K, C, M, Y) for selectively exposing the outer surface of the member  41  uniformly charged by the corona charger  42  (K, C, M, Y) to exposure light from an exposure unit  43  for each color, thereby forming an electrostatic latent image, a developing device  44  (K, C, M, Y) for imparting a developing agent that is a toner to the electrostatic latent image formed at this exposure site  43  (K, C, M, Y) to make a visible (toner) image, a primary transfer roller  45  (K, C, M, Y) for successively transferring toner images developed at this developing device  44  (K, C, M, Y) onto the intermediate transfer belt  30  for primary transfer purposes, and a cleaning device  46  (K, C, M, Y) working as cleaning means for removing the remnants of toner on the surface of the photosensitive member  41  (K, C, M, Y) after transfer. 
     Typically using a non-magnetic mono-component toner as the developing agent, the developing device  44  (K, C, M, Y) is constructed in the form of a developing cartridge  47  (K, C, M, Y) (see FIG.  31 ). Such a mono-component toner stored in the cartridge  47  is delivered to a developing roller  49  (K, C, M, Y) by way of a feed roller  48  (K, C, M, Y). The thickness of a developing agent film deposited onto the surface of the developing roller  49  (K, C, M, Y) is controlled by a control blade  50  (K, C, M, Y). Then, the developing roller  49  (K, C, M, Y) is brought into contact or engagement with the photosensitive member  41  (K, C, M, Y) so that the developing agent is deposited onto the photosensitive member  41  (K, C, M, Y) depending on the potential level of the photosensitive member, thereby developing the latent image in the form of a toner image. 
     The black, cyan, magenta and yellow toner images formed at four such monochromatic toner image-formation stations are successively primary transferred onto the intermediate transfer belt  30  by primary transfer biases applied on the primary transfer roller  45  (K, C, M, Y), so that they are superposed successively one upon another on the intermediate transfer belt  30 , yielding a full-color toner image. Then, the full-color toner image is secondary transferred onto a recording medium P such as a recording sheet at a secondary transfer roller  66 , passing between a pair of fixing rollers  61  that are fixing means so that the toner image is fixed on the recording medium P. Finally, the recording medium is ejected by way of a pair of ejecting rollers  62  on an output tray  68  mounted on the top of the system. 
     In FIG. 28, it is noted that reference numeral  63  is a sheet feed cassette for storing a multiplicity of recording media P in a superposed fashion,  64  a pickup roller for feeding recording media P from the sheet feed cassette  63  one by one,  65  is a pair of gate rollers for controlling the timing of when the recording medium P is to be fed to a secondary transfer site of the secondary transfer roller  66 ,  66  the secondary transfer roller behaving as secondary transfer means for defining the secondary transfer site between it and the intermediate transfer belt  39 , and  67  a cleaning blade working as cleaning means for removal of the remnants of toner on the surface of the intermediate transfer belt  30  after secondary transfer. 
     It is here noted that the reasons why the black developing device  44 K is located on the uppermost stream side of the intermediate transfer belt  30  in its endless direction and the yellow developing device  44 Y is positioned on the lowermost stream side are that when the toner image is transferred onto the recording medium P, black causes the most noticeable fogging whereas yellow causes the least noticeable fogging. In the case of reversal development or the like, fogging is caused by toner particles that are allowed to bear charges of polarity opposite to normal polarity at the developing device. However, black toner particles showing the most noticeable fogging are first transferred onto the intermediate transfer belt  30  as the lowermost layer. Of the black toner particles, fogging-prone toner particles remain firmly deposited onto the intermediate transfer belt  30  by means of image force or the like, so that they are less likely to be transferred onto the recording medium P at the secondary transfer site. On the other hand, toner particles that cause the least noticeable yellow fogging are deposited onto the intermediate transfer belt  30  as the uppermost layer. Although they are easily passed onto the recording medium P, yet they are less noticeable. Such an arrangement as explained above ensures that fogging is generally less noticeable because the black toner particles leading to the most noticeable fogging are relatively less likely to be passed onto the recording medium P whereas the yellow toner particles leading to the least noticeable fogging are passed onto the recording medium P with relative ease. 
     Since a mono-component developing agent such as a non-magnetic mono-component toner is used, there is no need of using a carrier such as a two-component developing agent. Accordingly, it is possible to reduce the volume of each developing device  44  (K, C, M, Y) and so achieve a color image formation system of small size. 
     In such a color image formation system as constructed as explained above according to the present invention, the four photosensitive members  41 K,  41 C,  41 M and  41 Y, the corona charger  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) disposed around the members, the intermediate transfer belt  30 , the driving roller  10 , follower roller  20  and tension roller  21  over which the intermediate transfer belt  30  are spanned, the primary transfer rollers  45  (K, C, M, Y) for bringing the intermediate transfer roll  30  in contact with the photosensitive members  41  (K, C, M, Y) and the cleaning blade  67  are all constructed in the form of the integral photosensitive member cartridge  40  that can be detached from or attached to the system proper, as shown in FIGS. 28 and 29. In this case, the developing devices  44 K,  44 C,  44 M and  44 Y that are appendixes to the photosensitive members  41 K,  41 C,  41 M and  41 Y are detachable from and attachable to the photosensitive member cartridge  40 . 
     Referring to FIG. 29, the photosensitive member cartridge  40  is provided on its frame  70  with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and their appendixes, i.e., the corona chargers  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) while they are relatively positioned with respect to one another. The intermediate transfer belt  30  spanned over the driving roller  10 , follower roller  20  and tension roller  21  and cleaned by the cleaning blade  67  is mounted together with these means on the frame  70  of the photosensitive member cartridge  40  in such a way that it comes in contact with the photosensitive members  41  (K, C, M, Y) via the primary transfer rollers  45  (K, C, M, Y). These members can be slid out of the system proper as shown by a double arrow. To this end, the pair of fixing rollers  61 , the pair of ejecting rollers  62  and the secondary transfer rollers  66  are mounted on a side plate  69  that can pivot on a rotary shaft  60 . The pair of fixing rollers  61 , the pair of ejecting rollers  62  and the secondary transfer rollers  66  are retracted, thereby defining an opening through which the photosensitive cartridge  40  is withdrawn out of the system. In the state where the photosensitive member cartridge  40  has been withdrawn out of the system proper, the photosensitive member cartridge  40  can be detached from the system and replaced by a new photosensitive member cartridge  40 . 
     FIG. 30 is a perspective view of the photosensitive cartridge  40  from which the developing devices  44 K,  44 C,  44 M and  44 Y are removed, and FIG. 31 is a perspective view illustrative of how the developing device  44 Y is detached from or attached to the photosensitive member cartridge  40  with the developing devices  44 K,  44 C and  44 M remaining mounted thereon. The frame  70  is in a rectangular box form, between both sides plates of which there are four photosensitive members  41 K,  41 C,  41 M and  41 Y that are positioned at a given interval and parallel with one another for rotation on their shafts  71 K,  71 C,  71 M and  71 Y. The shaft  71  (K, C, M, Y) of each photosensitive member  41  (K, C, M, Y) is provided at its one end with a gear  72  (K, C, M, Y). By way of the gear train to be referred to later, the photosensitive members  41  (K, C, M, Y) are rotatable in the (clockwise) direction indicated by the arrow in FIG. 28 at the same speed and in synchronism with one another. 
     Between the same two side plates of the frame  70 , the corona chargers  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) (which, in FIG. 30, are invisible because of being concealed by the photosensitive members  41  (K, C, M, Y) and frame  70 ), all appendixes to the photosensitive members  41  (K, C, M, Y), are mounted at given positions. On one side of the side plate of the frame  70  there are provided electrodes  75  (K, C, M, Y) for applying high voltages on the discharge wires of the corona chargers or Scorotrons  42  (K, C, M, Y) and electrodes  76  (K, C, M, Y) for applying high voltages on the grits of the Scorotrons. On the same one side of the side plate of the frame  70  there are also provided electrodes  77  (K, C, M, Y) for applying developing bias voltages on the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) in the state where the developing devices  44  (K, C, M, Y) are mounted on the photosensitive member cartridge  40  and electrodes  78  (K, C, M, Y) for applying developing feed bias voltages on the feed rollers  48  (K, C, M, Y) in the same state. 
     Between the side plates of the frame  70 , the driving roller  10 , follower roller  20  and tension roller  21 , over which the intermediate transfer roll  30  is spanned, are mounted parallel with one another at a given interval in such a manner that they are rotatable on shafts  22 ,  23  and  24 , and the primary transfer rollers  45  (K, C, M, Y), appendixes to the photosensitive members  41  (K, C, M, Y), are mounted at given positions (although not shown in FIGS.  30  and  31 ). On the same side of the side plate of the frame  70  there are mounted electrodes  80  (K, C, M, Y) for applying primary transfer voltages on the primary transfer roller  45  (K, C, M, Y). 
     On the same side plate, there is further provided an IC  110  as memory means for storing information about the fabrication and use of the photosensitive member cartridge  40 , color misalignments, etc. Upon the photosensitive member cartridge  40  mounted on the system proper, the electrodes  75  (K, C, M, Y), electrodes  76  (K, C, M, Y), electrodes  77  (K, C, M, Y), electrodes  78  (K, C, M, Y), electrodes  80  (K, C, M, Y) and IC  110  are automatically connected to the power source circuit and control circuit of the system proper. In this state, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are also automatically connected to ground for earth purposes. 
     At the inner upper sides of the same two side plates of the frame  70 , there are provided guide grooves  73  (K, C, M, Y) for receiving the developing devices  44  (K, C, M, Y) at constant positions corresponding to the photosensitive members  41  (K, C, M, Y). To fix the developing devices  44  (K, C, M, Y) received along the guide grooves  73  (K, C, M, Y), fixing levers  74  (K, C, M, Y) are pivotally provided. On both sides of the developing cartridge  47  (K, C, M, Y) of each developing device  44  (K, C, M, Y), there are guide ridges  79  (K, C, M, Y) that are to be inserted in the associated guide grooves  73  (K, C, M, Y) from the upper open ends thereof (see FIG. 31 where only one guide ridge  79 Y of the developing cartridge  47 Y is visible). To mount the developing devices  44  (K, C, M, Y) on the associated photosensitive members  41  (K, C, M, Y), the guide ridges  79  (K, C, M, Y) are inserted from above into the associated guide grooves  73  (K, C, M, Y) and the fixing levers  74  (K, C, M, Y) are then pivoted to fix the developing devices in place. To remove the developing cartridges  47  (K, C, M, Y) for replacement or other purposes, the fixing levers  74  (K, C, M, Y) are pivoted back to guide the developing cartridges  47  (K, C, M, Y) upward along the guide grooves  73  (K, C, M, Y). 
     According to the embodiment of FIG. 31, the developing cartridges  47  (K, C, M, Y) forming part of the individual developing devices  44  (K, C, M, Y) can separately be attached to or detached from the associated photosensitive members  41  (K, C, M, Y); of the developing devices  44  (K, C, M, Y), only an exhausted or dead developing device(s) can be replaced with no wasteful replacement of the rest, so that running cost reductions are achievable. 
     FIG. 32 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention wherein four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are constructed in the form of an integral development cartridge  47  for such a photosensitive member cartridge  40  as described above. In this embodiment, only one pair of guide grooves  73  are provided at the inner upper sites of both side plates of the frame  70  of the photosensitive member cartridge  40 , spanning between both side plates. Accordingly, only one pair of pivotal fixing levers  74  are provided. On the other hand, the four developing devices  44  (K, C, M, Y) are constructed in the form of an integrated single developing cartridge  47 . On each side of the developing cartridge  47  there is mounted a guide ridge  79  that is to be inserted into the associated guide groove  73  from the upper open end thereof (in FIG. 32, one guide ridge  79  alone is visible). To mount the developing cartridge  47  on the photosensitive member cartridge  40 , the guide ridges  79  are inserted from above into the guide grooves  73  and the fixing levers  74  are then pivoted to fix the developing cartridge in place. To remove the developing cartridge  47  for replacement or other purposes, the fixing levers  47  are pivoted back so that the developing cartridge  47  can be guided upward along the guide grooves  73 . 
     The embodiment of FIG. 32, wherein the four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are designed as the integral developing cartridge  47 , has the merit of reducing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. 
     FIG. 33 is a perspective view illustrative of the attachment/detachment mechanism for such a photosensitive member cartridge  40  as described above, wherein a black developing device  44 K is constructed in the form of one single developing cartridge  47 K that is detachable from or attachable to a black photosensitive member  41 K as is the case with FIG. 30 or FIG. 31, and three or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of an integral developing cartridge  47 YMC. At the inner upper sites of both side plates of a frame  70  of the photosensitive member cartridge  40  there are provided guide grooves  73 K for receiving the developing cartridge  47 K between both side plates and guide grooves  73 YMC for receiving the developing cartridge  47 YMC, and there are provided pivotal fixing levers  74 K and  74 YMC, accordingly. On the other hand, the black photosensitive member cartridge  40  is provided on both its sides with guide ridges  79 K and the three-color developing cartridge  47 YMC is provided on both its sides with guide ridges  79 YMC (in FIG. 33, only one guide ridge  79 YMC is visible on the developing cartridge  47 YMC). To mount the developing cartridge  47 K or  47 YMC on the photosensitive member cartridge  40 , the guide ridges  79 K or  79 YMC are inserted from above into the guide grooves  73 K or  73 YMC, whereupon the fixing levers  74 K or  74 YMC are pivoted to fix the developing cartridge in place. To remove the developing cartridge  47 K or  47 YMC for replacement or other purposes, the fixing levers  74 K or  74 YMC are pivoted back so that the developing cartridge  47 K or  47 YMC can be guided upward along the guide grooves  73 K or  73 YMC. 
     The embodiment of FIG. 33, wherein the three-color or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of the integral developing cartridge  47 YMC, has the merit of removing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. This embodiment has another merit of preventing the three-color or cyan, magenta and Y developing devices  44  (C, M, Y) from going to waste, because the black developing device  44 K most frequently used in general can be replaced in the form of the independent developing cartridge  47 K. 
     Next, an account is given of the mechanism of, upon the photosensitive member cartridge  40  mounted on the system proper, rotating the photosensitive members  41 K,  41 C,  41 M and  41 Y in the cartridge  40  in synchronism with one another, thereby preventing any color misalignment. FIG. 34 is illustrative of one construction for achieving this. As already mentioned, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are mounted at their one ends with gears  72 K,  72 C,  72 M and  72 Y, respectively, which are molded using the same mold. An idle gear  81  is interposed between the gears  71 K and  72 C, an idle gear  82  between the gears  72 C and  72 M, and an idle gear  83  between the gears  72 M and  72 Y, forming a gear train. The driving roller  10  is provided at its one end with a gear  97  rotating around a shaft  22 , and the gear  97  meshes with the gear  72 Y for rotating the photosensitive member  41 Y. The gears  72 K,  81 ,  72 C,  82 ,  72 M,  83 ,  72 Y and  97  thus form a series of gear train. A driving gear  91  in mesh with one gear in this gear train, for instance, gear  97 , is disposed at a driving source  90  on the side of the system proper, so that upon the photosensitive cartridge  40  mounted at a given position of the system proper, the driving gear  91  meshes with the gear  97 . 
     On the other hand, the shaft of the developing roller  49  (K, C, M, Y) of the developing device  44  (K, C, M, Y) is fixedly provided at its one end with a developing roller gear  84  (K, C, M, Y), and the shaft of the feed roller  48  (K, C, M, Y) is fixedly provided at its one end with a feed roller gear  85  (K, C, M, Y). An idle roller  86  (K, C, M, Y) is interposed between the developing roller gear  84  (K, C, M, Y) and the feed roller gear  85  (K, C, M, Y). The developing roller gear  84  (K, C, M, Y) meshes with the gear  72  (K, C, M, Y) of the photosensitive member  41  (K, C, M, Y), so that the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y), too, can be rotationally driven in synchronism with the rotation of the photosensitive member  41  (K, C, M, Y). 
     By rotating the driving gear  91  of the driving source at one site on the side of the system proper according to this arrangement, it is possible to rotationally drive the four photosensitive members  41  (K, C, M, Y) and the appendixes thereto, i.e., the developing rollers  49  (K, C, M, Y) and feed rollers  48  (K, C, M, Y) of the developing devices  44  (K, C, M, Y), all in synchronism with one another. 
     It is here desired that the diameter of the driving roller  10  be set in such a way to give a speed difference of 1 to 5% between the delivery speed of the intermediate transfer belt  30  by the driving roller  10  and the peripheral speed of the photosensitive member  41  (K, C, M, Y). With such a speed difference between the photosensitive member  41  (K, C, M, Y) and the intermediate transfer belt  30 , it is possible to increase the efficiency of transfer because the toner can be mechanically moved upon the primary transfer of the toner image. 
     When only the image carriers (photosensitive members) are replaced as is the case with the prior art, there is a fluctuation of the periphery speed of the image carriers with errors in image carrier shape, which in turn results in a change in the speed difference with the intermediate transfer belt. The fluctuations in the speed difference offer some problems; too small a speed difference renders the efficiency of transfer low whereas too large a speed difference causes deterioration in image quality. Therefore, if the photosensitive members  41  (K, C, M, Y) and intermediate transfer belt  30  are integrated with the photosensitive member cartridge  40  as contemplated herein, it is then possible to reduce the fluctuations in the speed difference between the photosensitive members  41  (K, C, M, Y) and the intermediate transfer belt  30  as by determining the shape of the driving roll  10  in conformity with the shape of the photosensitive member  41  (K, C, M, Y). It is thus possible to provide an imaging system with improved transfer efficiency and with no deterioration in image quality. 
     This embodiment ensures that the operating efficiency of attachment/detachment of the photosensitive member cartridge  40  is improved because the point of meshing of the gears for transmission of driving force upon attachment/detachment of the photosensitive member cartridge  40  is limited to one. Since the positioning criterion for the photosensitive member cartridge  40  is defined by this driving force transmission gear  91 , it is also possible to improve the precision of meshing and, hence, provide a system for forming high-quality images that are substantially free from any color misalignment or any banding (variations in densities, etc. at right angles with the feed direction). 
     It is understood that the mechanism for synchronized transmission of rotational force for the photosensitive members  41 K,  41 C,  41 M and  41 Y is not limited to such a gear train as shown, and so may be constructed using a belt or chain, for instance. 
     FIG. 35 is illustrative of one modification to the embodiment of FIG.  34 . In this modification, the driving gear  91  of the driving source  90  (FIG. 34) on the side of the system proper is designed to mesh with the gear  72 K in the gear train comprising the gears  72 K,  81 ,  72 C,  82 ,  72 M,  83 ,  72 Y and  97 , so that the intermediate transfer belt  30  as well as the four photosensitive members  41  (K, C, M, Y) and their appendixes, i.e., the developing rollers  49  (K, C, M, Y) and feed rollers  48  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) are all rotationally driven. Otherwise, the construction of FIG. 35 is the same as that of FIG.  34 . 
     FIGS. 36 and 37 are illustrative of an embodiment of the invention, wherein the photosensitive member cartridge  40  is mounted on the system proper and the photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40 , the intermediate transfer belt  30  and the developing devices  44  (K, C, M, Y) are driven by means of separate driving sources. FIG. 36 is similar to FIG.  34 . In this embodiment, the developing roller gears  84  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) are not in mesh with the gears  72  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) or separated therefrom, as can be seen from FIG.  36 . The embodiment of FIG. 36 is different from that of FIG. 34 only in terms of the gear train of the photosensitive member cartridge  40 . It is here understood that the gear  97  for rotating the driving roller  10  is in no direct mesh with the gear  72 Y for rotating the photosensitive member  41 Y; they are jointed to each other via two gears  98  and  99 . By rotating the driving gear  91  of the driving source  90  on the side of the system proper, the intermediate transfer belt  30  and the four photosensitive members  41  (K, C, M, Y) can thus be rotationally driven in synchronism, as can be see from FIG.  36 . 
     Although depending on the driving force of that driving source  90 , however, the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y) are kept from rotation. In this embodiment, there is another driving source  100  at another site on the side of the system proper, as shown in FIG.  37 . When the photosensitive member cartridge  40  is mounted at a given position of the system proper, four gears  101  (K, C, M, Y) of the separate driving source  100 , designed to rotate in synchronism and in the same direction, are positioned in such a way that they mesh with the developing roller gears  84  (K, C, M, Y) fixed at one ends of the shafts of the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) mounted on the photosensitive member cartridge  40 . Thus, the developing devices  44  (K, C, M, Y) are rotationally driven by the driving source  100  that is separate from that for the photosensitive members  41  (K, C, M, Y). 
     In such an arrangement as shown in FIG. 28, color misalignments and image banding are largely dependent on the precision of rotation of the image carriers and intermediate transfer belt; however, they are less dependent on the precision of rotation of the developing rollers. Therefore, if the driving source  90  for the intermediate transfer belt  30  and the photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40  is made separate from the driving source  100  for the developing devices  44  (K, C, M, Y) as shown in FIGS. 36 and 37, it is then possible to prevent rotation variations caused as by fluctuations in the torque of developing means from having influences on the rotation of the image carriers and, hence, provide a system for forming high-quality images with neither color misalignments nor image banding. 
     In the construction of FIGS. 36 and 37, too, it is acceptable to engage the driving gear  91  of the driving source  90  on the side of the system proper with the gear  72 K in the gear train comprising the gears  72 K,  81 ,  72 C,  82 ,  72 M,  83 ,  72 Y and  97  as shown in FIG. 35, thereby rotationally driving the intermediate transfer belt  30  and the four photosensitive members  41  (K, C, M, Y) in synchronism with one another. 
     FIG. 38 is illustrative of one embodiment of the mechanism for adjusting color misalignments occurring due to position misalignments between the photosensitive members  41 K,  41 C,  41 M and  41 Y in such a photosensitive member cartridge  40  as described above, especially skews in parallelism, when four different monochromatic toner images are transferred onto the intermediate transfer belt  30  in a superposed fashion. As shown in FIG. 38, while the shaft  51  (K, C, M, Y) of each primary transfer roller  45  (K, C, M, Y) extending from one side plate of the frame  70  is sandwiched between an adjustment screw  105  and the leading end of an extensible spring  106 , the other end of the extensible spring  106  is fixed to the side plate  70 . In this state, if the leading end of the adjustment screw  105  is adjustable in the direction opposite to the direction of extension of the extensible spring  106  to adjust the position of one end of the shaft  51  (K, C, M, Y), there are then changes in the primary transfer positions of the primary transfer rollers  45 K,  45 C,  45 M and  45 Y. Since there is such a speed difference as mentioned above between the intermediate transfer belt  30  and the photosensitive members  41  (K, C, M, Y), changes in the primary transfer positions cause changes in the transfer positions on the intermediate transfer belt  30  for the toner images of the corresponding colors; that is, color misalignments can be regulated. It is not always required to provide all the four photosensitive members  41 K,  41 C,  41 M and  41 Y with such color misalignment adjustment mechanisms. It is noted that it is acceptable to provide the opposite ends of the shafts  51  (K, C, M, Y) with such color misalignment adjustment mechanisms. However, this is not always necessary because misalignments can be electrically eliminated by controlling the timing of when color latent images formed on the photosensitive members  41  (K, C, M, Y) are to be written, as long as given parallelism is maintained between the photosensitive members  41  (K, C, M, Y). 
     It is here understood that color misalignments may also be regulated by providing similar adjustment mechanisms on the respective shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y). 
     By providing the photosensitive member cartridge  40  with the position alignment mechanism for the primary transfer rollers  45  (K, C, M, Y) or the photosensitive members  41  (K, C, M, Y) in this way, it is possible to make fine adjustments of the positions of the photosensitive members  41  (K, C, M, Y) onto which latent images are to be written and transferred, thereby reducing color misalignments. It is here noted that the color misalignment adjustment by this color (position) misalignment adjustment mechanism may be made upon shipment of the photosensitive member cartridge  40  or anytime after its attachment to the system proper. 
     Referring now to an electrographic system wherein latent images formed on image carriers are toner developed and the resulting toner images are transferred onto transfer media, there is a so-called “cleaner-less” mode wherein the remnants of toner not transferred onto the image carriers are recovered at developing devices without recourse to such cleaning devices as shown in FIG. 28 (for instance, see JP-B 06-77166). This “cleaner-less” mode is embodied as shown in FIG. 39, dispensing with the cleaning devices  46  (K, C, M, Y) of FIG.  28 . The embodiment of FIG.  29  is the same in construction as that of FIG. 28 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); any detailed account of its construction and action is not given. The construction of the photosensitive member cartridge  40  in this embodiment, too, is the same as that of FIGS. 28 and 29 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); four photosensitive members  41 K,  41 C,  41 M and  41 Y, corona chargers  42  (K, C, M, Y) disposed around the same and an intermediate transfer belt  30  are constructed in an integral form. 
     By use of the mode that dispenses with any cleaning device, it is possible to reduce the size of the photosensitive member cartridge  40  and the system proper. In addition, it is possible to diminish reaction force that may otherwise act on the photosensitive members  41  (K, C, M, Y) through the blades, etc. of cleaning devices, resulting in prevention of color misalignments. This is because the frame  70  is kept from deformation so that any position misalignment between the photosensitive members  41  (K, C, M, Y) can be avoided. 
     FIGS. 40 and 41 are views similar to FIGS. 28 and 29, showing another embodiment of the invention. In this embodiment, no single exposure unit  43  is used unlike the embodiment of FIG.  28 . An exposure device  43 ′ (K, C, M, Y) for performing selective exposure per color, corresponding to each photosensitive member  41  (K, C, M, Y), is integrated with a photosensitive member cartridge  40  between a corona charger  42  (K, C, M, Y) and a developing device  44  (K, C, M, Y). In accordance with this embodiment, the photosensitive member cartridge  40  is provided at its frame  70  with four photosensitive members  41 K,  41 C,  41 M and  41 Y and their appendixes, i.e., corona chargers  42  (K, C, M, Y), exposure devices  43 ′ (K, C, M, Y) and cleaning devices  45  (K, C, M, Y) while they are relatively positioned. An intermediate transfer belt  30  spanned over a driving roller  10 , a follower roller  20  and a tension roller  21  and cleaned by a cleaning blade  67  is attached together with these means to the frame  70  of the photosensitive member cartridge  40  in such a way that it comes into contact with the respective photosensitive members  41  (K, C, M, Y) through primary transfer rollers  45  (K, C, M, Y). 
     In this embodiment, the exposure unit  43  is dispensed with. Thus, as shown by a double arrow in FIG. 41, the photosensitive member cartridge  40  can be withdrawn from the system proper by lifting it substantially upward. To this end, the output tray  68  is mounted at its one end on the system proper in such a way that it can turn upwardly. The output tray  68  is retracted, thereby defining an opening through which the photosensitive cartridge  40  is withdrawn out of the system. In the state where the photosensitive member cartridge  40  has been withdrawn out of the system, the photosensitive member cartridge  40  can be detached from the system and replaced by a new photosensitive member cartridge  40 . 
     With such an arrangement wherein the exposure devices  43 ′ (K, C, M, Y), photosensitive members  41  (K, C, M, Y), intermediate transfer belt  30  and primary transfer rollers  45  (K, C, M, Y) are constructed in the form of the integral photosensitive cartridge  40 , it is possible to adjust nearly all of color misalignment factors at its production stage, thereby providing a system for the formation of images of high quality. 
     In the embodiment of FIGS. 40 and 41, the frame  70  of the photosensitive member cartridge  40  is provided with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and the appendixes thereto, i.e., the corona chargers  42  (K, C, M, Y), the exposure devices  43 ′ (K, C, M, Y), the intermediate transfer belt  30 , the driving roller  10 , follower roller  20  and tension roller  21  over which the intermediate transfer belt  30  is spanned, the primary transfer rollers  45  (K, C, M, Y) for bringing the intermediate transfer belt  30  in contact with the photosensitive members  41  (K, C, M, Y) and the cleaning blade  67  for cleaning the intermediate transfer belt  30  while they are relatively positioned. FIG. 42 is illustrative of one embodiment of how the exposure devices  43 ′ (K, C, M, Y) are attached to the frame  70  of the photosensitive member cartridge  40 . To be specific, FIG. 42 is a partly enlarged perspective view of only one end portions of the photosensitive members  41 Y and  41 M in the photosensitive member cartridge  40 . To mount the exposure devices  43 ′ (K, C, M, Y) at precisely located positions on the associated photosensitive members  41  (K, C, M, Y) and parallel therewith, mounting struts  111  (K, C, M, Y) are integrally provided, extending from the inside surfaces of both side plates of the frame  70  and opposing to each other. Each strut  111  (K, C, Y, M) is provided with locating holes for receiving locating pins and threaded holes, both holes not shown. Locating pins  115  provided at both ends of a long-length substrate  113  (FIG. 22) of each exposure device  43 ′ (K, C, M, Y) are inserted into the locating holes in the associated mounting strut  111  (K, C, M, Y) while fixing screws  112  (K, C, M, Y) are fixedly screwed into the threaded holes in the mounting strut  111  (K, C, M, Y) through screw-insertion holes in both ends of the long-length substrate  113  (FIG.  22 ), so that the each exposure device  43 ′ (K, C, M, Y) is fixed in place. 
     FIG. 22 is a perspective schematic of each exposure device  43 ′ (K, C, M, Y) constructed in the form of an LED line head comprising an LED array  116 . As mentioned above, each exposure device  43 ′ (K, C, M, Y) is mounted on the long-length substrate  113 , spanning between both side plates of the frame  70 . The LED array  116  for forming a line image on the photosensitive member  41  (K, C, M, Y) and parallel with its axis is mounted on the long-length substrate  113 , with each LED connected to a driver IC  117  for controlling light emission. The long-length substrate  113  is provided at each end with a locating pin  115  for the determination of a mounting position and a hole  114  for the insertion of a mounting screw. Thus, each exposure device is fixed at a precise position for the associated photosensitive member  41  (K, C, M, Y). In front of the LED array  116  there is integrally fixed a gradient index type rod lens array  118  having an image-formation action, by which a train of light emission points defined by the LED array  116  is allowed to form an image on the photosensitive surface of the associated photosensitive member  41  (K, C, M, Y). 
     FIG. 43 is illustrative of one embodiment of the mechanism for adjusting color misalignments occurring due to relative position misalignments between the exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y positioned and mounted on the photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40  of FIGS. 40 and 41, especially skews in parallelism, when four different monochromatic toner images are transferred onto the intermediate transfer belt  30  in a superposed fashion. As shown in FIG. 43, while the mounting ridge  111  (K, C, M, Y) of each exposure device  43 ′ (K, C, M, Y) extending from one side plate of the frame  70  or a long-length substrate  113  is sandwiched between an adjustment screw  105  and the leading end of an extensible spring  106 , the other end of the extensible spring  106  is fixed to the side plate  70 . In this state, if the leading end of the adjustment screw  105  is adjustable in the direction opposite to the direction of extension of the extensible spring  106  to adjust the position of one end of the exposure device  43 ′ (K, C, M, Y), it is then possible to adjust skews in parallelism between the exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y. It is not always required to provide all the four exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y with such color misalignment adjustment mechanisms. It is noted that it is acceptable to provide the opposite ends of the exposure devices  43 ′ (K, C, M, Y) with such color misalignment adjustment mechanisms. However, this is not always necessary because misalignments can be electrically eliminated by controlling the timing of when color latent images formed at the exposure devices  43 ′ (K, C, M, Y) are to be written, as long as given parallelism is maintained between the exposure devices  43 ′ (K, C, M, Y). 
     By providing the photosensitive member cartridge  40  with the position alignment mechanism for the exposure devices  43 ′ (K, C, M, Y) in this way, it is possible to make fine adjustments of the positions of the photosensitive members  41  (K, C, M, Y) onto which latent images are to be written and transferred, thereby reducing color misalignments. It is here noted that the color misalignment adjustment by this color (position) misalignment adjustment mechanism may be made upon shipment of the photosensitive member cartridge  40  or anytime after its attachment to the system proper. 
     In the embodiment of FIGS. 40 and 41, the write means that are integrally mounted together with the photosensitive members  41  (K, C, M, Y) on the photosensitive member cartridge  40  are not necessarily limited to such optical write means as shown in FIG.  22 . For instance, it is acceptable to make use of write means having recourse to charge transfer such as injection or elimination of charges, for instance, those proposed by the applicant in Japanese Patent Application Nos. 2000-298925 and 2000-298927, etc. FIG. 27 is a front schematic illustrative of the whole construction of a color image formation system wherein charge injection electrode line heads  3  (K, C, M, Y) are used as write means, and FIG. 27 is a perspective schematic illustrative of how the charge injection electrode line heads  3  (K, C, M, Y) are arranged and constructed with respect to photosensitive members  41  (K, C, M, Y). When writing is carried out by the injection of charges, it is not always necessary to use the chargers  42  (K, C, M, Y) of FIG.  40 . The charge injection electrode line head  3  (K, C, M, Y) comprises an array of electrodes  3   b  that come in contact with the associated photosensitive member  41  (K, C, M, Y) to create a potential profile therein and so form a latent image. Charges injected into each electrode  3   b  are controlled by a driver IC 119 . 
     In accordance with the inventive color image formation system wherein, as explained above, a plurality of photosensitive members  41  (K, C, M, Y) and the intermediate transfer belt  30  are mutually positioned and mounted on a photosensitive member cartridge  40  detachable from and attachable to the system proper and developing devices  44  (K, C, M, Y) are disposed in such a way as to be detachable from and attachable to the photosensitive members  41  (K, C, M, Y) mounted on the photosensitive member cartridge  40 , the precision of relative positions between the photosensitive members is so improved that color misalignments ascribable to misalignments between the photosensitive members and skews thereof can be prevented. 
     Gears can be associated with the photosensitive members in such phase relations as to reduce speed fluctuations due to the gears that drive the photosensitive member, so that the cartridge  40  can be constructed in an integral form. In addition, color misalignments due to the photosensitive member-driving gears can be considerably reduced (FIG.  34  and so on). Where the photosensitive members are individually mounted on the system proper, it is impossible to make phase adjustments of such gears because the photosensitive members rotate by themselves. 
     Further, the photosensitive member cartridge  40  can be finished up using photosensitive members of uniform performance singled out at the time of shipping, so that color changes due to variations in the properties of the photosensitive members of different colors can be prevented. In addition, the integrity of maintenance can be improved because a plurality of photosensitive members can be replaced at the same time. 
     Furthermore, the arrangement wherein the developing devices  44  (K, C, M, Y) are designed as detachable from and attachable to the photosensitive member cartridge  40  ensures that the developing devices  44  (K, C, M, Y) can be replaced independently of the photosensitive member cartridge  40 . Therefore, even when the developing devices  44  (K, C, M, Y) are exhausted or used up and so must be replaced with new ones, there is no need of making a replacement for the photosensitive members  41  (K, C, M, Y), so that running cost reductions are achievable. 
     What is necessary when the developing devices  44  (K, C, M, Y) are used up is only their replacement. There is no need of any color matching operation depending on the positions and configuration of the photosensitive members  41  (K, C, M, Y. It is thus possible to provide an image formation system having improved operating efficiency. 
     For replacement of the developing devices  44  (K, C, M, Y), only the withdrawal of the photosensitive member cartridge  40  is needed. Then, new developing devices are attached to the photosensitive member cartridge  40 . Thus, the operation for replacement of the developing devices  44  (K, C, M, Y) is so facilitated that the integrity of maintenance can be improved. 
     It is also acceptable to construct a plurality of photosensitive members  41  (K, C, M, Y) and the intermediate transfer belt  30  in the form of one single replacement and the developing devices  44  (K, C, M, Y) in the form of one single replacement  47  (FIG.  32 ), so that the integrity of maintenance can be much more improved. 
     The fourth aspect of the color image formation system according to the present invention is now explained with reference to some embodiments. 
     The color image formation system according to the third aspect of the present invention is now explained with reference to some embodiments. 
     FIG. 44 is a front schematic illustrative of the whole construction of a further color image formation system to which the invention is applied. As shown in FIG. 44, this image formation system comprises a recording medium carrier belt  30 ′ that is spanned in place with tensions applied thereon by a driving roller  10 , a follower roller  20  and a tension roller  21 , and driven endlessly in the (counterclockwise) direction shown by an arrow. Four photosensitive members (drums)  41 K,  41 C,  41 M and  41 Y having photosensitive layers on their outer surfaces, i.e., image carriers, are arranged at a given interval with respect to the recording medium carrier belt  30 ′. The capital letters K, C, M and Y added to the numeral reference mean black, cyan, magenta and yellow, indicating the photosensitive members for black, cyan, magenta and yellow, respectively. The same holds true for other members. The photosensitive members  41 K,  41 C,  41 M and  41 Y are rotationally driven in synchronism with the recording medium carrier belt  30 ′ in the (clockwise) direction indicated by an arrow. Around each photosensitive member  41  (K, C, M, Y), there is located a corona charger  42  (K, C, M, Y) comprising Scorotron acting as means for uniformly charging the outer surface of the photosensitive member  41  (K, C, M, Y), an exposure site  43  (K, C, M, Y) for selectively exposing the outer surface of the member  41  uniformly charged by the corona charger  42  (K, C, M, Y) to exposure light from an exposure unit  43  for each color, thereby forming an electrostatic latent image, a developing device  44  (K, C, M, Y) for imparting a developing agent that is a toner to the electrostatic latent image formed at this exposure site  43  (K, C, M, Y) to make a visible (toner) image, a transfer roller  45  (K, C, M, Y) for successively transferring toner images developed at this developing device  44  (K, C, M, Y) onto a recording medium P carried by the recording medium carrier belt  30 ′ for transfer purposes, and a cleaning device  46  (K, C, M, Y) working as cleaning means for removing the remnants of toner on the surface of the photosensitive member  41  (K, C, M, Y) after transfer. 
     Typically using a non-magnetic mono-component toner as the developing agent, the developing device  44  (K, C, M, Y) is constructed in the form of a developing cartridge  47  (K, C, M, Y) (see FIG.  47 ). Such a mono-component toner stored in the cartridge  47  is delivered to a developing roller  49  (K, C, M, Y) by way of a feed roller  48  (K, C, M, Y). The thickness of a developing agent film deposited onto the surface of the developing roller  49  (K, C, M, Y) is controlled by a control blade  50  (K, C, M, Y). Then, the developing roller  49  (K, C, M, Y) is brought into contact or engagement with the photosensitive member  41  (K, C, M, Y) so that the developing agent is deposited onto the photosensitive member  41  (K, C, M, Y) depending on the potential level of the photosensitive member, thereby developing the latent image in the form of a toner image. 
     The black, cyan, magenta and yellow toner images formed at four such different monochromatic toner image-formation stations are successively transferred onto the recording medium P carried by transfer biases applied on the transfer rollers  45  (K, C, M, Y), so that they are superposed successively one upon another on the recording medium P, yielding a full-color toner image thereon. Then, the recording medium P with the full-color toner image carried thereon is released from the recording medium carrier belt  30 ′ by a release roller  107 , passing between a pair of fixing rollers  61  that are fixing means so that the toner image is fixed on the recording medium P. Finally, the recording medium is ejected by way of a pair of ejecting rollers  62  on an output tray  68  mounted on the top of the system. 
     In FIG. 44, it is noted that reference numeral  63  is a sheet feed cassette for storing a multiplicity of recording media P in a superposed fashion,  64  a pickup roller for feeding recording media P from the sheet feed cassette  63  one by one,  65  is a pair of gate rollers for controlling the timing of when the recording medium P is to be fed to a transfer site of the transfer roller  45  (K, C, M, Y), and  104  a sheet absorption roller for absorbing the recording medium P carried by the pickup roller  64  onto the recording medium carrier belt  30 ′. 
     Since a mono-component developing agent such as a non-magnetic mono-component toner is used, there is no need of using a carrier such as a two-component developing agent. Accordingly, it is possible to reduce the volume of each developing device  44  (K, C, M, Y) and so achieve a color image formation system of small size. 
     In such a color image formation system as constructed as explained above according to the present invention, the four photosensitive members  41 K,  41 C,  41 M and  41 Y, the corona chargers  42  (K, C, M, Y, the cleaning devices  46  (K, C, M, Y), the recording medium carrier belt  30 ′, the driving roller  10 , follower roller  20  and tension roller  21  over which the recording medium carrier belt  30 ′are spanned, the transfer rollers  45  (K, C, M, Y) for bringing the recording medium carrier belt  30 ′ in contact with the photosensitive members  41  (K, C, M, Y), the sheet absorption roller  104  for absorbing the recording medium P onto the recording medium carrier belt  30 ′ and the release roll  107  for releasing the recording medium P with a toner image carried thereon from the recording medium carrier belt  30 ′ are all constructed in the form of the integral photosensitive member cartridge  40  that can be detached from or attached to the system proper, as shown in FIGS. 44 and 45. In this case, the developing devices  44 K,  44 C,  44 M and  44 Y that are appendixes to the photosensitive members  41 K,  41 C,  41 M and  41 Y are detachable from and attachable to the photosensitive member cartridge  40 . 
     Referring to FIG. 45, the photosensitive member cartridge  40  is provided on its frame  70  with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and their appendixes, i.e., the corona chargers  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) while they are relatively positioned with respect to one another. The recording medium carrier belt  30 ′, which is spanned over the driving roller  10 , follower roller  20  and tension roller  21  and from which the recording medium P with a toner image carried thereon, is mounted together with these means on the frame  70  of the photosensitive member cartridge  40  in such a way that it comes in contact with the photosensitive members  41  (K, C, M, Y) via the transfer rollers  45  (K, C, M, Y). These members can be slid out of the system proper as shown by a double arrow. To this end, for instance, the side plate  69  of the system proper is opened outwardly, thereby defining an opening through which the photosensitive cartridge  40  is withdrawn out of the system. In the state where the photosensitive member cartridge  40  has been withdrawn out of the system proper, the photosensitive member cartridge  40  can be detached from the system and replaced by a new photosensitive member cartridge  40 . It is here noted that one side plate of the frame  70  of the photosensitive member cartridge  40  is provided with a sheet inlet  108  for feeding the recording medium P supplied by the pickup roller  64  onto the recording medium carrier belt  30 ′ and the other side plate of the frame  70  is provided with a sheet port  109  for ejecting the recording medium P with a toner image carried thereon, which is released by the release roller  107  from the recording medium carrier belt  30 ′. 
     FIG. 46 is a perspective view of the photosensitive cartridge  40  from which the developing devices  44 K,  44 C,  44 M and  44 Y are removed, and FIG. 47 is a perspective view illustrative of how the developing device  44 Y is detached from or attached to the photosensitive member cartridge  40  with the developing devices  44 K,  44 C and  44 M remaining mounted thereon. The frame  70  is in a rectangular box form, between both sides plates of which there are four photosensitive members  41 K,  41 C,  41 M and  41 Y that are positioned at a given interval and parallel with one another for rotation on their shafts  71 K,  71 C,  71 M and  71 Y. The shaft  71  (K, C, M, Y) of each photosensitive member  41  (K, C, M, Y) is provided at its one end with a gear  72  (K, C, M, Y). By way of the gear train to be referred to later, the photosensitive members  41  (K, C, M, Y) are rotatable in the (clockwise) direction indicated by the arrow in FIG. 28 at the same speed and in synchronism with one another. 
     Between the same two side plates of the frame  70 , the corona chargers  42  (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) (which, in FIG. 46, are invisible because of being concealed by the photosensitive members  41  (K, C, M, Y) and frame  70 ), all appendixes to the photosensitive members  41  (K, C, M, Y), are mounted at given positions. On one side of the side plate of the frame  70  there are provided electrodes  75  (K, C, M, Y) for applying high voltages on the discharge wires of the corona chargers or Scorotrons  42  (K, C, M, Y) and electrodes  76  (K, C, M, Y) for applying high voltages on the grits of the Scorotrons. On the same one side of the side plate of the frame  70  there are also provided electrodes  77  (K, C, M, Y) for applying developing bias voltages on the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) in the state where the developing devices  44  (K, C, M, Y) are mounted on the photosensitive member cartridge  40  and electrodes  78  (K, C, M, Y) for applying developing feed bias voltages on the feed rollers  48  (K, C, M, Y) in the same state. 
     Between both side plates of the frame  70 , the driving roller  10 , follower roller  20  and tension roller  21 , over which the recording medium carrier belt  30 ′ is spanned, are mounted parallel with one another at a given interval in such a manner that they are rotatable on shafts  22 ,  23  and  23 , and the transfer rollers  45  (K, C, M, Y), appendixes to the photosensitive members  41  (K, C, M, Y), are mounted at given positions (although not shown in FIGS.  46  and  47 ). On the same side of the side plate of the frame  70 , there are mounted electrodes  80 ′ (K, C, M, Y) for applying transfer voltages on the transfer rollers  45  (K, C, M, Y). 
     On the same side plate, there is further provided an IC  110  as memory means for storing information about the fabrication and use of the photosensitive member cartridge  40 , color misalignments, etc. Upon the photosensitive member cartridge  40  mounted on the system proper, the electrodes  75  (K, C, M, Y), electrodes  76  (K, C, M, Y), electrodes  77  (K, C, M, Y), electrodes  78  (K, C, M, Y), electrodes  80 ′ (K, C, M, Y) and IC  110  are automatically connected to the power source circuit and control circuit of the system proper. In this state, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are also automatically connected to ground for earth purposes. 
     At the inner upper sides of the same two side plates of the frame  70 , there are provided guide grooves  73  (K, C, M, Y) for receiving the developing devices  44  (K, C, M, Y) at constant positions corresponding to the photosensitive members  41  (K, C, M, Y). To fix the developing devices  44  (K, C, M, Y) received along the guide grooves  73  (K, C, M, Y), fixing levers  74  (K, C, M, Y) are pivotally provided. On both sides of the developing cartridge  47  (K, C, M, Y) of each developing device  44  (K, C, M, Y), there are guide ridges  79  (K, C, M, Y) that are to be inserted in the associated guide grooves  73  (K, C, M, Y) from the upper open ends thereof (see FIG. 47 where only one guide ridge  79 Y of the developing cartridge  47 Y is visible). To mount the developing devices  44  (K, C, M, Y) on the associated photosensitive members  41  (K, C, M, Y), the guide ridges  79  (K, C, M, Y) are inserted from above into the associated guide grooves  73  (K, C, M, Y) and the fixing levers  74  (K, C, M, Y) are then pivoted to fix the developing devices in place. To remove the developing cartridges  47  (K, C, M, Y) for replacement or other purposes, the fixing levers  74  (K, C, M, Y) are pivoted back to guide the developing cartridges  47  (K, C, M, Y) upward along the guide grooves  73  (K, C, M, Y). 
     According to the embodiment of FIG. 47, the developing cartridges  47  (K, C, M, Y) forming part of the individual developing devices  44  (K, C, M, Y) can separately be attached to or detached from the associated photosensitive members  41  (K, C, M, Y); of the developing devices  44  (K, C, M, Y), only an exhausted or dead developing device(s) can be replaced with no wasteful replacement of the rest, so that running cost reductions are achievable. 
     FIG. 48 is a perspective view illustrative of the attachment/detachment mechanism for an embodiment of the invention wherein four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are constructed in the form of the integral development cartridge  47  for such a photosensitive member cartridge  40  as described above. In this embodiment, only one pair of guide grooves  73  are provided at the inner upper sites of both side plates of the frame  70  of the photosensitive member cartridge  40 , spanning between both side plates. Accordingly, only one pair of pivotal fixing levers  74  are provided. On the other hand, the four developing devices  44  (K, C, M, Y) are constructed in the form of the integrated single developing cartridge  47 . On each side of the developing cartridge  47  there is mounted a guide ridge  79  that is to be inserted into the associated guide groove  73  from the upper open end thereof (in FIG. 48, one guide ridge  79  alone is visible). To mount the developing cartridge  47  on the photosensitive member cartridge  40 , the guide ridges  79  are inserted from above into the guide grooves  73  and the fixing levers  74  are then pivoted to fix the developing cartridge in place. To remove the developing cartridge  47  for replacement or other purposes, the fixing levers  47  are pivoted back so that the developing cartridge  47  can be guided upward along the guide grooves  73 . 
     The embodiment of FIG. 48, wherein the four or black, cyan, magenta and yellow developing devices  44  (K, C, M, Y) are designed as the integral developing cartridge  47 , has the merit of reducing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. 
     FIG. 49 is a perspective view illustrative of the attachment/detachment mechanism for such a photosensitive member cartridge  40  as described above, wherein a black developing device  44 K is constructed in the form of one single developing cartridge  47 K that is detachable from or attachable to a black photosensitive member  41 K as is the case with FIG. 46 or FIG. 47, and three or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of an integral developing cartridge  47 YMC. At the inner upper sites of both side plates of a frame  70  of the photosensitive member cartridge  40  there are provided guide grooves  73 K for receiving the developing cartridge  47 K between both side plates and guide grooves  73 YMC for receiving the developing cartridge  47 YMC, and there are provided pivotal fixing levers  74 K and  74 YMC, accordingly. On the other hand, the black photosensitive member cartridge  40  is provided on both its sides with guide ridges  79 K and the three-color developing cartridge  47 YMC is provided on both its sides with guide ridges  79 YMC (in FIG. 49, only one guide ridge  79 YMC is visible on the developing cartridge  47 YMC). To mount the developing cartridge  47 K or  47 YMC on the photosensitive member cartridge  40 , the guide ridges  79 K or  79 YMC are inserted from above into the guide grooves  73 K or  73 YMC, whereupon the fixing levers  74 K or  74 YMC are pivoted to fix the developing cartridge in place. To remove the developing cartridge  47 K or  47 YMC for replacement or other purposes, the fixing levers  74 K or  74 YMC are pivoted back so that the developing cartridge  47 K or  47 YMC can be guided upward along the guide grooves  73 K or  73 YMC. 
     The embodiment of FIG. 49, wherein the three-color or cyan, magenta and yellow developing devices  44  (C, M, Y) are constructed in the form of the integral developing cartridge  47 YMC, has the merit of removing the number of consumable parts, thereby improving the integrity of maintenance and avoiding a risk of anything wrong happening upon mounting. This embodiment has another merit of preventing the three-color or cyan, magenta and Y developing devices  44  (C, M, Y) from going to waste, because the black developing device  44 K most frequently used in general can be replaced in the form of the independent developing cartridge  47 K. 
     Next, an account is given of the mechanism of, upon the photosensitive member cartridge  40  mounted on the system proper, rotating and carrying the photosensitive members  41 K,  41 C,  41 M and  41 Y in the cartridge  40  in synchronism with one another, thereby preventing any color misalignment. FIG. 50 is illustrative of one construction for achieving this. As already mentioned, the shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) are mounted at their one ends with gears  72 K,  72 C,  72 M and  72 Y, respectively, which are molded using the same mold. An idle gear  81  is interposed between the gears  71 K and  72 C, an idle gear  82  between the gears  72 C and  72 M, and an idle gear  83  between the gears  72 M and  72 Y, forming a gear train for transmission of rotational force. The driving roller  10  is provided at its one end with a gear  97  rotating around a shaft  22 , and the gear  97  meshes with the gear  72 Y for rotating the photosensitive member  41 Y via two gears  98  and  99 . The gears  72 K,  81 ,  72 C,  82 ,  72 M,  83 ,  72 Y,  99 ,  98  and  97  thus form a series of gear train. A driving gear  91  in mesh with one gear in this gear train, for instance, gear  97 , is disposed at a driving source  90  on the side of the system proper, so that upon the photosensitive cartridge  40  mounted at a given position of the system proper, the driving gear  91  meshes with the gear  97 . 
     On the other hand, the shaft of the developing roller  49  (K, C, M, Y) of the developing device  44  (K, C, M, Y) is fixedly provided at its one end with a developing roller gear  84  (K, C, M, Y), and the shaft of the feed roller  48  (K, C, M, Y) is fixedly provided at its one end with a feed roller gear  85  (K, C, M, Y). An idle roller  86  (K, C, M, Y) is interposed between the developing roller gear  84  (K, C, M, Y) and the feed roller gear  85  (K, C, M, Y). The developing roller gear  84  (K, C, M, Y) meshes with the gear  72  (K, C, M, Y) of the photosensitive member  41  (K, C, M, Y), so that the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y), too, can be rotationally driven in synchronism with the rotation of the photosensitive member  41  (K, C, M, Y). 
     By rotating the driving gear  91  of the driving source at one site on the side of the system proper according to this arrangement, it is possible to rotationally drive the four photosensitive members  41  (K, C, M, Y) and the appendixes thereto, i.e., the developing rollers  49  (K, C, M, Y) and feed rollers  48  (K, C, M, Y) of the developing devices  44  (K, C, M, Y), all in synchronism with one another. 
     It is here desired that the diameter of the driving roller  10  be set in such a way to give a speed difference of 1 to 5% between the delivery speed of the recording medium carrier belt  30 ′ by the driving roller  10  and the peripheral speed of the photosensitive member  41  (K, C, M, Y). With such a speed difference between the photosensitive member  41  (K, C, M, Y) and the recording medium carrier belt  30 ′, it is possible to increase the efficiency of transfer because the toner can be mechanically moved upon transfer of the toner image. 
     When only the image carriers (photosensitive members) are replaced as is the case with the prior art, there is a fluctuation of the periphery speed of the image carriers with errors in image carrier shape, which in turn results in a change in the speed difference with the recording medium carrier belt  30 ′. The fluctuations in the speed difference offer some problems; too small a speed difference renders the efficiency of transfer low whereas too large a speed difference causes deterioration in image quality. Therefore, if the photosensitive members  41  (K, C, M, Y) and recording medium carrier belt  30 ′ are integrated with the photosensitive member cartridge  40  as contemplated herein, it is then possible to reduce the fluctuations in the speed difference between the photosensitive members  41  (K, C, M, Y) and the recording medium carrier belt  30 ′ as by determining the shape of the driving roll  10  in conformity with the shape of the photosensitive member  41  (K, C, M, Y). It is thus possible to provide an imaging system with improved transfer efficiency yet with no deterioration in image quality. 
     Such an embodiment as shown in FIG. 50 ensures that the operating efficiency of attachment/detachment of the photosensitive member cartridge  40  is improved because the point of meshing of the gears for transmission of driving force upon attachment/detachment of the photosensitive member cartridge  40  is limited to one. Since the positioning criterion for the photosensitive member cartridge  40  is defined by this driving force transmission gear  91 , it is also possible to improve the precision of meshing and, hence, provide a system for forming high-quality images that are substantially free from any color misalignment or any banding (variations in densities, etc. at right angles with the feed direction). 
     It is understood that the mechanism for synchronized transmission of rotational force for the photosensitive members  41 K,  41 C,  41 M and  41 Y is not limited to such a gear train as shown, and so may be constructed using a belt or chain, for instance. 
     FIG. 51 is illustrative of one modification to the embodiment of FIG.  50 . In this modification, the driving gear  91  of the driving source  90  (FIG. 50) on the side of the system proper is designed to mesh with the gear  72 K in the gear train comprising the gears  72 K,  81 ,  72 C,  82 ,  72 M,  83 ,  72 Y,  99 ,  98  and  97 , so that the recording medium carrier belt  30 ′ as well as the four photosensitive members  41  (K, C, M, Y) and their appendixes, i.e., the developing rollers  49  (K, C, M, Y) and feed rollers  48  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) are all rotationally driven. Otherwise, the construction of FIG. 51 is the same as that of FIG.  55 . 
     FIGS. 52 and 53 are illustrative of an embodiment of the invention, wherein the photosensitive member cartridge  40  is mounted on the system proper and the photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40 , the recording medium carrier belt  30 ′ and the developing devices  44  (K, C, M, Y) are driven by means of separate driving sources. FIG. 52 is similar to FIG.  50 . In this embodiment, the developing roller gears  84  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) are not in mesh with the gears  72  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y) or separated therefrom, as can be seen from FIG.  52 . The embodiment of FIG. 52 is different from that of FIG. 50 only in terms of the gear train of the photosensitive member cartridge  40 . By rotating the driving gear  91  of the driving source  90  on the side of the system proper, the recording medium carrier belt  30 ′ and the four photosensitive members  41  (K, C, M, Y) can thus be rotationally driven in synchronism, as can be see from FIG.  52 . 
     Although depending on the driving force of that driving source  90 , however, the developing roller  49  (K, C, M, Y) and feed roller  48  (K, C, M, Y) of the developing device  44  (K, C, M, Y) are kept from rotation. In this embodiment, there is another driving source  100  at another site on the side of the system proper, as shown in FIG.  53 . When the photosensitive member cartridge  40  is mounted at a given position of the system proper, four gears  101  (K, C, M, Y) of the separate driving source  100 , designed to rotate in synchronism and in the same direction, are positioned in such a way that they mesh with the developing roller gears  84  (K, C, M, Y) fixed at one ends of the shafts of the developing rollers  49  (K, C, M, Y) of the developing devices  44  (K, C, M, Y) mounted on the photosensitive member cartridge  40 . Thus, the developing devices  44  (K, C, M, Y) are rotationally driven by the driving source  100  that is separate from that for the photosensitive members  41  (K, C, M, Y). 
     In such an arrangement as shown in FIG. 44, color misalignments and image banding are largely dependent on the precision of rotation of the image carriers and recording medium carrier belt; however, they are less dependent on the precision of rotation of the developing rollers. Therefore, if the driving source  90  for the recording medium carrier belt  30 ′ and photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40  is made separate from the driving source  100  for the developing devices  44  (K, C, M, Y) as shown in FIGS. 52 and 53, it is then possible to prevent rotation variations caused as by fluctuations in the torque of developing means from having influences on the rotation of the image carriers and, hence, provide a system for forming high-quality images with neither color misalignments nor image banding. 
     In the construction of FIGS. 52 and 53, too, it is acceptable to engage the driving gear  91  of the driving source  90  on the side of the system proper with the gear  72 K in the gear train comprising the gears  72 K,  81 ,  72 C,  82 ,  72 M,  83 ,  72 Y,  99 ,  98  and  97  as shown in FIG. 51, thereby rotationally driving the recording medium carrier belt  30 ′ and the four photosensitive members  41  (K, C, M, Y) in synchronism with one another. 
     FIG. 54 is illustrative of one embodiment of the mechanism for adjusting color misalignments occurring due to position misalignments between the photosensitive members  41 K,  41 C,  41 M and  41 Y of such a photosensitive member cartridge  40 , especially skews in parallelism, when four different monochromatic toner images are transferred onto the recording medium P absorbed onto the recording medium carrier belt  30 ′ in a superposed fashion. As shown in FIG. 54, while the shaft  51  (K, C, M, Y) of each transfer roller  45  (K, C, M, Y) extending from one side plate of the frame  70  is sandwiched between an adjustment screw  105  and the leading end of an extensible spring  106 , the other end of the extensible spring  106  is fixed to the side plate  70 . In this state, if the leading end of the adjustment screw  105  is adjustable in the direction opposite to the direction of extension of the extensible spring  106  to adjust the position of one end of the shaft  51  (K, C, M, Y), there are then changes in the transfer positions of the transfer rollers  45 K,  45 C,  45 M and  45 Y. Since there is such a speed difference as mentioned above between the recording medium carrier belt  30 ′ and the photosensitive members  41  (K, C, M, Y), changes in the primary transfer positions cause changes in the transfer positions on the recording medium P absorbed onto the recording medium carrier belt  30 ′ for the toner images of the corresponding colors; that is, color misalignments can be regulated. It is not always required to provide all the four photosensitive members  41 K,  41 C,  41 M and  41 Y with such color misalignment adjustment mechanisms. It is noted that it is acceptable to provide the opposite ends of the shafts  51  (K, C, M, Y) with such color misalignment adjustment mechanisms. However, this is not always necessary because misalignments can be electrically eliminated by controlling the timing of when color latent images formed on the photosensitive members  41  (K, C, M, Y) are to be written, as long as given parallelism is maintained between the photosensitive members  41  (K, C, M, Y). 
     It is here understood that color misalignments may also be regulated by providing similar adjustment mechanisms on the respective shafts  71  (K, C, M, Y) of the photosensitive members  41  (K, C, M, Y). 
     By providing the photosensitive member cartridge  40  with the position alignment mechanism for the transfer rollers  45  (K, C, M, Y) or the photosensitive members  41  (K, C, M, Y) in this way, it is possible to make fine adjustments of the positions of the photosensitive members  41  (K, C, M, Y) onto which latent images are to be written and transferred, thereby reducing color misalignments. It is here noted that the color misalignment adjustment by this color (position) misalignment adjustment mechanism may be made upon shipment of the photosensitive member cartridge  40  or anytime after its attachment to the system proper. 
     Referring now to an electrographic system wherein latent images formed on image carriers are toner developed and the resulting toner images are transferred onto transfer media, there is a so-called “cleaner-less” mode wherein the remnants of toner untransferred onto the image carriers are recovered at developing devices without recourse to such cleaning devices as shown in FIG. 44 (for instance, see JP-B 06-77166). This “cleaner-less” mode is embodied as shown in FIG. 55, dispensing with the cleaning devices  46  (K, C, M, Y) of FIG.  44 . The embodiment of FIG. 55 is the same in construction as that of FIG. 44 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); any detailed account of its construction and action is not given. The construction of the photosensitive member cartridge  40  in this embodiment, too, is the same as that of FIGS. 44 and 45 with the exception of the absence of the cleaning devices  46  (K, C, M, Y); four photosensitive members  41 K,  41 C,  41 M and  41 Y, corona chargers  42  (K, C, M, Y) disposed around the same and an recording medium carrier belt  30 ′ are constructed in an integral form. 
     By use of the mode that dispenses with any cleaning device, it is possible to reduce the size of the photosensitive member cartridge  40  and the system proper. In addition, it is possible to diminish reaction force that may otherwise act on the photosensitive members  41  (K, C, M, Y) through the blades, etc. of cleaning devices, resulting in prevention of color misalignments. This is because the frame  70  is kept from deformation so that any position misalignment between the photosensitive members  41  (K, C, M, Y) can be avoided. 
     FIG. 56 is a view similar to FIG. 44, showing another embodiment of the invention. In this embodiment, no single exposure unit  43  is used unlike the embodiment of FIG.  44 . An exposure device  43 ′ (K, C, M, Y) for performing selective exposure per color, corresponding to each photosensitive member  41  (K, C, M, Y), is integrated with a photosensitive member cartridge  40  between a corona charger  42  (K, C, M, Y) and a developing device  44  (K, C, M, Y). In accordance with this embodiment, the photosensitive member cartridge  40  is provided at its frame  70  with four photosensitive members  41 K,  41 C,  41 M and  41 Y and their appendixes, i.e., corona chargers  42  (K, C, M, Y), exposure devices  43 ′ (K, C, M, Y) and cleaning devices  46  (K, C, M, Y) while they are relatively positioned. An recording medium carrier belt  30 ′ spanned and endlessly driven over a driving roller  10 , a follower roller  20  and a tension roller  21  is attached together with these means to the frame  70  of the photosensitive member cartridge  40  in such a way that it comes into contact with the respective photosensitive members  41  (K, C, M, Y) through transfer rollers  45  (K, C, M, Y). 
     In this embodiment, the exposure unit  43  is dispensed with. Thus, the photosensitive member cartridge  40  can be withdrawn from the system proper by lifting it substantially upward. 
     With such an arrangement wherein the exposure devices  43 ′ (K, C, M, Y), photosensitive members  41  (K, C, M, Y), recording medium carrier belt  30 ′ and transfer rollers  45  (K, C, M, Y) are constructed in the form of the integral photosensitive cartridge  40 , it is possible to adjust nearly all of color misalignment factors at its production stage, thereby providing a system for the formation of images of high quality. 
     In the embodiment of FIG. 56, the frame  70  of the photosensitive member cartridge  40  is provided with the four photosensitive members  41 K,  41 C,  41 M and  41 Y and the appendixes thereto, i.e., the corona chargers  42  (K, C, M, Y), the exposure devices  43 ′ (K, C, M, Y), the cleaning devices  46  (K, C, M, Y), the recording medium carrier belt  30 ′, the driving roller  10 , follower roller  20  and tension roller  21  over which the recording medium carrier belt  30 ′ is spanned, the transfer rollers  45  (K, C, M, Y) for bringing the recording medium carrier belt  30 ′ in contact with the photosensitive members  41  (K, C, M, Y), the sheet absorption roller  104  for absorbing the recording medium P onto the recording medium carrier belt  30 ′ and the release roller  107  for releasing the recording medium P with a toner image carried thereon from the recording medium carrier belt  30 ′ while they are relatively positioned. FIG. 42 is illustrative of one embodiment of how the exposure devices  43 ′ (K, C, M, Y) are attached to the frame  70  of the photosensitive member cartridge  40 . To be specific, FIG. 42 is a partly enlarged perspective view of only one end portions of the photosensitive members  41 Y and  41 M in the photosensitive member cartridge  40 . To mount the exposure devices  43 ′ (K, C, M, Y) at precisely located positions on the associated photosensitive members  41  (K, C, M, Y) and parallel therewith, mounting struts  111  (K, C, M, Y) are integrally provided, extending from the inside surfaces of both side plates of the frame  70  and opposing to each other. Each strut  111  (K, C, Y, M) is provided with locating holes for receiving locating pins and threaded holes, both holes not shown. Locating pins  115  provided at both ends of a long-length substrate  113  (FIG. 22) of each exposure device  43 ′ (K, C, M, Y) are inserted into the locating holes in the associated mounting strut  111  (K, C, M, Y) while fixing screws  112  (K, C, M, Y) are fixedly screwed into the threaded holes in the mounting strut  111  (K, C, M, Y) through screw-insertion holes in both ends of the long-length substrate  113  (FIG.  22 ), so that the each exposure device  43 ′ (K, C, M, Y) is fixed in place. 
     FIG. 22 is a perspective schematic of each exposure device  43 ′ (K, C, M, Y) constructed in the form of an LED line head comprising an LED array  116 . As mentioned above, each exposure device  43 ′ (K, C, M, Y) is mounted on the long-length substrate  113 , spanning between both side plates of the frame  70 . The LED array  116  for forming a line image on the photosensitive member  41  (K, C, M, Y) and parallel with its axis is mounted on the long-length substrate  113 , with each LED connected to a driver IC  117  for controlling light emission. The long-length substrate  113  is provided at each end with a locating pin  115  for the determination of a mounting position and a hole  114  for the insertion of a mounting screw. Thus, each exposure device is fixed at a precise position for the associated photosensitive member  41  (K, C, M, Y). In front of the LED array  116  there is integrally fixed a gradient index type rod lens array  118  having an image-formation action, by which a train of light emission points defined by the LED array  116  is allowed to form an image on the photosensitive surface of the associated photosensitive member  41  (K, C, M, Y). 
     FIG. 57 is illustrative of one embodiment of the mechanism for adjusting color misalignments occurring due to relative position misalignments between the exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y positioned and mounted on the photosensitive members  41  (K, C, M, Y) of the photosensitive member cartridge  40  of FIG. 56, especially skews in parallelism, when four different monochromatic toner images are transferred onto the recording medium P absorbed onto the recording medium carrier belt  30 ′ in a superposed fashion. As shown in FIG. 57, while the mounting ridge  111  (K, C, M, Y) of each exposure device  43 ′ (K, C, M, Y) extending from one side plate of the frame  70  or a long-length substrate  113  is sandwiched between an adjustment screw  105  and the leading end of an extensible spring  106 , the other end of the extensible spring  106  is fixed to the side plate  70 . In this state, if the leading end of the adjustment screw  105  is adjustable in the direction opposite to the direction of extension of the extensible spring  106  to adjust the position of one end of the exposure device  43 ′ (K, C, M, Y), it is then possible to adjust skews in parallelism between the exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y. It is not always required to provide all the four exposure devices  43 ′K,  43 ′C,  43 ′M and  43 ′Y with such color misalignment adjustment mechanisms. It is noted that it is acceptable to provide the opposite ends of the exposure devices  43 ′ (K, C, M, Y) with such color misalignment adjustment mechanisms. However, this is not always necessary because misalignments can be electrically eliminated by controlling the timing of when color latent images formed at the exposure devices  43 ′ (K, C, M, Y) are to be written, as long as given parallelism is maintained between the exposure devices  43 ′ (K, C, M, Y). 
     By providing the photosensitive member cartridge  40  with the position alignment mechanism for the exposure devices  43 ′ (K, C, M, Y) in this way, it is possible to make fine adjustments of the positions of the photosensitive members  41  (K, C, M, Y) onto which latent images are to be written and transferred, thereby reducing color misalignments. It is here noted that the color misalignment adjustment by this color (position) misalignment adjustment mechanism may be made upon shipment of the photosensitive member cartridge  40  or anytime after its attachment to the system proper. 
     In the embodiment of FIG. 56, the write means that are integrally mounted together with the photosensitive members  41  (K, C, M, Y) and recording medium carrier belt  30 ′ on the photosensitive member cartridge  40  are not necessarily limited to such optical write means as shown in FIG.  22 . For instance, it is acceptable to make use of write means having recourse to charge transfer such as injection or elimination of charges, for instance, those proposed by the applicant in Japanese Patent Application Nos. 2000-298925 and 2000-298927, etc. FIG. 27 is a front schematic illustrative of the whole construction of a color image formation system wherein charge injection electrode line heads  3  (K, C, M, Y) are used as write means, and FIG. 27 is a perspective schematic illustrative of how the charge injection electrode line heads  3  (K, C, M, Y) are arranged and constructed with respect to photosensitive members  41  (K, C, M, Y). When writing is carried out by the injection of charges, it is not always necessary to use the chargers  42  (K, C, M, Y) of FIG.  40 . The charge injection electrode line head  3  (K, C, M, Y) comprises an array of electrodes  3   b  that come in contact with the associated photosensitive member  41  (K, C, M, Y) to create a potential profile therein and so form a latent image. Charges injected into each electrode  3   b  are controlled by a driver IC 119 . 
     In accordance with the inventive color image formation system wherein, as explained above, a plurality of photosensitive members  41  (K, C, M, Y) and the recording medium carrier belt  30 ′ are mutually positioned and mounted on a photosensitive member cartridge  40  detachable from and attachable to the system proper and developing devices  44  (K, C, M, Y) are disposed in such a way as to be detachable from and attachable to the photosensitive members  41  (K, C, M, Y) mounted on the photosensitive member cartridge  40 , the precision of relative positions between the photosensitive members is so improved that color misalignments ascribable to misalignments between the photosensitive members and skews thereof can be prevented. 
     Gears can be associated with the photosensitive members in such phase relations as to reduce speed fluctuations due to the gears that drive the photosensitive member, so that the cartridge  40  can be constructed in an integral form. In addition, color misalignments due to the photosensitive member-driving gears can be considerably reduced (FIG.  50  and so on). Where the photosensitive members are individually mounted on the system proper, it is impossible to make phase adjustments of such gears because the photosensitive members rotate by themselves. 
     Further, the photosensitive member cartridge  40  can be finished up using photosensitive members of uniform performance singled out at the time of shipping, so that color changes due to variations in the properties of the photosensitive members of different colors can be prevented. In addition, the integrity of maintenance can be improved because a plurality of photosensitive members can be replaced at the same time. 
     Furthermore, the arrangement wherein the developing devices  44  (K, C, M, Y) are designed as detachable from and attachable to the photosensitive member cartridge  40  ensures that the developing devices  44  (K, C, M, Y) can be replaced independently of the photosensitive member cartridge  40 . Therefore, even when the developing devices  44  (K, C, M, Y) are exhausted or used up and so must be replaced with new ones, there is no need of making a replacement for the photosensitive members  41  (K, C, M, Y), so that running cost reductions are achievable. 
     What is necessary when the developing devices  44  (K, C, M, Y) are used up is only their replacement. There is no need of any color matching operation depending on the positions and configuration of the photosensitive members  41  (K, C, M, Y) and write means  43 ′ (K, C, M, Y) or  3  (K, C, M, Y). It is thus possible to provide an image formation system having improved operating efficiency. 
     For replacement of the developing devices  44  (K, C, M, Y), only the withdrawal of the photosensitive member cartridge  40  is needed. Then, new developing devices are attached to the photosensitive member cartridge  40 . Thus, the operation for replacement of the developing devices  44  (K, C, M, Y) is so facilitated that the integrity of maintenance can be improved. 
     It is also acceptable to construct a plurality of photosensitive members  41  (K, C, M, Y) in the form of one single replacement and the developing devices  44  (K, C, M, Y) in the form of one single replacement  47  (FIG.  48 ), so that the integrity of maintenance can be much more improved. 
     While the color image formation systems of the present invention has been explained with their embodiments, it is understood that the present invention is not limited to these embodiments and so many modifications may be possible. 
     As can be appreciated from the foregoing, the first aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. Thus, the precision of relative positions of the image carriers is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means re replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     The second aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge, and write means are located and mounted at positions of said image carrier cartridge corresponding to a plurality of image carriers. Thus, the precision of relative positions of the image carriers and write means is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers and write means can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means re replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     The third aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper, an intermediate transfer belt is mounted contiguously to said plurality of image carriers, and developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. Thus, the precision of relative positions of the image carriers, and the precision of transfer positions is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers and transfer position misalignments can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means re replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved. 
     The fourth aspect of the present invention provides a system for forming color images, wherein a plurality of image carriers are mounted on an image carrier cartridge detachable from or attachable to a system proper while they are mutually positioned, and developing means is provided in such a way as to be detachable from or attachable to each image carrier mounted on said image carrier cartridge. Thus, the precision of relative positions of the image carriers is so improved that any misalignments ascribable to position and parallelism misalignments of the image carriers can be prevented. Since a plurality of image carriers can be replaced at the same time, the integrity of maintenance of the system can be improved. The developing means and the image carrier cartridge can be independently replaced so that running cost reductions are achievable because even when used-up developing means re replaced, there is no need of replacing the image carriers. For replacement of used-up developing means, their replacement alone is needed and so there is no need of color matching depending on the positions and shape of the image carriers. Thus, the system for forming color images according to this aspect can have high efficiency of operation. For replacement of the developing means, only the withdrawal of the image carrier cartridge from the system proper is needed, followed by detachment of used-up developing means and attachment of new one. Thus, the operation for replacement of the developing means is so facilitated that the integrity of maintenance of the system can be improved.