Color electrophotographic apparatus

Abstract: A color electrophotographic apparatus arranged as follows is disclosed. A plurality of image forming units (1BK, 1C, 1M, 1Y) each including a developing device having an electrostatic latent image holding member and toner of a different color are employed. Each of the image forming units is arranged to be displaceable so as to be moved to the same image forming position (50) for positioning. At the image forming position (50), the image forming unit is exposed to light image by an exposure device for image formation, with its toner image being transferred onto a transfer material through a confronting transfer transport device (31). The image forming unit at the image forming position (50) is sequentially exchanged, and by the reciprocation of the transfer material through the transfer/transport device (31), toner images of respective colors are transferred,as overlapped through positioning for coincidence, onto the same transfer material.

Description: The present invention relates to a color electrophotographic apparatus comprising a plurality of movable image forming means each provided with a rotatable photosensitive member, a charger for charging said photosensitive member, a developing material hopper for storing toner in different color, a developing means for developing a latent toner image on said photosensitive member by said toner, and a cleaner for cleaning said photosensitive member, thereby to form toner images in different colors respectively on said photosensitive member. Furthermore, the electrophotographic apparatus comprises transfer and transport means capable of supporting thereon a transfer material for reciprocating motion, an exposure means for effecting image exposure, and displacing means for successively displacing in a linear manner each of said plurality of image forming means. Such color electrophotographic apparatus may be particularly applied to a color copying apparatus, color printer or the like. Generally, for forming a color image by electrophotography, it has been a practice to form a color image by overlapping toner images of yellow, magenta, cyan and black respectively on a transfer material. As the method for effecting the overlapping of such toner images over the transfer material, there have been generally employed a transfer drum system (JP-A-62 287 264) in which the transfer material wound on a transfer drum is rotated and repeatedly brought into the same image forming position, whereat toner images of respective colors successively formed are overlapped for transfer, and a continuous transfer system wherein a plurality of image forming sections are disposed side by side, and the transfer material transported by a transport belt or the like (US-A-4 905 048) is caused to pass through the transfer position of each image forming section, thereby to successively transfer and overlap the toner image of the respective colors to obtain the colored image. A further example of a color image forming apparatus employing a transfer drum system is disclosed in JP-A-1252982. Furthermore, another example of a color electrophotographic apparatus based on the continuous transfer system is disclosed in JP-A-216580. Finally, EP-A-552 410, an application to be considered under Article 54 (3) EPC, shows a color electrophotographic apparatus comprising a plurality of movable image forming means, a transfer and transport means, an exposure means and displacing means, of the kind as described at the beginning of the description. It is an object of the present invention to provide a color electrophotographic apparatus comprising a plurality of movable image forming means which are successively displaced in a linear manner, which is compact in size as a whole inspite of increase of the capacity of the developing material hopper of each image forming unit, while the construction of the image forming unit including a photosensitive drum and developing unit is simple for easy replacement. In accordance with the invention, a color electrophotographic apparatus is structured as defined in claim 1, i.e. part of the developing material hopper of the image forming means is arranged to utilize a space above the charger and/or the cleaner of the neighboring image forming means. A preferable embodiment is characterized by said developing material hopper being wider at its upper part than at its lower part adjacent the charger and/or the cleaner. Another preferable embodiment is defined by said image forming means being of a shape which can be taken out slantwise in upward direction. Preferably, each of said image forming means has a side elevational shape generally in the form of a parallelogram. These and other features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which; Fig. 1 is a schematic side sectional view showing construction of a color electrophotographic apparatus, Fig. 2 is a schematic side sectional view showing on an enlarged scale, an image forming unit which is employed in the color electrophotographic apparatus of Fig. 1, Fig. 3 is a schematic side sectional view showing construction of a color electrophotographic apparatus according to an embodiment of the present invention, Fig. 4 is a schematic side sectional view of an image forming unit for a first example which may be employed in the color electrophotographic apparatus of Fig. 3, Fig. 5 is a schematic side sectional view of an image forming unit for a second example which may be employed in the color electrophotographic apparatus of Fig. 3, Fig. 6 is a schematic side sectional view of an image forming unit for a third example which may be employed in the color electrophotographic apparatus of Fig. 3, Fig. 7 is a schematic side sectional view showing construction of a color electrophotographic apparatus according to a further embodiment of the present invention, and Fig. 8 is a schematic side sectional view of an image forming unit which is employed in the color electrophotographic apparatus of Fig. 7. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. In Fig. 1, there is shown a color electrophotographic apparatus C1 mainly used with respect to a printer section for the image formation. In the first place, at the printer section, image forming units 1BK, 1C, 1M, and 1Y as four sets of image forming means for black, cyan, magenta and yellow are disposed side by side. Since the respective image forming units are constituted by the same members except for the developing materials accommodated therein, description will be given only with respect to the image forming unit 1M for magenta, and description for other image forming units is omitted for brevity of explanation, with like parts being designated by like reference numerals, and in the case where it is necessary to distinguish the construction of the unit for each color, symbols representing respective colors will be affixed to numerals. Fig. 2 shows the construction of the image forming unit 1M for magenta in detail. The image forming unit 1M includes a developing material hopper 14 containing a two-component developing material 26M, a photosensitive drum 9 having an organic photosensitive layer 9a on its outer peripheral surface and rotatably provided at the lower portion of the hopper 14, and a magnet 10 fixedly mounted on a shaft rotatably supporting the photosensitive drum 9. It is to be noted that although the photosensitive drum 9 is rotated around said shaft, the magnet 10 is fixed together with said shaft. Around the photosensitive layer 9a, there are sequentially disposed various processing devices such as a corona charger 11 for negatively charging the photosensitive layer 9a through a grid electrode 12 for controlling charge potential of the photosensitive layer 9a to be subjected to a laser beam scanning light 13, a collecting electrode roller 17 of aluminum rotatably provided adjacent to the photosensitive drum 9 and connected to an A.C. high voltage source 18 so as to be applied with a voltage thereby, an unrotatable magnet 16 coaxially fixed within said collecting electrode roller 17, a scraper 19 of a polyester film provided to scrape off toner on the surface of the roller 17, and a cleaner 27 for cleaning toner remaining on the photosensitive layer 9a after transfer. The organic photosensitive material layer 9a is prepared by dispersing phthalocyanin into polycarbonate group binder resin. The two-component developing material 26M is produced by mixing ferrite carrier 24M with particle diameter of 50µm coated on the surface by silicone, and toner 25M for attraction onto the surface of the photosensitive layer 9a by a magnetic force, while the toner 25M is prepared by dispersing a pigment in a polyester resin, with further addition of an additive thereto. Magnetic flux densities on the surface of the photosensitive material layer 9a and the collecting electrode roller 17 are respectively 800 gauss at maximum positions. The photosensitive drum 9 has a diameter of 30mm and is rotated in a direction indicated by an arrow at a circumferential speed of 120mm/sec., while the collecting electrode roller 17 has a diameter of 16mm, and is rotated in a direction of an arrow at a circumferential speed of 100mm/sec. By the above arrangement, the photosensitive layer 9a of the photosensitive drum 9 was charged to -500V by the corona charger 11, with an applied voltage at -5kV, and a voltage for the grid 12 at -500V. The laser beam scanning light 13 was projected onto the photosensitive layer 9a thus charged, thereby to form an electrostatic latent image thereon. At this time, the exposure potential for the photosensitive layer 9a was -100V. Onto the surface of the photosensitive layer 9a, the two-component developing material 26M was caused to adhere within the developing material hopper 14 by magnetic force. Subsequently, the photosensitive layer 9a was passed before the electrode roller 17 through rotation of the photoreceptor drum 9. During passing of the uncharged region of the photosensitive layer 9, an A.C. voltage (frequency 1kHz) of 750Vo-p (peak to peak 1.5kV) superposed with a D.C. voltage of 0V was applied to the electrode roller 17 by the A.C. high voltage source 18. Thereafter, during passing of the photosensitive layer 9a charged to -500V and written with the electrostatic latent image, an A.C. voltage (frequency 1kHz) of 750Vo-p (peak to peak 1.5kV) superposed with a D.C. voltage of -350V was applied to the electrode roller 17 by the A.C. high voltage source 18. Then, the toner attracted onto the carrier and the charged portion on the photosensitive layer 9a was collected by the electrode roller 17, and the toner image subjected to negative-positive inversion only at image portion was left on the photosensitive layer 9a. The carrier and toner adhering to the electrode roller 17 rotating in the direction of the arrow was scraped off by the scraper 19 and returned into the developing material hopper 14 again for use in the subsequent image formation. In the manner as described so far, the toner image in the magenta color is obtained on the photosensitive surface 9a. Each of the image forming units 1BK, 1C and 1Y other than the unit 1M also has a similar constructions and functions as described so far. Referring back to Fig. 1, the construction of the printer section will be described hereinbelow. The image forming units 1BK, 1C, 1M and 1Y disposed side by side are supported by a support member, and are displaceable as a whole in lateral direction (indicated by arrow X) by a motor 30 as a displacing means, and each of the image forming units 1BK to 1Y may be sequentially positioned in the vicinity of an image forming position 50 where the image forming unit 1BK is located in Fig. 1. This position confronts the transfer section 33 generally at a central portion of the transfer/transport belt 31. At the transfer section 33, the transfer/transport belt 31 is somewhat raised by a belt restricting member 32 as compared with other flat portion thereof, and is accurately restricted in its position. Fig. 1 shows the state where the image forming unit 1BK for black is brought into the position close to the image forming position 50, and the state before it is positioned at the image forming position. Upon positioning from the above state as described earlier, the image forming unit 1BK is lowered downwardly to a slight extent so that the photosensitive drum contacts the transfer/transport belt 31 to be described later. In the position above the group of the image forming units, there is provided a laser exposure device 3 which emits the laser beam scanning light 13 as modulated by the signal inputted to the printer section, and the laser beam 13 thus produced is reflected by mirrors 4 and 5 so as to be projected onto the photosensitive layer 9a of the photosensitive drum 9 of the image forming unit located at the image forming position for forming an electrostatic latent image on said photosensitive layer. The above function is effected on the image forming unit 1BK for black at the position lowered slightly downwardly as positioned from the state in Fig. 1. At a position for irradiating the photosensitive layer of the image forming unit after cleaning, located at the image forming position 50, there is provided an eraser lamp 8 fixed on the apparatus main body. The transfer/transport belt 31 constituted by a polyester film in an endless belt configuration of 100µm in thickness is directed around a driving roller 34 and a roller 35, and is adapted to be reciprocatingly movable in directions indicated by arrow W by attracting a paper sheet on its surface. It is to be noted here that in this embodiment, a distance between the driving roller 34 and the roller 35 is set to be slightly longer than a distance twice the length of an A4 size paper sheet in a direction of width thereof. At the right end of the transfer/transport belt 31 in a position above the roller 35, an adhering charger 37 is provided for attracting the paper sheet fed from the paper feeding section 36 onto the polyester film, and at the transfer section 33, a transfer charger 38 is disposed, while at the left end of the belt 31 in a position above the driving roller 34, a discharger 39 for discharging the paper sheet separated from the belt 31 and sent leftward and also, the transfer/transport belt 31 is provided as shown. As described earlier, at the transfer section 33, the transfer/transport belt 31 is raised by the belt restricting member 32 so as to be restricted in its upward and downward movements. In a position beside the transfer charger 38, a toner receptacle 40 is disposed to receive the waste toner sent out from the cleaner portion 27 when each of the image forming units 1BK to 1Y functions at the image forming position 50, while at the left end of the belt 31 below the driving roller 34, there is provided a belt cleaner portion 41 having a belt cleaner for cleaning the transfer/transport belt. The toner receptacle 40 is connected to the belt cleaner portion 41 at a connecting portion 42, and the waste toner discharged from each image forming unit at the image forming position 50 is collected into the belt cleaner portion 41. The transfer/transport belt 31, the transfer charger 38, and the belt cleaner portion 41, etc. are arranged to be displaceable to positions indicated by broken lines as a whole about the driving roller 34 for maintenance at paper jamming, etc. At the left side of the apparatus housing adjacent to the belt 31 directed around the driving roller 34, a fixing device 44 is provided for fixing the toner image on the paper sheet after transfer, and the paper sheet thus fixed with the toner image is discharged through a pair of discharge rollers 45. Driving of the driving roller 34 for the transfer/transport belt 31 and that of the fixing device 44 are respectively controlled by a transport control means (not shown). In the foregoing, the main construction of the electrophotographic apparatus have been described. Subsequently, functions of the above electrophotographic apparatus during formation of a color image in A4 size will be explained. An A4 size paper sheet (not shown) fed from the paper feeding section 36 in a direction of width is held on the transfer/transport belt 31 while being attracted onto said belt 31 by the action of the adhering charger 37, and is displaced in a leftward direction (referred to as a forward direction hereinafter) at a constant speed. At this time, since the paper sheet is positively attracted onto the belt 31, there is no slippage or deviation in positions between the transfer/transport belt 31 and the paper sheet even when the belt 31 is subjected to the reciprocating movement as described later, and thus, positioning may be readily effected when toner images of respective colors are overlapped. In the first place, the image forming units 1BK to 1Y are in positions as shown in Fig. 1, and the image forming unit 1BK is located in the vicinity of the image forming position 50. Fig. 1 shows the state before the image forming unit 1BK is positioned. Upon starting the function, the image forming unit 1BK for black is positioned at the image forming position 50, and also confronting the transfer section 33. In timed relation with the paper sheet transported from the right side on the transfer/transport belt 31, a signal light for black is applied to the image forming unit 1BK by the laser exposure device 3, and thus, image formation by the black toner is effected. It is so set that in the above case, the speed for the image formation of the image forming unit 1BK (equal to the circumferential speed of the photosensitive drum) becomes equal to the moving speed of the transfer/transport belt 31, and together with the image formation, the black toner image is transferred onto the paper sheet by the action of the transfer charger 38 as the paper sheet is displaced. Immediately after the trailing edge of the paper sheet has passed through the transfer section 33 upon completion of transfer of all the black toner image, the image forming unit 1BK at the image forming position 50 is released from the positioning, and the displacement of the belt 31 is once stopped. During such transfer function, the driving roller 34 for the transfer/transport belt 31 is connected with a flywheel, and smooth rotation with less speed variation can be effected. Just before stopping upon completion of the transfer, the driving roller 34 for the belt 31 is disengaged from the flywheel. Immediately after stopping, the belt 31 is displaced in the reverse direction at a speed sufficiently higher than the previous moving speed in the forward direction. In this case, since the driving roller 34 of the belt 31 is disengaged from the connection with the flywheel, quick stopping and reverse rotation at high speed may be effected. Since the transfer/transport belt 31 is displaced at high speed in the reverse direction, it is possible to return the paper sheet to the position before the transfer in a short period of time. It is to be noted that the leading edge of the paper upon stopping after completion of the transfer is located in the vicinity of the driving roller and does not come off from the belt 31 since said belt has a sufficient length. Meanwhile, during displacement of the belt 31 in the reverse direction, the group of the image forming units 1BK, 1C, 1M and 1Y is driven by the displacing motor 30 as a whole and is moved leftward in Fig. 1 as one unit and the next image forming unit 1C comes close to the image forming position 50. During the above time, since the image forming unit is located above the image forming position, there is no possibility that the black toner image on the moving paper sheet contacts the image forming unit for being disturbed. After the trailing edge of the paper sheet has passed the transfer section 33 towards the right side and the image forming unit 1C has arrived at the image forming position 50, the image forming unit 1C is positioned in the similar manner as in the case of the unit 1BK, and the belt 31 is again connected with the flywheel and displaced in the forward direction at a constant speed. In the similar manner as stated previously, the laser exposure device applies the signal light to the image forming unit 1C this time by the signal for cyan, and thus, formation and transfer of the toner image for cyan are effected. In this case, starting for displacement of the transfer/transport belt 31 and the starting of the signal light writing-in are so controlled in timing that subsequent toner image in cyan positionally coincides with the black toner image on the paper sheet. The function similar to the above are effected also for magenta and yellow, and on the paper sheet, toner images of four colors as positionally aligned are overlapped to form the resultant color image. After the last yellow toner image has been transferred, the belt 31 continuous to move in the forward direction, and the paper sheet formed with the color image is separated from the transfer/transport belt 31 while being electrically discharged by the action of the discharger 39 so as to be subsequently fixed with the color toner image thereon by a fixing device 44, and is then fed out of the apparatus through the discharge rollers 45. Meanwhile, the image forming unit group is displaced in the opposite direction to the previous direction, and returned to the initial position to prepare for the next image formation. So far, the electrophotographic apparatus of the present embodiment has been described with reference to the functioning during A4 color mode. Subsequently, the functioning of the above electrophotographic apparatus during single color mode will be described. In the single color mode, in the first place, before the paper sheet reaches the transfer position, the image forming unit of the predetermined color is displaced to and positioned at the image forming position. Then, in the similar manner as before, the image formation and transfer of the predetermined color are effected, and this time, the belt 31 is continuously displaced in the forward direction as it is even after the transfer for fixing and discharge of the paper sheet. Accordingly, during the single mode, a paper sheet larger than A4 size, for example, paper sheet of A3 size may be used. Meanwhile, waste toner discharged from the cleaner 27 at this time is collected in the belt cleaner portion 41 through the connecting portion 42 at any time. By making it possible to draw the image forming unit group out of the apparatus as one unit, and to exchange the respective image forming units independently, the exchange of the image forming units and maintenance thereof is simplified for facilitation of handling. Thus, according to construction of the above embodiment, since each image forming unit including the photosensitive member may be adjusted outside singly, for example, the unit already adjusted at the delivery from a factory may be simply exchanged at the site. Referring to Figs. 4 to 6, there are shown first to third examples for constructions of the image forming unit for magenta which may be employed in an electrophotographic apparatus C2 as shown in Fig. 3. In each of Figs. 4 to 6, the position of the neighboring image forming unit is shown by broken lines. Since the respective image forming units are constituted by the same members except for the developing materials accommodated therein, description will be given only with respect to the image forming unit 99M for magenta and explanation for other image forming units is omitted, with like parts being designated by like reference numerals, and in the case where it is necessary to distinguish the construction of the unit for each color, symbols representing respective colors will be affixed to numerals. Fig. 4 shows the construction of the image forming unit 99M for magenta according to a first example. The image forming unit 99M includes a developing material hopper 114 containing a two-component developing material 126M, a photosensitive drum 109 having an organic photosensitive layer 109a on its outer peripheral surface and rotatably provided at the lower portion of the hopper 114, and a magnet 110 unrotatably fixed to the same shaft for the photosensitive drum 109. Around the photosensitive layer 109a, there are sequentially disposed various processing devices such as a corona charger 111 for negatively charging the photosensitive layer 109a through a grid electrode 112 for controlling charge potential of the photosensitive layer 109a to be subjected to the laser beam scanning light 13, a toner restricting blade 120 of magnetic stainless material disposed close to the photosensitive layer 109a, a collecting electrode roller 117 of aluminum rotatably provided adjacent to the photosensitive drum 109 and connected to an A.C. high voltage source 118 so as to be applied with a voltage thereby, a scraper 119 of a polyester film provided to scrape off toner on the surface of the roller 117, and a cleaner 127 for cleaning off toner remaining on the photosensitive layer 109a after transfer. The two-component developing material 126M is produced by mixing ferrite carrier 124M with particle diameter of 100µm coated on the surface by silicone resin and toner 125M for attraction onto the surface of the photosensitive layer 109a by a magnetic force of the magnet 110, while the toner 125M is prepared by dispersing a pigment in a polyester resin, with further addition of an additive thereto. Magnetic flux density on the surfaces of the photosensitive layer 109a is 800 gauss at the maximum position. The photosensitive drum 109 has a diameter of 30mm and was rotated in a direction indicated by an arrow at a circumferential speed of 120mm/sec. Although the image forming unit of this type has an advantage in that when four units thereof are disposed side by side, it is possible to withdraw each unit in a direction indicated by an arrow D as shown in Fig. 4, there is such a drawback that an upper space E indicated by two broken lines above the corona charger 111 and the cleaner 127 can not be effectively utilized. Fig. 5 shows the construction of the image forming unit 100M according to a second example, in which like parts in the first example of Fig. 4 are designated by like reference numerals for brevity of explanation. In the image forming unit 100M of Fig. 5, the developing material hopper 114 in the image forming unit 99M in Fig. 4 has been replaced by a developing material hopper 114a arranged to effectively utilize the space by taking into account the shape of the neighboring image forming unit. In the image forming unit 100M, the capacity thereof can be increased to about 1.5 times that of the image forming unit 99M in Fig.4. However, when the image forming unit is to be replaced singly, it can not be drawn out in a direction of an arrow F or an arrow G in Fig. 5 due to contact with the neighboring image forming units. By way of example, in the case where the image forming unit disposed at the rightmost side of the four image forming units aligned side by side is to be drawn out upwardly, it is first required to draw out all of the neighboring units disposed at the left side thereof. Accordingly, in this case, there is such a restriction in designing that it is necessary to arrange to withdraw the image forming units towards the front side in the drawing. Fig. 6 shows the construction of the image forming unit 101M according to a third example, in which the problem in the image forming unit 100M in Fig. 5 has been eliminated. In the construction of Fig. 6 also, like parts in Fig. 4 are designated by like reference numerals for brevity of explanation. In the image forming unit 101M of Fig. 6, the developing material hopper 114 in the image forming unit 99M in Fig. 4 has been replaced by a developing material hopper 114b arranged to effectively utilize the upper space above the corona charger 111 and cleaner 127, and also to take into account, facilitation in drawing out the image forming unit singly. By this image forming unit 101M, the capacity of the developing material hopper 114b can be increased, and even when four image forming units of this type are arranged side by side, it is possible to independently take out the image forming unit in a direction indicated by an arrow H in Fig. 6. The image forming unit 101M includes the developing material hopper 114b containing a two-component developing material 126M, a photosensitive drum 109 having an organic photosensitive layer 109a on its outer peripheral surface and rotatably provided at the lower portion of the hopper 114b, and a magnet 110 unrotatably fixed to the same shaft for the photosensitive drum 109. Around the photosensitive layer 109a, there are sequentially disposed various processing devices such a corona charger 111 for negatively charging the photosensitive layer 109a through a grid electrode 112 for controlling charge potential of the photosensitive layer 109a to be subjected to a laser beam scanning light 13, a collecting electrode roller 117 of aluminum rotatably provided adjacent to the photosensitive drum 109 and connected to an A.C. high voltage source 118 so as to be applied with a voltage thereby, an unrotatable magnet 116 coaxially fixed within said collecting electrode roller 117, a scraper 119 of a polyester film provided to scrape off toner on the surface of the roller 117, and a cleaner 127 for cleaning toner remaining on the photosensitive layer 9a after transfer. Subsequently, the color electrophotographic apparatus according Fig. 3 will be described with reference to the drawings. In Fig. 3, there is shown a color electrophotographic apparatus C2 according to a further embodiment of the present invention mainly used with respect to a printer section for the image formation. Since the electrophotographic apparatus C2 is similar to that of Fig. 1 other parts having similar functions as those in Fig. 1 are designated by like reference numerals in Fig. 3 for brevity of explanation. In the first place, at the printer section, image forming units 101BK, 101C, 101M, and 101Y as four sets of image forming means for black, cyan, magenta and yellow are disposed side by side. Here, for the image forming units are constituted by the same members except for the developing materials accommodated therein, description will be given only with respect to the image forming unit 101M for magenta and explanation for other image forming units is omitted, with like parts being designated by like reference numerals, and in the case where it is necessary to distinguish the construction of the unit for each color, symbols representing respective color will be affixed to numerals. The image forming units as a whole can be displaced in the horizontal direction (in a direction indicated by an arrow X) as driven by the displacing motor 30 for the displacing means, and the respective image forming units may be successively positioned at the image forming position 50 confronting the transfer section 33 where the belt 31 is slightly pushed up by the belt restricting member 32. Since the construction for the displacement of the image forming units is similar to that as described earlier with reference to the embodiment of Fig. 1, detailed description thereof is abbreviated here for brevity. During image formation stand by period, the black unit 101BK of the image forming units 101BK, 101C, 101M and 101Y disposed side by side is disposed in the vicinity of the image forming position 50 as shown in Fig. 3. In the above case, according to the present invention, owing to the fact that each of the image forming units has a cross section generally in a parallelogram shape as shown in Fig. 6, it can be readily withdrawn from the support member if pulled up in a direction of the arrow H as shown in Fig. 6. Since the constructions and functions of the other exposure device portion, transfer belt portion, etc. are generally similar to those in the first embodiment, detailed description has been abbreviated here for brevity of explanation. It is to be noted here that, in the present embodiment, in the case where it is necessary to remove a paper sheet jammed within the apparatus, the four image forming units are displaced towards the right side end (as shown in Fig. 3) for the paper jamming at a portion L in Fig. 3, and towards the left side end for the paper jamming at a portion M for the removal of the paper sheet. Furthermore, when the space above the corona charger which normally becomes a wasteful space not utilized at all is utilized as the space for collecting the developing material of the neighboring image forming unit, such space is effectively utilized to the maximum degree without changing the size of the group of the image forming units as a whole, when the four image forming units are disposed side by side. In this case, if each of the image forming units is formed to have a side face configuration which allows withdrawal thereof slantwise upwardly, for example, generally a parallelogram shape, one image forming unit may be singly drawn out from the row of the four image forming units, and this provides a superior effect in the aspect of maintenance when the image forming unit is to be exchanged for each color. Hereinafter, a further embodiment according to the present invention will be described with reference to Figs. 7 and 8. This embodiment to be described hereinbelow differs from the first embodiment in the construction of the image forming units. Fig. 8 shows the image forming unit 151M for magenta. This unit 151M adopts the magnetic brush developing method generally employed for the developing apparatus in the conventional electrophotographic apparatus. In the construction of Fig. 8, like parts in Fig. 6 are designated by like reference numerals for brevity of explanation. In the image forming unit 151M of Fig. 8, there is provided a developing material hopper 114C arranged to effectively utilize the upper space above the corona charger 111' and cleaner 127', and also to take into account, facilitation in drawing out the image forming unit singly. By this image forming unit 151M, the capacity of the developing material hopper 114C is increased, and even when four image forming units 151BK, 151M, 151C and 151Y of this type are arranged side by side (Fig. 7), it is possible to independently take out the image forming unit in a direction indicated by an arrow I in Fig. 8. Subsequently, the construction of the above image forming unit as represented by the unit 151M for magenta will be described. The image forming unit 151M includes the developing material hopper 114C containing a two-component developing material 126M, and a photosensitive drum 159 having a photosensitive layer 159a on it outer peripheral surface and rotatably provided at the lower portion of the hopper 114C. Around the photosensitive layer 159a, there are sequentially disposed various processing devices such as a corona charger 111' for uniformly charging the photosensitive layer 159a through a grid electrode 112' for controlling charge potential of the photosensitive layer 159a to be subjected to the laser beam scanning light 13, a developing roller 117', rotatably provided adjacent to the photosensitive drum 159, and connected to an A.C. high voltage source 118' so as to be applied with a voltage thereby, magnet members 116' coaxially fixed within said developing roller 117', a developing material layer thickness restricting member 170 to form a developing material layer, on the surface of the roller 117', and a cleaner 127' for cleaning the photosensitive layer surface 159a. In the developing material hopper 114C, the two-component developing material 126M produced by mixing ferrite carrier 124M with particle diameter of 100µm coated on the surface by silicone resin and toner 125M is accommodated so as to be attracted onto the developing roller 117', having the magnet members 116' therein, thereby to form a developing material layer by the developing material layer thickness restricting member 170, and while the roller 117', is being rotated in the direction of an arrow, the electrostatic latent image on the photosensitive layer 159a is developed.

Claims: A color electrophotographic apparatus (C2; C3) comprising a plurality of movable image forming means (101BK, 101C, 101M, 101Y; 100M; 101M; 151BK, 151M, 151C, 151Y) each provided with a rotatable photosensitive member (109; 159), a charger (111; 111') for charging said photosenstitive member, a developing material hopper (114a; 114b; 114c) for storing toner in different color, a developing means for developing a latent toner image on said photosensitive member by said toner, and a cleaner (127; 127') for cleaning said photosensitive member, thereby to form toner images in different colors respectively on said photosensitive member (109; 159); a transfer and transport means (31) capable of supporting thereon a transfer material for reciprocating motion, and provided with a transfer means (38) for transferring the toner images on said photosensitive members (109; 159) onto the transfer material at the same transfer position (33); an exposure means (3) for effecting image exposure at the same exposure position corresponding to said transfer position (33); and a displacing means (30) for successively displacing in a linear manner each of said plurality of image forming means (101BK, 101C, 101M, 101Y; 100M; 101M; 151BK, 151M, 151C, 151Y) which are disposed to be aligned side by side in a horizontal direction, to an image forming position (50) corresponding to said exposure position and also, to said transfer position (33), whereby the toner images of different colors are overlapped and transferred on the transfer material for color image formation, thereby to obtain the color images on said transfer material: part of said developing material hopper (114a; 114b; 114c) of said image forming means (101BK, 101C, 101M, 101Y; 100M; 101M; 151BK, 151M, 151C, 151Y) being arranged to utilize a space above said charger (111; 111') and/or said cleaner (127; 127') of the neighboring image forming means. A color electrophotographic apparatus as claimed in claim 1, wherein said developing material hopper (114a; 114b; 114c) is wider at its upper part than at its lower part adjacent said charger (111; 111') and/or said cleaner (127; 127'). A color electrophotographic apparatus as claimed in claim 1 or 2, wherein said image forming means (101BK, 101C, 101M, 101Y; 101M; 151BK, 151M, 151C, 151Y) are of a shape which can be taken out slantwise in upward direction (H;I). A color electrophotographic apparatus as claimed in claim 3, wherein each of said image forming means (101BK, 101C, 101M, 101Y; 101M; 151BK, 151M, 151C, 151Y) has a side elevational shape generally in the form of a parallelogram.

Inventors: TERADA HIROSHI, YAMAMOTO HAJIME, TERADA, HIROSHI, YAMAMOTO, HAJIME
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G03G15
IPC codes: G03G15