Image forming apparatus having a plurality of vertically stacked image forming units and providing easily conducted jam clearing and maintenance
BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates to an image forming apparatus such as printers. 
     2. Description of Related Art 
     In recent years, there has been a growing demand for printers to be more sophisticated by adding such various functions as double-side printing function, composite printing function, and color printing function. On the other hand, a compact and inexpensive apparatus is also required though it is provided with only a single function. However, for such an apparatus with a single function, there is not prepared any optional unit of the above-mentioned functions to be attached to the apparatus. The user who has been using a printer which is provided with a single function is, therefore, obliged to prepare a high-grade apparatus besides the apparatus of a single function when it becomes necessary for the user to utilize sophisticated functions. 
     In constructing a high-grade printer, it may advantageously be arranged to provide a versatile printer with various functions basing on the inexpensive printer with a single function, however, such a printer has not been proposed yet. 
     In U.S. Pat. No. 4,972,236, there is disclosed an image forming apparatus wherein a plurality of image forming units are combined. In the apparatus, a plurality of image forming units are vertically stacked, and a paper feeding section and paper discharging section of an upper and lower image forming units are connected by a paper conveying unit provided with changeover means capable of changing over paper conveying paths. According to the image forming apparatus, double-side printing function, composite printing function, color printing function and the like may be arranged by means of conveying sheets of copy paper in various modes with the paper conveying unit. A sorting function may also be provided by utilizing the paper conveying unit which is provided with a sorter section. 
     In the image forming apparatus, however, when a sheet is jammed in the paper feeding path of the image forming unit and paper conveying unit other than the uppermost image forming unit and the paper conveying unit or when various maintenance operations are conducted, it is necessary to clear the jam and conduct a maintenance operation by opening upper frame of the image forming unit or opening upper cover of the paper conveying unit after each unit stacked thereabove is removed which causes the operations more complicated. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide an image forming apparatus wherein a plurality of image forming units with a single function are vertically stacked to have various functions, and jam clearing and maintenance operations can be easily conducted. 
     Another object of the present invention is to provide an image forming apparatus wherein jam clearing and maintenance operations can be easily conducted even if the units are vertically stacked for arrangement of various functions with a simple improvement of changing the direction of paper feed path in an image forming unit and changing the direction of opening and closing actions by utilizing the path. 
     These and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic structural view showing an image forming apparatus to which the- present invention is applied as first embodiment. 
     FIG. 2 is an exterior perspective view showing an image forming apparatus. 
     FIG. 3 is a perspective view showing an image forming apparatus wherein a paper feed path is opened. 
     FIG. 4 is a schematic structural view showing an image forming apparatus to which the present invention is applied as a second embodiment. 
     It is to be noted that like parts are designated by like numerals in each embodiment, and repeated description is omitted. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some of the embodiments of the present invention will now be described referring to the accompanying drawings. 
     FIGS. 1 through 3 show an image forming apparatus to which the present invention is applied as a first embodiment. 
     As illustrated in FIGS. 1 and 2, image forming units 1a and 1b are stacked vertically. The units are small-sized paper printers equipped with a single function. In each of the units 1a and 1b, there is provided a paper feed path 2 along a substantially vertical plane, and main body portion 3 and opening-closing portion 4 are divided and facing each other with the paper feed path 2 therebetween. As shown in FIG. 3, the opening-closing portion 4 is connected to the main body portion 3 with a hinge 31 at one side of the paper feed path 2, and with a rotation of the hinge 31 around its vertical axis, the paper feed path 2 is opened and closed. 
     At the lower portion of each opening-closing portion 4, there are provided a paper feed cassette 5 and paper feed roller 6, and a paper feed path 7 extending from the paper feed cassette 5 is connected to the lower portion of the paper feed path 2. In the paper feed path 2, there are subsequently disposed upward from the connecting section of the paper feed path 7, a register roller 8, an image forming cartridge 9 and a transfer charger 10, a fixing roller 11 and a changeover claw 12. 
     At the upper portion of each opening-closing portion 4, a paper discharge path 13 is provided to be connected with the paper feed path 2 through the changeover claw 12, and a paper discharge roller 14 and a paper discharge tray 15 are disposed. The image forming cartridge 9 is provided on the side of the main body portion 3 and the transfer charger 10 on the side of the opening-closing portion 4. The image forming cartridge 9 is integrally constructed with a photoconductive drum 16, unillustrated electrifying means, developing means and cleaning means, and an image is exposed onto the photoconductive drum 16 by an optical system unit 17 disposed on the side of the main body portion 3 to form an electrostatic latent image. The latent image is then developed with toner by the developing means to be transferred onto a transfer sheet by the transfer charger 10. 
     The optical system unit 17 is arranged to deflect the laser beam irradiated from a semiconductor laser which is modulated by an unillustrated image control section by deflecting means such as polygon mirror and form an image on the photoconductive drum 16 through a correcting lens and a folding mirror by performing main scanning. The photoconductive drum 16 is rotatively driven for a subscanning movement so that the image exposure is accomplished. 
     At four corners of the undersurface of the main body portion 3 of the lower image forming unit 1a, there are provided legs 32 to stably place the main body portion 3. At the undersurface of the opening-closing portion 4 which is connected to the main body portion 3, there is provided a support roller 18 to support the opening-closing portion 4. Since the opening-closing portion 4 is connected with and supported by the main body portion 3, it is stably opened and closed with the support of the support roller 18. The support roller 18 rolls on the surface 33 (refer to FIG. 1) on which the apparatus is placed so that the opening and closing of the portion 4 can be smoothly performed. 
     At the opening-closing end portion of the main body portion 3, engaging members 19 are provided at two locations, upper and lower portions, and corresponding to the engaging members 19, two lock claws 20 are provided at two locations of upper and lower portions of the opening-closing portion 4. The lock claws 20 are connected with n operating shaft 21 which is provided with an operating piece 22 arranged in the middle of the shaft. The upper and lower ends of the operating shafts 21 in the lower and upper image forming units 1a and 1b are further connected to each other with a connecting metal 23 so that both of the opening-closing portions 4 are correlatively opened and closed. 
     Description will now be made on printing operations. 
     In the case where a printing operation is performed on one side of a transfer sheet, a transfer sheet is fed from the paper feed cassette 5 to the paper feed path 2 by the paper feed roller 6 passing through the paper feed path 7 in either lower or upper image forming unit 1a, 1b, and is further fed to the location between the photoconductive drum 16 and the transfer charger 10 in a synchronous timing with an image forming process by the register roller 8 in the image forming cartridge 9, and an image formed on the photoconductive drum 6 is transferred onto the transfer sheet. The image transferred onto the transfer sheet is fixed by the fixing roller 11, and the sheet is guided to the side of the paper discharge path 13 by the changeover claw 12 and is then discharged onto the paper discharge tray 15 by the paper discharge roller 14. 
     In the case where a composite printing or a two-color printing operation is performed, a transfer sheet is fed from the paper feed cassette 5 of the lower image forming unit 1a, and a first colored-image is transferred and fixed on the transfer sheet in the lower image forming unit 1a in the same manner as described above. The transfer sheet on which the first coloredimage is transferred is further transported upward in the paper feed path 2 by the changeover claw 12 and forwarded into the paper feed path 2 of the upper image forming unit 1b. A second colored-image is then formed on the first colored-image and fixed on the sheet in the upper image forming unit 1b in the same manner as described above. At this stage of fixing process, the toner on the first-colored image is fused again together with the toner on the second-colored image so that they are mutually mixed at the portion overlapped each other, and a composite image is thereby formed by the lower and upper image forming units 1a and 1b. There forms a two-colored image in the case where images are not overlapped each other. The transfer sheet after the transfer process is discharged onto the paper discharge tray 15 of the upper image forming unit 1b by the changeover claw 12 passing through the paper discharge path 13. 
     In the case where both-side printing is performed, a transfer sheet is fed from the paper feed cassette 5 of the lower image forming unit 1a, and a first formed image is transferred and fixed on a first side of the transfer sheet the lower image forming unit 1a in the same manner as described above, and the sheet is then guided to the side of the paper discharge path 13 by the changeover claw 12. When the rear end of the transfer sheet has passed through the changeover claw 12, the paper discharge roller 14 is reversely rotated and the changeover claw 12 is switched over to return the sheet upward in the paper feed path 12 under the state that the sheet is reversed. The sheet is forwarded as it is into the paper feed path 2 of the upper image forming unit 1b, and a second formed image is transferred and fixed on a second side of the transfer sheet in the upper image forming unit in the same manner as described above, and images are formed on both sides of the transfer sheet by the lower and upper image forming unit 1a and 1b. Thereafter, the sheet is discharged onto the paper discharge tray 15 of the upper image forming unit 1b by the changeover claw 12 passing through the paper discharge path 13. 
     When a maintenance or jam clearing operation is conducted for the image forming unit 1a and 1b, the engagement of the engaging member 19 with the lock claw 20 is released by operating the engaging piece 22 to open the opening-closing portion 4 as illustrated in FIG. 3. At this time, the opening-closing portions 4 of the lower and upper image forming units 1a and 1b are correlatively opened to completely open the the paper feed path 2. The maintenance and jam clearing operations can thus be conducted easily. 
     A second embodiment of the present invention will now be described referring to FIG. 4. 
     In this embodiment, a paper feed cassette 5, paper feed roller 6 and paper feed path 7 are provided on the side of the main body portion 3 so that the weight of the opening-closing portion 4 is reduced and satisfactory weight balance of the opening-closing portion 4 can be maintained. The paper feed cassette 5 is mounted in an oblique position on the upper portion of the main body portion 3 so as to detach the cassette 5 from the front side. A transfer sheet can, therefore, be transported downward from the upper portion in the paper feed path 2. 
     According to each one of the embodiments of the present invention, image forming units are vertically stacked and disposed in a manner to connect each paper feed path of the units whereby the apparatus can be equipped with various functions such as both-side printing, composite printing, and multi-color printing. Since the opening-closing portion is arranged to be opened in the horizontal direction, jam clearing and maintenance operations can be conducted easily. It is advantageous that the apparatus can be constructed simply without the necessity of interposing a sheet transport unit between the image forming units. 
     Further, even if a copy paper is jammed in each of the units, it can be easily cleared by providing a means for correlatively opening and closing each of the opening-closing portions under the state that image forming units are vertically stacked and disposed. 
     In the embodiments described above, an example has been shown wherein the image forming units are vertically stacked in two stages, however, it may also be arranged to stack the units more than three stages for forming a composite colored-image in more than three colors. 
     In the above embodiment, it has been shown that the paper feed path 2 is vertically passed through the lower and upper image forming units 1a, 1b, however, it may also be arranged to connect the paper feed path 2 to the paper discharge path 13 without providing the changeover claw 12 at the upper portion of the unit wherein the paper feed path 2 of the lower image forming unit 1a is extended upward from the paper feed path 7 with its upper portion opened and lower portion of the paper feed path 2 of the upper image forming unit 1b is opened. With this arrangement, the image forming units in the same construction may be utilized. 
     In the above described embodiment, the upper and lower opening-closing portions 4 are usually connected with the connecting member 23, however, it may also be arranged to provide a means for properly connecting and releasing the connection corresponding to a jammed location when composite printing and both-side printing are performed. 
     It may also be arranged to provide the opening-closing portion 4 for only a limited region in the paper feed path 2 to be opened and closed not limiting to provide the opening-closing portion 4 over the entire vertical region of each image forming unit. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.