Abstract:
An image forming apparatus has a traveling unit carrying sheets of paper along a longitudinal path from a printing section to a stacker roller which guides sheets of paper having only one printed side to a stacker section. Selected sheets of paper are being displaced along a reverse path from the stacker roller back to the printing section for providing printing on the opposite side of the selected sheets, which are eventually guided by switching gates located along the reverse path to a sorting device juxtaposed with the switching gates.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an image formation apparatus, and in particular, to an image forming apparatus having a perfect printing paper line for carrying a sheet of paper having gone through a broadsheet printing to a printing section for the second time in order to have a reverse side of the paper printed, and a sorting device for sorting out the sheets of paper of which printing is finished. 
     DESCRIPTION OF THE RELATED ART 
     A structure of a conventional image formation apparatus of this type will be shown in FIG.  1 . The image formation apparatus comprises a printing unit  30 , a paper hopper  31 , a perfect printing paper travelling unit  41 , and a sorting device  44 . 
     In case of conducting a broadsheet printing, a sheet of paper is carried to the printing unit  30  from the paper hopper through a paper feeding roller  32 . When the printing is over, the sheet of paper is discharged along a path A to a stacker  40 . In case of sorting, the sheet of paper continues along a path B, and is discharged to the sorting device  44 . 
     In case of conducting a perfect printing, a sheet of paper having gone through a broadsheet printing travels from path A to a path C is turned over within the perfect printing paper travelling unit  41  (path D) to be carried to the printing unit  30  once again by path E and the paper carrier roller  43 . As printing is executed over the reverse side, and both sides of the paper are printed, the sheet of paper will be outputted to the stacker  40  or the sorting device  44  as in the case of the broadsheet printing. 
     For another structure of a conventional image forming apparatus of this type, it is possible to change the position of the sorting device either to a left side or to a right side of the printing unit instead of having it at the upper side of the printing unit as shown in FIG.  1 . In this way, it is possible to reduce the height of the whole image formation apparatus. 
     In the above-mentioned conventional image forming device, the sorting device is provided as a separate unit apart from the paper travelling line for the perfect printing. Therefore, whether it is a type having a paper travelling line for the sorting device and to be mounted on the upper side of the printing unit, or it is a type to be positioned on a side of the printing unit, the size of the apparatus as a while will become extremely large. This will result in requiring a huge set-up space. 
     SUMMARY OF THE INVENTION 
     It is therefore, an object of the present invention to provide an image forming apparatus which can maintain the whole apparatus as compact as possible even in case when the apparatus is to have both the perfect printing function and a sorting device, due to which the set-up area can be kept small. 
     In accordance with a first aspect of the preset invention, there is provided an image forming apparatus comprising: a perfect printing paper travelling line for carrying a sheet of paper having gone through a broadsheet printing to a printing section for the second time in order to execute a perfect printing on the sheet of paper; a sorting device for sorting the sheets of paper having gone through the broadsheet printing; and a switching gate for drawing in said sheets of paper having gone through the broadsheet printing to said sorting device, the switching gate provided in said perfect printing paper travelling line. 
     In accordance with a second aspect of the present invention, there is provided an image forming apparatus comprising: a perfect printing paper travelling line for carrying a sheet of paper having gone through a broadsheet printing to a printing section for the second time in order to execute a perfect printing on the sheet of paper; a sorting device for sorting the sheets of paper having gone through the broadsheet printing; and a plurality of switching gates for drawing in said sheets of paper having gone through the broadsheet printing to predetermined trays in said sorting device, the switching gates provided in said perfect printing paper travelling line. 
     In accordance with a third aspect of the present invention, said switching gate of the image forming apparatus comprises a solenoid and a lever operated by said solenoid. 
     In accordance with a fourth aspect of the present invention, the image forming apparatus further comprises a page order controlling means for firstly printing even numbered pages on one sides of the sheets of paper and then odd numbered pages on the opposite sides of the sheets of paper in case of executing a perfect printing. 
     In accordance with a fifth aspect of the present invention, the image forming apparatus further comprises an interface section for receiving printing data from a host device. 
     In accordance with a sixth aspect of the present invention, the image forming apparatus further comprises a scanner for reading a manuscript. 
     In accordance with a seventh aspect of the present invention, the image forming apparatus further comprises a facsimile receiving section for receiving facsimile data from a communication line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further objects and the novel feature of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings, in which: 
     FIG. 1 is a diagram showing a structure of a conventional image forming apparatus; 
     FIG. 2 is a side view showing the whole structure of an embodiment of the present invention; and 
     FIG. 3 is a detailed side view of a perfect printing paper travelling line and a sorting device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, a description of a preferred embodiment of the present invention will be given in detail. 
     With respect to an image forming apparatus used in a printer, a copying machine, a facsimile machine, and so forth, the options for the printing technology would be an electrophotographic system, an ink jet system, a thermal printing system, a thermal system, and so on. In this particular embodiment, the explanation will be given about a laser printer using the electrophotgraphic technology. 
     FIG. 2 is a side view showing the whole structure of the embodiment of the image forming apparatus in accordance with the present invention. A stack of paper for printing is set in a paper cassette  1 . A paper feeding roller  2  carries a sheet of paper to the inside of the apparatus. A resist roller  3  is used in passing over a sheet of paper carried from the paper feeding roller  2  to a photosensitive drum  4 . It is used for conducting accurate printing over a predetermined position on the sheet of paper. 
     The photosensitive drum  4  is attached to an EP (Electrophotography) cartridge  5 . A laser unit  6  scans a laser beam by a rotation mirror and form a latent image on the photosensitive drum  4 . The latent image formed on the photosensitive drum  4  is developed by a developer being integrated into the EP cartridge  5 . A transfer roller  7  transfers the toner image on the photosensitive drum  4  on a sheet of paper. A fixing unit  8  fixes the toner image on the sheet of paper by heat and a pressure by the upper and lower rollers. 
     A stacker discharge roller  9  carries the sheet of paper to the stacker  10  for discharge. In case when a perfect printing is conducted, a perfect printing paper travelling line  11  is a travelling line for carrying the sheet of paper having gone through a broadsheet printing to a photosensitive drum  4  for the second time in order to print on a reverse side of the sheet of paper. The perfect printing paper travelling line  11  is provided with a paper carrier roller  12  and a paper carrier roller  13 . The perfect printing paper travelling line  11  can be a line for carrying the sheets of paper having been printed to the sorting device  14 . A switching gate  15  switches the carrying between the photosensitive drum  4  and the sorting device  14 . The sorting device  14  has a plurality of trays  16  and a plurality of sorter discharge rollers  17 , and is further provided with a sorting function to cope with giving out multiple copies. It is also possible to let the apparatus have a mail box function in which each of the 16 trays is assigned to an individual or to a certain type of mail, on the basis of which the received mails can be sorted out. 
     An interface section  18  receives the printing data from a host machine. A control section  19  controls the printing process including the paper carrying. 
     Next the operation of the image forming apparatus of the present invention will be described. First of all, a description will be given about the case in which the sorting device  14  is not being used. 
     In a normal broadsheet printing, a sheet being set in the paper cassette  1  is carried to the inside of the apparatus through the paper feeding roller  2 , from which it is carried to the photosensitive drum  4  through the resist roller  3 . The sheet of paper having the image printed by the photosensitive drum  4  and the printing roller  7  is carried to the inside of the fixing unit  8  by the carrying force of the photosensitive drum  4  and the printing roller  7 . At the fixing unit  8 , the toner on the sheet of paper is fixed due to a heat and a pressure by the upper and lower rollers. The sheet of paper is then carried over to the stacker discharge roller  9  by a carrying forth of the fixing unit  8 , and then discharged from the stacker discharge roller  9  to a stacker  10  placed outside the apparatus. 
     Here, in case of conducting a perfect printing, at the time when the sheet of paper is discharged from the stacker discharge roller  9 , the stacker discharge roller  9  is reversed just before the last end of the paper completely comes off the stacker discharge roller  9 , by which the sheet of paper is carried in the opposite direction. At this time, the sheet of paper proceeds to a perfect printing paper travelling line  11  as P does as shown in FIG.  2  and then carried to the resist roller  3  by the paper carrier roller  12  and the paper carrier roller  13 . After that, the printing is conducted on the opposite side of the paper in the same manner as in the broadsheet printing, and the sheet of paper is discharged from the stacker discharge roller  9 . 
     FIG. 3 is a detailed side view of the perfect printing paper travelling line  11  and the sorting device  14 . Now with reference to FIG.  2  and FIG. 3, a description will be given on a switching of a paper travelling direction of the perfect printing paper travelling line  11 . 
     The sheet of paper having gone through the broadsheet printing, subjected to the printing on the opposite side is transmitted to the perfect printing paper travelling line  11 , and then carried over the perfect printing paper travelling line  11  by the paper carrier roller  12 . Likewise, the sheet of paper having completed with its printing and discharged to the tray  16  is transmitted to the perfect printing travelling line  11  by the stacker discharge roller  9 , and then carried over the perfect printing paper travelling line  11  by the paper carrier roller  12 . This process is all the same whether the sheet of paper has gone through the broadsheet printing alone or the perfect printing as well. 
     In the perfect printing paper travelling line  11 , there are switching gates  15  for pulling in the paper into the trays  16  of the sorting device  14 . With respect to the sheet of paper entering the perfect printing paper travelling line  11  which is not discharged to the tray  16 , the switching gates are all posited at the side of  15   a  as shown in FIG. 3, and the paper is to be carried to the resist roller  3  within the apparatus by the carrier roller  13 . 
     Here, when the sheet of paper is to be discharged to an arbitrary tray  16 , a switching gate to the desired tray  16  alone is moved to the side of  15   b  as shown in FIG. 13 by an actuator, etc. such as a solenoid and so forth (not shown). Thus the paper travelling line is switched so that the sheet of paper is carried to the tray  16 . The sheet of paper is then carried to the sorter discharge roller  17  along the switching gate  15 , such that it is discharged to the desired tray  16  by the sorter discharge roller  17 . This control is done by the control section  19 . 
     The discharges from the stacker  10  and the sorting device  14  are all face-down discharges in which the printed surface is facing down. Therefore, in case of the broadsheet printing, when the printing is done from page 1, the sheets of paper are all arranged in a right order when taken out after the printing. On the other hand, in case of the perfect printing, when the printing is done from page 1, the sheets of paper are arranged such that the page order becomes “2, 1, 4, 3, . . . ”, when they are taken out after the printing. In this case, the pages have to be rearranged. In order to prevent this from happening, a page order control is done in order to print the even pages first on one sides of the sheets of paper, and then print the odd page next on the other sides of the sheets of paper. This page order control is done by the control section  19 . The page order control can be executed by the host device which transmits the printing data to the printer. 
     In the present embodiment, although the description is given only with respect to the laser printer using the electrophotographic technology, the present invention is not limited to such embodiment. It is also possible to use other printers such as an ink jet printer and so forth. It is also possible that the present invention is applied to a copying machine which executes printing of data being read out by a scanner which is provided for reading out documents. Furthermore, it is also possible that the present invention is applied to a facsimile machine which executes printing of facsimile data being received from a communication line. 
     As described above, in the present invention, by sharing the paper travelling line for the perfect printing as the paper travelling line directed to the trays of the sorting device, it is possible to reduce the size of the apparatus as a whole. Accordingly, the apparatus can be set requiring a little space. 
     While the preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or the scope of the following claims.