Patent Publication Number: US-6661994-B2

Title: Electrophotographic image forming system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of U.S. application Ser. No. 09/801,847, filed Mar. 9, 2001, the subject matter of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an electrophotographic image forming system. 
     Generally, upon receipt of a printed data, the electrophotographic image forming system converts it into an image data and applies such luminous flux as laser beam to a photoconductor to form an image by electric charge, which is a so-called latent image. Then colored particles (toner) are deposited thereon on an selective basis by a development device, and latent image is formed into an manifest image, on the one hand. On the other hand, a medium such as form is fed to the photoconductor by a feed means such as a roller, and the image formed on the photoconductor is transferred to the medium. Then the image is fused onto the form by a fusing device, thereby completing printing. In such an electrophotographic image forming system, a form to guarantee print quality is normally specified to ensure stable printing operation. Therefore, the user is required to get a form specified for each system. There is no problem if such a form can be easily obtained. If not, the user has to be prepared for poor print quality. In addition to poor print quality, jamming occurs where the form is wound on the drum, depending on the case. Therefore, when other than specified forms are used, printing operation is performed by supplying the form from the manual feed tray to ensure that the form feed path will be shaped in a straight line wherever possible. However, this method cannot solve the problem of the drum wound by paper as described above. Even if the specified form is used, the form does not always exhibit predictable behavior when changes in form storage conditions and surrounding environment are taken into account. The form fed at a high speed may give vibration to parts inside the form feed path or may contact them by instantaneous behavior, causing the unfused image to be disturbed. Furthermore, paper used for printing includes a great variety of forms such as plain paper which is also called a copy form, OHP form, label form, envelope and post card. They may be used on the electrophotographic image forming system. The media greatly differing in the thickness, rigidity and the degree of curling of the form may be used. Thus, the system is required to cope with a great variety of forms. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an electrophotographic image forming system characterized by a mechanism of stabilizing the behavior of the tip of the form when the form with unfused colored particles (toner) deposited thereon is fed to the fusing device. 
     To achieve the above object, the present invention has a form posture correcting protrusion provided on the non-printing area of the surface of the form with unfused colored particles (toner) deposited thereon inside the feed path of the form with unfused colored particles (toner) deposited thereon, so that form behavior can be controlled when the form is fed to the fusing device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a printer with form guide representing one embodiment of the present invention; 
     FIG. 2 is a control block diagram of the printer representing one embodiment of the present invention; 
     FIG. 3 is a cross sectional view of a fusing device representing one embodiment of the present invention; 
     FIG. 4 is a cross sectional view showing the layout of the transfer drum and fusing device in a conventional example; 
     FIG. 5 is a drawing representing contact of the form with the fusing roller in a conventional example; 
     FIG. 6 is a drawing of correction of form posture representing one embodiment of the present invention; 
     FIG. 7 is a drawing of the printing area representing one embodiment of the present invention; and 
     FIG. 8 is a perspective view of the form posture correcting protrusion representing one embodiment of the present invention. 
     FIG. 9 is a cross sectional view representing the form wound on the fusing roller in a conventional example; 
     FIG. 10 is a cross sectional view representing the form separated by the form guide according to the present invention; 
     FIG. 11 is a cross sectional view of the form guide representing one embodiment of the present invention; 
     FIG. 12 is a perspective view of the form guide and fusing roller representing one embodiment of the present invention; and 
     FIG. 13 shows an embodiment of a form guide representing one embodiment of the present invention. 
     FIG. 14 is a drawing representing contact of the form with the fusing roller in a conventional example; 
     FIG. 15 is a perspective view of the form posture correcting protrusion representing one embodiment of the present invention; 
     FIG. 16 is a perspective view of the relation between the form guide and form representing one embodiment of the present invention; and 
     FIG. 17 is a cross sectional view of the relation between the form guide and form representing one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following describes one embodiment according to the present invention with reference to FIG.  1 . 
     The printer  25  has major components comprising development devices  1  to  4 , optical unit  5 , a charging device  8 , a photosensitive belt  22 , a transfer drum  21 , a paper feed roller  10 , a resist roller  12 , a transfer roller  13 , an electric charge eliminator  15 , a fusing device  19 , a paper eject roller  18  and a paper feed cassette  6 . FIG. 2 shows a control block. The control block can be broadly divided into two blocks; a printer controller  100  and a reversing paper feeder controller  101 . The printer controller  100  comprises an interface section to exchange data with the host, an exposure unit, a development unit, a fusing unit, a motor as power source, a solenoid drive unit, an operation/display unit, a paper feed controller, a sequence controller for control of some detectors and a form reversing controller, and reversing paper feeder controller  101 . The reversing paper feeder controller  101  comprises a motor as power source, solenoid, drive unit, some detectors, etc. 
     The following describes the operation of the printer  25 . 
     The photosensitive belt  22  is electrostatically charged by a charging device  8  uniformly in response to the printing start signal from a host (not illustrated). A latent image is formed on the photosensitive belt  22  by the optical unit  5  according to the printed data sent from the host. The latent image is developed by any one of development devices  1  to  4 , and colored particles (toner) in the development device are applied to the photosensitive belt  22 . The photosensitive belt  22  is rotated by the drive source (not illustrated), and colored particles (toner) on the photosensitive belt  22  are transferred onto the transfer drum  21 . Electric charge of the photosensitive belt  22  is eliminated by the erase lamp  160 , and excess colored particles (toner) remaining on the photosensitive belt  22  are removed by belt cleaner  23 . It is again electrostatically charged by the charging device  8 . For color printing, this process is repeated by switching the development device. A visible image of single or multi-colored particles (toner) is formed on the transfer drum  21 . Upon completion of the desired transfer operation or prior to completion, form  27  is pulled out of the form cassette  6  by the paper feed roller  10 , and is made to wait at the resist roller  12 . After the form is detected by the detector  161 , the paper feed roller  10  stops after the lapse of a specified time. When the position of the visible image formed on the transfer drum  21  has agreed with the transfer position on the form, the feed of the form waiting at the resist roller  12  is again started, and the visible image is transferred to the form at the transfer roller  13 . The form is separated from the transfer drum  21  by the electric charge eliminator  15 , and colored particles (toner) are fused onto the form  27  by the fusing device  19 . The form is then ejected to the paper eject tray  28 . Excess colored particles (toner) remaining on the transfer drum  21  are removed by drum cleaner  20 . FIG. 3 is a cross sectional view of the fusing device representing one embodiment of the present invention. The fusing device  19  has major components comprising a pressure roller  19   a , fusing roller  19   b , cleaning roller c, separator jaw  19   d , form guide  19   e , guide  182 , oil bottle  181  and oil drip pan  178 . The oil bottle  181  and oil drip pan  178  are getting less essential because oil-impregnated paper roll or oil-impregnated colored particles (toner) are coming to be used based on the recent technology, and the trend toward “oil-less” system is getting stronger. The form with unfused colored particles (toner) deposited thereon fed along the guide  182  is pressurized and heated by pressure roller  19   a  and fusing roller  19   b . Colored particles (toner) are molten to stick onto the form. FIG. 4 is a cross sectional view representing the layout of transfer drum  21  and fusing device  19  in the conventional example. There will be no problem if the form  27  with colored particles (toner) transfer from the transfer drum  21  is fed along the ideal locus  183  of a straight line formed by connecting the contact parts of transfer drum  21 , fusing roller  19   b  and pressure roller  19   a . However, the form is actually fed away from the ideal locus  183 , depending on the type of the form and the environment. FIG. 5 shows the contact of the form  27  to the fusing roller  19   b  in the conventional example. The form  27  having been fed along the guide  182  has the tip portion contacted by the pressure roller  19   a , and is caught in by the contact part between fusing roller  19   b  and pressure roller  19   a  through the rotation of the pressure roller  19   a  in the arrow direction. As a result of collision angle between pressure roller  19   a  and the tip of the form  27 , the tip of the form  27  instantaneously gives vibration and deformation to the fusing roller  19   b . As a result, colored particles (toner) in an unfused state are deposited on the surface of fusing roller  19   b . Then they are again transferred on the form  27  and fused there by re-contact between the form  27  and fusing roller  19   b . This will disturb an image about 7 to 8 mm on the tip of the form. FIG. 6 is a drawing representing correction of form posture representing one embodiment of the present invention. Regarding vibration and deformation given to fusing roller  19   b  by the form  27  when the form  27  with unfused colored particles (toner) deposited thereon contacts the pressure roller  19   a  described above, contact to the fusing roller  19   b  does not occur due to the effect of control guide  185  provided on the oil drip pan  178 . The form posture correcting protrusion  185  is provided on the non-printing portion of the printing surface of the form shown in FIG.  7 . It is located outside the printed area where image quality is guaranteed. FIG. 8 is a perspective view representing form posture correcting protrusion as one embodiment of the present invention. Form posture correcting protrusions  185   a  and  185   b  are provided on part of oil drip pan  178 . These protrusions are located at the place corresponding to the non-printing portion on the printed surface of said form. 
     The present invention provides an electrophotographic image forming system having a form posture correcting protrusion for form deformation on the side of the form with unfused colored particles (toner) deposited thereon. This feature prevents vibration and deformation caused by the form being fed to the fusing device, independently of the type of the form, and ensures excellent print quality. 
     Furthermore, in a fusing device as shown in FIG. 9, the oil bottle  181  and oil drip pan  178  are getting less essential because oil-impregnated paper roll or oil-impregnated colored particles (toner) are coming to be used based on the recent technology, and the trend toward “oil-less” system is getting stronger. The form with unfused colored particles (toner) deposited thereon fed along the guide  182  is pressurized and heated by pressure roller  19   a  and fusing roller  19   b.  Colored particles (toner) are molten to stick onto the form. The form passing between fusing roller  19   b  and pressure roller  19   a  is made to curl toward the fusing roller  19   b  by molten colored particles (toner), as shown in FIG.  9 . Depending on the degree of rigidity of form  27 , the paper is deformed to the extent of winding around the fusing roller  19   b , as shown in FIG.  9 . In FIG. 10, the deformed form after fusing is prevented by the form guide  19   e  from being wound in toward the fusing roll  19   b  and cleaning roller  19   c . Therefore, form  27  after fusing is fed out of the fusing device  19  along the form guide  19   e . FIG. 11 is a cross sectional view representing the form guide  19   e . The form guide  19   e  is composed of a dual structure consisting of a metallic member  19   f  such as stainless steel and aluminum and heat resistant resin  19   g  such as plastics. It is installed close to the fusing roller  19   b . The heat resistant resin  19   g  is installed with a clearance of about 0.5 m without contacting the fusing roller  19   b . FIG. 12 is a perspective view representing the form guide  19   e  and fusing roller  19   b . The protrusion  19   h  provided on the metallic member  19   f  contacts the surface of the fusing roller  19   b  to maintain clearance between the resin  19   g  of the form guide and fusing roller  19   b . Each end of the metallic member  19   f  is provided with a support joint which is held by the casing of the fusing device  19 . The heat resistant resin  19   g  has a concave  30  provided at the center as shown in FIG. 13, thereby avoiding possible contact between fusing device  19  and heat resistant resin  19   g  by thermal deformation. 
     The present invention provides an electrophotographic image forming system having a form guide on the form ejection side of the fusing device. This feature prevents the form from being wound on the fusing roller of a fusing device, and ensures correct form feed. 
     Furthermore, FIG. 5 shows the contact of the form  27  to the fusing roller  19   b  in the conventional example. The form  27  having been fed along the guide  182  has the tip portion contacted by the pressure roller  19   a , and is caught in by the contact part between fusing roller  19   b  and pressure roller  19   a  through the rotation of the pressure roller  19   a  in the arrow direction. As a result of collision angle between pressure roller  19   a  and the tip of the form  27 , the tip of the form  27  instantaneously gives vibration and deformation to the fusing roller  19   b . As a result, colored particles (toner) in an unfused state are deposited on the surface of fusing roller  19   b . Then they are again transferred on the form  27  and fused there by re-contact between the form  27  and fusing roller  19   b . This will disturb an image about 7 to 8 mm on the tip of the form. FIGS. 6 and 7 are perspective views representing the relationship between the form guides  179   a  and  179   b  and form  27 . As described above, deformation of the form caused by the form  27  contacting the pressure roller  19   a  results in not only the contact with the fusing roller  19   b  but also contact with the transfer drum  21 , depending on the type of the form fed. As for the state of printing in this case, colored particles (toner) once transferred onto the form  27  returns to the transfer drum  21  again, and the image of the portion in contract is removed after fusing. This results in serious deterioration of image quality. Form guide  179   a  and  179   b  are laid out so that they contact the end of the form  27  alone, in order to ensure that they do not contact the surface with colored particles (toner) deposited thereon, and do not re-contact transfer drum  21 . As a result, deposited colored particles (toner) are not affected. When the deformation of the form  27  is not very serious, these form guides  179  and  179   b  and the form  27  do not contact. FIG. 8 shows the relation between the form  27  and form guides  179   a  and  179   b . When form deformation has increased, the end of the form  27  contacts the sloping portion of form guides  179   a  and  179   b . Thus, further deformation of the form  27  is controlled at the time of contact. This makes it possible to avoid re-contact of transfer drum  21  with the surface having colored particles (toner) deposited thereon. The sloping portion of the form guides  179   a  and  179   b  can be either straight or curved. The shape is determined along the feed locus of the form  27 . Although not described herein, it can easily assumed that the distance between form guide A 179   a  and form guide B 179   b  can be changed automatically in conformity to the size of form  27 . 
     The present invention provides an electrophotographic image forming system having a form deformation control guide on the surface of the form with unfused colored particles (toner) deposited thereon. This feature allows deformation to be controlled, independently of the type of the form, and ensures excellent print quality.