Patent Publication Number: US-7715772-B2

Title: Image forming apparatus having print media-releasing member and fusing apparatus having same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2005-55362, filed Jun. 25, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Aspects of the present invention relate to an image forming apparatus and a fuser therefor, and more particularly, to an image forming apparatus having a print media-releasing member for releasing a print medium from a heating roller, and a fuser for such an image forming apparatus. 
   2. Description of the Related Art 
     FIG. 1  is a sectional view showing a conventional image forming apparatus. As shown in  FIG. 1 , the image forming apparatus  100  includes a print media feeder  110  for feeding print media, an image forming unit  120  forming a toner image on the print medium conveyed from the print media feeder  110 , and a print media ejector  130  discharging the print media conveyed from the image forming unit  120  to the outside. 
   Here, the image forming unit  120  includes a developer  121  having a photosensitive drum  122  for forming a toner image on a print medium  1 , a transfer roller  123  rotating correspondingly to the photosensitive drum  122  with the print medium  1  placed in-between, and a fuser  124  for fusing toner onto the print medium  1  having the toner image formed thereon. 
   The fuser  124  is composed of a heating roller  125  heating the print medium  1  being conveyed from the developer  121  and a press roller  126  pressing the print medium  1  towards the heating roller  125 . The toner formed on the print medium  1  is melted by the heating roller  125  and pressed by the press roller  126  therebelow to thereby be fused on the surface of the print medium  1 . The print medium  2  fused with the toner is conveyed to the print media-ejector  130  and discharged to the outside. 
   In the above conventional technique, however, the toner on the print medium  1  is in contact with and pressed on the heating roller  125 , so that the toner is likely to attach to the surface of the heating roller  125  during the fusing process. In this case, the print medium  1  sticks to the surface of the heating roller  125  by means of the toner and then rotates together with the heating roller  125 . Thus, the print medium  1  itself may be creased and consequently jammed inside the image forming apparatus  100 . 
   Moreover, in a case where the surface layer of the heating roller  125  is formed of a resilient material such as rubber, the print medium  1  attached to the heating roller  125  must be separated therefrom, without damaging the heating roller  125 . 
   SUMMARY OF THE INVENTION 
   Aspects of the present invention provide an image forming apparatus and a fuser therefor comprising a print roller having a resilient surface layer, in which a print medium attached to the print roller can be easily released therefrom without damaging the print roller. 
   According to an aspect of the present invention, there is provided an image forming apparatus having a print roller, in which a circumferential elastic contact part of the print roller contacts and presses a print medium to convey the print medium, the apparatus comprising: one or more push rollers pressing the print roller to elastically deform the circumferential elastic contact part; and one or more print media-releasing members comprising a claw member to be protruded into a space formed by the elastic deformation of the circumferential contact portion, the print medium being released from the print roller by use of the claw member. 
   The push roller may, although not necessarily, be provided on both sides of the print media-releasing member. 
   A rotating axis of the push roller may, although not necessarily, pass through the print media-releasing member. 
   The print media-releasing member may, although not necessarily, be provided with a rotation shaft where the push roller rotates. 
   The push roller may, although not necessarily, be provided with a rotation shaft which is formed to pass through the print media-releasing member. 
   The print roller may, although not necessarily, further comprise a central part having a predetermined radius, and the circumferential elastic contact part comprises a surface layer formed of an elastic material, the surface layer being formed in the circumferential face of the central part and having a predetermined thickness. 
   The print roller may, although not necessarily, comprise an elastic body. 
   The print roller may, although not necessarily, be a heating roller. 
   According to another aspect of the present invention, there is provided a fuser for an image forming apparatus comprising a heating roller having a circumferential elastic contact part and a heater generating heat by an electric power externally supplied, and a press roller conveying a print medium interposed in-between with the heating roller while contact-pressing the print medium towards the heating roller, the fuser comprising: one or more push rollers pressing the heating roller to elastically deform the circumferential elastic contact portion; and one or more print media-releasing members comprising a claw member to be protruded into a space formed by the elastic deformation of the circumferential contact portion, the print medium being released from the heating roller by means of the claw member. 
   Two push rollers may, although not necessarily, be provided on both sides of the print media-releasing member. 
   A rotating axis of the push roller may, although not necessarily, pass through the print media-releasing member. 
   The print media-releasing member may, although not necessarily, be provided with a rotation shaft where the push roller rotates. 
   The push roller may, although not necessarily, be provided with a rotation shaft which is formed to pass through the print media-releasing member. 
   The heating roller may, although not necessarily, further comprise a central part having a predetermined radius, and the circumferential elastic contact part comprises a surface layer formed of an elastic material, the surface layer being formed in the circumferential face of the central part and having a predetermined thickness. 
   The heating roller may, although not necessarily, comprise an elastic body. 
   Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompany drawings of which: 
       FIG. 1  is a sectional view showing a conventional image forming apparatus. 
       FIG. 2  is a sectional view of an image forming apparatus according to an embodiment of the invention. 
       FIG. 3  is a magnified sectional view of a fuser in the image forming apparatus of  FIG. 2 . 
       FIG. 4  is a plane view showing a push roller and a print media-releasing member in the fuser of  FIG. 3 . 
       FIG. 5  is an exploded sectional view explaining the operational procedures of the fuser of  FIG. 3 . 
       FIG. 6  is a sectional view showing a fuser for an image forming apparatus according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 2  is a sectional view showing an image forming apparatus  200  according to an embodiment of the present invention. 
   As shown in  FIG. 2 , the image forming apparatus  200  comprises a print media feeder  210  for supplying print media  11 , an image forming unit  220  forming a toner image on the print medium  13  conveyed from the print media feeder  210 , and a print media ejector  240  for ejecting the print medium  13  conveyed from the image forming unit  220 . 
   Other types of print media  13  aside from paper, such as transparencies, overheads, etc., may be used. 
   The image forming unit  220  includes a developer  221  having a photosensitive drum  222  for forming a toner image on a print medium  13 , a scanning unit  226  forming a latent image on the photosensitive drum  222  of the developer  221 , a transfer roller  227  rotating correspondingly to the photosensitive drum  222  with the print medium  13  placed in-between, and a fuser  228  for fusing the toner on the print medium  13  where the toner image is formed. 
   The print medium  11  loaded on a knock-up plate  211  of the print media feeder  210  is picked up by a pick-up roller  212  and supplied into a register roller  214  through a conveyor roller  213 . 
   The register roller  214  conveys the print medium  12  to between the photosensitive drum  222  and the transfer roller  227 , according to a print medium-advancing signal of a controller (not shown). 
   When the print medium  12  is conveyed, the scanning unit  226  generates a laser light corresponding to an image data, which is then radiated on the photosensitive drum  222 . Thus, an electrostatic latent image is formed on the surface of the photosensitive drum  222 . 
   In the developer  221 , toner stored in a toner storage  223  is transferred to the electrostatic latent image via a supply roller  224  and a developing roller  225  to thereby form a toner image. The toner image formed on the surface of the photosensitive drum  222  is transferred onto the surface of the print medium  13  by means of electric force of a transfer roller  227 . The print medium  13 , on which a toner image is transferred, passes through the fuser  228  and at the same time the toner is fused on the surface of the print medium. Thereafter, the print media is stacked, through the print media ejector  240 , on a print media stacker  250  provided on top of the image forming apparatus. 
   The fuser  228  comprises a heating roller  229  placed at the upper side thereof and a press roller  230  placed at the lower side thereof. 
   The heating roller  229  houses a heater (not shown), which generates heat through an electric power supplied from the main body of the image forming apparatus  200 . The print medium  13  being conveyed from the developer  221  is heated up by the heater and thus the toner transferred on the surface of the print medium  13  is melted. 
   The press roller  230  presses the print medium  13  being heated by the heating roller  229  towards the heating roller  229 . Thus, the toner on the print medium  13 , heated by the heating roller  229 , is fused on the surface of the print medium  13  by means of the press roller  230 . 
     FIG. 3  is an exploded sectional view of the fuser in the image forming apparatus of  FIG. 2 . 
   As shown in  FIG. 3 , the heating roller  229  includes a central part  229   a  having a predetermined radius, and a surface layer  229   b  formed along the circumference of the central part  229   a  so as to have a predetermined thickness. Here, the surface layer  229   b  is formed of a resilient material such as rubber, which can be easily elastically deformed, and provided as a circumferential elastic contact part. 
   In addition, a push roller  231  and a print media-releasing member  232  are provided in the print media-ejecting side of the heating roller  229 . The push roller  231  contacts and presses against the heating roller  229 , and has a rotation shaft, which passes through the print media-releasing member  232 . Thus, as shown in  FIG. 3 , the surface layer  229   b  of the heating roller  229  is pressed by the push roller  231  and thus elastically deformed to form a space A. 
   The print media-releasing member  232  is wedge-shaped and has a claw member  232   a , which is protruded inwards of the space A formed by the push roller  231 . 
     FIGS. 3 and 4  show a combined structure of the push roller  231  and the print media-releasing member  232 . As shown in the figures, the push roller  231  is disposed on both sides of the print media-releasing member  232  respectively and has a rotation shaft passing through the print media-releasing member  232  and connecting the two push rollers  231 . 
   Here, the rotation shaft may be protruded from both sides of the print media-releasing member  232  and the push roller  231  may be provided with a shaft hole, so that the rotation shaft may be inserted into the shaft hole. 
   As shown in  FIG. 4 , one print media-releasing member  232  and two pusher rollers  231  constitute a group, and one or more groups of print media-releasing member  232  and push roller  231  may be provided, if necessary.  FIG. 4  illustrates six groups. 
   On the other hand, body portions  232   b  of the respective print media-releasing members  232  may be inter-connected to form an integral body. In addition, the push roller  231  may have a smaller or larger diameter so as to form the space A having a desired size. 
   By the use of the above-structured push roller  231  and the print media-releasing member  232 , the print medium  13  passing through the fuser  228  can be prevented from sticking to the heating roller  229 . 
     FIG. 5  is an exploded sectional view explaining the operational procedures of the fuser of  FIG. 3 . 
   As shown in  FIG. 5 , toner t on the print medium  13  is fused on the surface of the print medium  13  while passing a contact point P (precisely, a contact plane) between the heating roller  229  and the press roller  230 . At this time, the fusing toner t may cause the print medium  13  to stick to the heating roller  229 . As shown in the figure, the surface layer  229   b  of the heating roller  229  is pressed and depressed by the push roller  231  to hereby form a space ‘A’, where the claw member  232   a  of the print media-releasing member  232  is placed. By means of the claw member  232   a , the leading end of the print medium  13  passing the contact point P is released from the surface layer  229   b  of the heating roller  229  and continues to advance. 
   In the above-described embodiment, the surface layer  229   b  of the heating roller  229  is formed of an elastic material, though part of or the entire heating roller  229 , in addition to the surface layer  229   b , may be formed of an elastic material. 
   In addition, the space A, which is formed by elastic deformation of the surface layer  229   b  in the heating roller  229 , may have various shapes, depending upon the size of the push roller  231 , the thickness of the surface layer  229   b , the material forming the surface layer  229   b , and the like. Therefore, these conditions must be considered when designing the claw member  232   a  of the print media-releasing member  232 . In particular, the claw member  232   a , in most instances, should not to protrude outside of the space A, so that the surface layer  229   b  can be prevented from being damaged due to the claw member  232   a.    
   On the other hand, the push roller  231  and the print media-releasing member  232  of this embodiment may be applied to any roller used in the image forming apparatus  200  as long as its surface layer is formed of a resilient material. For example, the push roller  231  and the print media-releasing member  232  can be applied to the conveyor roller  235  (in  FIG. 2 ), which conveys the print medium passed through the fuser  228 . 
   In addition, the fuser  228  including the above push roller  231  and the print media-releasing member  232  may be designed so as to be detachably mounted on the image forming apparatus  200 .  FIG. 6  schematically shows the configuration of a modular fuser  300  according to an embodiment of the present invention. As shown in  FIG. 6 , a print media-releasing member  332  may be designed to be fixedly supported by a casing  301  of the fuser  300 . 
   As described above, aspects of the present invention provide an image forming apparatus and a fuser therefor, in which a print roller having a resilient surface layer is pressed by a push roller to form a space in-between, and a print medium attached to the print roller can be easily released therefrom by using the space, without damaging the print roller. 
   Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.