Patent Publication Number: US-8121529-B2

Title: Sheet transport apparatus and fixing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 11/947,418 filed on Nov. 29, 2007, which claims the benefit of priority from Provisional application Ser. No. 60/867,930 filed on Nov. 30, 2006, the entire contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Related Art 
     The present invention relates to a sheet transport technique of clamping and transporting a sheet by a roller and a belt abutted against the roller. 
     2. Description of the Related Art 
     Hitherto, a fixing apparatus, etc., included in an image formation apparatus has adopted a sheet transport technique of clamping and transporting a sheet by a roller and a belt abutted against the roller. (For example, refer to U.S. Pat. No. 6,819,904.) 
     In the related art, to prevent the belt pressed against the roller from shifting in the rotation axis direction of the roller, it is a common practice to add special parts such as a shift prevention plate at both ends in the rotation axis direction of the roller. 
     Adding such special parts for shift prevention causes a problem because of hindering downsizing of the apparatus. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a sheet transport technique of clamping and transporting a sheet by a roller and a belt abutted against the roller, the technique capable of suppressing shift of the belt in the rotation axis direction of the roller without hindering downsizing of the apparatus. 
     To solve the above-described problems, according to one aspect of the invention, there is provided a sheet transport apparatus including a roller being formed with a tubular cavity having a predetermined length in a rotation direction and covered with an elastic body on the outer periphery in the rotation radius direction of the cavity; and a belt unit for abutting a belt of a width narrower than the width of the cavity in the rotation axis direction of the roller against a roller face of the roller so that it is positioned inside the range in which the cavity is formed in the rotation axis direction of the roller, and sandwiching a sheet between the belt and the roller and transporting the sheet. 
     According to one aspect of the invention, there is provided a fixing apparatus having a sheet transport apparatus of the configuration as described above; and a roller heating unit being placed in the proximity of the roller face of the roller for heating the roller face. 
     According to one aspect of the invention, there is provided a fixing apparatus having a sheet transport apparatus of the configuration as described above; and a belt heating unit being placed on a side of the belt in the belt unit not opposed to the roller face for heating a sheet to be transported through the belt. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a drawing to show the configuration of a fixing apparatus including a sheet transport apparatus according to a first embodiment of the invention; 
         FIG. 2  is a drawing to show the cross section of a roller  101  on a plane orthogonal to the rotation axis of the roller  101 ; 
         FIG. 3  is a drawing to show the cross section of the roller  101  on a perpendicular plane passing through the rotation axis of the roller  101  in the fixing apparatus according to the first embodiment of the invention; and 
         FIG. 4  is a drawing to show the configuration of a sheet transport apparatus and a fixing apparatus including the sheet transport apparatus according to a second embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the accompanying drawings, there are shown embodiments of the invention. 
     First Embodiment 
     To begin with, a sheet transport apparatus and a fixing apparatus including the sheet transport apparatus according to a first embodiment of the invention will be discussed. 
       FIG. 1  is a drawing to show the configuration of the fixing apparatus including the sheet transport apparatus according to the first embodiment of the invention. 
     As shown in  FIG. 1 , the fixing apparatus according to the embodiment is made up of a roller  101 , a belt unit  102 , a press unit  103 , an induction heating coil  104 , and a transport guide  105 . According to the configuration as shown in the figure, the fixing apparatus according to the embodiment clamps a sheet with an image formed thereon in a developer of toner, etc., by the roller  101  and the belt unit  102  and heats and fixes the developer image on the sheet. 
     In the fixing apparatus according to the embodiment, the roller  101  has a role as a heat roller and the belt unit  102  has a role in pressing the sheet against a roller face of the roller  101  heated by the induction heating coil  104 . The induction heating coil  104  is placed in the proximity of the roller face of the roller  101  for heating the roller face. 
     The components making, up the fixing apparatus according to the embodiment will be discussed below in detail:  FIG. 2  is a drawing to show the cross section of the roller  101  on a plane orthogonal to the rotation axis of the roller  101 , and  FIG. 3  is a drawing to show the cross section of the roller  101  on a perpendicular plane passing through the rotation axis of the roller  101  in the fixing apparatus according to the first embodiment of the invention. 
     Specifically, the roller  101  has a cross-sectional structure wherein a core  101   e , an elastic layer (corresponding to an elastic roller)  101   d  made of silicon expanded rubber, a metal layer  101   c , an elastic layer  101   b  made of silicon solid rubber, and a mold release layer  101   a  are laminated in order from the center. 
     The core  101   e  is formed of a material of iron, stainless steel, aluminum, etc., for example. The core  101   e  needs only to have a function as a shaft rotating on a rotation axis P and may be a solid structure or may be a hollow structure. 
     The elastic layer  101   d  is formed of a material resistant to heat and having elasticity, such as silicon expanded rubber, for example. 
     The elastic layer  101   d  can rotate on the rotation axis P and is formed with a concave shape groove M extending in the rotation direction on a roller face. The elastic layer  101   d  has a role in keeping the whole heat capacity of the roller  101  low by thermally insulating the metal layer  101   c  and the core  101   e  from each other. 
     The thickness of the elastic layer  101   d  in the rotation radius direction is set to a thickness of about 5 to 15 mm to keep wide the nip area formed between the roller  101  and the belt unit  102  and to keep such a distance for preventing a magnetic flux occurring from the induction heating coil from having an effect on the core  101   e . Preferably, the hardness of the silicon expanded rubber forming the elastic layer  101   d  is ASKER-C20 to 40°, for example. 
     The metal layer  101   c  is formed of a material of nickel electrocast, etc., for example, and has a thickness in the rotation direction set to 30 to 50 μm, for example. Of course, the material of the metal layer  101   c  may be any if it is good in the heating efficiency of induction heating; for example, magnetic stainless steel or iron can also be adopted. 
     The elastic layer  101   d  in the roller  101  is formed with a tubular cavity having a predetermined length in the rotation direction (see  FIG. 2 ) about the area where an image on a sheet passes through on the roller  101  considering an increase in the outer diameter caused by thermal expansion of the silicon expanded rubber at the heating time. 
     The elastic layer  101   d  formed with the groove M is covered with the metal layer  101   c  on the outer peripheral surface (roller face) in the rotation direction. The metal layer  101   c  is bonded to the outer periphery of the elastic layer  101   d  in an adhesive area shown in  FIG. 3 . Thus, the wall face of the groove formed in the elastic layer  101   d  and the metal layer  101   c  form the cavity. 
     The mold release layer  101   a  is formed of fluorocarbon resin of PFA, etc., for example, and has a layer thickness set to 0.05 to 0.2 mm, for example. 
     The outer periphery of the cavity provided in the roller  101  in the rotation radius direction (see  FIG. 2 ) is covered with elastic body that can become deformed by an external press force, as described above. 
     The belt unit  102  abuts a belt  102   c  of a width x 2  narrower than a width x 1  of a cavity in the rotation axis P direction of the roller  101  against the roller face of the roller  101  so that it is positioned inside the range x 1  in which the cavity is formed in the rotation axis P direction of the roller  101 , and sandwiches a sheet  7  between the belt  102   c  and the roller  101  and transports the sheet  7 . The belt  102   c  in the belt unit  102  is an endless belt placed on a plurality of rollers. 
     The press unit  103  has a role in pressing the belt  102   c  against the roller face from the position opposed to the roller face of the roller  101  through the belt  102   c  (see arrow F shown in  FIG. 1 ). 
     A width x 3  of the press unit  103  in the rotation axis P direction is set so that it becomes larger than the size of the sheet  7  to be transported (to which fixing treatment is applied) in the direction orthogonal to the transport direction. Accordingly, the whole sheet can be uniformly pressed against the roller  101  by the press force of the press unit  103  and occurrence of a fixing failure can be suppressed. 
     The width x 3  of the press unit  103  in the rotation axis P direction is set so that it becomes larger than the size of the area where an image can be formed (a developer image can be formed) in the sheet  7  to be transported in the direction orthogonal to the sheet transport direction. Accordingly, at least the area where a developer image is formed on the sheet which must be reliably heated can be uniformly pressed against the roller  101  and occurrence of a fixing failure can be suppressed. 
     The width of the press unit  103  in the rotation axis P direction means specifically the width of the area pressed by the press unit  103  in the belt  102   c  (the area where the press unit  103  abuts the belt  102   c ). Here, the area where the press unit  103  abuts the belt  102   c  is the same as the size of the press unit. 
     The width of the press unit  103  in the rotation axis P direction is set smaller than the cavity formed in the roller  101  in the rotation axis P direction as understood from the condition described above, needless to say. 
     In the configuration, if the belt  102   c  of the belt unit  102  is pressed against the roller face, a dent is caused to occur by elastic deformation in the cavity portion of the roller face of the roller  101  (see  FIG. 3 ). Then, the belt  102   c  narrower than the cavity is pressed against the roller  102  so as to fall within the range in which the cavity is formed as in the embodiment, whereby the belt  102   c  can be sunk in the dent. Accordingly, the position shift of the belt  102   c  in the rotation axis P direction is regulated and consequently the abutment position of the belt in the rotation axis P direction of the roller can be maintained at the regular position. 
     As shown in the embodiment, in the configuration adopting the roller formed with the cavity to absorb variations in the nip area range or the nip strength caused by an increase in the outer diameter of the roller caused by thermal expansion, the area where the cavity is formed in the roller can also be used for regulating the position shift of the belt. 
     Further, in the configuration for preventing the belt from shifting in the rotation axis direction of the roller, a strong frictional force acts on the side end part of the belt and there is a problem in the life of the belt. However, the tension of the belt is used to sink the belt in the moderate dent on the roller face produced by the press force as in the configuration of the embodiment, whereby the position shift can be suppressed without imposing excessive load on the belt. 
     The roller formed with the cavity therein is used as in the embodiment, whereby the frictional force added to the belt pressed against the roller can be lessened, resulting in contributing to the longer life of the belt. 
     The means for suppressing shift of the belt is provided by the cavity in the roller and the press unit placed inside the endless belt, so that downsizing of the apparatus is not hindered. 
     Second Embodiment 
     Subsequently, a second embodiment of the invention will be discussed. 
     The second embodiment of the invention is a modified example of the first embodiment described above and differs from the first embodiment in placement of heating means in configuring a fixing apparatus. Parts having identical functions with those previously described in the first embodiment are denoted by the same reference numerals in the second embodiment and will not be discussed again. 
       FIG. 4  is a drawing to show the configuration of a sheet transport apparatus and a fixing apparatus including the sheet transport apparatus according to the second embodiment of the invention. 
     As shown in the figure, in the embodiment, a ceramic heater  201  (corresponding to a belt heating unit) for fixing a developer image on a sheet at the fixing treatment time is placed on a side of a belt  102   c  in a belt unit  102  not opposed to a roller face (see  FIG. 4 ) for heating a sheet  7  to be transported through the belt  102   c . Therefore, in the embodiment, a roller  101  has a role as a pressurization roller. 
     The ceramic heater  201  is placed so as to abut the belt face on the side of the belt  102   c  not opposed to the roller face, whereby “surf fixing treatment” is realized. In the embodiment, preferably the belt  102   c  uses a material having a small heat capacity to efficiently transmit heat from the ceramic heater  201  to the sheet  7 . 
     The portion of the ceramic heater  201  abutting the belt face on the side of the belt  102   c  not opposed to the roller face is formed like a flat face. Accordingly, the area where the ceramic heater and the belt face are brought into intimate contact with each other can increase, contributing to improvement of the heating efficiency. 
     In the embodiment, the roller  101  bears the role as a pressurization roller and thus needs not necessarily to have a similar limination structure to that in the first embodiment and may be of a different structure if a pressurization characteristic required for pressing a sheet against a belt can be realized. 
     The configuration of the roller  101  in each of the embodiments described above is not limited to the example configuration; at least the outside in the rotation radius direction from the cavity portion formed in the roller needs only to be formed of a material that can become elastically deformed by the press force of the press unit or the belt heating unit. 
     In addition, an image formation apparatus (MFP: Multi Function Peripheral) including the fixing apparatus described above in each embodiment can also be provided, needless to say. 
     While the specific forms of the invention have been described in detail, it is to be understood that various changes and modifications will be apparent to those skilled in the art without departing from the spirit and the scope of the invention. 
     As described above in detail, according to the invention, there can be provided the sheet transport technique of clamping and transporting a sheet by the roller and the belt abutted against the roller, the technique capable of suppressing shift of the belt in the rotation axis direction of the roller without hindering downsizing of the apparatus.