Patent Publication Number: US-8526875-B2

Title: Roller and heating member configuration for a fixing device and an image forming apparatus

Description:
This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2010-102435 filed on Apr. 27, 2010, the contents of which are incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present invention relates to a fixing device including a pair of transport rollers that is disposed so as to face a heating member, and an image forming apparatus including the fixing device. 
     Hitherto, as a fixing device, a device has been known which has a configuration in which, in a downstream side of a paper transport direction of a heating roller (a heating member), a pair of transport rollers for transporting a paper is disposed so as to close a paper transport path. In the technique, one transport roller can move to a certain extent relative to another transport roller in a thickness direction of the paper. 
     SUMMARY 
     However, in the configuration of the related art, upon removing a paper jammed between the pair of transport rollers (at the time of jam handling), when one transport roller moves in the paper thickness direction more than necessary to greatly open the paper transport path, there is a concern that foreign objects will enter the paper transport path and become attached to a heating member, whereby an image quality may decline. In addition, it is considered that a movement amount of one transport roller is restricted so that a gap between the pair of transport rollers does not increase in size. However, in the case of bringing the transport rollers themselves into contact with the restriction member to restrict the movement, since the restriction member should be provided on the opposite side of the other transport roller with one transport roller interposed therebetween, there is a problem in that the device becomes larger. 
     Thus, an object of the present invention is to suppress the foreign matter from entering the heating member at the time of jam handling, while suppressing the device from becoming larger. 
     An aspect of the disclosure provides the following arrangement. 
     A fixing device comprising: 
     a frame forming a transport path for transporting a recording sheet in a transport direction; 
     a heating member that is disposed on the transport path and thermally fixes a developer image on the recording sheet; 
     first and second transport rollers which are disposed so as to face the heating member in the transport direction and hold the recording sheet between the first and second transport rollers to transport the recording sheet, the first transport roller including a rotation shaft; 
     a spring which includes a holding portion holding the rotation shaft of the first transport roller at one end side of the spring, a support portion supported by the frame at the other side of the spring and an arm part between the holding portion and the support portion, and is configured to bias the transport roller to the second transport roller; and 
     a restriction portion which contacts a part of the spring between the holding portion and the support portion and restricts the first transport roller from being moved in a direction separated from the second transport roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-sectional view that shows a laser printer according to an embodiment of the present invention. 
         FIG. 2  is an explanatory diagram that simply shows a fixing device. 
         FIG. 3A  is an explanatory diagram in which a pair of transport rollers is viewed from a downstream side of a paper transport direction. 
         FIG. 3B  is an explanatory diagram that shows a gap between the pair of transport rollers when a torsion spring is restricted by a restriction portion. 
         FIG. 4  is a perspective view in which a part is cut away in order to show a structure around an upper transport roller, a torsion spring and a transport roller of a frame. 
         FIG. 5A  is a rear view viewing the structure of  FIG. 4  from the rear. 
         FIG. 5B  is a cross-sectional view cut away along lines I-I of  FIG. 5A . 
         FIGS. 6A to 6D  are explanatory diagrams that show operations when a force facing upward is applied to the transport roller at the time of jam handling. 
         FIGS. 7A to 7C  are explanatory diagrams that show operations in which an arm portion of the torsion spring is guided to a restriction surface in a tilt surface of a restriction portion. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Next, an embodiment of the present invention will be described in detail with reference to suitable drawings. In addition, in the following description, firstly, after briefly describing the whole configuration of a laser printer as an example of an image forming apparatus, details of characteristic portions of the present invention will be described in detail. 
     Furthermore, in the following description, directions referring to a user at the time of using a laser printer will be described. That is, in  FIG. 1 , a right side is called “a front side (a head side)”, a left side is called “a rear side (inside)”, and an inside in a paper surface vertical direction is called “a right side” and a head side in the paper surface vertical direction is called “a left side”. Furthermore, an up-to-down direction toward the paper surface is called “an up-to-down direction”. 
     &lt;Whole Structure of Laser Printer&gt; 
     As shown in  FIG. 1 , a laser printer  1  includes a filter portion  4  for feeding a paper  3  as an example of a recording sheet into a device main body  2 , an image forming portion  5  for forming an image on the fed paper  3  or the like. 
     The filter portion  4  includes a paper feeding tray  6  that is mounted on a bottom portion in the device main body  2  in an attachable and detachable manner, and a paper pressing plate  7  that is provided in the paper feeding tray  6 . Furthermore, the filter portion  4  includes a paper feeding roller  8  and a paper feeding putt  9  provided in an upper part of a front end portion of the paper feeding tray  6 , and paper powder grasping rollers  10  and  11  provided in a downstream side of a transport direction of the paper  3  with respect to the paper feeding roller  8 . Moreover, the filter portion  4  includes a resist roller  12  provided in a downstream side with respect to the paper powder grasping rollers  10  and  11 . 
     Moreover, in the filter portion  4  configured as above, the papers  3  within the paper feeding tray  6  are made to approach the paper feeding roller  8  by the paper pressing plate  7 , are delivered by the paper feeding roller  8  and the paper feeding putt  9 , pass through the respective rollers  10  to  12  and then are transported to the image forming portion  5  one by one. 
     The image forming portion  5  includes a scanner portion  16 , a process cartridge  17 , a fixing device  18  or the like. 
     The scanner portion  16  is provided on an upper portion in the device main body  2  and includes a laser light emitting portion (not shown), a polygon mirror  19  that is rotated and driven, lenses  20  and  21 , reflectors  22 ,  23  and  24  or the like. Moreover, in the scanner portion  16 , a laser beam is scanned and irradiated on a surface photosensitive drum  27  of the process cartridge  17  through a path shown by dotted lines in the drawing at a high speed. 
     The process cartridge  17  is arranged on a lower part of the scanner portion  16  and is mounted on the device main body  2  in a freely attachable and detachable manner. Moreover, the process cartridge  17  is mainly constituted by a developing cartridge  28  and a drum cartridge  51 . 
     The developing cartridge  28  includes a developing roller  31 , a layer thickness restriction blade  32 , a supply roller  33  and a toner hopper  34 . Moreover, the toner in the toner hopper  34  is stirred by an agitator (not shown) and then is supplied to the developing roller  31  by the supply roller  33 , and, at this time, the toner is correctly frictionally electrified between the supply roller  33  and the developing roller  31 . The toner supplied onto the developing roller  31  enters between the layer thickness restriction blade  32  and the developing roller  31  due to the rotation of the developing roller  31 , and is carried on the developing roller  31  as a thin layer of a fixed thickness. 
     The drum unit  51  mainly includes a photosensitive drum  27 , a charger  29  and a transfer roller  30 . Moreover, in the drum unit  51 , a surface of the photosensitive drum  27  is similarly positively electrified by the charger  29  and then is exposed by the high speed scanning of the laser beam from the scanner portion  16 . As a result, an electric potential of the exposed portion is lowered, whereby an electrostatic latent image based on the image data is formed. Next, when the toner carried on the developing roller  31  contacts the photosensitive drum  27  due to the rotation of the developing roller  31 , the toner is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  27 . Moreover, the toner becomes a visible image by being selectively carried on the surface of the photosensitive drum  27 , whereby the toner image is formed by a solarization. 
     Thereafter, the photosensitive drum  27  and the transfer roller  30  are rotated and driven so as to interpose the paper  3  therebetween and transport the same, and the paper  3  is transported between the photosensitive drum  27  and the transfer roller  30 , whereby the toner image carried on a rear surface of the photosensitive drum  27  is transferred onto the paper  3 . 
     The fixing device  18  mainly includes a halogen heater HH, a heating roller  41  as an example of a heating member, a pressurization roller  42 , and two transport rollers  200  and  300 . 
     The halogen heater HH is arranged in a cylindrical heating roller  41  and heats the heating roller  41  from the inside thereof. 
     The heating roller  41  is a roller for thermally fixing the toner on the paper  3  and is disposed on the transport path  100  in the fixing device  18 . Specifically, the heating roller  41  is a metallic member formed in approximately a cylindrical shape, and is rotatably supported on the frame  180  of the fixing device  18 . In addition, as the heating roller  41 , for example, it is possible to adopt one in which a surface of a cylinder member of aluminum is subjected to a PTFE coating. 
     The pressurization roller  42  is pressed on the heating roller  41  by a spring (not shown), contacts the rotating heating roller  41 , and is rotated accordingly. In addition, as the pressurization roller  42 , for example, it is possible to adopt one in which a urethane rubber is provided around a core metal and the surface of urethane rubber is coated with a PTFE tube. 
     The transport rollers  200  and  300  are disposed so as to face the heating roller  41  in the transport direction in a position of the downstream side in the transport direction of the heating roller  41 , and are rotatably supported on the frame  180  of the fixing device  18 . Moreover, the driving force is input to any one roller, whereby the transport rollers  200  and  300  interpose the paper  3  therebetween and transport the paper  3  to the rear part. In addition, the structures around the transport rollers  200  and  300  will be described later in detail. 
     Moreover, in the fixing device  18  configured as above, the heating roller  41  is heated by the halogen heater HH, whereby the toner image transferred on the paper  3  when the paper  3  passes between the heating roller  41  and the pressurization roller  42  is thermally fixed. Thereafter, the paper  3  is transported to a paper discharging path  44  by the transport rollers  200  and  300 . In addition, the paper  3  transported to the paper discharging path  44  is discharged onto a paper discharging tray  46  by the paper discharging roller  45 . 
     &lt;Structure Around Transport Rollers&gt; 
     Next, a structure around the transport rollers  200  and  300  will be described in detail. 
     As shown in  FIG. 2 , the transport rollers  200  and  300  are disposed in a row up and down so as to close an exit on the transport path  100  for transporting the paper  3  formed on the frame  180 , specifically, an exit of a downstream side of the transport direction of the transport path  100 . Herein, the transport path  100  is formed by a plurality of plate-shaped ribs  181  arranged in a left to right direction (a width direction of the paper  3 ). 
     As shown in  FIG. 3A , a plurality of transport rollers  200  and  300  is arranged along the left to right direction at predetermined gaps, and a lower (the other side) transport roller  200  is supported on a shaft portion  210  extending from left to right and can be rotated integrally therewith. Moreover, the shaft portion  210  is formed to have a diameter smaller than that of the transport roller  200  and is rotatably supported on the frame  180 . 
     An upper (one side) transport roller  300  includes two disk-type roller portions  310 , and rotation shafts  320  that are formed integrally with the respective roller portions  310  so as to penetrate the centers of the respective roller portions  310 . Moreover, as shown in  FIG. 4 , both end portions  321  of the rotation shafts  320  are rotatably supported by the torsion spring  400  (specifically, a holding portion  430  described later), and the transport roller  300  is biased to the lower transport roller  200  by the torsion spring  400 . 
     The torsion spring  400  includes a pair of coil portions  410 , a pair of arm portions  420 , a pair of holding portions  430 , a pair of spring leg portions  440 , and one support portion  450 , and is formed to have approximately an L shape when viewed from the left to right direction and approximately an U shape when viewed from the up to down direction. 
     The respective coil portions  410  are coiled in a coil shape around an axis along the left to right direction and are disposed separately from each other so that a predetermined gap is empty in a left to right direction. 
     The arm portion  420  is formed so as to extend along approximately the front to rear direction (approximately the transport direction) from the coil portion  410  toward the transport roller  300 , whereby the arm portion  420  can oscillate in the up to down direction around the coil portion  410  (a part). 
     The holding portion  430  is formed (supported) integrally on the front end (one end side) of the arm portion  420 , and is bent and formed in approximately a circular ring shape so as to surround the end portion of the rotation shaft  320  of the transport roller  300 . That is, the holding portion  430  is formed in a ring shape which forms an elongated hole which is long approximately in the front to rear direction so as to support the rotations shaft  320  movably (see  FIG. 5B ). 
     The respective spring leg portions  440  extend in a direction (approximately the up to down direction) different from those from the respective coil portions  410  to the arm portions  420 , and the respective front end portions thereof are integrally connected by the support portion  450 . 
     The support portion  450  is disposed in an opposite side (the other end side) of the holding portion  430  with the coil portion  410  interposed therebetween, and is extended and formed in the left to right direction so as to bind the front ends of the respective spring leg portions  440 . Moreover, the support portion  450  is pressed and supported to a support wall  182  which is formed in the frame  180  by a biasing force of the torsion spring  400  of the time when the torsion spring  400  is attached to the frame  180  (the movement to the front is restrained: see  FIG. 5B ). 
     Furthermore, in the support wall  182 , on a position further up than the support portion  450  of the mounted torsion spring  400 , a protrusion portion  183  which, restricts the movement to the upper part of the support portion  450 , is formed so as to protrude rearward. 
     Furthermore, as shown in  FIGS. 4 ,  5 A and  5 B, on the frame  180 , a pair of restriction portions  190  is formed which is disposed on the upper part of the respective arm portions  420  (the position between the holding portion  430  and the support portion  450 ) of the mounted torsion spring  400 , and can contacts the respective arm portions  420  from above. Specifically, the lower surfaces of the respective restriction portions  190  are restriction surfaces  191  that contact the arm portions  420  to restrict the movement of the upper transport roller  300 . 
     As a result, as shown in  FIGS. 6A and 6B , at the time of the jam handling, when the upper transport roller  300  is moved to the upper part (a direction separated from the lower transport roller  200 ), firstly, the torsion spring  400  is also moved together with the transport roller  300 , and the support portion  450  of the torsion spring  400  contacts the protrusion portion  183 , whereby the movement of the support portion  450  of the torsion spring  400  is restrained by the protrusion portion  183 . 
     Thereafter, when an upward force is applied to the upper transport roller  300 , the upper transport roller  300  is moved to the upper part in resistance to the biasing force of the torsion spring  400 . That is, the arm portion  420  of the torsion spring  400  rolls to the upper part around the coil portion  410 , but, as shown in  FIG. 6C , when the arm portion  420  contacts the restriction portion  190  (the restriction surface  191 ), the movement of the transport roller  300  in excess of that is prevented, which makes it possible to actively reduce a gap between the pair of transport rollers  200  and  300 . 
     Furthermore, as shown in  FIGS. 5A and 5B , in the respective restriction portions  190 , tilt surfaces  192 , which are disposed at a side of the restriction portions  190  opposite to the lower transport roller  200  with the above-mentioned restriction surface  191  interposed therebetween and tilted with respect to the restriction surface  191 , are formed consecutively with the restriction surface  191 . Specifically, the respective tilt surfaces  192  are formed so as to be tilted to the inside (a direction approaching each other) of the left to right direction as they face downward. 
     As a result, as shown in  FIGS. 7A to 7C , at the time of the attachment of the torsion spring  400  to the frame  180 , it is possible to guide the pair of arm portions  420  to the restriction surface  191  while bending-deforming the arm portions  420  in the direction approaching each other by the respective tilt surfaces  192 . 
     That is, when the pair of arm portions  420  is moved up to the lower ends of the respective tilt surfaces  192  in the direction approaching each other while being bending-deformed, and climbs over the lower end (angular portion), due to the return force of the torsion spring  400 , the pair of arm portions  420  returns to an original posture and thus is disposed in the lower part of the restriction surface  191 . For that reason, the work of putting the respective arm portions  420  in the lower sides of the respective restriction portions  190  becomes easier. 
     In addition, as shown in  FIG. 4 , the protrusion portion  183  formed on the frame  180  is also formed to have a triangular cross-section that is approximately the same as that of the restriction portion  190 , and includes a stopper surface  183 A which restricts the movement of the support portion  450  of the torsion spring  400 , and a tilt surface  183 B which is tilted with respect to the stopper surface  183 A so as to guide the support portion  450  in the stopper surface  183 A. As a result, the work of putting the support portion  450  in the lower side of the protrusion portion  183  also becomes easier. 
     Furthermore, as shown in  FIG. 4 , on the frame  180 , a pair of support grooves  184  is formed which extends along the up to down direction (the movement direction of the upper transport roller  300 ) and movably supports both end portions  321  of the rotation shaft  320  of the upper transport roller  300 . The respective support grooves  184  are formed so that the upper sides thereof (opposite side of the lower transport roller  200 ) are opened. 
     Moreover, as shown in  FIGS. 4 and 5B , in a side (first side) of the support groove  184  opposite to the lower end portion  184 A (the end portion of the lower transport roller  200  side) with the restriction portion  190  interposed therebetween, and in a position which deviates from the support groove  184  in the left to right direction (the axial direction of the rotation shaft  320 ), a U-shaped concave portion  185  opening to the lower part is provided. As a result, as shown in  FIG. 6D , a strong force is applied to the transport roller  300  at the time of the jam handling, whereby even when the arm portion  420  of the torsion spring  400  is removed from the restriction portion  190 , it is possible to receive and accommodate the rotation shaft  320  of the transport roller  300  moving to the upper part at the concave portion  185 . 
     That is, if the concave portion  185  is not provided, the movement of the transport roller  300  to the upper part is not stopped, and the transport roller  300  falls out from the support groove  184 . However, by providing the concave portion  185  as in the present embodiment, it is possible to suppress the falling-out of the transport roller  300  from the support groove  184 . Furthermore, since the concave portion  185  is provided in a position which deviates from the support groove  184  in the left to right direction, as compared to a case where the up and down end portions of the support groove are formed so as to be closed at both sides, the mold release at the time of molding the frame  180  formed of resin becomes easier. 
     Furthermore, as shown in  FIGS. 4 and 5B , in the vicinity of the support groove  184  of the frame  180 , a guidance surface  186  is formed which is consecutively formed on the inner surface  184 B of the support groove  184  so as to guide the rotation shaft  320  into the support groove  184  at the time of attaching the upper transport roller  300  to the frame  180 . Specifically, the guidance surface  186  is formed so as to extend in a direction approximately orthogonal to the support groove  184  in a position further up from the restriction portion  190  (an opposite side of the lower transport roller  200 ). 
     Herein, in  FIG. 4 , in order to simply and easily show the structure of the support groove  184 , the right support groove  184  is shown so as to be penetrated from left to right, but, in practice, even in the right side of the right support groove  184 , a transporting rib  181  or the like is formed. 
     In other words, as shown in  FIG. 5B , in the open upper end portion  184 C of the support groove  184 , a guidance groove  187  is consecutively formed which is opened toward the inside of the upper part and the left to right direction (a middle side of the transport roller  300  in the axial direction) and extends in the front to rear direction (the transport direction). Moreover, the lower surface of the guidance groove  187  is the above-mentioned guidance surface  186 . 
     In this manner, the guidance surface  186  is formed so as to extend in the direction approximately orthogonal to the support grove  184 , whereby, even when the arm portion  420  is removed from the restriction portion  190  at the time of the jam handling, the rotation shaft  320  does not easily fall out along the guidance surface  186  (the mounting path of the rotation shaft  320 ) to the outside. 
     Furthermore, as shown in  FIG. 3A , the transporting rib  181 , which is disposed so as to face the shaft portion  210  of the lower transport roller  200  in the up to down direction, is disposed so that a predetermined gap G 1  is empty between it and the shaft portion  210 . Herein, the rib  181  facing the shaft portion  210  corresponds to an example of the wall portion. 
     On the contrary to this, as shown in  FIG. 3B , when the arm portion  420  is restricted by the restriction portion  190  at the time of the jam handling, a gap G 2  between the pair of transport rollers  200  and  300  is smaller than the above-mentioned gap G 1 . 
     That is, in a position where the gap G 2  of the time when the portion between two transport rollers  200  and  300  is widened until the torsion spring  400  contacts the restriction portion  190  is smaller than the gap G 1  between the shaft portion  210  and the rib  181 , the restriction portion  190  is provided. As a result, it is possible to further suppress the foreign matter from entering from the gap between the pair of transport rollers  200  and  300 . 
     As described above, in the present embodiment, the following effects can be obtained. 
     The torsion spring  400  contacts the restriction portion  190  at the time of the jam handling, whereby the movement of the upper transport roller  300  is restricted. Thus, it is possible to reduce the gap between the pair of transport rollers  200  and  300 . 
     Furthermore, since the torsion spring  400  contacts the restriction portion  190  to restrict the movement, for example, as compared to the structure in which the disk-shaped roller portion  310  of the transport roller  300  contacts the restriction portion to restrict the movement, the restriction portion  190  can be disposed in a lower position, and the size of the restriction portion  190  can also be formed to be small to suit the torsion spring  400 , and thus, miniaturization and weight-reduction of the fixing device  18  can be accomplished. 
     Since the restriction portion  190  contacts the arm portion  420  of the torsion spring  400 , that is, the restriction portion  190  contacts a part having an oscillating range smaller than the transport roller  300  (the holding portion  430 ) having a great oscillating range, the fixing device  18  can be miniaturized. 
     Since the tilt surface  192  is provided on the restriction portion  190 , it is possible to easily perform the attachment of the torsion spring  400  to the frame  180 . 
     Since the concave portion  185  is provided on the side of the support groove  184  opposite to the lower end portion  184 A with the restriction portion  190  interposed therebetween, even when the torsion spring  400  is removed from the restriction portion  190 , it is possible to suppress the falling-out of the transport roller  300  from the support groove  184 . 
     Furthermore, since the concave portion  185  is disposed in a position which deviates from support groove  184  in the axial direction of the rotation shaft  320  and the support groove  184  is opened to the upper part, as compared to a case where the up and down end portions of the support groove are closed in both sides, it is possible to easily perform the mold release at the time of molding the frame  180  made of resin. 
     Since the guidance surface  186  is extended in the direction approximately orthogonal to the support groove  184 , even when the torsion spring  400  is removed from the restriction portion  190  at the time of the jam handling, it is possible to suppress the rotation shaft  320  from falling out along the guidance surface  186  (the mounting path of the rotation shaft  320 ) to the outside. 
     Since the gap G 2  of the time when the portion between two transport rollers  200  and  300  is widened until being restricted by the restriction portion  190  is smaller than the gap G 1  between the shaft portion  210  and the rib  181 , it is possible to suppress the foreign matter from entering from the gap between the pair of transport rollers  200  and  300 . 
     In addition, the present invention is not limited to the above-mentioned embodiment but can be used in various formations as described below as an example. 
     In the above-mentioned embodiment, as an example of the recording sheet, the paper  3  such as a thick paper, a postcard, and a thin paper was adopted, but the present invention is not limited thereto, for example, the recording sheet may be an OHP sheet. 
     In the above-mentioned embodiment, the heating roller  41  was adopted as the heating member, but the present invention is not limited thereto, for example, the heating member may be a ceramic heater which heats the recording sheet via a cylindrical fixing film. 
     In the above-mentioned embodiment, the torsion spring  400  was adopted as the spring, but the present invention is not limited thereto, for example, the spring may be a leaf spring, a coil spring or the like. Furthermore, in the above-mentioned embodiment, the torsion spring  400  was adopted which has two holding portions  430  supporting both end portions  321  of the rotation shaft  320  of the transport roller  300 , but the present invention is not limited thereto, for example, a torsion spring may be adopted which has only one holding portion supporting the middle portion of the rotation shaft. 
     In the above-mentioned embodiment, the arm portion  420  was configured so that it can oscillate around the coil portion  410 , but the present invention is not limited thereto, for example, in the case of a V-shaped leaf spring, the arm portion may oscillate around the angular portion of the V shape. Furthermore, the part of the spring contacting the restriction portion is not limited to the arm portion, for example, in the case of the coil spring, the restriction portion can contact a part of the portion that is coiled in a coil shape. 
     In the above-mentioned embodiment, the plurality of ribs  181  was adopted as an example of the wall portion facing the shaft portion  210  of the lower transport roller  200 , but the present invention is not limited thereto, it is possible to adopt wall portions of various shapes. Furthermore, the frame forming the transport path or the frame supporting the support portion of the spring may be one body or separate bodies. 
     In the above-mentioned embodiment, two transport rollers  200  were provided, but the present invention is not limited thereto as long as at least two transport rollers are provided, for example, three or more transport rollers may be provided. Furthermore, two transport rollers may be two guidance rollers in which the driving force is not input only by guiding the paper on both sides. 
     In the above-mentioned embodiment, the present invention was applied to the laser printer  1 , but the present invention is not limited thereto, the present invention may be applied to other image forming apparatus, for example, a copier, a combiner or the like. 
     In the above-mentioned embodiment, the halogen heater HH was adopted as an example of the heat source, but the present invention is not limited thereto, for example, an induction heating type of IH (Induction Heating) heater, a heating resistor or the like may be adopted.