Patent Publication Number: US-9411308-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2011-184586 filed in Japan on Aug. 26, 2011, the entire contents of which are herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fixing apparatuses that are mounted in image forming apparatuses and the like such as electrophotographic copiers, printers, facsimiles, and their complex machines, and specifically to fixing apparatuses provided with a cooling mechanism that cools fixed paper sheets on a paper transport guide. 
     2. Description of the Related Art 
     In image forming apparatuses such as copiers and printers, high-speed operation along with high-quality image formation have been sought, but a given amount of heat is needed in order to have toner fixed to paper sheets. Moreover, cooling of paper sheets after fixing is not sufficiently performed with high-speed operation, and thus a toner blocking phenomenon will occur in which toner on one paper sheet sticks to another paper sheet loaded on a discharge tray. 
     Moreover, in duplex printing, hot paper sheets of which one side has been fixed are transported again to a photosensitive drum. When this duplex printing is used often, a temperature increase of the photosensitive drum is caused, and the life of the photosensitive drum may be shortened and poor cleaning and the like may be caused. 
     Some image forming apparatuses of this kind cool paper sheets which have been heated at the time of fixing. A method for cooling paper sheets after fixing is disclosed in which air vents are provided in a paper transport guide and air flow is formed to cool output paper sheets (for example, JP 2006-349755A, JP 2009-192998A, and JP 2010-30749A). 
     Moreover, some image forming apparatuses are disclosed in which solenoids are provided in a fixing apparatus as a separation claw driving means that makes a paper separation claw come into contact with and separate from the surface of a fixing roller and a pressure roller in order to reliably prevent occurrence of paper clogging (jam) at a fixing portion when paper sheets are wound around the fixing roller and the pressure roller of the fixing apparatus (for example, JP 2008-225223A, JP 2001-242738A, and JP 2007-225780A). 
     The solenoid serving as a drive source for separation/contact operations of a paper separation claw is required to ensure stable and long-time separation/contact operations of the paper separation claw even if the solenoid is incorporated in the fixing apparatus and used in a high temperature environment. Moreover, since the solenoid itself is an electric component and serves as a heat generating source, the solenoid is required to be cooled appropriately. 
     However, since paper sheets that retain unfixed toner images pass through the fixing apparatus, it is difficult to employ a method in which cooling air generated by a cooling fan is guided into the fixing apparatus via a ventilation channel and is blown directly to the heat generating source to cool it. Therefore, conventionally, a method is often employed in which heat generated at heat generating sources such as the fixing apparatus and other components is sucked by suction fans provided on the apparatus casing of an image forming apparatus through a suction duct, and is discharged to the outside of the apparatus to cool each portion of the inside of the image forming apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in view of the circumstances mentioned above, and it is an object to provide a fixing apparatus that can effectively perform cooling of the fixed paper sheets passing over the paper transport guide and a heat generating element (especially, solenoid) included in a drive source for driving the paper separation claw that is incorporated in the fixing apparatus to perform separation/contact operations without cooling air affecting paper sheets that retain unfixed toner images. 
     To solve problems above, the fixing apparatus of the present invention includes a fixing roller (a hot roller and a pressure roller), a paper separation claw, a drive source that switches between a state in which the paper separation claw is in contact with the fixing roller and a state in which the paper separation claw is separated from the fixing roller, and a paper transport guide that is disposed on the downstream side of the fixing roller, the drive source including a heat generating element, and further includes a main ventilation channel that channels cooling air to a fixed paper sheet passing over the paper transport guide and a sub ventilation channel that is branched from the main ventilation channel and channels a portion of the cooling air to the heat generating element. Here, it is preferable that the heat generating element is a solenoid. 
     According to a configuration mentioned above, it is possible to effectively perform cooling of the fixed paper sheets passing over the paper transport guide and the heat generating element (especially, solenoid) included in the drive source for driving the paper separation claw to perform separation/contact operations from/with the surface of the fixing roller without cooling air affecting paper sheets that retain unfixed toner images. 
     Moreover, in the present invention, it is preferable that the main ventilation channel is defined by a main duct and the sub ventilation channel is defined by a sub duct that is branched from the main duct. Since the main ventilation channel and the sub ventilation channel are configured to be defined by a main duct and a sub duct, it is possible to reliably channel air through the ventilation channels in the ducts without any air loss, and thus it is possible to effectively cool the fixed paper sheets and the heat generating element included in a drive source. 
     Also, in the present invention, it is preferable that the sub ventilation channel defined by the sub duct is configured to be formed in a tapered shape so as to be gradually narrowed from a branch portion of the main duct toward a leading end portion that faces the heat generating element. With this configuration, the occurrence of air accumulation in the sub duct can be prevented, and cooling air can be smoothly blown toward the heat generating element. 
     In addition, in the present invention, it is preferable that an air blowout port through which cooling air is blown to the heat generating element is provided in the leading end portion of the sub duct, and that the air blowout port is formed in a nozzle-shape in which the inner diameter on the branch portion side is larger and the inner diameter on the heat generating element side is smaller. With this configuration, air easily blows out from the inside of the sub ventilation channel, and it is possible to prevent hot air from flowing back from a space around the fixing roller in the fixing apparatus to the inside of the sub ventilation channel. Therefore, it is possible to effectively perform the cooling of the heat generating elements (especially, solenoids). 
     Moreover, in the present invention, it is preferable that a plurality of slits are provided in a casing portion of the heat generating element that faces the leading end portion so as to be arranged along the direction in which the cooling air that has passed through the sub duct flows. With this configuration, it is possible to guide cooling air in the sub ventilation channel into the casing portion due to slits provided in the casing portion of the heat generating elements (especially, solenoids), and thus it is possible to effectively perform cooling of the heat generating elements (especially, solenoids). Also, even if the amount of cooling air that is introduced into the casing portion through the sub duct is small, since the heat generating elements (especially, solenoids) are effectively cooled, it is possible to prevent excess cooling and thermal loss of the fixing apparatus from occurring and to maintain the temperature in the fixing apparatus appropriately. 
     In addition, in the present invention, the fixing apparatus may be configured to further include a heat insulating member that is disposed between the leading end portion of the sub duct and the casing portion that faces the leading end portion. With this configuration, heat generated by the fixing rollers in the fixing apparatus can be prevented from transferring directly to the sub duct by the heat insulating member, and thus a temperature increase in the sub duct is suppressed. As a result, cooling of the heat generating elements (especially, solenoids) can be further effectively performed. 
     Also, in the present invention, it is preferable that the main duct includes a ventilation opening, and that the ventilation opening is disposed on the lower face side opposite to the paper support face of the paper transport guide and projects toward the paper transport guide, and that a plurality of air vents in a slit-like shape are formed in the paper transport guide, and that a leading end opening portion of the ventilation opening is configured to be disposed so as to be in communication with a plurality of air vents in a slit-like shape. With this configuration, it is possible to effectively perform cooling of the fixed paper sheets passing over the paper transport guide and the heat generating elements (especially, solenoids) for driving the paper separation claw to perform separation/contact operations without cooling air affecting paper sheets that retain unfixed toner images. 
     Moreover, the fixing apparatus of the present invention may be configured to further include a heat insulating member that is disposed between the leading end of the ventilation opening and the paper transport guide. With this configuration, heat received by the paper sheet at the time of passing through the paper transport guide immediately after fixing can be prevented from transferring directly to the main duct by the heat insulating member, and thus a temperature increase in the main duct is effectively suppressed. As a result, cooling of the fixed paper sheet passing over the paper transport guide can be further effectively performed. 
     In addition, by using the present invention, an image forming apparatus can be realized that is configured to include an image forming portion that forms toner images on paper sheets and a fixing apparatus having any one of the above described configurations that fixes toner images formed on paper sheets. With this configuration, it is possible to provide an image forming apparatus that can effectively perform cooling of the fixed paper sheets passing over the paper transport guide and the heat generating element included in the drive source for driving the paper separation claw to perform separation/contact operations from/with the surface of the fixing roller without cooling air affecting paper sheets that retain unfixed toner images. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic view showing an overall configuration of an electrophotographic copier as one embodiment of image forming apparatuses in which a fixing apparatus according to one embodiment of the present invention is mounted. 
         FIG. 2  is a schematic cross-sectional view showing a peripheral structure of a fixing apparatus. 
         FIG. 3  is a schematic cross-sectional view showing schematically a peripheral structure of a fixing apparatus that includes a cooling duct portion, which is a feature of one embodiment of the present invention. 
         FIG. 4  is a plan view showing a main portion of a fixing apparatus that includes a cooling duct portion, which is a feature of one embodiment of the present invention. 
         FIG. 5A  is a schematic transverse cross-sectional view of a cooling duct portion, which is a feature of one embodiment of the present invention is viewed from above. 
         FIG. 5B  is a schematic transverse cross-sectional view of a cooling duct portion, which is a feature of one embodiment of the present invention is viewed from above. 
         FIG. 5C  is a schematic transverse cross-sectional view of a cooling duct portion, which is a feature of one embodiment of the present invention is viewed from above. 
         FIG. 5D  is a cross-sectional view showing an enlarged D portion of  FIG. 5C . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
     Description of Overall Configuration of Image Forming Apparatus 
     In the present embodiment, an example is described in which a fixing apparatus according to one embodiment of the present invention is mounted in an electrophotographic copier (hereinafter, simply referred to as “copier”) as one embodiment of an image forming apparatus. 
     In  FIG. 1 , a copier A is a copier that forms multicolored or monochrome images on a prescribed paper sheet (recording paper) according to image data transmitted from outside or image data obtained by reading originals. However, in the present embodiment, a copier that forms monochrome images is described as an example. 
     This copier A includes an original processing apparatus  10 , a paper feed portion  20 , an image forming portion  30 , and a discharge portion  15 . 
     The original processing apparatus  10  includes an original placement stage  11 , an original transport apparatus  12 , and an original reading portion  13  in an apparatus casing  1 . 
     The original placement stage  11  is made of transparent glass, and originals can be placed thereon. The original transport apparatus  12  transports originals page by page that are stacked on an original tray  12   a.  The original transport apparatus  12  is configured to be able to pivot rearward in the direction perpendicular to the paper plane in  FIG. 1 , and originals can be placed on the original placement stage  11  by opening above the original placement stage  11 . The original reading portion  13  can read originals that are being transported with the original transport apparatus  12  or are placed on the original placement stage  11 , and includes a mirror group  13   a , a condensing lens  13   b , and an imaging element (CCD)  13   c.    
     The paper feed portion  20  includes a paper feed cassette  21  and a pickup roller  22 . The pickup roller  22  is provided near an end portion of the paper feed cassette  21 , and picks up a paper sheet (recording paper) P from the paper feed cassette  21  page by page to feed the paper sheet to a paper transport path  25 . 
     The image forming portion  30  includes a photosensitive drum  31 , a charger  32 , a development unit  33 , a cleaner portion  34 , an exposing unit  35 , a transfer roller  36 , and a fixing apparatus  38  and the like. 
     The image forming portion  30  is an electrophotographic image forming apparatus, and the photosensitive drum  31  whose surface is uniformly charged by bias application to the charger  32  is irradiated with a laser beam from the exposing unit  35  based on image data transmitted from the outside of the copier A or image data generated by reading originals to form an electrostatic latent image. This electrostatic latent image undergoes toner development in the development unit  33  to form a visual image (toner image). Moreover, the pickup roller  22  picks up the paper sheet P loaded on the paper feed cassette  21  that is installed in the lower portion of the apparatus casing  1  in synchronization with toner image formation, and a transport roller  37  transports the paper sheet P to a nip portion between the photosensitive drum  31  and the transfer roller  36 . Then, a toner image on the photosensitive drum  31  is transferred to the paper sheet P by bias application to the transfer roller  36  and thus an image is formed on the paper sheet P. The paper sheet P to which the toner image is transferred is transported to the fixing apparatus  38 , and the toner image is fixed by applying heat and pressure in the fixing apparatus  38 , and then the paper sheet P is discharged onto the discharge portion  15  by a discharge roller  39 . 
     It should be noted that an suction fan  16  is provided on a back face la side of the apparatus casing  1  in order to suck heat generated mainly in the image forming portion  30  and to discharge the heat outside the copier, and that an suction duct (not shown in  FIG. 1 ) is provided in this suction fan  16  in order to effectively suck heat generated from the components in the apparatus casing  1 . 
     Description of Fixing Apparatus 
     Arrow signs Y in  FIGS. 2 through 4  show a paper transport direction. Moreover, arrows in  FIGS. 5A ˜ 5 C show the flow of air (cooling air). 
     The fixing apparatus  38  includes a fixing portion  40  configured with a roller pair consisting of an upper heat roller (hot roller)  41  and a lower heat roller (pressure roller)  42 . The upper heat roller  41  and the lower heat roller  42  are fixing rollers in each of which a heat generating element  43  such as a heater is provided and by which unfixed toner on the paper sheet P is molten by heating. While the paper sheet P is transported in a sandwiched manner by this roller pair, heat and pressure are applied to the paper sheet P, and thus unfixed tonner images that are transferred to the paper sheet P can be fixed. 
     A pre-fixing paper guide  44   a  is provided on the upstream side (upstream side in the paper transport direction; the photosensitive drum  31  side) of the fixing portion  40  in order to guide the paper sheet P from the photosensitive drum  31  to the nip portion N where the hot roller  41  is pressed against the pressure roller  42 . A fixing exit guide  44   b  is provided on the downstream side (downstream side in the paper transport direction) of the fixing portion  40  in order to guide the paper sheet P on which a toner image is fixed toward the discharge portion  15 . 
     Moreover, for each of the hot roller  41  and the pressure roller  42 , a separation claw unit  45  is provided on the downstream side of the nip portion N. These separation claw units  45  mainly include respective paper separation claws  46  that are movable paper separation claws which selectively come into contact with or separate from the peripheral surface of the hot roller  41  and the pressure roller  42 , respective drive shafts  47  that axially support the paper separation claws  46 , and respective solenoids  48  that serve as drive sources to drive respective drive shafts  47 . The solenoids  48  switch between a state in which the paper separation claws  46  are in contact with the hot roller  41  and the pressure roller  42  and a state in which the paper separation claws  46  are separated from the hot roller  41  and the pressure roller  42 . Each paper separation claw  46  is axially supported by the corresponding drive shaft  47  via a spring (not shown). An arm  49  is attached to one end portion of each drive shaft  47 . A plunger  48   a  of each solenoid  48  is axially supported by the corresponding arm  49 . 
     The separation claw unit  45  provided for the pressure roller  42  is disposed below the fixing exit guide  44   b , and the solenoid  48  is disposed so as to be adjacent to a lower partition plate  28   a  that extends vertically downward from the end portion on the downstream side of the fixing exit guide  44   b . In other words, the separation claw unit  45  is disposed in the fixing apparatus  38  so as to be contained within a casing portion defined by the fixing exit guide  44   b  and the lower partition plate  28   a.    
     Meanwhile, the separation claw unit  45  provided for the hot roller  41  is disposed above the fixing exit guide  44   b  and is disposed in the fixing apparatus  38  so as to be contained within an upper side partition plate  28   b  (the casing portion) formed in a squared U-shape. 
     Moreover, the cleaner portion  34  that includes a take-out roll  51 , a web roll  52  that is wound around the take-out roll  51 , and a take-up roll  53  that takes up the web roll  52  which has been wound off is provided in the hot roller  41 . Also, although not shown in the drawings, for example, a cleaning pad or the like serving as a cleaning means is provided in the pressure roller  42 . 
     Meanwhile, as shown in  FIGS. 3 and 4 , a paper transport guide  55  is provided on the further downstream side of the fixing exit guide  44   b  so as to transport the paper sheet P on which fixing has been completed. 
     The paper transport guide  55  is a lower transport guide serving as a guide member that supports the paper sheet P transported after the toner images are fixed on the paper sheet P. A plurality of air vents  56  in a slit-like shape passing through a paper support face  55   a  are provided in the paper transport guide  55  so as to be lined up in the width direction X that is perpendicular to the paper transport direction Y. 
     Moreover, a plurality of guide ribs  57  are provided in the paper support face  55   a  so as to be lined up in the width direction X in order to lower sliding friction by reducing the contact area between the paper transport guide  55  and the paper sheet P. The air vents  56  and the guide ribs  57  are disposed alternately in the width direction X. Also, the air vents  56  and the guide ribs  57  are arranged such that the dimensions of the air vents  56  and the guide ribs  57  along the paper transport direction Y are longer than along the width direction X. 
     A cooling duct  60  that is formed as a separate body from the paper transport guide  55  is provided on the lower face side opposite to the paper support face  55   a  of the paper transport guide  55 . The purpose of arranging this cooling duct  60  is to allow air to flow in order to cool the paper sheet P that is heated in the fixing portion  40  and is transported on the paper transport guide  55 . The cooling duct  60  includes a main duct  61  that is a main ventilation channel to channel cooling air to the fixed paper sheet P passing over the paper transport guide  55  and a sub duct  65  that is a branch of the main duct  61  and is a sub ventilation channel to channel a portion of the cooling air to the solenoid (heat generating element)  48  serving as the drive source of the separation claw unit  45  on the side of the pressure roller  42 . With this configuration, without cooling air affecting the paper sheet P that retains an unfixed toner image, it is possible to effectively cool the fixed paper sheet P passing over the paper transport guide  55  and to effectively cool the solenoid  48  serving as the drive source for driving the paper separation claw  46  to perform separation/contact operations. 
     The upper portion of the main duct  61  serves as a ventilation opening  62  whose shape is one step narrower than the other portion so as to face the air vents  56  provided in the paper transport guide  55 . A leading end opening portion (i.e., leading end opening portion that faces the air vents  56  of the paper transport guide  55 )  62   a  of the ventilation opening  62  is disposed so as to be in communication with the plurality of air vents  56  formed in the paper transport guide  55 . Moreover, the ventilation opening  62  is disposed so as not to project into the paper transport path side (i.e., above the paper support face  55   a ) of the paper support face  55   a  of the paper transport guide  55 . Therefore, the ventilation opening  62  does not come into contact with the paper sheet P that is transported on the paper transport guide  55 . 
     Air is sent from a cooling fan (not shown) to the cooling duct  60  having this configuration, and the air can be directly blown against paper sheets. 
     The suction fan  16  provided on the back face la of the apparatus casing  1  may be used as the cooling fan, or the cooling fan may be provided separately from the suction fan  16 . With this, the paper sheet heated in the fixing portion  40  is cooled. 
     When the paper sheet P is being transported, the cooling air directly hits the paper sheet P, and heat from the paper sheet P flows to the paper support face  55   a  of the paper transport guide  55 . Since the air at this time holds the heat of the paper sheet P and then is diffused, the paper transport guide  55  receives the heat hold by the paper sheet P after the fixing and is warmed. 
     Note that it is preferable that the paper transport guide  55  and the main duct  61  are formed as separate bodies so as not to be in contact with each other. Moreover, it is preferable that a heat insulating member  64  is disposed as a structure support body between the paper transport guide  55  and the main duct  61 . As the heat insulating member  64 , ceramics and non-woven fabrics and the like may be used. Arrangement of the heat insulating member  64  can prevent the heat received by the paper sheet P at the time of passing through the paper transport guide  55  immediately after fixing from transferring directly to the cooling duct  60  side, and thus a temperature increase in the cooling duct  60  is suppressed. It should be noted that the height of the guide ribs  57  may be heightened in order to increase the strength of the paper transport guide  55 . 
     Meanwhile, the sub duct  65  branched from the main duct  61 , as shown in  FIGS. 3 and 5A , may be in a shape of a simple cylinder or a simple quadrangular cylinder, or as shown in  FIGS. 5B and 5C , may be preferably formed in a tapered shape so as to be gradually narrowed from a branch portion  65   a  of the main duct  61  toward a leading end portion  65   b  that faces the solenoid  48  serving as the heat generating element. By forming the sub duct  65  in the tapered shape as above, the occurrence of air accumulation in the sub duct  65  can be prevented, and cooling air can be smoothly blown toward the solenoid  48 . 
     Moreover, an air blowout port  67  is provided in an end face  66  of the leading end portion  65   b  side of the sub duct  65  in order to blow cooling air toward the solenoid  48 . This air blowout port  67 , as shown in  FIGS. 5A and 5B , may be in a shape of a simple cylinder, or as shown in  FIGS. 5C and 5D , may be preferably formed in a nozzle-shape so that an inner diameter R1 of the branch portion  65   a  side (an interior of the leading end portion) is larger and an inner diameter R2 of the solenoid  48  side (an exterior of the leading end portion) is smaller (R1&gt;R2). Since the air blowout port  67  is formed in the nuzzled-shape as above in which the inner diameter of the branch portion  65   a  side (interior) is larger and the inner diameter of the solenoid  48  side (exterior) is smaller, air easily blows out from the inside of the sub duct  65  and it is possible to prevent hot air from flowing back from a space around the fixing portion  40  in the fixing apparatus to the inside of the sub duct  65 . Therefore, it is possible to perform cooling of the solenoid  48 . 
     Moreover, a plurality of slits  29  are provided in a lower partition plate  28   a  that faces the end face  66  of the sub duct  65  so as to be arranged along the direction in which the cooling air that has passed through the sub duct  65  flows. By also arranging the slits  29  in the lower partition plate  28   a  as above, it is possible to guide cooling air in the sub duct  65  from the slits  29  of the lower partition plate  28   a  into the casing portion, and thus it is possible to directly cool the solenoid  48 . Also, even if the amount of cooling air that is introduced into the casing portion through the sub duct  65  is small, it is possible to prevent excess cooling and thermal loss of the fixing apparatus from occurring because the solenoid  48  is effectively cooled. Therefore, the temperature in the fixing apparatus can be kept appropriately. 
     Moreover, as shown in  FIG. 3 , it is preferable that a heat insulating member  68  is disposed as the structure support body between the end face  66  of the sub duct  65  and the lower partition plate  28   a  that faces the end face  66 . As the heat insulating member  68 , ceramics and non-woven fabrics and the like may be used in a similar manner to the above. Arrangement of the heat insulating member  68  can prevent the heat generated in the fixing portion  40  in the fixing apparatus from transferring directly to the sub duct  65 , and thus a temperature increase in the sub duct  65  is suppressed. It should be noted that the sub duct  65  branched from the main duct  61  may be formed as a single body integrating with the main duct  61 , or formed as a separate body from the main duct  61 . 
     In the present embodiment, the cooling duct  60  is only disposed below the paper transport guide  55  and is not disposed above the paper transport guide  55 . In other words, the cooling unit  60  is configured to be unable to directly cool the solenoid  48  of the upper separation claw unit  45  with which the hot roller  41  is provided. This is because it is not necessary to arrange the cooling duct  60  on the upper separation claw unit  45  since the heat generated from the solenoid  48  of the upper separation claw unit  45  rises up and thus effects of the heat on the surface side of the paper transport guide  55  are relatively small. Moreover, as mentioned above, the suction fan  16  is provided on the back face la side of the apparatus casing  1  in order to suck air in the copier and to discharge air outside the copier. An suction duct  17  (see  FIG. 2 ) that is in communication with the suction fan  16  is disposed above the hot roller  41 , more specifically, above the cleaner portion  34 . Therefore, heat generated from the solenoid  48  of the upper separation claw unit  45  is discharged outside of the copier through the suction duct  17 , and thus without arranging the cooling duct  60  above the paper transport guide  55 , the solenoid  48  of the upper separation claw unit  45  is cooled sufficiently. However, quite naturally, the cooling duct  60  may be configured to be disposed above the paper transport guide  55  so that the solenoid  48  of the upper separation claw unit  45  is also cooled by the cooling duct  60 . 
     The present invention may be embodied in various other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all modifications or changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.