Abstract:
A fixing device includes a cylindrical rotating member rotating in a circumferential direction thereof and having a slot at an end thereof and a protruding section extending along an edge of the slot at a front side in a rotational direction of the rotating member, the rotating member receiving a rotational driving force via the slot; a pressing member pressing a recording medium bearing an unfixed toner image on a surface thereof by nipping the recording medium together with the rotating member so as to fix the toner image onto the surface; a heat source heating the recording medium; and a driving member having an engagement section engaged with the slot and in contact with the protruding section at a position separated from a peripheral wall of the cylinder by a certain distance, the driving member imparting the rotational driving force to the rotating member via the engagement section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-069243 filed Mar. 26, 2012. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to fixing devices and image forming apparatuses. 
       SUMMARY 
       [0003]    According to an aspect of the invention, there is provided a fixing device including a rotating member, a pressing member, a heat source, and a driving member. The rotating member has a shape of a cylinder and rotates in a circumferential direction of the cylinder. The rotating member has a slot at an end of the cylinder and a protruding section extending along an edge of the slot at a front side in a rotational direction of the rotating member. The rotating member receives a rotational driving force via the slot. The slot extends through the cylinder from an inside to an outside thereof and also extends from the end toward a center of the cylinder. The protruding section protrudes in a direction that intersects a peripheral wall of the cylinder. The pressing member presses a recording medium bearing an unfixed toner image on a surface thereof by nipping the recording medium together with the rotating member so as to fix the toner image onto the surface. The heat source heats the recording medium nipped between the rotating member and the pressing member. The driving member has an engagement section that is engaged with the slot in the rotating member and is in contact with the protruding section at a position separated from the peripheral wall of the cylinder by a certain distance. The driving member imparts the rotational driving force to the rotating member via the engagement section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
           [0005]      FIG. 1  schematically illustrates the configuration of a printer as an image forming apparatus according to a first exemplary embodiment of the present invention; 
           [0006]      FIG. 2  is a cross-sectional view of a fixing device and a sheet output device in the printer shown in  FIG. 1 ; 
           [0007]      FIG. 3  is a perspective view illustrating a heating roller; 
           [0008]      FIG. 4  illustrates the structure of keyways in the heating roller; and 
           [0009]      FIG. 5  illustrates a state where one of keys of a drive gear is engaged with one of the keyways in the heating roller. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    An exemplary embodiment of the present invention will be described below with reference to the drawings. 
         [0011]      FIG. 1  schematically illustrates the configuration of a printer as an image forming apparatus according to a first exemplary embodiment of the present invention. 
         [0012]    A printer  10  shown in  FIG. 1  is a monochrome printer, and a fixing device according to an exemplary embodiment of the present invention is incorporated in the printer  10 . 
         [0013]    The printer  10  receives an image signal, which is generated outside the printer  10  and expresses an image, via a signal cable (not shown). The printer  10  includes a controller  11  that controls the operation of each component included in the printer  10 , and the aforementioned image signal is input to this controller  11 . Under the control of the controller  11 , the image based on the image signal is formed in the printer  10 . 
         [0014]    Two sheet feed trays  21  are accommodated in a lower area of the printer  10 . The sheet feed trays  21  each accommodate therein sheets P of paper in a stacked state. The accommodated sheets P have different sizes between the two sheet feed trays  21 . The sheet feed trays  21  are ejectable so that new sheets P can be supplied thereto. 
         [0015]    From one of the two sheet feed trays  21 , a corresponding pickup roller  22  feeds sheets P with dimensions suitable for the dimensions of the image expressed by the image signal input to the controller  11 . The fed sheets P are separated into individual sheets by a corresponding separation roller  23 . Each of the separated sheets P is transported upward so that the leading edge of the sheet P reaches a standby roller  24 . The standby roller  24  has a role of transporting the sheet P while adjusting a subsequent transport timing. The sheet P that has reached the standby roller  24  is transported further while the standby roller  24  adjusts the subsequent transport timing. 
         [0016]    In the printer  10 , a photoconductor  12  that rotates in a direction indicated by an arrow A is provided above the standby roller  24 . A charging device  13 , an exposure device  14 , a developing device  15 , a transfer device  16 , and a photoconductor cleaner  17  are arranged around the photoconductor  12 . 
         [0017]    The photoconductor  12  is cylindrical and extends in the depth direction in  FIG. 1 . The photoconductor  12  bears an electric charge when the surface thereof is electrostatically charged, and releases the electric charge when the surface is exposed to light, whereby an electrostatic latent image is formed on the surface. 
         [0018]    The charging device  13  includes a charging roller that rotates by being in contact with the surface of the photoconductor  12 . The charging roller imparts an electric charge to the surface of the photoconductor  12  so as to electrostatically charge the surface. In the charging device  13 , a corona discharger not in contact with the photoconductor  12  may be employed as an alternative to the charging roller. 
         [0019]    The exposure device  14  includes a light-emitting unit that emits laser light (exposure light) modulated in accordance with the image signal supplied from the controller  11 , and a rotating polygonal mirror for scanning the laser light across the photoconductor  12 . The exposure light is output from the exposure device  14 . The photoconductor  12  is exposed to this exposure light so that an electrostatic latent image is formed on the surface of the photoconductor  12 . As an alternative to the laser-light emission type, a light-emitting diode (LED) array having multiple LEDs arranged in the scanning direction may be employed as the exposure device  14 . Furthermore, as an alternative to the exposure type, the latent-image forming unit may be of a type that uses multiple electrodes arranged in the scanning direction so as to directly form a latent image on the surface of the photoconductor  12 . 
         [0020]    The electrostatic latent image formed on the surface of the photoconductor  12  due to the surface thereof being exposed to the exposure light is subsequently developed by the developing device  15 . The developing device  15  includes a developing roller  15   c.  The developing device  15  is connected to a toner container  15   a  via a toner supply path  15   b.  The developing device  15  accommodates therein a developer containing a toner and a magnetic carrier. The toner contained in the toner container  15   a  is appropriately supplied to the developing device  15  via the toner supply path  15   b.  The magnetic carrier is, for example, iron powder coated with a resin coating. The toner particles are composed of, for example, binding resin, a colorant, and a releasing agent. The developing device  15  electrostatically charges the toner and the magnetic carrier by stirring the developer having a mixture of magnetic carrier particles and toner particles. The developer in the developing device  15  is supplied to the surface of the photoconductor  12  by the developing roller  15   c  so that the latent image on the surface of the photoconductor  12  is developed by the electrostatically-charged toner in the developer, whereby a toner image is formed. 
         [0021]    The aforementioned standby roller  24  transports the sheet P such that the sheet P reaches a position facing the transfer device  16  at a timing at which the toner image on the photoconductor  12  reaches that position. Then, the transfer device  16  transfers the toner image on the photoconductor  12  onto the transported sheet P. The transfer device  16  used may alternatively be of a type that indirectly transfers the toner image onto the transported sheet P via an intermediate transfer body. 
         [0022]    The toner remaining on the photoconductor  12  after the toner-image transfer process is removed from the photoconductor  12  by the photoconductor cleaner  17 . 
         [0023]    A combination of the photoconductor  12 , the charging device  13 , the exposure device  14 , the developing device  15 , and the transfer device  16  corresponds to an image forming unit according to an exemplary embodiment of the present invention. 
         [0024]    The sheet P with the toner image transferred thereto travels in a direction indicated by an arrow B and is heated and pressed by a fixing device  100 , whereby the toner image is fixed onto the sheet P. As a result, an image formed of the fixed toner image is formed on the sheet P. The fixing device  100  corresponds to a fixing device according to an exemplary embodiment of the present invention. 
         [0025]    The sheet P passing through the fixing device  100  travels toward a sheet output device  200  in a direction indicated by an arrow C, and is transported further in a direction indicated by an arrow D by the sheet output device  200  so as to be output onto a sheet output tray  18 . 
         [0026]      FIG. 2  is a cross-sectional view of the fixing device  100  and the sheet output device  200  in the printer  10  shown in  FIG. 1 . 
         [0027]    The fixing device  100  includes a heating roller  101  and a pressing roller  102 . The heating roller  101  is formed of a metallic cylinder whose outer peripheral surface is coated with a releasing material. Moreover, a heat source  103  is disposed within the heating roller  101 . The pressing roller  102  is also cylindrical, and the peripheral surface of the pressing roller  102  is pressed against the peripheral surface of the heating roller  101 . The sheet P that has reached the fixing device  100  by traveling in the direction of the arrow B enters a contact section between the pressing roller  102  and the heating roller  101 . The sheet P is nipped between the heating roller  101  and the pressing roller  102  at the contact section. In this case, the sheet P is disposed such that the surface thereof with the toner image faces toward the heating roller  101 . 
         [0028]    The heating roller  101  and the pressing roller  102  rotate in a direction indicated by arrows F while being in contact with each other. Therefore, the sheet P entering the contact section travels through the contact section due to the rotation of the heating roller  101  and the pressing roller  102 , thereby traveling toward the sheet output device  200  in the direction of the arrow C. While traveling through the contact section, the sheet P is heated by the heat source  103  disposed within the heating roller  101  and is also pressed by the pressing roller  102  so that the toner image is fixed onto the sheet P, whereby an image formed of the fixed toner image is formed on the sheet P. 
         [0029]    The heating roller  101  corresponds to a rotating member according to an exemplary embodiment of the present invention. The pressing roller  102  corresponds to a pressing member according to an exemplary embodiment of the present invention. The heat source  103  corresponds to a heat source according to an exemplary embodiment of the present invention. 
         [0030]    The sheet output device  200  is provided with a sheet output roller  203  that continuously transports the sheet P entering the sheet output device  200  in the direction of the arrow C and then further transports the sheet P in the direction of the arrow D. The sheet output roller  203  transports the sheet P in the direction of the arrow D from the sheet output device  200  so as to output the sheet P onto the sheet output tray  18 . 
         [0031]    The heating roller  101  will now be described in detail. 
         [0032]      FIG. 3  is a perspective view illustrating the heating roller  101 . 
         [0033]    A drive gear  104  that rotationally drives the heating roller  101  is fitted around one end of the heating roller  101 . The drive gear  104  has teeth (not shown) arranged therearound and receives a driving force from a motor via the teeth. Furthermore, the drive gear  104  is provided with inwardly-protruding keys  105 . The keys  105  are engaged with keyways  106  provided at the end of the heating roller  101 . The driving force received by the drive gear  104  from the motor is transmitted to the heating roller  101  via the keys  105 , so that the heating roller  101  receives the driving force at the keyways  106 . The heating roller  101  rotates in the direction of the arrow F due to the driving force. 
         [0034]    The drive gear  104  corresponds to a driving member according to an exemplary embodiment of the present invention. The keys  105  correspond to engagement sections according to an exemplary embodiment of the present invention. The keyways  106  correspond to slots in the rotating member according to an exemplary embodiment of the present invention. 
         [0035]    As demands for increasing the processing speed in image forming apparatuses are growing in recent years, it is desirable that the driving force imparted to the heating roller  101  by the drive gear  104  be maximized. Therefore, it is also desirable that the heating roller  101  have enough strength to withstand such a driving force. In order to increase the strength of the heating roller  101  to withstand the driving force, it is particularly desirable that the keyways  106  can withstand a large force. 
         [0036]      FIG. 4  illustrates the structure of the keyways  106  in the heating roller  101 . 
         [0037]    In  FIG. 4 , only the aforementioned end of the heating roller  101  is shown. The heating roller  101  is provided with a total of two keyways  106  located at half-perimeter positions of the heating roller  101 . Each keyway  106  extends from the end of the heating roller  101  toward a recess thereof, and is a so-called open slot that extends through the heating roller  101  from the inside to the outside thereof. The edges of the keyway  106  are provided with protruding walls  107  formed by bending the metallic material constituting the heating roller  101 . The protruding walls  107  protrude toward the inside of the heating roller  101  from a peripheral wall  108  of the heating roller  101 . The protruding walls  107  correspond to protruding sections of the rotating member according to an exemplary embodiment of the present invention. 
         [0038]      FIG. 5  illustrates a state where one of the keys  105  of the drive gear  104  is engaged with one of the keyways  106  in the heating roller  101 . 
         [0039]    The rotational direction of the drive gear  104  and the heating roller  101  is the direction of the arrow F shown in  FIG. 5 . The key  105  of the drive gear  104  is in contact with the protruding wall  107 , at the front side in the rotational direction, of the heating roller  101  at a position separated from the peripheral wall  108  by a certain distance. Therefore, a section of the protruding wall  107  from the base thereof to the contact area functions as a spring, so that stress generated due to the received driving force is dispersed. As a result, the heating roller  101  may withstand a large driving force. Specifically, in this exemplary embodiment, since a side surface  105   a  of the key  105  is in contact with an end of the aforementioned protruding wall  107 , the entire protruding wall  107  functions as a spring, whereby the heating roller  101  may withstand an even larger driving force. 
         [0040]    Based on simulation performed on the heating roller  101  having the above structure, it is confirmed that the safety factor is improved by about 1.4 to 1.9 times that of a comparative example in which the protruding walls  107  are entirely in contact with the keys  105 . 
         [0041]    Although the above exemplary embodiment relates to a monochrome printer as an example of an image forming apparatus, the image forming apparatus according to the exemplary embodiment of the present invention may be a color printer, a facsimile apparatus, a copier, or a multifunction apparatus. 
         [0042]    Furthermore, although the image forming unit in the above exemplary embodiment of the present invention is of a type that transfers a toner image formed on a photoconductor onto a recording medium, the image forming unit according to the exemplary embodiment of the present invention may alternatively be of a type that directly forms a toner image on a recording medium. 
         [0043]    Furthermore, although the rotating member in the above exemplary embodiment of the present invention is provided with two keyways, the rotating member according to the exemplary embodiment of the present invention may alternatively have a single keyway, or three or more keyways. 
         [0044]    The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.