PATENT ABSTRACT
An image forming apparatus includes a main assembly; a fixing unit including a fixing rotatable member for fixing an unfixed image formed on a recording material, and a frame for accommodating the fixing rotatable member, the fixing unit is detachably mountable to the main assembly; and an air feeding member for feeding air to the fixing rotatable member provided in the main assembly, wherein the frame is provided with an opening for applying the air fed from the air feeding member to the fixing rotatable member, and an openable member movable between a first position for closing the opening and a second position for opening the opening, wherein the openable member moves from the second position to the first position in response to an operation of taking the fixing unit out of the main assembly.

PATENT DESCRIPTION
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a fixing apparatus (fixing device) to be mounted in an electrophotographic image forming apparatus such as a copying machine, a printer, and the like. It relates to also an image forming apparatus equipped with a fixing apparatus (fixing device). 
     Generally speaking a fixing apparatus (device) to be mounted in an electrophotographic image forming apparatus is provided with a rotational fixing member, which contacts a sheet of recording medium which is bearing an unfixed toner image. 
     By the way, it has been known that in a case where a substantial number of images are continuously formed with the use of a printer equipped with a fixing device of the so-called contact heating type, that is, a fixing device having a rotational fixing member which contacts a sheet of recording medium, the portions of rotational fixing member, which are outside the path of a sheet of recording medium, excessively increase in temperature (unwanted temperature increase across out-of-sheet-path portions of recording medium). As the out-of-sheet-path portions of a rotational fixing member excessively increase in temperature, the structural components of a fixing device are sometimes damaged by the excessive amount of heat. 
     There is disclosed in Japanese Laid-open Patent Application 2003-076209, a fixing apparatus which is equipped with a cooling fan for preventing the portions of the heat roller and pressure roller of the fixing device, which are outside the path of recording medium, from excessively increasing in temperature. By the way, it has been thought to structure an image forming apparatus and the fixing device therefor so that the fixing device can be removably mountable in the main assembly of the image forming apparatus, for the maintenance or replacement of the fixing device. The fixing device disclosed in Japanese Laid-Open Patent Application 2003-076209 is provided with a cooling fan, and a duct for guiding cooling air. If an image forming apparatus equipped with a fixing device having a cooling fan, and a duct for guiding cooling air, is structured so that the fixing device is removably mountable in the main assembly of the image forming apparatus, it occurs that as the fixing device is replaced, the cooling fan and cooling air duct also are replaced. Thus, a fixing device configuration such as the one disclosed in abovementioned patent application is undesirable from the standpoint of cost. 
     On the other hand, in consideration of the cost related to the replacement of a fixing device, it is possible to structure an image forming apparatus and the fixing device therefor in such a manner that as the fixing device is removed from the main assembly of the image forming apparatus, the cooling fan for the fixing device remains in the main assembly of the image forming apparatus. In such a case, however, the frame of the fixing device has to be provided with an opening through which cooling air is guided from the cooling fan to the rotational fixing member. With the presence of this opening, it is possible for an operator (user) of the image forming apparatus to come into contact with the rotational fixing member. Thus, it is undesirable that when the fixing device is out of the main assembly of the image forming apparatus, the opening of the fixing device, which is for guiding cooling air to the rotational fixing member of the fixing device, remains exposed. 
     SUMMARY OF THE INVENTION 
     The present invention is made in consideration of the above-described problem. Thus, the primary object of the present invention is to provide a combination of an image forming apparatus which is low in cost and yet can send cooling air into its fixing device, and a fixing device which is removably mountable in the image forming apparatus. 
     Another object of the present invention is to provide a fixing device, the opening of which for cooling air can be open or closed, and an image forming apparatus structured so that the fixing device is removably installable in the main assembly of the image forming apparatus. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising a main assembly; a fixing unit including a fixing rotatable member for fixing an unfixed image formed on a recording material, and a frame for accommodating said fixing rotatable member, said fixing unit is detachably mountable to said main assembly; and an air feeding member for feeding air to said fixing rotatable member provided in said main assembly, wherein said frame is provided with an opening for applying the air fed from said air feeding member to said fixing rotatable member, and an openable member movable between a first position for closing said opening and a second position for opening said opening, wherein said openable member moves from the second position to the first position in response to an operation of taking said fixing unit out of said main assembly. 
     According to another aspect of the present invention, there is provided a fixing unit detachably mountable to a main assembly of an image forming apparatus, said fixing unit comprising a fixing rotatable member; and a frame accommodating said fixing rotatable member; wherein said frame is provided with an opening for applying air fed by an air feeding member provided in the main assembly to said fixing rotatable member, and an openable member movable between a first position for closing said opening and a second position for opening said opening, wherein said openable member moves from the second position to the first position in response to an operation of taking said fixing unit out of the main assembly. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of a typical image forming apparatus to which the present invention is applicable, as seen from the front side of the apparatus, and shows the general structure of the apparatus. 
         FIG. 2  is a perspective view of the fixing device, as seen from diagonally above the left and upstream corner (in terms of recording medium conveyance direction), after the removal of the fixing device from the main assembly of the image forming apparatus shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the fixing device, as seen from the front side of the image forming apparatus, when the fixing device is in the normal position in the image forming apparatus. 
         FIG. 4  is a schematic drawing of the essential portions of the fixing device. 
         FIG. 5  is a perspective view of the mechanism for controlling the shutter of the fixing device, and shows the general structure of the mechanism. 
         FIG. 6A  is a perspective view of the mechanism for controlling the rotatably movable entrance guide of the fixing device, and shows the general structure of the mechanism. 
         FIG. 6B  is a perspective view of the mechanism for controlling the rotatably movable entrance guide of the fixing device, and shows the general structure of the mechanism. 
         FIG. 6C  is a perspective view of the mechanism for controlling the rotatably movable entrance guide of the fixing device, and shows the general structure of the mechanism. 
         FIG. 6D  is a perspective view of the mechanism for controlling the rotatably movable entrance guide of the fixing device, and shows the general structure of the mechanism. 
         FIG. 7A  is a drawing (1) for describing how the fixing device is to be installed into the main assembly of the image forming apparatus. 
         FIG. 7B  is a drawing (2) for describing how the fixing device is to be installed into the main assembly of the image forming apparatus. 
         FIG. 7C  is a drawing (3) for describing how the fixing device is to be installed into the main assembly of the image forming apparatus. 
         FIG. 8  is a perspective view of the cooling device for cooling the lengthwise end portions of the rotational fixing member to prevent the lengthwise end portions of the rotational member from excessively increasing in temperature, and shows the general structure of the device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     (1) Example of Image Forming Apparatus 
     The image forming apparatus in this embodiment is an apparatus which forms an image on a sheet of recording medium, with the use of an appropriate image formation process, while the sheet is conveyed through the apparatus. Then, it outputs the print, that is, the sheet of recording medium on which the image has just been formed. The recording medium is in the form of a sheet of recording medium, on which an image can be formed. It includes a sheet of various ordinary paper, resin-coated paper, OHP film, envelops, postcards, etc, which are in a specific, or nonspecific form (which hereafter may be referred to simply as sheet). 
     Regarding the orientation of the image forming apparatus, the front side of the apparatus is the left side of the apparatus when the apparatus is seen from the upstream side of the sheet conveyance direction of the transfer nip of the image forming portion of the main assembly of the apparatus. The back side of the apparatus is the right side of the apparatus as seen from the upstream side of the apparatus in terms of the sheet conveyance direction of the transfer nip of the image forming portion of the main assembly of the apparatus. 
       FIG. 1  is a an example of image forming apparatus, as seen from the front side of the apparatus after the installation of a fixing device in accordance with the present invention into the main assembly of the apparatus. It shows the general structure of the apparatus. This image forming apparatus is an electrophotographic, digital, and monochromatic printer. 
     Referring to  FIG. 1 , designated by a numeral  100  is the main assembly of the image forming apparatus, which includes the external shell portion of the apparatus (which hereafter will be referred to simply as apparatus main assembly). There are an image forming portion  101  which forms a toner image (image) on a sheet S of recording medium, and a fixing portion (fixing device)  103  which fixes the unfixed toner image (image) formed on the sheet S, in the apparatus main assembly  100 . There are also in the apparatus main assembly  100 , a sheet feeder cassette  105  in which sheets S of recording medium (paper) are storable, and a sheet conveying portion  102  which conveys each sheet S of recording medium from the sheet feeder cassette  105  through the image forming portion  101  and fixing portion  103 . Further, there is: a sheet turning-and-conveying portion  126  which is for turning the sheet S over after the conveyance of the sheet S through the fixing portion  103 , and then, conveying the sheet S to the image forming portion  101 ; a control portion  200  which controls the entirety of the image forming apparatus; etc., in the apparatus main assembly  100 . 
     The control portion  200  comprises a CPU, and memories such as a RAM and a ROM in which image formation sequences, various tables necessary for image formation, etc., are stored. The control portion  200  makes the image forming apparatus to carry out one of the image formation sequences in response to a print command issued by an external apparatus (unshown) such as a host computer or the like. 
     First, a case in which the control portion  200  makes the image forming apparatus to carry out an image formation sequence in response to a print command for forming an image on only one of the two surfaces of a sheet S of recording medium is described. First, an electrophotographic photosensitive member (which hereafter will be referred to as photosensitive drum)  111 , which is in the form of a drum, is rotated at a preset peripheral velocity (process speed), in the image forming portion  101 . As the photosensitive drum  111  is rotated, the peripheral surface of the photosensitive drum  111  is uniformly charged to preset polarity and preset potential level by a charge roller (charging means)  112  (charging process). 
     Next, the uniformly charged portion of the peripheral surface of the photosensitive drum  111  is scanned by (exposed to) the beam of laser light outputted from a laser beam scanner (exposing means)  113  while being modulated (turned on and off) according to the information of the image to be formed, which is sent to the scanner  113  from an external apparatus (exposing process). Consequently, an electrostatic latent image, which reflects the information of the image to be formed, is effected on the peripheral surface of the photosensitive drum  111 , is formed. Then, the electrostatic latent image on the peripheral surface of the photosensitive drum  111  is developed into a visible image, that is, an image (toner image) formed of toner, by a developing device (developing means)  114  which uses toner. As for developing methods, there are jumping developing method, two-component developing method, or the like. Generally speaking, it is more likely that an electrostatic latent image is formed as an equivalent of a negative image of ordinary photography, and is reversely developed. 
     Meanwhile, the sheets S in the sheet feeder cassette  105  are moved out one by one from the cassette  105  with a preset sheet feeding timing by the rotation of the pickup roller  106 . Then, each sheet S is conveyed by the rotation of the sheet feeding roller  107  to a pair of registration rollers  110  through a sheet conveyance guide  109   a . The registration rollers  110  are rotated with a preset timing, whereby the sheet S is sent into the transfer nip N 1 , which is the area of contact between the peripheral surface of the photosensitive drum  111  and the peripheral surface of the transfer roller (transferring means)  115 . Then, the sheet S is conveyed toward the fixing device  103  by being pinched between the peripheral surface of the photosensitive drum  111  and the peripheral surface of the transfer roller  115 . While the sheet S is conveyed between the peripheral surface of the photosensitive drum  111  and the peripheral surface of the transfer roller  115 , remaining pinched by the photosensitive drum  111  and transfer roller  115 , a preset transfer bias is applied to the transfer roller  115 . Consequently, the toner image on the peripheral surface of the photosensitive drum  111  is transferred onto the sheet S (transferring process). 
     The sheet S which is bearing the toner image transferred from the peripheral surface of the photosensitive drum  111  is introduced into the fixation nip N 2  of the fixing device  103 , in which heat and pressure are applied to the unfixed toner image on the sheet S. As a result, the unfixed toner is thermally fixed to the sheet S. The structure of the fixing device  103  will be described later in detail, in Section (2). 
     After the sheet S is conveyed out of the fixing device  103 , the sheet S is discharged into a print stacking portion  124  provided outside the apparatus main assembly  100 , by the combination of a sheet discharge guide  109   b , and the rotation of a pair of discharge rollers  120 . 
     Designated by a numeral  125  is a lever for detecting whether or not the print stacking portion  124  is full with sheets S. As it is detected by the lever  125  that the print stacking portion  124  is full with sheets S, the control portion  200  controls the image forming portion  101  so that the image forming portion  101  does not form an image on a sheet S until all the sheet S on the sheet stacking portion  124  are removed. 
     After the separation of the sheet S from the peripheral surface of the photosensitive drum  111 , the photosensitive drum  111  is cleaned by cleaning blade  104  which is placed in contact with the peripheral surface of the photosensitive drum  111  to remove such substances as toner remaining on the peripheral surface of the photosensitive drum  111  after the transfer of the toner image from the photosensitive drum  111  (cleaning process), in order to make the peripheral surface of the photosensitive drum  111  ready to be repeatedly used for the following image formation. 
     In a case where the control portion  200  carries out an image formation sequence in response to a print command for forming an image on both surfaces of a sheet S of recording medium, after a sheet S is conveyed out of the fixing device  103 , it is conveyed to the sheet reception roller  123  by the sheet directing portion  122  of a sheet reversing-conveying portion  126 . Then, the sheet S is conveyed to a sheet reversing portion  124  through a bifurcation point  127  by the coordination between the sheet reception roller  123  and sheet reversing roller  122 , and is conveyed through the sheet reversing-conveying portion  124 . However, as soon as the trailing edge of the sheet S passes the bifurcation point  127 , the reversing roller  128  begins to be rotated in reverse so that the sheet S begins to be conveyed toward a reversal conveyance passage  121 , from the trailing edge side. Consequently, the sheet S is conveyed toward the registration rollers  110  by the rotation of a pair of sheet conveyance rollers  129 . 
     Then, the registration rollers  110  send the sheet S into the transfer nip N 1  of the image forming portion  101  with a preset timing. In the image forming portion  101 , each of the above described processes of charging, exposing, developing, and transferring is carried out to form an unfixed toner image on the surface of the sheet S, on which an image has not been formed. Then, the sheet S is introduced into the fixation nip N 2  of the fixing device  103 , in which heat and pressure are applied to the sheet S and the unfixed toner image thereon. Consequently, the unfixed toner image is thermally fixed to the surface of the sheet S. After being conveyed out of the fixing device  103 , the sheet S is discharged into the print stacking portion  124  by the coordination between the sheet discharge guide  109   b  and the rotation of the discharge rollers  120 . 
     Referring to  FIG. 1 , a referential code S 3  stands for a sheet sensor which detects a sheet S of recording medium. The apparatus main assembly  100  is provided multiple sheet sensors S 2 , which are positioned at the sheet feeder cassette  105 , and various preset points, one for one, of the recording medium conveyance passage of the apparatus main assembly  100 . 
     The image forming apparatus is enabled to deal with various types of sheet S of recording medium, in terms of width and length. Therefore, in an image forming operation in which a substantial number of sheets S, the width of which is narrower than the width of the widest sheet S conveyable through (introducible into) the apparatus, are continuously conveyed through the fixing device  103  in such a manner that in terms of the widthwise direction of the recording medium passage of the fixing device  103 , the center of each sheet S coincides with the center of the recording medium conveyance passage, or the edge of the sheet S coincides with the corresponding edge of the recording medium passage, there occurs the phenomenon that the portions of the rotational fixing member of the fixing device  103 , which are outside the recording medium path, excessively increases in temperature. As will be described later in detail, a widest sheet of recording medium conveyable through the fixing device  103  will be referred to as a largest sheet, and a sheet of recording medium which is narrower than the largest sheet will be referred to as a narrow sheet. Here, “sheet width” means the dimension of a sheet, in terms of the direction perpendicular to the sheet conveyance direction, when a sheet of recording medium is being conveyed through the sheet conveyance passage. 
     The image forming apparatus in this embodiment is provided with a cooling device Q for prevent the problem that in terms of the widthwise direction of the recording medium passage of the fixing device  103 , the portions of the rotational fixing member of the fixing device  103 , which are outside the recording medium path, excessively increase in temperature. The cooling device Q is positioned on the upstream side of the fixing device  103  in terms of the sheet conveyance direction. This cooling device Q will be described later in detail in Section (6). 
     (2) Fixing Device (Fixation Unit)  103   
     (2-1) General Structure of Fixing Device (Fixation Unit)  103   
       FIG. 2  is a perspective view of the fixing device  103  as seen from diagonally above the left and upstream (in terms of sheet conveyance direction) corner of the fixing device  103 , when the fixing device  103  is out of the apparatus main assembly  100 . It shows the state of the fixing device  103 , in which the shutter (member which can be opened or closed)  141  and rotationally movable entrance guide  151  of the fixing device  103  are closed.  FIG. 3  is a cross-sectional view of the fixing device  103 , as seen from the front side of the apparatus main assembly  100  when the fixing device  103  is in its normal position in the apparatus main assembly  100 . It shows the state of the fixing device  103 , in which the shutter  141  and rotationally movable entrance guide  151  of the fixing device  103  are open. The rotationally movable guide  151  plays the role of guiding a sheet S into the fixing device  103 . 
     A state in which the shutter  141  is closed is such a state that the shutter  141  is in a position (first position) in which its keeps covered the opening O 1  ( FIG. 3 ) of the fixing device  103 , which will be described later, as indicated by a single-dot chain line in  FIG. 3 . A state in which the shutter  141  is open is such a state that the shutter  141  is in a position (second position) in which its keeps exposed the opening O 1  as indicated by a solid line in  FIG. 3 . A state in which the rotationally movable entrance guide  151  is closed is such a state that the rotationally movable entrance guide  151  is in a position in which it keeps covered the nip entrance O 2  ( FIG. 3 ) of the fixing device  103 . A state in which the rotationally movable entrance guide  151  is open is such a state that the rotationally movable entrance guide  151  is in a position in which the rotationally movable guide  151  keeps the nip entrance O 2  exposed. 
       FIG. 4  is a schematic drawing of the essential portions of the fixing device  103 .  FIG. 4(   a ) is a cross-sectional view of the essential portions of the fixing device  103 , and shows the interior of the fixing device  103 .  FIG. 4(   b ) is a side view of the essential portions of the fixing device  103 , as seen from the upstream side of the fixing device  103  in terms of the sheet conveyance direction.  FIG. 4(   c ) is a side view of the ceramic heater  140  of the fixing device  103 , and shows the general structure of the heater  140 . This fixing device  103  is of such a type that has a fixation belt (which hereafter may be referred to as rotational fixing member or fixation film). It heats the unfixed toner image on a sheet S of recording medium with the use of the fixation belt. 
     Referring to  FIGS. 4(   a ) and  4 ( b ), designated by numerals  135  and  130  are a stay (rigid member) and a heater holder (heating member supporting member), respectively. Designated by numerals  131  and  116  are a ceramic heater (heating generating member) as a heat source, and a cylindrical fixation belt (first rotational member) as a rotational fixing member, respectively. Designated by numerals  117 ,  132 L, and  132 R are a pressure roller (second rotational member), and a pair of flanges (regulating members) which regulate the fixation belt  116  in lateral shift, respectively. 
     The stay  135  is roughly U-shaped in cross-section. It is formed by bending a piece of metallic plate. It is heat resistant and rigid. The heater holder  130  is formed of heat resistant resin. The stay  135  and heater holder  130  are put together so that the stay  135  is placed on the upwardly facing surface of the heater holder  130  to reinforce the heater holder  130  with the stay  135 . 
     The heater  131  has a long and narrow heater substrate (which hereafter will be referred to simply as substrate)  131   a  formed of highly heat resistant ceramic. The heater  131  has a heat generating resistor  131   b , which was formed on the downwardly facing surface of the substrate  131   a  by printing, in such an attitude that the lengthwise direction of the heat generating resistor  131   b  becomes parallel to the lengthwise direction of the substrate  131   a . The heat generating resistor  131   b  generates heat as electric current is flowed through it. Further, the heater  131  has a pair of electrically conductive portions  131   c  for supplying the heat generating resistor  131   b  with electric power, and a pair of electrodes  131   d  for supplying the heat generating resistor  131   b  with electric power through the electrically conductive portions  131   c . The electrically conductive portions  131   c  and electrodes  131   d  were formed also by printing, on the downwardly facing surface of the substrate  131   b . Further, the heater  131  is provided with a glass layer (protective layer)  131   e  coated on the downwardly facing surface of the substrate  131   b  in a manner to cover the heat generating resistor  131   b  to protect the resistor  131   b.    
     The heat holder  130  is provided with a groove  130   a , which is in the downwardly facing surface of the heater holder  130  and extends in the lengthwise direction of the holder  130 . It is in this groove  130   a  that the heater  131  is held. 
     The stay  135  and heater  131  are attached to the heater holder  130 , and the fixation belt  116  is loosely fitted around the combination of the stay  135 , heater  131 , and heater holder  130 . 
     Referring to  FIG. 4(   b ), there are disposed a pair of belt flanges  132 L and  132 R at the lateral edges of the fixation belt  116 , one for one. The belt flanges  132 L and  132 R have base portions  132 L 1  and  132 R 1 , regulating portions  132 L 2  and  132 R 2 , guiding portions  132 L 3  and  132 R 3 , etc., respectively. 
     The base portions  132 L 1  of the belt flange  132 L are supported by the frame  133 L of the fixation unit. The base portion  132 R 1  of the belt flange  132 R is supported by the frame  133 R of the fixation unit. 
     The regulating portions  132 L 2  and  132 R 2  are for regulating the movement of the fixation belt  116  in the thrust direction of the fixation belt  116 , which occurs as the fixation belt  116  is circularly driven. The guiding portions  132 L 3  and  132 R 3  are for guiding the fixation belt  116  from the inward side of the fixation belt  116  while the fixation belt  116  is circularly driven. 
     The pressure roller  117  has a metallic core  117   a , and an elastic layer  117   b  which covers most of the peripheral surface of the metallic core  117   a . As for the material for the elastic layer  117   b , heat resistant solid rubber such as silicone rubber, fluorinated rubber, or the like, can be used. Further, the pressure roller  117  is provided with a parting layer  117   c  which was formed of fluorinated resin or the like in a manner to cover the entirety of the outward surface of the elastic layer  117   b . The pressure roller  117  is disposed so that it opposes the heater  131 , with the presence of the fixation belt  116  between itself and the heater  131 . The lengthwise end portions of the metallic core  171   a  of the pressure roller  117  are rotatably supported by the frames  133 L and  133 R of the fixation unit, with the placement of a pair of bearings  133 L and  133 R between the metallic core  117   a  and frames  133 L and  133 R, respectively. 
     Further, the fixing device  103  is provided with a pair of pressure plates  136 L and  136 R, which are disposed so that they remain pressed upon the upwardly facing surfaces of the base portions  132 L 1  and  132 R 1  of the belt flanges  132 L and  132 R, respectively, by a pair of compression springs (unshown). 
     Since the pressure plates  136 L and  136 R are under the pressure from this pressure applying mechanism, the belt flanges  132 L and  132 R are made to press the heater holder  130  with the presence of the stay  135  between themselves and the heater holder  130 . Thus, the heater  131  is kept pressed upon the pressure roller  117  with the presence of the fixation belt  117  between itself and the pressure roller  117 . Thus, the elastic layer  3   b  of the pressure roller  3   b    117   b  of the pressure roller  117  is elastically deformed by the pressure applied to the pressure roller  117  by the heater  131 , creating thereby the fixation nip N 2  between the outward surface of the fixation belt  116  and peripheral surface of the pressure roller  117 . 
     The pressure applying mechanism has a pressure relieving mechanism which is for removing the pressure from the heater holder  130  to make it easier to remove a jammed sheet S from the fixing device  103 . 
     (2-2) Thermally Fixing Operation of Fixing Device  103   
     The control portion  200  begins to rotationally drive the motor (unshown) of the fixing device  103  in response to a print start command. The rotation of the output shaft of this motor is transmitted to a pressure roller gear  137  ( FIG. 2 ), with which the metallic core  1107   a  of the pressure roller  117  is fitted, through a preset speed reduction gear train (unshown). Consequently, the pressure roller  117  rotates in the direction indicated by an arrow mark ( FIG. 4(   a )). The rotation of the pressure roller  117  is transmitted to the fixation belt  116  by the friction which occurs between the peripheral surface of the pressure roller  117  and fixation belt  116 , in the fixation nip N 2 . Thus, the fixation belt  116  rotates in the direction indicated by an arrow mark ( FIG. 4(   a )), following the rotation of the pressure roller  117 , with the inward surface of the fixation belt  116  remaining in contact with the surface of the glass coat layer  131   e  of the heater  131 . 
     The inward surface of the fixation belt  116  is coated with grease (lubricant), which ensures that the fixation belt  116  smoothly slides on the combination of the heater  140  and heater holder  142 . 
     The control portion  200  takes in the detection signals (output signals) outputted from the thermistor (temperature detecting means)  210  disposed at the mid portion of the heater  131  in terms of the lengthwise direction of the heater  131 , and determines the duty ratio by which electric power is to be supplied to the heat generating resistor  131   b , based on these detection signals. Then, it controls a triac  202  based on this duty ratio, to maintain the temperature of the heater  131  at a preset fixation temperature (target temperature level). 
     As a sheet S on which an unfixed toner image is borne is conveyed through the fixation nip while the motor is rotationally driven, and the temperature of the heater  113  is kept at the target temperature level, the toner image is fixed to the sheet S. 
     After being conveyed out of the fixation nip N 2 , the sheet S is conveyed to the sheet conveyance passage, which is on the downstream side of the fixing device  103  in terms of the sheet conveyance direction, while remaining pinched by sheet discharge rollers  118  and  119  ( FIG. 3 ). 
     (3) Structure of Mechanism  140  for Opening or Closing Shutter  141   
     Referring to  FIGS. 3 and 7C , the frame (frame  133 ) of the fixing device  103  is provided with the openings O 1  which oppose the different portions of the fixation belt  116  from the fixation nip (N 2 ) portion of the fixation belt  116 , in terms of the circumferential direction of the fixation belt  116 . These opening O 1  are for allowing the cooling duct  171  of the cooling device Q with which the apparatus main assembly  100  is provided to cool the lengthwise end portions (out-of-sheet-path portions) of the rotational fixing member of the fixing device  103 , to be inserted into the fixing device  103 . Further, the frame ( 133 ) of the fixing device  103  is provided with a nip entrance O 2 , which is on the upstream side of the fixation nip N 2 , in terms of the sheet conveyance direction. This nip entrance O 2  is for guiding a sheet S of recording medium into the fixation nip N 2 . 
     Referring to  FIG. 2 , the fixing device  103  is provided with the first mechanism  140  having the shutter  141  for exposing or covering the openings O 1 , and the second mechanism  150  having the guide  151  which plays the role of guiding a sheet of recording medium to the fixation nip, and also, the role of exposing or covering the nip entrance O 2 . 
     The rotational axle  133 R 1  ( 133 L 1 ) of the first opening-closing mechanism  140  is disposed on the downstream side of the fixation nip N 2  in terms of the sheet conveyance direction. The shutter  141  is rotationally moved about the axle  133 R 1  ( 133 L 2 ) by the operation for installing the fixing device  103  into the apparatus main assembly  100 . 
     Further, the opening-closing mechanism  140  is structured so that as the fixing device  103  is moved out of the apparatus main assembly  100 , the shutter  141  is positioned above the fixation belt  116  to cover the opening O 1 , by the movement of the fixing device  103 . This shutter position above the fixation belt  116  is indicated by a single-dot chain line in  FIG. 3 . 
     That is, the apparatus main assembly  100  and fixing device  103  are structured so that as the fixing device  103  is inserted into the apparatus main assembly  100 , the shutter  141  is moved by the inward movement of the fixing device  103 , into the position in which the shutter  141  exposes the opening O 1 , and also, so that as the fixing device  101  is moved out of the apparatus main assembly  100 , the shutter  141  is moved by the outward movement of the fixing device  103 , into the position in which the shutter  103  covers the opening O 1 . 
       FIG. 5  is a perspective view of the opening-closing mechanism  140 , and shows the general structure of the opening-closing mechanism  140 . More specifically,  FIG. 5(   a ) is a perspective view of the opening-closing mechanism  140  when the shutter  141  is open, and  FIG. 5(   b ) is a perspective view of the opening-closing mechanism  140  when the shutter  141  is closed. 
     Referring to  FIGS. 2 and 6 , the opening-closing mechanism  140  has a long and narrow shutter  141 , a pair of arms  142 L and  142 R which support the lengthwise ends of the shutter  141 , one for one, etc. The shutter  141  is provided with a pair of shafts  141   a  and  141   b , which are integral parts of the length end portions of the shutter  141 , and are rotatably supported by the arms  142 L and  142 R, respectively. Further, the arms  142 L and  142 R are rotationally movable about a pair of rotational centers  142 Lb and  142 Rb, which are rotatably supported by the frame  133 L and  133 R of the fixation unit, making up the rotational axles  133 L 1  and  133 R 1 , respectively. 
     The arms  142 L and  142 R have engaging ends  142 La and  143 Ra, which are the top end portions of the arms  142 L and  142 R, respectively. They have also the rotational center portions  142 Lb and  142 Rb, which are the bottom portions of the arms  142 L and  142 R, respectively. The engaging end portions  142 La and  142 Ra of the arms  142 L and  142 R are provided with holes  143   a  and  144   a , respectively. The rotational center portions  142 Lb and  142 Rb are provided with shafts  143   b  and  144   b  having a hole (which hereafter may be referred to as hollow shafts). 
     The shaft portions  141   a  and  141   b  of the shutter  141  fit into the holes  143   a  and  144   a  of the engaging end portions  142 La and  142 Rra, whereby the shutter  141  is rotatably supported by the engaging end portions  142 La and  142 Ra. The shaft portions  133 L 1  and  133 R 1  of the frames  133 L and  133 R of the fixation unit ( FIG. 3 ) are fitted in the holes of the hollow shaft portions  143   b  and  144   b  of the arms  142 L and  142 R, whereby the arms  142 L and  142 R are rotatably supported by the frames  133 L and  133 R of the fixation unit, respectively. 
     The arms  142 L and  142 R are under the pressure generated by the torsional coil springs  146 L and  146 R, with which the hollow shaft portions  143   b  and  144   b  are provided, in the direction to rotate the arm  142 L and  142 R about the shaft portion  143   b  and  144 B, respectively. The direction indicated by the arrow mark A is the direction in which the shutter  141  is rotated to cover the opening O 1 . Further, the shutter  141  is under the pressure generated by the torsional coil springs  145 L and  145 R, with which the shaft portion  141   a  and  141   b  is provided, in the direction to rotationally move the shutter  141  about the shaft portion  141   a  and  141   b  in the direction indicated by an arrow mark B. The direction indicated by the arrow mark B is also the direction in which the shutter  141  is moved to cover the opening O 1 , like the direction indicated by the arrow mark A. 
     The engaging end portions  142 La and  142 Ra are provided with engaging portions  142 La 1  and  142 Ra 1 , which are located at preset positions of the peripheral surfaces of the engaging end portions  142 La and  142 Ra, respectively, to control the opening and closing of the shutter  141 . 
     (4) Structure of Mechanism  150  for Opening and Closing Guide 
     The guide opening-closing mechanism  150  is disposed on the upstream side of the fixation nip N 2  of the fixing device  103  in terms of the sheet conveyance direction. It is structured so that as the front door FD ( FIG. 6A ) of the apparatus main assembly  100 , which can be opened or closed is closed (moved in direction indicated by arrow mark P 1 ), the guide  151  is retracted into a position, which is a preset distance apart from a hypothetical extension (line) N 2 L of the fixation nip N 2  ( FIG. 3 ), to expose the nip entrance opening O 2 . This hypothetical extension (line) N 2 L is such a line that is perpendicular to the line which connects the center of the fixation belt  116  and the center of the pressure roller  117 , and is tangential to the outward surface of the fixation belt  116  and the peripheral surface of the pressure roller  117 . The position in which the guide  151  is after being retracted is contoured by a solid line in  FIG. 3 . The apparatus main assembly  100  is structured so that when the guide  151  is in this position of retraction, the guide  151  guides an upwardly curled sheet S of recording medium to the fixation nip N 2 . 
     Further, the guide opening-closing mechanism  150  is structured so that as the door on the front side (which hereafter will be referred to as front door) FD is opened (moved in direction indicated by arrow mark P 2 ), the guide  151  is moved in the direction perpendicular to the theoretical extension (line) N 2 L in a manner to cover the nip entrance opening O 2 . The position in which the guide  151  is when it became perpendicular to the theoretical extension (line) N 2 L is shown in  FIG. 6C . 
     That is, the guide opening-closing mechanism  150  is structured so that as the front door FD is closed, the guide  151  is rotationally moved into the position in which it keeps the nip entrance opening O 2  exposed, whereas as the front door FD is opened, the guide  151  is rotationally moved into the position in which it keeps the nip entrance opening O 2  covered. 
       FIGS. 6A-6D  are perspective views of the guide opening-closing mechanism  150 , which shows the general structure of the mechanism  150 . More specifically,  FIG. 6A  is a perspective view of the guide opening-closing mechanism  150  when the guide  151  is open, and  FIG. 6B  is an enlarged perspective view of the guide opening-closing mechanism  150 , as seen from the rear side of the mechanism  150  when the mechanism  150  is in the state shown in  FIG. 6A .  FIG. 6C  is a perspective view of the mechanism  150  when the guide  151  is closed, and  FIG. 6D  is an enlarged perspective view of the mechanism  150  when the mechanism  150  is in the state shown in  FIG. 6C . Incidentally, in order to prevent  FIGS. 6B and 6C  from appearing unnecessarily complicated, the guide  151  is not shown in the two drawings. 
     Referring to  FIGS. 2 and 6 , the guide opening-closing mechanism  150  has: the long and narrow guide  151 , an opening-closing button  152 , a camshaft  153 , a linkage plate  154 , a linkage plate  155 , etc. 
     The opening-closing button  152  is attached to the frame  133 L of the fixation unit in such a manner that it can be slid in the lengthwise direction of the guide  151 . The opening-closing button  152  is under the pressure generated by a spring (unshown) generated in the direction (indicated by arrow mark P 2 ) to make the button  152  protrude frontward (leftward in drawing) of the fixing device  103 . 
     The camshaft  153  is rotatably supported by the frame  133 L of the fixation unit, and is in contact with the opening-closing button  152 . The surface  152   a  of the opening-closing button  152 , which faces the camshaft  153 , and the surface  152   b  of the camshaft  153 , which faces the opening-closing button  152 , are slanted (hence, slanted surfaces  152   a  and  153   a ) at such angles that the linear movement of the opening-closing button  152  is converted into the rotational movement of the camshaft  153 . That is, as the opening-closing button  152  is moved in the direction indicated by the arrow mark P 1  (by being pushed by front door FD), the slanted surface  153   a  of the camshaft  153  is moved in the direction indicated by an arrow mark X, following the slanted surface  152   a  of the opening-closing button  152 . Consequently, the camshaft  153  rotates in the direction indicated by an arrow mark Y. 
     One of the lengthwise end portions of the linkage plate  154  is provided with a hole  154   a   1 , whereas the other lengthwise end portion of the linkage plate  154  is provided with an elongated hole  154   a   2 . It is in the hole  154   a   1  that a linkage plate shaft  156  fixed to the frame  133 L of the fixation unit is fitted. It is in the elongated hole  154   a   2  that the boss  153   b  with which the camshaft  153  is provided is fitted. The linkage plate  154  is rotationally moved about the linkage plate shaft  156  by the rotation of the camshaft  153 . 
     One of the lengthwise end portions of the linkage plate  155  is provided with a hole  155   a   1 , and the other lengthwise end portion of the linkage plate  155  is provided with an elongated hole  155   a   2 . It is in the hole  155   a   1  that the linkage plate shaft  156  is fitted in such a manner that the axial line of the hole  155   a   1  coincides with the axial line of the linkage plate shaft  156 . This linkage plate  155  is rotationally moved about the linkage plate shaft  156  by the rotational movement of the linkage plate  154 . 
     One of the lengthwise end portions of the guide  151  has a shaft  151   a , and the other lengthwise end portion of the guide  151  has a shaft  151   b . The shafts  151   a  and  151   b  are fitted in the holes (unshown) of the frames  133 L and  133 R of the fixation unit, being thereby rotatably supported by the frames  133 L and  133 R of the fixation unit, respectively. Further, the end of the shaft  151   a  of the guide  151  has a sub-shaft  151   a   1 , which is fitted in the elongated hole  155   a   2  of the linkage plate  155 . Thus, the guide  151  is rotationally moved about the shafts  151   a  and  151   b  by the rotational movement of the linkage plate  155 . 
     Further, there is disposed a return spring  157  between the frame  133 L of the fixation unit and the camshaft  153 . There is also disposed a return spring  158  between the linkage plates  154  and  155 . 
     With the provision of the above described structural arrangement, as the front door FD is closed, whereby the opening-closing button  152  is pushed inward of the apparatus main assembly  100 , the linkage plate  155  is rotated by the movement of the opening-closing button  152 , whereby the guide  151  is rotationally moved by the edge of the elongated hole  155   a   2  of the linkage plate  155  in the direction to expose the nip entrance opening O 2 . More concretely, the structural arrangement is such that the opening-closing button  152  is pushed inward of the apparatus main assembly  100  by the protrusion (unshown) with which the front door FD is provided. Therefore, when the front door FD remains closed (when apparatus is in normal operation), the guide  151  remains open ( FIG. 6A ), allowing a sheet S of recording medium to be introduced into the fixation nip N 2 .  FIG. 6B  shows the positions in which the linkage plates  154  and  155  are when the guide  151  is in the position shown in  FIG. 6A . 
     As the front door FD is opened, the opening-closing button  152  protrudes toward the front door FD, allowing thereby the linkage plate  155  to rotate. Thus, the guide  151  is rotationally moved by the edge of the elongated hole  155   a   2  of the linkage plate  155  in the direction to cover the nip entrance O 2 . That is, when the front door FD is open, the guide  151  remains closed ( FIG. 6C ), preventing thereby a sheet S of recording medium from being introduced into the fixation nip N 2 .  FIG. 6D  shows the positions in which the linkage plates  154  and  155  are when the guide  151  is in the position shown in  FIG. 6C . 
     (5) Structure of Rails  180 L and  180 R, and Guide  181 L and  181 R. 
       FIGS. 7A ,  7 B and  7 C are drawings for describing how to install the fixing device  103  into the fixation device space  100 S in the apparatus main assembly  100 . 
     Referring to  FIG. 7A , the apparatus main assembly  100  has a pair of rails  180 L and  180 R for guiding the fixing device  103  into the apparatus main assembly  100 , and a pair of guides  181 L and  182 R for rotationally moving the arms  142 L and  142 R of the opening-closing mechanism  140 . The rails  180 L and  180 R are attached to the left and right lateral plates (unshown) of the apparatus main assembly  100 , and are provided with guiding groove  180 La and  180 Rb, which are inwards side of the lateral plates, and along which the fixing device  103  can be roughly horizontally pulled out of, or inserted into, the fixation device space  100 S. Although  FIG. 7A  does not show the guiding groove  180 La of the rail  180 L, the guiding groove  180 La is the same in shape as the guiding groove  180 Rb. 
     The guides  181 L and  181 R also are attached to the left and right lateral plates (unshown) of the apparatus main assembly  100 , being positioned above the rails  180 L and  180 R, respectively. Further, the guide  181 L and  181 R have guiding surfaces  181 La and  181 Ra, which come into contact with the engaging portions  142 La 1  and  142 Ra 1  of the arms  142 L and  142 R, respectively. 
     The outward surfaces of the covers  133 L and  133 R of the fixing device  103  are provided with guiding protrusions  133 La and  133 Rb, respectively ( FIGS. 2 and 7A ). Although  FIGS. 2 and 7A  do not show the guiding protrusion  133 Rb of the cover  133 R, the guiding protrusion  133 Rb is the same in shape as the guiding protrusion  133 La of the cover  133 L. Further, the top stay  138 , which is one of the top portions of the fixing device  103 , is provided with a handle to be used to remove the fixing device  103  from the apparatus main assembly  100 . 
     When it is necessary to install the fixing device  103  into the apparatus main assembly  100 , an operator is to open the side cover (unshown), with which the apparatus main assembly  100  is provided, and which is placed on the sheet discharge guide ( 109   b ) side ( FIG. 1 ) of the apparatus main assembly  100 , to expose the fixing device space  100 S of the apparatus main assembly  100 . After the opening of the side cover, the operator is to grasp the handle  134  of the fixing device  103 , and fit the guiding protrusions  133 La and  133 Rb into the guiding grooves  180 La and  180 Rb of the rail  180 L and  180 R, respectively. Then, the operator is to roughly horizontally insert the fixing device  103  into the apparatus main assembly  100 , along the guiding grooves  180 La and  180 R. 
     Referring to  FIG. 7B , as the fixing device  103  is inserted into the apparatus main assembly  100  as described above, the engaging portions  142 La 1  and  142 Ra 1  of the arms  142 L and  142 R of the opening-closing mechanism  140  come into contact with the guiding surfaces  181 La and  181 Rb of the guides  181 L and  183 R. As the fixing device  103  is inserted further, the arm  142 L and  142 R are rotated in the counterclockwise direction, causing thereby the shutter  141  to upwardly rotate. Consequently, the shutter  141  is held by the guiding surfaces  181 La and  181 Rb in a manner to keep the opening O 1  of the fixing device  103  exposed, as shown in  FIG. 7C , and the fixing device  103  is moved into the normal position (preset position which allows sheet S to be introduced into fixing device) for the fixing device  101 , in the apparatus main assembly  100 . 
     Further, the apparatus main assembly  100  and fixing device  103  are structured so that as the fixing device  103  is moved into its normal position in the apparatus main assembly  100 , the electrodes (unshown) with which the apparatus main assembly  100  is provided come into contact with the electrodes (unshown) with which the cover  133 L (or  133 R) of the fixing device  103 , to establish electrical connection between the apparatus main assembly  100  and fixing device  100  so that the heater  131  is supplied with electrical power from the electrodes of the apparatus main assembly  100 , through the electrodes of the fixing device  103 . 
     As the shutter  141  is rotationally moved upward, it exposes the opening O 1 , and covers the handle  134  ( FIG. 3 ) to protect the handle  134  from contaminants and the like. 
     When it is necessary to take the fixing device  103  out of the apparatus main assembly  100 , the operator is to open the side cover (unshown) of the apparatus main assembly  100  to expose the fixing device space  100 S in the apparatus main assembly  100 . Then, the operator is to grasp the handle  134 , and roughly horizontally pull the fixing device  103  out of the apparatus main assembly  100  along the guide grooves  180 La and  180 Rb ( FIG. 7(   c )). 
     As the fixing device  103  is moved outward of the apparatus main assembly  100 , the engaging portion  142 La 1  and  142 Ra 1  of the arms  142 L and  142 R separate from the guiding surfaces  181 La and  181 Rb of the guide  181 L and  181 R, respectively. Then, as the fixing device  103  is moved further outward, the arms  142 L and  142 R rotate in the counterclockwise direction, causing thereby the shutter  141  to rotationally move downward. Consequently, the opening O 1  of the fixing device  103  is covered by the shutter  141  as shown in  FIG. 7A . 
     As described above, the frame of the fixing device  103  (fixation unit) is provided with the openings O 1  for allowing the air from the airflow generating member Q to be blown at the rotational fixing member  116 , and the shutter  141  which is movable into the first and second positions in which the shutter  141  keeps the opening O 1  covered, and exposed, respectively. Further, as the fixation unit is moved out of the apparatus main assembly  100 , the shutter  141  is moved from its second position to its first position by the outward movement of the fixation unit. Incidentally, a numeral  300  in  FIG. 7C  stands for a part of the frame of the fixation unit, which is at the center of the fixation unit (in terms of direction parallel to generatrix of rotational fixing member). Therefore, as the shutter  141  is moved into its second position (exposing position), the rotational fixing member  116  is exposed from the frame of the fixation unit, except for the center portion (which corresponds to center portion  300  of frame) in terms of the direction parallel to the generatrix of the rotational fixing member  116 . 
     (6) Structure of Cooling Device Q of Apparatus Main Assembly  100  for Preventing Out-of-Sheet-Path Portions of Rotational Fixing Member of Fixing Device from Excessively Increasing in Temperature 
       FIG. 8  is a perspective view of the cooling device Q for preventing the lengthwise end portions of the rotational fixing member (fixation belt  116 ) from excessively increasing in temperature. It shows the general structure of the device Q. More specifically,  FIG. 8(   a ) is a perspective view of the cooling device Q as seen from the side of the air outlet W of the duct  171  for cooling the lengthwise end portions of the fixation belt  116 .  FIG. 8(   b ) is a perspective view of the duct shutter mechanism located at the air outlet W of the duct  171 . It shows the overall structure of the duct shutter mechanism. 
     Regarding the cooling device Q for preventing the out-of-sheet-path portions of the rotational fixing member of the fixing device from excessively increasing in temperature, air (cooling air) is sent from the cooling fan (airflow generating member)  170  to the duct  171  for cooling the lengthwise end portions of the rotational fixing member  116 . Then, the air comes out of the air outlet W ( FIG. 3 ) of the duct  171  to be blown at the portions of the fixation belt  116 , which correspond to the out-of-sheet-path portions of the fixation nip N 2 , that is, the portions of the fixation nip N 2 , which a small sheet does not pass, to cool the out-of-sheet-path portions of the fixation belt  116 . That is, the airflow generating member  170  sends cooling air to the lengthwise end portions of the rotational fixing member  116  in terms of the direction parallel to the generatrix of the rotational fixing member  116 . 
     Referring to  FIG. 8(   a ), the cooling device Q for preventing the widthwise end portions of the fixation belt  116  from excessively increasing in temperature is provided with the ducts  171  located in the adjacencies of the widthwise end portions of the fixation belt  116  (unshown) to cool the widthwise end portions of the fixation belt  117 , and the cooling fan  170 . This cooling device Q is structured so that it blows air at the out-of-sheet-path portions of the fixation belt  116  to cool the out-of-sheet-path portions of the fixation belt  116  to prevent the out-of-sheet-path portions of the fixation belt  116  from excessively increasing in temperature, when a substantial number of small sheets are continuously conveyed through the fixation nip N 2 . 
     Referring to  FIG. 8(   b ), there are disposed in the cooling duct  171 , a pair of duct shutters  172 L and  172 R, which are supported so that they can be moved in the lengthwise direction of the frame  175 , and also, are in connection to a pair of racks  176 L and  176 R, respectively. The racks  176 L and  176 R are in engagement with a driving gear  174  with which the output shaft of a pulse motor  173  is provided. Thus, as the pulse motor  173  is driven, the duct shutters  172 L and  172 R are moved in the lengthwise direction of the frame  175  to open or close the air outlet W. That is, the shutters  172 L and  172 R can change in dimension, the ranges, in terms of the direction of the generatrix of the fixation belt  116 , across which air is blown at the fixation belt  116 . 
     Where the duct shutters  172 L and  172 R are to be positioned (stopped) is determined based on the size of a sheet of recording medium to be used for an image forming operation. That is, where the duct shutters  172 L and  172 R are to be moved is controlled by the amount by which the pulse motor  173  is driven. Thus, the air outlets W can be optimized in dimension in terms of the direction of the generatrix of the fixation belt  116  so that the dimension of the air outlet W matches the dimension (width) of the out-of-sheet-path portions of the fixation belt  116 . 
     Further, referring to  FIGS. 3 and 8 , as the fixing device  103  is installed into its preset position in the apparatus main assembly  100 , the duct  171  enters the fixation unit, and semi-cylindrically curved portions  172 LC and  172 RC of the shutter  172 , which faces the fixation belt  116 , are positioned in the adjacencies of the fixation belt  116 . That is, the apparatus main assembly  100  and fixation unit are structured so that as the fixation unit is installed into the main assembly of the printer, the tip of the duct is positioned close to the fixation belt  116 . Therefore, it is possible to precisely control at which portions of the fixation belt  116  the cooling air will be blown. 
     As described above, in the case of the fixing device  103  in this embodiment, it is the apparatus main assembly  100  that is provided with the cooling fan  170  and duct  171  for cooling the out-of-sheet-path portions of the fixation belt  116  of the fixing device  103 . Therefore, the fixing device  103  in this embodiment is less in manufacturing cost than any fixing device in accordance with the prior art. Further, it is structured so that during its maintenance, its opening O 1  is covered by its shutter  141 . Therefore, it can protect its fixation belt  116  during its maintenance. 
     (Miscellanies) 
     The present invention is also applicable to a fixing device, the rotational fixing member of which is a cylindrical and hollow fixation roller, and the heating member of which is a halogen heater. Further, it is applicable to a fixing device, the rotational fixing member of which is a cylindrical fixation belt having a heat generating layer which can be inductively heated, and the heating member of which is a coil (magnetic flux generating means) which generates magnetic flux to heat the fixation belt. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims priority from Japanese Patent Applications Nos. 087523/2013 and 063767/2014 filed Apr. 18, 2013 and Mar. 26, 2014, respectively which are hereby incorporated by reference.