Patent Publication Number: US-9835995-B2

Title: Fuser device and image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 USC 119 to Japanese Patent Application No. 2015-167810 filed on Aug. 27, 2015, the entire contents which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus, and more particularly to a configuration of a fuser device thereof. 
     BACKGROUND 
     Conventionally, in a fuser device of an image forming apparatus, a developer image was fused on a print medium by applying heat and pressure to a medium in which the developer image was transferred (For example, see Patent Document 1). 
     RELATED ART 
     [Patent Doc. 1] Japanese Laid-Open Patent Application Publication 2015-87624 (Page 7, FIG. 1) 
     However, with the conventional configuration, there were undesirable cases in which heat was applied to a medium for a long time when the print medium was stopped inside a fuser device. 
     SUMMARY 
     A fuser device that fuses a developer image on a recording medium that is carried along a carrying path includes: a first unit that is stable to the fuser device; a second unit that is movably arranged with respect to the first unit, the carrying path intervening between the first unit and the second unit; and a movement mechanism that moves the second unit between a first position and a second position with respect to the first unit, at least one of the first unit and the second unit providing heat on the recording medium. Wherein the first unit includes an endless first belt, and a fuser member that is rotatably held about a rotation shaft positioned on an inner side of the first belt, the second unit includes an endless second belt, a pressure application member that is rotatably held about another rotation shaft displaceable on an inner side of the second belt, and a first bias member that biases the pressure application member toward the fuser member, and the pressure application member, at the first position, presses the fuser member via the first belt and the second belt using the first bias member such that a nip part, where the developer image is fused on the recording medium, is formed between the pressure application member and the fuser member, and at the second position, is detached from the fuser member so that the nip part is eliminated. 
     According to the present invention, since a nip part is formed by a fuser member and a pressure application member as necessary and the rollers can be detached, an inconvenient situation in which heat is applied to a recording medium for a long time can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a main part configuration view showing a configuration of the main part of a printer of an example of an image forming apparatus equipped with a fuser device according to the present invention. 
         FIG. 2  is an external perspective view of a fuser device. 
         FIG. 3  is a front view of the fuser device as viewed from the upstream side of the sheet carrying direction (arrow A direction). 
         FIG. 4  is a front view showing a fuser device in which the external cover is removed. 
         FIG. 5  is an external perspective view of the fuser device in which the external cover is removed. 
         FIG. 6  is a right side view showing the fuser device in which the external cover is removed. 
         FIG. 7  is a right side view showing a state in which a drive transmission system is removed. 
         FIG. 8  is a view showing the A-A cross-section of  FIG. 3  as viewed from the arrow direction. 
         FIG. 9  is an exploded side view showing an upper stationary unit, a lower movable unit and a base unit constituting a fuser device in a state in which they are separated from each other, wherein (a) of  FIG. 9  is a right side view of an upper stationary unit, (b) of  FIG. 9  is a right side view of a lower movable unit, and (c) of  FIG. 9  is a right side view of a base unit. 
         FIG. 10  is an external perspective view of an upper stationary unit. 
         FIG. 11  is an external perspective view in which a drive transmission system including a fuser roller drive input gear is removed from the state shown in  FIG. 10 . 
         FIG. 12  is a right side view showing an upper stationary unit in which a sub-chassis of a drive transmission system is removed from the state shown in (a) of  FIG. 9 . 
         FIG. 13  is an external perspective view showing a lower movable unit. 
         FIG. 14  is an external perspective view of a base unit. 
         FIG. 15  is a front view of a base unit. 
         FIG. 16  is a view showing the F-F cross-section of  FIG. 15  as viewed from the arrow direction. 
         FIG. 17  is a view showing the B-B cross-section in  FIG. 4 , which is a front view of a fuser device with the external cover removed as viewed from the arrow direction. 
         FIG. 18  is a view showing the C-C cross-section of  FIG. 4 , which is a front view of a fuser device with the external cover removed as viewed from the arrow direction. 
         FIG. 19  is a view showing the D-D cross-section of  FIG. 4 , which is a front view of a fuser device with the external cover removed as viewed from the arrow direction. 
         FIG. 20  is a view showing the E-E cross-section of  FIG. 4 , which is a front view of a fuser device with the external cover removed as viewed from the arrow direction. 
         FIG. 21  is a view showing the B-B cross-section of  FIG. 4  as viewed from the arrow direction in a state in which a lower movable unit is slid to the lowermost position by a cam mechanism. 
         FIG. 22  is a view showing the E-E cross-section of  FIG. 4  as viewed from the arrow direction in a state in which a lower movable unit is slid to the lowermost position by a cam mechanism. 
         FIG. 23  is an external perspective view showing a pressure application roller and left and right arm portions holding the pressure application roller as viewed diagonally from above. 
         FIG. 24  is an external perspective view showing a pressure application pad and a pressure application pad holder holding the pressure application pad. 
         FIG. 25  is a configuration view schematically showing a position detection mechanism. 
         FIG. 26  is a block diagram showing a main configuration of a control system arranged inside a printer and configured to control main operations of the printer. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  illustrates a main part configuration of a printer of an Embodiment of an image forming apparatus equipped with a fuser device according to the present invention. The printer  1  is a color printer of an electrographic system configured to support a continuous print sheet. 
     As illustrated in  FIG. 1 , the printer  1  is equipped with a sheet holder  4  configured to hold a rolled sheet  5 , an introduction guide part  2  which is an introduction part of the rolled sheet  5 , and a print part  3  configured to execute printing on a recording medium. 
     The sheet holder  4 , for example, rotatably holds the axis of the rolled sheet  5 , rotates in accordance with the pulling of the leading edge side of the rolled sheet  5  toward the introduction guide part  2 , and continuously supplies the rolled sheet  5  to the introduction guide part  2 . 
     The introduction guide part  2  is equipped with a guide roller  21  for guiding the carrying of the rolled sheet  5 , a feeding roller pair  22  arranged on the carrying path of the rolled sheet  5  to carry the rolled sheet  5  to the downstream side, a sheet cutting part  23  arranged on the downstream side of the feeding roller pair  22  in the carrying direction of the rolled sheet  5 , and a sheet sensor  24  arranged on the downstream side of the sheet cutting part  23 . The introduction guide part  2  executes carrying and cutting of the rolled sheet  5  at a predetermined timing, and detects the presence or absence of a cut rolled sheet (hereinafter referred to as a recording sheet  6 ) to be sent to the print part  3  by the sheet sensor  24 . 
     On the carrying path of the recording sheet  6  in the print part  3 , carrying roller pairs  35  and  36  configured to carry the recording sheet  6  to a secondary transfer part  50  from the upstream side in the arrow A direction, which is the carrying direction of the recording sheet  6 , and a writing sensor  40  for obtaining the writing timing at the image forming part  30  are arranged. 
     The image forming part  30  of the print part  3  includes four process units  31 Y,  31 M,  31 C, and  31 K (simply referred to as  31  when there is no need to distinguish between them) each configured to form an each color toner image of yellow (Y), magenta (M), cyan (C), and black (K), and they are arranged in order from the upstream side along the arrow B direction showing the moving direction in which the intermediate transfer belt  41  of a later explained intermediate transfer belt unit  32  moves at the upper part of the intermediate transfer belt unit  32 . 
     The intermediate transfer belt unit  32  of the print part  3  is equipped with a drive roller  42  driven by an unillustrated driving part, a tension roller  43  configured to apply tension to the intermediate transfer belt  41  with a biasing method such as a coil spring, a secondary transfer backup roller  44  arranged so as to face the secondary transfer roller  34  and constituting the secondary transfer part  50 , and an intermediate transfer belt  41  stretched over the rollers, and further includes four primary transfer rollers  45 , etc., arranged so as to face the photosensitive drum  33  of each of the process units  31  and configured to apply a predetermined voltage for sequentially superimposing a toner image of each color formed on the photosensitive drums  33  to transfer it onto the intermediate transfer belt  41 . 
     The intermediate transfer belt unit  32 , as described above, sequentially superimposes and primarily transfers the toner image in each color formed by an image forming part  10  onto the intermediate transfer belt  41  and carries the primarily transferred toner images to the secondary transfer part  50 . At the secondary transfer part  50 , the toner image primarily transferred to the intermediate transfer belt  41  is transferred to a recording sheet  6  supplied and carried from the introduction guide part  2  by the secondary transfer roller  34  in which a predetermined voltage is applied. Therefore, the skew of the recording sheet  6  is corrected while passing through the carrying roller pairs  35  and  36 , and the writing sensor  40 , and the carrying timing is measured. 
     The fuser device  37  of the print part  3  is equipped with a fuser unit  210  and a pressure application unit  310  inside and is configured to apply heat and pressure to a toner image on the recording sheet  6  sent from the secondary transfer part  50  to melt and fuse it to the recording sheet  6 . After that, the recording sheet  6  is carried by the ejection roller pairs  38  and  39  and ejected outside the apparatus. Further, the fuser device  37  will be described in detailed later. Furthermore, here, the intermediate transfer belt unit  32  and the secondary transfer part  50  correspond to the image transfer part. 
     In  FIG. 1 , regarding the X, Y, and Z axes, the carrying direction (arrow A direction) when the recording sheet  6  passes the secondary transfer part  50  and the fuser device  37  is defined as an X axis, the rotation shaft direction of the carrying roller pairs  35  and  36  is defined as a Y axis, and the direction orthogonal to both axes is defined as a Z axis. Further, when the X, Y, and Z axes are shown in later explained other figures, the directions of these axes denote the same directions. In other words, in each of the figures, the X, Y, Z axes denote the arrangement direction when constituting the printer  1  as shown in  FIG. 1 . Here, it is assumed that the Z axis is arranged in an approximately vertical direction. 
       FIG. 2  is an external perspective view of the fuser device  37 ,  FIG. 3  is a front view of the fuser device  37  as viewed from the upstream side of the sheet carrying direction (arrow A direction),  FIG. 4  is a front view showing the fuser device  37  in which the external cover is removed,  FIG. 5  is an external perspective view of the fuser device  37  in which the external cover is removed,  FIG. 6  is a right side view showing the fuser device  37  in which the external cover is removed,  FIG. 7  is a right side view of the fuser device in which a drive transmission system is further removed, and  FIG. 8  is a view showing the A-A cross-section of  FIG. 3  as viewed from the arrow direction. It should be noted that, in some following descriptions, the front and back, left and right, and up and down directions of the fuser device  37  may be specified as viewed from the arrow A direction when viewing the fuser device  37  shown in  FIG. 2  from the front (plus end direction of X axis). 
     As shown in these figures, in the fuser device  37 , a sheet loading part  101  in which the recording sheets  6  are loaded, a fuser roller drive input gear  201  provided in an upper stationary unit  200  ( FIG. 9 ) to be described later and configured to receive an external rotation force for rotating the fuser roller  212  ( FIG. 8 ) provided in the upper stationary unit  200 , a cam drive input gear  401  provided in a base unit  400  ( FIG. 9 ) to be described later and configured to receive a driving force from the outside to drive the cam mechanism provided in the base unit  400 , and a handle  102 , are arranged so as to be capable of being contacted externally. 
     When the fuser device  37  is mounted to a predetermined position inside the print part  3  as shown in  FIG. 1 , the fuser roller drive input gear  201  meshes with a connecting gear of an unillustrated fuser roller drive source provided inside the print part  3  and receives a driving force, and the cam drive input gear  401  meshes with an unillustrated connecting gear of a motor drive transmission system connected to a cam drive motor  611  ( FIG. 26 ) to be described later and provided inside the print part  3 . 
       FIG. 9  is an exploded side view showing the upper stationary unit  200 , the lower movable unit  300 , and the base unit  400  constituting the fuser device  37  in a state in which they are separated. (a) of  FIG. 9  shows the right side view of the upper stationary unit  200 , (b) of  FIG. 9  shows the right side view of the lower movable unit  300 , and (c) of  FIG. 9  shows the right side view of the base unit  400 .  FIG. 10  is an external perspective view showing the upper stationary unit  200 .  FIG. 11  is an external perspective view in which a drive transmission system including a fuser roller drive input gear  201  is removed from the state shown in  FIG. 10 .  FIG. 12  is a right side view showing the upper stationary unit  200  in which a sub-chassis  206  of a drive transmission system is removed from the state shown in (a) of  FIG. 9 .  FIG. 13  is an external perspective view showing a lower movable unit  300 .  FIG. 14  is an external perspective view showing the base unit  400 .  FIG. 15  is a front view showing the base unit  400 .  FIG. 16  is a view showing the F-F cross-section of  FIG. 15  as viewed from the arrow direction. 
     As shown in the A-A cross-sectional view of  FIG. 8 , inside the fuser device  37 , a fuser unit  210  arranged in the upper stationary unit  200  and a pressure application unit  310  (see  FIG. 13 ) arranged in the lower movable unit  300 , extending in the left and right direction (hereinafter may be referred to as the longitudinal direction) are mounted. 
     The fuser unit  210 , similarly to the pressure application unit  310  as shown in  FIG. 13 , includes: a fuser belt  211  as a first belt mainly formed in an endless shape and extending in the longitudinal direction in a region exceeding at least the width of the recording sheet  6  that passes through; a fuser roller  212  in contact with the inner circumferential surface of the fuser belt  211  and configured to movably drive the fuser belt  211 ; a roller guide member  213  consisting of two guide rollers  217  and  218  and a guide member, and configured to guide the inner circumferential surface of the fuser belt  211  by being in contact with the inner circumferential surface of the fuser belt  211 , two heaters  214  arranged on the inside of the fuser belt  211  and configured to heat the fuser belt  211 ; a fuser pad  216  as a first pad; and a reflector  215  configured to reflect the heat from the heater  214  in a predetermined direction to the inner circumferential surface of the fuser belt  211 . 
     The pressure application unit  310 , as shown in  FIG. 13 , includes a pressure application belt  311  as a second belt mainly formed in an endless shape and extending in the longitudinal direction in a region exceeding at least the width of the recording sheet  6  that passes through, a pressure application roller  312  in contact with the inner circumferential surface of the pressure application belt  311  and configured to be driven by being contacted and pressed to the fuser roller  212  as described below to movably drive the pressure application belt  311 , a roller guide member  313  consisting of two guide rollers  317  and  318  and a guide member and configured to guide the inner circumferential surface of the pressure application belt  311  by being in contact with the inner circumferential surface of the pressure application belt  311 , a heater  314  arranged on the inside of the pressure application belt  311  and configured to heat the pressure application belt  311 , a pressure application pad  316  as a second pad, and a reflector  315  configured to reflect the heat from the heater  314  in a predetermined direction of the inner circumferential surface of the pressure application belt  311 . 
     The pressure application unit  310 , as described later, moves in the up and down direction so as to come in and out of contact with the fuser unit  210 , but as shown in  FIG. 8 , when the fuser roller  212  and the pressure application roller  312  are at a nip position forming a nip part, the pressure application pad  316  also comes into contact with the fuser pad  216 , and the fuser belt  211  and the pressure application belt  311 , and the fuser belt and the pressure application belt  311  each sandwiched between the fuser pad  216  and the pressure application pad  316 , respectively, form a linear carrying path. 
     In this state, when the fuser roller  212  obtains an external driving force and rotates in the arrow direction as described later, along with the pressure application roller  312  that is driven accordingly, the fuser roller  212  rotatably moves the fuser belt  211  and the pressure application belt  311  in the arrow direction. In this state, when the recording sheet  6  in which toner images were transferred is carried to the joining part of the fuser belt  211  and the pressure application belt  311  via the sheet loading part  101 , it is further sandwiched between the fuser belt  211  heated by the heater  214  and the pressure application belt  311  heated by the heater  314  and carried along a linear carrying path, and the toner images are fused to the recording sheet  6  due to the heat application and the pressure application received during that time, and the recording sheet  6  is ejected to a latter ejection roller pair  38  ( FIG. 1 ). 
     (Upper Fixed Unit  200 ) 
     The upper stationary unit  200  provided with the fuser unit  210  ( FIG. 8 ), as shown in (a) of  FIG. 9  and  FIGS. 10 to 12 , includes a main chassis  202  including a left side chassis  204  joined to an upper chassis  203  and an upper chassis  203 , and a right side chassis  205  joined to the upper chassis  203 , and the left and right side chassis  204  and  205  rotatably hold the rotation shaft  212   a  of the fuser roller  212  of the fuser unit  210  and each of the rotation shafts  217   a  and  218   a  of the guide rollers  217  and  218  at both end portions. Further, at a position of the left and right side chassis  204  and  205  facing the rear upper part of the fuser roller  212 , a left engagement post  220  (not illustrated) and a right engagement post  221  ( FIG. 12 ) protruding to the left and right, respectively, are provided. 
     The right side chassis  205  fixedly holds the sub-chassis  206 , and between it and the sub-chassis  206 , rotatbly holds a fuser roller drive input gear  201 , and as shown in  FIG. 12 , a first intermediate gear  207  which meshes to the fuser roller drive input gear  201 , and a second intermediate gear  208  which meshes with a fuser roller gear  212   b  fixedly arranged on a rotation shaft  212   a  of the first intermediate gear  207  and the fuser roller  212 . 
     From the aforementioned configuration, when the fuser roller drive input gear  201  meshes with a connecting gear of an unillustrated fuser roller drive source provided inside the print part  3  ( FIG. 1 ) and receives a rotation force in a predetermined direction, the rotation force is transmitted to the rotation shaft  212   a  of the fuser roller  212  via the first and second intermediate gears  207  and  208 , so that the fuser roller drive input gear  201  rotates the fuser roller  212  counterclockwise in the arrow direction ( FIG. 8 ). 
     (Lower Movable Unit  300 ) 
     The lower movable unit  300  provided with the pressure application unit  310  ( FIG. 8 ), as shown in (b) of  FIG. 9  and  FIG. 13 , includes a main chassis  302  including a left side chassis  304  joined to a lower chassis  303  and a lower chassis  303 , and a right side chassis  305  joined to the lower chassis  303 , and the left and right side chassis  304  and  305  rotatably hold each of the rotation shafts  317   a  and  318   b  of the guide rollers  317  and  318  of the pressure application unit  310  ( FIG. 13 ) and further, as described later, hold both end parts of the rotation shaft  312   a  of the pressure application roller  312  via the left and right arms  306  and  307 , which serve as supporting members. 
       FIG. 23  is an external perspective view showing a pressure application roller  312  and left and right arms  306  and  307  holding the pressure application roller  312  as viewed from diagonally above. 
     Here, the configuration in which the left and right side chassis  304  and  305  hold both end parts of the rotation shaft  312   a  of the pressure application roller  312  via the left arm  306  and the right arm  307  is configured to be a plane symmetry to the virtual central plane (vertical to the rotation shaft  312   a ) in middle of the left and right side chassis  304  and  305 , so here, only the configuration of the right side is illustrated, and it will be described with references to (b) of  FIG. 9 ,  FIG. 13 , as well as  FIGS. 17 to 20 . 
       FIG. 17  is a view showing the B-B cross-section in  FIG. 4 , which is a front view of a fuser device  37  with the external cover removed and viewed from the arrow direction.  FIG. 18  is a view showing the C-C cross-section of  FIG. 4  viewed from the arrow direction.  FIG. 19  is a view showing the D-D cross-section of  FIG. 4  viewed from the arrow direction.  FIG. 20  is a view showing the E-E cross-section of  FIG. 4  viewed from the arrow direction. 
     The right side chassis  305  is equipped with a rotation shaft  320  mounted slightly to the right direction from the upper part of the rear part, and the rotation shaft  320  is inserted into the shaft hole  307   c  of the right arm as an arm ( FIG. 23 ) to rotatably hold the right arm  307 . Similarly, the rotation shaft  319  of the left side chassis  304  is also inserted into the shaft hole  306   c  of the left arm  306  ( FIG. 23 ) to rotatably hold the left arm  306 . With this, the arms  306  and  307  can be pivoted about the rotation shafts  319  and  320 . 
     The right arm  307  is arranged so as to extend in the front and back direction (X-axis direction) as shown in  FIG. 19 , etc., and engaged with the upper end side of the first spring  321  as a first bias member arranged in the up and down direction by an engaging part  307   a  formed by bending in a right direction at the front end side upper part. In the first spring  321 , the lower end side is engaged with a spring engaging member  330  arranged in the right side chassis  305  and maintains the compressed state. 
     The right arm  307 , as shown in  FIG. 13  and  FIG. 20 , for example, forms a bearing  307   b  ( FIG. 23 ) at a position close to the rotation shaft  320  between the engaging part  307   a  and the rotation shaft  320  at the front edge, and rotatably holds one end side of the rotation shaft  312   a  of the pressure application roller  312  with the bearing  307   b , and the left arm  306  similarly rotatably holds the other end side of the rotation shaft  312   a  of the pressure application roller  312  with a bearing  306   a  ( FIG. 23 ). Therefore, the pressure application roller  312  is configured to be displaceable (slidable) to the main chassis  302  due to the revolution of the left and right arms  306  and  307 . As described later, the engaging part  307   a  of the right arm  307  biased by the first spring  321  is in contact with a regulation plate  341  (or regulation member) and the regulation plate  341  regulates the rotation of the right arm  307 . 
     The pressure application pad  316  ( FIG. 8 ) is arranged so as to extend in the longitudinal direction of the pressure application unit  310  in an approximately same region as the pressure application belt  311 .  FIG. 24  is an external perspective view showing a pressure application pad  316  and a pressure application pad holder  332  holding the pressure application pad. As shown in the figure, in the pressure application pad holder  332 , a pad fixture part  333  in which the pressure application pad  316  is fixed, a left end part  334  formed at both end parts of the pad fixture part  333  ( FIG. 13 ), and a right end part  335  are integrally formed. The pressure application pad holder  332  is slidably held by the main chassis  302  in the up and down direction, and its left and right end parts  334  and  335  are formed in a U-shape, respectively (see  FIG. 20 ). 
     The upper face portion  335   a  of the right end part  335  is adjacent to the first spring  321  and arranged in the up and down direction and engaged with the upper end side of the second spring, and the lower end side of the second spring  322  is engaged with the spring engaging member  330  arranged in the right side chassis  305  and is maintained in the compressed state. 
     In the left and right side chassis  304  and  305 , a left upper part slit  304   a  and a right upper part slit  305   a , in which the upper portions are open, are formed at opposing positions at the rear upper parts, and at the opposing position at the lower part, a left lower front part slit  304   b  and a right lower front part slit  305   b  as the first guide grooves in which the lower portions are open, and a left lower rear part slit  304   c  and a right lower rear part slit  305   c  as second guide grooves are formed. 
     (Base Unit  400 ) 
     The base unit  400  provided with a cam mechanism is equipped with a base chassis  402  extending in the left and right direction (longitudinal direction) as shown in (c) of  FIG. 9  and  FIGS. 14 to 17 . In the base chassis  402 , at both end parts in the longitudinal direction, a pair of supporting plates  402   a  and  402   b  rotatably holding the first cam shaft  403 , and a pair of supporting plates  402   c  and  402   d  rotatably holding the second cam shaft  404  arranged so as to be parallel and adjacent to the first cam shaft  403  are formed. 
     In the first cam shaft  403 , a cam  411  as a first cam and a cam gear  413  are fixedly arranged on the left side end part in a coaxial manner, and a cam  412  as a first cam and a cam gear  414  are fixedly arranged on the right side end part in a coaxial manner. In the second cam shaft  404 , a cam  421  as a second cam and a cam gear  423  are fixedly arranged on the left side end part in a coaxial manner, a cam  422  and a cam gear  424  are fixedly arranged on the right side end part in a coaxial manner, and the cam gear  413  and the cam gear  423 , and the cam gear  414  and the gear  424  are arranged so as to mesh with each other respectively at both end parts. 
     In the base chassis  402 , as shown in  FIG. 5 , screw holes  402   e  and  402   f  for screwing the holding plate  430  configured to rotatably hold the cam drive input gear  401  are formed, and as shown in  FIG. 5 , the holding plate  430  is arranged so as to be fixed by screwing so that the cam drive input gear  401  meshes with the cam gear  414 . 
     As shown in  FIG. 16 , the cams  412  and  422  are arranged so as to have plane symmetry shapes with respect to the virtual central plane between the first cam shaft  403  and the second cam shaft  404 . Further, the cam  411  is arranged on the first cam shaft  403  in the same shape and with the same angle as the cam  412 , and the cam  421  is arranged on the second cam shaft  404  in the same shape and with the same angle as the cam  422 . 
     Next, the attachment relationships of the upper stationary unit  200 , the lower movable unit  300 , and the base unit  400  will be described. 
     When the lower movable unit  300  is installed on the base unit  400 , as shown in  FIG. 9 , the right side of the fuser device  37  is arranged so that the first cam shaft  403  of the base unit  400  is slidably inserted into the right lower front part slit  305   b  formed on the right side chassis  305 , and similarly, the second cam shaft  404  of the base unit  400  is slidably inserted into the right lower rear part slit  305   c  (see  FIG. 18 ). Furthermore, the lower movable unit is installed so that the cam  412  of the first cam shaft  403  is in contact with the abutment projection plate  305   d  formed on the top part of the right lower front part slit  305   b  as a first engagement part, and the cam  422  of the second cam shaft  404  is in contact with the abutment projection plate  305   e  formed on the top part of the right lower rear part slit  305   c  as a second engagement part (see  FIG. 19 ). 
     At this time, the left side of the fuser device  37  is also arranged so that the first cam shaft  403  of the base unit  400  is slidably inserted into the left lower front part slit  304   b  formed in the left side chassis  304  ( FIG. 13 ), and similarly, the second cam shaft  404  of the base unit  400  is slidably inserted into the left lower rear part slit  304   c , and furthermore, the cam  411  of the first cam shaft  403  is in contact with the abutment projection plate  304   d  (not illustrated) formed on the top part of the left lower front part slit  304   b , and the cam  421  of the second cam shaft  404  is in contact with the abutment projection plate  304   e  (not illustrated) formed on the top part of the left lower rear part slit  304   c  (see  FIG. 19 ). 
     Next, the upper stationary unit  200  is fixed to the base unit  400 , but at this time, on the right side of the fuser device  37 , the right engagement post  221  arranged on the right side chassis  205  of the upper stationary unit  200  (see  FIG. 12 ) is arranged so as to be inserted into the upper right part slit  305   a  formed on the lower movable unit  300 , and similarly, on the left side of the fuser device  37 , the left engagement post  220  arranged on the left side chassis  204  of the upper stationary unit  200  is arranged so as to be inserted in the left upper part slit  304   a  formed on the lower movable unit (see  FIG. 13 ). 
     Further, as shown in  FIG. 9 , the attachment hole  205   a  formed at the lower part of the right side chassis  205  and the screw groove  402   g  formed in the base chassis  402  of the base unit  400  so as to face the attachment hole  205   a  are joined by a set screw  501  to fix the upper stationary unit  200  to the base unit  400 . Further, the fixture of the upper stationary unit  200  by the set screw  501  may be performed at other positions, such as a plurality of positions, for example, between an attachment hole  204   a  formed at a lower part of the left side chassis  204  ( FIG. 10 ) and a screw groove  402   h  formed in the base chassis  402  ( FIG. 14 ) as needed. 
     With the aforementioned configuration, the lower movable unit  300 , on the right side of the fuser device  37 , as shown in  FIG. 18 , is guided by the first cam shaft  403  and the second cam shaft  404  of the base unit  400  and the right engagement post  221  of the upper stationary unit  200 , and on the left side of the fuser device  37 , similarly, it is guided by the first cam shaft  403  and the second cam shaft  404  of the base unit  400  and the left engagement post  220  of the upper stationary unit  200  (not illustrated). Also, the lower movable unit  300  is held so as to be movable in the up and down direction, and furthermore, it moves in the up and down direction according to the rotation of the four cams  411 ,  412 ,  421  and  422  on the left and right. 
     Here, the base chassis  402  and the first and second cam shafts  403  and  404  of the base unit  400 , and the upper stationary unit  200  fixed to the base chassis  402  correspond to a first unit; the lower movable unit  300  movably held by the first unit corresponds to a second unit; the cams  411 ,  412 ,  421 , and  422 , the first and second cam shafts  403  and  404 , the cam gears  413 ,  414 ,  423 , and  424 , the cam drive input gear  401 , and the holding plate  430  correspond to a movement mechanism; and among them, the cam gears  413 ,  414 ,  423 , and  424 , the cam drive input gear  401 , and the holding plate  430  correspond to the drive transmission system. When the unit  200  and the unit  300  are attached, the position is defined as a first position of the invention where a fusing operation is performed. When the unit  200  and the unit  300  are not attached, the position is defined as a second of the invention where a fusing operation is not performed. 
     Further, the cam mechanism arranged on the left and right of the fuser device  37  and configured to move the lower movable unit  300  up and down is configured to be in plane symmetry with respect to the virtual central plane between the left and right side chassis  304  and  305  (vertical with respect to the cam shafts  403  and  404 ) with the exception of the holding plate  430  for rotatably holding the cam drive input gear  401 , and since the operations are the same, hereinafter, the operations will be described only for the mechanism on the right side. 
     (Explanation of Operations) 
     The first cam shaft  403  and the second cam shaft  404 , when the cam drive input gear  401  meshes with an unillustrated connecting gear of the motor drive transmission system connected to a cam drive motor  611  ( FIG. 26 ) to be described later and provided inside the print part  3  ( FIG. 1 ) and receives a rotation force in a predetermined direction, the rotation force is transmitted to the first cam shaft  403  and the second cam shaft  404  via the cam gears  414  and  424 , and for example, rotates the cam  412  and the cam  422  as shown in  FIG. 16  in the opposite directions at the same speed. 
       FIG. 17  and  FIG. 20  show states in which the lower movable unit  300  (see  FIG. 9 ) is slid to the lowermost position by the cam mechanism, and at this time as shown in  FIG. 17 , the pressure application roller  312  presses the fuser roller  212  and forms the nip part. At this time, the engaging part  307   a  and the regulation plate  341  are detached, and since the bottom end face  335   b  and the spring engaging member  330  are detached, the bias force of the first spring  321  can be applied to the nip part and the bias force of the second spring  322  can be applied to the pressure application pad  316 . 
     On the other hand,  FIG. 21  is a view showing the B-B cross-section in  FIG. 4 , which is a front view of a fuser device  37  in which the external cover is removed as viewed from the arrow direction, showing a state in which the lower movable unit  300  (see  FIG. 9 ) is slid to the lowermost position by the cam mechanism. Similarly,  FIG. 22  is a view showing the E-E cross-section in  FIG. 4  as viewed from the arrow direction, showing a state in which the lower movable unit  300  (see  FIG. 9 ) is slid to the lowermost position by the cam mechanism. At this time, as shown in  FIG. 21 , the pressure application unit  310  is in a state in which it is detached from the fuser unit  210 . 
     Hereinafter, the operations of each part when the lower movable unit  300  slides between the uppermost position and the lowermost position will be described. Further, all of the figures other than  FIG. 21  and  FIG. 22  show states in which the lower movable unit  300  is positioned at the uppermost position as a convenience. 
     For example, in  FIG. 19 , the abutment projection plates  305   d  and  305   e  of the lower movable unit  300  are maintained in a state in which they are in contact with the circumferential surfaces of the cams  412  and  422  at all times due to the self-weight of the lower movable unit  300 . Therefore, when the cams  412  and  422  are at a rotation position as shown in  FIG. 22 , in which the contact position is at the lowermost position, the lower movable unit  300  is at the lowermost position. Hereinafter, the lowermost position of the lower movable unit  300  may be referred to as a detached position. 
     At this time, the right arm  307  is biased in the clockwise direction by the first spring  321  ( FIG. 22 ), but the rotation in that direction is regulated in a state in which the engaging part  307   a  of the front edge is contacted and pressed against the regulation plate  341 . The rotation position of the right arm  307  at this time may be hereinafter referred to as an initial rotation position. 
     On the other hand, in the right end part  335  of the pressure application pad holder  332  ( FIG. 8 ), the upper face portion  335   a  is biased upwards by the second spring  322 , but the bottom face portion  335   b  is in contact with the bottom face of the spring engaging member  330  to regulate the movement in the direction. The movement position of the pressure application pad holder  332  at this time may be hereinafter referred to as an initial movement position. 
       FIG. 21  is a view showing the B-B cross-section of  FIG. 4  as viewed from the arrow direction when the lower movable unit  300  is at the detached position. As shown in the figure, the pressure application unit  310  arranged in the lower movable unit  300  is in a state in which it is detached from the fuser unit  210  arranged in the upper stationary unit  200  (see  FIG. 9 ). At this time, the uppermost portion of the pressure application roller  312  rotatably held by the right arm  307  in an initial rotation position and the uppermost portion of the pressure application pad  316  held by the pressure application pad holder  332  at the initial moving position are set to be approximately the same height and support the pressure application belt  311 . 
     When the lower movable unit  300  rotatably drives the cam drive input gear  401  in, for example, the arrow C direction ( FIG. 5 ) from the state shown in  FIG. 21  and  FIG. 22  in which it is at a detached position, the cams  412  and  422  rotate in different arrow directions ( FIG. 22 ) at the same speed and gradually push the abutment projection plates  305   d  and  305   e , that is, the lower movable unit  300 , upwards. Accordingly, for example, the pressure application unit  310  as shown in  FIG. 21  moves upwards and eventually presses the fuser unit  210  arranged in the upper stationary unit  200 . That is, the pressure application roller  312  and the pressure application pad  316  of the pressure application unit  310  each come in contact with the fuser roller  212  and the fuser pad  216  via the pressure application belt  311  and the fuser belt  211 . 
     When the lower movable unit  300  is further pushed up by the rotation of the cam  412  and the cam  422 , the pressure application roller  312  contacts and is pressed against the fuser roller  212  and the pressure application pad  316  contacts and is pressed against the fuser pad  216 , respectively, but both stop the upward movement. Accordingly, for example, the right arm  307  shown in  FIG. 20  and its engaging part  307   a , and the pressure application pad holder  332  ( FIG. 17 ) and its right end part  335  stop at the position as shown in the figure, but the main body of the lower movable unit  300  is further lifted. 
     With this, the right end part  335  of the pressure application pad holder  332  moves downward from the initial movement position relative to the right side chassis  305  and the bottom face portion  335   b  comes into a state in which it is detached from the bottom face of the spring engaging member  330 ; the right arm  307  rotates counterclockwise from the initial rotation position relative to the right side chassis  305  and its engaging part  307   a  comes into a state in which it is detached from the regulation plate  341 ; and the lower movable unit  300  eventually reaches the uppermost position as shown in  FIG. 20  and stops the upward movement. Hereinafter, the uppermost position of the lower movable unit  300  may be referred to as a nip position. 
     Therefore, when the lower movable unit  300  is at the nip position as shown in  FIG. 17  and  FIG. 20 , the pressure application roller  312  is further compressed and biased by the first spring  321  with an increased bias force, and presses the fuser roller  212  via the pressure application belt  311  and the fuser belt  211  to form a desired nip part. Further, the pressure application pad  316  is further compressed and biased by the second spring  322  with an increased bias force and presses the pressure application belt  311  and the fuser belt  211  against the fuser pad  216  with a predetermined pressure. 
     As described above, when the lower movable unit  300  is at the nip position, the pressure application roller  312  and the pressure application pad  316  are biased independently by separate springs, so the appropriate bias force can be applied separately to each of them, thereby contributing to the stability of the fusing process. 
     When the lower movable unit  300  further rotatably drives the cam drive input gear  401  in, for example, the arrow C direction ( FIG. 5 ) from the state in which it is at the nip position, the cams  412  and  422  rotate in different arrow directions ( FIG. 22 ) at the same speed and gradually push the abutment projection plates  305   d  and  305   e  in contact, that is, the lower movable unit  300 , downwards. 
     With this, the right end part  335  of the pressure application pad holder  332  moves upwards toward the initial movement position relative to the right side chassis  305  and the bottom face portion  335   b  comes into a state in which it is in contact with the bottom face of the spring engaging member  330 , and the right arm  307  rotates counterclockwise toward the initial rotation position relative to the right side chassis  305  and its engaging part  307   a  comes into a state in which it is in contact with the regulation plate  341 . 
     During this time, the nip part formed between the pressure application roller  312  and the fuser roller  212  is cancelled and the pressure by the pressure application pad  316  to the fuser pad  216  from the pressure application belt  311  and the fuser belt  211  is cancelled. 
     Hereinafter, the lower movable unit  300  integrally moves downwards and eventually reaches the lowermost position (detached position) as shown in  FIG. 21  and  FIG. 22  and stops the downward movement. 
     Further, here, in a direction parallel to the plane including the first cam shaft  403  and the second cam shaft  404  and orthogonal to these cam shafts (X-axis direction), the rotation shaft  312   a  of the pressure application roller  312  at the nip position is positioned between the first cam shaft  403  and the second cam shaft  404 . With this, the biasing by the pressure application roller  312  to the fuser roller  212  can be performed stably. 
     Further, in a direction perpendicular to the plane including the first cam shaft  403  and the second cam shaft  404  (Z-axis direction), the abutment projection plate  305   d  is positioned between the rotation shaft  312   a  of the pressure application roller  312  and the right lower front part slit  305   b  at the nip position, and the abutment projection plate  305   e  is positioned between the rotation shaft  312   a  of the pressure application roller  312  and the right lower rear part slit  305   c  at the nip position. With this, the sliding movement of the lower movable unit  300  may be performed stably. 
     Further, the bias force of the first spring  321  at the detached position is smaller than the bias force of the first spring  321  at the nip position, and the bias force of the second spring  322  at the detached position is smaller than the bias force of the second spring  322  at the nip position, so it is possible to reduce the strength of the regulation plate  341  receiving the bias force of the first spring at the detached position and the strength of the left and right end parts  344  and  345  of the pressure application pad holder  332  receiving the bias force at the second spring  322  at the detached position. 
     (Position Detection Mechanism) 
     Next, the position detection mechanism of the lower movable unit  300  which slidably moves in the up and down direction with respect to an integrated upper stationary unit  200  and the base unit  400  will be described.  FIG. 25  schematically illustrates the configuration of the position detection mechanism. 
     A position detection arm  450  which comes into contact with the engagement part  305   f  of the right side chassis  305  of the lower movable unit  300  which slidably moves in the up and down direction (see (b) of  FIG. 9 ) is rotatably held at the base unit  400 . The detection arm  450  is shaped into an L-shape and rotatably held by the base unit  400  with the bent portion as the rotation shaft  450   a , and one end part is in contact with the engagement part  305   f  of the right side chassis  305  and the other end part is provided with a detected part  450   b  (or a part to be detected). Further, it is assumed that the position detection arm  450  yields a force to rotate in the clockwise direction in a required rotation range from self-weight. 
     The detector  460  is arranged in the base unit  400  and configured to detect the detected part  450   b  of the position detection arm  450  at the detection position  460   a , and as shown by the solid line in  FIG. 25 , it is positioned to detect the detected part  450   b  of the position detection arm  450  when the lower movable unit  300  reaches the nip position at the uppermost position. Therefore, the detector  460  detects that the lower movable unit  300  has reached the nip position at the uppermost position and outputs the detection information to the image forming control part  600  ( FIG. 26 ) to be described later. 
     (Control of Cam Drive Motor) 
       FIG. 26  is a block diagram showing the main configuration of a control system arranged inside the printer  1  and configured to control the main operations of the printer  1 . 
     In the figure, the image forming control part  600  includes a processor  601 , a ROM  602 , a RAM  603 , input/output ports  604  and  605 , a counter, a timer, etc., and is configured to receive print data and control commands from a higher-level device to perform a sequential control of the printer  1  as a whole and perform the printing operation. Here, the description of these operations will be omitted. 
     Further, the control part  600  inputs the detection information from the detector  460  and based on the information, outputs an instruction signal to the cam drive motor control part  610  which drivingly controls the cam drive motor  611 . 
     The cam drive motor  611  is arranged inside the print part  3  ( FIG. 1 ) and meshes with the cam drive input gear  401  of the fuser device  37  similarly installed inside the print part  3  via an unillustrated motor drive transmission system to rotatably drive the cam drive input gear  401  in the arrow C direction ( FIG. 5 ). 
     Here, the image forming control part  600 , for example, at the time of carrying the recording sheet  6  accompanying the printing operation, instructs the cam drive motor control part  610  to rotatably drive the cam drive motor control part  610  to move the lower movable unit  300  of the fuser device  37  to the uppermost nip position, and instructs to stop the rotation after receiving the detection information from the detector  460  indicating that the lower movable unit  300  has reached the nip position. With this, the lower movable unit  300 , for example, can be maintained at the nip position as shown in  FIG. 17 . 
     Further, for the drive transmission system from the cam drive motor  611  to the cam drive input gear  401 , for example, a worm gear can be interposed so that when the cam drive motor  611  is stopped, the first and the second cam shafts  403  and  403  do not rotate from the load. 
     On the other hand, the image forming control part  600 , for example, when the recording sheet  6  is not being carried when the printing is stopped, instructs the cam drive motor control part  610  to rotate and drive the cam drive motor  611  for a predetermined amount to move the lower movable unit  300  of the fuser device  37  to the detached position at the lowermost position. Here, the number of rotations of the cam drive motor  611  or the driving time is set in advance so that the cams  412  and  422  revolve the lower movable unit  300  for a predetermined angle of rotation from the rotation position in which the lower movable unit  300  is maintained at the nip position as shown in  FIG. 20  to the rotation position in which the lower movable unit is maintained at the detached position as shown in  FIG. 22 . Here, the detector  460 , the image forming control part  600 , the cam drive motor control part  610 , and the cam drive motor  611  correspond to the drive control part. 
     In the aforementioned configuration, the image forming control part  600  repeats the movement of positions between the nip position and the detached position of the lower movable unit  300  according to operation and stopping of the printing operation of the printer  1 . 
     Further, in this Example, although it was described to perform printing on a recording sheet  6  in which a rolled sheet  5  is cut, it is not limited to that, and various embodiments can be used, such as printing on a rolled sheet  5  as it is. 
     As described above, according to the printer  1  of this Example, since the pressure application unit  310  can be moved to the nip position and the detached position with respect to the fuser unit  210  of the fuser device  37 , while the recording sheet is not carried, an undesired situation in which the recording sheet  6  or the rolled sheet  5  is sandwiched by the fuser unit  210  and the pressure application unit  310  and left there can be prevented. 
     Further, in the description of this Example, terms such as “top”, “bottom”, “left”, “right”, “front” and “rear” are used, but these are used for convenience and they do not limit the absolute positional relationship when arranging the fuser device. 
     In this Example, the present invention was described by using an example in which it is applied to a secondary transfer type color printer of an electrographic system, but the present invention is not limited to that, and may be applied to a facsimile device, a copier, an MFP (Multifunction Peripheral), and furthermore, a color printer, a monochromatic printer, etc., of a primary transfer system.