Abstract:
A device for fixing a sheet material to a cylindrical rotating member. Without using a suction mechanism and a vacuum, pressing portions of sheet material leading end clamps provided at a peripheral surface of the rotating member press the sheet material against the peripheral surface of the rotating member and fix the sheet material thereat. Each pressing portion has a region which deforms most due to centrifugal force generated by the rotating member. The pressing portion is formed in advance on the whole in a bow-like shape such that this region projects the most toward a center of the rotating member. Due to deformation caused by centrifugal force, the pressing portion changes from bow-shaped to planar, and uniformly presses the sheet material without a gap therebetween.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet material fixing device which fixes a sheet material onto the peripheral surface of a rotating member. 
   2. Description of the Related Art 
   Printing plate exposure devices have been developed which record (expose) an image directly by a laser beam or the like onto an image forming layer (e.g., a photosensitive layer or a heat-sensitive layer) of a sheet-shaped printing plate (e.g., photopoly plate or a thermal plate). 
   The printing plate exposure device is equipped with, for example, a rotating drum. The rotating drum is hollow cylindrical, and both ends thereof are closed. A printing plate is conveyed on the peripheral surface of the rotating drum. A pressure-reducing blower communicates with the interior of the rotating drum. A large number of suction holes and suction grooves are formed in the peripheral surface of the rotating drum. When a printing plate is being conveyed on the peripheral surface of the rotating drum, the pressure at the interior of the rotating drum is reduced by the pressure-reducing blower. The printing plate is thereby vacuum-adsorbed via the many suction holes and suction grooves, and is fixed to the peripheral surface of the rotating drum. 
   A recording head portion is provided in a vicinity of the rotating drum. While the rotating drum is rotated at high speed, a light beam from the recording head portion is irradiated onto the printing plate which is fixed on the peripheral surface of the rotating drum. The printing plate is thereby subjected to exposure processing. 
   However, in this printing plate exposure device, the machining for forming the large number of suction holes and suction grooves in the peripheral surface of the rotating drum is costly, and in addition, the pressure-reducing blower is required. Accordingly, problems arise in that the manufacturing costs increase, and that, due to the pressure-reducing blower, the surface area required for placement increases and noise is generated. 
   Yet another problem arises in addition to the aforementioned problems. In printing plate exposure devices which are currently being developed, the printing plate is fixed to the peripheral surface of the rotating drum by the leading end and the trailing end of the printing plate, which is being conveyed on the peripheral surface of the rotating drum, being pressed against the peripheral surface by leading end clamps and trailing end clamps, respectively. 
   However, in such a printing plate exposure device, the printing plate is not adsorbed to the peripheral surface of the rotating drum. Accordingly, at the time when the rotating drum is rotated at high speed, if the printing plate pressing portions of the leading end clamps and the trailing end clamps deform due to centrifugal force, it is difficult to uniformly press the leading end and the trailing end of the printing plate against the peripheral surface of the rotating drum. Thus, it is difficult to make the entire printing plate fit tightly to the peripheral surface of the rotating drum. 
   SUMMARY OF THE INVENTION 
   In view of the aforementioned, an object of the present invention is to provide a sheet material fixing device which, with a structure that is low-cost, requires little surface area for placement, and does not generate noise, can uniformly press a sheet material against the peripheral surface of a rotating member at the time the rotating member is rotated. 
   The sheet material fixing device has a rotating member, a holding member, and a pressing portion. The rotating member is rotatable, and a sheet material is disposed on the peripheral surface thereof. The holding member is provided at the peripheral surface of the rotating member. The pressing portion is provided at the holding member, and is formed so as to project progressively more toward the rotating member the further toward positions of the pressing portion where the amount of deformation thereof toward the side opposite the rotating member, due to the centrifugal force at the time when the rotating member rotates, increases. The pressing portion also presses the sheet material against the peripheral surface of the rotating member. 
   In the sheet material fixing device, the pressing portion of the holding member provided at the peripheral surface of the rotating member presses the sheet material against the peripheral surface of the rotating member. The sheet material is thereby fixed to the peripheral surface of the rotating member. Thus, not only are the conventional many suction holes and suction grooves not needed, but also, a pressure-reducing blower is unnecessary. Thus, it is possible to realize a structure which is low-cost, requires little space for placement, and does not generate noise. 
   Moreover, the pressing portion projects more and more toward the rotating member, the further toward positions of the pressing portion where the amount of deformation thereof toward the side opposite the rotating member, due to the centrifugal force at the time when the rotating member rotates, increases. Thus, even if the pressing portion deforms toward the side opposite the rotating member due to centrifugal force at the time when the rotating member is rotated, the pressing portion can press the sheet material without a gap therebetween. The pressing portion can thereby uniformly press the sheet material against the peripheral surface of the rotating member. 
   The sheet material fixing device of the present invention may have a plurality of the holding members and pressing portions. There are cases in which some of the pressing portions press one end of the sheet material against the peripheral surface of the rotating member, and the other pressing portions press the other end of the sheet material against the peripheral surface of the rotating member. 
   In the sheet material fixing device in this case, some of the pressing portions press one end of the sheet material against the peripheral surface of the rotating member, whereas the other pressing portions press the other end of the sheet material against the peripheral surface of the rotating member. Moreover, as described above, each pressing portion can press the sheet material uniformly against the peripheral surface of the rotating member. Thus, when the rotating member is rotated, floating-up of the sheet material from off of the peripheral surface of the rotating member due to centrifugal force and against the pressing force of the pressing portion can be suppressed. The entire sheet material can be made to fit tightly to the peripheral surface of the rotating member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing a leading end clamp of an automatic printing plate exposure device relating to an embodiment of the present invention. 
       FIG. 2  is a front view showing the leading end clamp of the automatic printing plate exposure device relating to the embodiment of the present invention. 
       FIG. 3  is a perspective view showing a trailing end clamp of the automatic printing plate exposure device relating to the embodiment of the present invention. 
       FIG. 4  is a front view showing a trailing end pressing plate of the automatic printing plate exposure device relating to the embodiment of the present invention. 
       FIG. 5  is a perspective view showing a rotating drum, the leading end clamps and the trailing end clamps of the automatic printing plate exposure device relating to the embodiment of the present invention. 
       FIG. 6A  is a cross-sectional view showing a method of attaching the trailing end clamp to the rotating drum of the automatic printing plate exposure device relating to the embodiment of the present invention, and shows a state in which an attaching/removing lever of the trailing end clamp is being inserted into a fixing hole of the rotating drum. 
       FIG. 6B  is a cross-sectional view showing the method of attaching the trailing end clamp to the rotating drum of the automatic printing plate exposure device relating to the embodiment of the present invention, and shows a state in which removal of the attaching/removing lever from the fixing hole is not possible. 
       FIG. 7  is a schematic side view showing the automatic printing plate exposure device relating to the embodiment of the present invention. 
       FIG. 8  is a front view showing another example of a pressing portion of the automatic printing plate exposure device relating to the embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An automatic printing plate exposure device  10 , which relates to the embodiment and to which the sheet material fixing device of the present invention is applied, is shown in side view in FIG.  7 . 
   The automatic printing plate exposure device  10  relating to the present embodiment exposes (records) an image onto an image forming layer (e.g., photosensitive layer or heat-sensitive layer) on a support of a printing plate  12  which is a photopoly plate or a thermal plate or the like and which serves as a sheet material. The automatic printing plate exposure device  10  is divided into a conveying guide unit  14 , a punching section  16 , and an exposure section  18 . The punching section  16  and the exposure section  18  are disposed in front of the conveying guide unit  14 , and the exposure section  18  is disposed beneath the punching section  16 . 
   The conveying guide unit  14  has a plate supplying guide  20 , which is formed as a substantially rectangular flat plate, and a plate discharging guide  22 , which is formed as a substantially rectangular flat plate. The plate supplying guide  20  and the plate discharging guide  22  are disposed relative to one another so as to form a sideways V shape. The conveying guide unit  14  is structured so as to be able to pivot over a predetermined angle, with a vicinity of the center in  FIG. 7  being the center of pivoting. Due to the conveying guide unit  14  pivoting, the plate supplying guide  20  and the plate discharging guide  22  can be selectively made to correspond to the punching section  16  or the exposure section  18 . The printing plate  12  is supplied onto the plate supplying guide  20 . 
   Here, due to the conveying guide unit  14  pivoting such that the plate supplying guide  20  corresponds to (faces) the punching section  16 , the leading end portion of the printing plate  12  on the plate supplying guide  20  is conveyed into the punching section  16 . A predetermined number of punch holes (not shown), e.g. round holes, long holes, or the like, are punched in the leading end portion of the printing plate  12  by the punching section  16 . When processing at the punching section  16  has been completed, the printing plate  12  is returned onto the plate supplying guide  20 . 
   The exposure section  18  has a rotating drum  24  serving as a rotating member. The rotating drum  24  is solid-cylindrical, and can rotate in the direction of arrow A and in the direction of arrow B in  FIG. 7. A  predetermined number of fixing holes  40  are formed in the peripheral surface of the rotating drum  24 . In the present embodiment, eight fixing holes  40  are formed. The fixing hole  40  is formed along the entire peripheral direction of the peripheral surface of the rotating drum  24 . The region of the fixing hole  40  nearer to the outer side of the rotating drum  24  is formed to be narrower in the left-right direction than the region of the fixing hole  40  nearer to the inner side of the rotating drum  24  (refer to  FIGS. 5 ,  6 A, and  6 B). This left-right direction is substantially orthogonal to the direction of conveying of the printing plate. Here, when the printing plate  12  is returned onto the plate supplying guide  20  from the punching section  16  as described above, the conveying guide unit  14  is pivoted such that the plate supplying guide  20  corresponds to the exposure section  18  (opposes the rotating drum  24  in a direction tangential to the rotating drum  24 ). In this way, the leading end of the printing plate  12  is conveyed onto (placed on) the peripheral surface of the rotating drum  24 , and the printing plate  12  is positioned. 
   A predetermined number of leading end clamps  26  serving as holding members are provided along the left-right direction (see  FIG. 5 ) on the peripheral surface of the rotating drum  24  at the position to which the leading end of the printing plate  12  is conveyed. In the present embodiment,  11  leading end clamps  26  are provided. The leading end clamp  26  is formed of plastic (in the present embodiment, an engineering plastic such as nylon  66  resin), and is formed in a plate shape which is V-shaped in cross-section. Elastic force in a direction of moving away from the peripheral surface of the rotating drum  24  is applied to the front side of the leading end clamp  26 . A leading end pressing portion  42  serving as a pressing portion is formed at the rear end of the leading end clamp  26 . 
   As shown in  FIG. 1 , a supporting member  44  is provided at each of the left-right direction sides of the leading end clamp  26 . Each supporting member  44  is fixed to the peripheral surface of the rotating drum  24 . A supporting shaft  46  is provided integrally with each left-right direction end of the leading end clamp  26 . Due to the respective supporting shafts  26  being supported by the respective supporting members  44 , the leading end clamp  26  is supported at the rotating drum  24  so as to be freely rotatable via the supporting members  44 . Thus, when the rotating drum  24  is rotated at high speed as will be described later, due to the centrifugal force, the leading end clamps  26  (including the leading end pressing portions  42 ) deform in a direction of moving away from the rotating drum  24 . The deformation becomes greater the further toward the left-right direction center of the leading end clamp  26 . 
   As shown in  FIG. 2 , the bottom end of the leading end pressing portion  42  (the end at the rotating drum  24  side) is formed in a bow shape (crown shape) in which the left-right direction center protrudes further downwardly (toward the rotating drum  24 ) than both left-right direction ends. The bottom end of the leading end pressing portion  42  protrudes toward the rotating drum  24  progressively more, the further toward positions of the leading end pressing portion  42  where the amount of deformation thereof toward the side opposite the rotating drum  24 , due to the centrifugal force at the time when the rotating drum  24  is rotated at high speed, increases. In this way, when the rotating drum  24  is rotated at high speed, the lower end of the leading end pressing portion  42  becomes planar due to the deformation of the leading end pressing portion  42 . 
   As shown in  FIG. 1 , the supporting shafts  46  are disposed at the rear side of the leading end clamp  26 . The mass of the leading end clamp  26  at the region thereof further toward the front than the supporting shafts  46  is greater than the mass of the leading end clamp  26  at the region thereof further toward the rear than the supporting shafts  46 . Thus, when the rotating drum  24  is rotated at high speed, the centrifugal force received at the region of the leading end clamp  26  at the front side of the supporting shafts  46  is greater than the centrifugal force received at the region of the leading end clamp  26  at the rear side of the supporting shafts  46 . In this way, torque, in a direction of directing the leading end pressing portion  42  toward the peripheral surface of the rotating drum  24 , is applied to the leading end clamp  26 . 
   As shown in  FIG. 7 , an attaching cam  28  is provided above each leading end clamp  26 . Due to the respective attaching cams  28  pressing the front sides of the leading end clamps  26 , the leading end pressing portions  42  at the rear ends of the leading end clamps  26  move away from the peripheral surface of the rotating drum  24  against the aforementioned elastic force. In this way, the leading end of the printing plate  12 , which has been conveyed onto the peripheral surface of the rotating drum  24  from the plate supplying guide  20  as described above, is inserted between the peripheral surface of the rotating drum  24  and the leading end pressing portions  42  at the rear ends of the leading end clamps  26 . In this state, positioning of the printing plate  12  is carried out. After positioning of the printing plate  12  has been completed, the respective attaching cams  28  are rotated such that their pressing of the front sides of the leading end clamps  26  is released. In this way, due to the aforementioned elastic force, the leading end pressing portions  42  at the rear ends of the predetermined number of leading end clamps  26  press substantially the entire leading end of the printing plate  12  against the peripheral surface of the rotating drum  24 , and the leading end of the printing plate  12  is fixed to the peripheral surface of the rotating drum  24 . Then, when the leading end of the printing plate  12  is fixed to the peripheral surface of the rotating drum  24 , the rotating drum  24  is rotated in the direction of arrow A in  FIG. 7  such that the printing plate  12  is trained around the peripheral surface of the rotating drum  24 . 
   A solid cylindrical squeeze roller  30  is disposed at the arrow A direction side in  FIG. 7  of the attaching cams  28 , in a vicinity of the peripheral surface of the rotating drum  24 . The squeeze roller  30  is moved toward the rotating drum  24 . In this way, while the printing plate  12  trained around the rotating drum  24  is pressed toward the rotating drum  24 , the rotating drum  24  is rotated and the printing plate  12  is made to fit tightly to the peripheral surface of the rotating drum  24 . 
   A trailing end clamp attaching/removing unit  32  is disposed between the attaching cams  28  and the squeeze roller  30  in a vicinity of the peripheral surface of the rotating drum  24 . The trailing end clamp attaching/removing unit  32  has a rising/falling frame  34 . The rising/falling frame  34  can move toward the rotating drum  24 . A predetermined number (four in the present embodiment) of trailing end clamps  36  serving as holding members are attached to the rising/falling frame  34  along the left-right direction (See FIG.  5 ). The trailing end clamp  36  is rectangular plate shaped. The upper end of a coil spring (not shown) is fixed to the bottom surface of the rear side of the trailing end clamp  36 . 
   As shown in  FIG. 3 , a trailing end pressing plate  48  serving as a pressing portion is provided at each of the right side region lower end and the left side region lower end of the front end of the trailing end clamp  36 . The surface of the trailing end pressing plate  48  is formed of a rubber-coated metal (aluminum in the present embodiment), and the coefficient of friction of the trailing end pressing plate  48  is high. 
   An attaching/removing lever  50  is rotatably provided at each of a substantial center of the right side region and a substantial center of the left side region of the trailing end clamp  36 . The trailing end clamp  36  is swingable around the pair of attaching/removing levers  50 . Nuts  52  are fixed to the upper ends of the attaching/removing levers  50 , and are exposed from the top surface of the trailing end clamp  36 . Further, the lower sides of the attaching/removing levers  50  project from the bottom surface of the trailing end clamp  36 . The bottom ends of the attaching/removing levers  50  are formed such that their front-rear direction dimension is long and their left-right direction dimension is short (see FIG.  6 A and FIG.  7 ). 
   Here, when the trailing end of the printing plate  12  trained on the rotating drum  24  opposes the trailing end clamp attaching/removing unit  32 , the rising/falling frame  34  is lowered, and the trailing end clamps  36  are moved toward the rotating drum  24 . In this way, as shown in  FIG. 6A , the attaching/removing levers  50  are inserted into the fixing holes  40  of the rotating drum  24 . Thereafter, as shown in  FIG. 6B , the attaching/removing levers  50  (the nuts  52 ) are rotated by  90 ° such that the longer side of the bottom end of each attaching/removing lever  50  extends along the left-right direction. Thus, it is not possible to remove the attaching/removing levers  50  from the fixing holes  40 , and the trailing end clamps  36  are attached to the peripheral surface of the rotating drum  24 . At this time, due to the lower ends of the aforementioned coil springs being pressed toward the peripheral surface of the rotating drum  24 , the trailing end pressing plates  48  at the front ends of the predetermined number of trailing end clamps  36  press substantially the entire trailing end of the printing plate  12  against the peripheral surface of the rotating drum  24  due to the urging force of the coil springs. The trailing end of the printing plate  12  is thereby fixed to the peripheral surface of the rotating drum  24 . Further, when the respective attaching/removing levers  50  are rotated by  90 ° as described above, the trailing end clamps  36  separate from the rising/falling frame  34 , and thereafter, the rising/falling frame  34  is raised to its origin position. 
   As shown in  FIG. 3 , the attaching/removing levers  50  are disposed at the front side of the trailing end clamp  36 . The mass of the trailing end clamp  36  at the region thereof toward the rear side of the attaching/removing levers  50  is greater than the mass of the trailing end clamp  36  at the region thereof toward the front side of the attaching/removing levers  50 . Therefore, when the rotating drum  24  is rotated at high speed, the centrifugal force received by the region of the trailing end clamp  36  at the rear side of the attaching/removing levers  50  is greater than the centrifugal force received by the region of the trailing end clamp  36  at the front side of the attaching/removing levers  50 . In this way, torque, in a direction of directing the trailing end pressing plates  48  toward the peripheral surface of the rotating drum  24 , is applied to the trailing end clamp  36 . 
   At this time, the vicinities of the left-right direction ends of each trailing end pressing plate  48  are pressed by the trailing end clamp  36 . In this way, each trailing end pressing plate  48  deforms in a direction of moving away from the rotating drum  24  due to the centrifugal force. The deformation becomes greater the further toward the left-right direction center of the trailing end pressing plate  48 . 
   As shown in  FIG. 4 , the bottom end of the trailing end pressing plate  48  (the end at the rotating drum  24  side) is formed in a bow shape (crown shape) in which the left-right direction center protrudes further downwardly (toward the rotating drum  24 ) than both left-right direction ends. The bottom end of the trailing end pressing plate  48  protrudes toward the rotating drum  24  progressively more, the further toward positions of the trailing end pressing plate  48  where the amount of deformation thereof in the direction of moving away from the rotating drum  24 , due to the centrifugal force at the time when the rotating drum  24  is rotated at high speed, increases. In this way, when the rotating drum  24  is rotated at high speed, the lower end of the trailing end pressing plate  48  becomes planar due to the deformation of the trailing end pressing plate  48 . 
   In this way, when the leading end and the trailing end of the printing plate  12  are fixed to the peripheral surface of the rotating drum  24  by the leading end clamps  26  and the trailing end clamps  36 , the squeeze roller  30  is moved away from the rotating drum  24 , and thereafter, the rotating drum  24  is rotated at high speed at a predetermined rotational speed. 
   As shown in  FIG. 7 , a recording head portion  38  is disposed in a vicinity of the rear side of the peripheral surface of the rotating drum  24 . The recording head portion  38  is, synchronously with the rotation of the rotating drum  24 , operated toward the rotating drum  24  which is being rotated at high speed. Then, the recording head portion  38  irradiates a light beam, which has been modulated on the basis of read image data, so as to expose the printing plate  12  on the basis of the image data. This exposure processing is so-called scan-exposure in which the recording head portion  38  is moved in the axial direction of the rotating drum  24  while the rotating drum  24  is rotated at high speed. Here, the rotation of the rotating drum  24  is main scanning, and movement in the axial direction of the rotating drum  24  is subscanning. 
   When the scan-exposure of the printing plate  12  has been completed, the rotating drum  24  is stopped temporarily at the position at which the trailing end clamps  36  oppose the rising/falling frame  34 . After the rising/falling frame  24  has been lowered toward the rotating drum  24 , the attaching/removing levers  50  (the nuts  52 ) are rotated reversely by 90°. In this way, the longer sides of the bottom ends of the attaching/removing levers  50  are disposed along the front-rear direction, and the attaching/removing levers  50  can be removed from the fixing holes  40 , and the trailing end clamps  36  are attached to the rising/falling frame  34 . Thereafter, by raising the rising/falling frame  34  to its origin position, the fixing of the trailing end of the printing plate  12  by the trailing end pressing plates  48  at the front ends of the trailing end clamps  36  is released. Moreover, the conveying guide unit  14  is pivoted such that the plate discharging guide  22  is made to correspond to the exposure section  18  (opposes the rotating drum  24  in a direction tangential to the rotating drum  24 ). Thereafter, by rotating the rotating drum  24  in the direction of arrow B in  FIG. 7 , the printing plate  12  is discharged, from the trailing end side thereof, onto the plate discharging guide  22 . At this time, the respective attaching cams  28  are rotated and press the front sides of the leading end clamps  26 . The fixing of the leading end of the printing plate  12  by the leading end pressing portions  42  at the rear ends of the leading end clamps  26  is thereby released. When the printing plate  12  is fed to the plate discharging guide  22 , the conveying guide unit  14  is pivoted, and the printing plate  12  is discharged from the plate discharging guide  22 . In this way, the printing plate  12  is conveyed to the developing device or printing device (neither is illustrated) which is the subsequent process adjacent to the automatic printing plate exposure device  10 . 
   Next, operation of the present embodiment will be described. 
   In the automatic printing plate exposure device  10  having the above-described structure, the printing plate  12  is placed on the plate supplying guide  20 . First, the conveying guide unit  14  is pivoted such that the plate supplying guide  20  correspond to the punching section  16 . Then, the leading end portion of the printing plate  12  is conveyed into the punching section  16 . A predetermined number of punch holes are formed by the punching section  16  in the leading end portion of the printing plate  12  which has been conveyed into the punching section  16 . Thereafter, the printing plate  12  is returned onto the plate supplying guide  20 . 
   Then, the conveying guide unit  14  is pivoted so that the plate supplying guide  20  corresponds to the exposure section  18 . The printing plate  12  is conveyed to the exposure section  18  and positioned. The leading end and the trailing end of the printing plate  12  which has been positioned are fixed to the peripheral surface of the rotating drum  24  by the leading end clamps  26  and the trailing end clamps  36 , respectively. Simultaneously, while the printing plate  12  is made to fit tightly to the peripheral surface of the rotating drum  24  by the squeeze roller  30 , the printing plate  12  is trained on the peripheral surface of the rotating drum  24 . When the printing plate  12  has been trained onto the peripheral surface of the rotating drum  24 , a light beam from the recording head portion  38  is irradiated onto the printing plate  12  in the state in which the rotating drum  24  is being rotated at high speed. In this way, exposure processing is carried out. 
   When exposure processing has been completed, the conveying guide unit  14  is pivoted such that the plate discharging guide  22  corresponds to the rotating drum  24 . Then, while the fixing of the printing plate  12  to the peripheral surface of the rotating drum  24  by the leading end clamps  26  and trailing end clamps  36  is released, the printing plate  12  is discharged from the rotating drum  24  to the plate discharging guide  22 . Thereafter, the conveying guide unit  14  is pivoted and the printing plate  12  is discharged out from the plate discharging guide  22 . 
   Here, in the exposure section  18 , the leading end clamps  26  and the trailing end clamps  36 , which are provided at the peripheral surface of the rotating drum  24 , press the printing plate  12  against the peripheral surface of the rotating drum  24  by the leading end pressing portions  42  and the trailing end pressing plates  48 . In this way, the printing plate  12  is fixed to the peripheral surface of the rotating drum  24 . Thus, not only the conventional large number of suction holes and suction grooves are unnecessary, but also, a pressure-reducing blower is not needed. Thus, the structure can be made to be lower cost, requires less space for placement, and does not generate sound. 
   When the rotating drum  24  is rotating at high speed, the leading end pressing portions  42  and the trailing end pressing plates  48 , due to centrifugal force, deform in directions of moving away from the rotating drum  24 . The further toward the left-right direction center of the leading end pressing portion  42  and the trailing end pressing plate  48 , the greater the deformation. Here, the left-right direction center of the bottom end of the leading end pressing portion  42  and the bottom end of the trailing end pressing plate  48  project in a bow-like manner further downward than the left-right direction both ends. In this way, the leading end pressing portions  42  and the trailing end pressing plates  48  protrude toward the rotating drum  24 . The leading end pressing portions  42  and the trailing end pressing plates  48  protrude progressively more, the further toward positions thereof where the amount of deformation in the direction of moving away from the rotating drum  24 , due to the centrifugal force at the time when the rotating drum  24  is rotated at high speed, increases. Thus, even if the leading end pressing portions  42  and the trailing end pressing plates  48  deform due to centrifugal force when the rotating drum  24  is rotated at high speed, the bottom ends of the leading end pressing portions  42  and the bottom ends of the trailing end pressing plates  48  become planar and can press the printing plate  12  without a gap therebetween. In this way, the leading end pressing portions  42  and the trailing end pressing plates  48  can uniformly press the printing plate  12  against the peripheral surface of the rotating drum  24  and make the printing plate  12  fit tightly against the peripheral surface of the rotating drum  24 . 
   Further, when the rotating drum  24  is rotated at high speed, the centrifugal force received by the region of the leading end clamp  26  at the front side of the supporting shafts  46  is greater than the centrifugal force received by the region of the leading end clamp  26  at the rear side of the supporting shafts  46 . Torque, in the direction of directing the leading end pressing portion  42  toward the peripheral surface of the rotating drum  24 , is applied to the leading end clamp  26 . Moreover, when the rotating drum  24  is rotated at high speed, the centrifugal force received by the region of the trailing end clamp  36  at the rear side of the attaching/removing levers  50  is greater than the centrifugal force received by the region of the trailing end clamp  36  at the front side of the attaching/removing levers  50 . Torque, in the direction of directing the trailing end pressing plates  48  toward the peripheral surface of the rotating drum  24 , is applied to the trailing end clamp  36 . In this way, the leading end pressing portions  42  and the trailing end pressing plates  48  can press the printing plate  12  against the peripheral surface of the rotating drum  24  at a high pressure. 
   Substantially the entire leading end of the printing plate  12  is pressed against the peripheral surface of the rotating drum  24  by the leading end pressing portions  42 . Moreover, substantially the entire trailing end of the printing plate  12  is pressed against the peripheral surface of the rotating drum  24  by the trailing end pressing plates  48 . In addition, as described above, the leading end pressing portions  42  and the trailing end pressing plates  48  uniformly press the printing plate  12  against the peripheral surface of the rotating drum  24  at a high pressure. Thus, when the rotating drum  24  is rotated at high speed, the printing plate  12  can be prevented from, due to centrifugal force, floating up off of the peripheral surface of the rotating drum  24  against the pressing force of the leading end pressing portions  42  and the trailing end pressing plates  48 . Accordingly, the entire printing plate  12  can be made to fit tightly against the peripheral surface of the rotating drum  24 . Thus, it is possible to prevent the recorded image from becoming blurry due to the distance between the recording head portion  38  and the printing plate  12  changing. 
   The present embodiment is a structural example in which, when the rotating drum  24  is rotated at high speed, the leading end pressing portions  42  and the trailing end pressing plates  48  deform in directions of moving away from the rotating drum  24  due to the centrifugal force, and the deformation is greater the further toward the left-right direction centers of the leading end pressing portions  42  and the trailing end pressing plates  48 . However, as shown in  FIG. 8 , in a case in which a pressing portion  60  is structured such that, when the rotating drum  24  (rotating member) rotates, the pressing portion  60  deforms due to centrifugal force such that the left-right direction center of the pressing portion  60  is pressed toward the rotating drum  24 , and the further toward the left-right direction both ends, the more the pressing portion  60  moves away from the rotating drum  24 , it suffices to form the bottom end of the pressing portion  60  (the end at the rotating drum  24  side) to be bow-shaped such that the left-right direction both end portions project further downward (toward the rotating drum  24  side) than the left-right direction center. In this way, the pressing portion  60  protrudes toward the rotating drum  24  progressively more, the further toward positions of the pressing portion  60  where the amount of deformation thereof in a direction of moving away from the rotating drum  24 , due to the centrifugal force at the time when the rotating drum  24  is rotated, increases. Even if the pressing portion  60  deforms due to centrifugal force at the time when the rotating drum  24  is rotated, the bottom end of the pressing portion  60  becomes planar, and can press the printing plate  12  without a gap therebetween. The pressing portion  60  can uniformly press the printing plate  12  against the peripheral surface of the rotating drum  24 . 
   In the sheet material fixing device of the present invention, due to the pressing portion of the holding member pressing the sheet material against the peripheral surface of the rotating member, the sheet material is fixed to the peripheral surface of the rotating member. Accordingly, there is no need for the conventional suction holes, suction grooves and pressure-reducing blower. A structure in which costs are reduced, less space is required for placement, and which does not generate noise can be realized. 
   Moreover, the pressing portion projects more toward the rotating member, the further toward positions of the pressing portion where the amount of deformation thereof toward the side opposite the rotating member, due to the centrifugal force at the time when the rotating member rotates, increases. Accordingly, even if the pressing portion deforms toward the side opposite the rotating member due to centrifugal force, the pressing portion can press the sheet material without a gap therebetween, and the pressing portion can uniformly press the sheet material against the peripheral surface of the rotating member. 
   In addition, when the sheet material fixing device of the present invention is provided with a plurality of holding members and pressing portions, some of the pressing portions press one end of the sheet material against the peripheral surface of the rotating member, whereas the other pressing portions press the other end of the sheet material against the peripheral surface of the rotating member. Accordingly, the entire sheet material can be made to fit tightly against the peripheral surface of the rotating member when the rotating member is rotated.