Patent Publication Number: US-6334392-B1

Title: Drawing apparatus having fixing member for clamping material on drum

Description:
This is a divisional of application Ser. No. 09/366,839, filed Aug. 4, 1999now U.S. Pat. No. 6,164,204. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drawing apparatus for fixing a sheet-shaped recording material to an outer peripheral surface of a drum to draw an image on the recording material. 
     2. Description of the Background Art 
     Drawing apparatuses have been used for drawing images upon irradiation of various types of photosensitive materials with light. In a drum-type drawing apparatus, a photosensitive material is mounted on a recording drum which is rotatable in a primary scanning direction, and a recording head comprising a laser diode and the like moves in a secondary scanning direction parallel to a rotary shaft of the recording drum to draw an image on the photosensitive material. 
     FIG. 34 is a schematic perspective view of a recording drum in a conventional drawing apparatus. A plate  160  made of aluminum serving as a photosensitive material is mounted on a recording drum  150  shown in FIG. 34. A front end clamp  170  for fixing one end of the plate  160  and a rear end clamp  180  for fixing the other end of the plate  160  are attached to an outer peripheral surface of the recording drum  150 . The rear end clamp  180  contains a magnet, and is fixed by a magnetic force to a position, on the outer peripheral surface of the recording drum  150 , corresponding to the size of the plate  160 . 
     The recording drum  150  having the plate  160  attached thereto is rotated at relatively low speed around a rotary shaft  190 , so that an image is drawn on the surface of the plate  160 . 
     In recent years, a request to improve the efficiency of processing for drawing an image on the plate  160  has been made. In order to improve the efficiency of the drawing processing, the recording drum  150  having the plate  160  attached thereto must be rotated at high speed. 
     However, the rear end clamp  180  is fixed to the recording drum  150  by the magnetic force. When the recording drum  150  is rotated at high speed, therefore, the rear end clamp  180  moves on the outer peripheral surface of the recording drum  150  or is detached from the recording drum  150 , so that the plate  160  fixed to the recording drum  150  may be shifted in position and detached. Therefore, the recording drum  150  cannot be rotated at high speed. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a drawing apparatus capable of reliably fixing a sheet-shaped recording material of arbitrary size to an outer peripheral surface of a cylindrical drum. 
     Another object of the present invention is to provide a drawing apparatus capable of uniformly bringing a sheet-shaped recording material into close contact with an outer peripheral surface of a cylindrical drum. 
     A drawing apparatus according to one aspect of the present invention for drawing an image on a sheet-shaped recording material comprises a cylindrical drum having a rotary shaft and an outer peripheral surface and having a groove extending in the circumferential direction provided on the outer peripheral surface, a rotation driving device for rotating the drum around the rotary shaft, a fixing member provided so as to be attachable and detachable to or from the groove of the drum and so as to be movable along the groove for fixing the recording material to the outer peripheral surface of the drum, and a drawing unit for drawing an image on the recording material fixed on the outer peripheral surface of the drum, the fixing member comprising a main body member having one side part for pressing one end of the recording material against the outer peripheral surface of the drum, an engaging member provided so as to project on the side of the lower surface of the main body member and engaged with the inside of the groove of the drum, and urging means for urging the other side part of the main body member in the direction away from the outer peripheral surface of the drum. 
     In the drawing apparatus, the fixing member is provided so as to be attachable and detachable to or from the groove of the cylindrical drum and so as to be movable along the groove. The sheet-shaped recording material is mounted on the outer peripheral surface of the drum, and is fixed by the fixing member. 
     The engaging member provided in the main body member of the fixing member is engaged with the inside of the groove of the drum, thereby making it possible to fix the fixing member to the drum. The one end of the recording material is interposed between the one side part of the main body member and the outer peripheral surface of the drum, and the other end of the main body member is urged in the direction away from the outer peripheral surface of the drum by the urging means. Thus, the one end of the recording material is pressed against the outer peripheral surface of the drum by the one side part of the main body member. In this state, the drum having the recording material fixed thereto can be rotated around the rotary shaft by the rotation driving device. 
     The engaging member can be released from the groove of the drum by releasing the engagement of the engaging member provided in the fixing member. Thus, the fixing member can be moved in the circumferential direction along the groove on the outer peripheral surface of the drum. Consequently, the recording material of arbitrary size can be reliably fixed to the outer peripheral surface of the drum. 
     It is preferable that the length of the one side part of the main body member which is determined on the basis of the engaging member in the circumferential direction of the drum is smaller than the length of the other side part of the main body member. 
     In this case, at the time of rotation of the drum, centrifugal forces are exerted, respectively, on the one side part and the other side part of the fixing member. Since the length of the one side part of the main body member is smaller than the length of the other side part of the main body member, a rotation moment generated by the one side part of the main body member centered around the engaging member is smaller than a rotation moment generated by the other side part of the main body member, so that a force is exerted in the direction in which the other side part of the main body member separates from the outer peripheral surface of the drum. As a result, the one end of the recording material is firmly pressed against the outer peripheral surface of the drum by the one side part of the main body member. 
     The higher the rotational speed of the drum is, the larger the force to separate the other end of the main body member from the outer peripheral surface is, and the larger a force for the one side part of the main body member to press the one end of the recording material against the other peripheral surface of the drum is. Even when the drum is rotated at high speed, therefore, the recording material on the outer peripheral surface of the drum is not shifted in position and detached. 
     A weight may be provided in the other side part of the main body member. In this case, at the time of rotation of the drum, a centrifugal force is exerted on the weight provided in the other side part of the main body member, and a force is exerted in the direction in which the other side part of the main body member separates from the outer peripheral surface of the drum. As a result, the one end of the recording material is firmly pressed against the outer peripheral surface of the drum by the one side part of the main body member. 
     The higher the rotational speed of the drum is, the larger the centrifugal force exerted on the weight on the other side part of the main body member is, and the larger the force for the one side part of the main body member to press the one end of the recording material against the outer peripheral surface of the drum is. Even when the drum is rotated at high speed, therefore, the recording material on the outer peripheral surface of the drum is not shifted in position and detached. 
     The urging means may comprise a spring provided between a lower surface of the other side part of the main body member and the outer peripheral surface of the drum, and the weight may be a metal provided in the spring. 
     In this case, the other side part of the main body member is urged in the direction away from the outer peripheral surface of the drum by a reaction force produced by the spring. In addition, at the time of rotation of the drum, the metal provided in the spring presses the other side part of the main body member in the direction away from the outer peripheral surface of the drum by a centrifugal force. Thus, the one end of the recording material is firmly pressed against the outer peripheral surface of the drum by the one side part of the main body member. 
     The urging means may comprise a spring provided between the lower surface of the other side part of the main body member and the outer peripheral surface of the drum. 
     The drawing apparatus may further comprise a fixing member driving device for operating the engaging member of the fixing member to fix the fixing member to the drum or release the fixing member from the drum. 
     In this case, the engaging member of the fixing member is operated by the fixing member driving device, so that the fixing member can be fixed to the drum or released from the drum. Consequently, it is possible to fix the fixing member to the drum and easily release the fixing member from the drum. 
     The fixing member driving device may hold the fixing member in a state where the engaging member of the fixing member is released from the groove of the drum. 
     In this case, the fixing member is held by the fixing member driving device when the engaging member of the fixing member is released from the groove of the drum, thereby making it easy to attach the fixing member to the drum and detach the fixing member from the drum. 
     The engaging member may be a rotating member provided so as to be rotatable in the main body member and fixed in the groove of the drum as it rotates. 
     In this case, the rotating member provided in the main body member of the fixing member is rotated, so that the rotating member can be fixed in the groove of the drum. In addition, the rotating member provided in the fixing member is rotated, so that the rotating member can be released from the groove of the drum. Thus, the fixing member can be moved in the circumferential direction along the groove on the outer peripheral surface of the drum. 
     The fixing member may further comprise a sliding member provided in the main body member so as to be slidable in a predetermined direction for rotating the rotating member as it slides, and the fixing member driving device may comprise a driving member engaged with the sliding member in the fixing member, and a driving member driving mechanism for moving the driving member in the predetermined direction. 
     In this case, the driving member of the fixing member driving device is engaged with the sliding member in the fixing member, and the driving member is moved in a predetermined direction by the driving member driving mechanism, so that the sliding member in the fixing member can be slid with respect to the main body member to rotate the rotating member. Thus, the rotating member in the fixing member can be fixed in the groove of the drum, or the rotating member in the fixing member can be released from the groove of the drum. 
     The driving member driving mechanism may comprise a moving member which together with the driving member, moves in the predetermined direction, and the fixing member driving device may further comprise a holding member for holding or releasing the main body member of the fixing member as the moving member moves. 
     In this case, the moving member in the fixing member driving device is moved, so that the main body member of the fixing member can be held by the fixing member or released. Thus, it is possible to hold the fixing member by the fixing member driving device when the rotating member of the fixing member is released from the groove of the drum and detach the fixing member from the fixing member driving device when the rotating member of the fixing member is fixed in the groove of the drum. Consequently, it is possible to easily attach the fixing member to the drum and detach the fixing member from the drum. 
     The engaging member may be a lock member having a press portion and an lock portion, the lock portion being insertable into the groove of the drum as the press portion is pressed, while being locked into the groove by releasing the pressing of the press portion. 
     In this case, the press portion of the lock member provided in the main body member of the fixing member is pressed, so that the lock portion of the lock member can be inserted into the groove of the drum. In addition, the pressing of the press portion of the lock member is released, so that the lock portion is locked into the groove of the drum. Thus, the fixing member can be fixed to the drum. Further, the press portion of the lock member provided in the fixing member is pressed, thereby making it possible to release the locking of the lock portion of the lock member in the groove of the drum. Thus, the fixing member can be moved in the circumferential direction along the groove on the outer peripheral surface of the drum. 
     The fixing member driving device may comprise a driving device for pressing the press portion of the lock member of the fixing member, and a driving member driving mechanism for moving the driving member toward the press portion of the lock member. 
     In this case, the driving member in the fixing member driving device is moved toward the press portion of the lock member by the driving member driving mechanism, thereby making it possible to press the press portion of the lock member by the driving member. Thus, it is possible to insert and lock the lock portion of the lock member into the groove of the drum or release the locking of the lock portion of the lock member in the groove of the drum. 
     The fixing member driving device may comprise a supporting member and a sliding member provided so as to be slidable in a predetermined direction with respect to the supporting member for moving the driving member toward the press portion of the lock member as it slides. 
     In this case, the sliding member in the fixing member driving device is slid in a predetermined direction with respect to the supporting member, thereby making it possible to move the driving member toward the press portion of the lock member. Thus, the driving member can press the press portion of the lock member. 
     The fixing member driving device may further comprise a holding member for holding or releasing the main body member of the fixing member as the sliding member slides. 
     In this case, the sliding member of the fixing member driving device is slid, so that the main body member of the fixing member can be held by the holding member or released. Thus, the fixing member can be held by the fixing member driving device when the lock member of the fixing member is released from the groove of the drum, the fixing member can be detached from the fixing member driving device when the lock member of the fixing member is locked into the groove of the drum. Consequently, it is possible to easily attach the fixing member to the drum and detach the fixing member from the drum. 
     The lock member may comprise first and second lock members having a press portion and a lock portion, a shaft for connecting the first and second lock members to each other so as to be rotatable, and a spring member for urging the first and second lock members in the direction in which the lock portion of each of the first and second lock members is locked into the groove of the drum, and the first and second lock members may be provided such that the locking of the lock portion in the groove is released by the pressing of the press portion. 
     The drawing apparatus may further comprise a strip-shaped lock plate provided in the groove of the drum, the spring member may urge the first and second lock members in the direction in which the lock portion of each of the first and second lock members is locked into the lock plate, and the first and second lock members may be provided such that the locking of the lock port ion by the lock plate is released by the pressing of the press portion. 
     The drawing apparatus may further comprise a moving mechanism for moving the fixing member driving device to a position spaced apart from the outer peripheral surface of the drum and a position in close proximity to the outer peripheral surface of the drum. 
     In this case, the fixing member driving device can be moved to the position spaced apart from the outer peripheral surface of the drum and the position in close proximity to the outer peripheral surface of the drum by the moving mechanism, thereby making it possible to smoothly attach the fixing member to the drum and detach the fixing member from the drum. 
     A drawing apparatus according to another aspect of the present invention for drawing an image on a sheet-shaped recording material comprises a cylindrical drum having a rotary shaft and an outer peripheral surface, a rotation driving device for rotating the drum around the rotary shaft, a fixing member provided on the outer peripheral surface of the drum for fixing the recording material on the outer peripheral surface of the drum, a drawing unit for drawing an image on the recording material fixed on the outer peripheral surface of the drum, a first roller arranged along the outer peripheral surface of the drum parallel to the rotary shaft of the drum, a second roller arranged along the first roller, and a roller moving mechanism for moving the first roller to a position spaced apart from the outer peripheral surface of the drum and the second roller and a position in contact with the outer peripheral surface of the drum and the second roller. 
     In the drawing apparatus, the sheet-shaped recording material is fixed on the outer peripheral surface of the cylindrical drum by the fixing member. In this state, the drum having the recording material fixed thereto can be rotated around the rotary shaft by the rotation driving device. 
     When the first roller is moved to the position in contact with the outer peripheral surface of the drum and the second roller by the roller moving mechanism, the first roller uniformly presses the recording material fixed on the outer peripheral surface of the drum. Thus, the recording material on the outer peripheral surface of the drum is uniformly brought into close contact with the outer peripheral surface of the drum. 
     In addition, dust or the like which adheres to the surface of the recording material on the outer peripheral surface of the drum is transferred to the first roller, and the dust or the like which has been transferred to the first roller is transferred to the second roller. Thus, it is possible to remove the dust or the like from the recording material on the outer peripheral surface of the drum. 
     When the first roller is moved to the position spaced apart from the outer peripheral surface of the drum and the second roller by the roller moving mechanism, the recording material on the outer peripheral surface of the drum is released from the first roller. At this time, the first roller is also spaced apart from the second roller, so that the dust or the like which has been transferred to the second roller is not transferred to the first roller again. 
     A drawing apparatus according to still another aspect of the present invention for drawing an image on a sheet-shaped recording material comprises a cylindrical drum having a rotary shaft and an outer peripheral surface and having a groove extending in the circumferential direction provided on the outer peripheral surface, a rotation driving device for rotating the drum around the rotary shaft, a first fixing member provided on the outer peripheral surface of the drum for fixing one end of the recording material on the outer peripheral surface of the drum, a second fixing member provided so as to be attachable and detachable to or from the groove of the drum and so as to be movable along the groove for fixing the other end of the recording material on the outer peripheral surface of the drum, a drawing unit for drawing an image on the recording material fixed on the outer peripheral surface of the drum, a first roller arranged along the outer peripheral surface of the drum parallel to the rotary shaft of the drum, a second roller arranged along the first roller, and a roller moving mechanism for moving the second roller to a position spaced apart from the outer peripheral surface of the drum and the second roller and a position in contact with the outer peripheral surface of the drum and the second roller. 
     The second fixing member may comprise a main body member having one side part for pressing the other end of the recording material against the outer peripheral surface of the drum, an engaging member provided so as to project on the side of the lower surface of the main body member and engaged with the inside of the groove of the drum, and urging means for urging the other side part of the main body member in the direction away from the outer peripheral surface of the drum. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic plan view of a drawing apparatus according to one embodiment of the present invention; 
     FIG. 2 is a schematic side view of the drawing apparatus shown in FIG. 1; 
     FIG. 3 is a perspective view of a recording drum in the drawing apparatus shown in FIG. 1; 
     FIG. 4 is an exploded perspective view of a front end clamp in the drawing apparatus shown in FIG. 1; 
     FIG. 5 is a side view of a front end clamp in the drawing apparatus shown in FIG. 1; 
     FIG. 6 is an exploded perspective view of a rear end clamp in the drawing apparatus shown in FIG. 1; 
     FIGS.  7 ( a ) and  7 ( b ) are partially sectional views along the length of the rear end clamp in the drawing apparatus shown in FIG. 1; 
     FIG. 8 is a cross-sectional view along the width of the rear end clamp in the drawing apparatus shown in FIG. 1; 
     FIG.  9 ( a ) is a cross-sectional view in a state before the rear end clamp is held in a first driving device in the drawing apparatus shown in FIG.  1  and FIG.  9 ( b ) is a plan view of the rear end clamp in such state; 
     FIG.  10 ( a ) is a cross-sectional view in a state where the rear end clamp is held in the first driving device in the drawing apparatus shown in FIG.  1  and FIG.  10 ( b ) is a plan view of the rear end clamp in such state; 
     FIG. 11 is a side view showing the construction of a clamp driving device in the drawing apparatus shown in FIG. 1; 
     FIG. 12 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIG. 13 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIG. 14 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIG. 15 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIG. 16 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIG. 17 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIG. 18 is a side view showing the operation of the clamp driving device shown in FIG. 11; 
     FIGS.  19 ( a ) and  19 ( b ) are cross-sectional views showing another example of the rear end clamp; 
     FIGS.  20 ( a ) and  20 ( b ) are cross-sectional views showing still another example of the rear end clamp; 
     FIG. 21 is a schematic plan view mainly showing a recording drum and a clamp driving device in a drawing apparatus according to another embodiment of the present invention; 
     FIG. 22 is a schematic side view of the drawing apparatus shown in FIG. 21; 
     FIG. 23 is a perspective view of a recording drum in the drawing apparatus shown in FIG. 21; 
     FIG. 24 is an exploded perspective view of the rear end clamp in the drawing apparatus shown in FIG. 21; 
     FIGS.  25 ( a )- 25 ( c ) are side views mainly showing a clamping mechanism of the rear end clamp in the drawing apparatus shown in FIG. 21; 
     FIG. 26 is a cross-sectional view along the width of the rear end clamp in the drawing apparatus shown in FIG. 21; 
     FIG. 27 is a cross-sectional view showing the construction and the operation of a driving device in the drawing apparatus shown in FIG. 21; 
     FIG. 28 is a cross-sectional view showing the construction and the operation of a driving device in the drawing apparatus shown in FIG. 21; 
     FIG. 29 is a cross-sectional view showing the construction and the operation of a driving device in the drawing apparatus shown in FIG. 21; 
     FIG.  30 ( a ) is a cross-sectional view and FIG.  30 ( b ) is plan view showing a state where the rear end clamp is held by the driving device in the drawing apparatus shown in FIG. 21; 
     FIG.  31 ( a ) is a cross-sectional view and FIG.  31 ( b ) is a plan view showing a state where a clamping mechanism of the rear end clamp is opened by the driving device in the drawing apparatus shown in FIG. 21; 
     FIG.  32 ( a ) is a cross-sectional view and FIG.  32 ( b ) is a plan view showing a state where the rear end clamp is detached from the driving device in the drawing apparatus shown in FIG. 21; 
     FIG. 33 is a schematic sectional view showing another example of the clamping mechanism of the rear end clamp in the drawing apparatus shown in FIG. 21; and 
     FIG. 34 is a perspective view of a recording drum in a conventional drawings apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic plan view of a drawing apparatus in a first embodiment of the present invention, and FIG. 2 is a schematic side view of the drawing apparatus shown in FIG.  1 . 
     In FIGS. 1 and 2, the drawing apparatus comprises a cylindrical recording drum  1 . The recording drum  1  is rotated in a direction indicted by an arrow A (in a primary scanning direction) around a rotary shaft  1   a  by a rotation driving device  4 . A plate  100  made of aluminum is mounted as a photosensitive material on an outer peripheral surface of the recording drum  1 . One end of the plate  100  is fixed to the outer peripheral surface of the recording drum  1  by a plurality of front end clamps  2 , and the other end of the plate  100  is fixed to the outer peripheral surface of the recording drum  1  by a plurality of rear end clamps  3 . 
     A recording head  8  comprising a plurality of laser diodes  81  is disposed ahead of the recording drum  1 . The recording head  8  is attached to a guide  82  so as to be movable, and moves in a direction indicated by an arrow B (in a secondary scanning direction) in synchronization with the rotation of the recording drum  1 . 
     The plurality of laser diodes  81  in the recording head  8  are driven by a laser diode driving circuit portion  110 . The laser diode driving circuit portion  110  comprises a plurality of laser diode driving circuits  111  corresponding to the plurality of laser diodes  81  in the recording head  8 . 
     An image signal generator circuit  130  generates a serial image signal. A serial/parallel converter  120  converts the serial image signal generated by the image signal generator circuit  130  into parallel image signals, and respectively feeds the image signals to the plurality of laser diode driving circuits  111  in the laser diode driving circuit portion  110 . Consequently, each of the laser diodes  81  in the recording head  8  is driven by the corresponding laser diode driving circuit  111 , to irradiate the plate  100  with laser light. 
     As shown in FIG. 2, a clamp driving device  5  is provided behind the recording drum  1 . The clamp driving device  5  is used for attaching the rear end clamps  3  to the recording drum  1 , detaching the rear end clamps  3  from the recording drum  1 , and releasing the front end clamps  2  on the recording drum  1 . 
     The clamp driving device  5  comprises a pair of clamp arms  6  which are swingable in a direction indicated by an arrow C. A driving bar  60  is attached between the pair of clamp arms  6 , and a plurality of first driving devices  7  are attached to the driving bar  60 . As shown in FIG. 1, the first driving device  7  is provided with a driving pin  75 , two holding pins  76 , and a release pin  78 . 
     In addition, as shown in FIG. 2, a conveying unit  9  is disposed so as to be swingable in a direction indicated by an arrow R above the recording drum  1 . The conveying unit  9  has a first conveying path  91  for carrying in a plate and a second conveying path  92  for carrying out a plate. At the time of carry-in of the plate  100 , the plate  100  is supplied onto the recording drum  1  through the first conveying path  91  in the conveying unit  9 . At the time of carry-out of the plate  100 , the plate  100  which has been detached from the recording drum  1  is carried outward through the second conveying path  92  in the conveying unit  9 . 
     A punching device  10  for forming positioning holes in the plate  100  is disposed on the side of a front end of the conveying unit  9 . The plate  100  is supplied to the punching device  10  through the first conveying path  91  in the conveying unit  9  before being supplied onto the recording drum  1 , so that the positioning holes are formed at a peripheral end of the plate  100 . The positioning holes of the plate  100  are engaged with positioning pins (not shown) provided on the outer peripheral surface of the recording drum  1 . 
     FIG. 3 is a perspective view of the recording drum  1  in the drawing apparatus shown in FIG.  1 . As shown in FIG. 3, the recording drum  1  has a plurality of clamp grooves  11  extending in its circumferential direction formed on its outer peripheral surface. The plurality of front end clamps  2  and the plurality of rear end clamps  3  are provided on the outer peripheral surface of the recording drum  1 . 
     The plurality of front end clamps  2  are arranged along the axis of the recording drum  1 , and are fixed to the outer peripheral surface of the recording drum  1 . The plurality of rear end clamps  3  are arranged along the axis of the recording drum  1 , and are respectively attached to the outer peripheral surface of the recording drum  1  so as to be movable in the circumferential direction along the clamp grooves  11 . 
     FIG. 4 is an exploded perspective view of the front end clamp  2 , and FIG. 5 is a side view of the front end clamp  2 . 
     In FIGS. 4 and 5, the front end clamp  2  is constituted by a clamp main body  20 , a rotary shaft  21 , two bearings  22 , four bolts  23 , two metal balls  24 , two springs  25 , and a plurality of pressing rubbers  26 . 
     The bearings  22  are fixed to the recording drum  1  by the bolts  23 . The clamp main body  20  is attached to the bearings  22  so as to be rotatable by the rotary shaft  21 . The pressing rubbers  26  are mounted on a lower surface of one side part  20   a  of the clamp main body  20 . As shown in FIG. 5, a recess  12  is formed in the recording drum  1  below the other side part  20   b  of the clamp main body  20 . The spring  25  is mounted between a lower surface of the other side part  20   b  of the clamp main body  20  and the recess  12  of the recording drum  1 , and the metal ball  24  is inserted into the spring  25 . 
     The lower surface of the one side part  20   a  of the clamp main body  20  may be coated with ceramic instead of mounting the pressing rubber  26  thereon. Consequently, the durability is improved without decreasing a frictional force. 
     The other side part  20   b  of the clamp main body  20  is urged in the direction away from the recording drum  1  centered around the rotary shaft  21 , as indicated by an arrow P 1 , by a reaction force produced by the spring  25 . Consequently, a force in the direction in which the one side part  20   a  of the clamp main body  20  is brought near the recording drum  1 , as indicated by an arrow P 2 , so that one end of the plate  100  on the recording drum  1  is pressed by the pressing rubber  26 . 
     The length L 1  of the one side part  20   a  of the clamp main body  20  which is determined on the basis of the rotary shaft  21  is set to a length smaller than the length L 2  of the other side part  20   b  of the clamp main body  20 . 
     At the time of rotation of the recording drum  1 , the metal ball  24  moves in the direction indicated by the arrow P 1  by a centrifugal force, to push the other side part  20   b  of the clamp main body  20  up in the direction away from the recording drum  1 . In addition, centrifugal forces are respectively exerted on the one side part  20   a  and the other side part  20   b  of the clamp main body  20 . Since the length L 1  of the one side part  20   a  of the clamp main body  20  is set to a length smaller than the length of the other side part  20   b  of the clamp main body  20 , a rotation moment generated by the one side part  20   a  of the clamp main body  20  centered around the rotary shaft  21  is smaller than a rotation moment generated by the other side part  20   b . Consequently, a force in the direction in which the other side part  20   b  of the clamp main body  20  is separated from the outer peripheral surface of the recording drum  1  is exerted, so that the one end of the plate  100  is firmly pressed against the outer peripheral surface of the recording drum  1  by the pressing rubber  26  in the one side part  20   a  of the clamp main body  20 . 
     The higher the rotational speed of the recording drum  1  is, the larger a force exerted on the other side part  20   b  of the clamp main body  20  is, and the larger a force for the pressing rubber  26  in the one side part  20   a  of the clamp main body  20  to press the one end of the plate  100  against the outer peripheral surface of the recording drum  1  is. Even when the recording drum  1  is rotated at high speed, therefore, the one end of the plate  100  is reliably fixed to the outer peripheral surface of the recording drum  100  by the front end clamp  20 , so that the plate  100  on the outer peripheral surface of the recording drum  1  is not shifted in position and detached. 
     FIG. 6 is an exploded perspective view of the rear end clamp  3 , FIGS.  7 ( a ) and  7 ( b ) are partially sectional views along the length of the rear end clamp  3 , and FIG. 8 is a cross-sectional view along the width of the rear end clamp  3 . 
     As shown in FIGS. 6 to  8 , the rear end clamp  3  is constituted by a clamp main body  30 , a clamp bolt connecting plate  31 , an engaging member  32 , two first clamp bolts  33 , two second clamp bolts  34 , two screws  35 , two leaf springs  36 , and four springs  37 . 
     A rectangular recess  38  is provided at the center of the clamp main body  30 , and rectangular recesses  39  are respectively provided on both sides of the recess  38 . Holding holes  40  are respectively provided in the vicinities of both ends of the clamp main body  30 . The holding holes  40  are composed of circular parts and narrow parts. The holding pins  76  in the first driving device  7 , described later, are respectively inserted into the holding holes  40 . 
     The clamp bolt connecting plate  31  is provided so as to be slidable in a direction indicated by an arrow S in the three recesses  38 ,  39  upon penetrating side surfaces of the recesses  38 ,  39 . The engaging member  32  is fixed to the clamp bolt connecting plate  31  in the recess  38 . The driving pin  75  in the first driving device  7  is engaged with an engaging hole  32   a  of the engaging member  32 . Long holes  31   a  are respectively formed in the vicinities of both ends of the clamp bolt connecting plate  31 . 
     The second clamp bolts  34  have projections  34   a  projecting toward both their sides provided on their outer peripheral surfaces. The second clamp bolts  34  are inserted into holes  39   a  provided on the bottom surfaces of the recesses  39  of the clamp main body  30 . The first clamp bolts  33  are attached to the heads of the second clamp bolts  34  by the screws  35 . Projections  33   a  are provided on the lower surfaces of the first clamp bolts  33 . The projections  33   a  of the first clamp bolts  33  are engaged with the long holes  31   a  of the clamp bolt connecting plate  31 . Consequently, when the engaging member  32  slides in the direction indicated by the arrow S, the clamp bolt connecting plate  31 , together with the engaging member  32 , slides in the direction indicated by the arrow S, so that the first clamp bolts  33 , together with the second clamp bolts  34 , rotate in a direction indicated by an arrow Q. 
     As shown in FIGS.  7 ( a ) and  7 ( b ), inner flanges  13  projecting inward are respectively provided at upper ends on both side surfaces of the clamp groove  11  formed in the recording drum  1 . As shown in FIG.  7 ( a ), when the projection portions  34   a  of the second clamp bolt  34  are positioned parallel to the clamp groove  11 , the projection portions  34   a  are not engaged with the inner flanges  13  of the clamp groove  11 . In this case, the rear end clamp  3  can be detached from the recording drum  1 . 
     On the other hand, as shown in FIG.  7 ( b ), when the projection portions  34   a  of the second clamp bolt  34  are positioned perpendicularly to the clamp groove  11  of the recording drum  1 , the projection portions  34   a  are engaged with the inner flanges  13  of the clamp groove  11 . Consequently, the rear end clamp  3  is fixed to the recording drum  1 . 
     As shown in FIG. 8, the other end of the plate  100  is inserted between the lower surface of one side part  30   a  of the clamp main body  30  and the outer peripheral surface of the recording drum  1 . A lead plate  42  is embedded in the other side part  30   b  of the clamp main body  30 . In addition, the leaf spring  36  and the spring  37  are mounted on the lower surface of the other side part  30   b  of the clamp main body  30 . 
     The other side part  30   b  of the clamp main body  30  is urged in the direction away from the recording drum  1  centered around the second clamp bolt  34 , as indicated by an arrow Y 1 , by reaction forces produced by the leaf spring  36  and the spring  37 . Consequently, a force in the direction in which the one side part  30   a  of the clamp main body  30  is brought near the recording drum  1 , as indicated by an arrow Y 2 , so that the one end of the plate  100  on the recording drum  1  is pressed by the lower surface of the one side part  30   a  of the clamp main body  30 . 
     The length L 3  of the one side part  30   a  of the clamp main body which is determined on the basis of the second clamp bolt  34  is set to a length smaller than the length L 4  of the other side part  30   b  of the clamp main body  30 . 
     At the time of rotation of the recording drum  1 , a centrifugal force is exerted in the direction indicated by the arrow Y 1  on the lead plate  42  embedded in the lower surface of the other side part  30   b  of the clamp main body  30 . In addition, centrifugal forces are respectively exerted on the one side part  30   a  and the other side part  30   b  of the clamp main body  30 . Since the length L 3  of the one side part  30   a  of the clamp main body  30  is set to a length smaller than the length L 4  of the other side part  30   b  of the clamp main body  30 , a rotation moment generated by the one side part  30   a  of the clamp main body  30  centered around the second clamp bolt  34  is smaller than a rotation moment generated by the other side part  30   b . Consequently, a force in the direction in which the other side part  30   b  of the clamp main body  30  is separated from the outer peripheral surface of the recording drum  1  is exerted, so that the other end of the plate  100  is firmly pressed against the outer peripheral surface of the recording drum  1  by the one side part  30   a  of the clamp main body  30 . 
     The higher the rotational speed of the recording drum  1  is, the larger a force to be exerted on the other side part  30   b  of the clamp main body  30  is, and the stronger a force for the one side part  30   a  of the clamp main body  30  to press the other end of the plate  100  against the outer peripheral surface of the recording drum  1  is. When the recording drum  1  is rotated at high speed, therefore, the other end of the plate  100  is reliably fixed to the outer peripheral surface of the recording drum  1  by the rear end clamp  3 , so that the plate  100  on the outer peripheral surface of the recording drum  1  is not shifted in position and detached. 
     FIG.  9 ( a ) is a cross-sectional view in a state before the rear end clamp  3  is held in the first driving device  7 , and FIG.  9 ( b ) is a plan view of the rear end clamp  3 . In addition, FIG.  10 ( a ) is a cross-sectional view in a state where the rear end clamp  3  is held in the first driving device  7 , and FIG.  10 ( b ) is a plan view of the rear end clamp  3 . 
     As shown in FIGS.  9 ( a ) and  9 ( b ), the first driving device  7  is constituted by a driving device main body  70 , a clamp bolt driving motor  71 , a driving member  72 , and a position sensors  73 . A gear  74  is attached to the clamp bolt driving motor  71 . A plane gear  72   a  which is meshed with the gear  74  is provided on a side surface of the driving member  72 . The driving member  72  is provided so as to be slidable in a direction indicated by an arrow U by the rotation of the clamp bolt driving motor  71 . In addition, driving pin  75  is provided at the center on the lower surface of the driving member  72 , and holding pins  76  are respectively provided in the vicinities of both ends of the lower surface of the driving member  72 . The position sensors  73  detect the position of the driving member  72 . 
     In the state of FIGS.  9 ( a ) and  9 ( b ), when the first driving device  7  is brought near the rear end clamp  3 , the driving pin  75  is inserted into an engaging hold  32   a  of an engaging member  32  in the rear end clamp  3 , and the holding pins  76  are inserted into the circular parts of the holding holes  40  in the rear end clamp  3 . 
     Thereafter, when the clamp bolt driving motor  71  rotates, the driving member  72  moves in a direction indicated by an arrow U 1 , so that the engaging member  32  which is engaged with the driving pin  75 , together with a clamp bolt connecting plate  31 , slides in the direction indicated by the arrow U 1 , as shown in FIGS.  10 ( a ) and  10 ( b ). Consequently, the first clamp bolts  33 , together with the second clamp bolts  34 , rotate in the directions shown by the arrows V 1  and V 2 . In addition, the holding pins  76  move to the narrow parts of the holding holes  40  in the rear end clamp  3 . Consequently, the rear end clamp  3  is held in the first driving device  7 , and the projection portions  34   a  of the second clamp bolts  34  are brought into the state parallel to the clamp groove  11  of the recording drum  1 , as shown in FIG.  7 ( a ). In this state, the second clamp bolts  34  in the rear end clamp  3  can be inserted into the clamp groove  11  of the recording drum  1 . 
     Subsequently, when the clamp bolt driving motor  71  rotates in the opposite direction, the engaging member  32  which is engaged with the driving pin  75 , together with the clamp bolt connecting plate  31 , slides in the opposite direction to the direction indicated by the arrow U 1 , so that the first clamp bolts  33 , together with the second clamp bolts  34 , rotate in the opposite direction. In addition, the holding pins  76  move to the circular parts of the holding holes  40  in the rear end clamp  3 . Consequently, the projection portions  34   a  of the second clamp bolts  34  are brought into the state perpendicular to the clamp groove  11  of the recording drum  1 , as shown in FIG.  7 ( b ). As a result, the second clamp bolts  34  in the rear end clamp  3  can be fixed to the clamp groove  11  of the recording drum  1 , and the first driving device  7  can be detached from the rear end clamp  3 . 
     By operations reverse to the above-mentioned operations, the rear end clamp  3  is detached from the recording drum  1 , and the rear end clamp  3  can be held in the first driving device  7 . 
     FIG. 11 is a side view showing the construction of the clamp driving device  5 . 
     A gear  51  is attached to a clamp arm driving motor  50 . The gear  51  is meshed with a gear  52 , and an engaging portion  52   a  provided in the gear  52  is engaged with a long hole  6   a  of the clamp arm  6 . The clamp arm driving motor  50  rotates, so that the clamp arm  6  swings in a direction indicted by an arrow C centered around a rotary shaft  61 . 
     In addition, the clamp driving device  5  is provided with a squeegee device  53  and a second driving device  62 . The squeegee device  53  is constituted by a squeegee driving motor  54 , a gear  55 , a swing member  56 , a gum roller  57 , and a squeegee roller  58 . The gear  55  is attached to the squeegee driving motor  54 , and the swing member  56  is meshed with the gear  55 . The swing member  56  is attached to the squeegee roller  58 . When the squeegee driving motor  54  rotates, the swing member  56  swings through the gear  55 , so that the squeegee roller  58  is brought into close contact with the outer peripheral surface of the recording drum  1 . 
     The second driving device  62  is constituted by a cam driving motor  63 , gears  64   a ,  64   b ,  64   c ,  64   d , and a cam  65 . The gear  64   a  is attached to the cam driving motor  63 . Torque generated by the cam driving motor  63  is transmitted to the gear  64   d  through the gears  64   a ,  64   b ,  64   c . The cam  65  is attached to the gear  64   d.    
     As shown in FIG. 11, the position of the clamp arm  6  in a state where the first driving device  7  is spaced apart from the outer peripheral surface of the recording drum  1  is referred to as an origin position, and the position of the clamp arm  6  in a state where the first driving device  7  is in close proximity to the outer peripheral surface of the recording drum  1  is referred to as a terminal position. 
     Next, description is now made of the operation of the clamp driving device  5  while referring to FIGS. 11 to  18 . 
     First, as shown in FIG. 11, after the recording drum  1  is rotated until the front end clamp  2  attached to the outer peripheral surface of the recording drum  1  reaches a position p 1  of the release pin  78  of the first driving device  7 , the rotation of the recording drum  1  is stopped. The clamp arm  6  swings from the origin position shown in FIG. 11 to the terminal position shown in FIG. 12 by the clamp arm driving motor  50 . Then, the first driving device  7  is brought near the front end clamp  2  attached to the outer peripheral surface of the recording drum  1 , so that the release pin  78  presses one side part of the front end clamp  2 . 
     Consequently, a clearance is formed between the other side part of the front end clamp  2  and the outer peripheral surface of the recording drum  1 , as shown in FIG.  13 . In this state, the plate  100  is carried inward through the first conveying path  91  in the conveying unit  9  shown in FIG. 2, and a front end of the plate  100  is inserted into the clearance between the other side part of the front end clamp  2  and the outer peripheral surface of the recording drum  1 . 
     Thereafter, the clamp arm  6  is returned to the origin position by the clamp arm driving motor  50 , so that the first driving device  7  separates from the outer peripheral surface of the recording drum  1 . Consequently, the front end of the plate  100  is fixed to the outer peripheral surface of the recording drum  1  by the front end clamp  2 . 
     The plate  100  is conveyed by the conveying unit  9  shown in FIG. 2 while rotating the recording drum  1 . When the front end clamp  2  reaches a position p 2  where the front end clamp  2  passes through the squeegee roller  58 , as shown in FIG. 14, the squeegee roller  58  is brought into close contact with the plate  100  on the outer peripheral surface of the recording drum  1  by the squeegee driving motor  54 . At this time, the squeegee roller  58  is also brought into contact with the gum roller  57 . Dust or the like is transferred onto an outer peripheral surface of the squeegee roller  58  from the surface of the plate  100  by the rotation of the recording drum  1 , so that the dust or the like which has been transferred to the squeegee roller  58  is further transferred to the gum roller  57 . 
     Thereafter, when a rear end of the plate  100  reaches a position p 3  of the rear end clamp  3  held in the first driving device  7  by the rotation of the recording drum  1 , as shown in FIG. 15, the rotation of the recording drum  1  is stopped. The stop position differs depending on the size of the plate  100  to be supplied. In the present embodiment, the plate  100  is fixed utilizing the groove  11  formed in the circumferential direction of the recording drum  1 , so that the plate  100  of arbitrary size can be reliably fixed on the outer peripheral surface of the recording drum  1 . 
     In this state, as shown in FIG. 16, the clamp arm  6  swings to the terminal position by the clamp arm driving motor  50 , and the rear end clamp  3  held by the holding pins  76  of the first driving device  7  presses the rear end of the plate  100  on the recording drum  1 . In this case, as shown in FIG.  7 ( a ), the second clamp bolts  34  of the rear end clamp  3  are inserted into the clamp groove  11  of the recording drum  1 , so that the plate  100  is pressed by the one side part of the clamp main body  30 . 
     Next, the clamp bolt driving motor  71  in the first driving device  7  shown in FIG. 10 is then rotated, and the clamp bolt connecting plate  31  in the rear end clamp  3  is slid by the driving pin  75 , to fix the second clamp bolts  34  in the clamp groove  11  of the recording drum  1  by the projection portions  34   a , as shown in FIG.  7 ( b ). Simultaneously, the holding pins  76  of the first driving device  7  shown in FIG. 10 move to the circular parts of the holding holes  40  in the rear end clamp  3 , so that the rear end clamp  3  is released from the first driving device  7 . 
     Thereafter, the clamp arm  6  is returned to the origin position by the clamp arm driving motor  50 , as shown in FIG.  17 . Consequently, the rear end clamp  3  is detached from the first driving device  7 . As a result, the rear end of the plate  100  is fixed to the outer peripheral surface of the recording drum  1  by the rear end clamp  3 . The plate  100  is thus fixed to the outer peripheral surface of the recording drum  1 , so that an image is drawn on the plate  100  by the recording head  8  shown in FIG.  1 . 
     When the drawing of the image on the plate  100  by the recording head  8  is completed, the rear end clamp  3  is moved to the position p 3 , shown in FIG. 17, of the holding pins  76  of the first driving device  7  by the rotation of the recording drum  1 , and the rotation of the recording drum  1  is then stopped. In addition, the squeegee roller  58  is brought into close contact with the plate  100  on the outer peripheral surface of the recording drum  1  by the squeegee driving motor  54 . Then, the clamp arm  6  swings to the terminal position, shown in FIG. 16, by the clamp arm driving motor  50 . 
     As shown in FIG. 10, the driving pin  75  of the first driving device  7  is inserted into the engaging hole  32   a  of the engaging member  32  in the rear end clamp  3 , and the holding pins  76  are inserted into the holding holes  40  of the rear end clamp  3 , so that the driving pin  75 , together with the clamp bolt connecting plate  31 , slides by the clamp bolt driving motor  71 , and the second clamp bolts  34  rotate. Consequently, the second clamp bolts  34  are released from the clamp groove  11  of the recording drum  1 . Simultaneously, the holding pins  76  of the first driving device  7  move to the narrow parts of the holding holes  40  of the rear end clamp  3 . Consequently, the rear end clamp  3  is held by the first driving device  7 . 
     In this state, when the clamp arm  6  swings to the origin position by the clamp arm driving motor  50 , the rear end clamp  3  is lifted up in a state where it is held by the first driving device  7 , to open the rear end of the plate  100 , as shown in FIG.  15 . 
     Furthermore, the plate  100  is carried outward by the conveying unit  9  shown in FIG. 2 while the recording drum  1  is being rotated in the opposite direction to the direction shown in FIG.  14 . 
     When the front end clamp  2  reaches a position p 4  of the cam  65  by the rotation of the recording drum  1 , as shown in FIG. 18, the rotation of the recording drum  1  is stopped. In this state, the cam  65  rotates by the cam driving motor  63 , to press the one side part of the front end clamp  2 . Consequently, the front end of the plate  100  is released from the front end clamp  2 . 
     In addition, the squeegee roller  58  is separated from the outer peripheral surface of the recording drum  1  by the squeegee driving motor  54 . In this case, the squeegee roller  58  also separates from the gum roller  57 . Thereafter, the plate  100  is carried outward through the second conveying path  92  in the conveying unit  9 . 
     FIGS.  19 ( a ) and  19 ( b ) are cross-sectional views showing another example of the rear end clamp  3 . As shown in FIGS.  19 ( a ) and  19 ( b ), an inner flange portion  13  projecting inward is provided at an upper end on one side surface of the clamp groove  11  formed in the recording drum  1 . A second clamp bolt  34  in the rear end clamp  3  has a projection portion  34   a  projecting toward its one side part provided on its outer peripheral surface. The construction of the other portions in the rear end clamp  3  shown in FIGS.  19 ( a ) and  19 ( b ) is the same as the construction of the rear end clamp shown in FIGS. 6 to  8 . 
     When the projection portion  34   a  of the second clamp bolt  34  is positioned parallel to the clamp groove  11 , as shown in FIG.  19 ( a ), the projection portion  34   a  is not engaged with the inner flange portion  13  of the clamp groove  11 . In this case, the rear end clamp  3  can be detached from the recording drum  1 . On the other hand, when the projection portion  34   a  of the second clamp bolt  34  is positioned perpendicularly to the clamp groove  11  of the recording drum  1 , as shown in FIG.  19 ( b ), the projection portion  34   a  is engaged with the inner flange portion  13  of the clamp groove  11 . Consequently, the rear end clamp  3  is fixed to the recording drum  1 . 
     When the rear end clamp  3  shown in FIG. 19 is used, the rear end of the plate  100  can be reliably fixed to the outer peripheral surface of the recording drum  1  even when the recording drum  1  is rotated at high speed, as in a case where the rear end clamp  3  shown in FIGS. 6 to  8  is used. 
     FIGS.  20 ( a ) and  20 ( b ) are cross-sectional views showing still another example of the rear end clamp  3 . As shown in FIGS.  20 ( a ) and  20 ( b ), the clamp groove  11  formed in the recording drum  1  has a rectangular cross section. An elliptical projection portion  34   b  is provided at a lower end of the second clamp bolt  34 . The construction of the other portions in the rear end clamps  3  shown in FIGS.  20 ( a ) and  20 ( b ) is the same as the construction of the rear end clamp  3  shown in FIGS. 6 to  8 . 
     When the projection portion  34   b  of the second clamp bolt  34  is positioned parallel to the clamp groove  11 , as shown in FIG.  20 ( a ), the rear end clamp  3  can be detached from the recording drum  1 . On the other hand, when the projection portion  34   b  of the second clamp bolt  34  is positioned perpendicularly to the clamp groove  11  of the recording drum  1 , as shown in FIG.  20 ( b ), both ends of the projection portion  34   b  are pressed against side surfaces of the clamp groove  11 . Consequently, the rear end clamp  3  is fixed to the recording drum  1 . 
     When the rear end clamp  3  shown in FIG. 20 is used, the rear end of the plate  100  can be reliably fixed to the outer peripheral surface of the recording drum  1  even when the recording drum  1  is rotated at high speed, as in a case where the rear end clamp  3  shown in FIGS. 6 to  8  is used. 
     As described in the foregoing, in the drawing apparatus according to the present embodiment, the plate  100  of arbitrary size can be reliably fixed to the outer peripheral surface of the recording drum  1  by the front end clamps  2  and the rear end clamps  3 , so that the plate  100  is not shifted in position and detached even when the recording drum  1  is rotated at high speed. 
     In addition, the fixing of the front end of the plate  100  by the front end clamps  2  and the fixing and the release of the rear end of the plate  100  by the rear end clamps  3  can be easily performed using the first driving devices  7  in the clamps driving device  5 . Further, the release of the front end clamps  2  can be easily performed using the second driving devices  62  in the clamp driving device  5 . 
     In addition, the plate  100  can be uniformly brought into close contact with the outer peripheral surface of the recording drum  1  by the squeegee device  53 , and the dust or the like adhering to the surface of the plate  100  can be transferred to the gum roller  57  through the squeegee roller  58 . Moreover, when the squeegee roller  58  is spaced apart from the outer peripheral surface of the recording drum  1 , the squeegee roller  58  is also spaced apart from the gum roller  57 . Accordingly, the dust or the like which has been transferred to the gum roller  57  is prevented from being transferred again to the squeegee roller  58 . 
     Although in the present embodiment, the rear end clamps  3  are fixed to the outer peripheral surface of the recording drum  1  by the grooves extending in its circumferential direction, the grooves may be replaced with a plurality of recesses formed in its circumferential direction. 
     FIG. 21 is a schematic plan view mainly showing a recording drum and a clamp driving device in a drawing apparatus in a second embodiment of the present invention, and FIG. 22 is a schematic side view of the drawing apparatus shown in FIG.  21 . 
     In FIGS. 21 and 22, the drawing apparatus comprises a cylindrical recording drum  1 . The recording drum  1  is rotated in a direction indicted by an arrow A (in a primary scanning direction) around a rotary shaft  1   a  by a rotation driving device  4  shown in FIG. 22. A plate  100  made of aluminum is mounted as a photosensitive material on an outer peripheral surface of the recording drum  1 . One end of the plate  100  is fixed to the outer peripheral surface of the recording drum  1  by a plurality of front end clamps  200 , and the other end of the plate  100  is fixed to the outer peripheral surface of the recording drum  1  by a plurality of rear end clamps  300 . 
     As shown in FIG. 22, a clamp driving device  500  is provided behind the recording drum  1 . The clamp driving device  500  is used for attaching the rear end clamps  300  to the recording drum  1 , detaching the rear end clamps  300  from the recording drum  1 , and releasing the front end clamps  200  on the recording drum  1 . 
     The clamp driving device  500  comprises a pair of clamp arms  600  which are swingable in a direction indicated by an arrow C. A driving device  700  is attached between the pair of clamp arms  600 . As shown in FIG. 21, the driving device  700  is provided with a plurality of sets of driving mechanisms  710 . Each of the sets of driving mechanisms  710  comprises two pairs of driving pins  750 , two holding pins  760 , and two pairs of pressing rollers  780 . 
     As described later, the two pairs of driving pins  750  are used for attaching the rear end clamp  300  to the recording drum  1  and detaching the rear end clamp  300  from the recording drum  1 , and the two holding pins  760  are used for holding the rear end clamp  300 . The two pairs of pressing rollers  780  are used for pressing the rear end clamp  300  on the recording drum  1 . 
     The drawing apparatus shown in FIGS. 21 and 22 is also provided with the recording head  8 , the conveying unit  9 , and the punching device  10  shown in FIGS. 1 and 2. 
     FIG. 23 is a perspective view of the recording drum  1  in the drawing apparatus shown in FIG.  21 . As shown in FIG. 23, the recording drum  1  has a plurality of clamp grooves  12  extending in its circumferential direction formed on its outer peripheral surface. A strip-shaped lock plate  13  having a predetermined length is mounted in each clamp groove  12 . A plurality of front end clamps  200  are attached to the outer peripheral surface of the recording drum  1 . The structure of each front end clamp  200  is the same as the structure of the front end clamp  2  shown in FIGS. 4 and 5. 
     FIG. 24 is an exploded perspective view of the rear end clamp  300 , FIG. 25 is a side view mainly showing a clamping mechanism of the rear end clamp  300 , and FIG. 26 is a cross-sectional view along the width of the rear end clamp  300 . 
     As shown in FIG. 24, the rear end clamp  300  is constituted by a clamp main body  301 , a pair of clamping mechanisms  302 , and four double torsion springs  303 . 
     The clamp main body  301  is provided with a pair of holes  320 . Holding holes  340  are respectively provided in the vicinities of both ends of the clamp main body  301 . The holding pins  760  of the driving device  700 , described later, are respectively inserted into the holding holds  340 . 
     Each clamping mechanism  302  is constituted by a pair of clamp members  321 ,  322 , a shaft  323 , a spring (not shown), a pair of pressing plates  324 ,  325 , and four screws  326 . The clamp members  321 ,  322  respectively have press portions  321   a ,  322   a  and hook portions  321   b ,  322   b . The clamp members  321 ,  322  in each pair are connected to each other so as to be rotatable by the shaft  323 , and are mounted in each hole  320  of the clamp main body  301 . Each shaft  323  is held in the clamp main body  301  by the pair of pressing plates  324 ,  325  and the four screws  326 . 
     The four double torsion springs  303  are attached to the rear surface of a side part  301   b  of the clamp main body  301 . Each of the double torsion springs  303  is attached so as to be rotatable in a case  331  by a shaft  332 , and the case  331  is fixed to the rear surface of the clamp main body  301  by four screws  333 ,  334 . 
     As shown in FIGS.  25 ( a )- 25 ( c ), the clamp members  321 ,  322  in the clamping mechanism  302  are urged in the direction in which the hook portions  321   b ,  322   b  are closed inward centered around the shaft  323  by the spring  327 . As shown in FIGS.  25 ( a )- 25 ( c ), the clamp groove  12  formed in the recording drum  1  is w-shaped in cross section, and can be formed at low cost by simple lathe forming. 
     Ends of the press portions  321   a ,  322   a  in a pair of clamp members  321 ,  322  are abutted against the upper surface of the clamp main body  301  from below. Consequently, a space between the hook portions  321   b ,  322   b  is slightly narrower than the lock plate  13  in the clamp groove  12  of the recording drum  1 , as shown in FIG.  25 ( a ). 
     When the press portions  321   a ,  322   a  in the clamp members  321 ,  322  are pressed downward by the driving pins  750  in the driving device  700 , the hook portions  321   b ,  322   b  are opened outward, centered around the shaft  323 , against a force produced by the spring  327 , as shown in FIG.  25 ( b ). In this state, the hook portions  321   b ,  322   b  can pass downward through both sides of the lock plate  13 . 
     Thereafter, as shown in FIG.  25 ( c ), when the clamp main body  301  is pushed downward, and the pressing of the press portions  321   a ,  322   a  by the driving pins  750  is released, the hook portions  321   b ,  322   b  are closed inward, centered around the shaft  323 , by the spring  327 . Consequently, the clamp members  321 ,  322  are engaged with the lock plate  13 , and the rear end clamp  300  is fixed to the recording drum  301 . Front ends of the hook portions  321   b ,  322   b  are firmly engaged with the lock plate  13  by the function of a centrifugal force exerted on the clamping mechanism  302  when the recording drum  1  is rotated at high speed. Therefore, the rear end clamp  300  can be firmly fixed to the recording drum  1 . 
     In addition, in a system of inserting the clamp bolts  33 ,  34  into the clamp groove  11  and then rotating the clamp bolts, and engaging the projection portions  33   a ,  34   a  with the inner flanges of the clamp groove  11 , as in the first embodiment, the thickness of the projection portions  33   a ,  34   a  (the length, in a direction perpendicular to the clamp groove  11 , of the projection portions  33   a ,  34   a  before the rotation) is limited to the width of the clamp groove  11 . On the other hand, in a system of simply opening or closing the hook portions  321   b ,  322   b  rightward or leftward, as in the second embodiment, the thickness of the hook portions  321   b ,  322   b  is the length thereof along the clamp groove  12 , so that it can be determined irrespective of the width of the clamp groove  12 . Therefore, the hook portions  321   b ,  322   b  can be caused to have such a thickness that it can withstand a larger clamping force. 
     As shown in FIG. 26, the one end of the plate  100  is interposed between a lower surface of the one side part  301   a  of the clamp main body  301  and the outer peripheral surface of the recording drum  1 . The double torsion spring  303  is urged in a direction indicated by an arrow Y 3 . 
     The other side part  301   b  of the clamp main body  301  is urged in the direction away from the recording drum  1  centered around a position between the clamp members  321 ,  322 , as indicated by an arrow Y 1 , by a reaction force produced by the double torsion spring  303 . Consequently, a force in the direction in which the one side part  301   a  of the clamp main body  301  is brought near the recording drum  1 , as indicated by an arrow Y 2 , is exerted, so that the one end of the plate  100  on the recording drum  1  is pressed by the lower surface of the one side part  301   a  of the clamp main body  301 . The lower surface of the one side part  20   a  of the clamp main body  301  is coated with ceramic. Consequently, the durability is improved without decreasing a frictional force. 
     The length L 3  of the one side part  301   a  of the clamp main body  301  which is determined on the basis of the position between the clamp members  321 ,  322  is set to a length smaller than the length L 4  of the other side part  301   b  of the clamp main body  301 . 
     At the time of rotation of the recording drum  1 , centrifugal forces are respectively exerted on the one side part  301   a  and the other side part  301   b  of the clamp main body  301 . Since the length L 3  of the one side part  301   a  of the clamp main body  301  is set to a length smaller than the length L 4  of the other side part  301   b  of the clamp main body  301 , a rotation moment generated by the one side part  301   a  of the clamp main body  301  centered around the position between the clamp members  301 ,  302  is smaller than a rotation moment generated by the other side part  301   b . Consequently, a force in the direction in which the other side part  301   b  of the clamp main body  301  is separated from the outer peripheral surface of the recording drum  1 , so that the one end of the plate  100  is firmly pressed against the outer peripheral surface of the recording drum  1  by the one side part  301   a  of the clamp main body  301 . 
     The higher the rotational speed of the recording drum  1  is, the larger a force to exert the other side part  301   b  of the clamp main body  301  is, and the stronger a force for the one side part  301   a  of the clamp main body  301  to press the one end of the plate  100  against the outer peripheral surface of the recording drum  1  is. Even when the recording drum  1  is rotated at high speed, therefore, the one end of the plate  100  is reliably fixed to the outer peripheral surface of the recording drum  1  by the rear end clamp  300 , so that the plate  100  on the outer peripheral surface of the recording drum  1  is not shifted in position and detached. 
     FIGS. 27,  28  and  29  are cross-sectional views showing the construction and the operation of a driving device  700 . In FIGS. 27 to  29 , one set of driving mechanisms  710  is illustrated. 
     As shown in FIGS. 27 to  29 , the driving device  700  comprises a driving stay  720  and a slider  730 . A flanged bearing  721  is attached to the driving stay  720 . A horizontal slit  731  is formed in the slider  730 . The flanged bearing  721  of the driving stay  720  is fitted in the slit  731  of the slider  730 . 
     Further, a slider driving motor  740  is fixed to the driving stay  720 . A pinion gear  741  is attached to the slider driving motor  740 . The slider  730  is provided with a rack gear  742  which is meshed with the pinion gear  741 . The slider  730  is provided so as to be slidable in a direction indicted by an arrow X with respect to the driving stay  720  by the rotation of the slider driving motor  740 . 
     The driving mechanism  710  is constituted by two pairs of driving pins  750 , two bearings  751 , two cam followers  752 , two cams  753 , and two holding pins  760 . 
     Each bearing  751  is fixed on the bottom surface of the driving stay  720 . One pair of driving pins  750  is respectively provided movably up and down so as to penetrate each bearing  751  and the driving stay  720 . Each cam follower  752  is attached to upper ends of one pair of driving pins  750 . The upper surface of the cam follower  752  is constituted by an upper horizontal surface  752   a , an inclined surface  752   b , and a lower horizontal surface  752   c . Each cam  753  is attached to the slider  730  so as to be abutted against the upper surface of each cam follower  752 . Each pair of driving pins  750  and each cam follower  752  are urged upward by a spring (not shown). 
     Each holding pin  760  penetrates the bottom surface of the slider  730 , and projects downward through a long hole provided on the lower surface of the driving stay  720 . Each holding pin  760  is urged downward by a spring (not shown). 
     Holding members  722 ,  723  projecting downward are provided on the lower surface of the driving stay  720 . A leaf spring  724  is attached to the holding member  723 . The rear end clamp  300  shown in FIG. 24 is held between the holding member  722  and the leaf spring  724 . In this case, the two holding pins  760  can be respectively inserted into the two holding holes  340  in the rear end clamp  300 , and the two pairs of driving pins  750  can be respectively abutted against the press portions  321   a ,  322   a  of the clamp members  321 ,  322  in the two clamping mechanisms  302 . 
     In addition, the pressing pin  725  which is urged downward by a spring (not shown) is provided on the lower surface of the driving stay  720 . The pressing pin  725  prevents the rear end clamp  300  held between the holding member  722  and the leaf spring  724  from being lifted. 
     A position detecting member  735  horizontally projecting is provided at one end of the slider  730 . Two tabs  735   a ,  735   b  are formed in the position detecting member  735 . Two sensors  736 ,  737  for detecting the tabs  735   a ,  735   b  of the position detecting member  735  are provided in the driving stay  720 . The position in the horizontal direction of the slider  730  with respect to the driving stay  720  is detected by the sensors  736 ,  737 . 
     FIGS.  30 ( a ),  30 ( b ) are respectively a cross-sectional view and a plan view of a state where the rear end clamp  300  is held by the driving device  700 . FIGS.  31 ( a ),  31 ( b ) are respectively a cross-sectional view and a plan view of a state where a clamping mechanism of the rear end clamp  300  is opened by the driving device  700 . FIGS.  32 ( a ),  32 ( b ) are respectively a cross-sectional view and a plan view of a state where the rear end clamp  300  is detached from the driving device  700 . The operations of the driving device  700  and the rear end clamp  300  will be described while referring to FIGS. 27 to  32 . 
     When the cam  753  in the slider  730  is positioned in the vicinity of a lower end of the inclined surface  752   b  of the cam follower  752 , as shown in FIG. 27, front ends of the driving pins  750  are at a first vertical position V 1 , and the holding pin  760  is at a first horizontal position H 1 . 
     In this case, the driving pins  750  are not abutted against the press portions  321   a ,  322   a  of the clamp members  321 ,  322 , as shown in FIG.  30 . Consequently, the hook portions  321   b ,  322   b  of the clamp members  321 ,  322  are in a closed state. In addition, the holding pin  760  is positioned in a narrow part of the holding hole  340  in the rear end clamp  300 . Consequently, the rear end clamp  300  is held by the holding pin  760 . 
     When the slider  730  slides in the horizontal direction by the slider driving motor  740  so that the cam  753  is positioned in the vicinity of an upper end of the inclined surface of the cam follower  752 , as shown in FIG. 28, the front ends of the driving pins  750  are lowered to a second vertical position V 2 , and the holding pin  760  moves to a second horizontal position H 2 . 
     In this case, the press portions  321   a ,  322   a  of the clamp members  321 ,  322  are pushed down by the driving pins  750 , as shown in FIG.  31 . Consequently, the hook portions  321   b ,  322   b  are opened outward, to pass through both sides of the lock plate  13  in the clamp groove  12 . Further, the holding pin  760  moves to the vicinity of a boundary between the narrow part and the circular part of the holding hole  340  in the rear end clamp  300 . 
     When the slider  730  further slides in the horizontal direction by the slider driving motor  740  so that the cam  753  is positioned on the upper horizontal surface  752   a  of the cam follower  752 , as shown in FIG. 29, the front ends of the driving pins  750  are pushed down to a third vertical position V 3 , and the holding pin  760  moves to a third horizontal position H 3 . 
     In this case, the holding pin  760  moves to the circular part of the holding hole  340  in the rear end clamp  300 , as shown in FIG.  32 . When the driving device  700  is moved upward, the holding pin  760  is detached from the rear end clamp  300 , and the pressing of the press portions  321   a ,  322   a  of the clamp members  321 ,  322  by the driving pins  750  is released. Consequently, the hook portions  321   b ,  322   b  of the clamp members  321 ,  322  are closed inward, and are engaged with the lock plate  13  in the clamp groove  12 . 
     In the above-mentioned manner, the rear end clamp  300  can be attached to the recording drum  1 , and the rear end clamp  300  can be detached from the driving device  700 . 
     By operations reverse to the above-mentioned operations, the rear end clamp  300  can be detached from the recording drum  1 , and the rear end clamp  300  can be held in the driving device  700 . 
     The construction of the other portions and the overall operation of the clamp driving device  500  in FIG. 22 are the same as the construction and the operation of the clamp driving device  5  described using FIGS. 11 to  18 . 
     As described in the foregoing, in the drawing apparatus of the present embodiment, the plate  100  of arbitrary size can be reliably fixed on the outer peripheral surface of the recording drum  1  by the front end clamps  200  and the rear end clamps  300 , so that the plate  100  is not shifted in position and detached even when the recording drum  1  is rotated at high speed. 
     In addition, the fixing of the front end of the plate  100  by the front end clamps  200  and the fixing and the release of the rear end of the plate  100  by the rear end clamps  300  can be easily performed using the driving device  700  in the clamp driving device  500 . 
     FIG. 33 is a schematic cross-sectional view showing another example of a clamping mechanism of the rear end clamp  300 . 
     As shown in FIG. 33, recesses  15   a ,  15   b  are formed on both sides of a clamp groove  14  in a recording drum  1 , and strip-shaped lock plates  16   a ,  16   b  are respectively attached on the recesses  15   a ,  15   b . A clamping mechanism  360  comprises a pair of clamping members  361 ,  362 . The clamp members  361 ,  362  respectively have press portions  361   a ,  362   a  and hook portions  361   b ,  362   b.    
     The clamp members  361 ,  362  are respectively provided in the clamp main body so as to be rotatable by the shafts  363 ,  364 , and are urged outward by a spring (not shown). Consequently, the hook portions  361   b ,  362   b  are respectively engaged with the lock plates  16   a ,  16   b  in the clamp groove  14 . When the press portions  361   a ,  362   a  are pushed down by the driving pins  750  of the driving device  700 , the engagement between the hook portions  361   b ,  362   b  and the lock plates  16   a ,  16   b  is released. 
     Although in the above-mentioned embodiment, the clamp groove  12  extending over the whole circumference of the outer peripheral surface of the recording drum  1  are provided, the clamp grooves  12  may be provided in a part, in the circumferential direction, of the outer peripheral surface of the recording drum  1 . Alternatively, the clamp grooves  12  may be intermittently provided in the circumferential direction of the outer peripheral surface of the recording drum  1 . 
     Although in the above-mentioned embodiment, a front end clamp and a rear end clamp are divided into a plurality of parts, they may have single structures, in which case the same function can be performed. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.