Abstract:
A sheet pressing apparatus includes a cam, lever, sheet press member, and first and second compression coil springs. The cam has a cam surface and is supported rotatably. The lever supports a cam follower that abuts against the cam surface and is pivoted by rotation of the cam. The sheet press member is movably supported by the lever and moves between a sheet press position to press a stacked sheet and a retreat position retreated from the sheet press position in accordance with swing motion of the lever. The first and second compression coil springs are arranged between the lever and a support, and bias the lever to bring the cam follower into tight contact with the cam surface. The second compression coil spring has a biasing force larger than that of the first compression coil spring. When the sheet press member is located at the sheet press position, only the first compression coil spring biases the cam follower with respect to the cam surface. When the sheet press member is located at the retreat position, the first and second compression coil springs cooperate to bias the cam follower with respect to the cam surface.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a sheet pressing apparatus used by a feed device or the like in a sheet-fed offset rotary printing press and, more particularly, to a sheet pressing apparatus in which a sheet press member moves between a sheet press position to press a stacked sheet and a retreat position retreated from the sheet press position.  
         [0002]     A sheet pressing apparatus in a conventional sheet-fed offset rotary printing press comprises a rotatably supported cam, a cam follower which abuts against the cam surface of the cam, a lever which is moved by rotation of the cam, a sheet press member which is supported by the lever and can be moved between a sheet press position to press a stacked sheet and a retreat position retreated from the sheet press position by rotation of the cam, and a biasing means which is arranged between the lever and a support member to bias the lever so as to bring the cam follower into tight contact with the cam surface.  
         [0003]     In the conventional sheet pressing apparatus described above, the cam follower is brought into tight contact with the cam surface by one biasing means. If the biasing force of the biasing means increases, the pressing force to press the sheet increases excessively, so the sheet press member may damage the sheet. If the biasing force of the biasing means decreases, the tight-contact force of the cam follower with respect to the cam surface becomes insufficient. Particularly, when the cam follower moves from a large-diameter portion to a small-diameter portion, the cam follower cannot follow the cam surface but separates from it, causing so-called cam detachment.  
       SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet pressing apparatus which does not damage a sheet and prevents cam detachment.  
       [0004]     In order to achieve the above object, according to the present invention, there is provided a sheet pressing apparatus comprising a cam having a cam surface and supported rotatably, a lever which supports a cam follower that abuts against the cam surface and is pivoted by rotation of the cam, a sheet press member which is movably supported by the lever and moves between a sheet press position to press a stacked sheet and a retreat position retreated from the sheet press position in accordance with swing motion of the lever, and first biasing means and second biasing means, arranged between the lever and a support member, for biasing the lever so as to bring the cam follower into tight contact with the cam surface, the second biasing means having a biasing force larger than that of the first biasing means, wherein when the sheet press member is located at the sheet press position, only the first biasing means biases the cam follower with respect to the cam surface, and when the sheet press member is located at the retreat position, the first biasing means and the second biasing means cooperate to bias the cam follower against the cam surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a front view of a sheet pressing apparatus according to the present invention;  
         [0006]      FIG. 2  is a side view of the sheet pressing apparatus according to the present invention to show a state wherein a sheet press member is positioned at a sheet press position to press a sheet;  
         [0007]      FIGS. 3A and 3B  are side views for explaining the operation of the sheet pressing apparatus according to the present invention, in which  FIG. 3A  shows a state wherein the sheet press member is switched between the sheet press position and a retreat position, and  FIG. 3B  shows a state wherein the sheet press member is positioned at the retreat position; and  
         [0008]      FIG. 4  is a view for explaining a state in the sheet pressing apparatus according to the present invention wherein the tight-contact force of a cam follower which is in contact with a cam surface is switched. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0009]     A sucker device in a sheet-fed offset rotary printing press according to an embodiment of the present invention will be described with reference to FIGS.  1  to  3 B.  
         [0010]     As shown in  FIG. 1 , a sheet pressing apparatus  1  comprises a sucker frame  2  including side plates  3  and  4  which oppose each other and a rod  5  horizontally extending between the side plates  3  and  4 . The side plate  3  is attached to the frame (not shown) of a feed device through a bracket  6 . A support  7  (support member) has one end fixed to the rod  5 . The other end of the support  7  has a support hole  8  ( FIG. 2 ).  
         [0011]     A shaft portion  9   b  integrally projecting from a spring retainer  9  having a through hole  9   a  is pivotally supported by the support hole  8  of the support  7  which engages with the spring retainer  9 . A rotating shaft  11  is rotatably supported between the two side plates  3  and  4  of the sucker frame  2  through bearings  12 . A swingable member  13  having one end which is axially mounted is supported by the rotating shaft  11  to be swingable about the rotating shaft  11  as a swing center. A connecting member  15  is pivotally mounted on the other end of the swingable member  13  through a shaft  16 . A sheet press member  18  is attached to the other end of the connecting member  15  through a screw  17 . The sheet press member  18  is supported such that it can move between the sheet press position (the solid line in  FIG. 2 ) to press a stacked sheet  19  and a retreat position (the alternate long and two short dashed line in  FIG. 2 ) retreated from the sheet press position when a cam  26  rotates, as will be described later.  
         [0012]     The center of a lever  22  is rotatably supported between the two side plates  3  and  4  of the sucker frame  2  through a shaft  23  ( FIGS. 3A and 3B ). The center of the connecting member  15  is pivotally mounted on one end of the lever  22  through a pin  24 . A cam follower  25  is pivotally mounted on the other end of the lever  22 . The cam follower  25  is brought into tight contact with a cam surface  27  of the rotating cam  26  by the spring forces of first and second compression coil springs  31  and  32  (first and second biasing means). The cam surface  27  of the cam  26  is formed of a small-diameter portion  27   a  as an iso-circular low cam, a large-diameter portion  27   b  as an iso-circular high cam, and an inclined portion  27   c  which links the small-diameter portion  27   a  to the large-diameter portion  27   b.    
         [0013]     A first spring retainer  28  having a through hole  28   a  is pivotally supported by a support hole  22   a , formed in the lever  22  between the shaft  23  and pin  24 , through a shaft portion  28   b  integrally projecting from the first spring retainer  28 . An engaging surface  28   c  is formed on that end face of the first spring retainer  28  which is in the direction of an arrow A (a direction to come close to the rod  5 ). A thin elongated shaft  30  has a threaded portion  30   a  at its one end and a large-diameter portion  30   b  at its intermediate portion. The large-diameter portion  30   b  has a flange  30   c  at its one end and a step  30   d  at its other end.  
         [0014]     The shaft  30  has one end slidably supported by a through hole  9   a  of a second spring retainer  9  and the other end slidably supported by the through hole  28   a  of the first spring retainer  28 . The step  30   d  of the shaft  30  opposes the engaging surface  28   c  of the first spring retainer  28  at a predetermined gap. The engaging portion  28   c  of the first spring retainer  28  and the step  30   d  of the shaft  30  form an engaging means.  
         [0015]     The first compression coil spring  31  is elastically mounted between the flange  30   c  of the shaft  30  and the first spring retainer  28 . The second compression coil spring  32  is elastically mounted between the flange  30   c  and the second spring retainer  9 . Hence, the shaft  30  is biased from the second spring retainer  9  by the spring force of the second compression coil spring  32  in the direction of an arrow B. Simultaneously, the shaft  30  biases the first spring retainer  28  in the direction of the arrow B (a direction to separate from the rod  5 ) with the spring force of the first compression coil spring  31 .  
         [0016]     The spring force of the first compression coil spring  31  is set smaller than that of the second compression coil spring  32 . The spring force of the first compression coil spring  31  is set to such a level that when the sheet press member  18  is located at the sheet press position to press the stacked sheet  19 , the sheet press member  18  will not deform the sheet  19 . The spring force of the second compression coil spring  32  is set to such a level that when the sheet press member  18  moves from the retreat position retreated from the sheet press position to the sheet press position, the cam follower  25  does not separate from the cam surface  27  of the cam  26 .  
         [0017]     As a double nut  33  (stopper member) threadably engaging with the threaded portion  30   a  engages with the second spring retainer  9 , it regulates movement in the direction of the arrow B of the shaft  30  biased by the spring force of the second compression coil spring  32 . When the threadable engaging amount of the double nut  33  with respect to the threaded portion  30   a  is adjusted, the gap between the second spring retainer  9  and the flange  30   c  of the shaft  30  is adjusted, so the spring force of the second compression coil spring  32  with respect to the shaft  30  can be adjusted.  
         [0018]     When the cam follower  25  is in contact with the small-diameter portion  27   a  of the cam  26 , the lever  22  pivots counterclockwise in  FIG. 2  about the shaft  23  as a center to form a gap L between the engaging surface  28   c  of the first spring retainer  28  and the step  30   d  of the shaft  30 . Therefore, the shaft  30  does not move until the first spring retainer  28  has moved for the gap “L” in the direction to come close to the step  30   d.    
         [0019]     In this state, the biasing force in the direction of the arrow B against the first spring retainer  28  consists of only the spring force of the first compression coil spring  31  elastically mounted between the flange  30   c  and second spring retainer  9 . Thus, the lever  22  is also biased counterclockwise about the shaft  23  as a center by the spring force of the first compression coil spring  31 .  
         [0020]     When the cam follower  25  is in contact with the small-diameter portion  27   a  of the cam  26 , the sheet press member  18  is located at the sheet press position to press the stacked sheet  19  through the connecting member  15 , as shown in  FIG. 2 . When the cam follower  25  is in contact with the large-diameter portion  27   b  of the cam  26 , the lever  22  is biased clockwise in  FIG. 2  about the shaft  23  as a center against the spring force of the compression coil spring  32 . Thus, the connecting member  15  pivots clockwise through the swingable member  13  about the rotating shaft  11  as a center to position the sheet press member  18  at the retreat position ( FIG. 3B ) retreated from the sheet press position.  
         [0021]     The operation in the sheet pressing apparatus having the above arrangement in which the sheet press member moves between the sheet press position and retreat position will be described.  
         [0022]     When the cam  26  rotates and the cam follower  25  comes into contact with the small-diameter portion  27   a  of the cam surface  27 , the sheet press member  18  is located at the sheet press position to press the stacked sheet  19 , as indicated by the solid line in  FIG. 2 . At this time, the engaging surface  28   c  of the first spring retainer  28  is spaced apart from the step  30   d  of the shaft  30  by the gap L, and no gap is formed between the compression coil spring  32  and second spring retainer  9 .  
         [0023]     As the spring force of the second compression coil spring  32  is set larger than that of the first compression coil spring  31 , the shaft  30  is inhibited by the spring force of the second compression coil spring  32  from moving in the direction of the arrow A, and the first spring retainer  28  becomes movable in the direction of the arrow A against the spring force of the first compression coil spring  31 . Therefore, while the cam follower  25  is in contact with the small-diameter portion  27   a , the biasing force (the tight-contact force of the cam follower  25  in contact with the cam surface  27 ) that the lever  22  receives through the first spring retainer  28  takes a minimal value of a tight-contact force P 1  obtained by the spring force of only the first compression coil spring  31 , as indicated by a point C in  FIG. 4 .  
         [0024]     According to this embodiment, the spring force of the first compression coil spring  31  is set to such a level that when the sheet press member  18  is located at the sheet press position to press the stacked sheet  19 , the sheet press member  18  does not deform the sheet  19 . Hence, the sheet press member  18  does not deform the sheet or damage the surface of the sheet.  
         [0025]     In this state, when the cam  26  further pivots and the cam follower  25  exceeds the small-diameter portion  27   a  and comes into contact with a slightly high cam before reaching the inclined portion  27   c , the sheet press member  18  is located between the sheet press position indicated by the solid line and the position indicated by the alternate long and two short dashed line in  FIG. 2 . At this time, the gap between the engaging surface  28   c  of the first spring retainer  28  and the step  30   d  of the shaft  30  becomes smaller than L, and no gap is formed between the double nut  33  and second spring retainer  9 . In this state, the biasing force that the lever  22  receives through the first spring retainer  28  is the tight-contact force P 1  from the point C to a point D in  FIG. 4  which is obtained by the spring force of only the first compression coil spring  31 .  
         [0026]     In this state, when the cam surface  27  further pivots and the cam follower  25  comes into contact with the inclined portion  27   c , the lever  22  pivots clockwise about the shaft  23  as a center against the spring force of the first compression coil spring  31 . Thus, the first spring retainer  28  moves in the direction of the arrow A so the engaging portion  28   c  engages with the step  30   d  of the shaft  30 . Therefore, the gap between the engaging surface  28   c  of the first spring retainer  28  and the step  30   d  of the shaft  30  disappears, and no gap is formed between the double nut  33  and second spring retainer  9 . In this state, as indicated by the point D in  FIG. 4 , the biasing force that the lever  22  receives through the first spring retainer  28  takes a maximal value of the tight-contact force P 1  obtained by the spring force of only the first compression coil spring  31 . At this time, the sheet press member  18  is located at the position shown in  FIG. 3A .  
         [0027]     After the engaging portion  28   c  engages with the step  30   d  of the shaft  30 , when the cam  26  further rotates, the cam follower  25  comes into contact with a cam slightly higher than the inclined portion  27   c . Then, the shaft  30  moves in the direction of the arrow A together with the first spring retainer  28 , and a slight gap is formed between the double nut  33  and second spring retainer  9 . Thus, the spring force of the second compression coil spring  32  is applied to the shaft  30 . The biasing force that the first spring retainer  28  receives is a tight-contact force P 2  as the sum of the spring force of the first compression coil spring  31  and the spring force of the second compression coil spring  32 .  
         [0028]     When the cam  26  further rotates and the cam follower  25  comes into contact with the cam  26  between the inclined portion  27   c  and large-diameter portion  27   b , the sheet press member  18  is located between the position shown in  FIG. 3A  and the position shown in  FIG. 3B . In this state, no gap is formed between the engaging surface  28   c  of the first spring retainer  28  and the step  30   d  of the shaft  30 , while a gap is formed between the double nut  33  and second spring retainer  9 . Thus, the tight-contact force which brings the cam follower  25  into tight contact with the cam surface  27  is the tight-contact force P 2  from the point E to a point F in  FIG. 4 .  
         [0029]     When the cam  26  further rotates and the cam follower  25  comes into contact with the large-diameter portion  27   b  of the cam  26 , the sheet press member  18  is located at the retreat position shown in  FIG. 3B . In this state, no gap is formed between the engaging surface  28   c  of the first spring retainer  28  and the step  30   d  of the shaft  30 , while a gap is formed between the double nut  33  and second spring retainer  9 . Thus, as indicated by the point F in  FIG. 4 , the tight-contact force P 2  which brings the cam follower  25  into tight contact with the cam surface  27  reaches a maximal value.  
         [0030]     According to this embodiment, the spring force of the second compression coil spring  32  is set to such a level that when the sheet press member  18  is moved from the retreat position in the direction so as to be located at the sheet press position, the cam follower  25  does not separate from the cam surface  27  of the cam  26 . Hence, cam detachment can be prevented while the cam follower  25  is in contact with the large-diameter portion  27   b.    
         [0031]     As described above, as the cam  26  rotates, the lever  22  pivots clockwise about the shaft  23  ( FIG. 2 ) as a center, and the tight-contact force of the sheet press member  18  shifts from the point C to the point F in  FIG. 4 . After that, when the cam  26  further rotates, the lever  22  pivots counterclockwise about the shaft  23  as a center, and the tight-contact force of the sheet press member  18  shifts from the point F to the point C in  FIG. 4 . In this manner, when the cam  26  continues rotating in one direction, the mode in which the tight-contact force shifts from the point C to the point F and the mode in which the tight-contact force shifts from the point F to the point C are repeated.  
         [0032]     As the sheet  19 , various types of sheet-type objects can be used, e.g., paper or a foil-type sheet, an aluminum sheet, or the like.  
         [0033]     As has been described above, according to the present invention, when the sheet press member is located at the sheet press position, it presses the sheet with the first biasing force which is a small biasing force. Thus, the sheet press member does not damage the surface of the sheet. When the sheet press member is located at the retreat position, the second biasing force which is a large biasing force and the first biasing force bring the cam follower into tight contact with the cam surface. Thus, cam detachment in which the cam follower separates from the cam surface can be inhibited.