Patent Publication Number: US-6334387-B1

Title: Stencil printer having carriage for guiding leading end of stencil sheet

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stencil printer, an more particularly, to an improvement of means for conducting a leading end of a stencil sheet perforated by stencil sheet perforation means to stencil leading end mounting means of a printing drum. 
     2. Description of the Prior Art 
     There has been proposed by Japanese Patent No. 2804695 a stencil printer having stencil sheet leading end holding and transporting means adapted to reciprocate between a vicinity of stencil sheet perforation means and a vicinity of stencil sheet leading end mounting means of a printing drum stopped at a stencil sheet mounting position, wherein the stencil sheet leading end holding and transporting means are operated to hold a leading end of a stencil sheet perforated by the stencil sheet perforation means at an outlet of the stencil sheet perforation means as projecting forward as much as can be clamped by stencil sheet leading end mounting means of the printing drum, and move to the vicinity of the stencil sheet leading end mounting means, and then the printing drum is rotated so as to wind up the stencil sheet therearound, with the stencil sheet leading end holding and transporting means holding the stencil sheet by a force weaker than a stencil sheet holding force of the stencil sheet leading end mounting means of the printing drum, so that thereby the stencil sheet is wound around the printing drum in an expanded condition. 
     When the stencil sheet leading end holding and transporting means for holding and transporting the stencil sheet leading end from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum are adapted also to serve as the means for expanding the stencil sheet during a winding-up thereof around the printing drum as in the above-mentioned patent, it is difficult to set up the friction condition of the clamping to be suitable for definitely and stably transporting the leading end of the stencil sheet from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum and also to be suitable for desirably expanding the stencil sheet without damaging it while it is wound around the printing drum, since these two conditions are not compatible with one another. 
     Further, when the leading end of the stencil sheet is transported by the stencil sheet leading end holding and transporting means from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum as projecting forward enough to be caught by the stencil sheet leading end mounting means of the printing drum, when the speed of the transportation increases, the forward projecting leading end of the stencil sheet is bent by a wind caused by the movement thereof, so that the leading end would not be correctly caught by the stencil sheet leading end mounting means of the printing drum. 
     SUMMARY OF THE INVENTION 
     In consideration of the above-mentioned problems, it is a primary object of the present invention to provide a stencil printer equipped with a stencil sheet leading end guiding carriage improved so as not to cause those problems. 
     In order to solve, the above-mentioned problems, the present invention proposes a stencil printer comprising: 
     a printing drum having means provided along a generatrix of a cylindrical circumference thereof for mounting a leading end of a stencil sheet, the printing drum being adapted to be stopped at a predetermined rotational position for mounting the stencil sheet thereon; 
     means for perforating the stencil sheet; and 
     a carriage guided to reciprocate between a vicinity of an outlet of the stencil sheet perforation means and a vicinity of the stencil sheet leading end mounting means of the printing drum stopped at the predetermined rotational position; 
     wherein the carriage has means for selectively clamping the leading end of the stencil sheet perforated by the stencil sheet perforation means, and a pair of rollers for feeding the stencil sheet when the stencil sheet leading end clamping means are not clamping the stencil sheet, the stencil sheet feeding roller pair being adapted to feed the stencil sheet which had been clamped at the leading end thereof by the stencil sheet leading end clamping means toward the stencil sheet leading end mounting means as starting from the leading end when the carriage is positioned in the vicinity of the stencil sheet leading end mounting means of the printing drum stopped at the predetermined rotational position and then to brake the stencil sheet while it is being wound around the circumference of the printing drum with the leading end thereof being held by the stencil sheet leading end mounting means. 
     By the stencil sheet leading end holding means for holding and pulling the leading end of the stencil sheet from the vicinity of the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum are constructed as means separate from the means for braking the stencil sheet to be expanded while it is being wound around the circumference of the printing drum according to a rotation thereof with the leading end of the stencil sheet being held by the stencil sheet leading end mounting means of the printing drum, the friction condition for ensuring the pulling by clamping of the leading end of the stencil sheet of the stencil sheet leading end clamping means can be determined independently of the friction condition for braking the stencil sheet being wound around the circumference of the printing drum, so that the pulling transportation of the leading end of the stencil sheet from the outlet of the stencil sheet perforation means to the stencil sheet leading end mounting means of the printing drum is definitely ensured, while the stencil sheet can be applied with a desirable expansion when it is wound around the circumference of the printing drum so as not to damage even highly delicately formed perforation images of the stencil sheet. 
     Further, by the clamping of the leading end of the stencil sheet by the stencil sheet leading end clamping means being released when reached the vicinity of the stencil sheet leading end mounting means of the printing drum, while in turn the leading end of the stencil sheet is fed out forward by the separate stencil sheet feeding roller pair so as to be fed into the stencil sheet leading end mounting means of the printing drum, there occurs no such deformation of the leading end of the stencil sheet as by a running wind during the transportation thereof from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum even when the speed of the transportation is increased. Further, by such an arrangement that the leading end of the stencil sheet is fed into the stencil sheet leading end mounting means of the printing drum by the stencil sheet leading end feeding roller pair in the vicinity thereof with a control of the stencil sheet leading end feeding roller pair for a very small distance of transportation independently of a control of transportation for a relatively large distance of transportation extended from the outlet of the stencil sheet perforation means to the stencil sheet leading end mounting means of the printing drum, the means for each of the two separate controls can be individually optimized with respect to the strength and the sensitivity of their constructions, so that the leading end of the stencil sheet is always mounted to the stencil sheet leading end mounting means of the printing drum in a predetermined correct mounting condition. 
     In more detail, the carriage may have a main frame, and an auxiliary frame pivotably supported by the main frame, the stencil sheet leading end clamping means having a lower clamping element and an upper clamping element, the stencil sheet feeding roller pair having a lower roller and an upper roller, the lower clamping element and the lower roller being mounted on the main frame, the upper clamping element and the upper roller being mounted on the auxiliary frame, the auxiliary frame being adapted to be pivoted relative to the main frame by an action of a cam follower engaging a cam when the carriage comes to the vicinity of the outlet of the stencil sheet perforation means so as to remove the upper clamping element and the upper roller from the lower damping element and the lower roller, respectively. 
     In such a construction, the auxiliary frame may be biased toward a regular position relative to the main frame by a spring. 
     The stencil printer of the above construction may further comprise a pair of guide rails extending between the vicinity of the outlet of the stencil sheet perforation means and the vicinity of the stencil sheet leading end mounting means of the printing drum stopped at the predetermined rotational position, the carriage being supported and guided by the guide rail pair at opposite side portions thereof. 
     In such a construction, the guide rails may have a branch portion adapted to be selectively branched in a way thereof, the carriage being capable of supplying the stencil sheet to at least two printing drums separately according to a non-branched state and a branched state. 
     Further, the guide rail pair may be deflected at an end portion thereof close to the stencil sheet perforation means so that the carriage coming to the vicinity of the outlet of the stencil sheet perforation means is inclined so as to bias an end of the main frame thereof close to the stencil sheet perforation means downward relative to the stencil sheet perforation means, so that thereby the lower clamping element and the lower roller are biased downward relative to the outlet of the stencil sheet perforation means, while the upper clamping element and the upper roller are biased upward relative to the outlet of the stencil sheet perforation means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, 
     FIG. 1 is a diagrammatical side view showing the general construction of the essential portions of an embodiment of the stencil printer equipped with the stencil sheet leading end guiding carriage according to the present invention; 
     FIG. 2 is a side view showing in an enlargement further details of the carriage and constructions therearound in the state shown in FIG. 1; 
     FIG. 3 is a diagrammatical side view similar to FIG. 1, showing the carriage in a state slightly moved from the state shown in FIG. 1; 
     FIG. 4 is a side view showing in an enlargement further details of the carriage and constructions therearound shown in FIG. 3; 
     FIG. 5 is a diagrammatical side view similar to FIG. 1, showing the carriage in a state slightly moved leftward from the state shown in FIG. 3 along the guide rail; 
     FIG. 6 is a diagrammatical side view similar to FIG.  1  and others, showing the carriage in the state operating in the vicinity of the stencil sheet leading end mounting means of the first printing drum; and 
     FIG. 7 is a diagrammatical side view similar to FIG.  1  and others, showing the carriage in the state operating in the vicinity of the stencil sheet leading end mounting means of the second printing drum. 
    
    
     DESCRIPTION OF THE EMBODIMENT 
     In the following, the invention will be described in more detail with respect to an embodiment thereof by referring to the accompanying drawings. 
     Referring to FIG. 1 diagrammatically showing a side view of only an essential portion of an embodiment of the present invention constructed as a two drum type stencil printer,  10  is a carriage for guiding a leading end of a stencil sheet. In FIG. 1, the carriage  10  is shown particularly in a condition where it has come to a vicinity of an outlet of stencil sheet perforation means  12 . This stencil printer is of a two drum type having a first printing drum  14  and a second printing drum  16  as shown in the figure, wherein a stencil sheet  20  fed out from a roll  18  serving as a source thereof is conducted through the stencil sheet perforation means  12  including a thermal head  22 , a platen roller  24 , a pair of stencil sheet feed out rollers  28  and a stencil sheet feed out port  30 , so that a perforated stencil sheet is mounted around the printing drum  14  or  16  to do a printing. 
     The stencil sheet fed out from the stencil sheet feed out port  30  is conducted by the carriage  10  running along a guide rail  32  supported by a support frame not shown in the figure toward stencil sheet leading end mounting means  34  of the printing drum  14  stopped at a predetermined rotational position for mounting the stencil sheet or to stencil sheet leading end mounting means  36  of the printing drum  16  stopped at a predetermined rotational position for mounting the stencil sheet. The stencil sheet leading end mounting means  34  and  36  have bar-like stencil sheet receiving bases  38  and  40  provided along a generatrix of each of the cylindrical shape of the printing drums, and clamps  46  and  48 , respectively, the clamps  46  and  48  being pivotable about pivot shafts  42  and  44  betweened an open position removed from the stencil sheet receiving base  38  and  40  as shown in FIG. 1 and a closed position pressed onto the stencil sheet receiving bases  38  and  40 , respectively. After the leading end of the stencil sheet conducted by the carriage  10  has been mounted to the printing drum  14  or  16  by the stencil sheet leading end mounting means  34  or  36 , the printing drum  14  or  16  is rotated so that the stencil sheet of a one sheet length is mounted around the printing drum, and a trailing end of the one sheet length stencil sheet is cut by a cutter  50 . 
     FIG. 2 is a diagrammatical side view showing the structure of the carriage  10  and the guide rail therearound in an enlargement at the position shown in FIG.  1 . The carriage  10  has a main frame  52  and an auxiliary frame  56  pivotably mounted to the main frame by a pivot shaft  54 . The main frame  52  is made of a pair of side plates  58  constructing opposite side edges of the width thereof and lateral bar members  60 ,  62  and  64  fixing the pair of side plates  58  to one another. Each of these lateral bar members  60 ,  62  and  64  provides a guide surface at a part thereof for guiding the stencil sheet therealong. The main frame  52  is equipped with rollers  70  and  72  mounted by shafts  66  and  68  to the outside of the pair of side plates  58 , respectively, the rollers  70  and  72  being engaged between a pair of parallel rail members  74  and  76  of the guide rail  32 , so as to be movable therealong. In the shown embodiment, the shafts  66  for the pair of rollers  70  are formed integral with the pivot shaft  54  for pivotably mounting the auxiliary frame  56  to the main frame  52 . In other words, opposite end portions of the pivot shaft  54  are formed as the shafts  66 . 
     The guide rail  32  formed of the pair of rail members  74  and  76  is inclined downwardly at a portion thereof located in the vicinity of the outlet of the stencil sheet perforation means  12 , i.e. the stencil sheet feed out port  30 , as shown in the figure, so that, when the carriage  10  comes to this position, the rollers  72  closer to the stencil sheet perforation means  12  lower relative to the other rollers  70 , thereby inclining the main frame  52  at this position downward in facing the stencil sheet perforation means  12 . On the other hand, the auxiliary frame  56  has a pair of rollers  80  rotatably supported by shafts  78  at opposite sides thereof, so that when these rollers ride on corresponding cams  82  supported by the supporting frame not shown in the figure, the auxiliary frame  56  is pivoted around the pivot shaft  54  in the counter clockwise direction in the figure relative to the main frame  52 . The pivotal movement of the auxiliary frame  56  about the pivot shaft  54  relative to the main frame  52  occurs against an elastic biasing force applied by a spring clip  84  provided around the pivot shaft  54  so as to elastically drive the auxiliary frame  56  in the clockwise direction in the figure around the pivot shaft  54  relative to the main frame  52 . Thus, when the carriage  10  has come to the vicinity of the outlet of the stencil sheet perforation means  12 , the main frame  52  is inclined so that the end thereof facing the stencil sheet perforation means  12  descends, while the auxiliary frame  56  is inclined so that the end thereof facing the stencil sheet perforation means  12  ascends, whereby the stencil sheet feed out port  30  of the stencil sheet perforation means  12  is deeply inserted into an open space formed between the main frame and the auxiliary frame. 
     The main frame  52  carries stationarily a lower clamping element  88  of stencil sheet leading end clamping means  86  as extending in the lateral direction of the carriage, and a lower roller  92  of a pair of stencil sheet leading end feeding rollers  90  as rotatably supported by a shaft  94  on the left side of the lower clamping element  88  as viewed in the figure in parallel thereto. On the other hand, the auxiliary frame  56  carries an upper clamping element  96  of the stencil sheet leading end clamping means  86  as extending in the lateral direction of the carriage and supported by a pair of actuators  98  at opposite ends thereof The auxiliary frame  56  also carries an upper roller  100  of the stencil sheet leading end feeding roller pair  90  as extending in the lateral direction of the carriage and supported by a pair of actuators  104  via an integrally rotatable shaft  102  at opposite ends thereof. The upper clamping element  96  is moved by an operation of the pair of actuators  98  supporting the opposite ends thereof between a position at which it is pressed against the opposing lower clamping element  88  and a position at which it is removed from the lower clamping element  88 . The upper roller  100  is moved by the pair of actuators  104  supporting the opposite ends thereof between a position at which it is pressed against the lower roller  92  and a position removed from the lower roller  92 . Further, the upper roller  100  is selectively driven in rotation by one or both of the actuators  104  via the shaft  102 . The lower roller  92  is provided with a gear  106  at one end thereof, while the upper roller  100  is provided with a gear  108  at one end thereof. These gears  106  and  108  mesh with one another when the upper roller  100  is pressed against the lower roller  92  by the actuators  104 , so that the lower roller  92  is driven in rotation in synchronization with the upper roller  100  in the direction opposite to that of the upper roller  100  when the upper roller is driven in rotation by one or both of the actuators  104 . 
     A part of the guide rail  32  shown in FIG. 2 forming a part thereof positioned in the vicinity of the outlet of the stencil sheet perforation means  12  is supported by a switching plate  110  which in turn is pivotably supported by a pivot shaft  112  from the support frame not shown in the figure so to be pivotable around a central axis of the pivot shaft  112 . 
     When the leading end of the perforated stencil sheet  20  was inserted into the carriage  10  positioned in the vicinity of the outlet of the stencil sheet perforation means  12  as shown in FIGS. 1 and 2, the carriage  10  is now moved by carriage self-driving means incorporated therein not shown in the figure or outside carriage drive means arranged along the guide rail  32  not shown in the figure to the position shown in FIGS. 3 and 4 at which the roller  72  comes out of the inclined end of the guide rail  32 , while the rollers  80  of the auxiliary frame  56  sliding off of the inclined surfaces of the cams  82 , thereby turning the auxiliary frame  56  correspondingly around the pivot shaft  54  in the clockwise direction in the figure relative to the main frame  52  by the action of the spring clip  84 , so that the auxiliary frame  56  reaches its regular mounting position relative to the main frame  52 . Here the actuators  98  are operated so that the upper clamping element  96  is moved toward the lower clamping element  88 , thereby clamping the leading end of the stencil sheet  20  therebetween as shown in FIGS. 3 and 4. At this time, the leading edge of the stencil sheet may reach a position slightly exceeding the nip region between the lower roller  92  and the upper roller  100  of the stencil sheet leading end feeding roller pair  90 . In this state, the upper roller  100  may still be held as removed from the lower roller  92  by the actuators  104 . 
     When the stencil sheet is to be mounted onto the printing drum  14 , the carriage  10  is moved from the portion of the guide rail  32  made of the rail members  74  and  76  supported by the switching plate  110  to a portion thereof made of rail members  114  and  116  as shown in FIG. 5, and to finally reach a position in the vicinity of the stencil sheet leading end mounting means  34  of the printing drum  14  stopped at a predetermined rotational position such as shown in FIG.  6 . When the carriage  10  has reached this position, the actuators  98  of the stencil sheet leading end clamping means  86  are operated so as to remove the upper clamping element  96  from the lower clamping element  88 , thereby releasing the clamping of the leading end of the stencil sheet by the stencil sheet leading end clamping means  86 , while at the same time the actuators  104  of the stencil sheet leading end feeding roller pair  90  are operated so as to press the upper roller  100  to the lower roller  92  with the leading end of the stencil sheet being clamped therebetween. At this time, the gear  106  provided at one end of the lower roller  92  meshes with the gear  108  provided at one end of the upper roller  100 . Then, one or both of the actuators  104  are operated to drive the upper roller  100  to rotate in the clockwise direction in the figure in a controlled manner, with the lower roller  92  being rotated in synchronization with the upper roller  100  in the counter clockwise direction in the figure, whereby the leading end of the stencil sheet clamped between the pair of rollers  92  and  100  is fed out from the carriage  10  so as to be fed into between the stencil sheet receiving base  38  and the opened clamp  46  of the stencil sheet leading end mounting means  34 . A trailing end of the stencil sheet of a one sheet length is cut by the cutter  50  in the way or after the end of the pulling out of the stencil sheet by the carriage  10  according to the length of the guide rail  32 . 
     When the leading end of the stencil sheet was introduced onto the stencil sheet receiving base  38  in a predetermined manner, the clamp  46  is closed over the stencil sheet receiving base  38 , thus completing the mounting of the stencil sheet leading end on the printing drum  14 . Then the printing drum  14  is rotated in the counter clockwise direction in the figure by a printing drum driving mechanism not shown in the figure for winding the stencil sheet therearound. During this process, one or both of the actuators  104  apply a braking of a predetermined strength to the upper roller  100  so that the stencil sheet wound around the printing drum  14  according to the rotation thereof is maintained at any optimum controlled condition of expansion which will never damage even highly delicate perforations formed in the stencil sheet. 
     In the case that the stencil sheet is to be mounted onto the printing drum  16 , when the carriage  10  has moved from the position shown in FIG. 1 to the position shown in FIG. 3, the switching plate  110  is turned around the pivot shaft  112  as shown in FIG. 7 by a switching-over mechanism not shown in the figure. In the shown embodiment, without further moving the carriage  10 , this is brought to a position in the vicinity of the stencil sheet leading end mounting means  36  of the printing drum  16 . Here the stencil sheet leading end clamping means  86  and the stencil sheet leading end feeding roller pair  90  are operated by the actuators  98  and  104 , respectively, so that the leading end of the stencil sheet is mounted to the stencil sheet leading end mounting means  36 , and then the printing drum  16  is rotated so that the stencil sheet is wound around the printing drum  16  in an expanded condition, in the same manner as described with respect to the printing drum  14 . 
     Although the present invention has been described in detail with respect to an embodiment thereof, it will be apparent for those skilled in the art that various modifications are possible with respect to the shown embodiment within the scope of the present invention.