Paper discharging device of screen printing machine

Information

  • Patent Grant
  • 6601501
  • Patent Number
    6,601,501
  • Date Filed
    Friday, December 21, 2001
    22 years ago
  • Date Issued
    Tuesday, August 5, 2003
    20 years ago
Abstract
A paper discharging apparatus, which is provided in a printing machine, for transferring sheets of paper having different thickness. The paper discharging apparatus has a first gripper unit fixed in a groove, which extends along the cylindrical surface of a printing cylinder, and a second gripper unit, which moves along a discharging rail. The second gripper unit has a gripper and a base to hold the sheet. The position of the base is adjusted in accordance with the thickness of the sheet. A relatively thin sheet of paper is held by the first gripper unit and a relatively thick sheet of paper is held by the second gripper unit.
Description




BACKGROUND OF THE INVENTION




The present invention is related to a cylinder type screen printing machine, and more particularly, to a paper discharging apparatus for transferring a printed paper.




However, the conventional discharging apparatuses have the following shortcomings.




Relatively thin paper tend to stick to the screen. Since papers are transferred along the screen in the first conventional discharging apparatus, it is difficult to separate paper from the screen. Further, printing is interrupted when a paper sticks to the screen.




The second conventional discharging apparatus transfers relatively thick paper along the printing cylinder. However, thick paper is relatively rigidity. Thus, when paper is separated from the printing cylinder, the end of the paper located on the opposite side of the end held by the discharging gripper may damage a screen during printing.




BRIEF SUMMARY OF THE INVENTION




It is an object of the present invention to provide a paper discharging apparatus of a printing machine that is capable of discharging papers of various thickness.




To achieve the above object, the present invention provides a paper discharging apparatus of a screen printing machine. The screen printing machine includes a rotatable printing cylinder for guiding a printed sheet of paper to one of a first discharging position and a second discharging position. The paper discharging apparatus includes a first gripper unit for receiving the sheet at a predetermined holding position and transferring the sheet to the first discharging position. A first holding portion is defined in the first gripper unit to hold the sheet. A second gripper unit receives the sheet at the holding position and transfers the sheet to the second discharging position. The second gripper unit is adjacent to the first gripper unit at the holding position. A second holding portion is defined in the second gripper unit to hold the sheet. The position of the second holding portion is selectively shifted between a first position and a second position relative to the second gripper unit. The second holding portion is allowed to hold the sheet when the second holding portion is in the first position. The first holding portion is allowed to hold the sheet when the second holding portion is in the second position.




A further aspect of the present invention is a paper discharging apparatus provided in a screen printing machine to receiving a sheet transferred from an upstream location and transfer the sheet to one of a first tray and a second tray in accordance with the thickness of the sheet. The screen printing machine includes a printing cylinder reciprocally rotated between a print start position and a print end position. The paper discharging apparatus includes a first gripper unit fixed in a groove extending axially along a cylindrical surface of the printing cylinder. The first gripper unit receives the sheet when the printing cylinder is arranged at the print start position and releases the sheet when the printing cylinder is arranged at the print end position and the first gripper is adjacent to the first tray. A first holding portion is defined in the first gripper unit for holding the sheet. A second gripper unit moves in synchronism with the printing cylinder. The second gripper unit is arranged in the groove adjacent to the first gripper unit when the printing cylinder is in the print start position and arranged adjacent to the second tray to release the sheet when the printing cylinder is in the print end position. A stopper is provided in the second gripper unit and has a positioning surface. The positioning surface contacts a front end of the sheet to position the sheet. A second holding portion is defined in the second gripper unit to hold the sheet. The second holding portion includes a base selectively shifted between a first position and a second position relative to the second gripper unit. A gripper holds the sheet with the base. The positioning surface is downstream of the base and the gripper and the base hold the sheet when the base is in the first position. The positioning surface is upstream of the base and the first holding portion holds the sheet when the second holding portion is in the second position.




Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention











BRIEF DESCRIPTION OF THE DRAWINGS




The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:





FIG. 1

is a schematic side view showing a printing machine according to a preferred embodiment of the present invention;





FIG. 2

is a plan view showing a printing cylinder and a first gripper unit of the printing machine of

FIG. 1

;





FIG. 3

is a plan view showing a second gripper unit;





FIG. 4

is a plan view showing the second gripper unit arranged in a holding position;





FIG. 5A

is a side view showing a holder and a first base when a thick paper is transferred;





FIG. 5B

is a plan view showing the holder and the first base of

FIG. 5A

;





FIG. 6A

is a side view showing the holder and the first base when a thin paper is transferred;





FIG. 6B

is a plan view showing the holder and the first base of

FIG. 6A

;





FIG. 7A

is a side view showing a lever of a second gripper unit;





FIG. 7B

is a side view showing a slider of the second gripper unit;





FIG. 8A

is a side view showing a remover of the second gripper unit;





FIG. 8B

is a plan view showing the remover of

FIG. 8A

;





FIG. 9

is a side view showing the second gripper unit moving along a guide rail;





FIG. 10

is a side view showing a slider that moves along a paper discharging rail;











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




Hereinafter, a cylinder type screen printing machine


1


according to a preferred embodiment of the present invention will be described referring

FIGS. 1

to


10


.




In this specification, a sheet of paper, or sheet P, is transferring is a downstream direction.




As shown in

FIG. 1

, the printing machine


1


has a printing mechanism


10


that is supported by a frame (not shown). A transferring device


20


is arranged upstream of the printing mechanism


10


. A first discharging apparatus


21


, which is used for relatively hard or thick paper, and a second discharging apparatus


22


, which is used for relatively flexible or thin paper, are arranged downstream of the printing mechanism


10


. A sheet feeder


23


is arranged upstream of the transferring device


20


. A control device (not shown) synchronously drives the printing mechanism


10


, the discharging apparatuses


21


,


22


, the transferring device


20


, and the sheet feeder


23


.




The printing mechanism


10


includes a screen frame


11


, a squeegee


12


, a doctor blade


13


and a printing cylinder


14


. A screen support (not shown) supports the screen frame


11


so that the screen frame


11


is reciprocally movable in the horizontal direction. A printing plate


15


is fixed to the screen frame


11


. The doctor blade


13


and the squeegee


12


are supported by the screen support so that they are vertically movable. The printing cylinder


14


is reciprocally rotated in the clockwise and counterclockwise directions in synchronism with the reciprocating movement of the screen frame


11


.




A groove


16


extending in the axial direction of the printing cylinder


14


along the surface of the printing cylinder


14


. A first gripper unit


30


for discharging thin papers and a second gripper unit


40


for discharging thick papers are accommodated in the groove


16


. The first gripper unit


30


is fixed to one side surface (the right side surface in

FIG. 1

) of the groove


16


. The second gripper unit


40


may be removed from the groove


16


. In the preferred embodiment, the first gripper unit


30


and the second gripper unit


40


form the paper discharging apparatus. When the groove


16


is arranged at a predetermined printing start position, the sheet P is held by the first gripper unit


30


or the second gripper unit


40


. When the groove


16


is arranged at a predetermined printing end position, the sheet is released from the first gripper unit


30


or the second gripper unit


40


. That is, when the groove


16


is arranged in the predetermined printing start position, the paper discharging apparatus is arranged at a holding position, and when the groove


16


is arranged at the predetermined printing end position, the paper discharging apparatus is arranged at a discharging position.




The squeegee


12


presses the printing plate


15


against the printing cylinder


14


. When the screen frame


11


moves horizontally, ink is applied to the sheet P by the squeegee


12


to perform printing. The doctor blade


13


is inclined relative to the printing plate


15


to wipes residual ink on the printing plate


15


after the printing.




A sheet feeder


23


holds a predetermined number of sheets P and supplies the sheets P one by one to the transferring device


20


. The transferring device


20


includes a supplying belt


24


. The belt


24


receives the sheets P from the sheet feeder


23


and supplies the sheets P to the printing mechanism


10


in synchronism with the rotation of the printing cylinder


14


.




The second discharging apparatus


22


includes an arcuate stripper plate


27


, which is adjacent to the printing cylinder


14


. A thin paper tray


221


is arranged downstream of the stripper plate


27


. When the groove


16


, or the first gripper unit


30


, reaches the predetermined first paper discharging position, the stripper plate


27


releases the sheet P from the printing cylinder


14


. The stripper plate


27


guides the sheet P into the thin paper tray


221


.




The first discharging apparatus


21


includes two paper discharging rails


25


and two guide rails


26


. The second gripper unit


40


has two sliders


41


(refer to

FIG. 3

) that are supported by the two discharging rails


25


. The second gripper unit


40


discharges the printed sheet P from the printing mechanism


10


in synchronism with the rotation of the printing cylinder


14


and transfers the sheet P along the discharging rails


25


to a thick paper tray


211


.




The two guide rails


26


are arranged under the discharging rails


25


parallel to the two discharging rails


25


. The second gripper unit


40


has two levers


42


that contact the upper surfaces of the two guide rails


26


(refer to FIG.


3


). The second gripper unit


40


moves along the guide rails


26


. The levers


42


are pivoted in accordance with the degree of contact with the guide rails


26


.




The thick paper tray


211


is arranged at the downstream end of the discharging rails


25


and the guide rails


26


. The second gripper unit


40


holds a relatively thick sheet P in the holding position and transfers the printed sheet P along the discharging rails


25


. When the second gripper unit


40


reaches a predetermined position, the sheet P is released from the second gripper unit


40


. The sheet P is moved along the discharging rails


25


and placed in the thick paper tray


211


.




The first gripper unit


30


and the second gripper unit


40


will be explained in detail. As shown in

FIG. 2

, the first gripper unit


30


is fixed to one side surface of the groove


16


. The first gripper unit


30


includes a plurality of first bases


31


and a plurality of rectangular suction members


32


, which function as a first holding portion. The first bases


31


and the suction members


32


are arranged alternately. The first bases


31


and the suction members


32


are arranged throughout the groove


16


except for locations corresponding to the two axial ends of the first gripper unit


30


.




As shown in

FIG. 4

, the second gripper unit


40


is arranged in the groove


16


of the printing cylinder


14


. The second gripper unit


40


has a plurality of holders


43


. When the second gripper unit


40


is in the holding position, each of the holders


43


is adjacent to an associated one of the first bases


31


. More specifically, as shown in

FIGS. 5A and 5B

, the second gripper unit


40


includes a second base


432


that contacts the first base


31


. As shown in

FIG. 5B

, each first base


31


has a projection


312


, which extends in the clockwise direction of the printing cylinder


14


as viewed

FIG. 1

, and a round small hole


311


. As shown in

FIGS. 5A and 6A

, the small hole


311


receives a piston rod


313




a


that is driven by an air cylinder


313


.




The piston rod


313




a


is normally received in the small hole


311


. When the air cylinder


313


lifts the piston rod


313




a


, the top end of the piston rod


313




a


extends out of the small hole


311


from the upper surface of the first base


31


. When the printing cylinder


14


is rotated by a predetermined angle, the air cylinder


313


lifts the piston rod


313




a


. A limit switch (not shown) detects the rotational angle of the printing cylinder


14


. The limit switch is actuated when the printing cylinder


14


is rotated by a predetermined angle. Further, the limit switch is arranged so that it is actuated and de-actuated in relation with the position of the stripper plate


27


and in synchronism with the rotation of the printing cylinder


14


.




Each of the suction members


32


has a plurality of suction holes


321


that are arranged in two rows along the longitudinal axis. The suction holes


321


are connected to a suction pump (not shown) by an air tube (not shown). When the suction pump is operated, the sheet P is drawn toward the suction holes


321


. When the sheet P is transferred to the first gripper unit


30


, the suction pump is operated and the sheet P is drawn to the suction holes


321


(suction members


32


). Thus, the first gripper unit


30


holds the sheet P. A limit switch (not shown) starts and stops operation of the suction pump in synchronism with the rotation of the printing cylinder


14


.




The second gripper unit


40


will now be discussed. As shown in

FIG. 3

, the second gripper unit


40


has a case


44


, a shaft


45


covered by the case


44


, two levers


42


fixed to the shaft


45


, two supports


48


respectively fixed to the two ends of the case


44


, two sliders


41


supported by the supports


48


, a plurality of sheet stoppers


46


, a plurality of holder


43


, and two separators


47


.




The case


44


extends in the axial direction of the printing cylinder


14


. The holders


43


and the sheet stoppers


46


are arranged with predetermined intervals in between and are fixed to the upper surface of the case


44


. The two separators


47


are fixed to the longitudinal ends of the case


44


.




The shaft


45


is rotatably supported by the case


44


. The ends of the shaft


45


extend out the case


44


. The two levers


42


are each fixed to one end of the shaft


45


. The distal end of each support


48


is located on the outer side the associated end of the case


44


. Each slider


41


is fixed to the distal end of each support


48


.




As shown in

FIGS. 5B and 6B

, each holder


43


is formed by a gripper


431


and a second base


432


, which is arranged under the gripper


431


. The gripper


431


has two parallel sides and two outwardly extending arcuate sides. The distance between the two arcuate sides is longer than the distance between the two parallel sides. In other words, the gripper


431


is a tonneau-shaped plate. As shown in

FIGS. 5A and 6A

, the gripper


431


has a convex upper surface and a flat bottom surface. A link rod


433


extends downward from the bottom surface of the gripper


431


. A pin


434


, which extends parallel to the axial direction of the printing cylinder


14


, is formed on the lower end of the link rod


433


.




A plurality of connecting plates


435


are fixed to the shaft


45


in association with the holders


43


. When the shaft


45


is rotated, the connecting plates


435


are rotated integrally with the shaft


45


. Each of the connecting plates


435


has a U-shaped notch


436


. The pin


434


of the corresponding link rod


433


is engaged with the notch


436


. A predetermined clearance is provided between the pin


434


and the notch


436


. The rotation of each connecting plate


435


is converted to the axial movement of the link rod


433


by the pin


434


. Therefore, the rotation of the shaft


45


lifts the grippers


431


. Normally, the grippers


431


are urged downward to a closed position by coil spring


451


, which are wound around the shaft


45


(refer to FIG.


3


).




As shown in

FIGS. 5B and 6B

, each U-shaped second base


432


has two elongated engaging holes


441


, which extend parallel to each other. The second base


432


is fixed to the case


44


by two bolts


442


, which are inserted through the two engaging holes


441


. The second base


432


slides along the engaging holes


441


when the bolts


442


are loosened. The second base


432


is arranged at a first position, which is shown in the state of

FIG. 5B

, to print a relatively thick sheet P. Further, the second base


432


is arranged at the second position, which is shown in the state of

FIG. 6B

to print a relatively thin sheet P. That is, the position of the second base


432


is shifted in accordance with the thickness of the sheet P.




The second base


432


has a notch


437


opened toward the first base


31


. The notch


437


prevents interference between the second base


432


and the link rod


433


. The second base


432


has two extensions


439


, which define the ends of the notch


437


. The two extensions


439


face each other with a predetermined space in between. As shown in

FIG. 5B

, the projection


312


of the first base


31


is arranged between the extensions


439


. A predetermined clearance is provided between the projection


312


and the extensions


439


. When the gripper


431


is in the closed position, the bottom surface of the gripper


431


contacts the upper surface of the two extensions


439


. A gripping portion


438


, which serves as a second holding portion (the parts shown with the slanted lines in FIGS.


5


B and


6


B), is defined by the bottom surface of the gripper


431


and the upper surface of the two extensions


439


.




The sheet stoppers


46


will now be explained referring FIG.


5


A and FIG.


6


A. Each sheet stopper


46


positions the sheet P transferred from the upstream of the printing mechanism


10


. More particularly, the sheet stopper


46


has a positioning surface


46




a


. The positioning surface


46




a


is arranged so that its middle portion is substantially aligned with the upper surfaces of the second bases


432


and the bottom surfaces of the grippers


431


. In other words, the sheet P transferred along the surface of the printing cylinder


14


is positioned along the upper surfaces of the second bases


432


or the bottom surfaces of the grippers


431


when contacting the positioning surface


46




a.






When the second bases


432


are located at the first position (FIG.


5


B), the upstream end surface of each second base


432


is upstream of the positioning surface


46




a


of the sheet stopper


46


. In printing, the sheet P contacts the sheet stopper


46


and the sheet P is in the position shown by the dashed line in FIG.


5


B. In this position, the sheet P is positioned between the upper surface of the second bases


432


and the bottom surface of the grippers


431


. When the gripper


431


moves to the lower position, the sheet P is held by the second base


432


and the gripper


431


.




When the second bases


432


are located at the second position (FIG.


6


B), the upstream end surface of each second base


432


is downstream of the positioning surface


46




a


of the sheet stopper


46


. During a printing operation, the sheet P contacts the sheet stopper


46


and is positioned as shown by the broken line in FIG.


6


B. At this position, the sheet P is not arranged between the upper surfaces of the second bases


432


and the bottom surfaces of the grippers


431


. In other words, the gripping portions


438


are downstream of the distal end of the sheet P. Therefore, the gripping portions


438


do not hold the sheet P.




The separators


47


will now be explained referring to

FIGS. 3

,


8


A, and


8


B. Each separator


47


includes a main body


471


, two arms


472


, and an arm actuator


473


. As shown in

FIG. 8A

, each arm


472


is bent and has a disk-like basal end. A rotation shaft


474


connects the basal ends of the two arms


472


. The arm actuator


473


has a head


475


, which contacts the basal ends of the two arms


472


. The head


475


, which contacts the basal ends of the arms


472


, is moved axially by the arm actuator


473


. Normally, the head


475


and the arms


472


are in a retracted position as shown by the solid line in FIG.


8


A. When the arm actuator


473


is driven, the head


475


pivots the arm


472


about the rotation shaft


474


in the direction indicated by the arrow. This moves the head


475


and the arm


472


to a lifted position, as shown by the broken lines. When the second gripper unit


40


contacts a limit switch


262


(refer to FIG.


9


), which is arranged on the discharging rail


25


, the arm actuator


473


is actuated to move the arm


472


to the lifted position.




As shown in

FIG. 7A

, each lever


42


has a basal end fixed to the shaft


45


and a distal end to which a roller


421


is coupled. The coil springs


451


urge the distal end of the lever


42


in a downward direction (the counterclockwise direction as viewed in FIG.


7


A). When the lever


42


receives an upward force greater than the urging force of the coil spring


451


, the lever


42


and the shaft


45


are rotated in an upward direction (the clockwise direction as viewed in FIG.


7


A). Accordingly, the grippers


431


are opened and closed by the pivoting of the lever


42


.




Referring to

FIG. 9

, the gripper unit


40


moves along the discharging rails


25


. During the movement of the gripper unit


40


, the rollers


421


contact the uneven upper surfaces of the guide rails


26


. The lever


42


is pivoted in accordance with the uneven surfaces of the guide rails


26


. Therefore, the gripper


431


is opened and closed by the uneven guide rails


26


.





FIG. 7B

is a side view showing the slider


41


. Each slider


41


has two upper wheels


411


and a lower wheel


412


. As shown in

FIG. 10

, each slider


41


is connected to one of the discharging rails


25


so that the discharging rail


25


is held between the upper wheels


411


and the lower wheel


412


. Therefore, the sliders


41


are movable along the two discharging rails


25


and enable the second gripper unit


40


to move between the holding position and the second paper discharging position.




The discharging rails


25


and the guide rails


26


will be explained with reference to

FIGS. 9 and 10

. The two discharging rails


25


are arranged at the axial ends of the printing cylinder


14


. Each discharging rail


25


is inclined at a predetermined angle from the upstream (the holding position or the print start position) to the downstream (the second paper discharging position). The arcuate upstream end of each discharging rail


25


and the printing cylinder


14


are concentric.




The two guide rails


26


are substantially parallel to the two discharging rails


25


. Accordingly, the two guide rails


26


are arranged at the axial ends of the printing cylinder


14


. The upstream end of each guide rail


26


rises gradually toward the discharging rail


25


. As the second gripper unit


40


approaches the upstream end of the rails


25


,


26


, the posture of the second gripper unit


40


is changed in accordance with the arcuate shape of the discharging rails


25


. Thus, the guide rails


26


shift the positions of the levers


42


.




A tapered portion


261


, which alters the height of the upper surface of the guide rail


26


, is defined in the longitudinally middle part of each guide rail


26


. Although the tapered portion


261


is located at a predetermined position on each guide rail


26


, the location of the tapered portion


261


may be changed as required. As shown in

FIG. 9

, the limit switch


262


is attached to one of the guide rails


26


(the guide rail


26


located on the left side relative to the downstream direction in the preferred embodiment). The limit switch


262


detects the passage of the second gripper unit


40


and rotates the separator


47


to the lifted position.




The discharging operation of the printed sheet P will be explained.




(A) When the Sheet P is Relatively Thick (Rigid)




The second bases


432


of the second gripper unit


40


are positioned in the first position. When the groove


16


is positioned at substantially the top of the printing cylinder


14


, the second gripper unit


40


is arranged in the groove


16


. As shown in

FIG. 5A

, each second base


432


contacts the associated first base


31


and the bottom surface of the second base


432


is substantially aligned with the upper surface of the first base


31


.




As shown in

FIG. 5B

, when the second gripper unit


40


is arranged in the holding position, the projection


312


of each first base


31


is accommodated in the notch


437


of the associated second base


432


. The gripper


431


is spaced from the second base


432


by a predetermined distance.




The sheet P, which is supplied from the transferring device


20


, is positioned when contacting the sheet stopper


46


. At this time, the sheet P is inserted between the gripper


431


and the second base


432


. The second gripper unit


40


moves along the arcuate discharging rails in synchronism with the counterclockwise rotation of the printing cylinder


14


. In other words, the gripper unit


40


is rotated in the same phase as the printing cylinder


14


. Therefore, contact between the second base


432


and the first base


31


is maintained.




When the second gripper unit


40


starts to move, the levers


42


contact the upper surface of the guide rail


26


. In this state, the high position of the guide rails


26


lifts the levers


42


. This lowers each gripper


431


to the closed position where the gripper


431


contacts the second base


432


and the gripping portion


438


of the associated holder


43


holds the sheet P.




When the printing cylinder


14


is further rotated and the gripper unit


40


reaches the lower linear portion of the discharging rails


25


, the second gripper unit


40


is separated from the groove


16


. Further, the second gripper unit


40


removes the sheet P from the printing cylinder


14


. The screen frame


11


moves in synchronism with the rotation of the printing cylinder


14


. This presses the printing plate


15


against the sheet P and performs printing on the sheet P.




As the second gripper unit


40


moves along the discharging rails


25


and reaches the tapered portions


261


, the levers


42


are pivoted downward (in the counterclockwise direction) along the tapered portions


261


. This rotates the shaft


45


of the second gripper unit


40


and lifts the gripper


431


to the open position by means of the connecting plate


435


and the link rod


433


. Thus, the holders


43


release the sheet P.




Further, when the second gripper unit


40


passes the limit switch


262


, each arm actuator


473


positions the associated arm


472


to the lifted position. This releases the sheet P from the holder


43


and drops the sheet P into the thick paper tray


211


, which is located under the guide rail


26


.




After the discharging, the second gripper unit


40


is moved to the upstream side and returned to its original position (the holding position), and the printing cylinder


14


is rotated in the counterclockwise direction and returned to its original position (the print start position).




(B) When the Sheet P is Relatively Thin (Flexible)




The second base


432


is positioned in the second position. In the same manner as case (A), when the groove


16


is positioned at substantially the top portion of the printing cylinder


14


, the second gripper unit


40


is arranged in the groove


16


. As shown in

FIG. 6A

, each second base


432


contacts the associated first base


31


, and the bottom surface of the second base


432


is flush with the upper surface of the first base


31


.




As shown in

FIG. 6B

, when the second gripper unit


40


is in the holding position, the first base


31


is separated from the second base


432


and the projection


312


of the first base


31


is not accommodated in the notch


437


of the second base


432


. Each gripper


431


is separated from the second base


432


by a predetermined distance.




The sheet P, which is supplied from the transferring device


20


, is positioned when contacting the sheet stopper


46


. Since each second base


432


is positioned downstream of the sheet stoppers


46


, the front end of the sheet P does not reach the second base


432


. In other words, the gripping portion


438


is not overlapped with the sheet P. Therefore, the sheet P is not inserted between the grippers


431


and the second bases


432


, and the holders


43


do not hold the sheet P.




The gripper unit


40


moves along the arcuate discharging rails


25


in synchronism with the counterclockwise rotation of the printing cylinder


14


. The suction pump is operated in synchronism with the rotation of the cylinder


14


. This draws the sheet P to the suction holes


321


of the first gripper unit


30


.




When the printing cylinder


14


is further rotated and the gripper unit


40


reaches the lower linear portion of the discharging rails


25


, the second gripper unit


40


is removed from the groove


16


. However, the second gripper unit


40


moves without the sheet P. The sheet P is held by the first gripper unit


30


and rotated integrally with the printing cylinder


14


. The screen frame


11


is moved in synchronism with the rotation of the printing cylinder


14


. This presses the printing plate


15


against the sheet P and performs printing on the sheet P.




When the printing cylinder


14


is rotated by a predetermined angle, the suction pump stops operating. Simultaneously, the air cylinder


313


of each first base


31


lifts the associated piston rod


313




a


. The top end of the lifted piston rod


313




a


extends from the small hole


311


of the first base


31


. As a result, the sheet P, which is supported by the first bases


31


, is released from the first gripper unit


30


. The released sheet P is guided by the stripper plate


27


and transferred to the thin paper tray


221


.




After the sheet P is released, the printing cylinder


14


is rotated in the clockwise direction and returned to its original position (the print start position). The second gripper unit


40


also returns to its original position (the holding position).




The following advantages are obtained in the cylinder type screen printing machine


1


of the preferred embodiment.




(1) The first gripper unit


30


or the second gripper unit


40


selectively holds a sheet P in accordance with the position of the second base


432


. Therefore, the paper discharging apparatus discharge sheets P of different thickness merely by changing the position of the second base


432


in accordance with the thickness of the sheet P.




(2) Each second base


432


is fixed to the case


44


by a bolt


442


. Therefore, the position of the second base


432


is easily adjusted by loosening the bolt


442


.




(3) The gripper unit


30


draws only relatively thin sheets P. Therefore, the suction pump need only a relatively weak suction force to draw the sheet P to the first gripper unit


30


.




(4) The second gripper unit


40


releases the held sheet P in accordance with the level of the upper surface of the guide rail


26


. Therefore, the position of the tapered portion


261


may be shifted to change the holding release position.




(5) The first gripper unit


30


releases the sheet P with the air cylinders


313


and their piston rods


313




a


. The relatively simple mechanism of the air cylinder


313


and the piston rod


313




a


ensures the operation for releasing the sheet P.




(6) The limit switch


262


operates the arm actuator


473


of each separator


47


. The relatively simple mechanism of the arm actuators


473


and their arms


472


ensures the releasing of the sheet P from the second gripper unit


40


.




(7) The first gripper unit


30


is fixed to the printing cylinder


14


. Thus, a mechanism for moving the first gripper unit


30


relative to the cylinder


14


is not necessary. Accordingly, the sheet P is discharged from the first gripper unit


30


in a stable and inexpensive manner.




(8) When the first gripper unit


30


and the second gripper unit


40


are arranged in the groove


16


, the upper surface of each first base


31


is flush with the upper surface of the associated second base


432


. The upper surface of the first base


31


and the upper surface of the second base


432


guide the sheet P to a predetermined position. This ensures that the sheet P be held.




(9) A relatively rigid sheet P is transferred in the tangential direction of the cylinder


14


by the second gripper unit


40


. This prevents the printing plate


15


from being damaged by the sheet P.




(10) A relatively thin sheet P is transferred along the surface of the cylinder


14


by the first gripper unit


30


. This facilitates the separation of the sheet P from the printing plate


15


. Accordingly, printing is not interrupted.




It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.




The shape of the first base


31


, the gripper


431


, and the second base


432


is not limited to the shapes described in the above embodiment. Further, the second bases


432


do not have to be moved horizontally. For example, the second base


432


may be rotated by 90 degree along a horizontal plane to change the distance between each first base


31


and the upstream end surface of associated the second base


432


.




The grippers


431


are lifted by the rotation of the shaft


45


, which cooperates with the pivoting of the levers


42


. However, for example, the grippers


431


may be lifted by other mechanisms such as an air cylinder.




The locations of the tapered portion


261


and the limit switch


262


may be changed. This would change the holding release position of the grippers


431


and the operation position of the arms


472


.




The depth and the width of the groove


16


may be altered. Further, the inclination of the walls of the groove


16


may be changed.




Instead of the piston rod


313




a


, the sheet P may be released by ejecting air from the small hole


311


. In this case, part of the suction mechanism (the pump or pipes) of the suction member


32


may be used to eject air.




The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.



Claims
  • 1. A paper discharging apparatus provided in a screen printing machine, wherein the screen printing machine includes a rotatable printing cylinder for guiding a printed sheet of paper to one of a first discharging position and a second discharging position, the paper discharging apparatus comprising:a first gripper unit for receiving the sheet at a predetermined holding position and transferring the sheet to the first discharging position; a first holding portion defined in the first gripper unit for holding the sheet; a second gripper unit for receiving the sheet at the holding position and transferring the sheet to the second discharging position, wherein the second gripper unit is adjacent to the first gripper unit at the holding position; and a second holding portion defined in the second gripper unit for holding the sheet, wherein the position of the second holding portion is selectively shifted between a first position and a second position relative to the second gripper unit, the second holding portion being allowed to hold the sheet when the second holding portion is in the first position, and the first holding portion being allowed to hold the sheet when the second holding portion is in the second position.
  • 2. The paper discharging apparatus according to claim 1, wherein the first gripper unit is fixed to the printing cylinder to rotate integrally with the printing cylinder, and the second gripper unit moves reciprocally between the holding position and the second discharging position in synchronism with the rotation of the printing cylinder.
  • 3. The paper discharging apparatus according to claim 1, wherein the first holding portion includes a suction portion defined in the first gripper unit for drawing the sheet.
  • 4. The paper discharging apparatus according to claim 1, wherein the second holding portion includes a gripper and a base, which engages the gripper.
  • 5. The paper discharging apparatus according to claim 4, wherein the position of the base is adjusted between the first position and the second position in accordance with the thickness of the sheet.
  • 6. The paper discharging apparatus according to claim 1, wherein the second gripper unit has a stopper including a positioning surface for contacting an end of the sheet and positioning the sheet.
  • 7. A paper discharging apparatus provided in a screen printing machine for receiving a sheet transferred from an upstream location and transferring the sheet to one of a first tray and a second tray in accordance with the thickness of the sheet, wherein the screen printing machine includes a printing cylinder reciprocally rotated between a print start position and a print end position, the paper discharging apparatus comprising:a first gripper unit fixed in a groove extending axially along a cylindrical surface of the printing cylinder, wherein the first gripper unit receives the sheet when the printing cylinder is arranged at the print start position and releases the sheet when the printing cylinder is arranged at the print end position and the first gripper unit is adjacent to the first tray; a first holding portion defined in the first gripper unit for holding the sheet; a second gripper unit for moving in synchronism with the printing cylinder, wherein the second gripper unit is arranged in the groove adjacent to the first gripper unit when the printing cylinder is in the print start position and arranged adjacent to the second tray to release the sheet when the printing cylinder is in the print end position; a stopper provided in the second gripper unit and having a positioning surface, wherein the positioning surface contacts a front end of the sheet to position the sheet; and a second holding portion defined in the second gripper unit to hold the sheet, wherein the second holding portion includes: a base selectively shifted between a first position and a second position relative to the second gripper unit; and a gripper for holding the sheet with the base; wherein the positioning surface is downstream of the base, and the gripper and the base hold the sheet when the base is in the first position, and the positioning surface is upstream of the base, and the first holding portion holds the sheet when the base is in the second position.
  • 8. The paper discharging apparatus according to claim 7, wherein the sheet is one of a relatively thin paper and a relatively thick paper, and the base is arranged at the first position when the sheet is a relatively thick paper, and the base is arranged at the second position when the sheet is a relatively thin paper.
  • 9. The paper discharging apparatus according to claim 8, wherein the first holding portion has a plurality of suction holes adapted to be connected to a suction pump that is operated when the base is in the second position, and the sheet is drawn to the plurality of suction holes.
  • 10. The paper discharging apparatus according to claim 7, wherein the base has an elongated groove extending perpendicular to the positioning surface, and the second gripper unit has a bolt inserted in the elongated groove, and wherein the bolt is loosened to move the base between the first position or the second position.
Priority Claims (1)
Number Date Country Kind
2001-111832 Apr 2001 JP
US Referenced Citations (1)
Number Name Date Kind
4509422 Nagatani Apr 1985 A
Foreign Referenced Citations (3)
Number Date Country
1 436 548 Apr 1969 DE
2 005 101 Aug 1971 DE
2 305 872 Aug 1973 DE