Note: Descriptions are shown in the official language in which they were submitted.
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POSITIONING DEVICE OF A FLEXIBLE PRINTING PLATE
ON A PLATE CYLINDER
The present invention relates to a positioning device of a flexible
printing plate on a plate cylinder, and more particularly to a device allowing
to
bias this flexible printing plate on the plate cylinder of a rotary printing
machine.
Machines of this kind, which are frequently used in the packaging
industry for printing plate-like workpieces such as sheets of paper or
cardboard, are usually called flexographic printing machines and comprise a
plurality of constitutive stations, i.e. according to a logical development
from
upstream to downstream referring to the travelling direction of the plate-like
workpieces, an infeed station, which successively seizes one sheet after
another from the top of a pile, followed by one or more printing groups, if
desired, with one or more dryers put in between these groups and, finally, a
delivery station collecting the printed workpieces. The sheets are conveyed
from one station or one group to another by means of a roller
train and a suction system thus entirely setting free the lower printed
surfaces
of the sheets.
The positioning device of a printing plate is used in the printing groups.
Each printing group, generally printing one colour, comprise a plate cylinder
round which winds and is tensioned thereto a flexible printing plate. Being
coated with ink owing to a screened cylinder, this printing plate prints at
each
rotation of the cylinder, according to the number of printing forms that it
comprises, one or more patterns on the sheet travelling between the plate
cylinder and a pressure roller both arranged such that the printing effects on
the tower surface of the sheets.
The printing form, consisting of a rubber or plastic material, is usually
glued on a flexible support base made of polyester such as Mylar in order to
form an assembly called printing plate. After the manufacturing of the
printing
form. its gluing onto the polyester base is a decisive operation. Being
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performed by the manufacturer, it directly conditions the quality of the
printing
register between the various colours. The upstream and downstream ends of
the flexible support base are equipped with a plastic strip, a longitudinal
edge
of which having an U-section and allows the fixing of the printing plate in a
claw secured to the plate cylinder. This claw is arranged in a parallel
direction
with the rotational axis of this cylinder. A thin metallic plate, attached on
the
strip and provided with an elongate aperture having a longitudinal
upstream-downstream axis, allows a rapid and accurate lateral positioning of
the printing plate on its cylinder by fitting on a centering pin secured to
the
claw.
At the time of gluing the printing form on its flexible support polyester
base, a lateral or longitudinal positioning error can easily be corrected,
respectively by a lateral movement or by a rotation of the plate cylinder
round
its axis, but this will not be the case if an error is caused by a biasing of
the
printing form. Then, the sides of the printing form are not orientated in a
parallel or perpendicular direction with the upstream and downstream edges
of the polyester base, resulting in an incorrigible biased positioning of the
printing form with respect to the direction given by the rotational axis of
the
plate cylinder.
If a plurality of printing forms are glued on a flexible polyester base,
each having the same biasing error, generally the upper edges of each
printing form are aligned and can thus be assimilated to a single large
printing
form affected by a positioning error resulting from a biased positioning.
In order to remedy to this problem, various known devices allow to
pivot the front and rear claws with respect to the rotational axis of the
plate
cylinder so as to bias the printing plate by the same amount but in opposition
to the registered error.
To this end, US Patent 5'488'904 describes a device comprising two
parallel bars clamping the ends of the printing plate. A mechanism, controlled
by the manual rotation of a graduated eccentric gauge, allows to impart a
lateral movement (parallel to the rotational axis of the cylinder) to the rear
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fixing bar of the printing plate and a pivoting of the front bar owing to an
assembly of bent pieces articulating round a plurality of pivots arranged at
its
ends. Owing to an articulation actuated by a spring placed at one end of the
rear bar, this latter is automatically pivoted in a position which is parallel
to the
position occupied by the front bar, when the printing plate is kept by its two
ends in this device. The whole mechanism is arranged in the plate cylinder
body at the bottom of a wide and deep groove which is machined in a parallel
direction with the rotational axis of the cylinder. The eccentric controlling
the
mechanism is mounted on one side of the plate cylinder.
Patent EP-232'730 provides another biasing device of a printing plate
suggesting a mechanism based on the pivoting of two tension bars in which
the ends of the printing plate are clamped. The ends of the tension bars are
connected to each other by two articulated plates having a triangular shape
and being mounted on two fixed pivots which are secured to the plate cylinder.
The pivots of the articulations have a rectangular configuration so that the
tension bars of the printing plate pivot about a virtual point P located in
the
center axis of the plate cylinder. The control means is arranged on one side
of
the plate cylinder and comprises a complex mechanism consisting of
articulated levers which can be actuated by a single-acting cylinder when the
plate cylinder is at standstill in a determined position.
Patent JP 62-56146 solves the biasing problem of a printing plate with
a device comprising two bars which are each actuated by two hydraulic
cylinders. When the position of the printing plate has to be diagonally
corrected, the oil pressure in these four hydraulic cylinders is reduced so
that
four springs, having been compressed by the four hydraulic cylinders, can
slacken and force back the fixing bars of the printing plate in an opening
movement. The correction value is input to a controller converting it in a
corresponding oil pressure applied to two other additional hydraulic cylinders
arranged on the same side at one end of the fixing bars. Under the action of
these two other hydraulic cylinders, two slanted planes can be independently
moved in a rectilinear movement so as to force, when closing the fixing bars
of
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the printing plate, one end of each bar in a perpendicular movement owing to
the triangular shape of the slanted plane. In a preferred embodiment, the
slanted planes can also be actuated by a motorized screw mechanism.
Several drawbacks arise with these devices, namely
- the presence of a so-called enclosed mechanism which is bulky and
needs, in the plate cylinder body, the arrangement of a groove having
important dimensions with respect to the diameter of the cylinder,
the existence of an undesirable unbalance, due to the importance of
the arrangement of such a mechanism, generating constraints which originate
in the bearings of the cylinder when the latter reaches a certain rotational
speed,
- a circumferential working surface about the cylinder which is reduced
by the important width of the groove that is required by the biasing device,
- the presence, in some case, of a manual adjustment which requires a
machine stop involving a prolongated adjustment time,
- the impossibility to resort to entire automation of adjusting the printing
plate when old jobs are to be restarted; for which jobs the adjustment values
could have been numerically saved and memorized,
- the necessity of controlling the mechanism leading to the biasing of
the printing plate, in the case of a non-manual adjustment, by means of an
additional actuator being independent of the one which enables the lateral or
circumferential movement of the plate cylinder.
The biasing device of a printing plate according to the invention is
meant to remedy these drawbacks by providing a simple and automatized
means, which occupies only a minimum volume in the plate cylinder body, and
with which the machine has not to be stopped. Advantageously, due to
the minimum volume occupied, the device is not depending on a biasing
mechanism of the printing plate actuated by an actuator arranged in the plate
cylinder body. Thus, for driving the biasing mechanism of the printing plate,
the device described in the present invention uses an electrical motor secured
to the frame of the machine being the same as the motor for moving the plate
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cylinder for lateral adjustment. This solution allows, on
the one hand, a more rational utilization of the actuator
that is already provided for lateral adjustment of the
printing plate, and, on the other hand, to a biasing
mechanism that is less expensive, less bulky, but strong and
reliable, and which is easy to adapt to plate cylinders
without such mechanism. Finally, owing to this mechanism,
the utilization of an external electronic controller, which
is connected to a plurality of position sensors arranged
outside the cylinder, allows measurement and memorizing of
the various adjustment positions adapted to respective jobs
which could easily be restarted subsequently without
requiring to register them. This latter variant offers an
additional asset being particularly suitable for the
mechanism of the present invention.
For this purpose, the present invention provides
positioning device of a flexible printing plate on a plate
cylinder in a printing machine frame, which device allows to
bias a printing plate in a rotary printing machine, the
plate cylinder, having a rotational axis, comprising a
groove which is disposed parallel to the rotational axis and
inside which said positioning device of a printing plate is
arranged, characterized by the fact that the device is
actuated by lateral movement of the plate cylinder, which is
set into operation by an external means secured to the frame
of the printing machine and by a cam-ring, which is arranged
outside the cylinder opposite said external means, said cam
ring having inner edges on which rests a roller that secured
to a movable base plate which is freely held with respect to
the plate cylinder by holding means and by two cams which
are rigidly attached on the bottom of the groove of the
plate cylinder and which control the movement of two
rollers, being attached to the base plate.
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In order to define some expressions used in the
present description for describing the position of some
elements within the printing machine, it should be understood
that the terms "operator's side" (C. C.) and "opposite
operator's side" (C.O.C.) make reference to a side as seen
from the longitudinal center axis of the machine. This in
order to avoid any confusions of the conventional terms
left-hand side and right-hand side which depend on the point
of view of the observer. In a similar way, for describing
the orientation of some axis or means, the usual terms
"longitudinal" and "lateral" will be used, still referring to
the center axis of the machine, the orientation of which
being determined by the travelling direction of the
plate-like workpieces. Finally, it should be noted that the
terms "upstream" and "downstream" refer to the travelling
direction of the plate-like workpieces within the printing
machine.
The invention will be better understood by the
study of an embodiment taken by way of nonlimiting example
and illustrated by the following drawings, in which:
Figs la and 1b are plan views, showing respectively
a third C.O.C. and a third C.C. of the biasing device mounted
on the plate cylinder,
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- Fig. 2 is a partial sectional view of the end C.C. of the positioning
device of a flexible printing plate on the plate cylinder,
- Figs. 3 and 4 are sectional views of the biasing device mounted on
the plate cylinder, respectively according to the lines A-A and B-B of Figs.
1a
and 1 b,
- Figs. 5a and 5b are plan views, showing respectively one half C.O.C.
and one half C.C. of the base plate and the claw support being fitted thereon,
- Fig. 6 is, in a parallel direction with the rotational axis of the plate
cylinder, a partial sectional view of this cylinder in the vicinity of the cam
C.C.,
- Fig. 7 is a plan view of the cam C.C. and of the corresponding stirrup,
- Fig. 8a is a schematical plan view of the biasing device of the printing
plate; more particularly when this mechanism is in an intermediate position of
non-biasing the printing plate,
- Fig. 8b differs from Fig. 8a in that the biasing mechanism of the
printing plate, after a clockwise rotation, is acting in a first end position,
- Fig. 8c differs from Fig. 8b in that the biasing mechanism of the
printing plate, after a anticlockwise rotation, is acting in a second end
position.
Figs. 1 a and 1 b are general plan views of the positioning device of a
printing plate arranged in a groove 1 machined in a parallel direction with
the
rotational axis 2 of a plate cylinder 3. As better shown in the corresponding
sectional views of Figs. 3 and 4, the biasing device is supported on a base
plate 4 on which an immovable front claw 5 is attached, which seizes, in a
notch 7, the front edge of a printing plate 19 arranged about the plate
cylinder
3. Facing the front claw 5, a movable rear claw 6, which seizes the rear edge
of the printing plate 19 in a notch 8, has at its end C.O.C. a slide 9 engaged
on a roller 10 screwed on a block 100 secured to the plate cylinder 3 by two
fastening screws. At the opposite end of the positioning device (Fig. 2), the
base plate 4 is attached to a roller 11, which is placed between the lateral
faces 12 and 13 of a circular cam-ring 14 mounted on the frame (not shown)
of the machine. As can be seen in Figs. 1 a and 1 b, two other rollers 15, 16
are
secured to the base plate 4 and slide respectively in two cams 17 and 18
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which are rigidly attached to the bottom of the groove 1 of the plate cylinder
3.
A means 101, consisting of an electrical motor, is mechanically joined with
the
plate cylinder 3 and allows to laterally move it along its rotational axis 2.
As illustrated in Figs. 1 a, 1 b and 3, the base plate 4 comprises a
plurality of supports 20 in the form of rectangular blocks kept at their base
by
screws 21 and above which are fixed, firstly and by means of screws 23, a
protection plate 22 bent in its length, then the front claw 5 kept by screws
24
which also clamp the protection plate 22. Opposite the front claw 5, the rear
claw 6 is attached by fastening means 103 (Fig. 4) onto a claw support 25
consisting of a metallic plate having a plurality of elongate apertures 26
(Fig.
5a, 5b) through which are arranged studs 27 allowing to maintain the rear
claw 6 on its claw support 25 by means of fastening screws 28. The
orientation of these elongate apertures 26 allows for the lateral movement of
the claw support 25 with respect to the rear claw 6 and drives this latter in
a
longitudinal perpendicular movement to the rotational axis 1 of the plate
cylinder. The closing and the opening of the rear claw 6 is achieved by this
movement which allows respectively to tighten or to liberate the printing
plate
19 of the plate cylinder 3. The claw support 25 is rigidly attached by means
of
screws 29 on two blocks 30 having a cuboidal rectangular form and sliding on
two axes 31. These axes are kept at each end by a support 32 attached to the
base plate 4 by screws 33. There is a fastening screw 34 above each support
for locking the axis 31 in its support 32. Therefore, the claw support 25 can
be
longitudinally moved along the axes 31 driving the rear claw 6 owing to the
perpendicular orientation of the elongate apertures 26.
The longitudinal opening movement of the rear claw 6 is controlled by
seven simultaneously working pneumatic cylinders 40 (Fig. 5a, 5b), which are
supplied by ducts 41 kept on the base plate 4 by fastening clamps 42, and
which are attached to each other by connections 43. These pneumatic
cylinders 40 are mounted by screws 45 on L-shaped supports 44, which may
also serve as fastening points for the protection plate 22 and the front claw
7.
These supports 44 are spaced at regular intervals and each positioned on
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the base plate 4 by two fastening screws. Plates 46, which are bent at right
angles in their ends, are positioned facing the pneumatic cylinders 40 and
welded, standing on one of their two main edges, to the claw support 25.
During pressurization of the pneumatic circuit supplying the pneumatic
cylinders 40, the axes 47 of these pneumatic cylinders (Fig. 1 a, 1 b),
resting on
the plates 46, push the claw support 25 in front of them. The rear claw 6,
associated with the claw support 25, is then opened.
The closing of the rear claw 6 is achieved, after having released the
pessure in the pneumatic cylinders, by a plurality of compression springs 48
pushing back.the claw support 25 in a longitudinal closing movement. Each
spring 48 is guided by thestem of a screw 49 extending through the bent plate
46 on which rests one end of these springs. The second end of the springs 48
rests on a plug 50 which is screwed in a retaining block 51 that is kept on
the
base plate 4 by two screws 52. The retaining blocks 51 also serve as fixing
support to a second bent protection plate 53 which partially covers the top of
the claw support 25. This protection plate 53 is attached to its base by a
plurality of screws 54 (Fig. 1 a, 1 b) arranged in the retaining blocks 51,
and
has circular openings to receive the plugs 50.
The lateral positioning of the printing plate 19 on the front claw 5 is
ensured by a centering pin 55 (Fig. 4) chased in the upper part of the front
claw 5 and accurately arranged on the longitudinal axis of the printing
machine.
Fig. 5b shows a fastener 60 attached to the end C.C. of the base plate
4 by screws 61. The roller 11 is positioned on the longitudinal axis of this
fastener by means of a screw 62. Two openings 63 in the vicinity of the first
and the last third of the base plate 4 have a diameter which is substantially
greater than the diameter of two bushings 64 extending through them (Fig. 3).
The overdimension of the openings 63 allows to provide the place required by
the movements of the base plate 4 while being flattened at the bottom of the
groove 1 by holding means 102; this in order to control the action of the
centrifugal force on the base plate 4 during rotation of the plate cylinder.
The
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holding means 102 consist of bushings 84 round which two bearing shells 65,
which are made of synthefical material having tow coeffiGent of friction,
seize
3ondwichod the base plate 4 enabling it to move e~sily. A compression spring
66, being arrangi~d between two other wnsttars 67 and 68, and a screw 89,
rusting on thv upper washer 88 and, after having extended through the
bushing 64, screwing tn the hattom at the groove t, maintain the clamping of
the base plate 4 in a parallel plan to the section of the plate cylinder. The
fastener 60 also has an opening 70 through which extends a screw 71, both
having the same respective functions as the openings 63 and the 3erows 69
described herein6efore.
As shown in Figs. 5a and 5b, two nclanguiat openings 72, cut out in
the base plate 4, allow t0 housA fhA spaced cams 17 and 18 secured to
the plate eyllndAr 3. These openings 72 have a larger size than the dirndnsion
of the bases 80 of the cams 17 and 18, this for irr~e 'movement of the base
plate 4 round these rams without abutting against one of them. The openings
72 aro widthwise bordered at each side with three aligned openings, the
center opening9 79 of which allow to accun~ly position a stirrup 74 by means
of two cylindrical pins 75, and the and openings 76 of which are adapted to
fix
the stirrup 74 on the base plate 4 by screws 77. A.s ilustrated in Figs. 6 and
7,
the stirrups 74 constitute twe bridges, which are secured to the base plate
and
arranged above the cams 16 and 17, and in the largest surface of which are
screwed from below the rollers 15 and 16 which slide in the respective cams
17 and 18. Screws 78 further allow to fhc the protection plate 22 and the
front
claw 5 above tire stimrp 74.
The cams 1 B and 17 aro symmetrical one with regard to the other and
consist of a stairtike tease 80 being provided, on the one hand, with an
opening adapted to receive a centering pin 81 and, on the other hand, with
two fixing openings 83 in which slide two screws 82 which are screwed in the
plate cylinder 3. Above thin base 80 rise two small salient parts 84 having N
triangular shape end constituting the core of the cams, betwaan which slides
the roller 15 or 16.
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In order to well grasp the working principle of the mechanism of the
present invention, Figs. 8a, 8b and 8c schematically illustrate three
different
positions which can be occupied by the positioning device of the printing
plate.
If no biasing is applied to the printing plate, the configuration of the
mechanism is in an intermediate position corresponding to the schematical
illustration of Fig. 8a.
If the printing plate has to be biased in one direction or another, a
simple lateral movement of the plate cylinder in the direction of its
rotational
axis 2 allows to actuate the biasing mechanism of the printing plate. The
lateral movement of the plate cylinder 3 is controlled by the means 101
comprising an electrical motor coupled to toothed wheels gearing in a worm.
This conventional mechanism allows to convert the circular movement of the
motor shaft into a rectilinear movement required by the lateral movement of
the plate cylinder. The movement of the plate cylinder by means of the motor
and this mechanism is moreover automatized owing to sensors detecting the
lateral position of the plate cylinder. These sensors are connected to an
external electronic controller (not shown) controlling the motor of the means
101. Thus for a given job, the biasing of a printing plate can easily be
controlled and memorized by the electronic controller, via position sensors,
by
simple memorization of the lateral movement of the plate cylinder.
As illustrated in Fig. 8b, when the cylinder is moved from C.O.C. to
C.C., the roller 11 rests, after a certain stroke, against the lateral side 12
of the
cam-ring 14. It follows a combined movement of the base plate 4, guided by
the rollers 15 and 16 which slide in the cams 17 and 18, consisting of both a
pivoting of the base plate 4 round the roller 11 and a translation of this
base
plate marked by the sliding motion upwards of this roller 11 along the lateral
side 12 of the cam-ring 14. The slide 9 of the rear claw 6, which only slides
longitudinally on the roller 10, solely permits a movement of translation and
rotation round the fixed pivot point consisting of this roller 10 secured to
the
plate cylinder 3. Due to the longitudinal orientation of this slide, no
movement
along the axis 2 can be transmitted to the rear claw 6. Therefore, owing to
this
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rear claw 6, which is not movable in a parallel direction with the axis 2 of
the
plate cylinder, and owing to the combined movement to which the front claw 5
is also liable, the front and rear edges of the printing plate can be biased,
as
subtly as simply, in a shearing movement while remaining parallel to each
other.
Fig. 8c illustrates, in the opposite direction, the same combined
movement resulting from the movement of the plate cylinder 3 from C.C. to
C.O.C. In this case, the roller 11 rests and slides along the opposite lateral
side 13 of the cam-ring 14.
To correct the biased positioning of a printing plate 19, the operator
acts on a control which slightly releases the pressure in the pneumatic
cylinders 40, so as to slacken and unglue the printing plate from the plate
cylinder, and which actuates the motor of the means 101 in order to move, in
one direction or another, the plate cylinder 3. Once the roller 11, being in
contact with one lateral side 12 or 13 of the cam-ring 14, has moved along
this
cam-ring 14 by a distance corresponding to the desired biasing, the plate
cylinder 3 moves in the opposite direction so as to reposition it according to
the lateral register suitable for the printing. The latter movement does not
at all
change the biasing of the printing plate 19 since, on this opposite movement,
the roller 11 is immediately loosened from the lateral side of the cam-ring
14.
Owing to the adherence of the printing plate tensioned on the plate cylinder,
the biased positon of the printing plate remains. The position of the lateral
register of the plate cylinder being known, it is thus easy to autmatize the
baising of the printing plate by an angular value, if desired, by simple
introduction of this value in the electronic controller.
Thus, the positioning and biasing operations of a printing plate on a
plate cylinder equipped with a device according to the present invention, are
limited to the following steps
a) Opening of the rear claw 6 by means of the pneumatic cylinders 40
which compress the springs 48.
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b) Fixing of the front edge of the printing plate 19 in the notch 7 of the
front claw 5 and in the centering pin 55.
c) Slow rotation of the plate cylinder 3 round its axis 2 so that the
printing plate 19 winds about the cylinder.
d) Fixing of the rear edge of the printing plate 19 in the notch 8 of the
rear claw 6.
e) Closing of the rear claw 6 by releasing of the pressure in the
pneumatic cylinders 40.
f) Rapid rotation of the plate cylinder 3 and actuation of the pneumatic
cylinders 40 to slightly unglue the printing plate 19 from the cylinder in
order to
allow for its biasing.
g) Actuation of the biasing of the printing plate 19 by lateral movement
of the plate cylinder 3 by a certain distance corresponding to the desired
slant.
h) Opposed lateral movement of the plate cylinder 3 so as to restore
the lateral register required for the printing.
i) Releasing of the pressure in the pneumatic cylinders 40.
Besides the fixing of the printing plate about its cylinder, each other
operation described hereinbefore can easily be automatized owing to the
conception and the specific mechanism for biasing the printing plate of the
present invention. When restarting an old printing job, advantageously, this
device does not require any manual adjustment of the printing plate if the
previously known adjustment values have been memorized. Finally, it should
be noted that this device also allows a biasing of the printing plate when the
plate cylinder rotates at maximum speed. Therefore, the printing machine
does not have to be stopped to correct the slanted position of the printing
plate, which fact allows to mainly reduce the costs for putting into service
when preparing a new printing job. Numerous improvements can be added to
this device within the scope of the claims.
