Note: Descriptions are shown in the official language in which they were submitted.
WH-7861-89 - 1 - 2000730
Device for correcting the register of sheet prints in a
sheet-fed rotary printing machine.
The invention relates to a device, provided before the
printing unit, for correcting the register of sheet prints
and for compensating for distorted sheets in a sheet-fed
rotary printing machine by deforming the leading sheet edge.
A device for correcting the register and compensating for
distorted sheets is known from the German Patent 31 12 964.
In this specification it is a sheet transfer cylinder which
comprises the aforementioned features. The bending device
engages the middle of the gripper bridge shaft of the sheet
transfer cylinder so that it bends the gripper bridge shaft
in accordance with the machine beat, whereby the leading
sheet edge is deformed in the middle in or against the
direction of rotation of the cylinder. The bending device
consists of a movable arrangement of a middle gripper bridge
shaft bearing and a cam mechanism including a cam roller and
a restoring spring, the instantaneous position of rotation
of the cam roller being adjustable by means of a control
shaft which, as is suggested in this specification, is
formed by the gripper bridge shaft. Such a bending device
causes relatively high costs and has above all the
disadvantage that an adjustment of the deformation of the
leading sheet edge cannot be effected while the machine is
running so that it is necessary to stop the machine a number
of times in the make-ready phase in order to perform
register corrections by deforming the leading sheet edge.
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The US Patent 2,577,099 shows a device for correcting the
register in which the gripper bridge shaft is held at its ends
in a sheet transfer cylinder and is also bent in the middle in
or against the travel direction of the sheet. For this purpose
the gripper bridge shaft is designed either in form of a tube
and supported in the middle of a channel in the sheet transfer
cylinder on a pair of rollers the axes of rotation of which
take different angular positions with respect to the axis of
the gripper bridge shaft and the rollers of which can be
pressed individually against the gripper bridge shaft by means
of an eccentric mechanism, or in form of a flexure rod which
cajn be deformed by an eccentric mechanism. Such a cam mechanism
for the bending device is also quite costly and, above all, it
cannot be regulated while the machine is running.
The German Application 23 14 302 and the German Patent 11 75
695 describe devices for deforming the leading sheet edge for
the purpose of correcting the register, in said devices the
gripper bridge shaft is subdivided and the neighbouring ends of
the shaft segments are mounted in a movable slide which can be
adjusted by means of specific structural members. These
devices, too, are very expensive and cannot be adjusted while
the machine is running.
Reference is also made to the known possibility of adjusting
respectively gripper pad bars and front stops provided at the
grippers of sheet transfer cylinders for the purpose of deform-
ing the leading sheet edge according to the German Patent 19 09
795 and the German Offenlegungsschrift 35 04 435. By means of
the devices known from these publications the leading sheet
edge is deformed in a sheet feed cylinder already during the
alignment of the sheet at the gripper pad bar and the front
stops of the grippers, respectively, thus abutting uniformly
against said gripper pad bars and front stops, respectively.
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WH-7861-89 - 3 - 2 0 0 0 7 3 0
However, these means which are designed so as to differ from
the prior art described above do not eliminate the
aforementioned disadvantages.
All prior art arrangements share the feature that the means
for deforming the leading sheet edge are provided at a
rotatingly driven cylinder including a gripper system which
is disposed in an axial channel at the circumference of this
cylinder and can be swivelled about a gripper bridge shaft
mounted eccentrically with respect to the cylinder axis.
Thus, practice and literature point out unequivocally that
the embodiment of such means is limited to rotatlng cylinders
and that an expensive production has to be accepted without
having the possibility of a simple adjustment of the means
while the machine is running.
It is the object of the invention to create a bending device
for deforming the leading sheet edge for the purpose of
correcting the register and compensating for distorted sheets
in a gripper system for taking over sheets in a sheet-fed
rotary printing machine, a bending device which can be
adjusted above all while the machine is running and which
requires hardly any additional structural members.
The present invention includes a bending device provided at
the gripper bridge of a pre-gripper which executes swinging
movements about an axis which is stationary with respect to
the machine frame but possibly adjustable with respect to its
position and the gripper bridge of which, by means of
flexurally stiff levers, is supported only at its two ends
on a gripper bridge shaft. The bending device has a stop
which is fixed to the machine frame but can still be
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adjusted with respect to its height and against which the middle
region of the gripper bridge abuts before the ends of the gripper
bridge which swivel further back reach their zero position in
which the sheet grippers grip the sheet. Since the stop is pro-
vided at a part of the machine frame, it can be adjusted any time
- even when the machine is running. This constitutes an essential
advantage as compared to any known prior art embodiment. Further-
more, the simplest embodiment of the stop can consist of an ad-
justing screw which can be screwed into a threaded part stationar-
ily fastened to the machine frame. In general, end stops for the
gripper bridge are not necessary; however, it is possible to
provide at the machine frame also stops for the ends of the grip-
per bridge against which the gripper bridge possibly abut in its
zero position. If the middle stop for the gripper bridge is with-
drawn behind the straight connection line between the two end
stops, the bending device will be ineffective. In case a register
correction should possibly be necessary, the middle stop is ad-
vanced with respect to the straight connection line so that the
middle of the gripper bridge already abuts against this stop
before the ends of the gripper bridge reach their zero position
and the outer stops, respectively, so that the gripper bridge is
slightly bent in the region of the middle stop. Such a gripper
bridge operates with gripper pad bars which do not feature any
stops so that, with the bending device being adjusted, the sheet
projects at its ends further into the grippers than at its middle
and that first of all, for the purpose of tensioning the sheet
during pre-gripper motion, the sides of the sheet are accelerated
more than is its middle, as in the case of other known devices.
In the simplest embodiment the stop for the middle region of the
gripper bridge is provided at a cross-bar of the machine frame.
According to a conception for a further embodimènt of the inven-
tion the middle stop for the gripper bridge is supported on the
gripper bridge shaft in order to permit a delay of several swivel
degrees. For this purpose there is provided, according to a par-
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ticular suggestion of the invention, a stop in form of a roller
mounted on a further lever which is firmly connected with the
gripper bridge, provided in the middle between the two flexurally
stiff levers disposed at the ends of the gripper bridge and ex-
tends approximately parallelly to the two flexurally stiff levers,
said lever featuring a self-aligning bearing which is connected
with the gripper bridge shaft so as to be fixed against rotation
and which is arranged eccentrically with respect to the axis of
the gripper bridge shaft. The distance of this roller from the
gripper bridge shaft can be adjusted by means of a cam embodied at
the circumference of a ring which is rotatable about the gripper
bridge shaft. According to the invention a particularly advanta-
geous solution is to be seen in the fact that the cam is provided
at the outer cylindrical surface of a ring surrounding the gripper
bridge shaft, the position of rotation of said ring being adjust-
able by means of an adjusting device, e.g. an adjusting screw,
which is attached to the machine frame. With the device not being
adjusted, the roller is not in contact with the cam, and the lever
is pressed against the stop screw by means of a spring.
The drawings show specimen embodiments of the invention:
Fig. 1 shows a vertical sectional view of a pre-gripper of a
sheet-fed rotary printing machine,
Fig. 2 is a plan view of a pre-gripper in direction of arrow X in
Fig. 1,
Fig. 3 is a vertical sectional view of a pre-gripper of a modi-
fied specimen embodiment as compared to Fig. 1,
Fig. 4 is a plan view of the pre-gripper according to Fig. 3 in
direction of arrow X in Fig. 3.
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The pre-gripper shown in the drawing grips the sheet 1 to be
printed from the feed table 2 on which the sheet has been aligned
at front and side lays (not illustrated). The pre-gripper acceler-
ates the sheet 1 to print speed and transfers it to the transfer
cylinder 3. The drive of the pre-gripper is effected by a cam 4
(illustrated in Fig. 1) via a roller lever 5 with a roller 6 being
mounted at its free end so as to be rotatable, said roller 6 being
pressed against the cam 4 by means of a spring 7. By designing the
cam 4 correspondingly the sheet is accelerated to print speed by
the pre-gripper when being transferred to the cylinder 3, while
the pre-gripper returns slowly to its other end position after a
respective delay in the last phase of motion and reaches its zero
position in which a new sheet 1 is taken from the feed table 2.
In the specimen embodiment of Fig. 1 a gripper bridge 8 which
extends across the machine width and is u-shaped in cross-section
is fastened at its ends to flexurally stiff levers 9 which, in
turn, are attached to the swivel shaft 10 of the pre-gripper. The
bending device for the gripper bridge 8 consists of a stop 12
which is adjustably arranged at a cross-bar 11 of the machine
frame, said stop 12 cooperating with a counter-stop 13 provided at
the gripper bridge 8. In this specimen embodiment the stop 12 is
designed as an adjusting screw 14 which can be screwed into the
cross-bar 11 extending transversely to the sheet-conveying direc-
tion or into another structural member of the machine frame, for
this purpose the free end of the adjusting screw 14 is connected
with a knurled head or means for using a tool which e.g. can be
driven by a motor. Further possibly adjustable stops 15 and 16 are
disposed in the region of the ends of the gripper bridge 8 and
cooperate with counter-stops 17 and 18 provided at the gripper
bridge, whereby - in the simplest case - "mushroom heads" are used
as stops 15 and 16 and screw heads as counter-stops 17 and 18.
With this arrangement the stop 12 can be withdrawn by the adjust-
ing scew 14 behind the straight connection line extending through
the planes in which the stops 15 and 16 are in contact with the
counter-stops 17 and 18 so that there is no bending of the gripper
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2000730
bridge 8. For register corrections the stop 12 can be advanced,
while the machine is running, beyond this straight connection line
by actuating the adjusting screw 14 so that the gripper bridge 8
is slightly bent at a varying degree, as shown by the dash-dot
lines in Fig. 2. Depending on the degree of bending the grip-
pers Z0 in the gripper bridge 8 which can be moved about their
swivel axis 19 grip the sheet further down in the margin than they
do in the middle so that during the pre-gripper motion there is a
greater acceleration at the margin, whereby the sheet is tensioned.
Another specimen embodiment is represented in Figs. 3 and 4 in
which the stop is formed by a roller 21 which is supported on the
cam 24 by a spring 31 and is mounted on a further lever 22 so as
to be freely rotatable, said lever 22 being provided in the middle
between the two flexurally stiff levers disposed at the ends of
the gripper bridge 8 and extending approximately parallely to said
flexurally stiff levers, one end of said lever being firmly con-
nected with the gripper bridge 8 and the other end of which
featuring a self-aligning bearing 23 which is connected with a
gripper bridge shaft 10 so as to be fixed against rotation and
being provided eccentrically with respect to the axis of said
gripper bridge shaft. Since the roller 21 is adjustable with
respect to its distance from the axis of the gripper bridge shaft
10, a bending device is provided by means of which the gripper
bridge 8 can be deformed via the lever 22. For adjusting the
distance of the roller 21 from the axis of the gripper bridge
shaft 10 the specimen embodiment provides a cam 24 which is em-
bodied at the circumference of a ring 25 being rotatable about the
axis of the gripper bridge shaft 10. This ring 25 can be rotated
by means of an adjusting screw Z6 which is held in the machine
frame so as not to be axially displaceable and the nut 27 of which
is connected with the ring Z5 so as to be able rotatable within
said ring. By means of this adjusting screw 26 the cam 24 can be
rotated into the region of the roller 21 acting as a stop so that,
with the swivelling back of the gripper bridge, the roller 21
abuts earlier against the cam 24, thus deforming the gripper
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bridge. With the bending device not being adjusted, the cam 24 is
moved out of the range of motion of the roller 21 as illustrated
in Fig. 3. The lever 22 the middle of which is connected with the
gripper bridge 8 cooperates with a further stop lever 28 provided
on the gripper bridge shaft 10 so as to be fixed against rotation.
In this lever 28 and in the lever 22 there is provided an adjust-
able stop screw 29 and 30, respectively, the heads of which are in
contact with each other and which can be set at a tension-free
zero position of the gripper bridge. With the bending device not
being adjusted, the two heads of the two screws 29 and 30 are held
together by ~eans of a spring 31.
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LISt OF REFERENCES
1 sheet
2 feed table
3 sheet transfer cylinder
4 cam
lever
- 6 roller
7 spring
8 gripper bridge
9 lever
gripper bridge shaft
11 cross-bar at the machine frame
12 stop
13 counter-stop
adjusting screw
stop
16 stop
17 counter-stop
18 counter-stop
19 gripper shaft
sheet gripper
21 roller
22 lever
23 ' self-aligning bearing
24 cam
ring
26 adjusting screw
27 nut
28 lever
29 screw
- 30 screw
31 spring
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