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Description  |
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FIELD OF THE INVENTION
The present invention is directed generally to a method and apparatus for
axially positioning a printing plate. More particularly, the present
invention is directed to a method and apparatus for axially positioning a
printing plate while it is being applied to a cylinder of a rotary
printing press. Most specifically, the present invention is directed to a
method and apparatus for axially positioning a printing plate as the plate
is being moved to a section of a plate cylinder by a conveying
arrangement. The printing plate is engaged by a plate gripping and
pressing device from a preliminary position at a printing plate
preparation device. As the plate is transported to the plate cylinder, its
axial position is finalized by the cooperation of lateral register stops
and axial plate positioning devices.
DESCRIPTION OF THE PRIOR ART
In the German Patent Publication DE 28 04 970 A1 there is described a
device that is used to mount and to remove printing plates from the plate
cylinder or cylinders of a rotary printing press. In this prior art
device, a suction member is utilized and performs a linear movement
between a delivery roller and a plate cylinder. This suction member thus
conveys the printing plate between the delivery roller and the plate
cylinder. A positioning table is located intermediate the delivery roller
and the plate cylinder. The suction member deposits the printing plate on
the delivery table as an intermediate step in the plate transfer path from
the delivery roller to the plate cylinder. The plate is positioned while
it is supported by the positioning table. Once the printing plate has been
positioned by the positioning table, it will again be engaged by the
suction member and will be conveyed on to the plate cylinder.
A limitation of this prior art device is that the positioning of the plate
can be adversely affected as the plate is picked up off the positioning
table by the suction member. Even though the plate may have been properly
positioned on the positioning table, it may still arrive at the plate
cylinder in an improper position due to errors that may have resulted from
the re-engagement of the plate by the suction transfer device. Once the
printing plate has left the positioning table, it cannot be again adjusted
or positioned during its transport to the printing cylinder.
It will thus be seen that a need exists for a method and apparatus that
will allow for the accurate axial positioning of a printing plate on a
plate cylinder of a rotary printing press. The method and apparatus in
accordance with the present invention provides such a process and a device
and is a significant improvement over the prior art.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus
for axially positioning a printing plate.
Another object of the present invention is to axially position a printing
plate while it is being applied to a plate cylinder of a rotary printing
press.
A further object of the present invention is to provide a method and
apparatus for axially positioning a printing plate while it is being
conveyed to a predetermined section of the plate cylinder by a plate
gripping and pressing conveying device.
As will be discussed in detail in the description of the preferred
embodiments which is set forth subsequently, the method and apparatus for
axially positioning a printing plate on a plate cylinder of a rotary
printing press, in accordance with the present invention utilizes a
plurality of lateral register stops, each of which is adjustable. The
printing plate is positioned on a printing plate preparation device and is
engaged by a plate gripping and pressing device. The printing plate is
transported to a set position in the plate cylinder, which is selected
from a plurality of possible preselectable positions. A position of the
printing plate in the axial direction of the plate cylinder, in relation
to a reference position on the cylinder is then determined. The printing
plate is brought into its preselected set position by being positioned as
it moves from the plate preparation device to the plate cylinder.
It is possible, in an advantageous manner, to position a printing plate in
various positions with an exact register on the plate cylinder by means of
the process or the device of the present invention.
By means of this, it is possible to compensate for the so-called "fan-out"
phenomenon. The axial register deviation of an image point from print
position to print position on a web of material to be printed in
multicolor printing is called the "fan-out" phenomenon. This register
deviation is a function, for example, of the gram weight and the
properties (penetration behavior, type) of the paper web, the type of the
subject to be printed and the printing speed. The result of this is that
axial registry deviations can be of different sizes with different print
jobs. To be able to compensate for these deviations, lateral register
stops associated with printing plates, which lie axially next to each
other, were appropriately adjusted up to now.
By means of the device in accordance with the present invention it is
possible to preselect different positions by remote control and to
position the printing plate on the cylinder accordingly. Expensive manual
adjustment work on the lateral register stops is avoided by this.
If a reference point for detecting the position of the printing plate is
disposed on the cylinder, inaccuracies as a result of the conveyance of
the printing plate by the conveying means are reduced. Thus the method and
apparatus for axially positioning a printing plate, in accordance with the
present invention overcomes the limitations of the prior art and is a
substantial advance in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
While the novel features of the method and apparatus for axially
positioning a printing plate on a plate cylinder of a rotary printing
press are set forth with particularity in the appended claims, a full and
complete understanding of the invention may be had by referring to the
detailed description of the preferred embodiments, as presented
subsequently, and as illustrated in the accompanying drawings, in which:
FIG. 1 is a schematic top plan view of a device for mounting printing
plates in accordance with the present invention;
FIG. 2 is a schematic perspective representation of a gripping and pressing
mechanism of the device of FIG. 1;
FIG. 3 is a schematic side elevation view of the device with the associated
cylinder and preparation devices of FIG. 1;
FIG. 4 is a schematic top view of a lateral register device in accordance
with a second preferred embodiment;
FIG. 5 is a schematic top view of an adjustable lateral register device in
accordance with a third preferred embodiment; and
FIG. 6 is a schematic top view of an adjustable lateral register device in
accordance with a fourth preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring initially to FIG. 1, there may be seen a cylinder 1 of a rotary
printing press in accordance with the present invention. The printing
cylinder 1 is utilized to support a plurality of easily bendable,
generally arcuately shaped objects 2, such as printing plates 2. As may be
seen in FIG. 3, on the oppositely located leading and trailing ends of
each easily bendable, arc-shaped object 2, there are provided front and
rear suspension edges 3 and 4, respectively. These suspension edges 3 and
4 have respective legs 6 and 7 which each enclose an opening angle of less
than 90.degree.. These suspension edges 3 and 4 are dimensionally stable;
i.e. during clamping of the objects 2 on the cylinder 1, these suspension
edges 3 and 4 are not bent open. These objects 2 designed in this way as
printing plates, can also consist of rubber blankets, which are provided
with suspension edges 3 and 4. These dimensionally stable suspension edges
3 and 4 of the rubber blankets can be beveled edges of a metal plate, on
which the rubber blanket is fastened by direct material contact, for
example by being glued on or vulcanized. Fabric inlays, in particular of
the rubber blanket, can be made of carbon fiber-reinforced plastic or of
fiberglass-reinforced plastic, and the suspension edges 3 and 4 can be
formed of this. For the sake of simplicity, this described object 2 will
be called a printing plate 2 for the remainder of the description of the
preferred embodiments.
An ink unit protector 11, which is positioned close to the cylinder and
which is fixed in the frame, is embodied as a first printing plate
preparation device 12, and is assigned to the cylinder 1 of the rotary
printing press, which is seated between two lateral frames 8 and 9 as seen
in FIG. 1. This first printing plate preparation device 12 has an upper
wall 13 and a lower wall 14 that is located opposite the upper wall 13.
These two walls 13 and 14 together constitute a chute 16. A suspension bar
19, which has a nose-shaped or angled cross section, and which extends
across the width of the cylinder 1 and is parallel with an axis of
rotation 18 of the cylinder 1, is fastened at an end 17, close to the
plate cylinder, of the upper wall 13. The end 17, close to the plate
cylinder, of the upper wall 13 is situated approximately parallel with a
tangent 21, which is determined by a cylinder jacket surface 22 of the
cylinder 1 and the suspension bar 19 of the printing plate preparation
device 12. It is also possible to locate a second printing plate
preparation device 23, besides the first printing plate preparation device
12, and whose end 24 close to the plate cylinder is also provided with a
suspension bar 26 of a nose-shaped or angled cross section, and which is
also situated approximately parallel with the tangent 21 determined by the
cylinder jacket surface 22 of the cylinder 1 and the suspension bar 19 of
the printing plate preparation device 12.
Again referring to FIGS. 1 and 3, above and parallel with this tangent 21
there is located one right and one left linear drive 27 and 28,
respectively, and which drives 27 and 28 are fastened in the lateral
frames 8 and 9, respectively. These linear drives 27 and 28 consist of
threaded spindles 29 and 31 respectively, which are rotatably seated in
brackets 32 and 33 or 34 and 36, that are fixed on the two lateral frames
8 and 9. In the same way, it is possible to employ other known linear
drives 27 and 28, for example belt or chain drives, toothed rack drives,
hydraulic or pneumatic servo cylinders or linear motors. A synchronous
rotating movement of the two threaded spindles 29 and 31 is generated by
means of a connecting belt 37, for example a toothed belt 37, which
mechanically synchronizes the right and left threaded spindles 29 and 31.
This synchronization can also take place, for example, mechanically by use
of chain or universal joints, or electronically via two separate drives 38
of the linear drives 27 and 28. The two threaded spindles 29 and 31 move a
cross-bar 39, which is positioned parallel with the axis of rotation 18 of
the cylinder 1, in a conveying plane, which is located above and
approximately parallel with the tangent 21 determined by the cylinder
jacket surface 22 of the cylinder 1 and the suspension bar 19 of the
printing plate preparation device 12. Threaded nuts 42 are respectively
disposed at both ends of this cross-bar 39, so that the cross-bar 39 is in
operative connection at right angles with the threaded spindles 29 and 31.
At least one gripping and pressing device, generally at 43 is fastened
along this cross-bar 39. In the embodiment depicted in FIG. 1, four such
gripping and pressing devices 43 are fastened along the cross-bar 39.
An independently movable gripping and pressing device 43 is associated with
each individual printing plate 2 assigned to an axial cylinder section. It
is also possible, by means of an additional linear drive, by which a
single gripping and pressing device 43 can perform an axial movement along
the cross-bar 39, to exchange several printing plates 2 disposed along the
cylinder 1 with only a single gripping and pressing device 43.
The elements of a gripping and pressing device 43 are depicted somewhat
schematically in FIG. 2. Each gripping and pressing device 43 consists of
at least one gripper unit 44 and at least one pressure roller 46. This
gripper unit 44 and the pressure rollers 46 can be displaced, in relation
to the cylinder 1, in the radial direction "D", and each gripper unit 44
can additionally be also displaced in an axial direction "C" of the
cylinder 1, independently of each other. In the depicted embodiment, the
gripping and pressing device 43 is arranged approximately symmetrically
with respect to the center line of the printing plate 2 which extends in
the direction of the cylinder circumference of the cylinder 1.
One gripper unit 44 is provided for each gripping and pressing device 43,
and is fashioned in the shape of two suction bars 47, for example, which
are axially displaceable, are fixed against relative rotation,
perpendicularly in respect to a guide bar 48 opposite the tangential
direction "b" of the cylinder 1, and which are pressed against a detent 51
in the direction "B" by means of pressure springs 49. These guide bars 48
are fastened on an upper guide bar 52 and can be displaced opposite the
direction "C" by means of a positioning device 53. A pneumatic cylinder 54
causes a position change of the upper guide bar 52 and thus of the suction
bars 47 along the direction "D". One pressure roller 46 is located next to
each of the suction bars 47 and can be placed against the printing plate 2
opposite the direction "D" by means of a pneumatic cylinder 56. The
positioning device 53 can be designed, for example, as a step motor with a
threaded spindle 55. An electric motor with an incremental sensor or
potentiometer cooperating with it is also possible. Therefore, means
preferably cooperate with the positioning device 53 for detecting its
position or the position of the printing plate 2.
In the subject invention, four plate end gripping assemblies or locks 57,
58, 59 and 61 are arranged in the cylinder 1 and extend in the axial
direction, parallel with the axis of rotation 18 of the cylinder 1. These
locks are disposed in cylinder pits or channels 62. The length of each of
the respective locks 57, 58, 59 or 61 is approximately half the cylinder
length. These locks 57, 58, 59 and 61 are each also divided in respect to
the width of the plates; so that respectively two printing plates 2 are
receivable by each lock 57, 58, 59 or 61, and each can be actuated
independently of each other within this division as well as in respect to
each other. The locks 57 and 58 are offset from each other by
approximately 90.degree. in the direction of the circumference of the
cylinder 1. A lock 59 or 61 is respectively associated with a
corresponding lock 57 or 58 on the opposite side of the cylinder 1.
For clamping a fresh printing place 84 in place, the cylinder 1 is rotated
into a clamping position which, as seen in FIG. 3, is defined by the
center line of the lock 57 being approximately congruent with a line 81
drawn from the axis of rotation 18 of cylinder 1 perpendicularly with the
direction of the linear drives 27 and 28. The cross-bar 39 is brought into
a position for receiving the fresh printing plate 84 by actuation of the
two linear drives 27 and 28. The suction bars 47 are thereby located in
the area of the end 17 of the upper wall 13, close to the plate cylinder,
of the printing plate preparation device 12. The gripper unit 44 is
displaced opposite to the direction "C" by actuating the positioning
device 53.
The printing plate 84 which is to be applied to the cylinder 1 had been
prepositioned and placed on the upper wall 13 and the suspension bar 19 of
the printing plate preparation device 12. The suction bars 47 are lowered
to the level of the printing plate 84 by venting the pneumatic cylinder 54
and are then charged with suction air. The print side of the printing
plate 84 is gripped by the suction bars 47 and is fixed in place on the
gripping and pressing device 43.
In accordance with the present invention, the axial alignment of a printing
plate 84 is accomplished in the following manner. In a first preferred
embodiment, each of a plurality of printing plates 84 which are placed
axially next to each other, has been assigned at least two lateral
register stops 66 and 86. At least one of these two lateral register stops
66 or 86 can be disposed directly on the suspension bar 19 of the printing
plate preparation device 12, or separately in an area between the printing
plate preparation device 12 and the cylinder 1, as shown in FIG. 3. In the
simplest case, this one lateral register stop 66 of the two lateral stops
66 and 68 is disposed on the suspension bar 19 in addition to the lateral
register stop 86 usually disposed on the cylinder 1. This lateral register
stop 66 is laterally offset in the axial direction of the cylinder 1 and
can be finely adjusted.
In a second preferred embodiment, a lateral register stop 86 on the
cylinder 1 is omitted. A lateral register arrangement 67 is disposed in
the area between the printing plate preparation device 12 and the cylinder
1 and consists of three lateral register stops 68, 69 and 71, which are
arranged behind each other, and which are disposed offset steplike in
respect to each other in the axial direction of the cylinder 1, as may be
seen in FIG. 4. These lateral register stops 68, 69 and 71 are embodied to
be finely axially adjustable, for example, by means of threaded screws 91,
92 or 93 and a linear bearing 94, 96 or 97.
In third and fourth preferred embodiments, only one lateral register stop
72 or 74 is displaceably disposed in a bearing 98 or 99, and can be placed
into different positions which are offset in respect to each other in the
axial direction of the cylinder 1. For example, the lateral register stop
72 can be fastened on a work cylinder 73, which is fixed in place, as
depicted in FIG. 5. A piston of this work cylinder 73 moves the lateral
register stop 72 into two positions. It is also possible to arrange a
lateral register stop 74 continuously displaceable in the axial direction
of the cylinder 1. To this end, the lateral register stop 74 can be
positioned, for example, by means of a threaded spindle 77 which is driven
by an electric motor 76, as illustrated in FIG. 6.
The printing plate 84 is axially aligned on the lateral register stops 66
to 69, 71, 72, 74 in the following manner. If, as discussed in connection
with the first and second preferred embodiments, several lateral register
stops 66 to 69, 71, 86 are arranged behind each other, the gripping and
pressing device 43 with the gripped printing plate 84 approaches a
preselected position assigned to the desired lateral register stops 66 to
69, 71, 86 in the direction "B", as shown in FIG. 2. With an adjustable
lateral register stop 72 or 74, the lateral register stop 72 or 74 is
brought into the preselected position by means of the work cylinder 73 or
the electric motor 76. The gripper unit 44 with the gripped printing plate
84 moves in the direction "A " into a position assigned to the lateral
register stop. The drive motor of the positioning device 53 moves the
gripper unit 44 in the axial direction until the printing plate 84 is
pressed with its suspension edge 3 against the respective lateral register
stop 66 to 69, 71, 72, 74, 86. Subsequently, the motor for the positioning
device 53 is switched off. This can take place, for example, by a
limitation of the current reception of an electrically driven motor of the
positioning device 53, or it is possible to dispose a sensor in the area
of the power flow for detecting the pressure force. In the same way, it is
possible to determine criteria for switch-off from the relationship
between the path travelled by the printing plate 84 or of the positioning
device 53 and the time needed for this.
In place of the lateral register stops 66 to 69, 71, 72, 74 and 86, it is
also possible to provide sensors for detecting the position of the
printing plate 84. A CCD sensor is particularly suited for determining the
position of the printing plate 84 and for controlling the positioning
drive of the gripper unit 44. This CCD sensor can be advantageously
fastened so it is partially covered by the lateral edge of the printing
plate and fixed in place in relation to the lateral frame. In the process,
the CCD sensor is aligned by being associated with a defined position of
the cylinder 1.
After the gripper unit has gripped the printing plate 84, the initial
position of the printing plate 84 is determined by means of the CCD
sensor. The drive of the positioning device 53 is operated, based on this
initial position, until the printing plate 84 has reached the desired
position in respect to the CCD sensor and therefore in respect to the
cylinder 1. Now the drive motor of the positioning device 53 is switched
off and the printing plate 84 is transported in the direction toward the
cylinder 1.
A further preferred embodiment, not represented, has two sensors on the
gripping and pressing device 43 and a reference point on the cylinder 1
for determining the position. The first sensor, which detects a lateral
edge of the printing plate 84, is fastened on the cross-bar 39 in the area
of a lateral edge of the printing plate 84. The second sensor, which
detects the reference point, is arranged, movable with the gripper unit
44, in the area of the reference point located on the cylinder 1.
The gripper unit 44, with the second sensor, is moved in the axial
direction until the reference point of the cylinder 1 has been reached.
This reference position is stored by the control of the drive motor of the
positioning device 53. If, in the course of this movement, the position of
the lateral edge of the printing plate 84 has been detected, this position
is also stored. Otherwise, the printing plate 84 is axially displaced
further until the lateral edge of the printing plate 84 is detected. Based
on these two position values and a preselected position in which the
printing plate 84 is intended to be mounted, the control of the drive
motor of the positioning device 53 calculates a path by which the printing
plate 84 still needs to be displaced. Subsequently the positioning device
53 performs the required axial movement of the printing plate 84.
Finally, in a further preferred embodiment, not shown, the reference point
is embodied on the cylinder 1 as a stop for a lateral edge of the printing
plate 84. The printing plate 84 suspended in the suspension edge 63 of the
cylinder 1, whose plate front suspension edge 3 is held by the gripper
device 44, is guided in the axial direction against the stop by means of
the positioning device 53. When the suspension edge 3 meets the stop, the
motor for the positioning device 53 is switched off. This switch-off can
occur, for example, by means of a current limiter or by evaluation of the
pulse sequences of an incremental sensor. Starting from this reference
position, the printing plate 84 is positioned in the axial direction in
the preselected position of the cylinder 1 by means of the positioning
device 53.
Further mounting of the plate 84 of the cylinder can take place, for
example, in accordance with the process described in German Patent
Publication DE 44 24 931 A1, which corresponds to U.S. patent application
Ser. No. 08/669,391, filed Jul. 17, 1996, the disclosure of which is
incorporated herein by reference.
If several printing plates can be mounted on a cylinder in the axial
direction next to each other in assigned cylinder sections, at least one
cylinder section has several selectable set positions located next to each
other. Several selectable set positions are assigned to each cylinder
section to which a printing plate is assigned. The "rough position" of the
plate is therefore determined by the selection of the cylinder section.
The "fine position" within the cylinder section is determined by the
selection of a set position from several set positions which are located
next to each other.
While preferred embodiments of a method and apparatus for axially
positioning a printing plate in accordance with the present invention have
been set forth fully and completely hereinabove, it will be apparent to
one of skill in the art that a number of changes in, for example, the size
of the cylinder, the type of plate secured to the cylinder and the like
can be made without departing from the true spirit and scope of the
present invention which is accordingly to be limited only by the following
claims.
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