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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device, in the form of a magazine, for removing
and/or supplying printing plates from or to a plate cylinder of a printing
press, in particular for the automatic or semi-automatic changing of
printing plates, with a plate-removing apparatus and a plate-supplying
apparatus.
A device of the initially mentioned kind is known from European patent
application 0 435 410. The purpose of said device is to automate the
changing of printing plates.
The magazine holds old, used plates. For removal, the used printing plate
is released from the plate cylinder at one end and is then--through
appropriate rotation of the plate cylinder--partially inserted into the
magazine. Subsequently, the other end of the printing plate is released by
the tensioning device of the plate cylinder and the entire printing plate
is introduced into the magazine with the plate-removing apparatus.
Subsequently, a new printing plate to be used is taken from the magazine
by means of the plate-supplying apparatus. First, one end of the printing
plate is inserted into the corresponding clamping device of the plate
cylinder, where it is clamped, and then--through rotation of the plate
cylinder--the printing plate is removed completely from the magazine and
is drawn around the outer cylindrical surface of the plate cylinder. Then,
the other end of the printing plate is clamped and the plate is tensioned
in the circumferential direction.
If the printing press comprises a plurality of printing units, a magazine
is associated with each printing unit. For the removal and/or supply of
printing plates, it is necessary for the magazine to be brought from a
more or less vertical position into an obliquely inclined position in
which the lower end of the magazine is opposite the outer cylindrical
surface of the plate cylinder. Since the space between the individual
printing units is tight on virtually all printing presses, only little
space is available for the magazines. Consequently, the removal of old,
used printing plates from-the magazine and/or the introduction of new, yet
to be used printing plates into the magazine is associated with
corresponding difficulties.
SUMMARY OF THE INVENTION
The object of the invention is to create a device of the initially
mentioned kind, said device, while being of simple construction, reliable
operation and small design, permitting the removal and/or supply of
printing plates and also allowing printing plates to be introduced into
and removed from the magazine in simple manner.
The object of the invention is achieved in that at least one cassette for
the printing plates is removably associated with the magazine. This has
the advantage that the new, yet to be used printing plates can be
introduced into the cassette outside of the magazine, with the result
that, in order to "load" the magazine, it is merely necessary to introduce
the cassette into the magazine. In similar manner, the simple removal of
old, used printing plates from the magazine is possible in that the used
printing plates are introduced by means of the plate-removing apparatus
into the cassette in the magazine, with the result that, for removal, it
is merely necessary to remove the cassette, filled with used printing
plates, from the magazine. The device according to the invention is
suitable either for the removal of old, used printing plates or for the
supply of new, yet to be used printing plates or, alternatively, also for
the removal and supply of printing plates; that is, there is then a change
of printing plates in which a used printing plate is accepted and a yet to
be used printing plate is supplied from the magazine.
If the cassette both accepts used printing plates and also delivers yet to
be used printing plates, it comprises a holding space for the used
printing plates and a holding space for the yet to be used printing
plates. To commence operation of the printing press, it is then merely
necessary for this one cassette to be associated with the corresponding
printing unit.
Alternatively, however, it is also possible for two cassettes to be
removably associated with the magazine, of which cassettes a first
cassette serves to accept used printing plates and a second cassette
serves to deliver yet to be used printing plates. Consequently, for
operation, two cassettes must be associated with each printing unit of the
printing press.
The association of the cassette or cassettes is particularly simple if the
magazine comprises at least one holding shaft for insertion of the
cassette or cassettes. If two cassettes must be associated with the
magazine, preferably two holding shafts are provided on the magazine.
Moreover, it is advantageous to employ a pressing-down device, said
pressing-down device engaging the yet to be used printing plates remaining
in the cassette transversely with respect to the planes thereof, in order
to prevent their tipping out from the cassettes. Otherwise, such
tipping-out might occur particularly when, after an automatic plate change
has been performed, the magazine is swiveled back into its vertical
position.
Preferably, at least the cassette holding the used (old) printing plates
comprises a base with adjoining, U-shaped upper and lower edge regions.
Preferably, the U-shaped leg of the upper edge region, forming a holding
edge, is longer than the corresponding U-shaped leg of the lower edge
region. This makes it possible for the rear edge of a used printing plate
first of all to be pushed far under the longer U-shaped leg of the upper
edge region and then be pulled back, with the result that the front edge
also comes under the corresponding U-shaped leg of the lower edge region,
without the rear edge of the printing plate being released by the longer
U-shaped leg in the upper edge region. Preferably, the cassette for the
new printing plates is of the same design as the cassette for the old
printing plates.
It has already been explained hereinbefore that the lifting of a new
printing plate from the pile of printing plates inside the cassette is
effected not simultaneously over the whole surface area, but is staggered
in such a manner that air is able to get between the plates, in order to
prevent the printing plates from "sticking together". For example,
suction-gripping by the rear, upper row of suckers may be effected first,
followed by the middle row and finally by the lower row of suction
elements. Moreover, it may preferably be provided that the cassette
holding the printing plates to be used comprises spacers, said spacers
being disposed between adjacent printing plates. Said spacers prevent a
vacuum from forming between the individual printing plates. They may be in
the form of plastic tabs. Preferably, they are adapted to be fixed on the
cassette in the locking seat. Consequently, when a cassette is being
filled, a spacer (or a plurality of spacers) is first clipped into the
cassette in such a manner that it is disposed on the surface of an
inserted printing plate. Only then is a further new printing plate
inserted into the cassette. The spacers are so flexible that they yield
when a below-lying printing plate is removed.
Moreover, it is particularly advantageous if the individual cassettes each
comprise a marking, particularly a color marking, which relates to the
associated printing unit, particularly to the color of the ink to be
printed with the printing unit. If all the cassettes for the individual
printing units have been furnished with printing plates outside of the
printing press, they can, on the basis of said marking, be inserted in
particularly simple manner into the magazines of the individual printing
units without there being any confusion.
The magazine according to the invention is preferably of layered
construction, with the cassette holding the used printing plates being
disposed in a lower layer and with the plate-removing apparatus associated
with the aforementioned cassette being disposed in a following layer and
with the cassette holding the yet to be used printing plates being
disposed in a further following layer and with the plate-supplying
apparatus associated with the aforementioned cassette being disposed in a
following, outer layer.
The invention relates further to a process for removing and/or supplying
printing plates from or to a plate cylinder of a printing press with a
plurality of printing units, in particular for the changing of printing
plates, wherein individual part-actions, such as, in particular,
unclamping of the printing-plate rear edges and/or unclamping of the
printing-plate front edges and/or removing of the used printing plates
and/or supplying of the yet to be used printing plates and/or clamping of
the printing-plate front edges and/or pressing-down and clamping of the
printing-plate rear edges, are effected consecutively, i.e. one after the
other, as a function of the smallest positioning travel of the individual
plate cylinders on the corresponding printing units before the next
part-action is performed in similar manner. Consequently, according to the
invention, the removal, supplying or changing of printing plates is not
performed in full on one printing unit of the printing press before then
being effected on the next printing unit of the printing press, but the
individual--preferably automatic--working steps (part-actions) are carried
out consecutively on the corresponding printing units, with the
printing-unit sequence in the performance of said part-actions being
determined by the criterion of the smallest positioning travel of the
plate cylinders. This makes it possible for printing plates to be removed
or supplied or changed in an extremely short time on all printing units.
Preferably, a start is made with the first-required part-action on that
printing unit whose plate cylinder needs to be moved by the smallest
positioning travel out of the current angular position in order to attain
the angular position necessary for performance of the part-action.
In the case of fully automatic operation, the operator may, preferably from
a control desk, trigger the fully automatic changing of printing plates or
the fully automatic unclamping of a used printing plate or the fully
automatic clamping of a new printing plate. For this purpose, it is
necessary first of all to select a command which defines the required
operation. Subsequently, the fully automatic operation is then started by
the operator (by pressing a button). The part-actions to be performed then
take place according to the aforementioned principle of optimization.
In addition to said fully automatic operation, however, a semi-automatic
operating mode is also conceivable. This is likewise carried out with a
minimum number of actions on the part of the operator and is intended at
the same time to involve the minimum potential for operator errors. The
operator merely uses control elements in order to control the process
relating to the changing of printing plates or the supply or removal of
printing plates; that is, the operator need not handle the printing plates
himself even in the case of semi-automatic operation.
In order, in semi-automatic operating mode, to render operation as
easy-to-follow and error-free as possible, the invention provides for only
a few control elements, with which, however, different functions can be
executed. Consequently, for example, a control element in the form of a
button permits, when pressed, the performance of different part-actions
(for example, the clamping of the printing plate or the unclamping of the
printing plate or, alternatively, various positioning operations of the
respective plate cylinder). For this purpose, the performance of
individual part-actions is stored in such a manner that the repeat
actuation of a control element that triggered the previous part-action
triggers another, different part-action when actuated again. This provides
maximum operational reliability with a minimum of control elements.
The invention is illustrated on the basis of a specimen embodiment with
respect to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a printing unit of a printing press in a schematic
representation with a magazine in the starting position;
FIG. 2 shows the magazine from FIG. 1 in a center position;
FIG. 3 shows the magazine in the plate-changing position while a new
printing plate to be used is supplied to the plate cylinder of the
printing press;
FIG. 4 shows a representation according to FIG. 3, with, however, the
printing plate already having been clamped onto the plate cylinder;
FIG. 5 shows the return of the magazine into the starting position;
FIG. 6 shows the movement to the center position in order to accept a used
printing plate;
FIG. 7 shows the magazine in the plate-changing position during acceptance
of the used printing plate;
FIG. 8 shows a representation according to FIG. 7, with, however, the
printing plate already being completely in a cassette of the magazine;
FIG. 9 shows the magazine once again in the starting position;
FIG. 10 shows a longitudinal section through the magazine;
FIG. 11 shows a longitudinal section through the magazine according to FIG.
10, but in a different plane;
FIG. 12 shows a cross section through the magazine;
FIG. 13 shows a schematic view in the longitudinal section during the
supply of a used printing plate to the magazine;
FIG. 14 shows a representation according to FIG. 13, but with the printing
plate introduced further;
FIG. 15 shows the magazine in the longitudinal section with the printing
plate completely introduced;
FIG. 16 shows a representation according to FIG. 15, but with the front
edge of the printing plate being introduced into a cassette of the
magazine;
FIG. 17 shows a cross section through the magazine in the region of a
plate-removing apparatus;
FIG. 18 shows a longitudinal section through the cassette;
FIG. 19 shows a control panel on the respective printing units of the
printing press;
FIG. 20 shows a flow diagram for the fully automatic changing of printing
plates;
FIG. 21 shows a flow diagram for the semi-automatic changing of printing
plates;
FIG. 22 shows a flow diagram for the semi-automatic removal of a printing
plate; and
FIG. 23 shows a flow diagram for the semi-automatic supplying of a printing
plate.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In order to provide for automatic or semi-automatic changing of printing
plates--that is, to remove an old, used printing plate and then to supply
a new printing plate to be used to the plate cylinder 1 of a printing unit
2 of a printing press 3--the printing unit 2 comprises a device in the
form of a magazine 4. The magazine 4, which, in the case of a printing
press 3 with a plurality of printing units 2, is provided on each printing
unit 2 of the printing press 3, may also be used merely to supply a new
printing plate to be used or merely to remove an already used printing
plate (FIG. 1 to 9).
In FIG. 1, the magazine 4 is in its starting position (vertical position).
In this idle position, the magazine 4 is secured (locked) against tilting.
Normal printing-press operation (printing mode) is possible only with the
magazine 4 in this lower, vertical position.
The magazine 4 comprises two holding shafts or receiving chutes 5 and 6,
into which cassettes 7 and 8, respectively, are insertable from above
(FIG. 1). The cassette 7 is used to hold old printing plates which have
already been used in the printing press 3. The cassette 7 is of such
design that it is capable of holding a plurality of, for example five,
used printing plates. Said printing plates form a printing-plate pile
inside the cassette 7; that is, the individual printing plates are in flat
contact with one another. The cassette 8 is used to hold new printing
plates that are yet to be used. It, too, is capable of holding a plurality
of, particularly five, printing plates simultaneously, with, once again,
said printing plates being in flat association with one another. In order
to remove the used printing plates, it is thus merely necessary to
withdraw the cassette 7 out of the holding shaft 5. Once outside of the
printing press 3, the cassette 8 can be furnished with new printing plates
yet to be used. Once this has been done, the cassette 8 is inserted into
the holding shaft 6 of the magazine 4, with the result that it is
available for supplying the plate cylinder 1 of the corresponding printing
unit 2.
Described hereinbelow are the individual positions of the magazine 4 which
are assumed for the removal and/or supply of printing plates. If the plate
cylinder 1 is to be supplied with a new printing plate 9, the magazine 4
moves--as shown in FIG. 2--vertically upwards into a center position and
then--as shown in FIG. 3--swivels into an oblique position (approximately
45.degree., for example). By means of a plate-supplying apparatus (still
to be described in greater detail) of the magazine 4, the printing plate 9
to be used is then supplied to the plate cylinder 1 and is clamped thereon
(FIG. 4). Subsequently, the magazine 1 then swivels back into its vertical
position and is then lowered again into the lower position (starting
position) as shown in FIG. 5.
The printing process can now be carried out. When the printing job has been
performed, the printing plate 9 must be removed from the plate cylinder 1.
For this purpose, a lifting device, in turn, lifts the magazine 4 into the
center position (FIG. 6). Subsequently, as shown in FIG. 7, the magazine 4
is swiveled into the oblique position and--through releasing of the plate
rear edge and backward rotation of the plate cylinder 1 --the used
printing plate 10 is partially inserted into the magazine 4 (FIG. 7). As
shown in FIG. 8, the used printing plate 10 is then pulled completely into
the cassette 7 by a plate-removing apparatus (still to be described in
greater detail) of the magazine 4. Next, the magazine 4 is again swiveled
into its vertical position and then--as shown in FIG. 9--is lowered into
the starting position.
Of course, it is also possible to combine the removal and supply of
printing plates in order to effect the changing of printing plates. This
means that, in the oblique position, a used printing plate 10 is first
accepted by the magazine 4 and a new printing plate is then supplied to
the plate cylinder 1. Once this has been done, the magazine 4 swivels back
into the vertical and is lowered into the starting position.
Hereinbelow, the design of the magazine 4 is to be described in greater
detail with reference to FIG. 10 to 12.
For graphical reasons, the magazine 4 is shown in FIG. 10 and 11 in a
horizontal position in relation to the side edges of the drawing sheet. It
should, however, be pointed out that the positions shown in FIG. 10 and 11
correspond to the oblique positions shown in FIG. 3, 4, 7 and 8.
The magazine 4 is of layered construction. It comprises an outer layer 11,
which holds the cassette 7. Accommodated in a following layer 12 is a
plate-removing apparatus 13, which is associated with the aforementioned
cassette 7. The cassette 8 is disposed in a following layer 14.
A further following layer 15 holds a plate-supplying apparatus 16, which
cooperates with the printing plates 9 of the cassette 8.
The plate-removing apparatus 13 comprises first holding means 17, which are
in the form of activatable first suction elements 18. The suction pads 19
of the first suction elements 18 can be extended towards the printing
plates 10 (for the sake of clarity, only one printing plate 9/10 is shown
in each of FIG. 10 and 11). The first suction elements 18 are disposed on
a first carriage 20, which is adapted to be moved along a first guide 21.
As shown in FIG. 17, the guide 21 comprises two spaced-apart,
parallel-extending guide parts 22, which are in the form of guide rods 23.
The guide rods 23 are encompassed with little play by guide parts 24 of
the first carriage 20.
The first carriage 20 is adapted to be moved along the first guide 21 by
means of a driving apparatus 25. The driving apparatus 25 comprises a
fixed, non-ferromagnetic tube 26 (an aluminium tube, for example), which
extends from the top side to the bottom side of the magazine 4. Situated
inside the tube 26 is a magnetic piston 27, which is adapted to be moved
backwards and forwards inside the tube 26 by means of a pressure medium in
addition to being positionable in desired positions. Situated on the first
carriage 20 is a ferromagnetic component which is in the form of a steel
ring 29. Consequently, a movement of the magnetic piston 27 has the effect
that the steel ring 29 and therefore the carriage 20 are moved through the
intermediary of the magnetic field. Such a design provides a flexible
coupling and, moreover, the carriage is movable from a position at the
extreme top in the magazine 4 (shown by solid lines in FIG. 10) into a
position at the extreme bottom (shown by broken lines in FIG. 10).
As shown in FIG. 17, a suction element 18 is disposed on either side of the
driving apparatus 25. Each suction element 18 is attached to a lever 30,
which is adapted to be swiveled towards the printing plate 10 by means of
a hinge 31. The position of the levers 30 is determined by a
forced-control device 32 (see also FIG. 13), which is formed by a roller
33 connected to each lever 30, said roller 33 running in a location-fixed
guide rail 34. Each guide rail 34 comprises in the upper region of the
magazine 4 a bevelled section 35 (FIG. 13), with the result that, with the
carriage 20 moving into an upper position, the rollers 33 contact the
bevelled sections 35 and thereby swivel the levers 30 and thus the suction
elements 18 towards the printing plate 10. Springs 115 serve to return the
lever 30 and to make the rollers 33 contact the bevelled sections 35.
Disposed on opposite sides in the lower region of the magazine 4 are
actuatable holders-down 36, which serve to engage the printing plate 10 in
said region. Furthermore, guide rollers 37, 38 and 39 are disposed in the
lower region of the magazine 4.
Hereinbelow, there is a functional description of the removal of a used
printing plate 10 from the plate cylinder 1 into the cassette 7 of the
magazine 4. For this purpose, first of all, the magazine 4 is--as shown in
FIG. 6 and 7--brought into the required oblique position. Subsequently, a
rear-edge clamping device 40 of the plate cylinder 1 opens and releases
the there-clamped, angled printing-plate rear edge 41. Owing to the
inherent elasticity, the rear end of the printing plate 10 consequently
strikes against the guide roller 37 (FIG. 13). Subsequently, through
backward rotation (arrow 42) of the plate cylinder 1, the printing plate
10 is inserted into the cassette 7 of the magazine 4. The guide rollers
37, 38 and 39 assist with the introduction of the rear-edge end of the
printing plate 10. Guide rails 116 may be provided, said guide rails 116
sliding in cutouts of the printing-plate rear edge 41. Said introduction
is shown by a dotted line in FIG. 13 and by an unbroken line in FIG. 14.
When approximately one-third of the printing plate 10 has been inserted
into the magazine 4, the suction elements 18 of the carriage 20 (the
carriage 20 being in the lowermost position inside the magazine 4) are
activated; that is, the suction pads 19 move towards the printing plate 10
to be held and firmly adhere by suction to the printing plate 10. Next,
with simultaneous further backward rotation of the plate cylinder 1, the
carriage 20 moves into its upper position, as a result of which the
printing plate 10 is pulled completely into the magazine 4, with the front
edge 44 of the printing plate 10 also being unclamped. When the carriage
20 enters the upper end region of the magazine 4, the rollers 33 contact
the bevelled sections 35 and swivel the levers 30, with the result
that--as shown in FIG. 15--the angled printing-plate rear edge 41 comes
under a holding edge 43 of the cassette 7. Subsequently, the holders-down
36 press down the printing plate 10 in the region of its front edge 44
(FIG. 16), with the result that the front edge 44 comes to lie at a lower
position than a holding edge 45 of the cassette 7. Through the force of
gravity and/or through movement of the carriage 20, the front edge 44 is
then brought under the holding edge 45 through pulling-down of the
printing plate 10. Consequently, the printing plate 10 is safely disposed
in the cassette 7. Particularly if a plurality of already used printing
plates 10 are to be accommodated in the cassette 7, it is necessary for
the last-inserted printing plates 10 to be pulled down by means of the
carriage 20 and to be held by the holders-down 36, so that they come under
the holding edge 45, since, owing to relatively great stresses at the
start of the printing plate, the force of gravity alone is no longer
sufficient to move the printing plates 10 into said position.
The removal of the used printing plates 10 from the magazine 4 is
accomplished ill simple manner in that the cassette 7 is withdrawn from
the associated holding shaft 5.
FIG. 18 shows a longitudinal section through a cassette 7. The cassette 7
comprises a base 46, which is adjoined by U-shaped upper and lower edge
regions 47, 48. The upper edge region 47 comprises a U-shaped leg 49 and
the lower edge region 48 comprises a U-shaped leg 50, which forms the
holding edge 45. The length x of the U-shaped leg 49 is greater than the
length y of the U-shaped leg 50. The clear distance between the ends of
the U-shaped legs 49 and 50 is selected such that a printing plate 10 to
be inserted is first slid under the U-shaped leg 49 and is then swung into
the interior of the cassette 7, with the front edge 44 passing the
U-shaped leg 50. Subsequently, the printing plate 10 is then displaced in
such a manner that its front edge 44 passes under the U-shaped leg 50,
without, however, the locating action of the U-shaped leg 49 being
lost--thanks to the greater length of the U-shaped leg 49. Consequently,
the printing plate 10 is safely accommodated inside the cassette 7. The
procedure is similar when removing a printing plate 9 from a cassette 8,
insofar as use is made also of a cassette with locating edges.
Each cassette 7 or 8 comprises in its upper region a handle 51 in order to
facilitate insertion and removal from the respective holding shaft 5 or 6
of the magazine 4. In addition, the handle 51 also makes it easier for the
corresponding cassette 7 or 8 to be transported to the printing press.
Furthermore, each cassette 7 or 8 is provided with a marking, particularly
a color marking (this may be disposed, for example, on the handle 51),
said marking relating to the respective printing unit 2 of the printing
press 3. For example, the handle 51 may be of a color corresponding to the
printing ink of the respective printing unit 2. Unambiguous identification
is made possible in this manner.
Reference may be made already at this point to a special feature of the
cassette 8 containing the new printing plates 9 yet to be used, although
the removal of the printing plates 9 from the cassette 8 will be discussed
at a later point hereinbelow. If there is a plurality of printing plates 9
piled one on top of the other inside the cassette 8, then it is possible,
when the uppermost printing plate 9 is removed, for a vacuum to be formed
with respect to the following printing plate 9. This may result in two
printing plates being removed simultaneously by mistake owing to the fact
that they "stick together". To prevent this, a special removal technique
is implemented and will be discussed in greater detail hereinbelow;
moreover, it is possible to provide spacers between the individual
printing plates 9, with the result that the formation of a vacuum is
prevented. The spacers are preferably in the form of plastic tabs. These
can be clipped preferably into locking seats ill the edge regions. An
advantageous further development of the invention provides that the
spacers are in the form of two rows of individual tabs, with, when the
printing plates are being inserted, a tab being placed between every two
printing plates on both sides. It is advantageous for said tabs to be
disposed in the region of the front row of suckers, which goes into action
first. Consequently, when a cassette 8 is being furnished with printing
plates, spacers are first of all clipped in position before a further
printing plate 9 is laid on a printing plate 9 already in the cassette 8.
The spacers are so flexible that they yield when the printing plate below
is removed.
If, after the removal of a printing plate 10, a new, as yet unused printing
plate 9 is to be clamped immediately onto the plate cylinder 1, then the
magazine 4 remains in its oblique position and a new printing plate 9 is
taken from the cassette 8. This is accomplished by means of the
plate-supplying apparatus 16.
In order for a printing plate 9 from the cassette 8 to be supplied to the
plate cylinder 1 by means of the plate-supplying apparatus 16, the
magazine 4 is--as mentioned hereinbefore--in its oblique position in which
support rollers 52 are supported on cylinder bearers 53 associated with
the plate cylinder 1. The plate-supplying apparatus 16 comprises on a
second carriage 54 second holding means 55, which are likewise in the form
of activatable suction elements 56 (second suction elements). As shown in
FIG. 10 and 12, the suction elements are each disposed spaced-apart in
rows in groups of four, with three rows being provided on the second
carriage 54. It is also possible for the lower row of suction elements 56
nearest to the plate cylinder 1 to be equipped with four suction elements
56 and for the other rows each to be provided with three. The suction
elements 56 disposed in the lower row associated with the plate cylinder 1
are attached to levers 57, which are adapted to be swiveled about shafts
58. Pneumatic cylinders 59 are provided for the actuation of the levers
57. Furthermore, the levers 57 are subjected to the force of a spring 60.
Disposed in the upper region of the magazine 4 is a preferably optical
sensor 61, which monitors the position of the associated printing plate 9,
particularly the position of the rear edge 41 thereof. Disposed between
the upper and middle rows of suction elements is an activatable
pressing-down device 62 for engagement of the printing plates 9. In
addition, the magazine 4 comprises at its lower end a displaceable
pressing-on element 63, which is in the form of a pressing-on roller 64
displaceable radially with respect to the plate cylinder 1.
The second carriage 54 is movable along a second guide 66 (FIG. 12) by
means of a piston/cylinder unit 65. The second guide is formed by fixed
profile rails 67, in which run guide rollers 68 of the carriage 54.
For the supplying of a printing plate 9, the lowermost suction elements 56,
associated with the plate cylinder 1, may first of all come into
operation, with the levers 57 being in their non-deflected positions.
Thereafter, the suction elements 56 of the middle row of suckers and then
the suction elements 56 of the upper row of suckers are activated. A
different sequence, such as first the middle row and then the row at the
edge, is conceivable. The non-simultaneous, but consecutive activation of
the rows of suction elements ensures that the uppermost, new printing
plate 9 is lifted in such a manner that no vacuum or only a very small
vacuum is formed with respect to the further printing plate 9 below. This
guarantees that only one printing plate 9 is lifted. As for the rest, the
aforementioned spacers (plastic tabs) may be disposed between the
individual printing plates 9, which additionally counteracts the formation
of a vacuum. When the printing plate 9 has been lifted, the carriage 54 is
pushed towards the plate cylinder 1 by means of the piston/cylinder unit
65. The front edge 44 of the printing plate 9 enters the front-edge
clamping device 69 of the plate cylinder 1, which was appropriately
positioned beforehand. During the above-depicted advance of the carriage
54, the angled printing-plate rear edge 41 slides through under the sensor
61, which registers the correct transport of the printing plate 9. During
the transport of the carriage 54, a bypass in the air supply to the
suckers of the suction elements 56 is activated, since a strong suction
air is required only for the suction-gripping of the printing plate 9.
After the carriage 54 has almost reached its outermost position facing the
plate cylinder 1, the suckers of the lowermost and middle rows of suction
elements 56 are rendered pressureless or are provided only with a weak
vacuum; the printing plate 9 is therefore held only by the uppermost row
of suckers. The purpose of this is so that the printing plate 9 can be
better aligned. Subsequently, the front-edge clamping device 69 is closed,
with the result that the front edge 44 of the printing plate 9 is firmly
clamped. Next, the plate cylinder 1 rotates in the forward direction,
pulling the printing plate 9 onto its outer cylindrical surface. Thanks to
the bypass, the suction elements are provided only with a weak vacuum,
with the result that they still hold the printing plate, but the printing
plate can still be displaced on the suction elements through the rotation
of the plate cylinder. Before the printing-plate rear edge passes the two
upper rows of suckers, the latter are rendered pressureless and brackets
70 ensure that the angled rear edge slides past the suction elements
without collision. Owing to its proximity to the plate cylinder 1, the
printing plate 9 is relatively rigid in the region of the lower row of
suction elements 56, with the result that, for the passage of the angled
printing-plate rear edge 41, a lever 57, in the form of a plate with hinge
and carrying the entire row of suckers, or a plurality of levers 57 are
swivelled into their positions shown in FIG. 10 by means of one or more
cylinders 59, with the result that the printing-plate rear edge 41 is able
properly to pass the row of suckers. Subsequently, the pressing-on roller
64 is moved radially towards the plate cylinder 1, as a result of which
the angled printing-plate rear edge 41 is pressed into the rear-edge
clamping device 40 of the plate cylinder 1. The rear-edge clamping device
40 closes and then tensions the printing plate through appropriate
displacement in the circumferential direction of the plate cylinder 1.
Thereafter, the carriage 54 is moved back to its original position in
order, at the appropriate time, to grip the next printing plate 9.
The device moves back into its starting position in that the cylinders 59
are rendered pressureless, with the result that the springs 60 are able to
ensure that the lever(s) 57 return to their original positions.
Subsequently, the pressing-down device 62 comes into action, ensuring that
the remaining printing plates 9 remain properly in the cassette 8 and are
unable to tip out, particularly when the magazine 4 is swiveled back into
its vertical position.
FIG. 10 shows that the upper and middle rows of suction elements 56 are
associated with elastic brackets 70. This, however, is necessary only for
such stiff printing plates, the rear edges of which do not drop down as a
result of their own weight. The elasticity of the brackets 70 permits the
suction-gripping of the printing plate 9 that is to be used; that is, the
brackets 70 do not disr | | |
