Mechanism for transporting printing plates

A mechanism for transporting printing plates includes a swiveling lifting cylinder carrying on its extendable and retractable piston rod a dish-shaped plate which is equipped with suction elements. The printing plates are stacked in inclined positions in a plate holder. When so stacked, the coated, photoconductive sides of the printing plates face downwards and are protected from damage by sheets. For transporting a printing plate to an exposure table, the dish-shaped plate of the lifting cylinder is lowered onto the uncoated side of the printing plate which lies on top of the stack in the plate holder until the suction elements rest on the printing plate. Then, reduced pressure is applied to the suction elements so that they grip the printing plate by suction, and the piston rod is partially retracted into the lifting cylinder. Then the lifting cylinder swivels to a vertical position and places the now horizontally lying printing plate on a conveyor track where it is engaged by rollers and is further transported, after the reduced pressure of the suction elements has been released.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Disclosure 
The present invention relates to a mechanism for transporting printing 
plates from a magazine or plate holder, in which the plates are stacked, 
to an exposure station with the aid of suction air. 
2. Description of the Prior Art 
Lettered and imaged printing masters which are directly suitable for 
printing are manufactured in such a way that the printing plates are first 
electrostatically charged and that an original is then projected imagewise 
upon the individual plate. After this exposing procedure, the printing 
master is developed with a developer, fixed and decoated and is then ready 
for printing. 
U.S. Pat. No. 4,006,984 discloses an apparatus for the manufacture of 
printing masters by electrophotographic means, in which the individual 
printing plate is picked up from a stack in a plate holder by a transport 
device comprised of a transport carriage with a reduced pressure-suction 
means. The transport carriage transfers the printing plate to an exposure 
platform. Charging of the individual printing plate and transporting it to 
the exposure station are combined in a time-saving manner by mounting at 
the front of the transport carriage a corona charging-station for the 
electrostatic charging of the printing plates. The corona charging-station 
extends transversely to the direction of motion of the carriage. The 
carriage runs on two guide rails and is driven by a motor positioned on 
top of it. The carriage engages via a gear wheel with a rack-and-pinion 
gear which is arranged parallel to the direction of motion of the 
transport carriage. The transport carriage has a vacuum plate which is 
attached to its underside and which is, by a number of holes, connected 
with a vacuum pump. When the transport carriage is placed upon the upper 
side of the printing plate which lies on top in the plate holder, reduced 
pressure is generated and the printing plate is sucked to the vacuum 
plate. The transport carriage is then displaced in the direction of the 
exposure platform by means of the motor. As soon as the carriage has 
reached its position above the exposure platform, it is lowered. The 
vacuum is then released so that the printing plate is set free and is 
deposited on the exposure platform. The exposure platform is also designed 
as a vacuum plate; and, under the action of reduced pressure, the printing 
plate is firmly urged against the platform. 
In this known apparatus, the printing plates are stacked in the plate 
holder with their photoconductive layer facing upwards. The coated side is 
thus sucked to the vacuum plate of the transport carriage. When a fresh 
supply of printing plates is placed into the plate holder or when the 
apparatus is opened, the printing plates which are still contained in the 
plate holder may be prematurely exposed by the light which falls in. As a 
result, the printing quality of the ready-developed master may be 
impaired. When the individual printing plate is removed from the stack, 
the photoconductive, coated side of the plate is contacted by suction 
means. Although these suction means allow a far gentler transport of the 
printing plate as compared with the rollers or webs in known apparatuses, 
mechanical or physical defects on the developed printing master cannot be 
precluded. 
In U.S. Pat. No. 4,149,798, a transport station for printing masters is 
described which includes a stacking area containing a supply of printing 
masters. A paper disposal area is provided for the sheets of paper which 
are interposed between the individual masters in the stack. By means of a 
control mechanism equipped with a number of suction cups, the printing 
masters are transported from the stacking area to a conveyor. The control 
mechanism is pivotally attached to a support arm which is connected to a 
motor via a gear mechanism. Thus, the control mechanism is adapted to 
perform a lateral sliding movement back and forth. The uppermost printing 
plate in the stack is picked up by at least four suction cups of the 
control mechanism. Then the control mechanism swings upwards; and, at the 
same time, the support arm mechanically approaches the conveyor. When the 
vacuum in the suction cups is released, the control mechanism pivots 
downwards and deposits the printing master on the conveyor. A second 
control mechanism positioned above the paper separation sheet engages the 
sheet, picks it up and conveys it to the paper disposal area. 
The conveyor transports the printing master to an exposure platform which 
has a plurality of holes on its upper surface and which comprises a lower 
chamber connected to a vacuum pump by a vacuum line. After the printing 
master has adopted the correct position on the surface of the exposure 
platform, a vacuum is applied; and the master is thus securely retained on 
the platform. The exposure system used to expose the printing master 
comprises a movable carriage to which a corona charging device and a light 
reflecting mirror are attached. A laser which emits modulated laser light 
is arranged in such a way that the light scan emitted by the laser is 
deflected by the mirror and impinges upon the printing master retained on 
the exposure platform in a plane which is approximately perpendicular to 
the surface of the master. 
Also, in this case, the printing masters are stacked in a magazine with 
their coated, photoconductive sides facing upwards. It may, therefore, 
happen that the master lying on top is prematurely exposed when the 
apparatus is opened or when the stack is replenished. In the subsequent 
exposure and development of the printing master, this may have a negative 
effect on the quality of the master which is ready for printing. Just as 
in the first-mentioned prior art apparatus, the photoconductive layer of 
the printing master is contacted by suction means when the topmost 
printing plate is removed from the stack. Again, this may lead to 
mechanical or physical defects on the finished printing master. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to improve a mechanism 
of the aforementioned kind in such a way that the coated, photoconductive 
side of the printing plate is not mechanically contacted during transport 
from the plate holder to the exposure platform and is, to a large extent, 
protected from premature exposure. 
According to the invention, this object is achieved by a mechanism of the 
kind described above, which has a swiveling lifting cylinder equipped with 
a piston rod which may be extended from and retracted into the lifting 
cylinder and which carries a dish-shaped plate for gripping by suction and 
depositing the uppermost printing plate in a stack of printing plates, the 
lifting cylinder being adapted to swivel about a pivotal point between a 
receiving position and a depositing position of the printing plate. 
In a preferred embodiment of the invention, the dish-shaped plate is 
provided with suction elements for gripping by suction, retaining, and 
depositing the printing plate on a horizontal conveyor track. This 
conveyor track may be a table. The printing plate is transported along 
this table to an exposure table arranged behind the track. The plate 
holder or magazine is arranged in an inclined position with respect to the 
perpendicular (i.e., the vertical) and the lifting cylinder, in its 
receiving position, points perpendicularly to the uncoated side of the 
uppermost printing plate. At the same time, the dish-shaped plate extends 
parallel to the uncoated side of the printing plate and is placed upon the 
plate in order to pick it up from the stack. 
To reiterate in somewhat different terms, the present invention provides a 
mechanism for transporting printing plates from a stack of plates in a 
plate holder to an exposure station with the aid of suction, the stack of 
printing plates including an uppermost printing plate. The mechanism 
includes a swivelable lifting cylinder and a piston rod coupled with the 
lifting cylinder. The piston rod is extensible from and retractable into 
the lifting cylinder. The mechanism includes means for selectively 
gripping by suction the uppermost printing plate in the stack of printing 
plates and for depositing that printing plate elsewhere. The selective 
gripping means includes a dish-shaped plate carried by the piston rod. The 
mechanism also includes means for accommodating swiveling movement of the 
lifting cylinder between a receiving position in which the uppermost plate 
is gripped by the selective gripping means and a depositing position in 
which that same printing plate is deposited elsewhere. 
A horizontal conveyor track cooperates with the lifting cylinder to receive 
printing plates which have been swivelably moved into the depositing 
position. The selective gripping means may be means for gripping by 
suction, retaining and depositing the uppermost printing plate on the 
horizontal conveyor track. This selective gripping means includes suction 
elements on the dish-shaped plate. 
Each printing plate includes an uncoated side. The horizontal conveyor 
track defines a vertical direction which is perpendicular to the conveyor 
track, and the plate holder is disposed in an inclined position with 
respect to this vertical direction. The lifting cylinder, when in the 
receiving position, points to the uncoated side of the uppermost printing 
plate and is disposed generally perpendicularly to the uppermost printing 
plate. The dish-shaped plate extends in parallel relationship to the 
uncoated side of the uppermost printing plate when the lifting cylinder is 
in the receiving position. Thus, the dish-shaped plate may be placed on 
the printing plate to pick it up from the stack of plates. 
The plate holder includes an upper end and a lower end, the upper end being 
disposed vertically above the lower end. Each printing plate has a coated 
side opposite the uncoated side. The coated side includes a 
photoconductive layer. Each printing plate has a protective sheet on the 
coated side to protect the coated side from damage. The mechanism includes 
an air jet at the upper end of the plate holder, the air jet cooperating 
with the lifting cylinder and being so disposed as to direct a stream of 
air almost tangentially with respect to the photoconductive layer on the 
coated side of the uppermost printing plate as soon as the lifting 
cylinder picks up the uppermost printing plate from the stack. Thus, the 
air jet contributes to detachment of the protective sheet from the coated 
side of the printing plate. 
The means for accommodating the swiveling movement of the lifting cylinder 
includes means for effecting movement through an angle of greater than 
90.degree. between the receiving position of the lifting cylinder, in 
which the uppermost printing plate is inclined with respect to the 
vertical direction, and the depositing position, in which position the 
printing plate is horizontally disposed for deposit on the horizontal 
conveyor track. 
The horizontal conveyor cooperates with an exposure table to which printing 
plates are transported by rollers. The exposure table is disposed at a 
certain level which is vertically above the lifting cylinder at least when 
the lifting cylinder is in the receiving position. Thus, the exposure 
table and the lifting cylinder together define an upward direction. In the 
depositing position of the lifting cylinder, the dish-shaped plate of the 
lifting cylinder extends horizontally. Specifically, in the depositing 
position, the photoconductive layer of that particular printing plate 
which is retained by the suction elements faces in the upward direction 
and the uncoated side of the printing plate is at the same level as the 
exposure table. 
The horizontal conveyor track is, of course, located generally in a 
horizontal plane. The aforementioned rollers are grooved rollers, and each 
printing plate includes opposite longitudinal edges. The grooved rollers 
are positioned in the plane of the conveyor track and engage by their 
grooves the opposite longitudinal edges of the printing plate during 
transport of the printing plate to the exposure table. 
It is an advantage of the present invention that the printing master, for 
example a printing plate, lying in the stack of plates with its 
photoconductive, coated side facing downwards, is, with the aid of the 
rotatable swiveling or lifting cylinder, gripped by suction exerted on its 
uncoated side, is then turned to adopt a horizontal position with its 
coated side facing upwards and is, in this position, transported to the 
exposure table. It is thus ensured that the photoconductive layer of the 
printing plate is neither mechanically contacted nor prematurely exposed 
during the entire transport from the plate holder to the exposure 
platform. 
BRIEF DESCRIPTION OF THE DRAWING 
One embodiment of the invention is now described in detail by reference to 
the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A transport station for the printing plates 9 includes a swiveling lifting 
cylinder 2 equipped with a piston rod 7 which may be extended from and 
retracted into the lifting cylinder. The printing plates 9 are stacked in 
a plate holder 10 in such a manner that each individual printing plate 
within the stack 1 is positioned with its photoconductive, coated side 
facing downwards. These sides of the plates, i.e., the undersides, are 
protected by a sheet 19 consisting of paper, plastic, film or similar 
material, so that any two plates 9 in the stack are separated by a sheet. 
At its end projecting from the lifting cylinder 2, the piston rod 7 
carries a dish-shaped plate 8 to which several suction elements 3 are 
attached. The lifting cylinder is adapted to swivel about a pivotal point 
11, from an oblique position to a vertical position, as indicated by the 
double arrow A--A. 
The plate holder 10 is arranged in inclined position with respect to the 
vertical. At the upper end of the plate holder 10, an air jet 13 is fixed 
to a bent support arm 20. The air jet 13 is adjusted in such a way that 
its air stream is almost tangentially directed to the underside of the 
printing plate 9 when the lifting cylinder 2 picks up the printing plate 
from the stack 1. The lifting cylinder 2, when in its receiving position 
(i.e., the position shown in solid lines), has been swiveled about the 
pivotal point 11 so that it points vertically to the uncoated side of the 
uppermost printing plate 9 of the stack 1. In the receiving position, the 
dish-shaped plate 8 extends parallel to the uncoated side of the printing 
plate 9 and is placed upon the printing plate. Then, reduced pressure is 
applied to the suction elements 3 so that they adhere to and retain the 
printing plate 9. The piston rod 7 is then partially retracted into the 
lifting cylinder until the printing plate 9 has adopted a position 
parallel to the plates 9 in the stack, which is indicated by a broken line 
in the drawing. In this position, the air stream from the air jet 13, 
which is almost tangentially directed to the photoconductive layer on the 
underside of the printing plate 9, has detached the greatest part of the 
sheet 19 (which sheet is for protecting the coated side of the printing 
plate from damage). The sheet 19, usually a sheet of paper, is blown by 
the air stream into a receiving tray 21 positioned below the exposure 
table 4. Then, the lifting cylinder 2 is swiveled (via a power source 
shown schematically at 22) about the pivotal point 11 into its vertical 
depositing position so that the printing plate 9 is moved into the plane 
of a conveyor track 12. 
The swiveling angle of the lifting cylinder 2, between the inclined 
receiving position of the printing plate 9 in the plate holder 10 and the 
horizontal depositing position on the conveyor track 12, is greater than 
90.degree. and ranges usually between 120.degree. and 150.degree.. 
Rollers 14 provided with grooves are arranged in the plane of the conveyor 
track 12. These rollers engage by their grooves the opposite longitudinal 
edges of the printing plate 9. As soon as the reduced pressure in the 
suction elements 3 is released, the printing plate 9 is set free and is 
transported by the driven rollers 14 along the conveyor track 12 towards 
the exposure table 4. On the exposure table 4, the printing plate 9 lies 
on a vacuum plate. As soon as the printing plate has adopted the correct 
position on the table, it is firmly retained thereon by creating a vacuum. 
A horizontally displaceable exposure carriage 16 is situated above the 
exposure table 4 and is equipped with optical means for scanning an 
original 18 and exposing the printing plate 9. Since these processing 
stations comprise devices which are known in the art, they are not 
described in further detail. 
A corona 15 is fastened to the underside of the exposure carriage 16. When 
the exposure carriage is horizontally displaced, the printing plate 9 is 
charged by the corona and is subsequently exposed. After exposure, the 
printing plate 9 is further conveyed to a developing table 5 by the 
rollers 14. The developing table 5 is connected to a drive shaft 6 
arranged below the table. The developing table 5 can be horizontally moved 
forward and backward along this drive shaft in the direction of the double 
arrow B--B. Via a developing unit 17 which is positioned above the 
developing table, a developer coat, composed of a mixture of carrier 
particles and toner, is applied to the surface of the printing plate by a 
magnetic brush, while the printing plate 9 is guided underneath the 
developing unit 17. The developed printing plate is then transported into 
a fixing device (not shown) where the toner in imagewise distribution is 
fixed, i.e., it is fused to the printing plate surface by the action of 
radiant heat. From the fixing station, the imaged printing master is taken 
to a decoating station for the removal of the image areas on the 
photoconductive layer and is subsequently suitable for use in an offset 
printing press.