Apparatus for fastening a flexible printing plate

A plate-clamping apparatus suitable for automatic exchanges of plates and has only a narrow clamping channel. The apparatus includes a tie beam, which has clamping bodies that are elastic in the clamping direction and on the ends of which radial forces can be applied by actuating devices, that is elastically disposed in the cylinder groove.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an apparatus for fastening a flexible printing 
plate, on the printing cylinder of a printing machine. 
2. Description of the Prior Art 
DE 31 16 506 C2 discloses an apparatus for fastening a flexible printing 
plate, which has a clamping groove with two groove walls running out at an 
acute angle to the cylinder-jacket surface. Two clamping bodies provide 
the clamping and are divided in the longitudinal direction of the groove 
and clamp the plate leg between themselves and a groove wall. Admittedly, 
this mechanism of clamping the plates permits an automatic exchange of 
plates, however, because of the space needed for the clamping bodies, it 
requires a wide clamping channel which is equivalent to a loss in printing 
area. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a plate clamping mechanism, 
which is suitable for exchanging plates automatically and which has a 
single narrow clamping channel. 
Pursuant to this object, and others which will become apparent hereafter, 
one aspect of the present invention resides in an apparatus for fastening 
a flexible printing plate on a printing cylinder of a printing machine, 
which apparatus includes a tie beam disposed in an axially extending 
groove in the printing cylinder. Springs elastically support the tie beam 
against the bottom of the cylinder groove. A clamping body is carried by 
the tie beam and has clamping surfaces which cooperate with the wails of 
the groove to hold the ends of the flexible printing plate therebetween. 
In another embodiment of the invention the clamping body is fixed to the 
tie beam. It is also possible to accommodate the clamping body in the tie 
beam so that it is movable in a clamping direction and is supported 
elastically on the tie beam so that it can be extended to a stop point. 
The tie beam extends approximately to the end of the cylinder shell and 
can be acted upon by actuating devices with forces directed radially on 
the printing cylinder. 
In still another embodiment of the invention, the clamping body is arranged 
in a groove in the tie beam and is braced elastically against the base of 
the tie beam groove. Sleeves are bolted to the bottom of the clamping body 
with the interpositioning of a stop ring, and the sleeves are inserted 
through a bore holes in the tie beam so as to cover the stop ring. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of the disclosure. For a better understanding of the invention, its 
operating advantages, and specific objects attained by its use, reference 
should be had to the drawing and descriptive matter in which there are 
illustrated and described preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The printing cylinder 1, shown sectionally in FIG. 1, has a cylindrical 
groove 2 which extends in the axial direction and contains acute-angled 
groove walls 3, 4, which extends approximately perpendicularly to the 
shell of the cylinder 1. A clamping body 5 cooperates with the groove 
walls 3, 4 and advantageously has clamping surfaces 6, 7, which are 
parallel to the groove walls 3, 4. The clamping body 5 is disposed fixed 
on a tie beam 8, which is braced by means of compression springs 9 against 
the bottom of the cylinder groove 2. The clamping body 5 may, for example, 
be bolted to the tie beam 8 or pressed into a groove. The tie beam 8, 
together with the clamping body 5, extends at least over the width of the 
printing plate 11 on the outer surface of the printing cylinder 1. 
The printing plate 11 is suspended with a leading plate leg 12 at a channel 
edge formed by the cylinder surface and the groove wall 3. In so doing, 
the plate leg 12 is clamped between the groove wall 3 and the clamping 
surface 6. During a revolution of the printing cylinder 1, which takes 
place subsequent to clamping of the leg 12, the printing plate 11 is 
rolled onto the printing cylinder 1 advantageously by using a 
counterpressure roller or the positioned rubber cylinder. Finally, a 
trailing leg 13 of the printing plate 11 is pressed between the groove 
wall 4 and the clamping surface 7 of the clamping body 5. The insertion of 
the plate legs 12, 13 is facilitated by providing the clamping body 5 with 
inclined slopes. To remove the printing plate 11, the clamping body 5 is 
pressed, together with the tie beam 8, against the force of the spring 9 
deeper into the cylinder groove 2 by a plate-detaching tool 14. In so 
doing, the wedging action of the clamping body 5 against the groove walls 
3, 4 is cancelled and the trailing leg 13 of the plate 11 springs out of 
the groove 2. After the printing plate 11 is uncoiled from the cylinder 
surface, the leading leg 12 of the plate 11 can also be removed by once 
again pressing on the clamping body 5. 
FIG. 2 shows a printing cylinder 16, for which a tie beam 17 extends into 
the cylinder groove 18 up to the ends of the cylinder shell and bearer 
rings 19, 20. Moreover, the clamping body is composed of clamping pieces 
21, which are joined together and accommodated elastically in the tie beam 
17. The division into clamping pieces is advantageous from a manufacturing 
point of view. In addition, good clamping of the printing plate 22 at the 
groove walls is achieved. Moreover, the cylinder groove 18 is 
geometrically identical with the cylinder groove 2 of FIG. 1. Only the 
width of the channel can, under certain circumstances, be kept narrower in 
the case of cylinder groove 18 since, for reasons given further below, the 
plate-detaching tool 14, which is required in FIG. 1, can be omitted. The 
tie beam 17 is braced by means of compression springs 23 in the base of 
the cylinder groove 18 (FIG. 3). Each clamping piece 21 is accommodated in 
a groove 24 of the tie beam 17 (FIG. 4) and is braced with springs 25 
against the bottom of the groove 24. Each clamping piece 21 has clamping 
surfaces, which are not labeled and are similar to those of the clamping 
body of FIG. 1. Two sleeves 27, with which the clamping pieces 21 are 
movably guided in the clamping direction in boreholes 28 of the tie beam 
17, are bolted with screws 26 to the underside of each clamping piece 21 
(FIG. 5). A stop ring 29, which covers the borehole 28, is interposed 
between the sleeve 27 and the head of the screw 26. The clamping pieces 21 
can also be guided differently, for example, by means of pins or the 
sidewalls of the groove 24. At each sidewall 30, 31 of the machine, a push 
rod 32, 33 is disposed, which can be moved through a borehole 34, 35 of 
the cylinder shell of the printing cylinder 16 in the radial direction and 
onto the tie beam 17. 
The printing plate 22 is clamped in the same way as described in the 
previous embodiment of FIG. 1. The plate legs are clamped by the clamping 
pieces 21, which are pressed by the spring-loaded tie beam into the wedge 
formed by the groove walls. So that they lie securely against the plate 
legs, the clamping pieces 21 are cushioned somewhat in the tie beam 17, a 
gap being formed between the stop ring 29 and the borehole 28. For the 
purpose of loosening the printing plate 22, the printing cylinder 16 is 
positioned so that the boreholes 34, 35 of the cylinder shell come to lie 
under the push rods 32, 33. When the push rods 32, 33 are extended, the 
tie beam 17 is pressed against the force of the compression springs 23 in 
the direction of the base of the clamping groove 18. After the gap between 
the stop ring 29 and the borehole 28 (FIG. 5) is overcome, the clamping 
pieces 21 are also carried along, that is, pulled out of the wedge formed 
by the groove walls and the plate legs are freed. Because plate-detaching 
means do not have to be introduced into it, the clamping channel can be 
kept very narrow, for example, 2 mm wide or less. Limits for the 
minimizing are set practically only by the thickness of the printing plate 
and the interests of the manufacturing process. 
FIGS. 6 and 10 show variations for actuating the tie beam, which are 
different from those of FIG. 2. In each case, only the actuating device at 
the left end of the printing cylinder shell is shown, a similar device 
being provided at the right end of the shell. In the case of the printing 
cylinder of FIG. 6, the tie beam 37 extends into the bearer ring 38 and 
ends in the region of a pressure chamber 39. The latter pressure chamber 
39 has a membrane 40, which can be deflected radially onto the tie beam 37 
and is connected with the outside atmosphere by a connecting borehole 41, 
which leads through the cylinder shell. A connection shoe 43 of a 
compressed air source can be placed on the borehole 41 by means of a 
lifting device 42. The connecting shoe 43 has the curvature of the 
cylinder shell (FIG. 7), and its connecting opening 44 advantageously has 
the shape of an elongated hole (FIG. 8). Due to this elongated shape of 
the hole 44, the connecting borehole 41 need not be positioned precisely 
below the connecting shoe 43 for loosening the printing plate. 
In accordance with FIG. 9, the connecting borehole 45 of a pressure chamber 
leads out of the front end of the printing cylinder 46. A connecting 
opening 47 of the connecting shoe 48 is constructed in the form of a 
circular segment here and the latter is surrounded by a fiat sealing 
surface. 
For the purpose of loosening the printing plate, the printing cylinder 36 
is positioned with its connecting borehole 41 under the connecting shoe 
43. After the connecting shoe 43 has been lowered onto the shell surface 
of the printing cylinder 36, the pressure chamber 39 is filled with 
compressed air, whereupon the membrane 40 presses the tie beam 37 inward. 
At the same time, the plate legs are released as in the previous 
embodiment. 
In accordance with FIG. 10, the tie beam 49 of the printing cylinder 50 has 
an inclined plane 51. A push rod 53, fastened to the side wall 52 of the 
machine, also has an inclined plane 54. When the push rod 53 is extended, 
the inclined planes 51, 54 slide upon one another and move the tie beam 49 
radially inward and release the plate legs. The further loosening and also 
the clamping of the printing plates takes place as indicated for the first 
embodiment. 
In the embodiments, the printing cylinder has only one cylinder groove for 
clamping a printing plate. Likewise, several grooves for clamping a 
corresponding number of printing plates can be disposed uniformly 
distributed over the circumference of the printing cylinder. Such 
arrangements also belong to the scope of the invention. 
The invention is not limited by the embodiments described above which are 
presented as examples only but can be modified in various ways within the 
scope of protection defined by the appended patent claims.