EP0057530B1

EP0057530B1 - Apparatus for securing a flexible printing plate to a printing cylinder

Info

Publication number: EP0057530B1
Application number: EP82300254A
Authority: EP
Inventors: Kevin Graham Davies; John Richard Marsh
Original assignee: Auto Masters Ltd
Current assignee: Auto Masters Ltd
Priority date: 1981-01-23
Filing date: 1982-01-19
Publication date: 1986-08-27
Also published as: DE3272789D1; EP0057530A1; EP0057078A2; EP0057078A3; ATE21652T1

Abstract

Apparatus for securing a flexible printing plate (4) to a printing cylinder (1) comprises holding means (5) for holding one edge (9) of the plate (4) on the cylinder (1). Locking means (12) include a pivotally mounted body (14) defining a retaining groove with a mouth (21) through which the opposite edge (13) of the printing plate (4) can be inserted into or removed from the retaining groove. The body (14) is pivotal in use between a locking position in which the printing plate (4) is locked under tension on the cylinder (1) and a release position in which the printing plate (4) can be fitted or removed.

Description

The present invention relates to apparatus for securing a flexible printing plate to a printing cylinder.
Conventionally, such printing plates are made of thin aluminium or mild steel sheets and attached either directly to a spacer element called a shim of a printing cylinder or to a spacer element called a saddle which is itself attached to the cylinder. Normally two plates are attached around the circumference of a cylinder and the securement mechanism thereof comprises a simple retaining means at the leading edge of the plate, as considered in the direction of rotation of the cylinder, and a tensioning means at the trailing edge of the plate. Owing to the strength of the printing plate, the tensioning means used in the past have made use of a rotary locking bar having a plurality of projections therealong which engage in holes made in the plate. Rotation of the bar by a tool after engagement with the plate tensions the plate pulling it tight against the surface of the shim or the saddle of the printing cylinder.
When the printing cylinder is fitted with shims the printing plate tensioning assembly may be detachably attached directly to the outer cylindrical surface of the printing cylinder between facing edge portions of the shims, as described in GB-A-1 575 016. In contrast, with a saddle arrangement, the tensioning means of the securement mechanism is mounted on the trailing edge of the saddle. In both cases, a disadvantage is that a special hand tool is required to rotate the locking bar of the tensioning means into the release position and the operator has only one hand free to fit the printing plate on the locking bar.
More recently, printing plates have been developed which are made of thick paper or plastics. However, when such plates are used with tensioning means of the kind described above they tend to tear or warp owing to the perforations therein.
In GB-A-1 403 053 these disadvantages are overcome in a rotary printing cylinder of the kind having a longitudinally extending recess formed in its circumferential surface. The recess accommodates a plate lock-up mechanism including a turnable plate-tightening bar with a slot which receives a preformed marginal tail portion of a thin, flexible and resilient printing plate. The plate-tightening bar lies wholly within the circumference of the printing cylinder in both the locked and unlocked positions. Such an arrangement is not suitable for the shallow recess available between the confronting edges of a pair of saddles or shims. Furthermore, the slot of the plate-tightening bar retains the printing plate by virtue of the hooked end of the plate engaging therein. Paper or plastics plates, with which the present invention is particularly concerned, rarely have sufficient rigidity to permit preformation of a hook portion which can be hooked over a suitable element as in FR-A-2 146 889. An obvious expedient is to clamp the end of the plate in the slot as in DE-B-2 759 434 but this makes the operation of the lock-up mechanism more awkward for the operator because of the need to open the clamping means for insertion and removal of the plate.
An object of the present invention is to provide an improved mechanism for securing a printing plate to a printing cylinder, which mechanism is suitable for use both with paper and plastics plates, and with metallic sheet plates.
According to the present invention there is provided apparatus for securing a flexible printing plate to a printing cylinder, comprising holding means for holding one edge of the plate on the cylinder, locking means including a pivotally mounted body defining a retaining groove with a mouth through which the opposite edge of the printing plate can be inserted into or removed from the retaining groove, said body being pivotal in use between a locking position in which the printing plate is locked under tension on the cylinder and a release position in which the printing plate can be fitted or removed, and biasing means acting on the body to urge it into the locking position, characterised in that the body of the locking means is attached to and extends over the full width of an end face of a spacer element on the printing cylinder for pivotal movement between the locking position, in which it lies wholly within a shallow recess defined by the outer surface of the cylinder, by said end face and by a confronting spacer element end face provided with said holding means, and the release position in which the body extends outwardly of said recess,
in that the groove is of sufficient width that said opposite edge of the printing plate can be freely and loosely inserted into and removed from the groove in the release position of the body and of sufficient depth that said edge is retained solely by friction in the groove on pivotal movement of the body into the locking position,
and in that said biasing means has over-centre action spring means which to the locking side of an intermediate position of the body urge the body into the locking position and to the release side of said intermediate position urge the body into the release position.
The retaining groove is preferably defined by opposed side walls which extend parallel to each other over part of the depth of the groove and diverge in the vicinity of the mouth so as to facilitate insertion of said opposite edge of the printing plate.
Preferably, that side wall which is overlapped by the printing plate in use is lower than the other side wall to further facilitate insertion of the printing plate.
The body preferably includes a spindle with exposed journal sections engaged by complementary bearing formations mounting means for the body. The spindle preferably has a flat surface.
The present invention will now be described by way of example with reference to the accompanying drawings, in which:-

Fig. 1 is a perspective view of a printing cylinder provided with locking mechanisms according to the present invention;
Fig. 2 is an exploded view to an enlarged scale of the locking mechanism shown in Fig. 1 seen from underneath; the inset shows the parts in the assembled condition;
Figs. 3 to 5 are diagrams showing different stages in the printing plate fitting and locking operation.

The drawings show a printing cylinder 1, which is rotatable, in use, in the direction shown by arrow 2 and which is provided with a pair of saddles 3 to each of which a printing plate 4 can be attached by a locking mechanism according to the present invention.
The locking mechanism comprises holding means 5 which is located along the leading edge 6 of the saddle 3 with respect to the direction of rotation of the cylinder 1. The holding means 5 comprises a simple clamp arrangement in which the edge 6 of the saddle 3 is undercut to provide an acute angle 7. Attached to the saddle 3 along the edge 6 is a metal or plastics strip 8 which is formed so as to define a clip with the edge 6. In this way, one edge 9 of the printing plate 4 can be retained by being pushed firmly between the strip 8 and the edge 6 so that the strip 8 clamps the plate 4 to the edge 6 and the plate 4 folds over the angle 7 against the surface 10 of the saddle 3.
At the trailing edge 11 of the saddle 3, the locking mechanism comprises a locking arrangement 12 to hold and tension the trailing edge 13 of the printing plate 4 opposing the leading edge 9 thereof against the surface 10 of the saddle. The arrangement 12 comprises a locking member 14 with a body having a heel 15 of part-circular profile. The trailing edge 11 of the saddle 3 is also formed with a part-circular profile, into which the heel 15 of the member 14 fits so that the locking member 14 has a degree of rotary motion with respect to the saddle 3 and thereby the cylinder 1. The locking member 14 is retained in position with respect to the saddle 3 by two hinges at opposite sides of the saddle only one of which is shown in Fig. 1.
The locking member body is made of sheet metal strip bent into shape with a spindle 16 inserted and secured thereto by suitable means (not shown). The curved heel 15 passes into side walls 17, 18 which defines therebetween a retaining groove 19 for the trailing edge 13 of the printing plate 4. The retaining groove 19 has a parallel-sided section 20 leading into a flared mouth 21 facilitating entry of the printing plate edge. That side wall 18 which is nearer to the associated holding means 5 is shorter than the other side wall 17 for the same reason. The body of the locking member has cut- outs 22, 23 exposing reduced diameter sections 24, 25 of the spindle 16 which provide journals for hooked ends 26, 27 of a hinge element 28. A generally circular split spring 29 is retained by the hinge element 28 and abuts with its one end against a lip 30 of the hinge element 28. The opposite end of the spring 29 has a U-shaped projection 31 of which the cross-piece 31a seats in a groove 32 in the body. The groove 32 has circumferential extensions 32a, b at each end for receiving the side pieces 31b, c of the spring projection 31 when necessary. The hinge element 28 is secured in a recess 33 at the trailing edge of the saddle 3 by means of screws 34, 35 extending through apertures 36, 37 in the hinge element 28 into engagement with tapped holes 38, 39 in the saddle 3. The recess 33 is U-shaped leaving an island of material 40 at the edge of the saddle 3 which is thus weakened little if at all by the two recesses in its trailing edge. The hinge element 28 has a cut-out 41 which fits over the island 40. It will be appreciated that the hinge at the opposide side of the saddle is constructed in the same way.
The construction of the hinges is such that the springs 29 have an over-centre action with respect to an unstable intermediate or neutral position which occurs when the line of action of each spring 29 is in line with the slot 32 and the axis of rotation of the body. When the locking member 14 is deflected to either side of this neutral position the springs act to urge the body in the same direction i.e. towards the locking or release position.
The spindle 16 has a flat surface 42 along one side thereof so as to provide an extension of the groove 19 (Figs. 3 to 5). The reduced diameter sections 24, 25 of the spindle 16 lie radially within the flat surface 42 so as to permit engagement by the hooked ends 26, 27 without obstructing the groove 19. Fig. 3 shows the locking member 14 in the release position ready for receiving the trailing edge 13 of a printing plate 4. The holding means 5 is about to receive the leading edge 9 of what may be assumed for the purposes of illustration to be the same printing plate 4. It will be seen that the locking member 14 projects generally radially with respect to the cylinder 1 and well above the surface 10 of the saddle 3 thus permitting a relatively deep retaining groove 19 which is increased in depth by the flat surface 42 on the spindle 16. Because of the depth of the groove 19 the trailing edge 13 is retained therein without any nipping or clamping action by the walls 17, 18 but merely by friction with the sides of the groove as the locking member 14 is turned into the fully locked position shown in Fig. 5.
The printing plate 4 is fitted to the saddle 3 by inserting the leading edge 9 in the direction of the arrow in Fig. 3 into the nip defined by the edge 6 of the saddle 3 and the clamping strip 8. The trailing edge 13 of the plate 4 is then inserted into the retaining groove 19 of the locking member 14 which is held in the release position by spring pressure urging the locking member 14 into abutment with the edge of the saddle. The operator can thus use both hands to fit the trailing edge 13 into the retaining groove 19.
Fig. 4 shows both leading and trailing edges 9, 13 of the printing plate 4 fully inserted and finger pressure being used to push the locking member 14 towards the locking position. The neutral or intermediate position of the over-centre springs is closely adjacent to the release position of the locking member 14 so that only a small rotational movement is required to push the locking member past the neutral position, i.e. over-centre, whereupon the springs snap the locking member 14 into the locking position (Fig. 5). The angular movement of the locking member 14 between the release and locking positions is approximately 90° and in the locking position the locking member 14 is more or less tangential to the printing cylinder 1. The exact amount of movement will depend upon the length of the printing plate 4 and slight variations in this dimension will produce corresponding changes in the angular orientation of the locking memer 14 in the locking position. It is important that the printing plate 4 should always hold the locking member 14 out of direct contact with the printing cylinder 1 in the locking position for otherwise insufficient tension is exerted on the plate.
When it is desired to remove the printing plate 4 from the cylinder 1, the locking member 14 is then rotated from the locking position (Fig. 5) back to the release position (Fig. 3) and the trailing edge 13 of the plate 4 removed from the mouth 21. The leading edge 9 of the plate 4 can then be removed by pulling from the holding means 5. It is possible to rotate the locking member 14 back into the release position by hand. However, as in practice it is awkward to grasp the locking member 14 with fingers often owing to the proximity of the leading edge of the adjacent saddle 3, a tool (not shown) may be used. Such a tool conveniently comprises an angled strip, the turned over angle portion of which can be engaged in the mouth 21 and the tool pulled to raise the member 14 back into the release position.
The advantage of having a locking member 14 which is movable at least from the first position into the second position by hand is twofold. Firstly, it permits the person fitting the plate 4 on the cylinder 1 to use both hands in the location of the trailing edge 13 of the plate 4 in the mouth 21 as the edge 13 can be held in the mouth 21 whilst pushing the member 14 over into the second position. This is in contrast to prior art arrangements wherein a tool is required to rotate the equivalent locking bar and only one hand can be used to hold the plate in the appropriate position with respect to the locking bar. Secondly, the comparative ease with which the locking member 14 rotates and the proximity of the centre position of the biasing springs to the release position prevent damage if the locking member 14 is accidentally left in the release position when the cylinder 1 is used. If this happens, the locking member 14 is automatically rotated into the locking position by contact with a cooperating press roller or cylinder. However, in prior art arrangements, the accidental use of a cylinder having an incorrectly positioned locking bar results in damage to the paper as the locking bar remains in the wrong position during printing.
It will be appreciated that several modifications can be made to the locking mechanism described above. Firstly, although the mechanism has been designed for incorporation in new printing equipment, it is possible to use the mechanism to convert existing equipment, which is an important advantage within the industry. In this case, the locking member 14 is used to replace the locking bar arrangements of existing printing cylinders and the holding means 5 can be included in a screw-on strip which can be added to the saddle or shim of the existing machine. In addition, it will be appreciated that the construction of the holding means may be different and instead of a clip arrangement or an undercut edge may comprise a slotted mouth cut into the leading edge of the saddle or shim at an acute angle to the surface.
Secondly, when the locking mechanism is cylinder-mounted as shown in Figs. 6 and 7 it is possible to provide for only one locking position at the trailing side of the release position of the locking member. In this case the biasing springs will act in the same way as in the first embodiment with the unstable neutral position adjacent the upright release position. Alternatively, two such locking members may be provided in each recess 150 to permit rotation of the printing cylinder in opposite directions, one of the locking members being used when the cylinder is rotated in one direction and the other locking member being used when the cylinder is rotated in the opposite direction.
Thirdly, instead of being mounted on a saddle or directly on the cylinder it is possible for the locking member to be mounted in the recess between two shims on a support which is detachably mounted on the confronting edges of the shims.

Claims

1. Apparatus for securing a flexible printing plate to a printing cylinder, comprising holding means (5) for holding one edge of the plate (4) on the cylinder (1), locking means (12) including a pivotally mounted body defining a retaining groove (19) with a mouth (21) through which the opposite edge (13) of the printing plate (4) can be inserted into or removed from the retaining groove (19), said body being pivotal in use between a locking position in which the printing plate is locked under tension on the cylinder and a release position in which the printing plate can be fitted or removed, and biasing means (29) acting on the body to urge it into the locking position,
characterised in that the body of the locking means (12) is attached to and extends over the full width of an end face (11) of a spacer element (3) on the printing cylinder (1) for pivotal movement between the locking position, in which it lies wholly within a shallow recess defined by the outer surface of the cylinder (1), by said end face (11) and by a confronting spacer element end face (6) provided with said holding means (5), and the release position in which the body extends outwardly of said recess,

in that the groove (19) is of sufficient width that said opposite edge (13) of the printing plate (4) can be freely and loosely inserted into and removed from the groove (19) in the release position of the body and of sufficient depth that said edge (13) is retained solely by friction in the groove (19) on pivotal movement of the body into the locking position,

and in that said biasing means (29) has over-centre action spring means (25) which to the locking side of an intermediate position of the body urge the body into the locking position and to the release side of said intermediate position urge the body into the release position.

2. Apparatus as claimed in claim 1, wherein the retaining groove (19) is defined by opposed side walls (17, 18) which extend parallel to each other over part (20) of the depth of the groove and diverge in the vicinity of the mouth (21) so as to facilitate insertion of said opposite edge (13) of the printing plate (4).

3. Apparatus as claimed in claim 2, wherein that side wall (18) which is overlapped by the printing plate (4) in use is lower than the other side wall (17) to further facilitate insertion of the printing plate (4).

4. Apparatus as claimed in any one of the preceding claims, wherein the body includes a spindle (16) with exposed journal sections (24, 25) engaged by complementary bearing formations (26, 27) of mounting means (28) for the body.

5. Apparatus as claimed in claim 4, wherein the spindle (16) has a flat surface (42) along one side thereof so as to increase the depth of the retaining groove (19), and the journal sections (24, 25) are reduced in diameter so as to lie radially within said flat surface (42) to avoid obstruction of the retaining groove (19) by the bearing formations (26, 27).

6. Apparatus as claimed in any one of the preceding claims, wherein the groove (19) of the locking means (12) is defined by a sheet metal strip bent into shape.