GB1584657A

GB1584657A - Trailing edge screen clamp

Info

Publication number: GB1584657A
Application number: GB3115277A
Authority: GB
Original assignee: Crosfield Electronics Ltd
Current assignee: Crosfield Electronics Ltd
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-02-18

Description

(54) TRAILING EDGE SCREEN CLAMP (71) We, CROSFIELD ELECTRONICS LIMITED, a British company of 766 Holloway Road, London N19 3JG, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: It is frequently required in printing to clamp a screen around a cylinder. The leading edge of the screen is held fast between bars, the lower one of which locates in a groove extending across the cylinder. The fixing of the trailing edge of the screen has in the past given rise to problems. Adhesive tape is troublesome to handle and relies upon the operator for secure fixing. Clamps constructed as an integral part of the drum result in a complicated drum structure.

The present invention provides a screen clamp for fixing the trailing edge of a printing screen on a cylinder, comprising: a bar for location in a recess in the cylinder surface and parallel to the cylinder axis, the bar being shaped to provide a longitudinal groove in one bar surface, for location at the base of the recess in the cylinder; a rod seating in the longitudinal groove, the cross-sectional shape of the bar and the diameter of the rod being such that the rod makes line contact with the bar on two sides of the groove; and a number of longitudinally spaced clamping claws pivotally mounted on the rod and extending through apertures in the surface of the bar opposite the grooved surface, the portion of each claw which extends through the aperture having a tongue which extends over the bar surface adjacent the aperture, the claw being resiliently mounted so that the trailing edge of the screen, placed around the cylinder and provided with apertures for the passage of the claws is clamped between the bar surface and the said tongues.

Preferably, the groove is V-shaped, the rod making line contact with each side of the groove.

The use of line contacts between the rod and the two sides of the groove allows greater tolerance and creates less alignment problems than there would be, for example, if the rod were running in a hole drilled throughout the length of the bar or through aligned longitudinally spaced holes.

In order that the invention may be better understood, two examples of clamps embodying the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates the use of a clamp embodying the invention for clamping the trailing edge of a screen, passing round the cylinder; Figure 2 is a cross-sectional view of the clamp at the location of one of the claws; Figures 3 and 4 are a bottom plan view and a side elevation, respectively of the clamp; Figure 5 is a section on the line A-A of Figure 3; and Figure 6 a section on the line B-B of Figure 3, and Figure 7 shows an alternative form of clamp.

In Figure 1, a screen is stretched around a cylinder 12, the leading edge of the screen being clamped in an attachment 14, a part of which seats in a recess 16 extending across the cylinder.

The cylinder is formed with a further groove 18 to house the trailing edge clamping device. As shown in the cross-sectional view of Figure 1, the clamping device comprises a bar 20 housing a pivoted claw 22 which extends through an aperture in the screen, close to the trailing edge of the screen, and has a tongue 24 which overlies the said trailing edge of the screen and clamps the latter between itself and the adjacent upper surface of the bar 20. A series of such claws is provided, spaced longitudinally on the bar 20, so that the trailing edge of the screen is clamped at a number of longitudinally spaced points.

The construction of the bar and clamping claw is shown in greater detail in Figure 2. The lower surface of the bar 20 is formed with a V-shaped groove, having sides 26 and 28, which extend for the whole length of the bar. A rod 30 seats in the V-shaped groove, making substantially line contact with the two sides of the groove. The free ends of spaced plates 29 support the rod 30 at intervals along its length.

The claws 22 are provided at intervals along the length of the rod; each claw has a circular hole by means of which it is mounted on the rod and an outwardly extending portion which passes through an aperture 31 in the bar and then turns at rightangles to form the tongue 24.

One end of a spring 32 is located in a bore 34 in the bar and abuts a spring-retaining screw 36. The other end of the screw enters a recess 37 in the claw. The spring 32 urges the clamping claw 22 into its clamping position, in which the trailing edge 10a of the screen is clamped between the flat lower surface of the tongue 24 of the claw and the flat upper surface of the portion 20a of the bar 20. The clamping claw is undercut beneath the tongue 24 to give more freedom for tolerances in the screen size without danger of the claw pulling on the edge of the hole in the screen or missing it altogether.

In Figures 3 and 4 recessed portions 38 of the lower surface of the bar 20 are formed to receive the longitudinally spaced plates 29 (Figure 2). Figure 3 also shows the apertures 34 for the passage of the clamping claws and the section shown in Figure 6 passes through such an aperture and through a tapped hole 36 for the spring-retaining screw.

As each claw is urged closed by a separate spring, all claws exert an effective clamping action without requiring tight tolerances on their angular position on the shaft.

The location of the rod in the V-shaped groove provided in the clamp body reduces tolerance and alignment problems. The rod is retained by a bearing block at each end of the clamping bar and by two intermediate retaining plates.

With a clamp assembly of the kind described, the only extra requirement for the drum is the provision of a groove to receive the assembly.

Figure 7 shows an alternative form of clamp utilising a torsion spring 40 to hold the claw 22 in its clamping position, in place of the compression spring 32 shown in Figure 2.

WHAT WE CLAIM IS: 1. A screen clamp for fixing the trailing edge of a printing screen on a cylinder, comprising: a bar for location in a recess in the cylinder surface and parallel to the cylinder axis, the bar being shaped to provide a longitudinal groove in one bar surface, for location at the base of the recess in the cylinder; a rod seating in the longitudinal groove, the cross-sectional shape of the bar and the diameter of the rod being such that the rod makes line contact with the bar on two sides of the groove; and a number of longitudinally spaced clamping claws pivotally mounted on the rod and extending through apertures in the surface of the bar opposite the grooved surface, the portion of each claw which extends through the aperture having a tongue which extends over the bar surface adjacent the aperture, the claw being resiliently mounted so that the trailing edge of the screen, placed around the cylinder and provided with apertures for the passage of the claws, is clamped between the bar surface and the said tongues.

2. A screen clamp in accordance with claim l, in which the said groove is V-shaped, the rod making line contact with each side of the groove.

3. A screen clamp in accordance with claim 1 or 2, comprising, for each claw, a spring acting in a direction such as to close the tongue of the claw on the bar surface.

4. A screen clamp, for fixing the trailing edge of a printing screen on a cylinder, substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

37 in the claw. The spring 32 urges the clamping claw 22 into its clamping position, in which the trailing edge 10a of the screen is clamped between the flat lower surface of the tongue 24 of the claw and the flat upper surface of the portion 20a of the bar 20. The clamping claw is undercut beneath the tongue 24 to give more freedom for tolerances in the screen size without danger of the claw pulling on the edge of the hole in the screen or missing it altogether.

In Figures 3 and 4 recessed portions 38 of the lower surface of the bar 20 are formed to receive the longitudinally spaced plates 29 (Figure 2). Figure 3 also shows the apertures 34 for the passage of the clamping claws and the section shown in Figure 6 passes through such an aperture and through a tapped hole 36 for the spring-retaining screw.

As each claw is urged closed by a separate spring, all claws exert an effective clamping action without requiring tight tolerances on their angular position on the shaft.

The location of the rod in the V-shaped groove provided in the clamp body reduces tolerance and alignment problems. The rod is retained by a bearing block at each end of the clamping bar and by two intermediate retaining plates.

With a clamp assembly of the kind described, the only extra requirement for the drum is the provision of a groove to receive the assembly.

Figure 7 shows an alternative form of clamp utilising a torsion spring 40 to hold the claw 22 in its clamping position, in place of the compression spring 32 shown in Figure 2.

WHAT WE CLAIM IS: 1. A screen clamp for fixing the trailing edge of a printing screen on a cylinder, comprising: a bar for location in a recess in the cylinder surface and parallel to the cylinder axis, the bar being shaped to provide a longitudinal groove in one bar surface, for location at the base of the recess in the cylinder; a rod seating in the longitudinal groove, the cross-sectional shape of the bar and the diameter of the rod being such that the rod makes line contact with the bar on two sides of the groove; and a number of longitudinally spaced clamping claws pivotally mounted on the rod and extending through apertures in the surface of the bar opposite the grooved surface, the portion of each claw which extends through the aperture having a tongue which extends over the bar surface adjacent the aperture, the claw being resiliently mounted so that the trailing edge of the screen, placed around the cylinder and provided with apertures for the passage of the claws, is clamped between the bar surface and the said tongues.
2. A screen clamp in accordance with claim l, in which the said groove is V-shaped, the rod making line contact with each side of the groove.
3. A screen clamp in accordance with claim

1 or 2, comprising, for each claw, a spring acting in a direction such as to close the tongue of the claw on the bar surface.
4. A screen clamp, for fixing the trailing edge of a printing screen on a cylinder, substantially as herein described with reference to the accompanying drawings.