GB2166388A

GB2166388A - Expandable work cylinder

Info

Publication number: GB2166388A
Application number: GB08524019A
Authority: GB
Inventors: Alan Keith Mccombie
Original assignee: ROTAPRINT PLC
Current assignee: ROTAPRINT PLC
Priority date: 1984-09-28
Filing date: 1985-09-30
Publication date: 1986-05-08
Also published as: GB8524019D0; GB2166388B

Abstract

A cylinder 1 has an expandable segment 2 mounted at its ends 7 on cantilever arms 9. The cantilever arms 9 are clamped at their bases 10 and can be deflected at their outer ends by screws 11 or helical wedges 12. The cantilever arms 9 and deflecting means 11 or 12 are oriented in such a way that as the outer ends of the expanding segment 2 are moved its radius of curvature changes, and it can be caused to expand or contract while remaining substantially co-axial with the cylinder 1. This arrangement is particularly suited to lithographic plate or impression cylinders in order to compensate for differing plate or paper thickness; other uses include embossing, cutting or creasing. <IMAGE>

Description

SPECIFICATION Expanding cylinder This invention relates to machinery in which revolving cylinders perform an operation on a process material which is in the form of a sheet or web; this includes machinery for embossing, cutting or creasing sheet materials as well as for printing. In particular, but not exclusively, the invention relates to those cylinders in printing machines which present a smooth cylindrical face as backing for a lithographic plate or as a counterpressure surface for printing.

Such cylindrical faces, which must not be interrupted by holes or slots, must be machined to a high accuracy of diameter and concentricity if high quality printing is to be achieved. Unfortunately, a standard diameter will not suffice if differing plate thicknesses and paper thicknesses are to be encountered. Rather than exchange the cylinder for another of different diameter, it has been the practice hitherto to change the cylinder's radius, if required, by the addition or removal of thin layers of sheet material. This is laborous and inaccurate.

It is therefore the object of the invention to provide means whereby the cylindrical surface itself may be expanded or contracted in radius steplessly, conveniently, quickly and by means which display the setting which has been selected.

The invention provides a cylinder with a surface segment of adjustable radius, comprising an arcuate member defining the said surface segment, legs extending inwardly from the circumferential extremities of the arcuate member, the inner end portions of the legs being secured to a substantially rigid mounting member, and means for deflecting the outer end portions of the legs relative to the mounting member, the legs being so arranged that, at least under small deflections, the arcuate member is caused to move and deform in such a way that its radius of curvature changes while its axis of curvature remains substantially fixed relative to the mounting member.

According to the present invention, the said cylindrical surface is machined on one or more segments which are fixed to the outside of a smaller subcylinder. The segment is of constant cross-section and may be manufactured by an extrusion process. This cross-section, which is important to the invention, comprises an outer cylindrical portion or shell, a sharp bend or elbow at each end of this, and two inner portions or legs projecting towards each other beneath the shell. The points of attachment to the sub-cylinder are situated at the extremities of these projecting inner portions. According to the invention, radial adjustment means such as jacking screws or wedges are provided so as to urge the respective elbows of the segment outwards.The segment is so proportioned that when this outward deformation is imposed, the legs deflect as simple cantilevers and thereby control the direction of outward movement of the two ends of the cylindrical shell. These directions are selected so that the resulting radial displacement of the ends is the same as that of the mid-point along the outer arc of the outer cylindrical portion.

With three points thus established on a larger common radius, it follows that the remainder of the curved surface will be on, or close to, the same radius because (a) an approximately uniform bending movement is applied around the outer portion, and (b) the deflections involved are very small anyway.

An embodiment of the invention will now be described with reference to the accompanying drawing, which represents a cross-section of a subcylinder 1 on which is mounted an expanding segment 2. The width of the cylinder is immaterial, so only one view is shown.

The sub-cylinder 1 is mounted on a shaft 3 and is of a substantially enclosed section supported by occasional webs 4. A segment 5 is machined to an accurate cylindrical form. Mounted on the sub-cylinder is the expanding segment 2 comprising a cylindrical shell 6 (which is unsupported by webs but may be relatively thick), two corners 7, two elbows 8 and two legs 9 whose extremities are rigidly fixed to the sub-cylinder by mounting screws 10.

In addition there is a jacking means comprising the screws 11 adapted to force the elbows 8 away from the sub-cylinder 1. In addition or alternatively there are rotating spiral wedges 12 which set a precise distance between pads 13 on the elbows 8 and pads 14 on the sub-cylinder. These wedges and the screws 11 may carry markings to indicate their settings.

It will be seen that if the elbows are forced outwards by these means, the entire section will deform and the elbows will move in the directions of the arrows 15 which are perpendicular to the legs 9. The legs will in fact deform in the manner of a leaf spring whose ends are "clamped and guided".

If the legs were parallel to each other (and therefore coplanar) the shell 6 would move bodily outwards without its radius changing; but because the legs are set at an angle, the shell will be forced into a larger radius. If the corners 7 move radially outwards the same distance as the mid-point of the shell, the shell will form a new radius which is still concentric with the central shaft 3.

Referring to the drawing, where the shell surface subtends an angle 26 and the legs are set to produce movement of the corners 7 at an angle pr to the radial, it can be shown that a concentric expansion of radius will be obtained if I = tan - cosec 6.

For all practical purposes, the deformations of the legs and shell will be small in comparision with the lengths of the legs and shell, but large in comparison with any deformations due to direct compression or tension of these parts. Thus the magnitude and direction of the deformations is not significantly affected by the thicknesses of the various sections, which may be selected to suit the particular requirements of the machine.

1. A cylinder with a surface segment of adjusta

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Expanding cylinder This invention relates to machinery in which revolving cylinders perform an operation on a process material which is in the form of a sheet or web; this includes machinery for embossing, cutting or creasing sheet materials as well as for printing. In particular, but not exclusively, the invention relates to those cylinders in printing machines which present a smooth cylindrical face as backing for a lithographic plate or as a counterpressure surface for printing. Such cylindrical faces, which must not be interrupted by holes or slots, must be machined to a high accuracy of diameter and concentricity if high quality printing is to be achieved. Unfortunately, a standard diameter will not suffice if differing plate thicknesses and paper thicknesses are to be encountered. Rather than exchange the cylinder for another of different diameter, it has been the practice hitherto to change the cylinder's radius, if required, by the addition or removal of thin layers of sheet material. This is laborous and inaccurate. It is therefore the object of the invention to provide means whereby the cylindrical surface itself may be expanded or contracted in radius steplessly, conveniently, quickly and by means which display the setting which has been selected. The invention provides a cylinder with a surface segment of adjustable radius, comprising an arcuate member defining the said surface segment, legs extending inwardly from the circumferential extremities of the arcuate member, the inner end portions of the legs being secured to a substantially rigid mounting member, and means for deflecting the outer end portions of the legs relative to the mounting member, the legs being so arranged that, at least under small deflections, the arcuate member is caused to move and deform in such a way that its radius of curvature changes while its axis of curvature remains substantially fixed relative to the mounting member. According to the present invention, the said cylindrical surface is machined on one or more segments which are fixed to the outside of a smaller subcylinder. The segment is of constant cross-section and may be manufactured by an extrusion process. This cross-section, which is important to the invention, comprises an outer cylindrical portion or shell, a sharp bend or elbow at each end of this, and two inner portions or legs projecting towards each other beneath the shell. The points of attachment to the sub-cylinder are situated at the extremities of these projecting inner portions. According to the invention, radial adjustment means such as jacking screws or wedges are provided so as to urge the respective elbows of the segment outwards.The segment is so proportioned that when this outward deformation is imposed, the legs deflect as simple cantilevers and thereby control the direction of outward movement of the two ends of the cylindrical shell. These directions are selected so that the resulting radial displacement of the ends is the same as that of the mid-point along the outer arc of the outer cylindrical portion. With three points thus established on a larger common radius, it follows that the remainder of the curved surface will be on, or close to, the same radius because (a) an approximately uniform bending movement is applied around the outer portion, and (b) the deflections involved are very small anyway. An embodiment of the invention will now be described with reference to the accompanying drawing, which represents a cross-section of a subcylinder 1 on which is mounted an expanding segment 2. The width of the cylinder is immaterial, so only one view is shown. The sub-cylinder 1 is mounted on a shaft 3 and is of a substantially enclosed section supported by occasional webs 4. A segment 5 is machined to an accurate cylindrical form. Mounted on the sub-cylinder is the expanding segment 2 comprising a cylindrical shell 6 (which is unsupported by webs but may be relatively thick), two corners 7, two elbows 8 and two legs 9 whose extremities are rigidly fixed to the sub-cylinder by mounting screws 10. In addition there is a jacking means comprising the screws 11 adapted to force the elbows 8 away from the sub-cylinder 1. In addition or alternatively there are rotating spiral wedges 12 which set a precise distance between pads 13 on the elbows 8 and pads 14 on the sub-cylinder. These wedges and the screws 11 may carry markings to indicate their settings. It will be seen that if the elbows are forced outwards by these means, the entire section will deform and the elbows will move in the directions of the arrows 15 which are perpendicular to the legs 9. The legs will in fact deform in the manner of a leaf spring whose ends are "clamped and guided". If the legs were parallel to each other (and therefore coplanar) the shell 6 would move bodily outwards without its radius changing; but because the legs are set at an angle, the shell will be forced into a larger radius. If the corners 7 move radially outwards the same distance as the mid-point of the shell, the shell will form a new radius which is still concentric with the central shaft 3. Referring to the drawing, where the shell surface subtends an angle 26 and the legs are set to produce movement of the corners 7 at an angle pr to the radial, it can be shown that a concentric expansion of radius will be obtained if I = tan - cosec 6. For all practical purposes, the deformations of the legs and shell will be small in comparision with the lengths of the legs and shell, but large in comparison with any deformations due to direct compression or tension of these parts. Thus the magnitude and direction of the deformations is not significantly affected by the thicknesses of the various sections, which may be selected to suit the particular requirements of the machine. CLAIMS

1. A cylinder with a surface segment of adjusta ble radius, comprising an arcuate member defining the said surface segment, legs extending inwardly from the circumferential extremities of the arcuate member, the inner end portions of the legs being secured to a substantially rigid mounting member, and means for deflecting the outer end portions of the legs relative to the mounting member, the legs being so arranged that, at least under small deflections, the arcuate member is caused to move and deform in such a way that its radius of curvature changes while its axis of curvature remains substantially fixed relative to the mounting member.

2. A cylinder as claimed in claim 1, wherein the said arcuate member and the said legs are formed integrally as a single member.

3. A cylinder as claimed in claim 2, wherein the said single member is formed by extrusion.

4. A cylinder as claimed in any one of claims 1 to 3, wherein the inner end portions of the legs are clamped rigidly to the mounting member, and the legs bend under the action of the deflecting means.

5. A cylinder as claimed in any one of claims 1 to 4, which comprises means for mounting it rotatably about an axis substantially co-axial with the said axis of curvature of the said surface segment.

6. A cylinder as claimed in any one of claims 1 to 5, wherein the deflecting means comprises wedges.

7. A cylinder as claimed in any one of claims 1 to 6, wherein the deflecting means comprises helical screw means.

8. A cylinder as claimed in any one of claims 1 to 7, wherein the deflecting means are provided with indicia showing the radius of the said surface segment.

9. A cylinder as claimed in any one of claims 1 to 8, wherein the lines of action of the deflecting means are in planes parallel to the said axis and so oriented that tan 8 = e = where: 20 is the angle subtended by the arcuate member at the axis; and PI is the angle between each said plane of action of the deflecting means and the radial plane through the respective extremity of the arcuate member.

10. A cylinder as claimed in any one of claims 1 to 9, wherein over at least part of that part of the circumference not occupied by the said arcuate member there is provided a member defining a cylindrical surface coaxial with the said surface segment and having a radius no greater than the minimum radius of the said surface segment.

11. A cylinder substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.