GB2283939A

GB2283939A - Printing machine motor drives

Info

Publication number: GB2283939A
Application number: GB9323643A
Authority: GB
Inventors: David Sawford
Original assignee: Cobden Chadwick
Current assignee: Cobden Chadwick
Priority date: 1993-11-16
Filing date: 1993-11-16
Publication date: 1995-05-24
Also published as: GB9323643D0

Abstract

A print cylinder (12) and impression cylinder (11) of a printing machine are independently driven using a single common main motor (14). A supplementary drive is provided using a control motor (18) linked to the printing cylinder (12) via a differential gear box (17) which acts on the print cylinder (12) to allow variation in the speed of rotation of the printing cylinder (12) relative to the impression cylinder (11). The printing cylinders may cooperate with the impression cylinder (11), each printing cylinder having a supplementary drive. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO PRINTING MACHINES The invention concerns printing machines, and has more particular reference to a drive arrangement for the print cylinders thereof.

In the continuous printing of a web material, the material is supported on a central impression cylinder and printing is effected by a print cylinder positioned in nip forming relationship with respect to the impression cylinder and between which and the central impression cylinder the material moves.

In multi-colour printing a plurality of individual print cylinder is arranged in angularly spaced disposition about the central impression cylinder, the material to be printed passing successively through the respective nips formed by the individual print cylinders and the central impression cylinder.

Accurate pattern register between the respective impressions of the successive print cylinders, in addition to requiring that a particular phase relationship be maintained between the individual print cylinders, also requires that the surface speed of the individual print cylinders matches that of the central impression cylinder, and conventionally this matching is achieved by providing a direct gear drive between the print cylinders and the impression cylinder.

Such direct gear drive between the print cylinders and the central impression cylinder gives good pattern register, but does impose engineering limitations on the print cylinders.

For example, the print cylinders must be of a circumference which corresponds to the pattern repeat length and, furthermore, such repeat length must be a multiple of the gear pitch of the direct drive between the print cylinder and the impression cylinder.

These limitations give rise to the need to provide print rollers specific to impression cylinders of a particular gear pitch and, moreover, to use print rollers wherein the circumference is equal to or a multiple of the pattern repeat.

The object of the present invention is to provide an arrangement which avoids the aforesaid limitations.

According to the present invention there is proposed a printing machine having a print cylinder in nip forming relationship to a central impression cylinder, characterised in that the print cylinder and central impression are driven from a common source through separate transmission paths and in that means is included to impose a supplementary drive to the print cylinder independently of that common source.

According to a preferred feature of the invention, the supplementary drive comprises a control motor the output of which is applied to a differential gear box provided in the drive transmission path to the print roller.

According to a further preferred feature, the control motor is adapted to apply a variable drive input to the differential gear.

According to a still further preferred feature, the output of the differential gearbox provides the drive to the print cylinder.

It is to be understood that a separate drive will ordinarily be provided for each respective print cylinder.

The invention will now be described further, by way of example only, with reference to the accompanying drawings which illustrate one embodiment thereof and in which : Fig. 1 is a schematic illustration showing two print cylinders in angularly spaced relationship about the periphery of the impression cylinder of a printing machine; and Fig. 2 shows, in diagrammatic manner, the drive for the print cylinder.

Referring now to the drawings and particularly to Fig. 1 thereof, an impression cylinder 11 receives two print cylinders 12 into nip forming relationship therewith, the print cylinders 12 being in predetermined angularly spaced disposition with respect to the impression cylinder.

In contradistinction to the prior art structures, wherein respective gears on the print cylinders and impression cylinder are in direct mesh, it is now proposed that the cylinders be independently driven from a common source, as is shown in Fig. 2. Thus, the drive to the impression cylinder 11 is from a drive gear 13 secured to the output shaft of a main motor 14 to an intermediate gear 15 and thence to a gear 16 secured in coaxial relationship with the impression cylinder 11. The printing cylinder 12 is also driven from main motor 14, but in this instance the drive transmission includes a differential gearbox 17 which receives a primary drive from intermediate gear 15 and a supplementary drive from a control motor 18, the output of the differential gear box being applied to print cylinder 12 through gearing comprising a supplementary drive gear 19, a supplementary intermediate gear 21 and a gear 22 secured in co-axial relationship with the print cylinder.

Supplementary drive gear 19 is similar to intermediate gear 15, whilst supplementary intermediate gear 21 is similar to gear 16 secured to the impression cylinder 11.

As will be appreciated, the control motor 18 will impose a drive motion on the print cylinder 12 additional to that provided by the main motor 14 and will allow of a variation in the speed of the print cylinder relative to that of the impression cylinder 11 but independently thereof.

Furthermore, the use of a different drive transmission path to the print cylinder 12 will avoid the constraints imposed by the direct gear connection between the impression cylinder and print cylinder of the prior art, and will enable use to be made of print cylinders having gears which are incompatible with the gear applied to the impression cylinders and thereby reduce the number of print cylinders required.

The peripheral speed of the print cylinder must be matched with that of the impression cylinder, but it has been found that a speed differential of, say, + 2% can be tolerated without discernable loss of definition. The invention thus provides a facility for a degree of variation in the repeat length applied by the print cylinder.

More -particularly, the invention introduces a versatility not available with prior art arrangements and, in consequence, provides an opportunity to reduce the number of print cylinders required to service a range of printing machines.

The invention is not limited to the detail of the embodiment herein disclosed, since alternatives will readily present themselves to one skilled in the art.

Thus, whilst it is proposed that the differential gear box, or an equivalent, be provided between the drive to the impression cylinder and the print cylinder, it may be found preferable, in some instances to provide such gear box within the drive to the print cylinder, such drive itself being taken from the main motor.

Claims

1. A printing machine having a print cylinder in nip forming relationship to a central impression cylinder, characterised in that the print cylinder and central impression are driven from a common source through separate transmission paths and in that means is included to impose a supplementary drive to the print cylinder independently of that common source.

2. A printing machine according to claim 1 wherein the supplementary drive comprises a control motor, the output of which is applied to a differential gear box provided in the drive transmission path to the print roller.

3. A printing machine according to claim 2 wherein the control motor is adapted to apply a variable drive input to the differential gear.

4. A printing machine according to claim 2 or claim 3 wherein the output of the differential gear box provides the drive to the print cylinder.

5. A printing machine according to any one of claims 1 to 4 wherein a separate drive is provided for each respective print cylinder.

6. A printing machine substantially as hereinbefore described with reference to Figures 1 and 2 of the drawings.