GB2145663A

GB2145663A - Method and apparatus for regulating printing in printing machines

Info

Publication number: GB2145663A
Application number: GB08420044A
Authority: GB
Inventors: Gunter Rogge
Original assignee: Windmoeller and Hoelscher KG
Current assignee: Windmoeller and Hoelscher KG
Priority date: 1983-08-29
Filing date: 1984-08-07
Publication date: 1985-04-03
Also published as: GB2145663B; DE3336792A1; DE3336792C2; IT1176553B; IT8422217A0; GB8420044D0; FR2550995A1; FR2550995B1

Abstract

For the proper printing of webs that are preprinted with registration marks, i.e. in conformance with the registration marks and to the correct printed lengths, a permanent change is made in the relative speed between the plate cylinder(s) and the or each backing cylinder 11 in a flexographic printing press. The backing cylinder 11 is driven from drive gear 31, and the plate cylinder(s) driven from coaxial gear 35 rotatably mounted relative to gear 31, adjustable transmission 27 allowing the difference in speed. <IMAGE>

Description

SPECIFICATION Method and apparatus for regulating printing in printing machines The invention relates to a method of regulating the printing in printing machines in conformance with registration marks and according to the proper printed lengths of webs preprinted with the registration marks or of other marked webs, e.g. by scoring or perforating, wherein the errors in registration and printed lengths are detected by comparing the signals emitted by a sensor scanning the markings with the signals emitted by equipment which detects the phase position of the plate cylinder relatively to the scanned markings, as well as to an apparatus for performing this method.

If a web that has already been printed once or otherwise marked, e.g. by scoring or perforating, is to be printed with a further image on the obverse and/or reverse side, it is necessary for the registration marks printed on the web to be in the correct phase in relation to the plate cylinders of the printing mechanisms that carry out the second printing.

Apart from this correct running of the preprinted web into the printing press as far as the phase is concerned, it is of course also necessary to adjust for printed lengths so that the lengths are adjusted to the printing already appearing on the web.

In a method of this kind known from DE-PS 27 11 744, printing in conformance with registration marks is conducted by a momentary pulse-like increase or reduction in the tensile force of the web.

Such momentary jerky increase or reduction in the tensile force of the web creates slip between the plate cylinder and the preprinted web, thereby eliminating the phase error. Displacement of the web as a result of the slip is effected only for a short time enabling phase errors to be eliminated, without thereby changing the size and producing registration errors. In the known method, printing to the correct lengths is effected by a stepwise increase or reduction in the tensile force of the web so that the length of the images already printed is adapted to the register by elongating or contracting the web.

Accordingly, it is a prerequisite for the known method that the preprinted web which is to be printed for a second time consists of a considerably stretchable material which must exhibit slight repeat shrinkage even in the relaxed condition so that regulation of the registration can also take place by a reduction in the tension in the web.

Thus, the known regulating method fails when printing on webs having only a slight stretchability, for example webs of paper and HD-PE or like materials.

It is therefore the problem of the invention to provide a method of the aforementioned kind for regulating the printing in flexographic printing machines in conformance with registration marks and according to the proper printed lengths of webs preprinted with the registration marks, such method being applicable for again printing on webs which have only a slight stretchability.

This problem is solved according to the invention in that to obtain printing in conformance with the registration marks in a short time and to achieve printing to the proper length, a permanent change is carried out if necessary in the relative speed between the plate cylinders and the or each backing cylinder.

Prior to printing, after a coarse adjustment has been made, the method of the invention provides for the printing in conformance with the registration marks by appropriate relative motion between the web to be printed and the plate cylinders, such motion being brought about by appropriately altering the relative speed between the plate cylinders and the or each backing cylinder, it being assumed that the web will not slip when changing the relative speed in relation to the or each backing cylinder. During this momentary change in the relative speed to establish the correct phase position between the preprinted images on the web and the plate cylinders, it is therefore possible for slip to occur leading to smudging of the printing. However, because of the small departures, this is acceptable.

To achieve printing to the proper length, a corresponding permanent change is made if necessary to the relative speed between the plate cylinders and the or each backing cylinder. However, this relative speed is so low that it results in such a small slip that does not markedly influence the quality of the printing.

Accordingly, in the method of the invention, a change in the tension of the web is dispensed with to regulate the registration. It is therefore also possible to obtain proper printing of webs consisting of a material that has only slight extensibility.

An apparatus for performing the method of the invention comprises plate cylinders set against a common backing cylinder and having associated inking mechanisms and a central gear for driving the backing cylinder, the pitch circle of the central gear being adapted to the diameter of the backing cylinder. This apparatus is characterised according to the invention in that the shaft of the central gear has freely rotatably mounted on it a second central gear which is in mesh with the gears driving the plate cylinders and that both central gears engage the output pinion of PI regulating gearing which drives both of them at the same speed or an adjustable relative speed. By means of the pinions of the differential gearing, the plate cylinders and the backing cylinder can be driven at the desired relative speed to each other.The speed difference of the output pinion of the differential gearing can be produced in that an additional drive is fed into same in known manner by way of a servo-motor.

One example of the invention will now be described in more detail with reference to the drawing, wherein: Figure 1 is a side elevation of a single cylinder flexographic printing machine according to the invention; Figure 2 shows the driving layout of the flexographic printing machine of Figure 1, and Figure 3 is a section on the line Ill-Ill in Figure 2.

A frame 1 of a printing mechanism is connected by a bridge 2 to a rear frame 3. This rear frame 3 is associated with a conventional unwinding device 4 equipped in known manner with a web tension measuring and regulating device. From the unwinder 4, the web 5 is first passed about a directionchanging roller 6 mounted in the rear frame 3 and fed to a feeder 7 led out of a driven feeding roller 8 and a likewise driven pressure roller 9 equipped with rubber rings. By way of further directionchanging rollers without references, the web is then fed by way of a feeder 10 about the backing cylinder 11 and thereby printed by six inking mechanisms 12, 13, 14, 15, 16, and 17. Each inking mechanism consists in known manner of a plate cylinder 18, a registration roller 19 and an immersion roller 20.

After printing, the web is fed through a dryer 21 above the bridge 2 and then reaches a cooling cylinder 22, after which it passes through a feeding device 23 and other unreferenced direction-changing rollers for example back to a coiler.

As is shown in Figure 1, a photocell device 24 on the bridge 2 scans markings applied to the web 5 and emits appropriate signals to a comparator 25.

This comparator also receives signals emitted by the contact points 26 connected to one of the plate cylinders. If the signals emitted by the photocell arrangement 24 and by the contact points 26 arrive at the comparator 25 simultaneously, no regulation takes place. However, if the comparator detects time differences, the PI regulating gearing 27 is actuated by way of a control lin 26'. Depending on whether the signals from the photocell arrangement 24 or from the contact points 26 first reach the comparator equipment 25, the speed of all the plate cylinders 18 is increased or reduced by the Pl regulating gearing 27.

Since the regulating gearing is PI regulating gearing, in addition to increasing or reducing the speed of the plate cylinders there is simultaneous momentary phase displacement. During an increase in speed, the phase displacement is in the direction of rotation and for a reduction in rotary speed the phase displacement is against the direction of rotation. The relative motion between the backing cylinder 11 and the plate cylinders 18 occurring during a regulating step does not markedly reduce the quality of printing because the relative movements that occur are extremely small. The driving scheme is evident from Figure 2 and 3, Fig ure 2 only representing one printing mechanism, namely the one equipped with the contact points 26.

As is shown in Figure 2, the feeder 7 as well as the cooling cylinder 22 and the feeder 23 are driven at the desired speed by way of the main drive motor 24', a V-belt drive 25', the bevel gearing 43, a plurality of pulleys with appropriate belts, as well as the regulators 44 and 28. Leading from the bevel gearing 43 there is a cardan shaft 29 extending to further bevel gearing 30. The central gear 31 is driven by this bevel gearing 30 by way of the inter mediate gear 32 and the drive gear 33. The central gear 31 is rigidly connected by a shaft 34 to the backing cylinder 11 of which the external diameter corresponds to the pitch circle diameter of the central gear 31. Next to the central gear 31 on the shaft 34 there is an additional central gear 35 of which the diameter corresponds to the diameter of the central gear 31.

It will be evident from Figure 3 that a further gear 36 engages the central gear 31. This gear 36 is rigidly keyed on a shaft 37 which, in turn, is rotatably mounted in the housing of the PI regulator 27. Between the gear 36 and the Pi regulator 27 there is a further gear 38 loosely rotatable on the shaft 37 and driven by the PI regulator gearing 27.

The teeth of gear 38 engage the teeth of the second central gear 35, whereby the latter is driven.

If, now, the comparator 25 shown in Figure 1 detects that the signals emitted by the photocell means 24 do not arrive at the same time as those emitted by the contact points 26, the PI regulator 27 changes the speed between the first central gear 31 and the second central gear 35 and at the same time effects mutual phase displacement between the two central gears. The speed of the second central gear 35 is now transmitted by way of gears 39 and 40 to the plate cylinder 18 and also to the registration roller 19. At the end of the registration roller 19 opposite to the gear 40, the roller carries a further gear 41 which is in mesh with the gear 42 connected to the immersion roller 20.

Although Figure 2 only shows one printing mechanism, it will be evident that all the other five printing mechanisms are similarly driven by the second central gear 35 because all the printing mechanisms are uniformly distributed about the backing cylinder 11.

It will be obvious that before the equipment of the invention is put in operation it is necessary to undertake coarse adjustment, i.e. the markings on the web 5 have to be brought into registry with the image to be printed, with the contact points 26 and the photo-cell means 24.

In the present example, regulation in accordance with the invention has been described in relation to a single cylinder flexographic printing press. It is, however, readily possible to apply the regulating means of the invention to multi-cylinder flexographic printing machines in which each plate cylinder is associated with its own backing cylinder.

The apparatus of the invention assumes that slip is possible between the plate cylinder and the web to be printed.

The equipment as described is used primarily in order properly to overprint in a second process webs which have already been preprinted or otherwise marked such as by scoring or perforating, i.e.

the reel of web provided in the unwinder 4 had al ready been preprinted or otherwise premarked in a preceding working operation. This marking is scanned by the photocell means 24 so that, after regulating by the PI regulating gearing 27, the printing mechanisms 12 to 17 correctly overprint the preprinted web 5 or apply further printing to the rear of the preprinted web 5 in conformance with registration marks.

Claims

1. A method of regulating the printing in printing machines in conformance with registration marks and according to the proper printed lengths of webs preprinted with the registration marks or of other marked webs, wherein the errors in registration and printed lengths are detected by comparing the signals emitted by a sensor scanning the markings with the signals emitted by equipment which detects the phase position of the plate cylinder relatively to the scanned markings, characterised in that to obtain printing in conformance with the registration marks in a short time and to achieve printing to the proper length, a permanent change is carried out if necessary in the relative speed between the plate cylinders and the or each backing cylinder.

2. Apparatus for performing the method of claim 1, comprising plate cylinders applied to a common backing cylinder and associated inking mechanisms, and comprising a central gear which drives the backing cylinder and has a pitch circle diameter adapted to the diameter of the backing cylinder, characterised in that the shaft of the central gear freely rotatably mounts a second central gear which engages the gears driving the plate cylinders, and that both central gears engage the two output pinions of PI regulating gearing which drives both of them at the same speed or an adjustable relative speed.

3. A method of regulating printing in printing machines, substantially as herein described with reference to and as illustrated in the accompanying drawings.

4. Apparatus for regulating printing in printing machines, substantially as herein described with reference to and as illustrated in the accompanying drawings.