GB2225750A

GB2225750A - Vibratory fluid transfer mechanism for a rotary printing machine

Info

Publication number: GB2225750A
Application number: GB8924230A
Authority: GB
Inventors: Heinz Skiera; Wolfgang Paul; Harald Rudolph
Original assignee: Kombinat Polygraph Werner Lamberz VEB; Polygraph Leipzig Kombinat Veb
Current assignee: Kombinat Polygraph Werner Lamberz VEB; Polygraph Leipzig Kombinat Veb
Priority date: 1988-10-31
Filing date: 1989-10-27
Publication date: 1990-06-13
Anticipated expiration: 2009-10-27
Also published as: FR2638394A1; GB2225750B; DD276455A1; DE3935215A1; GB8924230D0

Description

VIBRATORY FLUID TRANSFER MECHANISM FOR A ROTARY PRINTING MACHINE The

present invention relates to a vibratory fluid transfer mechanism for a rotary printing machine.

In a known inking mechanism, a continuously drivable duct roller is arranged at an ink duct and a vibratory roller pivotable in vibratory operation between the duct roller and a transfer roller feeding ink to the inking unit rollers arranged therebehind, the drive of the duct roller being adjustabl-e in rotational speed and the pivotal movement of the vibratory roller being continuously drivable by way of a cam. The vibratory roller lays itself in alternation against the.ink duct roller and the first ink transfer roller, wherein a narrow ink strip of a thickness sH, a length 1H (corresponding to the printing width of the machine) and a width bH is transferred over the entire width of the vibrator roller. The quantity of ink fed to the ink distributor system in each vibratory roller cycle (vibratory roller oscillation) corresponds to the volume of the ink strip transferred by the vibrator roller. If the ink layer thickness SH is fixed, the fed quantity of ink is proportional to the ink strip width bH (disregarding disturbing influences). For the absolute value of the ink strip width bH, the following equation applies:

bH UD. nD/nDZ ititH nH/nDZ tH wherein UD is the circumferential length of the ink duct roller, -nD/nDZ is the ratio of the rotational speed of the ink duct roller to the rotational speed of a printing plate cylinder of the machine, 25 nH/nDZ is the ratio of the rotational speed of the drive cam to the 2 rotational speed of the plate cylinder, and 4tH/tH is the keying ratio of the vibrator roller (ratio of the keying time to the period duration of the vibrator cycle period).

As is also evident from this equation, the quantity of ink fed to the inking unit in a single vibrator cycle changes proportionally to the rotational speed ratio nH/nDZ. This means that, if disturbing influences dependent on speed are disregarded, the ink feed for each vibrator cycle period is matched exactly to the ink requirement for each vibrator cycle period at any rotational speed ratio nH/nDZ. How- ever, the probability of occurrence of ink fluctuations in the printed image of the print sequence falling into.the individual vibrator cycle period increases with the number of printing cylinder revolutions fallinto a single vibrator cycle period, an effect of the principle of the discontinuous ink transmission from the ink duct roller into the ink distributor system at the vibratory inking unit.

This ink starvation occurring periodically with the vibrator cycle period is dependent on the ratio of the throughput quantity to the storage quantity of the printing ink in the ink distributor system, wherein the throughput quantity depends on the printing plate, the printing ink and the material to be printed on, and the storage quantity is a constant of the ink distributor system. It follows from this that the limit value, which is connected with a recognisable ink starvation, for the rotational speed ratio nHInDZ can be different for different ink applications.

In known vibratory inking mechanisms, the cam is driven at a fixed gear ratio by way of wheel gear by the main drive shaft of the prfn.tfrrg machine. Correspondingly, the vibrator cycle rate - a single -1k.

vibrator cycle corresponds to a single revolution of the cam - changes in the same ratio as the rotational speed of the printing cylinder.

The relatively low dynamic limit of the vibratory roller imposes an upper limit speed for the printing machine.

With the fixing of the constant rotational speed ratio nH/nDZ, it ensured that on the one hand the dynamic behaviour of the vibratory roller is fulfilled (upper limit of the rotational speed ratio) at the upper limit of the envisaged rotational speed range for the printing plate cylinder and on the other hand that no recognisable periodic ink starvation appears in the printing (lower limit).

The continuously operating film inking unit for a high-speed rotary printing machine has been developed as alternative to the discontinuously operating vibratory inking mechanism.

This inking mechanism, however, is extremely sensitive in adjust- ment and indifferent in ink conduction. Moreover, by contrast to a vibratory inking mechanism, it is not in a position to feed an emulsion of ink and moistening medium from the ink distributor system back to the ink duct, which amongst other things can lead to the defect of excessive build-up of such emulsion on the inking rollers and thereby a required interruption of continuous printing for the purpose of washing.

The specific disadvantages of the film inking mechanism led to the development of a combined vibrator-film inking mechanism, for example a resettable vibrator/film inking mechanism as disclosed in DE 30 08 980.

In this case, the printer has to decide, before work on a printing order, whether printing is to be carried outat full machine speed with the film inking mechanism or at reduced machine speed with the vibratory i S inking mechanism. The complication entailed by the pivot mechanism and the setting device is also disadvantageous and in film operation the above-mentioned disadvantages remain. In vibratory operation, an optimum matching of the ink metering to the use-dependent ink requirement is not possible and the machine speed is limited by the dynamic limit of the vibratory roller because of the cam drive being connected with the machine drive.

There is therefore a need for a vibratory fluid transfer mechanism for a rotary printing machine in which machine speeds can be used above an upper limit speed connected with the dynamic limit of the mechanism to the extent that the quality requirements in printing permit this. In particular, it would be desirable for the influencing magnitudes of the fluid transmission to be such that a maximum machine speed can be used with optimum matching of the fluid metering to the fluid require- ment of the machine printing plate and the storage capacity of the fluid distributor system, as well as with adequate dynamic behaviour of the vibratory roller.

According to the present invention there is provided a vibratory fluid transfer mechanism for a rotary printing machine, the mechanism comprising a continuously drivable duct roller arranged at a fluid duct and adjustable in rotational speed, a transfer roller for feeding fluid to fluid application rollers of the machine, a vibratory roller movable in oscillatory operation between the duct roller and the transfer roller to transfer fluid from the former to the latter, a rotary cam to oscillate the vibratory roller, a continuous drive electric motion to rotate the cam, and regulating means to regulate the rotational speed of the motor, the regulating means comprising - 5 first measuring means to provide a first signal having a value indicative of the rotational speed of a printing plate cylinder of the machine, a transmitter to provide a econd signal having a value indicative of target rotational drive speed of the cam, adding means for adding the first and second signal values and providing a third signal having a value indicative of the sum of the first and second values, second measuring means to provide a fourth signal having a value indicative of actual rotational drive speed of the cam, comparison means for comparing the third and fourth signal values and providing a fifth signal having a value indicative of the comparison result, and means to regulate motor speed in dependence on the fifth signal value, the ratio of the cam drive speed to plate cylinder speed being adjustable and controllable to remain constant for changes in the plate cylinder speed.

In a preferred embodiment, the drive means for the cam is an elect ric motor for continuous rotational movement and the regulating means for regulation of the rotational speed of the motor comprises a first measuring element for measuring the rotational speed of the printing plate cylinder, a transmitter for the rotational drive speed of the cam, a summation element for the signal of the first measuring element and the signal of the transmitter, a second measuring element for measuring the rotational drive speed of the vibrator, a comparison element for the signal of the summation element and the signal of the second measuring element, a regulator, and a setting member. The ratio of the rotational drive speed of the cam to the rotational speed of the plate cylinder is adjustable and can be regulated to be constant on changes in the rotational speed of the cylinder by means of the requating means.

Preferably, the electric motor is an asynchronous polyphase motor and the setting member is a frequency converter. This permits the combination of the advantages of a regulated direct current motor with the undemanding nature of a polyphase squirrel-cage rotor motor. In further refinement, a single regulating equipment is provided for regulation of rotational speed of the electric motor for the drive regulation of all cams in a printing unit or printing machine.

For the setting-up for continuous printing, the vibrator cycle rate one vibrator cycle corresponds to one revolution of a cam plate of the vibrator cam - is set into a defined ratio to the rotational speed of the printing plate cylinder by means of the transmitter for the rotationa] drive speed of the cam. Since this ratio is kept constant by the regulating means, the vibrator cycle rate grows in the same ratio as the rotational speed of the cylinder.

If the rotational speed of the cylinder is to be further increased, then the rotational speed ratio is to be made smaller, because of the dynamic limit of the vibratory inking mechanism, by means of the transmitter for the rotational drive speed of the cam, i.e. the number of printing cylinder revolutions falling into a single vibrator cycle period is increased. As is evident from the above, the quantity of fluid fed for each vibrator cycle period increases proportionally, i.e. the fluid feed remains adapted to the fluid requirement. The limit of adjustment is exceeded if an ink fluctuation, which is recognisable or impermissible for the respective printing order, occurs within the rinting sequence falling into a single vibrator cycle period.

A particular advantage of such a vibratory mechanism lies in the possibility, Df realising a high speed performance of the printing -1 machine with fulfilled quality criteria through targeted adjustment of the ratio of the v ibrator cycle rate to the rotational speed of the printing cylinder for a large number of printing orders. Moreover, high demands on the uniformity of the fluid application on the print- s ing plate can be fulfilled in the range of reduced machine speed.

it is also possible for the regulating means to provide a limit value regulation which keeps the rotational speed ratio constant until reaching the limit value, connected with the dynamic limit of the vibratory roller, for the vibrator cycle rate and beyond that reduces the rotational speed ratio by keeping the vibrator cycle rate constant.

The mechanism can be used for transferring ink or moistening medium.

An embodiment of the present invention will now be more particular ly described by way of example with reference to the accompanying draw ings, in which:

Fig. 1 is a schematic elevation of a vibratory inking mechanism embodying the invention; and Fig. 2 is a schematic diagram of a regulating circuit for the regulation of the rotational speed of a vibrator cam drive in the mechanism.

Referring now to the drawings, there is shown a vibratory inking mechanism which comprises a continuously drivable duct roller 2 arranged at an ink duct 1 and a vibratory roller 4 pivotable in oscillatory operation between the duct roller 2 and a transfer roller 3 feeding ink to an ink distributor system (not shown) arranged therebehind. The 'pivotal movement of the roller 4 is continuously effected by way of a vibrator cam gear 5.

The drive means for the cam gear 5 is an electric motor for continuous rotary movement, in this embodiment an asynchronous polyphase motor 6. Regulating equipment for regulation of the rotational speed of the motor comprises a first measuring element 7 for measuring the rotational speed of a printing plate cylinder of the machine, a transmitter 8 for the rotational drive speed of the cam gear 5, a summation element 9 for the signal of the first measuring element 7 and the signal of the transmitter 8, a second measuring element 10 for measuring the rotational drive speed of the cam gear 5, a comparison element 11 for the signal of the summation element 9 and the signal of the second measuring element 10, a regulator 12 for the rotational speed and an electronic frequency converter 13 intended as a setting member.

In a preferred construction of the frequency converter 13, the converter comprises a control part 13.1 and a power part 13.2. The power part 13.2 contains the components of mains rectifier, intermediate direct voltage circuit and DC-to-AC converter. The control part 13.1 in co-operation with the power part 13.2 provides a three-phase alternating voltage at controllable output frequency, wherein the ratio US/fS of the output voltage US to the output frequency fS is constant at the same time to ensure a constant magnetic flux in the motor 6 in the preferred regulating range of the output frequency.

For setting-up for continuous printing, the cam gear rotational drive speed nH is first set into a defined ratio to the rotational speed nDZ of the printing plate cylinder, for example a ratio of 1:5, by means of the transmitter 8 for the rotational drive speed nHSince this ratio is kept constant by the regulating equipment, the vibrator cycle rate nH increases in the same ratio as the cylinder rotational speed nDZ during running-up of the machine. After reaching the dynamic limit of the vibratory roller 4, a further increase in the cylinder rotational speed nDZ is possible for a reduction of the rotational speed ratio nH/nDZ. For example, a ratio of 1:7 is set by the transmitter 8 for the rotational drive speed nH, i.e. the number of printing cylinder revolutions falling into a single vibrator cycle period increases from 5 to 7 and the running performance of the machine could be increased by maximally 20% without exceeding the dynamic limit of the roller 4.

The limit of adjustment is exceeded if an ink fluctuation, which is recognisable or impermissible for the respective printing order, takes place within the printing sequence falling into a single vibrator cycle period.

A high running performance of the printing machine can be realised by a targeted adjustment of the rotational speed ratio nH/nDZ while observing the quality criteria applicable to the printing order concerned.

Claims

CLAIMS 1. A vibratory fluid transfer mechanism for a rotary printing

machine, the mechanism comprising a continuously drivable duct roller arranged at a fluid duct and adjustable in rotational speed, a transfer roller for feeding fluid to fluid application rollers of the machine, a vibratory roller movable in oscillatory operation between the duct roller and the transfer roller to transfer fluid from the former to the latter, a rotary cam to oscillate the vibratory roller, a continuous drive electric motor to rotate the cam, and regulating means to regulate the rotational speed of the motor, the regulating means comprising first measuring means to provide a first signal having a value indicative of the rotational speed of a printing plate-cylinder of the machine, a transmitter to provide a second signal having a value indicative of target rotational drive speed ofthe cam, adding means for adding the first and second signal values and providing a third signal having a value indicative of the sum of the first and second values, second measuring means to provide a fourth signal having a value indicative of actual rotational drive speed of the cam, comparison means for compar ing the third and fourth signal values and providing a fifth signal having a vIaue indicative of the comparison result, and means to regulate the motor speed in dependence on the fifth signal value, the ratio of the cam drive speed to plate cylinder speed being adjustable and controllable to remain constant for changes in the plate cylinder speed.
2. A mechanism as claimed in claim 1, wherein the motor is an "asynchronous polyphase motor and the means to regulate the motor speed comprises a frequency converter.

1
3. A mechanism as claimed in either claim 1 or claim 2, comprising a plurality of such duct rollers, application rollers, vibratory rollers and cams, the regulating means being arranged to regulate the drive of all of the cams.
4. A mechanism substantially as hereinbefore described with reference to the accompanying drawings.
5. A rotary printing machine provided with a mechanism as claimed in any one of the preceding claims.

T-1- Wr.l'R. 4TP 'Rirt.hp.r rnnies mavbe obtained from The Patent Office.