GB2192153A - Damping system in printing machines - Google Patents

Abstract

A printing machine (2) comprising a plate roller (4), a reservoir (6) for water (8), a fount roller (10) for transferring water (8) from the reservoir (6), and drive means (60) for driving the fount roller (10) at a first speed appropriate to provide that amount of water (8) necassary for damping the plate roller (4) during reproduction running conditions of the printing machine (2), and at a second speed appropriate to reduce that amount of water (8) provided to that necessary for damping the plate roller (4) during idle running conditions of the printing machine (2). <IMAGE>

Description

SPECIFICATION A printing machine This invention relates to a printing machine.

It is well known that during printing on printing machines, water is required to be present. The printing machines may be sophisticated large printing machines or relativeiy simple duplicator machines. The water can either be used alone or it can be used in admixture with alcohol. The amount of water employed should be precisely controlled to give good quality printing.

Known printing machines comprise a plate roller, a reservoirfor water, and a fount rollerfor transferring water from the reservoir to the plate roller. In the known machines, the fount roller is not able precisely to control the transfer of water from the reservoir to the plate roller and this poor control can disadvantageously affect the quality of printing.

One of the main causes ofthe poor printing resulting from the imprecise control ofthewater applied to the plate rollervia thefount roller, is that the fount roller usually rotates at a speed appropriate for providing adequate water damping for the plate roller during reproduction running conditions ofthe printing machine. When the printing machine is only operating at idle running conditions, the fount roller is still rotating as though the printing machine is operating under reproduction running conditions.

This means that the fount roller is rotating far too fast for idle running conditions of the printing machine and the result is thattoo much water is applied to the plate roller, giving poor quality printing.

It is an aim ofthe present invention to obviate or reduce the above mentioned problem.

Accordingly, this invention provides a printing machine comprising a plate roller, a reservoirfor water, a fount rollerfortransferring waterfrom the reservoir of the plate roller, and drive means for driving thefount roller at a first speed appropriate to provide that amount of water necessary for damping the plate roller during reproduction running conditions of the printing machine, and at a second speed appropriate to reduce that amount of water provided to that necessary for damping the plate roller during idle running conditions ofthe printing machine.

The fount roller may transfer water to the plate rollervia a plurality of other rollers.

The other rollers may be, for example, a ductor roller, an oscillator roller and a damp forme roller.

Thedampforme roller may be employed to effect a milling of waster and inkwhich is often desirableto give good quality printing.

The ductor roller may be a nitrile or a polyvinyl chloride nitrile roller. The oscillator roller may be a nylon covered aluminium roller.Thedampforme roller may be a nitrile roller or a polyvinyl chioride nitrile roller. Other materials forthe various rollers can be employed if desired Thedrivemeansforthefountrollerwill usuallybe an electric motor.

The electric motor may be arranged to directly drive the fount roller through a reduction gear box provided on the electric motor. The gear box may be connectedto a shaftofthefount roller bya solid coupling.

The printing machine may be one in which the drive means only operates at either the first speed or the second speed. Appropriate first and second speeds may be achieved by means of adjusting variable potentiometers providing appropriate currentforthe electric motor.

If desired, the drive means may be variable speed drive means, for example a variable speed electric motor, in which case the printing machine may include control means for varying the output speed ofthe drive means in proportion to the speed of operation of the printing machine. Thus, for example, the output speed ofthe drive means may be varied in proportion to the speed of operation of the printing machine from the idle running condition ofthe printing machine up to the reproduction running condition ofthe printing machine. The proportional variation of the output speed of the drive means may be effected by the use of information that is normally fed to a variable potentiometer or other device used to control the actual printing speed of the printing machine.This information may also be fed to a potentiometer or other variable device controlling the amount of current providedforthe electric motor.

Advantageously, the fount roller is able to be driven in a reverse direction forgiving improved milling of ink and water.

The printing machine of the present invention is preferably such that the water is fed via the fount rollerdirecttothe plate roller, ratherthan being fed into an ink reservoir.

Embodiments ofthe invention will now be described solely by way of example and with reference to the accompanying drawing which shows schematically the various printing rollers, water supply rollers and ink supply rollers in a printing machine.

Referring to the drawing, there is shown a printing machine 2 comprising a plate roller 4, a reservoir6 for water 8, and a fount roller 10 fortransferring water8from the reservoir 6to the plate roller4.

The reservoir 6 andthefount roller 10 form partof a water unit 12 which also comprises a ductor roller 14, a nitrile roller 16, an oscillating roller 18 and a Molleton roller 20. The direction of rotation ofthe various rollers in the water unit 12 is shown by arrowsinthewaterunit12.

The plate cylinder 4 receives inkfrom an inkunit 22. The ink unit 22 comprises an inkfount roller 24, a ductor roller 26, a rubber roller 28, idler rollers 30,32, inkforme rollers 34,36, a main oscillating roller 38, a rubber roller 40, and a distribution roller 42. The direction of rotation ofthe various rollers in the ink unit 22 is shown by arrows. The passage of inkfrom the inkfount roller 24to the inkforme rollers 34,36 is shown bytwo long arrows 44,46. it, the ink unit 22, the roller46 acts as an auxiliary oscillating roller.

Waterwhich is placed on the plate roller4viathe waterfount roller 10 and inkwhich is placed onthe plate roller4via the inkfount roller 24 aretransferred to the blanket roller 48. Paper 50 passes in the direction ofthe arrow 52throughthe nip 54 between the blanket roller48 and an impression roller 56. The impression roller 56 operates in conjunction with a transfer roller 58. An image on the plate roller4 is thus transferred to the paper 50. As is well known, the rollers 4,48 and 56 are sometimes referred to in the art as cylinders.

The printing machine 2 includes drive means in the form of an electric motor60. The electric motor60 drives a gear box 62which is attached to an outside housing part (not shown) ofthe electric motor 62.

The gear box 62 provides the appropriate gearing necessaryto directly drive the waterfount roller 10.

More specifically, an output shaft 64 from the gear box 62 is directly coupled to a shaft 66 ofthe water fount roller 10 by means of a solid mechanical coupling (not shown).

The electric motor 60 is able to drivethefount roller 10 at a first speed appropriate to that amount of water 8 necessary for damping the plate roller4 during reproduction running conditions ofthe printing machine 2. The electric motor 60 is also able to drive the fount roller 10 at a second speed appropriate to reduce that amount of water 8 provided to that necessary for damping the plate roller4 during idle running conditions ofthe printing machine 2. It will be understood that the second speed will be lowerthan the first speed. By having the two speeds, excess water8 is not provided on the plate roller4 during idle running conditions ofthe printing machine 2, as would be the case if the fount roller 10 were left running atthefirstspeed.

Similarly, by having the fount roller 10 able to operate atthe first and the second speeds, too little water 8 is avoided being provided on the plate roller 4 as would be the case if the fount roller 10 were left running at its second speed appropriate for idle running conditions ofthe printing machine and the printing machine was then operated at its reproduction running level. By controlling the amount of water8 provided on the plate roller 4 as described above, good quality printing can be achieved. Also, any need for operators to try and adjustthe machineryto getthe required amount of water8 onto the plate roller4forgiving running conditions ofthe printing machine 2 is obviated or reduced.

In a modification ofthe invention, the electric motor 60 can be such that it is a variable speed electric motor. If printing machine 2 then includes control means forvarying the output speed ofthe electric motor 60 in proportion to the speed of operation ofthe printing machine, itwill be apparent thatthe amount of water 8 provided on the plate roller4 can be progressively and incrementally increased from the minimum amount required at idle running conditions of the printing machine 2,to the maximum amount of water 8 required at the fastest running reproduction printing speed of the printing machine 2.The progressive control of the variable speed electric motor 60 may be achieved by providing a variable potentipmeter(not shown) which controls the powerto the electric motor 60 and which is automatically adjusted consequent upon information received as to the running speed ofthe printing machine 2 at any precise moment in time.

This information may be obtained from a main machine potentiometer(notshown)which is effective to vary the drive speed of main drive motor (not shown) for operating the entire printing machine 2.

Where the electric motor 20 is arranged to operate substantially solely at the two speeds appropriate to reproduction running conditions ofthe printing machine 2 and idle running conditions ofthe printing machine 2, then these two speeds may be adjusted as may be required, for example manually by the use of appropriate control potentiometers (not shown).

Itwill be seen from the drawing that the water unit 12 and the ink unit 22 are separate from each other so thatthe water and the ink is separately applied to the plate roller 4. The ductor rollers 14,26 move as indicated to be in driving engagement or non-driving engagement with the respective rollers 10,26 as will be understood. Obviously, as the plate roller4with its printing plate attached rotates inkfrom the ink unit 22 will be picked up by the cloth covered Mollerton roller 20. Thus at the roller 20, some milling ofthe ink and water will occur and this may be effective to give better printing under some printing conditions.Thefount roller 10 is advantageously constructed such that its direction of rotation can be reversed and this will obviously reverse the direction of rotation of the other rollers in the water unit 12, including the direction of rotation ofthe roller 20. This is effective to increasethe milling action ofthe water and the ink andthis increased milling may be effective to give yetfurther better quality printing. If desired, the direction of rotation of the output shaft 64 can be reversed to reverse the direction of rotation of the fount roller 10.

ThepapersOwill usuallycomefromapile(not shown) ofthe paper and, once the paper 50 is printed, it will be delivered to another pile (not shown).

It is to be appreciated that the embodiments ofthe invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effective. Thus, for example, the number of rollers in the water unit 12 and the ink unit 22 may be increased or decreased as may be required. Also, alcohol may be provided in the water 8. Generally, the printing machine 2 may be constructed to any desired degree of sophistication so thatthe printing machine 2 may be a large and complicated sophisticated colour printing machine or it may be a simple duplicating type of printing machine printing either black and wh lte or various colou rs, for examplefourcolours,as maybe required. Thus it will be understood that the printing machine may have as many printing heads as there are colours two be printed. Generally, the drive means may be controlled manually and/or automatically. For automatic control, all the required functions may be programmed into the printing machine, with the appropriate programme functions being caused two operate, for example by a sensor op the machine which would sense appropriate machine running conditions at any particular instant in time that would cause the operation of the programmed functions consequent upon the sensed machine running conditions. For example, the sensor could be employed to monitor the number of sheets of paper being printed per hour in order to enablethe water unit 1 2 to supply the required amount of water as described above.

Claims (12)

1. A printing machine comprising a plate roller, a reservoirforwater, a fount rollerfortransferring water from the reservoir of the plate roller, and drive means for driving the fount roller at a first speed appropriate to provide that amount of water necessaryfordamping the plate roller during reproduction running conditions of the printing machine, and at a second speed appropriate to reduce that amount of water provided to that necessary for damping the plate roller during idle running conditions ofthe printing machine.

2. A printing machine according to claim 1 in which the fount rollertransfers water to the plate rollervia a plurality of other rollers.

3. A printing machine according to claim 2 in which the other rollers are a ductor roller, an oscillator roller and a damp forme roller.

4. A printing machine according to claim 3 in which the damp forme roller is adapted to effect a milling of water and ink.

5. A printing machine according to any one ofthe preceding claims in which the drive means forthe fount roller is an electric motor.

6. A printing machine according to claim 5 in which the electric motor is arranged to directly drive the fount rollerthrough a reduction gear box provided on the electric motor.

7. A printing machine according to any one of the preceding claims in which the drive means only operates at eitherthefirst speed orthesecond speed.

8. A printing machine according to any one of claims 1 to 6 in which the drive means is a variable speed drive means.

9. A printing machine according to claim 8 and including control means for varying the output speed of the drive means in proportion to the speed ofoperation ofthe printing machine.

10. A printing machine according to any one of the preceding claims in which the fount roller is able to be driven in a reverse direction for giving improved milling of inkandwater.

11. Aprinting machine according to any one of the preceding claims and which is such that the water is fed via thefount roller direct to the plate roller.

12. A printing machine substantially as herein described with reference to the accompanying drawing.