Gearless flexo printing machine .

Drive technology for flexographic printing presses

Direct drive technology on printing presses is one of several developments in recent years that have helped flexo keep pace with other processes.   Looking at the printers’ main goals it can be seen that they are reduction of changeover times, production waste and production costs plus higher printing quality. 
 This press consists of central drum printing units and is characterised by the direct drive applied to the plate cylinder axis.  It is a gearless printing press suitable also for short runs and quick changeovers, designed to operate with sleeves for both plate cylinders and anilox rollers.

Advantages of direct drive
The advantages of direct drive are: higher print quality as it is possible to synchronise the surface web speed with the speed of the plate, regardless of its thickness; quick regulating at start-up as the printing decks go into register automatically with remote or automatic final adjustment to compensate for plate mounting errors; better performance of the anilox rollers which can rotate at the proper speed during printing, slow rotation and on-press washing. Another practical advantage of a direct driven flexo press is that the operator is able to print a differential repeat on a given repeat sleeve, in other words, he can print different repeats with the same sleeve.
When thin and quite flexible materials are being printed, it happens very often that the actual repeat gauged on the rewound reel is not exactly the one expected for the next packaging phases . Since it is possible to regulate the plate speed with the web speed to a certain extent, these print length errors can be rectified directly during the printing phase.
The limits of speed (repeat) corrections on a halftone print can be equal to ± 1-1.5% in relation to the repeat of the plate (sleeve) mounted on the press. If the differential repeat remains within the above limits, the operator can still get a good quality and good print dot. On exceeding these figures the colour dot loses its perfect roundness and the final outcome is a non-perfect print quality that is proportionate to the amount of variation described above.

Structural rigidity
A must in a gearless flexo press is the need for absolute rigidity between the direct motor and the plate mandrel. The register accuracy requirement of the packaging market necessitates that the motor plate should be in one block without any clearance or backlash between the two parts.
In order to achieve this, it is essential to eliminate any kind of transmission, either with gears or pulleys, between the motor and the plate sleeve mandrel. The plate sleeve mandrel is a rigid shaft coming out directly from the motor itself. The angle position of the motor matches the angle position of the plate. Only such a part of the machine design can guarantee that the whole system runs as if ruled by an absolutely rigid axis without any clearance or backlash, which assures perfect control, holding and precision of registers amongst all print units.
From this emerges another major feature to the operator’s advantage and it is that when starting a new job, all the decks or plates register one to the other automatically. The sleeves are mounted on their respective mandrels in their pre-registered position aided by reference pins. All data relating to the printing repeat, material thickness etc having been fed into the machine by the operator, therefore the system guarantees a very quick job start-up particularly on repeat runs. The system perfection is achieved by synchronising each component of the machine and the efficient transmission of the operational data to each component.
It is important to remember that the master motor is not a real motor and is not the main motor, which matches the CI drum turn. It is a virtual motor i.e. pulse shaper-generator, a perfect machine free from defects due to assembly or any other interference occurring during running. All motors connected to the master one can have their speed adjusted according to operator requirements. Furthermore the system controls both the speed and the position of all motors at any time during machine running.
To give an idea of the precision of these controls it is only necessary to remember that the loops of position and speed are checked every 250 microseconds. All machine control and command signals, as well as the data transmitted to the various parts of the press run in digital format. All data is transmitted through fibre optics.

The use of sleeves
Depending on what type of sleeve system is used, it might be advisable to use an intermediate sleeve (carrier). The remote adjustment of length registers to rectify any mistake to non-perfect assembly of the plate to the sleeves is always possible. The adjustment, which occurs directly on the plate motor, can be accomplished either on the printing group or on the video camera monitor by means of a palm top operator keyboard.
An alternative solution is an automatic register control system, which can be applied on the press to fine-tune the registers at every start-up. Start-up time and storing the parameters related to each job, including the printing positions and the register positions, into the supervisor reduces waste. The advantages of recalling the stored information and starting a job are only applicable if the plates remain mounted on the relative sleeves. Changeovers are then drastically reduced, if an on-press washing system is used, changeover times are reduced even further.

AC Motors

• The motors are AC, vectorially controlled, brushless, reliable and strong.
• The motor speed can be adjusted as can the DC motor, but AC motors are characterised by a higher static torque as well as by a more immediate reaction to any input given by the drives.
• The rotor axis angle of these motors can be adjusted, while the phase of the motor shaft is controlled to a pre-set position. This concept is quite important and is strictly related to the length register control and its precision in a gearless flexographic press.

The advantages, therefore, for the operator having no gears are as follows:

Quicker job changes as no gears have to be prepared, changed and meshed; no gears to be purchased and stocked;

 No imperial to metric options, infinitely variable and continuous printing repeat to match exactly any packaging process requirements not being limited to the gear pitch;

Material waste reduction due to the capacity of printing exactly the required repeat length.