Fig 1 : Automated plate feed on the printing unit
of a sheet-fed offset press.
a Feeding the plate;
b The structural design of a plate clamping mechanism
(SM 102/Autoplate, Heidelberg)
Removing the printing plates from the preceding job and mounting the printing plates for the next job can
take place at various stages of an automated process. Plate removal and feeding operations may be performed successively for individual plates with the assistance of the operator or fully automatically by means of cassette systems with no operator intervention once the change-over process has been initiated.The first designs for automatic plate changing systems for sheetfed presses came from Japan around 1990.
When mounting a set of printing plates for a multicolor job, it is essential that the printing plates are clamped in accurate register on the plate cylinder. This is achieved by means of the register holes on the printing plate and suitable guide systems. It implies, of course, that in prepress the color separations will have been exposed in accurate register on the printing plates.
Fig 2 : System for automated printing plate change on
a sheet-fed offset press (Lithrone/APC, Komori)
The requirements for the reliability and efficiency of automated plate feed systems are very exacting, since accurate positioning of the plate in the printing unit can be achieved even with manual plate feed because of the high-quality register systems available in prepress and the press. The particular advantage of automatic plate feed is that no manual clamping of the plate is required, no operator related factors are in effect, and plate change-over can take place on all printing units of the press at the same time (not always synchronously – this depends on the cylinder arrangement and cylinder position in the several printing units regarding the cylinder gap).
Fig 3 : Automated change of printing plate using a
cassette for plate removal and plate feed
for the next job on the printing unit of a
sheet-fed offset press (Rapida 105, KBA)
Various stages of the automated plate feeding operation are shown in figure 1. First, the plate is prepared/ placed ready in the printing unit for the new job, and then the plate is placed ready for mounting on the plate cylinder,which is followed by the automatic feeding and clamping process. Figure 1b shows how the plate is fed into the plate cylinder’s clamping system and how loading systems are designed.
Another system in cassette design is shown in figure 2. Figure 3 shows how plate removal and plate feed can be done automatically via a cassette system.
Fig 4 : Fully-automatic printing plate change on a
4-color sheet-fed offset press with multiplate
cassette system (SM 102/Multiplate,
Heidelberg)
There are designs for an automatic plate change, where the printing plates for several jobs can be stored in one cassette in the correct sequence. This means that the plates for several successive jobs can be ejected and loaded automatically. Such a system is shown in figure 4. However, these multi-plate cassette systems might prove to be troublesome in the case of malfunctions or if rescheduling measures have to be taken on short notice, for example changes in the press assignment or the processing sequence of orders.
Automated plate changing systems are also used on web offset printing systems. Figure 5 gives an example of how the plates for the upper and lower printing unit/couple on a blanket-to-blanket
Fig 5 : Automated printing plate change on a web offset printing system
(M-600, Heidelberg)