Graphic Design & Printing Technologythe sample taken from the run visually with the master proof. The function
keys of the control console corresponds to the ink zone of the printing unit,
which the operator can use to adjust the ink zone opening in individual printing
unit and to correct the colour with the master proof. The console has another
set of function keys that are used to set the ink register. The position of the
individual plate cylinders can be adjusted in circumference and lateral direction
in series of small steps. Some control console has the facility for downloading
job data such as colour settings from storage media. Sophisticated control
console systems can control the operations of dampening unit and air suction
and air blower.
Plate Image Scanners: They are used
for colour pre-setting operations.
They scan a plate to see how much
ink it require and the data is then input
into the control console for remote
adjustments of ink zone opening.
Control console also include
measuring devices for color, register
and match. Colour measurement and
control are done with the help of
measuring devices like densitometer
and colourimeter attached to the console. Register measurement and control is
done with the aid of optical magnifying glass attached to the control console.
Quality Control Devices
They are devices which are stripped, plated and printed in an off-image area of
the press. Under magnification, these images can aid the press operator in
determining overall press sheet image quality and in making press adjustments.
Most of the devices have been developed by the Graphic Arts Technical
Foundation (GATF), which is an American organisation at who are at the
forefront of researches and developments in graphic arts.
Colour Bar :A colour bar is a strip of colours printed in the trim area of a
press sheet. This strip usually consists of overprints of two- and three-colour
solids and tints. Press operators can monitor uniform ink distribution across
the press sheet by measuring the density of CMYK patches. A colour bar is
also used to monitor printing variables such as trapping, ink density, dot gain
and print contrast.
Star Target:Star targets are circular patterns of lines primarily used to detect
dot gain, slur, and dot doubling. Dot gain is the enlargement of printed dot due
to excessive ink film or pressure between cylinders. Slur is a stretching of half
tone dots caused by a slippage of the cylinders. Dot doubling is the printing of
the same dots twice.