Abstract
The printability problems in web-fed lithographic presses
attacked in the work. New types of on-press densitometers
for print quality monitoring have been designed and
implemented. The optical densitometer transducers have
incandescent lamps as light sources and silicon
photodiodes as detectors. For print on metal foils, the
concept of specular reflection density has been
introduced. For studies of ink transfer in a multi-roller
inking train, a non-contacting, capacitive ink-film
thickness monitor has been constructed. The data obtained
with the instrument have been used in the development of
smoothening algorithms for presetting procedures. Some
typical hazards of careless inker presetting with a duct
blade and inking screws are shown. An optical instrument,
the plate scanner, has been designed and constructed for
evaluation of the relative printing area distribution on
offset plates. A measuring method using polarized light
can be applied to presensitized and bi-metal plates,
whereas the conventional, diffuse measuring method can
only be used with presensitized plates. The plate scanner
is able to plot the resulted ink consumption profile on a
plastic foil with a marking pen. For actuation of the
various process control operations, a remote control
system has been constructed. Closed-loop control
algorithms have been implemented for a laboratory
web-offset press to regulate the print density within a
chosen target range. The control efforts are based on
density measurements anal the ink feed rate is used as a
control variable. After presetting, the screw positions
are controlled to maintain an even density profile. In
case of press speed changes, a master-acting duct roller
is used as a control device. The effect of dampening on
print contrast has also been studied, and the proposal of
an adaptive dampening control method has been suggested.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Award date | 30 May 1983 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-1768-7 |
Publication status | Published - 1983 |
MoE publication type | G4 Doctoral dissertation (monograph) |