Method and device for regulating a supply of dampening solution in an offset printing press

Method for regulating a supply of dampening solution in an offset printing press having a printing plate includes supplying at least one selected region of the printing plate with a well-defined amount of energy; determining and measuring scumming occurring in the selected region; comparing the measured scumming in the selected region with a prescribed scumming matched to the respective supplied amount of energy; and adjusting the supply of dampening solution, if the measured scumming and the prescribed scumming deviate from one another; and a device for performing the method.

The invention relates to a method and a device for regulating a supply of 
dampening solution in an offset printing press. 
The quality of printed products produced in an offset printing press 
depends essentially upon ink feed or inking and upon dampening-solution 
supply, which is adjusted to the inking. These variables, in turn, are 
dependent upon further parameters, such as temperature, ink composition, 
type of printing plate, grade of paper used, and so forth. While the 
inking decisively determines the color effect of a printed product, it is 
possible to influence contrast sharpness of the printed image by a correct 
supply of dampening solution. 
Print quality is optimal when the dampening-solution supply is set so that 
the printing process takes place in the vicinity of a so-called smearing 
limit. The printed image is distinguished by high contrast sharpness and 
brilliance thereat. 
Printing in the vicinity of the smearing limit is critical in that, if 
conditions should cause a drop below this limit, the non-printing regions 
of the printing plate begin to scum, i.e., ink deposits occur in the 
non-printing regions of the printing plate. If there is an excessive 
supply of dampening solution, as mentioned hereinbefore, the brilliance of 
the printed image is lost. In extreme cases, water marks occur in the 
printing regions which, like the aforedescribed scumming, results in the 
printing of rejected or waste sheets. 
In heretofore known proposals for regulating dampening solution, "indirect" 
or "direct" measuring methods are used. Thus, German Patent 38 30 732 
describes an "indirect" method for monitoring the supplying or feeding of 
dampening solution in an offset printing press. According to this 
heretofore known method, non-printing or subject-related ink-free areas 
and printing areas or subject-related areas covered with ink in the 
vicinity of an edge of a full-tone patch or patch are scanned by means of 
an opto-electric transducer. The resulting scanned signals are compared 
with setpoint or desired values. If there is a deviation between the 
scanned or measured values and the setpoint or desired values, necessary 
changes in the supply of dampening solution are determined in regard to 
the differences in the printing and non-printing area or surface 
coverages. 
The foregoing, heretofore known indirect method, has an advantage over 
heretofore known direct measuring methods which determine the amount or 
quantity of dampening solution directly, in that the printed product 
itself is used in order to evaluate the supply of dampening solution: 
necessary adjustments to the supply of dampening solution are evaluated on 
the basis of the printing results, i.e., the printed product, and are thus 
largely independent of further parameters. This heretofore known indirect 
method, however, is problematic during the setting-up phase of the 
printing press. 
It is accordingly an object of the invention to provide a method and a 
device for regulating the supply of dampening solution in an offset 
printing press which afford the possibility, even as early as during the 
setting-up phase, to effect a reliable setting or adjustment of the 
dampening-solution supply. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, a method for regulating a supply of 
dampening solution in an offset printing press having a printing plate, 
which comprises supplying at least one selected region of the printing 
plate with a well-defined amount of energy; determining and measuring 
scumming occurring in the selected region; comparing the measured scumming 
in the selected region with a prescribed scumming matched to the 
respective supplied amount of energy; and adjusting the supply of 
dampening solution, if the measured scumming and the prescribed scumming 
deviate from one another. 
In accordance with another aspect of the invention, there is provided a 
device for regulating a supply of dampening solution in an offset printing 
press having at least one printing plate, comprising at least one energy 
source for the one printing plate for supplying at least one selected 
region of the one printing plate with a well-defined amount of energy; 
measuring means for determining and measuring scumming occurring in the 
one selected region; evaluation means for comparing the measured scumming 
in the one selected region with a given scumming value matched to the 
well-defined amount of energy; and adjusting means for correcting the 
supply of the well-defined amount of energy in accordance with any 
deviation between the measured scumming and the given scumming value 
determined by the evaluation means. 
In accordance with alternative features of the invention, the one energy 
source is a laser, a microwave transmitter, a heat source, or a 
compressed-air source. In general, virtually all energy sources which 
permit the production of a well defined quantity of energy: such as 
lasers, microwave transmitters, heat sources, compressed-air sources, and 
the like, may form part of the inventive device. 
In accordance with another feature of the invention, the one selected 
region contains an oleophobic region of the one printing plate. 
In accordance with a further feature of the invention, the one printing 
plate has a full-tone patch thereon, and the oleophobic region is disposed 
in vicinity of an edge of the full-tone field or patch. The oleophobic 
region is situated in the vicinity of an edge of the fulltone field or 
patch on the printing plate, because, experience has shown that scumming 
tends to occur first in such regions. 
In accordance with an added feature of the invention, the one selected 
region is a half-tone field or patch. Likewise, it is also possible, 
however, to employ a specially formed half-tone field or patch, such as a 
line-screen field or patch, as the one selected region. Corrections in or 
adjustments to the supply of dampening solution are made when changes with 
regard to the scumming of the line-screen field or patch exceed or fall 
below a given or prescribed level which is matched to the well-defined 
amount of energy supplied. 
In accordance with an additional feature of the invention, the one selected 
region is disposed on a nonprinting margin of the one printing plate. In 
this regard, it is noted that the non-printing or print-free margin of the 
one printing plate whereon the one selected region is disposed comes into 
contact with the dampening-solution applicator rollers and inking rollers. 
Adjustments of the energy source and to the measuring means are thereby 
largely prevented. As a reference for determining the area or surface 
coverage, for example, a full-tone patch and a non-printing or ink-free 
patch can be measured in the same printing form, i.e., the one printing 
plate. 
In accordance with yet another feature of the invention, the printing press 
includes an inking unit with a plurality of successively disposed inking 
rollers, and a dampening unit with a plurality of successively disposed 
dampening-solution applicator rollers, and the one energy source is 
disposed between a last dampening-solution applicator roller of the 
plurality thereof and a first inking roller of the plurality thereof. 
In accordance with an alternate feature of the invention, the printing 
press includes a dampening unit with a plurality of successively disposed 
dampening-solution applicator rollers, and the one energy source is 
disposed before a first dampening-solution applicator roller of the 
plurality thereof. 
In accordance with another alternate feature of the invention, the printing 
press includes an inking unit with a plurality of successively disposed 
inking rollers, and the one energy source is disposed after a last inking 
roller of the plurality thereof. 
In accordance with yet a further feature of the invention, the measuring 
means for determining and measuring scumming occurring in the one selected 
region comprise means operatively associated with a sheet which has been 
printed from the one plate in the printing press for measuring scumming in 
a region of the sheet corresponding to the one selected region. Thus, the 
measuring means determine and measure the scumming of the one selected 
region off-line, i.e., the scumming of the one selected region is 
determined outside the printing press on a sheet which has been printed in 
the printing press. In accordance with an alternate embodiment, the 
scumming of the selected region is determinable on-line on the sheet. 
In accordance with yet an added feature of the invention, the printing 
press has a plate cylinder whereon the one printing plate is mounted, and 
wherein the measuring means is operatively associated with the plate 
cylinder of the printing press for measuring scumming in the one selected 
region on the printing plate mounted on the plate cylinder. 
In accordance with an alternate feature of the invention, the printing 
press has a blanket cylinder operatively engageable with the one printing 
plate, the measuring means being operatively associated with the blanket 
cylinder for determining and measuring scumming of the one selected region 
at a respective location on the blanket cylinder corresponding to the one 
selected region on the one printing plate. In this regard, it is noted 
that because the printed image, in offset printing, is transferred from 
the printing plate onto the blanket cylinder and, thereafter, in the 
printing gap between the blanket cylinder and the impression cylinder, 
onto a sheet, it is also possible to determine the scumming of the one 
selected region at a relevant location on the blanket cylinder which 
corresponds to the one selected region on the printing plate. 
In accordance with yet an additional feature of the invention, at least one 
cross-piece is mounted in the device and carries at least one of the 
energy source and the measuring means at a respective suitable location 
with respect to a plate of a plate cylinder, for example, which is being 
scanned.being scanned. The energy source and/or the measuring means are 
movable on the respective cross-piece to the desired measuring positions 
via an automatic or manual control. 
In accordance with a concomitant feature of the invention, means are 
provided for switching the energy source on and off, and the measuring 
means is actuatable for determining and measuring scumming of the one 
selected region in a scumming and in a non-scumming condition. This 
feature is applicable when the device according to the invention is 
intended for on-line regulation. 
Alternatively, in the immediate vicinity of the one selected region wherein 
the dampening-solution supply is influenced by the supply of energy, an 
identical selected region which is not influenced by a controlled supply 
of energy may be used for measuring purposes. In order to determine the 
area or surface coverage, it is furthermore possible to measure a 
full-tone region and a nonprinting or ink-free region. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
device and a method for regulating a dampening-solution supply in an 
offset printing press, it is nevertheless not intended to be limited to 
the details shown, since various modifications and structural changes may 
be made therein without departing from the spirit of the invention and 
within the scope and range of equivalents of the claims.

Referring now to the drawing and, first, particularly to FIG. 1 thereof, 
there is shown therein a printing unit with the device according to the 
invention. The printing unit includes conventional printing-unit 
cylinders, namely a plate cylinder 1 carrying a printing plate 2, a 
blanket cylinder 3 and an impression cylinder 4, the cylinders being in 
mutual rolling engagement. Only a last dampening-solution applicator 
roller 5 of an otherwise non-illustrated conventional dampening unit is 
shown in the figure; likewise, a representation of a conventional inking 
unit in the figure has been restricted to inking rollers 6 thereof, all in 
the interest of clarity. 
The device according to the invention includes an energy source 7, a 
measuring device 16 and an evaluation/control device 9. The energy source 
7 transmits energy to a selected region 14 (FIG&gt;3) of the printing plate 
2. The selected region 14 of the printing plate 2 is, quite generally, a 
region of the plate containing non-printing, i.e. oleophobic, locations. 
Both the energy source 7 as well as the measuring apparatus 16 may be 
displaced in axial direction of the plate cylinder 1 through the 
intermediary of traverses or cross-pieces 18. 
Controlled by the evaluation/control device 9, the energy source 7 
transmits a well defined quantity of energy to the selected region 14. 
Consequently, a small, precisely defined and always constant quantity of 
dampening solution is removed thereby from the selected region 14, so that 
a clearly visible scumming occurs in the region of the printed image. The 
evaluation/control device 9 regulates the supply of dampening solution so 
that, with a constant removal of dampening solution, the scumming in the 
selected region 14 reaches a given prescribed level during the setting-up 
phase and so that the given level is maintained during the production 
phase, respectively. With the device according to the invention, it is 
possible to adjust or set the supply of dampening solution for the 
printing process, more or less independently of other parameters such as 
type of plate, temperature, and so forth. 
FIG. 2 is a graph showing the required quantity W of dampening solution as 
a function of temperature T. In zone A, the dampening-solution supply is 
so small that ink deposits occur in the non-printing regions of the 
printing plate 2; scumming is a result thereof and, consequently, the 
printing of waste sheets. Zones B, C, D represent the working zone. In 
order to obtain a good printed product, the dampening-solution quantity 
must be set in this working zone B, C, D. The narrow zone B between the 
zones A and C forms the so-called smearing limit, i.e., the limit at which 
the non-printing regions start to accept ink. 
As mentioned hereinbefore, print quality in the vicinity of the smearing 
limit is optimal. Consequently, the printer will endeavor to maintain the 
dampening-solution quantity within the optimal working zone C. 
In zone E, the supply of dampening solution is so great that water marks 
appear in the printing regions and, just as the scumming, leads to the 
printing of waste sheets. 
As shown in the plot diagram of FIG. 2, an effect of an increase in 
temperature, when the inking is constant, is that the supply of dampening 
solution has to be increased in order to ensure that the printing process 
will continue to take place within the optimal working zone. With the 
device according to the invention, which uses as a controlled variable the 
controlled scumming of a selected region of the printing plate 2, the 
regulation of the dampening solution is more-or-less independent of all 
disruptive influences. 
FIG. 3 is a fanciful diagrammatic representation of a printing plate 2 
bearing an image or subject 10. According to possible embodiments of the 
device according to the invention, the selected region 14a is disposed in 
the vicinity of a full-tone patch 12 of a quality-control strip 11, or the 
selected region 14b is disposed in the vicinity of a region with high area 
coverage in the subject 10. Alternative embodiments provide for a selected 
region 14c to be a halftone patch, for example a line-screen patch, 
separately printed in the same form, or for a selected region 14d to be 
situated in the region of the non-printing or print-free border 15 of the 
printing plate 2. 
FIG. 4 is a flow diagram for controlling the device according to the 
invention for regulating a supply of dampening solution in an offset 
printing press. The program is started at 19. At 20, the 
evaluation/control device 9 of the energy source 7 specifies an amount or 
quantity of energy which is to be supplied to the printing plate 2, the 
amount of energy depending, among other things, on the rotational speed of 
the printing press. At point 21 in the flow diagram, the area or surface 
coverage F.sub.desired value or F.sub.setpoint of a selected region 14 of 
the printing plate 2 is determined as a function of the amount or quantity 
of energy supplied to the selected region 14, the area or surface coverage 
F.sub.desired value being the area or surface coverage which should occur 
as a result of the intentionally produced, controlled scumming for a given 
dampening-solution supply. 
Thereafter, at 22, the measuring device 16 is triggered so that, allowing 
for the angular offset between the energy source 7 and the measuring 
device 16 and taking into account the rotational speed of the printing 
press, the measuring device 16 determines the area or surface coverage 
F.sub.actual value in the selected region 14. At 23, the measured area or 
surface coverage F.sub.actual value is compared with the given area or 
surface coverage in the selected region 14. If there is a deviation 
between the area or surface coverages F.sub.actual value and F.sub.desired 
value' the evaluation/control device 9 initiates at 24 a suitable 
adjustment for correcting the supply of dampening solution. 
The determination of the area or surface coverage represents one possible 
way of determining the scumming. For this purpose, it is necessary to 
print and to measure reference patches with area or surface coverages of 
0% and 100%. Of course, it is also possible to compare the measured values 
directly with prescribed or given values.