Rotary offset printing machine system

To compensate for oscillations and bending of a blanket cylinder, and particularly oscillatory behavior under specific operating speeds, underlays between the rubber blanket and the cylinder surface are provided which are of differential thickness, so that, at any given operating speed where the blanket cylinder tends to move away from an associated impression cylinder, the underlay is thickened to thereby maintain essentially uniform printing pressure against the printing substrate (5) under all conditions. The system is equally applicable for plate cylinder - blanket cylinder systems of uniform diameter, as well as for plate cylinder - blanket cylinders of different diameter, and, in the latter case, preferably utilize an underlay blanket which tapers uniformly from a thinner portion to a thicker portion beneath the printed subject matter transferred to the blanket cylinder upon the second revolution of the plate cylinder.

The present invention relates to rotary offset printing machines, and more 
particularly to an arrangement to improve the quality of printed products, 
and the uniformity thereof, delivered by the printing machine system. 
BACKGROUND 
Rotary offset printing machines in which a plate cylinder together with a 
rubber blanket cylinder forms a printing couple are well known. It has 
been found that at high speeds of rotary printing machines--which may 
print on an elongated web or on sheets--cylinders tend to oscillate or 
otherwise not run exactly as intended, and the result of oscillation or 
otherwise differential behavior of the cylinders during printing results 
in printed copy which should be improved. Striations, stripings, 
differential inking and the like may be noticed. Printing machine 
cylinders, particularly blanket cylinders and plate cylinders, are excited 
to oscillate especially when the grooves in the cylinders in which the 
plates and the blankets are clamped run off against each other. Additional 
oscillations can be derived due to the drive gearing, that is, when 
meshing gears change from engagement of flanks of the gear teeth. Driven 
inkers and dampers, likewise subject to change in engagement of the flanks 
of the gear teeth, also may contribute to oscillatory behavior of printing 
cylinders. Many attempts have been made to prevent non-uniformity in 
printing, for example due to oscillation, see, for example, the following 
published patents: 
Fed. Rep. Germany Pat. No. 26 13 688 
Fed. Rep. Germany AS No. 11 93 516 
Fed. Rep. Germany Pat. No. 11 93 516 
German Dem. Republic (East Germany) Pat. No. 101,335 
In spite of many and extensive attempts, it has not been possible to 
entirely eliminate the effects of non-uniform rotation on printed subject 
matter. The various proposals which have been made--see the referenced 
patents, for example--were intended to suppress oscillations by directly 
affecting the respective cylinder. It is, of course, always possible to 
very accurately balance each individual cylinder in a printing machine 
system and arrange the balance with respect to all other printing 
cylinders. This, however, is extremely expensive and, in mass production, 
while balancing of the individual cylinders as they are made is part of 
the manufacturing process, a re-balancing of individual cylinders in any 
system then would be necessary. Furthermore, the behavior of the cylinders 
at different speeds differs, so that balancing the cylinders for all 
speeds is not always possible. Within specific series of printing machines 
which are made, similar efforts are undertaken for all the machines to 
balance the cylinders and to avoid vibrations and oscillations. It is 
always possible, however, that a specific machine of a series differs in 
its oscillatory characteristics from all the other machines of the similar 
series. Individual correction and rebalancing of such a machine is very 
difficult and costly. 
Various types of printing machines use rubber blanket cylinders which have 
a diameter larger than the diameter of the associated plate cylinder, for 
example twice the diameter. In such a machine, the plate cylinder revolves 
twice for each revolution of the rubber blanket cylinder, so that the 
rubber blanket cylinder will have two identical printed image information 
offset thereon. It has been found that there may be qualitative 
differences between the printed image transferred from such a rubber 
blanket cylinder which, for example, may be a difference in intensity or 
inking of a printed image transferred from one half of the rubber cylinder 
with respect to the adjacent half of the rubber cylinder, resulting from 
the second roll-off of the plate cylinder thereagainst. 
It is known to provide rubber blankets, stretched on rubber blanket 
cylinders, with underlays, or underblankets. 
THE INVENTION 
It is an object to improve printing machine systems such that the printed 
goods will have printed subject matter thereon which is improved by 
eliminating, or at least substantially reducing and rendering ineffective, 
oscillatory conditions of the printing cylinder-blanket cylinder 
combinations. 
Briefly, a rubber blanket underlay is located between the rubber blanket on 
the blanket cylinder and the surface of the blanket cylinder which is 
non-uniform throughout its longitudinal extent as it is applied on the 
blanket cylinder. 
In order to reduce vibrations, and in accordance with a feature of the 
invention, the rubber blanket underlay has regions of greater or lesser 
thickness, in which the arrangement of the respective regions of greater 
or lesser thickness--with respect to the position of the regions on the 
blanket, and the extent of the regions on the blanket--is matched to and 
associated with the oscillation characteristics of an individual machine 
system operating at some given speed, such that the effects of bending 
oscillations of the blanket cylinders are reduced or eliminated. 
The blanket may have a plurality of thickened and thinned regions or may 
taper from a thinner to a thicker region and taper off again to a thinner 
region at the end thereof or, conversely, may have thicker regions at the 
end portions where it is clamped to a clamping groove, and thinner regions 
therebeyond. In accordance with another feature of the invention, and 
particularly when used with blanket cylinders which have twice the 
circumference of the plate cylinder, the rubber blanket may have a 
tapering configuration, in which the thickness of the rubber blanket 
either gradually decreases from a leading point thereon towards the 
trailing point, or, for example, conversely increases from a leading point 
to a trailing point. The edge of the respective leading points may be 
either at the beginning of the blanket or, in some embodiments, may be 
located at half the circumference, that is, at the point where the plate 
cylinder rolls off against the rubber blanket cylinder a second time.

DETAILED DESCRIPTION 
The printing machine system of FIG. 1 utilizes a first plate 
cylinder-blanket cylinder combination or couple 1, 3, and a second plate 
cylinder-blanket cylinder combination or couple 2, 4. The respective 
blanket cylinders 3, 4 act also as impression or printing cylinders for a 
web or substrate 5, typically a paper web or paper sheets on which 
printing is to be carried out. 
The blanket cylinders 3, 4 have located thereon an underlay sheet or 
blanket 13 above which a rubber printing blanket 30 is located. The plates 
on the plate cylinders 1, 2 and the blankets on the blanket cylinders 3, 4 
are clamped in conventional axially extending clamping grooves by 
conventional clamping arrangements. The clamping grooves are identified 
only at positions 1a, 3a for simplicity and clarity of the drawing. The 
arrangement is entirely conventional. 
The invention is based on the realization that printing machines of a 
series of machines, for example of the same model, dimension and the like, 
have essentially similar oscillatory characteristics. On and beyond these 
common characteristics, however, any printing machine of the series may 
have an individual oscillatory characteristic with respect to that of any 
of the others, which, further, is speed dependent. This can be easily 
determined by checking the printed copy printed on diffferent machines of 
the same series or model, and made under different conditions of operating 
speed. It has been found that there are differences in intensity of inking 
which vary in accordance with position and strength depending on the 
operating speed of the machine. In accordance with the present invention, 
and based on the analysis of printed subject matter, underlay blankets 13 
were devised which, taken in the circumferential direction of the 
respective cylinders 3, 4, have different thicknesses. 
Referring to FIGS. 2a-2d, which illustrate side views of printing blankets: 
for any machine, and for selected operating speeds of the machine, special 
underlays 6, 7, 8, 9 were made. In accordance with the present invention, 
the position of variation of intensity of printing ink on the printed 
subject matter 5 is determined; striping of the subject matter is then 
determined and, in dependence on the position and intensity of the 
striping, the underlay 13 is constructed, as shown in FIGS. 2a to 2d, by 
providing underlays of different thickness regions, specifically designed 
for operation with a specific machine at a specific speed or speed range. 
FIG. 2a illustrates an underlay 6 for a specific machine at a given speed 
which has two long regions 11 which are comparatively thin and a somewhat 
thickened region 10 therebetween. The thickness of the region 10, and the 
position of the region 10, will be so placed that, at the particular 
speed, the cylinders 3, 4, between which the printed copy 5 is passed, 
would tend to separate or oscillate away from each other. The thickened 
region 10 counterbalances the slight movement of the cylinders away from 
each other to maintain uniformity of contact engagement of the surface of 
the blanket 30 on each one of the cylinders 3, 4. If the thickened region 
10 would not be present, the printing impression force between the two 
cylinders 3, 4, at the particular oscillatory point at which the cylinders 
3, 4 oscillate away from each other, would be reduced and, due to the 
reduced pressure, transfer of ink on the copy element 5 would likewise be 
reduced and the intensity of inking of the copy 5 would be reduced. The 
thickened region 10 on the underlay 6 counteracts the decrease in pressure 
between the cylinders. 
FIGS. 2b, 2c and 2d show, respectively, other embodiments of underlays 7, 
8, 9, having thin regions 11 and thick regions 10b, 10c, 10d, 
respectively, intended to be used for example with different machines, or 
with the same machine at different speeds in accordance with the 
oscillatory pattern of the particular cylinder in the machine. The 
oscillatory pattern can be readily determined by running a test copy at 
the intended operating speed, and determining uniformity of inking. In the 
region where the inking appears thinner or fainter, the underlay should be 
provided with an increased thickness. FIGS. 2a to 2d show typical side 
views of underlay blankets 6-9, respectively. The extent of thickening, 
and the particular position, is readily determined by a few test runs at 
the respective speed to obtain an essentially uniformly inked copy 5. 
The underlay blanket may be made of various materials, as desired, such as 
cardboard, plastic, metal, fabric, or the like. 
The system has the specific advantage that the expensive metal working of 
the cylinders 3, 4 is eliminated and, further, a much wider operating 
speed range is made possible without striping or differential inking of 
the copy; the effects of the cylinder oscillations can be essentially 
eliminated without the expensive machining of the printing machine 
cylinders and, additionally, by merely selecting an underlay from a set of 
underlays prepared for a specific machine at specific operating speeds 
provides substantial improvement in the quality of the printing on the 
printed copy 5. Shaping an underlay blanket to have, for example, the side 
aspect as shown in the respective FIGS. 2a to 2d is a simple matter, which 
can be easily made, by minor material removal, from a flat, easily 
machined and worked surface, for example of the materials referred to. The 
heavy steel cylinder forming the blanket cylinders 3, 4 remains untouched 
and assembled in the machine. 
FIG. 3 illustrates another embodiment of the invention in which plate 
cylinders 1', 2' have half the diameter of the associated blanket 
cylinders 3', 4'. The copy product 14' has the same subject matter printed 
twice, at adjacent locations A and B, also shown on the blanket cylinders 
3', 4', as the printing regions A, B. Upon one revolution of the blanket 
cylinders 3, 4, the plate cylinders 1, 2 revolve twice, so that the 
circumference of any blanket cylinder 3, 4 will carry two identical 
printed images, transferred to the substrate 5'. Theoretically, the two 
printed images A, B should be identical. In actual practice, this is not, 
however, frequently the case, due to the operating behavior of the 
respective cylinders in the printing system. 
In accordance with a feature of the invention, blanket underlays 15', 6', 
11' are used, in which, again, the thickness, taken in circumferential 
direction, differs from a uniform thickness, which was customary practice 
heretofore. The thickness may vary uniformly throughout the length of the 
underlay blanket, see FIG. 4c, at 12'. In accordance with a preferred 
feature of the invention, however, the thickness of only that portion of 
the blanket which is beneath the rubber cover carrying the second printed 
image B changes in thickness, while the region of the underlay blanket 
beneath the rubber cover associated with the first printed image A is of 
uniform thickness, so that the radius of the outer surface of the blanket 
on the region A will be uniform throughout. 
FIG. 4a shows the regions 7', 8' on the blanket, separated by a theoretical 
line x, which separates the respective images A, B on the rubber blanket. 
The radius of the underlay blanket 15' in the region 7', which is beneath 
the first half of the image A, is uniform; in the second region B, the 
thickness of the underlay, taken in circumferential direction, increases 
at a uniform rate, in wedge-shaped form, as seen at 8'. FIG. 4a 
illustrates the form of the underlay to be used with a double-diameter 
blanket cylinder which is most preferred. FIG. 4b illustrates another 
variation, in which the region 9' beneath the first printing portion A is 
of uniform thickness, whereas the region 10' beneath the second portion B 
decreases from an initially thickened region towards the end thereof. As 
seen in FIG. 4c, the underlay 11' is constructed in wedge-shaped form as 
seen at 12', the wedge-shaped tapering region extending over the entire 
length of the underlay blanket, that is, over the entire circumference of 
the respective blanket cylinder 3', 4' when placed beneath a rubber 
blanket. 
It has been found that a substantial improvement in quality can be obtained 
when using blanket underlays as shown in FIGS. 2a-2d and, for 
double-diameter blanket cylinders, especially as shown in FIG. 4a, the 
preferred form for this invention, but also as shown in FIG. 4b, the next 
one in order of preference, with the embodiment of FIG. 4c being assigned 
the lowest preference although it may be the easiest to make. The eventual 
choice will depend on the operating speed of the machine, and where and 
how non-uniformities in printed output result. 
The regions 11 (FIG. 2a-FIG. 2d) and 7', 9' (FIGS. 4a, 4b) usually and 
customarily have a thickness of: 1 mm. The regions 10, 10b, 10c, 10d 
(FIGS. 2a-2d) and 8', 10', 12' (FIGS. 4a-4c) may have a maximum thickness 
of: 0.5 mm. 
Various changes and modifications may be made, and features described in 
connection with any one of the embodiments may be used with any of the 
others, within the scope of the inventive concept.