Arrangement for reducing vibration of cylinders in printing press

A rotary printing press having first and second cylinders in rolling engagement, the first cylinder being rigid and the second cylinder being resiliently covered, both of the cylinders having a longitudinal groove defining a gap in the cylinder surface, the gaps being rotated in opposed synchronism with one another. The groove in the first cylinder defines leading and trailing end walls with the end walls terminating at lips at the cylinder surface, the lips on the end walls each having bead projections which extend longitudinally therealong and which project a small distance outwardly from the nominal radius dimension of the cylinder thereby causing the lip on the leading end wall of the first cylinder to engage the surface of the second cylinder earlier than it would in the absence of a bead and causing the lip on the trailing end wall to separate from the surface of the second cylinder later than it would in the absence of the bead thereby to extend the pressure build-up and pressure drop-off angles between the cylinders and to cause a more gradual build-up of pressure between them to the operating level as well as a more gradual decrease from the operating level.

In a conventional lithographic press the impression cylinder and blanket 
cylinders, which are in rolling engagement with one another, are biased, 
or pre-stressed, together to develop an operating level of printing 
pressure. It is customary in both of the impression cylinder and blanket 
cylinder to provide longitudinal grooves for the accommodation of take-up 
and tensioning devices for the blanket on the blanket cylinder and for the 
thin cover on the impression cylinder forming non-printing gaps in the 
surface. When the grooves in the two cylinders are opposite one another 
the mutual pressure is reduced to zero. As the leading edges of the 
printing area defined by the grooves engage one another there is a sudden 
build-up of pressure to the operating level. Conversely when a printing 
cycle has been completed and the grooves are again in opposed relation a 
sudden drop-off in pressure occurs from the operating level back to zero. 
The sudden increase in pressure at the beginning of a printing cycle 
produces relative outward shifting of the cylinder axes because of the 
play on the bearings and since the cylinders, being elastic, tend to 
retreat from the applied force. When the operating pressure is released at 
the end of the printing cycle, the cylinders tend to "drop" toward one 
another as the force which took up the bearing play is now released, and 
the cylinders, in addition, tend to elastically straighten back to their 
original condition. These rapidly succeeding displacements, first in one 
direction and then in the other, produce cylinder vibration which is 
particularly troublesome at high speeds, being evidenced by stripes in the 
printed product extending in the axial direction. At certain speeds a 
condition of resonance can be set up further aggravating the striping of 
the product. 
Much effort has gone into attempts to overcome cylinder vibration. For 
example, in U.S. Pat. No. 4,149,461 there is shown the use of rollers for 
providing artificial support of the cylinders in printing position during 
the interval of passage of the gaps. Also it has been conventional wisdom 
to cushion or relieve the "lip" portion of the printing surface, adjacent 
the leading and trailing edges defined by the groove, for the purpose of 
cushioning, or postponing, initial impact. Thus German Disclosure 
Specification 1,636,312 shows use of an elastically deformable cushion in 
the region of the leading edge of the printing zone while German 
Disclosure Specification 2,613,687 shows the provision of flatted areas 
along the edge of the gap. 
Thus emphasis in the past has been on relieving of the initial impact and 
not upon reducing the rate of change of force between the cylinders from 
zero to the operating level. 
Accordingly, it is an object of the present invention to provide a cylinder 
for printing presses having a groove but which instead of cushioning or 
flatting the lip at the edge of the groove, intentionally raises the level 
of the lip by forming it into a bead, the effect of which is to reduce the 
rate of build-up of printing force from zero to the operating level and 
conversely, to reduce the rate of drop-off from the operating force back 
to zero at the groove location. Stated in other words, it is the purpose 
of the present invention to enlarge the pressure build-up angle and 
pressure drop-off angle with the result that the rate of build-up and 
drop-off are decreased thereby bringing about reduction in cylinder 
vibration, particularly at high operating speeds. Thus it is an object of 
the invention to provide means for reducing the vibration of printing 
cylinders which not only constitutes an improvement over conventional 
vibration-reducing means and which, indeed, flies in the face of prior 
teachings. 
It is another object of the present invention to provide means for reducing 
vibration between cooperating grooved cylinders, which are respectively 
rigid and resiliently covered, by making a minor modification of the rigid 
cylinder in the region of initial impact, a modification which is 
inexpensive and which may be incorporated in both new cylinders and, by 
retrofit, cylinders already in the field. It is a related object to 
provide a modification which can be easily and cheaply performed and which 
brings about a disproportionate improvement in the smoothness of press 
operation, particularly when operating at a high production rate. 
It is a more detailed object to provide an upraised bead on a portion of a 
rigid cylinder which is conventionally cushioned or undercut but which is 
so formed, including an adjacent recess, as to be substantially 
non-wearing upon the cooperating blanket; in other words, it is an object 
to provide a vibration-reducing change which utilizes the resilient 
characteristics of a cooperating blanket but which does not result in any 
substantial increase in the degree of blanket wear. 
As a result of the above, it is an object of the invention to provide means 
for substantially reducing the degree of "striping" of the printed product 
due to cylinder vibration, and which therefore results in improved quality 
and value of the printed product.

While the invention has been described in connection with a preferred 
embodiment, it will be understood that I do not intend to limit the 
invention to the particular embodiment shown but intend, on the contrary, 
to cover the various alternative and equivalent forms of the invention 
included within the spirit and scope of the appended claims. 
Turning now to the drawings there is disclosed in FIG. 1 a first, or 
impression, cylinder 11 and a second, or blanket cylinder 12 having shafts 
13, 14, respectively, journaled in bearings 15, 16 mounted in the press 
frame, of which a fragmentary portion has been indicated at 17. 
The first cylinder has a longitudinal groove 20 defining leading and 
trailing end walls 21, 22 which are oriented at a generally radial 
direction as well as a bottom wall 23, the end walls terminating at the 
surface 24 of the cylinder in lips 25, 26. The groove 20 is normally 
provided for mounting of tensioning and take-up devices for a thin 
protective covering (not shown) which is usually stretched over the 
surface of an impression cylinder. 
Similarly, the second, or blanket, cylinder 12 has a groove 30 defining 
leading and trailing end walls 31, 32 which are radially oriented, and a 
bottom wall 33, with the end walls determining the limits of the outer 
surface 34. The end walls 31, 32 terminate in lips 35, 36 at the outer 
surface. Stretched over the outer surface 34 and about the lips 35, 36 is 
a resilient blanket of rubber or rubber-like material 37. It will be 
understood that the ends of the blanket are tensioned by tension and 
take-up devices (not shown) mounted on the bottom wall 33, as 
conventional. 
In the lithographic process a plate cylinder 38, having a plate mounted 
thereon, is in rolling engagement with the blanket 37. The image from the 
plate cylinder, following transfer to the blanket, is then "offset" onto a 
sheet of paper passing between the blanket and impression cylinders and 
held in place by grippers (not shown) on the latter. All three of the 
cylinders 11, 12, 38 are driven at the same peripheral speed by a press 
drive 39, adjacent cylinders being driven in opposed synchronous relation 
so that the grooves 20, 30 pass opposite one another, momentarily 
releasing the pressure between them. 
FIG. 1 shows a condition in which the grooves are passing one another, 
rotating in the directions shown, with the cylinders about to resume 
contact. Under such zero pressure conditions the shaft 14 of the upper, or 
blanket, cylinder, by reason of play P, occupies a position at the 
"bottom" of the bearing 16 in which it is journaled, dropping there of its 
own weight. This has moved the cylinder 12 closer to the cylinder 11. Also 
the cylinder 12 is in the relaxed state, rather than being elastically 
flexed upwardly, which serves to bring the cylinders a little closer to 
one another. Finally the two cylinders are intentionally adjusted toward 
one another into a slightly interfering relation so that the impression 
cylinder, with the sheet it supported upon it, slightly indents the 
blanket to establish printing pressure. These three factors, added 
together, produce a total radial interference indicated at I in FIG. 1 
when the cylinders are in the relaxed state, with grooves opposed, the 
interference being greatly magnified in this figure for purposes of 
illustration. 
In accordance with the present invention, rather than cushioning or 
flatting the lip on the leading end wall of the first cylinder 11, the lip 
is provided with a bead which extends longitudinally and which projects a 
small distance outwardly from the nominal radial dimension, of the 
cylinder thereby causing the lip on the leading end wall to engage the 
blanket surface of the second cylinder earlier in the cycle than it would 
in the absence of the bead thereby to enlarge the pressure build-up angle 
of the cylinders and to cause a more gradual build-up of pressure between 
them to the operating level. Thus, referring especially to FIGS. 2 and 2a, 
the lip 25 of the leading end wall 21, and which is at the outer surface 
24 of the cylinder, is formed with a longitudinal bead 40 which projects 
radially beyond the outer surface 24 of the cylinder. The bead is of 
rounded profile having an "outboard" side 41 which merges smoothly with 
the surface of the leading end 21 of the groove. Further in accordance 
with the invention there is provided a recess which extends continuously 
along the "inboard" side of the groove, such recess being indicated at 
42. The recess has a radius, from the center of the cylinder to its root, 
which is less than the nominal radius of the cylinder. 
Thus referring to FIG. 2a the significant dimensions of the bead and its 
recess, related to the surface 24 of the cylinder, are set forth. It will 
be seen that the bead 40 projects a distance P above the surface of the 
cylinder whereas the recess is depressed a distance R. The dimensions R 
and P are, in a practical case, of the same general order of magnitude, 
say between a sixteenth of an inch and an eight of an inch. The bead 
preferably has a width, measured in the circumferential direction of w 
while the recess has a width W. These are also of an equal order of 
magnitude, with the recess width W being at least as great as the width w 
of the bead. The bead and recess, taken together, are smoothly joined so 
as to resemble a sine wave which is, in turn, smoothly merged with the 
cylinder surface 24. 
The improvement brought about by the present invention may be understood 
and appreciated by comparing FIG. 3, which represents conventional 
construction, with the diagram in FIG. 4 which includes the bead of the 
present invention. Both diagrams are based upon the existence of the same 
amount of radial interference between the cylinders. Because of this 
radial interference the lip 25', which determines the beginning of the 
printing area, engages the blanket 37' on the impression cylinder at an 
angle ahead of dead center. This angle, which is indicated at .alpha., 
represents the angle during which build-up of force between the cylinders 
takes place prior to the lip 25' reaching its dead center position. This 
angle is relatively narrow resulting in a high rate of force increase. In 
other words the slope of the force curve is steep as indicated by the 
"full line" curve 50 in FIG. 6 where the slope has a maximum angle 
.gamma.. Note that one of the reasons for the steep slope is the fact that 
the force does not begin to rise until the point 51 is reached. 
By contrast, where a bead 40 is used, contact between the cylinders takes 
place earlier in the cycle so that more time is provided for the pressure 
build-up to occur which corresponds to a slower build-up of the pressure 
between the cylinders. This is shown by the dashed curve 52 in FIG. 6. All 
of the other factors being the same, presence of the bead 40 causes 
initial engagement between the cylinders to occur at an angle .beta., 
related to dead center, an angle which is substantially enlarged as 
compared to the angle .alpha.. In short, with use of the bead, build-up of 
force occurs earlier, at a point 53 on the pressure diagram. The force 
between the cylinders, rising from point 53, increases along a slope which 
is substantially more shallow than that at 50 where the bead is absent, 
the operating pressure, when finally achieved, however, being the same. 
The dashed curve 52, in addition, rises initially at a higher rate and is 
more linear than the curve 52. The reason for this is that the relatively 
deep initial penetration of the bead into the blanket develops a 
relatively high, although localized, reaction force. While the dashed 
curve 52 corresponding to the use of the bead is illustrated as being 
linear, such curve may, in a practical case, depart somewhat from true 
linearity, but analysis shows that, in any event, the maximum rate of 
force build-up utilizing the bead is less than in conventional 
construction and much less than where flatting or cushioning techniques 
are employed. The more shallow rate of pressure build-up characterizing 
the present invention seems to have a disproportionate effect in reducing 
"striping". This is believed due to the fact that striping is due to 
elastic vibration of the cylinder. Where the rate of change of pressure is 
reduced, substantially less energy is imparted to the cylinders and thus 
available for rebound. 
In practicing the invention in its preferred form a longitudinally 
extending recess is employed at the inboard side of the bead. The use of 
such recess does not have any direct effect upon the angle of pressure 
build-up, for example, the angle .beta.. The main purpose of the recess is 
to facilitate penetration by the bead and to enable the bead to develop a 
high reaction pressure when the bead is initially engaged and to 
neutralize the additional radial force exerted at the bead when the 
blanket rotates from a position shown in FIG. 4 to a position of full 
engagement with the printing surface, for example when the bead is 
approaching and passing the dead center condition. Under such condition of 
full engagement, the reduction in pressure upon the blanket over a 
longitudinal strip the width of the recess tends to neutralize the 
increase in pressure upon the blanket along the adjacent longitudinal 
strip occupied by the bead. 
While the above discussion has been concentrated upon the function of the 
bead 40 at the leading edge of the printing area, it is one of the 
features of the present invention that a similar bead 40a and recess 42a 
(FIG. 5) are used at the trailing edge 22 to enlarge the pressure drop-off 
angle thereby to prolong the drop-off period and thus reduce the rate of 
drop-off. 
Absent use of the bead the pressure drop off from the operating level is 
illustrated by the curve 55 in FIG. 6, with the drop-off being completed 
at the point 56. However, by using the bead the pressure drop-off angle is 
enlarged, and the drop-off time is extended. Thus the drop-off curve, 
indicated by the dashed line 57, extends all of the way out to point 58, 
having a slope which is substantially less than that which exists 
conventionally in the absence of a bead. 
In short, by using upraised beads at the leading and trailing edges of the 
printing area, the rate of pressure build-up and the rate of pressure 
drop-off are both substantially reduced to minimize vibration and 
"striping" without necessity for resorting to expensive support 
arrangements as disclosed, for example, in the above-mentioned U.S. 
patent. 
By making the bead of smoothly rounded profile merging smoothly with the 
recess and by merging the recess, in turn, smoothly into the cylinder 
surface, sharp edges are avoided and the blanket is protected against 
wear. It will be appreciated in that the benefits of the bead and adjacent 
recess can be achieved at low cost and without having to pay a penalty in 
the form of a change in some other one of the operating conditions. While 
it is true that the bead and recess slightly encroach upon the printing 
area, the extreme ends of the printing area are almost always employed for 
marginal purposes so the printing capacity is, as a practical matter, not 
affected. 
For incorporating the present invention into a cylinder conveniently and at 
lowest possible cost, it is proposed that the bead 40 and its recess 42 be 
incorporated in a bar-shaped insert such as illustrated at 60 in FIG. 2a 
fitted to and secured upon a ledge or shoulder 62 machined in the 
cylinder. 
While the invention has been described in connection with a combination of 
an impression cylinder and a blanket cylinder in a lithographic press, it 
will be apparent that the invention is not limited thereto and is usable 
wherever a rigid cylinder and a resiliently surfaced cylinder, with 
synchronously rotated grooves formed in both of them, are in pressure 
engagement with one another and where the effect of the resulting gap is 
to reduce the pressure momentarily to zero during each cycle of rotation. 
Also while the invention has been described assuming that the bead and its 
recess are of constant profile along the entire length of the cylinder, it 
will be appreciated by one skilled in the art that this is not an 
essential in the practicing of the invention. Similarly, although the bead 
and recess extend longitudinally of the cylinder they do not necessarily 
have to extend its entire length and minor variations in height and extent 
may be made as desired without departing from the invention.