Web tension control apparatus for use with a rotary press

The web tension control apparatus according to the present invention is provided with a biasing roller (6) adapted to be urged against the outer circumferential surface of a midway drag roller (4), a biasing means (7) adapted to apply an urging force in the biasing direction against the biasing roller (6) for the midway drag roller, a tension detecting means (7), (9) adapted to detect the tension of a running web (1) upstream and downstream of a printing unit (2), and a control means (10) adapted to control the urging force of the biasing device 7 in accordance with the signals from the tension detecting means (7), (9). If there is any difference in the signals from the tension detecting means (7), (9), the control device (10) controls the biasing roller (6) for the midway drag roller (4) by the aid of the biasing device (7) so as to eradicate the difference in the signals, so that the tensions web upstream and downstream of the printing unit (2) are equal with each other. Any losses of the tension in the web (1) as generated in the slotted section of a printing cylinder may be prevented from occurring, and any variations in the tensions of the web (1) may be relieved substantially so that defects in the printing such as the offset doubles and the deviations in cutting the printings, etc. may be obviated accordingly.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for controlling the tension 
of a running print sheet or web for use with a rotary press. 
2. Description of the Related Art 
A typical monochromatic perfecting unit and of a typical monochromatic 
perfecting and multicolor oneside printing unit for use with a 
conventional rotary press are shown in FIG. 1 and FIG. 2, respectively. 
According to the monochromatic perfecting unit as shown in FIG. 1, a 
running printing sheet or web of paper 1 is, after having been printed by 
the monochromatic perfecting unit 2, directed through a guide roller 3 
toward a midway drag roller 4, whereby the web of paper is subjected to 
traction to be delivered to following operations. 
According to the monochromatic perfecting unit and the multicolor one side 
printing unit as typically shown in FIG. 2, the running web 1 is, after 
having been printed by the monochromatic perfecting unit 2, directed 
through a guide roller 5 toward a midway drag roller 4, whereby the web is 
subjected to traction to be delivered to a multicolor one side printing 
unit 5, where the web is subjected to the multicolor printing operations 
and is then redirected to following procedures in the printing line. 
In the construction of the rotary press as schematically shown in FIGS. 1 
and 2, it is observed that there occurs a substantial variation in tension 
of the running web 1 extending in the upstream and downstream of the 
monochromatic perfecting unit 2 and the multicolor one-side printing unit 
5. This variation in tension of the web is considered to result from the 
possible loss of tension by way of the slots of the printing cylinder and 
of vibrations occurring per one operating cycle of the printing cylinder, 
and such variations in tension result in such faults such as deviations in 
the cutting of the printings and such as offset doubles, or the like. 
SUMMARY OF THE INVENTION 
In consideration of such problems as noted above, it is an object of the 
present invention to provide a tension control apparatus for use with a 
rotary press which can prevent the faults in the conventional printing 
units such as the occurrence of offset doubles and the deviation in the 
cutting of the printings, by eliminating possible variations in the 
tension of a running printing sheet or web upstream and downstream of the 
printing units incorporated in the rotary press line. 
According to the invention, there is provided a tension control apparatus 
for use with a rotary press, which comprises, as briefly summarized, a 
midway drag biasing roller adapted to be urged resiliently against the 
outer circumferential surface of a midway drag roller, a biasing device 
adapted to resiliently apply an urging pressure upon the midway drag 
biasing roller so that it may be urged properly in the biasing direction, 
a tension detecting device adapted to detect the tensions of the printing 
sheet or web extending upstream and downstream of a printing unit, and a 
control device adapted to control the urging force of the biasing device 
in accordance with due signals from the tension detecting device, so that 
the tensions of the running web upstream and downstream of the printing 
unit may be equalized, whereby there is attained such advantageous effects 
such as preventing a loss of tension in the printing web as would be 
encountered in the area of the slotted section of a printing cylinder, and 
such as reducing possible variations in the tension of the running web, 
thus resulting in the efficient prevention of defects such as offset 
doubles and variations in the cutting of the printings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A tension control apparatus according to the present invention for use with 
a rotary press shown in FIG. 3 is now described by way of a preferred 
embodiment, which is shown comprising a running sheet or web of printing 
paper designated at the reference numeral 1, a monochromatic perfecting 
unit at 2, a guide roller at 3, a midway drag roller at 4, a biasing 
roller at 6 which is not rotatably driven resiliently urged toward the 
midway drag roller 4, and a biasing device at 7 for causing the biasing 
roller 6 to be biased under a biasing force against the midway drag roller 
6. Also, a tension detector 8 is provided in the guide roller 3, and a 
floating or dancer roller 9 is provided upstream of the monochromatic 
perfecting unit 2. The detection of the tension in the running web 1 
passing through the monochromatic perfecting unit 2 and the guide roller 3 
is conducted in such a manner that a signal representing the tension 
detected as a load rendered by the dancer roller 9 upstream of the 
monochromatic perfecting unit 2 and a signal representing the tension as 
detected by the tension detector 8 are fed to a control unit 10 which is 
adapted to control the biasing device 7. 
Now, referring to the operation of the web tension control apparatus for 
use with the rotary press shown in FIG. 3, the running web of printing 
paper 1 is directed to extend toward to the monochromatic perfecting unit 
2, the web 1 being tensioned upstream of the unit 2, and thereafter fed 
into the unit 2 for printing. After printing, the running web 1 is then 
directed to pass through the guide roller 3, where the tension of the web 
1 on the delivery side of the monochromatic perfecting unit 2 is detected 
by the tension detector 8 which is provided in the guide roller 3, and 
then is sent out to the midway drag roller 4. It is arranged so that the 
outer circumferential speed of the midway drag roller 4 is set to be 1% 
greater than that of the monochromatic perfecting unit 2, and that the 
midway drag roller 4 slips with respect to the web 1 to an extent of a 
difference in the speeds of the two. With this arrangement, the midway 
drag roller 4 may render a dragging or friction force which is generally 
proportional to the biasing force of the biasing roller 6 upon the web 1, 
so that the tension of the web 1 may be controlled exclusively in 
accordance with the biasing force from the biasing roller 6, accordingly. 
If the tension signal which is detected by the dancer roller 9, for example 
a voltage signal, and the tension signal as detected by the tension 
detector 8, for example a voltage signal, are each proportional to the 
detected tension of the web 1, and these signals are fed into the control 
device 10, where they are compared with each other for any difference in 
magnitide of voltage, and if any, the control device 10 functions to 
generate a control signal which compensates for the difference in these 
signals, the control signal of the control device 10 is delivered to the 
biasing device 7 so that the biasing roller 6 may render an appropriate 
biasing force upon the midway drag roller 4 so as to control the tension 
of the web 1 accordingly. For instance, if the current tension as detected 
in the web 1 after passing the monochromatic perfecting unit 2 is found 
smaller than that upstream of the unit 2, the biasing device 7 is operated 
to urge the biasing roller 6 so as to increase the tension in the web 1, 
and vice versa. With such a tension control operation, the tensions 
present in the web 1 before and after passing through the monochromatic 
perfecting unit 2 are efficiently regulated to be equal to each other. 
Once the difference in the tensions in the web 1 across the monochromatic 
perfecting unit 2 is eliminated, there is no longer a chance of tension 
losses at the slotted section of the print cylinder, thus relieving 
possible variations in the tension of the web 1 and thus preventing 
defects such as the offset doubles, and deviations in cutting the 
printings, etc. from occurring. 
FIG. 4 shows another embodiment of the invention which is adapted to the 
rotary press employing the monochromatic perfecting unit 2 and the 
multicolor one-side printing unit 5 shown in FIG. 2. 
According to the construction of the multicolor one-side printing unit 5 
shown in FIG. 4, a plurality of sets of blanket cylinders 12 are urged 
toward the outer circumference of an impression cylinder 11. With such an 
arrangement, should a loss of tension in the web 1 by the slotted section 
in the printing cylinder occur while the web is held and fed in a 
sandwiched relationship between the impression cylinder 11 and the blanket 
cylinders 12, since some sets of blanket cylinders 12 may still serve to 
efficiently hold the web 1 in position around the circumference of the 
impression cylinder 11, only relatively small tension losses occur from 
the slotted section in the printing cylinder, thus efficiently preventing 
such faults in the printing from occurring as accomplished with the 
advantageous construction shown in FIG. 3, accordingly. 
Next, referring to a preferred embodiment of the midway drag roller 4 shown 
in FIGS. 5 and 6, a running web of printing paper 1, a midway drag roller 
4 having a flat portion 4a with a flat circumferential surface and a 
groove portion 4b formed with a plurality of grooves extending parallel to 
each other and disposed in alternate fashion with the flat portion, and a 
biasing roller 6 adapted to urge the web 1 upon the flat portions 4a of 
the midway drag roller 4 are provided. 
Now, the operation of the midway drag roller 4 as shown in FIGS. 5 and 6 
will be described. It is seen that the web 1 is urged against the outer 
circumferential surface of the midway drag roller 4 by the biasing roller 
6 while passing therethrough, with an appropriate tension value to 
following operations. At this stage, the web 1 would possibly proceed in 
zigzag manner with a too large of a tension rendered, which would result 
in a breakage of and wrinkle in the web 1. In this respect, it is required 
to maintain an appropriate tension within an optimal range. According to 
this embodiment, by virtue of such a unique construction of the midway 
drag roller 4 which is provided the flat portions 4a and the grooved 
portions 4b disposed in an alternate manner so that there are formed a 
plurality of grooves extending in parallel and in the circumferential 
direction in the outer circumferential surface of the roller 4, there is 
attained such an advantageous effect that the grooved portions 4b in the 
roller surface may let air entrapped by the web 1 escape, thus preventing 
the loss of frictional drive force from the circumferential surface of the 
midway drag roller 4 from occurring and thus, the biasing roller 6 serves 
to effiently urge the web 1 upon the flat portions 4a thereof so that the 
tension of the web 1 may be controlled optimally. Incidentally, it is 
empirically known that when the outer circumference of the midway drag 
roller 4 is made partly flat, the coefficient of friction is reduced 
merely from a few percent to tenths of a percent in comparison with a drag 
roller which is provided with a plurality of grooves in the entire 
circumferential area of thereof. 
As reviewed fully hereinbefore, with the improved construction such that 
the midway drag roller 4 is designed with its outer circumferential 
surface comprising the plurality of flat portions 4a sandwiched between 
the adjacent grooved portions 4b extending parallel to one another in the 
circumferential direction, and the biasing roller 6 is urged toward the 
flat portions 4a of the midway drag roller 4 so that the biasing roller 6 
may serve to urge the flat portions 4a of the midway drag roller 4 through 
the running web 1 sandwiched therebetween, there is no possibility that 
the grooves will leave any undesired marks or impressions on the surface 
of the web 1 even with a substantial urging force rendered thereupon, thus 
making it feasible in practice to have a substantially widened range of 
tension control for the running web 1 in comparison with the conventional 
construction in which there are formed a plurality of grooves the entire 
outer circumferential area of the drag roller 4. Also, it provides another 
advantageous feature in that the running web 1 may be held in an optimal 
condition while being fed along the printing line because it ensures that 
the web 1 is free from any marks of grooves in the urging roller.