BACKGROUND OF THE INVENTION
The present invention relates to tension control devices for a printing
Before the present invention, multi-color printing units have been
used in a printing press to print colored images on a paper web. The webs used
in the press unwind the web from a supply roll. Due to the relatively fast speed
of the press, the rolls have been completely unwound in a relatively short period
of time, such as 15 minutes.
In accordance with prior practice, a new roll of the web is pasted
onto the web of the previous roll when it is almost depleted. However, the rolls
each have different characteristics, such as different manufacture and different
winding tension. As a result, the tension on opposed sides of the new web becomes
significantly different, causing loss of registration in the press, and flapping
of the web which may cause a web break.
Adjustments must be made to the press in the event of loss of registration,
and due to the relative frequency of web pasting. This factor results in loss of
press time, wasted product, and inconvenience to the operator of the press.
SUMMARY OF THE INVENTION
The present invention relates to an improved tension control device
for a printing press.
The device of the present invention comprises an adjustment roller,
and means for measuring the tension on opposed sides of a web passing downstream
from the adjustment roller.
A feature of the invention is the provision of means responsive to
the measuring means for automatically approximately equalizing the tension of the
web on the adjustment roller on opposed sides of the adjustment roller.
Thus, a feature of the invention is that the device minimizes the
loss of registration otherwise due to a web paste.
Another feature of the invention is that the device minimizes flapping
of the web otherwise caused by the web paste.
A further feature of the invention is that adjustment to tension
of the adjustment roller are made to only one side of the adjustment roller.
Thus, a feature of the invention is that the device is of simplified
construction and reduced cost.
A feature of the invention is that the device minimizes the amount
of waste and time in operating the press otherwise due to the web paste.
Further features will become more fully apparent in the following
description of the embodiments of the invention and from the appended claims.
DESCRIPTION OF THE DRAWINGS
In the drawings:
DESCRIPTION OF THE PREFERRED EMBODIMENTS
- Fig. 1 is a diagrammatic view of a printing press for use of a tension control
device of the present invention;
- Fig. 2 is an elevational view of the tension control device;
- Fig. 3 is a diagrammatic view of a tension roller for the device of Fig. 2;
- Fig. 4 is a block diagram of a control system of the tension control device
of Fig. 2.
Referring now to Fig. 1, there is shown a printing press generally
designated 10 for printing an image on a paper web 14. The press 10 has a plurality
of printing units 28, 30, 32, and 34 for printing different colors of ink on the
web 10. As shown, the printing unit 28 may print an ink having a color Cyan C,
the printing unit 30 may print an ink having a color Magenta M, the printing unit
32 may print an ink having the color Yellow Y, and the printing unit 34 may print
an ink having a color black K in a four-color press 10.
The printing units 28, 30, 32, and 34 each have a plurality of print
rolls or cylinders 36 associated with a blanket cylinder or roll 40. During printing
by the press 10, an image of the ink is transferred from the print rolls 36 to
the associated blanket rolls 40 to print the image on one surface of the web 14.
In addition the press 10 may have a plurality of printing units having a plurality
of print rolls 38 associated with a plurality of blanket rolls or cylinders 42
on an opposed side of the web 14 in order to transfer the ink image from the print
rolls 38 to the blanket rolls 42 for printing an image on the other surface of
the web 14. The following description of the print rolls is equally applicable
to either the print rolls 36 or the print rolls 38 on the opposed sides of the
With reference to Fig. 2, the press 10 has a device 50 for controlling
tension of the web 14 of the press 10. As shown, the web 14 passes from a supply
roll around an adjustment roller 52 to a tension roller 54. The web 14 passes
from the tension roller 54 around a dancer roller 56 to an idler roller 58 and
then to the printing units of the press 10.
With reference to Fig. 4, the press 10 has a control system 62 having
a computer 60 or Central Processing Unit (CPU) having a Random Access Memory (RAM)
and Read Only Memory (ROM). As will be seen below, the control system 62 controls
operation of the device 50, as shown in Fig. 2.
As shown in Figs. 2 and 3, the tension roller 54 has transducers
64 and 66 on opposed sides of the tension roller 54. The transducers 64 and 66
are of known type, and measure the tension caused by the web 14 on opposed ends
of the tension roller 54.
With reference to Fig. 2, the adjustment roller 52 has a bearing
cup 68 on one side only of the adjustment roller 52, along with a bearing housing
70 for the cup 68. The bearing housing 70 has a bore 72 having inwardly directed
helical teeth 74. The device 50 has an elongated shaft 76 having outwardly directed
helical teeth 78 which mesh with the teeth 74. The device 50 has an elongated
shaft 80 having the teeth 78 in the region of the bearing housing 70, while the
housing 70 has the teeth 78 which meshes with the teeth 78 of the shaft 80. Thus,
rotation of the shaft 80 causes a displacement of the bearing cup 68 and the one
end of the adjustment roller 52 which has the bearing cup 68. In this manner, the
tension of the web 14 on the one end of the adjustment roller 52 may be adjusted,
which takes place automatically since the shaft 80 is rotated by a two-speed motor
82 attached to the shaft 80. The device 50 also has an elongated hand wheel 84
attached to an opposed end of the shaft 80 relative to the motor 82 in order to
make manual adjustments to the shaft 80, with the automatic system off, if desired.
The device 50 operates to sense a difference in tension on the transducers
64 and 66 on opposed ends of the tension roller 54. It is desired to obtain an
identical tension on the opposed ends of the tension roller 54 in order to compensate
for the paste of the web 14 from a depleted roll of web 14 to a new roll of the
web 14. The condition of pasting a new roll of web 14 usually causes the device
50 to determine a different tension on the transducers 64 and 66.
In the event of the differing tension of the transducers 64 and 66,
the device 50 actuates the motor 82 to rotate the shaft 80 and cause displacement
of the bearing cup 68 and the one end of the adjustment roller 52. The motor 82
operates on the shaft 80 in a direction which will minimize the difference in tension
on the transducers 64 and 66 of the tension roller 54. In this manner, the press
10 compensates for the web paste, and minimizes the occurrence of the loss of registration
and flapping of the web 14 due to the web paste.
In this manner, the device 50 minimizes the loss of registration
due to a web paste resulting in reduced waste of the printed web 14 and inconvenience
to the operating personnel due to the frequent web pastes.
As shown in Fig. 2, the device 50 also has a limit switch 86 which
signals the computer 60 in the event that a predetermined limit on adjustment of
the adjustment roller 52 takes place, in which case the motor 82 is deactivated.
The transducers 64 and 66 can measure when the web 14 is initially
pasted due to relatively high fluctuation of the tension on opposed ends of the
tension roller 54. In this case, the motor 82 runs at a first fast speed in order
to make coarse corrections to the one end of the adjustment roller 52 as controlled
by the CPU. Once the coarse corrections have been made by the motor 82, the CPU
causes the motor 82 to move at a second slow rate in order to make fine adjustments
to the one end of the adjustment roller 52. In this manner, the one end of the
adjustment roller may be adjusted in a rapid and accurate manner.
Fine adjustments are made as the expiring roll decreases to adjust
for small variations in tension.
The foregoing detailed description has been given for clearness of
understanding only, and no unnecessary limitations should be understood therefrom,
as modifications will be obvious to those skilled in the art.