Web tension monitor

A web tension monitoring system in which a guide roll is supported for rotation upon bearings which are mounted on stub shafts extending inwardly from frame members. Load cells which include strain gauges are cantilever-mounted adjacent the internal ends of said stub shafts within the guide roll. Guide rolls and frame spacing of different lengths are accommodated by adjustable casing sleeves which permit variation of the amount of insertion of the stub shafts into the guide roll without affecting the operation of the load cells. Adaptors are provided to permit the use of guide rolls of differing diameters.

This invention relates in general to the monitoring of tension in a moving 
web and in particular to an improved system which is self-adjusting to 
compensate for support frame spacing and misalignment, as well as guide 
roll loading. 
BACKGROUND OF THE INVENTION 
In various industries, continuous monitoring of tension in a web which may 
be moving at high speed is essential to avoid damage to the web or to 
maintain proper manufacturing controls on web-supported products. For 
example, in the manufacture of paper, endless webs are frequently used, 
and if tension is insufficient, the web tends to wrinkle, forming 
irregularities in the material being carried by the web. Conversely, if 
tension becomes too great, the web or product may be weakened or 
destroyed. In many other applications, such as printing and textile 
manufacturing, it is necessary to continuously observe and make necessary 
adjustments to maintain tension on a web within suitable limits. 
Numerous systems have been devised for such tension monitoring. One such 
system is exemplified in U.S. Pat. No. 3,260,106, in which the web is 
passed over a guide roll and exerts displacing forces upon that guide 
roll. The guide roll is mounted for rotation upon a support shaft, and the 
force exerted by the tensioned web upon the guide roll causes deflection 
of the support shaft which is sensed by a strain gauge or gauges. 
SUMMARY OF THE INVENTION 
In the present invention, the tension exerted by a moving web upon a guide 
roll is measured by continuously sensing the displacement force applied to 
the guide roll as it rotates. This basic technique is old in the art and 
considerable effort has gone into the improvement particularly of the 
force-sensing devices. In the present invention, unlike some of the prior 
art mechanisms, no support shaft extending through the length of the guide 
roll is employed. Rather, stub shafts which may be mounted in pillow 
blocks or directly supported by frame members, extend into the ends of a 
hollow guide roll, self-aligning bearings being interposed between the 
stub shafts and the guide roll to permit rotation. Well within the guide 
roll adjacent the inner end of one or both of the stub shafts, a 
transducer load cell is fixed within a casing and isolated from the guide 
roll by the self-aligning bearing. 
A wide range of adjustments may be made without changing the loading moment 
between the self-aligning bearing and the load cell. This is made possible 
by forming matching shoulders on the inside wall of the guide roll and the 
outside wall of the casing which permit variation of the setting of the 
guide roll axially relative to its supports. Also, guide rolls of 
differing diameters may be accommodated by adaptors in the form of sleeves 
of differing thicknesses which may be inserted between the inner surface 
of the guide roll and the outer surface of the casing which encloses the 
load cell. Axial expansion of either the stub shaft or the guide roll is 
accommodated without effect upon the load cell by a spring ring bearing 
upon the end of the guide roll and fixed to the end of the outer bearing 
retainer. Rubber O-rings are interposed between the outer casing of the 
transducer and the inner surface of the guide roll. These rings provide 
sufficient friction to cause the transducer casing to rotate under normal 
conditions with the guide roll. Under emergency conditions, such as might 
occur with a bearing freeze, the friction of the rubber rings is overcome 
and the guide roll turns relative to the transducer casing. 
The load cell consists of two double cantilever-mounted sensors, and its 
output varies with loading in the direction perpendicular to the cell; 
that is, loading caused by the web in its passage over the guide roll. The 
rubber rings noted above isolate the load cell from vibrations which occur 
during operation and which would otherwise work-harden the load cell and 
cause it to fatigue.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1 of U.S Pat. No. 4,052,891 granted Oct. 11, 1977 to the applicant 
here, there may be seen continuously moving webs passing over guide rolls. 
Between the guide rolls, a tension-monitoring roll 16 is positioned in 
such a fashion that the web passing under the guide rolls exerts a 
downwardly directed force upon the monitoring roll. The force exerted on 
the monitoring roll is a function of tension in the web and it is 
transmitted to a stub shaft which is mounted on a frame member. Sensors 
(not shown) are mounted on the stub shaft, and connections are made to 
suitable electrical circuitry to display continuously the amount of 
tension in the web or to provide a feedback signal to correct or modify 
web tension as desired. 
The present invention may be incorporated in similar apparatus and detail, 
including internally mounted elements of the system, is shown in FIG. 1. A 
stub shaft 12 may be fixed to a suitable frame member by a screw 14. At 
the opposite end of the stub shaft 12, a load cell is end-mounted, 
preferably by a screw 16. The load cell includes two diametrically 
oppositely disposed arcuate beams 18 and 20 on which surfaces are turned 
on the upwardly-facing portion of the beam 18 and on the downwardly-facing 
portion of the beam 20. Sensors in the form of semiconductor strain gauges 
are mounted on the beam surfaces, typical strain gauges 24 and 26 being 
seen on the upwardly facing surface of the beam 18. Comparable and similar 
elements on the surface of the beam 20 are not seen in this view. 
Electrical leads from the strain gauges such as those shown at 30 extend 
through a groove formed in the core of the stub shaft 12 and emerge 
adjacent the frame on which the stub shaft is mounted. 
To limit the movement in the vertical plane as shown in FIG. 1, oppositely 
disposed limit screws 32 and 34 are provided. Similar limit screws may be 
employed in the horizontal plane. These screws are threaded into the beam 
support member adjacent a cylindrical extension 36 thereof. An inner 
bearing race 38 is fixed to the outer surface of the extension 36 and is 
held in place by a snap ring 39 fitted into a groove formed in the 
extension 36. The bearing is of the self-aligning type and also includes 
rings of balls 42 and 44 as well as an outer bearing race 46. The outer 
bearing race 46 is fitted into a cylindrical transducer casing 48 and is 
held in place by a bearing retainer 50 which is attached to the end of the 
transducer casing 48 which is fitted into a guide roll 15 and is 
frictionally engaged therein by rubber O-rings 17. A spring-ring 52 which 
includes a hollow ring fastened to the end of the casing 48 has 
spring-loaded pistons 54 bearing against the end of the guide roll. The 
spring-ring assembly is designed to permit expansion and contraction of 
the guide roll 15 and the casing 48 without affecting the operation of the 
load cell. 
The stepped cylindrical shapes of the housing and the guide roll form 
matching shoulders adjacent the gap 56 and permit axial expansion of the 
roll with full insertion of the load cell sensing unit. The casing 48 may 
be adjusted in its axial position relative to the roll to match guide 
rolls and frame spacings of differing lengths. As a final step, the spring 
ring may be slid into position against the guide roll end and locked in 
place. These adjustments and accommodations can be made without changing 
the loading distance to the load cell. 
In FIG. 2, fragmentary detail is shown to illustrate the use of adaptors 
when it is desired to accommodate guide rolls of larger diameter. The 
adaptors are cylindrical sleeves in the outer peripheral surface of which 
a plurality of grooves are formed. Rubber O-rings are disposed in the 
grooves, the groove and O-ring 73 being typical and visible here By using 
adaptors of differing thicknesses, a wide range of sizes of guide roll may 
be utilized with a given support system. Also, as noted above., the extent 
of insertion of the transducer casing into the end of the guide roll may 
be adjusted to accommodate differing lengths of guide roll and spacings 
between frame members. Also, the use of the self-aligning bearing permits 
a degree of misalignment between frame members or rotational mismatching 
which may exist without creating any error in the transducer which is 
isolated at the end of the cantilever mount. 
The use of a pair of double cantilever mounted gauges provides four areas 
sensing the same loading force. Each area may be gauged in such a fashion 
that a broad range of sensitivity is achieved and a single transducer unit 
can cover forces ranging from very low to very great magnitudes. Also, the 
multiple units may be so arranged as to provide temperature compensation, 
cancelling out the effect of heat generated during operation which tends 
to be transferred to the load cell. 
The spring-loaded pistons 54 in the spring-ring 52 allow the guide roll or 
the stub shaft to expand or contract axially without affecting the output 
of the transducer. The only resistance to differential expansion axially 
is provided by the spring ring which tolerates the expansion or 
contraction without effect upon the output of the load cell. At the same 
time, however, the spring-ring 52 prevents the guide roll from shifting 
from side to side. The rubber rings interposed between the casing of the 
transducer and the guide roll provide sufficient friction to keep the 
transducer from turning relative to the guide roll under normal 
circumstances. However, if the bearing freezes or if for any other reason 
jamming occurs, the transducer will rotate within the guide roll without 
damaging the load cell. The rubber rings also serve to isolate the load 
cell from harmful roll vibration which can interfere with the precision 
and accuracy of its operation and its useful life. A dust seal 75 and end 
cap assembly 77 serve to prevent the entry of foreign material into the 
structure.