Sensing arrangement on a material roll

Sensing arrangements on material rolls are used to give advance warning when the material web forming the roll approaches its end. Usually this involves the sensing of the reduction of the the roll diameter with the help of a sensing device resting against the roll periphery. In the case of roll suspensions where the center of the roll is not fixed, these sensing arrangements cannot be used. The present invention uses a sensing arrangement which comprises a field-generating element, e.g. a permanent magnet, present in the center of the roll, together with a movable sensing device resting against the periphery of the roll, e.g. a heavy current switch which is acted upon at a certain predetermined field strength, and in a suitable manner indicates that a roll replacement is imminent.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to an arrangement for the sensing of the 
material thickness on a roll of weblike material. 
Weblike material is used very widely in various branches of industry. In 
the technique of packaging, for example, flexible weblike material is used 
as a starting material in the manufacture of packages, packing containers 
or the like. The conversion of the weblike material to finished packages 
takes place in packing machines which have a magazine to accommodate the 
web-like material in rolled-up condition. During operation of the machines 
the roll of weblike material is successively used up and has to be 
replaced, therefore, at regular intervals. To assist the machine operator, 
as he occasionally may have to handle several machines, the packing 
machines are generally provided with some form of indicating arrangement 
which visually or acoustically gives a signal when a roll diameter has 
been reduced to such an extent that roll replacement is imminent. 
Known arrangements for the sensing of the material thickness on a roll of 
weblike material are usually either of the mechanical or of the optical 
type. The mechanical arrangements generally make use of an arm resting 
against the roll periphery which as it approaches the roll centre, as the 
material is being used up or depleted, acts upon a limit switch to 
transmit an electric signal to an indicating arrangement. The optical type 
operates with a photocell which is located on one side of the material 
roll and which, after a certain consumption of material, is struck by a 
light beam from a light source situated on the opposite side of the roll. 
At this the photocell transmits a signal to an indicating arrangement of 
the known type. 
Both these known arrangements have proved to function well and provide a 
relatively reliable indication, so that the web splicing and the roll 
replacement can be done in good time and without the loss of an excessive 
quantity of residual material on the roll. The satisfactory operation 
fully depends, however, on the roll centre being in a fixed position in 
relation to the sensing element during the whole time of the material 
consumption. This condition can be achieved only if, in the first place, 
the axle which supports the material roll is rotatable in fixed bearing 
points on the frame of the machine and, in the second place, the outside 
diameter of the axle (possibly with intermediate elements, e.g. flanges or 
the like) corresponds to the inside diameter in the bobbin upon which the 
material is rolled up. The design and function of the sensing arrangement 
thus make demands on the suspension of the material roll which, otherwise, 
are not required, and it would be desirable, therefore, to provide a 
sensing arrangement which could operate with sufficient accuracy even on 
loosely suspended, radially movable material rolls. 
It is an object of the present invention to provide an arrangement for the 
sensing of the material thickness on a roll of weblike material, with the 
arrangement not subject to the disadvantages of earlier, similar 
arrangements. The present invention allowing a reading of the material 
thickness on a roll even if it is moved in an irregular manner in a radial 
direction during the consumption of material. 
It is a further object of the present invention to provide a sensing 
arrangement of the aforementioned type which is simple to manufacture and 
inexpensive and which gives such accuracy that the material wastage can be 
minimized. 
These and other objects have been achieved in accordance with the invention 
in that an arrangement of the type described provides a movable sensing 
device resting against the periphery of the roll and adapted so that at a 
predetermined distance from the centre of the roll it is acted upon by a 
field-generating element located in the central part of the roll. 
Owing to the sensing device present on the periphery of the roll being 
adapted to be acted on at a certain distance from the centre of the roll 
by a field-generating element present in the central part of the roll, the 
residual material thickness between the sensing device and 
field-generating element only will be registered. Any movements in the 
roll in radial direction will not affect the sensing device, since 
movements of the roll with respect to the point of suspension of the 
material roll have no consequence. Thus the material roll can be suspended 
in a very simple and labor-saving manner, e.g., an under-dimensioned axle 
is stuck through the bobbin of the roll and subsequently is placed freely 
movable between two V-shaped bearing elements. 
A preferred embodiment of the arrangement in accordance with the invention 
will now be described in detail with special reference to the enclosed 
schematic drawing which only shows the parts indispensable for the 
understanding of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In a machine for the manufacture of packages, weblike material 1 is rolled 
off from a material roll 3 which is supported so that it can freely rotate 
in the frame 2 of the machine. The material roll 3 is supported by an axle 
4 which extends through the bobbin 5 of the roll and is supported in 
V-shaped recesses 6 on either side of the roll 3. The V-shaped recesses 
are arranged in beams 7 which are firmly joined to the frame of the 
machine. 
The sensing arrangement in accordance with the invention comprises a 
movable sensing device 8 which is joined to the machine frame 2 by means 
of a vertically pivotable arm 9. The sensing device 8 is connected 
electrically to a unit 10 which e.g. may be a unit for automatic web 
splicing or a visual or acoustic indicating arrangement. 
In the central part of the material roll, that is to say in the bobbin 5, a 
field-generating element 11 is located which, for example, may be 
connected directly to the inside of the bobbin 5 or may be supported by a 
mounting device located in the roll center which, for example, is 
expandable or is adapted to be fixed centrally in the bobbin 5 by means of 
spring force. As shown in FIGS. 1 and 2, the element 11 is concentric with 
the bobbin 5. 
The sensing device 8 and the field-generating element 11 co-operate in such 
a manner that the sensing device is acted upon by the field generated by 
element 11 when it is at a certain distance from the field-generating 
element 11. This distance is adjustable e.g. by regulating the field 
strength of the generating element or the sensitivity of the sensing 
device. The field-generating element 11 is preferably a magnet, for 
example a permanent magnet, which generates a magnetic field acting upon 
the sensing device. The sensing device may be a heavy current switch which 
can be acted upon magnetically and which, at a certain field strength, 
closes the circuit and thus acts on the unit 10 so that the unit 10 
transmits a visual or acoustic indication or starts an automatic web 
splicing procedure, set up earlier. 
During operation of the arrangement in accordance with the invention, the 
material web 1 is consumed successively by the machine and the diameter of 
the roll 3 diminishes. As this happens the sensing device 8 resting 
against the periphery of the roll, due to the force of gravity (or 
possibly with the help of a spring, not shown), will approach the centre 
of the roll and the field-generating element 11 located there. As soon as 
the field strength is sufficiently great for the sensing device to be 
acted upon, the circuit to the unit 10 is closed which in turn influences 
the indicating arrangement or starts the web splicing. In practical 
experiments it has been found that the arrangement can be adjusted with 
great accuracy, and it is possible, for example with a material web 
thickness of approx. 0.4 mm to obtain an indication when only two turns of 
material remain on the roll which in a typical packing machine means that 
only approx. 6 packages remain unused on the roll when the splicing is 
carried out. 
Although a permanent magnet (e.g. of the self-holding band type) and a 
heavy current switch have proved very suitable in practical experiments, 
it is possible, of course, also to use other types of field-generating 
elements and sensing devices. Thus, for example, the field-generating 
element may be constituted of a radioactive isotope which with the help of 
a sensing device, sensitive to radioactive emission, may be used to give 
an indication when an appropriate quantity of material remains on the 
roll. Both these types of sensing arrangements have the advantage (in 
contrast to e.g. inductive-type transducers) that they operate also if, 
for example, a metal foil is included in the material web for which the 
arrangement is intended, which, in many cases is essential as e.g. 
aluminium foils are frequently included in the packing laminate. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing specification. The 
invention which is intended to be protected herein should not, however, be 
construed as limited to the particular forms disclosed, as these are to be 
regarded as illustrative rather than restrictive. Variations and changes 
may be made by those skilled in the art without departing from the spirit 
of the present invention. Accordingly, the foregoing detailed description 
should be considered exemplary in nature and not limited to the scope and 
spirit of the invention as set forth in the appended claims.