Apparatus for opening one layer of a tube-like material web

An apparatus for opening one layer of a tube-like material web comprises a cutting member and a straight support for guiding the material web, which support extends transverse to the longitudinal direction of the material web. The cutting member includes a cutting knife mounted on a carriage movable back and forth parallel to the support by means of a first driving member. The carriage carries a guiding element for guiding the carriage on the support during cutting open said one layer. The cutting knife projects with respect to the guiding element in the direction of the support along an adjustable length.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for opening one layer of a tube-like 
material web, comprising a cutting means and guiding means for guiding the 
material web. 
Such an apparatus is disclosed for example in EP-A-0 269 145. In this known 
apparatus the cutting means includes a perforating knife which perforates 
both layers of the tube-like material web, whereafter the perforation in 
the upper layer is torn open by mechanical auxiliary means. This known 
apparatus has the disadvantage that the adjustment of the apparatus to the 
material web to be used is rather cumbersome, whereas the construction of 
the apparatus is complicated due to the required mechanical auxiliary 
means. 
U.S. Pat. No. 4,586,318 discloses an apparatus of the above-mentioned type, 
wherein the cutting means includes a heated cutting wire which is pressed 
on said one layer of the tube-like material web. This known apparatus 
shows the disadvantage that the tube-like material web must be guided 
around a separation plate for separating both layers. 
SUMMARY OF THE INVENTION 
The invention aims to provide an apparatus of the above-mentioned type, 
wherein said disadvantages are obviated in a simple but nevertheless 
effective manner. 
To this end the apparatus according to the invention is characterized in 
that one of said guiding means is made as a straight support for the 
material web extending transverse to the longitudinal direction of the 
material web and in that said cutting means includes a cutting knife 
mounted on a carriage movable back and forth parallel to the support by 
means of a first driving means, said carriage carrying a guiding element 
for guiding the carriage on the support during cutting open said one 
layer, wherein the cutting knife projects with respect to the guiding 
element in the direction of the support along an adjustable length. 
In this manner an apparatus is obtained, by means of which the upper layer 
of the tube-like material web is cut open with certainty, wherein it is 
not necessary to make extremely high demands as to the tolerances in order 
to maintain the desired cutting depth, because the guiding element guides 
the carriage on the support during the cutting action, so that a fixed 
position of the carriage with respect to the support is guaranteed. By 
adjusting the projecting length of the cutting knife the desired cutting 
depth for cutting through the upper layer of the tube-like material web is 
then obtained. 
According to a favourable embodiment of the apparatus according to the 
invention the carriage is movable between a rest position and an operating 
position by means of a second driving means, said guiding element and said 
cutting knife being at a distance from the support in the rest position of 
the carriage, said guiding element being pressed against the material web 
guided on the support in the operating position of the carriage, wherein 
said carriage comprises a detector for detecting the presence and absence, 
respectively, of the material web opposite of the cutting knife and for 
actuating the second driving means in such a manner that the carriage is 
in its operating and rest position, respectively.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2 there is shown an apparatus for opening the one 
layer 1 of a tube-like material web 2 for example of plastic material, 
which material web is guided along a first roller 3 and a cutting shaft 4. 
The cutting shaft 4 functions as a support for the material web 2 during 
the cutting action and can also be made in a different manner. 
The complete apparatus is mounted between two support plates 5, one of 
which being shown in the drawings. 
A hollow shaft 6 is mounted at a distance under the cutting shaft 4, a 
carriage 7 being guided on this shaft 6. Said carriage 7 supports a 
cutting knife 8 with a cutting point 9 for cutting through the layer 1 of 
the material web 2. To this end the carriage 7 is movable back and forth 
on the shaft 6 by means of a first driving means 10. During each movement 
of the carriage 7 along the material web 2 the cutting knife 8 can cut 
through the upper layer 1. Means for transporting the material web 2 will 
move the material web along a predetermined distance after each cutting 
action. These means do not form part of the present invention. 
Said driving means 10 comprises a housing 11 which is slidably mounted on 
the shaft 6, whereas a magnet not shown in the drawing is movable back and 
forth within the hollow shaft by means of compressed air, which magnet 
cooperates with a magnet accommodated in the housing 11, so that the 
housing 11 will move together with the magnet driven by compressed air. 
Such driving means are known per se and need not to be described further. 
Of course, it is also possible to use another type of driving means for 
the carriage 7. 
The carriage 7 is mounted on the housing 11 and is made as a substantially 
L-shaped plate. On the one leg 12 a support block 13 is provided, on the 
upper side of which a knife support 14 is slidably mounted. The cutting 
knife 8 is attached on this knife support 14. The knife point 9 of the 
cutting knife 8 projects with an adjustable length with respect to a 
bearing 15 mounted on the support block 13 and functioning as a guiding 
element of the carriage 7. 
The carriage 7 is pivotable around the hollow shaft 6 by means of a second 
driving means 16, which in the embodiment shown is made as an 
electromagnet, which however can be replaced by any other suitable driving 
means. The driving means 16 actuates an excentric shaft 17 for moving the 
carriage 7 between a rest position shown in FIG. 3 and an operating 
position shown in FIG. 4. In the rest position of FIG. 3 the cutting knife 
8 lies at a distance from the cutting shaft 4, while in the operating 
position of FIG. 4 the bearing 15 is pressed against the material web 2, 
so that the cutting knife 8 sticks into the layer 1 of the material web 2. 
The excentric shaft 17 engages a boss 18 which is slidably mounted in a 
bush 20 against the action of a spring 19. The shaft 17 can be rotated by 
the driving means 16 from the position of FIG. 3 to the position of FIG. 
4, whereby the carriage 7 pivots towards the cutting shaft 4 and is 
pressed with the bearing 15 against the material web 2 with a force 
determined by the spring 19. The rest position of FIG. 3 is determined by 
a stop boss 22, which is screwed in the other leg 21 of the carriage 7. By 
adjustment of this boss 22 the centre line of the cutting knife 8 can be 
adjusted on the centre line of the cutting shaft 4, whereby a straight cut 
in the layer 1 of the material web as accurate as possible is obtained. 
The driving means 16 is energized by a detector made as a microswitch 23, 
of which a switch arm 24 projects into a slot 25 of a guiding plate 26 for 
the material web 2 in absence of this material web 2. As soon as the 
switching arm 24 reaches the material web 2, the driving means 16 is 
energized and the carriage 7 pivots from the rest position of FIG. 3 into 
the operating position of FIG. 4. 
In order to guarantee that the detector 23 only energizes the driving means 
16 if the cutting knife 8 has reached the material web 2, the detector 23 
is mounted on a slidable plate 27, by which the detector 23 is movable 
between two detection positions one at either side of the cutting knife 8. 
The plate 27 is slidable by means of a spring 28 operating as a lever, one 
end 29 of which is coupled with the plate 27 whereas the other end 30 is 
adapted to cooperate with a switching pin 31 mounted in the middle of the 
excentric shaft 17. 
When the carriage 7 is moving from the position shown in FIG. 1 to the 
left, the cutting knife 8 will be opposite of the material web 2 first, 
whereafter the switching arm 24 reaches the material web and energizes the 
driving means 16. Subsequently the plate 27 is slided because the spring 
28 is actuated by the switching pin 31, so that the switching arm 24 will 
lead with respect to the cutting knife 8 and de-energizes the driving 
means 16 as soon as the switching arm 24 will again enter into the slot 25 
of the guiding plate 26. Thereby the carriage 7 will pivot back into the 
rest position before the end edge of the material web 2 is reached. During 
the return movement from the left to the right according to the view of 
FIG. 1, the cutting knife 8 will first reach the material web and 
subsequently the switching arm 24. 
It is noted that the microswitch 23 with switching arm 24 can also be 
replaced by another type of detector, for example light detectors lying on 
either side of the cutting knife 8 with a corresponding logic control 
means. The detector should only guarantee that at detecting the presence 
and absence, respectively, of the material web 2 opposite of the cutting 
knife 8, the driving means 16 will be actuated in such a manner that the 
carriage 7 is in the operating and rest position, respectively. 
The requirements as to the tolerances of the described apparatus, in 
particular as to the cutting shaft 4 and the hollow shaft 6, to guarantee 
the required cutting depth are not extremely high because during the 
cutting action the bearing 15 guides the carriage 7 on the cutting shaft 4 
and the cutting knife 8 projects with respect to the bearing 15 along an 
adjustable length. 
The projecting length of the cutting knife 8 can be adjusted because the 
knife support 14 has at its side opposite of the cutting knife 8 a 
downwardly bent leg 32 with a threaded hole, in which an adjusting screw 
is rotatable. This adjusting screw is provided with a central threaded 
bore 34, with which the adjusting screw 33 is rotatably mounted on a fixed 
threaded rod 35. The pitch of the thread in the bore 34 is equal to the 
same at the outer side of the adjusting screw 33, so that the displacement 
of the cutting knife 8 is determined by the difference between the pitch 
of the outer and the pitch of the inner thread. Thereby an accurate 
adjustment of the projecting length of the cutting knife 8 is possible. 
The invention is not restricted to the above-described embodiment which can 
be varied in a number of ways within the scope of the claims.