[0001] The present invention relates to a dispensing system for a wrapping machine, wherein
the amount of film dispensed is mechanically controlled.
[0002] As known, wrapping machines are machines that are apt to package a load by wrapping
it in a plastic film. The wrapping of the load in the film may occur in different
ways, for example with a fixed film bobbin and a rotating load, or with a fixed load
and a rotating bobbin; in the latter case, the bobbin may be mounted onto a rotating
boom arrangement or onto a circular ring.
[0003] It is also known that most wrapping machines use very stretchable (up to 200%-300%)
film, which, for maximum yield, is pre-stretched by a pre-stretching unit before being
applied onto the load. The simplest pre-stretching units comprise rollers onto which
the film passes, which are broken in order to obtain the stretching of the film by
means of the tension applied while applying the film onto the load: however, this
system has some drawbacks that make it little effective, although very economical.
[0004] More effective devices provide that the film passes between a pair of rollers, the
downstream one of which has a higher peripheral speed, so as to obtain a uniform pre-stretching,
adjustable as desired.
[0005] The best results are obtained with a driving and controlling device for these rollers,
which establishes the film dispensing speed depending on the system requirements in
a given instant.
[0006] The most widespread solution on the market provides to adopt an electrical motor
to drive one of the two rollers - the two rollers being connected to each other, for
instance, by a pair of gears - and a dancing arm arranged between the pre-stretching
unit and the load to be wrapped, through which the tension in the film may be detected
and hence the electrical motor speed may be controlled. The dancing arm is usually
connected to a load cell, or to another position transducer, which generates a signal
that is proportional to the film tension and is then sent to a control unit of the
driving motor.
[0007] This way, when the film tension increases, i.e. when the wrapping operation requires
a larger quantity of film, the control unit makes the driving motor accelerate and
vice versa. However, these driving motor acceleration/deceleration phases must typically
(with a rectangular plan section load) occur 8 times per turn, and therefore require
a very prompt reaction from the system. The electronic control unit, no matter how
advanced and expensive, experiences set up problems in order to prevent the system
inertial moments and delays from dispensing a quantity of film differing from the
actual requirements.
[0008] Unfortunately, this type of problems is inherent in electronic control systems, where,
in addition, the reaction times of an electrical motor may not exceed certain thresholds,
unless in exchange for high costs and power consumption.
[0009] Furthermore, whenever the pre-stretching unit and the respective driving and controlling
device are mounted on a rotating support (for example in wrapping machines with a
rotating boom or provided with a ring track), it is necessary to provide wiping electrical
contacts in order both to supply the driving motor and to manage the controlling device.
However, these wiping contacts are often responsible for drawbacks and maintenance
charges.
[0010] US-A-4934123 discloses a dispenser according to the preamble of claim 1. In this
case a braking element is used to adjust the torque transmitted by the driving means,
but a planetary gear is required.
[0011] The object of the present invention is to solve the above-listed drawbacks. In particular,
it is meant to provide a film dispenser for a wrapping machine wherein the speed change
of the pre-stretching unit may be achieved in a completely mechanical way, without
the intervention of an electronic control unit; furthermore, according to another
aspect, it is meant to provide a film dispenser wherein wiping contacts may be completely
eliminated, and a wrapping machine comprising such a device.
[0012] Such objects are obtained with a device as described in its essential features in
the appended claim 1.
[0013] Further features and advantages of the device according to the invention will become
more evident from the following detailed description of preferred embodiments thereof,
given by way of example and illustrated in the appended drawings, wherein:
[0014] fig. 1 is a sectional view of a first embodiment of the device according to the invention;
[0015] fig. 2 is an enlarged view of a detail of fig. 1;
[0016] fig. 3 is a schematic plan view of a ring wrapping machine provided with a device
according to a second embodiment of the invention;
[0017] fig. 4 is an enlarged view of the device according to the invention shown in fig.
3;
[0018] fig. 5 is a sectional view taken along line V-V of fig. 4;
[0019] fig. 6 is a sectional view taken along the hatched line VI-VI of fig. 4; and
[0020] fig. 6A is an enlarged view of a detail of fig. 6.
[0021] As shown in fig. 1, a dispenser is comprised, in a
per se known manner, of a support plate 1 onto which a stretchable film bobbin 2, a pair
of pre-stretching rollers P
1 and P
2 and a movable roller B are mounted.
[0022] In the example shown, the movable roller B is mounted oscillating, by means of a
pair of arms 3a and 3b, onto a rotating shaft 4 provided with elastic return means
5. The latter balance the oscillation of the movable roller B against the tension
applied thereto by the stretchable film (not shown in fig. 1), which extends, passing
thereon, from the bobbin 2 and the pre-stretching rollers P
1 and P
2, to the load CA to be wrapped (fig. 3).
[0023] Rolls P
1 and P
2 are connected to each other, for example through a pair of gears P
1' and P
2' that set a gear ratio such that the downstream gear P
2 rotates faster than the upstream gear P
1, achieving the desired pre-stretching of the film.
[0024] According to a first embodiment of the invention (fig. 2), the rotating shaft 4 carries,
at one end thereof, a first geared wheel 6 engaging a second geared wheel 7 splined
onto a supporting shaft 8 by means of a helical engagement. In other words, a screw
coupling is provided between the hub of the second gear 7 and the supporting shaft
8, which transforms the rotation of gear 7 into a translation thereof along the longitudinal
axis of the shaft 8.
[0025] A lower half-clutch 10 - onto which a friction slipping element 11 is attached -
is mounted onto the second gear 7 through a suitable ring bearing 9. The friction
slipping element is in the form of a circular rim.
[0026] Opposed to the lower half-clutch 10, there is an upper half-clutch 12, axially fixed
but rotatively mounted onto the shaft 8 by means of bearings. The surface of the upper
half-clutch 12 opposed to the slipping element 11 also has an analogous friction slipping
element or is itself made of a friction slipping material.
[0027] The material with which the friction slipping element 11 is made is apt to transfer
a torque between the two half-clutches 10 and 12 in a progressive way as the compressive
force between said half-clutches varies. From this point of view, this material is
quite different from the one employed for the traditional automotive clutches, which
is apt to properly work in static condition only when high compressive force is applied
between the two portions of the clutch. The friction slipping material may be, for
example, Iglidur® marketed by Igus GmbH.
[0028] The half-clutch 12 is further connected with an electrical motor M, for example through
an engagement of gears 12a and Ma.
[0029] The lower half-clutch 10 is connected to the pre-stretching unit instead, preferably
with the downstream roller P
2, through a gear engagement 13.
[0030] Although the transmission to the pre-stretching unit may also be realised with the
upstream roller P
1, this would not be as much effective, because the operation would be affected by
potential oscillations in the degree of film pre-stretching.
[0031] When the device is in use, the motor M is excited and made to rotate at a constant
speed. Accordingly, the upper half-clutch 12 is made to rotate at a constant speed.
[0032] When no film is required, i.e. when no tension is applied to the movable roller B,
the translatable gear 7 is in its totally lowered position (in the view of fig. 2)
and therefore the two half-clutches 10 and 12 are kept spaced apart and no torque
is transferred from the motor M to the lower half-clutch 10.
[0033] When film is drawn by the system, a tension is applied to the movable roller B, the
shaft 4 is thus rotated by a certain angle depending on the ratio between film tension
and elastic force of the return means 5. The rotation of the shaft 4 results in a
rotation of the wheel 6 and of the translatable wheel 7, therefore in a translation
of the lower half-clutch 10 along the longitudinal axis of the shaft 8. This way,
the two engaging half-clutches 10 and 12 are brought closer to each other and the
friction slipping element 11 begins to work, transferring a torque that is proportional
to the displacement of the movable roller B or, in other words, proportional to the
tension applied onto the roller B by the film. In this condition, the motor M transfers
its motion to the pre-stretching unit P
1 and P
2, actively dispensing stretchable film.
[0034] As may be guessed, this arrangement represents a self-controlled dispensing system;
in fact, the more film the system requires - which corresponds to an increase in the
film tension - the more the movable roller B is biased, which results in more pressure
on the slipping contact 11 and in a higher torque being transferred from the motor
M to the pre-stretching unit, therefore in an increased dispensing of film; vice versa,
when the system requires less film, the tension loosens, therefore the movable roller
B returns towards its rest position, thus a lower pressure is applied between the
two engaging half-clutches 10 and 12, with a subsequent transfer of a lower torque
and a decrease in the dispensing of the film.
[0035] Through a proper adjustment of the gear ratio and of the elastic modulus of the return
means and through a suitable choice of the friction slipping element 11 material -
which is within the reach of an expert in the field, once having acquired the teachings
offered herewith - it is possible to obtain a progressive and regular operation of
the device.
[0036] The constant rotation speed of the motor M is advantageously set like the speed required
in order to dispense the maximum film quantity that the system is envisaged to require.
[0037] It is worth stressing that the engagement of the slipping rims does not occur in
the same way as a common clutch, which is by nature apt to work, in a steady state,
either in a disengaged or in a completely engaged way. In this case, instead, the
progressiveness of a "slipping" engagement is exploited, i.e. an engagement between
two surfaces apt to properly work while slipping, transferring a more or less high
torque, depending on the pressure applied. If it were not so, the control evenness
and progressiveness would be lost, resulting in an irregular and halting behaviour
of the dispenser.
[0038] Advantageously, in order to obtain the best outcome from the slipping clutch, i.e.
to obtain a prompt reaction and to prevent jams, the rotation direction of the translatable
wheel 7, which brings the two half-clutches 10 and 12 close to each other, is opposed
to the rotation direction of the half-clutch 12. This prevents the natural tendency
of the engagement to become tighter and thus favours a prompt release and an immediate
decrease of film dispensing as soon as the film tension onto the movable roller B
is released.
[0039] As may be guessed, the above described controlling device, being completely mechanical,
ensures a proportional, direct and virtually instant reaction, which does not cause
instability in the control cycle, as may occur with the prior art.
[0040] The embodiment shown so far may be applied onto a wrapping machine wherein the support
plate 1 is mounted onto a rotating boom or onto a ring track, or also in a fixed position
with a rotating load.
[0041] Another embodiment of the invention, typically applicable onto a ring track wrapping
machine, is shown in figs. 3-6.
[0042] In fig. 3 a typical annular structure A is schematically shown, which is vertically
translatable on two columns of a wrapping machine, onto which a supporting plate 100
is movably mounted.
[0043] The plate 100 is translatably mounted onto tracks of the annular structure A by means
of a series of rolling wheels R
1, R
2, R
3 and is fixed onto a rotating driving rim T, lying onto bearings Ci circumferentially
placed on the annular structure A.
[0044] The driving rim T and the plate 100 are made to rotate through a driving belt CT
driven by a motor MT (fig. 5), fixedly placed outside the annular structure A.
[0045] On the plate 100 there are substantially the same elements described above. A stretchable
film P is extended from a bobbin 102 to a pre-stretching unit P
10 and P
20, then around an intermediate roller 104a, and finally onto a movable roller B
10.
[0046] The movable roller B
10 is connected, through arms 103, to a rotating shaft 104, which also supports the
intermediate roller 104a, integral with a first driving wheel 106. The rotation of
the shaft 104 is opposed by elastic return means 105.
[0047] The gear wheel 106 is connected, through a chain 106a, to a translatable gear wheel
107, mounted through a helical engagement onto a supporting hollow stand 107a, wherein
a transmission shaft 108 is coaxially rotatably mounted. The translatable gear 107
carries a lower half-clutch 110 apt to engage another upper half-clutch 112 through
a friction slipping rim 111.
[0048] The upper half-clutch 112 is splined onto the transmission shaft 108, integral with
the downstream roller P
20 of the pre-stretching unit.
[0049] According to the present embodiment, the lower half-clutch 110 has the shape of a
bush, on the outer surface of which a groove 110a is provided.
[0050] A second driving belt D - winding as much as possible, with the assistance of a belt
tightener, around said bush 110 and then adhering to a track D1 integral with the
annualar structure A - is apt to be engaged into groove 110a (figs. 4 and 5).
[0051] When the supporting plate 100 is made to rotate by the motor MT around the annular
structure A, the second driving belt D, which is static relative to the track D1,
makes the bush 110 rotate.
[0052] Thus, the movement of the supporting plate 100 causes the rotation of the bush 110,
which is the driving member of the dispenser, similar to the function of the motor
M in the first embodiment illustrated.
[0053] This allows to avoid the use of a driving motor mounted on the supporting plate 100,
with all the advantages deriving from not having to supply electrical power to a moving
device.
[0054] Apart from this specific feature, the operation is otherwise identical to the one
described above. Through a suitable choice of the transmission ratio between the annular
track D1 and the rotating bush 110, it is ensured that the device is apt to dispense
the maximum quantity of film required by the system, depending on the peripheral rotation
speed of the device on the annular structure A.
[0055] This second embodiment also achieves the second object set in the premises, i.e.
that of totally avoiding the use of any sliding contacts in order to transfer electrical
power from outside the wrapping machine to the rotating dispenser.
[0056] It is however intended that the invention is not limited to the specific embodiments
illustrated above, which are only non-limiting examples of the scope of the invention,
but many alternatives are possible, all within the reach of an expert in the field,
without thereby departing from the scope of the invention.
[0057] It is for instance clear that the kinematic mechanism which causes the engaging half-clutches
to get closer to each other, depending on the movable roller displacement, may have
different shapes. Besides, it is not necessary that the movable roller be supported
oscillatorily, as it may also be translatable. Furthermore, the movable roller may
be equally substituted by other devices, the displacement of which depends on the
stretchable film tension.
[0058] Accordingly, the outer driving system, illustrated in figs. 4-6, it is to be considered
purely illustrative, as it is possible to adopt many different solutions to make the
dispenser rotate on the carrying ring structure.
[0059] Finally, the driving belt apt to drive the bush of the slipping clutch may be substituted
by similar elements, as long as the movement of the device around the annular structure
is exploited in order to drive the dispenser.
1. Dispenser of stretchable plastic material film for a wrapping machine, comprising
a bobbin of plastic film (2), a pre-stretching unit (1) driven by driving means (M)
and a movable controlling roller (B) apt to regulate torque transferred from said
driving means (M) to the pre-stretching unit (1) on the basis of the tension applied
thereon by the plastic material film, characterized in that
said movable controlling roller (B) is mechanically connected to a friction slipping
clutch,
the torque transferred by said slipping clutch being proportional to the pressure
applied thereon through said movable controlling roller (B),
said slipping clutch comprising a first half-clutch (12) and a second half-clutch
(10), which may be brought close to each other,
the first half-clutch (12, 110) being constantly rotating by means of said driving
means (M), while the second half-clutch (10, 112) is connected to said pre-stretching
unit, and in that an element (11, 111) of a material apt to work in a slipping condition is inserted
between said first and second half-clutches (12, 10; 110, 112).
2. Dispenser as in claim 1), wherein said first half-clutch is fixed in translation and
rotating onto a supporting shaft, while the second half-clutch is rotatably mounted
onto a translatable wheel coaxially mounted by a helical coupling onto said supporting
shaft, said translatable wheel being made to rotate by the displacement of said movable
controlling roller.
3. Dispenser as in claim 1), wherein said first half-clutch is rotating onto a translatable
wheel mounted, by means of a helical coupling, onto a supporting shaft, while said
second half-clutch is mounted fixed in translation, the displacement of said movable
controlling roller causing the rotation/translation of said translatable wheel.
4. Dispenser as in any one of the preceding claims, wherein said dispenser is movably
mounted onto an annular structure of a wrapping machine and said driving means comprise
a transmission element interposed between an annular track of said ring structure
and said second half-clutch.
5. Dispenser as in claim 4), wherein said transmission element is a transmission belt
that is wrapped around said track and around a bush that is integral with said second
half-clutch.
6. Dispenser as in any one of the preceding claims, wherein the two engaging half-clutches
are brought closer to each other, each one according to a rotation direction opposed
to that of the other.
7. Dispenser as in any one of the preceding claims, wherein the torque transferred is
applied to the roller downstream of said pre-stretching unit.
8. Wrapping machine comprising a dispenser as in any one of the preceding claims.
1. Abgabevorrichtung zur Abgabe einer dehnbaren Kunststoffolie für eine Umhüllungsmaschine,
mit einer aus einer aufgewickelten Kunststoffolie bestehenden Vorratsrolle (2), einer
von einem Antrieb (M) angetriebenen Vordehneinheit (1), und einer beweglichen Steuerrolle
(B), mittels welcher das von dem Antrieb (M) auf die Vordehneinheit (1) übertragene
Drehmoment auf der Basis der Spannung zu regulieren ist, welche durch die Kunststoffolie
auf sie ausgeübt wird, dadurch gekennzeichnet, daß die bewegliche Steuerrolle (B) mechanisch mit einer Reibungs-Schlupfkupplung verbunden
ist;
daß das von der Schlupfkupplung übertragene Drehmoment proportional zu dem Druck ist,
welcher durch die bewegliche Steuerrolle (B) auf sie ausgeübt wird;
daß die Schlupfkupplung eine erste Kupplungshälfte (12) und eine zweite Kupplungshälfte
(10) aufweist, welche nahe aneinander zu bringen sind;
daß die erste Kupplungshälfte (12, 110) durch den Antrieb (M) konstant dreht, während
die zweite Kupplungshälfte (10, 112) mit der Vordehneinheit verbunden ist, und daß
ein Element (11, 111) aus einem Material, welches unter Schlupfbedingung arbeiten
kann, zwischen den ersten und zweiten Kupplungshälften (12, 10; 110, 112) eingesetzt
ist.
2. Abgabevorrichtung nach Anspruch 1, wobei die erste Kupplungshälfte translatorisch
fixiert ist und auf einer Stützwelle dreht, während die zweite Kupplungshälfte drehbar
auf einem translatorisch beweglichen Rad angeordnet ist, welches durch eine Schraubkupplung
koaxial auf der Stützwelle angeordnet ist, wobei das translatorisch bewegliche Rad
durch die Verschiebung der beweglichen Steuerrolle zu drehen ist.
3. Abgabevorrichtung nach Anspruch 1, wobei die erste Kupplungshälfte auf einem translatorisch
beweglichen Rad dreht, welches mittels einer Schraubkupplung auf einer Stützwelle
montiert ist, während die zweite Kupplungshälfte translatorisch fixiert montiert ist,
wobei die Verschiebung der beweglichen Steuerrolle die Drehung/Translation des translatorisch
beweglichen Rades bewirkt.
4. Abgabevorrichtung nach einem der vorhergehenden Ansprüche, wobei die Abgabevorrichtung
beweglich auf einer ringförmigen Struktur einer Umhüllungsmaschine angeordnet ist,
und der Antrieb ein Transmissionselement aufweist, welches zwischen einer ringförmigen
Spur der ringförmigen Struktur und der zweiten Kupplungshälfte angeordnet ist.
5. Abgabevorrichtung nach Anspruch 4, wobei das Transmissionselement ein Transmissionsgurt
bzw. -riemen ist, der um die Spur und eine Buchse gewickelt ist, welche integral mit
der zweiten Kupplungshälfte ausgebildet ist.
6. Abgabevorrichtung nach einem der vorhergehenden Ansprüche, wobei die beiden miteinander
in Eingriff stehenden Kupplungshälften jeweils aufgrund einer Drehrichtung näher aneinandergebracht
werden, welche der Drehrichtung der anderen Kupplungshälfte entgegengerichtet ist.
7. Abgabevorrichtung nach einem der vorhergehenden Ansprüche, wobei das übertragene Drehmoment
auf die Rolle stromabwärts zu der Vordehneinheit aufgebracht wird.
8. Umhüllungsmaschine mit einer Abgabevorrichtung nach einem der vorhergehenden Ansprüche.
1. Distributeur de film de matière plastique étirable pour une machine d'emballage, comprenant
une bobine de film plastique (2), une unité de pré-étirage (1) entraînée par un moyen
d'entraînement (M) et un rouleau de commande mobile (B) apte à réguler le couple transféré
dudit moyen d'entraînement (M) à l'unité de pré-étirage (1) sur la base de la tension
appliquée dessus par le film de matière plastique, caractérisé en ce que
ledit rouleau de commande mobile (B) est relié mécaniquement à un limiteur de couple
à friction,
le couple transféré par ledit limiteur de couple à friction étant proportionnel à
la pression appliquée sur lui via ledit rouleau de commande mobile (B),
ledit limiteur de couple à friction comprenant un premier demi-embrayage (12) et un
deuxième demi-embrayage (10), qui peuvent être rapprochés l'un de l'autre,
le premier demi-embrayage (12, 110) étant constamment en rotation grâce audit moyen
d'entraînement (M), tandis que le deuxième demi-embrayage (10, 112) est relié à ladite
unité de pré-étirage, et en ce qu'un élément (11, 111) d'un matériau apte à opérer dans une condition de glissement
est inséré entre lesdits premier et deuxième demi-embrayages (12, 10 ; 110, 112).
2. Distributeur selon la revendication 1, dans lequel ledit premier demi-embrayage est
fixe en translation et tourne sur un arbre de support, tandis que le deuxième demi-embrayage
est monté avec possibilité de rotation sur une roue susceptible de translation montée
coaxialement par un accouplement hélicoïdal sur ledit arbre de support, ladite roue
susceptible de translation étant amenée à tourner par le déplacement dudit rouleau
de commande mobile.
3. Distributeur selon la revendication 1, dans lequel ledit premier demi-embrayage tourne
sur une roue susceptible de translation, montée, au moyen d'un accouplement hélicoïdal,
sur un arbre de support, tandis que ledit deuxième demi-embrayage est monté fixe en
translation, le déplacement dudit rouleau de commande mobile provoquant la rotation/translation
de ladite roue susceptible de translation.
4. Distributeur selon l'une quelconque des revendications précédentes, dans lequel ledit
distributeur est monté avec possibilité de mouvement sur une structure annulaire d'une
machine d'emballage et ledit moyen d'entraînement comprend un élément de transmission
intercalé entre une voie annulaire de ladite structure annulaire et ledit deuxième
demi-embrayage.
5. Distributeur selon la revendication 4, dans lequel ledit élément de transmission est
une courroie de transmission qui est enroulée autour de ladite voie et autour d'une
boîte de glissement qui est formée d'un seul tenant avec ledit deuxième demi-embrayage.
6. Distributeur selon l'une quelconque des revendications précédentes, dans lequel les
deux demi-embrayages d'engagement sont rapprochés l'un de l'autre, chacun selon un
sens de rotation contraire au sens de rotation de l'autre.
7. Distributeur selon l'une quelconque des revendications précédentes, dans lequel le
couple transféré est appliqué sur le rouleau en aval de ladite unité de pré-étirage.
8. Machine d'emballage comprenant un distributeur selon l'une quelconque des revendications
précédentes.