ES2256411T3 - MECHANICALLY CONTROLLED DISPENSER FOR PACKING MACHINES AND PACKING MACHINE EQUIPPED WITH SUCH DISPENSER. - Google Patents

Abstract

A dispenser of stretchable plastic material film and a wrapping machines equipped with such a dispenser are described. The dispenser comprises a bobbin (2) of plastic film, a pre-stretching unit (P1,P2) driven by driving means and a movable controlling roller (B) apt to control said driving means on the basis of the tension applied thereon by the plastic material film, said movable controlling roller being mechanically connected to a friction slipping clutch (10-12) apt to transfer a torque from said driving means to the pre-stretching unit, the torque transferred by said slipping clutch being proportional to the pressure applied thereon through said movable controlling roller. <IMAGE>

Description

Mechanically controlled dispenser for packaging machines and packaging machine equipped with said dispenser.

The present invention relates to a system of dispensing for a packaging machine, in which the amount of Dispensed film is controlled mechanically.

As it is known, the packaging machines are machines that are suitable for packing a load by wrapping it in a plastic film The wrapping of the load in the film it can be produced in different ways, for example with a coil of fixed film and a rotating load, or with a fixed load and a rotating coil; in the latter case, the coil can be mounted on a rotating boom arrangement or on a ring circular.

It is also known that most of the packaging machines use a very stretchable film (up to 200% - 300%), which, for maximum performance, are stretched previously by means of a prestressing unit before its application over load. The simplest pre-stretching units they comprise rollers on which the film passes, which are cut in order to get the film stretched by medium of the tension applied while applying the film on the load: however, this system has some drawbacks that They make it inefficient, although very economical.

More effective devices provide that film pass between a pair of rollers, presenting the roller downstream a higher peripheral speed, to obtain a Pre-stretched uniform, adjustable as desired.

The best results are obtained with a propulsion and control device for these rollers, which stabilizes the film dispensing speed according to the system requirements at a given time.

The most widespread solution in the market provides adopt an electric motor to drive one of the two rollers -the two rollers are coupled together, for example, by a pair of gears- and an oscillating arm arranged between the unit of pre-stretched and the load to be packed, by means of which detects the tension in the film and therefore can be controlled Electric motor speed. Swing arm normally is coupled to a piezoelectric battery, or to another transducer of position, which generates a signal that is proportional to the voltage of the film and then sends it to a control unit of the propulsion engine

In this way, when the tension of the film, that is, when the packing operation requires a more film, the control unit makes the engine of propulsion accelerate and vice versa. However, these phases of acceleration / deceleration of the propulsion engine must occur generally (with a rectangular section section load) 8 times per lap, and therefore require a very fast reaction of the system. The electronic control unit, no matter what advanced and expensive, experience preparation problems for avoid moments of inertia of the system and delays in the dispensing of a quantity of film that is different from that of Existing needs

Unfortunately, these types of problems are inherent in electronic control systems, in which, in addition, the reaction times of an electric motor cannot exceed certain minimum limits, unless it is in exchange for high costs and consumption.

In addition, provided that the prestressing unit and the respective propulsion and control device are mounted on a swivel stand (for example on packaging machines with a pen rotating or provided with an annular slide guide), results it is necessary to provide sliding electrical contacts for both feed the propulsion engine to run the control device However, these sliding contacts frequently involve certain inconveniences and burdens of maintenance.

The document US-A-4,934,123 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 drive means, but a planetary gear

The objective of the present invention is to solve the inconveniences indicated above. In particular, It is planned to provide a film dispenser for a machine packed in which the unit speed change prestressed can be achieved completely mechanically, without the intervention of an electronic control unit; also according to another aspect, it is planned to provide a film dispenser in the that the sliding contacts can be completely removed, and a packaging machine comprising such a device.

These goals are achieved with a device as described in its essential characteristics in the attached claim 1.

Other features and advantages of the device according to the invention will be more evident from the following detailed description of preferred embodiments of the same, provided by way of example and illustrated in the attached drawings, in which:

Figure 1 is a sectional view of a first embodiment of the device according to the invention;

Figure 2 is an enlarged view of a detail of figure 1;

Figure 3 is a schematic plan view of a circular packing machine provided with a device according to a second embodiment of the invention;

Figure 4 is an enlarged view of the device according to the invention represented in figure 3;

Figure 5 is a sectional view along the line V-V of Figure 4;

Figure 6 is a sectional view along the line of dots and stripes VI-VI of Figure 4; Y

Figure 6A is an enlarged view of a detail of figure 6.

As shown in Figure 1, a dispenser is composed, in a manner known per se, by a support plate 1 on which a coil of stretchable film 2, a pair of pre-stretched rollers P1 and P_ {2} and a mobile roller B.

In the example shown, the mobile roller B it is mounted oscillating, by means of a pair of arms 3a and 3b, on a rotating shaft 4 provided with elastic return means 5. The latter compensate the oscillation of the mobile roller B against the tension applied to it by the stretch film (not shown in figure 1), which extends, passing over it, from the bobbin 2 and the pre-stretched rollers P_ {{{}}} and P_ {{}} to the load AC to be wrapped (figure 3).

The rollers P1 and P2 are coupled each other, for example by a pair of gears P_ {1} 'and P_ {2} 'that establish a transmission relationship so that the downstream gear P_ {rotates faster than gear upstream P1, obtaining the desired prestress of the movie.

According to a first embodiment of the invention (figure 2), the rotating shaft 4 supports, at one end thereof, a first gear wheel 6 that meshes with a second gear wheel 7 keyed on a support shaft 8 by means of a helical coupling. That is, a spindle coupling between the hub of the second gear 7 and the support shaft 8, which transforms the rotation of gear 7 into a translation thereof along the longitudinal axis of the tree 8.

A lower clutch half 10, on which a friction sliding element 11 is coupled, it is mounted on the second gear 7 by means of a suitable annular bearing 9. The sliding friction element has the shape of a crown circular.

Opposite half of lower clutch 10, is provided with an upper clutch half 12, axially fixed but rotatably mounted on the shaft 8 by means of bearings. The surface of upper clutch half 12 opposite the element slide 11 also features a sliding friction element analogous or is made from a sliding material of friction

The material with which the element is made friction slider 11 is suitable for transferring a torque between the two clutch halves 10 and 12 progressively to as the compression force varies between said halves of clutch. From this point of view, this material is quite different from that used for traditional car clutches, which is suitable to function properly in static conditions only when high compression force is applied between two parts of the clutch. The sliding friction material can be, for example, Iglidur® marketed by Igus GmbH.

Clutch half 12 is further coupled with an electric motor M, for example by a coupling of gears 12a and Ma.

Instead, the lower clutch half 10 is coupled to the prestressing unit, preferably with the roller downstream P2, by means of a gear coupling 13.

Although the transmission to the prestressing unit it can also be done with the upstream roller P1, this would not be very effective, because the operation would not be affected by potential oscillations to the extent of pre-stretched from the movie.

When the device is used, the M motor and is rotated at a constant speed. Therefore, it spins upper clutch half 12 at a speed constant.

When no movie is required, that is, when no tension is applied to the mobile roller B, the transferable gear 7 is in its fully lowered position (in the view of figure 2) and therefore the two clutch halves 10 and 12 are kept separate and no torque is transferred from engine M to lower clutch half 10.

When the film is pulled by the system, a tension is applied to the mobile roller B, therefore the tree 4 is then rotated at a certain angle according to the relationship between film tension and force elastic of the return means 5. The rotation of the shaft 4 produces a rotation of the wheel 6 and the translatable wheel 7, therefore a translation of the lower clutch half 10 along the longitudinal axis of the tree 8. Thus, the two halves of clutch 10 and 12 approach each other and the sliding element of friction 11 starts to work, transferring a torque which is proportional to the displacement of the mobile roller B, that is, proportional to the tension applied on roller B by the movie. In this position, the motor M transfers its movement to the pre-stretching unit P_ {1} and P_ {2}, actively dispensing the stretchable film

As can be expected, this provision represents a self-controlled dispensing system; in fact, the more film requires the system, which corresponds to an increase in the film tension, plus the mobile roller B deviates, which gives as a result more pressure on the sliding contact 11 and that transfers a higher torque from the M motor to the drive unit prestressed, therefore an increase in film dispensing; vice versa, when the system requires less film, the tension is loosen, thus the mobile roller B returns to its position of rest, this way a lower pressure is applied between the two clutch halves in coupling 10 and 12, with subsequent transfer of a lower torque and a decrease in film dispensing.

By an appropriate adjustment of the ratio of transmission and elastic modulus of the return means and by a suitable choice of the material of the sliding element of friction 11, which is within the reach of an expert in subject, once the knowledge offered in this document, it is possible to obtain a functioning progressive and regular device.

The constant rotation speed of the motor M is fixed advantageously equal to the required speed in order to dispense the maximum amount of film that the system requires.

It should be stressed that the coupling of Sliding crowns does not occur in the same way as in a common clutch, which is by nature suitable for operation, in a firm position, decoupled or completely coupled. In this case, on the other hand, takes advantage of the progressive action of a "sliding" coupling, that is, a coupling between two surfaces suitable for proper functioning while sliding, transferring a higher or lower torque, depending on the pressure applied If that were not the case, regularity and progressive control action, resulting in a irregular and choppy behavior of the dispenser.

Advantageously, in order to obtain the best Sliding clutch result, that is, to obtain a Quick reaction and avoid seizures, the direction of rotation of the translatable wheel 7, which approximates the two clutch halves 10 and 12 with each other, it is opposite to the direction of rotation of the middle of clutch 12. This avoids the natural tendency of the coupling to tighten and thus favors a quick release and a immediate decrease in film dispensing as soon as the tension of the same is released on the mobile roller B.

As can be assumed, the device previously described, being completely mechanical, ensures a proportional, direct and virtually instantaneous reaction, which does not produces instability in the control cycle, as can happen with prior art

The embodiment represented so far It can be applied in a packaging machine in which the plate bracket 1 is mounted on a rotating boom or on a guide annular sliding, or also in a fixed position with a load swivel

In figures 3 to 6 another form of embodiment of the invention, generally applicable in a machine of annular slide guide packing.

Figure 3 shows schematically a typical annular structure A, which can be moved vertically in two columns of a packaging machine, on which it is mounted movably a support plate 100.

Plate 100 is removably mounted on sliding guides of the annular structure A by means of a series of movable wheels R_ {1}, R_ {2}, R_ {3} and is fixed on a rotating drive crown T, which is arranged on bearings Ci placed circumferentially in the annular structure A.

The drive crown T and plate 100 are they rotate using a CT drive belt driven by a MT motor (figure 5), fixedly arranged outside the structure cancel A.

In plate 100 there are substantially same elements described above. A stretchable film P extends from a coil 102 to a prestressing unit P_ {10} and P_ {20}, then around a roller intermediate 104a, and finally on a mobile roller B 10.

The mobile roller B 10 is coupled, by arms 103, to a rotating shaft 104, which also supports a intermediate roller 104a, integral with a first wheel of transmission 106. The rotation of the shaft 104 is opposed by means elastic return 105.

The gear wheel 106 is coupled, by a chain 106a, to a translatable gear wheel 107, mounted on a hollow support bracket 107a, in which it is mounted from rotating way coaxially a drive shaft 108. The translatable gear 107 supports a lower clutch half 110 suitable for coupling with another clutch half 112 by means of a sliding friction crown 111.

Upper clutch half 112 is keyed on the drive shaft 108, integral with the roller downstream P 20 of the prestressing unit.

According to the present embodiment, half of lower clutch 110 has the shape of a bushing, in whose outer surface has a groove 110a.

A second drive belt D, which coils as much as possible, with the collaboration of a tensioner belt, around said bushing 110 and then adheres to a sliding guide D1 integral with the annular structure A, is suitable for coupling in slot 110a (figures 4 and 5).

When the support plate 100 is rotated by the MT motor around the annular structure A, the second drive belt D, which is static with respect to the guide slip D1, rotates the bushing 110.

Thus, the movement of the plate support 100 produces the rotation of the bushing 110, which is the actuator element of the dispenser, similar to the function of the M motor in the first embodiment illustrated.

This allows to avoid the use of a motor propulsion mounted on support plate 100, with all advantages that arise from not having to supply energy electric to a moving device.

Apart from this particular feature, the Otherwise operation is identical to that described above. Through an appropriate choice of the transmission ratio between the annular slide guide D1 and the swivel bushing 110, are ensures that the device is able to dispense the maximum amount of film required by the system, depending on the speed of peripheral rotation of the device in the annular structure A.

This second embodiment also reaches the second objective set in the premises, that is, to avoid fully utilizing any sliding contacts with in order to transfer electrical energy from outside the packing machine to the rotating dispenser.

However, it is provided that the invention is not limit to the particular embodiments illustrated previously, which are only non-limiting examples of scope of the invention, but many alternatives are possible, all within the reach of an expert in the field, without departing hence the possibilities of the invention.

For example, it is clear that the mechanism kinematic that produces the coupling of the clutch halves to approximate each other, depending on the displacement of the roller mobile, can present different forms. In addition, it is not necessary that the mobile roller is oscillatingly supported, since It can be transportable. Moreover, the mobile roller can also be replaced by other devices, whose displacement It depends on the tension of the stretch film.

Therefore, the drive system exterior, illustrated in figures 4 to 6, must be considered For illustrative purposes only, since it is possible to adopt many different solutions to make the dispenser rotate in the support crown structure.

Finally, the drive belt suitable for Actuate the sliding clutch bushing can be replaced by similar elements, as long as the device around the annular structure to operate the dispenser.

Claims (8)

1. Film dispenser of stretchable plastic material for a packaging machine, comprising a plastic film coil (2), a pre-stretching unit (1) driven by drive means (M) and a mobile control roller (B) suitable for regulating the torque transferred from said drive means (M) to the prestressing unit (1) according to the tension applied to it by the plastic film, characterized in that said mobile control roller (B) is coupled mechanically to a friction sliding clutch, the torque being transferred by said sliding clutch proportional to the pressure applied to it by said mobile control roller (B), said sliding clutch comprising a first clutch half (12) and a second clutch half (10), that can approach each other, said first half of clutch being (12, 110) constantly rotating by means of said means of drive (M), while the second half of clutch (10, 112) is coupled to said prestressing unit, and because between said first and second clutch halves (12, 10; 110, 112) are introduces an element (11, 111) of a material suitable for working in a sliding position 2. Dispenser according to claim 1, in the that said first clutch half is fixed in translation and rotating on a support tree while the second half of clutch is rotatably mounted on a wheel transportable coaxially mounted by means of a helical coupling on said support shaft, said wheel being rotated translatable by moving said control roller mobile. 3. Dispenser according to claim 1, in the that said first clutch half is rotatable on a wheel Movable mounted, by means of a helical coupling, on a support shaft, while said second clutch half it is mounted fixed in translation, producing the displacement of said mobile control roller rotation / translation of said wheel transferable 4. Dispenser according to any of the previous claims, wherein said dispenser is movable mounted on an annular structure of a machine packed and said drive means comprise an element of transmission interposed between an annular slide guide of said annular structure and said second clutch half. 5. Dispenser according to claim 4, in the that said transmission element is a transmission belt that is wrapped around said slide guide and around of a bushing that is integral with said second half of clutch. 6. Dispenser according to any of the previous claims, wherein the two clutch halves they approach each other, each according to a direction of opposite rotation of the other. 7. Dispenser according to any of the previous claims, wherein the transferred torque it is applied to the roller downstream of said unit of pre-stretched 8. Packaging machine comprising a dispenser according to any of the preceding claims.