IDLER ROLLER AND CORRESPONDING PALLET WRAPPING MACHINE

Description

DESCRIPTION

This application claims priority to Italian Patent Application 102024000022173 filed October 7, 2024, the entirety of which is incorporated by reference herein.

The present invention relates to an idle roller and related pallet wrapping machine.

In the logistics industry, it is crucial to ensure the safe and efficient movement of goods.

For this purpose, the use of the pallet, a standardised platform used for transporting and storing goods that can be employed throughout the supply chain, is widespread. The pallet keeps goods elevated off the ground, protecting them from dust, moisture and damage during handling.

Once the goods are loaded onto the pallet, they are packaged.

The packaging is usually done by pallet wrapping machines, automated devices used to wrap pallets with stretch plastic film in order to stabilise and protect loads during transportation and storage.

The pallet wrapping machines in the prior art comprise at least one main roller, which holds the roll of plastic film.

The most common machines comprise a pre-stretching unit, consisting of at least one first mechanical roller, on which the plastic film is wound, and at least one second mechanical roller, over which the film passes before reaching the pallet. The first and second rollers are configured to rotate at different speeds, thus causing a controlled elongation of the film before packaging. The pre-stretching unit comprises at least one actuator configured to set the first and second rollers in rotation.

Pallet wrapping machines also comprise a load cell, usually consisting of an elastic body that deforms under load and comprises a strain gauge, that is, a sensor used to measure the deformation of the elastic body under mechanical stress. The strain gauge transforms the mechanical deformation into an electrical signal. This electrical signal is sent to a control unit for further processing. This enables the machine to adjust the film tension and the wrapping speed.

A common issue in the industry is the need to keep the tension of the film as even as possible when packaging the pallet, a complex task due to the non-circular shape of the pallet. Indeed, it is necessary for the plastic film to adhere to the load uniformly, so as to prevent movements and ensure the stability of the pallet during transportation and storage; this also provides complete protection against external contamination and optimises film consumption. Indeed, if the tension is too low, multiple layers of film may need to be applied to achieve sufficient stability, thus increasing wastage of material. Too high a tension, on the other hand, could cause tears in the film, requiring further applications.

There are multiple solutions in the prior art.

A first solution comprises a wrapping system based on a mechanical arm or moving roller ("dancer") that holds the plastic film and extends it around the pallet in a controlled and precise manner. The roller and the arm move in a continuous orbit around the load.

However, such a solution involves a sophisticated mechanical system with moving components such as rollers and rotating arms. This increases the risk of failure or malfunction, requiring more frequent and costly maintenance than simpler systems. In addition, such a system encounters difficulties in wrapping loads with irregular or non-standard shapes. Indeed, these types of loads require frequent adjustments, slowing down the process and reducing operational efficiency.

A second solution involves a load cell being placed in a fixed position relative to an idle roller, which is inserted into the path of the plastic film immediately after the pre-stretching unit and before reaching the load. In detail, the plastic film, wound in a roll positioned on a main roller, passes first through the rollers of the pre-stretching unit and then onto the idle roller before reaching the load. Generally, the load cell is inserted at the top or at the bottom of the idle roller. In this way, the load cell directly measures the tension applied by the film on the idle roller, allowing the system to automatically adjust the speed of the pre-stretching unit, through the actuator, in case of variations or irregularities.

However, this solution has some disadvantages.

First, since the strain gauge is only able to detect variations in tension along one direction, if the presence of the goods on the pallet requires a change in the maximum height of the film for wrapping, the electrical signal generated by the strain gauge would no longer be proportional to the mechanical deformation, which would occur in a different direction from that configured for detection. This occurs frequently due to the versatility of the pallet and of the goods it is intended to transport.

This limitation could be solved by joining a plurality of load cells to the idle roller, but this would result in very high production costs.

Second, the electrical signal generated by a strain gauge is directly proportional to the deformation detected. In this solution, the tension being measured is that of a plastic film, so the mechanical deformation of the elastic body of the strain gauge is a matter of millimetres. As a consequence, the electrical signal is extremely low. A signal amplification circuit is therefore needed before the signal is processed. In addition, such a weak signal significantly increases the risk of errors.

Therefore, the purpose of the present invention is to remedy the aforementioned drawbacks.

The invention, as it is characterised in the claims, achieves this aim thanks to a structural change of the idle roller.

The main advantage obtained by the present invention is that it enables a pallet with a constant tension to be packaged in a precise manner.

In addition, the invention makes it possible to effectively package loads having irregular or non-standard shapes.

Finally, the invention is mechanically compact and secure, since it does not include moving components. This also minimises the need for maintenance.

Further advantages and features of the present invention will become more apparent from the detailed description below with reference to the accompanying drawings, which show a non-limiting embodiment, in which:

FIG. 1 is a perspective front view of a first version of the invention;

FIG. 2 is a front view of the invention shown in FIG. 1;

FIG. 3 is a cross-section view along plane III-III as shown in FIG. 2;

FIG. 4 is a close-up view of a detail of the invention shown in FIG. 3;

FIG. 5 is a view from above of the invention shown in FIG. 1;

FIG. 6 is a cross-section view along plane VI-VI as shown in FIG. 2;

FIG. 7 is an exploded view of the invention shown in FIG. 1;

FIG. 8 is a cross-section view along plane VIII-VIII as shown in FIG. 5; this figure shows the invention in a use condition;

FIG. 9 is a perspective front view of a second version of the invention;

FIG. 10 is a prospective front view with a detail of the invention shown in FIG. 9 highlighted;

FIG. 11 is a front view of the invention shown in FIG. 9;

FIG. 12 is a cross-section view along plane XII-XII as shown in FIG. 11;

FIG. 13 is a close-up view of a detail of the invention shown in FIG. 12;

FIG. 14 is a cross-section view along plane XIV-XIV as shown in FIG. 11; and

FIG. 15 is a cross-section view along plane XV-XV as shown in FIG. 11;

FIG. 16 is a prospective side view of a variant of the invention;

FIG. 17 is a front view of the invention shown in FIG. 16;

FIG. 18 is a cross-section view along plane XVIII-XVIII as shown in FIG. 17.

As shown in the figures, the invention relates to an idle roller 1 comprising a hollow cylindrical body 10 configured to rotate around an axis 12.

Said idle roller 1 is configured to be installed in a pallet wrapping machine 40, comprising a carriage 50 supporting a main roller 53 configured to hold a roll of plastic film, at least one pre-stretching unit 60, provided with at least one pair of pre-stretching rollers 62a, 62b and at least one actuator 55 configured to drive the pair of pre-stretching rollers 62a, 62b. The idle roller 1 is configured to be installed immediately downstream of the pre-stretching unit 60 such that the plastic film passes first from the roll towards the pre-stretching unit 60, then through the idle roller 1 and, finally, onto the load. Therefore, the idle roller 1 is configured to be set in rotation by the passage of the plastic film, at a speed matching that of the last roller in the pre-stretching unit 60.

The roller 1 further comprises a load cell 20, provided with at least one rigid element 25 and at least one deformable element 26, and a fixed support 14, being coaxial to the cylindrical body 10 and being integral with the structure of the carriage 50 of the pallet wrapping machine 40.

Furthermore, the roller 1 is provided with connecting means 16 between the cylindrical body 10 and the load cell 20, comprising at least one bearing 17 capable of transferring to the load cell 20 the stress impressed on the roller 1 due to variations in its angular speed.

In the versions shown in the accompanying figures, the support 14 is configured to be fixed to a carriage 50 of a pallet wrapping machine 40. In addition, the support 14 traverses the cylindrical body 10 entirely and the connecting means 16 comprise two bearings 17 positioned at the ends of the cylindrical body 10.

The load cell 20 is interposed between the cylindrical body 10 and the support 14 and is configured to detect the difference in pressure exerted by the plastic film on the cylindrical body 10 and on the support 14. This makes the invention mechanically compact and secure, since it does not include moving components. This also minimises the need for maintenance.

The deformable element 26 of the cell 20 comprises at least one sensor 22 configured to detect a deformation of the load cell 20 itself.

The sensor 22 can be a strain gauge, a capacitive sensor, a piezoelectric sensor or an ultrasonic sensor. The presence of a sensor of this kind helps make the invention inexpensive.

In addition, the positioning of the load cell 20 between the cylindrical body 10 and the support 14 allows a cell 20 to be installed with dimensions larger than those of prior art solutions. Consequently, the cell 20 can be subject to major deformations, thus generating a higher electrical signal. This significantly reduces the risk of errors.

Preferably, the support 14 can comprise a recess 18 wherein the load cell 20 is housed. In this case, the load cell 20 is constrained to the support 14 through the rigid element 25. The constraint can be made, for instance, by screws. The recess 18 can be clearly seen in FIG. 7.

The connecting means 16 can comprise at least one elongated coupling element 30 having a surface 31 configured to be fixed to the deformable element 26 of the load cell 20. In this case, the coupling element 30 occupies the space between the load cell 20 and the cylindrical body 10, so as to ensure backlash for the deformable element 26 of the load cell 20. The cylindrical body 10 is configured to rotate, while thanks to the presence of the bearings 17 the coupling element 30 can be configured to remain in a static position, without taking part in the rotation.

As mentioned, when in use the plastic film passes from a roll installed on a main roller 53 of a pallet wrapping machine 40 towards the pallet to be wrapped through a pre-stretching unit 60 and the idle roller 1. The cylindrical body 10 of the idle roller 1 rotates idle together with and at the same speed as the rollers 62a, 62b, due to the passage of the film over it. The support 14 is fixed, being constrained at the top and at the bottom to the carriage 50 of the pallet wrapping machine 40, therefore being integral thereto.

As can be seen in FIG. 8, when in use the rotating cylindrical body 10 is subject to a force F exerted by the plastic film. The bearings 17 transmit force to the coupling element 30 that is integral to the cylindrical body 10, nevertheless maintaining an angular speed of nil. The support 14, on the other hand, remains fixed, being constrained to the carriage 50 of the pallet wrapping machine 40.

When, due to the shape of the pallet and/or of the load, the angular speed of the pre-stretching unit 60 does not match the speed imposed by the pallet wrapping machine 40, the wrapping tension of the plastic film is different from that desired. The result is a change in the pressure exerted by the plastic film on the cylindrical body 10, which consequently shifts in position, causing the deformable element 26 of the load cell 20 to deform. The deformation occurs because the cylindrical body 10 and, consequently, the coupling element 30 are shifted, whereas the support 14 remains in a fixed position.

The change in pressure occurs because the film tension is not even.

The coupling element 30 can have an at least partially semicircular cross-section so as to substantially adhere to the cylindrical body 10.

If the invention comprises at least one sensor 22 configured to detect a deformation of the cell 20, the roller 1 can comprise regulating means 24 connected to the load cell 20 and configured to orient in space the load cell 20 itself.

The regulating means 24 are useful to confer versatility on the roller 1, since most of the sensors configured to detect a deformation of a material are anisotropic, that is, their detection properties vary according to the direction in which the force or the stimulus deforming them is applied. In particular, said sensors have a preferred direction of detection. Using the regulating means 24, it is possible to configure the detection direction of the force causing the deformation. For exemplifying and non-limiting purposes, the accompanying figures contain regulating means 24 comprising a slot-and-screw mechanism. In particular, a washer with an at least partially circular-shaped slot is fixed on the shaft 14. A screw passes through the slot and is fixed to the load cell 20. When the screw is loosened, the cell 20 can be rotated along the slot. Once the desired position is reached, the screw is tightened so as to lock the cell 20 in that position.

Alternatively, as can be seen in FIGS. 9-15, the load cell 20 can have a cylindrical shape and comprise a through-hole 23 along its axis. In this case, the support 14 is inserted into the through-hole 23.

Furthermore, the roller 1 can comprise an additional hollow cylindrical body 40, configured to maintain a fixed position, interposed between, and connected to, the cylindrical body 10 and the load cell 20. The presence of a further element better enables the load cell 20 to keep its position.

Preferably, an external surface 19 of the main cylindrical body 10 is made of anti-slip material. This helps to keep the plastic film in position.

Also preferably, the roller 1 comprises at least one processing unit 21, which could also be remote, configured to process the signal received from the load cell 20 so as to change the rotational speed of the pre-stretching unit 60 and consequently of the cylindrical body 10 of the idle roller 1, based on the detected pressure difference, and to send out a signal containing indications regarding the required correction.

In this way, it is possible to wrap a pallet in a precise manner, keeping the tension of the film constant.

The present invention also describes a pallet wrapping machine 40 comprising a carriage 50 supporting a main roller 53 configured to hold a roll of plastic film, at least one pre-stretching unit 60, provided with at least one pair of pre-stretching rollers 62a, 62b and at least one actuator 55 configured to drive the pair of pre-stretching rollers 62a, 62b at different speeds and at least one idle roller 1 as described above.

The idle roller 1 is configured to be installed immediately downstream of the pre-stretching unit 60 such that the plastic film passes first from the roll towards the pre-stretching unit 60, then through the idle roller 1 and, finally, onto the load. Therefore, the idle roller 1 is configured to be set in rotation by the passage of the plastic film, at a speed matching that of the last roller in the pre-stretching unit 60.

In this case, as mentioned above, the idle roller 1 can comprise at least one processing unit 21, which could also be remote, configured to process the signal received from the load cell 20 so as to change the rotational speed of the pre-stretching unit 60 and consequently of the cylindrical body 10 of the idle roller 1, based on the detected pressure difference, and to send a signal containing indications regarding the required correction to the actuator 55, which consequently adjusts the speed of the pre-stretching rollers 62a, 62b.

As mentioned above, it is of fundamental importance that the tension of the plastic film is kept constant when wrapping the pallets. Nevertheless, during packaging, the required wrapping tension of the pallet can cause a misalignment between the speed of the rollers and that imposed by the actuator 55.

In this case, the load cell 20 detects a difference in pressure exerted by the plastic film on the cylindrical body 10 and on the support 14 of the idle roller 1. This means that the tension with which the plastic film is being applied is not constant and needs correction. At this point, the processing unit 21 of the idle roller 1 processes the required correction to change the rotational speed of the rollers, based on the pressure difference detected from the load cell 20 and sends a signal containing indications regarding the required correction to the actuator 55, which consequently adjusts the speed of the main roller 53 and/or the pre-stretching rollers 62a, 62b.

Where the load to be packaged has an irregular or non-standard shape, misalignment between speeds is more likely to occur. Therefore, a pallet wrapping machine according to the invention can also effectively package loads with irregular or non-standard shapes.