WO2013050832A1

WO2013050832A1 - Method and machine for wrapping stacks

Info

Publication number: WO2013050832A1
Application number: PCT/IB2012/000896
Authority: WO
Inventors: Luciano Butturini
Original assignee: Italdibipack S.P.A.
Priority date: 2011-05-09
Filing date: 2012-05-09
Publication date: 2013-04-11
Also published as: ITMI20110787A1

Abstract

A method for effecting the wrapping of stacks, which comprises the following phases: preparing a self- propelled winding machine comprising: a self-propelled motorized trolley, suitable for moving on the ground by means of at least two driving wheels whose rotation creates the movement trajectory of the machine, a control unit of the movement of the driving wheels and means suitable for supplying a wrapping material of the stack supported by the trolley, a distance detector assembled on the machine suitable for perceiving the distance from the stack. The method comprises the following phases: arranging the stack in a fixed position with respect to the ground where the machine moves, effecting the wrapping of the stack by releasing the wrapping material while the machine completes a series of revolutionary movements around the stack. The method comprises the following additional phases: establishing a main circular trajectory for the machine, having a constant diameter which is greater than the maximum dimension, in plan view, of the stack, so that the machine always moves at a distance from the stack, initially positioning the machine so that the centre of the main trajectory is conveniently close to the central and vertical geometrical axis of the stack; sending a correction signal to the control unit when the distance revealed by the distance detector falls below a predetermined threshold distance, establishing a corrective trajectory for the machine wherein the radius of the main trajectory is varied following the emission of said correction signal, said corrective trajectory being such as to move the centre of the movement trajectory of the machine towards the axis of the stack, and re-establishing said main trajectory for the machine.

Description

METHOD AND MACHINE FOR WRAPPING STAPELS

FIELD OF THE ART

The present invention relates to a method for effecting the wrapping of a stack by means of a self- propelled winding machine, wherein the stack is fixed with respect to the ground and the machine effects the winding by moving on the ground around the stack.

PRIOR ART

The known machines for the wrapping of stacks, in particular self-propelled winding machines used in the packaging industry for wrapping and stabilizing stacks, are generally configured for rotating around the stack following a predetermined trajectory.

The machine generally comprises means suitable for supplying a winding material, for example an extendable film, and a guiding system for moving the machine around the stack along a predetermined fixed and closed traj ectory .

Winding machines are known, which comprise a guiding system suitable for automatically and continuously regulating the trajectory of the machine, so as to automatically follow the profile of the stack, without the help of an operator. The guiding system of these machines generally comprises a control unit and a distance detector for monitoring the distance between the winding machine and stack. The trajectory of the winding machine is constantly regulated by the control unit in relation to the distance revealed by the distance detector. In this way, the trajectory of the machine is continuously regulated so as to keep the machine sufficiently close to the stack and favour the winding process of the stack. The distance detector can comprise an optical sensor, or a contact sensor. An example of a winding machine of this type is described by patent EP 1 740 462 "Self propelling machine for wrapping stacked load with protective films" . According to the disclosure of this patent, the trajectory of the winding machine is continuously regulated in relation to the distance of! the stack, said distance being revealed by means of a feeler device constantly in contact with the stack itself during the winding process. The correct functioning of the winding process is obtained by the continuous regulation of the trajectory, with the negative consequence that the rotation rate of the machine is limited by this and the efficiency of the process itself reduced. Furthermore, with every correction of the trajectory, there are slight decelerations and accelerations; these continuous changes in the rate cause an increase in the energy consumption of the feeding battery of the machine .

This type of functioning is difficult to effect if the stack has marked irregularities or if the load protrudes above the contact points of the probe with the stack.

An objective of the present invention is to provide a method for the functioning of a self-propelled winding machine which allows the self-propelled winding machine to also operate on irregular surfaces maintaining a velocity that is such as to improve the efficiency of the wrapping process and at the same time limit energy consumptions of the feeding battery.

A further objective of the present invention is to provide a method which allows the wrapping of protruding loads with respect to the dimensions of the sides of the stack.

In the invention, it is taken into account that the wrapping process normally takes place in deposits or warehouses whose floor can have irregularities such as holes or small ramps. These irregularities can cause the machine to be diverted from its pre-established trajectory with a consequent reduction in the efficacy of the wrapping process and in some cases also the interruption of the process, for example: if the machine ends up against the stack. These deviations from the pre-established trajectory can also be caused by different types of behaviour between the wheels and ground due, for example, to wear.

Another objective of the invention is to achieve said objective in the context of a simple, rational, reliable constructive solution, and with reduced encumbrance .

These objectives are achieved thanks to a method for wrapping a stack and a machine for wrapping a stack having the characteristics indicated in the claims.

DESCRIPTION OF THE INVENTION

The invention, in particular, provides a method for effecting the wrapping of a stack in a self-propelled winding machine which comprises:

■ a self-propelled motorized trolley, suitable for moving on the ground by means of at least two driving wheels whose rotation creates the movement trajectory of the machine,

^■ a control unit of the movement of the driving wheels, and

^■ means suitable for supplying a wrapping material of the stack supported by the trolley,

distance detector assembled on the machine : suitable for perceiving the distance from the stack which is in a fixed position on the ground where said machine moves; wherein

the wrapping of the stack is effected by releasing the wrapping material while the machine completes a series of revolutionary movements around the stack.

The method comprises the following phases:

a) establishing a main circular trajectory for the machine, having a constant diameter which is greater than the maximum dimension, in plan view, of the stack, so that the machine always moves at a distance from the stack,

b) initially positioning the machine so that the centre of the main trajectory is conveniently close to the central and vertical geometrical axis of the stack, ;

c) sending a correction signal: to the control unit when the distance revealed by the distance detector falls below a predetermined threshold distance, d) establishing a corrective trajectory for the machine wherein the radius of the main trajectory is varied following the emission of said correction signal, said corrective trajectory being such as to move the centre of the movement trajectory of the machine towards the axis of the stack, and

e) re-establishing said main trajectory for the machine . In this way, the wrapping process of a stack can be optimized as a substantially constant trajectory of the machine is established around the stack, along which the machine can advantageously move uniformly, modifying the trajectory of the machine only when strictly necessary, and consequently keeping the machine at a higher and more regular rate .

According to a particular aspect of the present invention, a method is provided for the wrapping of a stack in which the corrective trajectory is effected by making the velocity of the driving wheels more similar to each other, so as to increase the radius of the movement trajectory of the machine, and said corrective trajectory is activated after about 200-300 degrees from the point in which the alarm signal was sent from the distance detector.

In this way, not more than one correction is made per revolution of the machine around the stack and the machine can continue to rotate at an almost constant rate, thus reducing the energy consumptions of the battery.

According to another aspect of the present invention, a method is provided for the wrapping of stacks, in which the machine is positioned, at the beginning of the wrapping cycle, with its own i longitudinal axis parallel to a straight line tangent with respect to the main trajectory.

This reduces the necessity of having to modify the trajectory, by formulating the machine so that it can follow an initial circular trajectory with the stack exactly in the centre.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described with reference to the enclosed drawings, which illustrate a non- limiting embodiment example, in which:

- figure 1 represents a schematic side view of a self- propelled winding machine for wrapping stacks;

- figure 2 illustrates a schematic plan view of the machine of figure 1;

- figure 3 represents a distance detector according to an embodiment of the present invention; and

figures 4A, 4B and 4C represent three different states of the distance detector of figure 3;

- figure 5 represents, according to a plan view from above, a scheme of possible trajectories of the self- propelled winding machine according to an embodiment of the present invention and figure 5A is an enlarged detail of figure 5.

Said distance detector system can also be advantageously substituted by distance sensors with electrie/electronic functioning (see photocell, capacit ve/inductive radio- frequency or ultrasound sensors) , capable of sending a signal to the control unit if the machine moves too close to the edges of the stack.

DETAILED DESCRIPTION

In figure 1, number 1 indicates, as a whole, a self-propelled winding machine 1 of stacks 2 with a wrapping material 3, for example an extendable film, which is unwound from a bobbin 4, the machine 1 being suitable for autonomously rotating around said stacks 2.

Said self-propelled winding machine 1 comprises a motorized supporting trolley 5 suitable for moving on the surface of the floor, a handle (not shown in the figure) carrying manual guiding commands, and means (4,6,7) suitable for providing a wrapping material 3. These means comprise a lifting system 6, positioned on said motorized trolley 5, suitable for vertically moving a bobbin-holder slide 7 which supports a bobbin 4 of wrapping material 3.

With reference to figure 2, the self-propelled winding machine 1 comprises: two driving wheels 8a, 8b, positioned in the rear part of the motorized trolley 5 on the left■ and right side respectively, having an aligned rotation axis and each actuated by a respective independent motor (not shown in the figure) . The two wheels 8a, 8b are positioned behind an orientable wheel 9, suitable for supporting the machine and stabilizing the movement. The machine 1 comprises an automatic guiding system which acts by suitably regulating the velocity of the driving wheels 8a, 8b and which comprises a control unit 10 in the form, for example, of a microprocessor, a microcontroller or an electronic card, and two measurement sensors (not shown in the figure), for example two encoders, one for each wheel 8a, 8b and connected to the control unit 10. Each encoder measures the number of revs effected by the wheel 8a, 8b on which it is positioned. The control unit 10 in relation to the number of revs measured can calculate the distance covered by the wheel itself and control their functioning. The two wheels 8a, 8b can be regulated separately by the control unit 10.

Said guiding system also comprises a distance detector suitable for registering the distance between the machine 1 and stack 2, and sending a signal to the control unit 10 when this distances falls below a predetermined threshold distance ds . The distance detector 11 can comprise, but is not limited to, a feeler organ 12¹ or optical device, or another q equivalent device.

In the former case, figure 3, the feeler device 12 can be assembled on the machine 1 so that it protrudes laterally and outwardly with respect to the side surface of the machine 1 and is configured so as to send an alarm signal to the control unit 10 when it hits a point of the stack. The feeler organ 12 is free to oscillate on a horizontal plane and comprises one or more feeler rolls 13 and a supporting arm 14.

Said supporting arm 14 has one end hinged to the machine by means of a pin 15 screwed to the motorized trolley 5, and supports said feeler roll 13, in correspondence with the free end, and protruding from the machine. An actuator means 16 of a switch 17 is positioned and assembled integral with the end of the supporting arm 14 attached to the machine 1. When the feeler rolls 13 come into contact with the stack, the supporting arm 14 rotates around the pin 15, the actuator means 16 rotates integral with the arm 14 and activates the switch 17 thus closing an electric circuit (not shown in the figure) configured for sending an electric signal towards the control unit 10. • In this way, when the feeler organ 12 strikes the stack _' 2, a correction signal, in the form of an electric i signal, can be sent to the control unit 11.

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i n The supporting arm 14 can comprise two hinge- connected parts and a tension spring 18 for keeping the two parts aligned.

The functioning mechanism of the supporting arm 14 of the feeler organ 12 is shown in figures 4A to 4C. Figure 4A shows the feeler organ 12 before a contact with the stack 2, figure 4B shows the feeler organ 12 in contact with the stack 2. Figure 4C shows the feeler organ 12 following a further movement of the machine 1 after the initial contact of figure 4B. As can be seen in figure 4B, when the supporting arm 14 effects a maximum rotation around the pin 15, the hinge system allows further stress to be absorbed without damaging the supporting arm 14 itself.

According to an embodiment of the present invention, the distance detector 11 can comprise an optical device, for example an optical sensor. In this case, the distance between the machine 1 and stack 2 can be calculated in relation to the reflex time of an optical signal sent by the optical device towards the stack, reflected by the stack and sent back to the optical device. The optical device is also configured to send a correction signal when the distance revealed is less than the predetermined threshold distance ds.

The predetermined threshold distance ds depends on various factors such as, for example, but not exclusively, the type of distance detector 11 used, the material used for the wrapping, the dimensions of the stack 2, the type of floor where the wrapping process is effected, etc. This distance ds can be memorized in a memory unit 19 of the control unit 10 and established at the beginning of the wrapping process .

The distance detector 11 can also be used in an initial phase for regulating the initial distance at which the machine 1 is to be positioned with respect to the stack 2 to be wrapped, and subsequently for fixing the rotation diameter of the initial trajectory of the machine 1.

During functioning, figure 5, the machine 1 is configured to rotate around the stack 2 following an almost circular trajectory P (P1,P2), while the wrapping material 3 is being released onto the stack 2.

The method for effecting the wrapping of a stack 2 according to an embodiment of the present invention is now described (see figures 5, and 5A) .

A main circular trajectory P (indicated with PI, in figure 5) is established for the machine 1, having a constant diameter which is greater than the maximum dimension, in plan view, of the stack, and initially having its centre Al . The main initial trajectory P (PI) can be established by the operator and saved in the memory unit 19 of the control unit 10.

The machine is initially positioned so that the centre Al of the main trajectory P is conveniently close to the central and vertical geometrical axis Ac of the stack 2.

In particular, at the beginning of the wrapping cycle, the machine is positioned with its own longitudinal axis (M) parallel to a straight line tangent with respect to the main trajectory P (PI), and at a distance from the axis Ac of the stack which is conveniently equal to the diameter of the main trajectory P.

Once the machine 1 has been positioned in its pre- established starting position, the control unit 10 starts the machine 1 and establishes a main closed trajectory P (PI), preferably circular or sufficiently circular, having a constant diameter and centre Al which coincides with, or is sufficiently close to, the axis Ac of the stack 2. This result can be obtained by suitably regulating the power and rotation rate of each wheel 8a, 8b.

During ¹ functioning, the machine 1 maintains its own closed trajectory P, effecting a series of rotational movements around the stack 2 and releasing the wrapping material 3 onto the stack 2 to effect its wrapping.

In particular, the distance : detector 11 constantly reveals the distance between the machine 1 and stack 2.

If the movement conditions of the machine on the ground were to be ideal, the machine 1 would maintain the position of the centre Al of its trajectory PI (close to the axis Ac of the stack 2) unvaried; in this case, the distance revealed by the detector 11 would remain constant and equal to the initial value dl , and no correction signal would be sent to the control unit 10.

As real and actual conditions are rarely ideal, however, during functioning, the machine 1 can undergo deviations with respect to the main trajectory PI, due to various factors such as, for example, imperfections of the ground, or friction between the wheels 8a, 8b and the ground, which cause the machine to deviate from its predefined trajectory.

In this case, the machine 1 moves the centre of its trajectory P forming trajectories P, all the same, (having the same diameter) and centre which has shifted with respect to the centre Al . As the centre of the trajectory P moves away from the axis Ac of the stack, there is the possibility that at a certain point of the movement trajectory, the machine 1 will hit the stack 2.

When the distance detector 11 reveals a distance d2 from the initial distance dl , if the value of d2 is still higher than the predetermined threshold distance ds, the distance revealer 11 does not send any correction signal to the control unit 10. In this way, modifications and consequently slight slow-downs are necessary for small variations in the main trajectory, and the machine 1 can continue to function at the same rate.

If, on the other hand, the value of the distance revealed d2 becomes lower than the predetermined threshold distance ds , the distance detector 11 sends a correction signal to the control unit 10. ^;

This is the case illustrated in figure 5 : i the machine which was initially moving along the main trajectory PI, following a shift of the centre of the main trajectory, follows the main trajectory P2 , which almost touches a portion of the stack 2, without hitting the stack 2 however, which must be an edge of the same (should the stack 2 have a polygonal form) and the distance revealed is less than the threshold distance ds .

When the control unit 10 has received the correction signal_/ it adjusts the movement! trajectory of the machine 1 establishing a corrective trajectory R for the machine 1, which varies the rotation radius of the machine 1 around the stack 2, for a relatively short period. The corrective trajectory R is such as to move the centre of the movement trajectory of the machine 1 towards the axis Ac of the stack 2. In particular, according to an embodiment of the invention, the corrective trajectory R is established for the machine 1 by making the velocity of the driving wheels 8a, 8b more similar to each other, so as to increase the radius of the movement trajectory with respect to the trajectory P2 (see figure 5A) .

There can be various ways of controlling each driving wheel 8a, 8b with respect to the other; the velocity of one wheel can remain unvaried, for example, varying only the velocity of the other wheel (until it stops) ; or the velocity of one wheel can be increased and that of the other reduced.

According to a preferred embodiment of the present invention, the corrective trajectory R is activated after about 200-300 degrees of trajectory P2 from the point at which the alarm signal has been sent to the control unit 10 (see figure 4A) .

After this correction, the control unit 10 re- establishes the main trajectory P. The result of this correction is that the centre of the main trajectory of the machine is brought back to the initial centre Al , or in any case conveniently close to the axis Ac and the machine 1 thus returns to the main trajectory P and the wrapping process can be restarted, repeating, if necessary, the phases described, until the stack has been completely wrapped.

In practice, the machine 1 moves with a rotational movement around the stack 2 following various identical main trajectories P, whose centre tends to move from the initial centre Al ; only when the main trajectory moves close to the stack 2 as the distance of the machine has become dangerously close (in figure 5 this traj ectory i is indicated with P2), is a relatively short corrective : trajectory established, followed again by movement along a main trajectory P, which, after the correction, has a centre which is again closer to the axis Ac of the stack. At the beginning of the cycle, the machine 1 is positioned at a pre-established distance dl from the stack 2 to be wrapped.

In particular, a collimator (not shown in the figure) is assembled on the machine 1, for example a LED: pointer, which marks the position in which it is convenient to initially position the machine 1 \ with respect to the stack 2, in relation to the diameter of the main trajectory P and dimension of the stack 2. Said collimator, for example, emits a direct beam of light tilted towards the ground, where it indicates a reference point; in positioning the machine, this point must fall in correspondence with a prefixed point of the stack 2, for example in correspondence with a median point of the side of a pallet (not shown in the figure) on which the stack has been formed.

In practice, the machine 1 is positioned in correspondence with this median point of a side of the pallet, with its longitudinal axis M parallel to the side of the pallet, and also in such a position that the light emitted from the collimator strikes the base of the pallet in the median point of the side.

Alternatively, this distance dl can be controlled and regulated thanks to the distance detector 11, for example according to an embodiment of the present invention, by positioning the machine 1 at an initial distance from the stack 2, comparing the distance value revealed by the distance detector 11 with a predefined initial positioning distance, and finally moving the machine until the distance value revealed by the distance detector 11 more or less coincides with the t predefined initial positioning i distance .

The predefined initial positioning distance can ! vary, among other things, in relation to the dimensions of the stack 2, the type of wrapping material 3, the type of wrapping required, the type of ground on which the wrapping takes place, etc. Numerous modifications of a practical -applicative nature can obviously be applied to the invention in question, all included in the inventive concept as claimed hereunder.

Claims

1. A¹ method for effecting the wrapping of a stack (2), which comprises the following phases:

preparing a self-propelled winding machine (1) comprising :

^■ a self-propelled motorized trolley (5), suitable for moving on the ground by means of at least two driving wheels (8a, 8b) whose rotation creates the movement trajectory of the machine (1),

^■ a control unit (10) of the movement of the driving wheels (8a, 8b) and

■ means (6,7,4) suitable for supplying a wrapping material (3) of the stack (2) supported by the trolley (5) ,

^■ a distance detector (11) assembled on the machine (1) suitable for perceiving the distance from the stack (2) ;

arranging the stack (2) in a fixed position with respect to the ground where the machine (1) moves, - effecting the wrapping of the stack (2) by releasing the wrapping material (3) while the machine completes a series of revolutionary movements around the stack,

characterized by the following phases: <

a) establishing a main circular trajectory (P) for the machine (1), having a constant diameter which is greater than the maximum dimension, in plan view, of the stack (2), so that the machine always moves at a distance from the stack, b) initially positioning the machine (1) so that the centre ( Ai ) of the main trajectory is conveniently close to the central and vertical geometrical axis ( A_c ) of the stack (2) ,

c) sending a correction signal to the control unit (10) when the distance revealed by the distance detector (11) falls below a predetermined threshold distance (d_s) ,

d) establishing a corrective trajectory (R) for the machine (1) wherein the radius of the main trajectory (P₂) is varied following the emission of said correction signal, said corrective trajectory (R) being such as to move the centre ( A₂ ) of the movement trajectory of the machine (1) towards the axis ( A_c ) of the stack (2), and e) re-establishing said main trajectory (P) for the machine (1) .

2. The method according to claim 1, wherein the corrective trajectory (R) is effected by making the rate of the driving wheels (8a, 8b) more similar to each other, so as to increase the radius of the movement trajectory of the machine (1), and said corrective trajectory (R) is activated after about 200-300 degrees from the point in which the correction signal was sent by the distance detector (11) .

3. The method according to claim 1 or 2 , wherein the machine (1) , at the beginning of the wrapping cycle, is positioned with its own longitudinal axis (M) parallel to a straight line tangent to the main trajectory (P_x) , and at a distance from the axis (A_c) of the stack conveniently equal to the diameter of the main trajectory P.

4. The method according to one of the claims from 1 to 3, wherein the machine (1) comprises a collimator suitable for emitting a beam off light towards the

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ground and phase b) comprises the following phases:

bl) positioning the machine (1) near the stack (2) ; b2) revealing a point indicated by the beam of light emitted from the collimator;

b3) comparing the point revealed in phase b2) with a prefixed point of the stack (2) ;

b4) repeating phases bl) , b2 ) and b3) until the point revealed corresponds with the prefixed point of the stack (2 ) . !

1 5. A self-propelled wrapping machine (1) for actuating the wrapping method of stacks, according to one of the claims from 1 to 4 , which comprises:

^■ a self-propelled motorized trolley (5) , suitable for moving on the ground by means of at least two driving wheels (8a, 8b) whose rotation creates the movement trajectory of the machine,

^■ a control unit (8) of the movement of the driving wheels (8a, 8b) and

^■ means (4, 6,7) suitable for supplying a wrapping material (3) of the stack supported by the trolley (5) ,

^■ a distance detector (11) positioned on the machine (1) suitable for perceiving the distance between the machine (1) and the stack (2);

characterized in that:

the distance detector (11) is configured for

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emitting a correction signal to the control unit (10) when said distance falls below a predetermined threshold distance (ds) ; and

the control unit (10) is configured for varying the radius of the main trajectory (P, P2), for a relatively short period, following the emission of said correction signal, by imposing a corrective trajectory (R) which is such ^' that the centre of the main trajectory P moves towards^' the axis (Ac) of the stack, and subsequently re-establishing the main trajectory (P) for the machine .

6. The machine (1) according to claim 5, characterized in that the distance detector (11) comprises a feeler organ (12) oscillating on a horizontal plane, protruding sideways and outwardly with respect to a side surface of the machine (1) so as to be capable of striking a point of the stack (2) following the shift of the centre of the main trajectory (P, P2) with respect to the vertical axis A2 of the stack (2) during the wrapping of the stack (2) .

7. The machine according to claim 5, characterized in that the distance detector (11) comprises an optical device configured for sending an optical signal to the stack 2 and receiving the optical signal reflected by the stack.