TECHNICAL FIELD

The present invention relates to a power supply system for supplying heating elements for welding tubular lengths of web material, in particular for use in rotating machines during a packaging and labelling process for containers for pourable food products, such as bottles, cans etc.

BACKGROUND ART

Heating elements of the resistive type are known which can heat a material with short heating pulses (on the order of a few hundreds of milliseconds) by applying current. These heating elements are for example used for welding or sealing plastic films.

The known heating elements are generally configured in the form of rectilinear bars and have an active functional surface, which is heated and positioned in contact with the material which must be heated, for example for welding or sealing.

As diagrammatically shown in figure 1, a heating element 1 of the known type comprises a longitudinal metal support body 2, for example made of steel or aluminium, defining at-, a top portion thereof, a cooling duct 3, intended to be fed continuously with a refrigerant, such as water coming from a refrigerator (not shown.) The cooling duct 3 is closed on top by an insulating layer , for example of ceramic material, in turn externally coated by a heating layer 5, formed by a film of resistive material, such as for example a mixture of metal and glass . Heating layer 5 defines the above said active functional surface, and is supplied by means of electric wires connected thereto, by power supplying means (not shown) , which provi de short current pul s e s ( on the o rde r o f a few ]is) , for generating heating pulses having controllable temperature and duration. The function of cooling through cooling duct 3 is to maintain support body 2 at a substantially constant temperature, increasing thereby the efficiency of the heating and welding process.

Labelling machines are also known which are commonly used to apply labels on different kind of containers. In particular, sleeve labels are often used with bottles or other containers intended to contain pourable food products; such labels are obtained by the subsequent steps of: cutting a web unwound from a supply roll into a plurality of rectangular or square portions; winding each web portion in a tubular configuration so that opposite vertical edges overlap; and welding or sealing the overlapping edges to fix the web in a sleeve form.

In this connection, a labelling machine is known in which each sleeve label is formed about a relative cylindrical winding body (commonly known as "sleeve drum") and subsequently transferred onto a relative container, for example by introduction of the container within the sleeve label. The sleeve label is then fixed on the container by means of a thermal retraction process.

This kind of labelling machine comprises a conveyor (known as carousel) which rotates about a vertical axis to define a portion of substantially circular path, along which it can: receive respective sequences of unlabelled containers and of rectangular or square labelling material portions from respective input wheels; allow the application of sleeve labels onto corresponding containers, and release the labelled containers on an output wheel.

More in particular, the carousel comprises a number of operating units which are equally spaced about the rotation axis, are mounted along the periphery of the carousel and are moved by the latter along the above-mentioned said circular path portion.

Each operating unit comprises a supporting assembly adapted to support the bottom wall of a relative container, and a retaining element adapted to cooperate with the top portion of the container to maintain it in a vertical position during the rotation of the carousel.

Each supporting assembly comprises a vertical hollow support mount, fixed to a horizontal plane of a rotating frame of the carousel, and a cylindrical winding body, which engages the support mount in sliding and rotating manner with respect to its axis, and adapted to carry a relative container on its top surface, and a relative label on its side surface.

Each winding body is movable, for example under the control of cam means, between a raised position and a completely retracted position within the relative support mount .

In the raised position each winding body projects from a top surface of the relative support mount and is adapted to receive a relative label on its side surface from the label input wheel; in particular the label is wound about the winding body so that the opposite vertical edges of the label are overlapped to one another.

In the completely retracted position, which is reached at the container input and output wheels, the top surface of each winding body is flush with the top surface of the support mount, so that the containers are transferred on and from the carousel along the same transfer plane. After the welding of the overlapped edges of a sleeve label, the movement of the relative winding body from the raised position to the completely retracted position determines the insertion of the relative container within the label, thus making the container obtained thereby ready to be transferred on the output wheel.

In particular, to perform the welding of the overlapped edges of the labels, a respective sealing device is operatively coupled to a respective sealing device to each operating unit in the carousel. The sealing device is arranged in front of, and in a radially internal position with respect to the relative winding body about which the label is wound, so as to perform the welding of the relative overlapped ends.

For this purpose, each sealing device comprises a heating element, for example of the bar type previously disclosed with reference to figure 1, having an extension at least equivalent to the height of the overlapped edges to be welded of the label.

Currently, the electric power supply of the various heating elements (which can for example be forty in each carousel) is performed in sets, for example formed by four elements, by means of a respective power supply circuit.

As shown in figure 2, the above said power supply circuit comprises a three-phase converter 6, having three primary windings, each connected to a respective phase U, V, W, of the three-phase power supply network, and a secondary winding, on which it provides an AC voltage with a peak of 50 V (from the voltage of the power supply network, for example with a peak of 400 V) , with an output power of 2.5 kW.

Each heating element, indicated again with numeral 1, and of which bar support body 2 and heating layer 5 are shown, is selectively connected to the secondary winding of three-phase converter 6 by means of a respective power switch 7, in particular a TRIAC.

The power supply circuit also comprises a control unit 8, which is inputted with control signals from a supervising unit (not shown) of the labelling machine, in particular including a Programmable Logic Controlled (PLC) unit, and outputs appropriate control signals to the control terminals of power switches 7, in particular for managing welding time intervals and power for each heating element 1.

Control unit 8 also receives a feedback signal from a current sensor 9 , arranged on the return path of the current in the secondary winding of three-phase converter 6, for detecting the current absorbed by heating elements 1.

Each power supply circuit is entirely installed at the rotating carousel, on board of the labelling machine.

Although this power supply solution works and is technically simple, it also has some drawbacks.

In particular, it requires the presence on the rotating carousel of a plurality of electric converters, which are rather bulky and heavy (as they must output a power, for example equivalent to 2.5 k ) , one for each unit of four heating elements 1.

Furthermore, given the high values of current required and the low working frequencies, cables having a wide section are required for electrically connecting the heating elements.

In general, this solution implies considerable sizes and weights which result in any case disadvantageous for the freedom in the general design of the machine, and which cannot be ensured in the case of smaller machines.

Furthermore, this solution is also not easily manageable from a testing and failure search standpoint, in case of malfunction and does not allow in general to obtain an appropriate modularity of the machine.

DISCLOSURE OF INVENTION

It is an object of the present invention to therefore solve, at least in part, the problems previously highlighted.

According to the present invention a power supply system is provided as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, preferred embodiments thereof will now be disclosed by mere way of non-limitative example and with reference to the accompanying drawings, in which:

- figure 1 shows a partial cut-away perspective view of a resistive heating element of the known type;

- figure 2 shows an electric scheme of a power supply circuit for heating elements in a labelling machine of the known type;

- figure 3 shown a diagrammatic plan view with parts removed for clarity of a labelling machine;

- figure 4 shows a perspective view on an enlarged scale of a portion of the labelling machine of figure 3;

- figure 5 shows a diagrammatic partially sectional side view on an enlarged scale of a further portion of the labelling machine of figure 3;

- figure 6 shows an electric block diagram of a power converting circuit of a power supply system of the labelling machine of figure 3; - figure 7 shows an electric block diagram of a power supply module in the labelling machine of figure 3 ;

- figures 8 and 9 show graphs relating to electric quantities in the power supply module of figure 7; and

- figures 10 and 11 show diagrammatic block diagrams of variants of parts of the power supply system.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 3 shows a labelling machine of the rotating type, indicated in general with 10, operating so as to apply sleeve labels 12 (see also figures 4 and 5) on respective containers, in the example bottles, indicated with 13, each of which has a given longitudinal axis A, is joined at the bottom by means of a bottom wall 14 substantially perpendicular to axis A, and had a top neck 15 substantially coaxial with axis A.

Labelling machine 10 comprises a conveying device, for folding and welding portions of web material in a tubular configuration so as to form sleeve labels 12, and perform the insertion. of containers 13 in sleeve labels 12.

The conveying device comprises a conveyor (or carousel) 17, which is mounted to continuously rotate (in an anticlockwise direction in figure 3) about a respective vertical axis B perpendicular to the plane of figure 3. Conveyor 17 receives a sequence of unlabelled bottles 13, from an input wheel 18, which cooperates with conveyor 17 in a first transfer station 19 and is mounted to continuously rotate about a respective longitudinal axis C parallel to axis B.

Conveyor 17 also receives a sequence of portions, for example rectangular or square portions, of labelling web material (for example made of plastic film) from an input drum 20, which cooperates with conveyor 17 in a second transfer station 21 and is mounted to continuously rotate about a respective longitudinal axis D parallel to axes B and C.

Conveyor 17 releases a sequence of labelled bottles 13 on an output wheel 22, which cooperates with conveyor 17 in a third transfer station 23 and is mounted to continuously rotate about a respective longitudinal axis E parallel to axes B, C and D.

Conveyor 17 comprises a number of operating units 25, which are equally spaced about axis B (as better defined hereinafter) and are mounted on the periphery of conveyor 17, by means of which they are displaced along a portion of circular path P which extends about axis B and through transfer stations 19, 21 and 23.

With particular reference to figures 4 and 5, each operating unit 25 comprises a conveying module 26 adapted to receive a relative bottle 13 from input wheel 18 in a vertical position, i.e. with relative axis A parallel to axes B, C, D and to maintain bottle 13 in this position along path P from transfer station 19 up to transfer station 23.

Each conveying module 26 comprises a bottom supporting assembly 27 adapted to support bottom wall 14 of a relative bottle 13 and a top retaining element 28 adapted to cooperate with top neck 15 of bottle 13.

In particular, each supporting assembly 27 comprises:

- a hollow support mount 30, which has a vertical axis F, parallel to axes B, C, D and E and is fixed on a plane or a horizontal table of a rotating frame 31 of conveyor 17; and

- a substantially cylindrical winding body 32, which engages support mount 30 sliding and rotating with respect to axis F, and adapted to coaxially carry a relative bottle 13 on its top surface 33 and a relative label 12 on its side surface 34.

In particular, each winding body 32 can be displaced along axis F under the control of cam means (not shown) , between a completely retracted position within relative support mount 30 and a raised position.

In the completely retracted position, each winding body 32 is completely housed within relative support mount 30 so that top surface 33 thereof is flush with a top surface 35 of support mount 30.

In the raised position, each winding body 32 projects from top surface 35 of relative support mount 30 and is adapted to receive, on its side surface 34, a relative label 12 from input drum 20.

More specifically, the portions of web material are cut from a labelling web material 36 (figure 3) by means of a cutting device 37 (diagrammatically shown only in figure 3) and fed to input drum 20 to then be transferred on relative winding bodies 32.

As shown in figure 4, the cut portions of web material, indicated by numeral 38, are retained on side surface 40 of input drum 20 by suction; as a matter of fact, side surface 40 of input drum 20 is subdivided in a number of suction areas, which are equally spaced about axis D, are each provided with a plurality of through-holes 42 connected to a pneumatic suction device (known per se and not shown) and are adapted to cooperate with respective cut portions of web material 38.

Similarly, side surface 34 of each winding body 32 is provided with a plurality of through-holes 43 connected in turn to a pneumatic suction device (known per se and not shown) so as to retain the relative cut portion of web material 38 by suction.

In transfer station 21, each winding body 22 can be rotated in a known manner about relative axis F under the control of relative actuator means (not shown) in order to perform the complete winding of the relative cut portion of web material 38, coming from input drum 20, on side surface 34, so as to form a substantially tubular sleeve with opposite ends 44 overlapped.

With reference to figure 5, each operating unit 25 comprises a respective sealing device 48 arranged in front of, and in a position radially internal with respect to, relative conveying module 26; each sealing device 48 cooperates with the cut portion of web material 38 wound about corresponding winding body 32 for welding relative overlapped ends 44 so as to create sleeve label 12, which will then be arranged about bottle 13.

Each sealing device 48 comprises: a heating element, in particular of the bar type previously shown with reference to figure 1, again indicated with numeral 1, having an extension at least equal to the height of overlapped ends 44 to be welded of sleeve label 12, and comprising relative bar support body 2 (defining the cooling duct therein - not shown) and coated on top by heating layer 5; and an actuator unit 49, configured so as to displace heating element 1 towards and from overlapped edges 44 of relative sleeve label 12, along a direction X transversal to the portion of path P. As shown in figure 3, directions X, along which sealing device 48 are displaced, extend radially with respect to axis B and thus orthogonally to axes B-F.

According to an embodiment of the present invention, each sealing device 48 also comprises a respective power supply module 50, individually coupled thereto, and receiving appropriate control signals, indicated with S _c , from a supervising unit 51 of labelling machine 10 (and possibly of further machines, or parts thereof, cooperating with labelling machine 10) , in particular including a Programmable Logic Controller (PLC) unit. Each sealing device 48 also receives appropriate power supply signals from a converting circuit 52, which is single for the whole labelling machine 10 and for all power supply modules 50 of the various sealing devices 48.

In greater detail, as shown in figure 6, converting circuit 52 comprises a three-phase insulating converter 53, having three primary windings, each connected to a respective phase U, V, W of a three-phase power supply network of the electric system, providing for example a voltage having a maximum peak value of 400 V, and at least one secondary winding. The three-phase insulating converter 53 has a power sufficient to supply all sealing devices 48 of labelling machine 10 active at the same time during the welding step, providing for example an output power of 25 kW (in case labelling machine 10 has forty sealing devices 48) .

Converting circuit 52 also comprises: a first AC/DC converter 54, connected to the secondary winding of three- phase insulating converter 53 and outputting a first DC voltage Vali having a boosted value and adjusted, for example at 500 V, independent of the voltage and frequency values provided by the electric system; and a second AC/DC converter 55, of the insulated type, directly connected to the three-phase power supply network and outputting a second DC voltage Val ₂ having an adjusted value, for example of 24 V.

The first and second DC power voltages Vali, Val ₂ are outputted from converting circuit 52 to conveyor 17 of labelling machine 10 (diagrammatically shown herein) , where they are referred to a common ground voltage GND and filtered to eliminate electromagnetic disturbances in an EMI filter 56, and then supplied to various supply modules 50 of sealing devices 48 (not shown herein) . In particular, converting circuit 52 is arranged at a distance, externally to the rotating part of labelling machine 10, for example in a main transformer room or control box of labelling machine 10.

Each power supply module 50 forms a high efficiency resonant converter, capable of supplying respective heating element 1, in particular with a quasi-sinusoidal current at a high frequency (much higher to that of the power supply network) , for example of 200 kHz, and an appropriate peak power, for example in the range between 2.5 and 3 kW. Each power supply module 50 is advantageously formed by an electronic board, arranged on board of conveyor 17, at relative sealing device 48.

In detail, and as shown in figure 7, each power supply module 50 receives a third DC voltage Val ₃ , having logic value, for example of 5 V (i.e. adapted to supply logic gates and circuits) from a DC/DC converter 58, which generates such a voltage from second DC voltage Val ₂ . DC/DC converter 58 may be obtained not in the same printed circuit board, indicated herein with numeral 59, of power supply module 50.

Power supply module 50 comprises: a microprocessor control unit 60, supplied by third DC voltage Val ₃ , and inputted with control signals S _c from supervising unit 51 of labelling machine 10, in particular from a Controller Area Network (CAN) type bus. For this purpose it is provided with a CAN BUS interface 61; and a resonant power circuit including a bridge inverter 64 and a LC network 65.

Bridge inverter 64 is formed with a bridge of MOSFET transistors having power 64a- 64d, of the known type (not disclosed in detail herein) , each of which receives on a control terminal thereof a respective piloting signal Si or S ₂ , generated by a piloting stage (so-called driver) 66, controlled by microprocessor control unit 60 in order to control the welding steps and time intervals . In particular, piloting signals Si, S ₂ are shifted by 180° (they are inverted with respect to one another) , and formed by substantially rectangular pulse trains having a duration for example in the range between 2.5 and 5 με .

Bridge inverter 64 is connected between first DC voltage Vali and ground terminal GND, and outputs an alternating output voltage Vout, between a first and a second output terminal Outi, Out ₂ , to which LC network 65 is connected.

This LC network 65 includes a resonance capacitor 68 and a resonance inductor 69 connected in series between the first and the second output terminal Outi, Out ₂ , so as to generate a resonance condition, in the example at a high frequency of 200 KHz.

The above said resonance inductor 69 also forms the primary winding of an output transformer 70, having a secondary winding between the terminals of which heating element 1 is electrically coupled, and which may be schematised as a resistive element.

Power supply module 50 also comprises a feedback sensor 72, in particular a resistor, connected in series to heating element 1, so as to provide a measure of the current (and indirectly of the power) absorbed by heating element 1, in feedback towards microprocessor control unit 60, in order to maintain the power constant even upon variation of the operating conditions, for example due to a deterioration of heating element 1.

Figures 8 and 9 show graphs obtained by simulation, which highlight the performance of power supply module 50, respectively as regards the maximum power supplied to heating element 1 (figure 8) and the operating frequency in a resonance condition (figure 9) .

The advantages of the power supply system are clear from the preceding description.

In particular, the use of a single converting circuit 52 for all sealing devices 48, arranged at a distance with respect to the rotating part of labelling machine 10, allows to drastically reduce the size and the weight of the rotating part of labelling machine 10. Power supply modules 50, coupled to sealing devices 48, allow to subdivide the conversion of energy between various sealing devices 48, and the use of high-frequency ferrite for output converters 70 allows to reduce the weight and size thereof.

Furthermore, by supplying sealing devices 48 with high voltage and performing a conversion of voltage directly at relative heating elements 1, the length of the high current r cables can be reduced, increasing the efficiency of the system and the immunity to electromagnetic disturbances .

The use of a resonant feeder in power supply modules 50 allows to further increase the efficiency, reduce the power dissipated on the power MOSFET transistors and the spurious harmonics generated by the feeder.

The insulation of the three-phase voltage also allows to reduce the cost of the single resonant feeders.

The presence of intelligence localised in each power supply module 50 (in the relative microprocessor control unit 60) allows to manage the sequence and the power of the welding operation locally, taking up a minimum of the resources per supervising unit 51 of labelling machine 10. The same localised management of the welding operation also renders each sealing device 48 testable on its own and allows to identify failures and malfunctioning in a much easier way.

In general, the disclosed solution allows to increase the modularity of labelling machine 10.

It is finally apparent that modifications and variants may be made to what is disclosed and illustrated herein without, because of this, departing from the scope of protection of the present invention, as defined in the appended claims.

In particular, in a first variant, shown in figure 10

(in which conveyor 17, operating units 25 and sealing devices 48 of labelling machine 10 are shown), each power supply module 50 comprises, in the relative printed circuit board, a single signal stage (indicated with 50a, including relative control unit 60, not shown herein) and a dual power stage (indicated with 50b, 50b ¹ , including two resonant power circuits, each with a respective piloting stage 66, bridge inverter 64, LC network 65 and output converter 70, not shown herein), for supplying power to two heating elements 1 of a pair of adjacent sealing devices 48. In this variant, control unit 60 can manage the welding process of both sealing devices 48 on the basis of control signals Sc received from data bus 80. In particular, the number of power supply modules 50 results lower than the number of sealing devices 48.

As shown diagrammatically, converting circuit 52 is present also in this case outside the rotating carousel, for supplying the first and the second DC voltage Vali, Val ₂ to power supply modules 50 on board of the same rotating carousel; and also supervising unit 51 for supplying control signals Sc to power supply modules 50, through a data communication bus, indicated herein by numeral 80.

For ease of disclosure, only two power supply modules

50 are shown in figure 10 (similar considerations apply to the other power supply modules of the system) .

In a second variant, shown diagrammatically in figure 11, there is again provided a number of power supply modules 50 smaller than the number of sealing devices 48; in this case, each power supply module 50 comprises a single signal stage 50a and a single power stage 50b, which is controlled so as to alternatively supply (in distinct time intervals) at least two heating elements 1 for sealing devices 48 which are not active at the same time for performing the welding process. Output converter 70 of power supply module 50 is for this purpose connected electrically to heating elements 1 of such sealing devices 48. In this connection, it should be understood that operating units 25, to which respective sealing devices 48 are associated, are arranged along the periphery of conveyor 17 at a certain angular distance, or pitch, indicated by p in figure 11. The welding process of sleeve labels 12 requires, for its completion, a certain time interval, during which the carousel performs a certain number of rotation pitches. It is therefore clear that, in this variant, the same power supply module 50 can supply power to two sealing devices 48 which are positioned at an angular distance of at least the number of rotation pitches corresponding to the time required for the completion of the welding process.

For example, in the case of labelling machine 10 having forty-eight operating units 25, and with a welding process which requires twelve rotation pitches for its completion, a first power supply module 50 can control the supply of sealing devices 48 in position 1, 13, 25 and 37 (the numbers represent the position along the periphery of the carousel, from input wheel 18), i.e. of sealing devices 48 arranged in pairs in a diametrically opposite position.

In this variant, output converter 70 is connected to respective heating elements 1 by means of electric coupling means 81 (for example including a multiplexer) , which are appropriately controlled by control unit 60 of power supply module 50, to selectively and alternatively control the power supply of heating elements 1, in distinct time intervals.

For ease of disclosure, only one power supply module

50 is shown in figure 11 (similar considerations apply to the other power supply modules of the system) .

In general, the previously disclosed power supply module may also be used in other applications, other than labelling machine 10, for example in different rotating machines which handle a web material for processing tubular lengths to be used for different purposes, for example to wind articles in a film material.