FIELD OF THE INVENTION The present invention relates to the technical sector concerning the cutting of articles having a flat extension, for example leather sheets, by use of suitable tools, for example a vibrating or non-vibrating blade; in the following reference will be made, by way of non-limiting example, to leather sheets.

DESCRIPTION OF THE PRIOR ART The cut is carried out with the leather sheet stretched on an aspirating plane on which it is sealedly maintained with depression values that are known to the expert in the sector, for example comprised between a minimum value of about 3 Kpa and an optimal value of about 20 Kpa: the latter value ensuring a cutting velocity of about 50 m/min. The aspirating plane is divided into sectors, singly connectable to a source of depression; only the sectors totally or partly covered by the leather sheet are connected to the source (aspirating pump).

At the edges of the leather sheet there is a limited seal with respect to the sectors covered by the leather sheet, and this can lead to a displacing of the edges when they are subjected to the action of the blade.

The sectors of the aspirating plane that are partly uncovered, as they are involved by the edges of the leather sheet, can cause an anomalous increase in the flow rate of the pump (for example more than 3000 mc/h), sufficient to cause an overload of the motor activating the pump. Various technical solutions have been proposed for limiting the above- mentioned drawback. For example the edges of the leather sheet can be manually covered using a non-breathable covering material so as to cover the sectors involved by the edges entirely. This involves employing operators and the need to work on pieces of leather sheet obtained by the cut so as to clean them from the covering material which is in part cut; further, if the operators are inexpert the risk of waste of materials is significant.

Also possible is a reduction in the dimensions of the sectors, so as to reduce the pressure losses: this leads to a constructional complexity such as to make the technical-functional specification uneconomical. A known solution (see EP 1.178.120 by the same Applicant) teaches partialising the connection between the source and the sectors involved by the edges of the leather sheet, so as to reduce the pressure losses; this is a partly efficient specification, given the need to maintain a minimum depression level and flow rate in order to keep the edges of the leather sheet in adherence to the aspirating plane, which tend to lift.

It is not possible to use an aspirating pump able to supply a depression in the order of the best value (e.g. 20 Kpa) and a flow rate such as to involve the completely or partially covered sectors of the leather sheet, as that would lead to technical difficulties for realising an aspirating plane sturdy enough to support the 20 Kpa over the whole aspirating plane, as well as poorly- economical costs for the pump and the management costs thereof which have to constantly operate at maximum power.

The reduction of the cutting velocity at or in proximity of the edges of the leather sheet is inefficient for many types of leather sheet, poorly reliable and brings about a significant increase in cutting times.

SUMMARY OF THE INVENTION

The aim of the invention is to provided a system for cutting articles having a flat extension arranged adheringly on an aspirating work plane, which obviates the drawbacks of the prior art.

A further aim of the present invention is to provide a system for cutting articles which enables, with respect to the prior art, an increase in productivity, an increase in the performance of the leather sheet and a reduction in energy consumption due to the functioning of the aspirating means with which the leather sheet is removably blocked to the aspirating plane.

A further aim of the invention is to provide a method for cutting articles, for example leather sheets, that can be actuated with the above-described system.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the invention are specified in the following with particular reference to the accompanying tables of drawings, wherein:

- figures 1A, 1 B schematically illustrate a view of the aspirating work plane, in which the present invention is operative, and represent two moments relative to the cutting carried out along the profile of two shapes;

- figure 1 C illustrates a lateral view of detail Y of figures 1A, 1 B;

- figure 2 is a perspective view of a portion of the aspirating work plane, illustrated overturned with respect to a use configuration thereof, with some parts removed better to evidence others;

- figure 3 illustrates detail K of figure 2, in larger scale with respect to figure 2;

- figure 4 is a perspective view of a portion of the aspirating work plane, for example detail X of figure 1 B, illustrated overturned with respect to a use configuration thereof; - figure 5 is an illustration a perspective view of a connecting device between a sector of the aspirating plane and one or the other of two pneumatic circuits; - figure 6 is a perspective view of a cutaway of the device of figure 5;

- figures 7A, 7B, 7C illustrate, according to three sectioned plan views along a horizontal plane, the device of figures 5 and 6 in three characteristic use configurations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the figures, reference numeral 1 denotes an aspirating work plane comprising a plurality of sectors 2, not communicating with one another (figure 3), each of which sectors 2 affords through-holes 3 communicating on a side thereof with an upper surface of the plane 1 and on another side thereof with a gap 4 delimited by the lower surface of the plane 1 , by closing panels 5 and by a perimeter edge 6.

An outlet 7 opens into the central part of the panel 5 of a connecting device 8 provided with two inlets 9, 10, respectively a first and second inlet.

The first inlet.9 is connectable to a first pneumatic circuit, comprising a conduit 11 for each sector 2, connected to the first inlet, branching from a relative manifold 12 (of which only one is illustrated in the accompanying figures: see figure 4) supplied by a first piping 13 which is placed in depression by a first aspirating source (not illustrated) with a predetermined flow rate and depression. With reference to figures 2-4, reference numeral 14 denotes a supply chamber delimited by panels 5, by a wall 15 underlying the panels and by a perimeter edge 16.

The second inlets 10 of the connecting devices 8 are supplied by a second pneumatic circuit comprising the above-mentioned chamber 14, into which the second inlets open 10, and a second piping 17 connecting the chamber 14 with a second supply source, not illustrated, having a predetermined flow rate and depression. The depression generated by the second source is significantly greater than the depression generated by the first aspirating source.

By way of example the depression created by the second source is in the order of 20 Kpa, while the depression generated by the first source is in the order of 3Kpa.

A rotor 19 is arranged internally of each connecting device 8, which rotor 19 is activated by an actuator 18, for example an electric motor.

The motor 18 can impose three distinct configurations on the rotor 19:

- a first configuration C^ (figure 7A) in which the rotor intercepts (obstructs) both the inlets 9, 10: in this way the corresponding gap 4, and with it the relative sector, are not subject to aspiration;

- a second configuration C ₂ (figure 7B), in which the rotor 19 intercepts (obstructs) the second inlet 10:, while the first inlet 9 is free: it follows that the relative sector 2 is subjected to the flow rate and the depression generated by the first aspirating source;

- a third configuration C ₃ (figure 7C), in which the rotor 19 intercepts (obstructs) the first inlet 9:,while the second inlet 10 is free: it follows that the relative sector 2 is subjected to the flow rate and the depression generated by the second aspirating source. In prior-art applications, a cutting device operates above the aspirating plane 1 , not illustrated in detail as it is known to the expert in the sector, of which the blade 20 is schematically represented, which can be either vibrating or non- vibrating; this device is controlled and commanded by a suitable control unit 50 denoted schematically as of known type to the expert in the sector. This control unit controls and commands the actuators 18: see the connections "a". In the following the operating steps are illustrated that, with the system of the invention, lead to obtaining a plurality of pieces 70 of predetermined size and shape are obtained from a leather sheet P.

The leather sheet is arranged on the aspirating plane 1 ; using known methods the orientation and positioning of the leather sheet on the plane 1 is detected: the relative data is transmitted to the control unit 50.

The sectors 2A covered by the leather sheet, and the sectors 2B partly covered by the leather sheet, are connected using relative connecting devices 8 (located in the second configuration C ₂ : figure 7B) to the first aspirating source; the free sectors 2, i.e. those not involved by the leather sheet, are not subjected to aspiration (the relative connecting devices 8 are in the first configuration figure 7A).

In the above-described condition the operator operates on the edges B of the leather sheet to remove any creases. A pressure detector (not illustrated) is included, controlled by the control unit, with which the minimum depression guaranteeing that the leather sheet does not lift at the edges thereof is maintained.

Using known methods to the expert in the sector, the control unit 50 is used to memorise the profiles, or shapes, F,F (as well as the mutual positioning thereof with reference to the perimeter extension of the leather sheet) corresponding to the pieces 70, 71 that can be fashioned from the leather sheet; this is done either following the blocking of the leather sheet on the plane 1 or prior thereto: in this case a code is ascribed to the leather sheet, in combination with the detecting of the positioning of the leather sheet P on the plane 1 , so that the control unit contains the data relative to the positioning and orientation of each shape.

The control unit intervenes to command the cutting device so as to arrange it at the position of a shape F: see figure 1 A.

The shape totally or partially covers a series of sectors 2C; in figure 1A, from among the sectors, 2* is used to denote the sector that the blade 20 is involved with. The sector 2* is connected to the second aspirating source (the relative connecting device 8 is located in the third configuration C ₃ ) only for the time necessary for the blade 20 to pass through the sector.

Thereafter the blade passes through one of the above-mentioned sectors 2C (adjacent to sector 2*) which is subjected to the action of the second aspirating source, while preceding sector 2* is subjected to the depression of the first aspirating source or, if necessary, to no aspirating source (device 8 in the first configuration Ci: figure 7A): this reduces the system energy consumption.

The blade gradually passes through the various sectors 2C with the aim of involving the whole profile F: in this way the corresponding piece 70 is obtained.

Using a suitable detector (not represented in the figures) the depression generated in sector 2* involved in the cut is involved: the velocity of the blade 20 is adjusted as a function of this value. Figure 1 B illustrates both a further shape Ft (which defines a corresponding piece 71 ) and the sector 2* which, being subjected to the second source, enables cutting a portion of the shape and at the same time prevents lifting of the adjacent edge of the piece 70 previously cut.

The system of the invention is extremely versatile inasmuch as, when required, instead of only subjecting the sector 2* to the maximum aspiration, it is possible also to subject the sectors 2C, associated to the shape F, to a maximum aspiration. Definitively, an aspirating plane 1 is made available, subjected to two pneumatic circuits, with different diameters and rigidity, provided with relative depression sensors; the switching of the connection of the sectors 2 of the plane 1 is controlled by the control unit.

The first pneumatic circuit comprises the first aspirating source which generates a flow rate with a low depression.

The second pneumatic circuit comprises the second aspirating source which generates a high depression, but with a limited flow rate.

The system of the present invention provides various advantages.

In fact, an automatic management of the "leather sheet edge" is obtained, without the aid of manual and discretional coverings.

There is a reduction in cycle time consequent on the reduction of the positioning of the leather sheet on the work plane and a cutting velocity that is higher than that of the prior art.

There is an increase in the performance of leather sheets, as creases are eliminated (at the moment of positioning the leather sheet on the plane 1) and cutting is performed close to the edges and without waste.

Lastly, there is a reduction in energy consumption for the cutting of the leather sheet, consequent on the diversified management of the aspirating pumps: full coverage for fixing and a dynamic coverage for maximum seal of the leather sheet on the plane 1 during the cutting operation.