FOR THE CUTTING OF LEATHER

FIELD OF THE INVENTION

The present invention relates to the particular technical sector concerning cutting machines for cutting sheet or rolled materials, such as skins, leathers, hides, synthetic leather, etc.

In particular, the present invention relates to a cutting device having an improved pneumatically-powered oscillating blade destined to be mounted on the cutting machines.

DESCRIPTION OF THE PRIOR ART

Cutting machines comprise a work plane, where the materials to be cut are laid out, such as for example skins (hides, leather), synthetic skins and the like, a frame and mounted above the work plane and a cutting device mounted on the frame and interiorly provided with a cutting blade.

The cutting machines further comprise movement means, which are borne by the frame and mobile with respect thereto, so as to move the cutting device according to the three Cartesian axes above the work plane so that the cutting blade can be positioned above the skins, be lowered to score the skin and be moved according to a given cutting pathway so as to cut the skins on the basis of prefixed and/or desired profiles.

The cutting devices used for this purpose are predisposed so that the cutting blade can be made to oscillate vertically during the cutting of the material, from a lower cutting position to an upper cutting position, while always remaining within the thickness of the material to be scored/cut.

For this purpose, at present pneumatically-powered cutting devices are particularly used to cause the cutting blade to perform the requested oscillation needed to perform the cut.

Known-type pneumatically activated cutting devices are made in such a way as to comprise an oscillating chamber, having an upper end-run wall and a lower end- run wall, an oscillating piston, predisposed with the head thereof inserted in the oscillating chamber and with the relative rod thereof connected to the cutting blade, and a pneumatic activating system communicating with the oscillating chamber in order to cause the piston to oscillate between the upper end-run wall and the lower end-run wall, and therefore to cause the cutting blade to oscillate vertically.

In known cutting devices, the pneumatic activating system comprises a pneumatically-powered activating system and a discharge, which are predisposed and configured in such a way that the part of the oscillating chamber comprised between the piston head and the upper end-run wall and the part of the oscillating chamber comprised between the piston head and the lower end-run wall are alternatingly communicating with the pneumatic activating system and with the discharge so as to make the oscillation of the piston possible inside the oscillating chamber.

In this regard, in these known cutting devices, the oscillating chamber comprises two openings and the pneumatic activating system comprises conduits, which substantially have a same transversal section and which are respectively in communication with the openings and with the respective shutters or other valve organs activatable to open or close so as to make each of the two openings of the oscillating chamber, via the conduits, alternatingly in communication with the pneumatic supply and the discharge.

The switching of the oscillation of the piston is done by means of use of appropriate valve organs or external shutters.

This means that the switching of the piston stroke can take place with a certain delay with respect to the opening/closing of the switching member, a circumstance that can cause the entity of the oscillation run of the piston to be not always constant, i.e. sometimes shorter and sometimes longer than the desired run.

This circumstance can have a negative effect on the effectiveness of the cut.

The Applicant has obviated the above-described drawbacks by providing a special pneumatic cutting device with an oscillating blade, as described in Italian patent application for industrial invention no. 102017000038441.

The pneumatic cutting device (90) described in this patent application comprises a body (C), and a cutting blade (L) for cutting a leather sheet stretched on a work plane.

The pneumatic cutting device (90) in this regard is mountable on cutting machines, for example numerically controlled.

It is predisposed in such a way as to pneumatically activate the cutting blade (L) in order that it can oscillate vertically so as to score and cut the leather sheet.

Figures from 1A to 1C illustrate, in frontal views, the pneumatic cutting device (90), with the cutting blade (L) represented in different operating configurations attainable during oscillation thereof, respectively a lower cutting position (L1 ) (figure 1A), an intermediate cutting position (LM) (figure 1B) and an upper cutting position (L2) (figure 1C).

The cutting device (90) is provided, internally of the body (C), with an oscillating chamber (1 ), with an upper end-run wall (11 ) and a lower end-run wall (12), and an oscillating piston (10), having a head (13) and a rod (14), the oscillating piston (10) being predisposed with the head (13) thereof inserted in the oscillating chamber (1 ), between the upper end-run wall (11 ) and the lower end-run wall (12), the rod (14) being connected to the cutting blade (L).

When the head (13) of the oscillating piston (10) is in abutment against the lower end-run wall (12) of the oscillating chamber (1 ), the cutting blade (L) is in the lower cutting position (L1 ), while when the head (13) of the oscillating piston (10) is in abutment against the upper end-run wall (11 ) of the oscillating chamber (1 ) the cutting blade (L) is in the upper cutting position (L2).

The upper end-run wall (11 ) is predisposed in the body (C) at a distance with respect to the lower end-run wall (12) which is such that when the head (13) of the oscillating piston (10) reaches contact with the upper end-run wall (11 ), the cutting blade (L) reaches an upper cutting position (L2) such that it remains substantially in contact with, or slightly extracted from, the leather sheet (V) to be cut, with the purpose of guaranteeing continuity of the cutting operation.

For the pneumatic activating of the oscillation of the oscillating piston (10) in the relative oscillating chamber (1 ), and thus for the vertical oscillation of the cutting blade (L), the pneumatic cutting device (90) is provided with a relative pneumatic activating system (P) communicating with the oscillating chamber (1 ).

The pneumatic cutting device (90) realised according to what is described in this patent application is able to carry out the switching of the run of the oscillating piston (10) automatically without the presence of valve and/or switching organs, this is due to the following special characteristics: the particular conformation of the rod (14) o the piston (10), the special conformation of the head (13) of the piston (10) and the special conformation of the pneumatic supply system (P).

These aspects are illustrated in detail in figures from 2A to 2C which represent the views along section lines l-l, ll-ll and Ill-Ill of figures 1A, 1 B, 1C. The pneumatic activating system (P) comprises a pneumatic supply source (for example compressed air), denoted schematically by arrow (P1 ), and upper discharge (S1 ) and a lower discharge (S2).

The body (C) comprises a cylindrical cavity (16) while the rod (14) of the oscillating piston (10) is predisposed so as to be slidable alternatingly in the cylindrical cavity (16).

Further, the rod (14) of the oscillating piston (10) is conformed in such a way as to have: two annular portions (141 , 142), an upper annular portion (141 ) and a lower annular portion (142), in sliding contact with the walls of the cylindrical cavity (16), an annular recess (140), comprised between the two annular portions (141 , 142), and an internal conduit (17), the rod (14) being further provided with through-holes (18) which are predisposed along the rod (14) in a position beneath the lower annular portion (142) and such as to place the internal conduit (17) in communication with the outside of the rod (14).

The head (13) of the oscillating piston (10) is provided in turn with at least a hole (130) predisposed so as to place the internal conduit (17) of the rod (14) in communication with the part (1 B) of the oscillating chamber (1 ) comprised between the head (13) of the oscillating piston (10) and the upper end-run wall (11 ) of the oscillating chamber (1 ).

The pneumatic activating system (P) is predisposed and configured in the following way.

It comprises:

a switching chamber (8) of the oscillation of the oscillating piston (10) which comprises an upper annular chamber (8A) and a lower annular chamber (8B) realised in a portion of the walls of the cylindrical cavity (16); a main conduit (81 ) which is realised and predisposed in the body (C) so as to be in communication with the pneumatic supply source (P1 ) and with a part of the lower annular chamber (8B) of the switching chamber (8);

a secondary conduit (82) realised and predisposed in the body (C) so as to place the upper annular chamber (8A) of the switching chamber (8) in communication with the oscillating chamber (1 ) via a passage hole (83) realised in the lower end- run wall (12) of the oscillating chamber (1 ).

The upper discharge (S1 ) is made in a portion of the walls of the cylindrical cavity (16) above the upper annular chamber (8A) of the switching chamber (8), and communicating with the outside via a first discharge conduit (92) also realised and predisposed in the body (C).

In turn, the lower discharge (S2) is made in a portion of the walls of the cylindrical cavity (16) below the lower annular chamber (8B) of the switching chamber (8), and which communicates with the outside via a second discharge conduit (94) realised and predisposed in the body (C).

Further, the annular recess (140) of the rod (14) has dimensions so that, and with the holes (18) of the rod (14) being positioned with respect to the annular recess (140) in such a way that, with the alternating sliding of the rod (14) in the cylindrical cavity (16) the following conditions occur:

when the annular recess (140) of the rod (14) is positioned at the switching chamber (8) so as to place the lower annular chamber (8B) in communication with the upper annular chamber (8A), the holes (18) of the rod (14) are positioned at the lower discharge (S2) (see figure 2A), so that the main conduit (81 ) is in communication, via the lower annular chamber (8B), the annular recess (140) and the upper annular chamber (8A), with the secondary conduit (82) and therefore the pneumatic supply source (P1 ) is in communication with the part (1A) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the lower end-run wall (12) (the arrows in the unbroken line in figure 2A), while the part (1 B) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the upper end-run wall (11 ) is in communication with the lower discharge (S2),and therefore with the second discharge conduit (94) towards the outside, via the hole (130) of the head (13) of the piston (10), the internal conduit (17) of the rod (14) and the holes (18) of the rod (14) (see the arrows in the broken line in figure 2A), so that the oscillating piston (10) can be pneumatically pushed upwards;

and when the annular recess (140) of the rod (14) is positioned both at the upper discharge (S1 ) and at the upper annular chamber (8A) of the switching chamber (8) communicating with the secondary conduit (82), the holes (18) of the rod (14) are at the lower annular chamber (8B) of the switching chamber (8) and thus in communication with the main conduit (81 ) (see figure 2C), so that the pneumatic supply source (P1 ), via the main conduit (81 ), the holes (18) of the rod (14), the internal conduit (17) of the rod (14) and the hole (130) present in the head (13) of the oscillating piston (10), is in communication with the part (1 B) of the oscillating chamber (1 ) between the upper end-run wall (11 ) and the head (13) of the oscillating piston (10) (see the arrows in unbroken line in figure 2c), while the part (1A) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the lower end-run wall (12) is in communication with the upper discharge (S1 ) via the secondary conduit (82), the upper annular chamber (8A) of the switching chamber (8) and the annular recess (140), and therefore through the first discharge conduit (92) with the outside (see the arrows in broken line in figure 2c), so that the oscillating piston (10) can be pneumatically pushed downwards.

Figure 2B illustrates instead the situation in an intermediate position of the rod (14) of the oscillating piston (10) with respect to the end positions illustrated in figures 2A and 2C, con figure 2A illustrating the head (13) of the oscillating piston (10) in abutment against the lower end-run wall (12), while figure 2C illustrates the head (13) of the oscillating piston (10) in abutment against the upper end-run wall (11 ). In the position of figure 2B, the upper discharge (S1 ) is closed by the upper annular portion (141 ) of the rod (14) above the annular recess (140), while the lower annular chamber (8B), communicating with the main conduit (81 ), is closed by the lower annular portion (142) of the rod (14) below the annular recess (140). Consequently the oscillating piston (10) can continue in the downwards run thereof, if starting from the configuration illustrated in figure 2C, pushed by the pneumatic supply source (P1 ) which acts on the upper part of the head (13) of the oscillating piston (10) as described in the foregoing, or can continue in the upward runs, if starting from the configuration of figure 2A, pushed by the pneumatic supply source (P1 ) acting on the lower part of the head (13) of the oscillating piston (10), as previously described.

Therefore, owing to the special characteristics as set out in the foregoing, in the pneumatic cutting device (90) described in the above-mentioned patent application, the switching of the oscillation of the piston is activated and determined by the piston, according to the position of the relative rod with respect to the cylindrical cavity of the body, and in particular of the relative annular recess with respect to the switching chamber and the two discharges.

This has enabled obviating the drawbacks mentioned in the foregoing in pneumatic cutting devices which include the use of valve organs or shutters for commanding the switching of the oscillation of the piston.

In this particular technical sector, however, there is a growing need in the manufacturing industry of leather products for a significantly improved productivity, which can be achieved only with an ever-greater cutting speed.

This leads to the need to command the oscillation of the oscillating piston internally of the oscillating chamber with progressively-greater oscillation frequencies, for example up to in excess of 35000 cpm (cycles per minute).

The pneumatic cutting device (90) described in the foregoing, and object of the present patent application, is perfectly able to attain these oscillation frequencies; however, the Applicant has found that the high oscillation velocities that can be reached tend to create a good deal of potential energy in the piston which, consequently, strikes with its head with great force against the lower end-run wall and the upper end-run wall.

The Applicant has found that owing to the weight of the piston and the relative head, the lower end-run wall of the oscillating chamber is the one subject to more rapid wear, a circumstance that as well as compromising the correct and optimal functioning of the pneumatic cutting device, requires a consequent replacement of the components internal thereof.

The greater and more rapid wear of the lower end-run wall is also caused by the fact that the piston head is pushed by the compressed air with greater force downwards rather than upwards, as the upper surface of the piston head is greater than the lower surface, due to the presence of the rod.

Further, another drawback that can limit the attaining of higher oscillation frequencies is constituted by the inversion of the piston run from the lower cutting position to the upper cutting position; i.e. by the inversion of the run of the piston head from the lower end-run wall to the upper end-run wall.

In fact, as well as the weight of the piston, the head of the piston and the rod, the thrust of the compressed air acting on the lower surface of the piston head must overcome the resistance that the leather sheets, especially the stiffer and thicker ones, exert on the cutting blade which, in the lower cutting position, is inserted and forced into the entire thickness of the leather.

These factors tend to make the inversion of oscillating motion of the oscillating piston critical once it has reached abutment with the relative head against the lower end-run wall.

SUMMARY OF THE INVENTION

An aim of the present invention is therefore to disclose a new improved pneumatic cutting device having an oscillating blade for leather cutting machines able to guarantee high oscillation velocity of the cutting blade and at the same time reduces the onset of wear in the lower end-run wall of the oscillating chamber, and further guarantees and effective inversion of the oscillation of the oscillating piston when the head of the oscillating piston reaches abutment against the lower end- run wall.

The above-cited aim is attained with a pneumatic cutting device having an oscillating blade for leather cutting machines according to the contents of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the pneumatic cutting device with an oscillating blade for leather cutting machines of the invention are described in the following with reference to the accompanying tables of drawings, in which:

- figures from 1A to 1C illustrate, in respective frontal views, the pneumatic cutting device described in the patent application cited and filed by the same Applicant, with the cutting blade represented in three different operating configurations attainable during oscillation thereof, respectively a lower cutting position in figure 1A, an intermediate cutting position in figure 1 B, and an upper cutting position in figure 1C;

- figure 2A illustrates, in larger scale, the view along section plane l-l of figure 1A, figure 2B illustrates, in larger scale, the view along section plane ll-ll of figure 1 B, and lastly figure 2C illustrates, in larger scale, the view long section plane Ill-Ill of figure 1C;

- figures from 3A to 3C illustrate, in respective frontal views, the improved pneumatic cutting device of the present invention, illustrated with the cutting blade represented in three different operating configurations attainable during oscillation thereof, respectively a lower cutting position in figure 3A, an intermediate cutting position in figure 3B, and an upper cutting position in figure 3C;

- figure 4A illustrates, in larger scale, the view along section plane IV-IV of figure 3A, figure 4B illustrates, in larger scale, the view along section plane V-V of figure 3B, and lastly figure 4C illustrates, in larger scale, the view long section plane VI- VI of figure 3C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the appended tables of drawings, reference numeral (100) denotes the improved pneumatic cutting device with an oscillating blade for leather cutting machines of the present invention, in its entirety.

The improved pneumatic cutting device (100) comprises the same characteristics as the pneumatic cutting device of the above-mentioned and described patent application, concerning the activation in oscillation of the oscillating piston internally of the oscillating chamber and the switching modes of the inversion of the oscillation.

Therefore, in the following description, the parts of the improved pneumatic cutting device (100) of the present invention that correspond to those described in the foregoing for the cutting device of the mentioned patent application will be indicated using the same references.

The improved pneumatic cutting device (100) therefore comprises a body (C), a cutting blade (L) for cutting a leather sheet stretched on a work plane (leather sheet and work plane not illustrated).

The improved pneumatic cutting device (100) in this regard is predisposed and configured so as to be mountable on cutting machines, for example numerically controlled.

It is predisposed in such a way as to pneumatically activate the cutting blade (L) in order that it can oscillate vertically so as to score and cut the leather sheet.

Figures from 3A to 3C illustrate, in frontal views, the pneumatic cutting device (100), with the cutting blade (L) represented in different operating configurations attainable during oscillation thereof, respectively a lower cutting position (L1 ) (figure 3A), in which the cutting blade (L) crosses the whole thickness of the leather, an intermediate cutting position (LM) (figure 3B) in which the cutting blade (L) is internal of the thickness of the leather sheet, and an upper cutting position (L2) (figure 3C), in which the cutting blade (L) is substantially at the top of the leather sheet or slightly extracted from the leather.

The improved pneumatic cutting device (100) is also provided, internally of the body (C), with an oscillating chamber (1 ), with an upper end-run wall (11 ) and a lower end-run wall (12), and an oscillating piston (10), having a head (13) and a rod (14), which is predisposed with the head (13) thereof inserted in the oscillating chamber (1 ), between the upper end-run wall (11 ) and the lower end-run wall (12), the rod (14) being connected to the cutting blade (L).

When the head (13) of the oscillating piston (10) has reached abutment against the lower end-run wall (12) of the oscillating chamber (1 ), i.e. the cutting blade (L) is in the lower cutting position (L1 ), (see figure 4A), while when the head (13) of the oscillating piston (10) is in abutment against the upper end-run wall (11 ) of the oscillating chamber (1 ) the cutting blade (L) is in the upper cutting position (L2) (see figure 4C).

The upper end-run wall (11 ) is predisposed in the body (C) at a distance with respect to the lower end-run wall (12) which is such that when the head (13) of the oscillating piston (10) reaches contact with the upper end-run wall (11 ), the cutting blade (L) reaches an upper cutting position (L2) such that it remains substantially in contact with, or slightly extracted from, the leather sheet to be cut, with the purpose of guaranteeing continuity of the cutting operation.

For the pneumatic activating of the oscillation of the oscillating piston (10) in the relative oscillating chamber (1 ), and thus for the vertical oscillation of the cutting blade (L), the improved pneumatic cutting device (100) is provided with a relative pneumatic activating system (P) communicating with the oscillating chamber (1 ). The pneumatic activating system (P) comprises a pneumatic supply source (for example compressed air), denoted schematically by arrow (P1 ), and upper discharge (S1 ) and a lower discharge (S2), which communicate with the outside. The body (C) comprises a cylindrical cavity (16) while the rod (14) of the oscillating piston (10) is predisposed so as to be slidable alternatingly in the cylindrical cavity (16).

Further, the rod (14) of the oscillating piston (10) is conformed so as to have: two annular portions (141 , 142), the upper annular portion (141 ) and the lower annular portion (142), in sliding contact with the walls of the cylindrical cavity (16), an annular recess (140), which is comprised between the two annular portions (141 , 142), and an internal conduit (17).

The rod (14) is further provided with through-holes (18) which are predisposed along the rod (14) in a position below the lower annular portion (142) and such as to place the internal conduit (17) in contact with the outside of the rod (14).

The head (13) of the oscillating piston (10) is provided in turn with at least a hole (130) predisposed so as to place the internal conduit (17) of the rod (14) in communication with the part (1 B) of the oscillating chamber (1 ) comprised between the head (13) of the oscillating piston (10) and the upper end-run wall (11 ) of the oscillating chamber (1 ).

The pneumatic activating system (P) is predisposed and configured in the following way.

It comprises:

a switching chamber (8) of the oscillation of the oscillating piston (10) which comprises an upper annular chamber (8A) and a lower annular chamber (8B) realised in a portion of the walls of the cylindrical cavity (16);

a main conduit (81 ) which is realised and predisposed in the body (C) so as to be in communication with the pneumatic supply source (P1 ) and with a part of the lower annular chamber (8B) of the switching chamber (8);

a secondary conduit (82) realised and predisposed in the body (C) so as to place the upper annular chamber (8A) of the switching chamber (8) in communication with the oscillating chamber (1 ) via a passage hole (83) realised in the lower end- run wall (12) of the oscillating chamber (1 ).

The upper discharge (S1 ) is made in a portion of the walls of the cylindrical cavity (16) above the upper annular chamber (8A) of the switching chamber (8), and communicating with the outside via a first discharge conduit (92) also realised and predisposed in the body (C).

In turn, the lower discharge (S2) is made in a portion of the walls of the cylindrical cavity (16) below the lower annular chamber (8B) of the switching chamber (8), and communicates with the outside via a second discharge conduit (94) realised and predisposed in the body (C).

Further, the annular recess (140) of the rod (14) has dimensions so that, and with the holes (18) of the rod (14) being positioned with respect to the annular recess (140) in such a way that, with the alternating sliding of the rod (14) in the cylindrical cavity (16) the following conditions occur:

when the annular recess (140) of the rod (14) is positioned at the switching chamber (8) so as to place the lower annular chamber (8B) in communication with the upper annular chamber (8A), the holes (18) of the rod (14) are positioned at the lower discharge (S2) (see figure 4A), so that the main conduit (81 ) is in communication, via the lower annular chamber (8B), the annular recess (140) and the upper annular chamber (8A), with the secondary conduit (82) and therefore the pneumatic supply source (P1 ) is in communication with the part (1A) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the lower end-run wall (12) (see the arrows in unbroken lines in figure 4A), while the part (1 B) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the upper end-run wall (11 ) is in communication with the lower discharge (S2), and therefore via the second discharge conduit (94) with the outside, via the hole (130) of the head (13) of the piston (10), the internal conduit (17) of the rod (14) and the holes (18) of the rod (14) (see the arrows in broken lines in figure 4A), so that the oscillating piston (10) can be pneumatically pushed upwards;

and when the annular recess (140) of the rod (14) is positioned both at the upper discharge (S1 ) and at the upper annular chamber (8A) of the switching chamber (8) communicating with the secondary conduit (82), the holes (18) of the rod (14) are at the lower annular chamber (8B) of the switching chamber (8) and thus in communication with the main conduit (81 ) (see figure 4C), so that the pneumatic supply source (P1 ), via the main conduit (81 ), the holes (18) of the rod (14), the internal conduit (17) of the rod (14) and the hole (130) present in the head (13) of the oscillating piston (10), is in communication with the part (1 B) of the oscillating chamber (1 ) between the upper end-run wall (11 ) and the head (13) of the oscillating piston (10) (see the arrows in unbroken line in figure 4c), while the part ( A) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the lower end-run wall (12) is in communication with the upper discharge (S1 ) via the secondary conduit (82), the upper annular chamber (8A) of the switching chamber (8) and the annular recess (140), and therefore through the first discharge conduit (92) with the outside (see the arrows in broken line in figure 4C), so that the oscillating piston (10) can be pneumatically pushed downwards.

Figure 4B illustrates instead the situation in an intermediate position of the rod (14) of the oscillating piston (10) with respect to the end positions illustrated in figures 4A and 4C, con figure 4A illustrating the head (13) of the oscillating piston (10) in abutment against the lower end-run wall (12), while figure 4C illustrates the head (13) of the oscillating piston (10) in abutment against the upper end-run wall (1 ). In the position of figure 4B, the upper discharge (S1 ) is closed by the upper annular portion (141 ) of the rod (14) above the annular recess (140), while the lower annular chamber (8B), communicating with the main conduit (81 ), is closed by the lower annular portion (142) of the rod (14) below the annular recess (140). Consequently the oscillating piston (10) can continue in the downwards run thereof, if starting from the configuration illustrated in figure 4C, or can continue in the upward runs, if starting from the configuration of figure 4A.

The improved pneumatic cutting device (100) of the present invention further comprises the following special characteristics which enable attaining the above- described aims and obviating the drawbacks highlighted in the cases in which very high oscillation frequencies are desired.

The improved pneumatic cutting device (100) comprises an auxiliary chamber (3) which is realised in the body (C) in a position below the lower discharge (S2), and which is in communication in the upper part thereof with the lower discharge (S2). For example the auxiliary chamber (3) can be realised in such a way that the relative upper part is directly in communication with the lower discharge (S2), as illustrated in figures from 4A to 4C, or is placed in communication with the lower discharge (S2) via a relative connecting conduit.

The improved pneumatic cutting device (100) is such as to comprise a connecting conduit (31 ) which is realised in the body (C) and which is predisposed in the body (C) in such a way as to place the lower part of the auxiliary chamber (3) with a part of the upper annular chamber (8A) of the switching chamber of the pneumatic activating system (P).

Lastly, the improved pneumatic cutting device (100) is made in such a way that the rod (14) of the oscillating piston (10) comprises an annular projection (33) which is made in the rod (14) in a position below holes (18) afforded in the rod (14) and such that the annular projection (33) is arranged intemally of the auxiliary chamber (3).

The annular projection (33) is dimensioned in such a way as to be in sliding contact with the internal walls of the auxiliary chamber (3).

In particular, the annular projection (33) is realised on the rod (14) in a position such that:

when the head (13) of the oscillating piston (10) is in abutment against the lower end-run wall (12) of the oscillating chamber (1 ), the annular projection (33) of the rod (14) is in a lower end-run position (A1 ) internally of the auxiliary chamber (3) so as to leave a lower part of the auxiliary chamber (3) in communication with the connecting conduit (31 ) (see figure 4A);

and when the head (13) of the oscillating piston (10) is in abutment against the upper end-run wall (11 ) of the oscillating chamber (1 ), the annular projection (33) of the rod (14) is in an upper end-run position (A2) internally of the auxiliary chamber (3) so as to interrupt the communication between the auxiliary chamber (3) and the lower discharge (S2) (see figure 4C).

These special characteristics of the improved pneumatic cutting device (100) of the present invention enable obtaining the following advantages.

Let us consider, as the starting point, the one illustrated in figure 4C, with the head (13) of the oscillating piston (10) in abutment against the upper end-run wall (11 ) of the oscillating chamber (1 ).

The holes (18) of the rod (14) of the oscillating piston (10) are at the lower annular chamber (8B) of the switching chamber (8) and therefore communicating with the main conduit (81 ) (the internal conduit (17) of the rod (14) is therefore in communication, via the holes (18), with the main conduit (81 )), and when the annular recess (140) of the rod (14) is positioned both at the upper discharge (S1 ) and at the upper annular chamber (8A) of the switching chamber (8) and therefore the upper discharge (S1 ) is communicating with the secondary conduit (82).

In this situation, the main conduit (81 ), via the lower annular chamber (8B) of the switching chamber (8), the holes (18) of the rod (14), the internal conduit (17) of the rod (14) and the hole (130) present in the head (13) of the oscillating piston

(10) , is in communication with the second part (1 B) of the oscillating chamber (1 ) comprised between the head (13) of the oscillating piston (10) and the upper wall

(1 1 ) of the oscillating chamber (1 ), while the first part (1A) of the oscillating chamber (1 ) below the head (13) of the oscillating piston (10) is connected, via the passage hole (83), the secondary conduit (82), the upper annular chamber (8A) of the switching chamber (8) and the annular recess (140) of the rod (14), with the upper discharge (S1 ), and thus communicating with the outside.

The auxiliary chamber (3), via the connecting conduit (31 ), is in communication with the upper annular chamber (8A) of the switching chamber (8), and therefore, via the annular recess (140) of the rod (14), is in communication with the upper discharge (S1 ) and thus with the outside, and also with the part (1A) of the oscillating chamber (1 ) between the head (13) of the oscillating piston (10) and the lower end-run wall (12).

Consequently air can flow into the connecting conduit (31 ) (see the arrows in broken line in figure 4C) and reach and fill the part of the auxiliary chamber (3) below the annular projection (33) of the rod (14) which is located in the upper end- run position (A2) in the auxiliary chamber (3).

The pneumatic flow in arrival from the pneumatic supply source (P1 ), when flowing through the main conduit (81 ), reaches the lower annular chamber (8B) of the switching chamber (8), and as it passes from the holes (18) of the rod (14), flows through the internal conduit (17) of the rod (14) and crosses the hole (130) in the head (13) of the oscillating piston (10) to arrive in the part (1B) of the oscillating chamber (1 ), above the head (13) of the oscillating piston (10).

As the first part (1A) of the oscillating chamber (1 ) below the head (13) of the oscillating piston (10) is connected, via the passage hole (83), the auxiliary conduit (82), the upper annular chamber (8A) of the switching chamber (8) and the annular recess (140) of the rod (14), with the upper discharge (S1 ), the oscillating piston (10) is pushed downwards, with a contemporaneous downwards sliding of the rod (14) thereof in the cylindrical cavity (16) and a downwards displacement of the cutting blade (L).

The downwards sliding of the rod (14) of the oscillating piston (10) also determines the downwards displacement of the annular projection (33) internally of the auxiliary chamber (3).

The air present internally of the auxiliary chamber (3) below the annular projection (33) is thus compressed, constituting a sort of air cushion which slows the run of the rod (14) and, consequently, slows the descent of the head (13) of the oscillating piston (10) towards the lower end-run wall (12) of the oscillating chamber (1 ).

In the transition from the configuration of figure 4C and that of figure 4A, in which the head (13) of the oscillating piston (10) is in abutment against the lower end-run wall (12) of the oscillating chamber (1 ), in fact, as illustrated in figure 4B, the downwards sliding of the rod (14) is such that the upper annular portion (141 ) of the rod (14) closes the upper discharge (S1 ) and thus the communication with the outside of the part of the auxiliary chamber (3) is interrupted below the annular projection (33) which is descending downwards. Therefore, the air still present in this part of auxiliary chamber (3) is compressed by the further descent of the annular projection (33), constituting an air cushion, which contributes to slowing the descent of the head (13) of the oscillating piston (10) into the oscillating chamber (1 ), reducing the relative kinetic energy thereof. Consequently, the head (13) of the oscillating piston (10) will strike with less force against the lower end-run wall (12) which, therefore, will be subject to a lower degree of wear.

When the head (13) of the oscillating piston (10) has reached abutment against the lower end-run wall (12) of the oscillating chamber (1 ), i.e. the cutting blade (L) which is in the lower cutting position (L1 ), as illustrated in figure 4A, the following situations occur.

The rod (14) of the oscillating piston (10), with respect to the cylindrical cavity (16) of the body (C), is located in a position such that the annular recess (140) of the rod (14) is positioned at the switching chamber (8) so as to place the lower annular chamber (8A) and the upper annular chamber (8B) in mutual communication, while the holes (18) of the rod (14) are positioned at the lower discharge (S2). In this way, the main conduit (81 ), via the lower annular chamber (8B), the annular recess (140) of the rod (14), and the upper annular chamber (8A), is in communication with both the auxiliary conduit (82) and with the connecting conduit (31 ), as both are in communication with the upper annular chamber (8A).

Therefore, the source of pneumatic supply source (P1 ), via the main conduit (81 ), the lower annular chamber (8A), the annular recess (140) and the upper annular chamber (8B), the secondary conduit (82) and the passage hole (83), is in communication with the first part (1A) of the oscillating chamber (1 ) comprised between the head (13) of the oscillating piston (10) and the lower wall (12) of the oscillating chamber (1 ), and, at the same time, via the upper annular chamber (8B) and the connecting conduit (31 ), it is in communication with the lower part of the auxiliary chamber (3) below the annular projection (33) of the rod (14).

The part (1 B) of the oscillating chamber (1 ) comprised between the head (13) of the oscillating piston (10) and the upper wall (11 ) of the oscillating chamber (1 ), via the holes (130) of the head (13), the internal conduit (17) of the rod (14) and the holes (18) of the rod (14) itself, is instead in communication with the lower discharge (S2).

In this way, the pneumatic flow of compressed air coming from the pneumatic supply source (P1 ) then reaches both the first part (1A) of the oscillating chamber (1 ), below the head (13) of the oscillating piston (10), and in the lower part of the auxiliary chamber (3) below the annular projection (33) of the rod (14) (see the arrows in the unbroken line of figure 4A).

As the part (1 B) of the oscillating chamber (1 ), above the head (13) of the piston (10), is connected to the lower discharge (S2), the pneumatic flow can push the oscillating piston (10) upwards with a thrusting action that is exerted on the lower part of the head (13) of the oscillating piston (10) and also a thrusting action that is exerted on the lower part of the annular projection (33) of the rod (14).

Consequently, a supplementary upwards thrust is exerted on the rod (14) of the oscillating piston (10), which enables more rapid inversion of the oscillation of the piston from the lower endrun towards the upper endrun, and at the same time enables overcoming any resistance that the leather sheet might exert on the cutting blade.

The upwards push that the compressed air exerts, on the lower part of the annular projection (33) of the rod (14), encounters no resistance from any air present in the upper part of the auxiliary chamber (3) above the annular projection (33), as the upper part of the auxiliary chamber (3), as mentioned above, is in communication with the lower discharge (S2) and therefore with the outside.

The oscillating piston (10) is thus pushed upwards, with a contemporaneous upwards sliding of the rod (14) thereof in the cylindrical cavity (16) and an upwards displacement of the cutting blade (L): when the head (13) of the oscillating piston (10) reaches abutment against the upper end-run wall (1 1 ) of the oscillating chamber (1 ), the cutting blade (L) reaches the upper cutting position thereof (L2), while the upwards sliding of the rod (14) in the cylinder (16) of the body (C) newly determines the situation illustrated in figure 4C and described in the foregoing, with the inversion of oscillation of the piston from the upper endrun to the lower endrun.

The predisposing of the auxiliary chamber (3) below the lower discharge (S2), and communicating there-with, of the annular projection (33) on the rod (14) in such a position that the annular projection (33) is arranged in the auxiliary chamber (3), in sliding contact with the relative internal walls, and the presence of the connecting conduit (31 ), in order to place the lower part of the auxiliary chamber (3), below the annular projection (33) of the rod (14), with the upper annular chamber (8A) of the switching chamber (8) of the pneumatic activating system (P), thus enables a double technical advantage.

Firstly, as described in the foregoing, it is possible to slow down the run of the oscillating piston when it is pushed downwards, and therefore, consequently, to reduce the energy with which it impacts against the lower end-run wall, with a consequent advantage in terms of less wear.

Secondly, at the moment when the oscillating piston has reached abutment against the lower end-run wall, and thus at the moment when the inversion of the oscillation of the piston is to be effected, from the lower run towards the upper run, it is possible to exert on the oscillating piston a supplementary upwards thrust, which makes the inversion of the oscillation more rapid and immediate, including against any eventual resistance exerted on the cutting blade by the type and thickness of the leather sheet.