WO2019082110A1

WO2019082110A1 - Laser cutting head for machine tools

Info

Publication number: WO2019082110A1
Application number: PCT/IB2018/058320
Authority: WO
Inventors: Nicola MENEGHETTI; Enzo Gesuita
Original assignee: Salvagnini Italia S.P.A.
Priority date: 2017-10-26
Filing date: 2018-10-25
Publication date: 2019-05-02
Also published as: IT201700121656A1

Abstract

A laser cutting head (1), powerable by a laser emitting apparatus through optical transmission means (41) and associable to a machine tool, includes a collimating group (2) to collimate a laser beam (L) coming from the laser emitting apparatus and comprising at least one collimating lens (3) and a supporting element (4) that supports the collimating lens (3) and is movable along an adjusting direction (X); a focusing group (5) for focusing the laser beam (L) coming out from the collimating group (2); casing means (15, 16; 55) which forms an internal space (20) containing the collimating group (2) and the focusing group (5); actuator means (7; 17; 27) connected to the supporting element (4) with the collimating lens (3) in order to move them along the adjusting direction (X) and adjust a focal point of the laser beam (L) coming out from the focusing group (5); the supporting element (4) has an internal through cavity (40) for the passage of the laser beam (L), a first end (4a) that supports the collimating lens (3) inside the internal through cavity (40) and a second end (4c); sealing means (21, 22) connects the first and the second end (4a, 4c) to internal walls of the casing means (15, 16; 55) and is configured to enable the supporting element (4) to be movable along the adjusting direction (X); the sealing means (21, 22), the supporting element (4) and the internal walls of the casing means (15, 16; 55) form inside the internal space (20) a first chamber (20a) containing the collimating lens (3) and focusing group (5), and a second chamber (20b), containing the actuator means (7; 17, 27); the first chamber (20a) is closed and hermetically separated from the second chamber (20b) and from an external environment.

Description

Laser cutting head for machine tools

The invention concerns laser cutting devices for cutting machine tools, and in particular relates to a laser cutting head for use in a optical fibre laser cutting system in a cutting and/or punching machine tool for sheet metals.

In the field of machine tools for processing sheet metal and metal plates, the use of laser systems to cut, engrave and weld the pieces is well known and widespread.

As is known, the laser is a device capable of emitting, by means of a process of stimulated emission, a monochromatic light beam which is coherent in space namely concentrated in a rectilinear beam and having very high brightness (luminance). The possibility of concentrating a large amount of energy in a very small area allows the laser device to cut, engrave and weld metals. Metal materials are typically cut by vaporisation, and especially by fusion. In the latter case, the laser beam leads to the fusion of a small point of the metal and the fused metal (scum) is removed by a blow or jet of gas.

Different types of laser sources can be used to generate a beam of light which is suitable for cutting metals. Typically gas lasers are used (carbon dioxide C0₂, monoxide) and solid state lasers (laser diodes with doped glass and fibre lasers).

In machine tools, the high energy levels required for cutting sheet metals, also of great thickness, the dimensions and weight of the laser emitter apparatuses are such to prevent their placement on the machine. The laser beam is therefore focused on work pieces by a laser cutting head or focusing head which is connected to the emitting apparatus through an optical chain (C0₂ laser) or a transmission fibre (optical fibres, for example in YAG laser diodes). In virtue of its reduced dimensions and contained weight, the laser cutting head can in fact be moved by the machine tool with precision and speed to perform the cutting of the product.

In the so-called fibre laser cutting systems, in which a optical fibre cable is used to bring the laser beam to the cutting head, the latter typically comprises an optical collimating group that transmits the light beam coming out from the optical fibres to an optical focusing group capable of focusing the collimated laser beam on the piece to be cut.

The focused laser beam or ray comes out from the cutting head through a nozzle which concentrates the blow or jet of gas used to remove the scums generated by the fusion of the metal and limit the likelihood that the same can reach the focusing group. For this purpose, a transparent element or glass is provided at the nozzle, that separates the inside of the cutting head from the outside and allows the passage of the laser beam output by the optical focusing group. The latter makes it possible to focus the laser beam, that is, position its focal point or focus on a given point on the surface of the piece to be cut, or just below the surface.

The exact positioning of the focal point in which all the power of the laser beam is concentrated is required to perform the correct cutting of the material.

The optical focusing group typically comprises a focusing lens mounted on a drawer or lens-slide, movable along an adjusting direction which is parallel to the direction of the laser beam so as to allow it to focus. More precisely, the lens drawer is moved by a respective actuator that is controlled as a function of the distance between the cutting head and the surface of the piece, this distance being detected by a suitable sensor mounted on the same cutting head. The surface of the piece (for example a very large sheet) is in fact generally irregular, non-planar, curved.

Further laser cutting heads for machine tools are known in which the correct focusing of the laser beam, that is, the positioning of the focal point on the piece, is carried out by suitably moving the lens, or one of the lenses, of the optical collimating group, which is mounted on a respective drawer or lens-slide that is linearly movable. In this case, the focusing lens can be kept stationary.

In both configurations of the cutting head, the focusing lens or collimating lens and its relative lens-drawer are housed inside the cutting head, in a chamber that is suitably closed and separated from the external environment so as to prevent the entry of contaminants and foreign objects (in particular the scums generated by the cutting) which might dirty the lenses and therefore alter their optical characteristics.

The actuator which moves the lens -drawer is generally positioned on the outside of the chamber and connected to said drawer by means of mechanical connection elements that pass through one or more openings of the cutting head.

Suitable seals are provided at said openings to prevent the entry of contaminants and foreign objects in the internal chamber. However, the seals do not ensure the hermetic closure of the internal chamber, especially in cases of prolonged and intensive use of the cutting head, both because of their configuration and shape that must allow the linear sliding of the supporting elements and because of the degradation of the material subjected to heavy operating conditions. Periodically it is therefore necessary to clean the internal chamber and the focusing lens to remove any particles and scum which have penetrated therein.

Cooling systems are provided to cool the cutting head and in particular the focusing lens. A small fraction of the energy of the laser beam that passes through the lenses (collimating and focusing lenses) is indeed absorbed and converted into heat for several reasons, mainly due to the non-absolute transparency of the optics (coating and substrate). The heat generated by prolonged use causes a rise in the temperature of the entire head and in particular of the focusing lens, which is also very close to the piece to be processed, that is, the melting area of the same.

This increase in temperature causes a variation in the refractive index of the lens itself and therefore a shift of the focus. This phenomenon, commonly known with the term "thermal focus shift", then makes it impossible for the cutting system to focus the laser beam in the desired and optimal point on the surface of the piece, with a consequent decay of cutting characteristics up to the impossibility to perform the cutting itself.

The increase in temperature can also cause damages to the surface layer generally provided on the surfaces of the lenses, causing a further variation in the optical characteristics of the latter ones.

To resolve this problem, cooling systems are known which provide for the introduction of gas (typically nitrogen) at controlled temperatures inside the focusing head so as to lap and thus cool the focusing lens.

The external cooling of the casing of the head that encloses the focusing group is not in fact sufficient to ensure adequate cooling of the focusing lens.

However, the cooling systems with gas flow have the disadvantage of requiring the use of expensive technical gases (for example nitrogen) that are free of contaminants. Particles or foreign objects or contaminants contained in the gas can in fact settle on the focusing lens causing, in addition to a variation of the optic refractive index, absorption of the energy of the laser beam and therefore a reduction in the power available for cutting. Furthermore, due to the intense energy absorption at the areas where particles and contaminants have deposited, with a consequent increase in the local temperature, over time and with use the lens is damaged up to its destruction.

Moreover, said systems are rather complex and expensive to manufacture and require periodic maintenance.

An object of the present invention is to improve the known laser cutting heads for cutting machine tools, and in particular the cutting heads for optical fibre laser cutting systems. Another object is to provide a laser cutting head capable of ensuring effective and optimal isolation from an external environment to an internal chamber containing the optical collimating and focusing groups of the laser beam, so as to prevent the entrance therein of contaminating elements and particles, in particular solid and gaseous scum generated by laser cutting.

A further object is to obtain a laser cutting head which makes it possible to simply and effectively cool the optical collimating and focusing groups in the internal chamber, also with intense and prolonged use.

A further object is to provide a laser cutting head having a compact shape and particularly limited dimensions.

These and other objects are achieved by a laser cutting head according to the claims below. The invention can be better understood and implemented with reference to the accompanying drawings that illustrate a non-limiting exemplary embodiment, in which:

- figure 1 is a schematic sectional view of the laser cutting head of the invention;

- figure 2 is an enlarged detail of the laser cutting head of figure 1 which shows a collimating group of the laser beam and relative actuator means;

- figure 3 is a sectional view of another embodiment of the laser cutting head of the invention;

- figure 4 is an enlarged and partial view of a variant of the laser cutting head of figure 3;

- figure 5 is an enlarged and partial view of another variant of the cutting head of figure 3. With reference to figure 1, a laser cutting head 1 is shown according to the invention which can be powered by a laser emitting apparatus, of known type and not shown in the figures, through optical transmission means 41 and associable with a machine tool to perform cutting, engraving and welding on a piece 50. In particular, the emitting apparatus is a stimulated emission apparatus of a solid-state laser type and the optical transmission means 41 comprises an optical fibre cable capable of transporting the laser beam generated by the emitting apparatus to the laser cutting head 1.

The laser cutting head 1 comprises a collimating group 2 to collimate the laser beam L coming from the laser emitting apparatus and a focusing group 5 to focus the laser beam L coming out collimated from the collimating group 2.

The collimating group 2 comprises at least a collimating lens 3 and a supporting element 4 suitable to support the collimating lens 3 and movable along an adjusting direction X, which is substantially parallel to the direction of the laser beam coming out from the optical transmission means 41.

The focusing group 5 comprises at least one focusing lens 6 supported by a further supporting element 24. The laser beam L extends axially inside the laser cutting head 1 by a first input opening 39, coupled to the optical transmission means 41, to a second output opening 31 placed at a cutting nozzle 30. The collimating lens 3 and the focusing lens 6 are thus aligned along an optical axis F of the laser beam L and the adjusting direction X is parallel to the latter. The laser cutting head 1 further comprises casing means 55 which forms an internal space 20 adapted to contain the collimating group 2, the focusing group 5 and actuator means 7 connected to and suitable to move the supporting element 4 with the collimating lens 3 along the adjusting direction X, in order to adjust a focal point of said laser beam L coming out focused from the focusing group 5.

In the illustrated embodiment, the casing means comprises a single casing 55 which forms an internal space 20, closed and hermetically isolated, that is air-tight, from an external environment wherein the laser cutting head 1 is located. The casing means 55 therefore prevents the entrance inside the laser cutting head 1, inside the internal space 20, of contaminants and foreign elements, in particular scums and solid and gaseous residues generated by laser cutting, which could dirty the lenses of the collimating group 2 and focusing group 3. For this purpose, the casing means 55 is provided only with a first input opening 39 coupled to the optical transmission means 41, which allows entrance into the internal space 20 of the laser beam L generated by the emitting apparatus, and with a second output opening 31 placed at a cutting nozzle 30 and sealingly closed by a separating glass 32, as better explained in the following description, which allows the transmission of the laser beam collimated and focused by the laser cutting head 1. The casing means 55 does not have additional openings or holes for the passage of electrical or mechanical connection elements.

The actuator means 7 is entirely contained inside the internal space 20 and comprises, for example, a linear electromagnetic actuator 7 of the movable plunger type, which includes a fixed or static armature 8 which houses two coils or solenoids 8a powered by electric current and is fixed to a side wall of the casing means 55 and a movable armature 9, so- called core or plunger, which is provided with at least a body 9a made of ferromagnetic material and is integrated and formed by a portion of the supporting element 4. In other words, the body 9a is directly fixed to an external wall of the supporting element 4, which therefore acts as a movable armature.

It is also envisaged that the movable armature 9 is a distinct component fixed to the supporting element 4 by fixing means of a known type. In one variant of the laser cutting head 1 not shown in the figures, the fixed armature 8 is also integrated into, or formed by, the internal wall of the casing means 55 from which the polar expansions for the coils 8a extend radially toward the inside.

The movable armature 9 (that is, the supporting element 4) is linearly moved along the adjusting direction X when it is subjected to opposed magnetic fields generated by the two antagonist coils 8a, powered by electric current. By modulating and controlling the parameters of the electric current (intensity, voltage and frequency), it is possible to change the magnetic fields of the two antagonist coils 8a so as to adjust the direction and magnitude of the displacements of the movable armature 9, and therefore of the supporting element 4 and the collimating lens 3, along the adjusting direction X. In this way it is possible to adjust the focal point of the laser beam L on the piece 50 to be processed, as better explained in the following description.

Linear guiding means 11 is fixed to an internal wall of the casing means 55 to slidably support and guide the supporting element 4 along the adjusting direction X, preventing movements and/or oscillations that are transverse to this adjusting direction X which would cause a shift of the focal point of the laser beam L and/or a modification of the size and/or shape of this focal point on the piece 50.

The linear guiding means comprises, for example, a guiding bush 11 provided with spheres 12, in particular spheres made of ceramic material with low friction, slidable on an external wall 4b of the supporting element 4. The latter has an internal through cavity 40 for the passage of the laser beam L output from the optical transmission means 41. The supporting element 4, which has for example a hollow tubular shape, has a first end 4a, in particular furthest from the optical transmission means 41, adapted to support the collimating lens 3 inside the internal through cavity 40, and a second end 4c, in particular closest to the optical transmission means 41 and facing a connector 42 that connects the aforesaid optical transmission means 41 to the casing means 55.

It has to be noted that the guiding bush 11 with the spheres 12 made of ceramic material with low friction does not require for its operation, that is, for the linear sliding of the supporting element 4, the use of lubricants which could contaminate and dirty the lenses 3, 6. In addition, when the ceramic spheres 12 roll on the external wall 4b of the supporting element 4, they substantially do not generate particles that could also contaminate the internal space 20 of the laser cutting head 1.

The laser cutting head 1 also comprises anti-rotation means, of a known type and not shown in detail in the figures, housed inside the casing means 55 and arranged to prevent the supporting element 4 from rotating about an axis parallel to the adjustment direction X when moved by the actuator means 7. The rotation of the collimating lens 3 can in fact cause a shift of the focal point of the laser beam L and a variation in the size and/or shape of this focal point on the piece 50.

A position sensor 23 is provided inside the casing means 55 to measure the linear displacement of the supporting element 4 along the adjusting direction X. In this way, thanks to the position sensor 23, a control unit of the machine tool is able to perform a feedback control of the actuator means 7 which makes it possible to correctly position the collimating lens 3, that is the focal point of the laser beam on the piece 50. The position sensor 23 is, for example, an inductive sensor capable of detecting the position of a measuring element of an elongated shape along the adjusting direction X and fixed to an external wall of the supporting element 4. The position sensor 23 can however comprise an optical sensor.

The laser cutting head 1 of the invention further includes sealing means 21, 22 arranged to connect the ends 4a, 4c of the supporting element 4 to internal walls of the casing means 55 and configured to enable the supporting element 4 to be movable along the adjusting direction X. The sealing means 21, 22, the supporting element 4 and the internal walls of the casing means 55 form inside the internal space 20 a first chamber 20a containing the collimating lens 3 and the focusing group 5 and a second chamber 20b containing the actuator means 7; the first chamber 20a is closed and hermetically separated from the second chamber 20b and from the external environment. More specifically, inside the casing 55, the sealing means 21, 22 forms and delimits with the supporting element 4 the second chamber 20b with annular shape that houses, in addition to the actuator means 7, the guiding means 11, the position sensor 23 and the anti-rotation means.

The first chamber 20a, which includes the internal through cavity 40, formed by the supporting element 4 and containing the collimating lens 3, and the volume of the internal space 20 that houses the focusing group 5, is hermetically separated, that is, isolated from the second chamber 20b. In this way, any particles, foreign objects and contaminants, for example already present in the actuator means 7, guiding means 11, position sensor 23 and anti-rotation means in a step of mounting and assembling the laser cutting head 1, cannot reach and contaminate the collimating lens 3 and the focusing lens 6.

The sealing means 21, 22 comprises, for example, a first bellow gasket 21 and a second bellow gasket 22, in particular formed by respective cylindrical sleeves made of extendible material, for example rubber or silicone. The first bellow gasket 21 connects the first end 4a of the supporting element 4 to an internal wall of the casing 55, while the second bellow gasket 22 connects the second end 4c of the supporting element 4 to an internal wall of the casing 55 at the connector 42 of the optical transmission means 41.

Alternatively, the sealing means 21, 22 can comprise respective labyrinth seals formed by the ends 4a, 4c of the sealing element 4 with the internal walls of the casing 55.

Thanks to the sealing means 21, 22 it is therefore possible to ensure the complete isolation of the collimating group 2 and focusing group 5 from the external environment, minimizing the risks that particles and residues can contaminate and dirty the collimating lens 3 and focusing lense 6, thereby making it possible to increase the duration and have optimal performance in time, thus avoiding alterations of optical characteristics.

In this way, in a variant of the laser cutting head of the invention not shown in the figures, the second chamber 20b can be in connection with the external environment, for example, only partially containing the actuator means or for allowing the discharge of heat, since the first sealed chamber 20a ensures the proper isolation of the collimating group 2 and focusing group 5 from the external environment.

The laser cutting head 1 also comprises a further supporting element 24 fixed to an internal wall of the casing means 55 and arranged to support the focusing lens 6 of the focusing group 5. More precisely, the further supporting element 24 comprises a flange fixed to the internal walls of the casing 55 and able to house and support the focusing lens 6.

The laser cutting head 1 also comprises the cutting nozzle 30 fixed to the casing means 55 and through which the focused laser beam comes out. The cutting nozzle 30 concentrates a blow or jet of gas intended to distance the scum generated by the fusion of the work piece and at the same time limits the probability that the aforesaid scum can reach the focusing group 5 and the collimating group 2 inside the laser cutting head 1.

The cutting nozzle 30 is fixed to a lower portion of the casing means 55 that comprises the output opening 31 for the emission of the laser beam L and the separating glass 32 to hermetically close said output opening 31 while allowing the passage of the laser beam L which passes through the cutting nozzle 30 and strikes the work piece 50. The output opening 31 is carried out on a bottom wall 34 of the casing 55. The sealed closure of the output opening 31 through the separating glass 32 is guaranteed by a suitable sealing element 33.

The separating glass 32 together with the further supporting element 24 and the focusing lens 6 forms inside the internal space 20 of the casing means 55 an intermediate chamber 20c arranged to hermetically divide the collimating group 2 from the output opening 31. For this purpose the focusing lens 6 is tightly mounted on the further supporting element 24.

The intermediate chamber 20c constitutes a barrier that is interposed between the external environment (through the output opening 31) and the portion of the internal space 20 wherein the collimating group 2 is contained. In addition to the separating glass 32, the focusing lens 6 with the relative supporting element 24 also form a physical barrier that prevents entry into the laser cutting head 1 of any particles and foreign objects and, in particular, of solid and gaseous scums generated by the fusion of the work piece that could penetrate if the seal between the separating glass 32 and the bottom wall 34 were compromised, for example due to damage or degradation of the sealing element 33.

The laser cutting head 1 of the invention also includes a cooling unit 25 externally fixed to a respective internal wall of the casing means 55 and thermal-conductive means 26 that connects the supporting element 4 to an internal surface of said internal wall of the casing means 55 so as to extract by thermal conduction, through said internal wall of the casing means 55, from the supporting element 4 and the collimating lens 3, the heat generated in the latter when crossed by the laser beam L. For this purpose, the supporting element 4 and at least the respective internal wall of the casing means 55 are made of a material having high thermal conductivity.

The thermal-conductive means comprises at least one flexible thermal-conductive element 26 made of a material with high thermal conductivity, for example a ribbon of braided copper and/or a ribbon coated with graphite sheets or a ribbon of copper coated with a polyimide film (Kapton®). One end of the flexible thermal-conductive element 26 is fixed to a wall of the supporting element 4, while the remaining end is fixed to an internal surface of the internal wall of the casing means 55. The cooling unit 25 is instead fixed to an external surface of said internal wall of the casing means 55 at the end of the flexible thermal-conductive element 26 so as to extract the heat transmitted from the latter to the internal wall of the casing means 55. The flexibility of the thermal-conductive element 26 does not in any way hinder the movement of the supporting element 4 along the adjusting direction X in the operation of the laser cutting head 1.

The cooling unit 25 comprises one or more Peltier cells 37 and a heat sink element 38. The cold side of the Peltier cell 37 is externally fixed to the internal wall of the casing means 55, while the hot side of the Peltier cell 37 is connected to the heat sink element 38.

The laser cutting head 1 of the invention includes a further cooling unit 35 fixed externally to a respective internal wall of the casing means 55, in order to extract from the latter the heat which radiates by conduction from the focusing lens 6, warmed by the heat that is generated when crossed by the laser beam L. For this purpose, the further supporting element 24 and at least the respective internal wall of the casing means 55 are made of a material having high thermal conductivity.

The further cooling unit 35 comprises one or more Peltier cells 37 and a heat sink element 38. The cold side of the Peltier cell 37 is externally fixed to the internal wall of the casing means 55, while the hot side of the Peltier cell 37 is connected to the heat sink element 38. The further cooling unit 35 is also positioned on the wall of the casing means 55 also at said bottom wall 34, so as to extract by thermal conduction the heat that is generated in the separating glass 32 when crossed by the laser beam L. In fact, the heat radiates by conduction from the separating glass 32, through the bottom wall 34, to the wall of the casing means 55, to the exterior thereof the further cooling unit 35 is fixed. In this way, the separating glass 32 can also be cooled and its duration increases considerably.

In a version of the laser cutting head 1 of the invention not shown in the figures, the lenses 3, 6 of the collimating group 2 and focusing group 5 are cooled by a cooling system of a known type which envisages the introduction of gas (typically nitrogen) at controlled temperatures inside the laser cutting head 1 so as to lap and then cool the lenses.

In the operation of the laser cutting head 1 of the invention, the laser beam coming from the laser emitting apparatus through the optical transmission means 41 is collimated by the collimating group 2 toward the focusing group 3 from which said laser beam comes out focused and, through the cutting nozzle 30, strikes the piece 50 to be processed. The correct positioning of the focal point or focus of the laser beam L on the piece 50 to be cut (at a given point of the surface of the piece to be cut or just below said surface) is carried out by appropriately moving the collimating lens 3 along the adjusting direction X, the focusing lens 6 being fixed. This movement can be carried out in a precise and accurate manner by the actuator means 7 inserted and housed inside the casing means 55. Similarly, the guiding means 11 which supports and guides the supporting element 4 of the collimating lens 3 along the adjusting direction X, the anti-rotation means and the position sensor 23 are also housed inside the casing means 55. In this way the internal space 20 can be advantageously hermetically isolated, that is, air-tight separated from an external environment wherein the laser cutting head 1 is. In fact, it should be noted that the only openings envisaged on the casing means are the input opening 39 and the output opening 31 respectively for the input and output of the laser beam, closed by optical transmission means 41 and the separating glass 32. The laser cutting head 1 of the invention is therefore able to ensure the effective and optimal isolation of the internal space 20 containing the collimating group 2 and focusing group 5 of the laser beam L with an external environment, so as to prevent the entrance of either gaseous or solid contaminants and foreign objects, in particular of the scums generated by the cutting, in the laser cutting head itself.

It should also be noted that the actuator means 7, which comprises an electromagnetic actuator with movable plunger, and the guiding means 11, which comprises a guiding bush with ceramic spheres, substantially do not generate particles or debris in operation that can contaminate the internal space 20 of the laser cutting head 1 and thus dirty the lenses 3, 6. Thanks to the cooling unit 25, 35 provided with Peltier cells 37, placed on the exterior of the casing means 55 and connected to the supporting elements 4, 24 of the collimating lens 3 and focusing lens 6, it is possible to effectively extract by thermal conduction the heat generated in the lenses by the crossing of the laser beam L. Since the cooling units 25, 35 are externally fixed to the casing means 55 and extract the heat from the walls of the latter which spread from the lenses 3, 6 through the supporting elements 4, 24 and the thermal- conductive means 26 by thermal conduction, connection openings are not necessary on the casing means and the internal space 20 of the laser cutting head lis isolated from the external environment.

The particular configuration of the laser cutting head 1 of the invention makes it additionally possible to achieve numerous other advantages as described below.

The focusing lens 6 which is fixed and must not be moved to vary and adjust the focal point of the laser beam on the piece 50, can be positioned at a greater distance from the cutting nozzle 30, that is from the same piece 50 being processed(substantially at the maximum amount of adjustment stroke necessary in the case of laser cutting heads with fixed collimating lens). In this way the focusing lens 6 is subjected to a lower thermal gradient due to the heat generated by the fusion of the piece being processed, and its integrity and durability are better preserved.

Consequently also the separating glass 32 can be positioned at a greater distance from the piece 50, where it is more difficultly reached by splashes of melted material of the piece being processed. The duration of the separating glass 32 thus considerably increases and the time intervals between one maintenance service and the next also increases.

The separating glass 32 can also be positioned near the focusing lens 6, which is fixed, at a minimum distance from the latter and such to make it possible to minimize the power density of the laser beam L on said separating glass 32. The laser beam L, which comes out from the focusing lens 6 convergent to obtain the focal point on the piece 50, crosses an area of the separating glass 32 which progressively decreases with the increase of the distance of the latter from the focusing lens 6. At a minimum distance from the focusing lens 6 this area is at its maximum and the power of the laser beam L is distributed on said wider area, causing a lower power density and therefore a lower energy. The separating glass 32 is therefore less stressed from a thermal perspective and its duration increases. As already indicated above, using a fixed focusing lens 6 (mounted on the further supporting element 24), it is also possible to make inside the internal space 20 of the casing means 55 an intermediate chamber 20c that hermetically separates the collimating group 2 from the output opening 31 and is able to block the entry of particles and foreign objects in the laser cutting head 1 if the seal between the separating glass 32 and the relative supporting flange 34 is compromised, for example due to damage or degradation of the sealing element 33. It should also be noted that the two barriers formed, one by the separating glass 32 and the bottom wall 34 of the casing 55 and the other by the focusing lens 6 and the further supporting element 24, are also cooled by the further cooling unit 35. Finally, it is worth noting that the fixed focusing lens 6, in addition to being positioned furthest from the piece 50 being processed, can be positioned closer to the collimating lens 3. The smaller optical path that separates the two lenses makes it possible to obtain greater energy efficiency because of the less power of the laser beam L dispersed around the optical axis of the focusing lens 6.

Figure 3 shows a variant of the laser cutting head 1 of the invention which differs from the embodiment described above only for the fact that it comprises a reflective surface or mirror 10, located in the internal space 20 and interposed between the collimating group 2 and the focusing group 5 and arranged to reflect, in particular at about 90°, toward the focusing group 5 the laser beam L coming from the collimating group 2.

In this variant, the casing means 15, 16 comprises a first casing 15 adapted to contain the collimating group 2 and the actuator means 7 and a second casing 16 adapted to contain the mirror 10 and the focusing group 5. The first casing 15 and the second casing 16 have respective cavities that form the internal space 20. The first casing 15 has a substantially cylindrical shape, while the second casing 16 has the shape of a parallelepiped.

It should be noted that in this variant as well, the casing means 15, 16 prevents the entry into the internal space 20 of contaminants and foreign objects, in particular scums and solid and gaseous residues generated by the laser cutting, which could dirty the mirror 10. The laser beam L passes through the internal space 20 along a first portion parallel to the adjusting direction X (in the first casing 15) and a second portion which is substantially orthogonal to said direction (in the second casing 16) output from the cutting nozzle 30. The operation of this variant of the laser cutting head 1 is identical to that of the embodiment of figure 1.

With reference to figure 4, a further variant of the laser cutting head 1 of the invention is shown which differs from the embodiment described above and illustrated in figure 3, for the actuator means which comprises a linear motor with permanent magnets 17 which includes a fixed armature, or stator, 18 provided with coils 18a and fixed to an internal wall of the casing means 15, 16 and a movable armature 19 provided with permanent magnets 19a and fixed to an external wall of the supporting element 4. In particular, in the illustrated embodiment the movable armature 19 is integrated and formed by a portion of the supporting element 4 and the permanent magnets 19a are fixed directly to an external wall of said supporting element 4.

It is also envisaged that the movable armature 19 is a distinct component fixed to the supporting element 4 by fixing means of a known type.

In a further variant of the laser cutting head 1 not shown in the figures, also the fixed armature 18 of the linear motor with permanent magnets 17 is integrated in, or formed by, the internal wall of the casing means 55. More precisely, the fixed armature 18 is formed by an annular portion of the internal wall of the first casing 15, from which the polar expansions for the coils 18a radially extend toward the inside.

Linear guiding means 11 is fixed to an internal wall of the casing means 15, 16 for slidably supporting along the adjusting direction X the supporting element 4, thereby preventing transverse movements and/or oscillations to this adjusting direction X. The linear guiding means comprises a guiding bush 11 provided with spheres 12, in particular made of ceramic material with low friction, slidable on an external wall 4b of the supporting element 4.

A position sensor 23 is housed inside the casing means 15, 16, in particular the first casing 15, to measure the linear displacement of the supporting element 4 along the adjusting direction X in such a way as to allow a control unit of the machine tool to perform feedback control of the actuator means 17 for correctly positioning the collimating lens 3, that is, the focal point of the laser beam on the piece 50.

Also in this variant of the laser cutting head 1 of the invention, the sealing means 21, 22 in the internal space 20, in cooperation with the supporting element 4 and the walls of the first casing 5, forms and delimits a first chamber 20a and a second chamber 20b. The first chamber 20a contains the collimating lens 3, the mirror 10 and the focusing group 5 and is hermetically separated from the external environment and from the second chamber 20b, of annular shape, which contains the linear motor with permanent magnets 17, the guiding means 11, the position sensor 23, the anti-rotation means and the thermal-conductive means 26 that connects an external wall of the supporting element 4 to an internal surface of an internal wall of the first casing 15.

Figure 5 shows yet another variant of the laser cutting head 1 of the invention, which differs from the embodiments described above for the actuator means which comprises a rotary electric motor 27 fixed to an internal wall of the casing means 15, 16 and acting through screw- screw nut means 43 on the supporting element 4. More precisely, the electric motor 27 includes a fixed armature, or stator, 28 provided with coils 28a powered by electric current, fixed to an internal wall of the casing means 15, 16, and a rotating movable armature, or rotor 29, provided with permanent magnets 29a and connected to the supporting element 4 through the screw-screw nut means 43. More precisely, the movable armature 29 is connected to a nut screw 44 of the screw-screw nut means 43 in order to rotate the latter about a rotation axis parallel to the adjusting direction X.

The screw-screw nut means 43 comprises a ball screw wherein the nut screw 44 is provided with an internal helical groove for the sliding of spheres 46, in particular made of ceramic material, while the supporting element 4 acts as a screw and has on a respective external wall an external helical groove in which the aforesaid spheres 46 slide. The latter are preferably preloaded to reduce any errors and ensure a high level of precision in the transformation of the motion from rotary to linear.

Rolling bearings 45 are interposed between an internal wall of the casing means 15, 16 and the nut screw 44 for rotatably supporting the latter in its rotation.

Anti-rotation means, of known type and not shown in detail in the figures, is provided and housed inside the casing means 15, 16 to prevent the supporting element 4 from rotating with the nut screw 44 about the rotation axis during operation.

A further variant of the laser cutting head 1 of the invention provides that the fixed armature 28 of the rotary electric motor 27 is integrated and formed in the wall of the casing means 15, 16. More precisely, the fixed armature or stator 28 is formed by an annular portion of the wall of the first casing 15, from which the polar expansions for the coils 28a radially extend toward the inside. Similarly, it is also envisaged that the movable armature or rotor 29 is formed by a portion of the nut screw 44, the permanent magnets 29a being fixed directly to an external wall of an end of said nut screw 44.

The operation of the variants of the laser cutting head 1 described above and illustrated in figures 3 to 6 is substantially similar to that of the main embodiment of figures 1 and 2. With particular reference to the variants of the laser cutting head 1 of the invention described above, the actuator means 7, 17, 27 of the supporting element 4 which supports the collimating lens 3 thus comprises linear or rotary electromagnetic actuators wherein the respective fixed armatures 8, 18, 28 which bear the coils 8a, 18a, 28a powered by electric current can be advantageously integrated or formed in an internal wall of the casing means 15, 16, 55. More precisely, one or more annular portions of said internal wall serve as fixed armatures to which the coils can be fixed.

It is also envisaged that the movable armature (fixed or rotor) can be integrated into the supporting element 4, that is, formed by an end portion of said supporting element 4, the permanent magnets being fixed to an external wall of the latter.

These embodiments of the actuator means 7, 17, 27 substantially integrated into the casing means 15, 16, 55 and supporting element 4 of the collimating lens 3 make it possible to simplify the structure of the laser cutting head 1 of the invention and contain its sizes and dimensions. At the same time, the casing means 15, 16, 55 hermetically close the internal space 20.

Claims

1. Laser cutting head (1) powerable by a laser emitting apparatus through optical transmission means (41) and associable to a machine tool, comprising:

- a collimating group (2) to collimate a laser beam (L) coming from said laser emitting apparatus and comprising at least a collimating lens (3) and a supporting element (4) suitable to support said collimating lens (3) and movable along an adjusting direction (X);

- a focusing group (5) to focus said laser beam (L) coming out collimated from said collimating group (2);

- casing means (15, 16; 55) forming an internal space (20) adapted to contain said collimating group (2) and said focusing group (5);

- actuator means (7; 17; 27) connected to, and suitable to move said supporting element (4) with said collimating lens (3) along said adjusting direction (X), in order to adjust a focal point of said laser beam (L) coming out focused from said focusing group (5);

characterized in that said supporting element (4) has an internal through cavity (40) for said laser beam (L) passage, a first end (4a) adapted to support said collimating lens (3) inside said internal through cavity (40) and a second end (4c), and in that sealing means (21, 22) is provided to connect said first end (4a) and said second end (4c) of said supporting element (4) to internal walls of said casing means (15, 16; 55) and configured to enable said supporting element (4) to be movable along said adjusting direction (X), said sealing means (21, 22), said supporting element (4) and said internal walls of the casing means (15, 16; 55) forming inside said internal space (20) a first chamber (20a) containing said collimating lens (3) and said focusing group (5), and a second chamber (20b), containing at least partially said actuator means (7; 17; 27), said first chamber (20a) being closed and hermetically separated from said second chamber (20b) and from an external environment.

2. Laser cutting head (1) according to claim 1, wherein said sealing means comprises a first bellow gasket (21) and a second bellow gasket (22), in particular formed by respective cylindrical sleeves made of extendible material, said first bellow gasket (21) connecting said first end (4a) of said supporting element (4) to a respective internal wall of said casing means (15, 16; 55), said second bellow gasket (22) connecting said second end (4c) of the supporting element (4) to a respective internal wall of said casing means (15, 16; 55).

3. Laser cutting head (1) according to claim 1 or 2, wherein said actuator means (7;17; 27) is completely contained inside said casing means (15, 16; 55), in particular inside said second chamber (20b).

4. Laser cutting head (1) according to any preceding claim, wherein said internal space (20) is closed and hermetically isolated from an external environment.

5. Laser cutting head (1) according to any preceding claim, further comprising a reflecting surface (10) located inside said internal space (20) and interposed between said collimating group (2) and said focusing group (5) to reflect, in particular of about 90°, towards said focusing group (5) said laser beam (L) coming out from said collimating group (2).

6. Laser cutting head (1) according to any preceding claim, wherein said actuator means (7; 17; 27) comprises electromagnetic actuators provided with respective fixed armatures (8; 18; 28), which have coils (8a; 18a; 28a) powered by electric current and are integrated in an internal wall of said casing means (15, 16; 55) and/or provided with respective movable armatures (9; 19; 29), which have permanent magnets (9a;

19a; 29a) and are integrated in said supporting element (4).

7. Laser cutting head (1) according to any preceding claim, wherein said actuator means (7; 17; 27) comprises a linear electromagnetic actuator (7) that includes a fixed armature (8), which houses two coils (8a) powered by electric current and is fixed to an internal wall of said casing means (15, 16; 55), and a movable armature (9), which is provided with at least a body (9a) made of ferromagnetic material and is fixed to said supporting element (4), said movable armature (9) with said body (9a) being linearly moved along said adjusting direction (X) when subjected to magnetic fields generated by said coils (8a).

8. Laser cutting head (1) according to any of claims 1 to 6, wherein said actuator means (7; 17; 27) comprises a permanent magnet linear motor (17) that includes a fixed armature (18) provided with coils (18a) and fixed to an internal wall of said casing means (15, 16; 55) and a movable armature (19) provided with permanent magnets (19a) and fixed to an external wall of said supporting element (4).

9. Laser cutting head (1) according to any preceding claim, further comprising linear guiding means (11) positioned inside said casing means (15, 16; 55) and fixed to an internal wall of the latter to slidably support said supporting element (4) along said adjusting direction (X).

10. Laser cutting head (1) according to any of claims 1 to 6, wherein said actuator means (7; 17; 27) comprises a rotary electric motor (27) that includes a fixed armature (28), which is provided with coils (28a) powered by electric current and is fixed to an internal wall of said casing means (15, 16; 55), and a movable armature (29), which is provided with permanent magnets (29a) and connected to said supporting element (4) through screw-screw nut means (43).

11. Laser cutting head (1) according to any preceding claim, further comprising a further supporting element (24) fixed to an internal wall of said casing means (15, 16; 55) and suitable to support at least a focusing lens (6) of said focusing group (5).

12. Laser cutting head (1) according to claim 11, wherein said casing means (15, 16; 55) comprises an output opening (31) carried out on a bottom wall (34) of said casing means (15, 16; 55) for emitting said laser beam (L) from said laser cutting head (1) and a separating glass (32) to hermetically close said output opening (31) allowing the passage of said laser beam (L), said separating glass (32) together with said further supporting element (24) and said focusing lens (6) forming inside said internal space (20) an intermediate chamber (20c) arranged to hermetically divide said collimating group (2) from said output opening (31).