Patent Publication Number: US-2002003132-A1

Title: Focusing head for a laser machine

Description:
[0001] The present invention relates to a focusing head for a laser machine, for example a machine for laser cutting or welding of metal pieces.  
       [0002] Normally, a laser focusing head comprises a base body carrying a mirror, which, in use, receives a laser beam along a first axis and deflects said beam through 90° along a second axis. A focusing lens receives the laser beam along the second axis and sends a focused laser beam through a beam-exit nozzle.  
       [0003] In laser cutting and welding machines it is often necessary to vary the position of the focused area of the laser beam with respect to the workpiece. At the same time, for process reasons, it is necessary to maintain the distance between the laser-beam exit nozzle and the surface of the workpiece unvaried.  
       [0004] In order to meet the above requirements, laser machines for plane cutting (the so-called 2D applications) have already been built which have a focusing head provided with means that can vary the distance between the focusing area of the laser beam and the beam-exit nozzle. A known solution provided by the present applicant envisages making the body of the head in two distinct sections, one of which carries the nozzle, and the other carries the mirror and the focusing lens. In this known solution, the means for adjusting the position of the focusing area of the laser beam act in such a way as to vary the distance between the aforesaid sections of the body in the exit direction of the laser beam.  
       [0005] The purpose of the present invention is to provide a focusing head of the type specified above which is suitable for processes carried out on three-dimensional pieces (the so-called 3D applications) and which has an improved structure, i.e., one that is simpler and more compact than in the known solution.  
       [0006] According to the present invention, the above purpose is achieved by a laser focusing head having the characteristics that form the subject of the main claim. 
     
    
    
     [0007] The present invention will now be described in detail with reference to the attached drawings, which are provided purely by way of non-limiting example, and in which:  
     [0008]FIG. 1 is a schematic and partially sectioned side view of a laser focusing head according to the present invention;  
     [0009]FIG. 2 is a section according to the line II-II of FIG. 1;  
     [0010]FIG. 3 is a section similar to that of FIG. 2, with the main components exploded;  
     [0011]FIG. 4 is an exploded cross section of the part indicated by the arrow IV in FIG. 3; and  
     [0012]FIGS. 5 and 6 are cross sections respectively illustrating a second embodiment and a third embodiment of a focusing head according to the present invention. 
    
    
     [0013] With reference to FIG. 1, the number  10  designates a laser focusing head according to the present invention. The head  10  is designed to be connected, in a way in itself known, to a mobile element  12  of a laser machine. In the case where the laser machine has a cartesian-type structure, the mobile element  12  can be displaced along three mutually orthogonal directions, designated in FIG. 1 by X, Y and Z. The head  10  can be connected to the mobile element  12  so that it can turn about an axis A, as indicated by the arrow  14 .  
     [0014] The head  10  comprises a base  16  and a body  18 . The base  16  carries a first mirror  20  which is designed to receive a laser beam along the axis A and to deflect it through 90° along an axis B. The body  18  is mounted in such a way that it can turn with respect to the base  16  about an axis B. Control means, in themselves known (not illustrated), are provided for controlling rotation of the body  18  about the axis B, as indicated by the double-headed arrow  22 . The body  18  carries a second mirror  24  which is designed to receive a laser beam along the axis B and to deflect it by 90° along an axis F. In a known way, the mirrors  20 ,  24  are carried by respective supports  26 ,  28 , which are fixed to the base  16  and to the body  18 , respectively.  
     [0015] With reference to FIGS. 2 and 3, a nozzle  30  is fixed, in such a way that it can be removed, to the body  18 . In the example illustrated in the figures, the nozzle  30  is provided with locator pins  32  which insert into corresponding holes made in the body  18 . The nozzle  30  can be fixed to be body  18  by means of screws (not illustrated) which extend in a direction parallel to the axis F, extend through holes made in a flange  34  of the nozzle  30 , and engage respective threaded holes provided in the body  18 . The nozzle  30  has a through opening  36 , in a position corresponding to which, an end element  38  is fixed that comprises a capacitive sensor which is able to detect the distance, in the direction of the beam-exit axis F, between a front surface  40  of the end element  38  and the surface S of a workpiece, indicated by a dashed line in FIG. 2. A lens-holder unit  42  is mounted in the body  18  in such a way that it can move in the direction of the axis F. As illustrated in FIG. 4, the lens-holder unit  42  preferably comprises a first support  44 , a lens  46 , and a second support  48 . The first support  44  and the second support  48  are axially fixed together and withhold the lens  46  in a seat  50  provided in the first support  44 . Fixing together of the two supports  44 ,  48  may be obtained, for example, by means of an external thread  52  of the second support  48  which engages an internal thread  53  of the first support  44 . Preferably housed in the first support  44  is a seal  41  which acts on the lens  46  to create gas-tight contact with the lens  46 .  
     [0016] With reference to FIGS. 3 and 4, the lens-holder unit  42  has an external thread  54 , formed, for example, on the first support  44 , which engages an internal thread  56  of a nut screw  58  carried by the body  18  in such a way that it can turn about the axis F. The nut screw  58  is driven in rotation by an electric motor  60  carried by the body  18 . In the example illustrated in the figures, the drive mechanism between the motor  60  and the nut screw  58  comprises a pinion gear  62  which is mounted on the output shaft of the motor  60  and meshes with an external toothing  64  of the nut screw  58 . It will be understood that rotation of the nut screw  58 , controlled by the motor  60 , brings about a movement of the lens-holder unit  42  along the axis F. This movement causes approach or recession of the lens  46  with respect to the mirror  24  and modifies the distance between the focusing area of the laser beam and the front surface  40  of the end element  38 . This adjustment is useful above all for displacing the focusing area of the laser beam with respect to the workpiece, without, however, varying the distance between the front surface  40  of the end element  38  and the surface S of the piece.  
     [0017] Preferably, the nozzle  30  comprises a seal  66  which establishes gas-tight contact with a tubular portion  68  of the lens-holder unit  42 . During operation, in a way in itself known, into a chamber  70  of the nozzle  30  treatment gas is injected under pressure, which comes out, together with the laser beam, from an opening  72  (FIG. 3) of the end element  38 . The pressurized gas produces a force directed upwards on the lens  46 . This force depends upon the pressure of gas supply and can reach values in the region of 2700 N. One of the advantages of the lens-holder unit according to the present invention lies in the fact that the mechanism of transmission of motion to the lens-holder unit is irreversible. Consequently, the force that acts on the lens  46  is discharged onto the body  18  without producing any displacement of the lens-holder unit  42 . The lens-holder unit  42  is displaced only when there is a positive command sent through the motor  60 ; moreover, the absence of electrical supply to the motor does not modify the pre-existing position of the lens  46 .  
     [0018] The present invention enables adjustment of the position of the focal point of the laser beam by means of a very simple structure and with very small moving parts. The system according to the present invention moreover enables disassembly of the lens-holder unit  42  (for example, in order to replace it with a lens-holder unit of a different type) in an extremely simple way. To disassemble the lens-holder unit  42  it is just sufficient to remove the screws that fix the nozzle  30  to the body  18 , remove the nozzle  30 , and then activate the electrical motor  60  in the direction that produces a displacement downwards of the lens-holder unit. In this way, the lens-holder unit  42  is spontaneously ejected from the body  18  without any need to use tools. Re-assembly of the lens-holder unit is likewise simple, given that it is sufficient to position the new lens-holder unit  42  inside the body  18  and activate the motor  60  in the direction that controls a displacement upwards of the lens-holder unit. Next, the nozzle  30  is mounted and is fixed to the body  18  by tightening the screws provided.  
     [0019]FIGS. 5 and 6 illustrate, respectively, a second embodiment and a third embodiment of a head according to the invention. Items corresponding to those previously described are designated by the same reference numbers.  
     [0020] In the embodiment of FIG. 5, the lens-holder unit  42  is substantially identical to the one described with reference to FIGS.  2 - 4 . The only difference is that, in this case, the lens-holder unit  42  is set between the first mirror  20  and the second mirror  24  and is mobile with respect to the body  18  in the direction of the axis B.  
     [0021] In the embodiment illustrated in FIG. 6, the base  16  carries a sleeve  74  which can turn about the axis B and is controlled by a direct motor  76 . The body  18  carrying the second mirror  24  is mobile with respect to the sleeve  74  in a rectilinear direction coinciding with the axis B. For the movements of rotation about the axis B, the body  18  is integral with the sleeve  74 . A second direct motor  78  controls movement of the body  18  in the direction indicated by the double-headed arrow  80 . The structure of the head illustrated in FIG. 6 is described in detail in the Italian patent application No. TO2000A000252 filed by the present applicant. In the embodiment illustrated in FIG. 6, the focusing lens  46  is fixed with respect to the sleeve  74 . Movement of the second mirror  24  in the direction indicated by the arrow  80  makes it possible to vary the position of the focusing area of the laser beam with respect to the beam-exit nozzle in a way similar to what is obtained by moving the lens with respect to the mirror.