Abstract:
The present invention relates to an apparatus ( 1 ) for generating a rotating laser beam ( 5 ) which may used for various applications including welding, cutting, drilling or ablation of materials. More particularly, the apparatus according to the present invention is able to produce a fast rotating and accurate laser beam, because the main optical device ( 100 ) that is rotated consists of a first reflecting surface ( 102 ) rotating about an axis (X 1 ) at least a second reflecting surface ( 26 ), said first reflecting surface ( 102 ) intented to redirect said laser beam into the direction of the second reflecting surface ( 26 ), and a rotating lens ( 107 ) of optical axis (X 2 ) arranged to be tiltable, such that said optical axis (X 2 ) is able to be angled with respect to said axis (X 1 ).

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an apparatus for generating a rotating laser beam and, more particularly, to such an apparatus allowing accurate and fast circular machining and/or welding. Such an apparatus can also advantageously be applied to the visioning of circular machining and/or welding regions.  
       BACKGROUND OF THE INVENTION  
       [0002]     Although the following description relates specifically to a welding apparatus, it must be understood that, depending on the laser beam parameters, the apparatus according to the present invention can also been used for machining operations, such as cutting, drilling or ablation of materials.  
         [0003]     Systems for circular welding with a laser beam, for example, are known from the prior art.  
         [0004]     Some of these systems are based on the principle that the welding apparatus is arranged with respect to one or more workpieces to be welded in a stationary manner. The laser beam is directed to a welding region of the workpieces in a fixed direction, whereas the workpieces are driven in rotation by a support comprising motor means for that purpose.  
         [0005]     However, such systems present many drawbacks in that it is difficult to precisely adjust the position of the workpiece with respect to the laser beam, this being especially critical when the workpiece is rotated at a high speed of rotation.  
         [0006]     Further, the corresponding welding process takes a long time if there are a large number of workpieces to be welded successively. Indeed, in the process, the workpiece has to be positioned in its still support before the latter is driven in rotation with a high speed. Then the welding treatment is applied as soon as the workpiece is rotated faster than a predetermined rotating speed. After the welding treatment, the support has to stop rotating before the workpiece is removed from it and before the next workpiece is positioned.  
         [0007]     Other systems are known, in which the workpiece remains still during the welding process, the laser beam direction being changed to sweep the whole welding region. In order to cover the whole welding region with the laser beam, two mirrors are arranged in the optical path of the laser beam so that they can be tilted independently of each other, each between two end positions. Thus, one of the mirrors is responsible for a movement of the laser beam along a first direction X-X′ while the second mirror is responsible for a movement of the laser beam along a second direction Y-Y′, perpendicular to the first direction X-X′. Consequently, the combination of the respective tilts of the two mirrors covers the whole welding region of the workpiece.  
         [0008]     However, a drawback of such systems is that the larger the dimensions of the welding region, the further the end positions are from one another for each of the mirrors. Thus, the time necessary for a mirror to tilt from one end position to the other is longer, which leads to a decrease in the overall speed of the welding process.  
         [0009]     Futher, JP 60-236482A in the name of Mitsubishi Electric Corp. and published on Nov. 25, 1985, discloses an apparatus for generating a rotating laser beam comprising a large focal length lens standing in a still position as regards the apparatus and a first reflecting surface mounted on a rotating support for being driven in rotation. The light reflected by the first reflecting surface is directed toward a second reflecting surface and then toward a third reflecting surface.  
         [0010]     However, all three reflecting surfaces described in this document are of planar shape in cross-section and introduce thus an error in the shape of the image focus point formed on the workpiece to be welded, as they are combined with a large focal length lens.  
       SUMMARY OF THE INVENTION  
       [0011]     A first object of the present invention is to improve the systems of the aforementioned prior art by providing an apparatus for performing a circular machining on at least one workpiece in a fast and reliable manner.  
         [0012]     Thus, the present invention concerns such an apparatus comprising means for supplying a laser beam, said laser beam following an optical path through at least one optical system of the apparatus before emerging from said apparatus through an output before impinging onto an impact region of the workpiece. The optical system presents a central axis X 1  and is at least intended to adjust the position of an image focal point of said laser beam in the impact region. The optical system further comprises a first reflecting surface able to rotate with respect to the central axis X 1  and intended to redirect the laser beam into the direction of at least a second reflecting surface intended to reflect the laser beam towards the workpieces. The apparatus is characterised by the fact that it comprises means to drive the first reflecting surface together with the optical system in rotation. The apparatus according to the present invention is further characterised by the fact that the optical system comprises a rotating lens of optical axis X 2  arranged so as to be tiltable, such that the optical axis X 2  is able to be angled with respect to the central axis X 1 , to increase the quality of the image focus point on the workpiece.  
         [0013]     Thus, circular machining, welding for example, can be obtained by a simple rotational movement of a reflecting surface, allowing the implementation of high rotational speeds, the rotational speed being independent of the dimensions of the welding.  
         [0014]     Owing to its tiltable lens which is rotating together with the first reflecting surface, the quality of the image focus point on the workpiece can be finely adjusted. This last feature is thus an important additional improvement as regards the above mentioned known systems, in that with the latter no adjustment of the quality of the laser beam is provided, such adjustment taking into account the motion of the reflective surface.  
         [0015]     According to a preferred embodiment of the present invention, the first reflecting surface is arranged in a stationary manner in the optical system, the latter being able to rotate with respect to the central axis X 1  via the action of said motor means. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The present invention will now be described in more detail with reference to the accompanying drawings which illustrate the structure of the welding apparatus of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein.  
         [0017]      FIG. 1  is a cross-sectional schematic view of a laser welding apparatus in accordance with a prefered embodiment of the present invention.  
         [0018]      FIG. 2  is an enlarged cross-sectional view of an optical system centrally arranged in the apparatus of  FIG. 1 .  
         [0019]      FIG. 3  is a schematic diagram representing the optical path of the laser beam through the optical system of  FIG. 2 .  
         [0020]      FIG. 4  is an enlarged cross-sectional view of the further sleeve represented in the lower part of  FIG. 2  according to an alternate embodiment of the present invention.  
         [0021]      FIG. 4   a  is an enlarged cross-sectional view of the further sleeve of  FIG. 4 , the cross-section being perpendicular to that of  FIG. 4 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Referring now initially to  FIG. 1 , a laser beam welding apparatus  1  in accordance with the present invention is described. The apparatus  1  comprises a main housing  2  in which are enclosed most of the constituent elements of the apparatus. The main housing  2  comprises means (not shown), such as feet for example, to be positioned on a worktable  3  above a workpiece W holding tool (not represented in detail).  
         [0023]     The main housing comprises a side opening  4  through which a laser beam  5  passes, along a substantially horizontal direction, said beam being generated by a remote laser source (not shown). The laser beam  5  is, directed onto a semi-transparent mirror  6  at an angle of approximately 45 degrees with respect to the incident laser beam to redirect the latter in a substantially vertical direction.  
         [0024]     Further, a top opening  7  is provided above the back side of the semi-transparent mirror  6  to be used, in a conventional manner, as an observation window for the positioning of an optical sensor  200 , such as a CCD camera for example The optical sensor may be connected to a signal processing unit  201  comprising, in particular, a processor, the processing unit possibly being connected to a display  202 .  
         [0025]     Following the optical path of the laser beam downwards from the semi-transparent mirror  6  there is provided a main chamber  8 , in which a movable unit  9 , able to be translated in the direction of a central axis X 1  is partially enclosed. The movable unit  9  is connected to the main housing  2  through lateral arms  10  extending in a direction parallel to the central axis X 1  and cooperating with holes  11  of supporting extensions  12 , arranged on the inner surface of the main housing. Preferably, ball bearings  13  are inserted between each of the supporting extensions  12  and its corresponding arm  10  to improve a sliding movement between these two elements when the movable unit  9  is translated. The vertical position of the movable unit can be adjusted with respect to the housing, this being implemented by any suitable means, such as micrometric screws, for example.  
         [0026]     The movable unit comprises a centrally arranged optical system  100 , radially delimited by a sleeve  101 , which will be described later in more detail. The sleeve  101  comprises two distant annular step portions  16  on which bearings  17  abut, in order to maintain the position of the sleeve, in the direction of the central axis X 1  with respect to the movable unit  9 , and to radially guide the sleeve. An annular screw  18  cooperates with a thread portion provided at the front end  19  of the sleeve  15  to tighten the bearings  17  against the corresponding step portion  16 .  
         [0027]     A rotor  20  is directly arranged around the sleeve  101  in a stationnary manner, the rotor being for example made in the form of a permanent bipolar magnet.  
         [0028]     A stator  21  is concentrically arranged around the rotor  20 , the stator bearing a plurality of coils  22 , two of which are shown on the drawing. Thus, the combination of the rotor  20  and the stator  21  forms a motor whose power supply means are schematically shown by reference  23 . The operation of the motor induces a rotational motion of the optical system  100 , via rotation of the sleeve  101 .  
         [0029]     Further, the movable unit  9  comprises, in its lower part, a block  24  in which is provided a central cavity  25  comprising a first upper annular mirror  26  as well as a second lower annular mirror  27 . As can be seen from  FIG. 1 , both annular mirrors  26  and  27  have a planar shape in cross-section.  
         [0030]     Conventional means are provided for accurately adjusting the respective positions of the mirrors  26  and  27  such as, for example a set comprising a screw and a spring (not represented) arranged apart from the corresponding mirror. Thus, it is possible to adjust the inclination of the axis of each mirror  26 ,  27  with respect to the central axis X 1 , in order to control the quality of the laser beam before it impinges onto the workpiece W.  
         [0031]     The block  24  may be hold against the main housing  2  of the apparatus by the way of a plurality of screws  28 , for example.  
         [0032]     Further, the block  24  comprises a base central opening  29  closed by a cup shaped protection window  30 . The function of this window  30  is to prevent the optical elements of the apparatus being spoiled by dust or plasma during the welding process. Means are also provided for accurately adjusting the position of the protection window  30  with respect to the central axis X 1  and the annular mirrors  26  and  27 , for example by use of a screw  31 .  
         [0033]     It is to be noted that the protection window can take various forms as long as it fulfils the requirement of being substantially perpendicular to the central rays of the laser beam  5 . Thus, the protection window does not play any optical role in the laser beam propagation. In other words, the shape of the protection window is subject to variations, enclosed within the scope of the present invention, as a function of the direction of propagation of the laser beam  5  in the region of the protection window, i.e. as a function of the reflecting surface structure.  
         [0034]     Now with reference to  FIG. 2 , the rotating optical system  100  will be described in more detail. The optical system  100  is schematically represented in  FIG. 2 , the sleeve  101  being omitted to enhance the description of the optical parts.  
         [0035]      FIG. 2  shows a first tubular element  32  which is still with respect to the movable unit  9  and comprising a plurality of radial extensions  33  defining a supporting frame. In the region of the end  34  of the tubular element  32  there is arranged a lens  35 , the main function of which is to limit the divergence of the laser beam  5 .  
         [0036]     The first tubular element  32  is partially surrounded by a second tubular element  38 , the function of which will be explained later.  
         [0037]     The optical system  100  comprises a further sleeve  103  carrying, in particular, an optical device  104  having a planar input surface  105  and a hemispherical output surface  106 .  
         [0038]     In a prefered embodiment of the present invention, the optical device  104  is a block made of quartz, in which a planar gap, forming the reflecting surface  102 , is provided. The gap may be simply filled with air and is oriented with a certain angle with respect to the central axis X 1 , in order to change the direction of an incident laser beam as shown in  FIG. 1 . The optical device  104  may be simply maintained by friction inside the sleeve  103 .  
         [0039]     It is to be noted that the reflecting surface  102  may be made in any other suitable form by those skilled in the art, without departing from the scope of the present invention. However, the use of a mirror may not be as efficient as the use of a gap as regards the risk of heating due to the high power of the laser beam used. Thus, it is clear that the use of a conventional mirror is also possible, in particular in applications for which the use of a high power laser beam is not necessary.  
         [0040]     From another point of view, the disclosed shape of the optical device  104  is advantageous as regards its moment of inertia during the rotation of the optical system.  
         [0041]     Further, the sleeve  103  houses a correcting lens  107 , borne by a supporting member  108 . The supporting member  108  is mechanically connected to the sleeve  103  by two pivot pins (not shown) aligned to each other in the direction perpendicular to the plane of  FIG. 2 . The supporting member also comprises two pins  109  and  110  parallel to each other and to the direction of the central axis X 1 , arranged in adapted blind holes of the supporting member.  
         [0042]     A first pin  109  is supported in its hole by a helicoidal spring  111  while the second pin  110  is held in a fixed position with respect to its hole, for example by a threading (not shown).  
         [0043]     An annular element  112 , threaded in the sleeve  103 , abuts the pins  109  and  110  with its lower surface. Hence, it is apparent from  FIG. 2  that, if the annular element  112  is threaded down in direction of the supporting member  108 , pressure is exerted on the pins  109  and  110 . As pin  110  is fixed to the supporting member, it induces a pivoting motion of the latter while increasing the pressure exerted onto the pin  109 . Consequently, the pressure exerted on the pin  109  is transmitted to the spring  111  that becomes more compressed in order to absorb the pressure.  
         [0044]     As a result, the correcting lens  107  is tilted or, in other words, its optical axis X 2  is rotated with respect to the central axis X 1 . In the above example, the optical axis X 2  is rotated clockwise, as schematically shown in  FIG. 2 .  
         [0045]     The second tubular element  38  plays the part of a tool for operating the annular element  112  from outside the optical system  100 . Indeed, it can be seen in  FIG. 2  that the second tubular element  38  comprises a plurality of short rods  39  protruding from its lower surface for cooperating with corresponding blind holes  113  provided in the upper surface of the annular element  112 . Thus, the second tubular element  38  has to be lowered, by an operator, by compressing supporting springs  40  so that the short rods  39  enter the blind holes  113 . Then, and while the springs  40  remain under compression, the second tubular element  38  is rotated to induce a rotational movement of the annular element  112  and thus tilting of the correcting lens  107 . When the pressure on the second tubular element  38  is released, the short rods  39  are released from the blind holes  113  and the annular element  112  is maintained in a fixed angular position.  
         [0046]     The function of the correcting lens  107  is to act on the laser beam  5  to avoid the occurrence of any geometrical aberration of the image focal point in the welding region, i.e. to improve the quality of the image focal point.  
         [0047]     For the same reason, the respective surfaces of the annular mirrors  26  and  27  have to be treated very carefully during their preparation process. Due to the high quality of the mirror surface preparation, the quality of the image focal point is enhanced.  
         [0048]     As apparent from  FIG. 1 , the optical path of the laser beam  5  through the apparatus according to the present invention is such that it is possible to achieve circular welding when the optical system  100  is driven in rotation by the motor.  
         [0049]     Referring now to  FIG. 3 , the optical principles implemented in the apparatus according to the present invention will be described.  
         [0050]     When the movable unit  9  is in its neutral position, the image focal point in the impact region of the workpiece W is located at FO.  
         [0051]     Starting from this situation, the user has to make the movable unit  9  translate up or down to adjust the radius value of the circle swept by the laser beam during operation as a function of the dimensions of the workpiece W. The image focus point is thus translated along the optical path of the laser beam, together with the translation of the movable unit  9 . When the movable unit  9  is arranged in its highest position with respect to the housing  2 , the image focal point is located at F 1 ′ and when the movable unit is arranged in its lowest position, the image focal point is located at F 1 .  
         [0052]     Of course, the method that has just been described as regards the adjustment of the focus point position is given as an example and is not limiting. It could be subject to variations due to a choice of a different number of lenses for example or a choice of lenses of a different nature.  
         [0053]     Starting from the input of the optical system  100 , the laser beam  5  is slightly divergent when it impinges onto the first convergent lens  35 , the function of which is to decrease the beam divergence. The optical path extends then through the tiltable lens  107  which is convergent, its focal length being substantial. More particularly, the focal length of the tiltable lens is adapted to the dimensions of the apparatus according to the present invention, so as to form the image focus point on the surface of the workpiece W.  
         [0054]     Further, as previously mentioned, the tiltable lens  107  is able to pivot about an axis parallel to the first reflecting surface  102  so that its optical axis X 2  is able to be inclined with respect to the central axis X 1 . Thus, the quality of the image focus point formed on the surface of the workpiece W can be finely adjusted by pivoting the tiltable lens  107 , in order to avoid the formation of an ellipse-shaped focus point for example. This last feature is particularly advantageous since the tiltable lens  107  and the first reflecting surface  102  are rotated together so that their mutual orientation remains still during the operation of the apparatus.  
         [0055]     Referring now to  FIG. 4  and  FIG. 4   a , an alternate embodiment of the further sleeve  103  according to the present invention, which was described in relation with  FIG. 2 , will be described.  
         [0056]     More particularly, the present embodiment concerns changes in the structure supporting the correcting lens  107  and thus in the means provided for the adjustment of the orientation angle lying between optical axis X 2  and central axis X 1 .  
         [0057]     Here again, a supporting member  408  is mechanically connected to the sleeve  103  by means of two pivot pins  401  and  402  aligned with respect to each other in the direction perpendicular to the plane of  FIG. 4 , i.e. along the plane of  FIG. 4   a.    
         [0058]     Two elastic rings  403 ,  404  are provided respectively on both sides of the supporting member  408 , each of these rings being formed of a stack of a plurality of flat rings as can be seen from  FIGS. 4 and 4   a . Prefeably, the flat rings are made of metal and are welded or glued together at least partly around their periphery by any adapted known method.  
         [0059]     Each of the elastic rings  403 ,  404  comprises two holes  405 ,  406  traversing its thickness and located such as to be diametrically opposed, a screw  409 ,  410  being arranged in each of the holes.  
         [0060]     A first screw  409  of each elastic ring tightens the latter to the supporting member  408  in a region of connection, the respective regions of connection being diametrically opposed.  
         [0061]     The second screw  410  of each elastic ring simply ensures that the flat rings remain tightened to each other and is thus shorter than the corresponding first screw  409 . All screw heads protrude from the elastic rings on their respective sides opposite the supporting member  408 .  
         [0062]     Consequently, the screw heads of a first elastic ring  403  abuts against the annular element  112  (as disclosed in connection with  FIG. 2 ) while the screw heads of the second elastic ring  404  abuts against a step  411  provided inside the sleeve  103 .  
         [0063]     Then, the functionning of the assembly formed by the supporting member  408  together with the two elastic rings  403  and  404  will be described.  
         [0064]     In a similar fashion to that described in relation with  FIG. 2 , when the annular element  112  is screwed in the direction of the supporting member  408 , pressure is exerted on the screw heads of the first elastic ring  403 .  
         [0065]     Under the effect of the pressure, the first elastic ring  403  bends thus causing the second elastic ring  404  to bend, as the supporting member  408  is rigid and less prone to bending. As a result of the respective bendings of both elastic rings  403  and  404 , the supporting member  408  and thus the optical axis X 2  of the correcting lens  107  are inclined with respect to the direction of the central axis X 1 . More particularly, when the annular element  112  is screwed on  FIG. 4 , the correcting lens  107  is rotated anti-clockwise.  
         [0066]     As already mentioned above, the function of the correcting lens  107  is to act on the laser beam  5  to avoid the occurrence of any geometrical aberration of the image focal point in the welding region, i.e. to improve the quality of the image focal point.  
         [0067]     More generally, an important aspect of the apparatus according to the present invention lies in the fact that the tiltable lens  107  and the first reflecting surface  102  are rotated simultaneously.  
         [0068]     The apparatus according to the present invention can be used in many different applications. For example, it can be used as an examination apparatus by using the presence of the observation window in combination with an optical sensor  200  as mentioned above. In such a case, the side opening  4  of the housing  2  is not necessary as no laser beam needs to be input in the apparatus. However, this opening  4  can be kept and used as an input for a light source in order to light the region of the workpiece to be examined and enhance the contrast of the observation image.  
         [0069]     Another important advantage of the present invention lies in the fact that in order to treat a series of workpieces, the optical system can be kept rotating between two successive workpieces to be treated. The laser beam supply means need only be stopped for the time necessary to remove a treated workpiece and to position a new workpiece, which saves time for the user.  
         [0070]     Further conventional features can be added in the above described apparatus without departing from the scope of the present invention. For example, a cooling fluid supply circuit can be provided to cool the bearings  17  as visible in  FIG. 1 . A device for measuring the rotational speed of the optical system can also be provided.