Abstract:
This laser processing machine, which moves a work piece, which is mounted on a table, and an optical head, which shines a laser light, relative to each other, and processes the work piece by irradiating the work piece with the laser light, is provided with: a calibration camera that is fixed to the optical head; a probe that is fixed to the optical head; and a calibration unit that has measurement reference points (Pc 1 , Pc 2 , Pc 3 , Pp 1 , Pp 2 , Pp 3 ) for measuring the position of the calibration camera and the probe, and a processing portion that forms a processing mark (L 1 , L 2 ) due to the laser light.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Patent Application No. PCT/JP2015/052765, filed Jan. 30, 2015, which is hereby incorporated by reference in the present disclosure in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a laser beam machine and an alignment adjusting method therefor, the laser beam machine being configured to machine a workpiece by directing the laser beam through a liquid flow in the form of a pillar formed by a liquid discharged through a nozzle, wherein the laser beam machine has an alignment adjusting function for aligning the optical axis of the laser beam and the axis of the liquid flow. 
       BACKGROUND OF THE INVENTION 
       [0003]    Recently, a laser beam machine is developed, in which the dimensions and shape of a workpiece mounted to the laser beam machine are measured by a touch probe or an electric capacity sensor attached to the laser beam machine. For example, Patent Literature 1 describes a laser beam machine configured to control the gap between the laser beam machining head and the workpiece by an electric capacity sensor attached to the end of the laser beam machining head. 
       PATENT PUBLICATIONS 
       [0000]    
       
         
           
             Patent Literature 1: JP-A-H09-220685 
           
         
       
     
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In such a laser beam machine, provided with a touch probe or an electric capacity sensor, while the relative position between a touch probe or an electric capacity sensor and a laser beam machining head or an optical head is previously known as a designed value, an error is inevitably involved when a touch probe or an electric capacity sensor is attached to a laser beam machining head or an optical head. In the laser beam machine of Patent Literature 1, the optical axis of the laser beam irradiated from the laser beam machining head and the position of the electric capacity sensor relative to the Z-axis position of the end of laser beam machining head are not measured, and therefore the dimensions and shape of the workpiece measured by the electric capacity sensor includes errors based on the error involved when the electric capacity sensor is attached to the laser beam machining head. The measurement results including such errors cause the machining accuracy to be lowered. 
         [0006]    The invention is directed to solve the problem of the prior art, and the objective of the invention is to provide a laser beam machine and a laser beam machining method improved to measure the position of the touch probe relative to the optical axis of the laser beam, whereby machining with higher accuracy. 
         [0007]    In order to achieve the above described object, according to the invention, a laser beam machine configured to move a workpiece mounted to a table and an optical head for irradiating a laser beam to the workpiece, whereby machining the workpiece, comprising an optical sensor secured to the optical head, a probe secured to the optical head, and a calibration unit having a measurement reference for measuring positions by the optical sensor and the probe, and a to-be-processed part adapted to form a machined mark by the laser beam is provided. 
         [0008]    Further, according to the invention, a laser machining method for machining a workpiece by moving a workpiece attached to a table and an optical head configured to irradiate laser beam relatively to each other, and irradiating the laser beam to the workpiece, the method comprising the steps of providing a calibration unit secured to the table and having a measurement reference and a to-be-processed part, forming a machined mark with the laser beam on the to-be-processed part of the calibration unit, measuring, by an optical sensor mounted to the optical head, the position of the machined mark on the to-be-processed part and the position of the measurement reference of the calibration unit, measuring the position of the measurement reference by a probe mounted to the optical head, calculating the deviation between the position of the machining point of the laser beam and the position measured by the probe, based on the position of the machined mark and the position of the measurement reference, measured by the optical sensor, and the position of the measurement reference measured by the probe, obtaining the relative positions of the workpiece and the machining point of the laser beam, based on the calculated deviation between the machining point of the laser beam and the position measured by the probe, and the position of the workpiece measured by the probe, and machining the workpiece by moving the table and the optical head relatively to each other, based on the obtained relative positions of the workpiece and the machining point of the laser beam is provided. 
         [0009]    According to the invention, the deviation between the position of the machining point of the laser beam and the position measured by the probe is calculated by measuring the positions of the measurement reference by the optical sensor and the probe and the position the machined mark formed on the to-be-processed part by the laser beam, and the relative position between the machining point of the laser beam and the workpiece is obtained based on the deviation between the machining point of the laser beam and the measured position by the probe and the position of the workpiece measured by the probe, whereby the workpiece can be machined with high accuracy by moving the table and the optical head relatively to each other, based on the obtained relative position between the workpiece and the machining point of the laser beam. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic section of an example of a laser beam machine with a touch probe attached to an optical head. 
           [0011]      FIG. 2  is a perspective view of a calibration ring assembly according to a preferred embodiment of the invention. 
           [0012]      FIG. 3  is an image of the calibration ring assembly of  FIG. 2  captured by a calibration camera, for explaining the measurement by the calibration camera. 
           [0013]      FIG. 4  is a plan view of the calibration ring assembly, for explaining the measurement by the touch probe. 
           [0014]      FIG. 5  is a perspective view of an example of a laser beam machine to which the invention is applied. 
           [0015]      FIG. 6  is a schematic section of an optical head, similar to  FIG. 1 , of a water jet laser beam machine to which the invention is applied. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    With reference to the attached drawings, a preferred embodiment of the invention will be described below. 
         [0017]    With reference to  FIG. 5 , showing an example of a laser beam machine to which the invention is applied, a laser beam machine  100  comprises a table  108  to which a workpiece is attached, an optical head  10  configured to move linearly relative to the table  108  in three orthogonal X-, Y- and Z-aces directions. The optical head  10  and the table  108  are enclosed by a cover  102 . The cover  102  has a safety door  106 , slidable in the right-left direction (X-axis direction). Opening the safety door  106  allows an operator to access the optical head  10  and the table  108  through an opening  104 . The table  108  is provided with a calibration unit  50 . 
         [0018]    An operating panel  110  for the laser beam machine  100  is mounted to a front side wall of the cover  102 . The operating panel  110  has a display  112 , adapted to display parameters, indicating the condition and operation of the laser beam machine  100 , icons for teaching an operator the operation procedures and so on, and a various operating buttons  114 . The display  112  may be a touch panel, adapted to allow an operator to carry out a various operation to the laser beam machine  100  by touching an icon with his (her) finger. Further, the operating panel  110  is incorporated with a controller for controlling the laser beam machine  100  in accordance with the operator&#39;s input and a program contained in the controller. 
         [0019]    The laser head  10 , shown in  FIG. 1  as an example, comprises a laser irradiation head  16  which is enclosed in a housing  12  and configured to receive the laser beam from a laser oscillator  14  via an optical conduit  14  such as an optical fiber, and to irradiate the laser beam toward a collimation lens  18 . A downwardly tapered projection part  12   a  is provided at the lower end portion of the housing  12  of the optical head  10 . An orifice  12   b  is provided at the lower end of the projection part  12   a.    
         [0020]    The laser beam from the laser irradiation head  16  is parallelized by the collimation lens  18 , reflected to a second mirror  22  by a first mirror  20 , and reflected toward a focus lens  24  by the second mirror  22 . The laser beam is irradiated outside the housing  12  through the orifice  12   b  of the housing  12 , after being condensed by the focus lens  24 . At that time, the optical axis of the laser beam irradiated from the optical head  10  is substantially parallel to the Z-axis. 
         [0021]    The optical head  10  may be a water jet laser beam machine, as shown in  FIG. 6 , wherein a workpiece is machined by the laser beam is directed through a pillar-like liquid jet formed by liquid discharged through a nozzle. In this connection, in the optical head  10  of  FIG. 6 , the elements similar to those of the optical head  10  of  FIG. 1  are indicated by the same reference numbers, and the explanation thereof is omitted in order to avoid redundancy. Hereinafter, only the differences will be described. 
         [0022]    The optical head  10  of the water jet laser beam machine, shown in  FIG. 6 , comprises, in addition to the optical head  10  of  FIG. 1 , a nozzle head  34  configured to discharge liquid, for example water, outside the housing  12 . The nozzle head  34  comprises a tubular member configured to receive water supply from a water source  30  via a conduit  28 . Provided in a bottom wall of the nozzle head  34 , facing the table  108 , is a nozzle  34   b  for discharging a water jet. Opposite to the bottom wall, a top wall, facing the focus lens  24 , is provided with a window  34   a  formed of a transparent member such as glass. The nozzle  34   b  is fluidly communicated with the outside of the housing  12  of the optical head  10  via orifice  12   b  formed in the bottom wall of the housing  12 . 
         [0023]    The first and second mirrors  20  and  22  have planner reflecting surface, and motors  20   a  and  20   b  as a mirror orientation adjusting means for adjusting the orientations of the reflecting surfaces (the directions perpendicular to the reflecting surfaces), whereby adjusting the direction of the laser beam irradiated from the optical head  10 . The first and second mirrors  20  and  22 , in particular the second mirror  22 , adapted to reflect the laser beam toward the focus lens  24 , include(s) a dielectric multilayer suitable for the wave length of the laser beam irradiated from the laser oscillator  14  to reflect the laser beam and to transmit lights having wave lengths other than the wave length of the laser beam. In particular, it is formed by depositing a dielectric multilayer on a glass plate. Forming the second mirror  22  by such a dielectric multilayer enables the positions of the nozzle  34   b  and the laser beam irradiated through the nozzle  26  to be monitored by an alignment adjusting camera  26 . 
         [0024]    The calibration unit  50  is positioned at a position on the table  108  so as to be faced to the optical head  10  by moving the optical head  10  and the table  108  relatively to each other by three feed axes of X-, Y- and Z-axes of the laser beam machine  100 . The calibration unit  50  comprises a base member  48  configured to be secured to the table  108 , an annular lower holding member  46  secured to a top face of the base member  48 , an annular upper holding member  44  detachably attached to the lower holding member  46 , a reflecting plate  42  held between the upper and lower holding members  44  and  46 , and an annular light shielding member  34  fixed to a top face of the upper holding member  44 . 
         [0025]    On the lower end portion of the housing  12  of the optical head  10 , a touch probe  40 , having a contactor  40  for measuring the dimension and shape of a workpiece (not shown) attached to the table  108 , and a calibration camera  42 , providing an optical sensor, are mounted. The contactor  40   a  of the touch probe  40  extends downwardly in the Z-axis direction. The calibration camera  42  is oriented so that its optical axis is aligned with the Z-axis direction. 
         [0026]    The calibration unit  50  is positioned at a position on the table  108  so as to be faced to the optical head  10  by moving the optical head  10  and the table  108  relatively to each other by the three orthogonal X-, Y- and Z-aces feed devices of the laser beam machine  100 . The calibration unit  50  comprises a base member  52  configured to be secured to the table  108 , a touch switch  54  secured to a top face of the base member  48 , and a calibration ring assembly  60 . A reacting part  54   a , such as an electrostatic capacity switch or a non-contact microswitch is provided at the top end of the touch switch  54 . Further, the touch switch  54  is positioned at a level the same as a top face of a plate  68 , which provides a to-be-processed part of the calibration ring assembly  60 , and is inserted into slots  62   a.    
         [0027]    With reference to  FIG. 2 , the calibration ring assembly  60  comprises a cylindrical body  62 , an annular flange part  64  radially inwardly extending from the inner surface of the body  62 , and a plate  68  providing a to-be-processed part extending in the diametrical direction of the body  62 . The body  62  has a precisely machined cylindrical outer surface. Further, the cylindrical body  62  and the inner surface  64   a  of flange part  64  of the calibration ring assembly  60  are formed so as to be precisely concentrically aligned with each other. 
         [0028]    A pair of slots  62   a  are formed at diametrically opposite sides of the body  62 . The rectangular plate  68  is removably inserted into the slots  62   a  as a to-be-processed part. The slots  62   a  are disposed so as to allow the top face of the inserted plate  68  to contact intimately with the bottom face of the flange part  64 . The plate  68  is composed of a metallic member, such as stainless steel, of which top surface is finished to provide a reflecting surface reflecting the laser beam irradiated from the optical head  10 . 
         [0029]    The operation of the embodiment will be described below. 
         [0030]    When an operator presses a calibration start button on the operating panel  110 , the optical head  10  starts to be moved to a calibration adjustment position by the X-, Y- and Z-axes feed devices of the laser beam machine  100 . At the calibration adjustment position, the optical head  10  is located above the calibration unit  50 , then lowered along the Z-axis until the projection part  12   a  of the housing  12  of the optical head  10  contacts the reacting part  54   a  of the touch switch  54 . When the distal end of the projection part  12   a  contacts the reacting part  54   a  of the touch switch  54 , the lowering movement of the optical head  10  is terminated, and the currently Z-coordinate is stored in the controller (not shown) of the laser beam machine  100 . 
         [0031]    Then, the contactor  40   a  of the touch probe  40  is located above the touch switch  54  of the calibration unit  50 . Then, the contactor  40   a  is lowered until contacting with the touch switch  54 . When the distal end of the contactor  40   a  contacts the reacting part  54   a  of the touch switch  54 , the lowering movement of the optical head  10  is terminated, and the currently Z-coordinate is stored in the controller of the laser beam machine  100 . The focal position of the laser beam is previously adjusted based on the distal end of the projection part  12   a  of the housing  12  of the optical head  10 , thus the distance in the Z-axis direction from the distal end of the projection part  12   a  to the focal position of the laser beam is known. The distance between the focal portion of the laser beam and the contactor  40   a  in the Z-axis direction is calculated based on the Z-coordinate which is obtained when the distal end of the projection part  12   a  contacts the touch switch  54 , the Z-coordinate which is obtained when the distal end of the contactor  40   a  contacts the touch switch  54 , and the distance from the distal end of the projection part  12   a  to the focal position of the laser beam in the Z-axis direction. 
         [0032]    Then, the optical head  10  is moved to a position above the plate  68  of the calibration ring assembly  60 . Then, the laser beam is irradiated from the optical head  10 . An image of the irradiated laser beam is captured by the alignment adjusting camera  26 , and is displayed, along with the orifice  12   b , on the display  112  of the operating panel  110  as a laser spot. The operator adjusts the alignment of the laser beam relative to the orifice  12   b  of the optical head  10  by adjusting the orientations of the first and second mirrors  20  and  22  so as to align the images of the laser spot and the orifice  12   b  with each other, which are displayed on the display  112 . 
         [0033]    Then, two lines L 1  and L 2  are formed perpendicularly to each other, as shown in  FIGS. 3 and 4 , on the top face (reflecting surface) of the plate  68 , providing the to-be-processed part, by the laser beam irradiated from the optical head  10  fed in the X- and Y-axes direction relative to the table  108 . At that time, the output power of the laser beam is enough to machine the lines L 1  and L 2 , and higher than the output power irradiated for adjusting the alignment of the laser beam. The X-coordinate, when the optical head  10  is linearly fed in the Y-axis by the feed device whereby machining the line L 2 , and the Y-coordinate, when the optical head  10  is linearly fed in the X-axis by the feed device whereby machining the line L 1 , are stored as the coordinate of the intersection P between the lines L 1  and L 2 , the laser beam aligning with the intersection. 
         [0034]    Then, the calibration camera  42  captures an image of the top face of the plate  68  so that that the image is displayed on the display  112 . At that time, on the display  112 , cross lines Lc 1  and Lc 2  (refer to  FIG. 3 ), indicating the optical axis of the calibration camera  42 , are displayed at the center of the view field. Then, the optical head  10  is fed relative to the table  108  in X- and Y-axes so that the intersection Pc between the cross lines Lc 1  and Lc 2  is aligned with the intersection P between the lines L 1  and L 2 , i.e., the machined marks formed on the to-be-processed part, whereby the optical head  10  is positioned in the X- and Y-axes directions. The deviation, in the X-Y plane, between the optical axis of the laser beam and the optical axis of the calibration camera  42  is measured by calculation based on the current X-Y coordinate and the coordinate at which the laser beam aligns with the intersection P between the lines L 1  and L 2 . 
         [0035]    Then, as shown in  FIG. 3 , three measurement points Pc 1 , Pc 3  and Pc 3  are selected, as measurement reference points for the calibration camera  42 , along the inner periphery  64   a  of the flange part  64  of the calibration ring assembly  60 . In  FIG. 3 , although the three measurement points Pc 1 , Pc 2  and Pc 3  are shown so as to be equally located at an interval along the inner periphery of the flange part  64 , the present invention is not limited to this configuration, and the three measurement points Pc 1 , Pc 2  and Pc 3  can be selected at any points along the inner periphery of the flange part  64 . The cross lines Lc 1  and Lc 2 , indicating the optical axis of the calibration camera  42 , are displayed on the display  112 , on which the image captured by the calibration camera  42  is also displayed, as described above. The coordinates (xc 1 , yc 1 ), (xc 2 , yc 2 ) and (xc 3 , yc 3 ) of the three measurement points Pc 1 , Pc 2  and Pc 3  are successively measured by aligning the intersection Pc between the cross lines Lc 1  and Lc 2  successively with the measurement points Pc 1 , Pc 2  and Pc 3 . In  FIG. 3 , although the cross lines Lc 1  and Lc 2  are indicated at each measurement points Pc 1 , Pc 2  and Pc 3 , for convenience of explanation, actually, only one set of cross lines Lc 1  and Lc 2  is displayed. The read of the X-, Y- and X-axes digital scales may be used as the coordinates of the measurement points Pc 1 , Pc 2  and Pc 3 . The coordinate (x c , y c ) of the center of a circle extending through the three measurement points Pc 1 , Pc 2  and Pc 3  is obtained the following formulations. 
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         [0036]    Then, as shown in  FIG. 4 , three measurement points Pp 1 , Pp 2  and Pp 3  are selected, as measurement reference points for the touch probe  40 , at the same level in the Z-axis direction, along the outer peripheral surface of the body  62  of the calibration ring assembly  60 . In  FIG. 4 , although the three measurement points Pp 1 , Pp 2  and Pp 3  are shown so as to be equally located at an interval along the outer peripheral surface of the body  62 , the present invention is not limited to this configuration, and the three measurement points Pp 1 , Pp 2  and Pp 3  can be selected at any points along the outer peripheral surface of the body  62 , as long as they are located at the same level. 
         [0037]    The contactor  40   a  of the touch probe  40  is fixed at a level in the Z-axis direction, and the contactor  40   a  is moved to contact successively with the three measurement points Pp 1 , Pp 2  and Pp 3  on the outer peripheral surface of the body  62  of the calibration ring assembly  60 . The coordinates (xp 1 , yp 1 ), (xp 2 , yp 2 ) and (xp 3 , yp 3 ) of the respective measurement points Pp 1 , Pp 2  and Pp 3  are measured based on the read of the X-, Y- and X-axes digital scales when the contactor  40   a  contacts the three measurement points Pp 1 , Pp 2  and Pp 3 . The coordinate (x p , y p ) of the center of a circle extending through the three measurement points Pp 1 , Pp 2  and Pp 3  is obtained the following formulations. 
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         [0038]    As described above, the cylindrical body  62  and the inner periphery  64   a  of the flange part  64  of the calibration ring assembly  60  are formed so as to be precisely concentrically aligned with each other, and therefore the center of the circle extending through the three measurement points Pc 1 , Pc 2  and Pc 3  and the center of the circle extending through the three measurement points Pp 1 , Pp 2  and Pp 3  must be aligned with each other, within the machining accuracy of the calibration ring assembly  60 . Thus, the deviation, in the X-Y plane, between the optical axis of the calibration camera  42  and the contactor  40   a  of the touch probe  40  is measured by calculation based on the deviation between the coordinate (x c , y c ) of the center of a circle extending through the three measurement points Pc 1 , Pc 2  and Pc 3  and coordinate (x p , y p ) of the center of a circle extending through the three measurement points Pp 1 , Pp 2  and Pp 3 . 
         [0039]    The relative position between the workpiece, measured by the touch probe  40  and machining point of the laser beam can be obtained based on the deviation, in the X-Y plane, between the optical axis of the laser beam and the optical axis of the calibration camera  42  and the deviation, in the X-Y plane, between the optical axis of the calibration camera  42  and the touch probe  40 . Laser machining can be precisely carried out by moving the optical head  10  relative to the table  108 , based on the thus obtained relative position between the workpiece, measured by the touch probe  40 , and machining point of the laser beam. 
         [0040]    While the embodiment of the invention has been described in relation to the cylindrical calibration ring assembly  60  as an example, L-shaped or rectangular member, defining a measurement reference surface parallel to the Y-Z plane and a measurement reference surface parallel to the X-Z plane, may be used instead of the calibration ring assembly  60 . In this case, the X-axis position of the touch probe  40  is determined by contacting the contactor  40   a  of the touch probe  40  with the measurement reference surface parallel to the Y-Z plane and the X-axis position of the optical axis of the calibration camera  42  is determined by aligning the cross lines of the calibration camera  42  with the measurement reference surface parallel to the Y-Z plane, whereby the deviation in the X-axis direction is calculated. In the Y-axis direction, it can be similarly calculated by using the measurement reference surface parallel to the X-Z plane. In this case, it should be noted that it is difficult to install the L-shaped or rectangular member so that the surface is completely parallel to the Y-Z plane, and therefore an orientation error may be included. On the other hand, the cylindrical calibration ring assembly  60  is not affected by an inclination around the Z-axis, achieving high-accuracy measurement of the deviation. 
         [0041]    Further, while the embodiment of the invention has been described in relation to the calibration ring  60  having the cylindrical body  62  and the flange part  64  defining the inner periphery  64   a  concentric with the body, the body  62  and the inner periphery  64   a  of the flange part  64  may not be concentrically disposed. In this case, the deviation between the body  62  and the inner periphery  64   a  of the flange part  64  is previously obtained, and in the step of calculation, the deviation between the body  62  and the inner periphery  64   a  of the flange part  64  can be added. Concentric configuration of the body  62  and the inner periphery  64   a  of the flange part  64  facilitate the calculation, and allows the calibration ring assembly  60  to be machined by a lathe at higher machining accuracy. 
         [0042]    Further, while the embodiment of the invention has been described in relation to the calibration camera  42  providing an optical sensor, the optical sensor may be a laser length-measurement sensor. When measuring with a laser length-measurement sensor, the changes in displacement is detected by scanning during moving in the X- or Y-axis direction by the feed device. The positions of the lines L 1  and L 2 , i.e., the machined marks formed on the plate  68 , and the inner periphery  64   a  of the flange part  64  are detected as points where the displacement changes. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  Optical Head 
           12  Housing 
           14  Laser Oscillator 
           16  Laser Irradiation Head 
           18  Collimation Lens 
           20  First Mirror 
           22  Second Mirror 
           24  Focus Lens 
           26  Alignment Adjusting Camera 
           30  Water Source 
         
           34 
         
           34   a  Nozzle 
           40  Touch Probe 
           42  Calibration Camera 
           50  Calibration Unit 
           54  Touch Switch 
           60  Calibration Ring Assembly 
           62  Body 
           64  Flange Part 
           68  Plate 
           100  Laser Beam Machine 
           108  Table 
           110  Operating Panel 
           112  Display