Abstract:
In general, the present invention pertains to an apparatus and control system for working sheet material employs a tilting mechanism which automatically tilts a head about a theoretical point disposed upon the sheet material. In another aspect of the present invention, the head is defined as a laser head and the pivot point corresponds with the laser beam focal point. A further aspect of the present invention provides a seam tracking device and control system which automatically adjust a welding head height relative to the sheet material as a datum rather than relative to a gantry or other structure supporting the welding head. In yet another aspect of the present invention, an optical seam tracking device is employed to automatically tilt the welding head along differing rotational planes. In still another aspect of the present invention, various axial slides are employed in combination with a gantry. A further aspect of the present invention uses a seam tracking device and microprocessor to track a welding seam and move a welding head predetermined amounts due to sensed pre-weld gap widths. Another aspect of the present invention uses an automated tilting mechanism for creating a tailored blank butt weld between dissimilar materials. A method of operating the present invention is also provided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to an apparatus and control system for working sheet material and more specifically to a machine, control system and method for laser welding employing a tilting mechanism and a seam tracking device.  
           [0002]    It is common to employ a welding or cutting head in combination with an articulating robot arm or a moving gantry. However, most articulating robots suffer from a lack of precision and stability due to their inherent heavy moment arms extending a significant distance from their stationary bases. Furthermore, articulating robots usually only have a static movement accuracy of +/−100 microns, at best. This lack of accuracy and lack of stability detrimentally affects welding and cutting precision of a head mounted on the arm&#39;s end. In contrast, gantries tend to be more stable and thus more accurate than articulating robots, but usually require significantly expensive concrete reinforcement within the gantry and difficult to achieve bridge machining tolerances. Notwithstanding, the gantry bridges are still somewhat imprecise due to machining tolerances.  
           [0003]    To account for these tolerance and accuracy variations, optical seam tracking cameras and sensors have been recently used for various welding processes including gas metal arc welding, gas tungsten arc welding, plasma arc welding, submerged arc welding, flux-cord arc welding and laser beam welding. One such system is produced by Servo-Robot Inc. of Boucherville, Quebec, Canada. Other examples of such three dimensional vision seam sensing systems are disclosed in the following U.S. Pat. No. 5,168,141 entitled “Vision Guided Laser Welding” which issued to Tashjian et al. on Dec. 1, 1992; U.S. Pat. No. 4,969,108 entitled “Vision Seam Tracking Method and Apparatus for a Manipulator” which issued to Webb et al. on Nov. 6, 1990; and U.S. Pat. No. 4,621,185 entitled “Adaptive Welding Apparatus having Fill Control Correction for Curvilinear Weld Grooves” which issued to Brown on Nov. 4, 1986; all of which are incorporated by referenced herewithin. Most welding and cutting gantry devices employing optical sensing use the somewhat imprecise bridge as the Z axis (vertical) datum and accordingly automatically adjust a Z axis movement device. For articulating robots, each joint is moved to correlate Z axis changes in relation to the fixed base. A more traditional capacitive sensor has also been used to sense the distance between a welding head and the workpiece material. Such a capacitive sensor is disclosed within U.S. Pat. No. 5,428,280 entitled “Robotic Movement of Object over a Workpiece Surface” which issued to Schmidt et al. on Jun. 27, 1995, and is incorporated by reference herewithin.  
           [0004]    Laser welding and cutting with a CO 2  laser or a Yag laser are also becoming commonplace. Laser welding is highly advantageous over other types of welding methods since laser welding allows for deep and high speed welding without requiring the difficult to handle and somewhat costly filler material. Furthermore, laser welding devices are significantly less expensive as compared to other types of welding equipment. However, traditional laser welding and cutting systems use indexed turning or steering mirrors to redirect the laser beam along a curved workpiece or seam. Such mirrored systems are disclosed within the following U.S. Pat. Nos. 4,972,062; 4,855,564; 4,677,274; and 4,367,017. The necessity to rotate these types of mirrors about the laser beam requires complicated and costly computer programming while also being somewhat prone to damage in the workpiece environment. Furthermore, such redirecting mirrors also provide additional tolerance inaccuracies and tend to collect airborne debris. Additionally, a fixed pivot point positioned on or above the laser in traditional systems causes focal length and focal point inaccuracies in relation to the workpiece material when the laser is initially oriented or moved relative to the workpiece surface; this is the scenario disclosed in U.S. Pat. No. 5,190,204.  
           [0005]    Moreover, a large pre-weld gap between adjacent sheet material edges typically prevents adequate laser butt welding. This problem is usually observed with pre-weld gaps having a material edge-to-edge dimension greater than 10 percent of the material thickness. The welding machine is shut off and the material is scrapped if the maximum gap width is present. Such a gap problem is recognized in U.S. Pat. No. 5,204,505. Accordingly, it would be desirable to provide a laser welding apparatus and control system employing an improved, accurate and automated mechanism for welding across a large seam gap.  
         SUMMARY OF THE INVENTION  
         [0006]    In accordance with the present invention, the preferred embodiment of an apparatus and control system for working material employs a tilting mechanism which automatically tilts a head about a theoretical point disposed upon the sheet material. In another aspect of the present invention, the head is defined as a laser head and the pivot point corresponds with the laser beam focal point. A further aspect of the present invention provides a seam tracking device and control system which automatically adjust a welding head height relative to the sheet material as a datum rather than relative to a gantry or other structure supporting the welding head. In yet another aspect of the present invention, an optical seam tracking device is employed to automatically tilt the welding head along differing rotational planes. In still another aspect of the present invention, various axial slides are employed in combination with a gantry. A further aspect of the present invention uses a seam tracking device and microprocessor to track a welding seam and move a welding head predetermined amounts due to sensed pre-weld gap widths. Another aspect of the present invention uses an automated tilting mechanism for creating a tailored blank butt weld between dissimilar materials. An additional axis, controlled by the weld head processor may move or rotate a laser optic to orient a double spot optic to either increase welding speed or cover a larger area across the gap to ensure both metal sheets are melted. Also if two lasers are used (one for each spot), the weld head processor may selectively rise or lower each respective laser&#39;s power, or change one or both lasers to pulse mode from continuous wave mode. Moreover, in a further aspect of the present invention, an automatically adjusting laser is used to create tailored blank welds. Generally, tailored blank welds are essentially butt welds between pre-cut or previously blanked-out sheets of material of similar or dissimilar materials types and/or thicknesses. A method of operating the present invention is also provided.  
           [0007]    The laser welding apparatus and control system of the present invention have many advantages over traditional systems. For example, the automated nature of the present invention tilting mechanism, the closed-loop, actual condition sensing seam tracking device and the microprocessors allow for uninterrupted continuous welding along an arcuate seam regardless of even large seam gap widths. This automated tilting control system significantly lowers work material rejection, set-up time, operating time and operating costs while improving weld uniformity along material sheets having wide edge tolerances. Another advantage is the ability to rotate split laser beams in an automated manner. An integral electromagnetic laser optic member movement mechanism further aids welding across a large gap seam.  
           [0008]    The present invention tilting mechanism is also very cost effective, evenly balanced, dimensionally stable and extremely precise. Furthermore, the present invention tilting mechanism is extremely robust and resistant to abuse and environmental debris. The apparatus of the present invention is further advantageous by accurately maintaining the focal length of the laser beam such that the focal point is always maintained upon the desired workpiece seam location regardless of the tilted positioning of the laser optic. Another advantage of the apparatus of the present invention is that it can be tilted to weld across a pre-weld gap between adjacent sheet material edges even if the pre-weld gap is between 10 and 15% of the sheet material thickness. The present invention apparatus offers another advantage by being especially suitable for use in tailored blank butt welding of dissimilar material thicknesses or material types by providing a mechanism for accurately tilting the laser head in relation to the stepped sheet material seam. By tilting the laser head of the present invention, the harmful reflected laser beam is angularly offset from the incident laser beam emanating from the welding or cutting laser head. As another advantage, the present invention uses the sheet material and seam as datums thereby allowing wider and less costly tolerances and stiffness requirements within the bridge and gantry. In general, gantry systems provide static precision movement within +/−25 microns thereby offering superior accuracy relative to articulating robots. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a side elevational view showing the preferred embodiment of a laser welding apparatus and control system of the present invention;  
         [0010]    [0010]FIG. 2 is a side elevational view, taken perpendicular to that of FIG. 1, showing the preferred embodiment of the present invention laser welding apparatus and control system;  
         [0011]    [0011]FIG. 3 is an exploded perspective view showing the preferred embodiment of the laser welding apparatus and control system of the present invention;  
         [0012]    [0012]FIG. 4 is a diagrammatic side elevational view, similar to FIG. 2, showing the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0013]    [0013]FIG. 5 is an enlarged side elevational view, similar to FIG. 1, showing the preferred embodiment laser welding apparatus and control system of the present invention having a laser optic oriented perpendicular to the sheet material;  
         [0014]    [0014]FIG. 6 is an enlarged side elevational view, similar to FIG. 5, showing the preferred embodiment laser welding apparatus and control system of the present invention having the laser optic tilted in relation to the sheet material;  
         [0015]    [0015]FIG. 7 is a sectional view, taken along line  7 - 7  of FIG. 4, showing a goniometer employed in the preferred embodiment laser welding apparatus and control system of the present invention disposed in an untilted position;  
         [0016]    [0016]FIG. 8 is a sectional view, similar to that of FIG. 7, showing the goniometer employed in the preferred embodiment laser welding apparatus and control system of the present invention disposed in a tilted position;  
         [0017]    [0017]FIG. 9 is a top elevational view showing a tailored blank weld in the sheet material welded by the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0018]    [0018]FIG. 10 is a cross sectional view, taken along line  10 - 10  of FIG. 9, showing the tailored blank weld in the sheet material welded by the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0019]    [0019]FIG. 11 is a cross sectional view, similar to that shown in FIG. 10, showing an alternate orientation of the tailored blank weld welded by the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0020]    [0020]FIG. 12 is a top elevational view showing gap conditions between edges of adjacent sheets of material prior to being welded by the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0021]    [0021]FIG. 13 is a diagrammatic side elevational view showing a laser beam focal point and focal length for the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0022]    [0022]FIG. 14 is a schematic block diagram showing the interaction between electrical components employed within the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0023]    [0023]FIGS. 15A and B are a processing flow chart for the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0024]    [0024]FIGS. 16A and B are a processing flow diagram for the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0025]    [0025]FIG. 17 is a processing flow diagram for the preferred embodiment laser welding apparatus and control system of the present invention;  
         [0026]    [0026]FIG. 18 is a diagrammatic top elevational view showing a series of orientations of an alternate embodiment of the laser welding apparatus and control system of the present invention;  
         [0027]    [0027]FIG. 19 is a diagrammatic sectional view showing the alternate embodiment laser welding apparatus and control system of the present invention of FIG. 18;  
         [0028]    [0028]FIGS. 20A and B are electrical schematic diagrams showing the preferred embodiment laser welding apparatus and control system of the present invention; and  
         [0029]    [0029]FIG. 21 is an electrical schematic diagram showing the preferred embodiment laser welding apparatus and control system of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]    Referring to FIGS. 1 through 3, the preferred embodiment of a laser welding and cutting machine  31  employs a laser head assembly  33 , slide set  35 , seam tracking system  37  and gantry  39 . A tilting mechanism  41  is employed to tilt laser head assembly  33  relative to slide set  35 , gantry  39  and sheets of material  43 . Sheets of material  43  are held to a work table by clamps and/or magnets. Although machine  31  can be used to cut apertures and edges in sheets of material  43 , its use as a welding machine will be discussed in depth hereinafter.  
         [0031]    Laser welding head assembly  33  serves as a welding head and includes an Nd:Yag laser optic head  51  operably coupled to a laser microprocessor, laser light source (by way of a fiber optic cable) and laser cooling system  53 . Laser optic head  51  can be obtained from Haas Corporation of Germany with a power capability of 6 kilowatts, however, a laser with 2-6 kilowatts will also be suitable. Another Nd:Yag laser which would perform in an adequate manner is of the type disclosed in U.S. Pat. No. 5,434,880 entitled “Laser System” which issued to Burrows et al. on Jul. 18, 1995, and is incorporated by reference herewithin. As illustrated in FIG. 13, laser optic head  51  has a lens  61  which collates the nominally parallel laser beams  63  and preferably projects them toward a single focal point  65  corresponding to the upper surface of the desired weld seam. A specific collating lens  61  is preselected and installed depending upon the desired laser beam focal length Z f , as measured between lens  61  and focal point  65 . A focal length of 200 millimeters (7.87 inches) has been found satisfactory for performing tailored blank welding as will be discussed in greater detail hereinafter.  
         [0032]    Returning to FIGS.  1 - 3 , laser head assembly  33  further includes a high resolution CCD camera  71  affixed to the side of laser optic head  51 . CCD camera  71  aids in initial visual alignment of focal point  65  (see FIG. 13) with the abutting adjacent edges of sheets of material  43 , referred to as the welding seam  73  (although the term seam also refers to the cut edge when the present invention is employed to cut rather than weld material). The machine operator either looks through the CCD camera or observes an output LCD or CRT screen for aligning the laser beam focal point with the internally projected CCD camera cross hairs, by using a HeNe laser projected through a lens or by pulsing the Yag laser and measuring spot size. When the focal point is in registry with the X and Y axis cross hairs, laser head  33  and a bridge  75  of gantry  39  have been placed in their correct initialized position relative to the sheets of material  43 . One such CCD camera can be purchased from Pulnix, series TM-7/TM-6.  
         [0033]    A manually activated Z axis slide  77  has a fixed section  79  bolted onto a bracket  81 . A moving section  83  of Z axis slide  77  is oppositely bolted onto a laser optic head adaptor bracket  85  which holds laser optic head  51 . A manually rotated micrometer  89  is used in order to slide moving section  83  relative to fixed section  79 . This provides for minute manual fine positioning of laser optic head  51  and the focal point relative to sheets of material  43  during initial set up. Spring guides  87  assist in keeping moving section  83  snug against the micrometer  89 .  
         [0034]    Laser head assembly  33  further includes tilting mechanism  41 . Tilting mechanism  41  consists of a first primary goniometer  91 , a second slave goniometer  93  and a third primary goniometer  95 . These motorized goniometers are also more generally defined as radial bearings. The primary goniometers  91  and  95  are illustrated in more detail in FIGS. 7 and 8. Exemplary goniometer  91  has a driving bearing block  97  with a longitudinal bore  99  extending throughout its length. A worm gear or drive screw  101  is disposed within bore  99  and held in position by journalling plates  103  and  105  screwed to driving bearing block  97 . Additional bearing races may be employed. An armature shaft of an electric dc servomotor  107  is formed as part of or otherwise coupled to driving screw  101 . In another preferred embodiment, it is also envisioned that a knob (not shown) is affixed to driving screw  101  in place of motor  107  for manual actuation when only partial automation is desired. Goniometer  91  further has a driven bearing block  111  from which internally extends a set of teeth  113  arranged in a semi-circular manner having a radius equal to the focal length Z f . Teeth  113  are enmeshed with a portion of driving screw  101  such that when knob  107  is rotated, or an electric motor armature and armature shaft are rotated, driving screw  101  will simultaneously rotate for drivably rotating driven bearing block  111  in relation to driving bearing block  97 . The rotated positions can be observed by comparing FIGS. 7 and 8. As shown in FIG. 5, driving bearing block  97  and driven bearing block  111  are further secured to each other by mating dovetailed interlocks  115  and  117 . Teeth  113  (see FIG. 7) are centrally disposed along the center of interlock  115  in a longitudinal manner. Slave goniometer  93  is essentially the same as primary goniometer  91  except that the drive transmission, consisting of drive screw  101  and motor  107 , is omitted. Suitable manual knob actuated goniometers can be purchased from Chuo Seiki.  
         [0035]    As is illustrated in FIGS. 1 through 3 and  7 , driven bearing block  111  of each goniometer is bolted onto a lower plate  131  and oriented such that the longitudinal axis of first primary goniometer  91  is parallel to the longitudinal axis of slave goniometer  93  while third primary goniometer  95  is located perpendicular to goniometers  91  and  93 . Lower plate  131  is constructed from an aluminum sheet  133  adhered to a laminated sandwich  135  consisting of a pair of outer aluminum skins with either a balsa wood or aluminum honeycomb spacer therebetween. This laminated sandwich adds significant structural stiffness to lower plate  131 . Lower plate  131  has a U-like shape with an open cavity  137  for allowing free travel of the tilted laser optic head  51 .  
         [0036]    Bracket  81  is bolted upon driving bearing block  97  of third primary goniometer  95  such that manually actuated Z axis slide  77  operably tilts side-to-side. An upper plate  141 , constructed the same as lower plate  131 , is bolted upon driving bearing blocks  97  of first primary goniometer  91  and second slave goniometer  93 . Hence, lower plate  131  tilts and rotates in concert with goniometers  91  and  93 . Upper plate  141  has a central key-holed orifice  143  for receiving laser optic head  51 .  
         [0037]    Referring now to FIGS. 1 through 3, slide set  35  includes an automated Z axis slide  161 , an automated U axis slide  163 , a manually actuated T axis slide  165  and their associated mounting bracketry. A support bracket  167  is bolted onto an upper face of upper plate  141 . Furthermore, a stationary segment  169  of T axis slide  165  is bolted onto an upper shelf of support bracket  167 . A sliding segment  171  of T axis slide  165  has a sliding segment  183  (see FIG. 3) of U axis slide  163  bolted thereto. T axis slide  165  is constructed substantially the same as manually actuated Z axis slide  77 .  
         [0038]    U axis slide  163  has two rows of preloaded ball bearing races  175 , a central ball screw assembly  177 , four runner blocks (not shown), driving bearing end plates, floating bearing end plates and bellows  179 . Furthermore, an approximately 20 watt, dc servomotor  181  has an internal armature and armature shaft which rotatably drive ball screw assembly  177 . U axis slide  163  also has adjustable limit switches for determining the hardware travel limits of sliding segment  183  positioning relative to stationary segment  173 . Stationary and sliding segments, respectively  173  and  183 , are both machined from cast aluminum. Automated Z axis slide  161  is constructed similar to automated U axis slide  163  except that Z axis slide  161  has added structural stiffness and supporting ribs  185  as well as a longer linear travel. The electric servomotor employed with automatic Z axis slide  161  preferably has a power rating of approximately 60 watts. Two brackets  187  are bolted upon a sliding segment  189  of automated Z axis slide  161  and upon stationary segment  173  of automated U axis slide  163 . All of the brackets disclosed herein are preferably made from machined aluminum but may be provided with many differing shapes and configurations from those specifically shown.  
         [0039]    As can best be observed in FIGS. 3 through 5,  14  and  20 , seam tracking system  37  is preferably a Servo-Robot three-dimensional laser-camera  201 , type BIP- 20 . This Servo-Robot laser-camera  201  employs active optical triangulation principles using structured laser beam illumination and a photo sensitive illumination detection sensor. Laser-camera  201  further has a built-in 30 mW visible laser diode (independent from the welding laser) and has a 20 millimeter depth of view, 18 millimeter close plane field of view, 32 millimeter far plane field of view, 0.06 millimeter average depth resolution, and a speed of 30 profiles per second for 478 lateral sampling points and 60 profiles per second for 239 lateral sampling points. Laser-camera  201  has an air inlet  203 , a coolant outlet  205  and a coolant inlet (not shown). Laser-camera  201  utilizes the self-contained laser and sensor to optically track the welding seam in a non-contact and non-capacitive manner.  
         [0040]    A high performance pDSP parallel vision, laser-camera microprocessor and process controller  335  are compatible with an IBMPC ISA bus and are electrically connected to the self-contained laser and camera sensor within laser-camera  201 . Laser-camera microprocessor  335  employs a TMS320C40 parallel DSP which runs at 20 MIPS. The PILOT 3000 laser-camera microprocessor  335  coordinates the laser-camera  201  motion and three-dimensional data acquisition while also controlling the laser head servo controls, including automated slides  161  and  163 , in addition to CNC gantry controls, including an electric C axis rotation motor  211 , X axis gantry motor  501  and Y axis gantry motor  503 , through a gantry microprocessor  505 . The Servo-Robot laser-camera microprocessor  335  sends and receives information signals from and to an input/output/teaching pendant PC computer/microprocessor  337  running on a Windows® operating system.  
         [0041]    [0041]FIGS. 3 and 5 show laser-camera  201  mounted to a bottom of upper plate  141  within a square portion of orifice  143  by way of a pair of outer, inverted L-shaped brackets  223  cradling a central mounting cube  224  by way of threaded shoulder bolts  226 . Cube  224  is bolted onto laser-camera  201  and both are tiltable relative to outer brackets  223 , through temporary loosening of bolts  226 , to allow positional adjustment of laser-camera scanning relative to the welding beam focal point. A shield gas supply tube  225  is also affixed to upper plate  141  by suitable clamps (not shown). Argon shielding gas or the like is supplied to the welding seam through shield gas supply tube  225 . Laser camera  201  and tube  225  thereby move in concert with upper plate  141  and are thus, not tilted.  
         [0042]    Referring to FIGS. 1 and 2, gantry  39  includes a vertically rising pair of stationary structures or frames (not shown) upon which are movably mounted bridge  75 . Bridge  75  is moved along a Y axis, also known as the weld direction, by energization of one or more servomotors  503  (see FIG. 20B) which are mounted to bridge  75  or the structures and controlled by the gantry microprocessor  505 . A rotatable carousel  251  has an upper ring  253  with a set of outwardly extending teeth  255  driven by a chain  257 , belt or gear enmeshed with ring electric servomotor  211 . Carousel  251  further has a lower ring  259  bolted to upper ring  253  by a series of standoffs  261 . A 600 millimeter diameter rotary bearing  263  slidably couples lower ring  259  to the underside of bridge  75 . Hence, laser head  33  can be rotated relative to bridge  75  and sheet material  43  about C rotational axis. Automated Z axis slide  161  is bolted to an underside of lower ring  259 . Gantry  39  may be of the type generally disclosed in U.S. Pat. No. 5,229,571 entitled “High Production Laser Welding Assembly and Method” which issued to Neiheisel on Jul. 20, 1993, and U.S. Pat. No. 4,436,288 entitled “Metal Machining Device with Control Circuit Isolation” which issued to Kellogg et al. on Mar. 13, 1984, both of which are incorporated by reference herewithin. Additionally, a pneumatically actuated cylinder  271 , energized by a solenoid  507  (see FIG. 20B), a counterbalance assisting and counterbalancing Z axis movement of laser head  33 . Cylinder  271  has an intermediate portion bolted upon an upper surface of lower ring  259  and has a bottom member bolted to laser head  33  by way of Z axis slide  161 . A flexible electrical cable track  275  also has an end mounted to lower ring  259 .  
         [0043]    Reference should now be made to FIGS. 1 through 6 for an understanding of the function and operation of the present invention laser welding machine. As previously stated, teeth  113  of each driven bearing block  111  form a theoretically semi-circular shape having a radius equal to the focal length Z f . Therefore, tilting movement of goniometers  91  and  93  serve to tilt laser optic head  51  about its focal point  65  rather than about a traditional fixed mechanical pivot offset from the focal point. This provides superior accuracy in the focus of the laser beam despite various tilted orientations of laser optic head  51  in relation to the weld seam and sheet material. Further, no steerable or movable mirrors are used to redirect the laser beam.  
         [0044]    Structurally, driving bearing blocks  97  of goniometers  91  and  93  are fixed to upper plate  141  such that rotation of motor  107  or alternately, knob, causes the corresponding driven bearing blocks  111  to rotate and tilt lower plate  131 . This can best be observed by comparing FIGS. 5 and 6. The entire goniometer  95  tilts with driven bearing blocks  111  of goniometers  91  and  93  whereby bracket  81 , manually activated Z axis slide  77  and laser optic head  51  tilt in concert therewith about a first tilting plane.  
         [0045]    Third primary goniometer  95  can also be actuated to tilt laser optic head  51  in a second plane, perpendicular to that tilted by goniometers  91  and  93 . Regardless of the disposition of goniometers  91  and  93 , goniometer  95  can be actuated to rotate and tilt driving bearing block  97  relative to the driven bearing block  111  which is fixed to lower plate  131 . This causes bracket  81 , annually activated Z axis slide  77  and laser optic head  51  to tilt as shown by the arrow in FIG. 4. The goniometers preferably allow  14  degrees of laser tilting on either side of the vertical axis (see FIG. 2).  
         [0046]    Referring to FIGS. 1 through 3 and  14 , automated Z and U axis slides  161  and  163 , respectively, as well as C axis carousel  251 , are selectively moved by energization of their corresponding servomotors in order to have laser optic head  51  follow the welding seam when it is curved or the sheet material is bowed in the Z axis direction. The U and Z axis slide servomotors are controlled by a real-time, closed-loop feedback circuit through the weld head processor. The C axis movement is controlled by the gantry controls wherein a position feedback (encoder) signal is relayed to laser-camera processor  335  to allow the U axis movement to be corrected for the gantry programmed curve.  
         [0047]    As shown in FIGS. 9 through 12, the present invention is optimal for producing tailored blank butt welds. Tailored blank welds are those in which adjacent sheets of material  43  comprise similar or dissimilar metal types and/or thicknesses. For example, in automotive vehicle body side frames, it is desired to produce a butt weld between cold rolled steels  301  or on either lateral side of pieces of galvanized steel  303 . Galvanized steel  303  can be of a greater thickness than does cold rolled steel  301  thereby providing a somewhat difficult to access seam especially when they are placed in the orientation shown in FIG. 10.  
         [0048]    Laser optic head  51  is preferably tilted toward the open side of seam  73  when dissimilar sheets of material  43  are oriented as shown in FIG. 10, given a normal gap width. This provides significantly improved access to seam  73  while also reflecting laser beam away from the laser optic, thereby reducing harmful reflections from reaching the delicate optic lens. Alternately, laser optic head  51  is nominally oriented perpendicular to the upper coplanar surface of sheets of material  43  when oriented as shown in FIG. 11.  
         [0049]    Referring to FIGS. 1 through 3,  12 ,  14 ,  15 A,  15 B,  20  and  21 , the present invention significantly enhances tailored blank welding and similar material butt welding across large seam gaps which could not have been previously welded using conventional systems. The present invention laser welding machine accomplishes this large gap (greater than 10% of the material thickness) welding as follows. First, laser optic head  51  and laser-camera  201  are placed in their initialized position by use of the CCD camera  71 , manually activated Z axis slide  77  and automated U axis slide  163 . Second, laser-camera  201  and welding laser optic head  51  are energized such that laser-camera  201  projects and receives a triangulated and reflected laser beam along seam  73 . These first two steps are the procedures for initial set up of the axes and laser-camera reference. Laser-camera  201  projects its laser beam approximately 30 millimeters ahead of focal point  65  (see FIG. 13) from welding laser optic head  51  due to the laser-camera microprocessor  335  speed. However, it would be more desirable to orient the projected laser-camera beam focal point as close as possible to the welding laser beam focal point in order to achieve totally accurate actual condition sensing simultaneous with the welding. Third, laser-camera  201  and the Servo-Robot lasercamera microprocessor  335  controlled slides and servomotors track welding seam  73  as bridge  75  moves laser head  33  along the welding direction. This allows laser head  33  to accurately weld along a straight or curved seam  73 . Fourth, concurrently with the seam tracking function, laser-camera  201  senses the gap width Y between adjacent edges  331  and  333  of sheets of material  43 . Fifth, this sensed gap width Y is then output to a welding head microprocessor  401  for a comparison to a predetermined gap value X. Welding head microprocessor  401  stores the sensed gap value Y in RAM for a comparison to value X previously stored in ROM. Typically, gap value X is 10 percent of the lesser sheet material thickness. Sixth, welding head microprocessor  401  then determines if the sensed gap value Y is greater than a maximum non-weld value (for example, 25% of the lesser sheet material thickness). Seventh, if such a maximum non-weld value is observed, then welding laser and laser-camera  201  are de-energized for manual realignment or scrappage of the sheets of material  43 .  
         [0050]    Eighth, if sensed gap value Y is greater than predetermined value X but less than the maximum non-weld value, laser-camera microprocessor  335  and welding head microprocessor  401  will cause one or more combinations of the following events to occur: (a) servomotors  107  attached to each primary goniometer will be energized to automatically tilt the goniometers to predetermined rotational setting S depending upon the sensed value Y by reference to a ROM comparison table previously programmed into welding head microprocessor  401 ; (b) Laser microprocessor by way of a welding head microprocessor output signal, will increase the welding laser power a predetermined amount, through a laser microprocessor  509 , depending upon value Ybased on a preprogrammed welding head microprocessor  401  ROM chart; (c) Gantry processor by way of the welding head microprocessor  401  will slow down bridge  75  movement speed a predetermined amount, through gantry microprocessor  505 , depending upon sensed value Y based upon another ROM welding head microprocessor  401  table array or chart; (d) Welding head microprocessor  401  will energize then de-energize automated Z axis slide  161  to change the laser Z f  height relative to the sheet material an amount based upon another ROM table preprogrammed into welding head microprocessor  401  in light of the sensed value Y; this last step would be less desirable due to the mismatched focal length.  
         [0051]    The purpose in tilting, or further tilting, laser optic head  51  relative to the sheets of material  43  is that the effective material thickness (as measured along the angle of the welding laser centerline) is increased such that the weld gap Y would, in essence, be less than 10 percent of the angled material thickness. This would provide sufficient weld material flow for providing a strong butt weld. This laser tilting function is especially advantageous for a tailored blank weld wherein laser optic head  51  can be angled across the thicker sheet of material, thus, providing even greater weld material flow across a smaller effective percentage gap as compared to the angled material thickness.  
         [0052]    Moreover, the increased welding laser power and slowed bridge movement and raised welding laser height functions all provide increased welding material melting and flow to bridge the welding seam gap.  
         [0053]    The operational steps shown in FIGS. 16A and B are generally the same as those previously discussed and shown for steps  1  through  6  in FIGS. 15A and B, with the following subsequent differences. If a maximum-weld value is observed, then at least one of the following actions will occur: (a) welding head microprocessor  401  will cause energization of a laser beam servomotor  601  (see FIG. 19) for rotating or otherwise causing movement of split laser beams as will be described in greater detail hereinafter; laser beam servomotor  601  is energized a predetermined amount depending upon an energization time value correlating to sensed value Y as preprogrammed into ROM within welding head microprocessor  401 ; (b) the Y axis bridge movement speed will be slowed down a predetermined amount corresponding to sensed value Y preprogrammed into ROM within either welding head microprocessor  401  or gantry microprocessor  505 ; and/or (c) one or both servomotors  107  driving the goniometers will serve to tilt laser welding head  33  a predetermined amount depending upon a welding head microprocessor preprogrammed ROM motor energization time value corresponding to sensed value Y.  
         [0054]    [0054]FIG. 17 illustrates the initialized vertical axis height, Z i  which employs the sheet material and seam as the Z axis datum rather than the traditional use of the bridge as the datum. Accordingly, the initialized seam vertical height is initially established during welding laser head and laser-camera set up, thus defining Z i . Otherwise, the first through third steps of FIGS. 15A and B are generally the same for the process shown in FIG. 17. Subsequently, laser-camera microprocessor  335  (see FIG. 20) determines if a later sensed seam height Z s  is different than the datum Z i . This comparison is continuously and repetitively carried out throughout the entire welding path. If Z s  equals Z i  then no height adjustment is made and the sampling loop is continued as long as further welding is necessary. If Z s  is higher or lower than Z i  then the laser-camera microprocessor determines if Z s  is greater than maximum value height Z m , which would indicate undesirable excessive part warpage or bending. In this excessive situation, the welding laser and laser-camera are de-energized so the sheets of material can be scrapped (even if they could be properly welded). Finally, if Z s  is less than Z m , laser-camera microprocessor  335  will send a predetermined signal to welding head microprocessor  401  (see FIG. 21) which will concurrently cause energization of a Z axis motor  603  (also see FIG. 21) an amount equal to the difference between Z s  and Z i  in order to maintain the welding laser focal length and focal point upon the seam.  
         [0055]    [0055]FIGS. 18 and 19 illustrate an alternate embodiment laser optic head  611  employed within the present invention. Laser optic head  611  has a cylindrical housing  613  with a coaxially aligned internal passageway  615 . Electric motor  601  is mounted to housing  613 . Motor  601  has a fixed permanent magnet stator  617  and an internally disposed annular armature  619  surrounded by conductive copper wire windings  621 . Armature  619  has an internal bore  623  coaxially aligned and accessible to internal passageway  615  of housing  613 . Armature  619  is journalled within housing  613  by way of a pair of bearing races  625 . A casing (not shown) may surround motor  601 .  
         [0056]    Optic members are disposed within bore  623  of armature  619 . The optic members include a lens  641  and a prism  643 . Lens  641  has a circular periphery affixed to armature  619 . Prism  643  is located above lens  641  and retained either to lens  641  or armature  619  by various suspension brackets or the like. Electric motor  601  is preferably of a brushless type directly driving the optic members without additional gearing or belts. Optical members purchased from Trumf of Germany may also be employed for splitting the laser beams. Alternately, other beamsplitting devices may be used such as that disclosed within U.S. Pat. No. 5,478,983 entitled “Process and Apparatus for Welding or Heat Treating by Laser” which issued to Rancourt on Dec. 26, 1995, and U.S. Pat. No. 4,691,093 entitled “Twin Spot Laser Welding” which issued to Banas et al. on Sep. 1, 1987, both of which are incorporated by reference herewithin.  
         [0057]    The objective of this laser embodiment is to automatically move a pair of split laser beams, having focal points  651  and  653  from a first orientation  655 , with focal points  651  and  653  defining a line generally coaxial and parallel to a welding seam  657 , to a second orientation  655 ′, wherein focal points  651  and  653  define a line generally transverse to welding seam  657 . In second orientation  655 ′, focal point  651  is disposed on one side of welding seam  657  while the other focal point  653  is disposed on the opposite side of welding seam  657  (as viewed from above seam  657 ). This laser beam and focal point rotation are automatically achieved by welding head microprocessor  401  causing energization of motor  601  in either a counterclockwise or clockwise direction which rotates the beamsplitting optics. This rotation automatically occurs during Y axis welding movement without the need to turn off the machine or otherwise stop movement. Such focal point movement is ideal for welding across large seam gaps since the second orientation  655 ′ allows the welding laser beams to melt material from areas further away from the seam centerline to cause a larger molten pool and, thus, adequately weld across the larger seam. The focal points and laser beams are automatically returned to their nominal first orientation  655  when normal gap (less than 10 percent of the lesser sheet material thickness) welding conditions are sensed by the laser-camera. However, it should be appreciated that other beamsplitting optics and focal point movement actuators may be employed as long as automatic coaxial to transverse split beam positioning can be readily achieved. For example, multiple immediately adjacent laser heads, rather than the single split beam laser head disclosed, can be rotated or selectively energized and deenergized. Furthermore, a solenoid can be alternately energized to slide, rather than rotate, optic members within a beamsplitting laser.  
         [0058]    [0058]FIGS. 20A, 20B and  21  show the preferred electrical schematic diagram used to control the present invention laser welding apparatus. Servo-Robot pilot 3000 microprocessor, also known as the laser-camera microprocessor  335  is selectively connected to personal computer  337 . Personal computer  337  acts as a teaching pendant and includes a keyboard input device and a LCD output screen. Laser microprocessor  509  is further electrically connected to lasercamera microprocessor  335 . Laser-camera microprocessor  335  is also electrically connected to gantry microprocessor  505  by the following circuits or cables: Cable  1  provides alternating current into microprocessor  335 ; cable  2  provides lamp energization; cable  3  provides a safety alarm electrical interface; cable  4  provides X axis gantry encoder signals; cable  5  provides Y axis gantry encoder signals; cable  6  provides C axis gantry encoder signals; and cables  7  and  8  provide other digital interfaces between microprocessors  335  and  505 . Cables  10  and  11  electrically connect laser-camera microprocessor  335  to a junction box  701 , for sending and receiving U and Z axis slide signals. Additionally, cable  9  electrically connects junction box to gantry microprocessor. Also, laser-camera microprocessor  335  has CDU cables  1  and  2  electrically connected to a CDU box  703  which acts as an amplifier due to the cable distances between microprocessor  335  and laser-camera  201 .  
         [0059]    Gantry microprocessor  505  is electrically connected to and controls X, Y and C axis gantry encoders, respectively  705 ,  707  and  709 . These encoders transmit axial speed information based on each respective gantry motor or other separate linear slide movement sensing device by way of a feedback signal based on pulses/time. Gantry microprocessor  505  is also electrically connected to X, Y and C axis gantry brakes, respectively  711 ,  713  and  715 , which act as failsafe mechanical brakes for the device driven by each motor.  
         [0060]    A shielding gas solenoid  741  and an air knife solenoid  743  are electrically connected to junction box  701 . Junction box  701  is further electrically connected to welding head microprocessor  401  by way of cables  12  through  17 .  
         [0061]    Cables  20  and  21  electrically connect welding head microprocessor  401  with U and Z axis encoders, respectively  761  and  763 , a Z axis brake  767  (cable  21  only), and U and Z axis motors  181  and  603 , respectively. Left and right limit switches are part of the cable circuits  20  through  22  and  24  through  26 . Cable  22  serves to electrically connect a head retraction limit switch while cable  23  electrically connects welding head microprocessor  401  to shielding gas, air knife and counter balance solenoids. Finally, welding head microprocessor  401  is further electrically connected to tilting motors  107  by way of cables  24  and  25  as well as their limit switches. In the alternate embodiment, cable  26  electrically connects welding head microprocessor  401  to laser beam motor  601  through its respective limit switches.  
         [0062]    While the preferred embodiment of this laser welding apparatus has been disclosed, it will be appreciated that various modifications may be made without departing from the present invention. For example, only two goniometers may be required. Furthermore, greater or lesser numbers of plates, brackets and slides can be utilized as long as the laser head is provided with three-dimensional movement capability relative to the gantry. Also, tilting devices other than the disclosed goniometers can be employed as long as the laser is tilted about its focal point. It is also envisioned that the bridge may be stationary while the sheets of material are moved along the weld direction. An adhesive pumping, routing, grinding, milling, inspection or other heads may also employ the tilting mechanism of the present invention. Other electric control units such as MOSFETs, bipolars, or the like, or combined microprocessors can be substituted for the disclosed separated, modular microprocessors. Various materials have been disclosed in an exemplary fashion, however, other materials may of course be employed. It is intended by the following claims to cover these and any other departures from the disclosed embodiments which fall within the true spirit of this invention.