Abstract:
A positioning device for positioning a welding electrode near objects to be welded. A laser projects a light ray which is affixed to, and has a known spatial relationship with, the electrode. The laser is adjusted as to position, until the light ray strikes a target. At that time, the electrode stands in a corresponding position, which is the correct position for welding.

Description:
FIELD OF THE INVENTION 
     The invention concerns a device for positioning a welding electrode in an orbital tube-welding apparatus. Such apparatus are used to weld hollow objects to each other, such as a tube with a conical tube. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 illustrates a tube  3  which is to be welded to a conical structure  6 , which is hollow, and will be termed conic  6  herein. The tube  3  fits into a recess  9 , and is held concentric to the conic  6  by an annular flange  12 . FIG. 2 shows the tube  3  placed in position for welding. Dashed ellipse  15  represents a region which is shown in cross-sectional view in FIG.  3 . Tube  3  is shown, as are annular flange  12  and conic  6 . 
     The Inventor has identified a difficulty which occurs in welding the structures of FIG. 2 together, and has advanced a solution. 
     SUMMARY OF THE INVENTION 
     In one form of the invention, a laser is affixed to a welding electrode, and projects a laser beam in a predetermined spatial relationship with the electrode. A human operator positions the laser beam on a target, which has a predetermined spatial relationship with a spot to be welded. The electrode thereby becomes positioned at a predetermined spatial position with respect to the spot. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates two components  3  and  6 , which are to be welded together. 
     FIG. 2 illustrates the components of FIG. 2, in assembled form. 
     FIG. 3 is a cross-sectional view of region  15  in FIG.  2 . 
     FIG. 4 is a simplified schematic of a tube-welding apparatus. 
     FIGS. 5 and 6 are cross-sectional views of region  49  in FIG.  4 . 
     FIG. 7 illustrates a plane  60  into which the axis  57  of the electrode  46 , not shown in FIG. 7, must be positioned. 
     FIG. 8 illustrates how ring gear  43  blocks the view of eye  58 . 
     FIG. 9 illustrates a circle  79 , which indicates an allowable margin-of-error in positioning an electrode, not shown, at target  77 . 
     FIGS. 10 and 11 illustrate how parallax error occurs. 
     FIG. 12 illustrates parallax error in the device of FIG.  4 . 
     FIGS. 13 and 14 illustrate a process of bringing electrode  46  into contact with target  77 , and then creating a standoff distance between electrode  46  and the target  77 . 
     FIGS. 15 and 16 illustrate two forms of the invention. 
     FIGS. 17 and 18 illustrate alternate embodiments of the invention. 
     FIG. 19 is a flow chart illustrating processes undertaken by one form of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 4 shows the assembly  40  of FIG. 2, comprising tube  3  and conic  6 . The assembly  40  is positioned within a ring gear  43 . The ring gear  43  supports a tungsten welding electrode  46 . FIG. 5 shows a cross-sectional view of region  49  in FIG.  4 . 
     In FIG. 5, the electrode  46  is held at a standoff distance  52  from the flange  12 . After the electrode  46  is properly positioned, an electrical arc, not shown, is struck, by applying a momentary high voltage between the electrode  46  and the flange  12 . Next, after the arc is struck, a lower voltage is applied between the electrode  46  and the flange  12  which then maintains the arc, and the welding operation begins. 
     During welding, the ring gear  43  in FIG. 4 rotates as indicated by arrow  44 , while the assembly  40  remains stationary. During welding, the flange  12  is held at a positive potential, and the electrode  46  is held at a negative potential. 
     It is required that the electrode  46  in FIG. 5 be positioned accurately. For example, in one application, the tip  47  of the electrode  46  must be positioned in the plane of the junction  53  between the tube  3  and flange  12 . The plane includes the axis indicated by dashed line  56 . 
     If the electrode  46  is displaced from the proper position, as indicated by displacement  63  in FIG. 6, wherein the axis  57  of the electrode  46  is displaced from axis plane  56 , faulty welds can result. An axial displacement  63  as small as 0.015 inches, that is, 15 mils, is sufficient to prevent attainment of an optimal weld. 
     The term axial refers to movement in the direction of arrows  66  in FIG. 2, which are parallel to the axis  69  of the tube  3 . 
     It is difficult to position the electrode  46  so that any displacement  63  is within allowed limits. A primary reason is that the human operator&#39;s eye  58  in FIG. 7 cannot be placed in plane  60 , which contains axis  56  of FIG. 5, which coincides with junction  53 . That is, the eye  58  in FIG. 7 cannot sight along line  61  because the ring gear  43  obscures the view, as indicated by the break in line  61 . 
     Stated another way, if the operator could place the eye  58  in plane  60  in FIG. 7, the operator could perhaps determine whether axis  57  of the electrode  46 , not shown, coincides with axis  56 . However, ring gear  46  blocks the view of the operator. This overall problem will be explained in greater detail. 
     The axis of the junction point  53  in FIG. 5, indicated by dashed line  56  in FIG. 8, is obscured from eye  58  by the ring gear  43 . That is, dashed line  60 , running along the inside of the ring gear  43 , represents the plane that includes the axis indicated by dashed line  56 . In FIG. 8, the eye  58  of a human operator cannot see whether the electrode axis  57  is aligned with that plane  60 . Ring gear  43  prevents eye  58  from obtaining an edge-on view of plane  60 . 
     If the ring gear  43  were sufficiently large, the head of the operator could be positioned at point  75  in FIG.  8 . However, in the general case, the ring gear  43  is too small to allow such positioning. 
     A second reason for the difficulty in positioning electrode  46  is that, even if a human operator could gain access to an edge-on view of plane  60  in FIG. 8, that view does not necessarily solve the problem. One reason is that not all operators are sufficiently skilled to position the electrode  46  within the required 15 mils of a target position. For example, assume that the target position is represented by mark  77  in FIG. 9, which is scribed on the flange  12 . The operator is required to position the point of the electrode  46 , not shown, within circle  79 , which is 15 mils in radius. 
     However, circle  79  is not drawn to scale. A circle of 15 mil radius is extremely small: a human hair is about 3 to 5 mils in diameter, so that circle  79  has a diameter equal to the thickness of about six human hairs. Stated another way, circle  79  is much smaller than a pinhead, and is closer in diameter to the diameter of the shaft of the pin, rather than the pinhead. 
     Only a skilled operator can visually position the tip  47  of the electrode  46  in FIG. 5 within circle  79  in FIG.  9 . 
     A third reason why positioning the electrode  46  is difficult is that, even if an operator is sufficiently skilled to visually position the electrode  46 , manufacturing practicalities present an additional obstacle. The additional obstacle is caused by the fact that the tip  47  of the electrode  46  in FIG. 5 is not positioned adjacent mark  77  in FIG.  9 . Instead, the standoff distance  52  in FIG. 5 is maintained during the positioning process. This standoff distance generally lies in the range of 30 to 80 mils. 
     Under this requirement of maintaining the standoff distance  52 , parallax error creates problems for the operator. Parallax error is well known, and refers to the type of error which occurs when reading a needle on a volt meter. An accurate reading is best obtained when the reader&#39;s eye is directly above the needle, and looking perpendicular to the marks on a card beneath the needle. FIGS. 10 and 11 provide examples illustrating parallax error. 
     FIG. 10 is the view seen by a person whose eye is directly perpendicular to the meter  80 . The needle  81  is seen as indicating point  82 . In contrast, FIG. 11 illustrates the eye  84  of a person viewing needle  81  from the side, and sighting along line  85 . The needle  81 , which lies in plane  83 , appears to indicate point  86 . But in fact, the needle  81  indicates point  82 , as above. 
     A similar type of parallax error occurs when the eye  58  of the operator in FIG. 12 attempts to align the electrode  46  with mark  77 . 
     It may be thought that the electrode  46  could be brought into contact with the flange  12 , as in FIG. 13, to assist the operator in positioning the point of the electrode  46  against the mark  77 . Then, the electrode  46  would be withdrawn to the position shown in FIG.  14 . However, in practice, this is not done. The reason is that such a procedure would require that the standoff distance  52  in FIG. 5 be re-established, which is a time-consuming procedure. 
     Therefore, (1) the electrode must be positioned at an accurate axial position, (2) the ring gear  43  blocks a direct view of the tip of the electrode and introduces parallax error, (3) the parallax error is worsened by the fact that the tip of the electrode  46  is not adjacent flange  12 , and (4) even if an operator had a direct view, and the tip  47  were adjacent flange  12 , the tip  47  must be positioned within a very small distance from a target point. These factors make positioning electrode  46  difficult, or at least time-consuming. 
     The invention mitigates many of these difficulties. FIG. 15 illustrates one form of the invention. A laser  150  is affixed to the ring gear  43 , and shines a ray  153  onto the flange  12 . As shown in FIG. 15, the ray is displaced from the axis  57  of the electrode  46  by a distance  157 . Distance  157  equals the height  159  of the edge  155  of the flange  12  above the junction point  53 . The laser  150  is fixed in position with respect to the electrode  46 , and ray  153  is fixed with respect to the laser  150 . Thus, when the ray  153  is positioned so that it produces a spot on the edge  155  of flange  12 , the axis  57  of the electrode  46  will coincide with the axis indicated by dashed line  56 , as required. This positioning of ray  153  is achieved by moving the ring gear  43  up and down in FIG. 15, with respect to the assembly  40  in FIG. 15, as known in the art. 
     Ray  153  is parallel with axis  57  of the electrode  46 , and is perpendicular to the axis of rotation of the ring gear  43  in FIG. 4, which coincides with axis  69  of FIG.  2 . 
     Of course, edge  155  need not be used, and the system can be arranged so that ray  153  is required to shine on any suitable target, such as mark  77 , described in other Figures. 
     The laser need not be fixed to the ring gear  43 . FIG. 16 shows a removable laser  200 , projecting ray  153 . One or more indexing fingers  205  mate with teeth  208  of the ring gear  43 . Alternately, pins, not shown, on the laser  200  can mate with holes, not shown, in the ring gear  43 , to position the laser  200  in the desired position. The ring gear  43  is moved with respect to assembly  40 , as described above, to position the laser at the proper position. 
     Ray  153  need not be parallel with the axis of the electrode  46 . For example, as shown in FIG. 17, the laser  150  may be positioned so that ray  153  intersects the axis  57  of the electrode  46 . The distance between the intersection point  175  and the tip  47  coincides with the standoff distance. It is assumed that the electrode can be positioned on a radial line of the tube  3 . Therefore, when the laser- 150 /electrode- 46  assembly is brought toward the flange  12 , the assembly is correctly positioned when the laser dot coincides with mark  77 , as shown in FIG.  18 . 
     The intersection principle can be applied to the removable laser of FIG.  16 . 
     The standoff distance can be adjusted by adjusting distance  109  in FIG. 18, as by adjusting a screw, not shown. 
     The removable laser  200  of FIG. 16 is removable in a specific sense. In general, it could be said that anything is removable, because that thing can be unbolted, or cut, from its mounting. However, the laser of FIG. 16 is held in place by the operator&#39;s hand, not shown; gravity; a hand-operated wing nut, or the like. The laser is indexed in position by the teeth  205 , or the pins described above, or the like. Preferably, no tools are required by the operator to install, or remove, the laser. Thus, one definition of removable is that the laser can be properly positioned without the use of tools, and that, if fasteners are involved, the unaided human hand is sufficient to attain removal. 
     One form of the invention comprises a method of positioning electrode  46 . FIG. 19 is a flow chart of steps undertaken in the positioning process. In block  400 , a cylindrical assembly, such as that of FIG.  2 , is positioned coaxially within a tube welding apparatus. In block  405 , a laser is positioned, or maintained in a position, which bears a predetermined relationship with a welding electrode. FIGS. 15 and 17 illustrate two such relationships. 
     In block  410  in FIG. 19, the laser is activated, thereby producing a ray of light. In block  415 , the ray is moved so that it projects a laser dot onto a known target. FIG. 15 provides an example of a target, namely, edge  155  of the flange  12 . 
     Since the electrode  46  lies in a fixed physical relationship with the laser, placing the laser dot onto the target causes the tip of the electrode to assume its proper position. 
     Block  420  indicates that the laser is deactivated, and block  425  indicates that welding begins. One reason for the de-activation is that the welding arc (not shown) is an extremely intense source of electromagnetic radiation, including radiation in the visible spectrum. Such radiation may interfere with the lasing action of the laser, if not protected, as by a metal shield. 
     Another reason for de-activating the laser is that, as explained above, an initial high voltage pulse is applied to initiate the welding arc. In one embodiment of the invention, the laser is powered by the voltage difference between the electrode  46  and the conic  6 . FIG. 14 is a simplified schematic of the situation: a switch  450  connects laser  150  to the negative electrode  46  and the positive conic  6 . 
     In this embodiment, prior to actual welding, the normal welding voltage, of about 10 volts, is applied between the conic  6  and the electrode  46 . However, no arc has been struck at this time. This voltage only serves to power the laser  150 , which is used to position the electrode  46 . After positioning the electrode, the laser is disconnected, as by opening switch  450  in FIG. 14, and the welding operation begins. 
     This embodiment is represented by the optional path in FIG. 19 leading to block  430 , which indicates that the arc-maintaining voltage is used to power the laser. That is, block  430  indicates that the switch  450  in FIG. 14 is closed, in order to power the laser  150 . Blocks  435 ,  440 , and  445  in FIG. 19 correspond to blocks  410 ,  415 , and  420 , respectively. 
     Block  460  indicates that the arc-maintaining voltage is terminated, as by opening switch  450  in FIG.  14 . In block  425 , welding begins, wherein a high-voltage pulse is used to initiate the arc, and is then replaced by the arc-maintaining voltage. 
     Miniature lasers are commercially available, such as those used as gun sights for pistols and rifles. Rotary tube welding apparatus are also commercially available, such as those offered by Liburdi Dimetrics, in North Carolina, USA. 
     The preceding discussion has been framed in terms of an orbital welding system. However, this system should be considered exemplary only. The invention can be extended to most, if not all types of welding, wherein (1) an electrode, (2) a welding rod, or (3) a torch must be positioned accurately. Specifically included are gas tungsten arc welding, arc welding generally, and any welding process, including groove welding, fillet welding, and lap joint welding. 
     In addition, the weld joint need not be circumferential or curved, as occurs in orbital welding. The invention is also applicable to welding of flat plates, which can be viewed as orbital welding at an extremely large diameter. 
     Therefore, the invention presents an approach to positioning a probe involved in a welding operation. The particular use to which the probe is applied after the positioning, such as causing it to orbit about a tube, can be viewed as an ancillary matter. 
     Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims. For example, lasers were described herein. Collimated light may be used instead.