Patent Publication Number: US-2002005393-A1

Title: Multi-electrode welding system

Description:
CROSS-REFERENCES TO A RELATED PATENT &amp; A RELATED PATENT APPLICATION  
     [0001] The present Patent Application is related to an issued U.S. Pat. No. 5,837,968 and a pending U.S. patent application Ser. No. 08/852,324. The Applicant hereby claims the benefit of priority for any and all subject matter disclosed in a related U.S. Pat. No. 5,837,968 entitled Computer-Controlled Modular Power Supply for Precision Welding issued on Nov. 17, 1998; a related, pending U.S. patent application Ser. No.08/852,324, filed on May 7, 1997. 
    
    
     
       FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] None.  
       FIELD OF THE INVENTION  
       [0003] The present invention includes methods and apparatus for welding andj oining a wide variety of metal, plastic, composite or other types of workpieces. More particularly, the Multi-Electrode Welding System is a compact, versatile and highly effective machine tool that is capable of forming inside or outside welds on tubular stock.  
       BACKGROUND OF THE INVENTION  
       [0004] The worldwide aerospace industry is constantly confronted with obsolete fabrication technology and equipment that cannot keep pace with the technological requirements of today&#39;s and tomorrow&#39;s aircraft requirements. Each year the aerospace machine tool industry encounters new demands of engineers who specify increasingly complex machining processes for the manufacture of metal parts. One of greatest challenges confronting designers in the precision metal working industry is finding more precise and dependable techniques to join or to weld metal or plastic parts that may have exceedingly small dimensional tolerances or that may be fabricated from exotic metals and alloys, such as titanium, Inconel™ or hybrid stainless steels. The aircraft and aerospace industries are constantly confronted by difficulties that arise when hollow cylindrical metal, plastic or composite conduits need to be joined or welded.  
       [0005] The problem of providing a high-precision tool that can be used to weld or otherwise join metals, plastics, composites and other materials has presented a major challenge to engineers and technicians in the materials industry. The development of an accurate and versatile system that overcomes the difficulties encountered when conventional welders are utilized would constitute a major technological advance in the metal fabrication business. The enhanced performance that could be achieved using such an innovative device would satisfy a long felt need within the industry and would enable machine tool equipment manufacturers and users to save substantial expenditures of time and money.  
       SUMMARY OF THE INVENTION  
       [0006] The Multi-Electrode Welding System disclosed and claimed below solves many problems encountered by conventional welders. The Multi-Electrode Welding System is capable of precisely joining metal, plastics, composites and other materials. The present invention offers a compact, portable and easy-to-use tool for the welding industry. One of the preferred embodiments of the invention comprises a generally cubical tool that includes a weld head frame, a lid and a chamber base. The chamber formed within the frame, lid and base is designed to contain a volume of a generally inert gas that may be used for arc welding and for other joining operations. The chamber may be evacuated and back filled with a generally inert gas that is suitable for arc welding. The chamber may also be purged with an inert gas without evacuating.  
       [0007] In one embodiment of the invention, two electrodes situated within the chamber are utilized to perform inside and outside welds on a metal tube. Although one preferred embodiment of the invention uses one inside and one outside electrode, alternative embodiments of the invention may include any number and any combination of inside and/or outside electrodes. The invention includes a gear and power train which provides precise control of the orbital motion of the electrodes. The motion of each electrode is independently controllable, and one electrode may trail another as they move relative to the workpiece.  
       [0008] An appreciation of other aims and objectives of the present invention and a more complete and comprehensive understanding of this invention maybe achieved by studying the following description of preferred and alternative embodiments and by referring to the accompanying Drawings.  
     
    
    
     A BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] I. FIGS. 1 through 11A-Multi-Chamber Welder  
     [0010]FIG. 1 is a perspective front view of the outside of the Multi-Electrode Welding System, revealing a weld head frame, a chamber base and a lid. FIGS. 1A, 1B,  1 C and  1 D supply photographs of the invention.  
     [0011]FIGS. 2 and 2A offer perspective front views of the invention that reveals the weld head rotor and electrodes that occupy the chamber enclosed by the weld head frame, the chamber base and the lid.  
     [0012]FIGS. 3 and 3A present additional perspective front views like FIG. 2, but with the chamber base and workpiece inserts removed.  
     [0013]FIG. 4 supplies a cross-sectional view of one embodiment of the invention, revealing the electrode holders and associated elements. FIGS. 4A, 4B,  4 C,  4 D and  4 E furnish additional views of the invention.  
     [0014]FIG. 5 is a rear view of one embodiment of the invention that includes a dielectric housing, an I.D. spindle and I.D. and O.D. brush assemblies. FIGS. 5A and 5B provide cross-sectional views.  
     [0015]FIG. 6 provides a partially exploded rear view of the interior elements of one embodiment of the invention.  
     [0016]FIGS. 7 and 7A offer rear views of the internal workings of one embodiment of the present invention.  
     [0017]FIGS. 8, 8A,  8 B,  8 C and  8 D depict elements of various embodiments of a drive train.  
     [0018]FIG. 9 is a perspective front view of the invention that reveals the weld head rotor and electrodes that occupy the chamber enclosed by the weld head frame, the chamber base and the lid.  
     [0019]FIG. 10 is a perspective view of one embodiment of the drive train.  
     [0020]FIG. 11 reveals another view of a drive train. FIG. 11A supplies a cut-away cross-sectional view of one embodiment of the invention.  
     [0021] II. FIGS.  101 A through  112 -A Power Supply  
     [0022]FIGS. 101A, 101B,  101 C,  101 D,  101 E,  101 F,  101 G,  101 H and  101 I are isometric views of a preferred embodiment of the present invention.  
     [0023]FIGS. 102 and 103 are block diagrams which portray the functional capabilities of the present invention and the many possible connections to input, storage and peripheral devices.  
     [0024]FIGS. 104 through 109 are reproductions of photographs of the output of the display. This sequence of drawings illustrates the easy-to-use computer program which provides precise and automatic control of the present invention.  
     [0025]FIGS. 110, 111 and  112  furnish schematic diagrams of the electronic components of a preferred embodiment of the present invention.  
     [0026] III. FIGS. 201 through 212-Electronic Control Schematics  
     [0027]FIG. 201 is a schematic diagram of a welder micro-controller.  
     [0028]FIG. 202 is a schematic diagram which shows a current loop.  
     [0029]FIG. 203 is a schematic diagram which explains data conversion.  
     [0030]FIG. 204 is a schematic diagram that depicts motor control circuitry.  
     [0031]FIG. 205 is a schematic diagram that depicts motor power and control circuitry.  
     [0032]FIG. 206 is a schematic diagram of a processor.  
     [0033]FIG. 207 is a schematic diagram which shows circuitry related to memory and input/output decoding.  
     [0034]FIG. 208 is a schematic diagram of an input/output interface.  
     [0035]FIG. 209 is a schematic diagram of a motor control circuit.  
     [0036]FIG. 210 is a another schematic diagram which shows motor control circuitry. FIG. 211 is a schematic diagram of a power module current control circuit. FIG. 212 is a schematic diagram of a current source select circuit.  
    
    
     DETAILED DESCRIPTION OF PREFERRED &amp; ALTERNATIVE EMBODIMENTS  
     [0037] I. Multi-Electrode Welder  
     [0038]FIG. 1 presents an illustration of one of the preferred embodiments of the Multi-Electrode Welding System  10 , revealing a weld head frame  11 , a chamber base  14  and a lid  12  which closes down on the base  14  to form a tight seal. The frame  11 , lid  12  and base  14  form an enclosure or chamber  13 , which is designed to contain a volume of a generally inert gas that may be used for arc welding operations. Although FIGS. 1, 1A,  1 ,  1 B,  1 C and  1 D exhibit a generally cubical metal embodiment of the invention, any configuration or means which affords a readily accessible sealed chamber for gas welding will serve to implement the invention.  
     [0039] A workpiece is introduced into the chamber  13  through a pair of semi-annular inserts  16  that hold the workpiece (not shown), and maintain the chamber gas seal. In one embodiment of the invention, the workpiece is a generally cylindrical, tubular length of specialized aerospace metal such as titanium. Once the workpiece is securely in place, the chamber  13  may be evacuated and back filled with a generally inert gas that is suitable for arc welding. The chamber  13  may also be purged with an inert gas without evacuating. In one embodiment of the invention, argon is used as the inert gas.  
     [0040]FIGS. 2 and 2A reveal some of the working components of the present invention. A weld head rotor  18 , which is driven by a series of gears and motors depicted in other drawings, resides within the chamber  13  and controls the motion of inside and outside electrode holders  20  &amp;  22 .  
     [0041]FIGS. 3, 3A,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E reveal additional details of the interior of the present invention. In FIG. 3, the lid  12  and base  14  have been removed to show the rotor  18 , the inside electrode holder  20 , the inside and outside diameter electrodes ( 24 A &amp;  24 B) and the rotor and central drive shaft motor  26  which powers the rotor  18 . FIG. 4 supplies a cross-sectional view through the weld head frame  11  and base  14 , offering a detailed portrayal of a rotor outside diameter electrode holder  28 , an inside diameter spindle electrode holder  30 , flexing taper fingers  32  and a taper lock nut  34 .  
     [0042]FIGS. 5A and 5B are cross-sectional views of various embodiments of the invention. These views show a dielectric housing  40 , an inside diameter spindle  42  and outside diameter and inside diameter brush assemblies  36  &amp;  38 . The dielectric housing  40  serves as a insulator which electrically isolates the exterior of the invention form the active components within the chamber  13 .  
     [0043]FIGS. 6, 7,  7 A,  8 ,  8 A,  8 B,  8 C and  8 D offer views of the interior elements of one embodiment of the invention. These figures illustrate a rotor gear drive  44 , a rotor brush  46 , an outside diameter rotor brush assembly  48 , an idler gear  50 , a rotor drive motor pinion gear  52 , a rotor ring gear  54 , a central shaft gear  56 , a central shaft  58 , a rotor drive gear  60 , idler gears  62 , a meshing gear train  64 , a drive motor  66  and a drive motor gear  68 .  
     [0044]FIG. 9 is a perspective front view of the invention that reveals the weld head rotor and electrodes that occupy the chamber enclosed by the weld head frame, the chamber base and the lid. FIGS. 10, 11 and  11 A present views of the interior portions of the invention.  
     [0045] Although one preferred embodiment of the invention uses one inside and one outside electrode ( 24 A &amp;  24 B), alternative embodiments of the invention may include any number and any combination of inside and/or outside electrodes. When used in this Specification and in the claims that follow, the term “inside” refers to an electrode or other energy discharging means that supplies energy while it is located inside the chamber  13  and within the internal confines of a workpiece. The term “outside” refers to an electrode or other energy discharging means that supplies energy while it is inside the chamber  13 , but located outside the exterior of a workpiece. Although the preferred embodiment of the invention uses gta electrodes, alternative embodiments of the invention may employ plasma heads or any other means which uses energy to enable a welding or joining operation.  
     [0046] The invention includes a gear and power train which provides precise control of the orbital motion of the electrodes. The motion of each electrode is independently controllable, and one electrode may trail another as they move relative to the workpiece. Welding or joining operations may be performed on the inside or outside of a workpiece, or may be performed simultaneously. The number of drive motors used may vary with the complexity of the level of electrode control that is desired.  
     [0047] II. Power Supply  
     [0048]FIG. 101 A is an isometric view of a preferred embodiment of the Computer-Controlled Modular Power Supply for Precision Welding. A miniaturized, lightweight and portable aluminum enclosure  100  comprises rectangular frames  102  and  104  which provide support for the panels held within them. Compared to previous power supplies, the present invention represents a substantial improvement in the amount of space and volume that it occupies. Although the embodiment portrayed in FIG. 10A weighs only about forty-five pounds, it is capable of delivering from 25 to 200 amperes of high quality power for welding tasks. The invention may be used to control welding, induction heating an XY-table or CNC operations. When used to control welding tasks, the Power Supply may be used for longitudinal, multi-head and multi-axes procedures. The present invention may operate twin electrodes simultaneously.  
     [0049] The front panel  200  of the enclosure  100  includes a display with a touch screen  300  that allows the operator of the power supply to control and to monitor its functions. The operation of the power supply may also be monitored remotely using a cathode ray tube display. The embodiment shown in FIG. 1OlA has three modules: a Computer Control Module  400 , a Welding Power Module  500  and an Electrical Power Module  600 . A carbon steel enclosure  302  which prevents transients from disturbing the operation of the electronic components within the Module  400  resides inside Computer Control Module  400 . FIG. 100B offers another isometric view of the enclosure  100 , while FIG. 101C reveals a view of the interior  106 . Rails  108  span the enclosure&#39;s interior  106  and are capable of receiving a variety of modules  400 ,  500  &amp;  600  into bays  110  within the enclosure  100 . Figure lOlD exhibits the side walls of the Computer Control Module  400  and the Welding Power Module  500 . The Computer Control Module  400  includes a computer peripheral panel  402 . This panel furnishes external coupling hardware, including PCMCIA and remote display couplers; serial ports for connections to pointing devices, keyboards and modems; and parallel ports for connections to printers.  
     [0050]FIGS. 101E through 101I present detailed views of the components of the power supply enclosure  100 . Any number or combination of similar or different modules may be inserted into the enclosure. This modular design offers maximum flexibility and versatility to the customer, and is especially valuable when individual parts of the welding power supply need to be maintained, tested, repaired or replaced.  
     [0051] In the preferred embodiment of the invention, the Welding Power Module  500  comprises four drawers  502  which each contain an individual power unit. Although one embodiment utilizes four drawers  502 , the invention provides for many alternative configuration of a wide variety of different sized drawers. The outside walls of each of the drawers  502  the Welding Power Module  500  have a number of deep cut heat dissipating fins  504 . Unlike previous conventional power supplies which utilize heat sinks and fins located inside the power supply enclosure, the present invention has fins  504  on the exterior of the enclosure  100 . Heat produced by each of the drawers  502  is released by both conduction, convection and radiant cooling. These fins  504 , which are integrally formed on the drawers  502 , help the enclosure  100  to function as a very large heat sink. This innovative feature eliminates the need for cooling fans or vents, which would introduce dust, dirt and moisture into the environment within the enclosure. By keeping the Power Supply free from this contamination, the reliability and performance of the internal electronic components are greatly enhanced.  
     [0052]FIGS. 102 and 103 are block diagrams that reveal the functional capabilities of the present invention and the many possible connections to input, storage and peripheral devices  700 . In one embodiment of the invention, the Computer Control Module  400  includes a ports for a PCMCIA connector  702 , a keyboard  704 , a pointing device or mouse  706 , an external monitor  708  and a printer  710 .  
     [0053]FIGS. 104, 105,  106 ,  107 ,  108 ,  109 ,  110 ,  111  and  112  are reproductions of photographs of the output of the LCD with a touch screen. This sequence of drawings illustrates the easy-to-use computer program which provides precise and automatic control of the present invention.  
     [0054] Computer Control Module  400   
     [0055]FIG. 110 is a schematic diagram which shows the circuitry within the Computer Control Module  400 . FIGS. 111 and 112 provide schematic illustrations of the Microcontroller and Arc Starter circuits. The computer control circuits incorporate concurrent processing architecture and includes a micro-processor  406 , a non-volatile memory  408  and an embedded real time control processor. The microprocessor  406  controls and monitors the function of the Welding Power Module  500 . The Computer Control Module controls each module individually or in unison. In one embodiment of the invention, an 80486 chip is employed to produce a graphic user interface that is generated on the display  300 . Proprietary software developed by Creative Pathways™, Inc. of Torrance, Calif. creates an extremely user-friendly environment using the Microsoft™ Windows™ Operating System. Unlike some previous power supplies, the display is integrated into the Power Supply.  
     [0056] The Computer Control Module performs data logging, generates reports and stores and displays welding parameter and welding power calibration entries. Calibration data may be entered using the touch screen display  300 . The micro-processor then stores the calibration points in a non-volatile memory. These data points are then used during all subsequent welds. The processor monitors the weld data, and checks it against the stored calibration data. A report may be generated at the end of weld operation, which would report any errors that occurred during the sequence.  
     [0057] Welding Power Module  500   
     [0058] The Welding Power Module is capable of operating one, two or more welding arcs simultaneously.  
     [0059] Electrical Power Module  600   
     [0060] The Electrical Power Module  600  includes an on/off switch, an EMI filter, a motor control and provides circuitry for housekeeping and management functions. This module uses advanced switching mode current source supply technology. The system may operate at close to a 100% duty cycle at full load.  
     [0061] Applications in Cleanroom &amp; Aerospace Environments  
     [0062] The preferred and alternative embodiments of the present invention may be fabricated for bench-top operation, for use in a lightweight portable scaffold, as part of a cleanroom installation or as part of the specialized equipment that will be employed on the International Space Station.  
     [0063] The invention may be used as a stand-alone unit or may be used in combination with remote control equipment. The PCMCIA cards maybe transported back and forth between welding stations, quality control and inspection sites and engineering and staff meetings where the recorded data can be printed out and analyzed.  
     [0064] Operation of the Power Supply  
     [0065] One embodiment of the invention is specifically designed to be used for welding stainless steel and titanium tubes. The welding process begins with a burst of high voltage energy to start the arc after the purge gas has been turned on. This energy travels down the welding cables through the weld head and across the gap between the electrode and the tube. At the same time, arc start energy radiates off the welding cables and the weld head. This energy is called electromagnetic interference or “EMI noise.” In the present invention, the EMI noise is minimized by the following features:  
     [0066] 1) Careful isolation of each power converter, i.e., computer power supply, arc starter, power module, etc.;  
     [0067] 2) Proper single point grounding and tight EMI shielding of the entire box;  
     [0068] 3) Shielded weld cables;  
     [0069] 4) Regulating the amount of energy used for the Arc Start; and  
     [0070] 5) Separate shielded compartment for the 486 computer and embedded real time control processor. The individual power units in drawers  504  are programmed to begin delivering current to the weld work piece as soon as the Arc Start voltage ionizes the local atmosphere. When the Arc Start initiates the welding sequence, the power module output voltage drops to a typical voltage of approximately 12 VDC. The current is then regulated as previously programmed using the touch screen display  300 . The computer  400  can energize the drawer  504  at random and can sequence among them as required by the needs of a particular welding task.  
     [0071] In addition to the power module control, the embedded control processor  410  regulates the operation of the motor. This control includes speed, ramp speed up and down and home speed.  
     [0072] As is best seen in FIG. 110, the operator has several ways to control the welding sequence. The primary interface is the touch screen display  300 . The touch screen display overlays a VGA color monitor. The  486  computer weld software runs within the Microsof™ Windows™ Operating System. This provides the user with a familiar operating system, and minimizes training.  
     [0073] The keyboard  704  and mouse or pointing device  706  provide alternative interfaces to the welding equipment, thereby bypassing the touch screen  300 . The printer  710  enables the operator to print for record keeping any of the weld schedules.  
     [0074] In a preferred embodiment of the invention, the embedded real time control processor  410  is a Philips 87C552 or similar micro controller. The  486  computer  406  sends user commands to the embedded controller  410  via a serial interface. The embedded controller then commands and regulates the internal operation of the weld sequence by controlling the following components and variables:  
                                                  1) Gas Purge Solenoid Valve;           2) Motor Control;           3) Arc Starter;           4) Power Modules; and           5) Output Voltage and Current Sense.                      
 
     [0075]FIG. 111 is a block diagram that depicts the inputs and outputs of the micro controller  410 . This figure essentially shows how the micro controller is coupled to each of the power units in drawers  504 . The DAC outputs a linear control voltage that determines how much current is supplied to the weld workpiece. The signal is interfaced differentially as well as shielded. The on/off control of the power units is an open collector gate than can be disabled by the watch dog timer. Primarily, the interface is designed for safety and noise. The watch dog timer  412  gets an interrupt from the microcontroller each time the software routine is executed. If for some reason the software routine is not executed, i.e., the computer “hangs-up,” the watch dog timer  412  initiates a reset to the processor and turns off the power modules, thus instantly returning the welder to-a safe state.  
     [0076]FIG. 112 reveals the details of the novel Arc Starter Circuit  450 . It works directly off a conventional 110 VAC power source. A voltage doubler and rectifier is connected directly to the 110 VAC input. A capacitor stores the electrical energy to be used as arc start energy. A silicon-controlled rectifier (SCR) becomes a short to ground when commanded by the micro controller. The charge stored on the capacitor dumps to ground through the transformer and SCR. This capacitor discharges with a current spike of approximately 30 amps. The Hyman Trigger transformer  454  then generates a high voltage greater than 4000 volts.  
     [0077] Welding Schedules &amp; Input Parameters  
     [0078] Table One provides a typical set of current level data for a welding operation.  
               TABLE 1                          SET WELD SCHEDULE CURRENT       CREATIVE PATHWAYS       Micro-Impulsar 100                                 Schedule Name:   Date:   Misc:           Boeing Duct Weld   5/15/92   7′ .035 Ti 24 1PM                                         Impulse Current (0.0-100.0 A)   75.0           Impulse Start Level (2.0-100.0 A)   20.0           Maintenance Current (0.0-100.0 A)   65.0           Maint. Start Level (2.0-100.0 A)   18.0           Pulse Rate (0-100 PPS)   75.           Duty Cycle (0-100%)   50.                      
 
     [0079] A brief explanation of the parameters contained in Table One follows.  
                                      IMPULSE CURRENT:   (5 to 100 Amps) Arc Impulse Current. Impulse           current can be thought of as the arc penetrating           current. It is meant to penetrate through the           tube and form the inner weld bead. The user           may have to experiment with this setting by           making a test weld, then sectioning the tube           to examine the inner bead.       IMPULSE START   (5.0 TO 100.0 Amps). The impulse current at       LEVEL:   the start of upslope. This would normally be           about 10% of the impulse current or 5 Amps,           whichever is greater. When upslope is not           being used, set this value the same as the           impulse current.       MAINTENANCE   (3 to 100 Amps) Arc Maintaining Current.       CURRENT:   Maintenance current or background current is           the current that maintains the arc and heat input           between pulses.       MAINT START   (3.0 to 100.0 Amps). Maintenance current level       LEVEL:   at the start of upslope. Normally 10% of the           maintenance current level or 4 amps, whichever           is greater. When upslope is not being used, set           this value the same as the maintenance current.       PULSE RATE:   (1 to 100 Hz) The number of times per second           the current switches from impulse to           maintenance. Set the frequency so that you can           just notice each individual impulse overlap the           preceding one when inspecting the weld. If the           frequency is too high, the arc will wander and           the edges of the weld will be rough and un-           even. If the frequency is set too low, the weld           will resemble individual overlapping spot           welds.       DUTY CYCLE:   (2 to 98%) The percentage of time the current           is at the impulse level. This control allows a           convenient method for making small adjust-           ments in the weld schedule once it has been           developed. To slightly increase penetration,           increase duty cycle 1 or 2 percent; use the           reverse to decrease penetration.                  
 
     [0080] Table Two contains timing information for a welding sequence.  
               TABLE 2                          SET WELD SCHEDULE TIMING       CREATIVE PATHWAYS       Micro-Impulsar 100                                 Schedule Name:   Date:   Misc:           Boeing Duct Weld   5/15/92   7″, .035 Ti 26 1PM                                         Pre-Purge time (1-100.0 s)   4.0           Upslope time (0-100 s)   5.0           Dwell (0.0-180.0 s)   47.0           Taper Down Interval (0.0-100.0 s)   6.0           Taper Down Percent (0-100%)   50           Down Slope (0.0-100.0 s)   4.0           Post-Purge time (1-100 S)   4.0                             PRE-PURGE:   Set this control to allow enough           (2 to 100 seconds):   time for the gas to displace all               oxygen in the weld head, i.e. 25 to               40 seconds for CPI&#39;s smaller heads.               For the duct welding system, this               value should be at least 60 seconds.           UPSLOPE:   (0 to 100 seconds). Impulse and               maintenance current levels increase to the               dwell levels.           DWELL:   During this time, the output current           (1 to 180 seconds).   switches between the impulse and               maintenance levels at the frequency and               duty cycle entered. The dwell cycle forms               the main body of the weld.           TAPER:   Impulse and maintenance current levels           (0 to 100 seconds).   decrease linearly to a certain percentage of               their initial value. Taper can be used as a               second downslope cycle to slowly               decrease the heat input before the current               is finally downsloped to zero.           PERCENT TAPER:   The percentage decrease in impulse and           (0 to 100 percent).   maintenance current at the end of the taper               cycle.           DOWNSLOPE:   Impulse and maintenance current levels           (0 to 100 seconds).   decrease uniformly to zero. The               downslope cycle forms the end of the               weld.           POST-PURGE:   Set this control for enough time to ensure           (1 to 100 seconds).   that the weld does not oxidize or discolor               after it is completed, i.e. 30 to 50 seconds               for CPI&#39;s smaller heads, 60 seconds or               more for a duct weld.                      
 
     [0081] Table Three exhibits rotor control parameters.  
               TABLE 3                          SET ROTOR CONTROL PARAMETERS       CREATIVE PATHWAYS       Micro-Impulsar 100                                 Schedule Name:   Date:   Misc:           Boeing Duct Weld   5/15/92   7″ .035 Ti 24 1PM                                         Rotor Delay time (0-10.0 s)   1.0           Rotor Weld Speed (0-100%)   13           Rotor Start Speed (0-100%)   30           Rotor Ramp Time (0.0-100.0 s)   4.0           Rotor Home Speed (0-100%)   100                             ROTOR DELAY TIME:   Delay time from arc start to fixture           (0 to 10.0 seconds).   drive enable. This time period may               be used to delay the fixture drive               for short periods in order that the               arc can penetrate deep into the               material being welded. Rotor delay               is sometimes used with heavy wall               tubing or large diameter thin wall               ducting.           ROTOR WELD SPEED:   Weld speed. This is the fixture           (1 to 100 percent).   speed that is used during the weld.               Micro-Fit weld heads utilize an               optical encoder feedback system               for speed control accuracy of better               than ¼ percent.           ROTOR START SPEED:   This is the fixture speed at the start           (0 to 100 percent).   of the weld. The weld head will               start at this speed and ramp up to               the weld speed. If motor ramping               is not being used, set the rotor start               speed to the same value as the rotor               weld speed.           ROTOR RAMP TIME:   This is the time that the           (0.0 to 100.0 seconds).   weld head takes to ramp               from start speed to weld               speed. If motor ramping is               not required, set this value               to zero.           ROTOR HOME SPEED:   Weld head jog and return to           (1 to 100 percent).   home speed. For welding,               set this value to a fairly high               number so the weld head               will return to home quickly               at the end of the weld. For               jogging the weld head, set               this value to a lower               number.                      
 
     [0082] The present invention uses weld heads which utilize optical sensors for both speed and position control. To further simplify the head design, there are actually two home positions.  
     [0083] Table Four reveals data concerning the arc starter.  
               TABLE 4                          SET ARC STARTER PARAMETER       CREATIVE PATHWAYS       Micro-Impulsar 100                                 Schedule Name:   Date:   Misc:           Boeing Duct Weld   5/15/92   7″ .035 Ti 24 1PM                                         Arc Start Current (0.0-100.0 A)   50.0           Arc Start Duration (0.0-1.00 S)   0.15                             START CURRENT:   This is the current that flows           (20 to 90 amps).   during the arc start cycle. A setting               of 40 amps is optimal for most               applications. Large diameter thin               wall ducting requires around 50               amps.           START DURATION:   The length of time that the start           (.02 to .99 seconds).   current flows. This control is used               for setting arc start intensity. A               setting of 0.15 seconds is a good               starting point, although if you are               welding small diameter thin wall               tubing, a lower setting will be               required.                      
 
     [0084] III. Electronic Control  
     [0085] Twin electrode welding requires generating two arcs on two electrodes. This allows the operator to weld from the inside of a tube while simultaneously welding from the outside of the tube. This has many advantages, such as increased welding speed, less heat developed in the tube, and reduction in the amount of warpage due to welding.  
     [0086] Twin electrode welding may be implemented either by operating two single electrode power supplies together, or by a totally integrated computer controlled twin power source. Although the explanation that follows pertains to the use of two electrodes, any number of electrodes may be employed by the present invention.  
     [0087] The basic Welder Computer Controlled Power Supply is made up of three basic power source components: a Computer Section, a Power Module Section and an Electrical Section. In general, the Computer Section consist of all the elements typically found in a desktop computer. This computer operates from Microsof™ Windows™, and provides the basic user interface. The Power Module Section contains the power conversion electronics that convert the 110 volt input to low voltage high current weld power. The dynamic range of the power modules is from 2 amps to 100 amps. However, the dynamic range can be easily extended beyond those limits by simply replacing the power modules. The third section is the Electrical Section containing the microcontroller electronics, arc starter and basic interface electronics for the motor, foot pedal and purge solenoid.  
     [0088] Upon start of weld, the Arc Starter is enabled for a predetermined amount of time. At the end of this time, the arc voltage is measured to determine if the weld can continue. The starting current during the arc start is only valid during the arc start time. Initially, this stating current is programmable from the Microsof™ Windows™ control panel. Following the successful arc start, the system begins “up slope.” The starting current for up slope is the same for both impulse and maintenance. The current for impulse and maintenance ramp up together to their final dwell values. Down slope begins after dwell. Down slope is a mirror image of up slope. The impulse and maintenance currents ramp down to a final current value. The final current value is the same as the starting current value. When this value is reached, all of the power modules are turned off. The motor then returns to home at the “Home Speed.” 
     [0089] To perform two welds simultaneously using two computer controlled power supplies, the welding power supplies must be synchronized together. This is accomplished by connecting an interface cable between the two units. From the touch screen, the user selects one of the power supplies to be a “slave.” This means that the other power supply “master” can take control of the basic welder functions. The welders are set up using the same screens as before. The twin welding is initiated by pressing the “Start” weld button. The master microcontroller commands and controls the Arc Start time/duration as well as required welding currents.  
     [0090] Elements that make up the Welder include:  
                                                   1) Arc Starter            2) Power Modules: 15 and 30 amps            3) Motor control            4) Gas Purge Solenoid Valve            5) EMI Filtering            6) Output Voltage &amp; Current Monitor            7) Low Voltage Power            8) Microcontroller &amp; System I/O Hardware            9) Windows Computer Hardware           10) Harnesses, Cabling &amp; Connectors           11) Microcontroller Software           12) 486 Computer Windows Software           13) Touch Screen &amp; Display Hardware                      
 
     [0091] A. EMI Suppression  
     [0092] The welding process begins with a burst of high voltage energy to start the arc after the purge gas has been turned on. This energy travels down the welding cables through the weld head and across the gap between the electrode and the tube. At the same time, arc start energy radiates off the welding cables and the weld head into the air—“EMI Noise.” The EMI noise is minimized in this system by:  
     [0093] 1) Careful isolation of each power converter, i.e., computer power supply, arc starter, power module etc.;  
     [0094] 2) Proper single point grounding and tight EMI shielding of the entire box;  
     [0095] 3) Shielded weld cables;  
     [0096] 4) regulating the amount of energy used for the Arc Start;  
     [0097] 5) Separate shielded compartment for the computer and embedded real time control processor; and  
     [0098] 6) Twin electrode interface cable must be shielded with both ends tied to chassis and all signals heavily filter using ferrite beads.  
     [0099] The twin interface cable is especially susceptible given it close proximity and exposure to both ARC&#39;s.  
     [0100] B. Operational Details  
     [0101] The individual power modules are progranuned to begin delivering current to the weld piece as soon as the Arc Start voltage ionizes the local atmosphere. When the Arc Start initiates the welding, the power module output voltage drops to a typical voltage of approximately 12 VDC. The actual weld voltage is dependent on the amount of current being used in the weld process, and may vary from 7 volts up to 25 volts. The current is then regulated as previously programmed using the touch screen display.  
     [0102] In addition to the power module control, the embedded control processor regulates the operation of the motor. This control includes speed, ramp speed up and down and home speed. In one embodiment of the invention, the twin microcontroller electronics can control up to three independent motors. Typically, for twin operation, the motor is controlled by the master power supply.  
     [0103] The operator has several ways in which to interface to welder. The primary interface is the touch screen display. The touch screen display overlays a VGA color monitor. The computer weld software runs out of windows. This provides the user with a familiar operating system which minimizes training.  
     [0104] The keyboard and mouse provide alternative interfaces to the welder, bypassing the touch screen. The printer allows the operator to print for record keeping any of the weld schedules.  
     [0105] The Embedded Real Time Control Processor is a Phillips 87C52 or similar microcontroller. The 486 computer sends user commands to the embedded controller via a serial interface. The embedded controller then commands and regulates the internal operation of the weld sequence controlling the following:  
     [0106] 1) Gas Purge Solenoid valve;  
     [0107] 2) Motor Control;  
     [0108] 3) Arc Starter;  
     [0109] 4) Power Modules; and  
     [0110] 5) Output Voltage &amp; Current Sense.  
     [0111] The microcontroller via the “DAC,” outputs a linear control voltage that determines how much current is supplied to the weld piece. The on/off control of the power module is an open collector gate than can be disabled by the watch dog timer. Primarily, the interface is designed for safety and noise immunity. The watch dog timer gets an interrupt from the microcontroller each time the software routine is executed. If for some reason the software routine is not executed, e.g., the computer “hangs-up,” the watch dog timer initiates a reset to the processor, and turns off the power modules, instantly returning the welder to a safe state.  
     [0112] The following text provides brief explanations of modules controlled by the microcontroller:  
     [0113] 1. Power Modules  
     [0114] In one embodiment of the invention, the basic system contains as few as one module or as many as five. Module A can provide output currents from 1 amp to 15 amps. All other modules can deliver from 5 amps to 30 amps.  
     [0115] a. Module A is on all the time.  
     [0116] b. Module B is enabled for currents greater than 10 amps.  
     [0117] c. Module C is enabled for currents greater than 30 amps.  
     [0118] d. Module D is enabled for currents greater than 60 amps.  
     [0119] Each module must be individually turned on with an active high. The current command is provided through the 12 bit DAC. Full scale represents 100 amps. Individual power modules are only enabled when required by the current command. The sharing of current by each module is controlled by the microcontroller. Each module delivers the same percent of the modules full load capacity, maintaining relative component stress equally for all power modules. For example, Module A can deliver 15 amps, and Module B can deliver 30 amps. If both are on and the system is delivering 15 amps, then, the 15 amp module is generating 5 amps (33% of full load), and the 30 amp module is generating 10 amps (33% of full load).  
     [0120] The microcontroller uses a feed back control loop to regulate the amount of current used in the weld process. The microcontroller via the DAC outputs a voltage that corresponds to the amount of current required for the weld piece. This voltage is compared to the system output current sensor and the difference is an error signal or voltage. The current error signal is integrated and then is used to drive the current command signal of each of the power modules. The current command signal is continuously update until the system current exactly matches the current command signal from the microcontroller. The speed of this process is less than a millisecond which allows for the weld impulse frequency to achieve 100 Hz.  
     [0121] The microcontroller turns on enough power modules to provide tilt current required by the weld schedule. The current command signal is part of a control loop that precisely regulates the amount of current being delivered to the work piece. If the weld piece requires more or less voltage to achieve the programmed amount of current, the electronics automatically updates the command signal in less than a millisecond. The individual power modules are designed to turn on and slew to full load in less than a millisecond. This allows the impulse current to turn on and achieve its steady state value very quickly. The software is designed to share the load equally among all the power modules. The power modules only reach full capacity when the output current requirement exceeds 100 amps.  
     [0122] Other features include the ability of the system to start with an initial current less than 2 amps. The beginning of the current upslope is user selectable to the initial current. The end of downslope is hardcoded to 2 amps however, but may be programmed to be user selectable.  
     [0123] 2. Purge  
     [0124] This sub-system controls the flow of gas to the work piece. It is turned on with an active high. The user can enable/disable the purge from the Windows™ program. The user can also set-up prepurge and post purge times, such that the work piece purge can be automatically controlled by the computer.  
     [0125] 3. Motor Control  
     [0126] Motor control is similar to the Power Module. The Motor must be turned on with an active high. The speed of the motor is controlled through the  12  bit DAC. Full scale represents a speed of 100%. The motor on/off control prevents the motor from creeping while in idle. Motor speed is controlled independent of current. However, it can be ramped up and down same as current.  
     [0127] 4. Voltage Sense  
     [0128] This is an 8 bit number that is a measure of the weld head voltage. In one embodiment of the invention, full scale is set to 40 volts. This voltage is displayed on the monitor as part of the graph presented to the operator. The micro-controller needs to use this voltage to determine if the Arc Starter successfully struck an arc. The voltage will be below 25 volts if the arc has been successfully started. After the Arc Start has timed-out, the voltage is checked. If the voltage is less than 25 volts, then the weld process proceeds. If the voltage is above 25 volts, the power modules are all turned off and the motor proceeds to HOME using HOME SPEED.  
     [0129] 5. Foot Pedal Control  
     [0130] The foot pedal control is independent of the PC control. An FT Start signal indicates the user has depressed the pedal. At this time, the arc starter is turned on for a predetermined length of time (100 mSec). If the arc starts successfully, the current is controlled by the ADC that measures the voltage that is proportional to the position of the foot pedal. This continues until the FT Start signal goes away, indicating the operator has completed the weld.  
     [0131] IV. Integrated Twin Electrode Computer Controlled Power Supply  
     [0132] In one embodiment of the invention, the integrated power supply operates two electrodes simultaneously by allocating system resources in an optimal manner. For example, two independent arc start circuits are required to ignite the two electrodes. However, only one power converter is required to drive both are starters. The modular power supplies are allocated based upon impulse and maintenance programs for the two electrodes. If the impulse for the two electrodes are operated out of phase, the system can effectively double the welding power. A 100 amp power supply can be made to operate as an effective 200 amp supply. Typically, the impulse duty cycle is 50% or less. In this way, while one electrode is operating in maintenance, the other can be in impulse. The current from each of the power modules is routed to the required electrode as needed. This procedure affords the user a tremendous amount of capability in a very small light weight package.  
     CONCLUSION  
     [0133] The present invention will revolutionize the welding industry by providing a compact, low-cost and easy-to-use alternative compared to present conventional welding equipment. The present invention is also eminently capable of being integrated in a CNC System which could automatically accomplish a broad range of complex and precise welding or joining tasks.  
     [0134] Although the present invention has been described in detail with reference to a particular preferred embodiment, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements maybe made without departing from the spirit and scope of the claims that follow. The various materials that have been disclosed above are intended to educate the reader about one preferred embodiment, and are not intended to constrain the limits of the invention or the scope of the claims. Although the preferred embodiments have been described with particular emphasis on specific types of metal and tubular workpieces, the present invention may be beneficially implemented with other shapes and other materials such as plastics or composites. The List of Reference Characters which follows is intended to provide the reader with a convenient means of identifying elements of the invention in the Specification and Drawings. This list is not intended to delineate or narrow the scope of the claims.  
     LIST OF REFERENCE CHARACTERS  
     [0135] 10  Multi-Electrode Welding System  
     [0136] 11  Weld head frame  
     [0137] 12  Lid  
     [0138] 13  Chamber  
     [0139] 14  Chamber base  
     [0140] 16  Inserts  
     [0141] 18  Weld head rotor  
     [0142] 20  Inside electrode holder  
     [0143] 22  Outside electrode holder  
     [0144] 24 A Outside electrode  
     [0145] 24 B Inside electrode  
     [0146] 26  Rotor &amp; central drive shaft motor  
     [0147] 28  Rotor O.D. electrode holder  
     [0148] 30  I.D. spindle electrode holder  
     [0149] 32  Flexing taper fingers  
     [0150] 34  Taper lock-nut  
     [0151] 36  O.D. brush assembly  
     [0152] 38  I.D. brush assembly  
     [0153] 40  Dielectric housing  
     [0154] 42  I.D. spindle  
     [0155] 44  Rotor gear drive  
     [0156] 46  Rotor brush  
     [0157] 48  O.D. rotor brush assembly  
     [0158] 50  Idler gear  
     [0159] 52  Rotor drive motor pinion gear  
     [0160] 54  Rotor ring gear  
     [0161] 56  Central shaft gear  
     [0162] 58  Central shaft  
     [0163] 60  Rotor drive gear  
     [0164] 62  Idler gears  
     [0165] 64  Meshing gear train  
     [0166] 66  Drive motor  
     [0167] 68  Drive motor gear