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United States Patent (19) 11 3,978,311 Toth (45) Aug

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United States Patent (19) 11 3,978,311 Toth (45) Aug United States Patent (19) 11 3,978,311 Toth (45) Aug. 31, 1976 (54) VOLTAGE SENSOR CIRCUIT FOR AN ARC 3,258,596 6/1966 Green................................. 250/199 WELDING WIRE FEED CONTROL 3,488,586 11970 Watrous et al..................... 250/i99 w 3,604,884 9/197l Olsson .............................. 219/69 G 75 Inventor: Tibor Endre Toth, Florence, S.C. 3,794,841 2/1974 Consentino et al................. 250/99 73) Assignee: Union Carbide Corporation, New York, N.Y. Primary Examiner-J. V. Truhe Assistant Examiner-Clifford C. Shaw 22 Filed: Mar. 26, 1974 Attorney, Agent, or Firm-John R. Doherty (21) Appl. No.: 454,841 57 ABSTRACT 52 U.S. C. ............................. 219/131 F; 219/136 A sensor circuit coupled to an arc welding system and I5ll Int. Cl”............................................ B23K9/12 responsive to the arc welding voltage including an os (58) Field of Search. 219/131 F, 131 WR, 131 W, cillator and means for varying the frequency thereof in 219/135; 314/64; 250/199 response to the arc voltage, light emitting means re sponsive to the oscillator frequency, and detecting cir 56 References Cited cuit means responsive to the light emitting means for UNITED STATES PATENTS providing a DC voltage proportional to the arc voltage. 2,223,177 1 1/1940 Jones.................................... 3.14164 9. 2,636,102 4/1953 Lobosco.......................... 219/13 F 3 Claims, 2 Drawing Figures SENSOR CIRCUIT CONSTANT CURRENT O 8 AC/DC MOTOR CONTROL POWER SUPPLY O. O U.S. Patent Aug. 31, 1976 3,978,311 SENSOR CIRCUIT CONSTANT CURRENT o AC/DC POWER SUPPLYo O 3,978,311 1. 2 feed rate, cause a corresponding change in the wire VOLTAGE SENSOR CRCUT FOR AN ARC melt off rate which, if left uncorrected, may result in WELDING WIRE FEED CONTROL the arc stubbing out or cause burn back. Hence, it is necessary to compensate for variations in arc length in This invention relates to an arc stabilized wire feed 5 order to restore equilibrium to the system. The pre control and solid state arc voltage sensor circuit for ferred system of regulation involves adjusting the wire monitoring arc voltage fluctuations including means for feed rate in response to arc voltage changes. An arc electrically decoupling the wire feed control from the sensor circuit 16 senses the arc voltage and provides an welding power supply. output DC voltage Vo which is both proportional to the In constant current arc welding, compensation for 10 instantaneous level of the arc voltage and electrically variations in arc voltage is conventionally carried out isolated from the welding system. The output DC volt by adjustment of the electrode wire feed rate. Some age Vo is applied to the motor speed control 18 which prior art wire feed controls sense the arc voltage by a determines the speed of motor M and in turn the ac direct coupling across the arc. Such a direct coupling is companying wire feed rate. Thus the wire feed rate is inherently unsafe due to the fact that conventional wire 5 regulated in response to arc voltage variations. Al feed controls operate from a 110 volt or 220 volt line though any conventional motor speed control circuit power source, thus subjecting the welding operator to 18 may be used, the motor speed control shown and hazardous working conditions. In fact, the only safety described in U.S. Pat. No. 3,781,620 entitled Full precaution taken in most commercially available units Wave Governor Control System which issued on Dec. is the use of separate ground levels for the welding 20 25, 1973 in the name of T. E. Toth, is preferred. power supply and wire feed control respectively. Other The voltage sensor circuit 16 of FIG. 1, is schemati wire feed controls respond to predetermined changes cally illustrated in FIG. 2 and includes a full wave in the level of arc current in order to provide arc volt bridge rectifier circuit 15 for use when the power sup age compensation. Controls of the latter type are slow ply 10 is operated in the AC mode so as to convert the to respond to fluctuations in arc voltage. The wire feed 25 AC arc voltage into a DC signal. For DC power supply control should be capable of responding quickly to operation the bridge circuit 15 is unnecessary. A Zenor changes in arc voltage without loading down the weld diode Z1 is connected across the output of the bridge ing power supply or altering the arc characteristics. rectifier 15 to limit the detected arc voltage V to a It is therefore the primary object of the present in predetermined maximum level in order to place an vention to provide an arc voltage sensing circuit for 30 upper limit on the wire feed rate. Under ordinary oper monitoring arc voltage fluctuations across a constant ating circumstances the arc voltage will be substantially current arc and which is responsive to the magnitude of below such predetermined maximum level. The voltage the arc voltage variation. V, developed across the zenor diode Z1 is applied to a It is a further object to provide a wire feed control voltage controlled oscillator circuit 20. Oscillator cir system incorporating an arc voltage sensing circuit 35 cuit 20 is of the relaxation type whose frequency is which is electrically isolated from the welding power. controlled by the RC time constant of resistor R1 and supply circuit, responds quickly to arc voltage changes capacitor C1 and the level of applied voltage V. Capac and provides a signal proportional to the arc voltage itor C1 charges to a voltage during each cycle of oscil fluctuation. lation equal to the voltage across zenor diode Z2 plus Other objects and advantages of the present inven 40 about 0.7 volts at which level the programable unijunc tion will become apparent from the following detailed tion transistor (PUT) 24 fires. With the time constant description of the invention when taken in connection RC fixed the programmed firing level is reached in with the accompanying drawings of which: each oscillating cycle at a time which varies directly FIG. 1 is a block diagram of a constant current arc with changes in the applied voltage V. The program welding set up in combination with the wire feed con 45 able unijunction transistor (PUT) 24 is a commercially trol of the present invention; available solid state negative impedance device having FIG. 2 is an electrical schematic of the voltage isola a controlled firing potential which is preset by setting a tion circuit of FG. I. predetermined voltage at its gate 25. For the circuit The constant current welding system shown in FIG. shown in FIG. 2, the gate 25 is set by an appropriate comprises a conventional welding constant current 50 selection of zenor diode Z2. When the potential across power supply 10 which provides either AC or DC out capacitor C1, representing the potential at the anode put power respectively across the torch T to workpiece 23 of the programmed unijunction transistor 24, W. The workpiece W is usually at ground potential. reaches the potential set at gate 25 plus the junction Torch T is a conventional consumable electrode weld voltage of about 0.7 volts, programmed unijunction ing torch adapted to direct the electrode E to the work 55 transistor 24 fires discharging capacitor C1 through the piece W under the operation and control of a welding light emitting diode D1. As soon as the capacitor C1 is operator. An arc A is established between the electrode fully discharged the programmed unijunction transistor E and the workpiece W in a conventional manner such 24 turns off, providing a high impedance into capacitor as by inching the electrode into physical contact with C1. Capacitor C1 then once again begins to charge. As the workpiece W. The arc A is shielded from atmo 60 long as the voltage V impressed across the oscillator 20 spheric air by a substantially inert gas fed in a conven remains constant the frequency of the oscillator 20 will tional manner through the torch T. The consumable not vary. Any change however in voltage V will cause electrode E is drawn through a pair of feed rolls 12 and a corresponding change in the oscillator frequency. 14 respectively, from a supply spool S, and at a feed Thus the frequency of oscillator 20 is directly propor rate determined by the speed of motor M. 65 tional to voltage V and thus to the arc voltage. A change in voltage across the arc A, which may Light emitting diode D1, as its name implies, emits a occur, for example, by a variation in arc length due to pulse of light in response to each pulse of energy deliv a vertical movement of the torch T, will for any given ered from capacitor C1 during each cycle of oscilla 3,978,311 3 4. tion. The light emitting diode D1 is photocoupled to results in a predetermined increase in wire speed which the light detecting transistor Q1. The light emitting tends to decrease the arc voltage and restore equilib diode D1 is a conventional device and is commercially rium. S. sold in combination with a light detecting transistor What I claim is: such as Q1. The output at the collector terminal 26 of 5 1. A wire feed control for regulating the speed at light detecting transistor Q1 is connected to an inte which a consumable electrode is fed into an arc estab grating circuit consisting of resistor R2 and capacitor lished between said electrode and a workpiece from a C2.
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