An automatic transfer switch (ATS) controller is disclosed which includes a power supply circuit to regulate and filter input power, a transformer to convert utility and generator power sources into power supply voltages and voltage sensing sources and a voltage sense signal conditioning circuit. Caterpillar Automatic Transfer Switch Engine Division, MX Series Microprocessor Bated ATS Controllers, Oct.
BACKGROUND OF THE INVENTIONThis invention relates generally to electrical switches and, more particularly, to automatic transfer switches and control thereof.Many businesses use transfer switches for switching power sources, for example, from a public utility source to a private secondary supply, automatically within a matter of seconds.
A power supply for arc welding includes switching elements PTR, NTR for switching the polarity of the direct voltage from a power circuit PMC. Frost FreeFrost Free:Refrigeration appliances with this feature are easier to maintain because the build-up of ice inside is reduced, meaning you won't have to defrost the unit manually in most cases.
These alternatives are suggestions of similar items and may not have exactly the same specification.
Controller further implements a solenoid driver circuit to drive automatic transfer switch solenoids, an embedded microcontroller configured to monitor utility and generator voltages and a user interface interfaced to said microcontroller for operator entry of instructions. A controller according to claim 1 wherein said microcontroller comprises at least one analog-to-digital converter. A controller according to claim 2 wherein said voltage sense signal conditioning circuit comprises low pass filters configured to remove noise from the power supply voltages thereby enabling said microcontroller analog-to-digital converter to correctly sense voltage and frequency. A controller according to claim 1 wherein said solenoid driver circuit is configured with relays for powering automatic transfer switch drive solenoids. A controller according to claim 1 wherein said solenoid driver circuit is configured with solid state devices for powering automatic transfer switch drive solenoids. A controller according to claim 1 wherein said microcontroller is configured to recognize jumper selections for an exerciser clock adjustable for settings for a preselected number of days. A controller according to claim 1 wherein said microcontroller is configured to recognize jumper selections for supply voltages for at least one of 120 VAC, 208 VAC, 220 VAC and 240 VAC.
A controller according to claim 1 wherein said transformer is configured for supply voltages of at least one of 380 VAC, 415 VAC, 440 VAC and 480 VAC, said microcontroller is configured to recognize jumper selections for supply voltages for at least one of 380 VAC, 415 VAC, 440 VAC and 480 VAC. A controller according to claim 1 further comprising a generator control board configured to interface with said microcontroller and to sense at least one of oil pressure and temperature. A controller according to claim 1 further comprising a three phase sense board configured to expand single phase sensing capabilities of said controller to three phase sensing on utility and generator sources. A controller according to claim 1 wherein said microcontroller is configured with at least one of a generator cool down timer, a generator warmup timer, a loss of power delay timer, a generator fail-to-start timer, a generator crank timer, a generator pause timer, a generator overload timer and an utility stabilization before switchback timer.
A controller according to claim 1 wherein said microcontroller is configured to recognize jumper selections for frequencies of 50 Hz and 60 Hz. An automatic transfer switch system according to claim 15 wherein said microcontroller further comprises at least one analog-to-digital converter. An automatic transfer switch system according to claim 16 wherein said voltage sense signal conditioning circuit comprises low pass filters configured to remove noise from the power supply voltages thereby enabling said microcontroller analog-to-digital converter to correctly sense voltage and frequency. An automatic transfer switch system according to claim 15 wherein said solenoid driver circuit is configured with relays for powering automatic transfer switch drive solenoids. An automatic transfer switch system according to claim 15 wherein said solenoid driver circuit is configured with solid state devices for powering automatic transfer switch drive solenoids. An automatic transfer switch system according to claim 15 wherein said microcontroller is configured to recognize jumper selections for an exerciser clock adjustable for a preset number of days.
An automatic transfer switch system according to claim 15 wherein said microcontroller is configured to recognize jumper selections for supply voltages for at least one of 120 VAC, 208 VAC, 220 VAC and 240 VAC. An automatic transfer switch system according to claim 15 wherein said transformer is configured for supply voltages of at least one of 380 VAC, 415 VAC, 440 VAC and 480 VAC, said microcontroller is configured to recognize jumper selections for supply voltages for at least one of 380 VAC, 415 VAC, 440 VAC and 480 VAC. An automatic transfer switch system according to claim 15 wherein said controller further comprises a generator control board configured to interface with said microcontroller and to sense at least one of oil pressure and temperature. An automatic transfer switch system according to claim 15 wherein said controller further comprises a three phase sense board configured to expand single phase sensing capabilities of said controller to three phase sensing on utility and generator sources. An automatic transfer switch system according to claim 15 wherein said microcontroller is configured with at least one of a generator cool down timer, a generator warmup timer, a loss of power delay timer, a generator fail-to-start timer, a generator crank timer, a generator pause timer, a generator overload timer and an utility stabilization before switchback timer. An automatic transfer switch system according to claim 15 wherein said microcontroller is configured to recognize jumper selections for frequencies of 50 Hz and 60 Hz. An automatic transfer switch controller configured to control an automatic transfer switch that switches between providing power from a utility power source and from an alternate power source, said controller comprising a configuration section including a jumper panel that is built within said controller and that is configured to select a cycle for a clock. A controller in accordance with claim 29 wherein said clock is an exercise clock located within said controller. A controller in accordance with claim 29 wherein the cycle is one of a 7 day, a 14 day, a 21 day, and a 28 day cycle. A controller in accordance with claim 29 wherein said controller comprises a microcontroller and said configuration section is used to configure said microcontroller by selecting at least one of a voltage and a frequency provided to said microcontroller. A controller in accordance with claim 32 wherein the voltage is one of 120 volts, 208 volts, 220 volts, and 240 volts. A controller in accordance with claim 32 wherein the voltage is one of 380 volts, 415 volts, 440 volts, and 480 volts. A controller in accordance with claim 32 wherein the frequency is one of 50 hertz and 60 hertz.
A controller in accordance with claim 32 further comprising: jumpers installed to select one of the voltage and frequency provided to said microcontroller. An automatic transfer switch controller comprising at least one phase sense board configured to expand a capability of said controller from single phase voltage sensing to multiple phase voltage sensing of voltages generated from one of a utility and an alternate power source. A controller in accordance with claim 37 wherein the multiple phase sensing includes sensing three phase voltages. A controller in accordance with claim 37 further comprising a microcontroller configured to monitor voltages and frequencies of said utility and alternate power sources.
A controller in accordance with claim 39 wherein said microcontroller is located on a main control circuit board and said phase sense board is an option board. An automatic transfer switch controller comprising jumpers that are located on a main control board on which a microprocessor is located and that are configured to receive jumper selections of frequencies and voltage levels sensed by said controller. A controller in accordance with claim 41 wherein the jumper selections include a selection for a cycle of a clock within said controller. A controller in accordance with claim 29 wherein said controller is configured to be coupled to an option board that disconnects at least one load before said controller transfers at least one of a plurality of loads from said utility power source to said alternate power source.
A controller in accordance with claim 41 further comprising a generator control board separate from said main control board, coupled to said main control board, and configured to sense functions of an alternate source that provides power to a load via an automatic transfer switch controlled by said controller, wherein the functions of said generator control board are accessed by said controller when a control bit is enabled. Critical load businesses, such as, for example, hospitals, airport radar towers, and high volume data centers are dependent upon automatic transfer switches to provide continuous power. The element PTR is connected in parallel to a series unit of a switching element TR1 and a resistor R1.
Field of the InventionThe present invention relates to a power supply used for performing short-circuiting arc welding. A LED indicator is included and is configured to verify user interface entries and overall operation of the controller and ATS system. Transfer switches typically utilize a plurality of contacts that can be open or closed.Typically, automatic transfer switches are controlled using relay logic, programmable logic controllers (PLCs) or embedded controllers.
Likewise, the element NTR is connected in parallel to a series unit of a switching element R2 and a resistor R2. The present invention also relates to an automatic welding machine or welder utilizing such a power supply.
In known systems, the embedded controller monitors the public utility power source for a fault condition. A necking determination circuit ND determines whether a constriction occurs at the molten bridging portion between the welding wire and the base material.
The power supply of the present invention is designed to perform “necking current control” and “electrode polarity switching control”, as will be discussed later.2. When the constriction occurs during the “electrode positive” mode, the switching element PTR is turned off, while the switching element TR1 is brought into the conduction state.
Description of the Related ArtAs known in the art, arc welding is widely employed in the metalworking industries for joining two or more metallic parts.
When the constriction occurs during the “electrode negative” mode, the switching element NTR is turned off, while the switching element TR2 is brought into the conduction state.
Taking the automotive industry for example, an assembly of metallic pieces are welded together for constructing e.g.
It would be further desirable to have an automatic transfer switch controller with a communications interface to enable and select software options from an external device.BRIEF SUMMARY OF THE INVENTIONAn automatic transfer switch controller includes a power supply circuit to regulate and filter input power.
Also included is a transformer to convert utility and generator power sources into power supply voltages and voltage sensing sources for the controller.


The welded framework may have a number of coalesced joints each having a welding length of no greater than 50 mm. A voltage sense signal conditioning circuit is included as is a solenoid driver circuit used to drive automatic transfer switch solenoids. Typically, such a framework is constructed from pipes, reinforcing plates, etc., that may be connected together by automatic CO2-arc welding. The controller uses an embedded microcontroller to monitor utility and generator voltages which is interfaced to a user interface for operator entry of instructions. An LED indicator interfaced to said microcontroller is used to indicate operator entry of instructions at the operator interface.BRIEF DESCRIPTION OF THE DRAWINGSFIG. For reliable connection, the welds (that is, the coalesced joints) of the framework need to have a sufficient depth of fusion. 1 is a simplified schematic showing electrical routing within an automatic transfer switch system; andFIG. It is also required that spatters generated during the arc welding operation will not stick to the obtained weldment. Generally, CO2-arc welding is a short-circuiting arc welding, and spatters tend to be generated when the short-circuiting occurs and breaks. 3 is a detailed block diagram of a portion of the automatic transfer switch controller shown in FIG. In particular, when the short-circuiting breaks, a relatively great amount of spatters tend to be generated.JP-B2-Heisei 4-4074 discloses a technique for preventing the occurrence of spatters. In accordance with the conventional method, a welding wire (consumable electrode) is positively charged (“electrode positive” mode) for performing short-circuiting arc welding, and the welding current Iw is controlled for the purpose of reducing spatters. 1 is a simplified schematic diagram 10 showing electrical routing within an automatic transfer switch (ATS) system. 5 shows the waveform of the welding current Iw (Graph A), and illustrates how a molten globule 1a transfers from the welding wire 1 to the base material 2 (Phases B?E).As seen from FIG. Each of utility source 12 and generator source 14 are routed through circuit breakers 16 to a transfer switch 18. 5, the short-circuiting between the welding wire 1 and the base material 2 occurs when the globule 1a formed on the welding wire 1 comes into contact with the molten pool 2a of the base material 2 (see Phase B) At this instant, the welding current Iw is decreased to reduce spatter generation.Then, the welding current Iw is increased to exert a stronger electromagnetic pinching force on the molten bridging portion 2b (see Phase C). Transfer switch 18 is configured to route electrical power from utility source 12 through transfer switch 18 to a main breaker panel 20, through which electricity is distributed throughout a facility. This promotes the globule transfer from the wire 1 to the base material 2.Due to the increased pinching force, the molten bridging portion 2b is transformed into a constriction 2c (see Phase D). Transfer switch 18 is further configured with a controller (not shown) to monitor the power from utility source 12 for power quality, for example voltage, power factor, electrical noise and the like. When the constriction 2c is detected, the welding current Iw is dropped off immediately before the regeneration of arc.
When the transfer switch controller senses a problem with power quality, based upon preset limits, the transfer switch controller commands transfer switch 18 to switch to electrical power from generator source 14, on a temporary basis, until the transfer switch controller senses that the power quality from utility source 12 has returned to an acceptable level.FIG.
This current-dropping process, called “necking current control”, can significantly reduce the amount of spatters to be generated at the reoccurrence of arc. For achieving the current-dropping, the DC output of the power supply is connected to a switching element, with a resistor connected to the switching element in parallel. Controller 40 includes a microcontroller 42, a memory 44, a user interface 46, a power input section 48, an output section 50 which is configured to command one or more transfer switches 18 (shown in FIG.
When no constriction is detected, the switching element is held in the conduction state to short-circuit the accompanying resistor.
Upon detection of the constriction, the switching element is turned off so that the DC power supply will be inputted to the resistor.
Thus, the welding current Iw can be decreased rapidly.When the constriction 2c is formed, the resistance of the molten bridging portion 2b increases. In one exemplary embodiment, software options are to be enabled or disabled through the use of a factory configuration program via port 54, which is for example, an RS232 port.Controller 40 is configured with external connections (not shown in FIG. 1) into power supply voltages for powering controller 40 and into voltages to be sensed by controller 40. To maintain the arc 3, the welding current Iw is increased.During the short-circuiting period, the welding current Iw needs to be controlled precisely. Thus, the external characteristic of the power supply should be constant current characteristic. Filtering allows controller 40 to correctly sense voltage and frequency when utility source 12 or generator source 14 contain large amounts of harmonic distortion.In another exemplary embodiment of controller 40, output section 50 is configured as a solenoid driver circuit which includes two options of solenoid drivers, both of which are implemented on the main control board. During the arc-generating period, on the other hand, the power supply is caused to have constant potential characteristic so that the arc has a proper length.While the above-described prior art technique contributes to the reduction of spatters, it still may suffer a drawback illustrated in FIGS.
A first solenoid driver option is configured with on-board relays when the utility and generator power sources are 240Vac and below. A second solenoid driver option is configured with solid state devices when the utility and generator power sources are greater than 240Vac, but less than 600Vac. The solenoid driver circuit is used to control the power supplied to an ATS drive solenoid which causes swithcing from one electrical power source to another in transfer switch 18 (shown in FIG. 1).Using user interface 46 a user can momentarily energize a normal output causing the ATS to transfer to normal position, the position where utility power is used. Momentarily energizing an emergency output causes the ATS to transfer to the position where generator power is used. When the prior art welding is performed with the thin plates, the lower plate may be formed with burn through holes due to an excessive amount of heat input.Reference is now made to FIG.
In order to protect the ATS drive solenoid from damage, a solenoid saver scheme is implemented in controller 40 which controls the maximum on time and the number of tries a drive solenoid can be energized for before shutting down the drive circuit and initiating a diagnostic mode.All functions on the main control board are controlled by microcontroller 42 which uses custom written firmware to monitor the utility and generator voltages and frequency, monitor user interface updating indicator LEDs on user interface 46, perform real time clock functions, monitor ATS position and control the ATS. 7 showing the waveform of a conventional welding current Iw (see JP-A-Heisei 11-226730, for example). In a further embodiment, controller 40 is configured with a generator cool down timer, a generator warmup timer, a loss of power delay timer, a generator fail-to-start timer, a generator crank timer, a generator pause timer, a generator overload timer and an utility stabilization before switchback timer.Controller 40 includes a configuration section 52. Jumpers are installed by a user to select one of a seven, 14, 21, or 28 day cycle for a built in ATS exerciser. However, this alternative prior art method tends to produce a great amount of spatters at the time of the occurrence and breakage of the short-circuiting between the welding wire and the base material.SUMMARY OF THE INVENTIONThe present invention has been proposed under the circumstances described above.
The exerciser period can be adjusted for seven, 14, 21, or 28 days by selecting the appropriate jumpers setting located on the main control board.Configuration section 52 further includes jumper selectable voltage and frequency selections.
It is, therefore, an object of the present invention to provide a power supply for performing spatterless short-circuiting arc welding without causing burn through holes to be made even in a relatively thin base material.According to a first aspect of the present invention, there is provided a power supply for short-circuiting arc welding. The voltage controller 40 can sense is selectable from 120, 208, 220, and 240 Vac through the use of the correct jumper settings. Voltage ranges in the 380, 415, 440, and 480Vac are also selectable, but require that a different transformer be used in controller 40.
The robot controller controls the movement of the welding robot and also sends welding condition setting signals to the power supply. 1 is a block diagram illustrating a power supply for short-circuiting arc welding according to a first embodiment of the present invention;FIG. The three-phase sense board contains all of the necessary conditioning circuitry necessary for proper voltage and frequency detection.FIG. 3 is a detailed block diagram of a portion of the automatic transfer switch controller 40 shown in FIG. 3 schematically shows an automatic welding machine according to a second embodiment of the present invention;FIG. 4 shows an example of weldment composed of a reinforcing plate welded to a thin-walled pipe and to a thick-walled pipe;FIG. 5 illustrates the waveform of a welding current Iw employed for a conventional arc welding power supply and how a molten globule transfers from a welding wire to a base material;FIGS. 1 is a block diagram showing an arc welding power supply according to a first embodiment of the present invention. The illustrated power supply comprises the following features.A primary power circuit PMC converts an input alternating voltage to an output direct voltage.
Accordingly, automatic transfer switch controller includes power input section 48 that includes transformers 302 and 304 electrically coupled to utility source 12 and generator source 14, respectively. Transformers 302 and 304 are electrically coupled to a voltage sense signal conditioning circuit 306 that includes a low pass filter 308.
The primary power circuit PMC includes an inverter INV (incorporating an unillustrated rectifier for the input voltage), a high-frequency transformer INT, secondary rectifiers D2a?D2d, and a reactor WL. Specifically, the inverter INV changes the rectified input voltage to a high-frequency alternating voltage.


The transformer INT steps down this high-frequency voltage to a lower voltage suitable for performing the required welding operation. In one embodiment, output section 50 includes relay solenoid driver devices 312 coupled to microprocessor 42. The secondary rectifiers D2a?D2d rectify the reduced alternating voltage, to output positive and negative DC voltages. In an alternative embodiment, output section 50 includes solid state solenoid driver devices 314 coupled to microprocessor 42.Configuration section 52 includes a plurality of user selectable jumpers 316 to facilitate controlling the operation of controller 40. To achieve this selection, the switching circuit SWP includes an “electrode positive” switching element PTR and an “electrode negative” switching element NTR. When the “electrode positive” switching element PTR is in a conductive state, the positive voltage is applied to the wire 1.
Timers 328 may include, for example, a generator cool down timer 330, a generator warm-up timer 332, a loss of power delay timer 334, a generator fail-to-start timer 336, a generator crank timer 338, a generator pause timer 340, a generator overload timer 342 and an utility stabilization before switchback timer 344. On the other hand, when the “electrode negative” switching element NTR is in a conductive state, the negative voltage is applied to the wire 1.The “electrode positive” switching element PTR is connected in parallel to a combination of a switching element TR1 and a resistor R1 (connected to the switching element TR1 in series). Likewise, the “electrode negative” switching element NTR is connected in parallel to a combination of a switching element TR2 and a resistor R2 (connected to the switching element TR2 in series).The welding wire 1 extends through a welding torch 4. For supplement of the consumed portion, the welding wire 1 is fed forward through the torch 4 by the rotation of feeding rollers 5a. Arcs 3 are generated between the welding wire 1 and the base material 2 in accordance with the welding voltage Vw and the welding current Iw.A voltage detector VD detects the welding voltage Vw to output a voltage detection signal Vd corresponding to the absolute value of the detected voltage Vw.
A necking determiner ND determines whether a constriction occurs in the molten bridging portion extending between the welding wire 1 and the base material 2. When a constriction occurs, the necking determiner ND outputs a necking determination signal Nd.
In accordance with the driving signal Epd, the switching element PTR is brought into the conduction state only when the polarity setting signal Spn (supplied from outside the power unit) is at a prescribed “high” level and the necking determination signal Nd is not outputted (the low level of the signal Nd). In accordance with the driving signal Dv1, the switching element TR1 is brought into the conduction state only when the polarity setting signal Spn is at the high level and the necking determination signal Nd is outputted. In accordance with the driving signal Dv2, the driving circuit DV2 is brought into the conduction state only when the polarity setting signal Spn is at the low level and the necking determination signal Nd is outputted.With the above arrangement, when the polarity setting signal Spn is at the high level and no necking determination signal Nd is outputted (the “electrode positive” case), the “electrode positive” switching element PTR is in the conduction state, and the welding current Iw passes through the switching element PTR, the welding wire 1, the base material 2 and the reactor WL in this order. Then, when the necking determination signal Nd is outputted, the inverter is turned off to stop the output from the primary power circuit PMC. At the same time, the switching element PTR is brought into the non-conduction state, while the switching element TR1 is brought into the conduction state. As a result, the energy stored in the reactor WL is discharged along the path via the resistor R1, the switching element TR1, the welding wire 1, the base material 2 and the reactor WL.
1, the discharge rate (in other words, the current dropping rate) becomes faster about tenfold or more.As readily understood, the same current dropping operation as described above can be performed in the “electrode negative” case, too.
As a result, the inverter is turned off, the switching element NTR is brought into the non-conduction state, and the switching element TR2 is brought into the conduction state.A current detector ID detects the welding current Iw to output a current detection signal Id that corresponds to the absolute value of the detected welding current Iw. A primary controller MCC controls the output of the primary power circuit PMC and the wire feeding operation for supplement of the welding wire 1.
The primary controller comprises the following features.A short-circuiting determination circuit SD outputs a short-circuiting determination signal Sd based on the voltage detection signal Vd.
A voltage setting circuit VR outputs a voltage setting signal Vr for performing the desired voltage setting.
A current setting circuit IR outputs a current setting signal Ir for setting the welding current Iw during the short-circuiting period. A voltage error amplifier EV amplifies the difference between the voltage setting signal Vr and the voltage detection signal Vd, to output a voltage error amplification signal Ev.
A current error amplifier EI amplifies the difference between the current setting signal Ir and the current detection signal Id, to output a current error amplification signal Ei.
1) when the short-circuiting determination signal Sd is at a low level (the arc-generating period). At this time, the above-mentioned voltage error amplification signal Ev is outputted from the switching circuit SC as an error amplification signal Ea.
When the short-circuiting determination signal Sd is at a high level (the short-circuiting period), on the other hand, the external characteristic switching circuit SC switches to the b-side, thereby outputting the current error amplification signal Ei as an error amplification signal Ea. With this arrangement, the power supply is brought into the “constant potential characteristic” mode when in the arc-generating period, or into the “constant current characteristic” mode when in the short-circuiting period. Based on the error amplification signal Ea, a pulse-width modulation control circuit PWM outputs a control signal Pwm for performing PWM control with respect to the inverter INV.Reference is now made to FIG. 2 showing a timing chart for the above-described signals Spn, Iw, Sd, Nd, Epd, Dv1, End, Dv2 (A?H) of the power supply of the present invention. The necking determination signal Nd (D) is at the high level for t2?t3 when the necking occurs. The driving signal Epd (E) for the “electrode positive” switching element PTR is at the high level when the necking determination signal Nd is at the low level (t1?t2, t3?t4). The driving signal Dv1 (F) for the switching element TR1 is at the high level when the necking determination signal Nd is at the high level (t2?t3). At this time, the switching element TR1 is held in the conduction state.(2) Electrode Negative Period Ten—Polarity Setting Signal Spn (A) at Low LevelThe short-circuiting determination signal Sd (C) is at the high level when the short-circuiting period Ts (t5?t7), and at the low level when the arc-generating period Ta (t7?t8).
The necking determination signal Nd (D) is at the high level for t6?t7 when the necking occurs. The driving signal End (G) for the “electrode negative” switching element NTR is at the high level when the necking determination signal Nd is at the low level (t5?t6, t7?t8).
The driving signal Dv2 (H) for the switching element TR2 is at the high level when the necking determination signal Nd is at the high level (t6?t7). At this time, the switching element TR2 is held in the conduction state.With the use of the above-described power supply for a short-circuiting arc welding machine, it is possible to perform proper welding operation with respect to a very thin material (having a thickness of no greater than 1 mm, for example), as opposed to the conventional power supply. Specifically, to weld together thin metallic materials (plates, pipes, etc.), the polarity setting signal Spn is set to the low level, so that the welding operation is performed in the “electrode negative” mode. In this manner, the weld heat input to the base material can be reduced sufficiently to prevent defects (such as burn through holes) from occurring in the base material. Further, the necking current control in the “electrode negative” mode contributes to low-spatter welding. With respect to a relatively thick material (having a thickness of more than 1 mm, for example), the polarity setting signal Spn is set to the high level, so that the welding operation is performed in the “electrode positive” mode.
In this manner, it is possible to ensure a sufficiently great dept of fusion in the base material. Again, the accompanying necking current control contributes to performing low-spatter welding.FIG.
3 schematically shows an automatic welding machine according to a second embodiment of the present invention. The welding machine includes a power supply PS according to the above-described first embodiment, and a robot controller RC for controlling the operation of a welding robot RM.For causing the welding robot RM to work in accordance with work programs, the robot controller RC sends operation control signals Mc to the servo motors (not shown) incorporated in the welding robot RM. Further, the robot controller RC sends welding condition setting signals Ws to the power supply PS.
The welding condition setting signals Ws may include an output start signal, a voltage setting signal, a feeding rate setting signal, and a polarity setting signal Spn described above regarding the first embodiment of the present invention.
The supplement oaf the welding wire 1 through the torch 4 is performed by a wire feeding motor WM mounted on the welding robot RM. The polarity of the welding voltage Vw is switchable in accordance with the polarity setting signal Spn.FIG.
In light of the small thickness (no greater than 1 mm), the thin-walled pipe 6a is welded to the reinforcing plate 6c (see the weld area 7a) in the “electrode negative” mode (the polarity setting signal Spn at the low level).
On the other hand, due to the relatively great thickness, the other pipe 6b is welded to the reinforcing plate 6c (see the weld area 7b) in the “electrode positive” mode (the polarity setting signal Spn at the high level). Together with the “electrode negative” or “electrode positive” welding operation, the necking current control is also performed to reduce spatters. Thus, with the use of the welding machine of the present invention, the welding result is spatterless and suffers no burn through holes.The present invention being thus described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to those skilled in the art are intended to be included within the scope of the following claims.



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