Direct current power supply for manual arc welding

Abstract

A direct current power supply for manual arc welding comprising a polyphase transformer, a polyphase rectifier system including triggered rectifier valves, and a control system therefor which comprises means for setting the output current level by adjustment of a reference signal, means providing negative feed-back of the output voltage and the output current, and means for adjusting the slope of the characteristic by adjustment of the proportion between the amounts of feed-back of the voltage and the current. The current level setting means and the slope adjustment means are linked with each other to provide automatically a desired correlation between the slope and the current setting.

I claim: 
     
       1. A direct current power supply for manual arc welding having a steeply drooping, adjustable volt-ampere characteristic comprising a polyphase transformer having a plurality of secondary output leads carrying mutually phase displaced voltages, a polyphase rectifier system connecting said secondary output leads to a pair of D.C. welding current conductors for supplying a direct current to a welding arc struck between a welding electrode and a workpiece, said polyphase rectifier system comprising a set of triggered rectifier valves connected one in series with each of said secondary output leads, said triggered rectifier valves having each a trigger terminal for initiating current flow through the valve,   means for periodically supplying igniting pulses to each of said trigger terminals, including means for causing the angular position of said pulses to vary in response to a direct current control signal,   means for generating said direction current control signal comprising the following means, a. means for producing an adjustable direct current reference signal, including manually operable means for adjusting said reference signal,   b. means including a welding current sensing means for producing a welding current feed-back D.C. signal equal to the welding current flowing in the pair of welding current conductors multiplied by a first factor of proportionality,   c. means including a welding voltage sensing means for producing a welding voltage feed-back D.C. signal equal to the voltage between the welding current conductors multiplied by a second factor of proportionality,   d. summing means for combining said reference signal, said welding current feed-back signal and said welding voltage feed-back signal into a compound signal constituting said control signal, both of said feed-back signals being supplied to said summing means in opposing relationship to said reference signal,   e. slope adjustment means comprising means for adjusting the proportion between said first and second factors of proportionality, and,   f. means linking said manually operable means for adjusting the reference signal and said proportion adjusting means to provide automatically a desired correlation between the slope of volt-ampere characteristic of the power supply and the reference signal setting.     
     
     
       2. A direct power supply as claimed in claim 1 in which said linking means provides an automatic decrease of the slope of the volt-ampere characteristic of the power supply on increase of the reference signal. 
     
     
       3. A direct current power supply as claimed in claim 1 in which the correlation of the slope of the volt-ampere characteristic of the power supply and the reference signal setting is such as to provide a substantially constant current ratio I o  /I a  for all settings of the reference signal, I a  being the arc current in the welding current conductors, and I o  being the current in said conductors on short circuiting of the welding arc. 
     
     
       4. A direct current power supply as claimed in claim 3 in which said current radio has a value between 1.1 and 1.2. 
     
     
       5. A direct current power supply as claimed in claim 1 comprising a common manual control member and mechanical means connecting said control member to both said reference signal adjusting means and said proportion adjusting means. 
     
     
       6. A direct current power supply as claimed in claim 1 comprising means responsive to a control current for adjusting said proportion, and circuit means for supplying to said adjustment means a control current proportional to said reference signal. 
     
     
       7. A direct current power supply for manual arc welding having a steeply drooping, adjustable volt-ampere characteristic comprising a polyphase transformer having a plurality of secondary output leads carying mutually phase displaced voltages, a polyphase rectifier system connecting said secondary output leads to a pair of D.C. welding current conductors, said polyphase rectifier system comprising a set of triggered rectifier valves connected one in series with each of said secondary output leads, said triggered rectifier valves having each a trigger terminal for initiating current flow through the valve,   means for periodically supplying igniting pulses to each of said trigger terminals, including means for causing the angular position of said pulses to vary in response to a direct current control signal,   means for generating said direct current control signal comprising the following means, to wit, a. means for producing an adjustable D.C. reference signal, including manually operable means for adjusting said reference signal,   b. means including a welding current sensing means for producing a welding current feed-back D.C. signal equal to the welding current flowing in the pair of welding current conductors multiplied by a first factor of proportionality,   c. means including a welding voltage sensing means for producing a welding voltage feed-back D.C. signal equal to the voltage between the welding current conductors multiplied by a second factor of proportionality,   d. A capacitor connected in series with a resistor, means including a welding voltage sensing means for submitting said series connection to potential variations proportional to the variations of the welding voltage, and means for producing a transient feed-back signal equal to the voltage appearing across said resistor multiplied by a third factor of proportionality,   e. summing means for combining said reference signal, said welding current feed-back signal, said welding voltage feed-back signal and said transcent feed-back signal into a compound signal constituting the control signal aforementioned, said welding current feed-back signal and said welding voltage feed-back signal being supplied to said summing means in opposing relationship to said reference signal, transient feed-back signals caused by discharge of said capacitor on decrease of the welding voltage being supplied to said summing means in aiding relationship to said reference signal,   f. transient slope adjusting means comprising means for adjusting the proportion between said first and said third factors of proportionality, and,   g. means linking said manually operable means for adjusting the reference signal and said proportion adjusting means to provide automatically a desired correlation between the transient slope of the voltage-ampere characteristic of the power supply and the reference signal setting.     
     
     
       8. A direct current power supply as claimed in claim 7 which additionally comprises means for suppressing the transient feed-back signal caused by a flow of charge current through the series .[.conection.]. .Iadd.connection .Iaddend.of the capacitor and the resistor. 
     
     
       9. A direct current power supply as claimed in claim 7 which additionally comprises means including a fullwave rectifier bridge for reversing the polarity of the transient feed-back signal supplied to said summing means on charging of said capacitor, whereby the transient feed-back signal is supplied in aiding relationship to said reference signal irrespectively of whether it is caused by a charge or by a discharge of the capacitor. 
     
     
       10. A direct current power supply as claimed in claim 7 which has an open circuit voltage exceeding the voltage required for sustaining a welding arc and which additionally comprises a signal limiting means arranged to limit the maximum magnitude of the transient feed-back signal to a level substantially lower than the one corresponding to a sudden drop of the voltage between the welding current conductors from the open-circuit voltage to nil.