Direct current arc power supply

Claim 2

A direct current arc power supply for maintaining an arc between a pair of electrodes in which upon start of operation a startup direct current is applied to said electrodes for a sufficient time to allow said arc to become established, comprising power means operable for providing direct current to said electrodes, reference setpoint means to produce a set reference signal related to a desired value of said direct current, means for sensing said arc current and providing a current feedback signal, means for sensing the voltage across said electrodes and providing a voltage feedback signal, feedback control means coupled to said power means for summing said set reference signal, said current feedback signal and said voltage feedback signal for applying a control signal to said power means to control the volt-ampere charateristic of said direct current, start reference means for producing a start reference signal, and start means for comparing said current feedback signal with said start reference signal, said start means including switch means for varying said control signal upon start up to produce a value of said direct current different from said desired value, said start means including time delay means for switching said direct current to said desired value upon a determined time delay interval after said current feedback signal increases to a predetermined value with respect to said start reference signal.

Claim 3

The arc power supply of claim 1 in which said start means includes a first amplifier having one input coupled to said arc current sensing means, said switch means including relay means connected to an output of said first amplifier and having at least one relay contact, means producing a start level setting connected to said relay contact and to said feedback control means for said varying of said control signal.

Claim 4

The arc power supply of claim 2 in which said time delay means comprising a plurality of capacitors of differing capacitive values and switching means for connecting selected ones of said capacitors to said relay means for providing said desired value of time delay interval.

Claim 5

The arc power supply of claim 3 in which said relay means include a relay coil and in which there is further provided an additional capacitor connected across said relay coil to prevent said relay means from actuating upon occurrence of a short time duration outage of said arc which would decrease the current feEdback signal below said predetermined value.

Claim 6

The arc power supply of claim 2 in which said feedback control means includes a second amplifier having integrator capacitor means connected in a first feedback loop therewith and providing at an output said control signal, said start level setting means coupled in a second feedback loop whereby upon startup said start level setting is applied to the input of said second amplifier.

Claim 7

The arc power supply of claim 5 in which said integrator capacitor means comprises a plurality of integration capacitors selectively connected in said first feedback loop whereby a capacitance value is selected to provide a predetermined control response compatible with the type of welding process being performed.

Claim 8

An arc power supply for applying direct current to a pair of electrodes for establishing and maintaining an arc between said electrodes, comprising power means having controlled rectifiers operable for providing direct current to said electrodes, reference setpoint means to produce a set reference signal related to a desired value of said direct current, adjustable means for sensing said arc current and providing an adjustable current feedback signal, adjustable means for sensing the voltage across said electrodes and providing an adjustable voltage feedback signal, feedback control means coupled to said power means for summing said set reference signal, said adjustable current feedback signal and said adjustable voltage feedback signal for applying a control signal to said power means to control the volt-ampere characteristic of said direct current, first and second protection reference means for producing first and second protection reference signals, and overcurrent protection means comprising means for first comparing said adjustable current feedback signal with said first protection reference signal said first comparing means including integrating means having a time constant similar to the time current characteristics of said power means for integrating a surge of said adjustable current feedback signal, second means for comparing an output signal of said first comparing means for deactivating said power means when said output signal is of value greater than said second protection reference signal thereby to protect said arc power supply from current surges of excessive duration.

Claim 9

An arc power supply for applying direct current to a pair of electrodes for establishing and maintaining an arc between said electrodes, comprising power means having controlled rectifiers operable for providing direct current to said electrodes, reference setpoint means to produce a set reference signal related to a desired value of said direct current, adjustable means for sensing said arc current and providing an adjustable current feedback signal, adjustable means for sensing the voltage across said electrodes and providing an adjustable voltage feedback signal, feedback control means coupled to said power means for summing said set reference signal, said adjustable current feedback signal and said adjustable voltage feedback signal for applying a control signal to said power means to control the volt-ampere characteristic of said direct current, first and second protection reference means for producing first and second protection reference signals, and overcurrent protection means comprising means for first comparing said adjustable current feedback signal with said first protection reference signal said first comparing means including integrating means having a time constant similar to the time current characteristics of said power means for integrating a surge of said adjustable current feedback signal, second means for comparing an output signal of said first comparing means for deactivating said power means when said output signal is of value greater than said second protection reference signal thereby to protect said arc power supply from current surges of excessive duration.

Claim 10

The arc power supply of claim 7 in which there is provided switching control means connected to an output of said integration means, said switching control means being maintained normally turned off upon application of a high surge current of a shorter duration than said predetermined time interval and being turned on when said surge current is of at least said predetermined time duration.

Claim 11

The arc power supply of claim 8 in which there is provided relay means coupled to said switching control means for deactivating said power means when said switching control means is turned on.

Claim 12

The arc power supply of claim 9 in which there is provided means for resetting said overcurrent protection means after said power means is deactivated comprising means for turning off said switching control means.

Claim 13

The arc power supply of claim 7 in which there is provided start means for comparing said adjustable current feedback signal with a start reference signal for varying said control signal upon start up to produce a value of said direct current different from said desired value, said start means including time delay means for switching said direct current to said desired value upon a predetermined time delay interval after said adjustable current feedback signal increases to a predetermined value with respect to said start reference signal.

Claim 14

An arc power supply for controlling the direct current applied by way of lead means to a pair of electrodes which establishes and maintains an arc between said electrodes. comprising power means having controlled rectifiers and operAble for providing through said lead means direct current to said electrodes, reference setpoint means to produce a set reference signal related to a desired value of said direct current, first adjustable means connected to said lead means for sensing said arc current and providing an adjustable current feedback signal, second adjustable means connected to said lead means for sensing the voltage across said electrodes and providing an adjustable voltage feedback signal, pulse generator means for producing a series of pulses of predetermined pulse repetition frequency and amplitude, and feedback control means coupled to said power means for summing said set reference signal, said adjustable current feedback signal, said adjustable voltage feedback signal and said series of pulses for applying a control signal to said power means to control the firing of the controlled rectifiers thereby to vary their ON time and OFF time and thus the magnitude of said direct current.

Claim 15

An arc power supply for controlling the direct current applied by way of lead means to a pair of electrodes which establishes and maintains an arc between said electrodes. comprising power means having controlled rectifiers and operAble for providing through said lead means direct current to said electrodes, reference setpoint means to produce a set reference signal related to a desired value of said direct current, first adjustable means connected to said lead means for sensing said arc current and providing an adjustable current feedback signal, second adjustable means connected to said lead means for sensing the voltage across said electrodes and providing an adjustable voltage feedback signal, pulse generator means for producing a series of pulses of predetermined pulse repetition frequency and amplitude, and feedback control means coupled to said power means for summing said set reference signal, said adjustable current feedback signal, said adjustable voltage feedback signal and said series of pulses for applying a control signal to said power means to control the firing of the controlled rectifiers thereby to vary their ON time and OFF time and thus the magnitude of said direct current.

Claim 16

The arc power supply of claim 12 in which there is provided means for simultaneously adjusting both said first and second adjustable means to provide infinite and continuous control of a volt-ampere characteristic of said direct current between a constant current characteristic and a constant potential characteristic.

Claim 17

The arc power supply of claim 13 in which said pulse generator means includes an astable multivibrator and in which there is provided means for varying the frequency of oscillation and the pulse amplitude.

Claim 18

The arc power supply of claim 14 in which said power means comprises silicon controlled rectifiers for rectifying a source of alternating current for providing said direct current and firing means adapted to provide properly timed and spaced firing pulses to rectifiers of said recitifier means under the control of said control signal.