Capacitor-discharge stud welding apparatus

Claim 2

A stud welding apparatus, comprising capacitor means, charging means coupled to said capacitor means for charging said capacitor means, welding means, electronic switch means connecting said welding means to said capacitor means and capable of being rendered conductive and non-conductive for selectively discharging said capacitor means through said welding means, control means coupled to said switch means and variable between a first state and a second state for actuating said electronic switch means in the first state so as to render said switch means conductive and initiate welding, and protective means responsive to the conductivity of said switch means and the state of said control means and coupled to said capacitor means for reducing the voltage across said capacitor means when said switch means is conductive and when said control means is in the second state.

Claim 3

An apparatus as in claim 1, wherein said protective means includes voltage abating means coupled to said charging means for reducing the voltage applied by said charging means across said capacitor means.

Claim 4

An apparatus as in claim 2, wherein said protective means includes shunting means responsive to said switch means being conductive and said control means being in the second state for forming a shunt path through which said capacitor means can discharge.

Claim 5

An apparatus as in claim 2, wherein said protective means includes circuit means for forming a current path across said supply unit and including said electronic switch means, said circuit means including a cutoff device for responding to current through said circuit means, said cutoff device being connected to said capacitor means for cutting off the current to said capacitor means when said current device is cut off.

Claim 6

A stud welding apparatus, comprising welding current generating means including capacitor means, charging means coupled to said capacitor means for charging said capacitor means, welding means, said generating means including electronic switch means connecting said capacitor means to said welding means and capable of being rendered conductive and non-conductive for selectively discharging said capacitor means through said welding means, control means coupled to said switcH means and variable between a first state and a second state for actuating said switch means in the first state so as to render said switch means conductive and initiate welding, and protective means responsive to the conductivity of said switch means and the state of said control means and coupled to said generating means for reducing the voltage across said capacitor means when said switch means is conductive and when said control means is in the second state.

Claim 7

A stud welding apparatus, comprising welding current generating means including capacitor means, charging means coupled to said capacitor means for charging said capacitor means, welding means, said generating means including electronic switch means connecting said capacitor means to said welding means and capable of being rendered conductive and non-conductive for selectively discharging said capacitor means through said welding means, control means coupled to said switcH means and variable between a first state and a second state for actuating said switch means in the first state so as to render said switch means conductive and initiate welding, and protective means responsive to the conductivity of said switch means and the state of said control means and coupled to said generating means for reducing the voltage across said capacitor means when said switch means is conductive and when said control means is in the second state.

Claim 8

An apparatus as in claim 5, wherein said protective means includes voltage abating means coupled to said charging means for reducing the voltage applied by said charging means across said capacitor means.

Claim 9

An apparatus as in claim 6, wherein said protective means includes shunting means responsive to said switch means being conductive and said control means being in the second state for forming a shunt path through which said capacitor means can discharge.

Claim 10

An apparatus as in claim 6, wherein said protective means includes circuit means for forming a current path across said supply unit and including said electronic switch means, said circuit means including a cutoff device for responding to current through said circuit means, said cutoff device being connected to said capacitor means for cutting off the current to said capacitor means when said current device is cut off.

Claim 11

An apparatus as in claim 6, wherein said protective means includes sensor means sensing the voltage applied to said welding means, safety switch means responsive to said control means being in the second state and the existence of a predetermined voltage at said welding means for shunting said charging means, said safety switch means including a disconnect element responsive to current through said safety switch for disconnecting said charging means from said capacitor means.

Claim 12

An apparatus as in claim 9, wherein said safety switch means includes a thyristor, said sensor means being connected to said thyristor for turning said thyristor on when said sensor means senses a potential greater than a predetermined potential, said sensor means sensing a potential when said electronic switch means is conductive, said control means disconnecting said thyristor from said sensor means in the first state.

Claim 13

An apparatus as in claim 10, wherein protective means includes shunting means responsive to said switch means being conductive and said control means being in the second state for forming a shunt path through which said capacitor means can discharge.

Claim 14

An apparatus as in claim 11, wherein said charging means includes a series resistance, and wherein said path includes said series resistance.

Claim 15

An apparatus as in claim 12, wherein said protective means further includes overload means responsive to the voltage across said capacitor means and including comparator means for applying a signal to said safety switch means when the voltage across said capacitor means exceeds a predetermined value determined by said capacitor means.

Claim 16

An apparatus as in claim 10, wherein said safety switch means forms a shunt path across said charging means, said electronic switch means being outside of said path.

Claim 17

An apparatus as in claim 10, wherein said protective means further includes overload means responsive to the voltage across said capacitor means and including comparator means for applying a signal to said safety switch means when the voltage across said capacitor means exceeds a predetermined value determined by said capacitor means.

Claim 18

An apparatus as in claim 9, wherein said cutoff element is a fuse.

Claim 19

An apparatus as in claim 16, wherein said protective means further includes overload means responsive to the voltage across said capacitor means and including comparator means for applying a signal to said safety switch means when the voltage across said capacitor means exceeds a predetermined value determined by said capacitor means.

Claim 20

An apparatus as in claim 9, wherein said safety switch means Forms a shunt path across said charging means, said electronic switch means being outside of said path.

Claim 21

An apparatus as in claim 18, wherein protective means includes shunting means responsive to said switch means being conductive and said control means being in the second state for forming a shunt path through which said capacitor means can discharge.

Claim 22

An apparatus as in claim 9, wherein said protective means further includes overload means responsive to the voltage across said capacitor means and including comparator means for applying a signal to said safety switch means when the voltage across said capacitor means exceeds a predetermined value determined by said capacitor means.

Claim 23

An apparatus as in claim 5, wherein said protective means includes an auxiliary switch connected across said welding means and responsive to the state of said control means for shunting said welding means when said control means is in the second state.

Claim 24

A stud welding apparatus as in claim 21, wherein said protective means includes circuit means for forming a current path across said charging means and including said electronic switch means, said circuit means including a cutoff device for responding to current through said circuit means, said cutoff device being connected to said capacitor means for cutting off the current to said capacitor means when said cut off device is cut off.

Claim 25

An apparatus as in claim 5, wherein said charging means includes a current-limiting transformer and a rectifier circuit.

Claim 26

An apparatus as in claim 23 wherein said protective means includes voltage abating means coupled to said charging means for reducing the voltage applied by said charging means across said capacitor means.

Claim 27

An apparatus as in claim 24, wherein said protective means includes shunting means responsive to said switch means being conductive and said control means being in the second state for forming a shunt path through which said capacitor means can discharge.

Claim 28

An apparatus as in claim 23, wherein said protective means includes sensor means sensing the voltage applied to said welding means, safety switch means responsive to said control means being in the second state and the existence of a predetermined voltage at said welding means for shunting said charging means, said safety switch means including a disconnect element responsive to current through said safety switch for disconnecting said charging means from said capacitor means.

Claim 29

An apparatus as in claim 23, wherein said safety switch means includes a thyristor, said sensor means being connected to said thyristor for turning said thyristor on when said sensor means senses a potential greater than a predetermined potential, said sensor means sensing a potential when said electronic switch means is conductive, said control means disconnecting said thyristor from said sensor means in the first state.

Claim 30

An apparatus as in claim 23, wherein said charging means includes a series resistance, and wherein said path includes said series resistance.

Claim 31

An apparatus as in claim 23, wherein said transformer includes a primary winding and a secondary winding loosely coupled with said primary winding and having a core to form a leakage reactive transformer.