GB2220534A

GB2220534A - Welding current control apparatus

Info

Publication number: GB2220534A
Application number: GB8914066A
Authority: GB
Inventors: Calum Edward Medine
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-06-21
Filing date: 1989-06-19
Publication date: 1990-01-10
Anticipated expiration: 2009-06-19
Also published as: GB8914066D0; GB2220534B; GB8814722D0

Abstract

The apparatus comprises a welding plant 1, an arc starter unit 2 and a remote unit 4 controlled by switches 10, 11 on a welding torch 3. At the commencement of a welding operation the operator presses switch 10 which turns on the welding arc. Then, maintaining pressure on switch 10, switch 11 is pressed which operates a motor 9 to adjust a variable resistor 7 to increase the welding current. On releasing switch 11, but still maintaining pressure on switch 10, the welding current maintains a steady level. To decrease the current level, switch 10 is released, which reverses the motor 9, and the switch 10 is then repressed to maintain the current at a lower level. If the switch 10 is maintained released the current level gradually decreases to zero, and the welding arc is switched off in response to opening of a limit switch 8. <IMAGE>

Description

"Welding Current Control Apparatus" This invention relates to welding current control apparatus.

During an arc welding operation an operator may wish to vary the current supplied to the welding torch. Co-pending application No 8723806 describes apparatus which includes a finger operated switch control on the welding torch which operates a motor which drives a variable resistor in the welding current circuit. The operator is thus able to increase or decrease the welding current during a welding operation. The degree of control thus provided is most useful during a welding operation but it is an entirely manual process and thus as with conventional equipment not similarly equipped, the welding apparatus components remain live until a positive step is taken to switch off the supply to the torch.

According to the present invention there is provided welding current control apparatus comprising a current control device for varying welding current during operation of an electric arc welding plant, motor means for driving the current control device to vary the welding current and first and second control means for operating the motor means, the first control means having an on configuration in which the second control means is operable and an off configuration in which the second control means is inoperable and in which the motor means is operated to decrease the welding current, the second control means having an off configuration and an on configuration in which the motor means is operated to increase the welding current.

Preferably the first and second control means are in the form of push button switches which control a series of relays. Alternatively electronic switching means may be provided.

Preferably also limit switch means are included to disable the motor means when the welding current reaches a preset maximum or minimum level.

Preferably also the motor means is an electric motor.

Preferably also the current control device is a variable resistor.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of welding current control apparatus in accordance with the present invention; Fig. 2 is a circuit diagram of a first embodiment of welding current control apparatus in accordance with the present invention; Fig. 3 is a circuit diagram of a second embodiment of welding current control apparatus in accordance with the present invention; and Fig. 4 is a circuit diagram of a third embodiment of welding current control apparatus in accordance with the present invention.

Referring to the drawings, Fig. 1 illustrates welding apparatus incorporating welding current control apparatus in accordance with the present invention. The welding apparatus comprises a welding plant 1, an arc starter unit 2, a welding torch 3 and a remote unit 4 incorporating a transformer 5, to step the voltage down from the llOV supply to 24V; a circuit board 6; a variable resistor 7, for the welding current; a limit switch 8; and a control motor 9.

The torch 3 has a pair of push button switches 10 and 11.

The apparatus is designed to operate in the following manner. At the commencement of a welding operation the operator presses switch 10 which turns on the welding arc.

Then, maintaining pressure on switch 10, switch 11 is pressed which operates the motor 9 and hence the variable resistor 7 to increase the welding current. On releasing switch 11, but still maintaining pressure on switch 10, the current maintains a steady level. To decrease the current level switch 10 is released which reverses the motor 9 and then repressed to maintain the current at a lower level.

If the switch 10 is released again the current level gradually decreases to zero and the welding arc is switched off.

Referring now to Fig. 2 a circuit diagram of one embodiment of welding current control apparatus is illustrated. The circuit comprises, in addition to the components already described, a 110V supply 12 and an associated transformer which provides a 24V supply 13, indicator lamps 14 and 15, relays 1 to 4 and rectifiers 16.

The circuit achieves the required functions as described above in a manner which will now be described. Indicator lamp 14 lights to show that the apparatus is connected to the power supply. Pressing switch 10 causes relays 1 and 2 to close which starts the welding arc and causes indicator lamp 15 to light. Provided that switch 10 remains pressed subsequent operation of switch 11 closes relay 3 which provides power to the motor 9 which turns clockwise to operate the variable resistor 7 to increase the welding current. The limit switch 8 is closed which provides a back supply to relay 1 and closes relay 4 which makes an alternative arc circuit and provides a connection between relay 2 and the motor 9. Provided relay 2 remains closed however no power is provided to the motor via this circuit.

Releasing switch 11 when the desired current level has been achieved opens relay 3 which stops the motor and the current thus remains constant. To decrease the welding current switch 10 is released which opens relays 1 and 2 which in turn connects the back supply from the limit switch to the indicator lamp 15 and provides power to the motor 9 through relay 4. The motor 9 thus runs anticlockwise to increase the resistance of the variable resistor 7 and decrease the welding current.

Pressing switch 10 again causes the motor 9 to halt and the welding current to remain constant at a lower level. If however switch 10 remains released the motor 9 continues to operate and the welding current decreases until a point at which the limit switch opens and turns off relay 4. This in turn turns off the arc circuit, the motor 9 and the indicator lamp 15. The circuit thus operates in a manner whereby positive action must be taken to maintain the welding current and release of the switches 10 and 11 on the welding torch 3 causes the welding current to decrease and switch off.

The circuits illustrated in Figures 3 and 4 operate in a similar fashion but are provided with a DC supply 17 from the welding equipment-and have the addition of voltage regulators 18 for supply to the relays and to the motor.

Modifications and improvements may be incorporated without departing from the scope of the invention. For example the relays may be replaced by electronic switching circuits.

Claims

1. Welding current control apparatus comprises a current control device for varying welding current during operation of an electric arc welding plant, motor means for driving the current control device to vary the welding current and first and second control means for operating the motor means, the first control means having an on configuration in which the second control means is operable and an off configuration in which the second control means is inoperable and in which the motor means is operated to decrease the welding current, the second control means having an off configuration and an on configuration in which the motor means is operated to increase the welding current.

2. Welding current control apparatus as claimed in Claim 1, wherein the first and second control means are in the form of push button switches which control a series of relays.

3. Welding current control apparatus as claimed in Claim 1, wherein the first and second control means are in the form of push button switches which control electronic switching means.

4. Welding current control apparatus as claimed in Claim 1, 2 or 3, wherein limit switch means are included to disable the motor means when the welding current reaches a preset maximum or minimum level.

5. Welding current control apparatus as claimed in any one of the preceding claims, wherein the motor means is an electric motor.

6. Welding current control apparatus as claimed in any one of the preceding claims, wherein the current control device is a variable resistor.

7. Welding current control apparatus substantially as hereinbefore described, with reference to and as shown in the accompanying drawings.