GB2040118A - Welding control system - Google Patents

Abstract

A control system for an electric welding machine comprises: a power transformer 1 having a primary winding 2 for supplying welding power to the machine, a secondary winding 3 for connection to a pair of welding electrodes 9, 10, and a tertiary winding 4 for connection to a source of power for energising said secondary winding at low power insufficient to generate a welding arc; a sensor 6 coupled to the secondary winding for sensing the flow of current therethrough and generating a signal in response to said flow; and a dynamic member (e.g. electro-magnets 20, 21) for controlling the power supply circuit of the primary winding of the power transformer of the electric welding machine, the dynamic member being triggerable by said signal (SCR 19 fired). Short circuiting of said welding electrodes generates said signal, causing said dynamic member to enable said electric welding machine (triac 5 is triggered) and to move dark glasses 26 into their operative position. <IMAGE>

Description

SPECIFICATION Control systems The present invention relates to a control system for an electric welding machine, particularly a kind of electric welding machine that saves electricity and elevates work efficiently.

Generally speaking, the main structure of a conventional electric welding machine is, as indicated in Fig. 5, an iron core 1, with a primary winding 2 and a secondary winding 3 wound on it, this being a basic transformer structure. A high voltage low current supply is input to the primary winding through its two terminals, and a low voltage high density current output is induced in the secondary winding. An electric arc is created to generate high intensity heat by moving close to each other two electrodes connected to the two terminals of the secondary winding, the intense heat melting and joining work pieces to be welded as welding proceeds.Generally, during working time, the welder, desiring the convenience of creating an instant electric arc between the two electrodes, usually does not cut off the power supply to the primary winding even when the welding machine is not in use, hence, the supply circuit of the primary winding of the welding transformer is maintained in a constant state of closed circuit in spite of the intermittency of the welding work; so, obviously, it is uneconomical, for the primary winding of the welding transformer consumes electrical energy even when there is no welding. This is one of the main defects of the conventional electric welding machine; secondly, because the electric arc generates strong light when the electric welding machine is being used, the eyes of the welder have to be protected by a mask and dark glasses.Generally, when welding is in progress, the right hand is used to hold the electrode and the welding rod to do welding work, the left hand is used to hold the mask to protect the eyes, thus, only the right hand is employed to do the actual welding work, but both hands are occupied. If the surfaces of workpieces are flat this does not introduce any problems but if the work pieces are for example vertically perpendicular or angular, another person is needed to hold the work pieces in position and this is wasteful of manpower.

Thirdly, the welder must put on the mask and glasses before welding is started, for obvious reasons, but because the eyes are shielded by the dark glasses, the welder cannot see the correct position of the jointto be welded, so he has to depend on an experienced estimate to strike contact the electrodes to generate a strong electric arc light in order to locate the correct position. This not only poses a difficulty at the start of welding but in addition the surface which is not being welded is dirtied, marring the finished work. Furthermore, the secondary winding should not be shorted because the primary winding is generally maintained in a state of closed-circuit and the transformer may be damaged.To sum up, the conventional electric welding machine has four main defects: 1. wasting electricity; 2. wasting man power; 3. inconvenient to operate; 4. short circuiting of the welding electrodes can damage the transformer when the welding transformer is switched on to the power supply.

An object of the present invention is to provide an improved control system for an electric welding machine.

The present invention provides a control system for an electric welding machine comprising: a power transformer having a primary winding for supplying welding power to the machine, a secondary winding for connection to a pair of welding electrodes of the machine, and a tertiary winding for connection to a source of power for energising said secondary winding at lower power insufficient to generate a welding arc; a sensor coupled to the secondary winding for sensing the flow of current therethrough and generating a signal in response to said flow; and a dynamic member for controlling the power supply circuit of the primary winding of the power transformer of the electric welding machine, the dynamic member being triggerable by said signal whereby short circuiting said welding electrodes generates said signal and causes said dynamic member to enable said electric welding machine.

The present invention is applicable to electric welding devices such as: generally used electric welding machines, spot welding machines, seam welding machines and all types of resistance welding machines.

An advantage of the present invention is that the power supply for an electric welding machine may be automatically switched on when it is to be used, and automatically cut off from the machine when it is not in use, thereby to attain the object of electricity saving.

In a preferred form of the present invention an automatic eyes shielding control system is provided whereby the welder can have one hand holding the electrode and welding rod to do welding work and the other hand doing other related work, to elevate work efficiency.

A control system according to the present invention enables the right position of the joint to be welded to be located at the very first moment of the start of welding work.

An additional advantage of the present invention is the protection of the welding transformer from damage when a short-circuit occurs between the two welding electrodes at the start of the operation but before commencement of the actual welding.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of a control system according to the present invention; Fig. 2 is a sectional view of pneumatic cushioning electro-magnet; Fig. 3 is a structural view of dark glasses shielding mechanism of the present invention; Fig. 4 is an illustrated view of a lever operated switch of the present invention; and Fig. 5 is an illustrated view of the transformer structure of a conventional electric welding machine.

Fig. 1 depicts a circuit diagram of a control system of the present invention. A core 1 is the welding transformer core whereon are wound a primary wid ing 2 and a secondary winding 3, which are similar to those of the conventional welding transformer; on the core is wound a tertiary winding 4 which is a magnetic flux inciting winding. A Triac 5 is connected in series in the primary winding power supply circuit. The Triac 5 is normally off, therefore the primary winding does not normally generate magnetic flux. A core 7 of a sensor 6 encases the lead-out wire of the secondary winding, that is, the lead-out wire of the secondary winding 3 is the primary winding (one turn) of the sensor 6, and on the core of the sensor is wound an induction winding 8. Thus, the sensor functions as a current transformer.When the electrodes 9 and 10, connected to the two terminals of the secondary winding 3, come into close proximity to generate an electric arc during welding, the lead out wire of the secondary winding conducts heavy current and this induces a signal in the secondary winding 8 of the sensor 6. The signal is coupled to an amplifying circuit having a series of transistors 12, 13, 14 through a coupling capacitor 11. (The amplifying circuit is made up of 3 stages in this embodiment. However, the number of stages can be increased or decreased according to necessity). The amplified signal from transistor 14 is rectified by a full wave rectifier comprising diodes 15 and 16, and then amplified through a Darlington amplifier composed of transistors 17 and 18.The output signal of the Darlington amplifier can serve as a atrigger signal for different dynamic and time ele- ments. In this embodiment, the trigger signal is coupled to the gate of a SCR 19. The said SCR 19 is connected in series with two parallel dynamic ele ments, electro-magnets 20 and 21. When the SCR 19 is not triggered by a signal and is consequently off, the electromagnets 20 and 21 connected in series are not energized. Note that capacitor 33 is a delay capacitor.

The structure of each electro-magnet is shown in Fig.2, wherein frame 207, coil 202, spring 103, movable core 204 are generally similar to those of the conventional electro-magnet and will not be described here in detail, but at the bottom of the frame 201 is bored a very small hole 205 to limit the speed of the forward and backward movement of the movable core. This is a pneumatic type cushioning method. A steel wire 22 is connected to the top of the movable iron core 204.

The mechanism of the vertical movement of dark glasses on a mask is shown in Fig. 3, wherein the electromagnets 20 and 21 as depicted in Fig. 2 are disposed on the right and left sides respectively of a work cap 23. A lever 24 is fulcrumed about a joint bolt 25, and mounts the dark glasses 26 at one end. The glasses are biassed into their illustrated position by a spring 27. The movable core 204 of the electromagnet is connected to the lever 24 by means of the steel wire 22. When the electromagnet is energised, the dark glasses 26 are slowly pulled down to cover up a visual window 29 on the mask 28 (as indicated by the dotted line of Fig. 3) because of the actionof the pneumatic cushion and the delay capacitor 33.When the electro-magnet is de-energized, the lever 24 and the dark glasses 26 are slowly pulled back to their original positions by the restoring force of the spring 27. Though in the embodiment just described the electromagnets are disposed on the work cap, the electromagnets may be disposed on other parts of the welder's body if the normal functioning of the electromagnet and the dark glasses is not disturbed.

Referring to Fig. 4, the lever 24 has a lug 30 on its underside, and directly under the lug is disposed a press button switch 31 which is the switch shown in the lower left portion of Fig. 1 and is normally open.

The operation and functions of the present invention may be better understood by referring to Fig. 1 together with Figs.3 and 4. Because switch 31 is normally open, the Triac has no trigger signal input and is normally off, and the primary winding nor mally has no electric current. Primarily, the object of electricity saving is attained and the problem of damage of the transformer due to shorted electrodes is reduced.When operating, firstly bring the two electrodes 9, and 10 into contact to cause a currentto pass through the lead-out wire of the secondary winding 3, and subsequently to induce a signal in the winding 8 of the sensor 6, the signal is then amplified by the amplifiers and triggers the SCR 19 to turn on, and energizes the electro-magnets 20 and 21 which pulls down the lever 24 and the dark glasses 26 to cover up the eyes of the welder as shown in Fig. 3. The nose 30 of the lever 24 presses downwardly to close switch 31 and a voltage is induced in the secondary winding of the transformer 32 to trigger and turn on the Triac 5, consequently, a current passes through the primary winding of the welding transformer.When the dark glasses 26 come down slowly to position, the welder separates slightly the electrodes 9 and 10 and a welding arc is generated as a result of the switching on of the electric welding machine to the power supply. The sensor continues to induce signals because current continues to flow in the lead out wire of the secondary winding after an electric arc has been generated, and the signal after amplification by the amplifiers actuates the dynamic element to maintain the dark glasses in the covering position.When welding is over, the sensor 6 loses induced signals after the electrodes are separated turning off the SCR 29 and de-energizing the electromagnets 20 and 21, thus, the lever 24 and dark glasses 26 moves upward due to the restoring force of the spring 27, and the nose 30 moves away from switch 31 and turns it off, consequently, the trigger signal of the Triac 5 disappears, and the primary winding 2 of the electric welding machine is cut off from the power supply.

At the start of the operation, when the dark glasses are still not lowered to cover up the eyes and the electrodes 9 and 10 are being brought to contact, there is a time when the two electrodes are near to each other. However, no electric arc is generated, because at this moment, only the magnetic flux inciting winding 4 is on, the main primary winding is still off. Thus, electricity saving, using both hands in completing a welding work, correct position welding at the start of the welding, non-destructive shorting of the electrodes at the start of the welding process can be attained.

Claims (4)

1. A control system for an electric welding machine comprising: a powertransformerhaving a primary winding for supplying welding power to the machine, a secondary winding for connection to a pair of welding electrodes of the machine, and a ter tiary winding for connection to a source of power for energizing said secondary winding at low power insufficient to generate a welding arc; a sensor coupled to the secondary winding for sensing the flow of current therethrough and generating a signal in response to said flow; and a dynamic member for controlling the power supply circuit of the primary winding of the power transformer of the electric welding machine, the dynamic member being trig gerable by said signal whereby short circuiting said welding electrodes generates said signal and causes said dynamic member to enable said electric welding machine.

2. A control system as claimed in claim 1, wherein said dynamic member is adapted to control the shielding action of a pair of dark glasses disposed on a mask for an operator, the dynamic member being triggerable to move said glasses into a shielding position.

3. A control system for an electric welding machine, substantially as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.

4. An electric welding machine including a control system as claimed in any of claims 1 to 3.