JPH0569134A - Electric shock preventing circuit - Google Patents

Abstract

PURPOSE:To provide an electric shock preventing circuit which is a primarily turning-off type circuit without using an electric current detector (C. T), etc., and a high sensitivity type. CONSTITUTION:The electric shock preventing circuit is provided with a high-frequency generation circuit 1 for supplying the high-frequency voltage to the secondary side 4-2 of a welding transformer, a contact time detection circuit 2 which receives the voltage of both ends at the secondary side 4-2 of the welding transformer and detects the contact time between an electrode 6 and materials 7 to be welded by the change of the amplitude value and a driving circuit 3 which receives the signal of the contact time detection circuit 2 and drives a switch 5 when the electrode 6 comes into contact with the materials 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric shock preventive circuit for an arc welding machine, and more particularly to a circuit for preventing electric shock by interrupting a primary circuit of a main transformer of a welding machine.

[0002]

2. Description of the Related Art In an arc welding machine, it is necessary to keep the secondary voltage of the welding transformer below a safe voltage when it is not used. Various circuits have been proposed for that purpose, and roughly classified into primary cutting type circuits and secondary cutting type circuits. FIG. 2 shows an example of a primary cutting type electric shock protection circuit, which includes a welding transformer 21 and
It is composed of a down transformer (DT) 22, a magnet switch (MG) 23, a current detector (CT) 24, and the like. Here, the primary side 21 _-1 of the welding transformer 21
Is supplied with an AC voltage E, and the connection between the AC voltage E and the primary side 21 ₋₁ of the welding transformer 21 is ON / OFF controlled by a magnet switch 23. The down transformer 22 and the welding transformer 21 are connected in parallel with the primary and secondary circuits, and the current detector 24 is provided in the closed circuit on the secondary side of the down transformer 22 and the welding transformer 21. There is.

A welding rod 25 and an object to be welded 26 are connected in series to the secondary side 21 _-2 of the welding transformer 21. When arc discharge is to be performed, the two are brought into contact with each other (see the solid line in FIG. 2). When not in use, they are not in contact with each other (see the broken line in FIG. 2). The operation of the circuit of FIG. 2 will be described below. If the welding rod 25 and the object to be welded 26 are in a non-contact state, the magnet switch 2
Since 3 is in the OFF state, the secondary side 21 of the welding transformer
_No voltage is generated at _-2, and the secondary side of the down transformer 22 _-2
The specified safety voltage is generated only at. Therefore, a current having a predetermined value is flowing in the closed circuits of the secondary side 22 _-2 and 21 _-2 of the down transformer and the welding transformer.

In this state, when the welding rod 25 and the object to be welded 26 are brought into contact with each other, the secondary side of the down transformer 22 becomes
Since the short circuit is caused by the contact resistance between the welding rod 25 and the workpiece 26, the output of the current detector 24 increases. Current detector 24
Since a separate drive circuit is provided so that the magnet switch 23 turns on when the output of the welding transformer 21 increases, the AC voltage E is applied to the welding transformer 21 and the secondary side 2 of the welding transformer 2
1 _-2 to sustain properly the arcing predetermined voltage is induced in the.

FIG. 3 shows an example of a secondary cutting type electric shock protection circuit, which includes a welding transformer 21, a down transformer (DT) 22 and a magnet switch (M).
G) 23, and a voltage detection circuit 27 and the like. The major difference from the circuit of FIG. 2 is that the magnet switch 23 is provided on the secondary side 21 _-2 of the welding transformer.

The operation of the circuit shown in FIG. 3 will be described below. When the welding rod 25 and the object to be welded 26 are in a non-contact state, the magnet switch 23 is turned off and no current flows in the secondary side circuit. When the welding rod 25 and the object to be welded 26 are brought into contact with each other in this state, the secondary side 22 _-2 of the down transformer is short-circuited by the contact resistance between the welding rod 25 and the object to be welded 26, and current starts to flow. Therefore, this state is detected by the voltage detection circuit 27 and the magnet switch 23 is changed to the ON state,
The arc voltage is maintained by the secondary voltage of the welding transformer.

The electric shock protection circuit includes a low-sensitivity circuit that generates a predetermined secondary voltage when the contact resistance between the welding rod 25 and the work piece 26 is 2 ohms or less, and the contact resistance. There is a high-sensitivity type circuit that generates a predetermined secondary voltage when it reaches 2 to 500 ohms.

[0008]

However, the above-mentioned conventional circuits have the following problems, respectively. First,
Since the current detector 24 is indispensable in the circuit of FIG. 2, there is a problem that the device becomes large. Further, the circuit of FIG. 2 (primary cut type) has a problem that it cannot be a high sensitivity type circuit (particularly a circuit operating with a contact resistance of 300 ohms or more). This is because the impedance when the welding transformer secondary side 22 _-2 is viewed from the welding transformer secondary side 21 _-2 is about 4 ohms, so the contact resistance of the welding rod and the workpiece (about 300 ohms) is added to that impedance. This is because it is not easy to recognize that even if the resistance values of 1) are connected in parallel.

On the other hand, in the circuit of FIG. 3, a current does not flow when the welding rod and the object to be welded are not in contact, so a high-sensitivity type circuit can be constructed, but the exciting current (for example, 10 amperes) is always applied to the primary side of the welding transformer. However, there is a problem in that unnecessary power consumption (unnecessary heat generation) occurs. The present invention has been made in view of this problem, and an object thereof is to provide a high-sensitivity electric shock protection circuit which is a primary-cutting type circuit capable of interrupting an unnecessary exciting current. ..

[0010]

In order to achieve the above object, an electric shock preventive circuit according to the present invention comprises a high frequency generating circuit for supplying a high frequency voltage to the secondary side of a welding transformer and a secondary side of the welding transformer. The welding rod contacts the work piece under the control of the contact detection circuit that receives the voltage across both ends and detects the contact of the welding rod and the work piece by the change of this amplitude value, and the output signal of this contact detection circuit. For example, the welding transformer has a drive circuit for driving the switch on the primary side.

[0011]

The high frequency generating circuit oscillates a high frequency voltage and supplies it to the secondary side of the welding transformer. By the way, the equivalent load resistance of the high frequency generating circuit differs depending on whether or not the welding rod and the object to be welded are in contact with each other. That is, when the welding rod and the object to be welded come into contact with each other, this contact resistance is connected in parallel with the secondary impedance of the welding transformer, so that the combined impedance value decreases. Then, when the equivalent load resistance of the high frequency generation circuit decreases, the amplitude value of the high frequency voltage on the secondary side of the welding transformer also decreases.

Therefore, the contact detection circuit detects a change in the amplitude value on the secondary side of the welding transformer to detect the contact between the welding rod and the object to be welded. The drive circuit receives the output signal of the contact detection circuit and drives the switch on the primary side of the welding transformer when the welding rod and the object to be welded come into contact with each other. Then, a predetermined voltage value is generated on the secondary side of the welding transformer, and the welding machine operates normally.

[0013]

The present invention will be described in more detail based on the following examples. FIG. 1 is a diagram showing an embodiment of an electric shock prevention circuit according to the present invention, which includes a high frequency generation circuit 1, a contact detection circuit 2, a drive circuit 3, a welding transformer 4, a switch 5 and the like. Has been done. The switch 5 is a non-contact element such as a bidirectional three-terminal thyristor or a contact element such as a magnet switch.

The oscillation output of the high frequency generating circuit 1 is
De D₁Secondary side 4 of welding transformer 4 via_-2Supplied to
The secondary voltage of the welding transformer 4 is the diode D₂To
It is supplied to the contact detection circuit 2 via the contact. Also, contact inspection
The output of output circuit 2 is diode D ₃To drive circuit 3 via
Is supplied and the switch 5 is controlled by the output of the drive circuit 3.
To be done. In addition, the secondary side 4 of the welding transformer 4_-2Welding
The rod 6 and the object to be welded 7 are connected.

The high frequency generating circuit 1 includes a transistor Q ₁ ,
A multivibrator 8 which is formed by Q _2, the transistor Q ₃ to the ON operation only when the multivibrator 8 outputs the L level voltage, receiving the output of the transistor Q _3, a welding transformer secondary side 4 _-2 It is composed of a transistor Q ₅ etc. for supplying a high frequency voltage to. Here, the oscillation frequency f of the multivibrator 8 is, for example, 100K.
High frequency of about Hz. The transistor Q
_{When the} current flows through the closed circuit of the diodes D ₄ and D ₁ and the resistors R ₁ and R ₂ , ₄ turns on and the transistor Q
_This is a transistor that turns off ₅ .

The contact detection circuit 2 is composed of a transistor Q ₆ which performs an ON / OFF operation according to the amplitude value of the secondary side voltage of the welding transformer 4, a rectifying circuit 9 which rectifies the AC voltage AC in a half wave, and the like. ing. In this circuit, the transistor Q ₆ is but becomes an ON state charge of the capacitor C ₁ is discharged, the capacitor C ₁ when transistor Q ₆ is turned OFF is charged via the resistor R ₃ and the like. The switch SW is an inspection button for forcibly turning off the transistor Q ₆ and forcing the switch 5 into a driving state.

The drive circuit 3 is a circuit that starts driving the switch 5 when it receives an H level voltage, and then keeps driving the switch 5 when it receives an H level voltage at regular intervals. If the H-level voltage is not received for a certain time or longer, the switch 5 is shut off. FIG. 1 configured as described above
Hereinafter, the circuit operation of the circuit will be described separately for when the welding rod 6 and the workpiece 7 are not in contact and when they are in contact with each other. Note that this circuit is a high-sensitivity electric shock protection circuit, and it is assumed that the contact resistance between the welding rod 6 and the workpiece 7 is about 200 to 300 ohms.

[0018] In [noncontact time] welding rod 6 and the weld object 7 is in a non-contact state, the output signal of the high frequency generating circuit 1 is supplied to the input portion of the secondary side 4 _-2 and transistor Q ₆ of the welding transformer To be done. Then, the secondary 4 _-2 welding transformer, because it has an impedance with respect to the oscillation frequency f (e.g. 100kHz) of the high-frequency generating circuit 1, equivalent load resistance of the high-frequency generating circuit 1 is relatively large.

[0019] Therefore, even a relatively large amplitude (oscillation output of frequency f) welding transformer secondary side 4 _-2 voltage across (e.g. 4
Voltage), and the input of the transistor Q ₆
An H level voltage is applied in synchronization with the oscillation frequency f. On the other hand, since the AC voltage AC is applied to the rectifier circuit 9 of the contact time detection circuit 2, the collector of the transistor Q ₆ is
A power supply voltage whose amplitude changes at the commercial frequency is applied.

Therefore, the transistor Q ₆ repeats the ON operation in synchronization with the oscillation frequency f (when the positive power supply voltage is applied to the collector of the transistor Q ₆ ), so that the electric charge is stored in the capacitor C _1. It will not be charged. Since the capacitor C ₁ is not charged with electric charge, the output of the contact detection circuit 2 is always at the L level, and the drive circuit 3 does not drive the switch 5.

As described above, when the welding rod 6 and the object 7 to be welded are not in contact with each other, the switch 5 is always in the OFF state, and therefore, the secondary side _4-2 of the welding transformer 4 has a voltage higher than the safe voltage. No voltage is generated. [At the time of contact] When the welding rod 6 and the workpiece 7 come into contact with each other, the welding rod 6 is parallel to the secondary impedance of the welding transformer 4.
And the contact resistance of the workpiece 7 is added. Then, the combined impedance value decreases, so the secondary side of the welding transformer _4-2
The voltage across both ends (oscillation output of frequency f) also decreases, and the transistor Q ₆ is always in the OFF state.

Therefore, the capacitor C ₁ is charged by the output of the rectifier circuit 9, and after a predetermined time, a predetermined H level voltage is applied to the drive circuit 3. Then, the drive circuit 3 outputs a drive signal to the switch 5 and causes the secondary side of the welding transformer 4 to generate a predetermined voltage (for example, a no-load open voltage of 70 V). That is, when the welding rod 6 and the workpiece 7 are brought into contact with each other, the drive circuit 3 drives the switch 5 by the output signal (H-level voltage) of the contact detection circuit 2, so that the secondary side 4 of the welding transformer 4 is driven. _A certain voltage is generated at _-2 and the welder operates normally.

[During arc discharge] When a voltage of a predetermined value is generated on the secondary side of the welding transformer 4 and the welding machine is operating, a signal changing at the commercial frequency is applied to the input portion of the transistor Q _6. .. Therefore, the transistor Q ₆ repeats ON / OFF operation at the commercial frequency. When the transistor Q ₆ is in the OFF state, the power supply voltage of the transistor Q ₆ (the output voltage of the rectifier circuit 9) is 0 V, so that the output of the contact detection circuit 2 is always at the L level,
The H level voltage is not applied to the drive circuit 3.

However, during the arc discharge, the H level voltage is applied to the drive circuit 3 by another circuit (not shown), so that the switch 5 still maintains the drive state. During arc discharge, when a negative commercial frequency voltage is generated on the secondary side of the welding transformer 4, current flows in the closed circuit of the diode D ₄ , the resistor R ₁ , the resistor R ₂ and the diode D _1. , The transistor Q ₄ is turned on, so that the transistor Q ₅ is turned off, and the power consumption of the resistor R _{4 and the} like is suppressed.

[0025]

As described above, in the electric shock protection circuit according to the present invention, when the welding machine is not used, the primary side of the welding transformer is shut off to keep the secondary side voltage below the safe voltage. Therefore, the exciting current on the primary side of the welding transformer can be cut off, and the power consumption can be significantly reduced. Further, since the temperature rise due to an unnecessary exciting current can be reduced, the transformer can be downsized, and since the current detecting transformer and the like are not used, the entire circuit can be downsized.

Further, the electric shock prevention circuit according to the present invention is
When the welding rod and the object to be welded contact each other with a contact resistance of about 300 ohms, this is detected and a predetermined voltage is generated on the secondary side of the welding transformer. In other words, it is a primary cut type and realizes a high-sensitivity electric shock protection circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional electric shock protection circuit.

FIG. 3 is a circuit diagram showing another example of a conventional electric shock protection circuit.

[Explanation of symbols]

 1 High-frequency generation circuit 2 Contact detection circuit 3 Drive circuit 4 Welding transformer 5 Switch 6 Welding rod 7 Welding object

Claims (1)

[Claims] 1. A high frequency generating circuit for supplying a high frequency voltage to the secondary side of a welding transformer, and a voltage across the secondary side of the welding transformer. And a drive circuit that is controlled by an output signal of the contact detection circuit and that drives a switch on the primary side of the welding transformer when the welding rod contacts the workpiece. Electric shock protection circuit.