JPS59127976A - Power supply device to gun having built-in transformer for spot welding robot - Google Patents

Abstract

PURPOSE:To prevent accidental short-circuiting between flexible cables and to prevent electric shocks by providing an insulating transformer for step-down between a power source and a gun and grounding one point of the secondary side circuit of the transformer through impedance of low value. CONSTITUTION:The insulating transformer 4 for step-down is installed between the welding power source 10 of rated voltage 200 or 400V having an electronic switch 7 that controls welding current and the gun 1 having a built-in transformer fixed at the tip of the movable arm of a robot 2 to lower applied voltage between cable conductors of flexible cables 3. One point of the flexible cable is connected to ground 6 between the secondary coil side of the insulating transformer 4 and the primary coil side of the gun 1 through impedance 5 of low value, for instance, a resistor of about 100 ohm. By this way, prevention of occurrence of accidental short-circuiting between cables, and restriction of current at the time of short-circuiting become possible. Further, protection from electric shocks to the flexible cable is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device for automatic spot welding equipment such as spot welding robots.

It is well known that spot welding robots are used in many welding operations, including automobile body assembly lines;
However, in recent years, the use of so-called transformer-built-in guns, in which a welding transformer and spot welding head are integrated, has been increasing as a measure to save energy in spot welding and to prevent wear and tear on water-cooled cables for welding current circuits. .

Conventionally, the bath current was supplied to the spot welding gun, which was not attached to the tip of the robot arm, through a long water-cooled cable with a large cross-sectional area from a large welding transformer suspended from the ceiling. It was Therefore, the robot has to swing this thick cable and move at high speed, and the cable is subject to severe twisting and bending due to the posture control of the welding gun at each welding point. , cables have become a must-have consumable item.

On the other hand, in the transformer built-in gun described above, the secondary coil side of the welding transformer is integrated with the welding head with a pressurized 4S structure, so there is no need for a thick water-cooled cable for the welding current circuit. Since the impedance of the Oki 1 path through which a large welding current flows is extremely small, the welding transformer's current and capacity can be kept low νI, and its shape can be made extremely small and lightweight.

However, by attaching this transformer built-in gun to the tip of a welding robot arm and performing bath welding, a new problem arose. In other words, this 7-stem was unable to operate in a conventional low-voltage, high-current circuit. Instead of a cable, use a 200V or 400V rated v'i
:The voltage circuit was completely installed by robots, and the cable itself was not thin, so its lifespan was shortened. Robot with core wire and ground potential
The risk of dielectric breakdown between the arm, jig, etc. increases, and in addition, if such an accident occurs, the damage to peripheral equipment and the impact on the power supply system due to sparks will be significant and cannot be overlooked. It has become a fear.

These risks seriously hinder the practical use of guns with built-in transformers, which have many other disadvantages, but the present invention provides a drastic solution to these problems. It is.

The figure is an electric circuit diagram showing one embodiment of the present invention. Comparison of the prior art and the present invention using the figure is as follows.

Generally, the can (1) with a built-in transformer is identified at the tip of the movable arm of a spot welding robot (2) (not shown),
The workpiece is transferred at high speed according to the spot welding position dispersion, and the gun itself is also positioned according to the workpiece shape.
It will be a bold change.

Therefore, the nJ motion bracket 3) connected to the primary 1p11 of the welding transformer is forced to make extremely violent twists, turns, etc., and gradually wears out.

Conventionally, this movable cable (8) is internally connected to a welding power source (10) rated at 200V or 400V via an electronic switch (7) such as a thyristor contactor that controls the welding 7 electric current. When the thyristor/contactor (7) is in a conductive state due to the energization command from the timer (8), a good welding power source Ichikawa is directly applied to the VC between the cables of the pair of movable cables (3). So, father, example, thyristor contactor (7)
Even when the cable core is in a non-conducting state, the cable core will optionally be kept at a screen-to-ground potential.

As a result, a strong dielectric breakdown force acts even on the thin insulation that protects the outer periphery of the cable (8), causing short circuits between the cables and short circuits to the ground. If this happens, there is a danger that a very large short-circuit current will flow.

When these tPl scabbard θrc occur, in most cases, the breaker (9) installed in the welding cabinet τ111 will operate and cut off the power supply, but the large spark caused by the cable short circuit will cause the robot to This may cause damage to peripheral equipment such as arms and jigs, and in some cases may even affect power supply equipment such as substations, leading to major accidents such as factory power outages and fires.

- A so-called @i disconnector is effective against deterioration of the cable core wire's insulation against ground. If water scale accumulates and the insulation resistance of the electrical circuit decreases, the earth leakage circuit breaker may malfunction. Troublesome processing was required, including the use of special insulated Kasairitake mushrooms.

In contrast, in the present invention, by installing an insulating transformer (4) for step town in the middle ILi of the welding fixed angle (10) and the transformer built-in gun (1), the movable cable (3)
Since the voltage applied between the core wires can be reduced, the possibility of short-circuit accidents between cables is reduced, and even if a short-circuit between cables occurs in the movable cable (3), the isolation transformer (4) Due to internal impedance! lll
The short kT current that causes welding ionization can be limited.

- J, P edges) By keeping the secondary coil 1 of the lance (4) in the grounded state (~70-), even if the insulation on one side of the movable cable (8) breaks down, the cable core wire Even if some parts come into contact with parts at ground potential such as robot arms or jigs, the ground current will be 4t.
There will be no damage to the robot device due to sparks, etc., and no adverse effects on the power supply equipment.

However, if the potential of the terminal including this ijl'l'l+ +5--full (3) is grounded and kept in a floating state, the -primary coil and secondary coil of the isolation transformer (4) Due to leakage, innovation, etc. between the secondary coil and the primary coil (1111), for example, when the movable couple (3) crosses, the If a person touches the straight path, there is a fear of being attacked.

VC←r1 The supply impedance (5) for the electric circuit in this 70-ting state, for example, the 100 Ω resistor (earth (6) (l
All you have to do is connect it.

This kind of grounding can sufficiently reduce the subcurrent that flows through the ground even in the event of a ground fault in the ungrounded individual core wire of the J-type cable (3), and prevents the welded parts from being damaged by sparks, etc.
Total 1A: This is the secondary voltage of the two-prong, step-down isolation transformer (4), which can provide strong protection, that is, the normal pressure supplied to the welding transformer, but it is too low. If it is too thick, the movable cable (3) will become thick, resulting in poor workability and poor economic efficiency. Depending on these considerations and safety considerations, the optimal voltage for composing, for example several tens of volts, will be selected.

[Brief explanation of drawings]

Figure 1 is an electrical diagram showing a practical 7III example of the present invention. (O transformer internal gun ρ) Spot welding robot g) -+5J dynamic cable (4) Insulation transformer for step down ■ Grounding impedance ■ Earth ■ Thyristor contactor ■ Timer ■) Flaker (Iri 200vxu400v rated i-contact'ttta harp) Reverend Masahiro Kato

Claims (1)

[Claims] In an automatic spot bending device such as a spot welding robot that uses a so-called transformer-built-in gun in which a bath welding transformer and a spot welding head are integrated, A step-down isolation transformer is installed between the welding type shatter with a switch interposed therebetween and the bath contact transformer, and a fully flexible cable connects the secondary coil 111 of the isolation transformer to the primary coil side of the contact transformer. , connect one point of the electric path to the ground with a low impedance of 116, and melt it into the transformer built-in can with t￥fP.
#Power supply device.