JPS59159279A - Detector for short-circuiting and disconnection in electric circuit for gun containing welding transformer - Google Patents

Abstract

PURPOSE:To decrease the impressed voltage between the cores of a movable cable and to decrease the possibility of a short-circuiting accident between the cables by installing an insulating transformer for step down. CONSTITUTION:A control circuit 5 for timing in upply of a measuring voltage is introduced therein with the excitation signal for the solenoid 9 of a solenoid valve for pressurizing an electrode head from a welding timer 10, and interrupts an AC low voltage circuit 8 for measurement from the secondary circuit of an insulating transformer 4 during the period when said signal is inputted thereto, that is, during the period when the electrode head generates the pressurizing force for conducting the welding current, thereby preventing the malfunction and failure of this detector owing to the secondary voltage of the transformer 4 generated during the conduction of the welding current. The circuit 8 is again connected to the secondary coil side of the transformer 4 when the pressurizing period of the electrode head ends.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detection device for detecting a short circuit between core wires and a break in a conductor of a welding transformer-next cable in an automatic spot welding machine.

It is well known that spot welding robots and automatic spot welding equipment are used for many types of welding work, including automobile body assembly lines, but in recent years, spot welding energy saving measures and welding current circuit As a countermeasure against wear and tear on water-cooled cables, the use of so-called transformer-built-in cans, in which a welding transformer and a spot welding head are integrated, is increasing.

Conventionally, welding current was supplied to the spot welding head attached to the tip of the robot arm using a long water-cooled cable with a large cross section from a large welding truck or chair suspended from the ceiling. I was being bullied.

Therefore, the robot swings around a thick and heavy cable at high speed, and in order to control the posture of the welding head at each welding point, the cable itself is subject to sudden twists and bends. It has become a consumable item for Iffl.

On the other hand, because the transformer built-in can (the secondary coil side of the transformer is integrated with the welding head which has a pressurizing and welding mechanism of 1L), the welding current circuit is thick water-cooled. Since there is no need for a type cable, and the impedance of the circuit through which a large welding current flows becomes extremely small, the electric capacity of the welding transformer can be reduced, making it possible to make it extremely compact and lightweight.

However, when performing welding work by attaching this transformer-built-in can to the tip of the welding port arm, a new problem arose.

In other words, this method uses a robot to swing an Ml voltage circuit rated at 200V or 400V instead of the conventional low-voltage, high-current cable (the cable itself is thin and its lifespan is long). A short circuit between two cable core wires forming an electrical path, or a cable core wire at a high potential and the ground 7m (j'I.

The risk of dielectric breakdown between robot arms, jigs, etc. located in It has become a great blessing that cannot be achieved by others.

These dangers seriously impede the practical application of cans with built-in transformers, which have many other advantages, or the present invention provides a drastic solution to these problems. The present invention provides a useful device for monitoring disconnection, which is the most common accident when cables are moving around, while the cables are moving around.

The figure is an electrical circuit diagram showing one embodiment of the present invention, and the following is a comparative explanation of the conventional technology and the present invention using the figure.

Regarding the purpose and effects of a system in which a step-down isolation transformer (4) is installed between a 200V or 400V rated welding power source (13) and a gun with a built-in transformer (1), a patent application was filed in 1982 by the same applicant. No. 3153
SY is mentioned in the same specification filed as No. ``Power supply system for can with built-in transformer for spot welding robot fat''.

That is, this invention can reduce the voltage applied between the core wires of the movable cable (3) by installing the step-down lance (4), thereby reducing the occurrence of short circuits between the movable cables (3). Furthermore, even in the unlikely event that a short circuit occurs between cables in the movable cable (3), the short circuit current flowing into the welding power source can be limited by the internal impedance of the isolation transformer (4).

In addition, by insulating the electric path including the iJ movable cable (3) from the welding power supply circuit using the insulating transformer and grounding it with a low impedance, it is possible to prevent contact by sparks or the like when one wire of the movable cable (3) is grounded. It can prevent damage to the crystal, and the movable cable (3) can prevent damage to the crystal.
It is also extremely effective in terms of safety, as it can prevent electric shock accidents caused by forgetting to turn off the plate horn on the power supply side when replacing the power source.

The present invention utilizes the fact that the circuit including the movable cable (3) is insulated from the welding power source (13) by the insulating lance (4) of the invention, and the secondary coil of the insulating transformer (4) is 71i1i constant voltage supply timing control circuit (5
), a measurement current detection circuit (6), an alarm circuit (7), and a running AC low voltage circuit (8) are added, which prevents short circuits in the one-o-j motion cable (3) that is swung around by a robot arm, etc. The aim is to safely and reliably detect the occurrence of wire breakage or disconnection while the robot arm is moving around.

In conventional equipment that does not have a step-down isolation transformer (4), the short circuit of the iiJ dynamic cable (3) and the thyristor contactor (11) of the welding control timer (1) conduct the 1/1 wire. Short welding energization time,
For example, it was common to detect a change in the current flowing into the power supply circuit including the thyristor/contactor over a period of approximately 0.5 seconds.

In other words, if the movable cable (3) is short-circuited, it will cause a dead short in the 200V or 400V rated power line, and this short circuit will cause a large current to trip the power breaker.On the other hand, if the cable is disconnected, the current will flow to the Zyristor contactor. If the current stops flowing, methods such as detecting it with a current monitor or the like and obtaining a signal or notification have been taken.

In this method, to check for short circuits or lines in the movable cable (3), the robot/rm must be stopped,
This is only for a short period of time when the welding head or workpiece is pressurized and welding energization is carried out, and detection work must be performed during a longer period when the robot arm, etc. is moving around, which is likely to cause cable short-circuit or disconnection accidents. Not only is this method unreasonable, but it is also considered to be an extremely dangerous method, as short circuits in cables are detected by short circuits in high-voltage circuits that generate large currents that are likely to be accompanied by large sparks.

Contrary to this, the detection device of the present invention uses an extremely low alternating current voltage, for example, about 12 V AC, to detect the electric circuit including the movable cable (3) during the period when the movable cable (3) is being swung around. This system monitors short circuits and 1-1 wires.

The constant voltage H-supply timing control circuit 1i4j (5) in the figure introduces the magnetic shielding signal of the solenoid valve solenoid (9) for pressurizing the electrode head from the welding timer (1), and controls the period during which this signal is input. That is, during the period when the electrode head is generating pressure force for welding energization, the AC low voltage circuit (8) for measurement, which will be described later, is cut off from the secondary circuit of the isolation transformer (4), and the welding energization is stopped. This is to prevent malfunction or damage of this detection device due to the secondary voltage of the insulation transformer (4) generated inside the electrode. (8) again to the secondary coil side of the isolation transformer (4).

By applying this AC low current for measurement, an isolation transformer (4
) and a parallel circuit between the secondary coil circuit of the movable cable and another circuit that connects the movable cable to the primary coil of the welding transformer, a small alternating current for measurement according to each impedance flows.

The measured current detection circuit (6) shown in the figure monitors changes in this measured current, and detects a sudden increase in the measured current that occurs when the circuit under test including the movable cable (3) becomes short-circuited.
On the other hand, do measurements occur when the wire is disconnected? It detects a sudden decrease in current and transmits the signal "Ij" to the subsequent alarm circuit (7i).

The alarm circuit (7) mainly outputs short-circuit or line alarms in the movable cable (3) based on this number, and for example, in case of an emergency such as stopping the operation of an automatic machine or notifying the operator of the need for cable replacement. It is used as item 1).

As mentioned above, the detection device of the present invention is unrelated to welding energization, so it can detect short circuits in movable cables and 1tli wires that tend to occur while robot arms are moving or occur only for a moment when they are working. 200■ or 4.00V
Since the rated high voltage circuit can be easily readjusted even after 618 hours, damaged cables can be replaced reliably and in an extremely safe manner.

In this way, by adopting the present invention, the electrical danger associated with the use of a can with a built-in one-lance is completely eliminated, which greatly contributes to its practical application. .

[Brief explanation of the drawing]

The figure is an electrical circuit diagram showing an embodiment of the present invention. [Explanation of the issue] (1)...Can with built-in transformer (2)...Bottom capacity ↑ β month" Rojo Nt (3)
・・LJL work cable (4)・・Step-down insulation transformer (5)・・Measurement 71f, I:'t-Introduction u6 period system I wholesale circuit (6)・・・
・Measurement current detection circuit (7)...Alarm circuit (8)...Measurement AC low voltage circuit (9)...Solenoid valve solenoid for electric outlet J1-
10)...Timer for welding process (11)...Zyristor contactor (12)...
Flaka (13)・7 Hiiragibutsu? (1 source

Claims (1)

[Claims] In automatic spot welding and welding equipment such as spot welding Kawaguchi bots that use a so-called transformer built-in gun that integrates a welding transformer and a spot welding head, welding power sources that have an electronic switch that controls welding current and the A step-down isolation transformer is installed between the suction transformer and the spot is placed between the electrical circuits including the flexible cable that connects the secondary coil side of the isolation transformer and the primary coil side of the welding transformer. Applying a low alternating current voltage only during a period when the welding head is not under welding pressure, detecting a low current flowing according to the impedance between the electric circuits,
The secret feature is to detect a short-circuit condition of the electric circuit when the detected current suddenly increases from a predetermined rated value, and to detect a short-circuit condition of the electric circuit when the detected current suddenly decreases from a predetermined steady-state value. A device for detecting short circuits and disconnections in electric circuits for guns with five transformers.