JPH01130885A - Controller for resistance welding machine - Google Patents

Abstract

PURPOSE:To detect welding abnormality with high accuracy by detecting abnormality of a detector by a welding current value detected by a CT or a troidal coil arranged to primary side and secondary side cables and executing switching to a normal detector. CONSTITUTION:The CT11 or the troidal coil 2 is arranged to the primary side 10 and the secondary side 1 cables of a welding transformer. While the detected welding current value by these current detectors 11 and 2 is compared with a reference value set on a computer 9, a welding current is controlled. At this time, when the computer 9 detects the abnormality of the current value, the changeover to the normal current detector is executed via a switching means 5. By this method, the welding abnormality is detected with high accuracy and the productivity is improved.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention detects the secondary current flowing through a resistance welding machine with a current detector such as a toroidal coil inserted directly into the secondary side, and the detected current The control device for resistance welding machines compares the value with the set current value and controls the welding current to be constant to prevent a drop in welding conditions and welding defects. The present invention relates to a control device for a resistance welding machine that can automatically switch to a current detection circuit provided on the negative side to perform normal constant current control even if an abnormality occurs in a detector.

(Prior art) Conventionally, in spot welding machines, when detecting large currents ranging from several thousand amperes to tens of thousands of amperes in an extremely short energization time, a toroidal coil is generally inserted into the secondary cable or arm conductor of the welding machine. Welding current is detected directly from conductors such as cables. In this case, it is better to set the detection position of the toroidal coil, etc. near the electrode on the secondary side of the welding transformer rather than the primary side of the welding transformer, since there is no need to take into account errors caused by the setting of the coil turns ratio of the welding transformer or the excitation current. Moreover, it is desirable because it can also detect disconnections and short-circuit accidents in the secondary cable.

(Problems to be Solved by the Present Invention) However, the conventional current detection method as described above has the following drawbacks.

In other words, it is desirable to install the toroidal coil as close to the electrode as possible in order to detect disconnections and short circuits in the secondary cable. When the arm of a robot or the like moves in a complicated manner, the lead wire of the toroidal coil is forced to undergo complicated mechanical bending motion along with the secondary cable, and there is a problem of damage to the lead wire due to adhesion of spatter. It has come to the surface.

Damage to this lead wire is fatal to the toroidal coil, causing variations in the output voltage of the coil, and if an abnormality occurs in the detected value, normal constant current control will no longer be performed, resulting in a serious impact on welding quality. .

Until now, when a problem with a lead wire like this occurred, the only option was to temporarily stop the line in operation and replace the toroidal coil with a new one, and the incidental work required to replace it was a major hindrance to productivity. was.

(Means for Solving the Problems) Therefore, in the present invention, a novel constant current control circuit having the following configuration was developed to overcome the above problems.

That is, by detecting the welding current flowing to the primary or secondary side of the welding transformer and controlling the ignition phase of the AC power applied to the primary side of the welding transformer using an electronic switch such as Cyrisk, the secondary In the constant voltage regulation J11 circuit of a resistance welding machine that controls the welding current flowing to the side to be constant, current detectors for detecting the welding current are provided on the primary side and the secondary side of the transformer, and The technical measure is to provide a switching means on the input side of the control circuit that detects when one of the current detectors becomes abnormal and switches to the other normal current detector.

(Function) According to the present invention, the primary side of the welding transformer of the resistance welding machine is also provided with a toroidal coil or CT for auxiliary use.
A current detector, such as When an abnormality occurs in one of the current detectors due to the opening/closing operation of the switching means, the other normal current detector automatically turns on and continues to send the input signal to the control circuit. give. By doing this, even if the toroidal coil on the secondary side breaks or deteriorates and the output voltage from the coil changes, the normal current detector on the primary side will immediately switch to the normal current detector, so the normal constant current control function will not work. It is possible to maintain harmful (harmful) conditions, and continuous operation can be performed continuously without stopping the line in operation.

(Embodiments) Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram in which the control system of the present invention is applied to a spot welding robot.

As shown in Figure 1, a spot welding robot has a spot welding gun attached to the tip of a robot arm that moves freely, and a bipolar secondary wire between the welding gun and a welding transformer suspended from the ceiling. Connected via a secondary cable connected to a terminal. The controller then gives the welding gun the movements necessary for the welding operation according to memory, allowing even complex welding operations to be performed quickly. The control device connected to the welding power source has a built-in microcomputer and is connected to the primary side of the welding transformer via the primary cable, and controls the primary current flowing to the primary cable of the welding transformer or the secondary current flowing to the secondary cable. The next current is detected via CT or toroidal coil, the detected current value is compared with the current value required for welding set internally in advance, and the firing phase of the cyrisk is controlled according to the deviation, and the welding transformer The configuration is such that the primary current is controlled to be equal to or close to the set value so that a constant welding current always flows through the welding part.

The basic configuration of the welding robot and control device described above is numerically the same as that of a known manual machine or automatic dedicated machine and its mechanical or electrical components, but the present invention Characteristic components include, in addition, −next-side OCT
Conventionally, only one of the toroidal coils was installed, but in the present invention, current detectors are installed on both the primary cable and the secondary cable, respectively, as shown in the figure. installed.

Note that FIG. 2 is an electrical operational circuit diagram of the control device of the present invention.

It has a circuit configuration in which a current detector such as CTII is attached to the primary cable 10, and the secondary current is normally detected by a toroidal coil 2 attached to the secondary cable 1. A resistor 6 and a wire 2 are connected between the lead wire 30 of the toroidal coil and the lead wire 3' of the CT.
It is installed for adjusting the sensitivity of 1.

One lead wire of each current detector is connected to ground, and the other lease wire is a switching means 5 such as a relay or an analog switch provided in the control circuit (timer) 4.
connected to the contacts.

The output voltage from the lead wire 3 when the switch 5 is on is input to the A/D converter 8 via the operational amplifier 7, and is taken into the microcomputer 9. Based on this, the microcomputer 9 converts the electronic switch such as Cyrisk. The welding transformer performs constant current control so that the welding current on the secondary side of the welding transformer remains constant.

In this case, even though the control circuit ignited the cyrisk in the contactor and caused the welding current to flow, when there was no signal from the toroidal coil 2 immediately after welding started, or when the current value was abnormal. , this is detected by the microcomputer 9, and the output signal is sent to C via the switch 5.
Turn on the contact on the T11 side, repeat the welding operation from the beginning, and detect the primary current from the CT. −
If the next current is normal, constant current control is continued using the output signal, and an alarm output is issued in case of an accident in the toroidal coil.

Note that if the current values are abnormal on both the negative side and the secondary side, an emergency signal is issued and the line is stopped.

(Effects of the Invention) As explained above, according to the present invention, even if a problem occurs in the toroidal coil for current detection on the secondary side, welding work can be continued without stopping the production line. From this, productivity can be improved.

Furthermore, since the current detector switching operation is automatic, maintenance personnel do not have to worry about it. In addition, work can be continued while the alarm is output, and if the current detector is replaced during line downtime, the work can be streamlined.Furthermore, when investigating the cause of a malfunction, it is possible that the toroidal coil itself has a bad detection relationship. It is possible to clarify the cause analysis, such as whether it is caused by the welding machine itself or whether it is caused by other factors such as the welding machine itself.

Conventionally, pass/fail judgment was made based on the value of the detected current at the end of one welding point operation, so normal constant current control was not performed for that welding point and it was determined that the weld was defective. In the present invention, even if the toroidal coil is damaged during the process, it can be detected in the first cycle and the control operation can be switched to normal, so welding defects can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram in which the control system of the present invention is applied to a spot welding robot. 2 is an electrical block diagram showing an embodiment of the device of the present invention. (Explanation of symbols)

Claims (1)

[Claims] The welding current flowing to the primary or secondary side of the welding transformer is detected and the ignition phase of the AC power applied to the primary side of the welding transformer is controlled by an electronic switch such as a thyristor. In a constant current control circuit of a resistance welding machine that controls the flowing welding current to be constant, a current detector for detecting the welding current is provided on the primary side and secondary side of the transformer, and one of the A control device for a resistance welding machine, characterized in that a switching means is provided on the input side of the control circuit to detect an abnormality in one current detector and switch to the other current detector.