JPH0771751B2 - Control device for resistance welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention detects a secondary current flowing in a resistance welding machine by a current detector such as a toroidal coil directly inserted in the secondary side of a welding transformer, The present invention relates to a control device for a resistance welding machine, which compares a detected current value with a set current value and controls the welding current to be constant, and more specifically, a current detection device such as a toroidal coil provided on the secondary side of a welding transformer. The present invention relates to a control device for a resistance welding machine, which automatically detects disconnection / deterioration of a welder during non-welding and prevents welding defects.

(Prior Art) FIG. 1 is a system schematic view of a general spot welding robot.

As shown in the figure, the spot welding robot has a spot welding gun attached to the tip of a robot arm that can move freely, and a secondary electrode of both poles is installed between the welding gun and the welding transformer hung on the ceiling. It is connected via a secondary cable connected to the terminal. Then, the controller can give the welding gun the necessary movement for the welding work as memorized, and can perform the complicated welding work quickly. The control device connected to the welding power source has a built-in microcomputer and is welded to the primary side of the welding transformer via the primary cable.The secondary current flowing in the secondary cable of the welding transformer passes through the toroidal coil. Detected,
The detected current value is compared with the preset current value necessary for welding, and the ignition phase of the thyristor is controlled according to the deviation so that the primary current of the welding transformer is equal to or close to the set value. It is controlled so that a constant welding current always flows through the weld.

Conventionally, when performing constant current control in spot welding, as described above, a large current of several thousand amperes to tens of thousands amperes is detected in an extremely short energization time, and the ignition phase is controlled by an electronic switch such as a thyristor. Thus, the welding current flowing on the secondary side of the welding transformer is controlled to be constant.

When detecting the welding current, generally, the toroidal coil is inserted into the secondary cable or arm conductor of the welding machine and the welding current is directly detected from the conductor such as the cable.This toroidal coil is installed on the secondary side of the welding machine. Therefore, if the machine or robot is damaged by operation, spatter, etc., the coil will be disconnected or deteriorated and the resistance value will increase.
The accurate current value cannot be detected, which interferes with the constant current function and causes welding failure.

Therefore, in the conventional case, when the welding current cannot be detected due to the disconnection / deterioration of the coil, or the detected value is abnormally small, an alarm is usually issued after the welding is completed.

(Problem to be Solved by the Invention) However, in the conventional method of monitoring the abnormal state of the toroidal coil, even if an abnormal situation occurs in the toroidal coil, disconnection / deterioration must be made unless at least the first welding energization is completed. Could not be detected. Therefore, it is not possible to prevent the occurrence of welding failure from the first welding, and even if the output voltage from the toroidal coil is abnormal, the cause cannot always be identified as an abnormality of the toroidal coil. Since it is necessary to check the system of the entire welding machine including the above, there remains a big problem to be solved that it takes a lot of time and effort to analyze and investigate such a cause of trouble.

(Means for Solving the Problems) Therefore, the present invention has been developed to solve the above problems, and its gist is to detect the welding current flowing through the primary side or the secondary side of the welding transformer. Of the resistance welder that controls the welding current flowing to the secondary side of the welding transformer by controlling the ignition phase of the AC power applied to the primary side of the welding transformer by an electronic switch such as a thyristor. In the current control circuit, a constant current power supply for supplying a minute current is connected to the input terminal of the current detector provided on the primary side or secondary side of the transformer, and when switching means intervening in this DC constant current power supply is welded. Turns it off and switches it on during non-welding, and detects anomalies in the detector by measuring the minute current flowing to the detector during the closed period during non-welding. That is, technical measures have been taken.

(Operation) Then, in the present invention, the input side of the toroidal coil and the constant current power supply circuit are connected by a switching means before starting the welding operation, and the minute current flowing in the toroidal coil is checked during the closed period. Can detect the disconnection / deterioration of the lead wire of the toroidal coil, so that it is possible to prevent the occurrence of welding failure from the first welding.
In addition, when the cause of trouble is analyzed and investigated, it is possible to clearly distinguish whether the toroidal coil is abnormally generated or another factor, so that it is possible to improve efficiency of incidental work necessary for investigation of the cause.

(Embodiment) An embodiment of the present invention will be described below with reference to the electric operation circuit diagram shown in FIG. 2. The toroidal coil 1 is inserted in the secondary cable 2. One lead wire 3 of the toroidal coil is connected to the operational amplifier 4 and the other lead wire 3 '.
Is connected to earth. Between the lead wires 3 and 3 ', a resistor 5 for sensitivity adjustment is installed near the input connector of the control device. The operational amplifier 4 is connected to the computer 7 via the A / D converter 6. A DC constant current power supply 9 is connected to the input terminal of the toroidal coil via a switching means 8 such as a relay or an analog switch.

With the above configuration, when a welding current flows through the secondary cable, a voltage proportional to the welding current is input to the operational amplifier 4 via the one lead wire 3 of the toroidal coil 1. The resistor 5 finely adjusts the sensitivity of the toroidal coil. The output voltage value from the toroidal coil is input to the microcomputer 7 via the A / D converter 6, and the constant current control described above is performed based on this.

Although the above welding operation is the same as the conventional welding operation, in the present invention, the switching means 8 is automatically turned on by the microcomputer before the welding operation is started, that is, during the non-welding period, and the constant current power source 9 is toroidal. It is connected to the coil 1 and supplies a constant direct current of around 20 milliamps to the toroidal coil and its leads 3, 3 '.
The DC resistance of the toroidal coil and its lead wires 3 and 3'is about 100 ohms, and the calibration resistance is around 100 ohms. At this time, if the toroidal coil 1 and the lead wires 3 and 3'are normal, the operational amplifier 4 is used. Is input with a DC voltage of about 1 volt.

If the toroidal coil 1 or the lead wires 3 and 3 are disconnected, this DC current flows only through the resistor 4, so that the current voltage applied to the operational amplifier 4 becomes about 2 volts, and the microcomputer 7 and the A / D converter 6 Since this can be detected via, it is possible to immediately detect the defect. Further, when the coil starts to break, it is possible to judge from the detected voltage value whether the resistance value has increased or the resistance has decreased due to a short circuit of the coil.

During the welding operation, the microcomputer 7 automatically turns off the contact of the switching means 8 and inputs only the welding current to the operational amplifier 4.

(Effects of the Invention) As described above, according to the present invention, the constant current power source with the switching means interposed is connected to the input side of the toroidal coil, and the switching means forms an off circuit during welding,
Switch to the ON circuit during non-welding and detect a disconnection / deterioration of the toroidal coil and its lead wire by sending a small current to the toroidal coil only during the non-welding period, so even if an abnormal situation occurs in the toroidal coil and the lead wire. It is possible to prevent defective welding before starting the welding operation. Further, when analyzing and investigating the trouble factor of welding failure, it is possible to clearly distinguish whether the toroidal coil is abnormally generated or another factor, so that it is possible to improve efficiency of incidental work necessary for investigating the cause.

It should be noted that the same effect can be obtained not only in the detection of disconnection / deterioration of the toroidal coil, but also in a device using a sensor for detecting the current on the primary side of the welding transformer, such as a CT.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a system of a conventional spot welding robot. FIG. 2 is an electrical block diagram showing an embodiment of the device of the present invention. 1 ... Toroidal coil, 2 ... Secondary cable, 3,
3 '... Lead wire, 4 ... Operational amplifier, 5 ... Sensitivity adjusting resistor, 6 ... A / D converter, 7 ... Microcomputer, 8 ... Switching means, 9 ... DC constant current power supply

Claims (1)

[Claims] 1. A welding transformer by detecting a welding current flowing through a primary side or a secondary side of the welding transformer and controlling an ignition phase of AC power applied to the primary side of the welding transformer by an electronic switch such as a thyristor. In the constant current control circuit of the resistance welder for controlling the welding current flowing to the secondary side of the transformer to be constant, a minute current is supplied to the input terminal of the current detector provided on the primary side or the secondary side of the transformer. A DC constant current power supply is connected, and the switching means via this DC constant current circuit is turned off during welding and switched on during non-welding, and the minute amount that flows to the detector during the closed period during non-welding. A resistance welding machine control device having a circuit configuration for detecting an abnormal state of the detector by measuring an electric current.