JPH0646633Y2 - Control device for resistance welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is equipped with a device for detecting the voltage of a secondary circuit of a transformer, which is separated by both electrodes of a welding machine, from the voltage value detected by the device. The present invention relates to a control device for a resistance welding machine of a constant voltage control system, which compares a calculated voltage value between both electrodes and a set voltage and controls a welding voltage to a constant value by a thyristor control circuit.

[Prior Art] As a control device of this type, a thyristor control is performed by forming a voltage detection circuit on the secondary side of a transformer for a welding machine, particularly between both electrodes, and comparing the detected voltage value with a set voltage. For controlling the welding voltage to a constant value by a circuit, for example, Japanese Patent Publication
There is JP-A No. 60-2956 (hereinafter referred to as the first known technique).

Also, as a method for calculating the voltage value between the electrodes from the voltage value detected by the device for detecting the voltage of the secondary circuit portion of the transformer separated from both electrodes of the welding machine, for example, Japanese Patent Publication No.
There is JP-A-60-8912 (hereinafter referred to as the second known technique).

Further, in a constant current control system for a welding machine, as a device provided with an alarm when the welding current deviates from an allowable range and falls, for example, JP-A-61-216872 (hereinafter, referred to as third
There is a known technique).

By the way, in the case of the third known technique, since the constant current control method is used, the welding current largely depends on the reactance of the secondary circuit even if the resistance value thereof changes a little due to contact failure of the secondary circuit or the like. Therefore, as a result, a slight change in the resistance value does not particularly affect the change in welding current,
It is not possible to reliably warn of poor contact.

[Problems to be Solved by the Invention] In the control device for the resistance welding machine of the constant voltage control system as in the first and second known techniques, the secondary circuit portion of the transformer separated from both electrodes of the welding machine is provided. When detecting a voltage, the change in contact resistance at the electrical and mechanical connections in the secondary circuit directly affects the magnitude of the welding current, so the resistance in the circuit If the welding current deviates from the permissible range due to a sharp increase in the welding current, there is a problem that accurate welding cannot be performed due to insufficient welding current.

The present invention has been made in view of such problems of the conventional technology, and its purpose is to:
Sufficient voltage control is performed by detecting the voltage at the secondary circuit of the transformer, which is separated from both electrodes of the welding machine, and the current deviating from the permissible range is recognized with an alarm to ensure reliability. It is intended to provide a controller for a high resistance welding machine.

[Means for Solving the Problems] In order to achieve the above object, the control device for a resistance welding machine according to the present invention is a device for detecting a voltage at a secondary circuit portion of a transformer which is separated from both electrodes of the welding machine. A control device for a resistance welding machine of a constant voltage control system, which comprises a voltage value between both electrodes calculated from a voltage value detected by the device and a set voltage, and controls a welding voltage to a constant value by a thyristor control circuit. In the above, a device for detecting a welding current value is added to the secondary circuit, and a device for issuing an alarm when the current value falls outside an allowable range is connected to the welding current value detecting device. It is a thing.

[Operation] Since the voltage is detected at the position of the secondary circuit of the transformer, which is separated from both electrodes of the welding machine, the detection circuit interferes with the welding work, or is broken by contact, or due to welding heat. Does not burn out. At the same time, the welding current value is detected, and when the current value deviates from the permissible range, an alarm is issued to immediately detect a change in contact resistance or the like at the electrical and mechanical connection portion in the secondary circuit.

[Embodiment] An embodiment of the present invention will be described with reference to FIG.

In FIG. 1, 1 is a transformer 2 connected to a commercial power source.
Is an anti-parallel thyristor in the primary circuit of. A resistance welding machine 3 is arranged in the secondary circuit of the transformer 2. 4,5 are electrodes of this welding machine 3, 6 and 7 are parts of the secondary circuit of the transformer 2 separated from both electrodes 4 and 5, for example, 2 of the transformer.
It is a voltage detection point provided on the secondary output terminal or both arms.
Reference numeral 8 is a current detection point provided in the secondary circuit of the transformer.

The voltage detected by the voltage detection points 6 and 7 is guided to the induction removing circuit 9, and the voltage value between both electrodes is calculated in the induction removing circuit 9. The calculated voltage value is input to the constant voltage control circuit 10, and is compared with the reference voltage from the voltage setting unit 11 to input a desired correction value to the thyristor control circuit 12,
The thyristor control circuit 12 controls the thyristor 1 to keep the welding voltage constant.

By the way, the resistance in the secondary side circuit of the transformer is composed of the resistance RL of the object to be welded itself between the electrodes and the resistance R0 of the secondary circuit itself. Therefore, the voltage V detected at the voltage detection points 6 and 7 is V = (RL + R0) I, where I is the welding current.

Therefore, if R0 is known in advance, the voltage VP between both electrodes can be obtained by VP = RL1 = V-R0I.

This value should be kept constant, but since the resistance R0 of the secondary circuit changes depending on the temperature, a temperature sensor is installed at a predetermined location (not limited to one location) of the secondary circuit and the information is stored. It is recommended to correct R0 sequentially by receiving online.

Although the welding voltage can be controlled to a constant value by the above control circuit, the present invention further monitors the welding current value. That is, as described above, in the case of the constant voltage control method, a change in contact resistance or the like at the electrical and mechanical connection portion in the secondary circuit is immediately detected, so that a contact failure or the like at the connection portion is detected by the current detection. The current detected at the point 8 is guided to the current measuring circuit 13 and compared with the reference current from the current setting unit 14 to determine whether or not it deviates from the allowable range. Alarm circuit 15 if deviation occurs
Activates and issues an alarm.

[Effect of the Invention] According to this invention, the voltage is detected at the secondary circuit of the transformer, which is separated from both electrodes of the welding machine, so that the detection circuit interferes with the welding operation or makes contact. The constant voltage control can be performed easily and easily without disconnection or burnout due to welding heat, and at the same time, the welding current value is detected and the current value is within the allowable range. Since the alarm is issued when the deviation from the above, the constant voltage control system immediately detects the contact failure that most affects the current change and prevents the occurrence of defective welding due to insufficient welding current. And a highly reliable control device for the resistance welding machine.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. 1 ... thyristor, 2 ... transformer, 3 ... welding machine, 4,
5 …… electrode, 6,7 …… voltage detection point, 8 …… current detection point, 11
...... Voltage setting section, 14 …… Current setting section, 15 …… Alarm circuit.

Claims (1)

[Scope of utility model registration request] 1. A device for detecting a voltage of a secondary circuit of a transformer, which is separated from both electrodes of a welding machine, and a voltage value between both electrodes and a set voltage calculated from a voltage value detected by the device. In contrast to the constant voltage control type resistance welding machine control device for controlling the welding voltage to a constant value by a thyristor control circuit, a device for detecting a welding current value is added to the secondary circuit, and the current value is A controller for a resistance welding machine, characterized in that a device for issuing an alarm when it falls outside an allowable range is connected to the welding current value detecting device.