JPH1147947A - Control method for inverter type resistance welding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid saturation magnetization and to prevent generation of excessive current by constituting an energizing pattern in one welding cycle with a test current and a welding current, monitoring the tendency of a current value in the positive and negative current directions by the test current, and selecting the direction of the applied voltage of the next welding current. SOLUTION: With the starting switch 14 turned on, a weld sequence control circuit 11 operates, outputting a test energizing command and a test current value command to an oscillation circuit 9 and a current comparator circuit 7 following a pressurizing command. The oscillation circuit 9 applies a testing high frequency voltage to a welding transformer 4, with a load current picked up in a current transformer. This value and the test current value command are compared in the current comparator circuit 7, with the energizing pulse width automatically adjusted in a pulse width control circuit 12 so that the compared values are equalized. Simultaneously, the measured current is inputted in a magnetizing direction discriminating circuit 10, detecting the magnetizing direction at the start of energizing the welding transformer 4 and transferring it to the welding sequence control circuit 11. The energizing command for supplying the welding current is given from an inverter circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifier circuit for converting a commercial AC into a DC voltage, an inverter circuit for inversely converting the DC voltage to a high-frequency AC voltage, and a low-voltage / high-current converting the high-frequency AC voltage. The present invention relates to a welding current control method in an inverter type resistance welding machine having a welding transformer for converting a low voltage and a large current into a DC current.

[0002]

2. Description of the Related Art Conventionally, a rectifier circuit for converting a commercial AC into a DC voltage, an inverter circuit for converting the DC voltage back to a high-frequency AC voltage, and a welding for converting the high-frequency AC voltage into a low voltage and a large current. Inverter-type resistance welding machines having a transformer and a rectifier circuit for converting the low voltage / high current into a DC current are commonly known.

In the inverter type resistance welding machine, a current is applied by an inverter circuit so that a voltage initially applied to the welding transformer is magnetized in the same direction as the direction of the residual magnetization of the welding transformer. If it occurs, the transformer causes an excessive magnetization saturation phenomenon, and there is a risk that an excessive current flows due to a vector sum of the excessive magnetizing current and the original load current.

In view of the above, there has been proposed a method in which the voltage applied from the inverter circuit to the welding transformer is completed in one complete cycle to prevent the danger of the excessive current from flowing (for example, Japanese Patent No. 2507295). reference).

[0005]

However, for example, in an environment where welding conditions change every cycle, the voltage applied from the inverter circuit to the welding transformer is always completely reduced as described above. In order to perform control such that the control is completed in one cycle, the control circuit requires precision, becomes complicated, and requires an excessive cost.

The present invention has been made in view of such problems of the prior art, and has as its object to pay no particular attention to the final polarity of one welding cycle. , The direction of the remanent magnetization of the welding transformer at the start of energization is detected in advance, and a voltage of the opposite polarity to the direction is applied to the welding transformer. It is an object of the present invention to provide a control method of an inverter type resistance welding machine which can avoid the occurrence of an excessive current by avoiding the above problem.

[0007]

In order to achieve the above object, a control method of an inverter type resistance welding machine according to the present invention comprises a rectifier circuit for converting a commercial AC into a DC voltage, and a rectifier circuit for converting the DC voltage into a high frequency AC voltage. An inverter circuit for converting the high-frequency AC voltage into a low voltage and a large current; and a rectifier circuit for converting the low voltage and a large current into a DC current. In resistance welding machines,
An energization pattern in one welding cycle from the inverter circuit to the welding transformer is composed of a test current and a welding current, and a trend of a current value in both positive and negative current directions due to the test current is monitored. The present invention is characterized in that the direction of the first applied voltage of the next welding current is selected and executed from the current pattern.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In FIG. 1, reference numeral 1 denotes a rectifier circuit which receives a three-phase commercial AC power supply (or may be a single phase) and converts it into a DC voltage, 2 denotes a filter for waveform shaping, and 3 denotes a DC voltage from the filter 2. An inverter circuit including an IGBT or a large-capacity transistor for inversely converting to a high-frequency AC voltage, 4 receives the converted high-frequency AC voltage and converts it to a low-voltage / high-current suitable for a resistance welding machine. A welding transformer 5 is a rectifier circuit for converting the AC output voltage of the welding transformer 4 into a DC voltage and finally converting the output voltage into a DC welding current. This is an electrode section for passing a current.

Further, 7 is a current comparison circuit, 8 is a current transformer, 9
Is an oscillation circuit, 10 is a magnetization direction determination circuit, and 11 is a welding sheath.
A cans control circuit, 12 is a pulse width control circuit, 13 is an AND gate, and 14 is a start switch.

With the above configuration, first,
When the start switch 14 is turned on, the welding sequence control circuit 11 starts operating, and transmits a test energizing command and a test current value command to the oscillation circuit 9 and the current comparing circuit 7 following the pressurizing command. The oscillating circuit 9 applies a high-frequency voltage for testing to the welding transformer 4 through the AND gate 13 and the inverter circuit 3, picks up a load current flowing therewith by the current transformer 8, and measures the value and the test current. The current command circuit 7 compares the value command with the current command, and the pulse width control circuit 12 automatically adjusts the energizing pulse width so that the two are always equal. At the same time, the current measured by the current transformer 8 is input to the magnetization direction determination circuit 10,
Then check the polarity of the current or the pattern of the current,
The magnetization direction at the start of energization of the welding transformer 4 is detected and transmitted to the welding sequence control circuit 11.

If the direction of the remanent magnetization of the welding transformer 4 at the start of energization is previously detected by the test current, the high-frequency AC voltage from the inverter circuit 3 is supplied to supply the welding current. The welding sequence control circuit 11 issues an energization command so that a voltage having a polarity opposite to that direction is applied to the welding transformer 4.

Various control elements such as the magnitude, frequency, number of cycles, and rest time of the test voltage for flowing the test current are set in advance to numerical values in which the magnetization direction of the welding transformer 4 can be detected. . Then, the polarity is determined from the difference between the current values of the test currents in the positive and negative directions in each energizing cycle, the pattern of change during the entire energizing cycle, and the like. The pause time may be 0 if it is not particularly necessary. Further, by applying to the magnetization direction determination circuit 10 a RAM that stores the magnetization direction determined by the residual voltage of the capacitor or the voltage of the battery or an IC that stores the magnetization direction even in a no-power state, a sudden power failure or power off can be achieved. Even in such a case, by storing and storing the determined magnetization direction, the subsequent control becomes more reliable.

According to this embodiment, the direction of the remanent magnetization of the welding transformer 4 is detected in advance by a test current, and a high-frequency AC voltage for welding is applied to the welding transformer 4 from a voltage having a polarity opposite to the direction. Therefore, the magnetization saturation phenomenon in the welding transformer 4 can be reliably avoided by a simple control circuit.

[0014]

According to the present invention, the energization pattern in one welding cycle from the inverter circuit to the welding transformer is composed of a test current and a welding current, and both positive and negative currents based on the test current are provided. The trend of the current value in the direction is monitored and the direction of the first applied voltage of the next welding current is selected and executed from the current pattern, so special consideration is given to the final polarity of one welding cycle. A control method of an inverter type resistance welding machine which can avoid the magnetization saturation phenomenon in the welding transformer and prevent the occurrence of an excessive current by using a simple control circuit without paying a fee.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of an inverter type resistance welding machine according to the present invention.

FIG. 2 is a waveform diagram of one embodiment of a high-frequency AC voltage supplied to a welding transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rectifier circuit 3 Inverter circuit 4 Welding transformer 5 Rectifier circuit 6 Electrode part 7 Current comparison circuit 8 Current transformer 9 Oscillation circuit 10 Magnetization direction judgment circuit 11 Welding sequence control circuit 12 Pulse width control circuit

Claims (1)

[Claims] 1. A rectifier circuit for converting a commercial AC into a DC voltage, an inverter circuit for converting the DC voltage back to a high-frequency AC voltage, and a welding transformer for converting the high-frequency AC voltage into a low voltage and a large current. And an inverter-type resistance welding machine having a rectifier circuit for converting the low voltage / high current into a direct current, wherein an energization pattern in one welding cycle from the inverter circuit to the welding transformer is provided. It consists of a test current and a welding current, monitors the trend of the current value in both positive and negative current directions due to the test current, and selects and executes the direction of the first applied voltage of the next welding current from the current pattern. A control method of an inverter type resistance welding machine characterized by the above.