JPH0360877A - Controller for high-frequency resistance welding machine - Google Patents

Abstract

PURPOSE:To obtain a stable current in real time at every half cycle by providing an analog switch and a flip-flop circuit in the controller for a high-frequency resistance welding machine, controlling the analog switch by the flip-flop circuit, and thereby controlling a PWM control element. CONSTITUTION:The analog switch F which turns on and off the max. value of an external set voltage and the flip-flop circuit E which is triggered and turned on at every half cycle of an oscillation circuit for high frequencies and turns off upon attainment of the preset welding current necessary for welding are provided in the controller for the high frequency resistance welding machine provided with the oscillation circuit for high frequencies and the control element for PWM which can make phase control of an external set voltage at the phases proportional thereto alternately at every half cycle. The analog switch F is controlled by the flip-flop circuit E, by which the control element G for PWM is controlled in switching.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high frequency resistance welding machine that converts a commercial frequency into a high frequency and supplies it to a welding transformer to perform resistance welding.

Conventional technology A high-frequency resistance welding machine that performs welding by converting the commercial frequency to a higher frequency is generally known, and the output welding current is controlled by constant current control (a constant welding current is output in response to load fluctuations including the power source). control) is being carried out.

Here, as shown in FIG. 4, a voltage proportional to the output v0 of the reference voltage generation circuit 41 is applied to the PWM control element 42, and the inverter circuit is made conductive through the driver circuit at a phase determined by the voltage. Apply it to the welding transformer,
Obtain the welding current, detect the current, compare it with the voltage of the reference voltage generation circuit 41 through the comparison circuit 43, and add the difference to sample the new phase voltage! The current is held by the Reho Nd circuit 44, etc., and the next current is applied to the PWM control element 42. Repeating this, a constant current was obtained.

Problems to be Solved by the Invention This method uses the results of the first half cycle to determine the phase of the next half cycle, resulting in delayed control.
In response to changes, hunting was likely to occur as shown in Figure 3C.

Means for Solving the Problems In order to solve the above problems, 1. The control device for a high frequency resistance welding machine of the present invention has an analog switch for turning on/off the maximum value of an externally set voltage, and a half-switch for a high frequency oscillation circuit. The analog switch is controlled by the flip-flop circuit, and the PWM control element is controlled by switching. The configuration is such that a constant current is obtained in real time for each stroke.

Effect: The above means allows simple switching control.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the configuration of a resistance welding machine according to an embodiment of the present invention, FIG. 2 shows its specific configuration, and FIG. 3 shows signal waveforms of the main parts.

In FIG. 1, 1 is a rectifier circuit, 2 is an inverter circuit, and these constitute a high frequency conversion circuit. 3
is a welding transformer, 4 is a synchronous signal generator, 6 is a sequence timer circuit, 6 is a reference (welding current) voltage generation circuit, 7 is an SQL circuit, 8 is a cylinder, 9 is a welding current detection circuit,
10 is a comparison circuit, 11 is a switching circuit, 12 is a PW
A control element for M, 13 is an oscillation cycle setter, and 14 is a driver circuit.

In this way, the switching circuit 11 is provided at the output stage of the comparison circuit 1o that compares the welding current detection circuit 9 and the reference voltage generation circuit, and the PWM control element 12 is controlled by the H1 signal, instead of controlling the voltage. By controlling μ by switching the low signal, it is not a delay control,
It can be controlled in real time and performs stable constant current control.

Next, a specific example of the control device will be described with reference to FIGS. 2 and 3.

As shown in Fig. 2, the welding current is detected by CT,
A full-wave rectified welding current is obtained by B, compared with a reference voltage (welding current) VO by a comparator C, logic converted by an inverter D, and a flip-flop E is switched. Flip-flop E is from the PWM control element.
Upon receiving the oscillation period f0 (FIG. 3(q)), a trigger is set and the analog switch F is turned on and off.

By the switch F, the PWM control element G obtains an output a at an internal portion higher than the sawtooth wave (FIG. 3(d)), and drives the driver circuit 14 of FIG. next,
Again, the 7 lip-flop E is set at fo, and the analog switch F is turned 0FF at the same time as the reference voltage v0.
V is applied to L and PWM control element G. When it becomes equal to vo, the flip-flop E is reset and the analog switch F obtains an ONL output. In this way,
Obtain the inverter output alternately from the upper half wave a and the lower half wave a,
A voltage is applied to the welding transformer 3 shown in FIG. 1 to perform welding.

As a result, a stable welding current can be easily obtained using a complicated level control yv (conventional example) and delay control without causing hunting or the like.

Effects of the Invention As described above, according to the present invention, problems such as hunting can be avoided in the conventional level control that compares the reference voltage and the flowing current and then adds correction, despite the complex circuit configuration. However, by simply controlling switching, a stable current can be controlled in real time.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of a resistance welding machine showing an embodiment of the present invention, Fig. 2 is a block circuit diagram of a control device of the resistance welding machine, Fig. 3 is a signal waveform diagram of the main parts, and Fig. 4 is a block circuit diagram of a control device of the resistance welding machine. The figure is a block circuit diagram of a conventional control device for a resistance welding machine, and FIG. 6 is a signal waveform diagram of the main parts thereof. 6...Reference (welding current) voltage generation circuit, 9...
... Welding current detection circuit, 10 ... Comparison circuit, 11 ... Switching circuit, 12 ...
・PWM control element, 14 driver circuit.

Claims (1)

[Claims] Depending on the high frequency oscillation circuit and the externally set voltage,
A control device for a high frequency resistance welding machine equipped with a PWM control element capable of controlling a phase in proportion to an externally set voltage alternately every half cycle, an analog switch that turns on/off a maximum value of the externally set voltage; The analog switch is controlled by the flip-flop circuit, and is triggered on every half cycle of the high-frequency oscillation circuit, and is turned off when a preset welding current necessary for welding is reached, and the analog switch is controlled by the flip-flop circuit. A control device for a high-frequency resistance welding machine characterized by obtaining a constant current in real time every half cycle by controlling switching of a control element.