JPH0825018B2 - Inverter welding machine control device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a control device for an inverter welding machine.

Conventional technology With the advent of large capacity power transistors, several kHz ~
The inverter welding machine that controls the welding transformer at a frequency of several tens of kHz at a frequency higher than the commercial frequency has been realized, and the features of the inverter welding machine such as small size, light weight, and high-precision control make it possible to use conventional welding transformer secondary side thyristor control It's about to change.

Since the core of the welding transformer used in the inverter welding machine has a high normal frequency, the silicon steel sheet used at commercial frequencies has a large iron loss and the temperature rise is extremely large, so it is not used and the ferrite core is not used. Used.

However, in the case of ferrite core,
The change in the magnetic flux density with respect to the unit magnetizing force in the BH curve was several times as large, magnetic saturation was likely to occur, demagnetization occurred, and direct current excitation was likely to occur.

Therefore, the switching element on the primary side of the welding transformer may be destroyed, and as a countermeasure against this, there is a method of providing a gap in the welding transformer, increasing the self-inductance, and suppressing the DC exciting current.

It also detects the primary or secondary current of the welding transformer.
After I / V conversion, sample and hold and then ignite to the same positive and negative current to control the bias, or a welding transformer equipped with a third control winding to control the bias current. There was something that shed.

Problems to be Solved by the Invention However, the method of providing a gap in the welding transformer is a passive measure, and the structure of the welding transformer becomes complicated.

The method of controlling the firing bias requires a complicated control circuit and becomes expensive, and if the balance of feedback is broken, it has an adverse effect.

The method using the third control winding requires a control current of several tens of amperes or the like, resulting in a large power loss and is expensive.

Considering the DC excitation generation mode that was conventionally overlooked and not completely controlled, for example, after the welding machine input power is turned on, for example, the welding transformer is energized by one positive ignition energization. It starts, and after energization ends with the other negative ignition energization.

No matter how many times this energization is repeated, it will start with one positive ignition energization and end with the other negative, but there is no problem, but if the power supply to the welding machine is released and then re-energized, the other negative There is a 50% probability that it will start with the ignition current flowing in this case. In this case, the welding transformer was demagnetized and DC-excited, which sometimes destroyed the switching element.

That is, although there is no problem in the control after the input power is turned on, the synchronous control including the opening and turning on of the input power is not satisfied, leaving a big problem.

For the three points described as the DC excitation prevention measures, the ignition bias is sampled and held, not the passive or feedback control, and one and the other of the positive and negative ignition biases in one cycle are set. Similarly, there is an effective method of simultaneously performing synchronous control to actively prevent DC excitation, but even this method does not satisfy the synchronous control including opening and closing of the welding machine input power source.

As described above, in the conventional synchronous control, the ignition energization starts with, for example, one positive ignition energization and always ends with the other negative, but when the welding machine input power is once released and then turned on again, the other negative There is a case where it starts from the one and ends with one positive, and in this case, the welding transformer was demagnetized, was excited by direct current, and destroyed expensive switching elements such as power transistors.

The present invention completely synchronizes the ignition energization control of the welding transformer at any timing of the energization start signal except after the drawback of the conventional inverter welding machine, and after the input power of the welding machine is opened and closed. The purpose is to control so that

Means for Solving the Problems In order to solve the above problems, a control device for an inverter welding machine according to the present invention includes first switching means for supplying a current in one direction to a primary side of a welding transformer, and the one direction. A second switching means for supplying a current in a direction opposite to the above, and a controller for an inverter welding machine in which the welding transformer is controlled at a frequency higher than a commercial frequency, a first switching means for the first switching means. The ignition signal of the second
A circuit for generating a dead time signal generated in a non-conducting section in the middle of the second ignition signal to the switching means, a first flip-flop for controlling the first and second ignition signals, and the first flip-flop. The dead time signal generating circuit, comprising: an ignition signal circuit for generating a common ignition signal to the first and second switching means; and a second flip-flop for controlling an inhibition input of the ignition signal circuit. Is provided as a clock signal of the first flip-flop, the output of the first flip-flop and the common firing signal form the first and second firing signals, and The output of the flip-flop is supplied as a clock signal of the second flip-flop, and the output of the second flip-flop controls the inhibit input of the firing signal circuit, Scan is obtained so as to control the synchronization of the control of.

Operation With the above configuration, the output of the first flip-flop for ignition control and the first and second ignition signals to the first and second switching means are uniquely determined, and to the ignition signal circuit as before. One or the other of the positive and negative ignition signals is uniquely determined, and the prohibition input to the PWM switching control element can be controlled by the first flip-flop for ignition control as before. At this timing, or even after the input power of the welding machine is opened and closed, the ignition transformer energization control of the welding transformer can be made completely synchronous.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

In FIG. 1, the output of the welding power source 1 is the welding wire 2
And is supplied to the object to be welded 3. The welding wire 2 is continuously supplied by the wire feeding roller 4. 5 is a welding torch.

Fig. 2 shows the main circuit of an inverter welder.
AC200V is rectified by the rectifier 6, DC-smoothed by the reactor 7 and the capacitor 8, and the DC-smoothed voltage becomes a DC power supply for controlling the inverter.

The welding transformer 13 is inverter-controlled by the power transistors 9-12.

The voltage obtained on the secondary side of the welding transformer 13 is rectified by the rectifier 14, smoothed by the reactor 15 and becomes a welding output, which is supplied between the wire 2 and the workpiece 3.

FIG. 3 shows a synchronous control circuit when a PWM switching control element is used, and FIG. 4 shows the main waveforms of FIG.

Referring to FIG. 3, reference numeral 16 is a torch switch signal for starting welding, that is, an energization start signal.

17 is a signal for detecting the welding current with a shunt etc., comparing the magnitude of the fed back current with the set value, and controlling the missing current of the main circuit when the fed back current is too large. , 17 are given to the OR gate element 18, and the output of the OR gate element 18 is the second for inhibiting input control.
Given to the flip-flop 19 of.

The output of the second flip-flop 19 is given to the inhibition input terminal of the PWM switching control element 20.

A signal is generated from the OSCO of the PWM switching control element 20 in the non-conduction section in the middle of one positive ignition signal to the switching element and the other negative ignition signal, and the signal is expanded by the dead time expansion circuit 21. It

The output of the dead time extension circuit 21 is given to the Schmitt element 22, and the output of the Schmitt element 22 is given to the ignition control flip-flop 23 as a clock.

One of the outputs of the ignition control flip-flop 23 is NOR.
The gate element 25, the other inverted version, is applied to the NOR gate element 24, and one positive firing signal at the output of the NOR gate element 24 and the other negative firing signal at the output of the NOR gate element 25. Is supplied to the pulse transformer drive circuit 26 to drive the pulse transformers 27 and 28.

The outputs of the pulse transformers 27 and 28 are given to a base current amplifier circuit (not shown) which supplies the base currents of the power transistors 9 to 12 in FIG.

The output of the firing control flip-flop 23 is given to the second flip-flop 19 as a clock and synchronously controls the signals 16 and 17. The output of the firing control flip-flop 23 is also given to the AND gate element 29, and the output of the AND gate element 30 is also given to the gate of the AND gate element 29.
The output of the ND gate element 29 turns the analog switch 31 on and off.
Control.

By opening and closing the analog switch 31, the ignition switching bias sampled and held during the dead time is given to the PWM switching control element 20 every cycle.

32 is a firing bias that determines the magnitude of the welding current, 1.8V
It is in the range of ~ 3.4V.

A firing signal having a conduction width corresponding to the magnitude of the firing bias 32 is output from 33 and 34, and given to the NOR gate element 35.

The output of the NOR gate element 35 becomes a common positive and negative firing signal for one and the other and is given to the NOR elements 24, 25.

36 is an output of the protection circuit which is detected when an abnormal current flows in the main circuit.

The PWM switching control element 20 itself adopts a constant frequency pulse width modulation method, and the operating frequency is determined by externally providing timing components such as a capacitor and a resistor, and a sawtooth wave generated internally and a point to the NINV terminal The arc bias is compared by an internal PWM comparator, and a PWM pulse output, that is, an ignition signal is output.

 OSCO is output in synchronization with the oscillator output.

When the energization start signal 16 is generated and falls, at the rise of the Q output of the flip-flop 23, the inhibition input SD of the PWM switching control element 20 is released and the ignition signal is output.

At that time, the output of the NOR gate element 25 is "L", and a negative ignition signal is not output.

When a firing signal whose conduction width is controlled by any of the outputs 33 and 34 is given to the NOR gate element 35, its output becomes “L” and both inputs of the NOR gate element 24 become “L” and output. Becomes "H", and one positive ignition signal always comes out first.

When the energization start signal 16 ends and rises, the inhibition input SD of the PWM switching control element 20 is given at the rise of the Q output of the flip-flop 23, and the firing signal is not output at this point.

That is, when the Q output of the flip-flop 23 rises, NO
One of the positive firing signals of the R gate element 24 is sent to the NOR gate element 35.
I was waiting for the output of L to become L, but the inhibition input SD from the flip-flop 19 was first input to the PWM switching control element 20.
Is given, it will not fire.

Therefore, before the rise of Q of the flip-flop 23, the other negative firing signal was naturally issued, so that it always starts with one positive firing signal and ends with the other negative.

Release the input power of the welding machine and turn it on again to turn the power on and off
Even if it is repeated, the circuit configuration of FIG.
At the rising edge of Q, that is, the positive firing signal of the NOR gate element 24, and similarly, at the rising edge of Q of the flip-flop 23, it ends with the negative firing signal of the NOR gate element 25.

 FIG. 4 will be described.

The sawtooth wave in FIG. 4A and the comparator output in e are internal waveforms of the PWM switching control element 20 described above.

V ₁ and V _{2 of a} are ignition biases given to the NINV terminal of the PWM switching control element 20, and the conduction width of the two-dot chain line of V ₂ is larger than that of the solid line of V ₁ and the output of the main circuit The current is large.

The output of the comparator a is e, which is alternately output as f and g by the internal flip-flop of the PWM switching control element 20 and becomes a firing signal.

OSCO of b is output in synchronization with the sawtooth wave of a.
It is expanded by the dead time expansion circuit 21 in the figure to become c.

d is obtained from c, and the signal 16 or the signal 17 of h is lowered or raised in synchronization like i.

V ₁ of the solid line a, 2 points V ₂ of the chain line e, f, corresponds to V _1, V ₂ of g.

Also, for 8 μs for c, 33 μs for g, and 66 μs for g,
This is the value when the PWM switching basic frequency of the main circuit is 15 kHz.

Although FIG. 3 shows a synchronous control circuit, the conventional one is
Without the NOR elements 24, 25, 35, the outputs 33, 34 are directly applied to the pulse transformer drive circuit 26.

Therefore, after the power is turned on, the energization start signal 16 becomes “L” level, the inhibition input control flip-flop 19 synchronizes, and the inhibition input terminal of the PWM switching control element 20 becomes “L”.
However, at this time, the first firing signal is output 33
Can't decide whether the output is 34. That is, the relationship between d and f or g in FIG. 4 is not unique, and f may come earlier than g as timing when d rises, and the first ignition signal becomes disjointed. The reason is that the output states of the internal flip-flops of the PWM switching control element 20 that alternately distributes the rising of d and f and g in the transient rising state of the DC voltage immediately after the power is turned on do not match. .

In addition, in the present embodiment, the case where the PWM switching control element 20 is used has been described, but it goes without saying that the present invention can be applied to a configuration including discrete components such as a sawtooth wave oscillation circuit, a comparator, a flip-flop, and a gate element. .

Further, although an example in which power transistors are used as the switching elements 9 to 12 has been shown, SCR or power MOSFET elements may be used.

EFFECTS OF THE INVENTION As described above, according to the present invention, the ignition energization polarity of the welding transformer is always the same at any timing of the energization start signal and after the input power of the welding machine is opened and closed. Ignition energization starts from the one with polarity, and even when energization ends, ignition energization always ends with the other one with the same polarity, so that the welding transformer is not demagnetized and is not DC-excited.

As a welding machine to which the present invention can be applied, CO ₂
It can be applied to consumable electrode type welding machines such as gas arc welding or non-consumable electrode type welding machines such as TIG arc welding, and also to resistance welding machines.

In particular, some of these welding machines for welding precision parts such as IC elements and small parts have a welding time of about several hundred μs to several ms. It is extremely effective.

Further, since perfect synchronous control can be realized, B of the welding transformer and the magnetic flux density can be set high, so that the size, weight and cost can be reduced.

[Brief description of drawings]

FIG. 1 is a front view of an inverter welding machine showing an embodiment of the present invention, FIG. 2 is a main circuit diagram of the inverter welding machine, and FIG. 3 is a synchronization when a PWM switching control element is used in the main circuit. The control circuit diagram and FIG. 4 are the signal waveform diagrams of the main parts of FIG. 9,10,11,12 ... Power transistor, 13 ... Welding transformer, 19 ... Flip-flop, 20 ... PWM switching control element, 23 ... Flip-flop.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Koji Hamamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-64768 (JP, A) JP-A-57-171580 (JP, A)

Claims (1)

[Claims] 1. A welding transformer is provided with a first switching means for flowing a current in one direction on a primary side of the welding transformer and a second switching means for flowing a current in a direction opposite to the one direction. In a control device for an inverter welding machine configured to control at a frequency higher than a frequency, an intermediate between a first ignition signal to the first switching means and a second ignition signal to the second switching means. Circuit for generating a dead time signal generated in the non-conducting section of the above, a first flip-flop for controlling the first and second ignition signals, and a common ignition to the first and second switching means. An ignition signal circuit for generating a signal and a second flip-flop for controlling an inhibition input of the ignition signal circuit are provided, and an output of the dead time signal generation circuit is provided for the first flip-flop. It is given as a clock signal, the first
The first and second firing signals are formed by the output of the flip-flop and the common firing signal, and the output of the first flip-flop is given as the clock signal of the second flip-flop. The output of the second flip-flop controls the inhibit input of the firing signal circuit,
A control device for an inverter welding machine, wherein the control of the welding transformer is synchronously controlled.