JPS601116B2 - Resistance welding machine control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance welding machine control device that controls power supplied to a welding transformer by phase control.

Resistance welding machines are generally low power factor loads that apply high power for short periods of time, and the internal voltage drop in the power supply circuit during energization is large, causing not only large distortion in the power supply voltage waveform but also the internal impedance of the power supply circuit. Depending on the combination with the impedance of the welding machine, which is the load, the voltage phase at the input terminal of the welding machine may change between no load and load, so when controlling the phase of the power supplied to the welding transformer, Unbalanced current in the welding machine and saturation of the welding transformer core tended to cause abnormal excessive current to flow, sometimes destroying the welding machine and power supply.

FIG. 1 is an equivalent circuit diagram when a resistance welding machine is used to explain this phenomenon.

In the figure, a and b are the output terminals of the power transmission end, ro is the equivalent series resistance when the impedance of the power transmission and distribution line, the power transmission and distribution transformer, etc. is equivalently expressed, and Lo is the equivalent reactance. c and d are the input terminals of the welding machine, r is the equivalent resistance of the welding machine, wL is the equivalent IJ factor, and S
CR is a thyristor consisting of r and wL, which controls the phase of the power supplied to the welding machine, and H' is a thyristor phase control circuit that supplies an ignition signal to the thyristor SCR. Connected to terminals c and d. Here, the voltage at the transmission end at terminals a and b is Eo
, the voltage at welding machine input terminals c and d is E, , the current flowing through the line, thyristor, and welding machine circuit is 1, the angular frequency of the power supply is , the power factor angle of the entire circuit is , the power factor of the welding machine is Letting the angle be Q, each resistance drop rol,,r,1,, reactance drop wLol,,L1,, voltage Eo,E, and current 1,
A relationship as shown in the vector diagram of FIG. 2 occurs between them. Here, EF~+h 芋云j; E+LJF.

Therefore, E. = B 云iC ‐‐‐‐‐‐‐‐‐
Ni (r.

10rl) 2 10yama 2〈L. 10LI)2B=(r.10r,
) r, 10w2L (L. 10L) Cd L・r. One L. r
lHere, since A>0, C=wLro-Lr. <0
When E, is delayed in phase by 8=-Q than Eo.

FIG. 3 shows the relationship between Eo and E at the start of energization at each instantaneous value e. , e, in which a is the voltage at the sending end eo, b is the input voltage e of the phase control circuit, c is the instantaneous value i,, d of the current 1 flowing through the welding machine, and d is the phase control circuit. This is the output signal of the day. In the negative half cycle (not shown) of the first half cycle, energization has not started, so there is no line voltage drop, and the input voltage e of the phase control circuit is
and the sending end voltage eo are in phase. In the first positive half cycle after energization starts, the phase control circuit supplies an ignition signal to the thyristor SCR at a phase that is delayed by a predetermined control angle 8 from the zero point of the voltage e,=eo, and welds. Current i flows through the transformer. At the same time as the current starts flowing, the voltage e, is equal to -Q of 8,= as shown in the vector diagram in Figure 2.
Only late. In the next negative half cycle, the phase control circuit 4 supplies an ignition signal to the sirensor SCR at a further delay of a control angle a from the zero point of the input voltage e, which is delayed by B from the zero point of the sending end voltage eo. Therefore, the period of current i in this negative half cycle is shorter than that in the first half cycle, and the effective value of the current in this half cycle is reduced. The phase difference 82 generated by the current in this negative half cycle is 4.0 mm larger than the phase difference 8 generated in the previous positive half cycle because the current conduction period is short. Furthermore, in the next positive half cycle, ignition is delayed by a control angle of 8 from the zero point of the input voltage e, which is delayed by a phase difference of 62, so the energization period of this positive half cycle is shorter than that of the previous negative half cycle. becomes larger, and the effective value of this half-wave current increases. Therefore, the current value in the next negative half cycle becomes smaller, and as shown in Figure 3c, a DC component of △ldc flows through the primary winding of the welding transformer, which reduces the saturation of the iron core of the welding transformer. This causes abnormal excessive current to flow. As a method for preventing these, a method has been proposed in which the impedance of the power supply circuit and the impedance of the welding machine are adjusted so that Lr, ZO of C=Lro- of the above-mentioned m-formula.
The present invention proposes a control device that can perform stable phase control without changing the impedance of a welding machine. In order to prevent saturation of the welding transformer iron core due to the above-mentioned causes in a resistance welding machine that controls the power supplied to the welding transformer by phase control, the present invention changes the phase of the phase control signal to the voltage of the welding power source before starting energization. The power supplied to the welding transformer is controlled in synchronization with the oscillation phase of the oscillator, which oscillates in synchronization with the power supply voltage phase stored just before welding. It is characterized by

DESCRIPTION OF THE PREFERRED EMBODIMENTS The resistance welding machine control device of the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a configuration diagram showing a schematic configuration example when implementing the present invention.

In the figure, reference numeral 1 denotes a waveform shaping circuit that shapes the waveform of the input terminal voltage E of the welding machine, and outputs a constant pulse signal starting from the rising edge of the full-wave rectified waveform of E, for example. 2
is a phase comparator circuit which outputs a voltage signal corresponding to the phase difference between the input signals of the two input terminals P and P2.

3 is an integrator that integrates the output voltage of the phase comparator circuit 2; 4 is a voltage-controlled oscillator that generates a pulse with a frequency corresponding to the output voltage value of the integrator 3; 5 is an output of the waveform shaping circuit 1 that converts the output of the oscillator 4 into the output of the waveform shaping circuit 1; This is a frequency divider that lowers the frequency to the corresponding frequency.

Note that when the output frequency of the oscillator 4 is approximately the same as the output frequency of the waveform shaping circuit 1, this frequency divider is unnecessary. 6↓This is a phase shift adjuster for causing the trigger pulse generator T to generate a pulse with an arbitrary phase delay from the output pulse of the frequency divider 5.The trigger pulse generator 7 has a phase adjusted by the phase shift adjuster 6. Then, a first pulse is generated to fire the thyristors SCR1 and SCR2, which are phase control elements.

SI-1 and SI-2 are opening/closing elements such as relay contacts operated by a known welding time control device (not shown), and are respectively switched to the pocket point t2 side only when electricity is being applied. This switch may be of the contact type shown in the figure, but if a semiconductor switching element such as a transistor is used, the entire switch can be made contactless and reliability can be improved. Note that Tp is the trigger pulse generator 7 and the sirensor SCR1,
This is a pulse transformer for insulating between it and the SCR2, and this transformer is not necessarily required. Also WT
1 is a welding transformer, 10 is a welding electrode, and 11 is an object to be welded. In the above device, first, in a state before starting energization, the switching element SI-1 is on the side away from the contacts.

Therefore, the output phase of the waveform shaping circuit 1 and the output phase of the frequency divider 5 are compared in the phase comparator 2, and in order to correspond to the phase difference, for example, a proportional voltage is input to the integrator 3 via the switching element SI-1. be done. Here, when the output phase of the waveform shaping circuit 1 is ahead of the output phase of the frequency divider 5, the integration of the integrator 3 advances, its output increases, and the oscillation frequency of the voltage controlled oscillator 4 increases. Conversely, when the output phase of the waveform shaping circuit 1 lags behind the output phase of the frequency divider 5, the integration of the integrator 3 proceeds in the opposite direction, its output decreases, and the oscillation frequency of the oscillator 4 decreases. Let's do it like this. With this configuration, the phase comparator 2, the switching element SI-1
, an oscillator 4, and a frequency divider 5 form a waveform shaping circuit 1.
The signal becomes stable when the output phase of the frequency divider 5 becomes equal to the output phase of the frequency divider 5. Since the output of the frequency divider 5 is also input to the trigger pulse generator 7 via the phase shift adjuster 6, the trigger pulse generator 7 is synchronized with the output phase of the frequency divider 5 and is input to the phase shift adjuster 6. generate a pulse with an arbitrary phase difference determined by . Next, when switching the switching elements SI-1 and SI-2 to the rear point t2 side at the start of welding, the integrator 3 holds the output value immediately before switching the switching element SI-1, and therefore the frequency divider 5 also starts energizing. It continues to generate an output synchronized with the phase of the immediately preceding power supply voltage E.

Therefore, the trigger pulse generator 7 operates in synchronization with this.
Regardless of the phase of the power supply voltage during energization, a trigger pulse based on the power supply voltage phase immediately before the start of energization is generated, and the thyristors SCR1 and SCR2 are made conductive via the switching element SI-2 and the pulse transformer Tp. As a result, even if the phase of the voltage supplied to the welding machine is delayed due to the start of welding, the phase control is not disturbed at all and the control is performed normally. FIG. 5 is a block diagram showing another embodiment of the present invention.

In the figure, 8 is an adder having two input terminals Q, , Q2, and a reference voltage es, which can be set arbitrarily, obtained by a constant voltage source Eo and a variable resistor R, and a phase comparator 2.
through the switching element SI-1 to the integrator 3.
supply to. In this case, the output of the frequency divider 5 is the reference voltage e applied to the terminal P2 of the adder 8, compared to the embodiment of FIG.
The phase will be stabilized at a different value by the phase corresponding to s.
That is, in the embodiment shown in FIG. 5, the output phase of the frequency divider 5 is adjusted to the waveform shaping circuit 1 by changing the reference voltage es.
can be delayed by an arbitrary phase from the output phase (that is, the power supply voltage phase). Therefore, the phase shift adjuster 6 used in the case of FIG. 4 becomes unnecessary, and the output of the frequency divider 5 is directly supplied to the trigger pulse generator 7. At the start of energization, the switching elements SI-1 and SI-2 are activated as in the embodiment shown in FIG.
When switching to the contact t2 side, the frequency divider 5 continues to supply the output to the trigger pulse generator 7 at the phase immediately before switching.
Even if a delay occurs in the power supply voltage phase E due to energization, stable control can be performed without any disturbance in phase control. As described above, according to the device of the present invention, accurate phase control can always be performed regardless of the combination of the internal impedance of the power supply circuit and the impedance of the welding machine that is the load. There is no abnormal excessive current flowing due to saturation of the iron core, and there is no need to adjust these impedances, so there is an advantage that conventional power supply circuits and acid melting machines can be used as they are.

[Brief explanation of drawings]

Figure 1 is an equivalent circuit diagram when using a resistance welder, Figure 2
The figure is a vector diagram of the circuit in Figure 1, Figures 3a to 3d are waveform diagrams of various parts of the circuit in Figure 1 at the start of energization, and Figures 4 and 5 each show different embodiments of the present invention. FIG. 1... waveform shaping circuit, 2... phase comparator, 3... integrator, 4... voltage controlled oscillator, 5... frequency divider, 6...Phase shift adjuster "7...
...Trigger pulse generator, 8... Adder "SCR1, S
CR2...Thyristor (phase control element). Figure 3 Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] 1. A control device for a resistance welding machine that controls the effective value of a supply voltage using a phase control element, comprising: a waveform shaping circuit that generates a signal with a phase corresponding to the phase of an input terminal voltage of a welding machine;
a phase comparator that has two input terminals and outputs a voltage corresponding to a phase difference between signals input to each input terminal; an integrator that integrates the output voltage of the phase comparator; and an output voltage of the integrator. a voltage controlled oscillator that generates a signal with a frequency corresponding to the voltage controlled oscillator, and a pulse that has an arbitrary phase delay with respect to the output signal of the voltage controlled oscillator and controls conduction of the phase control element to the output signal of the voltage controlled oscillator. The phase comparator includes a trigger pulse generator that generates synchronized signals, and a switching element that is connected between the phase comparator and the integrator and transmits the output of the phase comparator to the integrator only when welding energization is stopped. 1. A resistance welding machine control device, characterized in that an output signal of a waveform shaping circuit is inputted to one input terminal of the device, and an output signal of a voltage controlled oscillator is inputted to the other input terminal of the device. 2. In a control device for a resistance welding machine that controls the effective value of the supply voltage using a phase control element, a waveform shaping circuit that generates a signal with a phase corresponding to the phase of the input terminal voltage of the welding machine;
A phase comparator that has two input terminals and outputs a voltage corresponding to the phase difference of the signals input to each input terminal, and outputs the sum of the output voltage of the phase comparator and an arbitrarily adjustable reference voltage. an integrator that integrates the output voltage of the adder; a voltage controlled oscillator that generates a signal with a frequency corresponding to the output voltage of the integrator; It includes a trigger pulse generator that generates a pulse to control conduction of the phase control element, and a switching element that is connected between the adder and the integrator and transmits the output of the adder to the integrator only when welding current is stopped. A resistance welding machine control device, wherein an output signal of a waveform shaping circuit is input to one input terminal of the phase comparator, and an output signal of a voltage controlled oscillator is input to the other input terminal.