JPS582745B2 - How to get started - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling a resistance welding machine that uses a thyristor or the like as a current-carrying element to control the phase, and when the welding current changes due to some factor, the welding can be stopped by controlling the firing angle of the thyristor. This relates to a welding current control method for a resistance welding machine that increases or decreases the current to always keep the heat generation amount at the welding point constant, and eliminates the drawbacks of the conventional method of compensating for the heat generation amount by increasing or decreasing the energization time. The purpose is easy to adjust. The present invention provides a highly reliable and valuable welding current control method for resistance welding machines.

Generally, in a resistance welding machine, when the welding current used for the workpiece changes due to various factors such as fluctuations in the voltage of the welding power source and secondary impedance of the welding transformer, the amount of heat generated at the welding point changes by the amount of change. To keep it constant, J=J%・R
-tw, a control method is used in which the energization (welding) time is increased or decreased by the square of the power to keep it constant.

The timer that normally controls the energization time is a CR timer that uses a time constant formed by a resistor and a capacitor, and the energization time ends when the potential of the capacitor reaches a certain set value.

Here, the method of keeping the heat generation amount at the welding point constant by increasing/decreasing the energization time by the square of the welding point is to generate a voltage proportional to the welding current with a current transformer (CT), and then to make the energization time constant. It is applied to the input of the element of the control circuit, and the fact that the internal resistance of this element increases or decreases depending on the magnitude of the CT voltage is used to increase or decrease the energization time at the set reference welding current.

That is, plate current Ip of vacuum tube etc. - grid voltage EG
In characteristics. This makes use of the region where the plate current changes with the square of the grid voltage.

In this case, ■, CT according to the squared curve part of the one-Eg characteristic
As the input signal increases or decreases, the internal resistance changes in proportion to the square of the bias, or if the grid bias is not correct in magnitude, it may exceed or fall short of the square.

Moreover, it is extremely difficult to adjust the bias because it utilizes the squared curve portion, and it is often the case that the energization time cannot be obtained as squared due to slight fluctuations in the power supply voltage of the vacuum tube circuit.

Also, even if the energizing time is actually obtained by squaring it. The thermal effect of the welded part was unfavorable, and a satisfactory welding result could not be obtained.

In addition to being difficult to adjust, the compensation effect varies due to slight fluctuations in circuit voltage, etc., and as a result, satisfactory welding results cannot be obtained, leading to a decline in welding quality, which remains a major problem.

The present invention eliminates these conventional problems and provides a control method that is easy to adjust, highly reliable, and valuable as described at the beginning. An example will be described.

First, Figures 1 to 3 show the conventional compensation method. Regarding Figure 1, if it starts at L8. Pressurization is started, and the welding current flows for a period of T1 after the effective pressurization time.

For period T2, when the welding current becomes lower than the set value. This shows the case where the energization time is increased by the square of the power.
FIG. 2 shows an energization time circuit that controls this energization time.

In the figure. VT is a vacuum tube, TH is a discharge tube, ■ is a voltmeter, and VR1 to VRμ variable resistor. R1 to R7 are fixed resistors, C1 and C2 are capacitors, S1 and S2 are switchboards, T
rl r Tr2 is a transformer, CT is a current transformer, and E3 is a DC power supply.

This compensation circuit is in use when the switch S2 is connected to the vacuum tube vT side.

First, when the switch S1 of the thyratron etc. is closed, a voltage is generated across the variable resistor VR1, so the vacuum tube V
At the same time that capacitor C1 is charged through T, the plate of discharge tube TH, such as a thyratron, is charged. As the potential between the cathodes increases, the bias voltage between the cathode of the discharge tube TH and the grid decreases, so the discharge tube TH is discharged by the synchronization pulse of the transformer Trp, and a welding completion pulse is generated in the transformer Trl.

At this time, a voltage proportional to the welding current is generated from the current transformer CT. When the grid K of the vacuum tube VT is given, its internal resistance changes by the square of the voltage of the current transformer CT, and it is possible to increase or decrease the energization time at the standard welding current.

The power source Es and the variable resistor VR3 determine the DC bias shown in FIG. 3, and are adjusted by the variable resistor VR3.

Also, the variable resistor VR1 has an Eg-Ip characteristic of 2 in Fig. 3.
It is adjusted to be closest to the power curve part,
Regarding adjustment of the energization time for compensation. While looking at the voltmeter y, select the output tap of the current transformer CT and the variable resistor VR4.
The magnitude of the input voltage of the vacuum tube VT grid is selected by:

In this case, if the desired voltage cannot be obtained, use the current transformer C.
Change the T tap. Adjustments can be made again using the variable resistor VR.

In addition. If no compensation circuit is used. Set the switch S2 to the capacitor C2 side.

In this case, the energization time is between capacitor C2 and variable resistor vR.
Set in 2.

The curves lt and l2 in Fig. 3 are the outputs of the current transformer CT in Fig. 2. For example, the output proportional to the set welding current is the curve l1, and the plate current at that time is Ipt.
In this case, if the welding current decreases for some reason, the output of the current transformer CT will become l2, and the plate current at that time will decrease by the square of the current, becoming Ip2, and therefore the energization time will become the square of It becomes more than it increases.

On the other hand, FIGS. 4 and 5 show the compensation method according to the present invention, with FIG. 4 showing its circuit diagram and FIG. 5 showing waveforms at various parts in FIG.

First, to explain Fig. 4, welding power source AC200
After V is set to 5V by a step-down transformer Trl, it is fully rectified by diodes D1 to D4 (FIG. 5A).

This fully rectified waveform is generated by the zero cross switch 1 on the line 13 as shown in the opening of FIG.

2 is a sawtooth wave generating circuit, and a voltage as shown in FIG. 5C is generated on line l4.

This voltage becomes an input to the inverted terminal of O of a differential operational amplification element (hereinafter referred to as OP amplifier) OP.

On the other hand, the non-inverting terminal of ■ has a variable resistor VR for setting the welding current.
1 and a potential 3 determined by the potential on the line 15 are applied, and the output from these inputs as shown in FIG. 52 is obtained on the line 1.

When the energization signal (Fig. 5 E) is transmitted. The output of NAND logic element 4 becomes 1 level and O level according to the output with line a, and capacitor C1 is output through elements 5, 6 and TR2.
is charged.

When the capacitor potential reaches a certain value, current flows from the unijunction transistor TR2 to the pulse transformer PT1, and a voltage is generated on the secondary side of the pulse transformer.

This voltage becomes the gate signal for the main thyristor that opens and closes the welding current (see Fig. 5), and the welding current can be controlled by changing the ignition position based on the output of the line 16.

Next, to explain the circuit that raises or lowers the potential of line l, current transformer CT generates a voltage proportional to the welding current in resistor R7, which is full-wave rectified by diodes D and D8. After that, the voltage is integrated by resistor R8 and capacitor C2, and the voltage divided by variable resistor VR2 becomes OP.
It is applied to the inverting terminal l of the amplifier OP2.

In addition, the voltage divided by the variable resistor VR is applied to the non-inverting terminal of ■, and in the OP amplifier OP2,
Compare the voltage proportional to the welding current obtained from variable resistor vR2 with the voltage obtained from variable resistor VR3, and if there is no increase or decrease in the welding current, that is, if the set value current is flowing, OP amplifier oP2 The voltage on line l7 at the output of is OV.

The variable resistors VR2 and vR3 are interlocked so that they change simultaneously in proportion to the magnitude of the welding current, so that the voltage obtained from the variable resistors VR2 and vR3 is the same at each scale of the welding current. It is composed of

When the welding current is small, the respective voltages applied to the ■ terminal of the OP amplifier by the variable resistors VR1 and VR3 are low, and as the welding current becomes larger, the voltage applied to the θ terminal becomes higher.

On line l7, the voltage of the difference between variable resistors VR2 and VR is amplified by amplifier OP2, and when relay contact CR1 is closed (to Fig. 5), on line l5, the voltage of the difference between variable resistors VR2 and VR is amplified by amplifier OP2. A voltage waveform as shown in Fig. 5G is obtained.

Considering the case when relay contact CR1 is closed, if the welding current set by variable resistor VR1 decreases for some reason, the output voltage of current transformer CT1 decreases, and this is caused by amplifier ℃P2. By being reversed and widened, the line l increases in level in the direction of increasing the positive potential welding current.

Conversely, if the welding current increases from the set current for some reason, the output voltage of current transformer CT1 increases, and the amplifier OP
2, the level of the line 1 is lowered in the direction of decreasing the welding current at negative potential.

Normally, if there is no fluctuation in the welding current, the variable resistor vR2
and VR. Since the voltages at the p movable connection terminals are set to have the same potential, the output of the amplifier OP2 is Ov, and therefore the line l, whose current is amplified by the transistor TR6, is also OV, and the output of the variable resistor VR .

Only the set welding current flows. When the compensation circuit is not used, when the switch S1 is turned OFF, the relay CR is turned OFF (hereinafter, the loss of coil voltage is referred to as OFF), and the variable resistor VR1 is connected to the relay contact C.
This means that it is grounded (OV line) by R'1.

In this case, the circuit from current transformer CT to transistor TR6 is disconnected, and no compensation is made for fluctuations in welding current.

To explain the switching timing of relay contacts CR1 and CR'1, when the energization signal is input, the transistor TR4 is activated through the gate elements of elements 7 and 8 to the ONL, the variable resistor VR, and the time constant set by the capacitor C3. After a certain period of time (usually set after 1 to 2 cycles), the transistor TR5 turns ON, and therefore the relay CR also turns ON (hereinafter, turning on the coil is referred to as ON).

That is, during 1 to 2 cycles after the energization signal is transmitted (which can be varied by the variable resistor VR4), the variable resistor VR is grounded by the relay contact CR'1, but the relay CR is ONt, When relay contact CR1 closes, closed-loop feedback control of the compensation circuit is performed.

As shown in Fig. 5G, this switching is possible because the welding current is not flowing before the start of energization, so the line l7 is +12
This is done to generate a voltage of about V.

Also, this switching circuit method is just an example;
For example, relay contact C is connected to the ■ and l input terminals of amplifier OP2.
It is also possible to connect R.

In addition, in the figure, TR1 is a transistor, R1 to R1
7 is a fixed resistor. D9. D10 is a diode.

The present invention provides a compensation circuit configured as described above.
Compensation for fluctuations in welding current can be achieved extremely easily and reliably using a feedback circuit using an OP amplifier.

In other words, conventional welding current variation compensation was to control the energization time, but the method according to the present invention controls the firing angle of the thyristor used in the most effective welding power supply circuit. It is extremely effective in terms of adjustment, compensation effect, certainty, etc.

With conventional compensation circuits, current transformer tap selection, vacuum tube D
There is no need to adjust the C bias, or to make extremely precise and precise adjustments of a variable resistor or the like to utilize the square curve portion.

Adjustment of the compensation circuit according to the invention is achieved by adjusting the variable resistor V in FIG.
The welding current set by R1 is simply adjusted by variable resistor VR2 so that the voltage obtained from current transformer CT1 and the voltage obtained by variable resistor VR3 linked to variable resistor VR1 become the same. .

Moreover, in the conventional method, the effectiveness of compensation is adjusted using the square curve portion, but the compensation effect can only be obtained within a certain limited range of the welding current circuit.

In the method according to the present invention. By replacing the fixed resistor R1 in FIG. 4 with a variable resistor, the degree of amplification can be easily increased. Because the degree of feedback can be varied. Compensation effects can be used extensively.

In addition, since the circuit does not use vacuum tubes, it requires a low DC power supply and is reliable without deteriorating over time.

From the above. The method according to the present invention eliminates all the drawbacks of the conventional methods and at the same time has sufficient practical effects by compensating for changes in welding current of a resistance welding machine with an extremely fast response.

Furthermore, it is effective against fluctuations in power supply voltage, making it highly industrially viable.

[Brief explanation of the drawing]

Figures 1 to 3 relate to conventional compensation methods,
Figure 1 is a timing diagram for compensation based on energization time, Figure 2 is a compensation circuit diagram based on energization time in Figure 1, and Figure 3 is an EG-IP of a vacuum tube that controls energization time by the square of the increase or decrease in welding current.
The characteristic diagrams, FIGS. 4 and 5 are related to the present invention,
Figure 4 shows a closed-lobe compensation circuit diagram that controls the phase control circuit and welding current by feedback. FIG. 5 is a diagram showing waveforms at various parts in FIG. 4. CT1...Current transformer, VR1, VR2, VR3-
...variable resistor. OPl, OP2...Comparators (differential operational amplifiers).

Claims (1)

[Claims] 1 The current-carrying element is configured to perform phase control using a thyristor, etc., and fluctuations in the welding current are detected by a current transformer connected to the welding power supply circuit, and the output voltage and welding current setting obtained by this current transformer are The voltage obtained from the variable resistor and the voltage obtained from another linked variable resistor are respectively applied to the input of a comparator such as a differential operation amplifier, and the output amplified by this comparator is used to set the welding current. It is applied to one end of the connection terminal of a variable resistor, and the output level of the comparator changes in accordance with the increase or decrease in the set welding current to cancel out the increase or decrease in the welding current, so that the welding current is always constant. Features a welding current control method for a resistance welding machine.