JPS6253267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output control device for giving an arc welding machine constant current characteristics or constant voltage characteristics.

Feedback control is generally used to provide arc welding machines with constant current or constant voltage characteristics. An example is shown in FIG. In the figure, 1
2 is a welding transformer, 2 is a control element using a thyristor for controlling the welding machine output current (AC), 3 is a current detection section using a current transformer, 4 is a welding load, and 5 is a current detection section 3. 6 is a rectifier that converts the current detection signal into direct current; 6 is an amplification section for the current detection signal; 7 is a reference voltage generation section for setting the output current; 8 is an error amplifier having a feedback circuit including a phase delay capacitor 9 and a resistor 10. , the reference voltage _E a given to the inverting input terminal from the reference voltage generating section 7 when the welding machine is loaded and the amplifying section 6
Current detection signal E _b given to the non-inverting input terminal from
Amplify the voltage _difference between _the
Output _d . Reference numeral 11 denotes a control signal generating section, which generates a control signal (thyristor firing signal) such that the smaller the output voltage E _d of the error amplifier is, the larger the welding machine output current I is. Added to element 2.

In the above device, when the welding machine is under no load, the current detection signal E _b is zero and only the reference voltage E _a is input to the error amplifier 8, so the output of the error amplifier 8 is E _d =0.
becomes saturated, and a control signal is applied to the control element 2 so that the output current I becomes maximum. When welding is started in this state, a phase delay element (capacitor 9) to prevent hunting is added to the feedback circuit of the error amplifier 8.
is inserted, the rise of the output voltage E _d is delayed, and an excessive lash current I _r flows through the welding machine output circuit as shown in Figure 2, causing problems such as burn-through of the welded part when welding thin plates. arise.

The above is a case of constant current control, but in constant voltage control, the signal that detects the output voltage is input to the error amplifier, so if the no-load output voltage of the welding machine is set high, the error amplifier will conversely increase the maximum output voltage. This causes the inconvenience that the rise of the output current at the start of welding is delayed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an output control device for an arc welding machine that can solve the above-mentioned problems and quickly stabilize the output current and voltage to a steady state at the start of welding.

In order to achieve the above object, the present invention short-circuits the input terminals of the error amplifier using a short-circuit element including impedance when the welding machine is not loaded, and transfers the voltage generated by the impedance of the short-circuit element between the input terminals of the error amplifier. By adding a differential voltage to the error amplifier, the error amplifier is put on standby in the output state when the welding machine is loaded.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate corresponding parts. In FIG. 3, the current detection signal generated by the current detection section 3 and converted into DC by the rectifier 5 is input to the amplification section 6 and the load state discrimination circuit 13, and the output voltage E _b of the amplification section 6 is input to the reverse blocking diode 14. The signal is applied to the non-inverting input terminal of the error amplifier 8 via. The load state determination circuit 13 is constituted by a level detector or a relay, and generates a signal S corresponding to a loaded state and an unloaded state of the welding machine depending on the presence or absence of a current detection signal.

15 is a shorting element including an impedance connected between the input terminals of the error amplifier 8, which turns on when the welding machine is under no load upon receiving the output signal S of the load state determination circuit 13, and turns off when the output current is detected. It has a switching function to Fig. 4 shows an example of the configuration of a shorting element that combines a transistor 16 and a resistor 17, but other examples include a single transistor, a combination of a mechanical switch and a resistor, a combination of a mechanical switch, a resistor, and a diode, etc. It can also be used.

18 is a power supply for generating a differential voltage between the input terminals of the error amplifier 8 when the welding machine is not loaded;
The voltage E _c is set higher than the voltage E _a of the reference voltage generating section 7 . 19 is a switch element connected to the power source 18, which turns on only when the welding machine is under no load in response to the output signal S of the load state determination circuit 13;
A voltage E′ _c is supplied to one end a of the shorting element 15 via the reverse blocking diode 20. The current flowing through the short-circuiting element 15 due to this voltage _E'c returns to the earthing terminal of the power supply 18 from the other end b of the shorting element through the resistor 21 and the ground. The internal resistances of the resistor 21 and the power source 18 are set to values that are sufficiently larger than the impedance of the shorting element 15.

Next, the operation will be explained with reference to the time chart shown in FIG. When the welding machine is not loaded (t ₁ in Fig. 5)
Previously), the output of the current detecting section 3 was zero, therefore the output voltage E _b of the amplifying section 6 was also zero, and the output signal S of the load state discriminating circuit 13 was at High level. This signal S turns on the shorting element 15 and the switch element 19, and the potential at point a becomes higher than the potential at point b by the impedance drop that occurs in the shorting element 15 due to the current flowing from the power supply 18 through the switch element 19 and the diode 20. Become. Since the differential voltage E _i is applied between the input terminals of the error amplifier 8, the error amplifier 8 generates a positive output voltage E _d corresponding to E _i and stands by in a non-saturated state.

When welding is started at time _t1 in FIG. 5, a current detection signal corresponding to the output current I is generated from the current detection section 3, and as a result, the output signal S of the load state discrimination circuit 13 is inverted to Low level. Short circuit element 15 and switch element 19 are turned off. Therefore, at the moment of starting welding, the error amplifier 8 is activated as shown in FIG.
The differential voltage E _i applied between the input terminals of decreases (-)
_However , since the capacitor 9 of the feedback circuit is charged by the output voltage E _d during no-load, the output voltage E _d does not fall suddenly, but gradually becomes steady as the output current I increases. With this, the output current I also quickly stabilizes to a steady state, and it is possible to prevent an excessive rush current from flowing as in the conventional case.

According to experiments conducted by the inventors, when the output voltage E _d of the error amplifier during no-load of the welding machine is maintained at approximately the same level as the steady state during welding or slightly higher, there is no lash current. It was found that good starting characteristics were obtained.

Such ideal characteristics are realized by appropriately setting the impedance of the shorting element 15 and the current flowing therein. For example, as the shorting element 15, a transistor 16 and a resistor 1 as shown in FIG.
7, and if the resistor 17 is 100Ω and the current flowing through it is 1mA, then the transistor 1
Collector saturation voltage caused by internal resistance of 6
Vcesat. (approximately 0.5V) and the voltage drop of resistor 17 V _r
(0.1V) is input to the error amplifier 8 as the no-load differential voltage E _i , making it possible to maintain the error amplifier 8 in an output state close to a steady state during welding. Here, the voltage E _a given from the reference voltage generator 7 changes depending on the set value of the output current I. When the voltage E _a increases, the current flowing through the shorting element 15 decreases, so the differential voltage E _i generated by its impedance decreases, and the output voltage E _d of the error amplifier 8 also decreases correspondingly, but the control signal generation Since the section 11 has a function of increasing the output current I as the voltage E _d becomes lower, the error amplifier 8 adjusts the output close to the steady state during welding in response to a change in the set value of the output current I. The condition will be maintained.

In this way, by using the shorting element 15 and appropriately selecting the voltage-current characteristics of its impedance, a slight difference voltage E _i corresponding to the set value of the output current can be input to the error amplifier when the welding machine is not loaded. It can be easily added between the terminals.

According to the above configuration, since the control element 2 stands by in a steady output state lower than the maximum output when there is no load, the output voltage at the time of starting welding may be too low and interfere with starting welding.

In such a case, a switch element 22 shown by a broken line in FIG.
It is preferable to clamp the input of 1 to approximately zero potential. If a resistor 23 is inserted between the output side of the error amplifier 8 and the connection point of the switch element 22, even if the input of the control signal generator 11 is clamped to zero potential, the error amplifier 8 will maintain its output. Since the system waits in a non-saturated state, the control element 2 is set to the maximum output state at the moment of starting welding, and the no-load voltage necessary to start welding is supplied, and after the output current I is detected, the switch element 23 is turned off. Natsute error amplifier 8
The control signal generator 11 is activated by the output voltage E _d of the output current I, and the output current I is quickly stabilized to a steady state without becoming excessive.

The current detection signal E _b and the reference voltage E _a are connected to the error amplifier 8.
Instead of comparing the current detection signal E _b and the reference voltage E _a using another adder 24 as shown in FIG.
In the case where the difference voltage is inputted to the error amplifier 8, the input terminals of the error amplifier 8 are short-circuited with the short-circuiting element 15 when the welding machine is not loaded, as in the previous embodiment. The effect of this can be obtained.
In FIG. 6, 25 is a resistor set to a value sufficiently larger than the impedance of the shorting element 15,
The voltage generated at the impedance of the shorting element 15 due to the current flowing from the inverting input terminal of the error amplifier 8 to the ground through the shorting element 15 and the resistor 25 is the difference in order to maintain the error amplifier 8 in an output state close to the steady state during welding. It is input to the error amplifier 8 as a voltage E _i .

In the above embodiment, the case of constant current control was described, but the present invention can be similarly applied to constant voltage control. In constant voltage control, the signal that detects the welding machine output voltage is input to the error amplifier, so if the no-load output voltage of the welding machine is set to a large value, the error amplifier will saturate at the maximum output, and when welding starts. However, by short-circuiting the input terminals of the error amplifier when the welding machine is not loaded with the above-mentioned shorting element 15, the error amplifier can be brought into an output state close to the steady state when the welding machine is loaded. By waiting at this time, the delay in the rise of the output current at the start of welding can be eliminated and the steady state can be quickly stabilized.

As explained above, according to the present invention, when controlling the output current or voltage to be constant in an arc welding machine, an excessive lash current may flow at the start of welding due to a control delay in the feedback control system, or the rise of the output current may be delayed. It can be quickly stabilized to a steady state without causing any damage, and problems such as burn-through of welds due to excessive current and poor starting due to insufficient current can be solved with a relatively simple circuit configuration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example of an output control device for an arc welding machine, Fig. 2 is a diagram showing its starting characteristics, and Fig. 3 is a block diagram of a control system showing an embodiment of the present invention. FIG. 4 is a diagram showing an example of the configuration of a short-circuiting element used in this, FIG. 5 is a time chart for explaining the operation of the embodiment of FIG. 3, and FIG. 6 is a main part showing another embodiment of the present invention. FIG. 1; Welding transformer, 2; Control element, 3; Current detection unit, 4; Welding load, 5; Rectifier, 6; Amplification unit,
7; Reference voltage generation section, 8; Error amplifier, 9; Phase delay capacitor, 10; Resistor, 11; Control signal generation section, 12; Amplification section, 13; Load condition determination circuit, 14; Reverse blocking diode, 15; shorting element,
16; transistor, 17; resistor, 18; power supply,
19; switch element, 20; reverse blocking diode,
21; Resistor, 22; Switch element, 23; Resistor,
24; Adder; 25; Resistor.

Claims (1)

[Claims] 1 An error amplifier having a feedback circuit including a phase delay element amplifies the voltage difference between the current or voltage detection signal and the reference voltage, converts the output into a control signal, adds it to the control element of the welding machine output circuit, and sends it to the control element of the welding machine output circuit. In an output control device for an arc welding machine that performs current control or constant voltage control, there is a load state discrimination circuit that emits signals corresponding to when the welding machine is loaded and no load, and a load state discrimination circuit that emits signals corresponding to when the welding machine is loaded and unloaded. a short-circuiting element that includes an impedance that shorts between the input terminals of the error amplifier only when the load is on, and applies a voltage difference between the input terminals of the error amplifier necessary to keep the error amplifier on standby in the output state when the welding machine is loaded; An output control device for an arc welding machine.