JPS6144594B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DC arc welding machine that uses a semiconductor switch element with a control pole to control the output at a constant current.

[Prior Art] Generally, as a method of controlling the output of a DC arc welding machine, a method of controlling the phase of AC power is widely adopted. By detecting the output voltage value and comparing it with a reference signal, and using the error signal to control the firing phase of a semiconductor switch element with a control pole such as a thyristor, a DC arc welding machine with constant voltage characteristics can be obtained, and the output current By detecting the value and comparing it with a reference signal, and controlling the firing phase of the thyristor using the error signal, a DC arc welding machine with constant current characteristics can be obtained. The stability of such a feedback system worsens as the gain of the system increases, but the system can be stabilized by inserting a time delay element such as an integrating circuit into the system. For example, as shown in FIG. 1, a welding power source transformer 1
The output terminal of the secondary winding TS' of 3 is connected to the thyristor SCR1.
A current value detection signal _{e f} is connected to the output terminal 2 via the semiconductor switch 8 with control pole consisting of ~SCR3 and the reactor L, and the output current value detector 3 is obtained.
and the reference signal _e obtained from the reference signal generator 4 are compared in a comparator 5 and amplified in an amplifier circuit 6.
I am trying to control 3.

In such a general DC arc welding machine, the ratio R3/R2 of the resistor R3 of the amplifier circuit 6 and the resistor R2 of the comparator 5 is made sufficiently large to increase the gain of the system and improve the constant current characteristics. In addition, by connecting a capacitor C as a time delay element 10, the system is stabilized.

[Problems to be Solved by the Invention] However, in the conventional welding machine shown in FIG. The current value detection signal _ef of the output current value detector 3 is zero, and the capacitor C is charged to a high voltage of (R3/R1) _es . In this state, when the electrode E is brought into contact with the workpiece W to start the arc and the current is started, the phase of the ignition signal _e1 obtained from the phase shifter 7 advances by a larger amount than during the steady output. Therefore, as shown by curve a in FIG. 2, an excessive output current flows at the start of startup. Since the capacitor C with the capacitance C is connected to the amplifier circuit 6, the time during which this excessive output current flows is determined by the time constant CR3, and generally reaches several hundred ms in a stabilized system.

If such an excessive output current flows for a long time, there is a risk of damaging the electrode rod E or the workpiece W to be welded. In particular, when welding thin plates using a low current, problems such as melting of the welded object occur due to the excessive current.

An object of the present invention is to provide a DC arc welding machine with constant current characteristics that prevents excessive output current from flowing for a long time when starting the arc.

[Means for Solving the Problems] The present invention attempts to solve the above-mentioned problems, and as shown in the block diagram of FIG. The configurations (a) to (g) of the welding machine are as follows: (a) a semiconductor switch 8 with a control pole that controls the output current flowing from the output terminal 2 to the welding load R, and (b) a switch corresponding to the output current value. an output current value detector 3 that outputs a current value detection signal e _f ; (c) a reference signal generator 4 that outputs a reference signal e _s corresponding to the output current value; (d) the reference signal e _s and the ( _e ) an operational amplifier Amp that amplifies the difference signal and a negative feedback device that provides negative feedback of the output signal of the operational amplifier Amp; Amplification circuit 6 consisting of resistor R3
(f) a phase shifter 7 that receives the output signal e ₀ of the amplifier circuit 6 as an input and outputs an ignition signal e ₁ to the semiconductor switch 8 with control pole; (g) the output signal e of the amplifier circuit 6; In addition to each configuration of the time delay element 10 consisting of a capacitor C for stabilizing ₀ , the following new configurations (h) and (i) are newly added, namely: (h) During energization to the welding load R Detection signal while energized
A _DC arc including: (i) a switch 9 that connects the time delay element 10 to the amplifier circuit 6 only when the current-on detection signal _e2 is output; It's a welding machine.

Further, in the DC arc welding machine of the present invention, as shown in the first embodiment of FIG. It consists of a series circuit of a capacitor C and a switch 9 which becomes closed or conductive when the current-on detection signal _e2 is input.

Furthermore, the DC arc welding machine of the present invention has a negative feedback resistor R3 as shown in the second embodiment of FIG.
A time delay element 10 and a switch 9 connected in parallel to each other are constructed from a parallel circuit of the capacitor C of the time delay element 10 and the switch 9 which becomes closed or non-conductive when the energization detection signal _e2 is input. has been done.

[Operation of the Invention] With the above configuration, in the DC arc welding machine of the present invention, the time delay element 10 is activated by the switch 9 only when the energization detector 11 is outputting the energization detection signal _e2 . Since it is connected to the amplifier circuit 6, it is possible to prevent an excessive output current from flowing for a long time when starting the arc.

[Example] The DC arc welding machine of the present invention will be explained in detail below with reference to the illustrated example.

FIG. 3 is a block diagram showing the structure of the DC arc welding machine of the present invention, in which 1 is an input terminal and 2 is an output terminal. 3 is an output current value detector for obtaining a signal e _f corresponding to the output current, and the current value detection signal e obtained from the output current value detector 3 is
_f is input to the comparator 5 together with the reference signal e _s obtained from the reference signal generator 4. The difference between the current value detection signal e _f and the reference signal e _s is obtained on the output side of the comparator 5 , and this difference signal is amplified by the amplifier circuit 6 . The difference signal amplified by the amplifier circuit 6 is supplied to the phase shifter 7 as is, or is supplied to the phase shifter 7 through the operation of a time delay element 10 connected to the amplifier circuit 6. 11 detects that current is being applied to the welding load R through the output terminal 2, depending on the presence or absence of the output current or a drop in the output voltage, and detects whether current is being applied while the welding load R is being energized. signal e ₂
This is a energized detector that outputs . Switch 9 is
It is turned on and off by the current-carrying detection signal _e2 output by the current-carrying detector 11, and while the current-carrying detector 11 detects energization to the welding load R, that is, the current-carrying detection signal _e2 is output. During this period, it is in the on state and sends the output signal e ₀ of the amplifier circuit 6 to the phase shifter 7 through the time delay element 10. Then, the energized detector 11
is not outputting the energization detection signal _e2 , the switch is turned off so that the output signal _e0 of the amplifier circuit 6 is sent directly to the phase shifter 7 without passing through the time delay element 10. 9 switches the output of the amplifier circuit 6.

The switch 9 does not immediately turn on because there is some time delay even when the current-on detector 11 detects the current. Therefore, at the moment when the electrode rod E contacts the workpiece W to be welded, the switch 9 is not yet activated, so the amplifier circuit 6 has a time delay element 1.
0 is not connected. Until just before this moment,
The current value detection signal e _f obtained from the output current value detector 3 is still zero. However, when the output current begins to flow, the switch 9 enters the operating state with a slight time delay because the energization detector 11 outputs the energization detection signal _e2 , and the time delay element 10 is activated in the amplifier circuit 6.
is connected. When the time delay element 10 is connected to the amplifier circuit 6, the amplification factor of the amplifier circuit 6 increases with a predetermined time constant and reaches steady operation.

Hereinafter, specific embodiments of the present invention will be described with reference to FIGS. 4 to 8.

FIG. 4 shows a first embodiment of the invention shown in FIG. In the figure, TS constituting the welding power source transformer 13 is the secondary winding of the Y-connected welding transformer, and this secondary winding is connected to the main winding L.
_u , L _v , L _w and auxiliary windings l _u , l v and _{l w} connected in series to the main winding constituting the auxiliary power supply circuit 12
It is made up of. The output ends of the main windings L _u , L _v , and L _w each have a thyristor whose cathode constituting a semiconductor switch element 8 with a control pole is connected in common.
The anodes of SCR1 to SCR3 are connected, and the cathodes of thyristors SCR1 to SCR3 are connected to the positive electrode side of the output terminal 2 of the welding machine via a DC reactor L.

Auxiliary windings l _u , l constituting the auxiliary power supply circuit 12
The terminals on the opposite side of the main windings of _v and l _w are connected to the anodes of diodes DR1 to DR3 whose cathodes are connected in common, and the cathodes of the diodes DR1 to DR3 are connected to the resistor R4 and the relay constituting the current-on detector 11.
Thyristor SCR1~ through the excitation coil of CR
Connected to the common connection point of the cathodes of SCR3. A neutral point N of the secondary winding TS is connected to the negative electrode side of an output terminal 2 of the welding machine via an output current value detector 3. The current value detection signal e _f obtained from the output current value detector 3 is applied to the resistor R2 that constitutes the comparator 5.
The operational amplifier Amp that constitutes the amplifier circuit 6 via
The reference signal e _s obtained from the reference signal generator 4 is input to the operational amplifier Amp via a resistor R1 forming a comparator 5.

The output signal _e0 of the operational amplifier Amp is input to the phase shifter 7, and the output of the phase shifter 7 is sent to the thyristors SCR1 to
It is given to the gate of SCR3. operational amplifier
A negative feedback resistor R3 is connected between the output end and the input end of the Amp, and a capacitor constituted by the normally open contact CRa of the relay CR constituting the switch 9 and the time delay element 10 is connected to both ends of this resistor R3. The series circuit with C is connected in parallel.

In the circuit shown in Fig. 4, the welding power source transformer 13
Auxiliary winding of secondary winding TS, diode DR1~
DS3 and current limiting resistor R4 constitute the auxiliary power supply circuit 12, and the excitation coil of the relay CR constitutes the energization detector 11. Further, the capacitor C constitutes the time delay element 10 of the operational amplifier Amp, and the normally open contact CRa of the relay uses the time delay element 10 for negative feedback only when the energization detection circuit 11 outputs the energization detection signal _e2 . It constitutes a switch 9 connected in parallel to the resistor R3.

In order to start the arc, the electrode rod E is connected to the workpiece W to be welded.
When contacted, a current flows through the auxiliary power supply circuit 12, and as a result, the relay CR is immediately energized, the contact CRa is closed, and the capacitor C is connected in parallel to the negative feedback resistor R3. Immediately before starting the arc, the current value detection signal e _f of the output current value detector 3 is zero, but the capacitor C is a relay contact.
It is not charged because it is disconnected by CRa. When the electrode E is brought into contact with the workpiece W, the output current begins to flow, and after a slight time delay, the relay contact CRa closes and the capacitor C becomes {(R3/R1) e _s − (R3/R2) e _f }. charged with voltage.

To explain in more detail, the electrode rod E is connected to the workpiece W.
Since the current value detection signal e _f is _zero until the relay contact CRa is brought into contact with As a result, a large current flows through the output. When the output current starts flowing, the relay contact CRa is closed with a slight time delay, but this large output current is caused by the DC reactor L.
The phase lags due to the presence of the thyristor, and the voltage in the main winding applied to the thyristor that is conducting at that time continues to flow until the voltage reaches the negative half-cycle thyristor. When the relay contact CRa is closed, the capacitor C is connected in parallel to the input/output terminals of the operational amplifier Amp, and charging of the capacitor C is started. If there is no charge on the capacitor C, the output signal e ₀ of the operational amplifier Amp drops to approximately zero, and then is charged with a time constant determined by the resistors R1, R2, R3 and the capacitor C. Therefore, as shown by curve b in FIG. 7, the output current initially flows as a large current, then decreases as the output signal _e0 of the operational amplifier Amp changes, and then settles down to the set value. As mentioned above, even after the relay contact CRa is closed, a large output current continues to flow for a certain period of time, so even if the output signal e ₀ of the operational amplifier Amp
Even if becomes a value close to zero, the output current will not fall to zero. Therefore, an excessive output current as shown in the conventional curve a in FIG. 2 does not flow for a long time, and a starting characteristic as shown in the curve b in FIG. 7 can be obtained.

Note that if a reed switch or the like is used as the relay CR, the response speed can be increased.

FIG. 5 shows a second embodiment of the present invention shown in FIG. 3, in which the welding power source transformer 13 shown in FIG.
The output current energizing circuit such as the auxiliary power supply circuit 12 is omitted, and in this embodiment, the capacitor C constituting the time delay element 10 is used together with the operational amplifier Amp.
and a negative feedback resistor R3 are connected in parallel, and a normally closed contact CRb constituting a switch 9 for shorting or operating the capacitor C is connected to the capacitor C.
are connected in parallel.

In the circuit shown in FIG. 5, before the start of welding, the current value detection signal e _f is zero and the contact CRb is closed, so the output signal e ₀ of the operational amplifier Amp is equal to the reference signal e _s . Therefore, when the electrode rod E is brought into contact with the workpiece W to generate an arc at the start of welding, the thyristors SCR1 to SCR3 conduct at the firing phase determined by the set value of the reference signal e _s and the welding load is reduced. Output current is supplied to R. Auxiliary power circuit 12
When current starts to flow from , the coil of the relay CR that constitutes the current-carrying detector 11 is excited, and its contact CRb is opened. When the contact CRb constituting the switch 9 opens, charging of the capacitor C starts, and the amplification factor of the amplifier circuit 6 starts to increase. Therefore, the output current is maintained at the set output current by amplifying the output signal e _{s -ef} of the comparator 5 in the amplifier circuit 6. In this case, when the output current starts flowing, a peak current as shown in curve b in FIG. 7 does not occur, and a smooth starting characteristic as shown in curve C in FIG. 8 is obtained.

In the embodiment shown in FIG. 4, the excitation coil of the relay CR constituting the energized detector 11 is connected in series with the current limiting resistor R4, but the resistor R in FIG.
By changing the connection between 4 and the excitation coil of relay CR and connecting the excitation coil of relay CR in parallel to both ends of resistor R4 as shown in Fig. 6, the welding load is energized. While resistor R
The coil of the relay CR may be excited by the voltage generated across the relay CR. In this case, the auxiliary windings l _u , l _v , l _w ,
The auxiliary output current flowing to the welding load R from the auxiliary power supply circuit 12 composed of the diodes DR1 to DR3 and the current-limiting resistor R4 makes it possible to improve the arc start and eliminate arc breakage.

In addition, the energization detector 11 may be configured by connecting a relay coil and a constant voltage diode in series between the output terminals 2 of the welding machine. In this way,
When the output voltage is high in a no-load state, the constant voltage diode becomes conductive, so the relay coil CR is excited and detects that the welding load R is not energized. Then, when the electrode rod E and the workpiece W are brought into contact and the welding load R is started to be energized, the output voltage decreases, the constant voltage diode becomes non-conductive, and the relay coil CR becomes de-energized. Detects whether the welding load R is being energized.

In the above embodiment, the relay coil constitutes the energized detector 11, and the relay contacts are used as the switch 9 that connects and disconnects the time delay element 10 to and from the amplifier circuit 6. The detector 11 may be of any type as long as it can detect that current is being applied to the welding load R and operate the switch 9 based on the current-carrying detection signal _e2 . Further, a semiconductor switch such as a thyristor or a transistor can be used as the switch 9, and the response speed can be further increased by using such a semiconductor switch.

Further, the time delay element 10 may be a first-order RC delay element consisting of a resistor and a capacitor, or a second-order delay element with other components interposed, or may include a reactor L.

[Effects of the Invention] As described above, according to the present invention, the switch 9 is provided to connect the time delay element 10 to the amplifier circuit 6 only when the energization detector 11 is outputting the energization detection signal _e2 . Therefore, there is an advantage that it is possible to reliably prevent an excessive output current from flowing for a long time when starting the arc.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of a conventional DC arc welding machine, Fig. 2 is a diagram showing temporal changes in the output current value at the time of starting the arc of a conventional DC arc welding machine, and Fig. 3 is a diagram showing the change in output current value over time of the conventional DC arc welding machine. 4 and 5 are a block diagram showing the configuration of the welding machine, and FIG. 6 is a connection diagram showing the first and second embodiments of the DC arc welding machine of the present invention shown in FIG. 3, respectively. is the auxiliary power supply circuit 1 of the DC arc welding machine of the present invention shown in FIG.
2 and a connection diagram showing a modification of the energizing detector 11, and FIGS. 7 and 8 are lines showing temporal changes in the output current value at the time of arc starting in the embodiment shown in FIGS. 4 and 5, respectively. It is a diagram. 3...Output current value detector, 4...Reference signal generator, 5...Comparator, 6...Amplification circuit, Amp...
Operational amplifier, R3...Resistor for negative feedback, 7...Phase shifter, 8...Semiconductor switch with control pole, 9...Switch, 10...Time delay element, C...Capacitor, 11...Currently conducting Detector, 12...Auxiliary power supply circuit, 13...Welding power source transformer, e _f ...Current value detection signal, e _s ...Reference signal, _e0 ...Amp output signal, _e1 ...Ignition Signal, e ₂ ...Electricity detection signal.

Claims (1)

[Claims] 1. A semiconductor switch 8 with a control pole that controls the output current flowing from the output terminal 2 to the welding load R, and an output current value detector that outputs a current value detection signal e _f corresponding to the output current value. 3, a reference signal generator 4 that outputs a reference signal e _s corresponding to the output current value, and a comparator 5 that receives the reference signal e _s and the current value detection signal e _f and outputs a difference signal. and an amplifier circuit 6 comprising an operational amplifier Amp that amplifies the difference signal and a feedback resistor _R3 that provides negative feedback to the output signal of the operational amplifier Amp; A direct current circuit consisting of a phase shifter 7 that outputs an ignition signal e ₁ to a polarized semiconductor switch 8, and a time delay element 10 consisting of a capacitor C for stabilizing the output signal e ₀ of the amplifier circuit 6. In the arc welding machine, when the welding load R is energized, an energization detection signal e ₂
A DC arc welding machine comprising: an energization detector 11 that outputs a energization detection signal _e2 ; and a switch 9 that connects the time delay element 10 to the amplifier circuit 6 only when the energization detection signal e2 is output. 2. The time delay element 10 and the switch 9 connected in parallel to the negative feedback resistor R3 are closed or conductive when the capacitor C of the time delay element 10 and the energization detection signal _e2 are input. The DC arc welding machine according to claim 1, which is a series circuit with. 3. The time delay element 10 and the switch 9 connected in parallel to the negative feedback resistor R3 are open circuited or non-conductive when the capacitor C of the time delay element 10 and the energization detection signal _e2 are input. The DC arc welding machine according to claim 1, which is a parallel circuit with.