JPH04224084A - Circuit for controlling electricity charging of capacitor type spot welder - Google Patents

Abstract

PURPOSE:To obtain the more stable controlling characteristic of the capacitor electricity charging voltage by controlling the charge voltage over all the controlling area at the initial period of charging and restricting the controlling area of the phase control rectifier circuit after reaching the prescribed voltage in the subject welder with capacitor charged by the phase control rectifier circuit. CONSTITUTION:The composition to operate the phase control rectifier circuit is obtd. by generating the detection signal with the voltage detecting means connected to both ends of the capacitor, comparing this with the reference electric voltage. And if the compared signal is beyond the threshold value, the pulse position of the pulse generating circuit to operate the phase control rectifier circuit is regulated and the moving area of the phase control rectifier circuit is limited.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging control circuit for a capacitor type spot welding machine.

0002

2. Description of the Related Art A capacitor-type spot welding machine is a device that instantly discharges the electric charge stored in a capacitor to weld opposing objects to be welded. The capacitor is normally charged by providing a phase control rectifier circuit including a thyristor and controlling the phase of the pulse fired by the thyristor. Generally, electrolytic capacitors are used for such capacitors.
There is no particular problem until charging to the target voltage is completed, but after charging is completed, a small amount of current must be passed to compensate for the drop in charging voltage due to leakage current of the capacitor, etc. but,
In the conventional phase control pulse generation circuit, since the control is performed in the same manner as the initial charging control, the voltage oscillates around the target voltage, and optimal control is not always possible.

0003

SUMMARY OF THE INVENTION An object of the present invention is to provide a control circuit for obtaining more stable characteristics regarding supplementary charging of a capacitor in a capacitor type spot welding machine. Another objective is to obtain a circuit that generates ignition pulses at high speed in order to perform fine control over the cycle of commercial AC power.

0004

[Means for Solving the Problems] In a capacitor-type spot welding machine including a phase-controlled rectifier circuit, the present invention charges a capacitor from an AC input power supply via a phase-controlled rectifier circuit in order to obtain stable supplementary charging characteristics. A charging control circuit for a capacitor type spot welding machine, comprising a circuit for
A voltage detection means connected to the capacitor, a comparison amplifier circuit that compares the detected voltage of the voltage detection means with a reference voltage, and an initial charge completion signal generation that generates a signal in response to the output voltage of the comparison amplifier circuit. circuit, a synchronous circuit that synchronizes with the rectification cycle of the input AC frequency, and a pulse generation circuit that starts with this synchronous circuit, and when there is no signal from the initial charge completion signal generation circuit, pulse generation starts in a time shorter than the synchronization point. and a pulse generation circuit that starts generating pulses after a time longer than the synchronization point when there is a signal from the initial charge completion signal generation circuit. This is what we propose.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A charging control circuit for a capacitor type spot welding machine according to the present invention will be explained with reference to FIGS. 1 to 4. Figure 1
is a block diagram of an embodiment of the charging control circuit of a capacitor-type spot welding machine according to the present invention, FIG. 2 is a waveform diagram showing an example of the operation results, and FIG. This is a specific circuit diagram, and FIG. 4 is a waveform diagram of each part. In FIG. 3, a commercial AC voltage is received from input terminals 11 and 12 and supplied to the primary winding of a transformer 13. The secondary winding of the transformer 13 consists of diodes 22 and 24 and thyristors 21 and 2 which are bridge-connected to each other.
It is connected to a phase control rectifier circuit 20 consisting of 3. The output terminal of this phase control rectifier circuit 20 is connected to a capacitor 30 via a resistor 31. Both ends of the capacitor 30 are connected to the primary winding 51 of the transformer 50 via the thyristor 40.
connected to. A secondary winding 52 of this transformer 50 is connected to a welding electrode 60. Here, the thyristors 21 and 23 are controlled by a control circuit to be described later so that the charging voltage of the capacitor 30 becomes a predetermined voltage. When the voltage of the capacitor 30 is charged to a predetermined voltage, the thyristor 4
When the ignition signal is applied to the gate of 0, the discharge current of the charge in the capacitor 30 flows to the primary winding 51 of the transformer 50, and the secondary winding 52 of the transformer 50 has a primary winding and a A large current value multiplied by the inverse ratio of the number of turns to the secondary winding flows, and Joule heat is generated in the workpiece sandwiched between the welding electrodes 60 and welded.

Next, a control circuit for driving and controlling the phase control rectifier circuit 20 will be explained. First, input terminals 11 and 12
is connected to the primary winding of the transformer 101, and the transformer 10
The secondary winding 1 is connected to the rectifier/constant voltage circuit 1 and supplied to each circuit. This rectifier/constant voltage circuit 1 is composed of bridge-connected diodes 102-105, a smoothing capacitor 106, and a constant voltage circuit (integrated circuit) 107. The input terminals 11 and 12 are also connected to the primary winding of the transformer 601, whose secondary winding is connected to the synchronous circuit 6, and the slope wave limiting generating circuit 7 is connected to the frequency of the input commercial power source.
It is synchronized with the rectification period of the double phase control rectifier circuit 20. To explain the synchronous circuit 6 in detail, the secondary winding of the transformer 601 is connected to bridge-connected diodes 602-604, and as shown in (1) of Fig. 4, a pulse with a frequency twice the input AC frequency is generated. Become a flow. This pulsating voltage is resistor 6
06-610, transistor 612, photocoupler 6
11, a circuit consisting of a diode 613 serves as an on/off signal for the light-receiving transistor of the photocoupler 611, which is transmitted insulated, and then transmitted to the subsequent transistor 616.
gives an on/off signal to the As shown in Figure 4 (2), the waveform is turned on only near electrical angles of 0° and 180°, turned off in other sections, and repeats at the same intervals thereafter.

Next, a resistor 201 is connected to the capacitor 30.
A voltage detecting means 2 consisting of and 202 is connected, and the detected voltage of the voltage detecting means 2 and the reference voltage 3 are compared by a comparison amplifier circuit 4 and the error signal thereof is amplified. To explain the details with reference to FIG. 3, the reference voltage circuit 3 is connected to the Zener diode 302 via the resistor 301 from the rectifier/constant voltage circuit 1.
A constant voltage is obtained by using resistor 303, variable resistor 304, and resistor 305 to obtain a desired reference voltage. This voltage is sent to the negative input terminal of operational amplifier 403 via resistor 402. Also, the voltage detection means 2
The detected voltage is applied to the operational amplifier 403 via the resistor 401.
is sent to the + input terminal of the These are compared and amplified in this operational amplifier 403. Resistors 404 and 40
5 applies negative feedback to the operational amplifier 403 to control the amplification factor.

Next, an initial charge completion signal generation circuit 8 is provided which generates a signal in response to the output voltage of the comparison amplifier circuit 4. To explain this initial charge completion signal generation circuit 8 in detail, the output voltage of the comparison amplifier circuit 4 is connected to resistors 801 and 804.
, 806, 807, 808 Diode 802, 803
After being amplified by a buffer amplifier consisting of a transistor 806 and an operational amplifier 813 via a resistor 812
is transmitted to the − input terminal of This operational amplifier 813
A low reference voltage obtained by dividing the substantially constant voltage supplied by the constant voltage circuit 1 by the resistors 810 and 809 is applied to the positive input terminal of the voltage regulator 809 via the resistor 812. The output terminal of this operational amplifier 813 is connected to the base of a transistor 815 through a resistor 814, and its collector is connected to the light emitting part of a photocoupler 817 through a resistor 816 from the positive power source. Therefore, when the voltage of the capacitor 30 is higher than the initial charging target value, the output voltage of the comparator/amplifier circuit 4 goes to H level, and then the collector of transistor 805 goes to L level, and the operational amplifier 8 goes to
The output of photocoupler 817 is at H level, and the output terminal of photocoupler 817 is turned on.

Next, the circuit of the slope wave limit generation circuit 7 will be explained. The collector of the transistor 616 of the synchronous circuit 6 is connected to the base of the transistor 701. The collector of this transistor 701 is connected to one end of a resistor 702 whose other end is connected to the + power supply, and further connected to the input terminal 2 of a timer circuit 704 (integrated circuit). This timer circuit 704 is connected to resistors 705, 707 and capacitors 703, 706 using a predetermined circuit connection method.
are connected as shown. This timer circuit 70
4 starts operating when its terminal 2 is opened, a triangular wave is generated across the capacitor 706 connected to its terminal 6, and when a predetermined value is reached, the timer output is turned off. The capacitor 706 is charged from the positive power supply through the resistor 707, but a transistor 709 and a resistor 708 are provided as another charging path. This path is activated when transistor 709 conducts. For its operation, a bias resistor 711 is connected to the base of the transistor 709, so the base only needs to be open. In other words, transistor 709
When the photocoupler 817, which is the output signal of the initial charge completion signal generation circuit 8 connected to the base of the capacitor 7, is off,
A route for charging 06 will be added. This situation can be easily understood by comparing (3) and (4) in FIG. 4 between the initial charging mode and the supplementary charging mode. In other words, the waveform of the output terminal 3 of the timer circuit 704 through the resistor 710 is as shown in (4) in Figure 4, and the timer starts at t1 and ends at t2, but when it is in the initial charging mode, it is in the supplementary charging mode. Compared to the above case, the timer end time t2 is early, and in the supplementary charging mode, t2 is late.

Transistor 71 receiving this timer output
3 has its collector connected to the + power supply via a resistor 711, and its emitter is connected to the - common potential via the collector-emitter of a transistor 714 and to the + power supply via a resistor 716. The base of transistor 714 is connected through resistor 712 to
(2) A synchronization signal with a waveform of (2) is connected. The circuit consisting of these transistors 713 and 714 has a so-called NA
An ND logic circuit is formed and its output is the same as the waveform of Figure 4 (2) (4), which is the same as the NAND logic (5).
Generates the waveform shown below. Time t2 is determined by this signal. In response to this signal, another set of similar transistors 717 and 719 are connected to a NAND logic circuit (FIG. 4).
6) Obtain the waveform shown below. This waveform is the transistor 72
The current is amplified by 3 and the collector has a current of 7
) appears. This voltage is applied to resistor 72
The capacitor 726 is charged via 4 and 725 to generate the slope wave shown in FIG. 4(8). This ramp wave is a ramp wave that is synchronized with the input AC cycle and is stopped by a timer from time t1 to t2, then starts from time t2 and returns to zero at time t3. In this way, this ramp wave starts at a time shorter than the synchronization point when there is no signal from the initial charge completion signal generation circuit 8 (initial charge mode), and when there is a signal from the initial charge completion signal generation circuit 8 (initial charge mode). Supplementary charging mode) starts after a period longer than the synchronization point.

Next, this slope wave is connected to the + input terminal of the comparator 503 in the pulse generating circuit 5 through the resistor 502.
applied via. Since the output voltage of the comparison amplifier circuit 4 is applied to the negative input terminal of the comparator 503 via the resistor 501, this slope wave and the output voltage (9) of the comparison amplifier circuit are applied as shown in FIG. 4(8). The comparator 503 is turned on at the intersection α, and the transistor 507 is turned on via the resistors 504 and 506.
Turn on. The collector of transistor 507 is +
A resistor 508 is connected to the power supply, and further a capacitor 509, a Zener diode 511, and a resistor 512 are connected.
connected in series with - connected to a common potential. Further, the connection point between the capacitor 509 and the Zener diode 511 is connected to the + power supply via the resistor 510. Further, the base and emitter of a transistor 514 are connected to both ends of the resistor 512, and a diode 513 having an opposite polarity is connected in parallel to this base-emitter junction. Therefore, normally the transistor 51
4 remains on, transistor 509 is off, and capacitor 509 is charged with the polarity shown. At this time, when the comparator 503 is turned on at the angle α mentioned above, the charge in the capacitor 509 is transferred to the transistor 507 and the transistor 514.
A discharge current flows through the emitter-base of the transistor 511, the Zener diode 511, and the capacitor 509, thereby reverse biasing the transistor 514. Therefore, after transistor 514 turns off rapidly, capacitor 509
When the charge on the zener diode 511 decreases and drops below the zener voltage of the zener diode 511, the zener diode 511 is turned on again. During this time, a rapidly rising off pulse is generated at the collector of the transistor 514. and transistor 5
The collector of 14 is connected to the positive power supply via a resistor 515, and the output of this transistor 514 becomes an on-pulse and is amplified by a circuit consisting of a transistor 517, resistors 516, 518, and a pulse transformer 519, and the two sets of The secondary winding is a diode 52
0 and 521 to the thyristors 21 and 23 of the phase control rectifier circuit 20. and pulse generation circuit 5
, a pulse is generated when the output signal of the comparison amplifier circuit 4 exceeds the output signal of the slope wave limit generation circuit 7.

A switch 505 connected in parallel to the resistor 506 is a switch contact that closes in conjunction with the operation of the thyristor 40, which is a discharging switching element, during welding work, and is used to stop charging when discharging the capacitor. It is provided in 1 and 3 described above show one embodiment of the present invention. For example, when the input AC power source is a three-phase AC, the control rectifier circuit 20, the synchronization circuit 6, the pulse generation circuit 5, and the slope wave limiting generator The circuit 8 etc. has a circuit configuration suitable for that case. Furthermore, both the pulse generation circuit 5 and the slope wave limitation generation circuit 7 can be constructed from a digital circuit. Further, the circuit shown in FIG. 3 is also an embodiment of the present invention, and can of course be modified within the scope of the spirit of the present invention.

[0013]

[Effect of the invention] The present invention has the features described above,
During the initial charging of the capacitor, the phase control rectifier circuit is freely controlled to almost the entire control angle, and after the initial charging is completed, the control range angle is limited to a range suitable for fine control, so the gain of the stabilizing loop is reduced. Stable characteristics can be obtained even if the voltage is increased, and charging is completed quickly during the first charge, and highly stable and highly accurate constant voltage characteristics are maintained during supplementary charging. In this way, control characteristics suitable for each mode of charging are obtained, and the voltage of the capacitor becomes more stable. Therefore, it has the effect of stabilizing welding energy and improving welding quality. Furthermore, since the reactive power component of the current that charges the capacitor is reduced, the life of the capacitor is extended and power consumption is also reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a charging control circuit for a capacitor-type spot welding machine according to the present invention.

FIG. 2 is a waveform diagram illustrating the operation of the charging control circuit of the capacitor spot welding machine according to the present invention.

FIG. 3 is a diagram showing an embodiment of a charging control circuit for a capacitor-type spot welding machine according to the present invention.

FIG. 4 is a waveform diagram illustrating the operation of the embodiment shown in FIG. 3;

[Explanation of symbols]

1... Rectifier/constant voltage circuit 2...Voltage divider 3...Reference voltage circuit 4...Comparison/amplification circuit 5...Pulse generation circuit 6...Synchronous circuit 7...Slope wave limit generation circuit 8...Initial charge completion signal generation circuit 11, 12...Input terminal 13...Transformer 20...Phase control rectifier circuit 21, 23...thyristor 22, 24...diode 30...Capacitor 31...Resistor 40...thyristor 50...Transformer 60...Welding electrode

Claims (4)

[Claims] 1. A charging control circuit for a capacitor-type spot welding machine, comprising a circuit for charging a capacitor from an AC input power source via a phase control rectifier circuit, comprising a voltage detecting means connected to the capacitor, and a voltage detecting means connected to the capacitor; A comparison amplifier circuit that compares the detection voltage of the means with a reference voltage, an initial charge completion signal generation circuit that generates a signal in response to the output voltage of the comparison amplifier circuit, and a synchronization circuit that synchronizes with the rectification cycle of the input AC frequency. The pulse generation circuit that starts with this synchronous circuit starts generating pulses in a time shorter than the synchronization point when there is no signal from the first charge completion signal generation circuit, and when there is a signal from the first charge completion signal generation circuit. This is a charging control circuit for a capacitor-type spot welding machine, characterized in that it is comprised of a pulse generation circuit that starts generating pulses after a long time has elapsed from the synchronization point. 2. A charging control circuit for a capacitor-type spot welding machine, comprising a circuit for charging a capacitor from an AC input power source via a phase control rectifier circuit, comprising a voltage detecting means connected to the capacitor, and a voltage detecting means for detecting the voltage. A comparison amplifier circuit that compares the detection voltage of the means with a reference voltage, an initial charge completion signal generation circuit that generates a signal in response to the output voltage of the comparison amplifier circuit, and a synchronization circuit that synchronizes with the rectification cycle of the input AC frequency. In the ramp wave limiting generation circuit that starts with this synchronization circuit, when there is no signal from the initial charge completion signal generation circuit, this ramp starts in a time shorter than the synchronization point, When there is a signal, a ramp wave limit generation circuit that starts after a time longer than the synchronization point, and a pulse that generates a pulse when the output signal of the comparison amplifier circuit exceeds the output signal of the ramp wave limit generation circuit. 1. A charging control circuit for a capacitor-type spot welding machine, comprising a generator circuit. 3. A timer circuit in which the slope wave limit generation circuit is started by a signal from the synchronous circuit; and a timer control circuit in which the duration of the timer circuit is controlled by a signal from the initial charge completion signal generation circuit. 3. The charging control circuit for a capacitor-type spot welding machine according to claim 2, further comprising a circuit that charges a capacitor with a constant current based on the duration of the timer circuit. 4. The pulse generation circuit includes a transistor whose emitter is connected to a common potential point and a load is connected between the collector and a power supply, a diode and a resistor connected to the base and emitter of this transistor, and the transistor. A resistor and a Zener diode connected between the base and the power supply and connected in series with each other, a connection point between these resistors and the Zener diode, a resistor and a capacitor connected between the power supply and connected in series with each other, 4. The charging control circuit for a capacitor-type spot welding machine according to claim 2 or 3, characterized in that it is comprised of a switching element connected to a connection point between the resistor and the capacitor and a common potential point.