JPH0898562A - Control device of resistance welding machine - Google Patents

Abstract

PURPOSE: To obtain a control device by which the erosion of an electrode is reduced by using an AC welding current, which enhances a current control characteristic and by which a high quality welding operation is performed. CONSTITUTION: An inverter 4 by which a DC voltage is converted into a square wave AC voltage to supply to the primary side of a transformer and by which an AC welding current is supplied from the secondary side, control parts 32 to 34 in which a current criterion is compared with the output current of the inverter 4 and by which control signal to reduce its error are output, pulse width modulation parts 35 to 38 by which continuity PWM signals are output at a constant modulation cycle and by which noncontinuity PWM signals are output according to the control signals, square wave generation parts 27, 28 which output square wave signals to decide the polarity and the frequency of the square wave AC voltage and drive parts 39 to 41 which drive the inverter 4 according to the PWM signals and the square wave signals are installed in a control device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding machine controller.

[0002]

2. Description of the Related Art Some control devices for resistance welding machines use an inverter, and a conventional device of this type is shown in FIG. The AC voltage of the AC power supply 1 is converted to DC by the rectifier 2, smoothed by the capacitor 3, and then converted to high-frequency AC of about 1 kHz by the inverter 4 composed of IGBTs (switch elements) 41 to 44, and transformed. After converting to a low AC voltage by the converter 5, it is converted to DC by the rectifier 7 and the welding electrode 9
DC welding current is supplied to. A stray inductance 8 is present in the wiring portion to the welding electrode and effectively acts to smooth the DC welding current.

The magnitude of the welding current is controlled by the current reference I ^* . That is, the welding current detects the primary current of the transformer 5 through the current transformer 6, and then simulates the DC welding current in the welding current simulator circuit 12 (the primary side of the transformer 5 has an internal rectifier of the welding current). The reflux current of 7 does not flow)
The current controller 13 outputs the current control signal a so as to reduce the error compared with the current reference I ^* . This signal a is compared with the triangular wave b output from the carrier generator 14 in the comparator 15, and becomes the PWM signal c. The carrier generator 14 outputs a signal d synchronized with the cycle of the triangular wave b, and the distribution circuit 16 activates one of the output signals e and f according to the signal d. This will drive the drive circuit through AND circuits 17 and 18.
The PWM signal c is alternately applied to 21 and 22.

On the other hand, when the drive signal g is input from the start-up circuit 19, the timer-20 operates and the energizing signal h is output only for the set time, and the drive circuits 21 and 22 are put into the operating state so that the switching signals j and k are changed. Alternately output, IGBT ₄₁ , I
Guru of GBT ₄₄ - flops and IGBT _43, IGBT ₄₂ of the guru -
Turns on alternately and a high-frequency AC voltage is applied to the primary side of the transformer 5, and the welding current and welding time are controlled.

[0005]

In the above-mentioned conventional device, the response of the current control is fast, the ripple of the current is small, and the inverter frequency is high, so that there is an advantage that the transformer can be miniaturized. However, because a welding current of direct current is applied, the welding electrode is subject to severe wear due to the electrolysis action, and when the welding process is robotized, frequent electrode replacement is required, so the line must be temporarily stopped and the operating rate decreases. It is a factor.

Further, a power loss of 10% to 20% occurs in the rectifier 7 for rectifying a current of tens of thousands of amperes, and the power loss occurs correspondingly, which causes a problem such as an increase in the amount of cooling water. The present invention has been made to solve the above problems, and an object thereof is to supply an alternating square-wave welding current to reduce wear of the welding electrode to improve the operating rate and reduce power loss. To improve efficiency, reduce fluctuations in heat generated when the polarity of welding current is reversed, improve welding quality, and reduce the ripple of welding current. To provide.

[0007]

According to the invention of claim 1,
Comparing the output current of the inverter with a current reference, which is an inverter that converts a DC voltage into a square wave AC voltage and supplies it to the primary side of the transformer and supplies an AC welding current from the secondary side. A control unit for outputting a control signal for reducing the error,
While outputting a PWM signal of conduction at a constant modulation cycle,
A pulse width modulator that outputs a non-conducting PWM signal according to the result of comparison between the control signal and the output current of the inverter, and a square wave signal that determines the polarity and frequency of the square wave AC voltage. A square wave generator and a driver for controlling the inverter according to the PWM signal and the square wave signal are provided.

According to a second aspect of the present invention, in the inverter, two switch elements each having a diode connected in anti-parallel are connected in series between the positive and negative sides of a DC voltage source, and an intermediate point thereof is an AC. It is composed of two sets of half bridge circuits as output terminals, and the drive section is configured so that one switching element of one half bridge circuit and the other switching element of the other half bridge circuit according to the PWM signal of conduction. Is turned on to output a voltage having a polarity corresponding to the square wave signal, and only one switch element of one half bridge circuit is made non-conductive according to the non-conductive PWM signal, and one half bridge is connected. The current flowing in the transformer is circulated through the diode connected in anti-parallel to the other switching element of the circuit.

According to a third aspect of the present invention, the current control section further integrates an error between the current reference of the amount of direct current and the absolute value of the output current of the inverter detected through the current detector. An integrator is provided, and a value obtained by adding the output of the integrator to the current reference is output as the control signal.

According to a fourth aspect of the present invention, the pulse width modulation section further includes a pulse generation section that outputs pulses at a constant modulation cycle, and a function generation section that outputs a sawtooth wave dither signal synchronized with the modulation cycle. And a PWM signal that is conductive when the pulse is generated, and a PWM signal that is non-conductive according to a difference value between the control signal and a value obtained by adding a dither signal to the output current of the inverter. And a signal holding unit for

According to a fifth aspect of the present invention, a reactor connected in parallel with the primary side of the transformer and having a characteristic close to the saturation characteristic of the magnetic flux density of the transformer, and an exciting current flowing through the reactor are detected. A current reference correction unit that outputs as a correction signal is provided, and the correction signal is added to the current reference to correct the current reference.

According to a sixth aspect of the present invention, the configuration of the third aspect further includes an arithmetic unit for obtaining an effective value of the output current of the inverter, and an amplifier for amplifying an error between the current reference and the effective value. , The output of the amplifier is added to the current reference to correct the current reference.

According to a seventh aspect of the present invention, in the configuration of the second aspect, the drive unit is further brought into a conducting state by a conducting PWM signal immediately before the square wave signal for a predetermined period from the time when the square wave signal changes. Of the half bridge circuit and the other switch element of the one half bridge circuit are provided with a polarity switching control unit for circulating a current flowing through the transformer through a diode connected in anti-parallel.

According to an eighth aspect of the present invention, in the configuration of the fourth aspect, the pulse width modulation section outputs a conduction PWM signal which is set by the pulse output from the pulse generation section, and the conduction PWM. A comparator, the output of which is reset to a predetermined value by a signal, and a differentiation circuit having a time constant longer than the modulation period, which outputs a sawtooth dither signal by resetting the output of the comparator to a predetermined value, are provided. , The output of the comparator is set according to the difference value between the control signal and the value obtained by adding the dither signal to the output current of the inverter, and the flip-flop is reset to output a non-conducting PWM signal. .

[0015]

According to the first aspect of the invention, the square wave generating section outputs a square wave signal having a binary state of a predetermined frequency. The current control unit outputs a current control signal that changes according to an error between the current reference and the output current of the inverter. The pulse width modulator outputs a PWM signal that is conductive at a constant modulation cycle, and outputs a PWM signal that is non-conductive within the modulation cycle according to the current control signal. The drive unit controls the inverter according to the PWM signal and the square wave signal, and supplies a square wave AC welding current.

In a second aspect of the present invention, the drive section of one of the half bridge circuits outputs the voltage having the polarity corresponding to the value of the square wave signal when the PWM signal for conduction is applied. When the switch element and the other switch element of the other half bridge circuit are made conductive and a non-conducting PWM signal is given, only one switch element of the one half bridge circuit is made non-conductive and the one half bridge circuit is made non-conductive. A thyroid connected in anti-parallel to the other switching element of the bridge circuit.
The current flowing to the primary side of the transformer is circulated through the switch and the other switching element of the other half bridge circuit.

In the invention of claim 3, the current control section is
The integrator integrates the error between the current reference of the DC amount and the absolute value of the output current of the inverter detected through the current detector, and outputs a signal whose change rate changes according to the error value. ,
This signal is added to the current reference and output as a current control signal.

In the invention of claim 4, the pulse width modulator outputs a pulse at a constant modulation cycle by the pulse generator, and the sawtooth wave pattern monotonically increases or decreases within the modulation cycle from the output time of the pulse by the function generator. The dither signal is output, and the signal holding unit outputs the PWM signal that is conductive at the time of outputting the pulse, and the PW that is non-conductive within the modulation cycle according to the difference value between the current control signal and the dither signal.
Output M signal.

In the invention of claim 5, the exciting current flowing in the reactor simulates the exciting current flowing in the primary side of the transformer, and the current reference correction section detects the exciting current flowing in the reactor and outputs it as a correction signal. Correct the current reference by adding it to the current reference.

In the invention of claim 6, the arithmetic unit outputs the effective value of the output current of the inverter, the amplifier amplifies the error between the current reference and the effective value, and adds the output to the current reference for correction. Get the current reference that you made.

According to another aspect of the invention, when the polarity switching control unit changes the value of the square wave signal, the drive unit is made conductive by the immediately preceding PWM signal for a predetermined period from that time. The other switching element of the half bridge circuit and the other switching element of the one half bridge circuit are caused to flow back the current flowing to the primary side of the transformer through the diode connected in anti-parallel, and the predetermined period has elapsed. At that time, the inverter is controlled so as to output a voltage having a polarity corresponding to the value of the square wave signal.

In the invention of claim 8, when the output of the comparator is reset to a predetermined value by the PWM signal of conduction,
A sawtooth dither signal monotonically decreasing with the time constant of the differentiating circuit is obtained, and this dither signal acts so as to be added to the output current of the inverter. The control signal and the inverter
The comparator operates according to the difference value between the output current of the inverter and the value obtained by adding the dither signal. When the output is set and changed, the flip-flop is reset and the non-conducting PWM signal is output.

[0023]

FIG. 1 shows an embodiment corresponding to claims 1 to 5 of the present invention. In FIG. 1, 23 is a small capacity reactor simulating the exciting current of the transformer 5, and the magnetic flux saturation characteristic of the iron core is approximated to the characteristic of the transformer 5. 24 is a current transformer, 25 is a level detector that outputs a signal s ₁ when the absolute value of the exciting current i ₀ flowing in the reactor 23 exceeds a predetermined value, and 26 is a polarity signal that determines the polarity of the exciting current i _0. POL output polarity detector, 27 includes a constant frequency clock pulse generator, outputs a pulse signal s ₂ each time a constant clock pulse is counted while the energization signal h is active, and clears and counts to zero. The pulse signal s ₂ is forcibly output by the signal s ₁ and is cleared to zero by the signal s ₁ , and is preset to a predetermined count number by the signal s ₄ . 28 is a pulse signal s ₂ while the energization signal h is active.
Is a square wave circuit that inverts the value of binary (1,0) every time is input and outputs a binary square wave signal s ₃ of a predetermined frequency.
The value of the square wave to be output first is determined by the signal s ₅ from the preset circuit. 29 is a latch circuit, which is a polarity signal PO at that time when the energizing signal h becomes inactive.
Hold L. A preset circuit 30 outputs signals s ₄ and s ₅ for initializing the counter 27 and the square wave circuit 28 according to the value of the polarity signal POL held in the latch circuit 29. Reference numeral 31 is a compensation circuit that outputs a compensation signal i _01, which is the polarity of the input signal i ₀ inverted according to the value of the square wave signal s ₃ , and 32 is compensated by adding the (welding) current reference I ^* and the compensation signal i _01. The adder for outputting the current reference I ₁ ^* (output of the inverter), 33 is the absolute value of the output current i ₁ of the inverter detected via the current reference I ₁ ^* and the current detector 11. An integrator that integrates the error from i _1d and outputs the control signal a, 34 is an adder that adds the current reference I ₁ ^* and the control signal a and outputs the current control signal b, and 35 is a constant modulation cycle. A pulse generator that outputs a pulse signal c and a rectangular-wave-shaped synchronizing signal d with a duty of 50%, and 36 outputs a sawtooth-shaped dither signal e that monotonically increases within the modulation cycle in synchronization with the synchronizing signal d. dither circuit, 37 is a control signal b and the inverter - plus dither signal e in absolute body value i _1d of data of the output current And a comparator that outputs a pulse signal f when the polarity of the difference value is inverted, 38 outputs a PWM signal j that is set and conductive with the pulse signal c, and is reset with the pulse signal f and is non-conductive. A flip-flop 39 that outputs the PWM signal j, and 39 is a distribution circuit that outputs the signals k and l that control the drive circuits 40 and 41 to control the inverter 4 according to the square wave signal s ₃ and the PWM signal j. is there. Others are the same as the conventional ones and are indicated by the same symbols.

The actions of the level detector 25, the polarity detector 26, the counter 27, the square wave circuit 28, the latch circuit 29, and the preset circuit 30 have been previously proposed (Japanese Patent Application No. 6-14372).
9) See the description for details. Here, parts related to the operation of the present invention will be described.

In the above structure, when the activation signal g for starting energization is input from the activation circuit 19, the timer 20 activates the energization signal h for the set welding time. As a result, the counter 27 starts counting internal clock pulses, outputs the pulse signal s ₂ at a predetermined cycle, and outputs the pulse signal s ₂
Is input, the square wave circuit 28 inverts the binary value and outputs a square wave signal s ₃ . The value of the square wave signal s ₃ acts as a signal that determines the polarity of the AC output voltage of the inverter 4, and the distribution circuit 39 operates according to the value of the square wave signal s _3.
The control signal k, l for turning on the corresponding switch element of the switch 4 is output. The functions of the drive circuits 40 and 41 are valid while the energization signal h is active, and the corresponding switch elements are made conductive in accordance with the control signals k and l, and the inverter 4 corresponds to the value of the square wave signal s _3. The voltage v ₁ having the above polarity is output, and the current i ₁ is supplied to the primary side of the transformer 5.

On the other hand, the pulse generator 35 has a constant modulation period T
_The pulse signal c is output at ₁ and the flip-flop 38
Outputs a PWM signal of conduction set by the pulse signal c, and its absolute value signal i _1d detected by the current detector 11 when the output current i ₁ of the inverter increases, i _1d
When the target value is increased, the pulse signal f is output from the comparator 37, the flip-flop 38 is reset and the non-conducting PWM signal j is output, and the power supply from the inverter 4 is stopped. As a result, the current i ₁ on the primary side of the transformer 5 starts to decrease. The flip-flop 38 is set at each modulation cycle and returns the inverter 4 to the original conductive state, so that so-called PWM control by so-called instantaneous value control is performed as shown in FIG.

When the target value of the welding current is given as the current reference I ^* , the target value of the output current i ₁ of the inverter is determined by the signal b output from the adder 34. That is, the current reference I ₁ ^{* obtained} by adding the compensation signal i ₀₁ output from the compensation circuit 31 to the primary side current reference I ^* corresponding to the welding current and compensating for the exciting current of the transformer 5 is added from the adder 32. Is output. Further, the integrator 33 outputs a signal a obtained by integrating the error between the current reference I ₁ ^* and the absolute value i _1d of the output current of the inverter, and the adder 34 outputs the current reference I ₁ ^* and the signal a. Is added and output as the target value of the output current i ₁ of the inverter.

The square wave signal s ₃ and the PWM signal j distributed according to the circuit 39, inverter as shown in FIG. 2 (a) - by controlling the switch elements of the motor 4 41-44, the square wave signal s ₃ When is 1, the switch elements 41 and 44 are operated and the positive voltage level v
_{When 1} is output and the square wave signal s ₃ is 0, the switch element 4
3 and 42 are operated to output the negative voltage v ₁ . Also, P
When the WM signal j is the conduction command (1), t ₁ -t ₂ , t ₃
-T ₄ or t ₆ -t ₇ , t ₈ -t ₉
Both switch elements 41 and 44 or 43 and 42 are made conductive,
When the PWM signal j is the non-conduction command (0), t ₂ −t ₃ ,
t ₄ - ₅ or t ₇ -t _8, t ₉ switching element 41 as shown in -t ₁₀ and 44 or 43 and 42 one of the switching element only to the non-conductive alternately. By performing the switching control in this way, when the PWM signal j is a non-conduction command, the current i ₁ flowing in the primary side of the transformer 5 is not regenerated to the DC power supply side and is recirculated through the inverter 4, The decrease of i ₁ is reduced and the ripple can be reduced, and the switching frequency of the switch element is equivalently 1
It can be / 2. When the square wave signal s ₃ changes from 1 to 0, the switch element 42 is conducted with a delay of several μs called dead time so that a DC short circuit does not occur due to an operation delay of the switch element 44. However, if switching control is performed in this way,
When the output current i ₁ of the controller reaches the target value and flows steadily, the fluctuation range of the deviation value between the signals b and i _1d becomes small, and as shown in FIG. vessel
The judgment time of 37 is affected by t _2A and t _2B , and PWM
The pulse width of the signal j may change significantly and the output current i ₁ of the inverter may become unstable. In this embodiment, the dither circuit 36 is provided in order to reduce the influence of this noise. The dither circuit 36 outputs a sawtooth-shaped dither signal e as shown in FIG. 2 (c) by the signal d output in synchronization with the modulation period T ₁ , and the comparator 37 outputs this signal e. In addition to the absolute value i _1d of the output current of the above, it acts to compare with the signal b. As a result, the apparent deviation value at a time point away from the target time point t ₂ at which the PWM signal j is made non-conductive is enlarged, and the influence of noise can be mitigated as t _2A and t _2B . The error between the current reference I ₁ ^* caused by the introduction of the dither signal e and the absolute value i _1d of the output current of the inverter is compensated by the signal a output from the integrator 33.

The inverter 4 outputs an AC voltage v ₁ as shown in FIG. 3 according to the period T ₂ of the square wave signal s ₃ and applies it to the primary side of the transformer 5 to generate an AC voltage from the secondary side. A square wave welding current i ₂ is supplied. On the primary side of the transformer 5, a current corresponding to the welding current i ₂ and a current i _{1 which} is the sum of the exciting current of the transformer 5 flow. An exciting current i ₀ similar to the exciting current of the transformer 5 flows through the reactor 23. The exciting current i ₀ of the reactor 23 detected through the current transformer 24 is generated by the compensating circuit 31 in accordance with the value of the square wave signal s ₃ to generate the compensating signal i ₀₁ whose polarity is inverted every half cycle, and the welding current i ₀ is generated. Is added to the current reference I ^* that determines the output current i ₁ of the inverter to become the current reference I ₁ ^* .

When the welding current i ₂ is large (close to 100%), the exciting current of the transformer 5 can be ignored, but when the welding current is small (20% or less), the exciting current of the transformer 5 becomes the welding current. On the other hand, the error becomes large by 5 to 10% or more, but according to the present embodiment, it is possible to eliminate this error and supply the welding current with high accuracy.

The integrator 33 also serves to compensate for the decrease in welding power during the transitional period when the polarity of the welding current i ₂ is reversed.
That is, when the integrator 33 is not provided, as shown in FIG. 4A, in the transition period T ₃ when the polarity is reversed, the welding current i
₂ changes at a predetermined current change rate determined by the circuit constant, and is controlled to be constant when the target welding current is reached. Accordingly, the welding power P (i ₂ squared) is reduced by the shaded portion of the transition period T ₃ , and the temperature of the welded portion is reduced. When the integrator 33 is provided, the welding current i ₂ is overshot for the period T ₄ immediately after the transient period T ₃ as shown in FIG. 4B.
And stabilizes at a constant value. The effect of this overshoot is that the current reference I ₁ ^* and the inverter during the transient period T ₃
This is done by integrating the error of the output current of the controller with the absolute value i _1d by the integrator 33 and adding the integrated value (signal a) to the current reference I ₁ ^* . As a result, the amount of decrease in the welding power P in the period T ₃ is immediately compensated for in the period T ₄ , and the temperature decrease of the welded portion can be recovered early.

An embodiment corresponding to claim 6 of the present invention is shown in FIG.
Shown in. In this embodiment, the effective value calculation circuit 51 calculates the effective value i _rms of the output current of the inverter from the output current i ₀₁ of the inverter detected by the current detector 11 to obtain the welding current reference I ^*. The difference between the effective value i _rms and the effective value i _rms is amplified by the amplifier 52 and added to I ^* to be used as the reference I ₁ ^* of the output current of the inverter. According to this embodiment, it is possible to compensate the decrease in the effective value during the transitional period when the polarity of the welding current is reversed, and to control the heat generation amount of the welded portion to be constant.

An embodiment corresponding to claim 7 of the present invention is shown in FIG.
(A). In this embodiment, a device is added to reduce the magnetic flux density of the transformer 5 after the polarity reversal in the transition period in which the polarity of the welding current is reversed. That is, to output the pulse signal P of the square wave signal s ₃ values one-shot circuit 45 from a predetermined width every time changes (T _5), a predetermined time period from the square wave signal s ₃ from the delay circuit 46 by the signal P ( While outputting a square wave signal s _3A that changes with a delay of T ₅ ),
PWM of non-conducting by closing the gate of AND circuit 47
Generate a signal. As a result, the distribution circuit 39 operates in the zero voltage output mode (the primary side current of the transformer 5 is the inverter when the value of the square wave signal s _{3 is} the value before the change of the value of the square wave signal s ₃ (the value of 1 in the figure) between t _{1 and} t ₂ . -The state in which the current flows through the inverter) is controlled so that the output voltage of the inverter 5 becomes zero voltage as shown in v ₁ (2) of Fig. 6 (b). Become. When the pulse signal P disappears at time t ₂ , the square wave signal s _3A output from the delay circuit 46 changes to the same value as the normal square wave signal s ₃ (state 0 in the figure), and the gate of the AND circuit 47 Is opened and the normal PWM signal j is output.
39 performs normal switching control. Therefore, the Inver
As shown in v ₁ (2), the output voltage of the output signal of the output signal of the input signal 4 is a negative voltage corresponding to the value of the square wave signal s _3A and reaches the target value t.
It is constant at a value that supplies the welding current after outputting the forcing voltage between _{2 and} t ₄ . For comparison, when inverting the polarity of the output voltage, the output voltage and welding current without the zero-voltage output mode are v ₁ (1) and i ₂ (1).
It was shown to.

According to this embodiment, the time for the welding current i ₂ (2) to reverse is slightly longer, but the time product of the voltage applied to the transformer 5 is zero between t _{1 and} t _2, and t _{1 to} t ₄
It becomes small when comparing between. This indicates that the magnetic flux density is low and that the transformer 5 can be miniaturized.

An embodiment corresponding to claim 8 of the present invention is shown in FIG.
(A). This embodiment simplifies the generation of the dither signal. That is, when the conduction PWM signal j is output, the bias amount applied to the input of the comparator 37 via the inverting circuit 63 and the resistor 62 is set to zero, and the output n of the comparator 37 is set to a predetermined value (in FIG. 7). Reset to high level).
When the output n changes to high level, the capacitor 64,
A displacement current flows through a differentiation circuit composed of resistors 65 and 66 to obtain a saw-toothed dither signal e. This dither signal e is applied to the in-phase input terminal of the comparator 37, and as a result, it is added to the absolute value i _1d of the output current of the inverter. Then, when the output n of the comparator 37 changes to a low level (-15 V) due to the difference value between the control signal b and the output current i _1d of the inverter plus the dither signal e, the flip-flop is provided via the inverting circuit 68. 38 is reset, the non-conducting PWM signal j is output, the bias amount is again applied to the comparator 37, and the capacitor 64 is charged with the voltage of the polarity shown.

[0036]

According to the present invention, since an alternating square-wave welding current is supplied, wear of the welding electrode is reduced and the frequency of electrode replacement is reduced, so that the operating rate can be improved. Further, it is possible to improve the response characteristics of the current control, improve the noise resistance characteristics, and reduce the ripple of the welding current. In addition, it is possible to compensate for the decrease in the temperature of the welded part when the polarity of the welding current is reversed, as well as to compensate the exciting current of the transformer, and it is possible to supply a highly accurate welding current and Good welding can be done. Further, it is possible to provide a control device for a resistance welding machine that can improve the magnetic flux utilization rate of the transformer and reduce the size thereof.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment corresponding to claims 1 to 5.

FIG. 2 is a waveform diagram for explaining the operation of the above embodiment.

FIG. 3 is a waveform diagram for explaining the function of the excitation current compensation of the above embodiment.

FIG. 4 is a waveform diagram for explaining the operation of the integrator 33 of the above embodiment.

FIG. 5 is a configuration diagram of essential parts of an embodiment corresponding to claim 6;

FIG. 6 is an embodiment corresponding to claim 7, (a) is a main part configuration diagram, and (b) is a waveform diagram.

FIG. 7 is an embodiment corresponding to claim 8, (a) is a configuration diagram of a main part, and (b) is a waveform diagram.

FIG. 8 is a block diagram of a conventional device

[Explanation of symbols]

1 ... AC power supply 2 ... Rectifier 3 ... Capacitor 4 ... Inverter 5 ... Transformer 6 ... Current transformer 8 ... Stray inductance 9 ... Welding electrode
11 ... Current detector 19 ... Starting circuit 20 ... Timer-23 ... Reactor 24 ... Current transformer 25 ... Level detector 26 ... Polarity detector 27 ... Counter 28 ... Square wave circuit 29 ... Latch circuit
30 ... Preset circuit 31 ... Compensation circuit 32, 34 ... Adder
33 ... Integrator 35 ... Pulse generator 36 ... Dither circuit 37
Comparator 38 Flip-flop 39 Distribution circuit 40
41 ... Drive circuit 45 ... One-shot circuit 46 ... Delay circuit
47 ... AND circuit 51 ... RMS value calculation circuit 52 ... Amplifier 60
~ 62, 65, 66, 69 ... Resistor 63, 68 ... Inversion circuit 64 ... Capacitor 67 ... Diode

Claims (8)

[Claims] 1. An inverter for converting a DC voltage into a square wave AC voltage and supplying it to the primary side of a transformer and supplying an AC welding current from the secondary side, a current reference and the output of the inverter. A control unit for comparing currents and outputting a control signal for reducing the error, and outputting a conduction PWM signal at a constant modulation cycle, and depending on the comparison result of the control signal and the output current of the inverter. A pulse width modulator that outputs a non-conducting PWM signal, and a square wave generator that outputs a square wave signal that determines the polarity and frequency of the square wave AC voltage.
A controller for a resistance welding machine, comprising a drive unit for controlling the inverter according to the PWM signal and the square wave signal. 2. The control device for a resistance welding machine according to claim 1, wherein the inverter has two switch elements, each of which has diodes connected in antiparallel, connected in series between positive and negative of a DC voltage source. However, it is composed of two sets of half bridge circuits having an AC output terminal at an intermediate point thereof, and the drive section responds to the PWM signal of the conduction, one switch element of one half bridge circuit and the other half bridge circuit. The other switch element of the half bridge circuit is turned on to output a voltage having a polarity corresponding to the square wave signal, and only one switch element of the one half bridge circuit is turned off according to the non-conducting PWM signal. A control device for a resistance welding machine, characterized in that a current flowing in a transformer is circulated through a diode connected in anti-parallel to the other switching element of one half bridge circuit. 3. The control device for the resistance welding machine according to claim 1, wherein the control unit has an absolute value of an output current of the inverter detected through a current reference of a direct current amount and a current detector. A controller for a resistance welding machine, comprising: an integrator that integrates an error between and, and outputting a value obtained by adding the output of the integrator to the current reference as the control signal. 4. The resistance welding machine control device according to claim 1, wherein the pulse width modulation section outputs a pulse at a constant modulation cycle, and a sawtooth wave dither synchronized with the modulation cycle. A function generator that outputs a signal,
A PWM signal for conduction is output when the pulse is generated, and a PWM signal for non-conduction is output according to a difference value between the control signal and a value obtained by adding a dither signal to the output current of the inverter.
A control device for a resistance welding machine, comprising a signal holding section for outputting a signal. 5. The control device for the resistance welding machine according to claim 1, further comprising a parallel connection to the primary side of the transformer,
A reactor having a characteristic close to the saturation characteristic of the magnetic flux density of the transformer, and a current reference correction unit that detects the exciting current flowing in this reactor and outputs it as a correction signal are added, and this correction signal is added to the current reference. A controller for a resistance welding machine characterized by correcting a current reference. 6. The resistance welding machine control device according to claim 3, further comprising: an arithmetic unit for obtaining an effective value of the output current of the inverter, and an amplifier for amplifying an error between the current reference and the effective value. The resistance welding machine control device is characterized in that the current reference is corrected by adding the output of the amplifier to the current reference. 7. The control device for the resistance welding machine according to claim 2, wherein the drive section is further brought into a conduction state by a conduction PWM signal immediately before the square wave signal changes for a predetermined period. A polarity switching control unit is provided to recirculate the current flowing through the transformer through the diode connected in anti-parallel to the other switching element of the other half bridge circuit and the other switching element of the one half bridge circuit. A control device for a resistance welding machine, which is characterized in that 8. The control device for the resistance welding machine according to claim 4, wherein the pulse width modulation section includes a flip-flop that outputs a PWM signal for conduction set by a pulse output from a pulse generation section, and the conduction. And a differentiating circuit having a time constant longer than the modulation period for outputting a sawtooth-shaped dither signal by resetting the output of the comparator to a predetermined value. The output of the comparator is set according to a difference value between the control signal and a value obtained by adding the dither signal to the output current of the inverter, and the flip-flop is reset to output a non-conducting PWM signal. A resistance welding machine control device characterized by outputting.