JPH07136776A - Inverter type resistance welding method and equipment therefor - Google Patents

Abstract

PURPOSE:To effectively suppress biased manetization and to prevent breakdown of a circuit element, etc., by outputting a biased magnetization detection signal by a determination part when comparative erroneous angles given in order from a comparison part exceed an erroneous angle threshold value from a setting circuit. CONSTITUTION:The comparison part 56 compares monitoring vectors IM1, IM2, IM3... in order with a reference vector IS and the comparative erroneous angles theta1, theta2, theta3... are generated in order. The determination part 58 determines in order whether or not the comparative erroneous angles theta1, theta2, theta3... given in order from the comparison part 56 exceed the erroneous angle threshold value thetaM from the setting circuit and when these angles exceed the threshold value, the biased magnetization detection signal MD is outputted. When the biased magnetization detection signal MD is outputted from the determination part 58, an inverter control circuit brings down an inverter control pulse at a point of that time. Consequently, since a primary current is suppressed before sufficiently increasing in an exponential function, this does not exceed a limitter value and the threshold value and there is no fear that a switching element, etc., in the inverter circuit are broken down.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type resistance welding control method and apparatus for automatically suppressing a magnetic bias phenomenon in a welding transformer of an inverter type resistance welding machine.

[0002]

2. Description of the Related Art Inverter-type resistance welding machines have the advantage that the cross-sectional area of the core of the welding transformer can be reduced and the size and weight of the transformer can be reduced because the frequency of the alternating current flowing through the welding transformer is high. is there. However, if the welding transformer is reduced in size and weight, a phenomenon of magnetic saturation depending on one of the positive and negative polarities, that is, a so-called magnetic bias phenomenon is likely to occur. If the current continues to flow as it is when the demagnetization phenomenon has occurred, it becomes as if a direct current component had been superimposed on the welding transformer, causing an excessive primary current due to residual saturation that has accumulated and causing a switching element in the inverter. It is extremely dangerous as it burns out etc.

Therefore, conventionally, the limiter function of the inverter controller is used to set the primary current of the welding transformer to a set value (limiter value) lower than the maximum allowable current value (limit value) of the switching element or the like by a predetermined value. When it reached, control was performed such that the inverter control pulse was made to fall (cut).

[0004]

However, in general, there is some time delay (primary current delay) from the fall of the inverter control pulse in the inverter control unit to the fall of the primary current pulse in the inverter resistance welding machine. There is. Therefore, in the case where the demagnetization phenomenon occurs, as shown in FIG. 6, even if the inverter control pulse falls at the time point te when the limiter value IL is reached, the inverter type resistance welding machine will experience the time delay (primary current delay). During the period ()), the primary current I1 exponentially increases exponentially and exceeds the limit value IL as well as the limit value Iu in a moment, and there is a possibility that the switching element or the like is destroyed.

In order to avoid such a problem, conventionally, as shown in FIG. 7, the limiter value is lowered to a value IL 'considerably lower than the original set value IL, in consideration of the primary current delay. Adjustments are made to accelerate the time from the occurrence of magnetic bias until the primary current I1 reaches the limiter value IL '. However, if such an adjustment is performed, the pulse width is limited by the lower limiter value IL 'even for a normal primary current pulse without a magnetic bias phenomenon, as indicated by a broken line I1' in FIG. There was a new problem that the maximum effective value of the welding current or welding power that could be supplied to the engine was limited.

The present invention has been made in view of the above-mentioned conventional problems, and effectively suppresses the magnetic bias without limiting the maximum possible pulse width of the normal primary current pulse without the magnetic bias phenomenon. It is an object of the present invention to provide an inverter type resistance welding control method and device which surely prevent destruction of elements and the like.

[0007]

In order to achieve the above-mentioned object, an inverter type resistance welding control method of the present invention rectifies a commercial alternating current into a direct current, and the direct current is converted into a pulsed high frequency alternating current of a predetermined frequency by an inverter. In the inverter resistance welding control method, wherein the high-frequency alternating current is passed through a welding transformer and then made into a direct current again through a rectifier, and this direct current is supplied to the material to be welded via a welding electrode,
A first step of detecting the primary current of the welding transformer; and a vector of a rate of change or an average rate of change of the primary current at a predetermined reference point or reference section in the first half or the middle of each pulse of the primary current. A second step for obtaining a vector, a third step for obtaining a vector of the rate of change of the primary current as a monitoring vector at predetermined time intervals after the reference point or the reference section, and the monitoring vector successively for the reference vector And a fourth step of determining whether or not the comparison error exceeds a predetermined value, and a fifth step of controlling the fall of each pulse of the primary current according to the determination result of the fourth step. And a step.

In order to achieve the above object, the inverter resistance welding control apparatus of the present invention rectifies commercial alternating current into direct current, and converts the direct current into pulsed high frequency alternating current of a predetermined frequency by an inverter, After passing the high-frequency alternating current through the welding transformer and then through the rectifier to make it direct current again, in the inverter type resistance welding control device for supplying this direct current to the material to be welded through the welding electrode, the primary current of the welding transformer is Current detection means for detecting, and receiving the output signal of the current detection means, the vector of the rate of change of the primary current in a predetermined reference point or reference section of the first half or the middle part of each pulse of the primary current as a reference vector Then, the vector of the rate of change of the primary current is sequentially obtained as a monitoring vector at predetermined intervals after the reference point or the reference section. Sequential comparison of the monitoring vector with the reference vector, and a bias magnetic detection means for determining whether or not the comparison error exceeds a predetermined value, and each pulse of the primary current according to the determination result from the bias magnetic detection means. And an inverter control means for controlling the fall of the power supply.

According to the present invention, the reference vector is determined in the first half or the middle of each pulse of the primary current in every predetermined cycle, and thereafter, each portion in the pulse is sampled at every predetermined time interval and the change rate vector ( (Monitoring vector) is successively obtained, and each time the monitoring vector is obtained, it is compared with the reference vector, and it is determined whether or not the comparison error exceeds a predetermined value, thereby detecting the magnetic bias at the initial stage of its occurrence. . Immediately upon detection of a bias, the inverter control pulse is dropped and the primary current is suppressed before it exponentially increases sufficiently. As described above, since the vector (magnitude and direction) of the rate of change of each part in the primary current pulse is dynamically monitored to detect and suppress the magnetic bias, it is not necessary to rely on the limiter function. Therefore, the limiter value can be set to the original optimum value, and the maximum possible pulse width of the normal primary current pulse without the magnetic bias phenomenon can be maximized.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 shows a main configuration of an inverter type resistance welding machine system according to an embodiment of the present invention.

A rectifier circuit 1 is connected to a three-phase commercial AC power supply terminal 10.
Two input terminals are connected, and direct current is obtained at the output terminal of the rectifier circuit 12. This direct current is smoothed by a smoothing circuit including the coil 14 and the capacitor 16, and then input to the inverter circuit 18. This inverter circuit 18 is a GT
This is a well-known device that uses R or IGBT as a switching element, and converts the input direct current into a pulsed (rectangular wave) high frequency alternating current by a high frequency switching operation. The switching of the inverter circuit 18, and thus the pulse width of its high-frequency AC output, is controlled by an inverter control circuit 42 via an inverter drive circuit 40, as will be described later.

The high frequency alternating current output from the inverter circuit 18 is supplied to the primary side coil of the welding transformer 20, and the reduced high frequency alternating current is obtained in the secondary side coil thereof.
This high-frequency alternating current is converted into direct current by the rectifier circuit 24 composed of a pair of diodes 22a and 22b, and this direct current Iw is passed through the welding electrodes 26a and 26b to the material to be welded 28.
a, 28b.

The inverter control circuit 42 controls the pulse width of the high frequency AC output of the inverter circuit 18 by the pulse width modulation (PWM) method, and the timing circuit 46.
When a start signal ST is received from the frequency generator 44, a modulation wave, for example, a triangular wave signal SF having a constant frequency is input to generate a PWM signal SPWM, and this signal SPWM is used as an inverter control pulse to turn on each switching element of the inverter circuit 18.・ Off control.

The current detecting means in this embodiment includes a current sensor, for example, a toroidal coil or a current transformer 30, which is hung on a conductor (primary conductor) connecting the primary coil of the welding transformer 20 and the output terminal of the inverter circuit 18. A primary current detection circuit 32 for obtaining an instantaneous value of the primary current I1 based on the output signal of the current sensor 30. The primary current detection value [I1] obtained by the primary current detection circuit 32 is used as the limiter detection circuit 34 and the magnetic bias detection circuit 3
6 and given to.

The limiter detection circuit 34 has a well-known circuit configuration, and the primary current detection value [I1] from the primary current detection circuit 32 is changed to the limiter value [IL] from the setting circuit 38.
], The limiter detection signal LG is given to the inverter control circuit 42 when the former [I1] reaches the latter [IL] level.

The limiter value [IL] is a level at which a normal pulse width of an inverter output pulse can be selected up to a maximum value within a range that does not damage the switching element in the inverter circuit 18 regardless of suppression of the magnetic bias phenomenon. Is set to. In this embodiment, as will be described later, the welding transformer 20 is used.
Even if the demagnetization occurs, the demagnetization detection circuit 36 and the inverter control circuit 42 perform the pulse fall control early in the demagnetization initial stage. For this reason, the limiter function can be made independent from the suppression of the bias magnetism, and the limiter value can be set to the original optimum value.

The bias magnetism detection circuit 36 is a circuit for detecting whether or not a bias magnetism phenomenon is occurring in the welding transformer 20.
This is a feature of this embodiment. FIG. 2 shows a specific configuration example of the bias magnetic detection circuit 36. This bias magnetic detection circuit 36
Is composed of an absolute value circuit 50, a reference vector calculation unit 52, a monitor vector calculation unit 54, a comparison unit 56, and a determination unit 58.

The absolute value circuit 50 is a circuit for converting the primary current detection value [I1] from the primary current detection circuit 32 into an absolute value, whereby the negative polarity pulse of the primary current I1 is also converted (inverted) into a positive polarity pulse. Moreover, each pulse is subjected to the same arithmetic processing every half cycle. The primary current detection value [I1] that has been converted into an absolute value by the absolute value circuit 50 is input to the reference vector calculation unit 52 and the monitor vector calculation unit 54.

FIG. 3 shows a method of vector calculation processing in the reference vector calculation section 52 and the monitor vector calculation section 54. The reference vector calculation unit 52 calculates the vector (magnitude and direction) of the rate of change of [I1] at the time tb after the elapse of the predetermined time Tb from the rising time t0 of each pulse of the primary current I1, or the predetermined time Ta from the time t0. The vector (gradient) of the average change rate of [I1] in the section Tc between the time point ta after the lapse of time and the time point tb is obtained as the reference vector <Is>. Monitoring vector calculator 54
Is [I at every predetermined time interval ΔTP after the time tb.
1] is sampled at high speed, and the vector (gradient) of the rate of change of the primary current I1 at each sampling point is sequentially obtained as monitoring vectors <IM1>, <IM2>, <IM3>, ....

Referring again to FIG. 2, the reference vector calculation unit 5
2 from the reference vector <Is> and the monitoring vectors <IM1>, <IM2>, <IM3 from the monitoring vector calculator 54.
>, ... Are provided to the comparison unit 56.

The comparator 56 monitors the monitor vectors <IM1>, <IM1>
, IM2>, <IM3>, ... are successively compared with the reference vector <Is>, and comparison error angles <θ1>, <θ2>, <θ3>, ... Are sequentially generated. The determination unit 58 sequentially determines whether or not the comparison error angles <θ1>, <θ2>, <θ3>, ... Given by the comparison unit 56 exceed the error angle limit value <θM> from the setting circuit 38. However, when it exceeds, the bias detection signal M
Output D. When the eccentricity detection signal MD is output from the determination unit 58, the inverter control circuit 42 causes the inverter control pulse SPWM to fall at that time.

The clock signal CK from the timing circuit 46 is applied to each of the arithmetic units 52 to 58 of the above-described bias magnetic detection circuit 36. In addition, each part of the bias magnetic detection circuit 36,
It may be configured by a high speed arithmetic hardware circuit such as a DSP, or may be realized by software by a microcomputer.

FIGS. 4 and 5 show the operation of bias detection by the bias detection circuit 36. As described above, the primary current I1
For each pulse of each half cycle, the reference vector <Is> is determined at a predetermined reference point in the intermediate portion, that is, at a time tb after a lapse of a predetermined time Tb from the rising time t0. After the time point tb, the rate of change of the primary current I1 is monitored vectors <IM1>, <I at every predetermined time interval ΔTP.
M2>, <IM3>, ... Sequentially obtained, and the comparison error angles <θ1>, <θ2>, <of the monitor vectors <IM1>, <IM2>, <IM3>, ... And the reference vector <Is>. θ
3>, ... are successively obtained.

As shown in FIG. 4, when the demagnetization occurs, the inclination and absolute value of the monitor vector <IM1> increase,
As a result, the comparison error angle <θi> also increases. Then, as shown in FIG. 5, when the comparison error angle <θj> exceeds the error angle limit value <θM>, the bias magnetic detection signal M is detected at the time te.
D is generated, and in response to this, the inverter control pulse S
PWM is turned off. As a result, all the switching elements in the inverter circuit 18 are switched to the OFF state, but because of the primary current delay, the primary current I1 does not fall immediately at the control pulse falling time te, but once reaches the peak value IP. It increases and then falls. But,
The peak value IP does not reach the limiter value IL or the limit value IU.

In the present embodiment, in each pulse of the primary current I1, after the reference point (tb) at the intermediate portion, the vector (magnitude and direction) of the rate of change of each pulse portion is dynamically monitored at minute time intervals by high-speed sampling. When the demagnetization occurs, the demagnetization detection signal MD is generated at the initial stage, and the pulse fall control is performed early. As a result, the primary current I1 is suppressed before it exponentially increases sufficiently, so that it does not exceed the limiter value IL or the limit value IL, and there is no fear that the switching elements or the like in the inverter circuit 18 will be destroyed.

In this embodiment, since each pulse of the primary current I1 is monitored in the half cycle period, the same as above is applied not only when the magnetic field is biased but also when the magnetic saturation occurs in both polarities of the welding transformer 20. By this action, the primary current I1 is effectively suppressed, and the destruction of circuit elements and the like is prevented. When suppressing only the biased magnetic field in the narrow sense, each pulse of the primary current I1 may be monitored in one cycle period. That is, since the bias magnetism always occurs in the odd-numbered pulse in relation to the residual magnetism, the above-mentioned bias magnetism detection and suppression function may be activated only for the odd-numbered pulse.

Further, in the above-described embodiment, the determination unit 58 in the magnetic bias detection circuit 36 determines whether or not the comparison error angle θi from the comparison unit 56 exceeds the set error angle limit value θM. However, instead of using such a set value θM, the bias magnetic detection signal MD is generated at the time when the inclination of the monitor vector IMi reaches a predetermined ratio, for example, three times the inclination of the reference vector Is. It can also be configured.

Further, since the waveform of the primary current pulse always rises along a certain function, this rising function or the behavior of the rise is predicted, and the actual waveform of each primary current pulse is the rising function. Whether or not the vehicle is on or off is monitored, and when it is off, control may be performed such that the primary current pulse is made to fall just before the degree of deviation exceeds the limit value.

[0029]

As described above, according to the inverter type resistance welding control method or apparatus of the present invention, the vector of the rate of change in the middle portion or the latter half portion of the primary current pulse is dynamically monitored. Can be detected at an early stage, and pulse fall control can be performed early. In addition, since bias magnetism can be suppressed without relying on the limiter function, the limiter value can be set to the original optimum value, and the maximum possible pulse width of a normal primary current pulse without bias magnetism phenomenon can be maximized. .

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an inverter resistance welding machine system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific configuration example of a bias magnetic detection circuit in the embodiment.

FIG. 3 is a waveform diagram for explaining a method of vector calculation processing in the bias magnetic detection circuit in the example.

FIG. 4 is a waveform diagram for explaining the action of bias magnetic detection in the example.

FIG. 5 is a vector diagram for explaining an operation of bias magnetism detection in the embodiment.

FIG. 6 is a waveform diagram showing a demagnetization phenomenon.

FIG. 7 is a waveform diagram for explaining an operation when suppressing magnetic bias by a conventional limiter function.

[Explanation of symbols]

 18 Inverter circuit 20 Welding transformer 30 Current sensor 32 Primary current detection circuit 36 Deflection detection circuit 38 Setting circuit 42 Inverter control circuit

Claims (2)

[Claims] 1. A commercial alternating current is rectified into a direct current, the direct current is converted into a pulsed high frequency alternating current of a predetermined frequency by an inverter, the high frequency alternating current is passed through a welding transformer, and then passed through a rectifier to be converted back into a direct current. In a resistance welding control method of the inverter type adapted to supply the material to the material to be welded via a welding electrode, a first step of detecting a primary current of the welding transformer, and a first half portion or an intermediate portion of each pulse of the primary current. Second step of sequentially obtaining a vector of the rate of change or average rate of change of the primary current at a predetermined reference point or reference section as a reference vector, and the primary current at predetermined time intervals after the reference point or reference section. The step of sequentially obtaining the vector of the change rate of the monitoring vector as a monitoring vector, and the monitoring vector is sequentially compared with the reference vector. A fourth step of determining whether or not the comparison error exceeds a predetermined value, and a fifth step of controlling the fall of each pulse of the primary current according to the determination result of the fourth step, An inverter-type resistance welding control method comprising: 2. A commercial alternating current is rectified into a direct current, the direct current is converted into a pulsed high frequency alternating current of a predetermined frequency by an inverter, and the high frequency alternating current is passed through a welding transformer and then passed through a rectifier to be turned into a direct current again. In the resistance welding control device of the inverter type adapted to supply to the material to be welded via the welding electrode, current detection means for detecting the primary current of the welding transformer, and an output signal of the current detection means, the primary current The vector of the rate of change of the primary current at a predetermined reference point or reference section in the first half or the middle of each pulse is obtained as a reference vector, and the change of the primary current at predetermined intervals after the reference point or reference section. A rate vector is sequentially obtained as a monitoring vector, the monitoring vector is sequentially compared with the reference vector, and the comparison error is a predetermined value. Means leaving polarized 磁検 determines whether obtain, an inverter control unit for controlling the falling edge of each pulse of the polarized 磁検 out the primary current in accordance with the determination result from the means,
An inverter type resistance welding control device comprising: