JP2732154B2 - Inverter type resistance welding control method - Google Patents

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 for controlling the energization of resistance welding using an inverter.

[0002]

2. Description of the Related Art In a general inverter type resistance welding machine, constant current control in which feedback is performed so that a constant current flows through a work (material to be welded) is most often used. However, inverter-type resistance welding machines that deal with precision electronic components require constant-voltage control that applies feedback so that a constant voltage is applied to the work, and constant-power control that applies feedback so that constant power is supplied to the work. Often used. Regardless of which control method is used, the parameters to be controlled (current, voltage, or power)
After reaching the set value, the inverter is controlled so as to be fixed (maintained) at the set value until the end of energization.

[0003]

However, even if the constant current, the constant voltage, or the constant power is controlled by the feedback as described above, the generation of the splash cannot be avoided.
This is considered because the growth speed of the nugget was too rapid, and the molten metal exploded from the work. That is, when energization is performed and resistance heat is generated in the work (material to be welded),
A nugget is formed near the joint surface of the work, and this nugget grows gradually with the passage of the energization time. In some cases, the nugget grows too quickly, causing the above-mentioned splash.

The occurrence of such a splash not only impairs the quality of the work itself, but also deteriorates the working environment and causes environmental problems such as industrial waste. Therefore, the generation of the splash at the current resistance welding site is suppressed. That is urgent.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an inverter-type resistance welding control method capable of appropriately controlling the nugget growth rate to prevent the occurrence of splash. I do.

[0006]

In order to achieve the above object, a first control method according to the present invention is directed to an inverter-type resistance welding control method for performing constant current control, wherein the method comprises the steps of: The inverter is intermittently turned off so that the current flowing through the material is temporarily dropped at predetermined intervals.

In order to reliably prevent the occurrence of splash with the minimum necessary control and to obtain a good weld joint, in the first control method, the resistance value between the electrode tips sandwiching the workpiece is reduced. When the peak value is reached, the intermittent turning off of the inverter is started, and when the resistance value between the electrode chips drops from the peak value by a predetermined value, the energization is terminated.

According to a second control method of the present invention, in the inverter-type resistance welding control method for performing constant voltage control, the voltage applied to the material to be welded for a predetermined time within the energization time is temporarily set at a predetermined interval. The inverter was turned off intermittently so that it would fall into.

According to a third control method of the present invention, in the inverter-type resistance welding control method for performing constant power control, electric power supplied to the material to be welded for a predetermined time within the energization time is temporarily set at a predetermined interval. The inverter was turned off intermittently so that it would fall into.

[0010]

In the first control method, the inverter is turned off intermittently for a predetermined time under a constant current control to temporarily reduce the current flowing through the welding material at a predetermined interval, thereby increasing the nugget. Growth can be suppressed or adjusted and the growth rate of the nugget can be controlled.

[0011] Further, since the splash is likely to occur between the time when the resistance value between the electrode tips sandwiching the material to be welded reaches the peak value and the time when the energization is terminated, the intermittent turning off of the inverter during this period is required. By doing so, splash can be reliably prevented by controlling the minimum necessary time. Then, by stopping the energization at an optimal timing based on the change in the resistance value between the chips by the ΔR control method, an optimal nugget diameter is obtained, and a good metal bonding is obtained.

In the second control method, under constant voltage control,
By turning off the inverter intermittently for a predetermined time and temporarily dropping the voltage applied to the welding material at predetermined intervals, the expansion and growth of the nugget can be suppressed or adjusted, and the growth speed of the nugget can be controlled. can do.

In a third control method, under constant power control,
By turning off the inverter intermittently for a predetermined time and temporarily lowering the power supplied to the welding material at predetermined intervals, the expansion and growth of the nugget can be suppressed or adjusted, and the growth speed of the nugget can be controlled. can do.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a main circuit configuration of an inverter-type resistance welding system to which an embodiment of the present invention is applied, FIG. 2 is a block diagram showing a functional configuration of a CPU for constant current control, and FIGS. FIG. 6 is a waveform chart showing the operation of each embodiment.

In FIG. 1, a commercial three-phase alternating current (S, T,
U) is input to the three-phase full-wave rectifier circuit 10, and the DC voltage obtained at the output terminal of the rectifier circuit 10 is input to the inverter circuit 14 after being smoothed by the capacitor 12. This inverter circuit 14 has four transistors TR1 to TR
4 and transistors TR1 and TR3 according to the inverter drive signals Fa and Fb from the inverter drive circuit 72.
And the transistors TR2 and TR4 are alternately turned on and off at a predetermined frequency sufficiently higher than the commercial AC frequency, whereby a high-frequency AC rectangular wave pulse is obtained at the output terminals OUT0 and OUT1.

The high-frequency AC rectangular wave pulse output from the inverter circuit 14 is supplied to the primary coil of the welding transformer 16, and a low-voltage, large-current AC pulse is obtained in the secondary coil. This secondary side AC pulse is converted into a direct current by a rectifier circuit comprising a pair of diodes D1 and D2, and this direct current secondary current (welding current) I2 is applied to the electrode tips 20, 22.
Then, the heat flows through the works 24 and 26, and resistance heat is generated in the works 24 and 26.

In the system of this embodiment, the workpieces 24, 2
A toroidal coil 32 is provided in the secondary side circuit to detect the secondary current 12 supplied to 6, and an output terminal of the toroidal coil 32 is connected to an input terminal of the secondary current detection circuit 34. When the secondary current I2 flows in the secondary circuit, the secondary current I2 is output from the output terminal of the toroidal coil 32.
Is obtained. Secondary current detection circuit 3
Reference numeral 4 restores the waveform of the secondary current I2 by integrating the differentiated waveform signal, finds an instantaneous current measurement value Si from the waveform, and supplies the current measurement value Si to the CPU 40.

In order to detect the voltage applied to the works 24 and 26, the electrode tips 20 and 22 are connected to the voltage detection lines 2
8 and 28 are connected to the input terminal of the inter-chip voltage detection circuit 30. The chip-to-chip voltage detection circuit 30 amplifies the input voltage detection signal and converts it into an instantaneous voltage measurement value Sv.
Give to 0. Strictly speaking, the measured voltage value Sv is the work 2
This value represents the voltage drop of the conductor path obtained by adding the tips of the electrode tips 20 and 22 to the electrode tips 20 and 22.
Since the voltage drop at the tip of the workpiece is practically negligible, the voltage measurement value Sv is approximately
Can be regarded as data representing the voltage drop (applied voltage) of

When the CPU 40 receives data such as various set values from the input unit 60, it stores them in the memory 62,
The set value, measured value, welding result, and the like are displayed on the display unit 64. The power supply circuit 66 generates various DC operating voltages from the AC power supply voltage and supplies them to the CPU 40 and other units. The current transformer 68 and the primary current detection circuit 70 are used when the welding current cannot be detected on the secondary side, and by multiplying the primary current detected by these current detection means by the turns ratio of the welding transformer 16, The value of the secondary current (welding current) is determined. The inverter drive circuit 72 receives the inverter control signals fa and fb from the CPU 40.
Are amplified into inverter drive signals Fa and Fb,
The switching of the transistors TR1 to TR4 of the inverter circuit 14 is controlled by these signals Fa and Fb.

The CPU 40 controls the whole and various parts of the resistance welding system according to a control program stored in the memory 62. In the present embodiment, when performing the constant current control, the CPU 40 functionally includes a current setting unit 42, a current comparison unit 44, and a resistance calculation unit 4 as shown in FIG.
6, a ΔR setting unit 48, a peak value detecting unit 50, a ΔR falling point detecting unit 52, a sequence control unit 54, an interval setting unit 56, and an inverter control signal generating unit 58.

The current setting section 42 supplies a current comparison section 44 with a set value Qi for constant current control input from the input section 60. In the present embodiment, as will be described later, control is performed so that the secondary current I2 drops at a predetermined interval in the latter half of the energization, so that the set value Qi may be selected to be somewhat larger than the normal value. The current comparison unit 44 compares the measured current value Si received from the secondary current detection circuit 34 with the current set value Qi, and gives the difference (current comparison error) δi to the inverter control signal generation unit 54.

The resistance calculating section 46 divides the voltage measurement value Sv from the inter-chip voltage detection circuit 30 by the current measurement value Si from the secondary current detection circuit 34 to obtain the electrode chip 2.
The instantaneous resistance value SR between 0 and 22 is determined.

The ΔR setting section 48 gives the ΔR control set value ΔRZ set and input from the input section 60 to the ΔR descent point detecting section 52. The ΔR control is a conduction time control for optimizing the nugget diameter or the welding strength in the constant current control. In the energization by the constant current control, the phenomenon that the resistance value of the work reaches a peak value at a certain point and then drops monotonously is seen. When the energization is stopped when an appropriate value (ΔR) drops from the peak value, The characteristic is that the optimum welding strength can be obtained. Thus, the peak value detection unit 50
Monitors the resistance measurement value SR calculated by the resistance calculation unit 46 to detect the peak value RMAX of the inter-chip resistance, and supplies the peak value RMAX to the ΔR drop point detection unit 52. The ΔR descent point detector 52 calculates the resistance measured value SR from the resistance calculator 46.
When the peak value RMAX is detected by the peak value detection unit 50, the resistance measurement value SR is monitored from that time, and when the value falls below the peak value RMAX by the set value ΔRZ, the sequence control unit 54 issues a predetermined timing. Output a signal.

In the interval setting section 56, a time interval for temporarily dropping the secondary current I2 to be controlled by the constant current control is set. Further, the degree of the drop or the like may be set. These set values are provided to the sequence control unit 54.

When the energization is started, the sequence control section 54 activates the inverter control signal generation section 58. Then, in response to the current comparison error δi from the current comparison unit 44, the inverter control signal generation unit 60
Inverter control signals fa,
Output fb. As a result, the secondary current I2 rises from the zero current value and reaches the set value Qi, and thereafter is kept at the set value Qi.

Some time after the start of energization, the peak value detector 5
When the peak value of the inter-chip resistance value is detected at 0, the sequence control unit 54 responds to the detection of the peak value of the inter-chip resistance value.
The set value from step 6 is supplied to the inverter control signal generator 58, and the inverter control signals fa and fb are intermittently stopped at regular intervals. Then, the inverter circuit 1
4 is turned off intermittently at that interval, whereby the secondary current Δi changes from the constant current value of the set value Qi such that it temporarily falls at a predetermined interval (waveform characteristic).
Is shown. The control for dropping the secondary current I2 at a predetermined interval is continued until the end of energization.
In the case of the present embodiment, when the chip-to-chip resistance value drops from the peak value RMAX by the set value ΔRZ, the ΔR drop point detecting unit 5
4 outputs a timing signal. In response to this, the sequence control unit 54 causes the inverter control signal generation unit 5 to output the timing signal.
8 stops the output of the inverter control signals fa and fb.

FIG. 3 shows waveforms of the secondary current I2, the voltage between chips, and the resistance between chips obtained by the control of the CPU 40 as described above. In this embodiment, since the constant current control is performed, control is performed to maintain the secondary current I2 at the set value Qi. Then, the chip-to-chip resistance value has a peak value R
From time ts when PEAK (RMAX) is reached, the output of the inverter control signals fa and fb is temporarily interrupted at predetermined intervals (#p), so that the secondary current I2 drops at predetermined intervals. i appears. Also, a drop #v appears in the inter-chip voltage at the same interval. The interval and the degree of the drop #i of the secondary current I2 are determined based on various conditions such as the thickness and material of the work, the current set value Qi, and the welding purpose, and are set in the interval setting section 56 as described above. .

As described above, in the present embodiment, the output of the inverter circuit 14 is intermittently stopped from the time when the resistance between the chips reaches the peak value, and the secondary current 12 is dropped at a predetermined interval so that the material to be welded is removed. The growth rate of the nugget is adjusted and controlled by controlling the amount of energy (resistance heating value) to be prevented from suddenly increasing, thereby preventing the occurrence of splash and obtaining good metal bonding. be able to. Further, since such control is performed in combination with the ΔR control method, it is possible to more reliably prevent the occurrence of splash and obtain better welding by controlling the minimum necessary time.

FIG. 4 is a waveform chart showing the operation of one embodiment of the constant voltage control. In the constant voltage control, control is performed to maintain the voltage between chips at the set value Qv. For this control, structurally, in FIG. 2, the current setting unit 42 may be changed to a voltage setting unit, and the current comparison unit 44 may be changed to a voltage comparison unit. Also in this embodiment, the output of the inverter control signals fa and fb is intermittently stopped after the inter-chip resistance value reaches the peak value RPEAK (RMAX) (#p), so that the inter-chip voltage drops at a predetermined interval. #V is obtained. The interval and degree of the voltage drop #v are determined by the thickness / material of the work and the current set value Qi.
Are determined based on various conditions such as welding purposes, and the set values are set in the interval setting section 56.

As described above, even if the output of the inverter control signals fa and fb is intermittently stopped under the constant voltage control and the voltage between the chips is dropped at a predetermined interval, the constant current control is not performed. Similarly, the nugget growth rate can be adjusted and controlled.

Under the constant power control, the output of the inverter control signals fa and fb is intermittently stopped so that the workpiece 2
Even if the power supplied to the power supplies 4 and 26 is decreased at predetermined intervals, the nugget growth rate can be adjusted and controlled in the same manner as described above. In this case, the waveforms of the secondary current, the voltage between chips, and the resistance between chips are shown in FIG.
Has the same waveform as

[0032]

According to the present invention having the above-described structure, the following effects can be obtained. According to the inverter-type resistance welding control method of the first invention, under constant current control, the inverter is turned off intermittently for a predetermined time within the energization time, and the current flowing through the workpiece is reduced at predetermined intervals. By controlling the speed and amount of heat generated, the growth and growth of the nugget can be appropriately suppressed or adjusted, and the growth speed of the nugget can be controlled, preventing the occurrence of splash and ensuring good weld joints. Obtainable. According to the inverter-type resistance welding control method of the second invention, by intermittently turning off the inverter in combination with the ΔR control method, it is possible to more reliably prevent the generation of splash by controlling the required minimum time, and Good weld joints can be obtained. According to the inverter-type resistance welding control method of the third invention, under constant voltage control, the inverter is intermittently turned off for a predetermined time within the energization time, and the voltage applied to the workpiece is changed at predetermined intervals. By controlling the speed and amount of heat generated by depressing, the growth and growth of the nugget can be appropriately suppressed or adjusted, and the growth speed of the nugget can be controlled. Can be obtained.
According to the inverter-type resistance welding control method of the fourth invention,
Under the constant power control, the inverter is turned off intermittently for a predetermined time within the energization time, and the power supplied to the workpiece is dropped at predetermined intervals to control the speed and amount of heat generation, thereby making the nugget Since the growth rate of the nugget can be controlled by appropriately controlling or adjusting the expansion growth of the nugget, it is possible to prevent the occurrence of splash and obtain a good welded joint.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main circuit configuration of an inverter type resistance welding system to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing a functional configuration of a CPU according to the embodiment for constant current control;

FIG. 3 is a waveform chart showing the operation of the embodiment with respect to constant current control.

FIG. 4 is a waveform chart showing the operation of the embodiment with respect to constant voltage control.

[Explanation of symbols]

 14 Inverter circuit 24 Work 26 Work 30 Voltage detection circuit between chips 34 Secondary current detection circuit 40 CPU 42 Current setting unit 44 Current comparison unit 46 Resistance calculation unit 48 ΔR setting unit 50 Peak value detection unit 52 ΔR drop point detection unit 54 Sequence Control unit 56 Interval setting unit 58 Inverter control signal generation unit

Claims (4)

(57) [Claims] 1. An inverter-type resistance welding control method for performing a constant current control, wherein an inverter is intermittently turned off so as to temporarily drop a current flowing through the material to be welded at a predetermined interval for a predetermined time within an energization time. And an inverter-type resistance welding control method. 2. An intermittent turning off of the inverter is started when a resistance value between the electrode tips sandwiching the material to be welded reaches a peak value, and power is supplied when the resistance value drops by a predetermined value from the peak value. 2. The method according to claim 1, wherein
2. The inverter-type resistance welding control method according to 1. 3. An inverter-type resistance welding control method for performing constant voltage control, wherein the inverter is intermittently interrupted such that a voltage applied to the material to be welded is temporarily dropped at predetermined intervals for a predetermined time within an energization time. An inverter-type resistance welding control method characterized by being turned off. 4. An inverter type resistance welding control method for performing constant power control, wherein the inverter is intermittently interrupted so that power supplied to the material to be welded is temporarily dropped at predetermined intervals for a predetermined time within an energization time. An inverter-type resistance welding control method characterized by being turned off.