JPH04300076A - Method and device for controlling resistance welding - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to energization control of a resistance welding machine, and more particularly to a control method and a control device regarding welding power and welding current.

0002

[Prior Art] In resistance welding, constant current control is often used to apply feedback so that a constant current flows through the welded material, but in precision electronic components, it is often used to supply a constant electric power to the welded material. Constant power control with feedback is considered advantageous. In constant current control, a temporary transient phenomenon occurs in which the current greatly exceeds the set value immediately after the start of energization, so if the workpiece (material to be welded) is small, the temporary excessive current causes splash (
However, there is a disadvantage that the welding quality deteriorates due to flying particles).
This is because such transient phenomena do not occur with constant power control.

0003

[Problems to be Solved by the Invention] However, in resistance welding, the voltage applied to the workpiece decreases as the energization time elapses, so constant power control has the property that the current increases as the energization time progresses. be. Therefore, if the voltage drop near the end of energization is large due to the material or structure of the workpiece, or if the energization time is relatively long, there is a risk of splash occurring just before the end of energization using constant power control. Ta.

The present invention has been made in view of these problems, and provides a resistance welding control method and a resistance welding control device that prevent splashing just before the end of energization when resistance welding is performed by constant power control. The purpose is to provide.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the resistance welding control method of the present invention applies constant power control to match the power supplied to the workpiece with the welding power setting value. When the current flowing through the material to be welded reaches a preset upper current limit during energization, the current is switched to constant current control to match the welding current setting value and energization is continued. .

The resistance welding control device of the present invention also includes a voltage detecting means for detecting a voltage applied to a material to be welded, a current detecting means for detecting a current flowing through the material to be welded, a voltage detecting means and a current detecting means. power calculation means for calculating the measured value of the electric power supplied to the welded material based on the voltage measurement value and the current measurement value respectively obtained from the means; and a welding power for providing a welding power setting value for constant power control. a setting means, a welding current setting means for giving a welding current setting value for constant current control, a current upper limit value setting means for giving an upper limit value of the welding current, a power measurement value obtained from the power calculation means; a constant power control means that performs constant power control to match the power supplied to the workpiece to the welding power set value based on the welding power set value; and a current measurement value obtained from the current detection means and the welding current setting. A constant current control means performs constant current control to make the current flowing through the welding material match the welding current setting value based on the welding current value, and a constant power control means starts energization, and the measured current value changes during the energization. The configuration includes energization control switching means that switches to constant current control means to continue energization when the current upper limit value is reached.

[0007]

[Function] According to the present invention, at the same time as the start of energization, the constant power control mechanism operates to perform energization control such that the electric power supplied to the workpiece matches the welding power setting value. In constant power control, the voltage transiently rises significantly at the start of energization, but the current rises relatively slowly, so
The current rarely becomes excessive from the initial stage of energization to the middle stage of energization. Therefore, energization by constant power control is continued at least until the middle period of energization. Then, when the current does not reach the upper limit value until the end time of energization, constant power control energization is performed throughout the entire energization time. However, when the current reaches the upper limit at a certain point (usually near the end of energization), constant power control is switched to constant current control at that point, and the constant current control is switched to maintain the current at the welding current setting value. Shifts to control energization. This prevents the risk of splashing from the workpiece due to a sudden increase in current at the end of energization.

As described above, according to the present invention, current is energized by constant power control throughout the entire energization time unless the current reaches the upper limit value. Then, when the current reaches the upper limit value during energization, the energization is thereafter switched to constant current control. However, even in this case, energization by constant current control is usually performed for a short time just before the end of energization, and the same welding result as when constant power control is performed throughout the entire energization period can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing the 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 the functions of the CPU in this embodiment, and Fig. 3 shows the operation of the embodiment. FIG. 4 is a waveform diagram of signals of various parts for purposes of illustration.

In FIG. 1, commercial three-phase alternating current (S, T,
U) is input to a three-phase full-wave rectifier circuit 10 , and the DC voltage obtained at the output terminal of this rectifier circuit 10 is smoothed by a capacitor 12 and then input to an inverter circuit 14 . This inverter circuit 14 includes four transistors TR1 to T
transistor T according to the inverter drive signals Fa and Fb from the inverter drive circuit 70.
By alternately turning on and off R1, TR3 and transistors TR2, TR4 at a predetermined frequency sufficiently higher than the commercial AC frequency, the output terminals OUT0, OUT
1, a high frequency AC rectangular wave pulse is obtained.

The high frequency alternating current rectangular wave pulse outputted from the inverter circuit 14 is supplied to the primary coil of the welding transformer 16, and a low voltage, large current pulse is obtained in the secondary coil. This secondary side pulse is transmitted through a pair of diodes D1,
This DC secondary current (welding current) I2 flows through the electrode tips 20, 22 and the works 24, 26, and resistance heat generation occurs in the works 24, 26.

In the system of this embodiment, the works 24, 2
In order to detect the secondary current I2 supplied to the secondary current I2, the secondary circuit is provided with a toroidal coil 28, and the output terminal of the toroidal coil 28 is connected to the input terminal of the secondary current detection circuit 30. When the secondary current I2 flows in the secondary circuit, the secondary current I2 flows from the output terminal of the toroidal coil 28.
A signal representing the differential waveform of is obtained. The secondary current detection circuit 30 restores the waveform of the secondary current I2 by integrating the differential waveform signal, and determines the instantaneous current measurement value Si from the waveform. This current measurement value Si is CP
It is applied to U40 and also to one input terminal of the welding power calculation circuit 36.

Further, in order to detect the welding power supplied to the works 24, 26, the electrode tips 20, 22 are connected to the input terminal of a welding voltage detection circuit 34 via voltage detection lines 32, 32. The welding voltage detection circuit 34 amplifies the input voltage detection signal, converts it into an instantaneous voltage measurement value Sv , and supplies this voltage measurement value Sv to the other input terminal of the welding power calculation circuit 36 . The welding power calculation circuit 36 calculates the voltage measurement value Sv from the welding voltage detection circuit 34.
By multiplying by the current measurement value Si from the secondary current detection circuit 30, the instantaneous power measurement value Sp supplied to the works 24 and 26 is determined, and this power measurement value Sp
is given to the CPU 40.

The CPU 40 takes in data such as various setting values from the input section 60 and stores them in the memory 62.
When displaying set values, measured values, welding results, etc., display data is sent to a display section (not shown). The power supply circuit 64 is
Various DC operating voltages are generated from the AC power supply voltage and supplied to the CPU 40 and other parts. current transformer 6
6 and the primary current detection circuit 68 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 secondary current is detected. The value of the next current (welding current) is determined. The inverter drive circuit 70 amplifies the inverter control signals fa and fb from the CPU 40 to provide inverter drive signals Fa and Fb, and controls the switching of the transistors TR1 to TR4 of the inverter circuit 14 using these signals Fa and Fb.

The CPU 40 controls the entire resistance welding machine system and each part according to a control program stored in the memory 62. Regarding the energization control of this embodiment, the CPU 40 functionally includes a power setting section 42, a power comparison section 44, a current setting section 46, a current comparison section 48, a switching section 50, and a sequence control section 52, as shown in FIG. and an inverter control signal generation section 54.

The power setting unit 42 supplies the constant power control setting value Qp input from the input unit 60 to the power comparison unit 44 . The power comparison unit 44 converts the welding power measurement value Sp received from the welding power calculation circuit 36 into the power set value Qp.
The difference (power comparison error) Δp is determined by the switching unit 50.
give to

The current setting section 46 supplies the constant current control set value Qi input from the input section 60 to the current comparison section 48 . The current comparator 48 converts the welding current measurement value Si received from the secondary current detection circuit 30 into the current set value Qi.
The difference (current comparison error) Δi is calculated by the switching unit 50.
give to In this embodiment, the current upper limit value IM is made to match the current set value Qi, and the current setting section 46 also serves as a current upper limit value setting section.

The sequence control section 52 controls the timing of the operation of the inverter control signal generation section 54.
When energization is started, first the switching unit 50 is connected to the power comparison unit 44.
Switch to the side. Then, the power comparison error Δp from the power comparison section 44 is given to the inverter control signal generation section 54 through the switching section 50. Thereby, the inverter control signal generation unit 54 outputs pulse width modulated inverter control signals fa and fb that have the frequency of the clock signal CK and make the power comparison error Δp zero. In this way, energization is started under constant power control.

After starting the energization, the sequence control section 52
monitors the current comparison error Δi from the current comparator 48. In the case of constant power control, the current increases over time, so the secondary current I2 does not reach the upper limit value IM from the start of energization until at least the middle of energization, so Δi>0 during that time, and the sequence control unit 52 is the switching section 5
0 remains on the power comparator 44 side, and continues to perform energization by constant power control. Therefore, if the secondary current I2 does not reach the upper limit value IM until the end of energization,
The energization is performed under constant power control throughout the entire energization time.

However, when the secondary current I2 reaches the upper limit value IM at a certain point during the energization period (generally at the end of the energization period), the current comparison error from the current comparator 48 becomes Δi
≦0, and in response to this, the sequence control unit 52 switches the switching unit 50 to the current comparison unit 48. This results in
The current comparison error Δi from the current comparison unit 48 is given to the inverter control signal generation unit 54 via the switching unit 50, and the inverter control signal generation unit 54 adjusts the secondary current I2 to the welding current so as to make Δi zero. Inverter control signals fa and f that are pulse width modulated to match the set value IM
Output b. In this way, when the secondary current reaches the current upper limit value IM during energization, constant power control is switched to constant current control at that point.

FIG. 3 is a waveform diagram showing the effect of the energization control in this embodiment. In the example in this figure, time t starts from the start of energization.
Current supply was performed under constant power control until time tx, but since the secondary current I2 reached the current upper limit value IM at time tx, the current supply was switched to constant current control. In the figure, dotted lines 80 and 82 are current and power characteristics (waveforms) when constant power control is continued without such switching,
In that case, there is a risk that splash may occur from the works 24 and 26 between time tx and energization end time te. However, in this embodiment, since constant current control is applied from time tx to end time te, the secondary current I2 is maintained at the current set value IM as shown by the solid line, and there is no risk of splashing occurring. do not have. In addition, Figure 3
In this case, the voltage increases significantly immediately after the start of energization, but since the current still remains at a low value, no splash occurs.

In this embodiment, the current setting value for constant current control is made to match the current upper limit value IM, but it is of course possible to set the two to different current values. Further, although the present embodiment relates to an inverter type resistance welding machine, the present invention is also applicable to control of other types of resistance welding machines such as an AC single-phase type and an AC three-phase type.

[0023]

[Effects of the Invention] By having the above-described configuration, the present invention achieves the following effects. When energization is started using constant power control to match the power supplied to the welding material with the welding power setting value, and the current flowing through the welding material reaches the preset upper current limit during energization, Since the current is switched to constant current control to match the welding current setting value, it is possible to carry out energization by constant power control throughout the entire energization time or most of it, and to prevent splashing just before the end of energization. , high quality welding results can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the 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 the functions of a CPU in the embodiment.

FIG. 3 is a waveform diagram of signals at various parts to show the operation of the embodiment.

[Explanation of symbols]

14 Inverter circuit 16 Welding transformer 20 Electrode tip 22 Electrode tip 24 Work 26 Work 30 Secondary current detection circuit 34 Welding voltage detection circuit 36 Welding power detection circuit 40 CPU 42 Power setting section 46 Current setting section 48 Current comparison section 50 Switching section 52 Sequence control section

Claims (2)

[Claims] [Claim 1] Start energization with constant power control to make the power supplied to the welding material match the welding power setting value,
When the current flowing through the welded material reaches a preset upper current limit during energization, the current is switched to constant current control to match the welding current setting value and energization is continued. Resistance welding control method. 2. Voltage detection means for detecting the voltage applied to the welded material, current detection means for detecting the current flowing through the welded material, and voltages respectively obtained from the voltage detection means and the current detection means. a power calculating means for calculating a measured value of the electric power supplied to the workpiece based on the measured value and the current measured value; a welding power setting means for providing a welding power setting value for constant power control; Welding current setting means for providing a welding current setting value for current control;
Current upper limit value setting means for giving an upper limit value of welding current; and electric power supplied to the welding material based on the electric power measurement value obtained from the electric power calculation means and the welding electric power setting value. a constant power control means that performs constant power control to match the set value, and a current flowing through the welding material based on the current measurement value obtained from the current detection means and the welding current set value. Constant current control means performs constant current control to match a set value, and the constant power control means starts energization, and when the current measurement value reaches the current upper limit value during energization, the constant current is increased. A resistance welding control device comprising: energization control switching means for switching to the control means to continue energization.