JPH04300077A - Method and device for controlling resistance welding - Google Patents

Abstract

PURPOSE:To stabilize the welding electric conduction and to allow it to have a high quality by the constant-current control for preventing a splash generated by a current overshoot in the beginning of the electric conduction. CONSTITUTION:A current comparing part 44 compares a current measured value Si from a secondary current detecting circuit 34 with a current set value Qi from a current setting part 42, and outputs a current comparison error deltai. A current comparing part 48 compares a power measured value Sp from a welding power arithmetic circuit 36 with a power set value Qp from a power setting part 46, and outputs a power comparison error deltap. A DELTAR fall point detecting part 54 outputs a prescribed timing signal for finishing the electric conduction at the time point when a measured value SR of an inter-tip resistance value arithmetic circuit 38 falls by a set value DELTARZ from a peak value RMAX. A sequence control part 56 switches a switching part 58 to 48 side and starts the electric conduction, and allows an inverter control signal generating part 60 to output inverter control signals (fa), (fb) for the constant-current control. When deltai from 44 becomes zero, 58 is switched to 44 side, and 60 is allowed to output (fa) and (fb) for the constant-current control.

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 method and apparatus for improving a constant current control system.

0002

[Prior Art] Constant current control, which applies feedback so that a constant current flows through the material to be welded, is most often used in resistance welding, and constant current control is also used in recently popular inverter-type resistance welding machines. has become mainstream. The main reasons for this are that current, along with pressure and energization time, are the three major welding conditions for resistance welding, and that current can be easily measured using toroidal coils, current transformers, etc., which form a feedback loop. For example, it is easy to use.

0003

[Problem to be solved by the invention] However, according to constant current control, at the beginning of energization, although temporary (transient),
A phenomenon occurs in which the current greatly exceeds the set value, that is, overshoot. In particular, in an inverter-type resistance welding machine, such a current overshoot phenomenon appears conspicuously despite high-speed feedback control.

[0004] In constant current control, the cause of the current overshoot phenomenon is that when energization starts, the current increases rapidly and rapidly from a zero value toward the set value due to feedback control, so that the current does not reach the set value. Possible causes include that the force of the current does not stop immediately, and that the inductance included in the secondary circuit of the resistance welding machine imparts an inertial force to the current. In any case, if such a current overshoot phenomenon occurs, there is a risk that splash will occur, which is inconvenient.

The present invention has been made in view of these problems, and it prevents the current overshoot phenomenon from occurring at the initial stage of energization, thereby preventing splash, and stabilizing and improving the quality of welding energization through constant current control. An object of the present invention is to provide a resistance welding control method and device for measuring resistance welding.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the first resistance welding control method of the present invention starts energization by constant power control so that the current supplied to the workpiece is a predetermined current. The method was to switch from constant power control to constant current control when the set value was reached.

Further, in the second resistance welding control method of the present invention, energization is started by constant voltage control, and when the current supplied to the material to be welded reaches a predetermined current setting value, the constant current is changed from constant voltage control. The method was to switch to control.

Further, in the third resistance welding control method of the present invention, in the first or second resistance welding control method, after the resistance value of the welded material reaches the peak value under constant current control, the resistance value is reduced to the peak value. The method was to stop energization when the value drops by a predetermined value.

The first resistance welding control device of the present invention further includes a current detection means for detecting the current supplied to the welded material, and a current detection means for detecting the current supplied to the welded material; constant current control means for performing constant current control to
A constant power control means performs constant power control to match the power supplied to the welding material with a welding power setting value, and the constant power control means starts energization, and the current measurement value obtained from the current detection means is The present invention is configured to include energization control switching means for switching to energization by constant current control means when a predetermined welding current setting value is reached.

The second resistance welding control device of the present invention further includes a current detection means for detecting the current supplied to the welded material, and a current detection means for detecting the current supplied to the welded material, and a current detection means for detecting the current supplied to the welded material. constant current control means for performing constant current control to
A constant voltage control means performs constant voltage control to match the voltage applied to the material to be welded with a welding voltage setting value, and the constant voltage control means starts energization, and the current measurement value obtained from the current detection means is set to a predetermined value. and energization control switching means for switching to energization by the constant current control means when the welding current set value is reached.

[0011]

[Operation] In the first resistance welding control method or the first resistance welding control device, when energization is started, constant voltage control is performed and the power supplied to the welded material matches (reaches) the set value.
As you like, it takes feedback. In this way, the current and voltage to the material to be welded rise, but since the voltage rises more rapidly when energizing is conducted under constant power control, the current rises slightly more suppressed. Therefore, no current overshoot phenomenon occurs. When the current reaches the set value, constant power control is switched to constant current control at that point, and from then on, energization is performed under constant current control until the end of energization.

In the second resistance welding control method or the second resistance welding control device, constant voltage control is performed instead of the constant voltage control as described above. Even in this case, since the current rises in a controlled manner, no current overshoot phenomenon occurs, and the control is switched to constant current control from the time when the current reaches the set value.

In the third resistance welding control method, after switching to constant current control in the first or second resistance welding control method, changes in the resistance value of the part to be welded are monitored by ΔR control, and Power can be turned off at the optimal point.

[0014]

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.

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
R4, and according to inverter drive signals Fa and Fb from the inverter drive circuit 70, the transistor TR
1, TR3 and transistors TR2, TR4 are turned on and off alternately at a predetermined frequency that is sufficiently higher than the commercial AC frequency, so that the output terminals OUT0 and OUT1
A high frequency AC rectangular wave pulse is obtained.

The high frequency alternating current 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 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 detection circuit 6, a toroidal coil 28 is provided in the secondary circuit, and an output terminal of the toroidal coil 28 is connected to an input terminal of a 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 a differential waveform of 2 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 voltage applied to the works 24 and 26 and the power supplied, the electrode tip 2
0 and 22 are connected to the input terminal of an interchip voltage detection circuit 34 via voltage detection lines 32 and 32, respectively. This interchip voltage detection circuit 34 amplifies the input voltage detection signal and then converts it into an instantaneous voltage measurement value Sv. This voltage measurement value Sv is applied to the other input terminal of the welding power calculation circuit 36 and also to the CPU 40.

The welding power calculation circuit 36 applies the voltage measurement value Sv from the welding voltage detection circuit 34 to the secondary current detection circuit 30.
The instantaneous power measurement Sp supplied to the workpieces 24, 26 is determined by multiplying by the current measurement Si from , and this power measurement Sp is provided to the CPU 40. Strictly speaking, the voltage measurement value Sv is a value representing the voltage drop in the conductor path including the workpieces 24 and 26 plus the tips of the electrode tips 20 and 22, but the voltage drop at the tips of the electrode tips 20 and 22 is Since Sv is practically negligible, the measured voltage value Sv can be approximately regarded as the value of the voltage applied to the works 24 and 26.

Furthermore, in order to detect the resistance values of the works 24 and 26, the voltage measurement value Sv from the inter-chip voltage detection circuit 30 and the current measurement value Si from the secondary current detection circuit 34 are used.
is applied to the input terminal of the inter-chip resistance value calculation circuit 38. The inter-chip resistance value calculation circuit 38 divides the voltage measurement value Sv by the current measurement value Si, thereby calculating the electrode tip 20.
, 22 is calculated, and this inter-chip resistance value SR is provided to the CPU 40. Electrode tip 20
, 22 is so low that it can be virtually ignored, the inter-chip resistance SR can be approximated by the workpieces 24, 26.
It can be regarded as data representing the resistance value of .

The CPU 40 takes in data such as various setting values from the input section 70 and stores them in the memory 72.
When displaying set values, measured values, welding results, etc., display data is sent to a display section (not shown). The power supply circuit 74 is
Various DC operating voltages are generated from the AC power supply voltage and supplied to the CPU 40 and other parts. current transformer 7
6 and the primary current detection circuit 78 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 80 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 72. Regarding the energization control of this embodiment, the CPU 40 functionally includes a current setting section 42, a current comparison section 44, a power setting section 46, a power comparison section 48, a ΔR setting section 50, and a peak value detection section, as shown in FIG. section 52, ΔR drop point detection section 54, sequence control section 56, switching section 58,
It consists of an inverter control signal generation section 60.

The current setting section 42 supplies the constant current control set value Qi input from the input section 70 to the current comparison section 44 . The current comparison unit 44 compares the current measurement value Si received from the secondary current detection circuit 34 with the current set value Qi, and provides the difference (current comparison error) δi to the switching unit 58 and also to the sequence control unit 56. give.

The power setting unit 46 supplies the constant power control setting value Qp input from the input unit 70 to the power comparison unit 48. The power comparison unit 48 converts the welding power measurement value Sp received from the welding power calculation circuit 36 into the power setting value Qp.
The difference (power comparison error) δp is determined by the switching unit 58.
give to

The ΔR setting section 50 provides the ΔR control setting value ΔRZ input from the input section 70 to the ΔR drop point detection section 54 . ΔR control is current application time control for optimizing the nugget diameter or welding strength in constant current control. When applying electricity using constant current control, there is a phenomenon in which the resistance of the workpiece reaches a peak value at a certain point and then drops monotonically, and if the electricity is stopped when the resistance falls by an appropriate value (ΔR) from the peak value, , it has the characteristic that optimum welding strength can be obtained. Therefore, the peak value detection section 52
is the resistance measurement value SR from the inter-chip resistance value calculation circuit 38
is monitored, the peak value RMAX of the inter-chip resistance is detected, and the peak value RMAX is provided to the ΔR drop point detection section 54. The ΔR drop point detection unit 54 receives the resistance measurement value SR from the inter-chip resistance value calculation circuit 38, and when the peak value detection unit 52 detects the peak value RMAX, it monitors the resistance measurement value SR from that time and detects the resistance measurement value SR. The value is the peak value R
A predetermined timing signal is output to the sequence control section 56 when the set value ΔRZ decreases from MAX.

When starting energization, the sequence control section 56 activates the inverter control signal generation section 54 and switches the switching section 58 to the power comparison section 48 side. Then, the power comparison error δp from the power comparison section 48 is given to the inverter control signal generation section 60 through the switching section 58. The inverter control signal generation unit 60 outputs inverter control signals fa and fb that are pulse width modulated at the clock frequency CK so as to make the power comparison error δp zero. In this way, energization is started under constant power control.

After starting the energization, the sequence control unit 56
monitors the current comparison error δi from the current comparator 44. Since the secondary current I2 rises from a value of zero, a comparison error of δi<0 is obtained during the rising period. and,
The rising has finished, and the secondary current I2 reaches the current setting value Qi
When δi=0, the sequence control section 56 switches the switching section 58 to the current comparison section 44 side in response. As a result, the current comparison error δi from the current comparison section 44 passes through the switching section 58 to the inverter control signal generation section 6.
0, and the inverter control signal generation unit 60 generates an inverter control signal fa that makes the current comparison error δi zero.
, fb. In this way, when the secondary current I2 reaches the current set value Qi, energization is performed by constant current control, and a constant current is supplied to the works 24 and 26. Then, when the timing signal is generated by the ΔR drop point detection section 54, the sequence control section 56 stops the operation of the inverter control signal generation section 60 at that point.

FIG. 3 is a diagram showing the operation of the energization control in this embodiment. In this figure, ts is the time when the secondary current I2 reaches the set value Qi, and te is the time when the energization stop command is issued by ΔR control. Therefore, the period from the energization start time to the switching time ts is a waveform due to constant power control, and from the switching time ts to the energization stop time te.
The period up to is a waveform based on constant current control. According to this embodiment, since energization is started by constant power control,
A current overshoot phenomenon as indicated by the chain line SH does not occur, and there is no risk of splash occurring.

In the above embodiment, the setting value for detecting the switching timing and the setting value for constant current control are shared by the same current setting value Qi, but it is also possible to select different values for both. It is possible. Furthermore, it is also possible to stop the energization after a preset energization time without using the ΔR control method.

Further, in the above-described embodiment, the energization was started by constant power control, but it is also possible to start by constant voltage control. In that case, for example, in FIG. 46, the power comparator 48 may be replaced with an interchip voltage detection circuit 30, a voltage setting section, and a voltage comparison section, respectively. Even when starting up using constant voltage control, a waveform similar to that shown in FIG. 3 can be obtained, and the same effects as when using constant power control can be obtained.

Although the present invention is particularly effective in the above-mentioned inverter type resistance welding machine, it is also applicable to other types of resistance welding machines such as single-phase AC type and three-phase AC type. Applicable.

[0032]

[Effects of the Invention] By having the above-described configuration, the present invention achieves the following effects.

According to the resistance welding control method according to claim 1 or the resistance welding control device according to claim 4, since the constant current control is executed after energization is started by constant power control, the current overshoot phenomenon and even the It is possible to weld without splashing, and high-quality welding results can be obtained.

According to the resistance welding control method of claim 2 or the resistance welding control device of claim 5, since the constant current control is executed after starting the current supply by constant voltage control, the current overshoot phenomenon and the It is possible to weld without splashing, and high-quality welding results can be obtained.

According to the resistance welding control method of claim 3, in the first or second resistance welding control method, after switching to constant current control, changes in the resistance value of the welded part are monitored by the ΔR control method. Since the current is turned off at the optimum time for nugget formation, good welding strength 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 chart showing the effect of the embodiment.

[Explanation of symbols]

14 Inverter circuit 20 Electrode tip 22 Electrode tip 24 Work 26 Work 30 Chip-to-chip voltage detection circuit 34 Secondary current detection circuit 36 Welding power detection circuit 40 CPU 42 Current setting section 44 Current comparison section 46 Power setting section 48 Power comparison section 50 ΔR setting section 52 Peak value detection section 54 ΔR descent point detection section 58 Switching section

Claims (5)

[Claims] [Claim 1] Starting energization by constant power control,
A resistance welding control method, characterized in that the constant power control is switched to constant current control when the current supplied to the workpiece reaches a predetermined current setting value. [Claim 2] Starting energization by constant voltage control,
A resistance welding control method, characterized in that the constant voltage control is switched to constant current control when the current supplied to the workpiece reaches a predetermined current setting value. 3. The current supply is stopped when the resistance value of the welded material reaches a peak value under the constant current control and then decreases by a predetermined value from the peak value. 2. The resistance welding control method according to 2. 4. Current detection means for detecting the current supplied to the welded material, and constant current control that performs constant current control to match the current supplied to the welded material with a welding current setting value. means, constant power control means for performing constant power control to match the electric power supplied to the welding material with the welding power set value, and a constant power control means for starting energization by the constant power control means, and a constant power control means for controlling the electric power supplied to the welding material to match the welding power setting value; 1. A resistance welding control device comprising: energization control switching means for switching to energization by the constant current control means when a measured current value reaches a predetermined welding current setting value. 5. Current detection means for detecting the current supplied to the welded material, and constant current control that performs constant current control to match the current supplied to the welded material with a welding current setting value. means, constant voltage control means for performing constant voltage control to match the voltage applied to the welding material with the welding voltage set value, and a constant voltage control means for starting energization by the constant voltage control means, and a voltage obtained by the current detection means. 1. A resistance welding control device comprising: energization control switching means for switching to energization by the constant current control means when a measured current value reaches a predetermined welding current setting value.