JPS60170583A - Method and device for monitoring welding strength in spot welding - Google Patents

Abstract

PURPOSE:To obtain always stable weld strength even if various factors fluctuate by monitoring the weld strength from the integrated value of the effective components of the voltage between chips with respect to individual weld points and interrupting the welding current when the target value is attained. CONSTITUTION:The decreased voltage of the voltage between chips in set time is obtd. by subtracting the output signal from an adder circuit 17 and the output signal from a min. voltage memory circuit 25 in the 3rd arithmetic circuit 36. The average value of the number of weld points is determined from the value set in a setting circuit 38 for the number of welding. The resulted average value of the decreased voltage and the value set in a setting circuit 39 for a target value are compared in an arithmetic circuit 40 and if the compared value is lower than the value set in the circuit 39, the welding current is increased from the next welding cycle and if said value is higher than the set value, the welding current is decreased by which the welding current is feedback-controlled to the stable current value.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention detects the welding voltage applied to the welding gun electrode, controls the welding current value and energization time from the voltage, and influences the welding strength. The present invention relates to a welding strength monitoring method in spot welding and an apparatus therefor, which makes it possible to always obtain optimal welding strength even if various factors that affect the welding strength vary.

[Prior art]

In order to obtain a high-quality product in spot welding, it is necessary to monitor overcurrent and control the current application time, regardless of the material of the workpiece. However, conventional control only applies energy under empirically determined conditions to the welding area, and is not necessarily linked to the welding result. That is, even if current is flowing, welding defects will occur if there are variations in various factors such as tip wear, shunt flow, pressure fluctuations, and the fit of the materials to be welded. Therefore, in order to reduce the influence of these factors as much as possible, current values and energization times are set with some margin. Therefore, there is a lot of power loss,
Another drawback was that the life of the chip was shortened.

[Purpose of the invention]

The object of the present invention is to provide a method and apparatus for monitoring weld strength in spot welding, which eliminates the above-mentioned drawbacks of the conventional methods.

[Structure of the invention]

The configuration of Silk 1 of this invention detects the welding voltage applied to the welding gun electrode, removes the induced noise component and the welding gun electrode resistance component from the detected welding voltage, and removes both of these components. The voltage difference between the effective welding voltage and the minimum voltage during the energization time is integrated during the energization time, and the integrated value is compared with the reference setting value, and when the integrated value reaches the reference setting value, the welding current is determined. At the same time, it detects a voltage drop within the set energization time, calculates the voltage difference due to the voltage drop as the average value of the set number of spot welding, and sets this voltage difference in advance near the limit where spatter occurs. The current value for the next spot welding is controlled when the voltage difference is out of a predetermined range, compared with a target voltage difference from the peak voltage based on the welding current.

Next, the configuration of the second invention of the present invention includes a voltage detection circuit that detects the voltage applied to the welding gun electrode, an inductive noise component removal circuit that is sequentially connected to the output side of this voltage detection circuit, and a welding A gun electrode resistance component removal circuit, an integration circuit that integrates the effective welding voltage during the energization time after removing ineffective components by these removal circuits, a minimum voltage memory circuit that stores the minimum voltage during the energization time, and a minimum voltage memory circuit that stores the minimum voltage during the energization time. An energization time memory circuit that stores time, a first arithmetic circuit that multiplies the minimum voltage and energization time stored in these memory circuits, and an output from the first arithmetic circuit that is used as an output from the integration circuit. a second arithmetic circuit for subtracting from
a comparison measurement circuit that compares and measures the output value from the arithmetic circuit and a preset reference value; an energization time control circuit that controls the energization time to the workpiece based on the output from the comparison measurement circuit; Subtract the output of the minimum voltage memory circuit from the output of the gun electrode resistance component removal circuit, divide this by a preset number of welding to obtain an average value, and subtract this value by a target value determined experimentally in advance. The welding current feedback circuit and the current control circuit that controls the current flowing to the workpiece in accordance with the output signal from the welding current feedback circuit are jiffed.

〔Example〕

Next, an embodiment of the second aspect of the present invention will be described with reference to FIG. When this device is operated, the first invention will be realized.

Reference numeral 1 denotes a welding transformer, and a primary coil 2 of the welding transformer 1 is connected in series with an energization time control circuit 3 and a current control circuit 4, which will be described later, and connected to a power supply terminal 5. Welding can electrodes 7 and 8 are connected to the secondary coil B of the welding transformer 1, and a workpiece 9 is connected between the tips of the welding can electrodes 7 and 8.
10 is held, and welding current flows.

A voltage detection circuit 11 detects the voltage applied between the welding gun electrodes 7.8.

An inductive noise component removal circuit 12 and a welding gun electrode resistance component removal circuit 15, which will be described next, are successively connected to the output side of the voltage detection circuit 11, followed by a processing circuit 14.

The induced noise component removal circuit 12 consists of sample water. The output signal of the voltage detection circuit 11 described above is received by the sample hold circuit i 5 , and its output is applied to one input terminal of the addition circuit 17 of the welding gun electrode resistance component removal circuit 13 . A l-loidal coil 18 is wound around the connection wire to the welding gun electrode 8, and the induction noise component removal circuit 1 is connected to the welding gun electrode 8 via a differential current detection circuit 19.
It is connected to the input side of the zero cross timing circuit 16 of No. 2. A part of the output of the differential current detection circuit 19 is also applied to the input side of the sample hold circuit 21 of the welding gun electrode resistance component removal circuit 13 via the integration circuit 2o.

The output side of the sample hold circuit 21 of the welding gun electrode resistance component removal circuit 13 is connected to the input side of the polarity inversion circuit 22. The output side of the polarity inversion circuit 22 is a variable resistor 2
3 is connected to one input of the adder circuit 170. The adder circuit 17 adds two signals input to two input terminals. The output side of the adder circuit 17 is connected to the input side of the integrating circuit 24 of the processing circuit 14 and the input side of the minimum voltage memory circuit 25. The processing circuit 14 is also provided with an energization time memory circuit 26, which receives the output signal of the zero cross timing circuit 16 of the induced noise component removal circuit 12. 27 is a first arithmetic circuit, and a minimum voltage memory circuit 2 connected to its input side.
5 by the minimum voltage stored in the energization time memory circuit 26 and the energization time.

28 is a second arithmetic circuit. This second arithmetic circuit 28
is for subtracting the output of the first arithmetic circuit 27 from the output of the integrating circuit 24, so these are connected to the input side. And on the output side, this second arithmetic circuit 28
The input side of a comparison/judgment circuit 3o is connected to compare the output of the target value setting circuit 29 with a target value set in advance in the target value setting circuit 29. The target value setting circuit 29 and the comparison judgment circuit 3° form a welding current cutoff circuit 31, and the comparison judgment circuit 3
The output side of 0 is connected to the control end of the aforementioned energization time control circuit 3. On the output side of the energization time memory circuit 26 of the processing circuit 14, in addition to the input side of the first arithmetic circuit 27, the other input of the comparison judgment circuit 63, which has one input side connected to the output of the upper and lower limit setting circuit 32, is connected. side is connected. The output side of the comparison/judgment circuit 33 is connected to an abnormality warning circuit 34.

35 is a welding current feedback circuit.

This welding current feedback circuit 35 receives the output signal from the adder circuit 17 described above from the minimum voltage memory circuit 2 described above.
5, an average value calculation circuit 37 that calculates an average value from the output signal of the third calculation circuit 36, and an average value calculation circuit 37 that calculates the average value. output of a welding number setting circuit 38 that provides a set value for the number of welding times that is separately set for the purpose of the process, a target value setting circuit 39 that sets a target value of welding current determined in advance by experiment, and an average value calculation circuit 37 from this target value. A fourth arithmetic circuit 4° for subtracting the signal is provided. The output side of the welding current feedback circuit 35 is connected to the control end of the current control circuit 4, and is also connected to the input side of the comparison/judgment circuit 41. The comparison and determination circuit 41 is also connected to an upper and lower limit setting circuit 42 and an abnormality notification circuit 43 .

Next, the operation of the device configured as described above will be explained together with the first invention. First, FIG. 2 shows the components of the detected voltage V taken out by the lead wires connected to the welding gun electrodes 7 and 8. As shown in this figure,
The detection voltage V contains the true interelectrode voltage component (effective component).
vllL, an induced noise component (including a reactance component) VN, and a welding gun electrode resistance component vr.

In order to know the value of the bath contact strength in spot welding, it is necessary to extract only the true interelectrode voltage component VB that acts as an effective component in spot welding. However, from the detection voltage ■ in Fig. 2, it is simply the induced noise component VN,
If only the welding gun electrode resistance component Vr is removed, a component VA remains that cannot be removed more accurately than l'-/ shown in FIG.

Therefore, in order to remove the component vA and find out the true welding strength,
As shown in FIG. 4, the induced noise component V is calculated from the detected voltage V.
Integrate the component after removing N and the welding gun electrode resistance component Vr (Fig. 4 (a)), and subtract from this value the value integrated during the minimum voltage application time (Fig. 4 (b)). Then, an integral value of the active ingredient as shown in FIG. 4(c) is obtained, and this is compared with a preset reference value.

The above operations are carried out by the voltage detection circuit 11, the induced noise component removal circuit 12, and the welding gun electrode resistance component removal circuit 13. Then, the current detected by the toroidal coil 1 is processed by the differential current detection circuit 19, and d
The voltage is detected when i/dt=0, and the induced noise component is removed. After this signal is integrated by an integrating circuit 2°, its polarity is inverted by a polarity inverting circuit 22, and the signal is added and subtracted. Processing circuit 14
The integrating circuit 24 integrates the effective component thus obtained. Further, the minimum voltage memory circuit 25 stores the minimum voltage during the energization time. On the other hand, energization time memory circuit 2
6 also stores the energization time.

The first arithmetic circuit 27 multiplies the energization time and the minimum voltage. Next, the second arithmetic circuit 28 subtracts the value obtained by integrating the output of the first arithmetic circuit 27 from the integral value of the integrator circuit 24 (
(See Figure 4 (a) or c)). This result is compared by the comparison judgment circuit 30 with the target value set by the target value setting circuit 29KI, and if the target value is exceeded, a signal is sent to the energization time control circuit 3 to cut off the welding current. . If the energization time to reach the target value is too long or too short, the comparison/judgment circuit 53 that receives the signal from the energization time memory circuit 26 compares it with the signal from the upper/lower limit setting circuit 32 and issues an abnormal output alarm. When the circuit 34 is caused to issue an abnormality alarm, it becomes K.

Next, a method for controlling welding current will be explained. First, in FIG. 5, the drop voltages V1 to V3 of the inter-chip voltage during the set time t$ are calculated. This reduced voltage (1) to (3)
The current value near the spatter generation limit is set to three levels: large, medium, and small.
This is what I chose for my manuscript.

This reduced voltage is obtained by subtracting the output signal of the adder circuit 17 and the output signal of the minimum voltage memory circuit 25 by the third arithmetic circuit 36. Next, the average value of the number of welding points is calculated from this voltage using a value preset in the welding number setting circuit 38 (see (4) in FIG. 6). This is obtained by dividing the output signal of the third arithmetic circuit 36 (see FIG. 6 (5)) by the set number. In this case, the number of spot welding points is preferably determined to be a number with a certain number of repetitions. Next, the average value of the voltage drop obtained in this manner is compared with an experimentally determined optimal value preset in the target value setting circuit 39.

This comparison is performed by the fourth arithmetic circuit 40. If this value is lower than the value set in the target value setting circuit 39, the welding current is increased from the next welding cycle, and if the noise is high, the welding current is decreased to perform feedback control to a stable current value. become. The welding current is controlled by a current control circuit 4. The optimal value for the voltage drop is
By setting the welding current close to the limit generated by spatter at the weld, the voltage drop at that time can be measured and claimed as an average value of 10 or more points. If the difference from the target value is too large, the upper and lower limit setting circuit 42 and the comparison judgment circuit 41 operate, and the abnormality notification circuit 45 issues an alarm.

〔Effect of the invention〕

As described above, this invention stabilizes the welding current by sequentially feeding back the welding current for each set number of spots, monitors the welding strength at each welding point using the integral value of the effective component of the inter-tip voltage, and when the welding current reaches the target value, the welding current Since the welding strength is controlled to be cut off, stable welding strength can always be obtained even if various factors that affect welding strength fluctuate. Furthermore, since excessive energy is not applied, it is possible to save energy and reduce wear on the electrode tip.

Fig. 1 is a circuit diagram of an embodiment of the second invention of this invention, and Fig. 2 is a line showing the relationship between voltage and time to theoretically explain the invention of Ml of this invention. Figure 3 is a diagram showing the state after removing some components of Figure 2; Figures 4 (a), (b), and (c) show the process of the first invention. Diagrams FIGS. 5 and 6 are diagrams for explaining the present invention in detail.

1... Welding transformer 3... Energization time control circuit 4... Current control circuit 7.8... Welding gun electrode 9.10... Work to be welded 11... Voltage detection circuit 12... Inductive noise component removal circuit 13... Welding gun electrode resistance component removal circuit 14... Processing circuit 20.24... Integration circuit 25... Minimum voltage memory circuit 26... Current application time memory circuit 27... First calculation circuit 28...Second calculation circuit 31...Welding current cutoff circuit 35...Welding current feedback circuit Patent applicant Toyota Auto Body Co., Ltd. Figure 2 Figure 3 Figure 5 Figure 4! 6@

Claims (1)

[Claims] 1) In spot welding, ``a welding voltage applied to a welding gun electrode is detected, an induced noise component and a welding gun electrode resistance component are removed from the detected welding voltage, and both these components are The voltage difference between the effective welding voltage after removal and the minimum voltage during the energization time is integrated during the energization time, and the integrated value is compared with a reference setting value, and when the integrated value reaches the reference setting value, welding is started. At the same time as cutting off the current, detecting the voltage drop within the set energization time, calculating the voltage difference due to the voltage drop as the average value of the set number of spot welding, and setting the voltage difference in advance near the limit where spatter will occur. In spot welding, the current value for the next spot welding is controlled when the voltage difference is out of a predetermined range by comparing the voltage difference from the peak voltage based on the welding current. Weld strength monitoring method. 2) A voltage detection circuit that detects the voltage applied to the welding gun electrode, an inductive noise component removal circuit and a welding gun electrode resistance component removal circuit that are sequentially connected to the output side of the voltage detection circuit, and these removal circuits. An integration circuit that integrates the effective welding voltage after removing ineffective components during the energization time, a minimum voltage memory circuit that stores the minimum voltage during the energization time, and an energization time memory circuit that stores the energization time; a first arithmetic circuit that multiplies the minimum voltage stored in the memory circuit by the energization time; a second arithmetic circuit that subtracts the output from the first arithmetic circuit from the output from the integrating circuit; a comparison measurement circuit that compares and measures the output value from the second arithmetic circuit with a preset reference value; and energization time control that controls the energization time to the workpiece based on the output from the comparison measurement circuit. The output of the minimum voltage memory circuit is subtracted from the output of the welding gun electrode resistance component removal circuit, and this is divided by a preset number of welding to obtain an average value, and this value is determined experimentally in advance. A welding current feedback circuit that subtracts by the target value, and a current that controls the current flowing to the workpiece according to the output signal from the welding current feedback circuit.