JPS603897B2 - How to detect voltage between welding electrodes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the welding electrode voltage (hereinafter referred to as welding voltage) as an effective control factor when monitoring the welding quality of resistance welding, especially spot welding, and when controlling the quality to a constant level. This invention relates to an improvement in the detection method of chip-to-chip voltage.

Conventional configuration and its problems It is a well-known fact that monitoring the inter-chip voltage is an extremely effective means of controlling spot welding quality (for example, see Resistance Welding Research Committee materials, “ Quality Assurance Method for Spot Welding” Osaka University, Shuji Nakata et al.
Published by the Welding Society of Japan on December 9, 1978).

By the way, in detecting the inter-tip voltage, due to constraints such as the shape of the object to be welded, the detection positions are set at points A and B, which are quite far from the tip of the welding electrode (tip), as shown in Figure 1.
The detection probe is also pulled out along the arm of the welder. Here, 1 is a welding electrode (tip), 2 is a workpiece to be welded, 3 is a detection bulb, 4 is a welding machine body, &P is a voltmeter. Now, the inter-chip voltage Vt actually detected is
Resistance drop between A and B in Figure 2 (V, 10V20V3
10V40V5) and induced voltage due to welding current (K groove)
, (where K: induced voltage coefficient, i: welding current, t: time)
It is given as the sum of

0 Of these, the voltage V3 between the objects to be welded, which is part of the resistance drop, is related to welding quality.

Therefore, to find this voltage V3, from the actually detected inter-chip voltage Vt, the induced voltage (K), the resistance drop within the chip (V, +V5), the resistance drop between the chip and the object to be welded. This is possible by subtracting (V2 + V4). However, in the conventional example, when detecting the chip-to-chip voltage, at most only the induced voltage (K voltage) is removed, and the detection accuracy cannot be said to be sufficient, and as a result, the chip-to-chip voltage is The weld quality monitoring utilized was also unsatisfactory. Purpose of the Invention In view of the above-mentioned related examples, the detection method of the present invention is intended to detect the resistance drop between the objects to be welded with higher accuracy.

Structure of the Invention As a structure for this purpose, the present invention detects the voltage between the welding electrodes for each energization cycle when the welding electrodes of resistance welding are short-circuited and energized, calculates the average value of the detected voltage between the welding electrodes, and calculates the average value of the detected voltage between the welding electrodes. The average value is corrected by a predetermined constant for each number of welding points and stored, the voltage between the welding electrodes is detected for each energization cycle during welding, and the voltage between the melting electrodes during welding and the stored value are detected. This is a method of detecting the voltage between welding electrodes, in which the difference value between the two electrodes is taken and the difference value is used as the detected value of the voltage between the welding electrodes.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described.

In the present invention, as shown in FIG. 3, the chip-to-chip voltage Vt at the time of chip short-circuit is sequentially detected for each power supply cycle of the energization time limit.

In this case, as a method for removing the induced voltage (K voltage generator), the chip-to-chip voltage Vt is input to an AC integrating circuit, and as shown in FIG. .
This is possible by setting the inter-chip voltage corresponding to each half-cycle energization to be energization (IVtE-VtFI, etc.). In this way, the chip-to-chip voltage from which the induced voltage has been removed is detected.

Here, since there is a difference in welding current between the chip short circuit and actual welding, the resistance drop within the chip (V, '
+V5') and the chip-to-chip voltage V6 are not strictly equal to the intra-chip resistance drop (V, +V5) and the chip-to-workpiece voltage (V2 + V4) shown in FIG. 2, respectively. Therefore, in order to correct this, a value obtained by subtracting a certain constant from the resistance drop (V, '10V60V;) at the time of a chip short-circuit is set as the inter-chip voltage at the time of a chip short-circuit.
Also, based on the inter-chip voltage for each energization cycle, the average value over the entire energization time period is determined, and this is taken as the inter-chip voltage at the time of chip short circuit. By the way, as is well known, when welding is repeated, the tip end deforms into a mushroom shape.

In such a case, since the inter-chip voltage at the time of chip short-circuiting differs, the average value must be corrected. This correction is performed by multiplying the average value by a certain constant for each predetermined number of welding points, and storing the result as an average value of inter-chip voltage at the time of a chip short circuit. If you do it like this,
The inter-chip voltage at the time of a chip short circuit need only be detected, for example, when the chip is replaced, and efficiency can be improved.
Now, next, the inter-tip voltage Vt detected during actual welding.
is input into the AC integration circuit, and the average value (memory value) of the chip-to-chip voltage at the time of the previous chip short circuit is subtracted from the value obtained by removing the induced voltage (K bag) for each power supply cycle of energization. If the inter-chip voltage value is determined for each power cycle, only the voltage drop between the objects to be welded, which is related to welding quality, can be detected more accurately.

FIG. 5 shows an embodiment of a detection circuit for carrying out the detection method of the present invention.

In the figure, an inter-chip voltage Vt is input to an AC integration circuit 1, and further input to a microcomputer W via a sample hold circuit 0 and an A/D conversion circuit m. On the other hand, the welding current is input to the zero point detection circuit via the current transformer V, and the welding current starts and ends flowing (fourth point).
(C, D, etc. in the figure) is detected and notified to the microcomputer N. The circuit board is a switch circuit that indicates whether the detected chip-to-chip voltage is the chip-to-chip voltage at the time of chip short circuit or the voltage at actual welding.

In addition, the number of welding points can be determined by inputting an electric signal that controls a pressure valve (electromagnetic valve) into a waveform shaping circuit and using a microcomputer W.
Inform the player of the dot status.

The microcomputer W has a fixed number of dots for correcting the chip-to-chip voltage when the chip is shorted according to the deformation of the chip, and when that number of dots is reached, the chip-to-chip voltage is sequentially adjusted by the method described above. I will correct it. With the above configuration, it is possible to very easily and easily detect the resistance drop between the objects to be welded, which is related to welding quality, with higher accuracy.

Effects of the Invention As described above, by using the detection method of the present invention, it is possible to more accurately detect the resistance drop between the objects to be welded, which is related to welding quality, in the inter-chip voltage, and it is possible to By storing the chip-to-chip voltage data at the time of chip short circuit, even if the chip deforms as the welding point progresses, the chip-to-chip voltage due to the deformation can be corrected. There is no need to store chip-to-chip voltage data when chips are shorted many times as the chips are deformed, and efficiency can be improved.

Therefore, as a result, by the method of the present invention, quality control of spot welding using inter-chip voltage can be carried out with higher precision and efficiency.

[Brief explanation of the drawings] Fig. 1 is a side view of a welding machine implementing the method for detecting the inter-chip voltage, Fig. 2 is an enlarged side view of the tip portion showing the inter-tip voltage during actual welding, and Fig. 3 The figure is an enlarged side view of the tip part showing the inter-chip voltage when the tip is short-circuited, FIG. 4 is a waveform diagram of the AC integral value of the welding current and the inter-tip voltage, showing an example of detecting the inter-chip voltage, and FIG. 1 is a block diagram of a detection circuit for implementing the detection method; FIG. 1... Welding electrode (chip), 2... Object to be welded,
3...Detection probe, 4...Welding machine body, 1...AC integration circuit, 0...Sample hold circuit, m...A/D conversion circuit, W... ...Microcontroller, V...Current transformer, W...Zero point detection circuit, skin...Switch circuit, skin...waveform shaping circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 Detect the voltage between the welding electrodes during the energization cycle when the welding electrodes of resistance welding are short-circuited and energized, calculate the average value of the detected voltage between the welding electrodes, and preset the average value for each number of welding points. The voltage between the welding electrodes is corrected and stored using a constant, the voltage between the welding electrodes is detected for each energization cycle during welding, the difference value between the voltage between the welding electrodes during welding and the stored value is calculated, and the difference value is calculated. A method for detecting a voltage between welding electrodes, characterized in that the detected value is a voltage between welding electrodes.