JPH0152115B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses welding electrode voltage (hereinafter referred to as inter-chip 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. related to the improvement of the detection method.

It is a well-known fact that monitoring the inter-chip voltage is an extremely effective means of controlling spot welding quality. (For example, as a document, resistance welding research committee material "Spot welding quality assurance method"
Osaka University, Shuji Nakata et al., published by the Welding Society of Japan, December 9, 1975). By the way, due to constraints such as the shape of the object to be welded when detecting the inter-chip voltage, the detection positions are set at points A and B, which are quite far from the tip of the welding electrode (chip), as shown in Figure 1. The detection probe is pulled out along the arm of the welder. Here, 1 is the welding electrode (chip), 2 is the object to be welded, and 3
is the detection probe, 4 is the welding machine body, and Vt is the voltmeter.

Now, the actual detected chip-to-chip voltage (Vt)
is the resistance drop (V ₁ +
V ₂ +V ₃ +V ₄ +V ₅ ) and the induced voltage component (Kdi/dt) due to the welding current (K: induced voltage coefficient, i: welding current, t: time). Of these, the voltage (V ₃ ) between the objects to be welded, which is part of the resistance drop, is related to the value of the welded product.

Therefore, from the actually detected inter-chip voltage (Vt), first calculate the induced voltage (K) due to the welding current.
di/dt), find the resistance drop, then subtract the resistance drop within the chip (V ₁ + V ₅ ) and the resistance drop between the chip and the workpiece (V ₂ + V ₄ ) to find the resistance drop. If only the resistance drop (V ₃ ) between welded objects can be extracted, welding quality can be monitored with the highest accuracy.

However, in the past, only the induced voltage component was removed, but the resistance drop within the chip was not removed, and although this detection accuracy was sufficient in terms of S/N ratio, Therefore, as a result, monitoring of welding quality using inter-chip voltage was by no means satisfactory.

In view of the above conventional examples, the detection method of the present invention efficiently removes the induced voltage component and the resistance drop inside the chip at the same time, and more accurately detects the resistance drop between the objects to be welded, which is directly related to welding quality. That is.

That is, in addition to the induced voltage component of the conventional example, it is also possible to remove the internal resistance drop component. For convenience of explanation, the welding current during chip short-circuiting and the welding current during actual welding are assumed to be equal. As shown in FIG. 3, the present invention sequentially calculates the chip-to-chip voltage (V'ti) when the chip is short-circuited for each energization cycle from the designated cycle (C ₁ ) to the designated cycle (C _o ) of the energization time limit. V′t ₁ ,
Detected as V′t ₂ , ...V′tn and stored in memory.
Here, V′ti=(V ₁ +V ₆ +V ₅ )i. Here, i is the energization cycle, (V ₁ +V ₅ ) is the resistance drop within the chip, and V ₆ is the resistance drop between the chips. Note that the induced voltage component Kdi/dt is deleted because the AC detection circuit is used for detection, and the reason will be described later.

Next, during actual welding, the inter-chip voltage (Vti) is detected for each energization cycle from the specified cycle (C ₁ ) to the specified cycle (C _o ) of the energization time limit, and _the The stored value V't ₁ is subtracted from the detected value Vt ₁ of the case, and the difference value is determined as (Vt ₁ −V't ₁ ), and this is taken as the inter-chip voltage of the energization cycle (C ₁ ). Below, (Vt ₂ −V′t ₂ ), (Vt ₃ −V′t ₃ )..., (Vtn−
Find the difference value for each cycle like V′tn),
This is taken as the inter-chip voltage for each cycle. Here, Vti=(V ₁ +V ₂ +V ₃ +V ₄ +V ₅ )i.
However, the induced voltage component Kdi/dt is deleted because an AC integrating circuit is used for detection, and the reason will be explained later.

Therefore, Vti-V'ti=( _V2 + _V3 + _V4 - _V6 )i, which is at least the resistance drop within the chip. (V ₁ +V ₅ ) and the induced voltage component (Kdi/dt) can be removed, so compared to the conventional method where only the induced voltage component (Kdi/dt) is removed, the voltage V ₃ , which is more closely related to welding quality, can be removed. This means that the detection accuracy has been improved.

Furthermore, in the present invention, when detecting the inter-chip voltage,
By inputting the signal from the detection probe into an AC integrating circuit, and subtracting the voltage at the point when the welding current stops flowing from the voltage at the point when the welding current starts flowing from the output voltage, and taking the absolute value. This removes induced voltage.

Note that, for example, when welding two mild steel plates with a thickness of 1 mm, the appropriate welding current is 8000 A.
In addition, if the welding current at the time of a chip short circuit and the welding current during actual welding are different, the voltage between chips at the time of a chip short circuit multiplied by a certain constant should be stored as the inter-chip voltage at the time of a chip short circuit. Bye.

FIG. 4 shows an embodiment of a detection circuit for carrying out the detection method of the present invention. In the figure, the inter-chip voltage is input to an AC integration circuit, and further input to a microcomputer via a sample-and-hold circuit and an A/D conversion circuit. On the other hand, the welding current is input to a zero point detection circuit via a current transformer, which detects the point at which the welding current begins to flow and the point at which it stops flowing, and inputs it to the microcomputer. The circuit is a switch circuit that indicates whether the detected inter-chip voltage is the inter-chip voltage at the time of a chip short circuit or the inter-chip voltage during actual welding.

Now, the inter-chip voltage via the AC integrating circuit has an integrated waveform as shown in FIG. Here, A shows the waveforms of the welding voltage and welding current.

Normally, the welding current in resistance welding is controlled by controlling the firing angle (current conduction angle) of thyristors arranged in antiparallel as current-carrying current control elements. In this example, as shown in FIG. 3A, the thyristor is ignited and energized at points C and E of the welding voltage. In resistance welding, the current lags behind the welding voltage due to reactance, so the welding voltage and current are slightly out of phase, as shown in Figure 3A. Also, since the thyristor is not firing between DE, the welding current does not flow during this period and becomes zero.

Next, FIG. 5B shows the inter-chip voltage (Vti) or (V'ti) obtained through the AC integrating circuit.
Here, the AC integrating circuit has a circuit configuration that uses an operational amplifier as an inverting amplifier, so when the signal for the welding current shown in Figure 5 A is input, the input and output of that signal have reversed signs. It becomes what it is. In other words, the AC integrating circuit is charged to the positive side by the signal corresponding to the negative CD. This charging value is the sum of the induced voltage (Kdi/dt) and the resistance drop.

Now, di/dt is positive when the welding current is increasing, negative when it is decreasing, and becomes zero just at the peak of CD.

The output of the corresponding AC integrating circuit rises from Vt _C , takes a peak value at the peak of CD, and after that decreases as di/dt becomes negative, and the welding current becomes zero at the point corresponding to D. Therefore, the output of the AC integrating circuit becomes Vt _D.

Also, since the welding current is zero between DE,
The output of this AC integrating circuit is held. but,
In reality, a slight discharge occurs, so the AC integrating circuit output values Vt _E and Vt _D at the next energization start point are not equal.

Similarly, when the next energization occurs at point E due to ignition of the thyristor, the welding current waveform is on the positive side, contrary to CD, so the AC integrator output starts to decrease from Vt _E and decreases at the peak of EF. The sign of di/dt of the induced voltage Kdi/dt reverses from here, so charging begins in the positive direction, and the welding current takes the value Vt _F at point F where it becomes zero. .

The AC integrating circuit output (Vt C , Vt E ) at the point when the welding current starts flowing (for example, points _C and _E ) and the values (Vt D , Vt F ) at the point when the welding current stops flowing (points _D and _F ) in each current cycle are calculated. The sample is held, A/D converted, and taken into a microcomputer, and for each energization cycle, the output value of the AC integrator circuit is calculated from the output value of the AC integrator circuit when the welding current begins to flow, and the output value of the AC integrator circuit when the welding current ends. Operations that subtract and take the absolute value (for example, Vt ₁ = |Vt _C −Vt _D |, Vt ₂ = |Vt _E −
Vt _F |,...) is performed by a microcomputer. This absolute value is obtained by removing the induced voltage Edi/dt. This is because, as already mentioned, the welding current waveform has a convex shape, and this di/dt takes positive and negative signs with the peak of the mountain as the boundary, and by integrating over one cycle of current, it becomes positive and negative. This is because Edi/dt becomes zero due to negative cancellation. Based on the chip-to-chip voltage corresponding to only the resistance drop obtained in this way, the chip-to-chip voltage (V′ti) at the time of a chip short circuit is calculated from the specified cycle (C ₁ ) to the cycle ( C _o ) is detected every customer cycle by the means shown in Figure 4, and it is stored in memory.
Store them as V′t ₁ , V′t ₂ , ...V′t _o .

Then, the inter-chip voltage (Vti) during actual welding is similarly detected by the means shown in Figure 4, and the stored value V′t ₁ in the memory is subtracted from the detected value Vt ₁ of the specified cycle (C ₁ ). , this is the chip-to-chip voltage of the cycle (C ₁ ). In this way sequential cycles (C ₁ )
Subtract from to (C _o ) in the same way,
This is to find the inter-chip voltage for each cycle.

There are various ways to designate the cycles (C ₁ ) and (C _o ), but here we have taken a method of storing the designated values in the ROM of the microcomputer.
Usually, the cycle (C ₁ ) is 1 and the cycle (C _o )
is set to be the energization time limit.

If the detection method of the present invention as described above is used,
Of the inter-chip voltage, it is possible to remove not only the induced voltage, which was conventionally considered a noise component and removed, but also the internal resistance drop within the chip, making it possible to more accurately measure the resistance drop between the objects to be welded, which is related to welding quality. This has an extremely large effect on improving the quality of resistance welding using chip-to-chip voltage.

[Brief explanation of drawings]

Figure 1 is a side view of a welding machine implementing the method for detecting the voltage between chips, Figure 2 is an enlarged side view of the chip section showing the voltage between chips during actual welding, and Figure 3 is a side view of the welding machine that implements the method for detecting the voltage between chips. FIG. 4 is a block diagram of a detection circuit for carrying out the detection method of the present invention, and FIGS. FIG. 3 is a waveform diagram of an AC integral value of the voltage between the two terminals. 1... Welding electrode (chip), 2... Work to be welded,
3...Detection probe, 4...Welding machine body,...
AC integrator circuit, sample hold circuit,
...A/D conversion circuit, ...microcomputer, ...alternator, ...zero point detection circuit, ...
...Switch circuit.

Claims (1)

[Claims] 1 In detecting the voltage between welding electrodes in resistance welding,
The absolute value of the difference between the output of the AC integrating circuit at the time when the welding current starts flowing and the output of the AC integrating circuit when the welding current stops flowing is detected via the AC integrating circuit, and the absolute value of the difference between the output of the AC integrating circuit at the time when the welding current starts flowing for each energization cycle and the output from the AC integrating circuit when the welding current ends is detected as the welding electrode for each energizing cycle. The voltage between the welding electrodes (V′ti) is detected for each energization cycle from the specified energization cycle (C ₁ ) to the specified energization cycle (C _o ) when the welding electrodes are short-circuited and energized. and sequentially V′t ₁ , V′t ₂ ,...
During actual _welding , the welding electrode voltage (Vti) is detected for each cycle from the specified energization cycle (C ₁ ) to (C _o ), and For each energization cycle from ₁ ) to (C _o ), the difference value obtained by subtracting the memorized welding electrode voltage (V'ti) from the welding electrode voltage (Vti) is calculated as the welding electrode voltage. A method for detecting voltage between welding electrodes, characterized in that the voltage is detected as a voltage.