JPS6359795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides resistance welding, particularly spot welding in which welding current is controlled by manipulating the firing angle of a switching element. ),
Regarding devices to improve welding quality, a standard inter-chip voltage is set as a guideline for welding quality, and the firing angle is manipulated to make the inter-chip voltage follow this reference value, or the inter-chip voltage is adjusted to this reference value. The present invention relates to a resistance welding control device characterized in that the reference value can be easily set in a control method based on a so-called reference inter-chip voltage value, in which current is cut off when the voltage reaches the reference value.

It has been well known that inter-chip voltage is an effective means for detecting spot welding quality. For example, as a document, there is a document by the Welding Society of Japan, Resistance Welding Research Committee, ``Quality Assurance Method for Spot Welding'' (December 1972).

Based on the results of these studies, a device has been devised that uses inter-chip voltage to control spot welding quality to a constant level.

For example, as shown in Figure 1A, the inter-chip voltage
This method detects the peak value Vp of Vt, sets a threshold level for cutting off current at a point Vc that has decreased by a certain percentage of X%, and cuts off current when the inter-chip voltage Vt drops to that point ( JP-A-52-114541) ``Method and device for controlling energization time in resistance welding'' and the like have been proposed. However, as is well known, in order to form a nugget (molten metal part), a current higher than a certain critical current is required. Furthermore, if the welding time is simply extended, uniform welding quality cannot be achieved.

Therefore, in order to make welding quality uniform, the absolute value of the inter-chip voltage must exceed a certain reference value within a limited time.

By setting this reference value and controlling the firing angle and energization time so that the inter-chip voltage follows or exceeds this value, good welding results can always be obtained.

However, setting this reference value is expected to be extremely complicated and difficult since there is no table of conditions based on past experience, as in the setting of welding current, pressing force, etc.

In view of the above conventional examples, the device according to the present invention sets a reference value of the inter-chip voltage as a measure of welding quality, and controls the inter-chip voltage to follow the reference value by manipulating the firing angle of the switching element. Alternatively, the present invention relates to a spot welding control device characterized in that a reference value can be easily set in control of bringing a part of the inter-chip voltage close to the reference value.

First, regarding the detection of the inter-chip voltage, since the induced voltage due to the welding current is detected superimposed on the resistance drop voltage between the chips, it is necessary to remove this induced voltage. To do this, for example, input the inter-chip voltage into an AC integrating circuit, and as shown in Figure 2, the integrated output value ( a _A ,
a _A ′,…), the point at which the flow ends (B, B′,…)
The integral output values (a _B , a _B ′, ...) corresponding to are detected, and the absolute value of each of the difference values, for example, |a _A ,
Let a _B |, |a _A ′, a _B ′|, ... be the inter-chip voltage corresponding to each half-cycle energization.

FIG. 3 shows an example of the apparatus of the present invention, which is constructed mainly of a microcomputer.

The configuration of the device of the present invention will be explained below using this circuit as an example.

The inter-chip voltage is taken into a microcomputer 5 via an attenuator 1, an AC integration circuit 2, a sample hold circuit 3, and an A/D conversion circuit 4. A capture timing signal is output from the microcomputer 5 to the sample hold circuit 3 and A/D conversion circuit 4, and this signal is used to transfer the welding current taken out via the current transformer 6 to the zero point detection circuit This is based on the signal C (FIG. 2C) which is input to the microcomputer 5 by detecting the start and end points of the welding current flow. That is, sample and hold is applied to the pulse signal C in FIG. 2, and A/D conversion is performed. The above is a means for detecting the inter-chip voltage.

Next, a timer time setting circuit 8, which is configured with a digital switch, for example, is provided for setting an initial pressurization time limit, an energization time limit, a holding time limit, and an opening time limit.
Each time limit value is input into the microcomputer 5, and the input voltage detected via the filter circuit 9 is input into the zero point detection circuit 10, and the obtained zero point detection pulse (FIG. 4 b) causes the microcomputer 5 to be The time limit is counted. Specifically, a value twice the time limit is set in the event counter in the microcomputer, and each time this pulse e is input, it is decremented by 1, and the point when a digit loss finally occurs is determined as the end point of the time limit. This is the way to do it.
In this way, each timer period is set, and the timing for setting the control signal of the electromagnetic valve that performs pressurization control and the gate trigger pulse of a switching element (for example, a thyristor, etc.) is determined. The above is the timer time limit setting means.

Next, regarding the setting of the welding current, first, welding current setting circuit 1 consisting of a digital switch etc.
The set value of 1 is taken into the microcomputer 5. In the microcomputer 5, the zero point pulse e detected by the zero point detection circuit 10 is
(Fig. 4B) is detected, and in synchronization with this, the microcomputer 5 generates a one-shot pulse f by a program based on the data of the circuit 11.
(Figure 4 C) is created and output. Specifically, as a method of setting the time limit programmatically, there is a method of setting "1" at the exit port while the same loop is looped the number of times equal to the data value of the circuit 11.

On the other hand, 12 in FIG. 3 is a ramp waveform setting circuit which uses the output f in FIG. 4 C as a reset signal. Therefore, as is clear from the output g in Figure 4D, if the width of the one-shot pulse f is changed,
The ramp output start point of the ramp waveform is changed, and this g waveform and the filter circuit 9 in FIG.
The waveform (fourth waveform) obtained by rectifying the output of
If the comparator circuit 14 compares the values (a) and (a) in FIG. 4 and outputs the pulse output h as shown in FIG. 4 (e) when g in FIG.
By changing the set value of the welding current setting circuit 11 shown in Fig. 3, the width of the pulse f of the one-shot output shown in Fig. 4 C can be changed, and therefore the pulse generation position of Fig. 4 E can also be manipulated. Become. This h
The signal is passed through a buffer circuit 15 and an electrically insulating circuit (for example, a pulse transformer) 16 to serve as a gate trigger signal for the thyristor.

As in this example, the ramp waveform output g in FIG.
If a method is adopted in which the firing angle is set by comparing the rectified waveform d of the input voltage with the rectified waveform d of the input voltage (Fig. 4 A), if the input voltage fluctuates, the firing angle will automatically compensate for the fluctuation. This means that an input voltage fluctuation compensation function has been added. If a DC constant voltage is used instead of the rectified waveform d, an input voltage fluctuation compensator etc. will be eliminated, but the firing angle can be set freely as in the case with the input voltage fluctuation compensation function.

The above are the means for setting the welding current and the means for compensating for input voltage fluctuations.

Now, the inter-chip voltage value during the energization process can be stored in the memory of the microcomputer 5 for each energization cycle by the above-mentioned timer time limit setting means, firing angle setting means, and inter-chip voltage detection means. In spot welding of mild steel or stainless steel, the data value at that time is approximately the value shown in FIG. 5, which is A/D converted and stored for each energization cycle. Now, here is the peak value of the inter-chip voltage (Vp in Figure 5) when welding is performed well.
Alternatively, the cumulative value (S in FIG. 5) from the beginning of energization is determined by searching or calculating using a program in the microcomputer 5, and is digitally displayed on the display 18 via the display interface circuit 17.

The operator can know by looking at the display 18 the peak value or cumulative value of the inter-chip voltage when welding has been performed satisfactorily.

Note that 19 in FIG. 3 is a chip-to-chip voltage setting circuit composed of a digital switch, etc., and the operator uses this setting circuit 19 to set the reference chip-to-chip voltage by referring to the above displayed data. Can be done. In addition, in the case of a method that uses this display content itself as a reference value, this circuit 1
9 requires only a key switch to notify that the displayed content has been accepted as the reference value.

The above are the inter-chip voltage display means and setting means.

In FIG. 3, 20 is a timer start switch circuit, and 21 is a buffer circuit. The reason why the device of the present invention is provided with an input voltage fluctuation compensation function is because setting a reference value is thought to be complicated in factories with poor power supply conditions. By using the circuit shown in Fig. 3, it is easy to set the reference value, and it is also possible to compare the reference value and the detected inter-chip voltage value at a specified time during the energization cycle, and if there is an excess or deficiency, By using a microcomputer, it is possible to manipulate the subsequent firing angle to make the inter-chip voltage follow or approach the reference value, and by doing this, welding quality can be made uniform. Needless to say, this can be achieved.

According to the resistance welding control device of the present invention as described above, since the inter-chip voltage as a reference value can be easily set to a high degree of integration as described above, welding quality can be controlled using the inter-chip voltage. High efficiency and high accuracy of quality control can be achieved, and the device itself can be configured at low cost.

[Brief explanation of the drawing]

Figures 1A and 2B are characteristic diagrams showing an example of a conventional quality control method using inter-chip voltage. Figure 3 is a circuit diagram of an embodiment of the welding control device according to the present invention, Figure 4 A, B, C,
D and E are output waveform diagrams of the main parts of the circuit in Figure 3, and Figure 5.
The figure is a diagram showing an example of a reference value of inter-chip voltage. 1...Attenuator, 2...AC integration circuit, 3
... Sample hold circuit, 4 ... A/D conversion circuit, 5 ... Microcomputer, 6 ... AC generator, 7 ... Zero point detection circuit, 8 ... Timer time limit setting circuit, 9 ... Filter circuit, 10 ... Zero point detection circuit, 11 ... Welding current setting circuit, 12 ...
...Ramp waveform setting circuit, 13... Rectifier circuit, 14
... Comparator circuit, 15 ... Buffer circuit, 16 ... Electrical isolation circuit, 17 ... Interface circuit, 18 ... Display, 19 ... Inter-chip voltage setting circuit, 20 ... Start switch, 21 ...
...Buffer circuit.

Claims (1)

[Claims] 1. A control rectifying element for controlling a welding current, a welding current setting means for determining a firing angle of the control rectifying element corresponding to the set welding current by inputting a set welding current, and a welding current setting means for detecting an input power supply voltage. The firing angle of the control rectifying element determined by the welding current setting means is advanced when the input power supply voltage is lower than a desired voltage, and the firing angle determined by the welding current setting means is advanced when the input power supply voltage is higher than the desired voltage. half-cycle input voltage fluctuation compensation means for delaying the firing angle of the control rectifying element, welding electrode voltage detection means for detecting the welding electrode voltage during welding, and the welding electrode voltage detection means detecting the welding electrode voltage. A resistance welding control device comprising display means for displaying a voltage between welding electrodes.