JPH0355230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method and apparatus for determining the quality of welding of a capacitor discharge type stud welding machine.
In particular, a capacitor discharge is configured to create an arc discharge between the base metal and the stud to melt the welded part, and then press the stud into resistive contact with the base metal to allow current to flow through the contact area. The present invention relates to a method and apparatus for determining the quality of welding in a type stud welding machine.

Conventional technology A capacitor discharge type stud welding machine creates an arc discharge between the base metal and the stud to melt the welded part, and then presses the stud into resistance contact with the base metal to weld the welded part. Capacitor discharge type stud welding machines are well known which are configured to apply current to the stud to reliably weld the stud to the base metal. The quality of welding with this welding machine is
It depends on the timing of pressing the stud to the base material,
If this timing is out of order, there is a risk of welding defects. This is because if the welded portion of the stud and base metal is not sufficiently melted by arc discharge, welding by resistance contact becomes unstable.

In the capacitor discharge type stud welding machine described above, the discharge current for welding has a single mountain-shaped waveform. This is due to the growth of the arc discharge and the charge stored in the capacitor decreasing as the discharge progresses. That is, at the beginning of discharge, the amount of charge in the capacitor is large and the discharge current increases at an upward slope as the arc discharge grows, but as the discharge continues, the amount of charge gradually decreases and the discharge current begins to decrease gradually. Eventually, the slope changes from positive to negative, and the discharge current continues to fall, resulting in the waveform of the discharge current becoming mountain-shaped.

For a capacitor discharge stud welding machine that exhibits such a discharge current waveform, the optimal pressure contact point should be in the range of 1/2 to 1/3 of the peak current value on the descending line past the peak of the discharge current waveform. This is known from experience. Although it appears that the current for melting is large at the point of the largest peak of the discharge current and the stud and base metal are most strongly melted, there is a time delay in the transfer of heat for melting both the stud and the base metal. Therefore, it has been found that the stud and base metal are most appropriately melted at 1/2 to 1/3 of the peak value on the descending line past the peak.

When the stud is optimally melted, it is preferable to press the stud into resistive contact with the base material. When the stud is press-fitted to the base material for resistance contact in this way, a small mountain or hump-like waveform appears in the discharge current waveform. This is because a current due to arc discharge flows before the pressure contact point, whereas a current flows due to the contact between the stud and the base material after the pressure contact point. In other words, the contact resistance between the stud and the base metal after pressure welding is lower than the resistance during arc discharge, so the current increases temporarily;
As the capacitor discharges, the current decreases again.

Problems to be Solved by the Invention Conventionally, in order to judge the quality of welding in this capacitor discharge type stud welding machine, the current of the pressure contact was measured and it was determined whether the pressure contact was within a preferable timing range. That is, in order to measure the pressure contact current, the welding current was detected and the current waveform of this welding current was observed using a residual image tube (CRT) oscilloscope. However, in such conventional methods, the operator must visually inspect the waveform on the screen of the oscilloscope, making it nearly impossible to inspect all welds. Also, due to visual inspection by the worker,
The current situation was far from achieving unmanned workers.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to provide a method and apparatus that can easily and automatically determine the quality of all welds for each weld.

Structure of the Invention In order to achieve the above object, according to the present invention,
In order to weld the stud to the base metal using the energy stored in the capacitor, an arc discharge is created between the base metal and the stud, and then the stud is pressed into resistance contact with the base metal and a current is applied to the contact area. In a method for determining the quality of welding in a capacitor discharge type stud welding machine, the capacitor discharge current of the stud welding machine is detected, the peak value of the discharge current is held, and the positive slope portion and the negative slope portion of the discharge current are detected. The gradient part is detected, and the pressure contact point for resistive contact between the stud and the base metal is found by the AND operation of both parts, and the value of the discharge current at the pressure contact point is held, and the peak value and the pressure contact point are found. A welding quality determination method for a capacitor discharge type stud welding machine is provided, which comprises comparing the current value with a point current value to determine whether or not the pressure contact current value is within a predetermined range of a peak value.

Further, according to the present invention, as a device for carrying out the above method, a peak current holding device receives a welding current of a welding current supply circuit that utilizes energy stored in a capacitor of a stud welding machine and holds the peak value of the current. a negative slope detector that receives the welding current, differentiates the current, and detects its negative slope portion; and a positive slope detector that receives the welding current, differentiates the current, and detects its positive slope portion. The output of the negative slope detector is connected to the control terminal of one element, the output of the positive slope detector is connected to the control terminal of the other element, and the welding current is input to the input side. two switch elements connected in series, and a pressure contact current value holder that is connected to the output side of the switch element and holds the current value of the welding current supplied by conduction of both elements. and connected to receive the output of the peak current holder and the output of the pressure contact current value holder,
A capacitor discharge type stud welding machine comprising: a comparison/judgment device that compares the peak value and the current value of the pressure contact to determine whether or not the pressure contact current value is within a predetermined range of the peak value. A welding quality determination device is provided.

Effect of the Invention As mentioned above, the pressure contact for resistance contact is as follows.
It is on the descending line that has passed the peak of the welding current waveform. At this point, a hump-like waveform appears in the welding current waveform. Looking at the slope of such a waveform of welding current, the peak is dark, the first half has a positive slope, and the second half has a negative slope except for the pressure contact point. Further, at the pressure contact point, the slope becomes positive, albeit slightly, at the hump-shaped portion, and then becomes negative again.
Therefore, if the positive slope part and the negative slope part are detected and their logical product (AND) is performed, only the pressure contact will be "1", and by holding the current value at this time, the pressure contact current value will be changed. can be obtained. On the other hand,
If the peak current value of the welding current is maintained, it is very easy to determine in which range of the peak current value the pressure contact current value falls. Therefore, if the pressure contact current value is 1/2 to 1/3 of the peak current value, it can be determined that the welding quality is "good".

Effects of the Invention According to the present invention, all types of welding can be performed extremely easily and without using expensive machines such as after-image type cathode ray tube oscilloscopes, and without forcing operators to perform visual inspections to observe waveforms. The welding quality of the capacitor discharge type stud welding machine is automatically determined. Further, if the welding machine is set to proceed to the next welding point only when the welding quality is good, and to weld again when the welding quality is poor, welding work can be automated. Furthermore, since the peak value of the welding current is held, it can also be determined whether the welding current is appropriate.

Furthermore, in the device of the present invention, the welding current is differentiated twice in order to detect a positive slope, and as a result, it is possible to clearly detect the hump-like wave of the resistance contact pressure contact, which does not appear at such a large level. There are also advantages.

Embodiments Examples of the present invention will be described below with reference to the drawings. In FIG. 1, a stud grasping part (not shown) of a capacitor discharge type stud welding machine 1 is shown.
The electrical energy stored in the capacitor 4 of the welding machine 1 is applied to the stud 2 and the base metal 3 attached to the welding machine 1, causing an arc discharge between the tip of the stud 2 and the base metal 3, and the stud 2 It is welded to the base material 3. The quality of this welding depends on the timing at which the tip of the stud 2 melted by arc discharge is pressed into resistance contact with the base metal 3, and it is known that if the timing is out of order, welding defects will occur. There is. The timing point of this pressure welding is preferably within the range of 1/2 to 1/3 of the peak value of the welding current on the descending line past the peak of the mountain-shaped welding current waveform.

In order to observe the welding current waveform, the present invention is provided with a peak and pressure contact current value holding circuit 5 that holds and outputs the peak welding current value and the resistance contact pressure contact welding current value. The voltage appearing at both ends of a resistor 6 installed in series between the welding machine 1 and the base material 3 is input to this circuit 5, and the voltage at both ends of the resistor 6 changes depending on the welding current. As a result, the welding current is input to the circuit 5. The peak welding current value from the circuit 5 is sent via the output terminal 7, and the pressure contact welding current value is sent to the comparison judgment circuit 9 via the output terminal 8. In this circuit 9, the pressure contact welding current is determined as the peak welding current. It is determined whether or not it is within a predetermined range (1/2 to 1/3), and a welding quality signal is output from the circuit 9. This welding pass/fail signal may be sent to a lamp, speaker, etc. to indicate pass/fail, or may be sent to an automatic welding control device (not shown) to automate the work, that is, to make it unmanned. You can do it like this.

FIG. 2 shows a block diagram of the peak and pressure contact current value holding circuit 5. The current waveform obtained by the resistor 6 in FIG. 1 is amplified by the amplifier 11. As shown in FIG. 4a, the welding current waveform is generally mountain-shaped as a whole, and a hump-like waveform appears at the resistance contact pressure contact Z. The welding current output from the amplifier 11 is sent to a peak current holder 12, where the current at the peak of the welding current (point y in FIG. 4a) is held and output to the output terminal 7. (See Figure 4i).

The output of the amplifier 11 is sent to a negative slope detector 13 and a positive slope detector 14 to detect the resistance contact pressure contact of the welding current. The negative slope detector 13 detects a portion where the welding current is decreasing, that is, a portion in the latter half from the peak, and outputs a pulse having a timing and width corresponding to this portion. In this case, it is preferable to set it to such an extent that it is insensitive to the positive slope at the press contact point. The positive slope detector 14 detects the part where the welding current is increasing, that is, the first half from the start of the welding current to the peak, and the part where it increases like a hump at point Z (insulation pressure contact) in Fig. 4a. It detects these parts and outputs two pulses with widths and timings corresponding to these parts. The outputs of both detectors 13 and 14 are sent to an AND gate 16, where they are ANDed,
A pulse corresponding to the pressure contact is output. This pressure contact pulse is sent to the control terminal of the switch circuit 17 to which the welding current from the amplifier 11 is input, and makes the switch 18 conductive. The output of the switch circuit 17 is input to a pressure contact current holder 19, which holds the input pressure contact welding current when the switch is turned on, and outputs it to the output terminal 8.

Note that the peak current holder 12 can use a circuit similar to that shown in FIG. 3, which will be described later, but is not limited to this, and it goes without saying that other peak value holding circuits may be used. . Further, the pressure contact current holder 19 can be realized by a similar circuit, but it may also be realized by another circuit, such as an analog hold circuit. The gradient detectors 13 and 14 may be either analog computing units or digital computing units as long as they can detect the gradient of the welding current waveform. In the case of analog computing units, a typical example is a combination circuit of a differentiator and a comparator. Will. Further, in the case of a digital arithmetic unit, an A/D converter will be required. AND
The gate 16 is not essential; for example, by using two switches 18 of the switch circuit 17 and arranging them in series and connecting the outputs of the detectors 13 and 14 to their respective control terminals, an AND operation can be performed. and in this case
AND gate 16 becomes unnecessary. switch circuit 1
The switch 18 of 7 may be a mechanical switch, but
It may be an electronic switch such as a semiconductor switch, and any switch element can be used as long as it can be controlled by an external signal.

In the comparison/judgment circuit 9 (Fig. 1), the peak welding current value is detected from the output terminal 7 of the circuit 5, and the peak welding current value is detected from the output terminal 8 of the circuit 5.
The resistance contact pressure contact welding current values are respectively inputted from . The input pressure contact welding current value is compared with the peak welding current value, and it is determined whether the pressure contact welding current value is within a predetermined range (1/2 to 1/3) of the peak welding current value. If it is within the range, for example, the welding quality signal is set to "1". This circuit 9 can be constructed of any circuit as long as it has the above function, and its detailed construction is omitted from illustration.
Regarding the comparison and determination, in a typical configuration, the above-mentioned comparison and determination can be performed using a simple voltage comparator. However, in addition to this, the peak welding current value and the pressure contact welding current value are each measured independently, and it is determined whether the peak welding current value is within a predetermined value. It may be determined whether the welding current is within a predetermined range. According to this, since the peak welding current value is also determined, it can be similarly checked whether the welding current is excessive or insufficient.

FIG. 3 shows another circuit that has the same effect as the peak and pressure contact current value holding circuit 5 shown in FIG. A current signal is input. This signal is inverted and amplified by the amplifier 23, and its output is
The signal is input to an inverting first differentiator 24 and a second amplifier 25 . The second amplifier 25 is also an inverting amplifier,
The output signal g is brought into phase with the waveform input to the amplifier 23 (FIG. 4a). The output of amplifier 25 is input to peak current holder 26 .

The peak current holder 26 consists of an operational amplifier 27, a diode 28, and an FET 29, and a capacitor 30 is provided at the gate of the FET. This type of holder is well known, but its operation will be briefly explained. After setting the output terminal 7 to zero using the reset circuit 31 or the like, when a signal is applied to the amplifier 27, the holder is connected to the capacitor 30 via the diode 28.
A current flows between the source and drain of the FET according to the charged voltage, and the voltage of the resistor 32 gradually increases. When the input signal exceeds its peak value and begins to decrease, the diode 28 and the high impedance of the gate of the FET hold the charge in the capacitor for a long time without escaping anywhere. Therefore, this retainer 26 holds the peak welding current value and outputs the peak welding current value from the output terminal 7.

The output of the second amplifier 25 is input to a switch circuit formed by photo transistors of two photo couplers 34 and 35 connected in series. These phototransistors act as switch elements, and as mentioned above, by connecting two switch elements in series, they function as a logical product operator (that is, an AND gate).

The welding current signal passing through the two phototransistors is sent to a current holder 36 having the same configuration as the first current holder 26, and outputs the value of the signal when both phototransistors of the photo couplers 34 and 35 are conductive. Output to terminal 8. As will be described later, since the two phototransistors are both conductive at the pressure contact, the output terminal 8 outputs a pressure contact welding current value.

The output of the first amplifier 23 is the reaction type first differentiator 2
4 is entered. The differentiator 24 is composed of a capacitor 38 and an inverting amplifier 39 connected in series, and differentiates the input signal to obtain its slope, inverts the slope signal, and outputs the inverted signal. The output of the first differentiator 24 is connected to the non-inverting input of the first comparator 41 via a diode 40.
Therefore, only a negative level signal is input to the comparator 41. A negative level reference voltage is applied to the inverting input of the comparator 41, and the output of the comparator 41 is approximately zero unless the input voltage from the first differentiator 24 becomes more negative than the reference voltage. The power supply voltage terminal of the comparator 41 is biased to a negative level by the ground potential and a negative voltage as shown in the figure, and the first differentiator 4
1 becomes a level more negative than the reference voltage applied to the inverting input of the comparator 41, the output of the comparator 41 outputs a negative voltage, which causes the second
A current flows through the light emitting diode of the photocoupler 35, causing it to emit light, thereby making the phototransistor of the second photocoupler, which serves as a switch element, conductive.

The output of the first differentiator 24 is transmitted to the second inverting differentiator 4
3 is input. This second differentiator 43 has the same configuration as the first differentiator, and functions to differentiate and invert the output of the first differentiator 24 again, and differentiates the once differentiated signal again, so that the welding current waveform at the pressure contact This is effective for highlighting the inflection point in a humped waveform. In other words, the second differentiator 43 can make the press contact point, which could not be sufficiently highlighted with the first differentiator 24, clear.

The output of the second differentiator 43 is inputted to the second comparator 45 which is the same as the first comparator 41 via the diode 44, and the output of the second differentiator 43 becomes more negative than the reference voltage of the second comparator 45. Then, the second comparator 45 outputs a negative voltage. As a result, the light emitting diode of the first photocoupler 34 emits light, and the phototransistor of the first photocoupler 34, which serves as a switch element, becomes conductive.

In the operation of the circuit shown in Fig. 3, the input terminal 2
When the welding current signal shown in FIG. 4a is input to 1 and 22, the amplifier 23 outputs the signal shown in FIG. 4b. When this signal is differentiated and inverted by the first differentiator 24, as shown in FIG. A signal c indicating a negative level is output in some parts. This signal c is the diode 4
0 to the first comparator 41, this comparator 41 outputs the signal f in FIG.
The light emitting diode is made to emit light, and the phototransistor of the second photocoupler 35 is made conductive. That is, the phototransistor of this photocoupler 35 detects the latter half (negative slope portion) of the welding current signal a.
It becomes conductive.

The signal c from the first differentiator 24 is transmitted to the second differentiator 43
It is differentiated again by and inverted. In FIG. 4, the signal c is made negative at the positive part and made positive at the negative part, as shown in the signal d, and the pressure contact Z
The inflection point at (see waveform a) is expanded, and the level becomes negative at that portion, albeit for a short time. The signal d is input to the second comparator 45 via the diode 44, and as shown in FIG.
outputs a pulse that has a negative level between the first half of the welding current and pressure contact z, and connects the first photocoupler 34.
make the light emitting diode emit light. This allows the first
The phototransistor of the photocoupler 34 is made conductive, passing the first half of the welding current and the signal from the second amplifier 25 at the pressure contact.

As mentioned above, the phototransistor of the second photocoupler 35 is conductive only in the latter half of the welding current, so the two phototransistors are conductive only at the pressure contact point z, as shown in FIG. 4h.
Only the signals corresponding to the pressure contacts are input to the holder 36. By inputting the signal h, the retainer 36 maintains the pressure contact welding current as it is, and outputs the signal shown in FIG. 4j to the output terminal 8.

On the other hand, the welding current signal g from the second amplifier 25 is also sent to the peak current holder 26, which outputs the peak value of the signal to the output terminal 7 (see FIG. 4i). Although the waveform of the output g of the second amplifier 25 is not shown, it is almost the same as that in FIG. 4a.

The peak welding current value i and the pressure contact welding current value j output from the output terminals 7 and 8 are compared by the comparison judgment circuit 9 shown in FIG. 1, and the quality of the welding is determined by outputting a welding quality signal. can be determined. Therefore, the quality of welding can be inspected over the entire welding process very easily and automatically without using an oscilloscope.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a welding quality determination device according to the present invention, Fig. 2 is a circuit diagram of a first embodiment of the peak and pressure contact current value holding circuit shown in Fig. 1, and Fig. 3 is a block diagram of the peak and pressure contact current values. FIG. 4 is a circuit diagram of the second embodiment of the holding circuit, and is a waveform diagram of each part of the circuit of FIGS. 2 and 3. 1...Capacitor discharge type stud welder, 2...
... Stud, 3 ... Base material, 5 ... Peak and pressure contact current value holding circuit, 7 ... Peak current output terminal,
8... Pressure contact current output terminal, 9... Comparison/judgment circuit, 11... Amplifier, 12... Peak current value holder, 13, 14... Gradient detector, 16... AND
Gate, 17... Switch circuit, 19... Pressure contact current holder, 23, 25... Amplifier, 24... First differentiator, 26... Peak current holder, 34...
1st photocoupler, 35... 2nd photocoupler,
36... Pressure contact current holder, 41... First comparator, 43... Second differentiator, 45... Second comparator.

Claims (1)

[Claims] 1. In order to weld the stud to the base metal using the energy charged in the capacitor, an arc discharge is created between the base metal and the stud to melt the welded part, and then the stud is welded to the base metal. In a method for determining the quality of welding of a capacitor discharge type stud welding machine, which is configured to make resistance contact with a stud welding machine and to flow a current through the contact part, the capacitor discharge current of the stud welding machine is detected and the peak of the discharge current is determined. The value is held, the positive slope part and the negative slope part of the discharge current are detected, and the pressure contact point for resistive contact between the stud and the base material is found by ANDing the two parts. Capacitor discharge type stud welding, characterized in that the value of the discharge current is held, and the peak value and the pressure contact current value are compared to determine whether the pressure contact current value is within a predetermined range of the peak value. How to judge the quality of welding of the machine. 2 In order to weld the stud to the base metal using the energy stored in the capacitor, an arc discharge is created between the base metal and the stud to melt the welded part, and then the stud is brought into resistance contact with the base metal. A welding quality determination device for a capacitor discharge type stud welding machine that is configured to apply pressure to the contact part and pass current through the contact part, receives a welding current from a welding current supply circuit that utilizes the energy stored in the capacitor of the stud welding machine. a peak current holder that holds the peak value of the current; a negative slope detector that receives the welding current, differentiates the current, and detects its negative slope portion; and a negative slope detector that receives the welding current and differentiates the current. a positive slope detector for detecting the positive slope portion; a control terminal of one element is connected to the output of the negative slope detector; and a control terminal of the other element is connected to the output of the positive slope detector. The welding current is inputted to the input side, and the welding current is connected to two switch elements connected in series with each other, and the output side of the switch element is connected to the welding current supplied by the conduction of both elements. a pressure contact current value holder for holding a value; and a pressure contact current value holder connected to receive the output of the peak current holder and the output of the pressure contact current value holder, and comparing the peak value and the current value of the pressure contact. 1. A welding quality determination device for a capacitor discharge type stud welding machine, comprising a comparison determination device for determining whether or not a pressure contact current value is within a predetermined range of a peak value. 3. The negative slope detector includes a first differentiator that differentiates and inverts the inverted welding current, and a first comparator that receives an output from the differentiator and detects that the output is at a negative level. The positive slope detector includes a second differentiator that redifferentiates and inverts the output from the first differentiator, and a second differentiator that receives the output from the second differentiator and detects that the output is at a negative level. 3. The apparatus of claim 2, further comprising a second comparator for sensing. 4. A patent claim in which each of the two elements is a photocoupler consisting of a light-emitting element and a light-receiving element, the light-receiving element is used as an analog switch, and the light-emitting element is connected to the first comparator or the second comparator. The device according to item 2 of the scope of the invention.