JPS6325876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance welding device that can control welding current in response to the condition of a welded location, particularly the occurrence of "splash" during AC resistance welding.

In general, in resistance welding, welding quality is determined by various electrical quantities: voltage and current, resistance which is the voltage divided by current, electric power which is the product of voltage and current,
Furthermore, it has been well known that this has a deep relationship with the value integrated over the energization time. Therefore, the amount of electricity when welding the material to be welded under specified welding conditions is received from both electrodes that hold the material to be welded, and this is stored as a standard amount of electricity, and this stored amount of electricity is A method of controlling the welding current so as to trace the standard quantity of electricity by detecting the difference in quantity of electricity during subsequent welding is being put into practical use.

As an apparatus to which this type of prior art is applied, there is a "resistance welding apparatus" as previously disclosed in Japanese Patent Application No. 1983-79989 filed by the present applicant. This device includes means for receiving an amount of electricity from both electrodes that sandwich the material to be welded, and converting the amount of electricity from analog to digital;
The amount of electricity obtained from both electrodes when the material to be welded is welded under the specified welding conditions is determined by the A/D.
means for receiving the quantity of electricity A/D converted by the A/D converting means and storing the quantity of electricity when the converting means receives the quantity of electricity; In a resistance welding apparatus comprising means for comparing the amount of electricity obtained from the A/D converting means and an AC welding power source for controlling the welding current according to the output of the comparing means, the output side of the comparing means A means for outputting phase conversion data is connected to the output means, and a phase conversion data table is stored in the output means for correcting the difference between the electric quantities compared by the comparison means. During welding, corresponding phase conversion data is searched according to the output of the comparing means, and the firing angle of the SCR in the AC welding power source is controlled based on the searched output, and the state of the welded part is controlled. Even if the welding current changes, the welding current is controlled to ensure reliable welding so that it quickly and reliably follows the reference electricity amount when welding under pre-specified welding conditions. .

Further, in the above-mentioned resistance welding apparatus, there is provided a means for monitoring fluctuations in the power supply voltage of the AC welding power source, and a means for automatically changing the search address of the phase conversion data table according to the amount of voltage fluctuation detected by the monitoring means. In order to quickly and reliably follow the standard amount of electricity when welding under pre-specified welding conditions, even if the power supply voltage of the AC welding power source changes, the welding current It has become possible to control the

According to this resistance welding device, it is true that even if there is a shunt caused by the proximity of the welded part to an already welded part or a change in the surface condition of the welded part, the standard electricity quantity can be quickly and reliably applied. In addition, even when the power supply voltage fluctuates greatly, the standard quantity of electricity can be traced in the same way. As a result, it is possible to always obtain the optimum nugget without being affected by fluctuations in the welding power source, welding materials, welding conditions, etc., and there is no damage to the electrode due to excessive current or insufficient welding strength due to insufficient current. , the effect is great. However, the phase of the welding current is determined by comparing the amount of electricity during welding under pre-specified welding conditions and the amount of electricity detected during subsequent welding at an appropriate sampling interval. When performing control, if the power supply voltage fluctuates greatly or if the difference between the standard quantity of electricity and the quantity of electricity detected during subsequent welding is large, the welding current must be rapidly increased or decreased. Taking as an example a case where there is a large difference between the standard quantity of electricity and the quantity of electricity detected during subsequent welding, the response characteristics of the above-mentioned conventional device are experimentally determined and are as shown in FIG. 1. In Figure A, a rectangular waveform that fluctuates from 5000 amperes to 7000 amperes in current equivalent is set as the standard voltage, and the standard voltage is traced using three types of phase conversion data of X, Y, and Z with different response characteristics. It is something. Figure b shows a trace of a standard voltage waveform equivalent to 5000 amperes, and figure c shows a trace of a rectangular wave varying from 5000 amperes to 3000 amperes.
Here, the response characteristic refers to the amount of increase or decrease in the welding current per appropriate sampling interval, and the characteristic is assumed to have a relationship of X<Y<Z. As is clear from this figure, the phase conversion data Z whose response characteristics are largely determined can sufficiently follow sudden changes in voltage. Furthermore, it can be seen that the phase conversion data X whose response characteristics are set small tends to be delayed in tracking.

By the way, during resistance welding, the amount of heat generated in the part to be welded is generally excessive due to causes such as excessive current, insufficient pressure, poor pressure response, and excessive surface contact resistance, causing the material to be welded to overheat. scattering,
So-called "scattering" may occur. This splintering includes front splintering and middle splintering, and when the former occurs, it damages the surface of the material to be welded and the electrode material.
Furthermore, when the latter occurs, a large "shrinkage cavity" is likely to be formed in the nugget portion. In particular, if large shrinkage cavities are formed, the strength of the welded portion will naturally be reduced. FIGS. 2a and 2b show, by solid lines, the changes in interelectrode voltage and interelectrode resistance, respectively, when expulsion occurs during welding in the conventional apparatus described above. As is clear from this figure, when expulsion occurs during welding, both the inter-electrode voltage and the inter-electrode resistance drop rapidly, but in this conventional device, the amount of drop in the inter-electrode voltage, that is, the standard inter-electrode voltage Converting the search address of phase conversion data having a response characteristic according to the difference Δ _v from the interelectrode voltage in actual welding from the phase conversion data table,
Since the welding current is controlled so that the interelectrode voltage waveform during actual welding follows the standard interelectrode voltage waveform, the supply of welding current increases rapidly, causing the nugget to overheat and cause expulsion. It had the disadvantage of creating a cause.

Therefore, an object of the present invention is to provide resistance welding that can compensate for welding strength by controlling the welding current so as to obtain as normal a nugget as possible even when splintering occurs during AC resistance welding. The goal is to provide equipment.

The resistance welding device according to the present invention includes a means for detecting a voltage between two electrodes that clamp a material to be welded, and a memory for storing the voltage obtained from the two electrodes when the material to be welded is welded under specified welding conditions. means for comparing the voltage stored by the storage means with the voltage obtained during subsequent welding; and means for comparing the voltage stored by the storage means with the voltage obtained during subsequent welding; means for searching and outputting the phase conversion data obtained by the search, a welding current control means for automatically tracing the stored standard voltage by the searched output, and means for monitoring fluctuations in the power supply voltage; A resistance welding apparatus comprising means for automatically shifting a search address of the phase conversion data table according to the amount of voltage fluctuation detected by the monitoring means, the voltage obtained when welding the material to be welded. means for detecting the point of occurrence of splintering during welding; and an output of the detection means to control the search address shifting means to select a search address having the smallest response characteristic in the phase conversion data table in the phase conversion data output means. The invention is characterized in that it has a means to do so. Furthermore, a standard amount of electricity is set in advance so that the area of the current-carrying path is such that the desired nugget diameter is obtained, and the amount of electricity obtained when welding the materials to be welded is the predetermined standard amount of electricity. The present invention is characterized in that a means is provided for controlling the current supply time by cutting off the welding current when the welding current reaches .

Next, embodiments of the resistance welding apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 3 is a block diagram showing the structure of a first embodiment according to the present invention. In the figure, 1a and 1b are materials to be welded such as mild steel plates, and 2a is a piston, etc. (not shown)
A movable electrode connected to 2b is a fixed electrode.

During the welding process, the materials to be welded 1a and 1b are sandwiched and pressurized by the electrodes 2a and 2b, and welding current from an AC power source 4 is applied thereto via the transformer 3. Symbol 5 is a voltage detection circuit that momentarily detects the voltage between the electrodes 2a and 2b (hereinafter referred to as "interelectrode voltage") as shown in FIG. 4a while the welding current is being applied;
6 is an A/D converter that performs full-wave rectification of the detected voltage as shown in FIG. 4b, peak-holds it in half-cycle sampling units as shown in FIG. 4c, and then A/D converts the value. It is a D converter. A/D
The output of the converter 6 is input to a standard voltage storage circuit 7 via a switch _SW1 to store the interelectrode voltage. This memory circuit 7 stores materials to be welded 1a and 1b.
It memorizes the inter-electrode voltage when welding under specified welding conditions. For example, magnetic type or RAM (Random Access
Memory) can be used. In addition, a display device (not shown), such as a normal pen-writing oscilloscope or an electromagnetic oscilloscope, is connected to the storage circuit 7 so that the stored digital values can be converted into analog voltage waveforms and displayed for observation. It can also be configured as

The voltage comparison circuit 8 compares the digitized standard voltage waveform stored in the standard voltage storage circuit 7 with the digital value of the interelectrode voltage newly detected in the subsequent welding process every half cycle. Phase conversion data output circuit 9 for the difference between both voltages
give to The phase conversion data output circuit 9 has a built-in phase conversion data bank in which the digital value of this differential voltage corresponds to the phase conversion amount of the current control circuit 10 that controls the welding current. When the digital value of the differential voltage is given, the amount of phase conversion corresponding to the differential voltage is retrieved and input to the current control circuit 10. The voltage data of the power supply 4 is also inputted to the phase conversion data output circuit 9 from the power supply voltage monitor 11, which will be described later.

As the phase conversion data bank of the phase conversion data output circuit 9, for example, a magnetic type or a ROM (Read Only Memory) made of a semiconductor is used. This ROM stores a phase conversion data table as schematically shown in FIG. In this figure, the numbers 1, 2,... in the leftmost column
m is the standard quantity of electricity when welding the materials to be welded 1a and 1b under the optimal welding conditions specified in advance, for example, the interelectrode voltage V _s and the interelectrode voltage V detected during subsequent welding. This is a number that encodes the absolute value of the differential voltage _Δv with _c . The method for determining this number is to first determine the maximum expected fluctuation value (width) of the differential voltage _Δv through experiments, and then limit the storage capacity of the phase conversion data table based on this.
It is divided into m equal parts. Also, the number 1 in the upper column,
2,...,n (referred to as table number or search address) is
For the control recovery rate (loop gain), consider the welding equipment, welding materials, or welding conditions that are expected to be used, find a value with an appropriate range through experiment, and divide the width into n equal parts. This is what I did. If the welding current to be controlled based on the differential voltage _Δv is Δi, then
There is the following relationship between the two.

Δi _p =kΔv _(p - ₁₎ where k is the control recovery rate (loop gain),
p is the number of repetitions of the half-cycle period during the welding time. In other words, this data table corresponds to the value of each loop gain k in the above equation based on the voltage difference Δ _v between the standard electrode voltage V _s and the inter-electrode voltage V _c detected during subsequent welding. The firing angle of the SCR in the current control circuit 10 is expressed as a coded value. This value is searched and read out from the phase conversion data output circuit 9,
A current control circuit 10 is provided with the current control circuit 10 .

The current control circuit 10 consists of a phase control circuit 10a, a thyristor trigger pulse generation circuit 10b, a switching element 10c, and an SCR 10d. The phase control circuit 10a will be described in detail later.
The output signal is given to the thyristor trigger pulse generation circuit 10b. The thyristor trigger pulse generation circuit 10b generates a trigger pulse during the operation period of the energization time control circuit 12. The output of the thyristor trigger pulse generation circuit 10b is applied to the SCR 10d via the switching element 10c, and the SCR 10d adjusts the voltage supplied from the AC power source 4, and the output is applied to the welding electrodes 2a and 2b via the transformer 3. Supplied.

Now, the absolute value of the differential voltage Δ _v , which is the output of the comparator circuit 8, is 3 in the differential voltage column of the phase conversion data table.
, the firing angle of SCR10d is corrected by an amount corresponding to the value "1" at the intersection with a separately selected table number (the selection of table numbers will be described later), for example, 2. It turns out. Note that the differential voltage Δ _v shown in the phase conversion data table is an absolute value, so when Δ _v > 0, the output value is positive, and Δ _v < 0.
The output value is negative when Δ v =0, and the output value is 0 when Δ _v =0.

The selection of table numbers 1, 2, . This compensation is made for variations in the supply voltage V _e by selecting the table number before the individual welding process is started. These controls will be explained in detail with reference to FIG. In the figure, it is a device for constantly monitoring the voltage V _e of the power source 4 of the power source voltage monitor 11, and for example, a known digital voltmeter or the like can be used. The voltage data digitized by the power supply voltage monitor 11 is given to the power supply voltage decoder 9a of the phase conversion data output circuit 9. The decoder 9a classifies the amount of variation in the input voltage with respect to a reference voltage value into signals of multiple levels and outputs the signals. For example, if the reference voltage when welding under optimal welding conditions is set to 100V, and the value that shifts the table number by one rank from the initially specified table number is 5% of the power supply voltage fluctuation value, then When the voltage is in the range of 105 to 109V, a selection signal is output to shift up the table number by one rank, when it is in the range of 110 to 114V, it is shifted up by two ranks, and when it is in the range of 115 to 119V, it is shifted up by three ranks. Outputs a selection signal to Also, when the power supply voltage is lower than the reference voltage and in the range of 95 to 91V, a selection signal is output that shifts down the table number by one rank, and when it is in the range of 90 to 86V, it outputs a selection signal that shifts down the table number by one rank, and if it is in the range of 90 to 86V, it outputs a selection signal that shifts down the table number by one rank, and if it is in the range of 85 to 81V. , a selection signal for downshifting by 3 ranks is output. In this way, the selection signals obtained from the decoder 9a are input to the data bank 9c, and a table number is selected (designated) according to the shift amount of each selection signal. Now, when performing welding, considering the fluctuation range at that time, if table number 2 is selected and the power supply voltage increases by 5%, table number 3 is selected by one rank shift up, and the 5% If the pressure has decreased, table number 1 is selected.

By selecting the table number selected in this way and the differential voltage number for the subsequent welding (by the differential voltage decoder 9b), when good welding is being performed, any fluctuations in welding conditions, e.g. Due to variations in the thickness of the material to be welded 1a or 1b, the welding current may be overcharged and spatter may occur. The reference voltage generation circuit 13 experimentally determines the amount of voltage drop in a half cycle at the time of occurrence of dissipation and sets it as _the reference voltage V _p . be compared. When the differential voltage Δ _v exceeds the reference voltage from the reference voltage generation circuit 13 , a control signal is input from the comparison circuit 14 to the phase conversion data output circuit 9 , and the signal from the power supply voltage monitor 11 is influenced by the control signal. Among the table numbers of the data bank 9c, the table number with the lowest response characteristic, for example, "1" in FIG. 6, is selected without being determined. As a result, the optimum table for changing the firing angle of the SCR 10d to the smallest value is selected.

The phase control circuit 10a in the current control circuit 10 is provided with a welding current setting circuit, and in the initial stage of welding, the welding current setting knob 10e controls the thyristor trigger pulse generation circuit 10b to set the welding current. . Note that the retrieved data output from the phase conversion data output circuit 9 input to the phase control circuit 10a has already been converted into a phase conversion amount, so it passes through the phase control circuit 10a as it is and is output to the thyristor. The signal is applied to the trigger pulse generation circuit 10b. In response to this, the trigger pulse of the thyristor trigger pulse generation circuit 10b is digitally shifted by an amount corresponding to the phase shift amount so that it follows the standard interelectrode voltage waveform stored in the storage circuit 7. , SCR
A firing angle of 10d is controlled.

The operating procedure of the control function performed via the phase conversion data output circuit 9 configured as described above will be described in detail below. First, prior to full-scale welding work, the materials to be welded are experimentally welded, the most suitable welding conditions (welding current, energization time, and pressure) are determined, and the welding conditions are determined. The conditions for welding current and energization time are set by the welding current setting knob 10e of the phase control circuit 10a and the welding time (energization time) setting knob 12a of the energization time control circuit 12. After that, the materials to be welded 1a and 1b are held between the upper and lower electrodes 2a and 2b installed in the welding machine head (not shown), and when pressurization is started, the micro-electrodes installed in the welding machine head
The switch operates at a preset pressure and gives a command to start energization to the energization time control circuit 12. In the control circuit 12, the welding time setting knob 12 is controlled based on the command from the micro switch.
Welding current is supplied to the materials to be welded 1a and 1b via the SCR 10d controlled by the thyristor trigger pulse generation circuit 10b for a period of time preset by a. The voltage waveform generated between the welding electrodes 2a and 2b during this first welding is the standard voltage waveform for subsequent welding, and is A/D converted by the A/D converter 6 via the voltage detection circuit 5. , are stored in the memory circuit 7 via the switch _SW1 . The waveform stored in the storage circuit 7 through such a process is referred to as a standard voltage waveform. After the standard voltage waveform most suitable for the material to be welded has been stored in the memory circuit 7 through the operations described above, the switch SW ₁ is opened to perform actual welding work.

Picks and
The inter-electrode voltage that has been uploaded and processed by the A/D converter 6 is input to a comparator circuit 8 and stored in a memory circuit 7.
compared to the standard voltage waveform of This comparison is made at every predetermined sampling interval (half cycle), and the difference value (differential voltage) between both voltage waveforms is determined and provided to the solution phase conversion data output circuit 9. In the phase conversion data output circuit 9, first, immediately before welding, the table number of the initially set phase conversion data table is corrected based on the amount of variation in the power supply voltage from the power supply voltage monitor 11, and then the table number of the compensated number is corrected. The phase conversion data (phase conversion amount) of the SCR 10d corresponding to the differential voltage within is searched. This retrieved data is input to a phase control circuit 10a, which will be described later, and is sent to the SCR 10 via a thyristor trigger pulse generation circuit 10b and a switching element 10c.
The firing angle of d is adjusted successively, and the value of the welding current is increased or decreased every half cycle. As a result, the welding interelectrode voltage waveform follows the standard voltage waveform, thereby
Welding quality remains constant. When the welding current is controlled in this way, the dissipation voltage comparator circuit 14 calculates the difference voltage Δ _v which is the output of the voltage comparator circuit 8.
and the voltage value generated by the reference voltage generation circuit 13, and if the difference voltage _Δv exceeds the voltage value of the reference voltage generation circuit 13, a control signal is output to the power supply voltage decoder 9a. While the input of this control signal continues, the power supply voltage decoder 9a does not respond to the input signal from the power supply voltage monitor 11, and the table number in the data bank 9c is "1" (the table with the lowest response characteristic). Select. Therefore, even if expulsion occurs during welding and the value of the differential voltage _Δv increases, the welding current will not increase suddenly as shown by the broken line in FIG. Therefore, the part to be welded is not overheated, so damage to the part to be welded can be prevented, and by applying appropriate heating and pressure, shrinkage cavities that have formed inside the nugget can be crushed, allowing the nugget to be repaired. can do.

According to the embodiment described above, even when the welded part is in close proximity to an already welded part, there is a shunt, a change in the surface condition of the welded part, and a large fluctuation in the power supply voltage. Not only can the standard voltage waveform be traced, but even if spatter occurs due to some variation in welding conditions, damage to the welded area can be prevented as much as possible.

FIG. 7 is a block diagram showing the configuration of a second embodiment according to the present invention. This example shows the signal generated when the difference resistance Δr between the interelectrode resistance value R _c mentioned earlier and the standard resistance value R _s stored as a standard value exceeds a predetermined reference resistance value R _p . By using this, the table number with the lowest response characteristic in the data bank 9c is selected when expulsion occurs at the welded location. In this figure, the same functions as those in FIG. 3 are indicated with the same symbols, and therefore, the explanation of those parts will be omitted. In FIG. 7, 15 is a current detection circuit that detects the welding current every moment, 16 is an A/D converter for A/D converting the detected current of the current detection circuit 15, and 17 is the detection voltage of the voltage detection circuit 5. A/D
This is an A/D converter for conversion. The current value that is the output of the A/D converter 16 and the A/D converter 17
The voltage value that is the output is input to the resistance value calculation circuit 18, and the voltage value is divided by the current value to detect the interelectrode resistance. The detected interelectrode resistance is the switch SW ₂
It is stored in the standard resistance value recording circuit 19 via.
These A/D converters 16, 17 and storage circuit 19 are similar to the A/D converter 6 used in the previous embodiment.
Also, a circuit equivalent to the standard voltage storage circuit 7 can be used. In the resistance value comparison circuit 20,
The digitized resistance value R _s stored in the standard resistance value storage circuit 19 and the digital value R _c of the resistance newly detected in the subsequent welding process are compared every half cycle, and the difference between the two resistances is calculated. Δr is scattered and output to the resistance comparison circuit 21. The reference resistance value generating circuit 22 is set as a reference resistance value R _p by experimentally determining the amount of resistance drop at an appropriate sampling interval when scattering occurs, and the above-mentioned difference resistance Δr is calculated by comparing this reference resistance value R _p and the comparison circuit. Comparisons are made in 21. When the differential resistance Δr exceeds the reference resistance R _p , a control signal is input from the comparison circuit 21 to the power supply voltage decoder 9a (FIG. 6) of the phase conversion data output circuit 9, and the power supply voltage monitor 11 Among the table numbers of the data bank 9c, the table number with the lowest response characteristic, for example "1", is selected without being influenced by the signal from the data bank 9c.

FIG. 8 is a block diagram showing the configuration of a third embodiment of the present invention. The above-mentioned first and second
In the example described above, the welding current was controlled by detecting either the voltage drop between the electrodes or the resistance value drop when splintering occurred, but as is clear from Fig. 2, Since the interelectrode voltage and resistance value drop at the same time, it is more accurate to control the welding current by assuming that expulsion occurs only when voltage and resistance drop at the same time than to detect only one of them. It is possible to detect the point in time at which expulsion occurs, making it possible to take accurate measures against expulsion.

Therefore, in FIG. 8, the outputs of the shunt voltage comparator circuit 14 in the first embodiment and the shunt resistance comparator circuit 21 in the second embodiment are outputted as phase conversion data via a newly provided AND circuit 23. The configuration is such that it is input to the circuit 9.
Since the AND circuit 23 outputs an output only when inputs are received from both the comparison circuits 14 and 21, occurrence of expulsion can be reliably detected. This makes it possible to more reliably take action after the occurrence of dispersion.

In the above embodiments, we have described a method for detecting the drop in interelectrode voltage or resistance value when splintering occurs and correcting the welding current to a smaller value after splattering occurs. It does not necessarily occur towards the end of the process, but may occur relatively early. If dispersion occurs early,
Since the supply of welding current per hour thereafter is reduced, a shortage of welding energy may occur if the welding current application time is fixed. In the present invention, in order to cope with such a situation, the reference amount of electricity is set in advance so that the area of the energized path is such that the desired nugget diameter can be obtained, and the welding material is welded. Means for controlling the energization time is also added so that the welding current is cut off when the amount of electricity obtained at the time reaches the predetermined reference amount of electricity.
This energization time control means will be explained below.

Figure 9 shows the temporal relationship between the interelectrode resistance and the reciprocal of the energized path area 1/S during welding under different welding conditions such as various electrode tip tip shapes and dimensions, electrode pressing force, and welding current. It shows the change. As seen in the figure, the interelectrode resistance changes moment by moment during welding. Note that the direction of the arrow of each curve indicates the direction in which time passes. Looking at the relationship with the reciprocal of the energized path area, there is an almost proportional relationship at the time after the interelectrode resistance passes the maximum value, and under any welding conditions, the relationship is almost proportional to the reciprocal of the current-carrying path area. There is a similar relationship.

Figure 10 shows the relationship between the interelectrode resistance at the initial stage of energization and the reciprocal 1/S of the energized path area under various welding conditions, but in this case as well, the proportional relationship is approximately along a single proportional straight line indicated by a broken line. It turns out that there is. As a result, the inter-electrode resistance R is R=ρ・/S
It is easily understood that the relationship is (ρ: specific resistance of material,: distance between electrodes, S: area of energizing path between materials to be welded).

The facts shown in these graphs indicate that the current carrying path area between the materials to be welded can be easily estimated during welding by measuring the interelectrode resistance. Note that even when other welding points already exist in the vicinity of the welding point of interest, the current carrying path area can be estimated within approximately the same error range based on the interelectrode resistance. In addition, the interelectrode voltage and interelectrode resistance include the value between the electrode tip and the welded material in addition to the value between the welded materials, but the latter is generally compared to the former. It is small at about 20 to 30%, and is almost constant over time, so it can be considered that the interelectrode voltage and resistance represent that between the materials to be welded.

The above facts always hold true regardless of the shape and dimensions of the electrode tip, the type of material to be welded, etc., and even if the thickness, thickness, number, etc. of the material to be welded change, the basic There is no change in the trend. Therefore, by detecting the inter-electrode resistance during the welding process, it is possible to detect the current carrying path area between the materials to be welded during welding. Since this energizing path area is closely related to the size of the nugget to be formed, a reference resistance value is set in advance so that the energizing path area provides the desired nugget diameter. If the welding current is cut off when the interelectrode resistance reaches its reference resistance value during welding, the desired nug diameter can be obtained even by controlling the reduction of the welding current due to the occurrence of expulsion. In addition, Fig. 11 shows the relationship between the diameter of the nugget and the integral value of the voltage between the electrodes, and curve A is for the CF type (planar type).
Curve B shows the case when an R type (curved) electrode tip is used. Thereby, the welding current can be cut off when the integral value of the voltage between the electrodes reaches a reference voltage integral value preset in accordance with the degree of formation of a necessary nugget while the welding current is being applied.

Now, the specific energization time control means will be explained with reference to FIGS. 3, 7, and 8.
First, in FIG. 3, the voltage integration circuit 24 connected to the A/D converter 6 time-integrates the inter-electrode voltage obtained during actual welding after welding the materials to be welded under specified welding conditions. and is applied to the voltage integral value comparison circuit 25. The reference voltage integral value generation circuit 26 is
A preset voltage integral value is generated so as to obtain a desired nugget diameter, and is output to the voltage integral value comparison circuit 25. Comparison circuit 25 compares both voltage integral values input from voltage integral circuit 24 and reference voltage integral value generation circuit 26, and cuts off the welding current when the voltage integral value of voltage integral circuit 24 reaches the reference voltage integral value. The welding current is cut off by giving a signal to the energization time control circuit 12 to cut off the welding current.

In addition, in FIGS. 7 and 8, the reference resistance value generation circuit 27 generates a reference resistance value that is preset so as to have an energized path area that provides a desired nugget diameter, and compares this with the resistance value. to circuit 28. The inter-electrode resistance value calculated by the resistance value calculation circuit 18 is also added to the resistance value comparison circuit 28, and this inter-electrode resistance value is compared with the reference resistance value.
When the interelectrode resistance value reaches the same value as the reference resistance value, a signal for cutting off the welding current is output to the energization time control circuit 12, and the welding current is cut off. By using such an energization time control means, the welding current energization time is automatically and always controlled to the optimum time, so that the desired nugget diameter can be obtained even if the welding current is decreased due to the occurrence of expulsion. , more appropriate weld quality can be obtained.

As is clear from the above explanation, the resistance welding apparatus according to the present invention has advantages such as shunting caused by the proximity of the welded part to an already welded part, the surface condition of the welded part, and the welding conditions (welding current, energization). Not only can you quickly and reliably trace the standard electrical quantity even if there are fluctuations in time, pressure, etc., but also compensate for the response characteristics for welding current correction even if expulsion occurs during welding. At the same time, by controlling the current application time, it is possible to avoid deterioration in the quality of nuggets. This makes it possible to always obtain the optimal nugget regardless of changes in welding equipment, welding materials, welding conditions, etc., and eliminates electrode damage due to excessive current and insufficient welding strength due to insufficient current, etc. In this case, the effect of improving the reliability of welding quality is significant.

[Brief explanation of the drawing]

Figures 1a, b, and c show the loop gains of a prior art resistance welding device in which the firing angle of the SCR in an AC welding power source is controlled by a phase conversion data table to follow a standard voltage waveform. 2A and 2B are diagrams showing the response characteristics, respectively, and FIG. FIGS. 4a, b and c are block diagrams showing the configuration of the embodiment of FIG. Figure 5 showing the waveform of
The figure is a schematic diagram of the phase conversion data table stored in the data bank of the phase conversion data output circuit in FIG. 3, and FIG. 6 is a schematic diagram for explaining the selection of the table number of the phase conversion data table in FIG. A more specific configuration diagram, FIG. 7 is a block diagram showing the configuration of the second embodiment according to the present invention,
FIG. 8 is a block diagram showing the configuration of the third embodiment of the present invention, and FIG. 9 shows the temporal change in the relationship between the interelectrode resistance and the reciprocal of the current carrying path area during welding under various different welding conditions. Figure 10 is a diagram showing the relationship between the interelectrode resistance at the initial stage of energization and the reciprocal of the energized path area under various different welding conditions.
The figure shows the relationship between the nugget diameter and the integral value of the voltage between the electrodes. Code explanation, 1a, 1b... material to be welded, 2a, 2
b... Upper and lower electrodes, 3... Transformer, 4... AC power supply, 5... Voltage detection circuit, 6, 16, 17...
A/D converter, 7... Standard voltage storage circuit, 8, 1
4, 20, 21, 25, 28...comparison circuit, 9...
... Phase conversion data output circuit, 10 ... Current control circuit, 11 ... Power supply voltage monitor, 12 ... Energization time control circuit, 13 ... Reference voltage generation circuit, 15 ...
Current detection circuit, 18... Resistance value calculation circuit, 19...
...Standard resistance value storage circuit, 22, 27...Reference resistance value generation circuit, 23...AND circuit, 24...Voltage integration circuit, 26...Reference voltage integral value generation circuit.

Claims (1)

[Scope of Claims] 1. Means for detecting the voltage between the two electrodes that clamp the material to be welded, and means for storing the voltage obtained from the two electrodes when the material to be welded is welded under specified welding conditions. a means for comparing the voltage stored by the storage means with a voltage obtained during subsequent welding; and a predetermined phase determined by the output of the comparison means corresponding to the difference between the two voltages obtained at the output. means for searching and outputting conversion data; welding current control means for automatically tracing the stored standard voltage by the searched output; means for monitoring fluctuations in power supply voltage; In the resistance welding apparatus, the resistance welding apparatus includes means for automatically shifting the search address of the phase conversion data table according to the amount of voltage fluctuation detected by the means, from the amount of electricity obtained when welding the materials to be welded. means for detecting the time point at which splintering occurs during welding; and controlling the search address shifting means using the output of the detection means to select the search address having the smallest response characteristic in the phase conversion data table in the phase conversion data output means. 1. A resistance welding device comprising: means. 2. As a means for detecting the point at which spatter occurs during welding, a spatter voltage comparison means is connected to a means for comparing the interelectrode voltage stored in the storage means and the voltage obtained during subsequent welding, and the comparison means is separately provided. receiving a reference voltage from a reference voltage generating means corresponding to the amount of voltage drop when splintering occurs during welding, and comparing the reference voltage with the output voltage of the voltage comparing means;
2. The resistance welding apparatus according to claim 1, wherein occurrence of expulsion is detected when the output voltage of the voltage comparison means exceeds the reference voltage. 3. As means for detecting the point at which splattering occurs during welding, there is a means for detecting the resistance value between the two electrodes that clamp the material to be welded, and a means for detecting the resistance value between the two electrodes that clamp the material to be welded, and a means for detecting the resistance value between the two electrodes when the material to be welded is welded under specified welding conditions. Means for storing the obtained resistance value, and means for comparing the resistance value stored by the storage means with the resistance value obtained during subsequent welding are provided, and a resistance comparison circuit is further connected to the comparison means. , the comparison circuit receives a reference resistance value from a separately provided reference resistance value generation means corresponding to the amount of resistance drop when expulsion occurs during welding, and calculates the reference resistance value and the output resistance value of the resistance value comparison means. 2. The resistance welding apparatus according to claim 1, wherein occurrence of expulsion is detected when the output resistance value of the resistance value comparison means exceeds the reference resistance value. 4. As a means for detecting the point at which spatter occurs during welding, a separately provided voltage drop amount at the time of spatter during welding is connected to a means for comparing the voltage stored by the storage means and the voltage obtained during subsequent welding. A scattering voltage comparison means receives a reference voltage from a reference voltage generation means corresponding to the reference voltage and compares the reference voltage with the output voltage of the voltage comparison means, and detects a resistance value between the two electrodes that clamp the material to be welded. means for storing a resistance value obtained from both electrodes when the material to be welded is welded under specified welding conditions; and a resistance value stored by the storage means and a resistance value obtained during subsequent welding. A means for comparing the resistance value,
The output of the reference resistance value and the resistance value comparison means is connected to the comparison means and receives a reference resistance value from a separately provided reference resistance value generation means corresponding to the amount of resistance drop when splintering occurs during welding. an AND connected to the output side of the dissipation resistance value comparison means and the dissipation resistance value comparison means;
A resistance welding device according to claim 1, comprising a circuit. 5 means for detecting the voltage between the two electrodes that clamp the material to be welded; means for storing the voltage obtained from the two electrodes when the material to be welded is welded under specified welding conditions; Means for comparing the stored voltage and the voltage obtained during subsequent welding, and an output of the comparing means to search and output predetermined phase conversion data corresponding to the difference between the two voltages obtained at the output. means for automatically tracing the stored standard voltage by the retrieved output; means for monitoring fluctuations in power supply voltage; and voltage detected by the monitoring means. In a resistance welding device comprising means for automatically shifting the search address of the phase conversion data table according to the amount of fluctuation, the time point at which splattering occurs during welding is determined based on the amount of electricity obtained when welding the materials to be welded. means for controlling the search address shift means using the output of the detection means to select the search address having the smallest response characteristic in the phase conversion data table in the phase conversion data output means; A standard amount of electricity is set in advance so that the area of the current-carrying path is such that the diameter can be obtained, and when the amount of electricity obtained when welding the materials to be welded reaches the predetermined standard amount of electricity, 1. A resistance welding device characterized by comprising means for interrupting welding current and controlling energization time. 6. As a means for controlling the energization time, there is provided a voltage integration means for time-integrating the interelectrode voltage obtained during subsequent welding, and a voltage integral value set in advance so as to obtain the energization path area such that the desired nugget diameter is obtained. The reference voltage integral value generated by the reference voltage integral value generating means is compared with the reference voltage integral value obtained from the output of the reference voltage integral value generating means and the voltage integral value obtained from the output of the voltage integrating means. 6. The resistance welding apparatus according to claim 5, further comprising voltage integral value comparing means for outputting a signal for cutting off the welding current when the reference voltage integral value is reached. 7. As a means for controlling the energization time, a resistance value comparison means is connected to the means for detecting the resistance value between the two electrodes that clamp the material to be welded, and the resistance value comparison means meets a separately provided standard for cutting off the welding current. A signal for receiving a reference resistance value from the resistance value generating means, comparing it with an output from the resistance value detecting means, and interrupting the welding current when the output of the resistance value detecting means reaches the reference resistance value. The resistance welding device according to claim 5, which outputs the following.