JP2002316269A - Monitoring device for spot welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monitoring device for a spot welding with which normal/ defective condition of the spot welding is stably decided on the basis of a vibration generated during the welding. SOLUTION: The monitoring device for the spot welding is provided with a vibration phase difference detection circuit 214 which detects the phase difference between the intermittent mechanical damping oscillation which is generated at the electrode part of a spot welding equipment 10 by an electromagnetic force which acts as a vibration source when the alternative welding current is supplied, and the alternate welding current, a reference setting circuit 215 for normal/defective decision which sets the reference value for the normal/ defective condition, and a normal/defective welding decision circuit 217 which decides the normal/defective condition of the spot welding by comparing the vibration phase difference detected with the vibration phase difference detection circuit 214 and the reference value given from the reference setting circuit 215 for normal/defective decision. The reliability for deciding the normal/ defective condition is enhanced by ensuring the detection of the vibration caused by the melting of metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding monitoring device used for determining in-process whether or not a welding condition is good or bad in spot welding for joining various materials such as steel plates.

[0002]

2. Description of the Related Art At present, spot welding is widely used for welding steel sheets in various products using steel sheets. Conventionally, in these products, since a mild steel plate is used as a material to be welded, welding defects are small, and it is possible to maintain welding quality relatively stable by managing predetermined welding conditions. However, in recent years, difficult-to-weld materials such as hot-dip galvanized steel sheets with improved rust prevention performance have been mainly used as materials to be welded, and this has led to wear of electrode tips of spot welding machines. Due to the occurrence of poor welding, there is a problem that it is difficult to control welding quality. Therefore, at the time of spot welding, it has been necessary to not only control welding conditions at a constant level but also control the quality of nuggets for each hitting point with high accuracy.

[0003] Therefore, various monitoring devices have been proposed to control the quality of nuggets. For example, in order to adapt to in-process monitoring of all welding spots, which is particularly required in a production line, metal monitoring during welding is performed. There has been a monitoring device that determines the quality of spot welding by focusing on a vibration phenomenon caused by a situation. (JP 2
001-25881)

[0004]

However, in a spot welding monitoring device that determines the quality of spot welding based on vibrations generated during welding, some types and structures of spot welding machines are caused by metal melting conditions. The vibration may be buried in the mechanical vibration of the spot welding machine, making it difficult to determine the quality. For example, in a spot welder having a hook-shaped arm generally called a C-type gun, the amplitude of mechanical vibration caused by electromagnetic force acting on the arm portion and the electrode tip due to energization is large because the arm rigidity is low. Become. This mechanical vibration is intermittent vibration accompanied by attenuation synchronized with twice the frequency of the current flow. For this reason, there is a problem that the vibration to be evaluated in the pass / fail judgment, that is, the vibration caused by the metal melting state is buried in the mechanical intermittent vibration of the spot welding machine, and the pass / fail judgment may be difficult. Has been an issue to solve various problems

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and is directed to a spot welding monitoring apparatus for determining the quality of spot welding based on vibration generated during welding. It is an object of the present invention to provide a spot welding monitoring device capable of stably determining the quality of spot welding even with such a low-rigidity AC spot welding machine.

[0006]

According to a first aspect of the present invention, there is provided a spot welding monitoring apparatus for judging the quality of spot welding based on vibration generated during welding. Vibration phase difference detecting means for detecting a phase difference (delay time) between an intermittent mechanical damping vibration of an electrode portion of the spot welding machine and an AC welding current generated when an electromagnetic force is generated as an excitation source when the electric current is applied,
A pass / fail judgment reference value setting means for setting a pass / fail judgment reference value, and comparing the vibration phase difference (delay time) detected by the vibration phase difference detecting means with the reference value from the pass / fail judgment reference value setting means to determine whether the spot welding is good or bad. The apparatus is provided with welding quality determination means for performing the determination, and the above-described configuration is used as means for solving the conventional problems.

[0007] This monitoring device for spot welding,
In spot welding, where an overlapped welding material (steel plate) is pressed with a pair of electrode tips, an AC welding current is applied to both electrode tips, and the two welding materials are welded to each other by resistance heating, the electrode tip or its vicinity. A vibration sensor is provided in the gun arm, and the vibration sensor detects intermittent mechanical damping vibration generated during welding.

According to a second aspect of the present invention, there is provided an apparatus for monitoring spot welding, wherein the vibration phase difference detecting means detects a phase difference of intermittent mechanical damping vibration a plurality of times per welding; Sample data optimizing means for deleting abnormal data corresponding to excessive vibration such as when scatter occurs or undervibration such as when preheating is applied from sample data of the detected vibration phase difference, and the mode (mode), arithmetic mean and geometric It is characterized in that it is provided with a judgment parameter determining means for obtaining a representative value of the sample data optimized using any one of the averages.

This spot welding monitoring device is:
In order to stably carry out a reliable quality judgment, in the vibration phase difference sampling means, the sample data of the vibration phase difference was detected a plurality of times per welding, and was detected earlier in the sample data optimization means. From the sample data, data such as “fluctuations” of accidental scattering vibrations or other vibrations or vibration phenomena, that is, abnormal data that is a hindrance to correct determination of good or bad, is eliminated to optimize the sample data. And
In the determination parameter determination means, a representative value for comparison with a pass / fail determination reference value is calculated from the sample data optimized in advance.

According to a third aspect of the present invention, there is provided a monitoring apparatus for spot welding, wherein the pass / fail judgment reference value setting means is means for setting a plurality of pass / fail judgment reference values. It is characterized in that it is means for judging "good welding" when the value is within the above range or within a predetermined range.

[0011] This spot welding monitoring device includes:
In order to judge the quality of spot welding without making an erroneous determination, a plurality of quality determination reference values are provided, and in the welding quality determination means, whether the representative value obtained by the determination parameter determination means is between the quality determination reference values. Determine whether or not.

According to a fourth aspect of the present invention, there is provided a monitoring apparatus for spot welding, wherein the pass / fail judgment reference value setting means sets an upper limit value of the pass / fail judgment reference value when a welding failure occurs due to either insufficient pressure of the electrode tip or wear. A corresponding vibration phase difference is set, and a vibration phase difference corresponding to the occurrence of welding failure due to insufficient current is set as a lower limit of the pass / fail judgment reference value. It is characterized in that it is means for judging "good welding" when it is between the lower limit values.

This spot welding monitoring device is:
In the pass / fail judgment reference value setting means, for example, a vibration phase difference that is increased due to an assumed insufficient pressure of the electrode tip,
In addition, the smaller value of the vibration phase difference that increases due to the wear of the electrode tip is set as the upper limit, and the vibration phase difference corresponding to the lower limit of the allowable welding current is set as the lower limit.

According to a fifth aspect of the present invention, there is provided a spot welding monitoring device, wherein the pass / fail judgment reference value setting means multiplies a value obtained by multiplying an amount of a vibration phase difference when welding is good by a predetermined coefficient obtained in advance. Claim 6 is characterized in that the pass / fail judgment reference value setting means multiplies a value obtained by multiplying a current estimation value calculated from the voltage between the electrodes by a predetermined coefficient obtained in advance. 8. The method according to claim 7, wherein the pass / fail judgment reference value setting means sets a thickness vs. pass / fail judgment reference value map set in advance based on a sheet thickness signal of the material to be welded input from outside. And a means for selecting and setting a pass / fail judgment reference value with reference to FIG.

These spot welding monitoring devices are intended to improve the operability and to simplify the setting of the pass / fail judgment reference value in order to prevent erroneous input. The apparatus stores a vibration phase difference when a good welding is being performed, such as when the electrode tip is new, by a switch operation, and as a coefficient previously obtained for the stored vibration phase difference, for example, 1.
5 is output as a pass / fail judgment reference value. In this coefficient example, it is determined that poor welding occurs when the vibration phase difference increases by 50% when good welding is performed.

[0016] The spot welding monitoring device according to claim 6 focuses on the characteristics of the welding current and the vibration phase difference,
A proportional multiplier between the welding current and the quality judgment reference value is obtained in advance, and the proportional constant is set as a coefficient. Then, the welding current value calculated from the inter-electrode voltage is multiplied by a proportional constant, and this is output as a pass / fail judgment reference value.

Further, the spot welding monitoring apparatus according to claim 7 focuses on the characteristics between the plate thickness of the material to be welded and the vibration phase difference, and obtains in advance a correspondence table between the plate thickness and the quality judgment reference value.
This correspondence table is set as a sheet thickness versus pass / fail judgment reference value map. Then, a corresponding pass / fail judgment reference value is output with reference to a sheet thickness vs. pass / fail judgment reference value map based on a sheet thickness signal input from the outside.

The spot welding monitoring apparatus according to claim 8 of the present invention compares the detection result of the vibration phase difference detecting means with a predetermined electrode shaping time determination reference value to detect the shaping time of the electrode tip and issues an alarm. It is characterized by comprising an electrode shaping time detecting means for outputting.

This monitoring device for spot welding includes:
Focusing on the characteristic that when the tip diameter increases due to the wear of the electrode tip, the vibration phase difference increases according to the size, and the vibration phase difference when the tip diameter becomes slightly before the welding failure occurs is calculated. The value is obtained in advance and set as the electrode shaping time determination reference value. Then, the vibration phase difference and the electrode shaping time determination reference value are compared in parallel with the quality determination of the spot welding, and when both match, an alarm is output to notify that the electrode tip has reached the shaping time.

In the spot welding monitoring apparatus according to the present invention, as a ninth aspect, a setting for judging whether or not a welding set condition for a workpiece is acceptable by comparing a change of a vibration phase difference for each cycle with a predetermined change pattern. Dispersion detecting means, characterized in that it comprises condition nonconformity detecting means, wherein the dispersion detecting means determines that vibration has occurred over a half cycle of the current waveform by detecting that vibration having a predetermined amplitude level or more continues for a half cycle, The method according to claim 11, further comprising: a dispersion generation cycle output unit that outputs a conduction cycle value when the dispersion is detected, wherein the conduction angle detected from the voltage between the electrodes is an appropriate value and the vibration amplitude is equal to or less than a predetermined amplitude. 13. An electrode tip welding detecting means for detecting the presence of the electrode tip and determining the welding of the electrode tip.
As a feature, current conduction failure detection means for determining that conduction is defective and outputting an alarm when the result obtained by dividing the conduction angle detected from the voltage between the electrodes by the vibration amplitude is a predetermined value or more is provided. According to a thirteenth aspect, when the current conduction failure detecting means does not determine that the conduction is defective, when the difference between the detected vibration phase difference and the moving average value is equal to or more than a predetermined value, the current is determined to be a shunt current and an alarm is issued. It is characterized by having a shunt detection means for outputting.

These spot welding monitoring devices output an alarm for notifying a welding defect relating to the quality of the spot welding, and the spot welding monitoring device according to the ninth aspect can share welding conditions. When welding to unspecified workpieces under the same welding conditions, it is detected that the workpieces that deviate from the applicable range of the set welding conditions are erroneously welded. In order to prevent the subsequent occurrence of poor welding, the setting condition nonconformity detecting means previously obtains a change pattern of the vibration phase difference for each cycle during good welding and sets it as a conformity determination reference value, and outputs the sample data optimizing means. The data is compared with the conformity determination reference value for each cycle, and if it is detected that the value is out of the predetermined fluctuation range, it is notified that the welding setting conditions are incompatible. Outputs an alarm that.

According to a tenth aspect of the present invention, there is provided a monitoring apparatus for spot welding, which outputs a cycle of occurrence of scattering in order to improve the quality of a finished appearance and to save power, in addition to determining whether the welding is good or bad. When the detection means detects a large-amplitude and low-damping-rate scattering vibration at the time of occurrence of the scattering with a preset threshold value for the detection of the scattering, and the detection of the scattering amplitude continues for a half cycle of the welding current. "Scattering" is detected. The scattering occurrence cycle output means measures the occurrence timing of the scattering in the energization cycle, and outputs the occurrence of the scattering in the number of energization cycles.

According to the eleventh aspect of the present invention, the spot welding monitoring apparatus focuses on the fact that the vibration amplitude becomes extremely small when the electrode tip is welded, and detects in advance the electrode tip welding detection based on the vibration amplitude at the time of electrode tip welding. A threshold value is set in advance, and when the amplitude of vibration falls below the threshold value while the current is at an appropriate value, it is determined that “electrode tip welding” has occurred.

In a twelfth aspect of the present invention, the spot welding monitoring apparatus focuses on the fact that the welding current and the vibration amplitude are in a proportional relationship, and determines the ratio between the welding current and the average value of the vibration amplitude when the current is normally supplied in advance. If the ratio between the estimated value of the current obtained from the voltage between the electrodes and the average value of the vibration amplitude is larger than the set value for each welding, it is determined that the current is poor and an alarm signal is output.

According to a thirteenth aspect of the present invention, the estimated value of the current detected from the voltage between the electrodes is within an appropriate range, and the moving average value of the vibration phase difference up to the previous time is a pass / fail judgment reference value or an electrode tip shaping. If the difference between the detected vibration phase difference and the moving average value exceeds a preset shunt judgment reference value while satisfying the condition that the timing judgment reference value is not reached, the shunt current is judged and an alarm signal is issued. Is output.

According to a fourteenth aspect of the present invention, there is provided an apparatus for monitoring spot welding, comprising the steps of: detecting a failure in any of the setting condition inconsistency detection means, the electrode tip welding detection means, the current conduction failure detection means and the branch current detection means; Equipped with welding failure alarm means for outputting a welding failure warning signal to welding quality judgment means, and when welding poor judgment means is input, outputs "poor welding" regardless of the result of quality judgment based on the vibration phase difference when a welding failure alarm is input. It is characterized in that it is a means for performing.

This spot welding monitoring device is:
In the case where any of the alarms for the defective welding conditions is output, it is considered that the alarm has an adverse effect on the nugget formation of the welded portion.
The logical sum of the alarm outputs described in No. 3 is input to the welding quality judgment means as a welding defect alarm signal.

In a spot welding monitoring apparatus according to a fifteenth aspect of the present invention, the vibration phase difference detecting means includes a representative value of the sampled data obtained by the determination parameter determining means and a detection threshold determined in advance from the start of energization. A means for switching and outputting the time up to the time when the above vibration is first detected, wherein the pass / fail judgment reference value setting means multiplies the amount of the vibration phase difference when welding is good by a predetermined coefficient obtained in advance. A pass / fail judgment reference value, and a pass / fail judgment reference value that is a value obtained by multiplying a current estimation value calculated from the inter-electrode voltage by a predetermined coefficient obtained in advance,
A steel plate having a quality judgment reference value selected and set by referring to a thickness-quality judgment reference value map preset based on a thickness signal of a material to be welded input from outside, and a surface coating layer having a lower melting point than the base material. Means for switching and outputting a good or bad judgment reference value at the time of welding failure judgment in the vibration phase difference detecting means and the good or bad judgment reference value setting means according to either the spot welding machine to be mounted or the workpiece to be welded. It is characterized by comprising a pass / fail judgment mode switching means for selecting output switching.

This monitoring device for spot welding includes:
The above configuration is provided in order to expand the applicable range of the spot welding machine or the workpiece to be mounted.

[0030]

According to the monitoring apparatus for spot welding according to the first aspect of the present invention, a monitoring apparatus for spot welding that determines the quality of spot welding based on vibrations generated during welding is, for example, a low rigidity monitoring apparatus. Even if the metal melting vibration corresponding to the nugget formation situation in an AC spot welding machine etc. is buried in the mechanical vibration of the spot welding machine and cannot be easily detected, large amplitude intermittent using the electromagnetic force during energization as the excitation source Since the target mechanical vibration damping vibration is detected, it is possible to easily detect a signal of the metal melting vibration, and it is possible to reliably determine the quality of spot welding. Further, since the vibration amplitude of the detection target is large, it is not necessary to use an advanced signal extraction technique for signal detection, and it is possible to adapt to spot welding of various materials to be welded. It is possible to conform to a wider range of welding conditions than in the case of, and it is possible to further improve the reliability of quality judgment.

According to the spot welding monitoring apparatus of the second aspect of the present invention, the same effect as that of the first aspect can be obtained. Detects phase difference sample data, eliminates abnormal data, and calculates the mode (mode) mean value, thereby reducing the effects of accidental scattering vibrations, other vibrations, or fluctuations in vibration phenomena. Thus, a highly reliable quality judgment can be stably performed.

According to the spot welding monitoring apparatus of the third aspect of the present invention, the same effects as those of the first and second aspects can be obtained, and vibration is detected by providing a plurality of pass / fail judgment reference values. Erroneous determination due to signal detection failure due to sensor failure or disconnection, drift of vibration phase difference data due to disturbance noise, or variation in welding conditions.

According to the spot welding monitoring apparatus of the fourth aspect of the present invention, the same effect as that of the third aspect can be obtained, and the accidental fluctuation of the pressure source of the electrode tip and the welding power source can be achieved. It is possible to prevent an erroneous determination due to a decrease in the pressing force or the welding current.

According to the monitoring apparatus for spot welding according to the fifth aspect of the present invention, the same effects as those of the first and second aspects can be obtained, and the vibration phase difference when good welding is performed. By simply operating so as to store the information, it is possible to easily set the pass / fail judgment reference value, thereby improving operability and preventing input errors.

According to the spot welding monitoring apparatus of the sixth aspect of the present invention, the same effect as in the first and second aspects can be obtained, and in addition, the proportional constant between the welding current and the pass / fail judgment reference value is determined in advance. By setting the value, the pass / fail judgment reference value according to the welding current can be automatically set, so that the operability can be further improved, and the welding current can be adjusted according to the material to be welded. You can also adapt to the case.

According to the spot welding monitoring apparatus of the seventh aspect of the present invention, the same effects as those of the first and second aspects can be obtained, and in addition, the thickness of the material to be welded and the reference value of the pass / fail judgment value are determined in advance. By inputting the corresponding map, it is possible to automatically set the pass / fail judgment reference value just by inputting the sheet pressure signal, and to improve the operability when continuously spot welding different thicknesses of workpieces. Can be improved.

According to the spot welding monitoring apparatus of the eighth aspect of the present invention, the same effects as those of the first to seventh aspects can be obtained, and the vibration phase difference is set to a predetermined electrode shaping time determination reference value. By comparing and judging, it is possible to detect an appropriate electrode tip shaping time, and by inputting an alarm signal notifying the electrode tip shaping time to an automatic electrode tip shaping device (auto tip dresser),
The electrode tip can be efficiently and automatically shaped.

According to the spot welding monitoring apparatus of the ninth aspect of the present invention, the same effects as those of the first to eighth aspects can be obtained, and in addition, the same welding can be performed on an unspecified workpiece. In the case where spot welding is performed under the conditions, it is possible to detect that the material to be welded exceeds the applicable range of the set welding conditions, thereby preventing a subsequent occurrence of poor welding, and Can be readjusted for welding conditions.

According to the monitoring apparatus for spot welding according to the tenth aspect of the present invention, the same effects as those of the first to ninth aspects can be obtained, and the occurrence of scattering can be detected. Reference data for improving the power consumption and saving power can be obtained. In addition, since the scattering occurrence cycle is output, the data can be input to the welding control device, and the cooling can be suppressed by performing the cool control of stopping the energization for the high frequency scattering occurrence cycle. it can.

According to the monitoring apparatus for spot welding according to the eleventh aspect of the present invention, the same effect as that of the first to tenth aspects can be obtained, and furthermore, the welding of the electrode tip to the material to be welded can be detected. In particular, it is possible to immediately detect electrode tip welding when spot welding is performed unattended, as in an automatic welding device, and it is possible to minimize the occurrence of problems associated with electrode tip welding.

According to the monitoring apparatus for spot welding according to the twelfth aspect of the present invention, the same effects as those of the first to eleventh aspects can be obtained, and in addition, poor current supply of the welding current can be achieved without using an expensive current sensor. Can be detected.

According to the monitoring apparatus for spot welding according to the thirteenth aspect of the present invention, the same effect as that of the twelfth aspect can be obtained. Since it is possible to estimate and output a warning of the generation of the shunt current, it is possible to prevent the welding failure due to the generation of the shunt current from being overlooked.

According to the spot welding monitoring apparatus of the present invention, the same effects as those of the ninth to thirteenth aspects can be obtained, and in addition, various welding defects can be obtained based on the judgment contents of each means. Is determined,
More strict welding failure can be prevented from being overlooked.

According to the monitoring apparatus for spot welding according to claim 15 of the present invention, the same effects as those of claims 2 to 14 can be obtained, and furthermore, according to the spot welding machine to be mounted or the material to be welded. By switching the pass / fail judgment mode, it is possible to immediately cope with a case where the metal melting vibration is relatively large, such as welding of a steel sheet having a surface coating layer by a DC welding machine.

[0045]

FIG. 2 and FIG. 3 show examples of spot welding monitoring for judging the quality of spot welding based on vibration generated during welding.

FIG. 2A shows a vibration signal An (t) SIN2πfn of a specific frequency during welding vibration from the start of energization.
(Tg) t, and FIG.
6A shows the relationship between the elapsed time Tr up to the amplitude expansion start time tr of the vibration signal and the nugget diameter in FIG.
As shown in FIG. 2 (b), focusing on the fact that the above relationship was obtained by an experiment result that can be approximated by an exponential curve, the amplitude expansion start time tr obtained at the time of welding and the elapsed time at the time of forming a pass nugget obtained at the preliminary experiment. By comparing Tr, it is possible to judge the quality of the nugget formation state before completion of the nugget formation. Further, by obtaining the approximate expression, the nugget diameter can be estimated at the time of the amplitude expansion start time tr.

FIG. 3 (a) shows the relationship between the event progress and the vibration signal from the start of energization in spot welding of a steel sheet having a surface coating layer having a lower melting point than the base material. (B) is a time tb at which an impact vibration is detected at the electrode tip portion at the beginning of welding after the start of energization.
3 shows the relationship between the elapsed time Tb and the nugget diameter. As shown in FIG. 3 (b), paying attention to the fact that the above-described relationship was obtained by an experimental result which can be approximated by an exponential curve, the impact vibration generation time tb obtained at the time of welding and the progress at the time of forming a passing nugget obtained in the preliminary experiment By comparing with the time Tb, it is possible to determine the quality of the nugget formation state before the nugget formation is completed. Further, the nugget diameter can be estimated at the time of the amplitude expansion start time tb by obtaining the approximate expression.

In each of these methods, the pass / fail judgment is made before the formation of the nugget is completed. Therefore, from the immediacy, the in-process control for controlling the welding current or the like to the optimum value based on the judgment result is performed. This is a suitable pass / fail judgment method or monitoring method.

Next, the basic principle of the pass / fail judgment according to the present invention will be described. FIG. 1A shows an example of a basic configuration of a spot welding monitoring apparatus according to the present invention and an example of a vibration waveform of an electrode tip portion detected during energization. In the figure, reference numeral 10 denotes a spot welding machine, 11 denotes a welding control device, and 12 denotes a welding transformer. It can be seen that the mechanical vibration Vs detected for the welding current waveform Iw has a vibration phase difference (delay time) dθ. further,
FIG. 1 shows the transition of the vibration phase difference dθ when continuous welding is performed until welding failure occurs at the same electrode tip.
As shown in (b), the characteristic of monotonically increasing up to about 1100 times, which is the first time to reach the minimum acceptable nugget diameter Dn, was observed.

The present invention focuses on this characteristic, and detects the timing at which a welding failure occurs by monitoring the vibration phase difference dθ of the mechanical vibration Vs of the electrode tip portion with respect to the welding current waveform Iw. Is what you do. The axis index of the vibration phase difference dθ in FIG. 1A indicates that the vibration phase difference angle (deg) is equal to one cycle (360) of the square wave of the welding current.
deg).

Here, considering the mechanism of the vibration phase difference dθ, FIG. 4 summarizes changes in physical phenomena in the electrode tip portion when the welding state is “good” and when the welding state is “bad”. Accurately representing actual physical phenomena is considerably complicated and includes many irregular elements. Therefore, here, macroscopic physical phenomena are considered using an ideal simple model.

The mechanical elements acting on the electrode tip portion during welding will be briefly described. The pressing force Fp by the pressurizing cylinder acts strongly on the electrode tip 15. Electromagnetic force induced by the application of the welding current Iw acts as a vibration source to the electrode tip 15, and the X-axis direction (Fmx) orthogonal to the axis of the electrode tip 15 and the Z-axis direction (Fmz) along the axis
A pulsating force is applied at twice the frequency of the welding current Iw.
Then, a molten pool having a nugget diameter (melting diameter) Dn is formed inside the workpiece Wp by resistance heating. Further, the electrode tip 15 bites into the material to be welded Wp by the pressing force Fp,
The composite force of the rigidity of the material to be welded Wp and the internal pressure of the molten pool and the pressing force F
The state where p is balanced is continued.

Therefore, looking at how the above-mentioned balance state changes at the time of poor welding with reference to typical mechanical parameters of the electrode tip portion, first, the shape change at the time of poor welding is caused by the change of the electrode tip 15. The tip diameter D due to wear
e increases and the tip shape becomes flat from the spherical surface of the dome.
In addition, the metal component and the attached matter of the material to be welded Wp are sintered, and the front end surface becomes smooth (surface smoothness Se). As a result, the indentation depth ie, which is the amount of bite into the material to be welded Wp, becomes shallower (decreases) because the pressure Fp is constant while the tip diameter De increases. Also, the friction coefficient μe of the pressing surface
Also decrease. Further, the formed nugget diameter Dn ′ is
Due to the decrease in the current density accompanying the increase in the tip diameter De 'of the electrode tip 15, the metal tip is reduced without promoting the melting of the metal. In terms of material mechanics, the viscous friction coefficient c of the nugget forming portion decreases because the nugget diameter Dn ′ is small and the heat generation temperature Tw is low. However, the spring constant k of the nugget forming part increases conversely.

The change in physical phenomena due to the quality of welding has been described above. As described in parentheses of each parameter in FIG. 4, each parameter has many correlations even in macro terms. These are major obstacles to the realization of the welding quality judgment. Note that the parentheses of the parameters in FIG. 4 indicate the main changing factors of the parameters. In FIG. 4, Pa is the air pressure, Pe is the welding power supply voltage, and Lz is the arm length (Z) of the spot welding machine in the Z-axis direction. Axis), Lx is the arm length in the X-axis direction of the spot welder, cm is the standard viscous friction coefficient of the workpiece, km is the spring constant of the workpiece, and tp
Is the total thickness of the material to be welded.

Further, according to the present invention, the pressing force Fp, the welding current Iw, and the electromagnetic forces Fmx, F can be individually monitored and controlled.
Since the detection of a change with time in the workpiece Wp and the electrode tip 15 that cannot be monitored or controlled is a problem to be solved, the pressing force Fp, the welding current Iw, and the electromagnetic force Fm are compared with mz.
Although it has been described that x and Fmz are constant, there is an accidental decrease in the pressurizing source (air pressure) Pa and the welding current Iw at the actual welding site, and the fluctuation factors cannot be ignored. The output of the effect is shown in FIG.

In general, it is sufficient to consider the direction in which the pressure is reduced. As shown in FIG. 5A, when the pressure source Pa decreases, the vibration phase difference dθ tends to increase. FIG.
As shown in (b), when the welding current Iw decreases, the vibration phase difference dθ tends to decrease. Further, as shown in FIG. 5 (c), even when spot-welded materials having different thicknesses are welded under the same welding conditions, the vibration phase difference dθ is proportional to the thickness.
Tend to increase.

Therefore, it is necessary not only to compare and determine the vibration phase difference dθ with a predetermined pass / fail judgment reference value, but also to adopt a pass / fail judgment method taking into account the above-mentioned variable factors. In the present invention, an erroneous determination is prevented by devising a method of setting a pass / fail determination reference value for a variable element.

Based on these relationships and considering the mechanism of increasing the vibration phase difference at the time of welding failure based on FIG.
The electrode tip 15 has a pressing force Fp with respect to the fixed end of the arm.
And a solid friction force consisting of a circle having a tip diameter De and a friction coefficient μe acts on the tip. In addition, in the X-axis direction orthogonal to the axis of the electrode tip 15, the electromagnetic force Fm
The force of x acts, and the viscous frictional force of the nugget forming part is generated, and the resistance R to the electromagnetic force Fmx acts together with the solid frictional force. In addition, a model in which a restoring force S due to a spring constant of the nut forming portion acts can be considered.

The equation of motion of this model is given by the following equation 1, and the phase difference between the vibration in the X-axis direction and the external force (electromagnetic force) is given by the following equation 2.

[0060]

(Equation 1)

[0061]

(Equation 2)

The resistance R and the restoring force S are given by the following equations (3) and (4).

[0063]

(Equation 3)

[0064]

(Equation 4)

Therefore, the equivalent viscous friction coefficient C and the equivalent spring constant K of the equation of motion are expected to be functions of the parameters shown in the following equations 5 and 6 from the above equations 3 and 4.

[0066]

(Equation 5)

[0067]

(Equation 6)

When the parameters of the above equations 5 and 6 were evaluated for increase and decrease assuming the quality of welding, the following Table 1 was obtained.
become that way.

[0069]

[Table 1]

From this study, it can be understood that, when a welding defect occurs, the equivalent viscous friction coefficient and the equivalent spring constant at the tip of the electrode tip are both larger than at the time of good welding. This is the reason for the increase in the vibration phase difference dθ shown in FIG. In Table 1, the reasons for excluding the standard viscous friction coefficient cm of the material to be welded, the spring constant km of the material to be welded, and the indentation depth ie from the evaluation items are as follows. This is because the parameter does not change depending on the quality, and the indentation depth ie overlaps the pressing force Fp and the tip diameter De.

The spot welding machine shown in FIG. 7 has an air cylinder 19 in which a pressure shaft 17 is integrally provided on a cylinder rod.
And the welding gun arm 18 are connected via the electric insulator 14. The pressing shaft 17 and the welding gun arm 18 are provided with opposing electrode tips 15 and 16, and are not shown. Are pressed between the electrode tips 15 and 16, and the materials to be welded are welded by resistance heating by energization. The pressure shaft 17 is driven by air pressure by an air cylinder 19, and the other gun arm 18 is in a fixed state at least during welding.

The above-mentioned spot welding machine is a two-electrode tip 1
The welding current, energizing time (cycle number) and energizing angle for 5 and 16 are controlled by the welding control device 11, and the primary current, which is the output thereof, is amplified in the welding transformer 12 to the current Iw required for welding stomach. The welding current Iw is generated by the pressurizing shaft 17, the welding gun arm 18, and the electrode tips 15, 16.
A welding current circuit is constituted by a material to be welded, not shown. The vibration sensor 20 for detecting the intermittent mechanical damping vibration of the electrode tips 15 and 16 employs, for example, an acceleration sensor using a piezoelectric element, and does not interfere with the material to be welded at the time of welding. Use a bracket or attach directly to a position where vibration of the part can be detected with appropriate sensitivity.

The monitoring device 21 for spot welding performed by using the above-described spot welding machine is roughly composed of a conduction angle detection circuit (conduction angle detection means) 211, a current value estimation circuit (current value estimation means) 212, and a vibration detection circuit. (Vibration detecting means) 213, vibration phase difference detecting circuit (vibrating phase difference detecting means) 214, pass / fail judgment reference value setting circuit (pass / fail judgment reference value setting means) 215, poor welding alarm circuit (welding poor alarm means) 216, welding Pass / fail judgment circuit (welding pass / fail judgment means) 2
17, an electrode tip shaping timing detection circuit (electrode tip shaping timing detection means) 218 and a spill detection circuit (splash detection means) 219.

The energization angle detection circuit 211 calculates the voltage Ve between the electrodes.
To generate an energization angle signal φi used to estimate the energization current and an energization timing signal φc used to measure the phase difference between the current waveform and the detected vibration wave. The current value estimating circuit 212 calculates an estimated current value Ie from the angle signal φi. The vibration detection circuit 213 inputs the detection signal Vs of the vibration sensor 20 attached to the spot welding machine,
Unnecessary frequency components are removed from the detection signal Vs, and the detection signal Vs is amplified by a subsequent circuit to an appropriate signal level to output a detection vibration signal Vm.

The vibration phase difference detection circuit 214 detects the energization timing signal φc and the vibration signal Vm detected by the vibration detection circuit 213.
And measure the phase difference dθ between both signals φc and Vm,
It is output as a vibration phase difference signal (judgment parameter) Jp. The pass / fail judgment reference value setting circuit 215 sets and outputs a pass / fail judgment reference value Jr to be used for the pass / fail judgment of spot welding. The welding failure alarm circuit 216 includes a current value estimation circuit 212
Outputs the estimated current value Ie, the detected vibration signal Vm, and the vibration phase difference signal Jp output from the vibration phase difference detection circuit 214.
And various welding failure alarms Wo, We, Wi, Wb
Is output.

The welding pass / fail judgment circuit 217 compares the vibration phase difference signal Jp with the pass / fail judgment reference value Jr output from the pass / fail judgment reference value setting circuit 215 to judge whether the welding is good or not. If all the alarm signals Sw to be output have no alarm, a pass / fail judgment result is output, and if there is an alarm, a judgment signal Sj of “poor welding” is output regardless of the pass / fail judgment. Electrode tip shaping time detection circuit 218
Compares the vibration phase difference signal Jp with an externally input electrode tip shaping time determination reference value Se, determines that the electrode tips 15 and 16 have reached the shaping time, and generates the electrode tip shaping signal Sd. Output. The scatter detection circuit 219 includes:
Input detection vibration signal Vm and energization timing signal φc,
When the detection vibration signal Vm is continuously input for one cycle of the energization timing φc, the occurrence of scattering is detected, and the number of energization cycles at that time is detected as the occurrence cycle signal Ss of the scattering.
Output as

The basic processing procedure of the monitoring device 21 will be described with reference to the flowchart of FIG.

In step S1, the form and value Jr of the pass / fail judgment standard are selected and set according to the pass / fail judgment mode.
In step S2, the energization timing signal φc is read, and the estimated energization current Ie [n] is measured.
3, the energization timing signal φc and the detected vibration signal V
m is read and both vibration phase differences dθ [n] are measured. Note that the array variable n indicates an energization cycle index.

Next, in step S4, the estimated current Ie [n], the detected vibration signal Vm, and the vibration phase difference dθ
Based on the information of [n], whether pass / fail of “setting condition inconsistency”, presence / absence of “electrode tip welding”, presence / absence of “current conduction failure”, and presence / absence of “shunt current” are detected, and welding failure is determined according to these results. An alarm is determined. Then, in step S5, the quality determination is started by comparing the quality determination reference value Jr with the vibration phase difference dθ [n]. In step S5, a determination process corresponding to the form of the quality determination criterion and the value Jr is performed.

Next, in Step S6, Step S
It is determined whether or not the warning item is detected in the determination of the welding failure warning of No. 4 and when it is determined that there is no failure warning (Ye)
s): In Step S7, it is determined whether or not the spot welding is good, and when it is determined that the spot welding is good (Ye).
In step s), a determination result of good welding is output in step S8. If it is determined in step S6 that there is a failure alarm (No) or if it is determined in step S7 that welding is not good (No), step S6 is performed.
In step 9, the result of the determination of poor welding is output, and an alarm of the corresponding alarm item is output.

Next, in step S10, the determination of the electrode tip shaping time is started by comparing the vibration phase difference dθ [n] with the electrode tip shaping time determination reference value Se. That is, the vibration phase difference dθ [n] is equal to the electrode tip shaping time determination reference value S.
e is determined, and if it is determined that the shaping time has been reached (Yes), an alarm of electrode tip shaping is output in step S12. If it is determined in step S11 that the shaping time has not been reached (N
After the alarm is output in step o) and step S12, in step S13, the presence or absence of dispersion is detected from the amplitude level of the detected vibration signal Vm, and the occurrence cycle of dispersion is detected and output from the energization timing signal φc.

Thus, the pass / fail judgment processing in one welding is completed. In order to continuously prepare for the next welding, the process returns from step S13 to step S2 to be in a standby state.
Thereafter, the processing is continued until the software is stopped.

Here, the energization angle detection circuit 211 and the current value estimation circuit 212 will be described. The inter-electrode voltage Ve is detected as a waveform obtained by differentiating the welding current Iw (1) by the inductance of the conduction path of the spot welding machine 10, as shown in (2) in the timing chart of FIG. In this embodiment, the inter-electrode voltage Ve excellent in time resolution
Is detected, and the energization timing signal φc is output by processing so that a thin pulse signal is output only at the sharp voltage change point. Note that a high-pass filter can be used to generate a thin pulse signal.

In the thin pulse signal thus obtained, the first signal Po corresponds to the energization start timing (hereinafter referred to as "ignition"), and the next signal Pc corresponds to the energization stop signal (hereinafter "arc extinguishing"). ), And is used as an operation timing signal of a subsequent processing circuit.

Next, an energization timing signal φc is used for the energization angle φi, the first signal Po is at a high level, the next signal P
A signal having a pulse width corresponding to the conduction angle φi by alternately changing the level so as to be low level at c (4)
And Note that a flip-flop element can be used to generate the pulse signal. Thus, the energization angle signal φi and the energization timing signal φc are output from the energization angle detection circuit 211.

Next, the current value estimation circuit 212 receives the energization angle signal φi updated every half cycle of the energization current, measures the pulse width thereof, and sequentially updates and outputs the estimated welding current value Ie ( 5). In this process, a Miller integration circuit (time integration) is used for measuring the pulse width, and a sample and hold circuit that operates at the timing of extinguishing is used to generate the welding current estimated value signal Ie.

In the software, as shown in FIG. 16, in step S21, a signal Po of the firing time is detected, and in step S22, the signal Pc of the extinction time is detected.
Is detected, and in step S23, information corresponding to the estimated welding current value Ie can be obtained by subtracting the firing time from the arc extinguishing time. Further, by multiplying the detected subtraction value by the welding current conversion coefficient If, a welding current estimated value Ie converted into a physical value can be output. The conversion coefficient at this time is obtained by the following equation (7).

[0088]

(Equation 7)

The above processing is repeated every half cycle of energization in one welding operation. In step S24, the waiting time Ph until the next ignition is measured.
At 25, it is determined whether or not the energization has ended. In step S25, for example, when the energization has been performed for three cycles or more, it is determined that the energization has ended. When it is determined that the energization has ended (Yes), the measured firing time, extinguishing time, and energization amount information To return to the main routine of FIG. If it is determined that the energization has not ended (No), the process returns to step S21. If the waiting time Ph until the ignition time is set to be equal to or longer than the maximum value of the set cool cycle value, the process does not return to the main routine even during welding with a cool cycle.

Next, the vibration phase difference detection circuit 214 will be described with reference to the flowcharts shown in FIGS. In step S31 in FIG. 17, a processing procedure is selected according to the pass / fail determination mode Sm before the vibration phase difference measurement. This corresponds to the pass / fail judgment mode switching means.

If the object to be detected is the intermittent mechanical damping vibration Vm, the processing proceeds from step S31 to the vibration phase difference detection procedure. In step S32, the ignition time Po of the energization timing signal φc is detected. Step S3
In 3, it is determined whether or not the amplitude of the intermittent mechanical damping vibration Vm is equal to or larger than the detection threshold value Ath. At this time, when it is determined that the intermittent mechanical damping vibration Vm is larger than the detection threshold value Ath (Yes), the detection time Tv is detected in step S34. Then, in step S35, the firing phase time Po is subtracted from the vibration detection time Tv to obtain the vibration phase difference dθ [n]. An example of the detection timing at this time is dθ [1.5] in (7) of FIG.
Shown in In FIG. 19 (7), the amplitude corresponds to the phase difference, and the magnitude is normalized with one cycle of the conduction current as one cycle.

On the other hand, if it is determined in step S33 that the intermittent mechanical damping vibration Vm is smaller than the detection threshold value Ath (No), step S36 is executed.
In step S3, it is determined whether or not the elapsed time from the detection of the ignition time Po has reached the half cycle of the conduction current. If it is determined that the half cycle of the conduction current has not been reached (No), the process proceeds to step S3.
3, the process waits for detection of vibration, and when it is determined that the half cycle of the energizing current has been reached (Yes), in step S37, the detection cycle is determined to be impossible to detect vibration, and is normalized to the vibration phase difference dθ [n]. Is substituted for the maximum value of 1.

The above process is repeated in each welding half cycle until the end of energization is detected in one welding operation. The array variable of the vibration phase difference dθ [n] is updated every half cycle, and at the end of energization, twice as many phase difference data as the total number of energization cycles are detected. This is the vibration phase difference sampling means.

Then, in step S38, the waiting time Ph at the firing time Po is measured. In step S39, it is determined whether or not the energization is completed. If it is determined that the energization is completed (Yes), the process proceeds to step S310. To eliminate abnormal data and determine that power supply has not ended (N
In o), the process returns to step S32.

Here, the abnormal data is defined as the vibration phase difference dθ [0.5] or dθ [1.0] shown in FIG. As shown by the data [1] substituted for dθ [n] when the detection becomes impossible and the vibration phase difference dθ [3.5] and dθ [4.0] in FIG. As a result, vibration is detected immediately after ignition, and dθ [n] is

This is data that has a value close to [0], and indicates data that greatly deviates from the average detected phase difference. Therefore, in step S310, a process of removing abnormal data from the sample data (population) is performed. This is the sample data optimizing means.

Then, in step S311, a representative value is calculated from the last remaining sample data and used as a determination parameter Jp. At this time, as means for obtaining the determination parameter Jp, in addition to the arithmetic mean which is advantageous in the calculation time, a geometrical value which can obtain a representative value as an effective value without being affected by low-frequency, large-deviation, noise-like sample data is used. The average or mode (mode) is valid. This is the determination parameter determining means.

Next, if the object to be detected is a metal melting vibration as shown in FIG.
From step 31, the process proceeds to the metal melting time processing procedure, and step S31
In step 2, the ignition time Po of the energization timing signal φc is detected, and in step S313, the time Tv at which the amplitude value of the metal melting vibration has exceeded the detection threshold value Ath is detected. In step S314, the metal melting detection time Tv
Is subtracted from the firing time Po to obtain a time Tb from the start of energization to the detection of the first vibration wave, and this is used as a determination parameter. FIG. 13 shows the determination parameters obtained in this manner.
Return to the main routine.

Next, FIGS. 8 and 9 show block diagrams of another embodiment of the vibration phase difference detection circuit 214 which is constituted by hardware. In the embodiment shown in FIG. 8, the oscillation phase difference sampling circuit 214a corresponds to steps S32 to S38 in FIG.
Is a time counter that starts counting the firing time Po and stops counting when the intermittent mechanical damping vibration Vm becomes equal to or greater than the detection threshold value Ath. The time counter is executed every half cycle of the supplied current to obtain sample data of the vibration phase difference. After that, sample data optimization circuit 2
14b determines a determination parameter by the same logic as in step S310 of FIG.
For c, a determination parameter is obtained by the same logic as in step S311 in FIG.

A burst wave detection time detection circuit 214d for obtaining a determination parameter when the object to be detected is metal melting vibration corresponds to steps S312 to S314 in FIG. 17, and corresponds to the firing time of the first energization timing signal φc. Po
Starts counting, and the metal melting vibration reaches the detection threshold value At.
h is a time counter that stops counting when it reaches h or more, thereby obtaining a time Tb until the first vibration wave is detected. Finally, in accordance with the pass / fail determination mode Sm, it is determined whether the determination parameter is based on intermittent mechanical damping vibration or the determination parameter based on metal melting vibration.
The output is switched at 4e.

In the embodiment shown in FIG. 9, the cross-correlation calculating circuit 214f calculates the time-base transition (Rxy (t)) of the cross-correlation between the energization timing signal φc and the intermittent mechanical damping vibration Vm, and firstly calculates the phase relation. The time tc at which the number reaches the maximum peak is obtained, and the time tcW is set as the vibration phase difference dθ [n] r.
This process is executed every half cycle of the conduction current to obtain sample data of the vibration phase difference. The calculation time width τ of the cross-correlation
Is a half cycle of the conduction current, and the reference time is the ignition time P
As for o, when the intermittent mechanical damping vibration Vm has an envelope waveform, a clear peak of the correlation coefficient is easily obtained.

The determination parameter tb based on the metal melting vibration is the vibration phase difference dθ [n] which becomes the first or less among the sample data obtained by the cross-correlation calculation circuit 214f in the burst wave detection time detection circuit 214g. Is extracted, and the cycle time for the number of cycles before the vibration phase difference dθ [n] is extracted is obtained.

Next, an embodiment of the pass / fail judgment reference value setting means will be described with reference to the flowchart of FIG.

In step S110, a reference value setting mode is selected. Here, a fixed mode for fixedly setting the pass / fail judgment reference value, an automatic setting mode for automatically setting the pass / fail judgment reference value by multiplying the detection amount by a preset adjustment coefficient Sk, and an external input signal The external input mode in which a pass / fail judgment reference value is retrieved from a reference value map set in advance in accordance with the external input mode can be selected according to the application.

In the fixed mode, in step S111, a processing procedure is selected according to the pass / fail judgment mode Sm.
This is switched in conjunction with the selection of the quality judgment mode of the vibration phase difference detection circuit 214, and corresponds to a quality judgment mode switching means. If the quality determination target is the phase difference Jp of the intermittent mechanical damping vibration Vm, step S112
At the lower end of the pass / fail judgment reference value Jr
(L) is read. In setting the lower limit at this time, the vibration phase difference dθ at the allowable lower limit of the welding current is used as a guide.
Further, as described above with reference to FIG. 5B, when the welding current value is insufficient, the vibration phase difference d detected at that time is determined.
θ also decreases. Therefore, the vibration phase difference dθ when good welding is performed at the allowable lower limit current of insufficient current is the lower limit for determining “good welding”. The vibration phase difference dθ at this time is obtained in advance, and set to the lower limit value of the pass / fail judgment criterion.

Next, in step S113, the upper / lower quality judgment reference value is read. To set the upper limit at this time, the vibration phase difference d at the time of the allowable lower limit force of the pressing force of the electrode tip is set.
θ, and vibration phase difference d at the limit of continuous use of electrode tip
Use the smaller of θ as a guide. As described above with reference to FIG. 5A, the vibration phase difference dθ increases when the pressing force is insufficient, and the vibration phase difference dθ also increases at the time of continuous use limit due to wear of the electrode tip. . Therefore, the allowable lower limit of the pressing force or the vibration phase difference dθ at the time of the continuous use limit of the electrode tip is the upper limit for determining “good welding”. The vibration phase difference dθ at this time is obtained in advance, and set to the upper limit of the pass / fail judgment criterion. As a result, as shown in FIG. 22, two pass / fail judgment reference values of the upper limit Jr (U) and the lower limit Jr (L) are set.

When the metal melting vibration is judged as a good or bad in the good or bad judgment mode Sm, the vibration phase difference dθ becomes large even if the current is insufficient, and the setting of the lower limit becomes unnecessary. Therefore, the reading of the lower limit is omitted. are doing. As a result, FIG.
As shown in FIG. 1, one pass / fail judgment reference value is set.

In the automatic setting mode, the reference parameter for calculating the pass / fail judgment reference value can be selected by the phase difference and the current value according to the application. First, when the phase difference is selected as the reference parameter, in step S115, a previously obtained adjustment coefficient Sk is read. This adjustment coefficient S
k is a ratio between the vibration phase difference when good welding is performed and the vibration phase difference to be determined as a defect, and is set using the following equation 8 as a guide.

[0108]

(Equation 8)

Subsequently, in step S116, the vibration phase difference (determination parameter Jp) when good welding is performed is read. For this reading, a previously stored vibration phase difference may be called, but a switch is provided on the welding gun, and when the welding conditions are in a good state after replacing the electrode tip or the like, the switch is pressed. In this case, the quality determination reference value can be adapted to the vibration phase difference that changes each time the electrode tip is replaced. Then, in step S117, the read / write adjustment coefficient Sk is multiplied by the vibration phase difference to calculate and output a pass / fail judgment reference value Jr by the following equation 9. FIG. 23 shows the relationship between the number of weldings and the phase difference as this setting.

[0110]

(Equation 9)

If the welding current has been selected as the reference parameter, the adjustment coefficient Sk 'determined in advance is read in step S118. This adjustment coefficient Sk '
Is a ratio between the set welding current value and the vibration phase difference to be determined as a defect, and is set using the following Expression 10 as a guide.

[0112]

(Equation 10)

Then, in step S119, the vibration phase difference (determination parameter Jp) when good welding is being performed is read. For this reading, a previously stored vibration phase difference may be called, but if the welding current Ie detected each time the welding quality is determined is used, the quality is determined according to the vibration phase difference dθ (i) due to the current fluctuation. Judgment reference value Jr
(I) can be adapted. And step S
At 120, the read / write adjustment coefficient Sk 'is multiplied by the vibration phase difference Jp (i) to calculate and output a pass / fail judgment reference value Jr (i) according to the following equation 11. FIG. 24 shows the relationship between the number of weldings, the energizing current, and the phase difference as this setting.

[0114]

[Equation 11]

In the external input mode, in step S121, a sheet pressure signal input from the outside is read, and in step S122, the sheet thickness read with reference to a preset sheet thickness versus pass / fail judgment reference value map is used. Search and
In step S123, the corresponding pass / fail judgment reference value is read. At this time, in the map, a thickness-to-goodness determination reference value map as shown in FIG. 15 is set. For example, if the thickness input from the outside is 2.0 mm, the quality determination corresponding to this is made. Reference value Jr = 0.5 is set.

Although not described in the flow chart of FIG. 14, the thickness and vibration phase difference of the material to be welded are shown in FIG.
Since there is a proportionality relationship as shown in FIG. 7, an adjustment coefficient Sk ″ may be used in place of the sheet thickness versus the quality judgment reference value map, and a quality judgment reference value may be set similarly to the automatic setting mode based on the welding current. FIG. 25 shows the relationship between the number of weldings, the plate thickness, and the phase difference as this setting.

Next, an embodiment of the welding failure alarm means will be described with reference to FIG. First, an embodiment of the setting condition non-conforming means relating to the welding defect alarm means will be described.
θ [n] indicates the transition of the energization cycle of the vibration phase difference at the time of welding conforming to the set conditions. Ln [n] and Ll [n] indicate the upper limit phase difference and the lower limit phase difference of the matching determination reference value, respectively. Therefore, the detected vibration phase difference dθ [n] is Ln [n] in each energization cycle.
And Ll [n], it is determined that the material to be welded at that time conforms to the set conditions. On the contrary,
If the detected vibration phase difference dθ [n] is out of the range between Ln [n] and Ll [n] in each energization cycle, it is determined that the vibration phase difference is nonconforming, and the set condition nonconformity alarm Wo is output.

In this embodiment, the shift register 216a is used to sequentially send the conformity determination reference value to the comparator 216b in accordance with the progress of the energizing cycle. An adaptation determination reference value for each energization cycle is set in advance, and this is set in response to the energization start signal t0.
Set to. At the time of comparison, the firing time Po of the energization timing signal φc is used as a shift lock, and the vibration phase difference dθ
Conformity determination reference value Ln of energization cycle corresponding to [n]
[N] and Ll [n] are sent to the comparator 216b, and the vibration d
It is determined whether θ [n] is out of the range of the matching determination reference value Ln [n] and Ll [n].

Next, an embodiment of the electrode chip welding detecting means will be described. At the time of electrode tip welding, the amplitude of the intermittent mechanical damping vibration Vm becomes extremely small despite the proper energization. Therefore, the intermittent mechanical damping vibration V
After rectifying m through a diode 216c, an average amplitude value is extracted by a low-pass filter 216d, and a voltage comparator 216e detects an electrode chip welding detection threshold Ath.
Compare with Also, the energizing current value is determined by comparing the estimated current value Ie obtained from the voltage between the electrodes and the appropriate energizing value Vi with a voltage comparator 216f.
In the AND element 216g, a case where the amplitude average value is smaller than the electrode chip welding detection threshold value Ath and the energizing current is equal to or more than an appropriate value is extracted, and the electrode chip welding alarm We is output.

Next, an embodiment of the current conduction failure detecting means will be described. FIG. 27 shows a transition in the number of weldings of a value obtained by dividing a conduction angle proportional to a conduction current by an average value of vibration amplitude. Normally, the current value is controlled to be constant by the welding control device 11, but the vibration amplitude increases with an increase in the number of weldings. Therefore, FIG. 27 shows a downward-sloping transition. However, when the power supply voltage decreases or the electrical resistance of the material to be welded increases, the predetermined amount of current cannot be obtained, so that the welding control device 11 increases the current flowing angle. As a result, in the case of an energization failure, as shown in FIG. 27, the value obtained by dividing the energization angle by the vibration amplitude becomes large due to the increase in the energization angle and the attenuation of the vibration amplitude due to insufficient energization. In order to detect this energization failure, the current estimation value Ie obtained from the inter-electrode voltage in the divider 216h is divided by the average value of the vibration amplitude, and is compared with a preset comparison voltage Vi in the voltage comparator 216f. Is determined to be "power failure" and the alarm signal W
Output i.

Next, an embodiment of the branch detection means will be described. FIG. 28 shows the transition in the number of weldings of a value obtained by subtracting the past average value of the vibration phase difference from the vibration phase difference. Normally, the vibration phase angle changes to the right as the number of welding increases with the deterioration of the tip of the electrode tip. However, when a shunt of the energizing current to the already welded portion occurs, the energizing current value viewed from the welding control device 11 is in an appropriate range, but the energizing current of the pressurizing portion is shunted to a nearby welding point. Decrease. As a result, the nugget formation of the pressurizing portion is not promoted at the time of the occurrence of the branch flow, so that the vibration phase difference suddenly increases as shown in FIG.

Therefore, in order to detect this branch flow,
First, the moving average value of the past vibration phase difference is
6i, the moving average value is subtracted from the current vibration phase difference (judgment parameter Jr) by the subtracter 216j, and the absolute value of the change amount of the current vibration phase difference is calculated. Next, the voltage comparator 16k determines whether or not the amount of change is greater than a preset branch determination reference value Vb. Then, in order to make a distinction from other fluctuation factors, the logical product element 21 determines that the energization amount is at an appropriate value and that it does not reach a pass / fail judgment reference value or an electrode tip shaping time judgment reference value.
Comprehensive determination is made at 6 m, and if the current vibration phase difference is larger than the shunt determination reference value Vb, it is determined that a shunt current has occurred and an alarm signal Wb is output.

Further, in the embodiment of the welding failure alarm means, the logical sum of each alarm output of the setting condition nonconformity detection means, the electrode tip welding detection means, the current conduction failure detection means and the branch current detection means is used by using the OR element 216n. This is output as the welding failure alarm Sw. Further, this welding failure alarm Sw is shown in FIG.
As shown in FIG. 3, the process is executed before the welding quality determination (step S5), and when the welding failure alarm Sw is output, the welding quality determination is not performed. Therefore, in this case, the quality of the welding is determined forcibly as a poor welding and output with an alarm (step S).
9).

Next, an embodiment of the electrode tip shaping time detecting means will be described. As described above, in the flowchart of FIG. 13, it is determined whether or not the determination parameter Jp, which is the representative value of the vibration phase difference dθ [n], has reached the electrode tip shaping time determination reference value Se. If the time has been reached, an electrode tip shaping alarm is output. FIG. 10 shows an embodiment in which this means is constituted by hardware. Here, the moving average circuit 218a
Is provided in order to reduce a large variation in the determination parameter of the electrode tip shaping time and to stabilize the comparison with the electrode tip shaping time determination reference value Se in the comparator 218b. When an automatic electrode tip shaping device (auto tip dresser) is used, efficient electrode tip shaping can be performed by inputting this electrode tip shaping alarm output as an event signal for shaping execution.

Next, an embodiment of the scatter cycle output means will be described with reference to FIGS. First,
In step S130, the firing time Po of the energization timing signal φc is detected, and in step S131, 0.5 is added to the counter for detecting the scattering occurrence cycle. This is because scattering occurs every half cycle of the welding current cycle. Next, in step S132, the amplitude of the intermittent mechanical damping vibration Vm is set to the detection threshold At.
h. At this time, when it is determined that the amplitude of the intermittent mechanical damping vibration Vm is larger than the detection threshold value Ath (Yes), the vibration detection time Tv is detected in step S133. I do.

Subsequently, in step S134, it is determined whether or not the result of subtracting the firing time Po from the stored vibration detection time Tv is 0. If it is determined that the result is 0 (Yes), In step S135, the value of the scattering occurrence cycle counter at that time is stored. An example of the detection timing of this scattering is dθ [3.
5]. FIG. 20 (3) shows the result of comparing the intermittent mechanical damping vibration Vm with the detection threshold value Ath after rectification, and shows a state where the high level is Vm> Ath. Therefore, during the period of 3.5 to 4.5 cycles during which the high level is detected at the time of detection of the firing time Po, the firing time Po
And the difference between the vibration detection time Tv and dθ [n] is zero.

On the other hand, when the high level is Vm <Ath
, The firing time P is determined in step S136.
It is determined whether or not the elapsed time from the detection of o has reached the half cycle of the conduction current. Here, if it is determined that it has not reached (No), the process returns to step S132 and waits for detection of vibration. When it is determined that the half cycle of the energizing current has been reached (Yes), in step S137, the detection cycle is determined to be incapable of detecting vibration, and the vibration phase difference dθ [n] is determined.
Is substituted for the maximum value 1 of the normalization. The above processing is repeated every half cycle of energization until the end of energization is detected in one welding operation. This process is performed in the same procedure as the flowchart of the energizing current estimation circuit 212 described with reference to FIG.

Then, in step S138, the ignition waiting time Ph is measured. In step S139, it is determined whether or not the energization is completed. If it is determined that the energization is not completed (No), the process proceeds to step s130. Returning to step S14, if it is determined that the energization has ended (Yes), the process proceeds to step S14.
At 0, it is determined whether or not a scatter has been detected. If a scatter has occurred, the value of the scatter generation cycle counter is output in step S141, and thereafter, the process returns to the main routine shown in FIG.

FIG. 11 shows an embodiment in which the scatter detection circuit 219 is constituted by hardware. Here, the dispersion detection circuit 219a performs steps S130 to S130 in FIG.
The scattering is detected by the same logic as in S139, and the number of cycles in which the scattering occurs is counted by the counter 219b. Note that the counter 219b counts the firing time Po of the energization timing signal φc from the energization start t0, and stops counting based on the dispersion detection signal of the dispersion detection circuit 219a. That is, the cycle in which the counting is stopped is output as the scattering occurrence cycle Ss.

The configuration of the monitoring apparatus for spot welding according to the present invention is not limited to the above embodiments, and various modifications can be made.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the principle of spot welding according to the present invention, and FIG. 1B is a graph showing a relationship between the number of weldings and a vibration phase difference.

FIG. 2 is a diagram for explaining a welding defect determination method based on a vibration amplitude expansion start time.

FIG. 3 is a diagram illustrating a method for determining a welding defect based on initial vibration observed in a low melting point plated steel sheet.

FIG. 4 is a diagram illustrating a physical phenomenon in a welded portion.

FIG. 5 is a graph (a) showing a relationship between a pressing force and a vibration phase difference as characteristics of a variation factor, a graph (b) showing a relationship between a welding current and a vibration phase difference, and a relationship between a plate thickness and a vibration phase difference. It is a graph (c) which shows.

FIG. 6 is a diagram for explaining the principle verification of the present invention.

FIG. 7 is a basic block diagram illustrating an embodiment of a spot welding monitoring apparatus according to the present invention.

FIG. 8 is a block diagram illustrating an embodiment of a vibration phase difference detection unit.

FIG. 9 is a block diagram for explaining another embodiment of the vibration phase difference detecting means.

FIG. 10 is a block diagram illustrating an embodiment of an electrode tip shaping time detecting unit.

FIG. 11 is a block diagram illustrating an embodiment of a scatter detection unit.

FIG. 12 is a block diagram illustrating an embodiment of a welding failure alarm unit.

FIG. 13 is a flowchart illustrating a basic processing procedure performed by the spot welding monitoring apparatus according to the present invention.

FIG. 14 is a flowchart illustrating a processing procedure when setting a pass / fail determination reference value.

FIG. 15 is a diagram showing an example of a sheet thickness versus pass / fail judgment reference value map.

FIG. 16 is a flowchart illustrating a processing procedure for measuring an energization amount.

FIG. 17 is a flowchart illustrating a processing procedure for measuring a vibration phase difference.

FIG. 18 is a flowchart illustrating a scatter cycle output processing procedure.

FIG. 19 is a timing chart illustrating a procedure for detecting a current estimated value and a vibration phase difference.

FIG. 20 is a timing chart illustrating a procedure for detecting electrode tip welding and scattering.

FIG. 21 is a graph showing a relationship between the number of times of welding and a vibration phase difference as a setting of a pass / fail judgment reference value.

FIG. 22 is a graph showing the relationship between the number of weldings and the phase difference as the setting of the upper and lower limits of the pass / fail judgment reference value.

FIG. 23 is a graph illustrating a method for setting a pass / fail judgment reference value from a vibration phase difference, showing a relationship between the number of weldings and the vibration phase difference.

FIG. 24 is a graph for explaining a method of setting a pass / fail judgment reference value from an energizing current, and is a graph showing a relationship between the number of weldings, an energizing current, and a vibration phase difference.

FIG. 25 is a graph for explaining a method of setting a pass / fail judgment reference value from a plate thickness, showing a relationship between the number of times of welding, the plate thickness, and a vibration phase difference.

FIG. 26 is a graph illustrating a method of detecting a setting condition non-conformity, showing a relationship between an energization cycle and a vibration phase difference.

FIG. 27 is a graph for explaining a method for detecting an energization failure, and is a graph showing the relationship between the number of weldings and the energization angle / vibration amplitude.

FIG. 28 is a graph illustrating a method of detecting a branch flow, showing a relationship between the number of times of welding and a vibration phase difference-average phase difference.

[Explanation of symbols]

Reference Signs List 10 spot welding machine 21 monitoring device 214 vibration phase difference detection circuit (vibration phase difference detection means) 214a vibration phase difference sampling circuit (vibration phase difference sampling means) 214b sample data optimization circuit (sample data optimization means) 214c Judgment Parameter determination circuit (determination parameter determination means) 214e Pass / fail judgment mode switch (pass / fail judgment mode switching means) 215 Pass / fail judgment reference value setting circuit (pass / fail judgment reference value setting means) 217 Weld pass / fail judgment circuit (welding pass / fail judgment means) 218 Electrode Chip shaping timing detecting circuit (electrode tip shaping timing detecting means) 219 Scattering detecting circuit (scattering detecting means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01R 25/00 G01P 15/00 A (72) Inventor Shuji Torii 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor F term in reference (reference) 2G030 AA01 AG00 2G060 AA10 AF03 AF20 EA06

Claims (15)

[Claims] An electrode of a spot welding machine for generating an electromagnetic force as an excitation source when an AC welding current is applied in a spot welding monitoring device for determining the quality of a spot welding based on vibration generated during welding. Vibration phase difference detection means for detecting the intermittent mechanical damping vibration of the portion and the phase difference between the AC welding current, pass / fail determination reference value setting means for setting a reference value for pass / fail determination, and vibration level detected by the vibration phase difference detection means A spot welding monitoring device, comprising: welding quality judgment means for comparing the phase difference with a reference value from a quality judgment reference value setting means to judge the quality of spot welding. 2. A vibration phase difference detecting means for detecting a phase difference of intermittent mechanical damping vibration a plurality of times per welding, a vibration phase difference sampling means for detecting a phase difference between the detected vibration phase differences, etc. Sample data optimizing means to delete abnormal data corresponding to excessive vibration and under-vibration such as during preheating energization, and representative values of sample data optimized using either mode, arithmetic mean or geometric mean The spot welding monitoring apparatus according to claim 1, further comprising: a determination parameter determining unit that obtains the following. 3. The pass / fail judgment reference value setting means is means for setting a plurality of pass / fail judgment reference values, and the welding pass / fail judgment means is configured to determine whether the vibration phase difference is less than, greater than, or within a predetermined range with respect to the reference value. The spot welding monitoring apparatus according to claim 1 or 2, wherein the means is a means for determining "good welding" when. 4. A pass / fail judgment reference value setting means sets a vibration phase difference corresponding to a welding failure caused by insufficient pressing force or wear of the electrode tip as an upper limit of the pass / fail judgment reference value. Means for setting a vibration phase difference corresponding to the occurrence of welding failure due to insufficient current as the lower limit of the value, and the welding quality determination means determines that "welding is good" when the vibration phase difference is between the upper limit and the lower limit. The spot welding monitoring apparatus according to claim 3, wherein the apparatus is a determination unit. 5. A pass / fail judgment reference value setting means for setting a pass / fail judgment reference value to a value obtained by multiplying an amount of a vibration phase difference when welding is good by a predetermined coefficient obtained in advance. 3. The monitoring device for spot welding according to 1 or 2. 6. The pass / fail judgment reference value setting means is a means for setting a value obtained by multiplying a current estimation value calculated from a voltage between electrodes by a predetermined coefficient obtained in advance as a pass / fail judgment reference value. 3. The monitoring device for spot welding according to 1 or 2. 7. A pass / fail judgment reference value setting means selects and sets a pass / fail judgment reference value by referring to a predetermined thickness-to-pass / fail judgment reference value map based on a sheet thickness signal of a material to be welded inputted from outside. 3. The apparatus for monitoring spot welding according to claim 1, wherein the apparatus is a means. 8. An electrode shaping time detecting means for detecting a shaping time of an electrode tip by comparing a detection result of the vibration phase difference detecting means with a predetermined electrode shaping time determination reference value and outputting an alarm. The spot welding monitoring device according to claim 1. 9. A setting condition inconsistency detecting means for comparing a change of the vibration phase difference for each cycle with a predetermined change pattern to determine whether or not a welding setting condition for a workpiece is suitable. The monitoring device for spot welding according to any one of claims 1 to 8. 10. A dispersion detecting means for detecting that vibration having a predetermined amplitude level or more continues for a half cycle of a current waveform to determine dispersion, and a dispersion generation cycle for outputting an energization cycle value when the dispersion is detected. The spot welding monitoring apparatus according to claim 1, further comprising an output unit. 11. An electrode tip welding detecting means for detecting that an energization angle detected from an inter-electrode voltage is at an appropriate value and that a vibration amplitude is equal to or less than a predetermined amplitude and which determines electrode tip welding is provided. The spot welding monitoring device according to any one of claims 1 to 10. 12. A current-carrying fault detecting means for judging a faulty current and outputting an alarm when a result obtained by dividing a current-carrying angle detected from an electrode voltage by a vibration amplitude exceeds a predetermined value, is provided. The monitoring apparatus for spot welding according to claim 1, wherein 13. When the current conduction failure detecting means does not determine that the conduction is defective, when the difference between the detected vibration phase difference and the moving average value is equal to or greater than a predetermined value, the current is determined to be a shunt current and an alarm is output. The apparatus for monitoring spot welding according to claim 12, further comprising a shunt detection means for detecting the spot welding. 14. A welding device for outputting a welding failure alarm signal to a welding quality determination unit when a failure is detected in any of the setting condition inconsistency detection unit, the electrode tip welding detection unit, the current conduction failure detection unit, and the branch current detection unit. 10. A defect alarm means, wherein the welding quality judgment means is means for outputting "poor welding" regardless of the result of the quality judgment based on the vibration phase difference when a welding defect alarm is input. The monitoring device for spot welding according to any one of claims 13 to 13. 15. The vibration phase difference detecting means detects a representative value of the sampled data obtained by the determination parameter determining means and a time from the start of energization to a time when vibration equal to or more than a predetermined detection threshold is first detected. The pass / fail judgment reference value setting means calculates the pass / fail judgment reference value, which is a value obtained by multiplying the amount of the vibration phase difference when welding is good by a predetermined coefficient, and the voltage between the electrodes. The quality judgment reference value, which is a value obtained by multiplying the obtained current estimated value by a predetermined coefficient obtained in advance, and a thickness-quality judgment reference value map preset based on a thickness signal of the workpiece to be welded input from outside. A means for selectively switching and outputting a quality determination reference value selected and set, and a quality determination reference value at the time of welding failure determination in a steel sheet having a surface coating layer having a lower melting point than the base material, and a spot welding machine to be attached and Melted 15. A good or bad judgment mode switching means for selecting switching of output of a vibration phase difference detecting means and a good or bad judgment reference value setting means according to any of the contact members. A spot welding monitoring device as described.