JPS6356367A - Method and device for adaptive control for resistance welding - Google Patents

Abstract

PURPOSE:To perform the satisfactory resistance welding in a prescribed time at all times even if a welding condition is different by detecting the time of the welding resistance maximum value between electrode tips after electrification is started and integrating the quantity of decrease of the resistance extending to the prescribed time after that to control a welding current. CONSTITUTION:The resistance between the electrode tips 1 after the electrification is started is reduced by the fitting of the pressing surface and the resistance is increased by the rise of the temperature after that. Next, an electrification area is increased by the generation of a nugget and the resistance is decreased gradually. When this resistance maximum value is R2, a point of time T2 is detected by a peak detection circuit 4 and the quantity S2 of integration of the resistance decrease till the prescribed time DELTAT by a timer is calculated by an integration circuit 9 and transmitted to a welding current control circuit 8 as the correct setting quantity. The control circuit 8 gives instructions on a correction current value DELTAI to a welding current regulator 3 to finish the welding after the lapse of the prescribed time. Accordingly, the satisfactory resistance welding is performed in the prescribed time at all times regardless of changes of welding materials, a surface condition and the number of laminations.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides an adaptive control system for resistance welding that changes welding conditions based on changes in resistance or voltage between electrode tips during welding current application time. METHODS AND APPARATUS.

(Prior art) As is well known, in lap resistance welding such as general spot welding of thin steel plates, the workpiece (object to be welded)
The resistance between the electrode tips for pressurizing and energizing the electrode changes with the elapsed energization time in a pattern as shown in FIG. 1(A).

At the very beginning when the welding current starts to be applied, the contact resistance between the tips rapidly decreases as the large contact resistance caused by foreign matter existing at the tip of the electrode tip or between the workpieces decreases drastically. However, P immediately occurs due to the temperature of the workpiece due to energization, and as a result, the inter-chip resistance changes to increase. Here, a local minimum value R1 is generated.

When the temperature of the workpieces becomes high enough, weld nuggets begin to form between the workpieces. When this happens, the cross-sectional area of the welding current flow path expands, so the inter-chip resistance changes from increasing to decreasing. Here, a maximum l1iIR2 occurs.

Research has been actively conducted on the correlation between the above-mentioned change in inter-chip resistance and the degree of growth of weld nogets. In particular, it has been found that the manner in which the resistance decreases after the above-mentioned maximum value [2] is produced corresponds well to the manner in which weld nuggets grow.

Based on these research results, for example,
Resistance welding control techniques such as those described in Japanese Patent Application Laid-open No. 6185 and Japanese Patent Application Laid-Open No. 118393/1988 have been developed. In these methods, the welding current is changed so that the decrease in the inter-electrode tip resistance after it reaches its maximum value falls within a set change pattern.

(Problem that the invention attempts to solve) Type of workpiece metal, thickness 2. presence or absence of plating on the surface.

Even if the conditions of the objects to be welded (referred to as work conditions), such as the number of stacked pieces, are the same, the degree of familiarity between the work pieces,
The welding quality and welding time that can be obtained will vary depending on the implementation conditions, such as the degree of contamination on the workpiece surface or the degree of wear on the tip of the electrode.

Conventional control technology C can provide approximately constant welding quality within a fairly constant period of time as long as the range of variation in implementation conditions as described above is not too large. However, if there is a large variation in the execution status, the welding time may become extremely long or the welding quality as intended may not be obtained. In other words, conventional control technology has a very narrow allowable range of variation depending on work conditions and implementation conditions.

This invention was made in view of the above-mentioned conventional problems, and the first is that even if the implementation conditions such as the familiarity of each workpiece or the dirt on the surface vary considerably, the process can be performed within approximately the same amount of time. Optimum welding quality (!
13= By providing a method and apparatus for adaptive control for resistance welding that has a wide range of applicability.

(Means for solving the problem) Therefore, in the present invention, after starting energization under certain welding conditions, changes in resistance (or voltage) between electrode tips are monitored,
In addition to capturing the timing when the value does not show a maximum value, quantitatively analyze the decreasing change in the above value over a certain period of time,
Based on the analysis results, welding strip f after the above-mentioned certain period of time has elapsed.
The control method was to determine 1.

A device for carrying out this control method; and a peak detection means for monitoring the change in resistance (or voltage) between the electrode tips after the start of energization and detecting the J timing T2 when the value shows the maximum value. , an integrating means that performs a Δ-difference operation for a predetermined period of time from this timing T2 and integrates a decrease in the resistance (or voltage) from the maximum value, and welding conditions corresponding to the integral value obtained by this integrating means. Characteristic setting means for generating information and J-recording timing T2'-recording interval Δ
A control means for changing the welding conditions according to the output of the characteristic setting means after T has elapsed is provided.

(Function) The period in which the inter-electrode tip resistance reaches the maximum value R2 and begins to decrease is called the period of rapid growth of weld nuggets. The degree of decrease in interchip resistance during this period corresponds to various external factors (work conditions, implementation status, etc.) related to the growth and expansion of Naguchi. For example, if the tip diameter of the electrode tip expands due to wear, or if the thickness of the workpiece plate increases,
If there is a galvanized layer on the workpiece surface, if the workpiece does not fit well, or if the surface is extremely dirty, weld nuggets will be difficult to grow and expand, and the resistance will decrease more slowly. This tendency is that the above-mentioned integral value becomes smaller.

In this invention, after the interchip resistance shows the local maximum value R2 at timing T2, the decrease change in the above value of Δt for a certain period of time is quantitatively analyzed, and based on the analysis result, after the time Δt has elapsed, By determining the welding conditions, it is possible to provide welding conditions that match the growth and expansion conditions of the nuggets, and to obtain approximately constant welding quality within a approximately constant time.

(Embodiment) FIG. 2 shows the configuration of a control device according to an embodiment of the present invention. The welding current regulator 3 is controlled by a welding current control circuit 8, and causes a predetermined test current 11 to flow between the electrode tips 1 at the start of energization. The voltage between the electrode tips 1 is input to a resistance calculation circuit 2, and the inter-tip resistance Rx is calculated from this voltage and the welding current.

The peak detection circuit 4 monitors the change in the interchip resistance Rx after the start of energization, and first detects a minimum value R1 where RX suddenly decreases and then increases.

At timing T1 when the local minimum value R1 is detected, the detection circuit 4 activates the integrating circuit 5 and provides the detected local minimum value R1 to the integrating circuit 5.

After the integrator circuit 5 is activated at time T1, the integrator circuit 5 calculates the increase (1- or even RX-R1) from the minimum value R1 of the inter-chip resistance RX.
) is integrated.

The peak detection circuit 4 then detects a local maximum value R2 at which the inter-chip resistance Rx changes from increasing to decreasing.

When the local maximum value R2 is detected at time T2, the detection circuit 4 stops the integrating operation of the integrating circuit 5. Upon receiving this number, the integrating circuit 5 outputs the integration result S1 from time point 1 to time point I2.

The above-mentioned integral value S1 is inputted to a level discrimination circuit 6, and divided into several classes depending on its magnitude.

The level discrimination result becomes an input to the basic control amount setting circuit 7.

The basic control amount setting circuit 7 is composed of a memory, and sets the optimum welding current value after time I2 for each integral value S1 divided into several classes. This data setting is based on appropriate data obtained from actual measurements of changes in interchip resistance for various workpiece lines f1 and implementation conditions.

At time T2, an integral value S1 is calculated, and based on it, a welding current command value 2 is applied from the basic control amount setting circuit 7 to the welding current control circuit 8.

The welding current command value I2 at this time is the basic control amount.

In response, the control circuit 8 controls the welding current regulator 3 to switch the welding current flowing between the chips from the test current (1) to the commanded current value (2).

By this control, the welding current I2 during fermentation after time T2, that is, the period when nuggets are generated, grows and expands.
is determined. This value 12 is a value that is approximately commensurate with the work conditions and other implementation conditions observed up to time T2.

The above is the first-stage control function in this embodiment.

The gist of the present invention is the control function described below.

At time T2 when the peak detection circuit 4 detects the local maximum value R2, it activates another integrating circuit 9 and gives the local maximum value R2 to it. The integration circuit 9 integrates the decrease (R2-Rx) of the inter-chip resistance Rx from the maximum value R2 for a certain period of time T after being activated. Note that the integration time ΔT can be arbitrarily set using a timer.

When the time elapses from time T2 to time, the integrating operation of the integrating circuit 9 stops and an integral signal S2 is output.

The integral value S2 is input to the level discrimination circuit 10, and is classified into a plurality of levels according to its magnitude. The level discrimination result becomes an input to the correction m setting circuit 11. The correction amount setting circuit 11 has the same method as the basic control amount setting circuit 7,
The amount of compensation (or correction factor) for the welding current is determined for the level-discriminated integral (iFj S2).

At time point 2+8T, the correction amount corresponding to the integral value S2 is output from the correction amount setting circuit 11, and is manually input to the welding current control circuit 8. In response to this correction instruction, control circuit 8 controls welding current regulator 3 to increase or decrease the welding current value from I2 by an appropriate correction amount ΔI. And if a certain period of time passes after the power is turned on.

The control circuit 8 controls the welding current regulator 3 to stop energization.

By setting the basic control amount at time T2 and making corrections at time + knee j1-2 + ΔK as described above, it is possible to obtain a welding nugget of approximately the set size at the time when the current supply is stopped. This can be achieved even if the work conditions described above basically fluctuate greatly, and it also works effectively against wear of the electrode tip and large foreign particles between the workpieces, and can be achieved even when the work conditions fluctuate widely. However, it is possible to perform welding with almost constant quality in a constant amount of time.

In the above embodiments, only the welding current value was controlled as the welding condition, but the present invention is of course not limited to this. In addition to the welding current value, welding conditions such as the welding current waveform and the pressure applied to the electrode tip may be controlled by the method of the present invention.

(Effects of the Invention) As explained in detail above, in the method and apparatus for adaptive control for resistance welding according to the present invention, the decreasing change in inter-chip resistance is measured for rapid growth of weld nuggets, and the resulting Since the welding conditions from then on are controlled by

Even if the welding conditions such as the number of stacked sheets2, the presence or absence of plating on the surface, the degree of familiarity between the workpieces, the presence or absence of foreign matter9, the degree of contamination on the surface, and the diameter of the tip of the electrode tip, welding conditions can vary considerably. The adaptive control of the present invention works effectively, and resistance welding of substantially constant quality can be performed within a substantially constant time.

[Brief explanation of the drawings] Figure 1 (A) is a graph showing the change in interchip resistance over time.
FIG. 2B is a graph showing a change in welding current over time according to the present invention, and FIG. 2 is a block diagram showing the configuration of a control device according to an embodiment of the present invention. 1... Electrode tip 2...
...Resistance value calculation circuit 3...Welding current regulator 4...Peak detection circuit 5.9...Integrator circuit

Claims (2)

[Claims] (1) After starting energization under certain welding conditions, monitor the change in resistance (or voltage) between the electrode tips, capture the timing when the value shows the maximum value, and check the decrease in the above value for a certain period of time thereafter. An adaptive control method for resistance welding, characterized in that the welding conditions are determined after the predetermined period of time has elapsed based on the quantitative analysis results. (2) Resistance (or voltage) between electrode tips after energization starts
Timing T2 when a change in is monitored and the value shows a maximum value
a peak detecting means for detecting the peak detecting means; an integrating means that operates for a predetermined time ΔT from this timing T2 and integrates the decrease in the resistance (or voltage) from the maximum value; and an integral value obtained by the integrating means. An adaptive control device for resistance welding, comprising a characteristic setting means for generating corresponding welding condition information, and a control means for changing the welding conditions according to the output of the characteristic setting means after the time ΔT has elapsed from the timing T2. .