JPS622914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to adaptive control for obtaining healthy weld nuggets using a resistance welding device, and more specifically, to detect the amount of change in the voltage value between electrode tips, etc. that occurs when weld nuggets are generated. However, by feeding back the signal to the welding equipment, welding conditions are controlled to ensure appropriate welding strength.

Currently, adaptive control devices for lap resistance welding include those that detect the interelectrode voltage or interelectrode resistance as changes associated with the generation of weld nuggets, those that detect the amount of electrode expansion, and those that detect the amount of electrode expansion. Various methods have been studied, such as methods that detect temperature rise or ultrasonic transmittance between electrodes, but most of them detect a predetermined intensity by adjusting the flow time of the welding current. This is a method to obtain weld nuggets.

However, according to this method, when considering the crushing of the tip of the electrode tip as the number of welding points increases in spot welding, the energization time gradually increases in order to obtain a nugget of a predetermined strength, and eventually Situations that have a negative impact on work takt time are a particular problem.

The present invention aims to improve the efficiency of the welding operation by improving these drawbacks and extending the interval between forming operations for the tip of the electrode tip while ensuring a welding nugget of better quality.

To explain the embodiments shown in the drawings below, Fig. 1 is for explaining the concept of the present invention, and the horizontal axis shows the number of consecutive spot welding points immediately after dressing the chip tip, with the maximum number of 6000 points. This is an example of a combination of two surface-treated rigid plates.

One of the vertical axes in the figure shows the change in energization time in each spot welding. In the example in the figure, 10 cycles is the reference value, and the number of dots (several tens of points) for 11 cycles of energization is shown in a convex shape here and there. ing.

The other vertical axis shows the change in welding current (8000A to 10500A as an example) at the top, which shows that the welding current gradually increases as the number of welding points progresses.

The operating principle of the present invention will be explained below using the example shown in the figure.

First, immediately after chip dressing, the welding current was 8000 A under a certain predetermined electrode pressure, and the average welding time was 10.
Adaptively controlled spot welding is carried out under cycle conditions.

The adaptive control device may change the energization time by 1 to 2 cycles due to disturbances such as changes in plate thickness or the shunting effect of welding current due to proximity of the welding point position, but on average, the energization time is 10 cycles. do.

The number of welding points is now the NI point in Figure 1 (approximately 700 points)
The area increases due to the crushing of the chip tip, and the current density decreases, making it difficult to form a weld nugget with the same current.The adaptive control device automatically increases the energization time by one cycle to 11 cycles.

The device of the present invention detects this one-cycle increase in the energization time, and in order to return it to the original value of 10 cycles, the welding current is gradually increased at each welding point as the number of welding points increases. It increases little by little. The rate of increase in this current can be determined empirically as a percentage (%) of the initial current (8000A in the figure), or as the number of dots NI that changed in 11 cycles.
(about 700 points in the figure) may be calculated and controlled.
The welding current gradually increased to a certain value (in the figure approximately
When the current (approximately 8500A) is reached, the adaptive control device automatically returns the energization time to the initial value (10 cycles).

The device of the present invention detects the return of the energization time to the initial value (10 cycles), stops increasing the welding current in that state, and performs control to maintain the value at that time (approximately 8500 A).

As mentioned above, since the adaptive control device adjusts the energization time for each time in response to various disturbances,
Although the actual energization time is not always exactly constant, the gradual change in welding current mentioned above
These fluctuations in energization time can be averaged and considered.

At the number of dots N2 in FIG. 1 (approximately 1400 dots in the figure), the energization time increases by one cycle in the average value, again as described above. As a result, the welding current increases again, this time at 9000A for 10 hrs.
This shows a state in which the operation to maintain the cycle has been automatically performed.

Current application time Tw′ and welding current shown by dotted lines in the figure
Iw' indicates the case of normal adaptive control not attached to the device of the present invention. That is, it can be seen that the welding current does not increase, but the current application time gradually increases as the electrode chip becomes crushed.

In contrast, in the device of the present invention, the welding current is automatically increased by an amount corresponding to one cycle of the energization time, and the energization time is kept at the initial state, so there is no need to worry about interfering with the work takt. You don't have to think about it.

In addition, in order to compensate for the decrease in current density due to an increase in the chip tip area, it is more rational to increase the welding current itself and perform adaptive control than to extend the energization time, and it also improves the quality of weld nuggets. Good results can be expected.

FIG. 2 shows an electrical block diagram of one embodiment of the invention.

In the figure, the welding detector 29 is anything that can electrically detect the amount of change related to the generation of weld nuggets, such as the inter-electrode voltage, electrode expansion, temperature at the tip of the electrode, or ultrasonic transmittance between the electrodes, as described at the beginning. Well, the following energization time control type adaptive control device 3
0 can be applied to any device in which the completion of the weld nugget is adjusted by the energization time based on the information from the welding detector 29.

When performing spot welding by flowing a welding current under a predetermined electrode pressure, the welding current is set by a reference welding current setting device 22, fed back by a current detector 21, and stabilized by an ignition phase calculator 26. controlled. Adaptive control device 30 described above
transmits a energization stop signal at the same time as the welding nugget is completed, and this signal passes through the energization time controller 31 and locks the ignition signal transmitter 25, interrupting the alternating current electronic switch circuits such as thyristors and stacks, and stopping the welding energization. An operation is performed to stop the.

The energization time in the adaptive control spot welding immediately after the dressing operation of the tip of the electrode tip is performed is measured and set as the reference energization time by manual operation or automatic operation using an electronic circuit.
3 is stored.

As mentioned above, the adaptive control device 30 responds to disturbances such as changes in plate thickness and shunts by changing the energization time.
is compared with a reference value and transmitted to the current increase/decrease rate calculator 27 at the next stage. However, the current increase/decrease rate calculator 27 does not increase or decrease the welding current in response to these one-off recoverable information inputs. When the tip of the electrode tip begins to collapse as the number of welding points increases, the actual energization time by the adaptive control device will frequently increase by one cycle from the initial value, and soon the increased energization time will become average. It becomes a value. The aforementioned current increase/decrease rate calculator identifies this state as a one-off state and transmits a command to temporarily increase the welding current to the ignition phase calculator 26 at the next stage.

This current temporary increase command is issued by the reference welding current setting device 22.
Since the welding current is increased little by little as the number of welding points progresses, the adaptive control device 30 does not need to extend its energization time and returns to the initial value again. This state is identified by the comparator 28, and the current increase/decrease rate calculator 27 receives no input, so that the current is held constant at the value at that time.

In this way, as the state of crushing of the electrode tip progresses, the welding current increases little by little by an amount corresponding to one cycle as the average value of the current application time, and eventually due to the welding conditions or the current capacity of the welding equipment. The upper limit value is reached.

In this state, the device will issue an alarm (not shown) to prompt the dressing of the electrode tip.

The welding operation will proceed again with the tip diameter of the electrode tip formed, but at this time the welding current remains at the upper limit value. When welding current is applied under such conditions, so-called "scattering" may occur.
However, the adaptive control device 30 detects the completion of the weld nugget in an extremely short energization time.

Information on this energization time, which is much lower than the value set by the reference energization time setting device 23, is transmitted to the current increase/decrease rate calculator 27, and based on this information, the welding current is immediately specified by the reference welding current setting device 22. It will be automatically reset to the initial value.

FIG. 3 is an electrical block diagram of an embodiment of the present invention, in which only the welding detector 29 and the energization time-controlled adaptive control device 30, which are different from FIG. 2, are shown in detail. The parts after the time controller are completely the same as in FIG. 2, so they are omitted.

The interelectrode voltage detector 1 shown in FIG. 3 is for detecting voltage changes between electrodes due to the generation of weld nuggets, and the induced noise voltage of the welding current received by the detection cable is removed by an internal electronic circuit.

In spot welding using a stabilized constant value welding current, the output voltage of this voltage detector 1 has a maximum value when weld nuggets are sprouting, and gradually decreases as the area increases due to nugget growth. It is a well-known fact that

The voltage decrease time integrator 2 shown in the figure is for time-integrating the difference between the maximum value of the voltage curve and the voltage that decreases over time, and this integral value has a correlation with the nugget diameter of spot welding. It has also been found that it is resistant to disturbances such as sudden changes in the welding power source, and has excellent characteristics as an adaptive control parameter for spot welding.

When a proper weld nugget is obtained by spot welding performed under the standard conditions immediately after the electrode tip tip forming operation, the output of the voltage reduction time integrator 2 during that spot welding is measured and can be controlled manually or by an electronic circuit. It is stored in the reference integral value setter 4 by automatic operation.

Thereafter, this adaptive control device transmits a welding energization stop signal to the next stage energization time controller 31 when the output of the voltage decrease time integrator 2 matches the value of the reference integral value setting device 4, The output performs the same function as the energization time controller 31 shown in FIG. 2, and stops the welding energization. As the electrode tip collapses as the number of welding points progresses, the output of the inter-electrode voltage detector 1 becomes
The aforementioned maximum voltage value itself becomes lower, and at the same time, the degree of decrease in the voltage with respect to time becomes smaller.

Therefore, in order for the output of the voltage decrease time integrator 2 to match the value of the reference integral value setter 4, a longer energization time is required, and the energization time is calculated as an average value at a large number of welding points. A state of one cycle increase occurs.

The operation of the apparatus of the present invention after the occurrence of this state of extension of the energization time is exactly the same as in the case of FIG. 2 described above, and therefore will not be described here.

In addition, in Fig. 1, we have explained only the case where the current application time is kept constant at 10 cycles as an example, but if it does not have a large effect on the welding work tact, it is possible to change the number of dots where the electrode tip has been crushed. For example, after 4000 dots, the energization time is extended by 1 to 2 cycles, i.e. 11 cycles or
It is also possible to switch from 12 cycles to the standard energization time and proceed with the work with less welding current.

Also, in the operation of keeping the energization time at a constant value,
In many cases, it is not always necessary to control the welding current by increasing or decreasing it on a cycle-by-cycle basis. In such a case, the gist of the present invention is to provide a control method in which a permissible range of change in the energization time is determined within a range that does not interfere with the work tact, and the welding current is increased or decreased within a range that does not exceed that range. I would like to add that.

As described above, the present invention not only realizes adaptive control that can ensure sufficient welding strength in the welding nugget generation process, but also prevents the work tact from being extended by keeping the energization time constant, and maintains the electrode tip. The number of operations can be reduced and work efficiency can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between welding current and the number of times of welding in the device of the present invention, and FIG.
FIG. 3 is an electrical block diagram showing an example of a device according to the present invention, and FIG. 3 is an electrical block diagram showing an example of an energization time control type adaptive control device among the devices according to the present invention.

Claims (1)

[Claims] 1. In an adaptive control device for resistance welding that constantly forms a weld nugget with a predetermined tensile strength by adjusting the flow time of welding current, 1. A method for controlling a resistance welding machine, comprising: measuring an energization time; and increasing or decreasing a welding current so that the energization time remains as constant as possible. 2. In resistance welding performed using a stabilized welding current, the voltage between the welding electrodes during the current-carrying period is detected, and the maximum value of the voltage at the time when welding nuggets occur and the voltage that gradually decreases as the nuggets grow. The difference is integrated over time, and when the integral value reaches a predetermined constant value, the welding current is stopped, the actual energization time for each welding energization is measured, and the energization time is kept at a predetermined constant value as much as possible. A method for controlling a resistance welding machine according to claim 1, wherein the welding current is controlled to increase or decrease so that the welding current is maintained constant. 3. Comparison means is interposed between the adaptive control means that controls the energization time based on the detection information of the voltage between the electrode tips and the reference energization time setting device set in advance, and the above-mentioned comparison means with respect to the reference energization time is A control device for a resistance welding machine, comprising means for detecting an increase or decrease in welding current application time due to an adaptive control means and compensating the welding current accordingly. 4. In the item set forth in claim 3, the adaptive control means for controlling the energization time is:
A reference integral value setter that sets the value necessary to form a weld nugget with a predetermined strength, an interelectrode voltage detector, and the detection signal actuate the voltage reduction time after the voltage peak at the time when a nugget occurs. A control for a resistance welding machine comprising an integrator and a device for comparing the integral value of the integrator with a reference integral value issued by the reference integral value setting device, and controlling the energization time based on the comparison signal. Device.