JPH04158987A - Resistance welding controller - Google Patents

Abstract

PURPOSE:To improve welding quality, to evade a dancer to an operator and to properly maintain control of the degree of wear of equipment by detecting whether or not splash is generated during energizing and controlling welding conditions in the direction where the splash is not generated. CONSTITUTION:A differentiation circuit 13 generates a pulse DP when the voltage VC between welding chips falls. A flip flop 15 is reset at the time t0 of starting energizing and a signal G is supplied to a gate circuit 14 from a point of time t3 when the voltage VC is stabilized up to t4 right before energizing completion. In this way, a pulse DP2 generated at the time t1 of energizing completion is blocked at the circuit 14 and only a pulse DP1 is supplied to the flip flop 15. Consequently, the output Q of the flip flop 15 is made to zero or one when there is no splash and there is splash, respectively and the presence or absence of splash can be detected.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a resistance welding control device, and more particularly to a resistance welding control device for controlling various welding conditions (welding current, energization time, welding tip pressure force, etc.) in resistance welding.

[Conventional technology]

In resistance welding, the tip of the welding tip wears out each time weld, and
Its diameter gradually increases. Therefore, there is a risk that the current density will decrease and the welding strength will decrease. To prevent this, conventionally the tip of the welding tip is polished every certain number of welding points. In addition, so-called step-up control is added in which the current is increased at a predetermined rate for each predetermined number of welding points so that the number of times of polishing can be minimized.

[Problem to be solved by the invention]

Incidentally, the rate of increase in current in this step-up control is determined experimentally and empirically. For this reason, there are differences in the characteristics of each welding machine, variations in the plate pressure of the workpiece (object to be welded),
It is difficult to accurately respond to variations in surface conditions. Furthermore, it is difficult to check the quality of the welding, especially whether the welding strength is sufficient, on the actual product at the production site. For this reason, at many sites, the presence or absence of splash is used as a guideline for setting welding conditions. In this case, if there is no splash at all, it is visually indistinguishable from the case of no electricity or insufficient melting. Further, the splash may not be produced due to the above-mentioned variations or incorrect setting of the step-up rate. For this reason, the person in charge of the work tends to set the energizing current and energizing time too high. Such a condition setting, together with the above-mentioned inappropriate step-up rate setting, will likely cause a strong splash. Strong splash causes a decrease in weld strength. It also shortens the life of the welding tip. Furthermore, it also increases the danger to workers. It also promotes deterioration and insulation deterioration of cables, hoses, welding machine bodies, control equipment, etc.

[Means to solve the problem]

Therefore, in the present invention, a detection means for detecting the occurrence of splash splash, a continuity detection means for detecting continuous occurrence or non-occurrence of splash, and predetermined welding conditions are controlled so that the continuous occurrence or non-occurrence of splash does not occur. A control means is used to solve the above problem.

[Effect]

If the welding conditions are set so that splash occurs moderately, the state in which it occurs will be random to some extent. When controlling welding conditions using splash as a guide, it is most preferable to maintain this state. In order to do this, in the present invention, first, the detection means checks whether or not splash occurs during energization. Then, the continuity detection means detects whether or not there are a predetermined number of consecutive welding points that generate splash, or whether there are a predetermined number of consecutive welding points that do not generate splash. Welding conditions such as welding current and energization time are controlled in a direction that does not occur.

【Example】

The details of the present invention will be explained below based on illustrated embodiments. 1st
In the figure, 1 is a rectifier circuit that rectifies three-phase AC 3φ to generate DC voltage DC. 2 is a choke coil, 3 is an electrolytic capacitor, and these smooth the DC voltage DC. 4 is an inverter that generates an AC AF of around 1000H2 whose duty ratio changes according to the control signal C8. A transformer 5 steps down the AC AF supplied from the inverter 4 to generate low voltage LV. 6.7 is a diode that performs full-wave rectification of the low voltage LV. A welding tip 8.9 is supported by the resistance welding machine main body (not shown), is brought into close contact with the workpiece 10 by pressure, and supplies the welding current I to it. 11 is a current detection coil;
A minute current i corresponding to the variation (differential value) of the welding current I is generated. 12 is an integrating circuit which integrates the minute current i and generates a digital value DI. This value DI is the welding current I
corresponds to 13 is a differential circuit that generates a pulse DP in response to the fall of the welding tip voltage VC. 14 is a gate circuit, and while the gate signal G is supplied, the input terminal IN and the output terminal OUT are electrically connected. A flip-flop 15 is set by the output of the gate circuit 14 and reset by the signal R. When set, its output Q becomes "1". Reference numeral 16 denotes a central processing unit (CPU), a so-called microcomputer, made of an integrated circuit, which uses a random access memory (RAM) 17 and executes processes described below according to programs in a read-only memory (ROM) 18. 19 is a so-called RAM card, which is used to store data and programs. 20 is a printing device, 21 is a display device, and each CPU1
Control data supplied from 6 (time of change of welding current, welding point number at that time, device operating status, etc.) is printed out or displayed. 22 is the keyboard, CPU 16
used for data input to. 23 is an input/output board, which is connected between each of the above-mentioned circuits and the CPU 6, between the resistance welding machine main control circuit (not shown) and the CPU 6, and between the external computer, etc. (not shown) and the CPtJ 16. Transfer data. Next, referring to FIG. 2, a splash detection method in this embodiment will be explained. In FIG. 2, diagram (A) shows an example of welding current (2), in which constant current control is performed from time point to when energization starts to time point t1 when it ends. Note that the magnitude of the current I is increased or decreased by the CPU 6 (described later). Figures (B) and (C) show examples of changes in the welding tip voltage VC at this time. Figure (B) Example of VCI energized without splashing, Figure (C) VO2
shows an example in which a splash occurs during energization, and in this example, the splash occurs at a time point t2 in the middle, so that the voltage between the welding tips C2 suddenly decreases. In this embodiment, occurrence of splash is detected using such characteristics. Specifically, a differentiating circuit 13, a gate circuit 14, and a flip-flop 15 are used. That is, the differentiating circuit 13 generates the pulse DP when the welding tip voltage VC falls as described above (FIG. 2(D)). Therefore, the flip-flop 15 is reset to the time to when energization starts, and the gate signal G is supplied to the gate circuit 14 from an appropriate time t3 when the voltage VC between welding tips is stabilized to time t4 immediately before the end of energization (see FIG. (E)). In this way, the pulse DP generated at t1 at the end of energization
2 is blocked by the gate circuit 14, and only the pulses generated during this time, such as pulse DPI, are supplied to the flip-flop 15 (FIG. 2(F)). As a result, the output Q of the flip-flop 15 is "O" when there is no splash, and "1" when there is splash.
(The same applies when there are two or more splashes), and with this, the presence or absence of a splash can be detected. The operation of the first embodiment will be explained with reference to FIG. First, when the work 10 is positioned on the welding machine main body by a robot or the like, the welding machine main body control circuit supplies a work start command JS to the CPU 16. In response to this, the CPU 16 starts this processing routine and first sets the target value MI of the energizing current to the initial value MO (step Sl). The initial value MO is roughly set to a value that will produce a moderate amount of splash depending on the characteristics of the workpiece and welding machine. Next, the first sample flag S and the consecutive number C are set to "0" (step 52) (how to use these will be described later). Next, it waits for an energization command ST to arrive from the welding machine main body control circuit (step SS). The energization command ST is the welding tip 8,
9 is brought into contact with a predetermined welding point and a predetermined time (squeeze time) has elapsed, the signal is sent from the welding machine main body control circuit. When the energization command ST arrives, the CPU 16 supplies a reset signal R to the flip-flop 15 (step S4).
. As a result, the output Q of the flip-flop 15 becomes rOJ. Next, the switch signal SW is supplied to the inverter 4, and the application of the welding current I is started (step S5. FIG. 2, 10). The magnitude of welding current I is represented by a digital value DI. Based on this digital value DI, the CPU 16 controls the duty ratio of the AC AF using a control signal C8 so that the welding current ■ becomes the target value MI. Next, the process advances to step S6 and waits for a predetermined time T1 to elapse from the energization start time to. Generally welding tip voltage VC
I and VC2 change as shown in FIGS. 2(B) and 2(C) after the start of energization. Therefore, in this embodiment, the gate circuit 14 is not made conductive immediately after the start of energization, but is made conductive after a delay of time T1. In this way, even if a pulse DP is generated due to a voltage drop at the beginning of energization, it will not be erroneously detected as a splash. Note that this time T1 is preferably made changeable to accommodate differences in the shape and material of the workpiece. After time T1 has elapsed, gate signal G is supplied to gate circuit 14 (step S7). Next, the process advances to S8 and waits for the predetermined time T2 to elapse (FIG. 2(E)). This time T2 is set to be slightly shorter than the difference between the predetermined energization time T3 (FIG. 2(A)) and the time T1. If a splash occurs within this time T2, the output of the gate circuit 14 (OU
A pulse DPI appears at T) (FIG. 2(F)), and the flip-flop 15 is set. When the predetermined time T2 has elapsed, the supply of the gate signal G is stopped (step S9). Next, the process proceeds to step S10, where the supply of the switch signal SW to the inverter 4 is stopped and the energization is ended. Then, an energization completion signal E is sent to the welding machine main body control circuit (step 511). The welding machine main body control circuit moves the welding tip 8.9 to the next welding location in response to this signal E. Next, the process proceeds to step S12, and the CPU 16 checks whether the leading sample flag S at this time is rOJ. In the present invention, when a predetermined number of consecutive splashes occur,
Alternatively, if such a phenomenon does not occur for a predetermined number of consecutive times, the predetermined welding conditions are controlled in a direction in which such a phenomenon does not occur. Therefore, immediately after the welding operation is started, or for the first welding point after adjusting the welding conditions, the splash occurrence situation for that welding point is simply recorded, and the welding conditions are not adjusted. The first sample flag S is used to determine whether the welding point is the first one, and is set to "0" in step S2. Therefore, the answer here is "yes" and the CPU 16 proceeds to step S13. After setting the first sample flag S to "1" here, the value of Q indicating the splash occurrence situation at this time is taken into the variable F in the next step S14. This variable F is used as data indicating the splash occurrence status of the previous welding point when processing the next welding point. Next, the CPU 16 proceeds to step S15, and sets the variable C to "
1". This variable C is the point where the splash occurs, or
is used as a counter to count the number of consecutive non-occurring dots. After this, the CPU 16 returns to step S3. Upon receiving the energization completion signal E in step S11, the welding tip 8.9 is brought into contact with the next welding location and pressurized, and the welding machine main body control circuit supplies the energization command ST to the CPU 16. In response to this, the CPU 16 executes steps 84 to Sll for the next welding location, and proceeds to step S12. In step S13, the first sample flag S is set to "1". So now the answer to this step is "no"
becomes. Therefore, the CPU 16 proceeds to step S16 and inputs the variable F representing the presence or absence of splash at the previous welding point and the flip-flop 15 representing the status of the current welding point.
The difference between the output Q and the output Q is calculated, and the process proceeds to the next step S17. If the difference is not "0", that is, the answer here is "No".
When , the splash occurrence situation at the previous welding point and the current welding point is different (when F=1 and Q=O, D=1
, since D=1 when F=O and Q=1. ). In this case, the CPU 16 proceeds to step S14, takes in the new content of Q at this time to F, proceeds to the next step S15, resets the consecutive number C to "1" again, and returns to step S3. When the difference is "0", that is, when the answer is "yes" in step S17, the splash conditions of the previous welding point and the current welding point match (F=0 and Q=O, or F=1). Therefore, when Q=1, D=0.) In this case, the CPU 16 proceeds to step 318 and adds "1" to the consecutive number C. Then, the process advances to step S19, and it is determined whether or not this consecutive number C has reached "5". In this embodiment, the welding conditions are not changed when the consecutive number C has not reached "5". Here, we are still assuming the second welding point, so the answer is "no." Therefore, CPtJ1
Step 6 returns to step S3 and repeats the same process for the third and subsequent welding points. As mentioned above, if the welding conditions are appropriately set, for example, if splash occurs at one welding point, no splash will occur at the next two welding points, and no splash will occur at the next two welding points.
The occurrence of splash is random, such as another splash occurring at one welding point. Therefore, if the welding conditions are set appropriately and the welding tip is in good condition, while welding is performed at several welding points, the splash situation at that welding point and the splash situation at the previous welding point will be different. If , there is a mismatch, and the answer is "no" in step S17, and step S1
When the number is 5, C=1, and it is repeated that the number is consecutive or the number is broken. However, as mentioned above, the welding conditions for the workpiece 10 do not always match the welding conditions, and the condition of the welding tip also changes as the number of welding points increases. For this reason, as the number of hits increased, the number of consecutive runs reached C.
It happens that the value of reaches "5". In this case, the answer in step S19 is "yes" and the CPU
l6 proceeds to step S20. Then, the contents of Q at that time are examined. When the answer in this step is "yes", that is, Q or "1", it means that there are five consecutive welding points with "splash" including that welding point. Therefore, in the next step S21, the CPU 16 subtracts a predetermined adjustment value MA from the target value MI, returns to step S2, sets the consecutive number C and first sample flag S to rOJ, and then proceeds to step S3 again. Further, if the answer in step S20 is "no", it means that there are five consecutive welding points where no soubrune occurs. Therefore, CPtJl 6 proceeds to step S22 and adds a predetermined adjustment value MA to the target value Ml. Note that if the welding current I is too large, there is a risk that defects may occur in the nugget. Also, there is a limit to the current supply ability. Therefore, in this embodiment, in step S22, the target value M
If l is increased, it is checked in the next step S23 whether it exceeds the upper limit value MM. If the target value Ml exceeds the upper limit value MM, step S2
4, a maximum current attainment signal M is supplied to the welding machine main body control circuit, and this routine is temporarily terminated. If Ml after the increase does not exceed the upper limit value MM, the process returns to step S2. The adjustment value MA is determined based on the characteristics of the workpiece and the welding machine, following the example of manual adjustment in the past. Next, the operation of the second embodiment will be explained with reference to FIG. In this example, when the number of consecutive welding points that generate splash reaches 3, and when the number of consecutive welding points that do not generate splash reaches 6, the target The value MI is changed (steps 331 to 533). For other flows, please refer to the 1st page.
This is the same as in the embodiment, and the same step numbers are given. As mentioned above, when welding conditions are appropriate, splashes occur randomly to some extent. Therefore, as in the first embodiment, the number C of consecutive welding points that generate splash and the number C of consecutive welding points that do not generate splash are judged based on the same standard (=5) without distinction (step 519), and this is maintained. If the welding conditions are controlled so that the welding conditions are controlled, the number of welding points where splash occurs and the number of welding points where no splash occurs will be roughly 5 minutes and 5 minutes. On the other hand, in this second embodiment, the number of consecutive welding points that generate splash and the number of consecutive welding points that do not generate splash are set to different values (C20 in step S32, step S
33, the judgment is based on C≧6). Therefore, in this embodiment, for every one welding point that generates splash, there are approximately two welding points that do not generate splash, that is, one out of three welding points.
Welding points where splash occurs occur at a rate of 1. If it is desired to adjust the splash occurrence status, different judgment criteria are set for the number of consecutive occurrences C and the number C of consecutive non-occurrences as in the second embodiment. The third embodiment will be described with reference to FIG. In this embodiment, the process of calculating the ratio of the number of splash occurrence points to the number of welding execution points and adjusting the target value MI based on the result is added to the first embodiment (
Steps 842-549). Note that the same steps as in the first embodiment are given the same step numbers. By controlling the welding conditions based on a predetermined number of consecutive welding points that generate splash or a predetermined number of consecutive welding points that do not generate splash, it is possible to quickly respond to changes in the conditions of the workpiece 10, welding tip 8.9, etc. This is a major advantage of the present invention. On the other hand, since the process added here is control based on the splash generation status of many welding points, it has the advantage of creating welding conditions that are even more suitable for the conditions of the workpiece 10 and the welding tip 8.9. . The third embodiment aims at a synergistic effect of these two advantages. That is, in this third embodiment, in step S41 instead of step S2 in the first embodiment, the CPU 16 sets the variable P indicating the number of welding points in addition to the same variable S10 as in the first embodiment. Variables Y indicating the cumulative number of dots where splashes have occurred are each set to "0". In step S42 following step S15, CPU1
6 checks whether the value of Q at this time is "1" or not. If the answer is "yes", "1" is added to the cumulative number Y of welding spots where suvlance occurs (step 543). If the answer is "no", step S43 is bypassed and the process proceeds to step S44. Here, 1 is added to the number of welding points P. Then, in the next step S45, it is checked whether the number of welding points P has reached 100 or not. In this third embodiment, the number of splash points occurring during every 100 welding points is added up, and the splash generation ratio is determined based on this. If the welding execution points P have not reached 100, the answer here is "no". In this case, the CPL 116 returns to step S3 and repeats the same process. When the integration of the number of splash occurrence points for 100 welding points is completed, the answer in step S45 becomes "yes". Thereby, the CPU 16 proceeds to step S46. In this example, the center value is ``30'', which is the number of splash points for 100 welding points, and ``33'' is the control upper limit, and ``33'' is the control limit.
27'' is the lower control limit. Steps S46 and S47 are for determining these. When the management upper limit is exceeded, the answer in step S46 is "yes", and the CPU 16 subtracts a predetermined adjustment value MB from the target value MI (step 5
47) Then return to step 541. If it is within the control limits, the answers in steps S46 and S48 will be "no", and the CPU 16 will return to step S41 without changing the target value MI. If the value falls below the lower control limit, the answer in step 846 is "no", the answer in step S48 is "yes", and the process proceeds to step S49, where the CPU 16 adds a predetermined adjustment value MB to the target value MI. . When the target value MI is increased, that is, this step S49
If the above is executed, the process proceeds to step S23 and it is checked whether the target value MI has reached the upper limit value MM, as in the first embodiment. Adjustment value MB is set to a smaller value than adjustment value MA. In this way, the adjustment value MA corresponds to large fluctuations, and the adjustment value MB corresponds to small fluctuations, making it possible to perform more fine-grained control.

[Other Examples]

Although the welding current is controlled in this embodiment, other welding conditions such as welding time may be controlled. Furthermore, two or more welding conditions may be controlled simultaneously. In addition, the method of taking samples, the number of samples, the method of determining the ratio, the control limits, etc. should be devised according to the characteristics of the workpiece and welding machine. Furthermore, regarding splash detection, for example, a light receiving element detects its occurrence, a pressure sensor detects fluctuations in pressurizing force, a position sensor detects welding tip movement, and A-D.
Techniques other than those in the embodiment may be used, such as using a converter and a CPU, or detecting the resistance change by dividing the integral value of the welding current I by the integral value of the welding tip voltage VC for one AC cycle. Furthermore, although this embodiment applies the present invention to an inverter system, the present invention can also be applied to other systems such as an AC system and a capacitor system.

【Effect of the invention】

As explained above, in the present invention, the splash generation point,
The welding conditions were controlled so that no more than a predetermined number of welding points continued where no splash occurred. Therefore, even if there are variations in the condition of each workpiece, such as plate thickness or surface condition, this can be quickly dealt with and the welding conditions can be maintained at appropriate values. In addition, even when the tip of the welding tip gradually becomes thicker, this change is reflected in the generation of splash, so if the welding conditions are controlled using the present invention, the diameter of the welding tip can be increased quickly. , and the conventional step-up control becomes unnecessary. Furthermore, under such welding conditions where a moderate amount of splash is generated, the splash is much weaker than that of conventional welding. Therefore, the degree of danger to workers, the degree of wear and tear on equipment, and the degree of wear on welding tips can be further reduced. Furthermore, since a moderate amount of splash is generated, there is no need to set welding conditions to excessive values that would cause splash to occur every time, and welding quality can be improved and made more uniform. Furthermore, by adding control such that the ratio of the number of splash points to the predetermined number of welding points falls within a predetermined range (third embodiment), even more fine-grained control of welding conditions can be performed.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, Fig. 1 is a block diagram showing the circuit configuration, Fig. 2 is a waveform diagram showing each signal, and Figs. 3 to 5 respectively show the first to third embodiments. 2 is a flowchart showing a processing procedure. 13-15...Detection means, 16-19.23...Continuity detection means, 4.11, 12
．． 16-19.23... Control means. Patent applicant Myachi Technos Co., Ltd.

Claims (3)

[Claims] (1) Equipped with a detection means for detecting occurrence of splash, a continuity detection means for detecting continuous occurrence or non-occurrence of splash, and a control means for controlling welding conditions so that the continuous occurrence or non-occurrence of splash does not occur. A resistance welding control device characterized by: (2) The resistance welding control device according to claim 1, wherein the predetermined number for continuous occurrence and the predetermined number for non-continuous occurrence are different values. . (3) In a state in which the continuous occurrence or non-occurrence of splash does not occur for a predetermined number of welding points, the control means controls the control means so that the ratio of the number of splash generating points to the predetermined number of welding points is within a predetermined range. 2. The resistance welding control device according to claim 1, wherein the welding conditions are controlled so that the welding conditions are satisfied.