JPH0751278B2 - Resistance welding control device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a resistance welding control device, and more particularly, to a resistance welding control device suitable for use in a welding process in which work is performed while adjusting welding current, energizing time and other welding conditions so that welding quality is accurately maintained.

[Prior art]

Welding conditions for resistance welding, such as welding current and energizing time,
It can be determined experimentally and logically to some extent. However, in reality, since there are various variations in the properties of the welding location, such as the plate thickness and surface condition, the characteristics of the welding machine, etc., it is possible to set these on site based on the intuition and experience of a skilled person. Many. It is difficult to confirm whether or not the welding conditions are set properly, in other words, whether the quality (strength, surface condition, etc.) of the welding made under these conditions is good at the production site for the actual product. . For this reason, the presence or absence of splash is used as a guide for setting welding conditions at many sites. By the way, the state without splash is indistinguishable from the case of no electricity or insufficient welding. In addition, there may be cases where the splash does not occur halfway due to inaccurate settings of the step-up control or the step-up amount setting, variations in the properties of the welding location, and the like. For this reason, the operator inevitably sets the welding condition to a relatively large value so that the splash will almost certainly come out at each welding position. Such a tendency causes deterioration of welding quality. Therefore, to prevent such a thing, monitor the welding condition,
Welding work is performed while adjusting various welding conditions based on the result. For example, the situation of splash occurrence at 10 welding spots is monitored, and the welding current is controlled so that it is 3 to 5 new. Various methods are possible.

[Problems to be Solved by the Invention]

By the way, when the wear deformation of the tip of the welding tip reaches a certain limit or the number of welding points reaches a predetermined value, the welding operation is temporarily interrupted, and the tip of the welding tip is polished or the welding tip is replaced. As a result, the tip of the welding tip has a predetermined initial shape (hereinafter referred to as "update"). The welding conditions set at this time are for the shape of the tip of the welding tip before the polishing and replacement thereof. Therefore, when polishing or replacement is performed, it is necessary to return the welding condition to an appropriate initial value adapted to this initial shape. Intuition and experience of an expert are required to set the initial value. However, it is difficult to train a skilled person. Further, the setting by the expert is not always accurate at all times. Even if the welding condition is controlled by feeding back the breakage splash occurrence status etc., if the initial value is set incorrectly, the welding condition is purposely returned to an inappropriate one each time the tip of the welding tip is updated. It produces a strange state.

[Means for Solving the Problems]

Therefore, in the present invention, condition adjusting means for adjusting the welding conditions so that the splash occurrence rate for a predetermined number of welding spots is a predetermined value, and the welding conditions are set to initial values when the tip of the welding tip is in an initial shape. The condition initializing means to be set and the splash occurrence rate at the initial stage after the tip of the welding tip is made into the initial shape and before reaching the predetermined number of welding spots are compared with the predetermined splash occurrence rate, and the error is compared. The initial value correction means for correcting the initial value so as to reduce the number is used to solve the above problem.

[Action]

In the present invention, the initial value of the welding condition at the time of updating the tip of the welding tip is corrected by looking at the adjustment content of the welding condition at the final stage after updating the tip of the welding tip. That is, when the tip of the welding tip is updated, the welding condition, for example, the welding current is also returned to the preset initial value. Under this initial welding condition, the initial stage of welding, that is, the welding up to a predetermined welding point number is executed. The initial value correction means compares the splash occurrence rate at this stage with a predetermined occurrence rate. This "predetermined rate of occurrence" is determined in order to maintain good welding quality, and is defined, for example, "splash generation 5 welding points for 10 welding points". The initial value correction means compares the occurrence rate of splash in the initial stage with this predetermined occurrence rate. Then, the initial value of the welding condition is corrected so that the error is reduced. For example, if the welding current is an adjustment target and the splash occurrence rate is higher than a predetermined splash occurrence rate at the initial stage, the initial value of the welding current is reduced by an amount commensurate with the error. As a result, the initial value reset in the next update becomes more appropriate than the initial value in the previous update, and appropriate welding can be executed immediately after the update.

【Example】

Hereinafter, the details of the present invention will be described based on illustrated embodiments. The welding condition adjusted in this embodiment is the welding current. Specifically, the generation or non-occurrence of splash is inspected at each welding spot, and the welding current is controlled so that the number of splash spots per 10 welding spots is within the range of 3 to 5. Further, in this embodiment, the function of each of the above means is realized by using a so-called microcomputer. Thus, in FIG. 1, 1
Is a rectifier circuit that rectifies the three-phase alternating current 3φ and generates a direct current voltage DC. Reference numeral 2 is a choke coil, and 3 is an electrolytic capacitor, which smoothes the DC voltage DC. 4 is an inverter,
The AC AF of about 1000 Hz whose duty ratio changes according to the control signal CS is generated. A transformer 5 steps down the AC AF supplied from the inverter 4 to generate a low voltage LV. Reference numerals 6 and 7 are diodes that perform full-wave rectification of low-voltage LV. Numerals 8 and 9 are welding tips, which are supported by a resistance welding machine main body (not shown), and are brought into close contact with the work 10 by a pressing force, and a welding current I is supplied thereto. 11
Is a current detection coil, which generates a minute current i corresponding to the variation (differential value) of the welding current I. An integrating circuit 12 integrates the minute current i to generate a digital value DI. This value
DI corresponds to the welding current I. A differentiating circuit 13 generates a pulse DP in response to the fall of the welding tip voltage VC. Reference numeral 14 is a gate circuit, and while the gate signal G is supplied, the input terminal IN and the output terminal OUT
Conducts. 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 is a central processing unit (CPU) composed of an integrated circuit, and while using a random access memory (RAM) 17, a read only memory (ROM) 18
The functions of the respective means are realized in accordance with the program. A so-called RAM card 19 is used to store data and programs. Reference numeral 20 is a printing device, and 21 is a display device, which prints out or displays the control data (welding tip update time, work or welding position number at that time, device operating status, etc.) supplied from the CPU 16, respectively. . A keyboard 22 is used to input data to the CPU 16. Reference numeral 23 is an input / output port for data between the above-mentioned circuit differences and the CPU 16, between the resistance welding machine control circuit (not shown) and the CPU 16, and between the external computer (not shown) and the CPU 16. To deliver. Next, a splash detection method in this embodiment will be described with reference to FIG. In FIG. 2, FIG. 2A shows an example of the welding current I, in which constant current control is performed from the energization start time t ₀ to the end time t ₁ . The magnitude of the current I is adjusted by the CPU 16. FIGS. 9B and 9C show an example of changes in the welding tip voltage VC at this time. Examples of energization is finished without drawing (B) VC1 is splash occurs, FIG. (C) VC2 is an example splash occurs during energization, in this example splash at the time t ₂ in the middle The welding tip voltage VC2 drops sharply because of the occurrence. In this embodiment, the occurrence of splash is detected by utilizing such characteristics. Specifically, the differentiating circuit 13 and the gate circuit 14
And a flip-flop 15 is used. That is, the differentiating circuit 13 generates the pulse DP when the voltage VC between the welding tips falls as described above (FIG. 2 (D)). Therefore, the flip-flop 15 is reset at the start of energization t ₀ , and the gate signal G is supplied to the gate circuit 14 from an appropriate time t ₃ when the welding tip voltage VC stabilizes to a time t ₄ immediately before the end of energization ( FIG. 2 (E)). In this way, the pulse DP2 generated at the end of energization t ₁ is blocked by the gate circuit 14, and a pulse generated during that period, for example, a pulse
Only DP1 is supplied to the flip-flop 15 (FIG. 2 (F)). As a result, the output Q of the flip-flop 15 becomes "0" when there is no splash and "1" when there is splash (the same applies when the number of times is two or more), and the presence or absence of splash can be detected. The operation of this embodiment will be described with reference to FIG. First, when the work 10 is positioned on the main body of the welder by a robot or the like, the control circuit of the main body of the welder supplies a work start command JS to the CPU 16. At this time, the tips of the welding tips 8 and 9 are assumed to be in the initial shape (updated). In response to the work start command JS, the CPU 16 starts this processing routine, first sets the target value MI of the welding current to the initial value M0, and sets the flag N to 0 (step S1). The initial value M0 of the welding current corresponding to the case where the tips of the welding tips 8 and 9 are in the initial shape is input from the keyboard 22 in advance. The value is roughly set according to the characteristics of the work 10 and the welding machine so that the splash will be moderate. The flag N is used to distinguish between the first adjustment of the welding current after the tips of the welding tips 8 and 9 are updated and the subsequent adjustment of the welding current. Next, the number of splash occurrences Y and the number of welding spots P are set to "0" (step S2). Next, it waits for the energization command ST to arrive from the welding machine control circuit (step S3).
The energization command ST is sent from the welding machine main body control circuit when a predetermined time (squeeze time) elapses after the welding tips 8 and 9 are brought into contact with a predetermined welding location. When the energization command ST arrives, the CPU 16 causes the flip-flop 15
Reset signal R, and inverter 4 switch signal SW
Is supplied (step S4). As a result, the output Q of the flip-flop 15 becomes "0", and the inverter 4 starts passing the welding current I (t _{0 in} FIG. 2). The magnitude of the welding current I is represented by a digital value DI. CPU16 is step S5
Then, the digital value DI is inspected, and the duty ratio of the AC AF is controlled by the control signal CS so that the welding current I matches the target value MI. Then a predetermined time from the energization start time point t ₀ the process proceeds to step S6 T1
Check whether has passed. Within time T1
The CPU 16 returns to step S5 and controls the welding current I. Generally, the welding tip voltages VC1 and VC2 change as shown in FIGS. 2B and 2C after the start of energization. Therefore, in the present embodiment, the gate circuit 14 is not made conductive immediately after the start of energization, but is made conductive by delaying the time T1. In this way, even if the pulse DP is generated due to the voltage drop at the beginning of energization, it will not be erroneously detected as a splash. When the time T1 has elapsed, the gate signal G is supplied to the gate circuit 14 (step S7). Next, in S8, it is inspected whether or not a predetermined time T2 has elapsed. CPU16 before time T2 elapses
Returns to step S5 and controls the welding current I. In this case, step S7 is executed again. This is for simplifying the procedure, and there is no problem even if the gate signals G are overlapped and supplied. This time T2 is the predetermined energization time T3 (Fig. 2 (A)) and time T1.
The time is slightly shorter than the difference (Fig. 2 (E)). This time
When a splash occurs in T2, a pulse DP1 appears at the output (OUT) of the gate circuit 14 (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). Then it stops supplying the switch signal SW to the inverter 4 proceeds to step S10 to end the energization (first 2t _1). Then, the energization completion signal E is sent to the welding machine control circuit (step S11). In response to this signal E, the welding machine control circuit moves the welding tips 8 and 9 to the next welding position. Next, in step S12, the CPU 16 checks whether or not the value of Q at this time is "1". When the answer is "yes", "1" is added to the number of splash occurrences (step S1.
3). If the answer is "no", then this step S13 is bypassed and the process proceeds to step S14. Here, 1 is added to the number P of welding execution spots. Then, in the next step S15, it is inspected whether the number P of welding execution spots has reached 10. If the number of welded points P has not reached 10, the answer here is "No". In this case CPU16
Return to 3 and repeat the same process. When the addition of the number of splash generation spots for the first 10 welding spots is completed, the answer in this step S15 is "Yes". As a result, the CPU 16 proceeds to step S16. In this embodiment, with respect to 10 welding-executed spots, the number of splash-generated spots "4" is the central value, "5" is the control upper limit, and "3" is the control lower limit. If the number of splash points is within the control limit, steps S16 to S17, step S1
Go to 8. In this welding work started with the tips of the welding tips 8 and 9 updated, the fact that the occurrence of splash at the first 10 RBIs is within the control limits means that the welding that was set Indicates that the initial value of current M0 is appropriate and does not need to be modified. Therefore, the CPU 16 sets this initial value M0 as its side, and only performs the process of setting the flag N to 1 in this step S18. When the flag N is set to 1, even if the welding current target value MI is adjusted in other steps thereafter, the initial value M0 is not corrected (described later). Then, the CPU 16 proceeds to steps S20 and S21. Here, the return command RT and the signal FR indicating that the tips of the welding tips 8 and 9 have been updated
To see if it has arrived. Since these signals do not arrive at the initial stage, the CPU 16 returns to step S2 and
Splash for 0 RBI is monitored. For the next 10 RBIs, if the occurrence of splash is within the control limit, execute step S18 again,
This is to simplify the procedure, and there is no problem even if N = 1 is overwritten. On the other hand, when the occurrence status of the splash of the first 10 RBI exceeds the management upper limit, the answer in step S16 is "Yes". Therefore, the CPU 16 proceeds to step S22 and subtracts a predetermined adjustment value MA from the target value MI. The adjustment value MA is determined in accordance with the characteristics of the work 10 and the welding machine, following the example of the conventional manual adjustment. Then, it proceeds to step S23. Here, the content of the flag N is inspected. The answer is yes when the first 10 RBIs have been completed. Therefore, the process proceeds to step S24 and the flag N is set to 1
Then, the process proceeds to step S25. It is preferable that the initial value M0 of the welding current that has been set is that the occurrence status of the splash of the first 10 welding points of the welding work started with the tips of the welding tips 8 and 9 being updated exceeds the control upper limit. It means greater than the value. Therefore, the CPU 16 subtracts the adjustment value MA from the initial value M0 in this step S25. Then, the process returns to step S2 through steps S20 and S21 described above. When the number of splashes is below the lower control limit, the situation is just opposite. In this case, the answer in step S16 is “No” and the answer in step S17 is “Yes”.
Therefore, the CPU 16 proceeds to step S26 and adds the predetermined adjustment value MA to the target value MI. Then from step S27 to step S28
Then, the flag N is set to 1, and then the process proceeds to step S29. The CPU 16 now subtracts the adjusted MA from the initial value M0. If the welding current I is too large, the nugget may be defective. In addition, the current supply capacity is naturally limited. Therefore, in this embodiment, when the target value MI is increased in step S26, it is increased in step S30.
To check if the Here, the target value MI is the upper limit value
If it exceeds MM, the CPU 16 proceeds to step S31, supplies the maximum current arrival signal M to the welding machine main body control circuit, and once ends this routine. When the increased MI does not exceed the upper limit value MM, steps S20 and S21 are performed, and then step S2.
Return to. The result of the adjustment of the target value MI for every 10 RBI from the second time is not reflected in the correction of the initial value. Cover step S18, S24 or S2
This is because the flag N is set to 1 in any of 8 and the answer in step S17, S23, or S27 becomes "No", and step S25 or step S29 is not executed. . Further, the target value MI is originally adjusted in order to compensate for the decrease in the current density at the welded place which is caused by the wear deformation of the tips of the welding tips 8 and 9 as the number of welding execution spots increases. . Therefore, as the number of welding execution spots increases, the target value MI contains a large amount of the wear deformation. Therefore, in the present invention, the welding tips 8, 9
Target value MI for the first 10 RBI after the tip of is updated
Only the adjustment result of is reflected in the correction of the initial value M0. In this way, welding is sequentially performed on each welding point, and when the number reaches a predetermined value, for example 2000 points, the main body control circuit interrupts the welding operation and moves the welding tips 8 and 9 to a grinder (not shown). Then, the tip is polished and renewed to the initial shape. Then, the update signal FR is supplied to the CPU 16. When the update signal FR is supplied, the answer in step S21 is "Yes". Therefore, in this case, the CPU 16 returns to step S1 and returns the target value MI to the initial value M0. At this time, the initial value M0 reflects the result of the first 10 welding points of the welding operation started with the tips of the welding tips 8 and 9 updated. Therefore, even if the situation of occurrence of splash for the first 10 RBIs is not within the control limit, the number of splashed RBIs for the first 10 RBI after this welding tip update is within the normal control limit. In addition, the initial value M0 deviates considerably from the preferable value, and even if it exceeds the control limit at this time, it corresponds to the adjustment of the target value MI for the first 10 RBI at this time. Then, the initial value M0 is corrected again, and then the next, and then the next, until the splash occurrence situation for the first 10 RBI after the tip update of the welding tips 8 and 9 is within the control limit. The correction of the value M0 is repeated. In this embodiment, the welding current is controlled, but the present invention can be applied to welding time, applied pressure, welding tip voltage, and other welding conditions.

【The invention's effect】

As described above, in the present invention, the initial value of the welding condition at the time of updating the tip of the welding tip is corrected by looking at the adjustment content of the welding condition at the first stage after updating the tip of the welding tip. Therefore, even if an inexperienced person sets this initial value, the improper portion is immediately corrected, and good quality is maintained over the entire welding point. Further, even if the expert sets the initial value, it is not necessary to pay special attention as before, and the skill of the expert can be utilized for other work.

[Brief description of drawings]

1 shows an embodiment of the present invention, FIG. 1 is a block diagram showing a circuit configuration, FIG. 2 is a waveform diagram showing each signal, and FIG. 3 is a flow chart showing a processing procedure. 11-19, 23 ... Condition adjusting means, 16-19, 23 ... Condition initializing means, 16-19, 23 ... Initial value correcting means.

Claims (1)

[Claims] 1. Condition adjusting means for adjusting welding conditions so that a splash occurrence rate with respect to a predetermined number of welding spots has a predetermined value, and when the tip of the welding tip has an initial shape, the welding conditions are set to initial values. The condition initializing means to be set and the splash rate at the initial stage after the tip of the welding tip is made into the initial shape and before reaching the predetermined number of welding spots are compared with the predetermined splash rate, and the error is compared. A resistance welding control device, comprising: an initial value correction means for correcting the initial value so as to reduce the initial value.