JPH0651235B2 - 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 for controlling multi-condition resistance welding.

2. Description of the Related Art When performing resistance welding on a workpiece, such as a car body, in which the properties of the portion to be welded, such as the thickness and thermal conductivity of the material, differ depending on the location, multi-condition resistance welding Done. In the multi-condition resistance welding, for example, a welded portion having a thickness th ₁ of two sheets is identified by an identification code ID ₁ , and a welded portion having a thickness th ₂ of three sheets is identified by an identification code ID ₂ , respectively. An identification code for distinguishing the property of the place is given. For this identification code, for example, the welding current is I ₁ for ID ₁ , the energization time is T ₁ , and the welding current is I _{2 for} ID ₂ and the energization time is T ₂ , for example. A control target value having a size corresponding to the property of is determined. Then, when performing welding, one that matches the identification code of the welding location is selected from among the plurality of control target values, and the respective welding conditions are controlled so as to match this. In resistance welding, so-called step-up control is performed in which the current is increased at a predetermined rate for each predetermined number of welding points. This control is performed in order to correct a decrease in current density at the welding point due to wear of the tip of the tip each time welding is performed and the diameter thereof gradually increases. This step-up control is also used in combination with the above-mentioned multi-condition resistance welding.

[Problems to be Solved by the Invention]

The magnitude of each control target value corresponding to the property of the welded portion and the current increase rate in this step-up control can be determined experimentally and logically to some extent. However, in reality, since there are various variations in the properties of the welded part, such as the thick plate and surface condition, or the characteristics of the welding machine, most of these values are set on site based on the so-called intuition and experience of a skilled person. To be done. It is not possible to confirm whether the setting of the control target value etc. is appropriate, in other words, whether the welding made with that value is good, especially whether there is sufficient welding strength at the production site for the actual product difficult. Therefore, in many sites, the presence or absence of splash is used as a guide for setting the control target value. By the way, the state without splash is indistinguishable from the case of non-energization or insufficient melting. It is empirically known that the splash may not occur in the middle of the process due to improper setting of the control target value or the step-up rate and variations in the properties of the welded spot. For this reason, the operator inevitably sets the control target values such as the energization current and the energization time and the step-up rate to be relatively large so that the splash will almost certainly come out at each welding point. This tendency, together with the improper setting of the control target value and the step-up rate, causes a strong splash. A strong splash causes a decrease in welding strength. It also shortens the chip life. Furthermore, the degree of danger to the worker is increased. It also promotes deterioration and insulation deterioration of cables, hoses, welder bodies, control equipment, and the like.

[Means for Solving the Problems]

Therefore, in the present invention, an energization control unit that selects one from a plurality of control target values based on the identification code given to each place to be welded, and performs energization according to the target value,
Detecting means for detecting the occurrence of splash, a calculating means for calculating the ratio of the number of spots of splash generation to the predetermined number of welding spots to be welded for the welding portion having the same identification code
The above problem is solved by using an adjusting unit that adjusts the control target value corresponding to each identification code so that the ratio falls within a predetermined range.

[Action]

That is, in the present invention, one of a plurality of control target values is selected according to the identification code given to each place to be welded, and the welding condition is controlled by the energization control means so as to match the control target value. Is performed. During the period of this energization, the detection means detects whether or not a splash has occurred. Based on the result, the calculating means calculates the ratio of the number of splashed spots to the predetermined number of welding spots to be welded for the welded portion having the same identification code. If the ratio does not fall within the predetermined range, the adjusting means adjusts the control target value corresponding to the identification code.

【Example】

Hereinafter, the details of the present invention will be described based on illustrated embodiments. First
In the figure, reference numeral 1 is a rectifying circuit, which rectifies a three-phase alternating current 3φ to generate a direct current voltage DC. Reference numeral 2 is a choke coil, and 3 is an electrolytic capacitor, which smoothes the DC voltage DC.
Reference numeral 4 denotes an inverter, which generates an AC AF of about 1000 Hz whose duty ratio changes according to the control signal CS. 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 for full-wave rectifying the low voltage LV. Reference numerals 8 and 9 denote 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. Reference numeral 11 denotes a current detection coil, which generates a minute current i corresponding to a change amount (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. Reference numeral 13 is a differentiating circuit, which generates a pulse DP in response to the fall of the inter-chip voltage VC. Reference numeral 14 is a gate circuit, and the input terminal IN and the output terminal OUT are electrically connected while the gate signal G is supplied. 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". 16
Is a central processing unit (CPU) that is an integrated circuit, a so-called microcomputer, and random access memory (RAM)
Read only memory (ROM) while using 17
The following processing is executed according to 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.
The control data (identification code IDx, the dot number at that time, the operation status of the device, etc.) supplied from 6 is printed out or displayed. A keyboard 22 is used to input data to the CPU 16. Reference numeral 23 denotes an input / output port, which is used for data between the above-described circuits and the like and the CPU 16, between the resistance welding machine control circuit (not shown) and the CPU 16, and between the external computer and the like (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. (A) 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 increased / decreased by the CPU 16 (described later). FIGS. 9B and 9C show an example of changes in the inter-chip 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 Because of the occurrence, the inter-chip voltage VC2 drops sharply. In this embodiment, the occurrence of splash is detected by utilizing such characteristics. Specifically, the differentiating circuit 13, the gate circuit 14, and the flip-flop 15 are used. That is, the differentiating circuit 13 generates the pulse DP when the inter-chip voltage VC falls as described above (FIG. 2 (D)). Therefore, the reset signal R is supplied to the flip-flop 15 at the start of energization t ₀ to reset it, and the gate circuit 14 is supplied from an appropriate time t ₃ when the inter-chip voltage VC stabilizes to a time t ₄ immediately before the end of energization. A gate signal G is supplied (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 only the pulse generated during that time, for example, the pulse DP1 is supplied to the flip-flop 15 (FIG. 2 (F)). ). As a result, the output Q of the flip-flop 15 is "0" when there is no splash and "1" when there is splash.
Then (the same applies when the number of times is two or more), the presence or absence of splash can be detected. The operation of the first embodiment will be described with reference to FIG. First, when the workpiece 10 is positioned on the main body of the welder by the robot or the like, the control circuit of the main body of the welder supplies a work start command JS to the CPU 16. In response to this, the CPU 16 starts this processing routine. First, the control target values MI _{0 to} MIn of the energizing current are set to the initial values MS _{0 to} MSn (step S1). The initial values MS _{0 to} MSn are roughly set to a value indicating whether or not a splash is generated according to the properties of the respective welded portions distinguished by the identification codes ID _{0 to} IDn. Then a splash of occurrences _Y 0 -Yn every welding point that each identification code _ID 0 ～IDn is attached, the RBI number accumulated value _P 0 to PN respective to "0" (Step S2). Next, the welding machine control circuit waits for the supply of the identification code IDx and the energization command ST attached to the portion to be welded at that time (step S3). The identification code IDx is stored in the memory of the welding machine main body control circuit together with the position information of the welding location. According to the welding tip drive program, the control circuit abuts the welding tips 8 and 9 on a predetermined welding point, then reads out this identification information attached to the welding point from the memory and supplies it to the CPU 16. The CPU 16 stores the received identification code IDx in the RAM 17. Here, the identification code is n + 1 from ID _{0 to} IDn.
The type is defined. At this time, the IDx is selected by the control circuit of the welding machine main body and supplied to the CPU 16. In the following description, the variables or constants with the subscript "x" are the variables or constants corresponding to the selected identification information IDx. Further, the energization command ST is supplied from the welding machine main body control circuit to the CPU 16 when the welding tips 8 and 9 are brought into contact with a predetermined welding point and a predetermined time (squeeze time) has elapsed. When the energization command ST arrives, the CPU 16 supplies the reset signal R to the flip-flop 15 (step S
4). As a result, the output Q of the flip-flop 15 becomes "0". Then switch signal SW to the inverter 4
Is supplied, and the welding current I is started to be supplied at the control target value MIx corresponding to the identification code IDx at this time (step S).
5, FIG. 2 t ₀ ). The magnitude of the welding current I flowing through the work is represented by a digital value DI. The CPU 16 controls the duty ratio of the AC AF by the control signal CS so that the welding current I becomes the control target value MIx based on the digital value DI. Then wait for the energization start time point t ₀ the process proceeds to step S6 for a predetermined time T1 elapses. Generally, the chip-to-chip voltage VC1,
VC2 changes 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. It should be noted that this time T1 is preferably changeable so as to correspond to each property of the welded portions to which the identification codes ID _{0 to} ID _n are attached. When the time T1 has elapsed, the gate signal G is supplied to the gate circuit 14 (step S7). Next, the process proceeds to S8 and waits for the predetermined time T2 to elapse (FIG. 2 (E)). This time T2 is 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
The pulse DP1 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, in step S10, the supply of the switch signal SW to the inverter 4 is stopped and the energization ends. 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 body control circuit moves the welding tips 8 and 9 to the next welding point. Then, the process proceeds to step S12, where the CPU 16 performs the Q
Check whether the value of is "1". When the answer is "yes", "1" is added to the number Yx of splash occurrences corresponding to the identification code IDx at that time (step S1).
3). If the answer is no, then this step S1
3 is bypassed and the process proceeds to step S14. Here, 1 is added to the dot number integrated value Px corresponding to the identification code IDx at this time. Then, in the next step S15, this dot number integrated value Px is 2
Check whether it has become 0 or not. In the first embodiment integrating separately variable P ₀ to PN corresponding to these welding run number strike for people identification code ID ₀ ~IDn husband. Then, the number of welding spots at which splash has occurred until this value reaches 20 is integrated by the variables Y _{0 to} Yn corresponding to the respective identification codes ID _{0 to} IDn, and the splash ratio is obtained based on this. If the number of welded spots Px has not reached 20 in step S14, the answer here is "No". In this case, the CPU 16 returns to step S3 and performs the same processing, that is, the current value I = M corresponding to the identification code IDx supplied at that time.
The process of energizing Ix, adding "1" to the corresponding Yx when a splash occurs, and adding "1" to the corresponding dot number integrated value Px is repeated. Then, when the control target values MI _{0 to} MIn are selected according to the identification codes ID _{0 to} IDn of the respective welding points and welding is executed, one of the dot number integrated values P _{0 to} Pn is eventually “20”.
Reach As a result, the answer in step S15 is "Yes", and the CPU 16 proceeds to step S16. In this embodiment, the welding spots 20 belong to the same identification code IDx.
When managing the number of dots that generate splashes relative to the number of dots, "6" is the central value, "7" is the upper management limit, and "5" is the lower management limit. Steps S16 and S17 determine these, and when the management upper limit is exceeded, this step S17
The answer is YES, and the CPU 16 subtracts the predetermined adjustment value MA from the control target value MIx corresponding to the identification code IDx at that time (step S18). Then, the process returns to step S2. If it is within the control limit, the answer in steps S16 and S17 is "No", and the CPU 16 returns to step S2 without changing the control target value MIx at that time. When the value is below the control lower limit, the answer in step S16 is "No", the answer in step S17 is "Yes", and the process proceeds to step S19 where the CPU 16 sets the control target value MIx at that time to the predetermined adjustment value. Add MA. 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 control target value MIx at that time is increased in step S19, the next step S2
At 0 it is checked whether it exceeds the upper limit MM. If the control target value MIx at that time exceeds the upper limit value MM, the process proceeds to step S21, the maximum current arrival signal MX is supplied to the welding machine main body control circuit, and this routine is once ended. If the increased MIx does not exceed the upper limit value MM, the process returns to step S2. The processing of these steps S16 to S21 is performed by the dot number integrated value P _0.
Every time any one of ~ to Pn reaches "20", it is executed for the corresponding control target values MI _{0 to} MIn. The adjustment value MA is determined in accordance with the conventional example in which the adjustment value MA is manually adjusted in light of the characteristics of the welding points belonging to the identification codes ID _{0 to} IDn, the work, and the characteristics of the welding machine. Next, the operation of the second embodiment will be described. In this embodiment, the ratio of the number of spots for splash generation to the number of spots for welding is calculated as a moving average. RA, which is the recording means for this purpose, is shown in FIG.
The memory allocation of M17 is shown. In this embodiment, the presence / absence of splash is recorded for each of 20 welding spots for each of the identification codes ID _{0 to} IDn, and 20 addresses each having the head addresses of AS _{0 to} ASn are used for this recording. Used for. (In FIG. 5, AS ₀
Only the 20 addresses each having the leading address of ~ AS ₁ are shown. The numbers displayed in each address indicate an example of the recorded data. “0” indicates no splash and “1” indicates splash. The operation of the second embodiment will be described with reference to FIG.
First, the CPU 16 sets the values of the variables A _{1 to} An (for memory address instruction) set for the identification codes ID _{0 to} IDn to the respective head addresses AS _{0 to} ASn (step S30). Then, step S1 having the same contents as in the first embodiment is executed. Next, the identification code ID _{0 to} ID
Number of occurrences of splash Y _{0 to} Yn for each of n
And respective flags R _{0 to} Rn indicating whether or not the number of welding dots belonging to the same identification code IDx has reached the first 20 dots.
Is set to "0" (step S31). After this, steps S3 to S11 having the same contents as in the first embodiment are executed. Next, the CPU 16 recognizes whether or not the flag Rx corresponding to the identification code IDx at that time is "1" (step S3).
2). In the present embodiment, regarding the welding points belonging to the same identification code IDx, the value of the address Ax is incremented from ASx to ASx + 19 up to the first 20th dot, and the presence or absence of splash of each welding dot at that time is recorded in the address. If there is a splash at this time, "1" is added to the number of times Yx of splash occurrence at that time.
On the other hand, even for welding spots belonging to the same identification codes ID _{0 to} IDn, after the 21st spot, the value of the address A is returned to ASx every 20 spots so that the range of this address extends from the welding spot to 20 spots before. Circularly record the occurrence of splashes. For each of the 21st welding point and thereafter, every time the welding welding point increases by one, the splash generation ratio for the 20th welding point before that is checked and the welding current control target value MIx is adjusted. Therefore, it is necessary to change the flow for each of the identification codes ID _{0 to} IDn with the first 20 hit points as a boundary, and the flags R _{0 to} Rn are used for this determination. Thus, in step S31, Rx is initially set to "0". Therefore, the answer to this step S32 is "no". As described above, the CPU 16 stores the output Q of the flip-flop 15, that is, the data indicating the presence or absence of splash at the address indicated by Ax (step S33). And the first
The steps S12 and S13 having the same contents as those in the above embodiment are executed. In the next step S34, the CPU 16 determines that the address Ax is AS
It is inspected whether it becomes x + 19, that is, whether the recording of the first 20 RBIs is finished. If the 20 hit points have not been reached, the answer here is "no", and the CPU 16 increments the value of Ax (step S35) and then proceeds to step S35.
Returning to step 3, the same processing is repeated for the identification code IDx supplied at that time. When the result of the first 20 dots for the same identification code IDx is recorded, the answer in this step S34 is "Yes". As a result, the CPU 16 proceeds to step S36 to set the flag Rx to "1" and then returns the value of Ax to "ASx" (step 37). Then, the process returns to step S3. After Rx becomes "1", the process proceeds from step S32 to step S38. Here, the CPU 16 reads the value stored in the address indicated by Ax as B. Then this B
Is subtracted from the output Q of the flip-flop 15 at that time (step S39). In this step S39, the value of the output Q of the flip-flop 20 (B as a variable) 20 points before the same identification number is compared with the value of the output Q of the flip-flop 15 at the welding point at that time. The value of the splash occurrence frequency Yx corresponding to the identification code IDx at that time is increased or decreased according to the result. First, the difference D
Indicates that the presence or absence of the splash at that time and the presence or absence of the splash before 20 RBI match. Therefore, in this case, it is not necessary to change the value of Yx, which is the number of splashes generated, and the CPU 16 executes step S40,
The process proceeds from S41 to S16 having the same contents as in the first embodiment. When the difference D shows "1", there is no splash this time,
There is a splash before 20 RBI. Therefore, in step S43, the value of the number Yx of splash occurrences corresponding to the identification code IDx at that time is subtracted by “1”, and in the next step S44, a new Q is added to the address indicated by Ax.
Record (= 0). When the difference D indicates "-1", it is in the opposite state.
Therefore, the CPU 16 proceeds to step S45, adds "1" to the number of times Yx of splash occurrence corresponding to the identification code IDx at that time, and records a new Q value (= 1) at the address indicated by Ax in the next step S44. To do. Then, the CPU 16 executes steps S16 to S21 having the same contents as in the first embodiment. After executing step S18, and when the answer is "no" in steps S17 and S20, the process proceeds to step S34, respectively. or,
Since the flag Rx is set to "1" when the first 20 hit points belonging to the same identification number IDx are finished, it is not necessary to set the flag Rx to "1" again in step S36 for the subsequent welding hit points. Here, the same routine is used and step S36 is executed again in order to reduce the amount of the program.

Other Embodiments In the present embodiment, each control target value was adjusted for the welding current, but each control target value may be adjusted for other welding conditions such as welding time. Further, each control target value may be simultaneously adjusted for two or more welding conditions. Moreover, it is advisable to devise the method of obtaining the samples, the number of the samples, and the method of obtaining the ratio according to the characteristics of the work and the welding machine. Further, regarding the detection of splash, for example, the light-receiving element detects the occurrence thereof, the pressure sensor detects the fluctuation of the pressing force, the position sensor detects the welding tip movement, and A-D.
A method other than the embodiment may be used, such as using a converter and a CPU or detecting the resistance change by dividing the integrated value of the welding current I by the integrated value of the inter-chip voltage VC for one AC cycle. Further, although the present embodiment relates to the inverter system, the present invention can be applied to other systems such as an AC system and a capacitor system.

【The invention's effect】

As described above, in the present invention, each control target value is adjusted for one or more welding conditions so that the splash occurs at a predetermined ratio. Therefore, even if there are variations in the properties between the workpieces or the welding locations belonging to the same identification code, it is possible to flexibly cope with this and maintain each control target value at an appropriate value. Can be done. Further, even with respect to the phenomenon that the tip of the welding tip gradually becomes thicker, the change is reflected in the occurrence state of splash, so if the respective control target values are adjusted in the present invention, the diameter of the welding tip increases. This naturally corresponds, and the conventional step-up control becomes unnecessary. Further, under the welding conditions in which a splash is moderately generated in this way, the splash becomes far weaker than the conventional one. Therefore, the degree of danger to the operator, the degree of wear of the equipment, and the degree of wear of the tip can be further reduced. Furthermore, since the splashes are moderately present, it is possible to improve the welding quality and make the welding quality uniform without setting each control target value to an excessive value that causes the splashes every time.

[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, FIG. 3 is a flow chart showing a processing procedure of the first embodiment, FIG. FIG. 4 is a flow chart showing the processing procedure of the second embodiment, and FIG. 5 is a diagram showing memory allocation. 4, 11, 12, 16-19, 23 ... energization control means,
13-15 ...... detecting means, 16～19,23 ...... calculation means, adjusting means, _ID 0 ~IDn, IDx ...... identification code, _MI 0 ~MIn ...... control target value.

Claims (1)

[Claims] 1. An energization control means for selecting one from a plurality of control target values on the basis of an identification code given to each welding location, and energizing in accordance with the target values, and a detection means for detecting the occurrence of splash. And a calculating means for calculating the ratio of the number of spots for splash generation to the predetermined number of welding spots to be welded for the welding points having the same identification code, and the control target value corresponding to each identification code so that the ratio falls within a predetermined range. A resistance welding control device comprising an adjusting means for adjusting.