JPH0796158B2 - 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 projection welding.

[Prior art]

In the resistance welding, when the welding current is changed in response to the change in the pressing force, the timing (synchronization) must be well matched. For example, energization will deteriorate the welding quality unless the work is started after it has been sufficiently pressed.
In addition, the wear of the welding tip becomes faster. On the other hand, the work efficiency is reduced unless the energization is started promptly after the sufficient pressure is applied. Further, in the projection welding which requires the two-step pressurization, good welding cannot be expected unless the welding current is increased at the same timing as shifting to the second-step pressure. For this reason, conventionally, for example, at the start of welding, the squeeze time is adjusted to adjust the timing. Further, in the case of projection welding, the timing is adjusted by adjusting the waiting time after the pressure increase command to the pneumatic servo circuit until the welding current control circuit is commanded to increase the current. .

[Problems to be Solved by the Invention]

By the way, the urging means for urging the welding tip, especially the generally used pneumatic (pneumatic) cylinder, the movement of its piston becomes faster or slower depending on the season, temperature, machine temperature and the like. Further, even in the case of cylinders of the same type, the speed of movement differs depending on the welding machine. For this reason, the squeeze time and the waiting time after the pressure boosting instruction have to be frequently checked and adjusted, which is complicated. Moreover, there is no method to easily check the goodness and badness of these synchronizations at the site, and intuition and experience are required for the adjustment.

[Means for Solving the Problems]

Therefore, in the present invention, in a resistance welding control device used for resistance welding in which the applied pressure is changed during energization, the resistance welding control device is disposed between the welding tip and the biasing means for biasing the welding tip, Pressing force detection means for detecting the actual pressing force applied to the welding tip from the biasing means via
Welding current control means for changing the welding current in response to the output from the pressing force detection means (claim 1). Further, the welding current control means switches the welding current to a predetermined value when the output of the detection means reaches a predetermined value to conduct electricity (claim 2).

[Action]

In the resistance welding control device of the present invention, the pressing force detecting means is arranged between the welding tip and the urging means for urging the welding tip. By doing so, the actual pressing force applied to the welding tip, that is, the actual pressing force applied to the workpiece is detected by the pressing force detecting means. Then, in resistance welding in which the welding pressure is changed during energization, the timing of the welding pressure change is accurately grasped using the output of this welding pressure detection means, and the welding current is changed in accordance with the timing of this welding pressure change. It

【Example】

Hereinafter, the details of the present invention will be described based on illustrated embodiments. First
In the figure, reference numeral 1 is a rectifier 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. 4 is an inverter, which has a pulse width of 10 according to the designated pulse width value WP.
00Hz AC AF 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 on this low-voltage LV. 8 and 9 are welding tips,
It is supported by a welding machine main body (not shown) and adheres to the work 10 by a pressing force F, and a welding current I is supplied thereto.
11 is a current detection coil, which is the amount of change in welding current I (differential value)
Generates a minute 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 pneumatic servo circuit 13 controls each pressure P1, P2 in the pneumatic cylinder 14 according to a designated pressure value supplied from a welding machine body control circuit (body control circuit) (not shown). Reference numeral 15 is a strain resistor as a pressing force detecting means, which is attached to a connecting rod 17 which connects the piston 16 and the welding tip 8.
The resistance value changes according to (distortion). A constant current circuit 18 supplies a constant current CI to the distortion resistor 15.
An analog-digital converter (A / D converter) 19 converts the terminal voltage VR of the distortion resistor 15 into a digital value DP. This digital value DP represents the pressing force F. Reference numeral 20 denotes a clock circuit, which executes clocking from "0" when the reset signal R is supplied. Reference numeral 21 is a central processing unit (CPU), which is an integrated circuit, called a microcomputer, and random access memory (RAM) 22
The following processing is executed according to the program of the read only memory (ROM) 23 while using the. The so-called RAM card 24 is used for storing data and programs. Reference numeral 25 is a printing device, and 26 is a display device, which prints out or displays control status data (welding current, welding spot number, operation status of each part, etc.) supplied from the CPU 21, respectively. A keyboard 27 is used for data input to the CPU 21. Reference numeral 28 denotes an input / output port, which exchanges data between the above-described circuits and the like and the CPU 21, between the main body control circuit and the CPU 21, and between an external computer or the like (not shown) and the CPU 21. 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 welding machine by the robot or the like, the main body control circuit executes the processing as follows. First, a work start command JS is supplied to the CPU 21. Next, the welding tips 8 and 9 are brought into contact with the first welding point. Next energization command ST
Is supplied to the CPU 21. Then, the first stage pressing force F is applied to the work 10.
Prescribed pressure specified value VP1 to pneumatic servo circuit 13 so that P is applied
To supply. Wait for the predetermined time TP to elapse from there.
This time TP is the time for maintaining the first stage pressure FP.
When the predetermined time TP elapses, a predetermined pressure designated value VP2 is supplied to the pneumatic servo circuit 13 so that the second stage pressing force FS is applied to the work 10. After that, wait for the energization end signal E to arrive from the CPU 21,
After a lapse of a predetermined time TH from the arrival of the signal, the cylinder pressure P1 is opened and the cylinder pressure P2 is set to a predetermined value so that the welding tips 8 and 9 are separated from the welding spot and the next welding spot is provided with these. The procedure is repeated and the same processing is repeated. The time TH is the hold time. In response to these processes of the main body control circuit, the CPU 21 executes the processes as follows. First, in response to the work start command ST
The CPU 21 enters the control main routine shown in FIG. Then, in steps S1 and S2, the return instruction RT or the energization instruction ST arrives. When the energization command ST arrives and the answer at step S2 is "Yes", the CPU 21 proceeds to step S3 and outputs the output DP of the A / D converter 19.
Wait until (pressurization force F) reaches a predetermined value PM1. Predetermined value PM1
Is 90% of the digital value DP1 corresponding to the 1st stage pressure FP
It should be a value before and after. If the answer in step S3 is "Yes", that is, if 90% of the first-stage pressing force FP is actually applied to the workpiece 10, the CPU 21 proceeds to steps S4 and S5, where the control target of the welding current I is set. value
MI is set to the target value MI1 when the first-stage pressure FP is applied, and the current control pulse width specified value WP is set to the initial value WP1 corresponding to this target value MI1. Next, in step S6, the switch signal SW is supplied to the inverter 4 to activate it. Next, the CPU 20 proceeds to step S7 and executes the current I control subroutine (FIG. 4). CP in this subroutine
U21 first obtains the difference D between the digital value DI indicating the welding current I at that time and the target value MI (step S71). In this embodiment, when the absolute value of the difference D is smaller than the predetermined value DS, the pulse width adjustment value WA is set to "0" (steps S72 → S).
74 → S76). Further, when the absolute value of the difference D is larger than the predetermined value DS but does not reach the larger predetermined value DL, the pulse width adjustment value WA is set to the small predetermined value WS (steps S72 → S74). → S75). When the absolute value of the difference D exceeds the larger predetermined value DL, the pulse width adjustment value WA is set to the larger predetermined value WL (step 72 → S7).
3). Next, the CPU 21 proceeds to step S77 from any of steps S73, S75 and S76, and determines the polarity of the difference D. When the difference D is positive, the digital value DI corresponding to the welding current I at that time
Is larger than the target value MI. Therefore, to reduce this,
The CPU 21 subtracts the pulse width adjustment value WA from the pulse width specification value WP at that time and sets it as a new pulse width specification value WP (step S78). If the difference D is negative, the reverse process is performed (step S79). Note that the difference D of "0" is processed in step S78. Then, the CPU 21 proceeds to step S80, supplies a new pulse width designation value WP to the inverter 4, and returns to the main routine of FIG. In the next step S8, the CPU 21 causes the digital value DP indicating the applied pressure.
Whether or not the predetermined value PM2, which is larger than the digital value DP1 when the first-stage pressure FP is applied, is reached. This predetermined value PM2 determines the timing when the welding current I is increased in accordance with the increase of the pressing force F, and in the present embodiment, it is an intermediate value between the pressing force FP of the first stage and the pressing force FS of the second stage. And the digital value corresponding to this is the predetermined value PM2. When the pressing force F exceeds this digital value PM2, the answer in step S8 is "Yes". So CPU21 is step S
Proceeding to 9, the reset signal R is supplied to the timing circuit 20. In response to this, the timing circuit 20 starts timing from "0". Subsequently, the target value MI of the welding current I is set to the value MI2 for applying the second-stage pressure FS, and correspondingly, the pulse width designation value WP is also set to the initial value WP2 corresponding to this target value MI2. (Steps S10, S11). Next, in step S13, the current I control subroutine of FIG. 4 is executed. The process of maintaining the value of the welding current I at the target value MI2 is continued until the output T of the timing circuit 20 reaches the predetermined value TM (step S14). When the output of the timing circuit 20 reaches TM, that is, when the energization at the target value MI2 is maintained for the time TM, the answer in step S14 is "Yes". Then, the CPU 21 proceeds to step S15 to cut off the switch signal SW supplied to the inverter 4 and stop its operation. Then, a signal E indicating that the energization is finished is supplied to the main body control circuit. The time TM is determined according to the characteristics of the work 10. When the signal E arrives, the main body control circuit waits for the hold time TH to elapse from that point as described above. This time TH is also determined according to the characteristics of the work 10. When this time TH has elapsed, the main body control circuit separates the welding tips 8 and 9 from the workpiece 10 and moves the welding tips 8 and 9 to the next welding point, as described above. Such processing is executed up to the final welding spot, and when the CPU 21 supplies the energization end signal E to the main body control circuit for the welding spot, the circuit supplies the CPU 21 with a return command RT. Upon receipt of this instruction RT, the CPU 21 shifts from step S1 to an upper routine (not shown) and finishes the processing shown in FIG.

【The invention's effect】

As described above, in the present invention, the pressing force detecting means is arranged between the welding tip and the biasing means for biasing the welding tip, and the output timing of the pressing force detecting means is used to accurately determine the timing of change in the pressing force. , And changed the welding current. Therefore, in resistance welding used for resistance welding in which the applied pressure is changed during energization, for example, poor welding quality caused by a mismatch between the timing of transition to the second stage applied pressure and the timing of increase in welding current, welding tip It is possible to reliably prevent wear of the steel, deterioration of work efficiency, and the like, and it is particularly useful for projection welding that requires two-step pressing and resistance welding of sintered metal, aluminum, and the like. The resistance welding control device of the embodiment is applied to an inverter type resistance welding machine, but may be applied to an AC type and a capacitor type resistance welding machine.

[Brief description of drawings]

FIG. 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 changes in welding pressure and welding current, and FIG. 3 is a flow chart showing a control main routine. FIG. 4 is a flow chart showing the current I control subroutine. 8, 9 ... Welding tip, 13, 14 ... Energizing means, 15, 18, 19 ... Pressurizing force detecting means, 11, 12, 21-23 ... Welding current control means.

Claims (2)

[Claims] 1. A resistance welding control device used for resistance welding in which the applied pressure is changed during energization, the resistance welding control device being arranged between a welding tip and an urging means for urging the welding tip. Pressurizing force detecting means for detecting the actual pressurizing force applied to the welding tip from the biasing means via the welding force, and welding current controlling means for changing the welding current in response to the output from the pressurizing force detecting means. A resistance welding control device comprising: 2. The resistance welding control device according to claim 1, wherein the welding current control means switches the welding current to a predetermined value to supply electricity when the output of the detection means reaches a predetermined value.