JPS62176688A - Adaptive control method in resistance welding machine - Google Patents

Abstract

PURPOSE:To accurately detect and measure the resistance or voltage between electrode chips by disusing the lead wire for measuring voltage between electrodes for the electrode chip, by finding a voltage displacement factor and current displacement factor, by taking the resistance value between the electrode chips by multiplying this difference by the reference resistance value and by performing adaptive control with repeating this measurement extending over all electrifying period. CONSTITUTION:An arc ignition circuit 11 performs the constant current control which adjusts an ignition phase angle to a thyristor 8 by finding the variation in the welding current. A division circuit 14 finds a power source voltage displacement factor by detecting the welding power source voltage. A division circuit 16 finds the welding current displacement factor by dividing the welding current by the reference current value by detecting it. A substraction circuit 17 finds the resistance value between the electrode chips by substracting the power source voltage displacement factor fed from the division circuit 14 from the circuit 16. A multiplication the resistance displacement factor between electrode chips by the reference resistance value. The arc ignition circuit 11 monitors the resistance between electrode chips fed from the multiplication circuit 18 with performing the constant current control and performs the adaptive control by controlling the welding current and/or welding time according to the prescribed algorithm from the propulsion thereof.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention continuously detects the resistance between electrode tips that changes from moment to moment during the spot welding process, and generates a nugget of an appropriate size. Regarding an adaptive control method for controlling welding current and/or energization time, etc., more specifically, an adaptive control method using an electrode tip resistance measurement method that eliminates the need for a lead wire for detecting and measuring the electrode tip voltage. Regarding the method.

(Prior Art) Recently, as a control method to guarantee the quality of spot welding, welding current and/or Alternatively, an adaptive control method has been put into practical use that guarantees the size of the nugget by automatically controlling the energization time.

In order to detect and measure the voltage between electrode tips, most spot welding guns usually have a small tapped hole near the tip holder, and one end of the insulated lead wire is screwed into that small hole. Then, the lead wires are fixed and wired along the arm.

(Problems to be Solved by the Invention) However, in the electrode tip voltage measurement method using lead wires as described above, the lead wires may be damaged or disconnected due to handling of the spot welding gun or mechanical interference with external equipment. Happens often. Furthermore, since the lead wire will be routed near the secondary cable where a powerful welding current flows,
The drawback is that the electromagnetic induction generates a large amount of noise, making it difficult to accurately detect and measure the voltage between the electrode tips.

(Means for Solving the Problems) The present invention solves the above problems, and its specific method is to detect the resistance between the electrode tips that changes from time to time during the welding process, and to In the so-called resistance welding adaptive control method, which automatically controls various conditions such as welding current and/or current application time while continuously monitoring the transition of the resistance between electrode tips, so as to obtain the nugget diameter, the IF voltage is Detected every half cycle or predetermined cycle.

The detected voltage value is divided by a preset reference voltage value to obtain the voltage displacement rate, and the current value on the primary side or secondary side of the welding transformer is detected, and the detected current value is set in advance. Find the current displacement rate by dividing by the reference current value,
Furthermore, the value obtained by subtracting the voltage displacement rate from the current displacement rate is multiplied by a preset reference resistance value, and the value obtained thereby is regarded as the inter-electrode tip resistance value during welding, The present invention provides a technical means of performing adaptive control while repeating this measurement over the entire energization time.

(Operation) Next, the principle and operation of the present invention will be explained with reference to FIGS. 1 and 2.

In spot welding, for example, as shown in the main circuit shown in FIG.
The pressure device 6 applies the pressure necessary for welding to the electrode tip.
3 and 4, and an electronic control element such as Cylisk 8 inserted between the welding transformer and the welding power source 7.
The main current is opened and closed by controlling the ignition circuit included in the control device 9, and the current necessary for welding is passed between the electrode tips for a certain period of time to form a nugget 10 at the welding part and join.

Factors that cause current fluctuations during nugget generation can be roughly divided into power supply fluctuations and load fluctuations.

Of these, for load fluctuation, ■resistance value of secondary cable,
■Divided into variations in resistance between electrode tips.

The above power fluctuations may also occur irregularly during the welding process. The resistance value of the secondary cable gradually increases as the secondary cable wears out due to long-term use, and the resistance value does not dynamically change during the welding process.

On the other hand, regarding the resistance between electrode tips, as is well known, in general spot welding, the resistance between electrode tips during the welding process typically shows a transition as shown in FIG.

Section C shown in the figure is an unstable region immediately after the start of energization, and the behavior of the resistance between the electrode tips during this period is determined by the contact condition of the welded material (fitting in) and the contamination of the surface of the welded material such as oil and rust. Depends on etc. This surface contact resistance is 1 to 2 after the start of energization.
It disappears in cycles, and the resistance between the electrode tips rapidly decreases.

Next, in section b, the resistivity of the welded object increases due to the temperature rise of the weld, and the current carrying path area increases simultaneously due to softening and crushing of the weld. During this period, the increase in weld resistance due to the increase in specific resistance exceeds the decrease in resistance value due to the expansion of the current carrying path area, and as a result, the inter-electrode tip resistance increases, reaching a maximum value near the end of this process. During this period, nuggets begin to form and are in the early stages of growth.

Next, in section C, the current carrying path area continues to expand as the nugget grows, but the resistivity remains constant after reaching the saturation value, so the resistance between the electrode tips decreases.

Most of the current fluctuations during the welding process are the result of power supply fluctuations and the sum of the resistance between the electrode tips. Therefore, for example, in the case of AC welding, the power supply voltage is detected every half cycle, and in the case of DC welding, at every predetermined time interval, and this detected value is set as a preset reference voltage value, that is, a state with no fluctuation. The voltage change rate from the reference voltage value is determined by dividing the power supply voltage at By dividing by , the current displacement rate from the reference current value is obtained, and by subtracting the voltage displacement rate from the current displacement rate, the displacement rate of the inter-electrode tip resistance can be calculated.

If the displacement rate of the inter-electrode tip resistance obtained in this way is multiplied by a predetermined reference resistance value, that is, the electrical resistance value in a state where there is no fluctuation due to temperature rise, softening, crushing, etc. of the welded part, then The absolute value of the inter-electrode tip resistance can be obtained. Thus, by repeating the above operation every half cycle or at predetermined time intervals, it is possible to monitor the change in resistance between the electrode tips during the welding process.

Therefore, when implementing adaptive control of spot welding, l
In this way, the resistance or voltage between the electrode tips can be easily and accurately determined without connecting a lead wire for detecting the inter-electrode voltage to the electrode tip.

(Example) Hereinafter, a configuration example of an apparatus for carrying out the method of the present invention will be described based on FIG. 3.

FIG. 3 is an electrical block diagram of a general single-phase AC welding device. In this figure, the same components as those of the main circuit shown in FIG. 1 are given the same reference numerals, and the details are omitted.

The ignition circuit 11 of the control device 9 sends an ignition signal to the thyristor 8 and connects the CT 12. Alternatively, the welding current is detected by the toroidal coil 13 installed on the secondary side of the welding transformer, and fluctuations in the welding current due to fluctuations in the welding power source and load impedance are determined, and a point to the thyristor 8 is set to compensate for this. Performs so-called constant current control to adjust the arc phase angle.

At the same time, the divider circuit 14 inputs a power supply voltage detection transformer 15 inserted between the welding power source 7 and the welding transformer 1 every half cycle.
The welding power supply voltage is detected and divided by a preset reference voltage value, that is, the power supply voltage value in a state with no fluctuation, to obtain the power supply voltage change rate.

At the same time, the dividing circuit 16 detects the welding current by the CT 12 or the toroidal coil 13 every half cycle, divides this by a preset reference current value, that is, the current value in a state without disturbances such as load fluctuation, and calculates the welding current. Find the displacement rate. In addition, as mentioned above, if you add a word to this,
The constant current control performed during the welding process compensates the welding current to the set value every half cycle by controlling the firing phase of the thyristor. Since compensation is performed during the next half cycle, there is always a half cycle response delay and the welding current is not always maintained at the set value.

Therefore, for an instantaneous half cycle, if any disturbance occurs, the current displacement will occur.

Next, the subtraction circuit 17 subtracts the power supply voltage change rate output from the division circuit 14 from the other division circuit 16. This calculated value corresponds to the resistance change rate between the electrode tips.

Next, the multiplier circuit 18 uses the calculation result output from the subtraction circuit 17, that is, the reference resistance value set in advance for the resistance displacement rate between the electrode tips, that is, in a state where there is no fluctuation due to temperature rise, softening, crushing, etc. of the welded part. multiplied by the resistance value between the electrode tips. This calculated value corresponds to the inter-electrode tip resistance value.

The ignition circuit 11 performs constant current control as described above, and also monitors the inter-electrode tip resistance output from the multiplier circuit 18, and controls the welding current and/or energization time based on the transition according to a predetermined algorithm. and performs adaptive control.

As is well known, the predetermined algorithm is
A method that integrates the waveform of the transition of the resistance between electrode tips and stops energization when it reaches a preset value, and energizes when the transition of the resistance between electrode tips drops by a preset value from the highest value of the transition of the electrode tip resistance. There are many methods, such as a method in which the welding current is truncated, or a method in which the welding current is adjusted every half cycle so that the waveform of the transition of the electrode tip resistance matches the waveform that yields the appropriate nugget determined in advance by experiment. The example is applicable to either.

As described above, as a result of carrying out the method of the present invention based on the following experimental values, changes in the inter-electrode tip resistance value as shown in FIG. 4 were observed.

◎ Material to be welded Alloyed hot-dip galvanized steel plate (45g/4
5g) Plate thickness: 0.7tX2 ◎ Welding conditions Pressure: 250kgf current
: 11.0OOA Current application time; 10~ (Effects of the invention) As described above, according to the method of the present invention, there is no need to connect a lead wire for measuring interelectrode voltage to the electrode tip of a resistance welding machine, which is different from the conventional method. It is possible to detect and measure the resistance or voltage between the electrode tips during the welding process, regardless of the effects of breakage of lead wires and noise caused by electromagnetic induction, as seen in .

[Brief explanation of drawings]

FIG. 1 is a main configuration circuit diagram of a resistance welding machine. FIG. 2 is a diagram showing a typical change in resistance between electrode tips. FIG. 3 is an electrical block diagram showing a configuration example for implementing the method according to the present invention. FIG. 4 is a diagram showing changes in inter-electrode tip resistance based on experimental values. 1... Welding transformer 2... Secondary conductor 3.4
... Electrode tip 5 ... Welded object 6 ... Pressure device ゛ 7 ... Welding power source 9 ... Control device 10 ... Nugget 11 ... Ignition circuit
12...CT13...Troidal coil
14.16...Division circuit Figure 2 Figure 4 Part 3

Claims (1)

[Claims] The resistance between the electrode tips during the welding process is detected, and various conditions such as welding current and/or energization time are automatically adjusted while continuously monitoring the transition of the resistance between the electrode tips so that the appropriate nugget diameter can be obtained. In the so-called resistance welding adaptive control method, the power supply voltage is detected every half cycle or every predetermined cycle, the detected voltage value and a preset reference voltage value are calculated to determine the voltage displacement rate, and the welding transformer is Detects the current value on the primary side or secondary side of
Then, calculate the current displacement rate by calculating the detected current value and a preset reference current value, and further subtract the voltage displacement rate from the current displacement rate, and set the preset standard to the value obtained by subtracting the voltage displacement rate from the current displacement rate. Adaptive control in a resistance welding machine, characterized in that the value obtained by multiplying the resistance value is regarded as the inter-electrode tip resistance value during welding, and thereafter this measurement is repeated over the entire energization time. Method.