JPS62107877A - Constant current control method in spot welding machine - Google Patents

Abstract

PURPOSE:To pertinently set the current in starting without performing a trial electrification, etc. by fixing the approximate value of the maximum current and power factor angle of a welding machine and by performing the initial electrification at the firing angle which is decided from a thyristor firing angle - relative welding current characteristics. CONSTITUTION:Since the power factor angle of a spot welding machine is generally 50-70 deg. it is given at 60 deg. as the approximate value and the approxi mate value of the maximum current is decided by the shape of the welding machine. For instance, in case of selecting 8KA for the approximate value the relative current to the set current value makes 0.5, so the corresponding firing angle makes about 105 deg. from the thyristor ignition angle - relative welding current characteristics relation chart. And the initial welding cycle electrification is performed at this ignition angle and after the 2nd cycle and on the ignition angle is controlled so as to eliminate the error in the welding current measuring value and set current. Consequently, the current at the starting time can be made optimum without performing a pilot electrification, etc.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a constant current control method in a spot welding machine, and in particular to a method for controlling a constant current in a spot welding machine, particularly at the start of welding to perform pilot energization that delays main energization or complicated test energization. It is designed to flow an appropriate welding current.

(Prior art) In a general spot welding machine, as shown in FIG. Welding current I is applied from the side coil to weld material 1.
6.18 is melted by Joule heat generation, and the materials to be welded 16°18 are metallurgically joined.

In FIG. 3, 20 is a welding control device or a welding timer that applies gate drive signals Ga, Gb to the thyristors 10.12 to control the firing angle or firing phase of these thyristors. Further, 22 is a toroidal coil used for measuring the welding 7Ti flow I.

4 and 5 show the principle of a system for controlling the welding current by changing the firing angle φ of the cylindrical rJ stars 10 and 12. FIG. 4 shows a case where the firing angle φ is made to match the power factor angle θ, and the welder aI at this time becomes a substantially continuous positive wave, a so-called full heat current waveform. Fig. 5 shows the case where the firing angle φ is made larger (delayed) by ζ than the power factor angle θ, and at this time, a period in which no voltage is applied to the primary side of the welding transformer 14 occurs, and the welding current I is discontinuous. At the same time, its peak value also decreases, resulting in a so-called heat control current waveform. If the delay ζ of the firing angle φ is further increased, the voltage rest period is increased, and the magnitude of the welding current I is further reduced. In this way, the magnitude of the welding current (■) can be controlled by changing the firing angle φ.

By the way, although only one cycle is shown in FIGS. 4 and 5, in reality, the welding current I is flown for a number of cycles, for example, 10 cycles, and in each cycle, the welding current I reaches the set current value IO.
The firing angle φ is controlled so as to match the ignition angle φ, and so-called constant current control is performed.

However, if the welding current (2) flowing in the first (first) cycle deviates significantly from the set current value Io, it will have a negative effect on the welding quality even if it gradually becomes stable in the later cycles. That is, if the initial welding current I is too large, sparks will fly, and if it is too small, the welding current will increase slowly (slowly) resulting in a slow slope.

Therefore, in constant current control, it is important to flow an appropriate welding current I close to the set current value IO in the first cycle.

For this purpose, conventionally, before the regular energization (main energization), one cycle of energization was performed at a predetermined appropriate firing angle φ, and the measured value (effective value) of the welding current flowing at that time and the lag. Calculate the power factor angle θ and the optimal firing angle φm from the angle (γ),
In the main energization immediately after that, the first cycle of energization is performed at the optimum firing angle φl.

Alternatively, when the welding current control device 20 is installed, test energization is performed for several cycles, and the power factor angle O and the optimum firing angle φm are calculated and stored in the memory. During welding, the optimum firing angle φm is read out and the first cycle of current is applied.

(Problem to be solved by the invention) However, according to the former method, there is always a delay of one cycle in pilot energization before main energization for each welding, so it is difficult to perform continuous high-speed welding work. It was inconvenient.

Furthermore, the latter method has the inconvenience of complicating adjustment work when installing the timer.

The present invention has been made in view of the above-mentioned problems of the prior art, and is a constant current that allows an appropriate welding current to flow at the start of welding without carrying out pilot energization or complicated test energization that causes a delay in main energization. The purpose is to provide a control method.

(Means for Solving the Problems) The method of the present invention for achieving the above object is to perform welding with a current value equal to a set value in a spot welding machine having a constant thyristor firing angle-relative welding current characteristic using the power factor angle as a parameter. A constant current control method for controlling the thyristor firing angle of each welding cycle so that current flows, the method determines approximate values of the maximum current and power factor angle of a spot welding machine, and determines the thyristor firing angle corresponding to these approximate values. is determined based on the thyristor firing angle-relative welding current characteristics, and in the first welding cycle, the thyristor is energized at the determined firing angle, and in the second
After the cycle, the welding current is energized at such a thyristor firing angle as to cause a comparison error between the measured value of the welding current flowing in the previous welding cycle and the set current value.

(Function) FIG. 1 shows the thyristor firing angle-relative welding current characteristics of a spot welding machine. As shown in the figure, when the power factor angle θ changes, the characteristic curve also changes, but since the power factor angle θ of a general spot welding machine does not differ much between 50° and 70°, it can be set to, for example, 60° as an approximate value. can. Further, the maximum current is determined by the structure or connection form of the slot welding machine, but is generally known and it is easy to determine its approximate value.

Therefore, for example, if the approximate value of the maximum current is 16 KA (kiloampere), and the set current value is selected to be 8 KA, then the relative current corresponding to the set current value with the characteristics shown is 0°5, the corresponding thyristor firing angle φ in the characteristic curve (θ=60') is approximately 105°.

In the present invention, the firing angle determined in this way (approximately 10
Since the first welding cycle is energized at 5°), there is no need to conduct pilot energization or test energization. In the second and subsequent welding cycles, the measured value of the welding current that flowed in the previous welding cycle is compared with the set current value, and the thyristor is energized at a firing angle φ that eliminates the comparison error. Even if the welding current in the welding cycle slightly deviates from the set value, or even if an error occurs due to fluctuations in the power supply voltage, distortion of the voltage waveform, changes in resistance of the welded object (load fluctuations), etc., it is immediately corrected and stabilized. Highly accurate constant current control is performed.

(Embodiment) FIG. 2 shows a circuit configuration of a welding current control device (welding timer) suitable for implementing the present invention.

In FIG. 2, the toroidal coil 22 is the same as that in FIG. 3, and when the welding current I flows, it generates a voltage signal El having a waveform corresponding to its differential value.

The terminals of the toroidal coil 22 are connected to resistors 30, 32, and 34 selected by the first switch 36 for changing the measurement range.
The inverting input terminal of the operational amplifier 38 is connected to the inverting input terminal of the operational amplifier 38 via one of the following. The non-inverting input terminal of the operational amplifier 38 is grounded, and a capacitor 40 is connected between the output terminal and the inverting input terminal, so that the operational amplifier 38 operates as an integrating circuit, and a voltage is applied to the output terminal. Signal E1
A voltage signal E2 having a waveform corresponding to the welding current I is obtained. In this embodiment, the resistance values R30, R32, and R34 of the resistors 30, 32.34 are 1
:2:4 ratio is selected. The integration constant of this integration circuit is 1/CR (C is the capacitance of the capacitor 40, R
is the resistance value of the resistor 30.32 or 34), so the level of the voltage signal E2 when the resistors 30 and 32°34 are respectively selected is <E 2a> and <E 2b>
, < E 2c>, then their levels < E
2a>, <E 2b>, <E 2c
> becomes a ratio of 1: 0.5: 0.25. Therefore, the level of the voltage signal E2 when the resistor 30 is selected and the welding current I of 10 KA flows is the reference level < E
2S>, if resistor 32 is selected and a welding current of 20 KA flows, and if resistor 34 is selected and a welding current of 40 KA flows, then
Even when the welding current I of KA flows, the reference level < E
2S> voltage signal E2 is obtained. In this embodiment, the resistor 30 is for the 5 to 10 KA range, and the resistor 32 is for the 10 to 10 KA range.
For the 20KA range, resistor 34 is selected for the 20-40KA range.

The output terminal of the operational amplifier 38 is connected to the inverting input terminal of the operational amplifier 54 via one of the resistors 42 to 50 selected by the second switch 52 for changing the measurement range. The non-inverting input terminal of the operational amplifier 54 is grounded, and a resistor 56 is connected between the output terminal and the inverting input terminal, so that the operational amplifier 54 operates as an amplifier circuit, and the voltage signal E2 is supplied to the output terminal of the operational amplifier 54. Predetermined times (R5
8/R42 to R50) is obtained.

In this embodiment, the resistance value R of the resistors 42 to 50, 5f3
42, R44, R4Ei, R48, R50, R2H
is 1.0:1.2:1.4:1. G: 1.
The ratio of 8:2.0 is chosen and it is 0. Therefore, when resistor 42 is selected, the amplification factor is 2.0/1.0, and when resistor 44 is selected, the amplification factor is 2.0/1.2.
When resistor 46 is selected, the amplification factor is 2.0/1.4, and when resistor 48 is selected, the amplification factor is 2.0/1. G and the resistor 50 is selected, the amplification factor becomes 2.0/1.8. In this way, the multi-stage amplification factor allows the rough measurement range by the resistors 30 to 34 and the switch 36 to be refined in multiple stages, and can correspond to virtually any maximum current value IN. The level of the voltage signal E3 can be set to the reference level <E3S>.

That is, for example, when the maximum current value IM is 16 KA, the level of the voltage signal E2 obtained at the output terminal of the operational amplifier 38 is Reference level < E
The maximum value is 16/20 times 2S>. However, the second switch, Chi52, amplifies $2゜0/1. [By selecting the resistor 48 for i, the level of the voltage signal E3 obtained at the output terminal of the operational amplifier 54 becomes a reference level <E 3s> corresponding to the reference level <E 2S>. Similarly, for example, if the maximum current value IN is 12KA, the first
By selecting the resistor 32 for 10 to 20 KA with the switch 36, the level of the voltage signal E2 is lower than the reference level.
The maximum value is 12/20 times E2s>, but by selecting the resistor 44 for the amplification factor of 2.0/1.2 with the second switch 52, the level of the voltage signal E3 becomes the reference level<
The reference level <E 3s> corresponds to E 2s>.

In this way, in this embodiment, substantially any maximum current value I
Since the level of the voltage signal E3 can be set to the reference value or the maximum value for N, signal processing and accuracy in the analog-to-digital (A/D) converter 58 and the central processing unit 60 at the subsequent stage can be improved. . That is, since the input voltage of the A/D converter 58 can always be set to the maximum value (full range) with respect to the maximum current value IN, the resolution of the digital signal e3 obtained at its output terminal does not deteriorate. Regarding this point, conventionally only 10KA
, 20KA, and 40KA, so if the maximum current value is, for example, 16KA, the input voltage of A/D converter S8 (
E3) is reduced to 16/20 times the reference level, and the A/D
There was a problem in that the resolution of the converted digital signal was small and the measurement accuracy was low. In addition, in this example, if the maximum current value IN (for example, 18 KA) is relatively 1, the set current value (for example, 8 KA) becomes 0.5, which corresponds to the thyristor firing angle-relative welding current characteristic shown in Fig. 1. This is convenient for arithmetic processing in the CPU 60.

Note that from the second cycle onward, the CPU 60 calculates the effective value (measured value) of the previous welding current I based on the digital signal e3.
is calculated, and the measured value is compared with the set current value IO to calculate the error, and gate trigger signals Ga and Gb are generated at timings such that the comparison error is made. Data of approximate values of value Io + maximum current value IN and power factor angle θ are stored, and thyristor firing angle-relative welding current characteristics of the spot welding machine are stored as numerical data or calculation formula.
60, when the approximate values of the maximum current value IN and the power factor angle θ are input from an input device (not shown), the ignition to be used in the first cycle is determined based on the thyristor firing angle-relative welding current characteristic. Determine the angle φ. The CPU 60 also switches the switches 36 and 52.

(Effects of the Invention) As described above, in the present invention, the approximate values of the maximum current and power factor angle of the spot welding machine are determined, and the firing angle determined from the thyristor firing angle-relative welding current characteristic is used for the first cycle. Since energization is carried out appropriately, good welding quality can be obtained while eliminating the need for pilot energization and complicated test energization that accompany main energization.

[Brief explanation of drawings]

FIG. 1 is a diagram showing thyristor firing angle-relative welding current characteristics for detailed explanation of the present invention, and FIG. 2 is a diagram showing a circuit configuration of a welding current control device (welding timer) suitable for implementing the present invention. Block diagram, Figure 3 is a circuit diagram showing the circuit configuration of a general spot/8 welding machine, Figures 4 and 5 are diagrams showing the principle of the method of controlling welding current by changing the thyristor firing angle φ. It is. 10.12... Thyristor, 14... Welding transformer 20... Welding control device, 22... Toroidal coil, 30-34... Resistor, 36... First
switch, 38... operational amplifier, 40... capacitor, 42-50, 56... resistor, 52... second switch, 54... operational amplifier, 58... analog Goodinotal (A/D) converter, 60...Central processing unit, 62...Memory. Patent applicant Miyaji Electronics Co., Ltd.
Company agent Patent attorney Takashi Sasaki Figure 1 → "Iris 7 voices, Yuji angle Figure 3 7"'--/'' 5th country procedural amendment (voluntary) 1985/119\・2 Patent Agency Director Michibe Uga 1, Indication of the case Patent Application No. 249496 of 1985 2, Name of the invention Constant current control method in a spot welder 3, Relationship with the person making the amendment case Patent applicant address Noda, Chiba Prefecture No. 95-3 Ichi Nitsuka Name: Miyaji Electronics Co., Ltd. Representative Keiji Nishizawa 4 Agent address: 2-11-16 Kanda Surugadai, Chiyoda-ku, Tokyo 101
Surugadai Saikachizaka Building No. 302 Telephone: Tokyo (233) 3191 Drawing 6, details of amendments Drawing 5 will be amended as attached. , +, /:
“Heto Figure 5

Claims (1)

[Claims] Controlling the thyristor firing angle of each welding cycle so that a welding current equal to a set current value flows in a spot welding machine having a constant thyristor firing angle-relative welding current characteristic using the power factor angle as a parameter. A constant current control method comprising: determining approximate values of the maximum current and power factor angle of the spot welding machine; and determining a thyristor firing angle corresponding to these approximate values based on the thyristor firing angle-relative welding current characteristic. In the first welding cycle, the thyristor is energized at the determined firing angle, and in the second and subsequent welding cycles, the comparison error between the measured value of the welding current flowing in the previous welding cycle and the set current value is substantially reduced. A constant current control method characterized by energizing a thyristor at a firing angle that makes the thyristor zero.