JPH0253155B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a resistance welding machine that calculates the current usage rate of a single-phase AC resistance welding machine from the power factor of the load and the firing phase of an electric valve using a computer. The present invention relates to a current usage rate calculation device.

[Technical background of the invention and its problems]

Single-phase AC resistance welding machines are often used for welding thin steel plates, and in the automobile industry in particular, a large number of resistance welding machines are used in parallel for welding vehicle bodies.

A single-phase AC resistance welding machine controls the phase of an external AC power source using an electric valve (for example, a thyristor) connected in reverse parallel, and flows the welding current through a welding transformer, but the primary current of the welding transformer during welding is 100～
The welding current is approximately 600A, and when the power supply voltage drops, the welding current is controlled at a constant level by advancing the ignition phase. However, if the voltage drop exceeds approximately 10%, full ignition occurs, and the welding current cannot be increased any further. It becomes impossible to prevent the decline.

Therefore, if a large number of resistance welding machines are connected in parallel to one power source as described above, when the welding currents of each welding machine overlap, a voltage drop of nearly 20% will occur due to the impedance of the power supply system. Sometimes,
A problem arises in that the welding current of the resistance welding machine is insufficient. Here, the current usage rate η of the resistance welding machine is as follows (1)
Formula η = Welding current (effective value) / Welding current at full ignition (effective value) × 100% ...... (1) When welding with full ignition current, η =
When welding with a current of 100% and half of the total ignition current, η = 50%.

Conventionally, the current usage rate η was calculated from the welding current and the total ignition current using equation (1), and this was used as a guide to control the entire welding machine while monitoring the allowable fluctuation range of the power supply voltage.

However, the above method (a) requires a welding current measuring device, (b) requires measurement of both the welding current and the total ignition current, and (c) requires measurement of both the welding current and the total ignition current, and (c) It has the disadvantage that the measurement error increases because the arc current changes.

[Object of the Invention] An object of the present invention is to provide a current usage rate calculating device for a resistance welding machine that directly calculates and displays the current usage rate without using a welding current measuring device.

[Summary of the invention]

The present invention calculates the load power factor from the zero point phase of the welding current for a specific firing phase angle of a single-phase AC resistance welding machine that controls the welding current by adjusting the firing phase of electric valves connected in antiparallel. A current usage rate calculation circuit is provided to calculate the current usage rate of the welding machine from the load power factor calculated above and the firing phase angle during actual welding, and to measure the welding current. This is a current usage rate calculation device for resistance welding machines that can calculate and display the current usage rate without any hassle.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

In FIG. 1, 1 is a microprocessor for controlling a resistance welding machine, and is used as an arithmetic circuit in the present invention. 2 is a current usage rate indicator.

The microprocessor 1 is mainly used to control the firing phase of an anti-parallel thyristor 4 for controlling a resistance welding machine, but since this is not directly related to the present invention, its details will be omitted.

The AC voltage V supplied from the AC power source 3 is applied to the primary side of the welding transformer 5 via the anti-parallel thyristor 4, and the secondary side of the welding transformer 5 causes welding current to flow through the welding electrode 6.

The primary current I is detected by a current transformer 7, rectified by a rectifier 8 to become a voltage across a resistor 9, and further
The data is converted into a digital value via the D converter 10 and read into the microprocessor 1.

The voltage V _Q across the anti-parallel thyristor 4 is approximately zero when the welding current is flowing, and is equal to the power supply voltage V when the welding current is not flowing.

The voltage rise detector 11 detects the rise of the voltage _VQ , that is, the point in time when the welding current becomes zero, and uses this as an interrupt signal Q to interrupt the microprocessor 1. Voltage zero cross detector 12 detects power supply voltage V
When zero crosses, an interrupt signal P is generated and the timing counter 14 is reset.

The pulse oscillator 13 has a pulse interval at a frequency corresponding to a phase angle of 1° (18 kHz when the power frequency is 50 Hz, 60 kHz).
Generates a pulse train of 21.6kHz (Hz).

The timing counter 14 is reset to zero by the interrupt signal P, counts the pulse train, and inputs the count value R to the microprocessor 1.

FIG. 3 is a timing chart showing these voltage waveforms.

The primary current I obtained by controlling the firing phase of the anti-parallel thyristor 4 by the microprocessor 1
is given by the following equation (2).

Here, E is the amplitude of the power supply voltage V, ω is the angular velocity of the power supply voltage, R is the equivalent resistance of the load, L is the equivalent inductance of the load, T is the load circuit time constant (=L/R),
φ is the power factor angle, and using equation (2), the firing angle θ and I
If the time t at which =0 is known, the power factor angle φ can be calculated.

For example, if θ=90°, when I=0 sin(ωt−π/2−φ)=θ−t/Tsin(π/2−φ) ...(3) becomes.

As shown in the time chart in Figure 3, the interrupt signal Q is generated when I = 0, so read the count value R at this time and use it as t in equation (3),
If the value of φ with respect to t is stored in advance as a data table, the power factor angle φ can be instantaneously determined.

Also, in equation (2), when θ=φ, the transient term θ−
t/Tsin(θ-φ) becomes zero, and the effective value of I becomes maximum, resulting in current usage rate η=100%.

Next, the effective value of I is determined sequentially by setting θ = φ + 1° and θ = φ + 2°, and this is graphed as a percentage of the effective value of I at full firing, ie, η, as shown in Figure 2. The current usage rate η corresponding to the firing angle θ is obtained using the rate angle φ as a parameter.

For example, when φ = 80° and θ = 80°, η = 100%, and φ
= 80°, θ = 110° and η = 51%.

Moreover, the dotted line indicates that η=88% when φ=50° and θ=65°.

Therefore, if the data table shown in FIG. 2 is stored in the microprocessor 1, the power factor angle φ and firing angle θ
The DC usage rate η can be immediately calculated from .

Note that the above characteristic data was previously calculated using another large-scale computer, and the results were transferred to the microprocessor 1.
It can be stored in the main memory of

The microprocessor 1 first sets θ=90° and reads the contents R of the counter 14 at the interrupt timing Q to obtain the power factor angle φ, and then calculates the firing angle θ and the power factor angle φ when the welding current is applied. The current usage rate η is calculated from the data table in the main memory.

Approximately 4 Kbytes of memory capacity is required to store data every 1° over the entire range of φ = 30° to 80° and θ = 30° to 110°.
If there are only 6 points every 10 degrees, the memory capacity will be about 330 bytes.

In this case, linear approximation may be used for the intermediate φ.

The current usage rate η calculated by the microprocessor 1 is displayed on the display 2.

〔Effect of the invention〕

As explained above, according to the present invention, in a single-phase AC resistance welding machine that controls welding current by controlling the firing phase of electric valves connected in reverse parallel, the welding current for a specific firing phase is zero. The power factor angle of the load is calculated by detecting the point phase, and the current usage rate is calculated from this load power factor angle and the firing angle during actual welding. (b) Calculation of current usage rate is performed by a microprocessor using a data table created in advance, so no special work is required and labor is saved; (c) Power supply voltage is not required for calculation. Therefore, a reasonable current usage rate calculation device for resistance welding machines can be obtained, which has advantages such as no measurement errors due to fluctuations in power supply voltage.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the current usage rate calculating device for a resistance welding machine according to the present invention, FIG. 2 is a diagram showing an example of characteristic data used for calculation in the present invention, and FIG. 3 is a diagram showing an example of the characteristic data used in the calculation according to the present invention. This is a time chart showing the operating voltage of each part in the. 1... Microprocessor, 2... Current usage rate indicator, 4... Anti-parallel thyristor, 5... Welding transformer, 6... Welding electrode, 10... A/D converter, 11... Voltage rise detection device, 12... Voltage zero cross detector, 13... Pulse oscillator, 14...
…counter.

Claims (1)

[Claims] 1 A load that calculates the load power factor from the zero point phase of the welding current for a specific firing phase angle of a single-phase AC resistance welding machine that controls the welding current by adjusting the firing phase of electric valves connected in reverse parallel. A resistance welding machine comprising a power factor calculation circuit and a current usage rate calculation circuit that calculates the current usage rate of the welding machine from the load power factor calculated above and the firing phase angle during actual welding. Current usage rate calculation device.