KR900002369B1 - Method of current control - Google Patents

Abstract

detecting a welding current; comparing, at least, 2 adjacent half waves of the current; and delaying a phase control angle of the next half wave of the higher current peak to compensate the unbalanced welding current.

Description

Constant current control method of resistance welding machine

1 is a graph showing waveforms of power supply voltage and welding current for explaining the present invention.

2 is a block diagram showing an embodiment of a control device for realizing the method of the present invention.

3 is a graph showing the relationship between the phase control angle and the current value (formula (2) in the specification is expressed as a ratio to the maximum current value when the uncontrolled ignition device is taken 100%).

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current control method of a resistance welder, and more particularly, to a constant current control method having higher accuracy than the conventional method when there is a change in load during welding, especially a power factor change.

In the conventional method of controlling the constant current of a resistance welding machine, the welding current is controlled by the following method. That is, the first half-wave or the second half-wave of the welding current is started at a phase control angle of about 90 ° -120 °, and the power factor of the welder is the current value and current at the first and second half-waves. The next phase control angle is calculated using the power factor already calculated and the difference between the current value and the preset current value. The calculated phase control angle is used to move the switch component. It was to ignite.

However, the conventional control method in this arrangement has the following defects. 1. The load power factor cannot be compensated for during welding, resulting in insufficient accuracy. 2. At the start of current conduction, a relatively large amount of current flows to the work site, causing dust to adhere to the welded site, thus degrading the welding quality. 3. Since the power factor is calculated from the conduction angle in the unstable state where the work area is high at the start of current conduction, the calculated power factor is not accurate and the high-precision constant current control work cannot be performed.

It is an object of the present invention to provide a higher response accuracy and a better welding quality level even when ignition is performed under the condition that the control angle of the first or second half wave at the start of welding current conduction is 120 ° or more. To provide a control method. This invention is performed based on the following viewpoints. That is, the reason why a relatively large amount of current is required at the start of current conduction in the conventional method is as follows. In other words, when calculating the power factor from the conduction angle at 120 ° or more of the phase control angle (delayed phase), the inverse of the change of the conduction angle is very small, thereby reducing the extraction accuracy.

More specifically, the features of the present invention are as follows. That is, the method for controlling the constant current of the welding machine is a feedback loop for ignition of the positional component in order to minimize the difference between the current flowing into the first coil or the second coil of the welding transformer and the preset welding current. In the method for controlling a constant current having a current, the first half wave of the welding current is applied to the delayed phase to the work site to be welded, that is, the phase control angle α 120 ° -150 °, and the current value I _L and the conduction angle. (δ) is extracted, and then the power factor angle (ø) of the resistance welder is calculated from the already obtained conduction angle (δ) and phase control angle (α), and the next phase control angle (α) is already calculated The current value corresponding to the set current value of the next half wave is obtained by calculating from the obtained power factor angle (ø), the conduction angle (δ) and the current value (I) already obtained, and the already calculated value of the phase control angle (α) is Ignite the switch parts for half wave Used to Thus, the phase control angle α of the next half-wave current is calculated based on the pre-calculated data regarding the phase control angle α, conduction angle δ and welding current I _L of the previous half-wave current. The process is carried out repeatedly during the exclusive period.

The above and other objects, features and advantages of the present invention will become more apparent as described below with reference to the accompanying drawings.

2 is a block diagram illustrating one embodiment of a control device embodying the method of the present invention. 2 shows a welding transformer 1 and a power supply 2, and an electronic switch component 3 such as a thyrister disposed between the welding transformer 1 and the power supply 2 is shown. It is. The welding current is extracted from the current flowing into the first coil or the second coil of the welding transformer (1), and the current of the first coil is the current extraction disposed between the die Lister (3) and the welding transformer (1). The current of the second coil is retrieved by the machine 4 (CT) and is retrieved by the annular coil 6 disposed between the welding transformer 1 and the welding gun 5.

The output signal from the current extractor 4 and the annular coil 6 is input to the color extractor 7 in order to extract the effective current value and the conduction angle. The calculation signal relating to the conduction angle extracted by the color extractor 7 is input to the power factor angle calculating circuit 8, while the calculation signal relating to the effective current value extracted by the color extractor 7 is calculated by the maximum current value calculating circuit ( 9) is put into. The power factor calculation circuit 8 is provided between the maximum current value calculation circuit 9 and the control angle calculation circuit 10 for the control angle calculation of the next half-wave current. The power factor angle ø of the welder can be calculated by using the first phase control angle α and the delay phase 120 ° -150 ° to be used for the first half-wave current according to the following formula (1). The angle α is already stored in the control angle calculation circuit 10 for the next half wave, and the conduction angle δ is extracted by the color extractor 7.

The maximum current value calculation circuit 9 uses the current value I _L extracted by the color extractor 7 and the power factor angle? And the ignition control angle α obtained by the formula (1) in the case of an uncontrolled ignition device. Calculate using the following formula (2).

The next half wave control angle calculation circuit 10 is provided between the ignition circuit 11 and the set circuit 12 connected to the thyristor 3, and the circuit 10 is set for the next half wave stored in the circuit 12. One value is preserved, and the circuit 10 calculates the phase control angle α to obtain a current value corresponding to the current value set by this angle.

The ignition circuit 11 controls the thyristor 3 by receiving the phase control angle α calculated by the calculation circuit 10.

In the control device thus configured, the current value set for each half wave has already been stored in the set circuit 12 before the electric conduction starts. In general, the value of each half wave is always constant during the conduction period, and up to two half waves are used. However, in the beginning of the conduction, about three cycles of upward inclination (six half-waves) are often used to ensure that the work site is melted. In this case, the first half wave starts with a current of 10% -35% of the maximum current value I _LO when using the uncontrolled ignition device and the phase control angle uses 150 ° -120 °.

When the welding start signal is input from the outside, the first half wave of the phase control angle 150 ° -120 ° is applied to the work. In this case, if the power factor angle of the commonly used welding machine is 45 ° -70 °, the welding current will be 10% -35% of the maximum current when the uncontrolled ignition device is used. That is, the present invention is effective in preventing sudden large currents from flowing into the welding transformer by conduction of a large amount of current, and also in preventing dust from adhering to the work site at the beginning of melting of the welding material. If the phase control angle is 150 ° or more, it is difficult to ensure ignition of the thyristor 3. Therefore, the initial current value hardly decreases further.

According to the present invention, as is clearly shown in FIG. 3, the effective current value is controlled within a section where the effective current value is not significantly affected by the change of the power factor angle of the welder (typically about 45 ° -70 °), and the effective current value is uncontrolled ignition. In the case of a device, starting with a relatively small current corresponding to 10% -35% of the maximum current value, such as dust adhesion and the like are removed.

While the welding current flows, the effective current value I _L and the conduction angle δ are located on the full color generator 4 located on the first coil side of the welding transformer 1 or on the second coil side of the welding transformer 1. The calculation signal is retrieved from the annular coil by being stored in the color extractor 7.

The extracted conduction angle δ signaled from the color extractor 7 is input to the power factor calculation circuit 8 and the circuit 8 uses the received conduction angle δ and the ignition control angle α Based on (1), the power factor angle ø is calculated. The practical way to perform this calculation is as follows. In other words, a large power factor (ø) is calculated in advance and a data table is created and stored in advance in an appropriate storage device. The power factor angle is derived by determining the phase control angle α and the conduction angle δ as parameters. This method is very effective for reducing the computation time.

On the other hand, when the current value I _L extracted by the color extractor 7 is input to the maximum current value calculation circuit 9, in the case of the uncontrolled ignition device, the maximum current value is calculated by the phase control angle α calculated by the calculation circuit 10. Circuit 9 calculates using the formula (2) based on the power factor angle (ø) obtained from The above-described method based on the data table can be effectively applied to the calculation work of the circuit 9, thereby reducing the calculation time.

The calculation signals, i.e., the power factor angle ø and the maximum current value I _LO obtained from the calculation circuits 8 and 9 are input to the calculation circuit 19. The circuit 10 calculates the control angle α based on the current device set for the two signals and the next half wave stored in the set circuit 12 and using formula (2). The above-described method according to the data table can also be applied to the calculation work of the circuit 10 to shorten the calculation time.

The ignition circuit 11 is operated by the control angle calculated by the circuit 10 to ignite the thyristor 3. The control operation described above is repeated during the entire welding period.

As is apparent from the above description, the present invention has the following advantages. (1) In a welding machine in which a large amount of current flows through the thyristor, the first half wave of the welding current is delayed by a phase control angle of 120 ° -150 ° so that a large amount in the initial conduction (first half wave or the next half wave) is obtained. It is not necessary to supply the current (60% -70% of the maximum current value), and thus it is possible to eliminate the adhesion of dust which degrades the welding quality.

(2) As clearly shown in Fig. 3, the power factor is related to the change in the ignition angle for the active current error component, that is, the so-called response gain, and thus can compensate for the change in the load power factor compared to the conventional constant current control method. This improves the accuracy of the response.

(3) According to the present invention, the power factor angle when the melted volume is still in an unstable state at the beginning of conduction is not used over the entire welding time. Therefore, the accuracy of the power factor angle itself is increased and full control of constant current is achieved.

Although the present invention has been described above in detail by way of examples, it should be understood that embodiments of the present specification have already been modified in detail, and that the combination and arrangement of parts do not depart from the spirit and scope of the invention as set forth in the claims below. You will be able to modify it within limits.

Claims (4)

A method of controlling the constant current of a resistance welder, the method comprising: extracting current flowing into a first coil or a second coil of a welding transformer; applying a first half wave having a predetermined phase control angle; Extracting the conduction angle, calculating the power factor angle of the resistance welder using the already-conducted conduction angle and the phase control angle, the next half wave based on the already calculated power factor, the already-conducted conduction angle, and the already extracted current value. Calculating a control angle to obtain a current value corresponding to a preset value of the current, circulating the next electric wave through a die thruster to a work site to be welded by the control angle, and controlling the welding time. Constant current control method of a resistance welder, characterized in that consisting of repeating the process. The method of claim 1, wherein the predetermined phase control angle is within about 120 ° -150 °. The method according to claim 2, wherein in the case of an uncontrolled ignition device, another step of calculating a maximum current value is calculated in order to calculate the control angle. The method of claim 3, wherein the preset value of the next half-wave current is used to calculate the control angle.

Images