KR100266040B1 - Apparatus for testing welding state of welder - Google Patents

Abstract

PURPOSE: A welding quality deciding device is provided to decide the welding quality of a spot welder using the power factor angle of the spot welder. CONSTITUTION: A welding quality deciding device of a spot welder, which controls effective current fed to electrodes(2-1,2-2) by controlling the firing angle of thyristors, comprises a communication detecting unit(5) that detects a communication state between electrodes; a first table(71) that stores effective current about the firing angle in a power factor angle; a second table(72) that stores the information of the power factor angle about the firing angle and a communicating angle; a controller(6) that detects the communicating angle of the thyristors according to the communicating state of the communication detecting unit, detects the power factor angle corresponding to the firing angle and the communicating angle by using the second table and detects the firing angle corresponding to the power factor angle by using the first table to supply effective current to the electrodes; and an artificial neural net(8) that decides welding quality by the change of the power factor angle.

Description

APPARATUS FOR TESTING WELDING STATE OF WELDER

The present invention relates to an apparatus for evaluating the quality of a weld (hereinafter, referred to as weld quality) by a spot welder, and more particularly, to an apparatus for evaluating weld quality using a power factor angle of a spot welder. will be.

Spot welding melt-bonds the contact parts of the base material by Joule heat using contact and compression resistance generated between the base materials by supplying a large current (8,000 ~ 30,000A) while pressing two or more thin sheets by air pressure between the electrodes. It is a welding method to obtain a simple but clean joint.

The three basic elements of spot welding are pressurization, energization time and energization. Therefore, the spot welding control device must sequentially perform operations such as pressurized cylinder operation, initial pressurization, energization, holding, and cylinder depressurization for the welding start request.

In spot welding, weld quality is indicated by weld marks remaining on the surface, weld size, strength, internal defects, and cracking of the metal surface as the welding base material. Among them, the weld marks and the flare of the plate are the externally exposed appearance quality, and the weld strength and the internal defect are the items directly related to the quality of the actual welded structure. The weld quality generally refers to the weld strength rather than the externally revealed quality, and the evaluation method can be roughly classified into a fracture test method and a non-destructive test method.

In order to inspect the weld quality accurately, it is inevitable to cut the weld and observe and measure the metal structure of the melt. However, such a fracture inspection method has a limitation in inspection since the inspection object is sampled, and it is a general trend to grasp the welding state by examining welding variables that qualitatively indicate the formation process of the molten metal.

What was conceived as a method of determination of weld quality using welding parameters is a method of using the dynamic resistance characteristic during welding. In spot welding, the welding material undergoes a change in resistance of the welding material (referred to as dynamic resistance), and the change state of the resistance reflects the formation of the molten portion. Therefore, by measuring the copper resistance, it is possible to detect the size and the like of the melted portion that can exhibit weld quality.

In the related art, the size of the melted portion was estimated by learning the dynamic resistance characteristics of the artificial neural network.

On the other hand, in order to measure the copper resistance, conventionally, a method of measuring the resistance value using the Ohm's law is measured by measuring the potential difference between the welding electrodes and the amount of energized current in half cycle units. In other words, the copper resistance is obtained by dividing the voltage signal at both ends of the electrode that changes during the welding process into a current signal and changing the curve for each welding cycle. Therefore, there is a problem that a conventional apparatus for determining weld quality using an artificial neural network requires a separate device for measuring voltage and current at both ends of an electrode.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a welding quality judging device capable of judging welding quality using a power factor angle in a spot welding machine.

1 is a schematic block diagram of a spot welder.

2 is a schematic block diagram of a spot welder with variable taps.

3 and 4 are diagrams for showing the phase difference between voltage and current in an alternating current circuit having resistance and inductance.

5 and 6 are diagrams for illustrating a method of controlling current trauma in a spot welder using a thyristor.

7 is a block diagram of the welding quality judgment device of the spot welder according to the present invention.

8 and 9 are diagrams showing examples of information stored in a table constituted in a welding quality judgment device of a spot welder according to the present invention.

10 is an operation flowchart of the welding quality judgment device of the spot welder according to the present invention.

* Explanation of symbols for main parts of the drawings

2-1, 2-2: electrode 5: energization detecting unit

6: control device 7: ROM

8: artificial neural network

The present invention for achieving this object is a device for determining the weld quality in a spot welder that controls the amount of effective value current applied to the electrode while controlling the ignition angle of the thyristors, connected to the electrode to detect the energized state between the electrodes An energization detection unit; A first table storing an effective current for an ignition angle at a predetermined power factor; A second table storing power factor angle information on the ignition angle and the energization angle; In response to the energization state of the energization detector, the energization angle of the thyristors is detected, and a power factor angle corresponding to the ignition angle and the energization angle of the thyristors is detected using a second table, and a current having a predetermined effective value is applied to the electrode. Control means for detecting the ignition angle corresponding to the detected power factor angle using the first table to ignite the thyristor; It includes an artificial neural network that receives the power factor angle of the control means, and determines the weld quality in accordance with the change of the power factor angle.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, a point welder for carrying out the present invention will be described schematically.

1 shows a schematic diagram of a welder. As shown, currents are provided to the electrodes 2-1 and 2-2 for welding the member 1 through the transformer T.

In this case, the power source used for spot welding is AC 220V, 380V, 440V, which is generally lowered by a large turns ratio transformer to obtain a high current. The relationship is as follows.

Where V1, I1, N1: primary voltage, current and number of turns of transformer

V2, I2, N2: secondary voltage, current and number of turns of transformer

That is, since the primary and secondary power of the transformer is always constant, the voltage on the primary side is dropped by a transformer to generate a high current on the secondary side. Therefore, the voltage applied between the two electrodes on the secondary side is lowered to about several volts. Since the magnitude of the current that can be obtained from the secondary side is determined by the turn ratio (N2 / N1) of the transformer, the conventional welding machine is provided with the variable taps 3-1, 3-2, and 3- as shown in FIG. 3) was installed and the amount of energization was adjusted by changing the turn ratio with the switch (4).

When the tap is used as shown in FIG. 2, welding can be performed by varying the amount of current, but as shown, the step of varying the current is limited, and inconveniences in use such as manually rotating the tab are involved. .

In order to alleviate this inconvenience, a method of controlling the amount of current by controlling the energization time of the AC power source through a power element (Thyrister, SCR) has been proposed.

Specifically, the welder has impedances of the resistance component R and the inductance component L, as shown in FIG. 3. Accordingly, as shown in FIG. 4, a current i having a phase difference with respect to the welding voltage V flows, and this phase difference θ is referred to as a power factor and COSθ is referred to as a power factor.

As a method for controlling the current (i) in the welding machine, the thyristors (SCR1, 2) are used as shown in FIG. 5, and the signal (i) at the gate terminal of the die Lister (SCR1, 2) as shown in FIG. _The application of a _gate is called firing. The current i is provided from the firing angle α, and the provision of the current i ends at the extinction angle β. The extinction angle β depends on the characteristics of the welder circuit. The conduction angle λ means the angle driven from the ignition angle α to the extinction angle β, that is, the thyristor.

Therefore, the user can control the amount of current i by adjusting the ignition angle α when the power factor angle θ is determined, but the power factor angle θ changes even during welding (the shape of the welded material and the welded material). The length and shape to be inserted into the pocket, variations in resistance components during welding, etc.).

Here, as described above, the spot welding system can be idealized by R and L circuits. In the idealized welding machine, voltage and current have the following relationship, and the power factor angle θ is varied.

The power factor (θ) is

R: resistance of the whole welder

L: Inductance of the whole welding machine

ω: angular velocity of input power

Here, the resistance R and the inductance L may vary depending on the type of welding operation. The resistance (R) depends on the specimen located between the two electrodes of the welder, that is, the type and thickness of the welding member, and during the welding, the molten part has a sudden temperature change, so the resistance value depends on the temperature and specific resistance constant of the specimen material. Also changes.

Inductance (L) also varies depending on the shape and size of the specimen introduced between the electrodes, but maintains the same value during welding because the same specimen is located between the electrodes.

라는 일정한 값을 가진다. 따라서, 용접도중 변동하는 요인은 저항(R) 뿐이라는 결론을 내릴 수 있다.Angular velocity (ω) is the angular velocity of the welding power source.

Has a constant value. Therefore, it can be concluded that the only factor that changes during welding is resistance (R).

Since the change in the resistance R mainly occurs between the electrodes, the amount of change in the resistance R can be regarded as the change in resistance between the electrodes.

Here, Equation 1 described above may be changed as Equation 2.

In Equation 2, θ is a power factor angle monitored every half cycle as described above, and is a value calculated using an ignition angle and an energization angle as described below. That is, ω L is a constant, and the change in cot θ can be thought of as a change in resistance R. The determination of weld quality by an artificial neural network can use the power factor angle θ.

7 is a schematic block diagram of an apparatus according to the present invention.

As shown, the current provided to the electrodes 2-1 and 2-2 through the transformer T is controlled by the signal i _gate applied to the gates of the thyristors SCR1 and SCR2. An energization detection unit 5 is configured at one end of the electrode 2-1 or 2-2, and the energization detection unit 5 detects an energization state between the electrodes 2-1 and 2-2 to control the device 6. It is configured to apply to.

The control device 6 is composed of a microprocessor and the like, and is configured to adjust the ignition angle α of the thyristors SCR1 and 2 in response to the set current amount I _SET input from the user. The control device 6 uses the information of the tables 71 and 72 in the ROM 7 according to the energization state of the energization detector 6 to adjust the ignition angle α.

In the table 71, as shown in FIG. 8, the effective value current I _RMS for the ignition angle α is stored at a predetermined power factor angle θ.

Further, in the table 72, as shown in FIG. 9, information on the power factor angle θ with respect to the ignition angle α and the conduction angle λ is stored.

Information according to FIG. 9 can be obtained by solving the relationship between the power factor angle θ and the ignition angle α by numerical analysis, as shown in Equation 3 below.

Moreover, the artificial neural network 8 is comprised in the control apparatus 6 of this invention, The control apparatus 6 detects the change of the power factor angle (theta), and applies it to the artificial neural network 8, as mentioned later, The artificial neural network 8 determines the weld quality by using the variation of the power factor angle θ.

10 shows a flowchart performed by the control device 6 in the device having the above-described configuration.

As shown in the drawing, the control device 6 reads the set current value and the welding cycle n at the time of its initial driving, and sets the ignition angle α corresponding to the desired effective value current value i _RMS in the table 71. Read out (step 12). The power factor angle θ at this time can be set to any value.

The control device 6 that reads the ignition angle α in step 12 applies the signals i _gate to the thyristor SCR at the read ignition angle α, thereby applying the electrodes 2-1 and 2-2. ) And a current is supplied (step 13), and it is judged whether the electricity supply between the electrodes 2-1 and 2-2 has ended by the output of the energization detecting section 5 (step 14).

If energization is detected in step 14, the control device 6 can easily detect the energization angle [lambda], and the thus applied energization angle [lambda] and ignition angle [alpha] to the table 72. Substituting the power factor angle θ at this time can be detected (step 15).

The control device 6 having detected the power factor angle θ detects the ignition angle α corresponding to the desired current value i _RMS and the detected power factor angle θ i in the table 71 (step 15). .

Then, the control device 6 increases the arbitrary variable i by 1 (step 16) and determines whether the increased variable i is equal to or greater than the welding cycle n (step 17). End the welding process (step 18).

Then, the control device 6 applies this stored power factor angle θ i to the artificial neural network 8 to cause the artificial neural network to determine the weld quality (step 19), and the weld quality estimated by the artificial neural network 8. Output is via an output device (not shown) or the like (step 20).

That is, in the present invention, when the weld quality of the spot welding machine is determined by using an artificial neural network, it is determined by using the power factor angle θ, not using dynamic resistance. The quality can be judged.

Claims (1)

An apparatus for judging weld quality in a spot welder that controls the amount of effective value current applied to an electrode while controlling the ignition angle of the thyristors, An energization detector connected to the electrode to detect an energization state between the electrodes; A first table storing an effective current for an ignition angle at a predetermined power factor; A second table storing power factor angle information on the ignition angle and the energization angle; Detects the energization angle of the thyristors corresponding to the energization state of the energization detector, detects the power factor angle corresponding to the ignition angle and the energization angle of the thyristors using the second table, the current of the preset effective value Control means for detecting an ignition angle corresponding to the detected power factor angle by using the first table so as to be provided to the electrode and igniting the thyristors; And a artificial neural network receiving the power factor angle of the control means and determining the weld quality according to the change of the power factor angle.

Images