JP3274157B2 - Method and apparatus for measuring secondary resistance in resistance welding control - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a change in resistance between electrode tips corresponding to electrode tip exchange and a change in resistance of a welding cable corresponding to welding cable exchange, and a change in a secondary resistance of a welding transformer. The present invention relates to a method for measuring a secondary resistance value of a welding transformer from a primary side of a welding transformer in order to perform an adaptive control, an electrode tip replacement, and a cable diagnostic function based on the above.

[0002]

2. Description of the Related Art Conventionally, it is necessary to automatically increase the current by compensating for a decrease in welding current density due to wear of an electrode tip, or to replace a welding cable in response to a partial disconnection of the welding cable. As a method of measuring or estimating a change in the secondary resistance value of the welding transformer, there is a method of accurately detecting a change in load power factor during welding and relatively detecting a change in resistance value.

[0003]

However, the change in the load power factor is for detecting the relative change between the resistance component and the reactance component of the load impedance, and is not for detecting the change in the resistance value itself. Therefore, it cannot be used for a welding machine where the inductance component changes due to the kicking of the welding cable due to the repulsive force caused by the welding current, or a welding machine where the inductance changes depending on the welding location. However, since the magnitude of the change in the resistance value and the detection accuracy vary depending on the magnitude of the resistance, there is a drawback in that a number of parameters must be adjusted by cut-and-try in practical use. Therefore, an object of the present invention is to attach a special additional device to the outside of the resistance welding control device when calculating a resistance value change between electrode tips corresponding to electrode tip replacement and a resistance value change of a welding cable corresponding to welding cable replacement. Without welding transformer 2
It is an object of the present invention to provide a secondary resistance measuring method in resistance welding control that can easily measure a secondary resistance value from a primary side of a welding transformer.

[0004]

A resolution means for] That is, the present invention measures the welding transformer primary voltages V ₁ and the primary current I ₁ at the timing of the rate of change of primary current in the welding 0, for example,
Di / dt to enter the primary current I ₁ welding transformer
= 0, when the di / dt = 0 signal is generated from the detection circuit, the primary voltage V ₁ and the primary current I ₁ of the welding transformer are sampled and held and input to the computer, and the secondary voltage is V ₂ , The secondary current is I ₂ , and the turns ratio of the welding transformer is m
From the equation V ₂ = V ₁ ÷ m I ₂ = I ₁ × m, the secondary resistance R ₂ of the welding circuit is calculated as follows: R ₂ = V ₂ / I ₂ = V ₁ / (I ₁ × m ² ) In the secondary resistance measurement method and apparatus in the resistance welding control obtained by calculating the following.

[0005]

In the resistance welding control constructed as described above, 2
In the case of the secondary-side resistance measurement method, in the RL AC circuit, there is a relation of V = R ・ i + L ・ di / dt between the voltage V and the resistance R, the inductance L, and the current i. Therefore, at the moment of di / dt = 0, R =
The relationship of V / i is established, and the component of the inductance L is not included. That is, by sampling the voltage and the current at the moment when the current change rate is 0, the resistance value of the RL AC circuit can be easily obtained by the following equation. From V ₂ = V ₁ ÷ m I ₂ = I ₁ × m, the secondary resistance R ₂ of the welding circuit is become.

The resistance value obtained here is the sum of the internal resistance of the primary cable and the welding transformer, the resistance value of the secondary cable, the welding gun, the work to be welded, and the like.
The internal resistance of the transformer is constant during energization except for a small change in resistance value due to self-heating.Therefore, if the difference between the resistance values obtained per unit time during a series of welding is calculated, In addition, the deterioration amount of the welding cable can be detected by determining the relative change amount of the welding transformer secondary-side resistance value over a long period of time.

[0007]

As a result, according to the present invention, when a change in resistance between electrode tips corresponding to electrode tip replacement or a change in resistance of a welding cable corresponding to welding cable replacement is determined, a special method is provided outside the resistance welding control device. The resistance of the secondary side of the welding transformer can be easily measured from the primary side of the welding transformer without installing any additional equipment, and only the resistance value of the secondary side impedance of the welding circuit is detected as an absolute value. Therefore, the inductance changes during welding,
Even when the inductance is different for each welding point, the welding control operates accurately, and even if the power supply voltage changes, there is an effect that a stable operation can be secured without being affected by the change. Further, there is an effect that the present invention can be used not only for an application utilizing a change in resistance between electrodes during a series of welding but also for an application utilizing a change in resistance of the entire welding machine at each welding point.

[0008]

Next, the structure of an embodiment of the present invention will be described with reference to the drawings. Figure 1 detects a secondary resistance value of the pressure is connected to the resistance welding control apparatus 3 for conducting a welding current to the welding subject 2 weld transformer WT between electrode tips 1,1 at the primary side, 2 FIG. 3 is a block circuit diagram of the secondary-side resistance measuring device, and FIG.
The secondary current transformer CT is an air-core CT for detecting a current flowing to the primary side of the welding transformer WT. A differential signal of an actual current waveform is input to this circuit, and this differential signal is integrated by an integrating circuit I.
The current waveform is restored by C. The primary voltage input is level-adjusted by the amplifier circuit AMC with a signal obtained by stepping down the welding power supply by the measuring transformer MT, and the current and voltage signals are converted from the primary current transformer CT waveform by the sample-and-hold circuit SHC to di. / Dt = 0 The sampling circuit is sampled and held for each timing signal of di / dt = 0 detected by the detection circuit DDC. The timing signal is input to the microcomputer MC to generate an interrupt, and the A / D converter ADC generates the interrupt. A / D converted current and voltage data are sampled, and the secondary resistance value R2 of the welding transformer WT is obtained from the sampled data.
Is calculated by the microcomputer MC according to the following equation.

[0009] The difference ΔR ₂ in the resistance value in one welding cycle from the maximum value of the resistance value R to the end of welding is also calculated.

Next, the operation of this embodiment will be described.
In the case of the secondary resistance measurement method in the resistance welding control configured as described above, in the RL AC circuit, V = R ・ i + L ・ di / dt between the voltage V, the resistance R, the inductance L, and the current i. There is a relationship. Therefore, di / dt = 0 indicated by x in FIG.
At the moment, the relationship of R = V / i is established, and the component of the inductance L is not included. That is, by sampling the voltage and the current at the moment when the current change rate is 0, the resistance value of the RL AC circuit can be easily obtained by the following equation. From V ₂ = V ₁ ÷ m I ₂ = I ₁ × m, the secondary resistance R ₂ of the welding circuit is become.

The resistance value R ₂ obtained here is the sum of the internal resistance of the welding transformer WT and the resistance value of the secondary cable, the welding gun of the electrode tips 1, 1 and the workpiece 2 to be welded. The internal resistance of the transformer is constant during energization, except for a small change in resistance value due to self-heating. Therefore, the difference between the resistance values R ₂ obtained for each unit time during a series of welding can be calculated. , The amount of change in the voltage between the electrode tips 1 and 1 during welding can be obtained.
By determining the relative change amount of the secondary-side resistance value, it is possible to detect deterioration of the welding cable and the like. As a result, the electrode tips 1, 1 corresponding to the replacement of the electrode tips 1, 1
In determining the change in resistance [Delta] R ₂ and the resistance value changes in welding cable corresponding to the welding cable replacement [Delta] R ₂ between the secondary side resistance welding transformer WT without attaching special additional equipment to the outside of the resistance welding control apparatus 3 can be easily measured values R ₂ from the primary side of the welding transformer WT, moreover, in order to detect only the resistance value R ₂ of the secondary side impedance welding circuit in absolute value, the inductance is changed during the welding Also, even when the inductance differs for each welding point, the welding control operates accurately, and even if the power supply voltage changes, there is an effect that a stable operation can be secured without being affected by the change. Further, the present invention can be used not only for an application utilizing a change in resistance value between the electrode tips 1 and 1 during a series of welding, but also for an application utilizing a change in resistance value of the entire welding machine at each welding point.

[Brief description of the drawings]

1 is a secondary resistance R ₂ detection block circuit diagram of a resistance welding control circuit.

FIG. 2 is a waveform diagram of a primary welding current and a welding voltage of a resistance welding control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode tip 2 Workpiece 3 Welding control device CT Primary current transformer WT Welding transformer IC Integrator MT Transformer for measuring instrument MC Microcomputer AMC Amplification circuit SHC Sample hold circuit DDC di / dt = 0 Detection circuit ADC A / D conversion vessel

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-229482 (JP, A) JP-B-5-16551 (JP, B2) JP-B 5-49952 (JP, B2) Yoneichiro Sakaki et al. ： University course electrical circuit (1) Second edition, page 85, Ohmsha, published on September 20, 1980 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 27/00-27/32 B23K 11/24 B23K 11/25

Claims (2)

(57) [Claims] The rate of change of the primary current of the welding transformer is zero.
, The primary voltage V ₁ and the primary current I ₁ , the welding transformer
[R ₂ = V ₁ / (I ₁ × m ² )]
A secondary resistance measuring method in resistance welding control for obtaining a secondary resistance of a welding transformer according to the following . 2. A method for measuring a primary voltage of a welding transformer.
Measures the primary voltage of the welding transformer and the secondary voltage measuring means
A primary-side current measuring means, and a computer.
The computer measured 1 by the primary side current measuring means.
When the change rate of the secondary current is 0, the
Output from the primary side voltage V ₁ and primary side current measuring means.
Sampling and holding of the primary current I ₁
Primary voltage V ₁ and primary current I ₁ , welding
Based on the turns ratio m of the transformer, the formula [R ₂ = V1 / (I ₁ ×
m ² )] to determine the secondary resistance of the welding transformer
Secondary side resistance measurement device for welding control.