JPH0438312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an eddy current flaw detection device for detecting flaws in metal materials and foreign substances mixed therein.

"Prior art" In the manufacturing process of copper wire, etc., if foreign objects such as iron pieces are mixed into the copper wire or if there are scratches, this is undesirable as it may cause wire breakage in each wire drawing process. . Therefore, before starting each wire drawing process, it is necessary to inspect the wire for the presence of foreign objects and scratches.

Conventionally, an eddy current flaw detection device has a copper wire 1 running through detection coils La and Lb as shown in FIG. A device has been developed in which scratches and foreign objects are detected based on the output signal between terminals B and D of this bridge circuit. The detection principle of this device is as follows. In other words, if the copper wire 1 passing through the coils La and Lb is not damaged, adjust the bridge circuit in advance so that the output signal between terminals B and D is zero balanced, and then When a scratch or a foreign object passes through the copper wire 1, the zero balance is disrupted due to changes in the eddy current within the copper wire 1 due to this passage, and a detection signal is output. Further, the zero balance adjustment of the AC bridge is performed with the copper wires 1 in the coils La and Lb kept stationary.

"Problems to be Solved by the Invention" By the way, when the copper wire 1 is stationary, the magnetic field generated in the coils La and Lb has a magnetic field distribution as shown by the solid line in Fig. 6, corresponding to the coil length. However, when the copper wire 1 is running,
Due to the drag effect, the base of the distribution curve extends in the traveling direction according to the conveyance speed, resulting in a magnetic field distribution as shown by the broken line in the figure. That is, the magnetic field distribution in the coils La and Lb differs between when the copper wire is stationary for zero balance adjustment and when the copper wire is running for detection.

Due to the shift in the magnetic field distribution due to the drag effect, the eddy currents generated near the coils La and Lb change differently, and as a result, when the conveyance speed is high, the defect-free portion of the copper wire 1 passes through. Even if
An abnormality detection signal may be output.

In other words, conventional eddy current flaw detection devices have the disadvantage of being susceptible to malfunctions due to the influence of the drag effect, and in particular, when the copper wire 1 is conveyed at high speed, the influence of the drag effect becomes more significant, which is a problem. .
In addition, in the conventional eddy current flaw detection apparatus, when a vibration occurs in the copper wire 1 being conveyed, the detection signal is directly affected by the vibration, resulting in a problem that the signal-to-noise ratio deteriorates.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an eddy current flaw detection device that is not affected by the drag effect or the shaking of the inspected material and has an extremely high signal-to-noise ratio.

"Means for Solving the Problems" In order to solve the above-mentioned problems, this invention
In an eddy current flaw detection device that generates an eddy current by the detection coil in a conductor passing through the detection coil and detects a defective part of the conductor from a change in the eddy current, the length direction of the conductor is A pair of detection coils installed along the two sides of the bridge are provided, and when the eddy current in the conductor changes, the bridge becomes unbalanced and two AC bridge circuits are provided to output a detection signal. It is equipped with an arithmetic circuit that adds the detection signals of the AC bridge circuit with opposite polarities.

"Function" If similar eddy current changes occur simultaneously in the vicinity of each of the above detection coils, the addition result of the arithmetic circuit becomes 0 and this change is ignored; on the other hand,
When the eddy current changes with a time difference in the vicinity of each of the detection coils, the addition result of the arithmetic circuit does not become 0, and a signal corresponding to the change in the eddy current is output.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 5 is a bridge circuit similar to the AC bridge circuit shown in FIG.
A copper wire 1 passes through the detection coils L ₁ and L ₂ .
In this case, the detection coils L ₁ and L ₂ are similar to the detection coils La and Lb shown in FIG. 5, respectively.
Further, 6 is an AC bridge circuit similar to the AC bridge circuit 5, and the detection coils La and 6 shown in FIG.
It has detection coils L ₃ and L ₄ similar to Lb. In this case, if the output signal of the AC bridge circuit 5 is (jωL ₁ -jωL ₂ ), then the output signal of the AC bridge circuit 6 is -(jωL ₃ -jωL ₄ ). The output signal is (jωL ₂ −
jωL ₁ ), the output signal of the AC bridge circuit 6 is set to be −(jωL ₄ −jωL ₃ ). The arithmetic circuit 7 includes an AC bridge circuit 5
and 6 are added, and this added signal is output. That is, in the arithmetic circuit 7, the output signals of the AC bridges 5 and 6 are added with opposite polarities. Moreover, the above-mentioned AC bridge circuits 5 and 6
Similar to the AC bridge circuit shown in FIG. 5, zero balance adjustment is performed while the copper wire 1 is stationary.

Next, the operation of this embodiment with the above-described configuration will be explained.

First, make sure that the part of copper wire 1 that has no defects such as scratches is the coil.
While passing through _L1 to _L4 , if there is no drag effect, the output signals of the AC bridge circuits 5 and 6 are both 0, so the output signal of the arithmetic circuit is also 0. However, if there is a drag effect, the zero balance of the AC bridge circuits 5 and 6 will be disrupted, and the output signal will have a magnitude corresponding to the drag effect. In this case, the speed of the copper wire 1 is also near the coils L ₁ and L ₂ .
Since they are also equal near the coils L ₃ and L ₄ , the absolute values of the output signals of the AC bridge circuits 5 and 6 due to the influence of the drag effect are both equal to Δv. Therefore, voltages Δv and -Δv are applied to each input terminal of the arithmetic circuit 7, and as a result, Δv+
(-Δv) is performed, and its output signal becomes 0 without being affected by the drag effect.

Furthermore, when considering the influence of conveyance vibration (shaking) of the copper wire 1, it is found that since the state of conveyance vibration is uniform in any part of the copper wire 1, the coil L ₁ ,
The vibration of the copper wire near L ₂ and the vibration of the copper wire near coils L ₃ and L ₄ are similar, and as a result, the output signals of the AC bridge circuits 5 and 6 due to the influence of the conveyor vibration are always the same. the sizes will be equal. That is, the voltage applied to both input terminals of the arithmetic circuit 7 is:
As in the case described above, the voltages are equal in magnitude and opposite in polarity, and as a result, the output signal of the arithmetic circuit 7 becomes 0 without being affected by the carrier vibration.

As mentioned above, in this embodiment, the output signal of the arithmetic circuit 7 is not affected by drag effects or conveyance vibrations, so when the defect-free portion of the copper wire 1 passes through the coils _L1 to _L4 , In this case, the output signal of the arithmetic circuit 7 is always stable at 0.

Next, the defective part of copper wire 1 is connected to coil L ₁ ~ coil
The operation when passing through L ₄ will be explained.

Since the copper wire 1 is conveyed in the direction of the solid arrow shown in FIG. 1, the defective part is transferred from coil L ₁ to coil L ₂
→ Coil L ₃ → Coil L ₄ They pass in this order.
Then, in the coil through which the defective part passes, an impedance change occurs due to a change in eddy current, and as a result, the zero balance of the AC bridge circuit 5 or AC bridge circuit 6 is lost, and the impedance from each AC bridge circuit 5, 6 is lost. A detection signal of a voltage value corresponding to the change is output. In this case, the impedance changes of each coil do not occur at the same time, but occur sequentially according to the above-mentioned passing order, so the same voltage of opposite polarity is not supplied to both input terminals of the calculation circuit 7, and as a result, the calculation The circuit 7 outputs a detection signal corresponding to the passage of the defect. Here, FIG. 2 shows an example of the output signals of the AC bridge circuits 5 and 6 and the output signal of the arithmetic circuit 7 corresponding to the passage of a defect. In FIG. 2, A and C indicate the positions of coils L ₁ and L ₂ and coils L ₃ and L ₄ , respectively, B and D indicate the output signals of AC bridge circuits 5 and 6, respectively, and E indicates the calculation The output signal of circuit 7 is shown. As shown in this figure, when the defective part passes from left to right, first a sinusoidal detection signal is output from the AC bridge circuit 5, and then,
The AC bridge circuit 6 outputs a sinusoidal detection signal having a polarity opposite to that of the detection signal, partially overlapping.
The output signal of the arithmetic circuit 7 is a composite waveform of the waveforms shown in FIG. .

In the above-described embodiment, two sets of detection coils are provided, but for example, four sets may be provided as shown in FIG. 3. 10 and 11 shown in this FIG.
AC bridge circuits 12 and 13 are each configured similarly to AC bridge circuits 5 and 6, and arithmetic circuits 12 and 13 are each configured similarly to arithmetic circuit 7. In addition, the coils _L1 to _L4 , the AC bridge circuit 5,
6 and the arithmetic circuit 7 constitute a correction detection means 20, which includes coils _L5 to _L6 , AC bridge circuits 10, 1
1 and the arithmetic circuit 12 constitute a correction detection means 21.

According to the above-described configuration, even if an in-phase error occurs in the arithmetic circuits 7 and 12, this error is canceled out by the arithmetic circuit 13.
This provides the advantage of an extremely high signal-to-noise ratio. Also,
Based on the same principle, the SN ratio can be further improved by further increasing the number of detection coils.

"Effects of the Invention" As explained above, according to the present invention, an eddy current is generated by the detection coil in a conductor passing through the detection coil, and from a change in this eddy current, the conductor In an eddy current flaw detection device that detects a defective part of a conductor, a pair of detection coils provided along the length of the conductor are used as two sides of a bridge, and when the eddy current in the conductor changes, the balance of the bridge is lost. In addition to providing two AC bridge circuits that output detection signals at the same time, an arithmetic circuit that adds the detection signals of each of the AC bridge circuits with opposite polarities is also provided. It is possible to provide an eddy current flaw detection device that is not affected by vibration and has an extremely high signal-to-noise ratio.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a waveform diagram showing waveforms during defect detection in the same embodiment, and Fig. 3 shows the configuration of a modified example of the same embodiment. 4 is a schematic configuration diagram showing the configuration of a conventional eddy current flaw detection device, FIG. 5 is a circuit diagram showing the configuration of an AC bridge circuit, and FIG. 6 is a characteristic diagram showing the magnetic distribution of the detection coil. . 1...Copper wire (conductor), 5, 6, 10, 11...
AC bridge circuit, 7, 12... Arithmetic circuit, 2
0, 21...Correction detection means.

Claims (1)

[Scope of Claims] 1. An eddy current flaw detection device that generates an eddy current by the detection coil in a conductor passing through the detection coil, and detects a defective part of the conductor from a change in the eddy current. , an AC bridge circuit in which a pair of detection coils provided along the length direction of the conductor are used as two sides of the bridge, and when an eddy current in the conductor changes, the balance of the bridge is disrupted and a detection signal is output. An eddy current flaw detection device comprising: two pieces of the AC bridge circuit, and an arithmetic circuit that adds the detection signals of the respective AC bridge circuits with opposite polarities.