JPS6236532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic foreign matter detection device that detects magnetic foreign matter mixed in a non-magnetic material.

In the manufacturing process of copper wire (non-magnetic material), etc., if non-magnetic foreign matter such as iron pieces is mixed into the copper wire, this will cause wire breakage in each wire drawing process. Therefore, it is necessary to inspect the presence or absence of magnetic foreign matter in advance before each wire drawing process or the like.

Conventionally, the following methods have been adopted to inspect this magnetic foreign material. That is, as shown in FIG. 1, the copper wire 1 is run at a high speed, for example, V=900 m/min, in a DC high magnetic field H _p . Further, a detection coil 2 is arranged along the traveling route of the copper wire 1 in the DC high magnetic field H _p . Then, a magnetic foreign substance 3 is found in the copper wire 1.
If this magnetic foreign object 3 passes through the magnetic field H _p , the magnetic flux φ in the detection coil 2 will change, and as a result, the detection coil 2 will have e=-Ndφ/dt...( 1) However: N is the number of turns of detection coil 2.

An electromotive force is generated. The magnetic foreign object 3 is detected based on the electromotive force generated in the detection coil 2.

By the way, a problem with the above-described method of detecting magnetic foreign matter is noise caused by the vibration of the copper wire 1. That is, when the copper wire 1 in the magnetic field _Hp vibrates, an eddy current is generated in the copper wire 1, and this eddy current changes the magnetic flux φ in the detection coil 2, and a noise voltage is generated in the detection coil 2. . Such noise can be roughly divided into the following two types. Part 1
is the noise generated when the copper wire 1 vibrates with a relatively long wavelength (hereinafter referred to as long wavelength noise)
This long wavelength noise is relatively low frequency noise. The second noise is noise (hereinafter referred to as traveling wave noise) generated by a traveling wave with a short wavelength occurring in the copper wire 1, and this traveling wave noise has a relatively high frequency. Incidentally, the frequency components of the two types of noise mentioned above and the frequency components of the detection signal generated by the iron piece 3 are shown in FIG. In this figure, curve A shows the frequency component of long wavelength noise, curve B shows the frequency component of the detection signal, and curve C shows the frequency component of traveling wave noise. Furthermore, actual noise is a complex mixture of the two types of noise described above. Due to these two types of noise, the magnetic foreign object detection method using one detection coil shown in Fig. 1 has a practically sufficient detection ability, or in other words, a satisfactory S/N (signal component to noise component ratio). can't get it.

Therefore, conventionally, various configurations have been considered in order to remove these noises. For example, the third
The figure shows detection coils 2a and 2b arranged at different positions along the travel path of copper wire 1, and these detection coils 2a and 2b are differentially coupled.This configuration eliminates long wavelength noise. It is possible to do so. That is, suppose that the copper wire 1 vibrates, and this vibration generates a noise signal as shown in FIG. 4A in the detection coil 2a, for example. In this case, assuming that the wavelength of the vibration of the copper wire 1 is relatively long, a signal having the same phase as the signal shown in FIG. 4A is also generated in the detection coil 2b at approximately the same time (see FIG. 4B). Since the detection coils 2a and 2b are differentially coupled, these noise signals are mutually canceled within the detection coils 2a and 2b and are not output to the outside. By adopting such a configuration, the long wavelength noise is reduced to 1/10 to 1/1 compared to the case of one detection coil shown in Figure 1.
It is possible to set it to 20.

However, even with the above-described configuration, it is impossible to remove traveling wave noise. That is,
When a traveling wave with a short wavelength is generated in the copper wire 1, the noise signals generated in the detection coils 2a and 2b by this traveling wave are out of phase as shown in Figure 5 A and B. . Therefore, it is impossible to cancel these noise signals by differential coupling.

FIG. 6 shows an example of a conventional configuration in which the configuration shown in FIG. 3 is further improved so that traveling wave noise can also be removed.
A copper sleeve 4 is inserted between the sleeve 2b and the sleeve 2b. In this figure, when the copper wire 1 vibrates at a high frequency and this generates a noise signal in the detection coils 2a, 2b, the energy of this noise signal is consumed to cause a ring current to flow in the sleeve 4, and therefore , is not output from both terminals of the detection coils 2a and 2b. (i.e. 2 of the transformer
The result is the same as when the next side is shorted. )on the other hand,
Since the detection signal of the magnetic foreign object 3 has a frequency lower than that of traveling wave noise, it is not canceled by the annular current flowing through the sleeve 4, and is outputted from both terminals of the detection coils 2a and 2b. Further, long wavelength noise is canceled by the differentially coupled detection coils 2a and 2b. In this way, in the configuration shown in FIG.
It is possible to remove both long wavelength noise and traveling wave noise. However, this configuration requires the sleeve 4 and has the drawback of complicating the mechanism.

In view of the above-mentioned circumstances, the present invention is capable of removing long-wavelength noise and almost completely removing traveling wave noise. The present invention provides a device for detecting magnetic foreign matter in magnetic materials, which includes:
A second detection coil and first to third arithmetic circuits are provided, and both long wavelength noise and traveling wave noise are removed from the first to third arithmetic circuits.
This is characterized in that it is electrically canceled by a third arithmetic circuit.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a block diagram showing the configuration of a magnetic foreign object detection device according to the present invention. In this diagram,
Copper wire 11 (non-magnetic material) running in DC high magnetic field H
First and second detection coils 12a and 12b are arranged at mutually shifted positions along the traveling route of the vehicle. These detection coils 12a,
Each output of 12b is supplied to the in-phase amplifier 14 and the inverting amplifier 15 of the first arithmetic circuit 13, respectively. The in-phase amplifier 14 in-phase amplifies the output of the detection coil 12a, and connects one input terminal of the adder circuit 16 and the high-pass filter (hereinafter referred to as
(abbreviated as HPF) 18. The inverting amplifier 15 inverts and amplifies the output of the detection coil 12b and supplies it to the other input terminal of the adder circuit 16 and the HPF 19. The adding circuit 16 adds the respective outputs of the in-phase amplifier 14 and the inverting amplifier 15 and supplies the addition result to one input terminal of the adding circuit 23 of the third arithmetic circuit 20 . The second arithmetic circuit 17 is HPF1
8 and 19, and an adder circuit 22 that adds the respective outputs of the HPFs 18 and 19. In this case, the cutoff frequencies of the HPFs 18 and 19 are both the frequency f _c at the intersection of curves B and C shown in FIG. Further, the output of the adder circuit 22 is supplied to the inverter circuit 21 of the third arithmetic circuit 20. The inverting circuit 21 inverts the output of the adding circuit 22 and supplies it to the other input terminal of the adding circuit 23. Addition circuit 23
adds the output of the inversion circuit 21 and the output of the addition circuit 16, and outputs the addition result to a subsequent signal processing circuit (not shown).

In the above configuration, the detection coils 12a, 12
b and the first arithmetic circuit 13 constitute a differential bridge circuit, and this circuit configuration makes it possible to remove long wavelength noise. That is, when the copper wire 11 vibrates at a relatively long wavelength, and as a result, in-phase noise signals shown in FIG. 8A and 8B are generated in the detection coils 12a and 12b, respectively. and is amplified by the inverting amplifier 15, resulting in the signals shown in FIG. 8C and D. In other words, the outputs of the in-phase amplifier 14 and the inverting amplifier 15 are out of phase with each other. When these outputs are added by the adder circuit 16, the output of the adder circuit 16 becomes approximately zero as shown in FIG. 8E. In this way, the long wavelength noise generated in each of the detection coils 12a and 12b does not appear at the output end of the adder circuit 16.

On the other hand, when the iron piece 25 (magnetic foreign matter) mixed in the copper wire 11 passes through the detection coils 12a and 12b in sequence, detection signals with shifted phases as shown in FIG. 9 A and B are generated in the detection coils 12a and 12b, respectively. do. These detection signals are each input to an in-phase amplifier 14.
and is amplified by the inverting amplifier 15, resulting in the signals shown in FIG. 9C and D. When these signals are added by the adder circuit 16, the adder circuit 16 outputs the signal shown in FIG.
That is, the iron piece 25 is connected to the detection coils 12a, 312.
When passing through b sequentially, the ninth
The magnetic foreign object detection signal shown in Figure E is obtained.

Next, removal of traveling wave noise will be explained. A traveling wave with a short wavelength is generated in the copper wire 11, and when this traveling wave passes through the detection coils 12a and 12b sequentially, the detection coils 12a and 12b produce high-frequency noise with a phase shift shown in FIG. As a result, the in-phase amplifier 14 and the inverting amplifier 15 output the signals shown in FIG. 10C and D, respectively. Since these signals are each supplied to the adder circuit 16, the adder circuit 16 outputs the signal shown in FIG.
The signals shown in Figure 0 C and D are HPF 18 and 1, respectively.
9 to the adder circuit 22, the adder circuit 22 outputs the signal shown in FIG.
In this case, the signals shown in FIG. 10 E and F are substantially the same. Then, the output of the adder circuit 22, that is, the signal shown in FIG.
When added to the output of the adder circuit 16 (FIG. 10E), the output of the adder circuit 23 becomes approximately zero as shown in FIG. 10H. That is, the addition circuit 23
No traveling wave noise appears in the output.

On the other hand, the iron piece 25 in the copper wire 11 is connected to the detection coil 12.
When passing through a and 12b sequentially, as mentioned above,
The signal shown in FIG.
At this time, at the same time, each output of the in-phase amplifier 14 and the inverting amplifier 15 (FIG. 9 c, d) is
However, these outputs are not supplied to the adder circuit 22 because their frequencies are lower than the respective cutoff frequencies of the HPFs 18 and 19, and therefore the outputs of the adder circuit 22 and the inverting circuit 21 The outputs of both become zero. As a result, the output of the adder circuit 16 is output from the output end of the adder circuit 23. In this way, the magnetic foreign object detection signal shown in FIG. 9E is obtained at the output end of the adder circuit 23.

As described above, the magnetic foreign object detection device according to the present invention uses the first calculation circuit 13 to remove long wavelength noise, and the second and third calculation circuits 17 and 20 to remove traveling wave noise. are doing.

In addition, although the inverting amplifier 15 is used in the above embodiment, an in-phase amplifier is used instead,
Exactly the same effect can be obtained even if a subtraction circuit is used for each of the addition circuits 16 and 22. Further, although the inverting circuit 21 is used in the above embodiment, the same effect can be obtained by omitting this circuit and replacing the adding circuit 23 with a subtracting circuit. Further, the inverting circuit 21 may be inserted on the output side of the adding circuit 22.

For reference, the experimental results of the example shown in FIG. 7 are shown in FIG. 11. In this figure, the vertical axis is the S/N, and the horizontal axis is the size (mmφ) of the iron piece 25. In addition, in this experiment, a copper wire of 8 mmφ was used.
It is running in a magnetic field at a speed of 900m/min.

As explained above, according to the present invention, since both long wavelength noise and traveling wave noise are electrically canceled, traveling wave noise can be almost completely eliminated, and the ability to detect magnetic foreign objects is improved compared to that of the present invention. It can be much improved compared to the previous one.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the method of detecting magnetic foreign matter in non-magnetic materials, and Figure 2 conceptually shows the frequency components of noise generated when detecting magnetic foreign matter and the frequency components of the magnetic foreign matter detection signal. Figures 4 and 5 are waveform diagrams for explaining the operation of the device shown in Figure 3, respectively. 7 is a diagram showing another example of the configuration of a conventional magnetic foreign object detection device, FIG. 7 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
10 are waveform diagrams for explaining the operation of the embodiment shown in FIG. 7, and FIG. 11 is a diagram showing experimental results of the embodiment. 11... Copper wire (non-magnetic material), 12a... First detection coil, 12b... Second detection coil, 13
...first arithmetic circuit, 17...second arithmetic circuit,
20...Third arithmetic circuit.

Claims (1)

[Claims] 1. A non-magnetic material is caused to run in a DC magnetic field, and magnetic foreign matter mixed in the non-magnetic material is detected based on changes in the DC magnetic field caused by the magnetic foreign matter. In the magnetic foreign object detection device, (a) first and second detection coils are arranged with positions shifted from each other along the travel path of the non-magnetic material in the DC magnetic field; (b) the second detection coil; (c) a first arithmetic circuit that inverts the output of the first detection coil and adds it to the output of the first detection coil;
(d) a second arithmetic circuit that extracts each component of a predetermined frequency or higher of the inverted output of the detection coil and adds each of the extracted components; home,
A device for detecting magnetic foreign matter in a non-magnetic material, comprising: a third arithmetic circuit that inverts one output and adds the inverted output to the other output.