JPH0211864B2 - - 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/mm, in a DC high magnetic field H ₀ . In addition, DC high magnetic field
A detection coil 2 is arranged along the running path of the copper wire 1 in H ₀ . If a magnetic foreign substance 3 is mixed into the copper wire 1, when this magnetic foreign substance 3 passes through the magnetic field _H0 , the magnetic flux φ in the detection coil 2 changes,
As a result, the same detection coil 2 has the following equation: e=-Ndφ/dt (1) where: N is the number of turns of the 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 H ₀ 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. The first type is noise generated when the copper wire 1 vibrates with a relatively long wavelength (hereinafter referred to as long wavelength noise), and 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 represents the frequency component of long wavelength noise, and curve B represents the frequency component of long wavelength noise.
curve C indicates the frequency component of the detection signal, and curve C indicates the frequency component of the 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 1/20 compared to the case of one detection coil shown in Figure 1.
It is possible to do so.

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 Fig. 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 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. (In other words, the result is the same as if the secondary side of the transformer were short-circuited.) On the other hand, the detection signal of the magnetic foreign object 3 is caused by the annular eddy current flowing in the sleeve 4 because its frequency is lower than that of traveling wave noise. It is not canceled and is output 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, this invention can remove long wavelength noise, almost completely remove traveling wave noise, and further improve the amplitude of the magnetic foreign object detection signal compared to the conventional one. , provides a device for detecting magnetic foreign matter in a non-magnetic material that can double or more, in which at least three detection coils are provided at equal intervals along the travel path of the non-magnetic material, and these detection coils are An arithmetic circuit, an adder/inverter circuit, and an adder circuit are provided to process the output of the detector, and both long wavelength noise and traveling wave noise are canceled by the electric circuit. It is characterized by a large signal amplitude.

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

FIG. 7 is a block diagram showing the configuration of the first embodiment of the present invention. In this figure, three detection coils 12a, 12b, and 12c are arranged at equal intervals with their positions shifted from each other along the travel path of a copper wire 11 (non-magnetic material) that travels in a DC high magnetic field H. There is. Then, the output of the detection coil 12a is sent to the in-phase amplifier 14 of the arithmetic circuit 13.
The output of the detection coil 12b is supplied to the inverting amplifier 15 of the arithmetic circuit 13 and the inverting amplifier 17 of the arithmetic circuit 16, and the output of the detection coil 12c is supplied to the in-phase amplifier 18 of the arithmetic circuit 16, respectively. Further, the output of the in-phase amplifier 14 and the output of the inverting amplifier 15 are each supplied to an adder circuit 19, and the output of the inverting amplifier 17 and the output of the in-phase amplifier 18 are each supplied to an adder circuit 20. Adder circuit 19 adds the output of in-phase amplifier 14 and the output of inverting amplifier 15, and its output is supplied to adder circuit 33. Addition circuit 20
is for adding the output of the inverting amplifier 17 and the output of the in-phase amplifier 18, and the output is added to the adder circuit 33.
supplied to Adder circuit 33 adds the outputs of adder circuits 19 and 20, and outputs the addition result to a signal processing circuit (not shown).

In the above configuration, the detection coils 12a, 12
b, arithmetic circuit 13 and detection coils 12b, 12
c. Each of the arithmetic circuits 16 constitutes 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 19, the output of the adder circuit 19 becomes approximately zero as shown in FIG. 8E. In this way, the detection coil 12
The long wavelength noise generated in each of a and 12b is added to the adder circuit 1.
It does not appear on the output terminal of 9. Similarly, detection coil 1
The long wavelength noise generated at 2b and 12c is canceled out by the adder circuit 20 and does not appear at the output end of the adder circuit 20.

That is, the in-phase long wavelength noise generated in the detection coils 12a to 12c is all removed by the arithmetic circuits 13 and 16.

Next, a case will be described in which the iron piece 23 (magnetic foreign substance) mixed in the copper wire 11 is detected. When the iron piece 23 passes through the detection coils 12a to 12c in sequence, the detection coils 12a to 12c are respectively
Detection signals shown in c are generated whose phases are shifted by 180 degrees. These detection signals are amplified by the in-phase amplifier 14, inverting amplifiers 15, 17, and in-phase amplifier 18, respectively, and become the signals shown in FIG. In addition,
FIG. 9E shows both the outputs of the inverting amplifiers 15 and 17. Then, when the signal shown in FIG. 9D and the signal shown in E are added by the adder circuit 19,
When the signal shown in FIG. 9G is output from the adder circuit 19, and the signal shown in FIG. 9H and the signal shown in F are added by the adder circuit 20, the signal shown in FIG. It is output from the adder circuit 20. Each output of these adder circuits 19 and 20 (FIG. 9 G and H)
are added by the adder circuit 33, and the adder circuit 3
From 3 to 9, magnetic foreign object detection signals shown in FIG. 9 are output.

Here, the amplitude of this magnetic foreign object detection signal will be considered. For example, suppose that in the conventional configuration shown in FIG. 3, when the iron piece 3 passes through the detection coils 2a and 2b in sequence, the detection signals shown in FIGS. 9A and 9B are obtained at the detection coils 2a and 2b, respectively. Since the detection coils 2a and 2b are differentially coupled, these detection signals are inverted and added, and the signal shown in FIG. 9G is obtained between the terminals T ₁ and T ₂ (FIG. 3). As is clear by comparing the signal shown in FIG. 9G and the magnetic foreign object detection signal shown in FIG. 9L,
The magnetic foreign object detection signal shown in FIG. 9 can have an amplitude twice that of the detection output obtained by the conventional configuration. In addition, the detection output from the conventional configuration is amplified by an amplifier,
It is of course possible to increase the amplitude, but in this case the noise signal is also amplified at the same time, so the S/
This will not improve N.

Next, a configuration for removing traveling wave noise will be explained.

In FIG. 7, reference numerals 26 and 27 indicate addition/inversion circuits having the same configuration. Addition/inversion circuit 26
is a high pass filter (hereinafter abbreviated as HPF)
28a, 29a and these HPF28a, 29a
an adder circuit 30a that adds each output of the adder circuit 30a, and an inverter circuit 3 that inverts and outputs the output of the adder circuit 30a.
1a, and HPF28a,
The cutoff frequency of 29a is curve B shown in FIG.
This is the frequency at the intersection of and C. and,
The HPFs 28a and 29a each have an in-phase amplifier 14,
Each output of the inverting amplifier 15 is supplied, and the inverting circuit 3
The output of 1a is supplied to an adder circuit 33. Also,
The HPFs 28b and 29b of the inverting/adding circuit 27 have
The outputs of the inverting amplifier 17 and the in-phase amplifier 18 are respectively supplied, and the output of the inverting circuit 31b is supplied to the adder circuit 33.
supplied to The adder circuit 33 includes the outputs of the inverting circuits 31a and 31b described above and the adder circuits 19 and 2.
The outputs of 0 are added together, and the output is supplied to a signal processing circuit (not shown).

In the above configuration, a traveling wave with a short wavelength is generated in the copper wire 11, which causes the detection coils 12a to
A case where the traveling wave noise signals shown in FIGS. 10A to 10C are generated at 12c will be explained. These noise signals are transmitted through an in-phase amplifier 14, an inverting amplifier 15, and an inverting amplifier 15, respectively.
17. After being amplified by the in-phase amplifier 18, adder circuits 19, 20 and HPFs 28a, 29a,
It is supplied to each input terminal of 28b and 29b. The adder circuit 19 adds the respective outputs of the in-phase amplifier 14 and the inverting amplifier 15, and produces the signal shown in FIG.
It is output to the adder circuit 33. The adder circuit 20 adds the respective outputs of the inverting amplifier 17 and the in-phase amplifier 18, and outputs the result to the adder circuit 33 as a signal shown in FIG.
Output to. On the other hand, since the frequencies of these signals are higher than the cutoff frequencies of HPFs 28a and 29a (see Fig. 2), the signals supplied to the input terminals of HPFs 28a and 29a, respectively, are
29a to the adder circuit 30a, and as a result, a signal substantially the same as the signal shown in FIG. 10D is output from the output end of the adder circuit 30a. and,
This signal is inverted by the inverting circuit 31a and applied to the adding circuit 33 as a signal shown in FIG. Similarly, the signals applied to each input terminal of the HPFs 28b and 29b are added by an adding circuit 30b, and then inverted by an inverting circuit 31b.
The signal is applied to the adder circuit 33 as a signal shown in FIG. The outputs of the adder circuits 19 and 20 and the outputs of the inverter circuits 31a and 31b (first
When the signals (signals shown in Figure 0) are added by the adding circuit 33, the output of the adding circuit 33 becomes zero.

That is, when traveling wave noise signals occur in each of the detection coils 12a to 12c, these noise signals are all canceled out by the adder circuit 33 and do not appear at the output end of the adder circuit 33.

Note that the signals emitted when the iron piece 23 mixed in the copper wire 11 passes through the detection coils 12a, 12b, 12c are the HPFs 28a, 29a,
It is also supplied to 28b and 29b, but HPF28a
Since the cutoff frequency of ~29b is set higher than the frequency of the signal generated by the iron piece 23, the signal is cut off there.

In this way, in the circuit shown in FIG. 7, the amplitude of the magnetic foreign object detection signal can be doubled compared to the conventional method, and both long wavelength noise and traveling wave noise can be removed. .

Above, the embodiment of the present invention has been described with reference to the case where there are three detection coils.
Of course, it is also possible to make it individual. In this case, the amplitude of the magnetic foreign object detection signal can be made larger than in the case where there are three detection coils. For reference, FIG. 11 shows the circuit configuration when the configuration shown in FIG. 7 is changed to four detection coils, and FIG. 12 shows the waveforms of various parts in this case. In FIG. 12, A to D are the outputs of the detection coils 12a to 12d in FIG. 11, H to H are the outputs of the adder circuits 35 to 37 in the figure, respectively, and H is the output of the adder circuit 38 in the figure. are shown respectively.

In the first embodiment described above, the same effect can be obtained even if in-phase amplifiers are used in place of the inverting amplifiers 15 and 17, and subtraction circuits are used in place of the adder circuits 19, 20, 30a, and 30b. Obtainable.

As explained above, according to the present invention, at least three detection coils are arranged along the travel path of the non-magnetic material, so the amplitude of the magnetic foreign object detection signal can be more than doubled compared to the conventional method. Can be done. Also,
According to this invention, since the traveling wave noise is canceled by the electric circuit, the traveling wave noise can be almost completely eliminated. And these results,
The magnetic foreign matter detection device according to the present invention can have a much superior magnetic foreign matter detection ability compared to conventional devices.

[Brief explanation of drawings]

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, and FIG. 7 is a block diagram showing the configuration of the first embodiment of the present invention.
8, 9, and 10 are waveform diagrams for explaining the operation of the same embodiment, FIG. 11 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 12 is the same. FIG. 3 is a waveform diagram showing output waveforms of each part in the example. 11...Copper wire (non-magnetic material), 12a to 12d...
...Detection coil, 13, 16...Arithmetic circuit, 23...
...Iron piece (magnetic foreign material), 26, 27... Addition/inversion circuit, 33, 38... Arithmetic circuit.

Claims (1)

[Claims] 1. Magnetism in which a non-magnetic material is 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 foreign object detection device, (a) at least three detection coils arranged at mutually shifted positions along the travel path of the non-magnetic material in the DC magnetic field; (b) two detection coils adjacent to each other; (c) at least two arithmetic circuits that invert the output of one of the detection coils and add the inverted output to the output of the other detection coil; (c) two of the detection coils adjacent to each other; At least one of the coils, extracting components having a predetermined frequency or higher from the inverted output of one detection coil and the output of the other detection coil, adding each of the extracted components, and inverting and outputting the addition result. A device for detecting magnetic foreign matter in a non-magnetic material, comprising: two adding/inverting circuits; (d) an adding circuit for adding each output of the arithmetic circuit and the adding/inverting circuit.