JPS6236540B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a differential magnetic head. Differential magnetic heads are small and have high sensitivity (ratio of output value when the object to be detected is in contact with the gap part to output value when there is no object to be detected).
It has advantages such as a large amount of paper, and is advantageously used for identifying banknotes and the like. FIG. 1 is a simplified front view of the prior art. In FIG. 1, the magnetic core 1 is constructed by adhering a pair of E-shaped magnetic core portions 2 and 3 facing each other. Leg portion 2a of one magnetic core portion 2,
Excitation coils 4 and 5 are wound around 2b, respectively. The excitation coils 4 and 5 are excited by an AC power source 7. Legs 3a, 3 of the other magnetic core portion 3
Detection coils 8 and 9 are wound around b. The detection coils 8 and 9 are connected in series to a voltmeter 10 so that their induced electromotive forces cancel each other out. The magnetic core parts 2, 3 have the same shape, with the magnetic core part 2 shown enlarged in FIG. The magnetic core part 2 is connected to the end face 11 of the connecting part 6,
end surfaces 12 forming the gap of the legs 2a, 2b;
13 means that if the gap length is d, then the length is d/2.
There is a size difference of just Therefore, the fine magnetic core portion 2 requires precise polishing. Also, when assembling, 3 of the end faces 11, 12, 13
It is necessary to assemble the magnetic core part 3 so that the magnetic core part 3 faces the corresponding surface of the other magnetic core part 3. Therefore, careful attention must be paid during assembly, resulting in poor productivity. The prior art shown in FIG. 1 and 2 has an H-shaped magnetic core 14.
1, and parts corresponding to those of the prior art in FIG. 1 are given the same reference numerals. This prior art technique is used when less resolution is required than that of FIG. In these prior art shown in FIG.
A differential magnetic head that is small and has good sensitivity is desired in actual industry. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a differential magnetic head with good sensitivity. The present invention, described in connection with the embodiment of FIGS. 3 to 6, for example, has a magnetic core 15 having a generally S-shaped overall shape, and this magnetic core 15 has a single magnetic core 15. Elongated central part 18
and two elongated legs 16, 17, one longitudinal end of each leg 16, 17 is connected to both longitudinal ends of the central part 18, and the other longitudinal end of each leg 16, 17 is connected to both longitudinal ends of the central part 18. A gap is formed between the ends (the lower end of the leg portion 16 and the upper end of the leg portion 17 in FIG. 3) and both longitudinal ends of the central portion 18, and the central portion 18 is energized by the AC power source 7. An excitation coil 21 is wound around each leg 16, 17, and a detection coil 22, 23 is wound around each leg 16, 17.
These detection coils 22 and 23 are connected in series so that the induced electromotive force cancels each other out, and the detection coils 22 and 23 are connected in series so that the induced electromotive forces cancel each other out. 17 (upper end in FIG. 3). FIG. 3 is a front view of one embodiment of the present invention.
The flat magnetic core 15 has two legs 16 and 17.
and a central portion 18. One end of the leg portion 16 is connected to one end of the central portion 18 to form a connecting portion 19 . Further, one end of the other leg portion 17 and the other end of the central portion 18 are connected to each other to form a connecting portion 20. The magnetic core thus has a generally S-shaped shape. A magnetic coil 2 that is excited by an AC power source 7 is provided in the center portion 18 of the magnetic core 15.
1 is wound. Detection coils 22 and 23 are wound around the legs 16 and 17, respectively. These detection coils 22 and 23 are connected in series so that their induced electromotive forces cancel each other out. Detection coil 2
The outputs of 2 and 23 are detected by the voltmeter 10. In a differential magnetic head having such a structure, when an object M to be detected approaches or comes into contact with the free end of the leg portion 17 and the connecting portion 19, the voltmeter 10 shows a voltage as shown in FIG. It was confirmed that an output more than 10 times greater than that of the prior art shown in 2 was obtained, and the sensitivity was extremely good. According to the inventor's experiments, the length l of the legs 16, 17 was 6 mm, the distance l2 between the legs 16, 17 and the center part 18 was 2.6 mm, and the legs 16, 17, the center part 1
When the axis-perpendicular cross section of 8 and their connecting portions 19 and 20 was 0.6 mm x 1.0 mm, the experimental results shown in Table 1 were obtained when the object to be detected M was brought close as shown by the imaginary line. The frequency of the AC power supply 7 is 2KHz. The excitation coil 21 is 600T (turn), and the excitation current has a peak to peak value of 20mA. Each detection coil 22, 23 is 300T. In Table 1, voltage indicates the peak to peak value detected by voltmeter 10.

[Table] For comparison, in the prior art shown in Figure 1 and 2,
l3 = l4 = 6.0 mm, l5 = 2.6 mm, and the axis-perpendicular cross section of the magnetic core 14 is 0.6 mm x 1.0 as in the embodiment shown in Fig. 3.
The experimental results when mm is also shown in Table 1.
Each excitation coil 4, 5 is each 300T, and each detection coil 8, 9 is also each 300T.
The frequency and excitation current of the AC power source 7 are the same as those shown in the third diagram. The wires of excitation coils 4, 5; 21 and detection coils 8, 9; 22, 23 are 0.03 mm
It is φ. In Table 1, when the object M to be detected is sendust, the magnetic core is saturated, so no difference in voltage values was observed in either FIG. 3 or FIG. 1. The experimental results shown in Table 1 show that the output of the differential magnetic head of the present invention has significantly better sensitivity than that of the prior art. The inventor of the present invention inferred the reason for this through the following experiment. As shown in FIG. 4, a U-shaped magnetic core 24 is prepared, an excitation coil 25 is wound around it and excited by an AC power supply 7, and a detection coil 2
Connect a voltmeter 10 to 6. An object M to be detected is brought close to the free end of the magnetic core 24, and the output of the voltmeter 10 is read. Next, as shown in FIG. 4, the magnetic core 24
The scale of the voltmeter 10 is read when the object M to be detected is brought close to the connecting portion of the voltmeter 10. Voltmeter 1 when the detected object M is a ferromagnetic material such as iron and a non-magnetic material such as aluminum or copper
The reading of 0 is shown in Table 2.

[Table] In Table 2, the frequency of AC power supply 7 is
50KHz, and the excitation current of the excitation coil 25 is
The peak to peak value is 20mA. Also voltmeter 10
The output by is a peak to peak value. From Table 2, it should be noted that according to the experiment shown in FIG.
, the output voltage read by the voltmeter 10 decreases, and in the case of a non-magnetic object M, the output voltage read by the voltmeter 10 decreases. This is an increase compared to when there is no M. FIG. 4 3 shows a differential magnetic head constructed by combining FIGS. 4 1 and 4 2 . The differential magnetic head of FIG. 4 is equivalent to the embodiment of the present invention shown in FIG. That is, the fourth
In the differential magnetic head shown in FIG. 3, the parts where the excitation coils 25 of the two magnetic cores 24a and 24b are wound are overlapped to form the central part 18 in FIG. 3, and these coils 25 are made into a single piece. Thus, the differential magnetic head shown in FIG. 3 is realized. Referring to the differential magnetic head shown in FIG. 4,
When the detected object M is a ferromagnetic material, both free ends of one magnetic core 24a and the other magnetic core 24
When the detected object M faces across the connecting portion of b, the output from one detection coil 26a is larger than when there is no detected object M, as shown in Table 2.
The output of the other detection coil 26b is the detected object M.
It is smaller than when there is no. The voltmeter 10 is connected to detect the difference in induced electromotive force between these detection coils 26a and 26b. Therefore, voltmeter 1
0 has a differentially connected detection coil 26
The output is the sum of the absolute values of the output voltages a and 26b. Further, when the detected object M is a non-magnetic material, the output of the detection coil 26a is smaller than when there is no detected object M, and the output of the detected object 26b is larger than when there is no detected object M. Therefore, the reading of the voltmeter 10 representing the sum of the absolute values of the outputs of the detection coils 26a and 26b is large. From the above, it is understood why the differential magnetic head having the structure shown in FIG. 3 has better sensitivity than the prior art shown in FIG. The reason why the embodiment shown in FIG. 3 has better sensitivity than the prior art shown in FIG. 1 can be explained by another speculation as follows. In FIG. 5, the distribution of the leakage magnetic flux 27 when the detected object M is not present in the prior art of FIG. 1 and FIG. 2 is shown with diagonal lines for convenience. Therefore, even if a ferromagnetic detected object M approaches, the leakage magnetic flux is almost the same as when the detected object M is not present, as indicated by reference numeral 28. In contrast, according to the embodiment of the present invention shown in FIG. 3 as shown in FIG. 6, leakage magnetic flux 29 is present when the detected object M is not present. Here, when the detected object M, which is a ferromagnetic material, approaches, a leakage magnetic flux 30 having a large amount of magnetic flux is obtained near the connecting portion 19 of the magnetic core 15. As a result, the magnetic resistance between the detected object M and the magnetic core 15 becomes significantly smaller than in the state shown in FIG. 61. Therefore, as can be seen from the explanation of FIGS. 5 and 6, the differential magnetic head according to the present invention has a large difference in magnetic resistance between when there is an object M to be detected and when there is no object M to be detected. It is understood that good sensitivity can be achieved. In FIGS. 5 and 6, when the object M to be detected is a diamagnetic material, the decrease rate of the leakage magnetic flux 30 is larger than the decrease rate of the leakage magnetic flux 28. It is understood that the magnetic head according to the present invention has good sensitivity. FIG. 7 is a front view of another embodiment of the invention. A pair of legs 31 and 32 of the same shape having a roughly C-shape, and a straight rod-shaped central part 3
3 constitutes a magnetic core 34. This leg 3
1 and 32, the detection coils 22 and 23 are connected as described above.
are wound and differentially connected. The excitation coil 21 is wound around the central portion 33 . Excitation coil 2
1 is excited by an AC power source 7. Detection coils 22 and 23 are connected to voltmeter 10. What should be noted in this embodiment is the shape of the magnetic core 34. The legs 31 are shown enlarged in FIG. This leg portion 31 is formed symmetrically with respect to a symmetry plane 35 at the center in the longitudinal direction, and both end surfaces 36 and 37 are simultaneously polished into flat surfaces. Magnetic core 3 shown in FIG.
4, the end face 37 or 36
and an end face 36 or 37 forming a gap 38.
and may be tightly fixed at the same time while facing the central portion 33. This also applies to the other leg 32. In this embodiment, the magnetic core 34
When assembling the two end faces 36, 3 at the same time,
You should pay attention to number 7. Therefore, the embodiments shown in FIGS. 7 and 8 do not adhere the three end surfaces 11, 12, and 13 at the same time, as in the prior art described in connection with FIG. 2 above. So,
This embodiment has the advantages of easy assembly and excellent productivity. FIG. 9 is a perspective view of a magnetic core 40 according to another embodiment of the invention. Central part 4 where the excitation coil is wound
1 are connected to one end of each of legs 42 and 43 around which a detection coil is wound, respectively, and these connecting portions are indicated by reference numerals 44 and 45. In this way, the magnetic core 40 is formed into a roughly S-shape. It should be noted that the legs 42, 43 are arranged in a plane perpendicular to the axis of the central part 41 and offset by 90 degrees about that axis. In other embodiments, the angle may be other than 90 degrees. Such embodiments are also within the spirit of the invention. As described above, according to the present invention, the magnetic core is formed in an S-shape, and the exciting coil is wound around the central part,
Since the detection coils wound around both legs are differentially connected, the sensitivity can be significantly improved compared to prior art differential magnetic heads. This also allows the magnetic core to be made smaller in order to obtain a given sensitivity, which is especially true when the magnetic core is made of relatively expensive materials such as sendust or ferrite. This will make a particularly large contribution to the reduction. Further, in the present invention, since only a single excitation coil is provided in the central portion, the number of bobbins and the like used therefor is reduced compared to the prior art. Furthermore, in the prior art shown in Figure 1, there are two excitation coils, so it takes time to connect the wires, but in the present invention, there is only a single excitation coil, so the wiring work is simplified. This greatly contributes to productivity, especially when creating a so-called ultra-small magnetic head in which the excitation coil has extremely thin wires.

[Brief explanation of the drawing]

FIG. 1 is a simplified front view of the prior art; FIG. 2 is a magnetic core portion 2 of the prior art shown in FIG.
3 is a simplified front view of one embodiment of the present invention, FIG. 4 is a front view for explaining the operating principle of the differential magnetic head of FIG. 3, and FIG. 5 is a simplified front view of an embodiment of the present invention. 1 is a front view for explaining the operation of the prior art shown in FIG. 2, FIG. 6 is a front view for explaining the operation of the differential magnetic head shown in FIG. 3, and FIG. 7 is a front view for explaining the operation of the differential magnetic head shown in FIG. Simplified front view of another embodiment of the invention, No. 8
This figure is an enlarged front view of the magnetic core 31 in the differential magnetic head of FIG. 7, and FIG. 9 is a perspective view of another embodiment of the present invention. 7... AC power supply, 10... Voltmeter, 15, 34, 4
0...Magnetic core, 16, 17; 31, 32; 42,
43... Leg part, 18, 33, 41... Center part, 21...
Excitation coil, 22, 23...detection coil.

Claims (1)

[Claims] 1. A magnetic core having a generally S-shaped overall shape, the magnetic core having a single elongated central portion and two elongated legs, each leg having a single elongated central portion and two elongated legs. One longitudinal end of each leg is connected to both longitudinal ends of the central part, forming a gap between the other longitudinal end of each leg and both longitudinal ends of the central part, and an AC power source is connected to the central part. An excitation coil is wound around each leg, and a detection coil is wound around each leg, and these detection coils are connected in series so that the induced electromotive force cancels out. 1. A differential magnetic head, characterized in that an object to be detected extending from a connecting portion between the head and the center portion to the other end of the other leg is detected.