JPS60174966A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To obtain a magnetic sensor simple in the manufacture of a magnetic head by arranging the magnetic head so as to run a high frequency current through a ferromagnetic fine wire. CONSTITUTION:As an external magnetic field H is applied to a magnetic detection head 1, a magnetic flux passes through a ferromagnetic fine wire 3 with a high magnetic permeability so that the flux density in the magnetic body 3 rises to lower the magnetic permeability. The change in the magnetic permeability causes the impedance of a detection head 1 to lower with a drop in the magnetic permeability. Thus, the voltage at the point (b) becomes such that the output voltage [voltage at the point (a)] of an oscillator 6 is resistance-divided with a resistance R1 and the impedance of the detection head 1. Therefore, the voltage at the point (b) is detected and rectified with a detection diode D1, a smoothing capacitor C and a smoothing resistance R2 to take out the voltage at the point (c) as output.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a magnetic sensor capable of detecting an external magnetic field.

(Prior art and its problems) Conventionally, there is a magnetic sensor that detects magnetic flux density by winding a saturable core, saturating the saturable core by an external magnetic field, and detecting the change in actance of the winding. . Although this magnetic sensor has good sensitivity and stability, it is difficult to manufacture one with a relatively long two-dimensional detection range because it is wound with wire, so it is mainly used as an element for point detection.

In addition, winding itself tends to cause layer short circuits in the coil, which makes automation of production relatively difficult and increases costs.

In addition, there are conventional magnetoresistive elements that utilize the magnetoresistive effect, in which the resistance of a ferromagnetic material changes when an external magnetic field is applied to a thin film of ferromagnetic material. This is similar in structure to the present invention, but
The disadvantage is that the magnetic resistance coefficient is very small and the sensitivity is poor. Therefore, the film thickness of the ferromagnetic material must be made extremely thin.
It is difficult to create a relatively long two-dimensional magnetic sensor, and it is still at the stage of a point detection element.

(Object of the Invention) In view of the above-mentioned points, the present invention aims to provide a magnetic sensor that can be easily made two-dimensional and whose magnetic detection head is easy to manufacture (low cost). (Summary of the Invention) The present invention provides a method for forming 7
4-A thin wire of ferromagnetic material such as Malloy is formed into a zigdeg shape,
Electrodes for flowing high-frequency current are provided at both ends or at the midpoint of this thin ferromagnetic wire. A high frequency current (for example, 50 kHz to IMHz) was passed through the magnetic detection head constructed in this way, and the detected rectified result was taken out as an output. The magnetic sensor of the present invention extends position measurement and is used for positioning cranes, mobile carts, tables of machine tools, etc., detecting passage (or presence/absence) of arm reds, detecting scratches on wire irons, etc.

(Embodiment of the Invention) FIG. 1-1 is a perspective view showing a first example of a magnetic detection head used in the present invention. In the figure, (1) shows the magnetic detection head as a whole, (2) is a substrate made of plastic or ceramic, (3) is a thin wire made of ferromagnetic material such as ferromagnet or mono-malloy, (4) and (5) are Electrodes (terminals) provided at both ends of the thin wire (3), H indicate an external magnetic field. The thin wire (3) is, for example, about 0.1 mm square or OJ mm in diameter, and is formed in a zigzag shape on the substrate (2) by an appropriate method.

FIG. 1-2 is a circuit diagram showing a typical configuration of a magnetic sensor using the magnetic detection head of FIG. 1-1. In the figure, (6) is a 50 kHz to IMHz oscillator, R1 is a resistor, Dl is a detection diode, C is a smoothing capacitor, and R2 is a smoothing resistor. When an external magnetic field H is applied to the detection head (1), the magnetic flux passes through the inside of a ferromagnetic material with a high magnetic permeability μ, the magnetic flux density B inside this magnetic material increases, and the magnetic permeability μ becomes low. The situation is shown in Figures 1-3 and 1-4. The impedance of the detection head (1) changes as the magnetic permeability μ changes, as shown in FIGS. 1-5, and as the magnetic permeability μ decreases, the impedance of the detection head also decreases.

Therefore, the voltage at point ■ in FIG.
The output voltage V at the 0 point obtained by detecting and rectifying the voltage at the 0 point is as shown in Fig. 1-β.

Next, a detailed explanation will be given with reference to Figures 1-5.・2°R,L
Assuming that are the impedance, pure resistance, and self-inductance of the detection head (1), respectively, the impedance 2 can be expressed as follows.

Z=R+L Pure resistance R is 5kin depth (
It can be expressed as a function of skin thickness) δ as follows.

L=Full table of ferromagnetic wires ρ = resistivity of ferromagnetic wire 8 - Area through which current flows in a ferromagnetic wire a = epidermal thickness f - frequency of the current flowing in the ferromagnetic wire Magnetic permeability of μ-rich ferromagnetic wire Radius of ferromagnetic wire Self-inductance L can be expressed as follows.

r From the above equation, it can be seen that both RIL decreases as the magnetic permeability μ decreases. L = 04m, ρ = 55μ.

If r = 6 x 10-5 m, the permeability-impedance curve shown in Figures 1-5 is obtained.

FIG. 2-1 is a circuit diagram showing an application example of the magnetic sensor shown in FIG. 1-2. In this example, a switching circuit (7) including a voltage comparison circuit is added after the output shown in FIGS. 1-2, and is used as a magnetic proximity switch. FIG. 2-2 is an explanatory diagram of the operation, and Vo in the figure indicates a threshold level.

Figures 2-3 are schematic diagrams showing other applications of the magnetic sensor of Figures 1-2. In this example, the magnetic detection head (1) is configured to be long so as to be able to detect the passage of a moving object such as red or red. In the figure, (8 is moving) and let, (9) is the magnet attached to the back of the motherlet (8), and Q is the non-magnetic conveyor belt. With this configuration, the mother red No matter what direction (8) is, it can be detected when it passes through the dirt of the detection head. ◎ Figure 3-1 shows a second example of the magnetic detection head used in the present invention. is a perspective view, and B is a side view. With the above-mentioned detection head, it was impossible to distinguish between the N pole and the S pole of the external magnetic field H, but by providing a bias magnet α of an appropriate strength near the detection head (1), the external magnetic field can be reduced. It becomes possible to determine the polarity of FIG. 3-2 is an explanatory diagram of the operation.

In the figure, HO indicates a bias magnetic field. A detection head provided with such a bias magnet is used as a point detection, line or two-dimensional magnetic detection element capable of distinguishing between north and south poles.

FIG. 4-1 is a perspective view showing a third example of the magnetic detection head used in the present invention. This example is configured so that it can be used as a verifier for a magnetic plate or magnetic card, which has three-value encoded information based on a combination of the north pole, south pole, and non-magnetized part of the magnet. In this example, the detection head (1) is divided into, for example, four parts, and each part has a bias magnet coded with an N pole, a S pole, and a non-magnetized part (N1 none, NX5 in the figure). A board or magnetic card (6) is provided. Each part of the detection head (1) has a bit 1. Bit 2. Bit 3. It can be called bit 4. The object to be detected 0 is a magnet plate magnetized with the opposite polarity in correspondence with the bias magnet plate 0 turret. FIG. 4-2 is an explanatory diagram showing the operation.

When the magnet plate 0 to be detected does not exist opposite the detection head (1), each bit portion is magnetized by the bias magnet plate α, and the impedance of the entire detection head is reduced. At this time, the detected magnet plate (to) is moved to the detection head (1
) on the opposite side of the bias magnet plate α■.
1), if the polarity of the detected magnet plate (to) is such that it cancels the magnetization of each bit part by the bias magnet plate (2), the detection head as a whole will not be magnetized by the external magnetic field. In this state, the impedance is highest in the state 〇 In this way, the detection head becomes high impedance only by the proximity of the magnet plate α → which has the opposite magnetization sign to the bias magnet plate α. By setting the threshold level of the voltage comparator of the switching circuit so that the switching circuit operates when

Figure 4-3 is a circuit diagram of the above-mentioned collation device;
FIG. 3 is an explanatory diagram showing the relationship between the voltage level at point ■ in Figure 3 and the degree of matching. For transporting the detected magnet plate aI.
When attached to the noglet, it is necessary to detect the magnetization code, which enables sorting in the conveyor line of the noglet. In addition, a magnetic card collation machine can be constructed by using a magnetic card made by kneading plastic and magnetic powder as the magnetic plate (a).

FIG. 5-1 is a perspective view showing a fourth example of the magnetic detection head used in the present invention. In this example, a balance circuit is constructed by providing a center point on the detection head, which works differentially with respect to the external magnetic field H, making it less susceptible to the external magnetic field applied in parallel to the entire detection head. . Figure 5-2 shows
It is a circuit diagram showing the electrical connection. In the same figure, z
l is the impedance between the electrodes in Figure 5-1, z2
represents the impedance between the electrodes
′ shows the change in . In the figure, XI and X2 are X in Figure 5-1.
i and X2, respectively. That is, the external magnetic field H
When is moved along the X direction as shown in Figure 5-1, the output in Figure g5-2 is obtained as the voltage difference between A' and B' in Figure 5-3, and as shown in Figure 5-4. become. The output is O voltage when the external magnetic field H is applied equally on both sides of the center point ◎ of the detection head, a positive voltage when a large amount is applied between ◎ on the left side, and a positive voltage when a large amount is applied between ◎ and ◎ on the right side. becomes a negative voltage. FIG. 5-5 shows a case where the detection head is divided into two left and right head elements (11) and (12) at the above-mentioned 0 point. In this case, electrodes ◎ and O are short-circuited and the 5th-
Connect ■ and ■ to the 0 point in Figure 2, respectively. In this way, when the magnet α→ moves in the X direction as shown in FIG. 5-6, an output similar to that shown in FIG. 5-4 can be obtained.

A magnetic sensor using a balance circuit as described above is very stable and sensitive, and can perform highly accurate positioning by attaching an appropriate magnet to a moving object.

An example is shown in Figures 5-7.

In the figure, (b) indicates a magnet plate. The magnetic detection head (1) has a structure in which a thin ferromagnetic wire is sandwiched between glass films. The thickness can be approximately 1.0 m. The zero output point is particularly stable against changes in temperature characteristics and power supply voltage, and positioning at this point provides the highest accuracy. This makes it suitable for a thin position detection device and for determining the angular position of a rodet joint.

FIG. 6-1 is a perspective view showing an application example of the above-described differential analog output type magnetic sensor.

In this figure, parts corresponding to those in FIG. 5-5 are given the same reference numerals. αQ is constructed by twisting together a large number of steel wires using wire rope. The wire rope αQ becomes fatigued by long-term use, and the wires gradually crack or break, forming lines, and eventually the wire rope itself breaks. Before such a situation occurs, it is necessary to inspect the wire rope for wire breakage and fatigue to prevent wire rope breakage. The present example is constructed to suit this purpose. When a wire rope is magnetized in the axial direction, there is a sudden change in magnetic permeability at the point where the strands are broken or where the wire is fatigued, and a relatively strong leakage magnetic flux is generated from that point to the outside of the wire rope. ,well known. Conventionally, a method for detecting this leakage magnetic flux is to wind an induction coil around a wire rope, move the induction coil and the wire rope relative to each other, and detect changes in magnetic flux density due to the leakage flux as electromotive force induced in the induction coil. . In this case, the wire rope and the induction coil must be moved relative to each other at relatively high speeds, and detection at low speeds close to stationary conditions is not possible. In order to perform low-speed detection near a stationary state using this method, it is necessary to apply AC magnetization to the wire rope using an electromagnet.
There are drawbacks such as high power consumption and the size of the device. Therefore, a method of detecting leakage magnetic flux by placing multiple magnetically sensitive elements around the wire rope was considered, but since the wire rope is a twisted wire, the surface is extremely uneven and the flow of magnetic flux due to magnetization is complicated. By adjusting the arrangement of the magnetically sensitive elements to the pitch of the twist, or by arranging a large number of magnetically sensitive elements as densely as possible, the S/N ratio (signal due to leakage magnetic flux and signal due to disturbance of magnetic flux caused by twisting) can be improved. Efforts were made to increase the ratio of

However, as long as the magnetically sensitive element is a point detection element that detects magnetic flux in a narrow range! There was a limit to the improvement of the 1.87N ratio.

The example of Figure 6-1 overcomes the drawbacks of wire rope testers using such point sensing elements.゛In this example, the detection head element (11) is configured thinly.

(12) is placed around the wire rope α as shown in the figure. The detection elements (11) and (1-) are configured to act differentially with respect to the magnetic field in the axial direction of the wire rope. When leakage magnetic flux due to wire breakage passes through the detection elements (11) and (1g) as the wire rope moves, a positive output voltage is detected at the detection element (11), and a positive output voltage is generated at the detection element (12). So we get a negative output voltage. The situation is shown in Parts 6-2 and 6.
- Shown in Figure 3. In the figure, α indicates a permanent magnet for wire rope magnetization, and Ql indicates leakage magnetic flux. According to this example, since the detection element (Il) - (1g) works differentially and exhibits continuous magnetic sensitivity along the periphery of the wire rope, the leakage magnetic flux due to the twisting of the wire rope is almost completely averaged. Furthermore, the difference in detection sensitivity of leakage magnetic flux due to vibration of the wire rope is also averaged, making it possible to detect wire breakage and fatigue points with an extremely good S/N ratio.

Figure 7-1 shows the magnetic detection head of Figure 5-1 with a long
00cym to 1m) is a diagram showing an example of a case where it is formed in a linear shape. In this case, if the folding pitch of the ferromagnetic thin wire (3) is equal as before, the detection head (1)
When the width of the magnet α is small compared to the total length of the magnet α, only a small portion is magnetized by the magnet α), and the impedance reduction of the detection head (1) due to magnetization remains constant. The relationship between the position of the magnet α and the output voltage is shown in the lower part of the figure. The folding pitch of thin wire (3) is 7-2.
As shown in the figure, if the detection head (1) is configured so that it gradually becomes denser from coarser to both sides from the center, the width of the part magnetized by the magnetic α field is constant, but the folding pitch is The impedance decreases greatly in areas where the detection head (1) is dense, and as shown in the lower part of the figure, a linear monotonically increasing characteristic can be obtained over the entire length of the detection head (1). In addition to measuring the position of movable objects with attached magnets, such magnetic sensors can also be used to monitor heavy objects. Suitable for positioning.

Figure 7-3 is a schematic diagram showing an example of its application. In this example,
Heavy moving objects such as cranes 6! A magnetic detection head (1) as shown in Figure 7-2 is attached to the main body, and a magnet (20
1), (202), (20g), ... are buried. FIG. 7-4 is a schematic diagram showing another example of application of the detection head (1) of FIG. 7-2. In this example, this detection head (1) is attached to an unmanned trolley (foundation), and the sensor is adjusted so that the center of the traveling axis of the unmanned trolley (a) matches the belt-shaped rubber magnet buried on the floor or under the floor. This guides the unmanned trolley.

The magnetic sensor according to the invention can also be used for reading magnetic scales. FIG. 8-1 is a schematic diagram showing an example of a magnetic scale. In this example, a rubber magnet or a plastic magnet (goods) made of a mixture of magnetic powder such as barium ferrite with high holding power and resin such as vinyl chloride is attached to an iron base (c). The S poles are alternately magnetized and the checkered magnetic scale is constructed at 0.8 dragon pitch (λ). FIG. 8-2 is a plan view showing an example in which the present invention is applied to a magnetic scale reading head. In this example, we use two sets of magnetic sensors, each with channel 1 (C).
11') and channel 2 (CH2), and was configured with a folding pitch as shown in the figure. Now, considering only the channels and moving the detection head (1) close to the magnetic scale as shown in Figure 8-3, the detection head ■-
The impedance between ◎ and ◎ is shown by the solid line in Fig. 8-4, with respect to the scale pitch λ of the magnetic scale (dotted line in Fig. 8-4). Therefore, the signal shown in FIG. 8-5 is obtained as the channel 1 sensor output. channel 2
Similarly, channel 2 outputs a sine wave whose phase lags the phase of channel l by -.

However, by using two sets of magnetic sensors of the present invention,
When a two-phase scale reading output with a phase difference of 90 degrees is obtained, it has a period of Q and 4111 (J), and a magnetic scale with a resolution of QJfil+ can be constructed by 1/4 interpolation.

(Effects of the Invention) As explained above, the magnetic sensor according to the present invention has two
It has the advantage of being easy to dimension, making the magnetic detection head simple (low cost), and having an extremely wide range of applications. In particular, when used for detecting flaws in wire ropes, etc., power consumption is low (the S/N ratio is improved).

[Brief explanation of drawings]

Fig. 1-1 is a perspective view showing a first example of the magnetic detection head used in the present invention, and Fig. 1-2 is a circuit diagram showing a typical configuration of a magnetic sensor using the magnetic detection head shown in Fig. 1-1. , Figures 1-3 to 1-6 are characteristic diagrams for explaining its operation, Figure 2-1 is a circuit diagram showing an application example of the magnetic sensor in Figure 1-2, and Figure 2-2 is its operation. Explanatory diagram, Figures 2-3 are the first
- Schematic diagram showing another application example of the magnetic sensor in Figure 2, 3rd =
) is a diagram showing a second example of the magnetic detection head used in the present invention, Figure 3-2 is an explanatory diagram of its operation, and Figure 4-1 is a third example of the magnetic detection head used in the present invention. FIG. 4-2 is a diagram illustrating its operation, FIG. 4-3 is a circuit diagram showing an example in which the magnetic detection head of FIG. 4-1 is used as a collation device, and FIG.
Fig. 5-4 is an explanatory diagram of its operation, Fig. 5-1 is a perspective view showing a fourth example of the magnetic detection head used in the present invention, Fig. 5-2 is a circuit diagram showing its electrical connection, and Fig. 5- Figure 3 and 5-4
5-5 is a perspective view showing a modification of the magnetic detection head of FIG. 5-1, FIG. 5-6 is an explanatory diagram of its operation, and FIG. Figure 6-1 is a perspective view showing an application example of the magnetic detection head shown in Figure 5-5, and Figures 6-2 and 6-3 show its operation. An explanatory diagram, FIG. 7-1 is a diagram showing an example of the magnetic detection head of FIG. 5-1 formed in a linear shape, and FIG. 7-2 is a diagram showing a modification of the magnetic detection head of FIG. 7-1. Figure 7-
Figure 3 is a diagram showing an application example of the magnetic detection head in Figure 7-2;
FIG. 7-4 is a diagram showing another application example of the magnetic detection head of FIG. 7-2, FIG. 8-1 is a diagram showing an example of a magnetic scale,
Fig. 8-2 is a plan view showing an example in which the present invention is applied to a magnetic scale reading head, Fig. 8-3 is a diagram showing its usage situation, and Figs. 8-4 to 8-6 are explanations of its operation. In the diagram ◎ (1)... Magnetic detection head, (2)... Substrate,
(3)...Thin wire of ferromagnetic material, (4) + (5)-■
, ■, ■, @), @... Electrode for flowing high frequency current, H... External magnetic field. Figure 1-3 Difference 1-4 Figure 1-6 Luck 1-20 ψ>i & gain

Claims (1)

[Claims] A magnetic detection head is formed by forming thin ferromagnetic wires on a substrate in a zig-deg shape, a high frequency current is passed through the thin ferromagnetic wires, and the impedance of the thin ferromagnetic wires is changed by applying an external magnetic field. A magnetoresistive sensor that detects external magnetic fields by using changes in the magnetic field.