JPS6331117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a proximity switch using permalloy elements.

It has been known that a permalloy element made of an iron-nickel alloy has an anisotropic magnetoresistance effect when a magnetic field is applied to the element. FIG. 1 shows the characteristics of this anisotropic magnetoresistive effect.

In recent years, with the advancement of semiconductor technology, a device has been announced in which a thin film of permalloy is deposited on a silicon wafer and an internal magnet for biasing is attached closely to the thin film. However, permalloy is extremely sensitive to temperature changes, and changes due to temperature are much larger than changes due to magnetic fields, so it is common to use it in a bridge. FIG. 2 shows a conventional circuit in which a bridge circuit is formed using permalloy elements. In this bridge circuit, due to the anisotropic magnetoresistive effect of permalloy, when a magnetic field H1 is applied in the direction of the arrow, the permalloy elements R1 and R3 that intersect with the magnetic field are affected by the magnetic field H1, and their resistance value decreases. , the permalloy elements R2 and R4 parallel to the magnetic field H1 do not change, so a bridge output is obtained. Its operating principle is shown in FIGS. 9, 10 and 11.

That is, in FIG. 9, current terminals a and c are connected to the power supply, and now permalloy elements R1,
A magnetic field H of sufficient strength to saturate magnetize R2,
In the plane formed by permalloy elements R1 and R2,
When added at an angle θ to the direction of the straight line portion of the permalloy element R1, that is, the current direction, the electric resistances ρA and ρB of the permalloy elements R1 and R2 change, and the change is expressed by the following equation using the angle θ. .

ρA＝ρ _V sin ² θ＋ρ _H cos ² θ ……(1) ρB＝ρ _V cos ² θ＋ρ _H sin ² θ ……(2) However, ρ _V saturates permalloy elements R1 and R2 in the direction perpendicular to the current. The electrical resistance of permalloy elements R1, _R2 when
2 electrical resistance. Also, the voltage V of output terminal b
Since permalloy elements R1 and R2 are connected in series, if the power supply voltage is Vo, it is expressed by the following equation.

V = ρB / ρA + ρBVo ... (3) Substituting equations (1) and (2) into equation (3) and rearranging, we get V = Vo / 2 - Δρ / 2 (ρ _H + ρ _V )・cos2θ・Vo ...(
4) (However, Δρ = ρ _H - ρ _V ) In this equation (4), the first term on the right side represents the reference voltage, and the second term represents the amount of change ΔV〓, so ΔV〓 = Δρ/ 4ρ _p cos2θ・Vo ...(5) However, 2ρ _p = ρ _H + ρ _V , and ρ _p is the electrical resistance in the demagnetized state. Therefore, the voltage V at output terminal b changes depending on the direction of the magnetic field H, and the output change has a minimum value at 0 degrees and 180 degrees, as shown in Figure 10.
It becomes a normal waveform with maximum values at 90 degrees and 270 degrees.
Figure 11 shows an equivalent circuit in which the permalloy elements R1 and R2 are variable resistances, and the resistance value is the magnetic field H.
It can be thought of as changing depending on the direction of. Note that this operating principle is based on the specification and drawings of Utility Model Application Publication No. 149971/1983 (applicant: Sony Corporation).

Further, FIG. 3 shows the relationship between the bridge output and the magnetic flux density in FIG. 2. However, as is clear from this graph, this bridge output has hysteresis. Now, for example, suppose the output is biased to the internal magnet and is at point A when the target is far enough from the proximity switch. Assume that the output circuit is set to operate when the target approaches the proximity switch and reaches point B. At this time, here is the internal magnetic field from the outside.
When an external magnetic field with an inclination of 90 degrees is applied, the output is at point C.
After the external magnetic field is removed in this state, it moves to point A1 and does not return to point A.
This means a drift in the bridge output, which has the drawback of changing the sensitive distance, especially when applied to a proximity switch. Note that such an external magnetic field is easily generated by a motor solenoid or the like in an actual location where a proximity switch is used.

The present invention is intended to solve these conventional drawbacks.

First, regarding the hysteresis, if hysteresis of permalloy in each element constituting the bridge circuit is unavoidable, it must be prevented from appearing in the bridge output. Therefore,
In Figure 2, an external magnetic field of H1 is applied to this bridge.
permalloy element R2
and R4 are affected by the magnetic field, but the other permalloy elements R1 and R3 are not affected by it.

However, due to this external magnetic field, the permalloy element R2
and R4 and permalloy elements R1 and R
Due to the repeated energization of 3, a small amount of magnetic resistance remains in the permalloy element parallel to the external magnetic field. This is the cause of bridge output hysteresis. Here, this hysteresis should be eliminated if all four elements are made to receive the same influence from the external magnetic field. For everything to work the same way, the permalloy elements must be placed in the same direction. However, if all the elements are arranged in the same direction, the internal magnetic field will not change, and the bridge output will not change. FIG. 4 shows how the magnetic flux density around the magnet 2 changes depending on the target 6. This figure shows the change in magnetic flux density due to the target 6 at a position 4 mm away from the magnetic flux 2, for example, along a line L that intersects the axial center line of the magnetization direction of the magnet 2 and 4 mm away from the magnet 2. ing. According to this graph, as the target 6 approaches, the magnetic flux density from the center of the magnet 2 to the target 6 side increases, and conversely decreases from the opposite side.

Therefore, multiple permalloy elements R1, R2, R
3, R4 are arranged parallel to each other in the first direction intersecting the magnetic sensing direction, that is, the longitudinal direction of each element, as shown in Fig. 5, and a bridge circuit is formed by these elements. In addition, the target 6 is disposed in a second direction intersecting the first direction so as to be relatively close to or away from one of the outer permalloy elements, for example, the permalloy element indicated by the symbol R1. . A magnet 2 is disposed close to the bridge circuit, and this magnet applies a magnetic bias to the bridge circuit. Moreover, in that bridge circuit,
Elements R1 and R3 of the first set of sides facing each other
From the center of the magnet 2 to the target 6 side, elements R2 and R4 of the second set of sides facing each other,
It is arranged on the opposite side of the target 6 from the center of the magnet 2.

Thereby, the magnetic flux generated by the bias magnet 2 crosses elements R1 and R4 with equal magnetic field strength, and also has equal magnetic field strength with respect to elements R2 and R3. cross. That is, all elements R1, R2, R
3. This means that an equal bias magnetic field is applied to R4. In this state, all elements are balanced and no output from the bridge circuit is produced. That is, it shows that the target 6 is located far from the bridge circuit. From this state, target 6
When the biasing magnet 2 approaches the bridge circuit, for example, the element R1 as shown in FIG. In other words, the magnetic flux flows from the center of magnet 2 to target 6 in FIG.
Because it is tilted to the side, more magnetic flux crosses elements R1 and R3, and conversely more magnetic flux crosses elements R2 and R4. As a result, the bridge circuit loses its balance and generates an output corresponding to the amount of approach of the target 6.

When the target 6 moves away from the bridge circuit, the magnetic field applied to each element R1, R2, R3, R4 becomes only the bias magnetic field from the magnet 2, so the bridge circuit is balanced again and no output is produced.

The function of this bridge circuit will be explained with reference to FIG. Now, when the target 6 is sufficiently far away from the bridge circuit, the locations where elements R1 and R3 are placed are points A and B, and the locations where elements R2 and R4 are placed are
Points C and D are the cases in which . Then, each element R, that is, R1, R2, R3, R4, is biased with the magnetic flux density at that point, and a bridge output is produced. When the target approaches here, the magnetic flux density changes, and the bias of each element becomes A1, B1, C1,
D1, and among the four elements of the bridge circuit, the resistances of the two elements R1 and R3 on the sides of the first set facing each other decrease, and conversely, the resistance of the two elements R2 and R4 on the sides of the second set facing each other decreases. increases. This causes a change in the bridge output.

7 and 8 show the specific structure of the proximity switch according to the present invention. A cap 4 is fitted into the case 3, and the end surface of this cap forms a sensitive surface. A printed circuit board 5 to which electronic circuit components are attached is housed within the case 3, and a circuit element 1 provided with the bridge circuit described above is provided on this board. A magnet 2 that applies a magnetic bias to the circuit element 1 is provided within the case 3 at a predetermined distance from the circuit element 1.

FIG. 12 shows an air cylinder in which the proximity switch shown in FIGS. 7 and 8 is applied, and in this figure, a piston rod 12 is supported in a cylinder 11 so as to be able to reciprocate along its axis. , this rod has a cylinder piston 13
is fixed, and furthermore, a target 6 is fixed to this cylinder piston. Further, a proximity switch 20 according to the present invention is provided outside the cylinder 11 in close proximity to the target 6.

Then, the cylinder piston 13 moves in a certain direction, for example, to the right in FIG. When the target 6 moves away from the proximity switch 20, the proximity switch no longer generates an output.

Figure 13 is the block circuit diagram of Figure 12, and Figure 14 is the block circuit diagram of Figure 12.
The figure is a specific circuit diagram.

As described above, the present invention arranges a plurality of permalloy elements parallel to each other in the longitudinal direction along the first direction, forms a bridge circuit with these elements, and connects the target to the first direction. The permalloy elements are brought close to or separated from one of the outer permalloy elements in a second direction intersecting the direction of the permalloy element, and a magnetic bias is applied to the bridge circuit by a magnet,
Since the first set of opposing sides are arranged from the center of the magnet to the target side, and the second set of opposing sides are arranged from the center of the magnet to the opposite side from the target, the permalloy element This has the advantage of being able to eliminate systeresis caused by the magnetoresistive effect.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the anisotropic magnetoresistive effect of permalloy, Figure 2 is a diagram showing the bridge circuit of a conventional proximity switch, and Figure 3 is the relationship between the output of the bridge circuit and magnetic flux density in Figure 2. A graph showing,
FIG. 4 is a diagram showing changes in the magnetic flux density around the magnet depending on the target, FIG. 5 is a diagram showing a bridge circuit in the proximity switch of the present invention, and FIG.
7 is a front sectional view of the proximity switch to which the present invention is applied, FIG. 8 is a sectional view of the same side, and FIGS. 9, 10 and 11 are diagrams explaining the operation of the bridge circuit in the figure. Figures 12, 13 and 14, which illustrate the principle of the permalloy element, are diagrams illustrating application examples of the proximity switch of the present invention. 1...Circuit element, 2...Magnet, 3...Case,
4...Cap, 5...Printed circuit board, 6...
...Target, R1, R2, R3, R4... Permalloy element.

Claims (1)

[Claims] 1. In a device in which a bridge circuit is formed by a plurality of permalloy elements and the output of the bridge circuit is changed by moving a target made of a magnetic substance toward or away from the bridge circuit, each of the permalloy elements are arranged so that their longitudinal directions are parallel to each other along the first direction, and the target is located inside the permalloy element, and at least outside the permalloy element, in a second direction intersecting the first axis. A magnet is provided close to or away from one of the permalloy elements and is close to the bridge circuit to apply a magnetic bias to the bridge circuit, and in the bridge circuit, the first set of opposing sides are arranged as described above. A proximity switch characterized in that a second set of opposite sides are arranged from the center of the magnet toward the target, and a second set of opposing sides are arranged from the center of the magnet to the opposite side from the target.