JPH0127368B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a position detector using a magnetoresistive element or a magnetic change element whose output changes in response to a change in the magnetic field of a Hall element.

An example of a conventional position detector using a magnetoresistive element as a magnetic change element is shown in FIGS. 1 and 2. In Fig. 1, 1 is a magnetoresistive element (for example, Siemens differential sensor product number
FP211D155)
a is a housing, 1b and 1c are magnetic resistance elements, 1
d is a resin for mounting the magnetoresistive elements 1b and 1c. 1e is a cylindrical permanent magnet.
Reference numeral 2 is a disk made of a magnetic material and has one protrusion 2a, and this protrusion 2a is the reference position of the rotating shaft. FIG. 2 shows the magnetoresistive element 1b in FIG.
This is a view seen from the direction A shown in FIG. 1 to show the arrangement of the disk 1c, and the portion indicated by the two-dot chain line in the drawing shows the state of the protrusion 2a portion of the disk 2 in FIG. FIG. 3 is an electrical circuit diagram for electrically extracting the change in resistance value of the magnetoresistive elements 1b and 1c. The magnetoresistive elements 1b and 1c are elements with the same characteristics. FIG. 4 shows a voltage waveform generated when the disc 2 rotates in the direction of the arrow in FIG.

In FIG. 3, magnetoresistive elements 1b and 1c are connected in series, a constant voltage Vc is applied to one end of magnetoresistive element 1c, and one end of magnetoresistive element 1b is grounded. On the other hand, fixed resistors R ₃ and R ₄ are also connected in series, the constant voltage Vc is applied to one end of the fixed resistor R ₄ , and one end of the fixed resistor R ₃ is grounded. The potential difference ΔV between the connection point between the magnetoresistive elements 1b and 1c and the connection point between the fixed resistors _R3 and _R4 is output. Each magnetoresistive element 1b,
1c and fixed resistors R ₃ and R ₄ constitute a bridge circuit, and if the resistance values of the magnetoresistive elements 1b and 1c are R ₁ and R ₂ , respectively, then the voltage △V is as follows: △V=Vc×( R ₁・R ₄ −R ₂・R ₃ )/(R ₁ +R ₂ )×
(R ₃ + R ₄ )...Equation (1) is obtained. In this case, the setting is such that R ₁ ×R ₄ =R ₂ ×R ₃ when the projections 2a are not close to each other.

To explain its operation with the above configuration, in FIG. 1, if the permanent magnet 1e emits magnetic flux shown by the dotted line, if the protrusion 2a of the disk 2 is not close, the magnetic flux will flow through the magnetic resistance. Element 1b,1
It passes evenly through c. Then, the disk 2 rotates and the protrusion 2a portion becomes the magnetoresistive element 1 as shown in FIG.
When approaching b, the magnetic flux passing through the magnetoresistive element 1b increases, and the resistance value of the magnetoresistive element 1b increases,
Conversely, the magnetic flux passing through the magnetoresistive element 1c decreases, and the resistance value of the magnetoresistive element 1c becomes smaller. Therefore, the voltage ΔV in FIG. 3 has the waveform A shown in FIG. 4. On the other hand, when the protrusion 2a portion passes through the magnetoresistive element 1c, the waveform becomes C shown in FIG. Therefore, the switching point B between waveform A and waveform C may be used as the reference position.

However, when the position detector is used in this way, each magnetoresistive element 1b and 1c is divided into two parts as shown in FIG. It will be a problem if they are not placed side by side in the direction of rotation, as shown in the figure. Therefore, from the relative positional relationship between the position detector 1 and the disc 2, in order to make the position detector 1 have the directionality as shown in Fig. 2 while maintaining the distance between the detection part and the disc 2, the position detection method is necessary. There is a problem that it is difficult to attach the device. for example,
When fixing the detector 1 to the mounting part 3 by cutting a screw 1b in the housing 1a as shown in FIG. It becomes difficult to hold it. In particular, when accuracy is required for the distance l, if you turn the detector 1, l will not come out due to the properties of the screw 1b, and if you turn the detector 1, the direction will not come out, so the detector 1
There is a disadvantage that it cannot be easily attached using such screws 1b. Another possible method is to attach a support plate to the attachment part 3 and make a hole in the housing 1a of the detector 1.
In either case, there are problems with sealing and the size of the support plate becomes large, making it difficult to install it easily.

In addition, there are position detectors without directionality that use an oscillation type coil to generate magnetic flux, and when a magnetic material passes through, the magnetic flux is interrupted. However, the drawbacks of this type of detector are: oscillation circuit,
This requires an amplification switching circuit, etc., which makes the circuit complicated and expensive, and due to the relationship with the oscillation frequency, the response frequency is below 10KHz, resulting in no response when the detected value rotates at high speed. The disadvantage is that it is difficult to adjust the distance l from the body.

In order to solve the above-mentioned drawbacks, the present invention uses one permanent magnet having a hollow cylindrical shape, that is, a donut shape, with its end face facing the object to be detected, and the magnetic flux generated by the permanent magnet is A magnetic change element such as a magnetoresistive element or a Hall element is placed near the point on the central axis of the interface between the magnetic flux passing through the inside of the cylinder and the magnetic flux passing outside the cylinder, and the magnetic change element, such as a magnetoresistive element or a Hall element, is placed on the end face. It is fixed to the permanent magnet on the side, and by utilizing the fact that the electrical output of the magnetic change element changes because the zero point moves when a magnetic body approaches, it is possible to detect a non-directional and proportional detection object. It is an object of the present invention to provide a small and lightweight position detector that does not require accurate measurement of the distance.

The present invention will be described below with reference to embodiments shown in the drawings. FIG. 6A is a diagram showing the principle of operation, and 5 is a hollow cylindrical permanent magnet, its axial cross section is shown, and the direction of the magnetic field is shown by the solid arrow line.
The permanent magnet 5 is made of ferrite and is magnetized in the axial direction to have N and S poles as shown in the figure. In such a permanent magnet 5, the junction point _P0 between the magnetic flux going inside the permanent magnet 5 and that going outside of the magnetic flux going from the N pole to the S pole is always on the center line of the permanent magnet 5, The strength of the magnetic flux at this junction point P ₀ is 0. Figure 6B shows the strength of the magnetic flux. In FIG. 6B, the horizontal axis represents the distance in the axial direction, and the vertical axis represents the strength of the magnetic flux. As shown by the solid line in FIG. 6B, the magnetic flux inside the permanent magnet 5 is almost parallel. The strength of the magnetic field decreases in inverse proportion to the square of the distance as the distance from the P ₀ point increases, and the change in the magnetic field is greatest near the P ₀ point. In this state, when the detection object 6 made of magnetic material approaches the closest during its rotation, the P ₀ point will move down on the central axis toward the permanent magnet 5 side, creating a magnetic field as shown by the dotted line, and the magnetic flux 0 point will be the P ₀ point. becomes P ₀ ′. I'm following now
If a magnetic change element that responds to changes in the magnetic field is placed at the P ₀ point, a magnetic flux of Hx will be applied to the magnetic change element when the detection object 6 approaches. As a result, the amount of electricity in the magnetic change element changes. Naturally, the magnetic flux is rotationally symmetrical, so the direction is irrelevant.
In addition, the point P ₀ of zero magnetic flux has a hollow cylindrical shape, that is,
It is determined by the inner mold, outer diameter, and length, and has nothing to do with the strength of the magnetizing magnetic flux.

FIG. 7 shows the configuration of an embodiment of the present invention. 2 is a rotating disk, 2a is a protrusion made of a magnetic material provided on the rotating disk 2, 3 is an attached part to which the position detector 10 is attached, 5 is the above-mentioned permanent magnet with a hollow inside; As shown in the figure, the protrusion 2a side is the N pole,
The opposite side is magnetized to the S pole. 11 is the Sony Corporation product number used as the magnetic change element.
It is a magnetoresistive element made of DM101A, and 12 is an amplification switching circuit as an amplification circuit.
13 is an adhesive made of Araldite (trade name). An amplification switching circuit 12 is built inside a cylindrical housing 10a of the detector 10 made of non-magnetic material such as aluminum or copper.
A permanent magnet 5 is built into the open end side of the housing 10a, and a ring-shaped protection member 15 made of a non-magnetic material is provided at the outer end of the permanent magnet 5. As is well known, the magnetoresistive element 11 is made by depositing a horizontal pattern and a vertical pattern on a very small substrate. The resistance value changes depending on the magnetic field on the same surface. This magnetoresistive element 11
As shown in FIG. 8, the center line 11c of the pattern that distinguishes the horizontal pattern 11a and the vertical pattern 11b is located at the center of the ring-shaped protective member 15 near zero magnetic flux on the center line of the permanent magnet 5. horizontal pattern 11 so that it coincides with the central axis of
The magnetoresistive element 11, the permanent magnet 5, and the ring-shaped protective member 15 are disposed such that the substrate surface on which the vertical pattern 11b is evaporated is perpendicular to one end surface of the permanent magnet 5. The protective member 15 and the adhesive 13 filled in the housing 10a securely hold the housing 10a. The detector 10 is screwed onto the attached part by a screw 10c formed on the outer periphery of the housing 10a,
It is locked by a lock nut 14 screwed onto the screw 10c.

The shape of the hollow cylindrical permanent magnet 5 has an outer diameter of 8φ,
The inner diameter is 3.5φ, the length is 4 mm, and the distance d of zero magnetic flux is approximately 0.5 mm from the end face of the permanent magnet 5.

Figure 8 shows the amplification switching circuit 1 shown in Figure 7.
2 shows the internal circuit of No. 2. In FIG. 8, input terminals 120, 121, and 122 are connected to one bias voltage terminal, the output voltage terminal, and the other bias voltage terminal of the magnetoresistive element 11 in this order, respectively. One end of the capacitor 123 is connected to the input terminal 121, and the other end is connected to the inverting input of an operational amplifier (hereinafter referred to as an operational amplifier) 128. The resistor 124 and the resistor 125 are connected in series, the other end of the resistor 124 is connected to the input terminal 120, and the other end of the resistor 125 is connected to the input terminal 122. Input terminal 120 is power supply terminal 131
It is connected to , and a constant voltage Vc is applied to it.
Input terminal 122 is connected to ground terminal 133. A connection point between resistor 124 and resistor 125 is connected to a non-inverting input of operational amplifier 128. resistance 12
6 is connected to the other end of the capacitor 123 and the connection point between the resistor 124 and the resistor 125, and the resistor 127
is connected between the other end of the capacitor 123 and the ground terminal 133. The operational amplifier 128 is a Siemens IC with product number TAA765W.
A positive feedback resistor 129 is inserted between the non-inverting input and output of the operational amplifier 128. A load resistor 130 is connected between the output of the operational amplifier 128 and a power supply terminal 131. The operational amplifier 128 has a positive power terminal connected to a power terminal 131 and a negative power terminal connected to a ground terminal 133. The output of the operational amplifier 128 serves as an output terminal 132 of the amplification switching circuit 12.

To explain its operation with the above configuration, when the rotating disk 2 in FIG. 7 rotates and the protruding portion 2a approaches, the hollow cylindrical permanent magnet 5 from the N pole to the S
Since the zero point of the magnetic field toward the pole changes, the magnitude and direction of the magnetic field change significantly. The change in the magnetic field appears as a change in the resistance value of the magnetoresistive element 11, and the voltage at the input terminal 121 changes depending on whether or not the protrusion 2a portion approaches. In other words, as the protrusion 2a approaches, the permanent magnet 5 moves away from the protrusion 2a.
As the magnetic flux in the partial direction increases, its direction becomes parallel to the center line of the permanent magnet 5. Accordingly, each pattern 11a,
11b has the property that the resistance value is maximum when it is parallel to the direction of the magnetic field, and minimum when it is perpendicular to the direction of the magnetic field, so the resistance value of the horizontal pattern decreases and the resistance value of the input terminal 121 The voltage increases.
Then, the change is detected by the capacitor 123. In this case, the resistor 124 and the resistor 125 have the same resistance value, so the voltage at the connection point is 1/2Vc, and this voltage is applied to the non-inverting input of the operational amplifier 128, and at the same time, the resistor 126 is The voltage on the operational amplifier 128 side of the capacitor 123 is set to 1/2Vc through the capacitor 123. However, in this case, since the operational amplifier 128 is used as a comparator, whether a low level is a high level is determined by the offset voltage of the operational amplifier 128. To prevent this, resistor 127 connects 1/2Vc to resistor 126 and resistor 12.
By applying a voltage divided by 7 to the operational amplifier 128 and the capacitor 123, the output of the operational amplifier 128 is set to a high level. In this state, when the protrusion 2a approaches, the resistance value of the magnetoresistive element 11 changes, the voltage at the input terminal 121 increases, the voltage at the inverting input of the operational amplifier 128 becomes greater than 1/2Vc, and the output of the operational amplifier 128 increases. will be at a low level. As the protrusion 2a moves away, the voltage at the input terminal 121 decreases, and the operational amplifier 12
The output of 8 goes from low level to high level. In this way, the amplification switching circuit 12 amplifies the change in resistance value of the magnetoresistive element 11 and outputs it to the output terminal 132.
outputs high-level and low-level switching signals. Position detection can be performed by using this change from high level to low level as a position detection signal.

Note that when the projections 2a are at the closest position, or when the projections 2a are far enough apart that they do not affect the magnetic flux generated by the permanent magnet 5, the magnetic flux generated by the permanent magnet 5 is centered around the central axis of the permanent magnet 5. It is subject to rotation as Therefore, as long as the center line 11c of the pattern of the magnetoresistive element 11 coincides with the central axis of the permanent magnet 5, the magnetoresistive element 11 will be The magnetic flux detected by 11 is always constant. In other words, no matter from which direction the protrusion 2a of the disc 2 approaches,
The magnetic flux detected by the magnetoresistive element changes from zero magnetic flux to disk 2.
The magnetic flux increases to the maximum magnetic flux that is detected when the protrusion 2a portion approaches the closest. At this time, how the magnetic flux increases from zero to maximum varies slightly depending on the mounting direction of the board, but
Since the substrate of the magnetoresistive element 11 is very small, the change is very small and does not substantially have any effect. Therefore, the detector 10 can be screwed into the attachment part 3 and attached without considering the directionality.

In addition, the amplification switching circuit is connected to the position detector 10.
Since the S/N ratio can be increased by incorporating the signal into the circuit, the influence of external noise can be reduced.

In this case, if the shape of the protrusion 2a in FIG. 7 is made of S15C iron with a length of 4 mm, a width of 5 mm, and a depth of 9 mm, the distance between the protrusion 2a and the tip of the position detector 10 is independent of the direction of the magnetoresistive element 11. The distance l could be detected from 0 to 2.5 mm.

The smaller the magnetic change element 11, the better, but the size of the magnetic sensing part in this example is 1.18 x 2.36.
[mm ² ], and the thickness is 1 mm or less, but it can be sufficiently used as a magnetic change element according to the present invention.

In addition, in this example, Sony Corporation product number DM101A was used as the magnetic change element, but it goes without saying that a magnetoresistive element manufactured by Siemens Corporation may also be used. It is clear from the principle that a Hall element may be used instead. Although an AC amplification switching circuit was used as the amplification switching circuit 12, what is possible with a DC amplification switching circuit that applies the output ΔV of the bridge circuit to the inverting input and non-inverting input of the comparator as shown in FIG. As those skilled in the art will naturally understand, the explanation will be omitted here.

In addition, in the embodiment, the magnetic resistance element was placed at the zero magnetic flux point on the N pole side of the permanent magnet 5, but the permanent magnet 5
It is clear that the position can be detected even if the direction of is reversed and the magnetoresistive element is placed at the zero magnetic flux point of the S pole.

Further, in the embodiment described above, the amplification switching circuit 12 is inserted into the housing 10, but it may be provided in another location.

As described above, in the present invention, one hollow cylindrical permanent magnet is arranged with its end face facing the detected object, and out of the magnetic flux generated by the permanent magnet, the magnetic flux passing through the inside of the cylinder of the permanent magnet and the magnetic flux passing through the outside. Since the magnetic change element is placed near the zero magnetic flux point on the central axis, which is the junction point with the magnetic flux, and fixed to the permanent magnet on the end face side, the directionality that conventionally existed in this type of position detector can be improved. It has the advantage of being small and lightweight, in addition to being able to eliminate the need for a sensor and allowing a great deal of leeway in setting the distance between the detection object and the detection part of the position detector.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view showing the main parts of a conventional detector, Fig. 2 is a right side view of Fig. 1, Fig. 3 is an electric circuit diagram of the detector shown in Fig. 1, and Fig. 4 is the same as that shown in Fig. 1. An output waveform diagram of the magnetoresistive element in the illustrated detector; FIG. 5 is a partially sectional front view showing the mounting state of the conventional detector;
6A and 6B are the principle configuration diagram of the detector of the present invention and its magnetic flux waveform diagram, FIG. 7 is a partially sectional front view showing an embodiment of the detector of the present invention, and FIG. 8 is the detector shown in FIG. 7. FIG. 5... Permanent magnet, 10a... Housing, 11
... Magnetoresistive element as a magnetic change element, 12...
...Amplification switching circuit as an amplifier circuit.

Claims (1)

[Scope of Claims] 1. A single hollow cylindrical permanent magnet that closely opposes the circumferential portion of the rotating body, has a protrusion on one end surface, is magnetized in the axial direction, and is fixed to a member to be attached, and this permanent magnet The magnetic field of the magnetic flux passing through the outside from the N pole to the S pole of the permanent magnet near the zero magnetic flux point on the central axis, which is the junction point of the magnetic flux passing inside and the magnetic flux passing outside among the magnetic flux generated by a magnetic change element that is disposed near the zero magnetic flux point to detect the strength, is fixed to the permanent magnet on the one end surface side, and generates an output change according to a change in the magnetic field; A position detector comprising: an amplifier circuit that amplifies the amount of change in electrical output near a magnetic flux point to generate a signal indicating the rotational position of the rotating body.