JPH0868662A - Magnetic stroke sensor - Google Patents

Abstract

PURPOSE: To obtain a magnetic stoke sensor in which the direction of displacement of a magnetic scale can be detected by arranging the sensor and the scale to come into surface contact thereby enhancing the sensitivity and increasing the detectable distance. CONSTITUTION: Since a magnetic body has detection surfaces, i.e., a pair of arcuate end faces 1a, 1b, facing the circular cross-sectional profile of a magnetic scale 28, a sensor comes into face contact with the scale 28. Since a uniform gap can be set entirely between the end faces 1a, 1b and the scale 28, the average distance is decreased as compared with conventional one and the sensitivity is enhanced. Distribution of magnetic lines 9 of force is also made uniform as compared with a conventional one and flux leakage, i.e., the flux not interlinking with the scale 28, is reduced. Since the increase rate of leakage flux is low and the lowering rate of sensitivity is low even if the distance h2 to the scale 28 is long, the detectable distance can be increased. Furthermore, since two pairs of detection faces 1a, 1b, 2a, 2b are arranged at a predetermined interval P0 in the moving direction of the scale 28, the direction of displacement can be determined based on the phase difference between two detection signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic stroke detection sensor for detecting an axial movement amount of a magnetic scale,
In particular, it relates to the one having improved detection sensitivity.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 6, a magnetic detecting device of this type is arranged such that side cores 11 and 12 made of a U-shaped magnetic body are opposed to both sides of a center core 10 made of a flat magnetic body. Also, the center core 10 and the side cores 11, 1
Non-magnetic body 13, 14 for forming a gap between the two
It is configured to sandwich each. A bias coil 15 for supplying a bias magnetic flux is wound around the center core 10, and the side cores 11 and 12 change the magnetic flux of the bias coil 15 (electromagnetic induction).
The detection coils 16 and 17 that generate a predetermined voltage are wound around each.

The above-mentioned magnetism detecting device includes side cores 11 and 1.
The change in the magnetic resistance due to the passage of the object to be detected (magnetic material) 18 moving in the direction orthogonal to the facing surfaces 11a and 12a of 2 was detected by the voltage change in the detection coils 16 and 17.

[0004]

By the way, in the above apparatus, as shown in FIG. 7, the end face 10a of the center core and the upper faces 11b and 12 of the side cores 11 and 12, which are detection faces, are provided.
As shown by the dotted line 19 ', the distribution state of the magnetic force lines 19 passing between and b is a convex shape centering on the end surface 10a of the center core, and the detected object 18 is, for example, a rod-shaped magnetic scale having a circular cross section. In some cases, it is in the form of point contact with the object 18 to be detected. Therefore, there is a problem that the average distance between the object to be detected 18 and each detection surface becomes large and the sensitivity becomes low. Further, due to the distribution of the magnetic force lines 19 being convex, the density of the magnetic force lines is higher as it is closer to the detection surface, as indicated by the dotted line 19 '. Therefore, when the distance h ₁ to the object to be detected 18 increases, the leakage magnetic flux 20 that does not interlink with the object to be detected 18 increases, the rate of increase thereof is high, and the rate of decrease in sensitivity is high. Therefore, there is a problem that the detectable distance cannot be set large.

Further, when used as a stroke detection sensor for detecting the displacement or moving direction of the object to be detected, two or more magnetic detecting devices are required, and as shown in FIG. It was necessary to arrange the magnetic detection devices A and B so that the longitudinal direction of the upper surface to be detected is in a line. For this reason, the distance L between the center cores 10A and 10B of the magnetic detection devices A and B needs to be about 5 mm. For example, when the magnetic detection device is used in a limited space such as an automobile, the space occupied by the devices is small. However, there was a problem that

The present invention has been made in view of the above problems of the prior art. The object of the present invention is to enhance the sensitivity, increase the detectable distance, and change the displacement direction of the magnetic scale. It is to provide a magnetic type stroke detection sensor that can detect.

[0007]

In order to solve the above problems, a magnetic stroke detection sensor according to the present invention comprises two semi-annular magnetic members each having a pair of end faces, and a pair of the magnetic members. A common bias coil that supplies a magnetic flux for bias to two closed magnetic paths that are respectively formed between the end faces, and two detection coils that are respectively provided in the magnetic body and that detect changes in the magnetic flux are provided. A magnetic stroke detection sensor for passing a magnetic scale that changes an external magnetic flux by axial displacement between a pair of end faces, wherein the pair of end faces of the magnetic body is at least partially a cross section of the magnetic scale. It has a cross-sectional shape along the shape, and a pair of end faces of two magnetic bodies are arranged at a predetermined interval in the displacement direction of the magnetic scale.

Further, the pair of end faces may have a cross sectional shape along the cross sectional shape over substantially the entire circumference of the cross section of the magnetic scale.

[0009]

Since the pair of end faces of the magnetic body that is the detection surface has a cross-sectional shape that follows the cross-sectional shape of the magnetic scale that is the object to be detected, the magnetic stroke detection sensor (apparatus) and the magnetic scale are, so to speak, surface contact. As compared with the conventional point contact type, the average distance between the detection surface and the magnetic scale becomes smaller and the sensitivity becomes higher. In addition, as a result of the surface contact shape, the density of magnetic field lines becomes more uniform compared to the conventional point contact shape,
Even if the distance from the magnetic scale increases, the rate of increase in leakage flux is low and the rate of decrease in sensitivity is low. Further, since the pair of detection surfaces of the two magnetic bodies are arranged at a predetermined interval in the displacement direction of the magnetic scale, the displacement direction can be determined by the phase difference between the two detection signals.

Further, if the detection surface has a cross-sectional shape along substantially the entire circumference of the cross section of the magnetic scale,
As the area of the detection surface increases and the sensitivity further increases, the leakage magnetic flux decreases, and the rate of decrease in sensitivity with respect to the distance from the magnetic scale becomes smaller.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a front view and a plan view of a magnetic stroke detection sensor of the present invention, FIG. 2 is a detection circuit diagram of the magnetic stroke detection sensor of FIG. 1, and FIG. 3 is an output showing the operation of the magnetic stroke detection sensor of FIG. 4 is a waveform diagram, FIG. 4 is an output waveform diagram showing a comparison with the prior art, and FIG. 5 is a front view and a plan view showing another embodiment of the magnetic stroke detection sensor of the present invention.

First, the structure will be described with reference to FIG. FIG.
In Fig. 1, the magnetic stroke detection sensor is
As shown in (a) and (b), a pair of end faces 1a, respectively.
.1b, 2a, 2b having two U-shaped (semi-annular) magnetic bodies 1 and 2 sharing the base 30;
In addition, each magnetic body 1, 2 and a pair of end faces 1a, 1b, 2a thereof
A common bias coil 3 that supplies a magnetic flux for bias to two closed magnetic paths formed between 2b, and a detection coil 4 that detects a change in the magnetic flux in one of the columnar portions of the magnetic bodies 1 and 2. 5 are provided respectively.
Here, the bases 30 of the magnetic bodies 1 and 2 may be separate. Then, as shown in FIG. 1A, both magnetic bodies 1,
A magnetic scale 28 having a circular cross section passes between the pair of two end faces 1a and 1b, 2a and 2b. That is, each of the pair of end faces 1a, 1b, 2a
-2b constitutes a detection surface. As shown in FIG. 1B, the pair of end faces 1a · 1b, 2a · 2b of the magnetic bodies 1 and 2 are
It has an arc-shaped cross-sectional shape that follows the cross-sectional shape of the magnetic scale, and is arranged at a predetermined distance d. And FIG.
(A), the two magnetic bodies 1, the pair of end faces 1a · 1b, 2a · 2b are arranged at predetermined intervals P ₀ to the displacement (movement) direction of the magnetic scale 28 . The magnetic scale 28 may be any one that changes the external magnetic flux by axial displacement. For example, an iron-chromium-cobalt alloy or the like magnetized at a predetermined pitch, or a rod made of a high-manganese non-magnetic steel material. It is possible to use, for example, those in which magnetic portions are formed in stripes at a predetermined pitch, or rods made of a magnetic material are grooved in stripes at a predetermined pitch. In the present embodiment, the description will be made assuming that the magnetic portions are formed in stripes on the rod made of a non-magnetic material at a predetermined pitch.

The cores (magnetic bodies 1 and 2) are made of, for example, a heat-resistant magnetic material (permalloy, sendust, etc.). In addition, in the present embodiment, the electrical specifications are that the bias coil 3 has a wire diameter of 0.06 mm for 200 turns, the detection coils 4 and 5 have a wire diameter of 0.06 mm for 300 turns, and the magnetic members 1 and 2 have column-shaped disconnection. The area was 0.6 mm ² , and the current value of the bias coil 3 was 40 mA.

Next, the structure of the detection circuit of the above-mentioned magnetic stroke detection sensor will be described with reference to FIG. In FIG. 2, the bias coil 3 is connected to the AC power supply 30 and is applied with an AC bias voltage. On the other hand, the detection coils 4 and 5 are connected to the differential amplifier circuit 32, generate a predetermined voltage according to the applied voltage of the bias coil 3 by electromagnetic induction, and generate each voltage of the differential amplifier circuit 32. Outputs to the + and-terminals. Then, the differential amplifier circuit 3
2 outputs the difference of each voltage input to each terminal via the detection circuit 33. The resistors shown in the figure are resistors that adjust the level of each voltage output from the detection coils 4 and 5 so that the output voltage from the differential amplifier circuit 32 is set to 0 V in a state where the magnetic scale is not detected. is there.

Next, the detection operation will be described with reference to FIG. FIG. 3A is a diagram showing a state in which the magnetic scale is passing over the magnetic stroke detection sensor, and FIG. 3B is a diagram showing the output of the detection circuit. In FIG. 3A, reference numerals M _{1 to} M ₄ are magnetic scales 28 that move in the arrow direction.
Is the magnetic part of. The pitch P of the magnetic parts M _{1 to} M ₄ is determined by the two detection surfaces 1a of the magnetic stroke detection sensor.
-The pitch is such that magnetic parts do not exist simultaneously in 1b and 2a-2b. In the position shown, the detection surface 1a · 1b of the magnetic stroke detecting sensor has detected a magnetic unit M _4, the detection surface 2a · 2b has not detected the magnetic unit. That is, the magnetic portion M is provided only above the detection surfaces 1a and 1b.
_Since there is _4, the magnetic resistance between the detection surfaces 1a and 1b becomes small, and the voltage output from the detection coil 4 becomes higher than the voltage output from the detection coil 5 and is input to the differential amplifier circuit. Therefore, from the differential amplifier circuit, as shown in FIG.
The voltage on the + side indicated by the symbol w ₄ is output. When there is no magnetic portion above any of the detection surfaces 1a and 1b and 2a and 2b, the output voltages from both detection coils 4 and 5 are at the same level, and the output voltage from the differential amplifier circuit is 0
V.

Next, this will be described in time series with reference to FIGS. Now, the magnetic part M ₁ is changed to the magnetic part M ₄
, The output voltage w from the differential amplifier circuit is
₁ is output. Next, when the magnetic part M ₁ advances to the position of the magnetic part M ₃ , the magnetic part M ₂ outputs the output voltage w ₂ . When the magnetic part M ₁ reaches above the detection surfaces 2a and 2b, the voltage output from the detection coil 5 becomes higher than the voltage output from the detection coil 4 and is input to the differential amplifier circuit. from the differential amplifier circuit, - side output voltage w ₁ 'is output. Similarly, the magnetic parts M _{1 to} M ₄
Output voltage w ₃ , w on the + side at a cycle T corresponding to the pitch P of
_4, and - side output voltage w ₂ 'are output. And
The time difference T ₀ between the + side output voltage and the − side output voltage due to the same magnetic portion corresponds to the pitch P ₀ of the two detection surfaces 1a · 1b and 2a · 2b, and as shown in the figure, the − side output voltage w output timing of ₁ '+ side output voltage w _2, deviates from the middle of the w ₃ are set (figure t) as. Therefore, the moving direction of the magnetic scale can be known from the deviation direction. That is, in the present invention, the magnetic scale 28
Two pairs of detection surfaces 1a, 1b and 2a.
Since 2b are arranged at a predetermined interval P ₀ , the displacement direction can be determined by the phase difference between the two detection signals. Further, by outputting the difference between the two detection signals, the variation in the absolute value of the detection signal due to the temperature is canceled out, so that there is an advantage that the temperature characteristic is compensated.

Next, the effect of the shape of the detection surface is shown in FIG.
This will be described with reference to FIG. In FIG. 1B, the pair of end faces 1a and 1b of the magnetic body, which are the detection surfaces, have an arc-shaped cross-section along the circular cross-section of the magnetic scale 28. Is, so to speak, in the form of surface contact. Therefore, the detection surface 1a
The distance between b and the magnetic scale 28 is uniform at each place,
Compared with the conventional point contact type, the average distance is smaller and the sensitivity is higher. That is, as shown in FIG. 4, in the present embodiment, the output voltage 22 of the detection circuit described above is about 25 times (V ₂ / V ₁ ) as compared with the conventional output voltage 21. Returning to FIG. 1, and as a result of the surface contact shape, as shown by the dotted line 9 ', the distribution state of the magnetic force lines 9 becomes more uniform as compared with the conventional point contact shape, and does not interlink with the magnetic scale. Leakage magnetic flux is reduced. Therefore, the distance h to the magnetic scale 28
_{Even if 2} is increased, the rate of increase in leakage flux is low and the rate of decrease in sensitivity is low. That is, it becomes possible to secure a large detectable distance as compared with the conventional case, and the result of this embodiment is about 1.5 times.

Next, another embodiment of the present invention will be described with reference to FIG. 5 is substantially different from FIG. 1 in that
As shown in FIG. 1B, the detection surfaces 41a, 41b, 42a, 42b have a semicircular shape along the circular cross section of the magnetic scale 48 over substantially the entire circumference thereof. Is. In addition, 43 is a bias coil, 44,
Reference numeral 45 is a detection coil for each of the magnetic bodies 41 and 42. By doing so, the area of the detection surface is increased and the sensitivity is further enhanced, and the magnetic force lines 49 are formed on the detection surfaces 41a, 41b, 4 and 4.
Since the magnetic flux passes straight between 2a and 42b, the leakage flux is further reduced, and the rate of decrease in sensitivity with respect to the distance from the magnetic scale is further reduced. Therefore, it becomes possible to secure a larger detectable distance.

Although the magnetic scale has a circular cross-sectional shape in the above description, the present invention is not limited to this, and other shapes can be similarly applied.

[0020]

As described above, in the magnetic stroke detection sensor of the present invention, the pair of end faces of the magnetic body as the detection surface has a cross-sectional shape along the cross-sectional shape of the magnetic scale which is the object to be detected. The stroke detection sensor and the magnetic scale are in a so-called surface contact form, and the average distance between the detection surface and the magnetic scale is smaller than in the conventional point contact form, so that the sensitivity can be increased. Also, as a result of the surface contact type, the leakage magnetic flux is smaller than that of the conventional point contact type, and the decrease rate of the sensitivity with respect to the distance to the magnetic scale is small, so the detectable distance can be increased. is there. Furthermore, since the pair of detection surfaces of the two magnetic bodies are arranged at a predetermined interval in the displacement direction of the magnetic scale, the displacement direction can be determined by the phase difference between the two detection signals.

When the detection surface has a cross-sectional shape that conforms to the cross-sectional shape of substantially the entire circumference of the cross section of the magnetic scale,
Since the area of the detection surface is increased, the sensitivity can be further increased, and since the leakage magnetic flux is reduced, the detectable distance can be further increased.

[Brief description of drawings]

FIG. 1 is a front view and a plan view of a magnetic stroke detection sensor of the present invention.

FIG. 2 is a detection circuit diagram of a magnetic stroke detection sensor of the present invention.

FIG. 3 is an output waveform diagram showing an operation of the magnetic stroke detection sensor of the present invention.

FIG. 4 is an output waveform diagram showing a comparison with the related art.

5A and 5B are a front view and a plan view showing another embodiment of the magnetic stroke detection sensor of the present invention.

FIG. 6 is a perspective view of a conventional magnetic detection device.

FIG. 7 is a front view of a conventional magnetic detection device.

FIG. 8 is a diagram showing a method of using a conventional magnetic detection device.

[Explanation of symbols]

P ₀ Predetermined interval 1 Magnetic substance 1a End face 1b End face 2 Magnetic substance 2a End face 2b End face 3 Bias coil 4 Detection coil 5 Detection coil 9 Magnetic field line (equivalent to magnetic flux) 28 Magnetic scale

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mio Uda 684 Shimobu, Kagami-cho, Kami-gun, Kochi Prefecture 1 Minerva Kochi factory

Claims (2)

[Claims] 1. A semi-annular two each having a pair of end faces.
One magnetic body, a common bias coil that supplies a magnetic flux for biasing to two closed magnetic paths formed respectively between the magnetic body and a pair of end faces, and a change in magnetic flux provided in each of the magnetic bodies is detected. A magnetic stroke detection sensor, comprising: two detection coils; passing a magnetic scale that changes an external magnetic flux by axial displacement between a pair of end surfaces of the magnetic body; Has a cross-sectional shape that at least partially conforms to the cross-sectional shape of the magnetic scale, and a pair of end surfaces of the two magnetic bodies are arranged at predetermined intervals in the displacement direction of the magnetic scale. And a magnetic stroke detection sensor. 2. The magnetic stroke detection sensor according to claim 1, wherein the pair of end faces has a cross-sectional shape along the cross-sectional shape over substantially the entire circumference of the cross section of the magnetic scale.