JP2016133336A - Distance measuring system, and distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-contact type distance measuring system using a permanent magnet that can be improved in the accuracy of distance measuring without having to increase the size of the permanent magnet and a distance measuring method using this system.SOLUTION: A distance measuring system 1 for measuring the distance between a first member 11 and a second member 12 which can be moved relative to each other in a prescribed approaching or departing direction is equipped with a permanent magnet 2 that is partly fitted into a concave 110 formed in the first member 11 and a magnetic field sensor 3 that is fixed to the second member 12 and detects the intensity of a magnetic field generated by the permanent magnet 2. The first member 11 is formed of soft magnet material, and its concave 110 opens toward the second member 12, and the permanent magnet 2 is fixed to the first member 11 by its own magnetic force with its motion in a direction crossing the approaching or departing direction being regulated by its fitting into the concave 110.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a distance measuring system and a distance measuring method for measuring a distance between a first member and a second member that are relatively movable in a predetermined contact / separation direction.

  2. Description of the Related Art Conventionally, a non-contact type distance meter is known that can measure the distance to a measurement object by the magnetism of a permanent magnet (see Patent Document 1).

  The distance meter described in Patent Literature 1 includes a permanent magnet that generates a magnetic flux that passes through a measurement target, a magnetic sensor that is disposed between the permanent magnet and the measurement target, and a change amount of the distance from the magnetic sensor to the measurement target. And a distance calculation circuit for calculating from a change amount of magnetic flux density detected by the magnetic sensor. The magnetic sensor comprises a core formed in a cylindrical shape and a detection coil wound around the core, and the distance calculation circuit is based on the positive and negative peak values of the output voltage at both ends of the detection coil. The amount of change in distance is calculated.

JP-A-3-243801

  In the distance meter described in Patent Document 1, since the magnetic sensor is disposed between the permanent magnet and the measurement object, there is a large gap between the permanent magnet and the measurement object. For this reason, the magnetic flux passing through the measurement target cannot be increased, and the ratio of the change in the magnetic flux density in the magnetic sensor to the change in the distance from the magnetic sensor to the measurement target is small. It was difficult to improve distance accuracy.

  Further, for example, if the size of the permanent magnet is increased, the magnetic flux passing through the measurement object can be increased. In this case, however, the installation space is increased in size and cost.

  Therefore, an object of the present invention is to provide a distance measuring system and a distance measuring method capable of improving the distance measurement accuracy without increasing the size of the permanent magnet.

  The present invention is a distance measuring system for measuring a distance between a first member and a second member that can be moved relative to each other in a predetermined contact / separation direction for the purpose of solving the above-described problem, and is formed on the first member. A permanent magnet partially fitted into the recessed portion, and a magnetic field sensor that is fixed to the second member and detects the strength of the magnetic field generated by the permanent magnet, wherein the first member is made of a soft magnetic material. The concave portion opens toward the second member, and the permanent magnet is fixed to the first member by its own magnetic force, and intersects the separation / contact direction by fitting into the concave portion. Provided is a distance measurement system in which movement in a direction is restricted.

  Further, the present invention is a distance measuring method for measuring a distance between a first member and a second member that can be relatively moved in a predetermined contact / separation direction for the purpose of solving the above-described problem, wherein the first member A magnetic field sensor that detects a strength of a magnetic field generated by the permanent magnet by forming a concave portion that opens toward the second member, disposing a permanent magnet so that a part of the concave portion is fitted in the concave portion. The first member is made of a soft magnetic material constituting a part of the magnetic path of the permanent magnet, the permanent magnet is fixed to the first member by its own magnetic force, and the concave portion The movement in the direction intersecting the separation / contact direction is restricted by the fitting to and the distance between the first member and the second member is measured based on the strength of the magnetic field detected by the magnetic field sensor. Provide a distance measurement method.

  According to the distance measuring system and the distance measuring method according to the present invention, the distance measurement accuracy can be improved without increasing the size of the permanent magnet.

(A) is a disassembled perspective view which shows the structural example of the distance measuring system which concerns on this Embodiment, (b) is a perspective view which shows the magnetic field sensor used for this distance measuring system. It is sectional drawing which shows the peripheral part of the recessed part of a 1st member, and the permanent magnet fitted and fixed to the recessed part. (A) And (b) is explanatory drawing shown in order to demonstrate operation | movement of a distance measurement system. In (a) to (e), the fitting ratio of the permanent magnet to the recess is 1.0 (100%), 0.5 (50%), 0.25 (25%), 0.1 (10 %) And 0 (0%) are schematic views schematically showing lines of magnetic force radiated from the permanent magnet. It is a graph which shows the relationship between the distance between the 1st member 11 and the 2nd member 12, and the intensity | strength of the magnetic field detected by a magnetic field sensor.

[Embodiment]
Hereinafter, a distance measurement system according to an embodiment of the present invention and a distance measurement method using the distance measurement system will be described with reference to FIGS.

  FIG. 1A is an exploded perspective view showing a configuration example of a distance measuring system according to the present embodiment. FIG.1 (b) is a perspective view which shows the magnetic field sensor used for this distance measuring system.

  The distance measuring system 1 includes a first member 11 and a second member 12 that are relatively movable in a predetermined contact / separation direction, and can measure the distance between the first member 11 and the second member 12 in a non-contact manner. It is. In the present embodiment, a case will be described in which the second member 12 is fixed to a fixing member such as a frame (not shown) and the first member 11 is a moving body that moves relative to the second member 12. The distance measuring system 1 is preferably used for short distance measurement that measures the position of the first member 11 within a range within 20 mm from the closest position where the first member 11 is closest to the second member 12, for example. be able to.

  The distance measuring system 1 includes a permanent magnet 2 that partially fits into a recess 110 formed in a first member 11 and a magnetic field sensor that is fixed to the second member 12 and detects the strength of a magnetic field generated by the permanent magnet 2. 3 and a calculation unit (described later) that calculates the distance between the first member 11 and the second member 12 based on the detection result of the strength of the magnetic field by the magnetic field sensor 3. The distance measuring system 1 is used in an environment where the ambient temperature of the permanent magnet 2 is 100 ° C. or higher. That is, the permanent magnet 2 is disposed in a space where the temperature is 100 ° C. or higher.

  The first member 11 is a moving body that is a measurement target of the distance from the second member 12, and moves forward and backward with respect to the second member 12 in response to a moving force from an unillustrated moving force generation mechanism. The first member 11 is formed with a recess 110 formed in a part of the facing surface 11a facing the second member 12 so as to be recessed in a direction perpendicular to the facing surface 11a. In the present embodiment, the internal space of the recess 110 is cylindrical and opens toward the second member 12.

  The first member 11 is made of a soft magnetic material that constitutes a part of the magnetic path of the permanent magnet 2. Specifically, iron-based metal, martensite-based or ferrite-based stainless steel can be used as the soft magnetic material.

  In the following description, the case where the first member 11 moves linearly with respect to the second member 12 will be described. However, the present invention is not limited to this, and the first member 11 swings around a support shaft (not shown) (predetermined angle). It may be supported so that it can rotate within a range. In this case, the distance measurement system 1 can measure the distance between the second member 12 and the position of the recess 110 that changes as the first member 11 swings.

  The permanent magnet 2 is a samarium cobalt magnet or a neodymium magnet. The samarium-cobalt magnet is also called a samacoba magnet, and is a rare earth magnet mainly composed of samarium (Sm) and cobalt (Co). The neodymium magnet is a rare earth magnet mainly composed of neodymium (Nd), iron (Fe), and boron (B). The samarium cobalt magnet and the neodymium magnet can obtain a higher residual magnetic flux density than, for example, a ferrite magnet. In the present embodiment, the residual magnetic flux density of the permanent magnet 2 is 1.0 T (Tesla) or more. In addition, nickel or the like may be plated on the surface of these magnets for rust prevention or the like.

  In the present embodiment, the permanent magnet 2 has a cylindrical shape, and a pair of magnetic poles (N pole and S pole) are formed side by side in the central axis c direction. In the permanent magnet 2, one end 21 in the direction of the central axis c along the direction in which the pair of magnetic poles are aligned is fitted into the recess 110 of the first member 11. The end surface 2 b of the permanent magnet 2 at the other end 22 opposite to the one end 21 faces the second member 12.

  In the present embodiment, the second member 12 is made of a mold resin, and the magnetic field sensor 3 is insert-molded in the mold resin. In the present embodiment, the second member 12 has a quadrangular prism shape. However, the second member 12 may be any non-magnetic material that can fix the magnetic field sensor 3, and various materials and shapes may be used. Can be used.

  In the present embodiment, the magnetic field sensor 3 is a Hall IC, and a main body 30 formed by sealing a Hall element that converts the intensity of a magnetic field into an electric signal by using a Hall effect by an insulator such as a resin or ceramic. And first to third lead wires 31 to 33 led out from the main body 30. The first lead wire 31 is a power supply line, the second lead wire 32 is a signal line, and the third lead wire 33 is a ground line. The main body 30 is disposed at a position and orientation where the intensity of the magnetic field along the central axis c of the permanent magnet 2 can be detected. The magnetic field sensor 3 outputs an electrical signal corresponding to the strength of the magnetic field from the second lead wire 32.

  FIG. 2 is a cross-sectional view showing the peripheral portion of the concave portion 110 of the first member 11 and the permanent magnet 2 having one end 21 fitted and fixed to the concave portion 110 in a cross section including the central axis c.

  The end surface 2 a of the one end portion 21 of the permanent magnet 2 is in surface contact with the bottom surface 110 a of the recess 110. The permanent magnet 2 is fixed to the first member 11 by its own magnetic force. That is, the permanent magnet 2 is fixed to the first member 11 by the attractive force of the permanent magnet 2 itself without using a fixing means such as an adhesive.

  Further, the permanent magnet 2 is restricted from moving in a direction intersecting the direction of separating from and coming into contact with the second member 12 by fitting into the recess 110. In FIG. 2, this separation / contact direction is indicated by an arrow A. In the present embodiment, this separation / contact direction is parallel to the central axis c of the permanent magnet 2.

As shown in FIG. 2, when the diameter of the permanent magnet 2 is D ₁ and the inner diameter of the recess 110 of the first member 11 is D ₂ , the inner diameter D _{2 of the} recess 110 is slightly smaller than the diameter D ₁ of the permanent magnet 2. The diameter difference ΔD (ΔD = D ₂ −D ₁ ) is, for example, 0.5 mm. The depth of the recess 110, i.e. the fitting depth of the permanent magnet 2 in the recess 110 when the _{D 3,} the depth _{D 3} is deeper than the diameter difference [Delta] D. That is, the diameter D ₁ of the permanent magnet 2, the inner diameter D _{2 of} the recess 110, and the fitting depth D ₃ of the permanent magnet 2 in the recess 110 satisfy the following relational expression (1).
D ₂ -D ₁ <D ₃ (1)
Thereby, even when a vibration or impact is applied to the first member 11, the permanent magnet 2 is suppressed from being detached from the recess 110.

Incidentally, the fitting depth _{D 3} of the permanent magnet 2 in the recess 110 is desirably 0.5mm or more. When the fitting depth _{D 3} is less than 0.5 mm, for example, when a vibration or shock is applied to the first member 11, over the side surface 110b of the recess 110 the permanent magnet 2, the positional deviation of the permanent magnet 2 This is because it tends to occur.

Furthermore, if the thickness of the permanent magnet 2 in the direction of the central axis c is t, the thickness t is smaller than the diameter D ₁ of the permanent magnet 2 (t <D ₁ ). That is, the permanent magnet 2 is formed in a flat cylindrical shape. Thereby, compared with the case where the thickness t in the central axis c direction of the permanent magnet 2 is larger than the diameter D _{1 of} the permanent magnet 2, the end surface 2 a at the one end portion 21 of the permanent magnet 2 is in relation to the bottom surface 110 a of the recess 110. The tilt and the permanent magnet 2 are prevented from falling.

Further, the ratio of the length (fitting depth D ₃ ) of the portion fitted in the recess 110 to the total length (thickness t) in the central axis c direction of the permanent magnet 2 is the fitting ratio R (R = D ₃ / t). Then, it is desirable that the fitting ratio R is 0.1 to 0.5. That is, in the present embodiment, the ratio of the length of the portion fitted in the recess 110 to the total length of the permanent magnet 2 in the direction of the central axis c is 10 to 50% (10% or more and 50% or less). If this ratio is less than 10%, it is not preferable because the permanent magnet 2 is easily pulled out from the recess 110. On the other hand, if the ratio exceeds 50%, the magnetic field of the permanent magnet 2 is difficult to reach the magnetic field sensor 3, which is not preferable.

In FIG. 2, the thickness t of the permanent magnet 2 is 3 mm, fitting depth _{D 3} is 0.75 mm, is illustrated for the case the fitting ratio R is 0.25 (25%).

FIGS. 3A and 3B are explanatory views shown for explaining the operation of the distance measuring system 1. Figure 3 (b), the distance _{L 2} between the first member 11 and second member 12, the distance _{L 1} between the first member 11 in the state shown in FIG. 3 (a) and the second member 12 The smaller state is illustrated.

  3A and 3B, the magnetic field sensor 3 inside the second member 12 and the cable 4 connected to the magnetic field sensor 3 are shown by solid lines, and two lines of magnetic force indicating the magnetic field of the permanent magnet 2 are shown. Shown with a chain line. The magnetic field sensor 3 is connected to the calculation unit 5 by a cable 4.

  The permanent magnet 2 has an S pole at one end 21 and an N pole at the other end 22. The lines of magnetic force radiated from the end surface 2 b in the other end portion 22 are curved and enter the first member 11. Further, a part of the lines of magnetic force radiated from the end surface 2 a in the one end portion 21 is linked to the main body portion 30 of the magnetic field sensor 3.

  The cable 4 includes first to third electric wires 41 to 43 and a sheath 40 that collectively covers the first to third electric wires 41 to 43. Each of the first to third electric wires 41 to 43 is an insulated electric wire formed by insulatingly coating a core wire, and the core wire of the first electric wire 41 is connected to the first lead wire 31 of the magnetic field sensor 3 and the second electric wire. The core wire 42 is connected to the second lead wire 32 of the magnetic field sensor 3, and the core wire of the third electric wire 43 is connected to the third lead wire 33 of the magnetic field sensor 3.

  When the first member 11 approaches the second member 12, the strength of the magnetic field detected by the magnetic field sensor 3 increases, and when the first member 11 moves away from the second member 12, the strength of the magnetic field detected by the magnetic field sensor 3. Becomes weaker. The calculation unit 5 measures the distance between the first member 11 and the second member 12 by calculation based on the strength of the magnetic field detected by the magnetic field sensor 3.

  The calculation unit 5 performs analog-digital conversion on the output signal of the magnetic field sensor 3 transmitted by the CPU (Central Processing Unit), a storage element constituted by a ROM, a RAM, and the like, and the second electric wire 42 of the cable 4. The storage element has relation information indicating the relationship between the strength of the magnetic field detected by the magnetic field sensor 3 and the distance between the first member 11 and the second member 12. It is remembered. The CPU refers to the relationship information stored in the storage element based on numerical information indicating the intensity of the magnetic field detected by the magnetic field sensor 3 and digitally converted by the AD conversion element, and between the first member 11 and the second member 12. Is obtained by calculation.

(Consideration about the fitting ratio R of the permanent magnet 2)
Next, for a suitable range of the fitting ratio R, which is the ratio of the length (fitting depth D ₃ ) of the portion fitted in the recess 110 to the total length (thickness t) in the central axis c direction of the permanent magnet 2, This will be described with reference to FIGS.

  4A to 4E, the fitting ratio R is 1.0 (100%), 0.5 (50%), 0.25 (25%), 0.1 (10%), And 0 (0%) are schematic views schematically showing magnetic lines of force radiated from the permanent magnet 2 in each case, and FIG. 5 is a distance between the first member 11 and the second member 12 in each case. 4 is a graph showing the relationship between L and the magnetic field intensity B detected by the magnetic field sensor 3. 4A to 4E, the distance between the end face 2b on the N pole side of the permanent magnet 2 and the second member 12 in the direction along the central axis c of the permanent magnet 2 is constant.

  As shown in FIGS. 4A to 4E, as the fitting ratio R is smaller, the magnetic lines of force radiated from the permanent magnet 2 greatly extend along the central axis c of the permanent magnet 2 and are detected by the magnetic field sensor 3. The strength of the magnetic field increases. Further, the distance between the first member 11 and the second member 12 can be obtained with higher accuracy as the amount of change in the strength of the magnetic field detected by the magnetic field sensor 3 accompanying the movement of the first member 11 is larger. That is, as apparent from FIG. 5, the smaller the fitting ratio R, the larger the magnetic field intensity B detected by the magnetic field sensor 3 in accordance with the change in the distance L between the first member 11 and the second member 12. It changes, and it becomes possible to raise the detection accuracy of the distance L between the 1st member 11 and the 2nd member 12. FIG.

However, when the permanent magnet 2 is not fitted in the recess 110, i.e. the fitting depth D ₃ is zero, the positional deviation of the permanent magnet 2 is generated by the permanent magnet 2 slides relative to the first member 11 As a result, the distance between the first member 11 and the second member 12 cannot be measured accurately. Even if the permanent magnet 2 is fitted in the recess 110, if the fitting ratio R is too small, the permanent magnet 2 is likely to fall. Therefore, in the present embodiment, by setting the fitting ratio R to 0.1 to 0.5 (10 to 50%), it is possible to prevent the positional displacement and the collapse of the permanent magnet 2, and the first member 11 and the second member. This is to achieve both improvement in measurement accuracy of the distance to the member 12.

(Operation and effect of the embodiment)
According to the embodiment described above, the following operations and effects can be obtained.

(1) Since the permanent magnet 2 is fixed to the first member 11 to be measured and moves with respect to the second member 12 together with the first member 11, the magnetic field intensity that changes as the first member 11 moves is changed. The change can be directly detected by the magnetic field sensor 3 fixed to the second member 12. Thereby, the change amount of the magnetic field intensity detected by the magnetic field sensor 3 accompanying the movement of the first member 11 can be increased, and the measurement accuracy of the distance between the first member 11 and the second member 12 can be increased. Is possible.

(2) Since the permanent magnet 2 is fixed to the first member 11 by its own magnetic force, the permanent magnet 2 can be fixed without providing fixing means such as an adhesive. As a result, the number of man-hours for attaching the permanent magnet 2 to the first member 11 can be reduced, and the permanent magnet can be used without concern for a decrease in the adhesive strength of the adhesive even in a high temperature environment exceeding 100 ° C. 2 can be stably fixed to the first member 11.

(3) Since the permanent magnet 2 is fitted into the concave portion 110 of the first member 11, it is possible to prevent a positional shift and a fall with respect to the first member 11.

(4) The fitting ratio R, which is the ratio of the length (fitting depth D ₃ ) of the portion fitted in the recess 110 to the total length (thickness t) in the direction of the central axis c of the permanent magnet 2 is 0.1-0. .5 (10 to 50%), it is possible to achieve both the prevention of positional displacement and falling of the permanent magnet 2 and the improvement of the measurement accuracy of the distance between the first member 11 and the second member 12.

(5) By using a samarium cobalt magnet or a neodymium magnet as the permanent magnet 2, it is possible to obtain a higher attractive force than when the permanent magnet 2 is a ferrite magnet, and the first member 11 is subjected to vibration or impact. However, it is possible to suppress the permanent magnet 2 from being inclined or detached with respect to the first member 11.

(6) By setting the residual magnetic flux density of the permanent magnet 2 to 1.0 T or more, the permanent magnet 2 can be more securely fixed to the first member 11.

(Summary of embodiment)
Next, the technical idea grasped from the embodiment described above will be described with reference to the reference numerals in the embodiment. However, each reference numeral in the following description does not limit the constituent elements in the claims to members or the like specifically shown in the embodiment.

[1] A distance measuring system (1) for measuring a distance between a first member (11) and a second member (12) that can be relatively moved in a predetermined contact / separation direction, wherein the first member (11) A permanent magnet (2) partly fitted in the formed recess (110), and a magnetic field sensor (fixed to the second member (12) and detecting the strength of the magnetic field generated by the permanent magnet (2) ( 3), the first member (11) is made of a soft magnetic material, the recess (110) opens toward the second member (12), and the permanent magnet (2) itself The distance measuring system (1) is fixed to the first member (11) by the magnetic force of and the movement in the direction intersecting the separation / contact direction is restricted by the fitting to the recess (110).

[2] In the permanent magnet (2), one end (21) in the direction of the central axis (C) along the direction in which the pair of magnetic poles are aligned is fitted in the recess (110), and the center of the permanent magnet (2) The distance measuring system (1) according to the above [1], wherein the ratio of the length of the portion fitted in the recess (110) to the total length in the axis (C) direction is 10 to 50%.

[3] the permanent magnet (2) and the recess (110) are both cylindrical, the diameter of the permanent magnet (2) and _{D 1,} the inner diameter of the recess (110) and _{D 2,} the recess ( when the fitting depth of the permanent magnets (2) in 110) was _{D 3,} satisfy the following formula, the distance measuring system according to [1] or [2] (1). _{D 2} -D ₁ <D ₃

[4] The distance measuring system (1) according to any one of [1] to [3], wherein the permanent magnet (2) is a samarium cobalt magnet or a neodymium magnet.

[5] The distance measuring system (1) according to any one of [1] to [4], wherein the permanent magnet (2) has a residual magnetic flux density of 1.0 T or more.

[6] The distance measuring system (1) according to any one of [1] to [5], wherein the permanent magnet (2) is disposed in a space having a temperature of 100 ° C. or higher.

[7] A distance measuring method for measuring a distance between the first member (11) and the second member (12) that can be moved relative to each other in a predetermined contact / separation direction, wherein the second member is attached to the first member (11). A concave portion (110) that opens toward the member (12) is formed, a permanent magnet (2) is arranged so that a part of the concave portion (110) is fitted, and a magnetic field generated by the permanent magnet (2). A magnetic field sensor (3) for detecting the intensity of the permanent magnet (2) is disposed on the second member (12), and the first member (11) is made of a soft magnetic material constituting a part of the magnetic path of the permanent magnet (2). The permanent magnet (2) is fixed to the first member (11) by its own magnetic force, and moves in a direction intersecting the separation / contact direction by fitting into the recess (110). Is controlled based on the strength of the magnetic field detected by the magnetic field sensor (3). The distance between the first member (11) and said second member (12) is measured, the distance measuring method.

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

  Further, the present invention can be appropriately modified and implemented without departing from the spirit of the present invention. For example, in the above-described embodiment, the case where the second member 12 is fixed and the first member 11 moves relative to the second member 12 has been described. However, the present invention is not limited to this, and the first member 11 is a device frame or the like. The distance measuring system may be configured such that the second member 12 is moved relative to the first member 11.

DESCRIPTION OF SYMBOLS 1 ... Distance measuring system 11 ... 1st member 110 ... Recess 12 ... 2nd member 2 ... Permanent magnet 3 ... Magnetic field sensor

Claims (7)

A distance measuring system that measures a distance between a first member and a second member that are relatively movable in a predetermined approaching / separating direction,
A permanent magnet partially fitted in the recess formed in the first member;
A magnetic field sensor fixed to the second member and detecting the strength of the magnetic field generated by the permanent magnet,
The first member is made of a soft magnetic material, and the concave portion opens toward the second member,
The permanent magnet is fixed to the first member by its own magnetic force, and movement in a direction intersecting the separation / contact direction is restricted by fitting into the recess.
Distance measuring system. The permanent magnet has one end in the direction of the central axis along the direction in which the pair of magnetic poles are aligned, and is fitted into the recess.
The ratio of the length of the portion fitted in the concave portion to the total length in the central axis direction of the permanent magnet is 10 to 50%.
The distance measuring system according to claim 1. The permanent magnet and the recess are both cylindrical.
The diameter of the permanent magnet and D _1, the inner diameter of the recess and D _2, when the fitting depth of the permanent magnets in the concave portion was set to D _3, satisfy the following formula,
The distance measuring system according to claim 1 or 2.
_{D 2} -D ₁ <D ₃ The permanent magnet is a samarium cobalt magnet or a neodymium magnet.
The distance measuring system according to any one of claims 1 to 3. The permanent magnet has a residual magnetic flux density of 1.0 T or more,
The distance measuring system according to any one of claims 1 to 4. The permanent magnet is disposed in a space having a temperature of 100 ° C. or higher.
The distance measuring system according to any one of claims 1 to 5. A distance measuring method for measuring a distance between a first member and a second member that are relatively movable in a predetermined approaching / separating direction,
Forming a recess opening in the first member toward the second member;
A permanent magnet is arranged so that a part thereof fits in the recess,
A magnetic field sensor for detecting the strength of the magnetic field generated by the permanent magnet is disposed on the second member;
The first member is made of a soft magnetic material constituting a part of the magnetic path of the permanent magnet,
The permanent magnet is fixed to the first member by its own magnetic force, and movement in a direction intersecting the separation / contact direction is restricted by fitting into the recess,
Measuring the distance between the first member and the second member based on the strength of the magnetic field detected by the magnetic field sensor;
Distance measurement method.

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