JP2006300902A - Stress detection method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To put a stress sensor utilizing a reverse effect of magnetostriction to practical use, and to provide a stress detection method superior in robust properties and a high-performance and inexpensive stress detection device based on such a detection method. <P>SOLUTION: A thin cylindrical permanent magnet 2 magnetized in the axial direction is attached to the surface of a shaft 1 as a magnetic material having magnetostriction and a magnetic sensor 3 is disposed at an end position of the permanent magnet 2 to detect the variation of spatial magnetic flux leaking out to the outside of the shaft 1 among the magnetic flux generated from the permanent magnet 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for detecting stress acting on members of various machines, and more specifically, to a stress detection method and apparatus for detecting a stress applied to a member having magnetostriction in a non-contact manner by utilizing an inverse effect of magnetostriction. Is.

  For example, if the axial force of an undercarriage in an automobile can be detected by an inexpensive and highly robust sensor, it may lead to the realization of new vehicle control. It is thought that there are many requests, but at present there are no such sensor candidates.

As a method of detecting the stress of a member having elasticity, a method of attaching a strain gauge is well known, but in order to detect the axial force (tensile, compressive force) of a link around an automobile or the like, it is robust. Therefore, the above method using a strain gauge is not suitable for this.
On the other hand, although a sensor using magnetostriction has been proposed as a stress sensor, none seems to be put into practical use (for example, see Non-Patent Document 1).
I. J. et al. Garshelis: SAE, Paper No. 910856, 1991

That is, FIG. 13 is an explanatory diagram of a stress sensor using the inverse effect of magnetostriction proposed by Non-Patent Document 1 above. In FIG. 13A, PM is a permanent magnet, and FS is a magnetic sensor. The core located at the center has magnetostriction. The magnetic flux from the permanent magnet PM is distributed as shown in the figure, magnetizing the core as shown by the arrow, and the magnetic flux also passes through the core.
When tensile stress is applied to the core, the magnetic flux passes through the core more, so the magnetic flux passing through the magnetic sensor FS decreases. On the other hand, when compressive stress acts on the core, the magnetic flux is difficult to pass through the core, and thus the magnetic flux passing through the magnetic sensor FS increases. In this way, the magnitude of the signal from the sensor FS reflects the magnitude of the stress acting on the core.

The above is the principle of the proposed stress sensor, which is characterized in that no power source is required to generate magnetic flux. It is stated that the position of the magnetic sensor FS may be the position of A or B as shown in FIG.
In tensile stress and compressive stress, the data shows that the signal of the sensor FS changes more greatly in compression, and in the rated range of the sensor, there is a change of 30 to 80% in compression. .

  However, in the above proposal, the cylindrical alnico magnet is arranged in the pipe-shaped core, and the Hall element is placed on the surface of the pipe, and the data is taken. Thus, it cannot be said that it is a proposal at the practical application stage.

  The present invention has been made in view of the above-described problems in conventional stress sensors, and the object of the present invention is to commercialize a stress sensor using the inverse effect of magnetostriction and to provide a stress detection method with excellent robustness. Another object of the present invention is to provide an inexpensive stress detection apparatus to which such a detection method is applied.

  As a result of intensive studies aimed at solving the above problems, the present inventors have found that if a magnetized magnetic body is on the side of a magnetic body having magnetostriction, the present invention can be a practical stress sensor, and the present invention has been completed. I arrived.

  The present invention is based on the above knowledge, and the stress detection method of the present invention is such that the magnetic flux generated from the permanent magnet is in the vicinity of the permanent magnet and passes through the magnetic body having magnetostriction, and the magnetic body. Phenomenon in which the amount of spatial magnetic flux that flows in the space outside the magnetic material changes when the amount of internal magnetic flux that passes through the magnetic material changes due to the stress acting on the magnetic material that is distributed to the space without flowing through the space It is characterized in that the stress acting on the magnetic body is detected by detecting such a change in the spatial magnetic flux on a side different from the magnetic body with respect to the permanent magnet. Yes.

  The stress detection apparatus of the present invention can be suitably used for carrying out the above detection method, and includes a magnetic body having magnetostriction, a permanent magnet disposed in the vicinity of the magnetic body, and the magnetic body. Including a magnetic flux detection means for detecting a change in the magnetic flux generated from the permanent magnet and flowing in the space outside the magnetic material without passing through the magnetic material, for example, a magnetic sensor The spatial magnetic flux detection means such as is arranged on the side different from the permanent magnet with respect to the magnetic body.

When a magnetic body having magnetostriction and a permanent magnet are arranged close to each other, the magnetic flux emitted from the permanent magnet flows in a distributed manner with the internal magnetic flux passing through the magnetic body and the spatial magnetic flux flowing in the space outside the magnetic body. When the stress acts on the magnetic material, the amount of the internal magnetic flux passing through the magnetic body changes, and as a result, the amount of the spatial magnetic flux flowing through the space changes, so that the change in the spatial magnetic flux is detected by a spatial magnetic flux detecting means such as a magnetic sensor, Specifically, the stress acting on the magnetic material can be detected by detecting with a Hall element or Hall IC.
According to the present invention, such a change in the spatial magnetic flux is detected on the side different from the magnetic body with respect to the permanent magnet, so that a minute magnetic field change can be detected and acts on the magnetic body. Stress detection sensitivity can be improved. In addition, by arranging the permanent magnet integrally with the magnetic body, or by making the magnetic body into a shaft shape, it is possible to realize a compact and inexpensive device with a small number of parts, and it is also possible to detect stress in a rotating state. It becomes possible and the usefulness can be dramatically improved.

  Hereinafter, the stress detection method and the stress detection apparatus of the present invention will be described in more detail together with specific embodiments thereof.

  The stress detection method and apparatus according to the present invention basically have the above-described configuration. However, the magnetic body is axial, or the permanent magnet is disposed in contact with the surface of the axial magnetic body. Is desirable.

  That is, the stress detection device of the present invention has a structure as shown in FIG. 1A, for example, and includes a shaft 1 (magnetic material) having magnetostriction. A permanent magnet 2 is fitted. The permanent magnet 2 is magnetized in the axial direction.

In FIG. 1A, reference numeral 3 denotes a magnetic sensor as spatial magnetic flux detection means, and specifically, a Hall sensor is used.
As the magnetic sensor 3, in addition to the Hall sensor described above, a power-saving and small Hall IC or MI sensor can be used. From the viewpoint of increasing detection sensitivity, as shown in the figure, a permanent magnet is used. It is desirable to detect the magnetic flux in the radial direction by disposing it at a position close to the end portion of 2 (see FIG. 1B). The Hall IC here is a type that can obtain linear output.

  FIG. 1B is a cross-sectional view of the permanent magnet 2, and the magnetic flux of the permanent magnet 2 is closed by flowing in the space inside the shaft 1 and the space outside the shaft 1.

When an axial tensile stress acts on the shaft 1, the magnetic flux passing through the shaft 1 increases (the magnetic flux easily passes through the inside of the shaft), so that the spatial magnetic flux leaking outside decreases, and therefore the magnetic flux passing through the magnetic sensor 3. Will be reduced. This is an explanation of the case where the magnetostriction is positive (hereinafter the same), and of course the opposite is true when the magnetostriction is negative.
On the other hand, when compressive stress is applied to the shaft 1, the magnetic flux passing through the shaft 1 decreases (the magnetic flux becomes difficult to pass through the shaft), so that the spatial magnetic flux leaking outside increases and the magnetic flux passing through the magnetic sensor 3 increases. Therefore, the signal of the magnetic sensor 3 corresponding to the stress is obtained.

In the stress detection device of the present invention having such a structure, since it is not necessary to bring the magnetic sensor 3 into contact with the shaft 1, it is possible to detect axial force (tensile and compressive stress) in a non-contact state.
In addition, the axial force (tensile and compressive stress) in the rotating state can be measured by using a magnetic material on which the stress acts as a shaft. The permanent magnet 2 functions as a magnetic flux supply source and does not need to be deformed together with the shaft 1 under stress.

As shown in FIGS. 2A and 2B, a yoke 5 made of a soft magnetic material having a small coercive force, such as a silicon steel plate, electromagnetic soft iron, soft ferrite, or permalloy, is provided on the back side (on the opposite axis side) of the magnetic sensor 3. Can also be provided.
When such a yoke 5 is used, resistance against external electromagnetic noise is improved and the magnitude of the signal of the magnetic sensor 3 can be increased by about a factor of two.

Also, as shown in FIG. 3, two magnetic sensors can be used. That is, it is desirable to arrange the second magnetic sensor 4 in the axial direction in addition to the magnetic sensor 3 and to dispose these at positions near both ends of the concavo-convex portion 2. In this case, since the sensor sensitivity sense is reversed for the second magnetic sensor 4, the two sensor signals can be added and doubled by subtraction.
By arranging the two sensors 3 and 4 in this way, even if an almost uniform magnetic field from the outside is applied, the input is in-phase, so that it can be canceled by subtraction, and resistance to disturbance is improved. To do.

FIG. 4 shows a case where a sheet-like permanent magnet 2 is arranged on the surface of the shaft 1. The permanent magnet 2 is magnetized in the longitudinal direction (axial direction) of the shaft 1 as indicated by an arrow in the figure. The permanent magnet 2 may be a bond magnet or a sheet metal magnet such as alnico. The sheet-like magnet 2 is advantageous because the magnet characteristics when magnetized in the longitudinal direction are extremely stable.
The magnetic sensor 3 may be disposed above the end of the sheet magnet magnet 2.

Further, as shown in FIG. 5, another permanent magnet 2 can be arranged on the back surface side (180 ° position) of the permanent magnet 2.
In this case, the signal of the magnetic sensor can be doubled, and when the bending stress is applied to the shaft 1 such as when the diameter of the shaft 1 is small, the bending stress can be canceled and only the axial force can be detected. Occurs.

  FIG. 6 is a cross-sectional view when the reduced diameter portion 1a is provided on the shaft 1. By forming the reduced diameter portion 1a in this way, the position of the permanent magnet 2 can be easily fixed.

Further, in the above description, an example in which a shaft-like magnetic body is used as a magnetic body having magnetostriction has been shown. However, as shown in FIG. 7, even a plate-like magnetic body 10 is used as a stress detection device. Needless to say, it works.
As shown in the drawing, a sheet-like permanent magnet 2 magnetized in the longitudinal direction is arranged on the plate surface, and a magnetic sensor 3 is similarly arranged above the end of the permanent magnet 2.

Since it is desired that the magnetic material having magnetostriction has little hysteresis with respect to stress, the magnetic material needs to undergo an appropriate process. For example, it is desirable to perform a heat treatment process after machining, or to perform machining so that non-uniform residual stress does not enter after heat treatment. Magnetizing in the circumferential direction can also be said to be an effective means.
That is, as shown in FIG. 8, the shaft 1 is magnetized in the circumferential direction (the direction of magnetization is perpendicular to the permanent magnet 2), and there is much magnetization directed in the circumferential direction, which reduces hysteresis. It is thought that it works for. The merit of magnetizing in the circumferential direction is that the sensitivity of tension and compression is the same (the stress magnetic effect is generally greater in compression). It is estimated that this reason is the same.

When the shaft material is energized, when the current density is uniform, the magnitude of the circumferential magnetic field is proportional to the radius inside the shaft and attenuates inversely proportional to the distance from the center outside the shaft. .
In general, a portion to which a magnetic field twice or more as large as the coercive force of the shaft material is applied is generally magnetized. Therefore, when a sufficiently large current is passed, the cylindrical region including the surface is surely magnetized in the circumferential direction.

  Further, since a larger output signal is obtained when the stress applied to the magnetic body is larger, the sensitivity can be increased by using a hollow shaft in the case of a shaft.

FIGS. 9A and 9B show examples in which a multipolar magnetized portion is provided at the end of a thin cylindrical magnet so as to function as a rotation sensor.
That is, a slightly longer bonded magnet is employed as the thin cylindrical permanent magnet 2, and the left end in the figure is an NS multipolar magnetized portion 2a. The magnetization direction at this time is the radial direction as shown in FIG.

On the other hand, the magnetization direction of the portion supplying the magnetic flux for stress detection in the thin cylindrical permanent magnet 2 is the axial direction as shown in FIG. The bond magnet constituting the permanent magnet 2 may be a ferrite bond or a rare earth bond magnet.
Then, by making the Hall IC 7 face the multipolar magnetized portion 2a of the permanent magnet 2, the rotation signal of the shaft 1 can be taken simultaneously with the stress detection.

  In this way, a stress detection device that also serves as a rotation sensor can be realized. Here, as the Hall IC 7, a digital output type that is a pulse output is adopted.

In the stress detection apparatus, in order to stabilize the sensor characteristics, aging is preferably performed at a temperature higher than the use temperature.
By aging the sensor for about 1 hour at, for example, 160 ° C., stable characteristics can be obtained when used at a temperature equal to or lower than that temperature.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples.

Example 1
As a magnetic material having magnetostriction, maraging steel (trade name YAG300, manufactured by Hitachi Metals, Ltd., 18% Ni-9% Co-5% Mo-Fe) is used, and as shown in FIG. = 19 mm shaft 1 was made by machining.
After machining, solution treatment and aging heat treatment were performed. The solution treatment was held at 820 ° C. × 1 h in vacuum, the aging treatment was held at 490 ° C. × 5 h in vacuum, and then air-cooled.

  As the permanent magnet 2, a thin cylindrical ferrite magnet having a width of 12 mm and a thickness of 1 mm was magnetized in the width direction. The leakage magnetic field at the end face after magnetization of the thin cylindrical ferrite magnet alone was about 1.5 kG.

Then, as shown in FIG. 1, the thin cylindrical permanent magnet 2 is fitted to the shaft 1, the hall sensor 3 is disposed at the upper position of the end of the permanent magnet 2, and tensile and compressive stress is applied to the shaft 1. The output of the Hall sensor 3 was examined. The result is shown in FIG. The magnetic sensor area of the hall sensor 3 was about 2 mm ² , and the center position of the area was about 0.5 mm from the surface of the shaft 1. The Hall sensor 3 detects a radial magnetic field.
It was confirmed that the output from the Hall sensor 3 decreased when the shaft 1 was subjected to tensile stress, increased due to compressive stress, and obtained a characteristic with almost no hysteresis with respect to a stress load of ± 40 MPa.

There is no data for stress 0, but this is due to the convenience of the testing machine used in this example. That is, in the test machine in which tensile stress and compressive stress are continuously applied, play occurs and continuous output cannot be obtained. Therefore, it is considered that the problem can be solved by adding a device to the apparatus so as to prevent the occurrence of play.
Moreover, although the stress load range is narrow, this is also due to the convenience of the testing machine. If a testing machine with a large capacity is used, the stress range can be easily expanded.

In a stress sensor using the inverse effect of magnetostriction, hysteresis appears when the shaft 1 causes micro-yield. Therefore, if the load stress is about half or less of the yield stress of the magnetic material constituting the shaft 1, Characteristics with good reproducibility can be obtained.
In this example, since the yield stress of the maraging steel used as the material of the shaft 1 exceeds 2 GPa, it is considered that sufficiently reproducible data can be obtained up to at least about 1 GPa.

(Example 2)
The same shaft material 1 as in Example 1 was used, and magnetized in the circumferential direction by passing 10000 A through it.
Except for this, the same operation as in Example 1 was repeated, and the output from the Hall sensor 3 was examined. As a result, it was confirmed that a characteristic having almost no hysteresis was obtained with respect to a stress load of ± 40 MPa. Note that the sensitivity was slightly inferior to that of Example 1 shown in FIG.

(Example 3)
As a material for the shaft 1, carbon steel for mechanical structure S45C specified in JIS G4051 was used, induction hardening was performed as a heat treatment, and then a tempering treatment at 170 ° C. for 1 hour was performed. Except for this, the output characteristics of the Hall sensor 3 were investigated by repeating the same operation as in Example 2.
In addition, as the aim of the above heat treatment, the effective hardened layer depth at which the surface hardness after tempering is HRC50 or more and HRC45 or more is aimed at 0.8 mm.

  As a result, characteristics with almost no hysteresis were obtained. The sensitivity was confirmed to be the same as in Example 2 above.

(A) It is explanatory drawing which shows the example which fitted the thin cylindrical magnet to the axis | shaft as an example of embodiment of the stress detection apparatus by this invention. (B) It is expansion explanatory drawing in the permanent magnet part shown to Fig.1 (a). It is the front view (a) and top view (b) which show the other embodiment which has arrange | positioned the yoke behind the magnetic sensor. It is explanatory drawing which shows the example of an embodiment which has arrange | positioned two magnetic sensors. It is explanatory drawing which shows the embodiment example which has arrange | positioned the sheet-like magnet as a permanent magnet. It is explanatory drawing which shows the embodiment example which has arrange | positioned the sheet-like magnet of 2 sheets as a permanent magnet in the circumferential direction. It is explanatory drawing which shows the example of embodiment which has arrange | positioned the permanent magnet to the diameter reducing part of an axis | shaft. It is explanatory drawing which shows the example of an embodiment using a plate-shaped magnetic body instead of the shaft-shaped magnetic body. It is explanatory drawing which shows the example of an embodiment magnetized in the circumferential direction of the axis | shaft. (A) It is explanatory drawing which shows the embodiment of the stress detection apparatus which served as the rotation sensor. (B) It is an enlarged view which shows the magnetization state of the multi-pole magnetized part shown to Fig.9 (a). It is a graph which shows the output characteristic data obtained by Example 1 of this invention. (A)-(c) is explanatory drawing which shows the structure and principle of the conventional stress sensor.

Explanation of symbols

1 axis (magnetic material)
DESCRIPTION OF SYMBOLS 1a Reduced diameter part 2 Permanent magnet 2a Multipolar magnetized part 3, 4 Magnetic sensor (space magnetic flux detection means)
5 York

Claims (21)

  Of the magnetic flux generated from the permanent magnet and distributed to the internal magnetic flux passing through the magnetic body having magnetostriction and positioned in the vicinity of the permanent magnet, and the magnetic flux flowing in the space outside the magnetic body, the magnetic body A stress characterized by detecting a stress acting on the magnetic material by detecting a change in the spatial magnetic flux resulting from the change of the internal magnetic flux caused by the stress acting on the side different from the magnetic material with respect to the permanent magnet. Detection method.   The stress detection method according to claim 1, wherein a change in the spatial magnetic flux is detected by a magnetic sensor.   The stress detection method according to claim 1 or 2, wherein a shaft-like material is used as the magnetic body.   A magnetic flux having magnetostriction, a permanent magnet located in the vicinity of the magnetic body, and a spatial magnetic flux generated from the permanent magnet and flowing into the space outside the magnetic body by applying a stress to the magnetic body. A stress detection device comprising spatial magnetic flux detection means for detecting the change of the magnetic flux, wherein the spatial magnetic flux detection means is disposed on a side different from the magnetic body with respect to the permanent magnet.   A shaft having magnetostriction, a permanent magnet disposed near the surface of the shaft, and disposed near the permanent magnet, and stress is applied to the shaft so that the shaft is generated from the permanent magnet without passing through the shaft. The stress detection device according to claim 4, further comprising a magnetic sensor that detects a change in a spatial magnetic flux flowing in an outside space.   The stress detection apparatus according to claim 5, wherein the permanent magnet is disposed in contact with the surface of the shaft.   The stress detection apparatus according to claim 5 or 6, wherein the permanent magnet has a thin cylindrical shape or a sheet shape and is magnetized in an axial direction.   The stress detection device according to claim 5, wherein the shaft includes a reduced diameter portion, and a permanent magnet is disposed in the reduced diameter portion.   The stress detection device according to any one of claims 6 to 8, wherein a tensile stress and a compressive stress acting in an axial direction are detected.   The stress detection apparatus according to any one of claims 6 to 9, wherein the shaft is rotatably held.   The stress detection apparatus according to claim 5, wherein the shaft is magnetized in the circumferential direction.   The stress detection device according to any one of claims 5 to 11, wherein the magnetic sensor is disposed at an end portion of the permanent magnet and detects a magnetic flux in a radial direction.   The stress detection device according to claim 12, wherein the magnetic sensor is an end portion of a permanent magnet and is disposed above the permanent magnet.   The stress detecting device according to any one of claims 5 to 13, wherein a yoke is disposed at a position opposite to the axis of the magnetic sensor.   15. The stress detection device according to claim 14, wherein the yoke is made of a soft magnetic material.   The stress detecting device according to any one of claims 5 to 15, wherein the shaft having magnetostriction is made of heat-treated steel or surface-treated steel.   The stress detection apparatus according to claim 5, wherein the magnetic sensor is a Hall element or a Hall IC.   The stress detection device according to claim 4, wherein the permanent magnet is a bonded magnet.   The permanent magnet has a cylindrical shape, and has multipolar magnetized portions alternately magnetized in the circumferential direction at the end of the cylindrical magnet, and is disposed to face the multipolar magnetized portion. The stress detection device according to claim 18, further comprising a magnetic sensor for detecting rotation.   The stress detection device according to any one of claims 5 to 19, wherein the shaft is hollow.   The stress detecting device according to any one of claims 5 to 20, wherein the shaft and the permanent magnet are subjected to an aging treatment.

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