JP2007040956A - Stress sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stress sensor of magnetostrictive type utilizing the opposite effect of magnetostriction, provided with a detection part which is compact and easy to operation, low in cost and excellent in robustness. <P>SOLUTION: The stress detection part 1 comprising the plate-like permanent magnet 2, the magnetic sensors 3 and 4 for detecting variation of a magnetic flux generated by the plate-like magnet 2 flowing outside of the magnetic body 8, and the plate-like yoke 5 for enhancing the detection sensitivity of the magnetic sensors 3 and 4 by its magnetic flux collection effect is attached on the magnetostrictive magnetic body 8. The magnetic sensors 3 and 4 are arranged closely to the magnetic body 8 at the neighbor of ends of the plate-like magnet 2 and also the magnetic body side to the yoke 5 arranged at the other side of the magnetic body regarding the plate-like magnet 2 and except the place between the plate-like magnet 2 and the magnetic body 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for sensing stress acting on various mechanical parts, for example, and more specifically, to a stress sensor capable of detecting stress acting on a member having magnetostriction by utilizing the inverse effect of magnetostriction. It is.

  For example, if the axle 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. However, there are currently no such sensor candidates.

As a method of detecting the stress applied to the elastic member, a method of attaching a strain gauge is generally well known, but in order to monitor the axial force (tensile and compressive force) of the link in the undercarriage part such as an automobile. However, since robustness is required, the strain gauge method is not suitable.
On the other hand, as a stress sensor, a sensor using magnetostriction has been proposed, but 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. 9 is an explanatory diagram of a stress sensor using the inverse effect of magnetostriction proposed by Non-Patent Document 1, and in FIG. 9A, PM is a permanent magnet and FS is a magnetic sensor. The core located at the center has magnetostriction. Permanent magnet PM magnetizes the core in the direction indicated by the arrow. The magnetic flux of the permanent magnet PM is distributed as shown in the figure and also passes through the core.
When tensile stress is applied to the core, the magnetic flux from the permanent magnet PM passes through the core more, so the magnetic flux passing through the magnetic sensor FS decreases. On the other hand, when compressive stress is applied to the core, the magnetic flux becomes difficult to pass through the core, so that the magnetic flux passing through the sensor FS increases. In this way, the magnitude of the signal from the magnetic 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 A or B as shown in FIG.
In tensile stress and compressive stress, the data shows that the change in the signal of the magnetic sensor FS is greater in compression, and there is a change of 30 to 80% in compression within the rated range of the sensor. Yes.

  However, in the above proposal, although the cylindrical alnico magnet is arranged in the pipe-shaped core and the Hall element is placed on the surface of the pipe, data is taken, but it does not go out of the principle confirmation stage. However, there are various mounting problems such as the placement of these magnetic sensors and permanent magnets on the core and specific mounting methods, and it is practical to use these stress sensors to solve these problems. It was a problem to make it.

  The present invention has been made in view of the above-mentioned problems in the magnetostrictive stress sensor, and the object of the present invention is to commercialize a stress sensor using the inverse effect of magnetostriction, and to provide a compact and easy-to-handle detection unit. An object is to provide a magnetostrictive stress sensor which is inexpensive and excellent in robustness.

  As a result of intensive studies on the arrangement and mounting method of a magnetic sensor, a permanent magnet, and a yoke for improving the detection sensitivity, the inventors of the present invention have made a thin plate-like permanent magnet and a Hall element. And a plate-like yoke having a predetermined arrangement, it has been found that a compact and excellent handling unit can be realized, and the present invention has been completed.

  The present invention is based on the above knowledge, and the stress sensor according to the present invention includes a magnetic flux generated from a permanent magnet arranged close to a magnetic body having magnetostriction, and a magnetic flux passing through the inside of the magnetic body. When the amount of magnetic flux that passes through the magnetic body changes due to the stress acting on the magnetic body, the amount of magnetic flux that flows outside the magnetic body changes and the magnetic flux distribution A magnetostrictive stress sensor that utilizes a phenomenon in which the plate-shaped permanent magnet is disposed in proximity to the magnetic material for stress measurement, the plate-shaped yoke disposed on the diamagnetic side of the plate-shaped magnet, and A stress detection unit having a magnetic sensor disposed near the end of the plate magnet on the magnetic body side of the yoke and at a position other than between the plate permanent magnet and the magnetic body; It is a feature.

  When a permanent magnet is placed close to a magnetic body having magnetostriction, the magnetic flux emitted from the permanent magnet flows in a distributed manner into an internal magnetic flux passing through the magnetic body and a spatial magnetic flux flowing in a space outside the magnetic body. When stress is applied to the magnetic material, the amount of internal magnetic flux that passes through this magnetic material changes, and as a result, the amount of spatial magnetic flux flowing through the space changes and the distribution of internal and external magnetic flux changes. By detecting with a simple magnetic sensor, the stress acting on the magnetic material can be detected.

  According to the present invention, a plate-like permanent magnet disposed close to a magnetic body, a magnetic sensor that detects a change in magnetic flux generated from the permanent magnet and flowing outside the magnetic body, and a diamagnetism of the plate magnet The plate-shaped yoke arranged on the body side constitutes a stress detection unit, and the detection sensitivity is improved by the magnetic flux collecting effect of the yoke, and the magnetic sensor is located near the end of the plate-shaped magnet on the magnetic body side relative to the yoke. In addition, since the sensor is disposed at a position other than between the plate-shaped permanent magnet and the magnetic body, that is, between the plate-shaped yoke and the permanent magnet or between the plate-shaped yoke and the magnetic body, The sensor can be small and highly sensitive, and a stress sensor can be easily configured by simply attaching the detection unit to a magnetic body having magnetostriction, so that the stress acting on the magnetic body can be detected. And its useful The thing is very high.

  Hereinafter, the stress sensor of the present invention will be described in more detail together with specific embodiments thereof.

  In the stress sensor of the present invention, a magnetic sensor for detecting a change in magnetic flux generated from a permanent magnet and flowing outside the magnetic body is preferably integrated into the shield case together with the permanent magnet and the yoke for improving detection sensitivity. As a result, a stress detection unit (detection head) can be obtained. As the detection head, a structure as shown in FIG. 1A can be exemplified.

That is, the detection head shown in the drawing, that is, the stress detection unit 1 includes a thin plate-like permanent magnet 2, Hall elements 3 and 4 as magnetic sensors, and a yoke 5, which are inside an electromagnetic shield case 6. Are housed in one piece.
And such a detection head 1 is attached to the magnetic body 8 which has a magnetostriction as shown, for example in FIG.1 (b), and when a stress acts on the magnetic body 8, based on the principle as mentioned above, The stress acting on the magnetic body 8 can be detected.

  As shown in FIG. 1 (a), the shield case 6 is a box-type whose lower side surface is released in the figure, and the plate-like permanent magnet 2 is formed on the lower end surface of the shield case 6 which is released. It is desirable to arrange the plate-like magnets 2 so that the lower end surfaces thereof coincide with each other or are parallel and close to each other.

As the material of the shield case 6, a soft magnetic metal material, for example, an iron-based metal material such as permalloy or silicon steel plate can be used. It is also possible to use a plastic material mixed with a magnetic filler having an electromagnetic shielding effect. Furthermore, a metal material having no magnetism such as an aluminum material or a copper material can be used.
In other words, the magnetic metal material case and the magnetic filler-containing plastic case have an electromagnetic shielding effect, so the resistance to electromagnetic noise from disturbance is significantly improved, and there is also a shielding effect against magnetic noise. Resistance to disturbance is improved. A nonmagnetic metal case also has an electromagnetic noise shielding effect.

Regarding the size of the shield case 6 and the positional relationship with the plate-shaped magnet 2 and the yoke 5, when the shield case material is a magnetic material, the magnet is used when the case 6 is near the plate-shaped magnet 2 and the yoke 5. Since the magnetic flux from 2 passes through the shield case 6, it is not preferable in terms of sensitivity and influence of disturbance. Accordingly, when the plate magnet 2 and the yoke 5 are separated from each other as shown in FIG. 1A, the inner surface of the case 6 is equal to or more than the distance between the plate magnet 2 and the yoke 5. Is preferably separated from the yoke 5. Further, it is desirable that the end of the plate magnet 2 and the inner surface of the case 6 be separated by a similar distance.
The disturbance referred to here means that when a stress is applied to the case 6, the magnetic flux is disturbed because a part of the magnetic flux passes through the case, and the sensor signal rides as noise.

  The inside of the shield case 6 can be filled with a resin material such as an epoxy resin, and the weather resistance of the detection head 1 can be ensured by molding the sensor portion with the resin 7. become.

  The shield case 6 can be provided with a collar portion 6a on the lower end portion thereof, that is, on the release surface side. When the detection head 1 is attached to the magnetic body 8 as described above, for example, a screw is inserted into the collar portion 6a. While providing a hole, the detection head 1 can be easily fixed in a state where the release surface of the shield case 6, in other words, the lower end surface of the plate magnet 2 is in contact with the magnetic body 8 by providing a screw hole in the magnetic body 8. Will be able to.

The plate-like magnet 2 is magnetized in the longitudinal direction as shown by arrows in FIGS. 2 (a) and 2 (b).
Further, the length dimension L is suitably from several millimeters to 20 mm, and the width dimension W is suitably several millimeters. The aspect ratio L / W is 1.0 in order to maintain the stability of magnetization in the longitudinal direction. It is desirable to make it larger.

  Further, the thickness T (see FIG. 2B) of the plate-like permanent magnet 2 is preferably in the range of 0.5 mm to 3.0 mm.

  That is, FIG. 3 (a) shows an example in FIG. 3 (b) using an Fe—Cr—Co based magnet in which the length dimension L and the width dimension W are fixed to 20 mm and 10 mm, respectively, and the thickness T is changed. The result of having investigated the relationship between the detection sensitivity and the magnet thickness in the stress sensor of the structure as shown is shown. At this time, the height from the surface of the plate-like permanent magnet 2 to 0.5 mm from the surface of the plate-like permanent magnet 2 is applied to the magnetic element, and a tensile stress from 50 MPa to 100 MPa is applied to the magnetic body. did. In addition, the vertical axis in FIG. 3A indicates a relative ratio where the sensitivity when the thickness T = 1 mm is “1”.

  As is clear from the results of FIG. 3A, the sensitivity shows the maximum value when the thickness T of the plate-like magnet 2 is 1.0 mm, and the sensitivity is lowered if the thickness is too thin or too thick. Therefore, it was found that the range of 0.5 mm to 3.0 mm is suitable as described above.

  As described above, the Hall elements 3 and 4 can be used as the magnetic sensor, but in addition to this, a small Hall IC or MI sensor that saves power can be used. The Hall IC here is a linear output type.

  Further, in FIG. 1A, two Hall elements 3 and 4 are arranged as a magnetic sensor in the length direction of the plate magnet 2, and the signals of both sensors 3 and 4 whose senses are opposite to each other are subtracted. As a double signal, the stress detection sensitivity is doubled and the resistance to disturbance is improved by being insensitive to the same-phase magnetic flux passing through both sensors 3 and 4. The stress sensor is not necessarily limited to one using two sensors, and it goes without saying that even if one magnetic sensor is used, stress detection can be performed with reasonable sensitivity.

  Note that, from the viewpoint of increasing detection sensitivity, the magnetic sensor is desirably disposed at an intermediate position between the plate-shaped magnet 2 and the yoke 5, and is disposed at a position near the end of the plate-shaped permanent magnet 2 from the same viewpoint. It is desirable.

Next, the shape of the yoke 5 will be described.
FIG. 2 (c) shows the positional relationship between the plate-shaped magnet 2, the Hall elements 3, 4 and the yoke 5 (viewed from above). The length of the yoke 5 is the same as that of the plate-shaped magnet 2. It is desirable that the length is sufficient to cover the length.

On the other hand, it is not preferable that the width of the yoke 5 is too narrow or too wide. The range of the outer dimensions of the resin-molded Hall elements 3 and 4 is 1 to 5 times, and further 2 to 4 times. It is more desirable to do.
That is, if the width is narrow, the yoke 5 has insufficient resistance to the magnetic flux collection effect and disturbance, while if the width is wide, the magnetic flux collection effect and disturbance resistance are sufficient, but the detection head is downsized. Or it becomes disadvantageous in terms of material cost.

  Further, the thickness of the yoke 5 is more preferably in the range of 0.05 mm to 2.0 mm, and further preferably in the range of 0.1 mm to 1.0 mm. When it is too thin, the yoke 5 is in a state close to magnetic saturation. Therefore, not only the magnetism collecting effect and disturbance resistance become insufficient, but also mechanical distortion tends to occur, so that excessive consideration is required for handling, which is not preferable. On the other hand, if it is too thick, it is not preferable in terms of material cost and size reduction.

The distance between the yoke 5 and the plate-like permanent magnet 2 is suitably in the range of 0.5 mm to 5.0 mm, more preferably in the range of 1.0 mm to 3.0 mm. To do.
That is, if it is too narrow, it will be disadvantageous in terms of sensitivity, and it will be disadvantageous in terms of cost to use a specially thin Hall element. This is because it is not preferable in terms of miniaturization.

  As described above, an example in which the shield case 6 is used and the stress detection unit is housed in the case has been described as a preferred example of the present invention. However, in the stress sensor of the present invention, the plate-like yoke 5 has a considerable shielding effect. Use of the shield case 6 is not necessarily an essential requirement because it fulfills the level.

Further, the arrangement of the magnetic sensors (Hall elements 3 and 4), the yoke 5 and the plate-like permanent magnet 2 and the mounting state with respect to the magnetic body 8 are not limited to the form shown in FIG. Various types can be adopted.
4A to 4H show various arrangement examples of the plate-shaped magnet 2, the yoke 5, and the Hall elements 3 and 4 with respect to the magnetic body 8, respectively, along the longitudinal direction of the plate-shaped magnet 2. It is sectional drawing in a surface perpendicular | vertical to a magnet plate surface.

FIG. 4A shows an arrangement similar to that shown in FIG. 1A except that it is not housed in the shield case 6.
On the other hand, FIG. 4B shows a case where the magnetic sensors 3 and 4 are arranged at positions deviating from the position directly above the plate magnet 2 with respect to FIG. By adopting such an arrangement, the amount of magnetic flux passing through the magnetic sensors 3 and 4 is increased, so that there is an advantage that sensitivity is improved.

  FIG. 4C shows an example in which the magnetic sensors 3 and 4 are located at the same level position as the plate-shaped magnet 2 and are arranged on the magnet end face side. 2 can be arranged at a position close to 2, and the stress detection unit can be made more compact. In particular, it is suitable when it is necessary to use a thicker magnet to increase the amount of magnetic flux in order to ensure sensitivity.

  Furthermore, as shown in FIG. 4 (d), the plate-like yoke 5 can be arranged so as to be in contact with the plate-like magnet 2, thereby further reducing the size of the stress detecting portion. In particular, it is suitable when a thick magnet and a magnet with a short longitudinal direction are employed.

  The plate magnet 2 is not only attached to the state in contact with the magnetic body 8, but can also be disposed in a state of being separated from the magnetic body 8. FIGS. 4E to 4H show examples in which the plate-like permanent magnet 2 is attached in a state of being separated from the magnetic body 8, and are shown in FIGS. 4A to 4D, respectively. Correspond.

The separation distance at this time is preferably a distance within the thickness dimension of the plate-like magnet 2.
That is, if the gap between the plate-like magnet 2 and the magnetic body 8 is too large, the magnetic flux passing through the magnetic body 8 is reduced, so that the sensitivity is lowered and the size of the stress detection unit is increased. But it is not preferable.

FIG. 5A is a diagram illustrating a specific flow of magnetic flux in the arrangement shown in FIG. 4D, and the function as a stress sensor is basically the same as described above.
FIG. 5B shows the size and positional relationship of the plate magnet 2, the yoke 5, and the magnetic sensors 3 and 4 shown in FIGS. 4B to 4D and 4F to 4H. FIG.

FIG. 6 is a cross-sectional view showing an example in which the components shown in FIGS. 4D and 5 are molded in the case 6, thereby further improving the weather resistance of the stress detection unit. be able to.
As described above, when the plate-like yoke 5 and the permanent magnet 2 that are arranged in contact with each other are stored in the shield case 6, the center distance between the yoke 5 and the plate-like magnet 2 is twice or more. It is desirable to dispose the inner surface of the case 6 so as to be separated from the yoke 5 and the plate-like magnet 2 by this distance.

  As for the influence of the thickness of the plate magnet 2 on the detection sensitivity of the stress sensor, a gap is provided between the plate magnet 2 and the magnetic body 8 when the positions of the magnetic sensors 3 and 4 are changed. Even in this case, it has been confirmed that the data is almost the same as in FIG.

Furthermore, as shown in FIG. 7, the signal processing circuit 10 can be housed in the shield case 6 in the detection head 1.
As described above, since it is necessary to provide a distance between the inner surface of the shield case 6 and the yoke 5, the signal processing circuit 10 can be accommodated in this space.

As a result, it is only necessary to take out the three lead wires of the power supply line, the ground line, and the signal line from the detection head 1. For example, when the power supply is DC 5 V, the signal is 2.5 V. The stress can be reduced to zero, decreased by a tensile stress, and increased by a compressive stress.
Moreover, it can be said that housing the signal processing circuit 10 in the electromagnetic shield case 6 is extremely preferable from the viewpoint of electromagnetic noise.

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

(1) Magnetic material (see FIG. 1B)
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 the magnetic material has a thickness of 5 mm and a width of 50 mm. 8 was produced by machining.
After machining, a solid solution treatment at 820 ° C. for 1 hour in a vacuum and an aging treatment at 490 ° C. for 5 hours in a vacuum were performed, followed by air cooling.

(2) Detection head (see FIG. 1 (a))
As the plate-like permanent magnet 2, an Fe—Cr—Co magnet having a width W = 7 mm, a length L = 15 mm, and a thickness T = 0.8 mm was magnetized in the length direction. In addition, the said magnet was not an isotropic magnet, but the thing which gave the anisotropy in the longitudinal direction was used. The leakage magnetic field at the end face after magnetization of the plate magnet 2 alone was about 2.0 kG.

  As Hall elements 3 and 4 which are magnetic sensors, those having a mold outer shape, width: 2.4 mm, length: 2.7 mm, and thickness: 1.0 mm were used.

  The yoke 5 was made of PB permalloy and had a width of 6 mm, a length of 20 mm, and a thickness of 0.5 mm.

  The shield case 6 is manufactured by machining electromagnetic soft iron, and the outer dimensions excluding the collar portion 6a are as follows: width: about 20 mm, length: about 30 mm, height: about 10 mm, and wall thickness: about 1 mm. It was supposed to be.

  The distance between the plate magnet 2 and the yoke 5 was 3 mm, and the distance between the yoke 5 and the inner surface of the shield case 6 was 4 mm. Furthermore, the distance between the end of the plate magnet 2 and the inner surface of the case 6 was also 4 mm.

  By positioning the yoke 5, the hall elements 3 and 4 and the plate magnet 2 in the shield case 6 as described above by the inner frame made of bakelite, and filling the space with epoxy adhesive, the detection head (Stress detection part)

(3) Performance Evaluation After the detection head 1 is screwed to the magnetic body 8 made of maraging steel obtained as described above, as shown in FIG. 1B, tensile and compressive stress is applied to the magnetic body 8. The performance as a stress sensor was evaluated. An example of the result is shown in FIG.
As is clear from this figure, it has been confirmed that sufficient sensitivity and reproducibility as a stress sensor can be obtained.

Although the detection head 1 in the above embodiment has been shown to be relatively large, it goes without saying that further downsizing can be achieved by using a small Hall element.
In the above embodiment, an example in which the detection head 1 is attached to the magnetic body 8 (on the plane thereof) having a rectangular cross section has been described. However, a thin plate magnet having a curvature in the vertical direction (width direction) is employed. Thus, it can be applied to a magnetic body having a cylindrical surface, and it goes without saying that the stress applied to the axis of the circular cross section can be detected.

(A) It is sectional drawing which shows the structural example of the detection head (stress detection part) used for the stress sensor of this invention. (B) It is a perspective view which shows the state which attached the detection head shown to Fig.1 (a) to the magnetic body which has a magnetostriction. (A) It is a top view which shows the shape of the plate-shaped magnet shown to Fig.1 (a). (B) It is a perspective view which shows the shape of the plate-shaped magnet shown to Fig.1 (a). (C) It is a top view explaining the magnitude | size and positional relationship of a plate-shaped magnet and a yoke which were shown to Fig.1 (a). (A) It is a graph which shows the relationship between the thickness of a plate-shaped magnet, and the detection sensitivity of a stress sensor. (B) It is sectional drawing which shows the structure of the stress sensor used for calculating | requiring the relationship of Fig.3 (a). (A)-(h) is sectional drawing which shows the various example of arrangement | positioning of the plate-shaped magnet 2, a yoke, and a Hall element. (A) It is explanatory drawing which illustrated the flow of the magnetic flux in the detection part shown in FIG.4 (d). (B) It is a top view which shows the magnitude | size and positional relationship of the plate-shaped magnet and yoke 5 which were shown to FIG.4 (b)-(d) and (f)-(h). It is sectional drawing which shows the example which molded each component shown in FIG.4 (d) and FIG. 5 in the case. It is sectional drawing which shows the structural example of the detection head which accommodated the signal processing circuit in the shield case. It is a graph which shows the output characteristic data of the stress sensor obtained by the Example of this invention. (A) And (b) is explanatory drawing which shows the structure and principle of the conventional magnetostrictive stress sensor.

Explanation of symbols

1 Detection head (stress detection unit)
2 Permanent magnet 3, 4 Hall element (magnetic sensor)
5 Yoke 6 Case 6a Collar 7 Resin 8 Magnetic body 10 Signal processing circuit

Claims (24)

Of the magnetic flux generated from a permanent magnet close to the stress detecting magnetic body having magnetostriction and flowing separately to the magnetic body and the outside of the magnetic body, the magnetic flux flowing through the magnetic body is caused by the stress acting on the magnetic body. A magnetostrictive stress sensor for detecting a change in magnetic flux distribution resulting from a change,
A stress detection unit having a plate-shaped permanent magnet, a magnetic sensor, and a plate-shaped yoke, wherein the magnetic sensor is in the vicinity of an end of the plate-shaped magnet disposed in proximity to the magnetic body, A stress sensor, wherein the stress sensor is disposed on a magnetic material side of a plate-shaped yoke disposed on a diamagnetic material side and at a position other than between the magnetic material and the plate-shaped magnet.   2. The stress sensor according to claim 1, wherein the plate magnet is magnetized in the longitudinal direction.   The stress sensor according to claim 1 or 2, wherein the yoke has a length sufficient to cover the magnetic sensor and the plate magnet in the longitudinal direction.   The stress sensor according to any one of claims 1 to 3, wherein the plate magnet is separated from the magnetic body at a distance within a thickness of the magnet.   The stress sensor according to any one of claims 1 to 3, wherein the plate magnet is in contact with the magnetic body.   The stress sensor according to any one of claims 1 to 5, wherein an aspect ratio of the plate magnet is larger than 1.0.   The thickness of the said plate-shaped magnet is 0.5-3.0 mm, The stress sensor as described in any one of Claims 1-6 characterized by the above-mentioned.   The stress sensor according to any one of claims 1 to 7, wherein a distance between the plate magnet and the yoke is 0.5 to 5.0 mm.   The stress sensor according to claim 1, wherein the plate magnet is in contact with the yoke.   The stress sensor according to claim 1, wherein a width of the yoke is 1 to 5 times an outer dimension of the magnetic sensor.   The stress sensor according to any one of claims 1 to 10, wherein the yoke has a thickness of 0.05 to 2.0 mm.   The stress sensor according to claim 1, wherein the stress detection unit is molded with a resin.   The stress sensor according to claim 12, wherein the stress detection unit is housed in a case.   The stress sensor according to claim 13, wherein the case is an electromagnetic shield case.   The stress sensor according to claim 13 or 14, wherein one surface on the magnetic body side of the case is in an open state, and the open surface and one surface of the plate magnet are arranged in parallel.   The stress sensor according to claim 15, wherein the case is provided with a flange portion for fixing the stress detection portion to the magnetic body on the open surface.   17. The item according to claim 13, wherein the yoke and the plate magnet are separated from each other, and the inner surface of the shield case is separated from the yoke by a distance greater than the distance between the yoke and the plate magnet. The stress sensor described.   The yoke and the plate magnet are separated from each other, and the inner surface of the shield case is separated from the end of the plate magnet by a distance greater than the distance between the yoke and the plate magnet. The stress sensor according to any one of the items.   The yoke and the plate-shaped magnet are in contact with each other, and the inner surface of the shield case is separated from the yoke at least twice the center distance between the yoke and the plate-shaped magnet. The stress sensor according to one item.   The yoke and the plate-shaped magnet are in contact with each other, and the inner surface of the shield case is separated from the end of the plate-shaped magnet at least twice the center distance between the yoke and the plate-shaped magnet. The stress sensor according to any one of -16 to 19 and 19.   21. The stress sensor according to claim 1, wherein the plate magnet is a magnet having anisotropy in a longitudinal direction.   The stress sensor according to any one of claims 13 to 21, wherein the shield case is made of a metal, a metal having soft magnetism, or a plastic material containing a filler having an electromagnetic shielding effect.   23. The stress sensor according to claim 13, wherein a signal processing circuit is accommodated in a space between the yoke and the inner surface of the shield case.   The stress sensor according to any one of claims 1 to 23, wherein the magnetic sensor is a Hall element or a Hall IC.

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