JP4569764B2 - Stress detector - Google Patents

Description

The present invention relates to a technique for detecting stress acting on various machine parts, for example, and more specifically, to a stress detection apparatus capable of detecting stress acting on a member having magnetostriction by utilizing the inverse effect of magnetostriction. Is. In addition, the present invention relates to a stress detection device that can detect stress even in a non-contact manner on a rotating shaft or the like.

  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 a link around an automobile or the like Since the 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. 10 is an explanatory diagram of a stress sensor using the inverse effect of magnetostriction proposed by Non-Patent Document 1 above. In FIG. 10A, 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 of 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, 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 put into practical use a stress sensor utilizing the inverse effect of magnetostriction, and to provide an inexpensive stress excellent in robustness. It is to provide a detection device.

  As a result of diligent investigations aimed at solving the above problems, the present inventors have magnetized a shaft member having a large number of parallel grooves on its surface in the circumferential direction, and the peaks between the grooves are magnetized in the longitudinal direction. As a result, it has been found that good sensor characteristics can be obtained by using such a shaft material as a stress sensor, and the present invention has been completed.

The present invention is based on the above knowledge, and the stress detection device of the present invention includes a magnetized first magnetic body, a second magnetic body having magnetostriction, and stress applied to the second magnetic body. It is provided with a spatial magnetic flux detection means that detects a change in the spatial magnetic flux generated from the first magnetic body and flowing in the space outside the second magnetic body without passing through the second magnetic body. The first magnetic body is integrated with the second magnetic body to form a part of the second magnetic body, and an angle of 0 degree or more and less than 90 degrees with respect to the longitudinal direction of the second magnetic body A plurality of grooves or ridges that are formed in parallel, and are characterized in that the inter-groove portions or ridges of the concavo-convex parts are magnetized in the longitudinal direction . .

When the magnetized first magnetic body and the second magnetic body having magnetostriction are placed close to each other, the magnetic flux emitted from the first magnetic body passes through the second magnetic body, and the second magnetic body. When the stress is applied to the second magnetic body, the amount of the internal magnetic flux passing through the second magnetic body changes, and as a result, the spatial magnetic flux flowing through the space flows. Since the amount of the magnetic flux changes, the change in the spatial magnetic flux is detected by a spatial magnetic flux detection means such as a magnetic sensor, more specifically by a Hall element or a Hall IC. Can be detected.
According to the present invention, since the first magnetic body and the second magnetic body are integrated, a compact and inexpensive apparatus with a small number of parts can be realized. In particular, by using the second magnetic body as a shaft, it is possible to detect stress in a rotating state, and the usefulness thereof can be greatly improved.

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

The stress detection device of the present invention basically uses the first magnetic body and the second magnetic body, and the first magnetic body forms part of the second magnetic body. to, it is possible to make such a second magnetic body and that of the axial.

That is, the stress detection apparatus of the present invention has a structure as shown in FIG. 1A, for example, and includes a shaft 1 (second magnetic body) having magnetostriction. A plurality of grooves 2a forming 45 degrees with respect to the direction of the central axis of the shaft 1 are formed in parallel, and the grooves 2a and the inter-groove portions remaining between them become ridges 2b, and these grooves 2a and ridges The uneven portion 2 is formed in a band shape by 2b.
In the drawing, since the groove 2a has a 45 degree spiral shape, it should be accurately expressed in an S shape, but is schematically represented as a straight line for the convenience of drawing.

When a large current is applied to the shaft 1 from the right side in the drawing as shown in FIG. 1B, the shaft 1 is magnetized in the circumferential direction as indicated by an arrow in the drawing. However, in the concavo-convex portion 2, since there is a groove 2 a (because it is a space), the peak portion 2 b is not magnetized in the circumferential direction, and is polarized in the direction of 45 degrees with respect to the longitudinal direction of the peak portion 2 b, that is, the axial direction. Magnetized.
That is, when magnetized in the circumferential direction of the shaft 1, a pole appears on the side surface of the peak portion 2b, so that a demagnetizing field is generated and the magnetization direction is directed to the longitudinal direction of the peak portion 2b (shape effect or shape magnetism). anisotropy). Therefore, the magnetized state in the peak portion 2b is as shown in FIG. 1C, and the peak portion 2b functions as the first magnetic body.

In FIG. 1A, reference numeral 3 denotes a magnetic sensor as a 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 the detection sensitivity, as shown in FIG. It is desirable that the magnetic flux in the radial direction is detected by disposing it at a position close to the end portion 2 (see FIG. 2). The Hall IC here is of a linear output type.

FIG. 2 shows a cross section obtained by cutting the crest 2b of the concavo-convex portion 2 in a longitudinal direction. The crest 2b is magnetized (magnetized) as indicated by the arrows in the figure, and the magnetic flux is a space inside and outside the axis. Is leaking.
Note that “+” shown in FIG. 1C indicates the N pole, and “−” indicates that the S pole appears.

When an axial tensile stress is applied to the shaft 1, the magnetic flux passing through the shaft 1 increases (the magnetic flux easily passes through the shaft), so that the spatial magnetic flux leaking to the outside decreases, and therefore the magnetic flux passing through the magnetic sensor 3. Will be reduced. This is an explanation when the magnetostriction is positive (hereinafter the same), and 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 to the 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 the second magnetic body on which the stress acts as a shaft.

As shown in FIGS. 3A and 3B, 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.
By using such a yoke 5, resistance against external electromagnetic noise is improved, and the magnitude of the signal of the magnetic sensor 3 can be increased by a factor of about two.

Also, as shown in FIG. 4, two magnetic sensors 3 and 4 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.

  And as shown in FIG. 5, the uneven | corrugated | grooved part 2 made to oppose the inclination direction of the groove part 2a can also be made to approach two places of the axis | shaft 1, and in this case, the signal of the magnetic sensor 3 can be arranged. The size of can be doubled.

Furthermore, as is clear from the above description, the angle of the groove 2a in the concavo-convex portion 2 does not necessarily need to be 45 degrees, and can be any angle as shown in FIG.
Further, instead of forming the groove 2a in the concavo-convex portion 2, as shown in FIG. 7, a spiral protrusion 2c is formed on the surface of the shaft 1 so as to have a shape like a helical gear. It is also possible. In this case, the protrusion 2c is magnetized along the longitudinal direction (first magnetic body).

In the above description, an example in which a second magnetic body having magnetostriction has a shaft shape is used. However, as shown in FIGS. 8A and 8B, a plate-shaped magnetic body is used. It goes without saying that even if it is 10, it functions as a stress detection device.
As shown in the figure, with the grooves 2a formed in parallel, a large current is passed in the direction of the arrow in the figure to magnetize, so that the inter-groove portion 2b is magnetized, and the first stress detecting device in the first embodiment It functions as a magnetic material.

As the material of the second magnetic body having magnetostriction, there is a relationship in which the magnetized portion is integrally held, and it is desired to stably maintain the magnetized state.
Therefore, as such a magnetic material, steel subjected to heat treatment such as precipitation hardening or quenching / tempering, and steel subjected to surface treatment such as carburization, surface nitriding, induction quenching / tempering are suitable. This is because these steels generally have a coercive force of about 20 to several tens of Oe.

Moreover, since it is desired that the hysteresis with respect to the stress is small, the material needs to undergo an appropriate process. In other words, it is desirable to perform a heat treatment step after machining, or to perform machining so that non-uniform residual stress does not enter after heat treatment. In addition, if a large stress causing plastic deformation is applied, a non-uniform residual stress distribution is brought about, leading to an increase in hysteresis, so plastic working should be avoided.
Magnetizing in the circumferential direction can also be said to be an effective means. That is, it is considered that a large amount of magnetization directed in the circumferential direction is effective in reducing hysteresis. 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 inversely proportional to the distance from the center outside the shaft. Attenuates.
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. In the case of a grooved shaft, the groove bottom portion is magnetized in the circumferential direction.

  In addition, since the output signal is larger when the stress applied to the second magnetic body is larger, the hollow shaft is more convenient for increasing the sensitivity in the case of the shaft. In the case where the groove portion is provided, since the groove bottom diameter determines the stress, the sensitivity can be increased accordingly.

In the above example, the magnetization is performed by energization. However, since the peak portion (inter-groove portion) only needs to be magnetized in the longitudinal direction, it can be magnetized by another means. It is.
When the protrusion 2c is formed as shown in FIG. 7, for example, it is easy to magnetize only the protrusion (leaving only the protrusion in the longitudinal direction).

  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 the material of the second magnetic body, using maraging steel (trade name YAG300, manufactured by Hitachi Metals, Ltd., 18% Ni-9% Co-5% Mo-Fe), as shown in FIG. A shaft 1 with D = 19 mm was produced by machining.
Next, by using an end mill having a diameter of 1 mm, 20 grooves 2a inclined in the direction of 45 degrees in the axial direction are formed in two locations on the shaft 1 in the circumferential direction so as to have a width of 1 mm and a depth of 1.5 mm. Parts 2 and 2. Note that the widths of the concavo-convex portions 2 and 2 in which the 20 spiral grooves 2a were formed were 11 mm each (the distance between the centers of the end mills was 10 mm). In addition, the distance between both uneven | corrugated | grooved parts 2 and 2 was 1 mm (distance between centers of an end mill is 2 mm).

After these machining processes, 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.
Next, the obtained shaft 1 was magnetized by passing a current of 10,000 A.

Then, as shown in FIG. 5, the Hall sensor 3 was arranged at an intermediate position between the concavo-convex portions 2 and 2, and the output of the Hall sensor 3 when tensile and compressive stress was applied to the shaft 1 was examined. The result is shown in FIG. The magnetic sensitive 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 of the Hall sensor 3 decreased due to the tensile stress and increased due to the compressive stress, and a characteristic having almost no hysteresis was obtained 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 is generated and continuous output cannot be obtained, so that play can be prevented. It is thought that this problem can be solved by modifying the device.
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 the case of a stress sensor using the inverse effect of magnetostriction, hysteresis appears when the shaft 1 undergoes micro-yield, so the load stress should be about half or less of the yield stress of the magnetic material constituting the shaft 1. In this case, 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)
Using the maraging steel as the material of the second magnetic body, the shaft 1 having a shaft diameter D = 19 mm was produced by machining as described above.
Next, as shown in FIG. 1, the concavo-convex portion 2 having 20 grooves 2a inclined at 45 degrees in the axial direction is formed at one location of the shaft 1 as in Example 1, and the same heat treatment is performed. Further, magnetization was performed by energization of 10,000 A.

  And the hall sensor 3 was arrange | positioned in the position shown in FIG. 1, and the output from the hall sensor 3 when stress was applied to the axis | shaft 1 was investigated similarly. As a result, it was confirmed that a characteristic having almost no hysteresis was obtained with respect to a stress load of ± 40 MPa. The sensitivity was about half that of the embodiment shown in FIG.

(Example 3)
Example 2 except that carbon steel for mechanical structure S45C specified in JIS G4051 is used as the material of the shaft 1, induction hardening is performed as heat treatment, and then tempering treatment is performed at 170 ° C. × 1 hour. Using the shaft 1 obtained by repeating the same operation, the output characteristics of the Hall sensor 3 were similarly investigated under the same conditions.
In addition, as the aim of the heat treatment, the surface hardness after tempering is HRC50 or more, the effective hardened layer depth that becomes HRC45 or more is aimed at 0.8 mm, and the surface hardness and the hardened layer depth after tempering are aimed. The condition was satisfied.

  As a result, a characteristic having almost no hysteresis was obtained. It was confirmed that the sensitivity was slightly inferior.

(A) It is explanatory drawing which shows an example of embodiment of the stress detection apparatus by this invention. (B) It is explanatory drawing which shows the magnetization direction when it supplies with electricity to an axial direction. (C) It is an expanded explanatory view which shows the magnetization state in the groove part of an uneven part. It is sectional explanatory drawing which shows the magnetization state in the groove part of an uneven | corrugated | grooved part. It is the front view (a) and top view (b) which show 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 example of embodiment which formed the uneven | corrugated | grooved part in two places of the axis | shaft. It is explanatory drawing which shows embodiment example from which the inclination angle of the groove | channel in an uneven | corrugated | grooved part differs. It is explanatory drawing which shows the example of embodiment which replaced with the groove | channel of the uneven | corrugated | grooved part and formed the protrusion part. 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 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 (second magnetic body)
2 Concave and convex portions 2a Groove 2b Mountain portion (inter-groove portion: first magnetic body)
2c Projection (first magnetic body)
3,4 Magnetic sensor (space magnetic flux detection means)
5 York

Claims (14)

The first magnetic body magnetized, the second magnetic body having magnetostriction, and the stress acting on the second magnetic body causes the first magnetic body to generate and pass through the second magnetic body. A spatial magnetic flux detection means for detecting the change of the spatial magnetic flux flowing in the space outside the second magnetic body without any change,
The first magnetic body is integrated with the second magnetic body to form a part of the second magnetic body, and forms an angle of 0 degree or more and less than 90 degrees with respect to the longitudinal direction of the second magnetic body. Stress detection characterized in that it is a strip-shaped uneven part formed by forming a plurality of grooves or protrusions in parallel, and the inter-groove part or protrusions of the uneven part are magnetized in the longitudinal direction apparatus. The stress detection device according to claim 1 , wherein the second magnetic body has an axial shape, and the groove or the ridge portion forms the angle with respect to an axial direction . The stress detecting device according to claim 2 , wherein the groove or the ridge portion forms an angle of 45 degrees with respect to the axial direction. 4. The stress detection according to claim 3 , wherein the second magnetic body having an axial shape is magnetized in the circumferential direction, and the spatial magnetic flux detecting means is disposed in the vicinity of the belt-shaped uneven portion. apparatus. 5. The stress detecting device according to claim 4 , wherein the second magnetic body having an axial shape has the strip-shaped uneven portions provided at two positions close to each other. The stress detection apparatus according to claim 4 or 5 , wherein a tensile stress and a compressive stress acting in the axial direction are detected. The stress detection device according to any one of claims 4 to 6 , wherein the second magnetic body having an axial shape is rotatably held. The stress detection device according to any one of claims 4 to 7 , wherein the spatial magnetic flux detection means is arranged at an end of the belt-shaped uneven portion and detects a magnetic flux in a radial direction. The stress detection device according to any one of claims 4 to 8 , wherein a yoke is disposed on the opposite side of the spatial magnetic flux detection means with respect to the second magnetic body. The stress detection apparatus according to claim 9 , wherein the yoke is made of a soft magnetic material. The stress detection apparatus according to any one of claims 4 to 10 , wherein the second magnetic body is hollow. The stress detection apparatus according to any one of claims 1 to 11 , wherein the spatial magnetic flux detection means is a magnetic sensor. The torque detection device according to claim 12 , wherein the magnetic sensor is a Hall element or a Hall IC. The stress detection apparatus according to any one of claims 1 to 13 , wherein the second magnetic body is made of heat-treated steel or surface-treated steel.

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