JP2006049516A - Magnetostrictive element and bias magnetic field applying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve miniaturization of a magnetostrictive element and suppress the influence of a leakage flux from a permanent magnet by efficiently applying the magnetic flux generated from the permanent magnet to a magnetostrictive material. <P>SOLUTION: The magnetostrictive element is provided with the magnetostrictive material 1, the permanent magnet 3 for applying a bias magnetic field to the magnetostrictive material 1, and a coil 2 for carrying out electromagnetic conversion. The permanent magnet 3 is a tubular (e.g. a cylindrical) permanent magnet, and the coil 2 is wound about this tubular permanent magnet 3 as a bobbin. Rubber O rings 4, for example, may be interposed between the magnetostrictive material 1 and the permanent magnet 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetostrictive element such as a magnetostrictive actuator or a magnetostrictive sensor, and more particularly to an improved structure and method for applying a bias magnetic field with a permanent magnet.

  Magnetostrictive materials with Joule effect (deformation by applying a magnetic field) and barrier effect (change in permeability due to stress change) are expected to be applied to various actuators and sensors. As it is developed, its demand tends to increase more and more.

  Here, specific applications of the magnetostrictive material include a linear actuator, a vibrator, a pressure torque sensor, a vibration sensor, a gyro sensor, and the like. When used in a linear actuator, vibrator, etc., the dimensions change with changes in the applied magnetic field and generate a driving force. When used in a pressure torque sensor, vibration sensor, gyro sensor, etc., the magnetic permeability changes with a change in externally applied stress, and pressure, torque, vibration, etc. are detected by sensing this.

  When the magnetostrictive element is used as a vibrator, for example, it is necessary to apply a bias magnetic field in addition to the input of a signal magnetic field by a coil or the like. Due to the characteristics of the magnetostrictive material, if a signal magnetic field is applied without applying a bias magnetic field, for example, two cycles of vibration are output for one cycle of the signal magnetic field, which may cause problems in actual use. Therefore, normally, in this type of magnetostrictive element, a predetermined bias magnetic field is applied by some means.

  As a typical method for forming the bias magnetic field, there are a method of generating a bias magnetic field by applying a constant direct current to the coil, a method of arranging a permanent magnet, and the like. However, in the former case, the coil may be overheated due to Joule heat caused by a direct current, which may cause a decrease in the amount of vibration of the magnetostrictive element. In this respect, the latter is advantageous.

  In addition, as a method of applying a bias magnetic field by a permanent magnet, there are a method of installing a plurality of permanent magnets at both ends in the vibration direction of the magnetostrictive material, a method of arranging a cylindrical permanent magnet outside the magnetostrictive material and the coil, and the like. As is known, in the case of the method of installing permanent magnets at both ends in the vibration direction of the magnetostrictive material, the permanent magnet will increase the length in the vibration direction of the element, leading to an increase in the length of the entire element, There is an inconvenience that miniaturization is hindered. In addition, the permanent magnet itself vibrates, and the mass (vibrating mass) of the vibrating member increases, resulting in a disadvantage that vibration energy is reduced.

From such a situation, a method using a cylindrical permanent magnet is widely adopted (see, for example, Patent Document 1). In the invention described in Patent Document 1, the permanent magnet is formed into a cylindrical shape having at least one end opened, and is disposed outside the coil as shown in the figure.
Japanese Patent Laid-Open No. 3-60176

  However, if the permanent magnet is disposed outside the coil, the magnetic flux generated from the permanent magnet does not effectively act on the magnetostrictive material, and the ratio of the magnetic flux applied to the magnetostrictive material is reduced, so that a predetermined bias magnetic field is applied. Therefore, it is necessary to use a permanent magnet having a large magnet volume according to the ratio. In addition, when the permanent magnet is arranged outside, the magnetic flux generated by the permanent magnet leaks not only inside the cylindrical permanent magnet but also outside, and the magnetic flux leaking outside the permanent magnet may be reduced to other parts, etc. There is also a risk of adverse effects on the surroundings.

  The present invention has been proposed in view of such a conventional situation, does not generate heat when forming a bias magnetic field, does not increase vibration mass, and efficiently generates magnetic flux generated from a permanent magnet as a magnetostrictive material. An object of the present invention is to provide a magnetostrictive element that can be applied and that can keep the ratio of leakage magnetic flux low, and further to provide a bias magnetic field application method.

  In order to achieve the above-described object, a magnetostrictive element according to the present invention is a magnetostrictive element including a magnetostrictive material, a permanent magnet that applies a bias magnetic field to the magnetostrictive material, and a coil that performs electromagnetic conversion. The magnet is a cylindrical permanent magnet, and a coil is wound around the cylindrical permanent magnet as a bobbin.

  Further, the bias magnetic field applying method according to the present invention includes arranging a cylindrical permanent magnet around the magnetostrictive material, winding a coil around the cylindrical permanent magnet as a bobbin, and using the permanent magnet to magnetostrictive material A bias magnetic field is applied to the above.

  As described above, the present invention is characterized in that a cylindrical permanent magnet for applying a bias magnetic field is arranged inside the coil, and further, this is used as a bobbin and the coil is wound around it. . By adopting such a configuration, the distance between the cylindrical permanent magnet and the magnetostrictive material can be significantly reduced as compared with the case where the permanent magnet is disposed outside the coil. Here, for example, in the case of a cylindrical permanent magnet having a cylindrical end as a magnetic pole, the magnetic flux passing through the inside of the cylinder is efficiently applied to the magnetostrictive material, leading to, for example, reduction of the magnet volume. That is, downsizing of the permanent magnet is realized. In addition, by using a permanent magnet as a bobbin and winding a coil directly around it, there is no need to prepare a separate bobbin, the number of parts is reduced, and the combined volume of the permanent magnet and the coil This also leads to a reduction in the magnetostrictive element in combination with the downsizing of the permanent magnet for the above reason. In addition, regarding the provision of the coil on the outside of the permanent magnet, one word is also described in Patent Document 1, but the superiority is not recognized in Patent Document 1 (the coil is composed of a permanent magnet and a magnetostrictive material). It is said that it is preferable to be provided in between.) As described in the present invention, there is no description about using a permanent magnet as a bobbin for further miniaturization.

  In addition to the above, the magnetostrictive element and bias magnetic field applying method of the present invention also have the following advantages. First of all, the bias magnetic field is applied by a permanent magnet, and it is not necessary to pass a constant DC voltage through the coil, so that performance degradation due to heat generation of the coil is avoided. Secondly, if the permanent magnet is arranged inside the coil as described above, the leakage magnetic flux from the permanent magnet does not affect the outside. Thirdly, since the permanent magnet is not in contact with the magnetostrictive material, for example, a vibrator having a small size and high magnetomechanical conversion efficiency is realized without the mass of vibration.

  According to the present invention, it is possible to provide a magnetostrictive element and a bias magnetic field applying method capable of efficiently applying a magnetic flux generated from a permanent magnet to a magnetostrictive material without generating heat when forming a bias magnetic field. Further, according to the present invention, the installation of the permanent magnet does not cause an increase in length, an increase in vibration mass, and the like, and further, the magnet volume and the number of parts can be reduced, and the magnetostrictive element can be reduced in size. It is possible. Furthermore, since the magnetostrictive element of the present invention is less affected by the leakage magnetic flux to the outside, it is possible to realize high-density mounting.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In the following, a magnetostrictive vibrator will be described as an example of the magnetostrictive element.

  As shown in FIG. 1, a magnetostrictive element (magnetostrictive vibrator) to which the present invention is applied is displaced by applying an external magnetic field and applies a signal magnetic field to the magnetostrictive material 1 that functions as a vibrator. And a permanent magnet 3 for applying a bias magnetic field to the magnetostrictive material 1 as main components.

  Here, the magnetostrictive material 1 is preferably a magnetostrictive material having so-called supermagnetostrictive characteristics. For example, terbium-dysprosium can be manufactured at a low cost by using powder metallurgy. -A magnetostrictive material made of a sintered body of iron (Tb-Dy-Fe) alloy powder is suitable.

The magnetostrictive material manufactured using the powder metallurgy method will be described. For example, the magnetostrictive material is represented by the formula RT _y (where R is one or more rare earth elements, T is one or more transition metals, and y is 1 <y <4.) Obtained by sintering an alloy powder having a composition represented by:

  In the formula, R represents one or more selected from lanthanoid series and actinoid series rare earth elements including Y. Among these, R is preferably a rare earth element such as Nd, Pr, Sm, Tb, Dy, or Ho, more preferably Tb or Dy, and these can be used in combination. In the formula, T represents one or more transition metals. Among these, as T, transition metals such as Fe, Co, Ni, Mn, Cr, and Mo are particularly preferable, and these can be mixed and used.

Of the alloys represented by the formula RT _y , the RT ₂ Laves type intermetallic compound in which y = 2 is suitable for a magnetostrictive element because it has a high Curie temperature and a large magnetostriction value. Here, when y is 1 or less, the RT phase is precipitated by the heat treatment after sintering, and the magnetostriction value is lowered. When y is 4 or more, the RT ₃ phase or the RT ₆ phase increases and the magnetostriction value decreases. Therefore, in order to RT ₂ is more rich phase, y is 1 <range of y <4 is preferable.

R may be a mixture of two or more rare earth elements, and it is particularly preferable to use a mixture of Tb and Dy. Specifically, in the alloy represented by Tb _a Dy _(1-a) , a is more preferably in the range of 0.27 <a ≦ 0.50. As a result, (Tb _a Dy _(1-a) ) T _y alloy has a large saturation magnetostriction constant and a large magnetostriction value. Here, when a is 0.27 or less, a sufficient magnetostriction value is not exhibited at room temperature or less, and conversely when it exceeds 0.50, a sufficient magnetostriction value is not exhibited near room temperature.

As T, Fe is particularly preferable, and Fe forms a Tb, Dy and (Tb, Dy) Fe ₂ intermetallic compound to obtain a sintered body having a large magnetostriction value and high magnetostriction characteristics. At this time, a part of Fe may be substituted with Co and Ni. However, Co increases magnetic anisotropy but decreases magnetic permeability, and Ni lowers the Curie temperature. Reduce the magnetostriction value at room temperature and high magnetic field. Therefore, Fe is preferably 70% by weight or more, and more preferably 80% by weight or more.

  The magnetostrictive material 1 has, for example, a cylindrical shape, and a coil 2 and a permanent magnet 3 are concentrically disposed around the magnetostrictive material 1. Of course, the shape of the magnetostrictive material 1 is not limited to the columnar shape, but may be any shape such as a rod shape having various cross-sectional shapes, a cylindrical shape such as a cylindrical shape, or an annular shape. In addition to a single sintered body or the like, the form thereof is arbitrary, such as a laminate of a plurality of thin plate-like magnetostrictive materials, and a laminate of linear magnetostrictive materials that are bonded together.

  On the other hand, the permanent magnet 3 for applying a bias magnetic field to the magnetostrictive material 1 needs to be disposed around the magnetostrictive material 1 and the cylinder so that a magnetic field can be efficiently applied to the magnetostrictive material 1. For example, a cylindrical shape. The shape of the permanent magnet 3 is not limited to the cylindrical shape, and may be any shape as long as it has a cylindrical shape. For example, a cylindrical body having a polygonal cross section in which the outer peripheral surface or the inner peripheral surface is a polyhedron, or a cylindrical body having one end surface closed. However, it is preferably a cylindrical permanent magnet with both ends open for reasons such as easy manufacture and easy magnetization.

  Here, in the conventional magnetostrictive element, it is normal that the coil 2 is arranged on the inner side and the cylindrical permanent magnet 3 is arranged on the outer side, but in this arrangement, the magnetic flux of the permanent magnet 3 is applied to the magnetostrictive material 1. It does not act effectively, and the magnetic flux generated from the permanent magnet 3 always leaks to the surroundings. Therefore, in the magnetostrictive vibrator of the present embodiment, the cylindrical permanent magnet 3 is disposed on the inner side, and the coil 2 is disposed on the outer side.

  In this case, the permanent magnet 3 is preferably as close to the magnetostrictive material 1 as possible. However, if the permanent magnet 3 comes into contact with the magnetostrictive material 1, vibration energy may be wasted due to friction or the like. Therefore, the magnetostrictive material 1 and the permanent magnet 3 do not come into contact with each other, and it is necessary to maintain a minimum interval. is there.

  As described above, in order to keep the magnetostrictive material 1 and the permanent magnet 3 from contacting each other and keeping a minimum distance, it is effective to interpose, for example, an O-ring between the magnetostrictive material 1 and the permanent magnet 3. . FIG. 2 shows a state in which the O-ring 4 is interposed between the magnetostrictive material 1 and the permanent magnet 3. The O-ring 4 functions as a spacer by interposing the O-ring 4, and the contact between the magnetostrictive material 1 and the permanent magnet 3. To prevent. The O-ring 4 may be provided at two or more locations in the vibration direction of the magnetostrictive material 1, whereby the distance between the magnetostrictive material 1 and the cylindrical permanent magnet 3 can be stably maintained. The O-ring 4 is preferably a rubber O-ring or the like. By using the rubber O-ring 4, the vibration of the magnetostrictive material 1 is not hindered and smooth vibration can be realized. is there.

  On the other hand, it is preferable that the coil 2 be as close as possible to the magnetostrictive material 1. Therefore, it is one of preferred embodiments that the cylindrical permanent magnet 3 is used as a coil bobbin and the coil 2 is directly wound around the outer peripheral surface thereof. It is. In other words, in other words, the cylindrical portion of the bobbin of the coil 2 for driving is composed of a permanent magnet, and a bias magnetic field is applied to this portion. When the permanent magnet 3 is a metal magnet, there is a concern that the coil 3 may be short-circuited. However, the winding of the coil 2 is usually covered with an insulating film, and there is no particular problem. If necessary, the surface of the permanent magnet 3 may be covered with an insulating film.

  Although it seems that placing the coil 2 outside the permanent magnet 3 is disadvantageous in applying the signal magnetic field, the coil 2 is actually used as the permanent magnet as demonstrated in the examples described later. 3 is almost the same as the case where it is arranged inside 3. Therefore, the change in the arrangement hardly hinders application of the signal magnetic field.

  The coil 2 applies a signal magnetic field to the magnetostrictive material 1, and the permanent magnet 3 applies a bias magnetic field to the magnetostrictive material 1. Hereinafter, the application of these magnetic fields and the operation of the magnetostrictive material 1 as a vibrator will be described.

In the magnetostrictive material 1, its length l expands and contracts by Δl according to the external magnetic field H. The relationship between the external magnetic field H and the displacement amount Δl is, for example, as shown in FIG. 3, where the external magnetic field H is symmetrical on the plus side and the minus side, and tends to increase nonlinearly as the external magnetic field H increases. Here, when applying a signal magnetic field S _H flowing alternating current (current of a sine wave) to the coil 2, in the state where a bias magnetic field is not applied, as shown in FIG. 3 (a), a signal magnetic field S _H 1 cycle In contrast, two cycles of output (vibration) are generated. Thus, if the signal magnetic field _SH and the output do not correspond one-to-one, it is a serious problem in actual use.

In contrast, as shown in FIG. 3 (b), when the signal magnetic field S _H applies a bias magnetic field B _H as not negative, with respect to the signal magnetic field S _H 1 cycle, 1 cycle output (vibration ), And the signal magnetic field _SH and the output have a one-to-one correspondence.

The application of the bias magnetic field B _H is also effective for improving the output (amplitude). When the bias magnetic field B _H is not applied, vibration is performed using a region near the zero point where the gradient of the displacement Δl is gentle. In other words, in the magnetostrictive vibrator, the amplitude of vibration of the magnetostrictive material 1 becomes small, and there is a possibility that a sufficient output cannot be obtained. On the other hand, if the bias magnetic field BH is applied and vibration is performed using a region where the gradient of the displacement amount Δl is large, a large displacement amount can be obtained with the same signal magnetic field, and a large output can be obtained. is there.

  In the magnetostrictive element having the structure shown in FIG. 1 or FIG. 2, it is preferable to set the magnitude of the bias magnetic field in consideration of the aforementioned matters. Therefore, a magnet material capable of applying a necessary bias magnetic field may be used for the cylindrical permanent magnet 3, and for example, a ferrite magnet or a metal magnet may be appropriately selected and used.

  In the magnetostrictive element (magnetostrictive vibrator) having the above-described configuration, the permanent magnet 3 is disposed inside the coil 2 and a bias magnetic field is efficiently applied. Therefore, the size of the permanent magnet 3 should be small. In addition, since it is not necessary to provide a coil bobbin separately, it is possible to reduce the size of the entire magnetostrictive element. In addition, since the permanent magnet 3 that always generates magnetic flux is arranged on the inner side, the leakage magnetic flux leaking to the outside of the magnetostrictive element can be suppressed, and its adverse effect can be suppressed. Furthermore, even if the permanent magnet 3 is disposed on the inner side and the coil 2 is disposed on the outer side, the signal magnetic field applied by the coil 2 does not decrease.

  As described above, the embodiments of the magnetostrictive element to which the present invention is applied have been described taking the magnetostrictive vibrator as an example, but it goes without saying that the present invention is not limited to this embodiment. For example, as a magnetostrictive element, various actuators that displace a magnetostrictive material by a magnetic field generated from a coil, such as a linear actuator, and a magnetic permeability change accompanying a stress change applied to the magnetostrictive material such as a pressure torque sensor, a vibration sensor, a gyro sensor, etc. The present invention can also be applied to a magnetostrictive sensor or the like that is detected by the above.

  Hereinafter, specific examples of the present invention will be described based on experimental results.

Comparative Example As shown in FIGS. 4A and 4B, a cylindrical rod-shaped magnetostrictive material 11 is arranged at the center, a coil 12 is arranged outside thereof, and a cylindrical permanent magnet 13 is arranged outside thereof. Further, iron pressing plates 14 are provided at both ends of the magnetostrictive material 11, and the magnetostrictive material 11 and the permanent magnet 13 are positioned by a counterbore formed on the pressing plate 14.

  The dimension A (the outer diameter of the permanent magnet 13 which is the outermost diameter of the magnetostrictive element) shown in FIG. 4A is 12 mm, the dimension B (the outer diameter of the coil 12) is 8 mm, and the dimension C (the outer diameter of the magnetostrictive material 11). Is 3.5 mm. The length of the magnetostrictive material 11 was 30 mm, and the length of the permanent magnet 13 was 29 mm.

EXAMPLE As shown in FIGS. 5A and 5B, a cylindrical rod-shaped magnetostrictive material 11 is arranged at the center, a cylindrical permanent magnet 13 is arranged outside thereof, and a coil 12 is arranged outside thereof. Further, iron pressing plates 14 are provided at both ends of the magnetostrictive material 11, and the magnetostrictive material 11 and the permanent magnet 13 are positioned by a counterbore formed on the pressing plate 14.

  Dimension A (the outer diameter of the coil 12 that is the outermost diameter of the magnetostrictive element) shown in FIG. 5A is 11 mm, dimension B (the outer diameter of the permanent magnet 13) is 8 mm, and dimension C (the outer diameter of the magnetostrictive material 11). Is 3.5 mm. As in the comparative example, the length of the magnetostrictive material 11 was 30 mm, and the length of the permanent magnet 13 was 29 mm.

The λ-H characteristics of the magnetostrictive elements (comparative examples and examples) produced by evaluation were examined. In the λ-H characteristic, the bias magnetic field is 400 (Oe), and in condition 1, ± 1000 (Oe) by the coil 12, in condition 2, ± 300 (Oe) by the coil 12, and in condition 3, ± 100 (Oe) by the coil 12. A displacement amount Δl (ppm) of the magnetostrictive material 11 at that time was measured. FIG. 6 shows the λ-H characteristic in the comparative example, and FIG. 7 shows the λ-H characteristic in the example.

  Comparing FIG. 6 and FIG. 7, there is almost no change in the λ-H characteristic between the comparative example and the example. Therefore, in the example, by disposing the permanent magnet 13 inside the coil 12, the characteristics equivalent to those of the comparative example can be obtained while reducing the outermost diameter dimension of the magnetostrictive element. It has been proved effective for miniaturization.

It is a schematic sectional drawing which shows an example of the magnetostrictive element (magnetostrictive vibrator) to which this invention is applied. It is a schematic sectional drawing which shows the other example of the magnetostrictive element (magnetostrictive vibrator) to which this invention is applied. It is a figure which shows the relationship between the applied magnetic field and displacement amount in a magnetostrictive vibrator, and the relationship between a signal magnetic field and an output, (a) is a case where a bias magnetic field is not applied, (b) is a case where a bias magnetic field is applied. It is a figure which shows the structure of the magnetostriction element produced by the comparative example, (a) is a top view, (b) is sectional drawing. It is a figure which shows the structure of the magnetostriction element produced in the Example, (a) is a top view, (b) is sectional drawing. It is a characteristic view which shows the (lambda) -H characteristic in a comparative example. It is a characteristic view which shows the (lambda) -H characteristic in an Example.

Explanation of symbols

1,11 magnetostrictive material, 2,12 coil, 3,13 permanent magnet, 4 O-ring, 14 holding plate

Claims (6)

A magnetostrictive element comprising a magnetostrictive material, a permanent magnet that applies a bias magnetic field to the magnetostrictive material, and a coil that performs electromagnetic conversion,
The permanent magnet is a cylindrical permanent magnet, and a coil is wound around the cylindrical permanent magnet as a bobbin.   2. The magnetostrictive element according to claim 1, wherein an O-ring is interposed between the magnetostrictive material and the permanent magnet.   The magnetostrictive element according to claim 2, wherein the O-ring is made of rubber.   4. The magnetostrictive element according to claim 1, wherein the magnetostrictive element is a magnetostrictive actuator that displaces the magnetostrictive material by a magnetic field generated from the coil, or a magnetostrictive vibrator that vibrates the magnetostrictive material. 5.   4. The magnetostrictive element according to claim 1, wherein the magnetostrictive element is a magnetostrictive sensor that detects a change in magnetic permeability associated with a change in stress applied to the magnetostrictive material by the coil. 5. A cylindrical permanent magnet is arranged around the magnetostrictive material, and a coil is wound around the cylindrical permanent magnet as a bobbin,
A bias magnetic field applying method, wherein a bias magnetic field is applied to the magnetostrictive material by the permanent magnet.

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