JP2003143879A - Actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low cost actuator capable of attaining a simple structure of which control position accuracy is not affected by temperature. SOLUTION: This actuator includes a coil for generating a magnetic field, a magnetostrictive member for generating magnetostriction with the generated magnetic field, and a driving rod for taking out variances in the length of the magnetostrictive member by the magnetostriction. One end of the magnetostrictive member is supported by a hole side of an actuator casing into which the driving rod pierces, a flange lower surface of the driving rod is brought into contact with the other end of the magnetostrictive member, an upper surface of the flange is energized by an elastic member in a hole direction in which the driving rod of the actuator casing pierces, and a ratio of a length ranging from the driving rod flange lower surface to an end surface of the driving rod in which the hole pierces to a length of the magnetostrictive member is made equal to the ratio of the linear expansion coefficient of the magnetostrictive member to a linear expansion coefficient of the driving rod material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator for controlling a minute movement amount, and more particularly to an actuator using a magnetostrictive material (particularly a giant magnetostrictive material).

[0002]

2. Description of the Related Art As an actuator for controlling a minute movement amount, there is a linear actuator which drives an actuator driving rod by utilizing a phenomenon in which a giant magnetostrictive material is distorted by a change in an external magnetic field and expands. When the temperature fluctuates, the control position accuracy of the drive rod cannot be ensured.

Further, in Japanese Patent Laid-Open No. 9-144706, two magnetostrictive materials are attached from both end surfaces of a magnetostrictive material holder and tandem connection is performed through the magnetostrictive material holders, whereby the substantial length of the magnetostrictive material is 2 mm. There is disclosed an actuator that cancels temperature fluctuation during use by doubling and forming the magnetostrictive material holder material with a material having a thermal expansion coefficient that is twice the thermal expansion coefficient of the magnetostrictive material.

[0004]

Since the movement amount of the drive rod of the actuator using the conventional giant magnetostrictive material is small,
When used in an atmosphere in which the temperature fluctuates, the thermal expansion of the giant magnetostrictive material had a large effect on the control position of the drive rod, and the positioning accuracy could not be ensured. In addition, JP-A-9
The actuator disclosed in Japanese Patent No. 144706 has the advantage that the length of the actuator required to obtain the same drive rod control amount can be shortened, but it requires deep hole drilling in the base body into which the magnetostrictive material is fitted, and the structure is also It is inevitable that it becomes complicated and the manufacturing cost increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an actuator which is easy to process and has a simple structure, and in which the control position accuracy of the drive rod is not affected by temperature fluctuation during use.

[0006]

In order to achieve the above object, the present invention provides a coil for generating a magnetic field, a magnetostrictive member in which magnetostriction is generated by the generated magnetic field, and a drive for extracting a change in length of the magnetostrictive member due to magnetostriction. An actuator comprising a rod, wherein one end side of the magnetostrictive member is supported by a hole side of an actuator casing through which the drive rod passes, and the other end side of the magnetostrictive member is brought into contact with a lower surface of the flange of the drive rod, The upper surface of the flange is biased by an elastic member in the direction of the hole through which the drive rod of the actuator casing penetrates, and the length from the lower surface of the drive rod flange to the end surface of the drive rod that penetrates the hole and the length of the magnetostrictive member. Is equal to the ratio of the coefficient of thermal expansion of the magnetostrictive member and the coefficient of thermal expansion of the drive rod material.

According to this invention, even when the actuator is arranged in a place where the temperature fluctuates during operation, the thermal expansion amount of the magnetostrictive member and the thermal expansion amount of the drive rod are always equal and the expansion directions are opposite. Therefore, the control position of the drive rod does not change due to temperature fluctuation, and the control position of the drive rod can be maintained regardless of the temperature.

The invention according to claim 2 is characterized in that a dipole of a magnet is arranged at both ends of the magnetostrictive member, and an initial magnetostriction is generated in the magnetostrictive member by a magnetic field of the magnet. For example, an N magnetic pole is arranged on one end side of the magnetostrictive member, and an S magnetic pole is arranged on the other end side of the magnetostrictive member so that magnetostriction is generated in advance through magnetic force lines in the axial direction of the magnetostrictive member. This makes it possible to change the drive direction of the drive rod from the initial position depending on whether the direction of the magnetic field generated when a current is applied to the coil is made to coincide with or opposite to the direction of the magnetic field generated by the magnet.

In the structure of the present invention, since the length of the drive rod is longer than the length of the magnetostrictive member, the length of the drive rod can be reduced by using a material whose linear expansion coefficient is smaller than that of the magnetostrictive member. The ratio with the length of the magnetostrictive member can be set to be equal to the ratio between the linear expansion coefficient of the magnetostrictive member and the linear expansion coefficient of the drive rod.

It is preferable that the magnetostrictive member has a hollow cylindrical shape, for example, a hollow cylinder, having a hole through which the output member penetrates in the central portion. Also, a plurality of magnetostrictive members may be arranged around the drive rod. Further, in the drive rod that penetrates the hollow portion of the hollow cylindrical magnetostrictive member or when a plurality of magnetostrictive members are arranged around the drive rod, the magnetic force lines of the coil (electromagnet) efficiently pass through the magnetostrictive member in the drive rod. As described above, it is preferable to use a material whose relative magnetic permeability is as small as possible than the relative magnetic permeability of the magnetostrictive member.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples.

FIG. 1 shows a schematic configuration of a first example according to the embodiment of the present invention, in which a drive rod penetrates a hollow cylindrical magnetostrictive member. FIG. 2 shows a schematic configuration of a second example according to the embodiment of the present invention, in which a plurality of magnetostrictive members are arranged around the drive rod. FIG. 3 is a diagram for explaining that the control position of the drive rod is not affected by the temperature of the actuator, and FIG. 4 shows a schematic configuration of a third example according to the embodiment of the present invention.

In FIG. 1, 1 is a casing of an actuator, 2 is a magnetostrictive member, 3 is a drive rod, 4 is a flange of the drive rod, and 6 is a coil. The magnetostrictive member 2 is formed in a hollow cylindrical shape, and one end of the magnetostrictive member 2 has a hole 1 in the casing 1.
The lower surface of the flange 4 of the drive rod 3 penetrating the hollow portion of the magnetostrictive member 2 abuts on the other end of the magnetostrictive member 2. The upper surface of the flange 4 is biased by a spring 5 in the direction of the hole 1a of the casing 1. An appropriate gap is provided between the hollow hole of the magnetostrictive member 2 and the outer circumference of the drive rod 3 so that the magnetostrictive member 2 and the drive rod 3 can move relative to each other. A seal member (not shown) may be provided in the gap between the hole 1a of the casing 1 and the drive rod 3. A coil 6 is arranged around the magnetostrictive member 2. The lower end surface 3a of the drive rod 3 is the control position of the actuator 10.

The magnetostrictive member 2 has a magnetostrictive constant (saturated amount of strain).
A large magnetostrictive material is used. When an electric current is applied to the coil 6, a magnetic field is generated, and the magnetic flux passes through the magnetostrictive member 2 and the magnetostrictive member 2
Then, a strain corresponding to the magnitude of the current is generated, the magnetostrictive member 2 expands, and the drive rod 3 is lifted against the biasing force of the spring 5, so that the lower end surface 3a moves upward. The giant magnetostrictive material has a characteristic of exhibiting a large magnetostriction constant when an appropriate axial compressive stress (prestress) is applied in advance, and the lower surface of the flange 4 of the drive rod 3 of the spring 5 is always in contact with the upper surface of the magnetostrictive member 2. Thus, the pre-stress is given to the magnetostrictive member 2 as well.

FIG. 2 shows a second embodiment of the present invention, and FIG.
Is that the magnetostrictive member is composed of a plurality of magnetostrictive members 2 ′ and is arranged around the drive rod 3. In the present embodiment, a plurality of magnetostrictive members 2'having the same magnetostrictive characteristics and having the same height (length) are arranged so as to surround the drive rod 3 instead of the hollow cylindrical magnetostrictive member in FIG. The shape of the magnetostrictive member 2'may be a cylinder or any other shape, and it is not necessary to form a hollow hole in the magnetostrictive member.

FIG. 3 is a diagram for explaining that the control position of the drive rod is not affected by the temperature of the actuator.
Shows a state at a certain temperature, and (B) shows a state at a temperature higher by ΔT ° C. than (A). In FIG. 3A, the length of the magnetostrictive member 2 is Lm and the length of the drive rod 3 is Lr. In FIG. 6B, the magnetostrictive member 2 extends upward by ΔLm and the drive rod 3 extends downward by ΔLr due to thermal expansion, as compared with FIG.

Therefore, the linear expansion coefficient of the magnetostrictive member 2 is set to α
m, and the linear expansion coefficient of the drive rod is αr, ΔLm = αm · Lm · ΔT ΔLr = αr · Lr · ΔT ΔLm-ΔLr = (αm · Lm-αr · Lr) · ΔT. Therefore, αm · Lm−αr · Lr = 0, that is, L
By setting r / Lm = αm / αr, ΔLm−Δ
Lr is always 0 regardless of ΔT. Therefore, the extension due to the thermal expansion of the magnetostrictive member 2 and the extension due to the thermal expansion of the drive rod 3 are always canceled out, and the drive rod 3 at the control position is set.
The position of the lower end surface 3a of is not affected by temperature. The change in the magnetostrictive characteristic (relationship between the strength of the magnetic field applied to the magnetostrictive member and the magnitude of the magnetostriction generated) with temperature can be corrected by the current flowing through the coil 6.

The flange 4 of the drive rod 3 is in contact with the upper end surface of the magnetostrictive member 2 and is preferably made of a ferromagnetic material having a high magnetic permeability so that the magnetic flux generated by passing a current through the coil 6 can easily pass therethrough. . Also, the hole 1a of the casing 1
Similarly, the side should be made of a ferromagnetic material or a ferromagnetic material member should be provided. The other parts of the casing are preferably made of non-magnetic material to prevent leakage of magnetic flux. The drive rod 3 is preferably made of a material having a smaller magnetic permeability than that of the magnetostrictive member 2 in order to reduce the leakage of the magnetic flux into the drive rod and to efficiently pass the magnetic flux through the magnetostrictive member 2.

For example, the linear expansion coefficient αm of the magnetostrictive member 2 is 1
If the linear expansion coefficient αr is 8.4 ppm / ° C. and the material of the driving rod 3 is pure titanium, the ratio of the length Lr of the driving rod 3 to the length Lm of the magnetostrictive member 2 is Lr / Lm = αm / αr = 12 / 8.4 = 1.428 ... That is, the length of the drive rod 3 is about 1.4 times the length of the magnetostrictive member 2.
It may be tripled.

The magnetostrictive member 2 has a relative magnetic permeability of about 4 to 10, whereas pure titanium has a small relative magnetic permeability of about 1 and is a material suitable for the drive rod material of the present invention. Titanium alloy Ti-6Al-4V and the like are also suitable materials.

FIG. 4 shows a schematic configuration of a third example according to the embodiment of the present invention. The difference from FIG. 1 is that magnets 7 (permanent magnets) sandwiching the magnetostrictive member 2 from both ends are provided. The same components as those in FIG. 1 are designated by the same reference numerals. An initial magnetostriction is generated in the magnetostrictive member 2 by the magnet, and the direction of the magnetic field generated when a current is applied to the coil is matched with or opposite to the direction of the magnetic field by the magnet, that is, the direction of the current is changed. Thus, the drive direction of the drive rod from the initial position can be changed. Of course, a conventional method in which a bias magnet is provided on the outer circumference of the coil may be used. In FIG. 4, the fact that the spring 5 and one pole of the magnet 7 overlap does not mean that the spring 5 is embedded in one pole of the magnet 7,
It only indicates that one pole of the magnet 7 may be arranged independently of the spring 5.

[0022]

The present invention is carried out in the form as described above and has the following effects.

When the length Lm and linear expansion coefficient αm of the magnetostrictive member and the length Lr and linear expansion coefficient αr of the driving rod are L,
By selecting the length and linear expansion coefficient of the magnetostrictive member and the length and linear expansion coefficient of the drive rod so that r / Lm = αm / αr, it is possible to obtain an actuator in which the influence of thermal expansion is completely eliminated.

By disposing a plurality of magnetostrictive members around the drive rod, it is possible to eliminate the processing of the elongated through holes in the magnetostrictive member, and the manufacture of the magnetostrictive member is facilitated.

By disposing the dipoles of the magnet on both ends of the magnetostrictive member, the initial magnetostriction can be effectively generated in the magnetostrictive member.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first example according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a second example according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating that the control position of the drive rod is not affected by the temperature of the actuator.

FIG. 4 is a diagram showing a schematic configuration of a third example according to the embodiment of the present invention.

[Explanation of symbols]

1 casing 2 Magnetostrictive member 3 drive rod 4 flange 5 springs 6 coils 7 magnet 10 actuators

Claims (6)

[Claims] 1. An actuator comprising a coil for generating a magnetic field, a magnetostrictive member for causing magnetostriction due to the generated magnetic field, and a drive rod for taking out a length change of the magnetostrictive member due to the magnetostriction, wherein one end of the magnetostrictive member. Side is supported by the hole side of the actuator casing through which the drive rod penetrates, the lower surface of the flange of the drive rod is abutted on the other end side of the magnetostrictive member, and the upper surface of the flange is penetrated by the drive rod of the actuator casing. Direction is urged by an elastic member, and the ratio of the length from the lower surface of the drive rod flange to the end surface of the drive rod penetrating the hole to the length of the magnetostrictive member is defined as the linear expansion coefficient of the magnetostrictive member and the drive rod material. An actuator characterized by being made equal to the linear expansion coefficient. 2. The actuator according to claim 1, wherein dipoles of a magnet are arranged at both ends of the magnetostrictive member, and an initial magnetostriction is generated in the magnetostrictive member by a magnetic field of the magnet. 3. The actuator according to claim 1, wherein the linear expansion coefficient of the drive rod is smaller than the linear expansion coefficient of the magnetostrictive member. 4. The actuator according to claim 1, wherein a relative magnetic permeability of the drive rod is smaller than a relative magnetic permeability of the magnetostrictive member. 5. The actuator according to claim 1, wherein the magnetostrictive member is formed in a hollow cylindrical shape having a hole through which the drive rod penetrates in a central portion thereof. 6. The actuator according to claim 1, wherein the magnetostrictive member comprises a plurality of magnetostrictive members arranged around the drive rod.