JPH03239150A - Voice coil type linear motor - Google Patents

Abstract

PURPOSE:To reduce the unevenness of magnetic spaces by fixing a hollow cylindrical auxiliary ring of ferromagnetic material to the inner face of a hollow cylindrical permanent magnet, which is provided at the inner face of the outer yoke of a voice coil type linear motor and has anisotropy in the radial direction. CONSTITUTION:A voice coil type linear motor is composed of a peripheral yoke 1, a rear yoke 2, and a center yoke 3 each consisting of ferromagnetic substance. The yokes 1 and 3 are made hollow cylindrical, and the yoke 2 dislike. These pieces of hollow cylindrical permanent magnets 4 having anisotropy in radial direction are fixed to the inside periphery of the peripheral yoke 1 so as to assemble magnetic circuits. Furthermore, a hollow cylindrical auxiliary ring 5 of ferromagnetic substance consisting of an iron plate, a steel plate, or the like is fixed to the inside periphery of the permanent magnet 4. Hereby, the unevenness in the circumferential or axial magnetic spaces of the permanent magnets are reduced sharply, and thrust moment is equalized. This is suitable for a magnetic disc device.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a voice coil type linear motor used as a means for positioning a magnetic node in a magnetic disk drive, and in particular to This invention relates to an improved voice coil type linear motor.

[Prior Art] Voice coil type linear motors have been used in many applications because they have a simple structure and are excellent as a drive source for high-speed linear motion. In particular, in magnetic disk drives, it is necessary to move the magnetic head from any track position on the magnetic disk to another track position at high speed and with high precision. Voice coil type linear motors, which have short access times, are often used.

In general, such voice coil type linear motors are composed of two cylindrical outer yokes, one center yoke, and five permanent magnets fixed to the inner peripheral surfaces of the outer yokes, and a moving coil (for example, Japanese Patent Publication No. 504241, Japanese Unexamined Patent Publication No. 1983-
(See Publication No. 123361, etc.).

FIG. 6 is a vertical cross-sectional view of a main part of an example of the conventional voice coil type linear motor. In FIG. 6, reference numeral 1 denotes an outer yoke, which is formed into a hollow cylindrical shape from a ferromagnetic material such as soft iron or F4. Reference numeral 2 indicates a rear yoke. Reference numeral 3 indicates a center yoke, both of which are made of the same ferromagnetic material as the outer peripheral yoke 1 and formed into a disk shape and a columnar shape, respectively. Then, a rear yoke 2 is fixed to the right end of the outer yoke 1, and a center yoke 3 is attached to the center of the rear yoke 2 coaxially with the outer yoke 1.
to fix. Next, reference numeral 4 denotes a permanent magnet, which has anisotropy in the radial direction, is formed into a hollow cylindrical shape, and is fixed to the inner surface of the outer circumferential yoke 1. A voice coil 7 is provided in a magnetic gap 6 formed between the permanent magnet 4 and the center yoke 3 to be connected to a carriage (none of which is shown) that supports a magnetic head. The voice coil 7 is formed by winding a coil 9 around a bobbin 8 made of an insulating material such as plastic.

With the above configuration, the coil 9 constituting the voice coil 7
When a current is applied to the permanent magnet 4, the magnetic flux lines (indicated by broken lines in the figure) generated by the permanent magnet 4 are perpendicular to the current, so the voice coil 7 moves linearly in the axial direction based on Fleming's left-hand rule. Since the direction of this linear motion can be changed by reversing the direction of the current flowing through the coil 9, the voice coil 7 can be moved forward and backward.

In the voice coil type linear motor having the above configuration, as the permanent magnet 4, an alnico magnet, a ferrite magnet, a rare earth cobalt magnet, or the like is generally used. In addition, in the voice coil type linear motor, the operating point cannot be set high due to the limited wall thickness of the permanent magnet 4 (the permeance coefficient is generally about 0.8 to 3, although it varies depending on the configuration of the magnetic circuit). It is necessary to use a ferrite magnet or rare earth cobalt magnet with a large coercive force. In particular, with the miniaturization and higher performance of magnetic disk devices, there are similar demands for voice coil type linear motors as drive sources in these devices, so rare earth cobalt magnets are often used (e.g. (See Japanese Patent Application Laid-Open No. 56-74077). Furthermore, in recent years, there has been a demand for further miniaturization and higher performance of 2-point coil type linear motors, so in order to obtain high magnetic flux density within the magnetic gap 6, permanent Magnets (for example, see Japanese Patent Publication No. 61-34242)
Voice coil type motors or linear motors using
No. 10862 and No. 61-266056).

[Problem to be solved by the invention]

The R-Fe-B permanent magnet 4 described above has anisotropy in the radial direction, but even if there is a slight difference in the packing density of the material powder during molding, the There is a tendency for variations in magnetic properties to increase, causing variations in magnetic force in the circumferential direction of the permanent magnet 4, which manifests as variations in magnetic flux density within the magnetic gap 6. Therefore, there is a problem that a difference occurs between the thrust on one side of the plane including the axis and the thrust on the other side, which disturbs the linear balance of the linear motion of the voice coil 7.

Furthermore, since it is difficult to manufacture permanent magnets 4 made of R-Fe-B material as described above with a large length in the axial direction, 1 usually there are a plurality of permanent magnets in the axial direction as shown in FIG. Individual(
For example, the structure is such that it is divided into three pieces, molded, and joined within the outer circumferential yoke l.

For this reason, a seam exists between the permanent magnets 4, 4 in the axial direction, causing variation (8 to 10%) in the magnetic flux density within the magnetic gap 6 at the axial position, reducing the driving performance of the voice coil 7. There is a problem.

Moreover, the permanent magnet 4 made of R-Fe-B material has excellent magnetic properties.

Since it contains a large amount of rare earth elements (particularly Nd) and iron that are easily oxidized in the atmosphere, if it is stuck to the outer yoke l as it is, oxides will be generated on the surface of the permanent magnet 4 and the magnetic gap 6 will be
This leads to a decrease in the magnetic flux density inside.

For this reason, when using an R-Fe-B permanent magnet 4, it is common to form an oxidation-preventing film on its surface by various methods (for example, Japanese Patent Laid-Open No. 60-153109).
No. 1 No. 61-130453, No. 61-150201
(Refer to the publication number, etc.) However, in a voice coil type linear motor, the magnetic gap 6 is limited to a few millimeters, so even if an anti-oxidation film is formed on the surface of the permanent magnet 4 as described above, the bobbin 8 or coil 9 and the permanent magnet 4 interfere, and the permanent magnet 4
Chips may occur. Therefore, there are also problems in that the assembly work is extremely complicated and requires a large amount of man-hours and time.

The present invention solves the problems existing in the prior art described above, and significantly reduces the variation in magnetic flux density of the magnetic gap in the circumferential direction and axial direction of the permanent magnet.

The purpose of the present invention is to provide a voice coil type linear motor that eliminates variations in thrust moment and has excellent thrust linearity.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a center yoke formed in a cylindrical shape made of a ferromagnetic material is magnetically coupled to the outer yoke within an outer yoke formed in a hollow cylindrical shape made of a ferromagnetic material. A permanent magnet having radial anisotropy and formed into a hollow cylindrical shape is fixed to the inner surface of the outer peripheral yoke, and a hollow cylindrical shape is formed within the magnetic gap formed between this permanent magnet and the center yoke. In a voice coil type linear motor having a coil movable in the axial direction, an auxiliary ring formed in a hollow cylindrical shape made of a ferromagnetic material is fixed to the inner surface of a permanent magnet. A technical method was adopted.

In the present invention, the permanent magnet can be formed from an R-Fe-B material. In this case, the content of the element R in the intermediate material of the RFe-B material is preferably in the range of 10 to 30 atomic %. If R is less than 10 atomic %, the magnetic properties (especially coercive force) deteriorate.

On the other hand, if the amount is more than 30 atomic %, the R-rich nonmagnetic phase increases and the residual magnetic flux density decreases, which is not preferable. In this case, the rare earth element R is usually Nd.

Rare earth elements such as Pr are used, but Nd, which is particularly abundant in resources and relatively inexpensive, is the most common.

In addition, in order to improve the coercive force, a part of R (1 to 30%
degree) can be replaced with heavy rare earth elements such as Dy, Ho, and Tb. Furthermore, R is La, Ce, Sm, Gd,
It can contain at least one of Er, Eu, Tm, Tb, and Y.

The content of Fe is preferably in the range of 65 to 85 at.%. F
When e is less than 65 at%, the residual magnetic flux density decreases, and 8
If it is more than 5 atomic %, the coercive force decreases, which is not preferable.

The content of B is preferably in the range of 2 to 28 at.%.

When B is less than 2 at%, the coercive force decreases, and B is less than 28 at%.
If the amount is larger, the amount of B-rich nonmagnetic phase increases and the residual magnetic flux density decreases, which is not preferable.

In addition to the above-mentioned essential components, impurities (for example, Ot) that are unavoidable during production may be included. Further, known additive elements (for example, Co, Aj!, Ti, etc.) can also be contained in R-Fe-B-based materials. Such additive elements include 2, for example, JP-A-60-162754.

It is disclosed in Japanese Patent No. 61-87825.

The hollow cylindrical permanent magnet in the present invention can be manufactured, for example, as follows. First, the RFe-B alloy is melted in Ar or in vacuum using the usual method.
may be added as ferroboron. It is preferable to add the rare earth element last. After melting, the ingot is crushed by coarse and fine crushing. Coarse crushing is done by stamp mills, show crushers, brown mills, disc mills, etc., and fine crushing is done by jet mills, vibration mills, etc.

This is done using a ball mill, etc. Both are carried out in a non-oxidizing atmosphere to prevent oxidation, and for this reason it is preferable to use an organic solvent or an inert gas. The particle size after grinding is 2-5 um (Fischer 5ubsiveS
It is preferable to set the value to 1. The magnetic powder produced as described above is molded into a predetermined hollow cylindrical molded body using a magnetic field molding device. This molded body is then sintered, and the sintering is carried out at a temperature of 950 to 115 o''c for 20 minutes to 2 hours in an inert gas such as Ar or He, in vacuum, or in hydrogen. After sintering If necessary, heat treatment is performed in an inert gas atmosphere.The preferred heat treatment conditions are 500 to 700°C for 30 minutes to 3 hours.Finally, the direction of orientation of the magnetic particles (radial direction in this case)
Perform magnetization in alignment with Magnetizing magnetic field strength is 5 to 30 kOe
A range of is good.

[Effect]

With the above configuration, even if there are variations in the magnetic properties of the permanent magnet in the circumferential direction and/or the axial direction, the magnetic flux density distribution within the magnetic gap can be made uniform by the auxiliary ring made of one ferromagnetic material.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of the present invention, and the same parts are designated by the same reference numerals as in FIG. 6. In FIG. 1, reference numeral 5 denotes an auxiliary ring, which is made of a ferromagnetic material such as soft iron or steel and has a hollow cylindrical shape, and is fixed to the inner surface of the permanent magnet 4. In this example, the permanent magnet 4 was formed as follows. That is, an alloy having a composition of 13% Nd, 2% Dy, 87% Fe, and 78% Fe in atomic % was cast by vacuum melting, and then coarsely and finely pulverized in a Nz gas atmosphere to obtain an alloy powder with an average particle size of 3 μm. Obtained. The obtained alloy powder was heated to 20 kOe in the radial direction into the molding cavity using a magnetic field molding device.
It was press-formed at a pressure of It/cm" without applying a pulsed magnetic field. Next, it was sintered in a vacuum at a temperature of 1100°C for 2 hours, and then heat-treated in an Ar gas atmosphere at a temperature of 600'C for 1 hour. After polishing the inner and outer peripheries of this sintered body, one magnetization was performed to obtain an outer diameter of 99 mm, an inner diameter of 92 mm,
A hollow cylindrical permanent magnet 4 having a length of 23 mm was obtained. This permanent magnet 4 has a residual magnetic flux density Br=1.1.000G and a coercive force+Hc=10.0000e.

Maximum magnetic x-2 Lugie product (BH) max = 26MGO
The magnetic properties of e. A magnetic circuit as shown in FIG. 1 was assembled using three of the above permanent magnets 4. Each yoke is made of soft iron, and the outer diameter of the outer yoke l is 117 m.
m, center yoke 3 has an outer diameter of 84 mm and an inner diameter of 60 mm.
mm. In addition, the thickness of the auxiliary ring 5 made of an iron plate was varied to evaluate the cable characteristics.

FIGS. 2(a) and 2(b) are diagrams showing the relationship between the axial position of the permanent magnet and the magnetic flux density of the magnetic gap, and the right side is the first
This is the side of the rear yoke 2 shown in FIGS. First, what is shown in Fig. 2(b).

This is a conventional structure shown in FIG. 6, and it is recognized that there are variations in the magnetic flux density within the magnetic gap 6 depending on the axial position of the permanent magnet 4. On the other hand, the one shown in FIG. 2(a) has a structure in which an auxiliary ring 5 (with a wall thickness of 0.9 mm) is fixed to the inner surface of the permanent magnet 4 as shown in FIG. 1.

Variations due to the axial position of the permanent magnet 4 are drastically reduced.

It is recognized that the magnetic flux density is almost linear. That is, due to the fixation of the auxiliary ring 5.

It is clear that the influence of the joint between the permanent magnets 4.4 is almost eliminated.

3(a) and 3(b) each show the relationship between the circumferential position of the permanent magnet and the magnetic flux density of the magnetic gap, and correspond to those shown in FIG. 1 and FIG. 6, respectively. In these cases, the center yoke 3 is provided with an axial slit (not shown) divided into six equal parts in the circumferential direction, and a is the position corresponding to the slit. Figure (b) corresponds to the above-mentioned Figure 6, but the difference ΔBr in the peak value of the magnetic flux density of the air gap 6 is 500G.

It is recognized that there is a large variation in the circumferential direction.

It is presumed that this is because the difference in packing density and the difference in orientation during molding of the permanent magnets 4 directly appear as variations in the magnetic flux density in the air gap 6. On the other hand, the third
As shown in FIG. 1, the difference in the peak value of magnetic flux density between the five gaps 6 is due to the configuration in which the auxiliary ring 5 (thickness 0.9 mm) is fixed to the inner peripheral surface of the permanent magnet 4, as shown in FIG. △Br
remains at only 50G, and it can be seen that the variation in one circumferential direction has been significantly reduced.

FIG. 4 is a diagram showing the relationship between the wall thickness and the difference in thrust moment, and shows the difference in thrust moment between the upper and lower parts of the plane including the axis when the wall thickness of the auxiliary ring 5 in FIG. 1 is changed. (absolute value). In FIG. 4, curves F and R correspond, respectively, to the withdrawal and entry directions of the voice coil (not shown) in FIG. As is clear from Fig. 4, the wall thickness is 0. In other words, in the case of the one lacking the auxiliary ring 5 in Fig. 1 (corresponding to the conventional structure shown in Fig. 6), the difference in thrust moment is 50 gf.
-cm and 80 gf-cm, but it is recognized that by providing the auxiliary ring 5 and increasing its wall thickness, the difference in thrust moment is drastically reduced. However, if the wall thickness of the auxiliary ring 5 is increased to 1 mm or more, the dimension of the air gap 6 shown in FIG. This is undesirable because it is easy to occur, or the thickness of the permanent magnet 4 has to be reduced in order to ensure the gap 6 has a predetermined size, resulting in deterioration of the magnetic properties.

FIG. 5 is a diagram showing the relationship between wall thickness and thrust linearity. As is clear from FIG. 5, it can be seen that by providing the auxiliary ring 5 shown in FIG. 1, the thrust linearity can be significantly improved.

Although the thrust linearity can be improved by increasing the wall thickness of the auxiliary ring 5, it is recognized that the thrust linearity tends to be substantially saturated when the wall thickness exceeds 0.5 mm.

In the above experiment, 163 square aluminum wires with a width of 1 mm and a thickness of 0.3 mm were attached to the bobbin as the voice coil.
A tan-wound coil (length 30 mm) was used, the input current to the coil was LA, and the stroke was 38.7 mm.

Although this example describes an example in which the permanent magnet is made of Nd-Fe-B-based material, it may also contain other rare earth elements, and the effect will be the same even if it is a ferrite magnet. .

Furthermore, a part of the auxiliary ring may extend to the end face of the permanent magnet.

〔Effect of the invention〕

Since the present invention has the configuration and operation described above, it is possible to significantly reduce variations in the magnetic gap in the circumferential direction and/or axial direction of the permanent magnet, reduce the difference in thrust moment, and improve the linearity of the two thrusts. It can be expected to have the effect of significantly improving the

Kumagnet 55: Auxiliary ring, 6: M1 air gap, 9: Coil.

Claims (2)

[Claims] (1) A center yoke formed in a cylindrical shape made of a ferromagnetic material is magnetically coupled to the outer yoke within an outer yoke formed in a hollow cylindrical shape made of a ferromagnetic material, and anisotropic in the radial direction is provided on the inner surface of the outer yoke. A hollow cylindrical permanent magnet having a magnetic field is fixed thereto, and a hollow cylindrical coil is provided in a magnetic gap formed between the permanent magnet and the center yoke so as to be movable in the axial direction. What is claimed is: 1. A voice coil linear motor characterized in that an auxiliary ring formed in a hollow cylindrical shape made of a ferromagnetic material is fixed to the inner surface of a permanent magnet. (2) The voice coil type linear motor according to claim (1), wherein the permanent magnet is formed of an R (one or more rare earth elements such as Nd, Pr, Dy, etc.)-Fe-B material.