JPS63148854A - Magnetic circuit for linear motor - Google Patents

Abstract

PURPOSE:To realize a high speed response by forming a through hole which is wide at the center and narrowed toward the periphery at the magnetic yoke of a voice coil, thereby reducing the impedance of the coil without reducing a magnetic flux density in a magnetic air gap. CONSTITUTION:A through hole 6 which has a penetrating direction substantially parallel to permanent magnets 3a, 36 and substantially perpendicular with respect to the moving direction designated by an arrow A of a voice coil 1, and is wide at the center and narrowed toward the periphery is formed at a magnetic yoke 2b disposed at the center of the coil 1. Thus, magnetic fluxes generated from the permanent magnets 3a, 3b and guided from magnetic yokes 2a, 2c toward the yoke 2b are substantially saturated. Accordingly, since the magnetic flux generated by a current flowing in the coil 1 is scarcely conducted to reduce the inductance of the coil 1, a high speed response can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic circuit for a linear motor capable of moving at high speed.

Conventional technology: Place the voice coil in a magnetic air gap with an equal magnetic field,
Linear motors that can move a voice coil linearly by passing current through it are used in various fields, such as traverse motors for data memory devices. A conventional linear motor of this type has a structure as shown in FIG.

In FIG. 6, 1 is a voice coil, 2a, 2b.

2c is a magnetic yoke made of soft magnetic material, 3a and 3b are permanent magnets, and 4 is a coil bobbin around which a voice coil is wound. The permanent magnets 3a and 3b are magnetized in the thickness direction, and generate an equal magnetic field in the magnetic gap sandwiched between the magnetic yoke 2b at the center and the permanent magnets 3a and 3b. A driving force is generated by passing a current through the voice coil 1 wound around the magnetic yoke 2b at the center, and the voice coil 1 and the coil bobbin 4 are moved.

Problems to be Solved by the Invention However, in such a structure, there is a magnetic yoke 2b inside the voice coil 1.
b forms a closed magnetic loop together with the external magnetic yokes 2a and 2c. Therefore, due to the closed magnetic loop structure, the magnetic flux generated by the current flowing through the voice coil 1 rarely leaks to the outside (and the self-inductance is extremely large), which hinders the high-speed response of the linear motor.

In addition, in order to reduce self-inductance, as shown in the cross-sectional view of the linear motor in FIG. Sometimes used. This reduces self-inductance by causing the magnetic loop generated in the magnetic yoke 2b by the current flowing through the voice coil 1 to be consumed as an eddy current in the steel cap 5, and reducing the amount of magnetic flux generated in the magnetic yoke 2b. This is what it aims to do. Voice coil 1 when using this steel cap 5
The frequency response of the effective resistance R1 and reactance XI of is shown in FIG. FIG. 5 shows that the reactance X1 can be reduced at high frequencies by the steel cap 5. However, the effective resistance R1 becomes large at high frequencies due to eddy current loss, and there is a problem in that it actually makes high-speed response difficult.

The present invention enables high-speed response by lowering the inductance of the voice coil without using a copper cap, and also prevents the non-uniformity of the air gap magnetic field caused by the magnetic flux generated in the voice coil. The purpose is to obtain a stable driving force.

Means for Solving the Problems In order to achieve the above object, the first invention provides a magnetic yoke arranged at the center of the voice coil that is substantially parallel to the permanent magnet and with respect to the moving direction of the voice coil. A through hole having a substantially perpendicular penetration direction is provided, and the cross-sectional area of the cross section perpendicular to the penetration direction of the through hole is wide at the center (and narrows toward the periphery. The part of the magnetic yoke located at the center of the coil that is opposite to the permanent magnet has a small thickness at the center and becomes thicker toward the periphery.

Effects The present invention has the above-mentioned configuration, which reduces the amount of magnetic flux generated at the center of the voice coil by passing a current through the voice coil and converges on the magnetic yoke disposed at the center of the voice coil. Reduce magnetic coupling (by
This reduces the inductance of the voice coil. In other words, a through hole is provided in the magnetic yoke located at the center of the voice coil, or a magnetic yoke is formed on the opposite side of the permanent magnet so that the center part is thinner. By setting the magnetic flux generated by the magnet to a state of magnetic saturation, the magnetic permeability of the magnetic yoke can be lowered, thereby reducing the inductance.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a sectional view of a magnetic circuit for a linear motor according to a first embodiment of the present invention, taken along the moving direction of the linear motor. In the figure, components having the same configuration as those of the conventional example are designated by the same numerals and explanations thereof will be omitted.

The voice coil 1 is placed in a magnetic gap between permanent magnets 3a and 3b and a magnetic yoke 2b at the center, and is moved in the direction of arrow A in the figure by a current flowing through the voice coil 1. When a current is applied to the voice coil 1, a magnetic flux is generated by the current applied to the voice coil 1 in the magnetic yoke 2b arranged at the center of the voice coil. This magnetic flux passes through the central magnetic yoke 2b and the external magnetic yokes 2a+2c, forming a closed magnetic path. The magnetic resistance of the yoke is small, and the magnetic flux generated in the voice coil 1 flows easily, forming a closed magnetic path, resulting in an increase in inductance. A way to prevent an increase in inductance is to increase the magnetic resistance of the yoke to make it difficult for magnetic flux to flow. That is, a method for increasing magnetic resistance is to provide a magnetic gap in the middle of a closed-loop magnetic yoke.

A feature of the present invention is that the magnetic yoke 2b disposed at the center of the voice coil 1 has a penetrating direction that is substantially parallel to the permanent magnets 3a and 3b and substantially perpendicular to the moving direction of the voice coil 1. , the through hole 6 is formed to be wide at the center and narrow toward the periphery.

The operation of this embodiment configured as above will be explained below. First, the magnetic flux generated by the permanent magnets 3a and 3b is guided to the central magnetic yoke 2b through the external magnetic yokes 2a and 2c. At this time, the magnetic flux density inside the yoke is high at the periphery of the magnetic yoke 2b at the center, and as it moves toward the center, the magnetic flux leaks through the magnetic gap, so the magnetic flux density inside the yoke decreases. Therefore, by providing a through hole on the side surface of the magnetic yoke at the center, the area of the through section perpendicular to the penetration direction is large at the center and becomes smaller toward the periphery. The magnetic yoke 2b maintains a constant magnetic flux flowing within the yoke without reducing the magnetic flux density within the magnetic gap.
The magnetic flux can be set to approximately the saturation magnetic flux. Bringing the magnetic yoke 2b closer to the saturation magnetic flux state means bringing the magnetic permeability of the magnetic yoke 2b closer to 1, equivalently equivalent to providing a magnetic gap inside the magnetic yoke. Therefore, by providing a through hole in the magnetic yoke at the center as shown in Figure 1, the magnetic flux generated by the current flowing through the voice coil 1 can pass through it. Therefore, the inductance of the voice coil 1 decreases. The impedance characteristics at this time are shown in Fig. 5.The effective resistance X2 of this example is the reactance component of the actual fiR2.Compared with R1 and XI of the copper cap method described above, it is The influence can be reduced and the impedance can be reduced.

The relationship between the impedance of the voice coil and the driving force F of the linear motor is: Bg: magnetic flux density in the magnetic air gap) V: voice coil length in the magnetic air gap V: drive voltage Zv: impedance of the voice coil, so drive The relationship between force and impedance is inversely proportional, and it is necessary to reduce the high frequency component of impedance, especially in devices that require high-speed response.

Therefore, in this embodiment, the impedance of the voice coil can be reduced without lowering the magnetic flux density of the magnetic air gap, and high-speed response can be achieved.

FIG. 2 shows a second embodiment of the present invention, in which a through hole 7 with a large diameter is formed in the central magnetic yoke 2b, and through holes with smaller diameters are formed in order toward the periphery. It was opened. Even with the configuration of this embodiment, the same effects as those described in FIG. 1 can be expected.

FIG. 3 shows a third embodiment of the invention. 1st
In the embodiment described in FIG. 2, two permanent magnets 3a, 3
Fig. 3 shows the case where one permanent magnet 3a is provided.
This shows the case where only . In this example,
The magnetic yoke 2b at the center of the voice coil 1 forms a closed magnetic loop together with the external magnetic yoke 2a. Therefore, in this case as well, the same effects as in the case described above can be expected.

FIG. 4 shows a fourth embodiment of the present invention. Rather than providing a through hole in the magnetic yoke 2b at the center, the thickness of the part opposite to the permanent magnet 3a is made thinner toward the center.This reduces the magnetic flux density of the magnetic gap. (Also, the flow of magnetic flux generated by the voice coil 1 can be reduced, and the same effect as the embodiment described in FIG. 1 can be expected.

Effects of the Invention The present invention provides a magnetic yoke disposed at the center of the voice coil with a through hole that is wide at the center and narrows toward the periphery, or a magnetic yoke disposed at the center of the voice coil. The opposite side of the magnetic yoke to the permanent magnet is made thinner in the center and thicker towards the periphery, thereby reducing the magnetic flux density within the magnetic gap. It can reduce the inductance of the voice coil and realize a linear motor with high-speed response.In addition, the change in magnetic flux density of the magnetic air gap caused by the current flowing through the voice coil can be reduced by providing a through hole. Alternatively, it can be made smaller by changing the thickness as described above, and a constant driving force that does not depend on the position of the voice coil can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a magnetic circuit for a linear motor according to a first embodiment of the present invention, and FIGS.
A sectional view of a magnetic circuit for a linear motor according to a fourth embodiment, a fifth embodiment.
6 is a perspective view of a conventional magnetic circuit for a linear motor, and FIG. 7 is a sectional view of a conventional magnetic circuit for a linear motor. 1...Voice coil, 2a-2c...
Magnetic yoke, 3a, 3b...Permanent magnet, 4...
...Voice coil bobbin, 5...Steel cap, 6...Through hole, 7...Through hole, 8
・・・・・・Excision part. Name of agent: Patent attorney Toshio Nakao and 1 other person / --- Whisgoyle Zw ~, 2c ---'a 'a 4' 3, 3b-Hiku Katsu 2 Ishiyoshi 1 17I 4- Coil bobbin Otsu-Kan jΔkidney-JLI 3b 2Q Fig. 2 7--11 holes Fig. 3 Fig. 4 Fig. 5 (KH B) Fig. 6 WJ7 Fig. 5 3b Zc

Claims (3)

[Claims] (1) A magnetic yoke is arranged so as to surround a permanent magnet, and a part of the magnetic yoke is arranged in the center of the voice coil, and the magnetic yoke is provided with a magnetic yoke that is substantially parallel to the permanent magnet and that is connected to the voice coil. A through hole having a penetration direction substantially perpendicular to the moving direction of the through hole is provided, and the cross-sectional area of the through hole in the direction perpendicular to the penetration direction is wide at the center and narrows toward the periphery. A magnetic circuit for linear motors featuring: (2) Claim (1) characterized in that a through hole with a large diameter is provided near the center of the magnetic yoke disposed at the center of the voice coil, and a through hole with a small diameter is provided in the peripheral area.
Magnetic circuit for linear motors described in section. (3) A magnetic yoke is arranged to surround a permanent magnet, and a part of the magnetic yoke is arranged in the center of the voice coil, and the permanent magnet of the magnetic yoke is arranged in the center of the voice coil. The magnetic circuit for a linear motor is characterized in that the opposite part has a smaller thickness at the center and a larger thickness at the periphery.