JPH03273531A - Lens actuator - Google Patents

Abstract

PURPOSE:To simplify construction and to decrease the number of parts as well as to improve the responsiveness to a control current by forming the main part of a moving part to a rotational axisymmetrical shape and the yoke of a magnetic circuit to a rotational axisymmetrical shape and winding coils around the axis of revolution. CONSTITUTION:The main part of the moving part is formed into the rotational axisymmetrical shape and is constituted of the assembly formed by joining a ring 1 consisting of a soft magnetic material, a cylindrical magnet 2 and a ring 3 consisting of a soft magnetic material in this order. The yoke 4 of the magnetic circuit fixed and provided to and on the outer side of the moving part is made into the rotational axisymmetrical shape having a symmetrical axis parallel with the symmetrical axis of the moving part and exists in the part where the gap part of the magnetic circuit faces the two rings, 1 3 respectively in the central position. The coils 6, 7 are wound around the axis of revolution in the space enclosed by the yoke 4 of the magnetic circuit. The number of the parts is decreased in this way. In addition, the construction is simple and further, the lens is driven with the good response with the control current without generating higher order resonance, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lens actuator used in an optical head of an optical memory such as a magneto-optical memory 1 or a phase change optical memory.

[Prior Art] Conventional lens actuators are roughly divided into two types: an MC (moving coil) type in which a coil moves and an MM (moving magnet) type in which a magnet moves.

For the MC type, for example, JP-A-57-210456, JP-U-61-145334, and JP-A-64-37734 are disclosed.
There is a public notice.

The MM type is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-37830.

[Problem to be solved by the invention] In addition, m, μ, ni, and α are all constants 0
m is the mass of the moving part, μ is the friction coefficient, and is generally called a spring constant. The right side is the force generated by passing current through the coil, and is proportional to the current value. When designing an actuator, each constant m in equation (1),
Determine μ, and α, respectively.

Typical numerical values that characterize a lens actuator, such as the primary resonance value M, primary resonance frequency f, obtained from the measurement results, can be expressed using the four constants mentioned above, so the performance of the actuator can be expressed using the four constants described above. It is possible to design an index. The required performance index of the actuator, for example when applied to an optical head of an optical memory, varies depending on changes in specifications such as surface runout and rotation speed of the disk, but can be accommodated by changing the design of the four constants mentioned above.

Although there are various methods for driving an actuator, the actuator of the present invention is a conventional actuator generally called an electromagnetic actuator. However, electromagnetic
As mentioned above, actuators are classified into MC type in which a coil moves and MM type in which a magnet moves, and among these, the present invention belongs to the MM type. Also, in this example, 1
The conventional example described above is a two-dimensional actuator that moves in two mutually perpendicular planes. However, the above-mentioned problem to be solved is an essential problem that is not affected by whether the actuator is two-dimensional or one-dimensional. Furthermore, even if the present invention were to be applied to a two-dimensional system, the magnetization pattern of the cylindrical magnet would basically be changed for the movable part, as in, for example, Toku IJi63-33170/32717.

Therefore, since it is two-dimensional like the MC type, there is no need for an extra coil and an increase in the mass of the moving parts.

The mainstream of conventional lens actuators is the MC type.

However, in the case of a spring support type actuator as disclosed in Japanese Patent Application Laid-Open No. 57-210456, a support spring is provided for α in equation (1) by designing a magnetic circuit.

In such an example, higher-order resonances due to the support springs may occur. On the other hand, since the present invention uses a so-called magnetic spring,
αMomo can also be designed by magnetic circuit, so
There is no such worry.

The dynamic characteristics of the actuator according to the present invention were evaluated using an FFT analyzer and a laser displacement meter by replacing the lens with a flat mirror having the same mass as the lens.

From the resulting Bode diagram, the frequency response of gain and phase can be evaluated. Then, the above-mentioned primary resonance value M
, primary resonance frequency f, and other figures of merit. According to this, high-order resonance was not observed in the actuator of the example according to the present invention at frequencies below 40 kHz. This means that there is no need to specially provide a damper or the like in order to suppress the above-mentioned high-order resonance. This characteristic is a very important characteristic when applied to optical heads of optical memories such as magneto-optical memories and phase-change memories, even if specifications such as disk surface runout and rotation speed change. It is.

Furthermore, the lens actuator of the present invention can also independently control α and χ in equation (1) within one magnetic circuit. Of course, if the magnet in the movable part is made stronger, α will also become larger. However, by changing the ratio of ring 1, cylindrical magnet, and ring 20 in the movable part, it is possible to change independently of α. These are the results of measuring changes in the primary resonance frequency f of lens actuators made by changing the f.

All have the basic structure of Figure 1, Table 1, A, B of 1,
In both case C, the height of the movable part is 6.6 mm. However, the only difference is the height ratio of the ring top, the cylindrical magnet, and the ring 2.
The heights are expressed in mm in this order. Here, the acceleration performance refers to the acceleration (α/m) of the movable part when a unit current is passed through the coil. From this table, α
It can be seen that it is possible to change ``independently''.

Table 1 Furthermore, the present invention is superior in the following points compared to an MM type actuator (an example of which is shown in FIG. 2), which similarly does not exhibit high-order resonance below 40 kHz. FIG. 1 is a cross-sectional view of an embodiment of the actuator according to the invention evaluated by the method described above, but with significant differences -
It has the shape of a yoke of a magnetic circuit fixed to the outside of the movable part in FIG.

As you can clearly see by comparing the cross-sectional view of the conventional example in Figure 2, the center yoke differs from the conventional example in that it extends up and down to cover the movable range of the movable part, and this part creates a difference from the conventional example. .

Table 2 compares the performance of the actuators of FIGS. 1 and 2. All other conditions that significantly affect the magnetic circuit, such as the number of coil turns, yoke material, and magnet material, remain the same. However, each yoke shape (Fig. 1,
The only difference is 4) in Figure 2.

In the actuator having the structure shown in FIGS. 1 and 2, it is necessary to insert a sliding member between the movable part and the yoke of the magnetic circuit fixed to the outside thereof.

Making this sliding member thinner will reduce the gap in the magnetic circuit, and the force acting on the movable part (the right side of equation (1)) will increase. However, making this sliding member thinner has disadvantages in terms of its structure, such as deterioration of durability and the occurrence of hysteresis in the relationship between the force acting on the movable part and displacement. . Therefore, the present invention was designed to obtain sufficient force acting on the movable part without impairing the thickness of the sliding member.

Table 2 shows the results of acceleration performance determined from the measured Bode diagrams while ensuring the same wall thickness of the sliding member at 0.8 mm.

Table 2 As will be seen, the acceleration performance of the embodiment according to the present invention is more than 10% higher, and this acceleration performance is comparable to that of the conventional MC type (for example, the 50th
-Society of Applied Physics Academic Lecture Preliminary Lecture Collection 30a-PB-
In other words, as mentioned above, the mass of the moving parts of the MM type is large, and there is no problem of large power consumption or large heat generation in the coil part. Regarding this performance, the specifications such as disk surface runout and rotation speed, etc. Even if the change is made, smaller is not necessarily better, and the present invention is advantageous in terms of power consumption and heat generation in the coil portion.

[JI! As described above, according to the present invention, despite the MM type actuator, sufficient sensitivity comparable to that of the MC type can be obtained.
There is no need to worry about power consumption or heat generation in the coil part, and since there is no high-order resonance, there is no need to install parts such as dampers to prevent it, and there is no need for power supply lines to moving parts. Therefore, no soldering work is required for that purpose.
Furthermore, there is no need for a land for soldering on the movable part, and miniaturization can be achieved.

Furthermore, among the MM type actuators of the present invention, This is advantageous in terms of sensitivity.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens actuator according to an embodiment of the present invention. FIG. 2 is a sectional view of a lens actuator that is an example of a conventional MM type. 1... Ring 1 2... Cylindrical magnet 3... Ring 2 4... Yoke 5 of the magnetic circuit fixed to the outside of the movable part... Sliding member 6... Coil 1 7...・Coil 2 or more

Claims (1)

[Claims] The main part of the movable part to which the lens is fixed is rotationally symmetrical, and includes a ring 1 made of a soft magnetic material, a cylindrical magnet magnetized in the axial direction of the cylinder, and a soft magnetic material. The yoke of the magnetic circuit fixedly provided on the outside of the movable part is rotationally symmetrical with the axis of symmetry parallel to the axis of symmetry of the movable part. a shape in which the gap portion of the magnetic circuit exists in a portion facing each of the two rings made of soft magnetic material constituting the movable portion in the neutral position, and a coil is disposed in a space surrounded by the yoke of the magnetic circuit. A lens actuator characterized in that the lens actuator is wound around the rotation axis.