JPH03288339A - Lens actuator - Google Patents

Abstract

PURPOSE:To reduce the number of parts, to make structure simple and to drive a lens with satisfactory responsiveness in respect to a control current by using glassy carbon with fine and uniform structure for a sliding member. CONSTITUTION:The sliding members of soft magnetic materials 4 and 5 at a fixed part are vertically moved while getting contact each other. In coils 6 and 7, a current flows mutually oppositely. These coils are wound so as to surround movable parts 1,2,3 and 5. The glassy carbon is applied also onto the surface of the soft magnetic material part 4 at the fixed part in contact with the sliding member 5 composed of the glassy carbon with the fine and uniform structure. The lens actuator can independently control acceleration performance and the primary resonance frequency in one magnetic circuit.

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 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.

[Problems to be Solved by the Invention] However, in examples such as the above-mentioned MC type, in order to supply a driving current for control to the coil, which is a movable part, it is necessary to provide a connection line between the coil and the fixed part. . It is necessary to use an extremely thin wire for this connection line so as not to hinder the movement of the movable part. Since such wire rods do not have sufficient mechanical strength, it is difficult to connect and solder them. Furthermore, the elasticity of the power supply line affects the vibration characteristics of the movable part, and it is difficult to design the vibration characteristics by taking this into consideration, and complicated adjustment work is required. In addition, as mentioned above, the connection between the power supply line and the coil is generally done by soldering.
For this purpose, a land for soldering must be provided on the movable part, which is an obstacle to reducing the size and weight of the movable part. Furthermore, heat generated by the current flowing through the movable coil may adversely affect the optical characteristics of the lens.

In addition, some MC type actuators include a spring support that supports the lens and supports the bobbin to which the coil is attached using a support rod with spring properties, a leaf spring, a molded hinge, etc., and drives the lens by elastic deformation of these. There are several types of actuators. In this spring support type lens actuator, high-order resonance is likely to occur during driving due to the nature of the spring materials such as the leaf springs and support rods that support it. Since a damper and the like are provided in the structure, the structure becomes complicated and assembly becomes difficult.

On the other hand, in the conventional MM type, the trade I of the movable part is generally larger than that in the MC type. Therefore, a large current is required for the servo current, and power consumption and heat generation in the coil portion become problems.

Then, regardless of MC type or MM type, for example, JP-A-57
A type of actuator called a shaft sliding type such as -210456 has a problem in that hysteresis occurs in the relationship between the force acting on the movable part and displacement. There is also the problem that the frictional force gradually increases due to changes in the sliding portion over time, resulting in changes in acceleration performance.

Therefore, the present invention aims to solve these problems.
The objective is to create a lens actuator that reduces the number of parts, has a simple structure, and can drive the lens with good response to the control current without causing higher-order resonance. It is about providing.

[Means for Solving the Problems] The lens actuator of the present invention has a main movable part that is rotationally symmetrical and includes a ring 1 made of a soft magnetic material, a cylindrical magnet, and a ring 1 made of the soft magnetic material. It is composed of rings 2 of the same shape and properties joined in this order, and is a soft magnetic material part of the fixed part of the magnetic circuit provided for the purpose of vibrating the movable part in the direction along the rotation axis. is rotationally symmetrical with the same axis of symmetry as the movable part,
and a sliding member located outside the movable part, the sliding member having an inner diameter larger than an outer diameter of the movable part,
The outer diameter is smaller than the inner diameter of the soft magnetic material portion of the fixed portion of the magnetic circuit, and the rotating shaft is symmetrical about the rotational axis that is the same as the movable portion and the soft magnetic material portion of the fixed portion of the magnetic circuit, and the material thereof is is glass-like carbon having a dense uniform structure, and the glass-like carbon is surface-treated on the surface of the portion that contacts the sliding member, and the soft carbon of the fixed magnetic circuit is made of glass-like carbon. ! The present invention is characterized in that a coil is wound around the rotating shaft in a space surrounded by a flexible material.

[Example: There are various methods for driving a core actuator, but the actuator of the present invention is a conventional type generally called an electromagnetic actuator. However, as described above, an electromagnetic actuator can be an MC type in which a coil moves, or a magnet type. The present invention is divided into the MM type in which the
It belongs to type M. Therefore, there is no problem arising from the need to connect the power supply line to the movable part as described above. Also, the present embodiment is a one-dimensional actuator, and the conventional examples described above are all two-dimensional actuators perpendicular to each other. This is an example of a two-dimensional actuator that moves in two planes. but,
The above-mentioned problem to be solved is a more fundamental problem that is not affected by whether the actuator is two-dimensional or one-dimensional. Also, suppose that the present invention is
Even if it is applied to a dimensional actuator, basically it is sufficient to change the magnetization pattern of the cylindrical magnet for the movable part, as in, for example, Japanese Patent Application No. 63-33170/32717.
Therefore, since it is two-dimensional like the MC type, an extra coil is not required and the mass of the moving part does not increase.

Most conventional lens actuators are of the MC type, and in the case of a spring-supported actuator, such as that disclosed in Japanese Patent Laid-Open No. 57-210456, there is a possibility that higher-order resonance may occur due to the support spring. On the other hand, since the actuator of the present invention uses a so-called magnetic spring, there is no such concern, and there is also no structural resonance as in, for example, JP-A-64-37733.

Hereinafter, the present invention will be explained in detail based on the embodiment shown in FIG. The parts 1, 2, 3 and 5 in FIG. 1 are movable parts. The sliding members made of soft magnetic materials 4 and 5 of the fixed part move up and down while being in contact with each other. The coil is shown in Figure 16.
and 7 are used. 6 and 7 are passing current in opposite directions. Both are wrapped around the moving parts. Fig. 1 5 shows a sliding member made of glass-like carbon having a dense uniform structure, and the glass-like carbon is also applied to the surface of the soft magnetic material part of the fixed part of Fig. 1 4 that comes into contact with the sliding member. It is.

The dynamic characteristics of the actuator according to the present invention shown in FIG.
Using an FFT analyzer and a laser displacement meter, evaluation was performed 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. It is also possible to know the figures of merit such as the above-mentioned primary resonance value M and primary resonance frequency f.

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 to suppress high-order resonance as described above. This characteristic is extremely important when applied to optical heads for optical memories such as magneto-optical memories and phase change memories, and is unaffected by changes in specifications such as disk surface runout and rotational speed. .

Furthermore, the lens actuator of the present invention can independently control the acceleration performance and the primary resonance frequency within one magnetic circuit.Of course, by increasing the strength of the magnet in the movable part, both the acceleration performance and the primary resonance frequency can be controlled independently. However, by changing the ratio of the soft magnetic ring 1, cylindrical magnet, and soft magnetic ring 2 in the movable part, it is possible to change the primary resonance frequency independently of the acceleration performance. The primary resonance frequency f of a lens actuator made by changing the ratio of the soft magnetic ring 1, the cylindrical magnet, and the soft magnetic ring 2 in the movable part,
These are the results of measuring changes in . In all of A, B, and C of Tables 0 and 1 whose basic structure is the structure shown in FIG. 1, the height of the movable part is 6.6 mm.

However, soft 6ji ring 1, cylindrical magnet, soft magnetic ring 2
Table 1 shows the heights of soft magnetic ring 1, cylindrical magnet, and soft magnetic ring 2 in mm in this order.
It is expressed in units. Here, the acceleration performance refers to the acceleration of the movable part when a unit current is passed through the coil.

While the yoke of the magnetic circuit provided on the outside of the movable part shown in Table 1 moved in contact with each other, in the actuator shown in Figure 2, the ring made of soft magnetic material shown at 1 and 3 is shown at 5. It moves in contact with the sliding member. That is, in the case of FIG. 1, the sliding members 5 were moving together, but in the case of FIG. 2, the sliding members 5 were fixed without moving. Therefore, the mass of the movable part in FIG. 2 is slightly smaller.

Table 2 FIG. 2 also shows the force τ, which is an embodiment of the present invention, and the actuator shown in FIG. There is a force of 5 depending on the shape of the yoke of the magnetic circuit. Therefore, the sliding member 5 in FIG. 1 and the actuator 4 shown in FIG. 2 were evaluated in the same manner as the actuator in FIG. 1 as described above.

There was also no high-order resonance below 40 kHz.

Table 2 compares the acceleration performance of each actuator. The number of coil turns, thread material, and magnet material conditions were all the same. For the purpose of mounting in an optical memory drive, the overall size of the actuator is the same in both FIGS. 1 and 2. That is, the thickness of the sliding member indicated by 5 in each figure is different. The acceleration performance shown in Table 2 is comparable to that of the conventional MC type (for example, compared with the 50th Japan Society of Applied Physics Academic Conference Preliminary Lecture Proceedings 30a-PB-20). As shown in the figure, the mass of the moving parts of the MM type is large, and there is no problem of large power consumption or heat generation in the coil part.As for this acceleration performance, even if the specifications such as the surface runout of the disk and the rotation speed are changed, it will be smaller. The present invention is advantageous in terms of power consumption and heat generation in the coil portion.

In the present invention, since the sliding member shown by 5 in each figure is made of glass-like carbon having m-dense uniform cross paths, even if a thin member as shown in FIG.
Good acceleration performance as shown in 2 can be obtained, but if conventionally commonly used resin materials such as 4-fluoroethylene resin, polyimide resin, or polyamide resin are used, warping may occur after processing or the durability may deteriorate. The problem of inferiority arises. Figure 3 compares the changes in acceleration performance over time in the actuator having the structure shown in Figure 2, in which the glass-like Gabon of the present invention is used for the sliding member 5 and in which bulk polyamide resin is used. be.

FIG. 4 shows an actuator having the structure shown in FIG. 1, in which the sliding member 5 is made of bulk ethylene resin, and the outer surface of the aluminum ring is made of 47. This is a comparison of changes in acceleration performance over time for products coated with ethylene chloride resin.

It can be seen from both FIG. 3 and FIG. 4 that the product using glassy carbon has superior durability. These evaluations were performed by continuously driving the actuator with a 40 Hz sine wave.

[Effects of the Invention] 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 adjust the installation of parts such as dampers to prevent it, and there is no need for power supply lines to the moving parts. Therefore, there is no need for soldering work, and there is no need for soldering lands on the movable parts, allowing for miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a lens actuator of Example 1 according to the present invention. FIG. 2 is a sectional view of a lens actuator according to a second embodiment of the present invention. 3 is a diagram showing changes over time in acceleration performance of various sliding members in the lens actuator having the structure shown in FIG. 2. FIG. FIG. 4 is a diagram showing changes over time in acceleration performance of various sliding members in the lens actuator having the structure shown in FIG. 1. 1... Soft magnetic ring 1 2... Cylindrical magnet 3... Soft magnetic ring 2 4... Soft magnetic part of fixed magnetic circuit 5... Sliding made of glassy carbon having a dense uniform structure Member 6...Coil 1 7...Coil 2 and above

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. the sliding member has an inner diameter larger than an outer diameter of the movable part,
A glass-like carbon whose outer diameter is smaller than the inner diameter of the soft magnetic material part of the fixed part of the magnetic circuit, and whose axis of symmetry is the same as that of the movable part, and whose material has a dense and uniform structure. The surface of the part that comes into contact with the sliding member is surface-treated with the glassy carbon, and the coil is placed in a space surrounded by a yoke of a magnetic circuit fixedly provided outside the movable part. A lens actuator characterized by being wound around a rotating shaft.