JPH02301023A - Lens focusing actuator - Google Patents

Abstract

PURPOSE:To obtain an actuator with simple structure and miniaturized and of light weight by using a cylindrical magnet separated to two areas and in which each part is radial-magnetized in directions opposite to each other as a movable part, and supporting the movable part with a superconducting bearing. CONSTITUTION:An objective lens 1 is fixed on the cylindrical magnet 2, and the movable part consisting of the objective lens 1 and the magnet 2 is supported so that it can be moved rectilinearly at a contactless state in the direction of cylindrical shaft made of a superconductor, and the focal point of a laser beam can be moved in a focusing direction. Since the shaft and the bearing 3 are formed in contactless type, no friction occurs, and stable rectilinear motion can be obtained even a device is driven at high speed. The magnet 2 is separated to two areas in the direction of cylindrical shaft, and it is radial-magnetized so that each magnetizing direction can be set in the directions opposite to each other, and protective rings 4 and 5 are provided at the end faces of the magnet 2 in the direction of cylindrical shaft, and coils 8 and 9 are provided at the outside of the magnet, and a magnetic circuit is comprised of a yoke 10, and focusing is performed by permitting currents in opposite directions to flow on the two coils 8 and 9 and displacing a movable magnet in a fine distance in the neighborhood of a neutral position.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a magnet movable lens focusing actuator (hereinafter referred to as L) used in an optical head of an optical memory device.
(denoted as FA).

[Prior art] Conventionally, LFA in an optical memory device is disclosed in Japanese Patent Application Laid-Open No. 63-1.
As described in Publication No. 0331, many of them were of a movable coil type and had a structure with a support spring.

[Problems to be solved by the invention] However, in the conventional technology, disconnection of the power supply line to the moving coil,
Bonding failure due to overheating of the coil and associated thermal deformation of the coil are likely to occur.Furthermore, the process of connecting the power supply line is complicated and time-consuming, and depending on the power supply method, the power supply line itself may have a negative effect on the high-speed operation of the moving parts. It has the problem of causing problems. In addition, variations in the coil shape tend to cause an imbalance in the mass of the movable part, which causes high-order resonance and other problems that impede high-speed operation. Therefore, the rotational speed of the optical disk cannot be increased, and the data transfer speed is limited. Furthermore, since changes in coil specifications (number of turns, wire diameter, etc.) lead to changes in the mass of the movable part, it is necessary to repeatedly cut and try with changes in the design of the actuator in order to find the optimum specifications for the coil. Furthermore, high-speed response deteriorates due to high-order resonance caused by the support spring.

Therefore, the present invention is intended to solve these problems, and its purpose is to provide an LFA with excellent high-speed operation by creating a structure that does not have a support spring and does not require power supply to the movable parts. It's there to provide. This results in
It becomes possible to realize an optical memory device with high reliability and high data transfer speed.

[Means for Solving the Problems] The LFA of the present invention is an LFA that drives an objective lens of an optical head. a magnetized cylindrical magnet; (b) a cylindrical superconductor provided on the fixed portion side of the optical head with a desired gap between the outer peripheral surface or the inner peripheral surface of the magnet; (C) The present invention is characterized in that it includes a coil and a yoke that are spaced a certain distance MllIffl around the magnet and are installed on the fixed part side.

[Function] According to the above configuration of the present invention, the cylindrical magnet divided into two regions and radially magnetized in opposite directions, and the coil and yoke on the outside of the cylindrical magnet maintain the magnet neutrally and further maintain the magnet near the neutral position. can be driven in the axial direction of the cylinder. Furthermore, by installing a superconductor near the outer circumference or inner circumferential surface of the magnet, the magnet can be supported in a non-contact manner so as to be able to move linearly in the axial direction using the Meissner effect.

[Example] The present invention will be described in detail below based on examples.

FIG. 1 is a main sectional view of an embodiment of the LFA of the present invention. All parts are ring-shaped. The objective lens 1 is fixed to a cylindrical magnet 2. This movable part consisting of an objective lens and a magnet is supported in a non-contact state by a cylindrical bearing 3 made of a superconductor so that it can move linearly in the direction of the cylinder axis, and the focal point of the laser beam moves in the focusing direction. I can do it. Since the shaft and bearing are non-contact using superconducting materials and magnets, there is no friction and stable linear motion can be obtained even during high-speed driving. Although it was installed on the outer circumferential side of the magnet, it can be similarly supported in a non-contact state even if it is installed on the inner circumferential side. As shown in FIG. 1, the magnet is divided into two regions in the cylindrical axis direction (vertical direction in the figure) and radially magnetized so that the magnetization direction of each region is opposite. A protective ring 4.5 is attached to the cylindrical end face of the magnet in order to prevent the magnet from directly colliding with the stopper 6.7. Coils 8 and 9 are arranged outside the magnet, and a yoke 10 constitutes a magnetic circuit.

By passing currents in opposite directions through the two coils, the movable magnet is slightly displaced near the neutral position, and focusing is performed by passing a control current corresponding to the surface runout of the optical disk.

Next, we will discuss the magnets and superconductors used before this implementation. S allows for highly productive production of anisotropic magnets with high magnetic performance.
m-Go resin-bonded magnets are very advantageous. Also,
This magnet is lightweight and can easily achieve high dimensional accuracy. In this example, an Sm-Co resin bonded compression molded magnet was used, but the magnet material and molding method are not limited thereto. is S m (CO@, 5r2c
u ++, isF e@, 222 r a, @2s)
The raw material is melted in an induction furnace so that it becomes 1120 to 1180
Solution treatment was carried out at 850'C for 5 hours, followed by 4 hours at 850'C.
Time aging treatment was performed. This 2-17 rare earth intermetallic alloy is pulverized to an average particle size of 20 μm (by Fischer subsieve cider), and 98% by weight of this powder is mixed with 2% by weight of a thermosetting two-component engineered poxy resin. A magnetic composition prepared by adding . This was subjected to radial magnetization in two areas. It is desirable that the superconductor has a high critical temperature.
Although an oxide superconductor was used in this example, it is not limited to this. First, the composition is B i +, 4P b s
, ss r zCa2c ua Ov The acetate salts of each component are added to pure water and stirred and dispersed. This liquid is dried using the dry-sew-sea method and simultaneously combusted to obtain a fine powder.

Next, this fine powder is calcined in an oxygen atmosphere at 800°C for 2 hours. Further, the fired fine powder was pressed into a cylindrical shape, and then sintered in air at 845°C.

When the LFA of the present invention using the thus obtained magnet and superconductor bearing was mounted on an optical head and cooled to liquid nitrogen temperature, the dynamic characteristics of the moving part showed extremely excellent high-speed response. . Note that tracking is performed by slightly changing the angle of the laser beam incident on the objective lens using a galvano mirror.The present invention does not use supporting members such as springs to maintain the neutral position of the movable part, so assembly is easy, and compared to conventional methods. The problematic high-order resonance of the support member can be avoided, and the optical head can be made smaller and lighter because there is no need for support springs or complicated magnetic circuits to maintain neutrality.

Furthermore, since the movable part is supported in a non-contact manner, stick-slip on the sliding surface can be avoided and stable high-speed operation can be achieved.

In addition, all parts can be made into ring shapes, making it easy to achieve high dimensional accuracy, realizing a structure with good mass balance, and eliminating unnecessary parasitic vibrations.

As described above, by using a movable magnet and a superconductor, it is possible to downsize and improve the performance of the LFA. Moreover, the LFA of the present invention
By mounting only the mirror and mirror on the carriage, and fixing the optical system such as a semiconductor laser and photodiode, as well as the tracking actuator, the weight of the access section can be reduced and high-speed access can be facilitated.

[Effects of the Invention] As described above, according to the present invention, a cylindrical magnet divided into two regions and radially magnetized in opposite directions is used for the movable part, and the movable part is supported by a superconducting bearing. This brings about the following advantages.

(1) There is no disconnection in the power supply line.

(2) Assembly is easy because there is no connection process for power supply lines.

(3) There is no need to worry about thermal deformation of the coil or poor adhesion.

(4) Good mass balance of moving parts.

(5) There is no support spring.

(6) Simple structure, small size, and light weight.

(7) There is no friction in the moving parts.

Therefore, the LFA of the present invention, which provides an LFA with excellent high-speed response and high reliability, can be applied to optical memory devices such as computer memory, optical disk files, CDs, CD-ROMs, and LVDs, and can be applied to optical memory devices such as computer memories, optical disk files, CDs, CD-ROMs, and LVDs. It has great effects such as higher performance and smaller size.

[Brief explanation of drawings]

FIG. 1 is a main sectional view showing an embodiment of the LFA of the present invention. 1 ... Objective lens 2 ... Magnet 3 ... Bearing 8.9 ... Coil 10 ... More than yoke

Claims (1)

[Claims] (1) In a lens focusing actuator that drives an objective lens of an optical head, (a) a cylindrical magnet to which the objective lens is fixed, divided into two areas in the cylindrical axis direction and radially magnetized in opposite directions; (b) a cylindrical superconductor provided on the fixed part side of the optical head with a desired gap from the outer peripheral surface or inner peripheral surface of the magnet; (c) a cylindrical superconductor provided at a fixed distance around the magnet; A lens focusing actuator characterized by comprising a coil and a yoke installed on the fixed part side.