JPH04184723A - Lens actuator - Google Patents

Abstract

PURPOSE:To reduce the number of components, improve assembly workability and, further, facilitate lens driving highly responsive to a control current without generating high degree resonance by a method wherein a bearing which is made of glassy carbon having a precise structure is provided and a cylindrical ruby is employed as a component of a movable part and friction surfaces are provided between the bearing and the ruby. CONSTITUTION:A movable part to which an object lens 9 is fixed is symmetrical around a rotation axis and is mainly composed of a ring 1 made of soft magnetic material, a cylindrical ruby 5, a cylindrical magnet 2 which is fitted into the ruby 5 and magnetized along a cylinder axis and a ring 3 made of soft magnetic material which are jointed together in this order. A fixed bearing 8 which is fitted onto the cylindrical ruby 5 is symmetrical around a rotation axis parallel with the rotation axis of the movable part and is made of glassy carbon having a precise structure. Further, a yoke 4 which is so fixed as to fit onto the bearing 8 and is made of soft magnetic material and coils 6 and 7 for magnetizing the rings 1 and 3 made of soft magnetic material are provided. With this constitution, high degree resonance can be eliminated and assembly workability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lens actuator mounted on an optical head of an optical memory or the like.

[Prior Art] Conventional lens actuators, particularly electromagnetic actuators, can be roughly divided into two types: an MC (moving coil) type in which a coil is the movable part, and an MM (moving magnet) type in which a magnet is the movable part.

For the MC type, for example, JP-A-57-210456.64-
37734 and Utility Model Application Publication No. 61-145334. On the other hand, for the MM type, there is, for example, Japanese Patent Application Laid-Open No. 63-37830.

[Problems to be Solved by the Invention] However, in the MC type, since a control current is passed through the coil, which is a movable part, it is necessary to provide a connecting wire between the coil and the fixed part. This connecting wire uses an extremely thin wire material so as not to adversely affect the movement of the movable part. Since such wire rods do not have sufficient mechanical strength, connection and soldering operations are difficult. Furthermore, heat generated by the current flowing through the movable coil may have an adverse effect on the optical characteristics of the lens.

Furthermore, many MC type actuators are spring-supported, and in these cases high-order resonance is likely to occur. Furthermore, since a damper or the like is provided for the purpose of suppressing the high-order resonance, the structure becomes complicated and assembly becomes difficult.

On the other hand, in the MM type, the mass of the movable part is generally larger than in the MC type, the servo current is larger, and power consumption and heat generation of the coil become problems.

In addition, regardless of MC type or MM type, JP-A-57-2104
A so-called shaft sliding type actuator such as No. 56 has a problem in that hysteresis occurs in the relationship between the force acting on the movement and the displacement. There was also a problem in that the acceleration performance changed due to changes in the sliding portion over time.

Therefore, the present invention aims to solve these problems.
The purpose is to provide a lens actuator that can reduce the number of parts, improve assembly efficiency, and drive a lens with good response to a control current without generating higher-order resonance.

[Means for Solving the Problems] The lens actuator of the present invention has a movable part to which the objective lens is fixed, which is symmetrical about the rotational axis, and
A ring 1 whose main part is made of a soft magnetic material, a part consisting of a cylindrical ruby and a cylindrical magnet circumscribed to the ruby and magnetized in the axial direction of the cylinder, and a ring 2 made of a soft magnetic material
It is composed of three parts joined in this order,
The fixed bearing inscribed in the cylindrical ruby is made of glass-like carbon having a rotational axis symmetrical shape with an axis of symmetry parallel to the axis of symmetry of the movable part, and has a dense and uniform structure; A yoke made of a soft magnetic material fixed to be inscribed in the bearing in a rotationally symmetrical shape having an axis of symmetry parallel to the axis of symmetry of the part, and a coil installed for the purpose of exciting the soft magnetic material 3. It is characterized by

[Embodiments] Examples of the present invention will be described below based on the drawings. 1st
The figure is a sectional view of an embodiment of a lens actuator according to the invention. 1.2.3.5 and 9 constitute the movable part. 9 is an objective lens, l and 3 are rings made of soft magnetic material, and 2 is a cylindrical magnet. Also, 5 is a cylindrical ruby. 8 is a bearing made of glassy carbon. 1.2.3.5 and 9 and the bearing 8 made of glassy carbon rub against each other as it moves. The movement of this movable part is controlled by a coil current of a magnetic circuit consisting of a yoke 4 made of a soft magnetic material and a coil 6.7. In this example, current flows through the coils 7 and 6 in opposite directions, and depending on the direction of this current and the direction of magnetization of the magnet 2, it is determined whether the movable part moves upward or downward in this drawing. In addition, in this Figure 1, the direction in which the current flows in the coil is shown as the direction perpendicular to the paper and the direction perpendicular to the paper, but if the direction in which the movable part moves is reversed, Of course, all currents flow in opposite directions.

In the actuator according to the present invention, the movable part is made of a magnet and the part made of a coil is fixed. There is no need to use a wire, and the wire does not adversely affect the movement of the movable part.

Further, since the actuator according to the present invention is basically cylindrical as described above, assembly is very simple. Furthermore, as a result of measurement with a measurement system consisting of an actuator using almost the same shape of aluminum instead of the objective lens in Fig. 19, a laser displacement type, and an FFT analyzer, 2
No higher-order resonance was observed below 0 kHz. This is also because all actuators of this invention are basically cylindrical.

In addition, as mentioned above, the MM type has a larger mass of moving parts than the MC type, so there is a problem that the servo current increases.In this embodiment, in order to improve the sensitivity of the moving parts as much as possible, A rare earth-cobalt magnet was used for the cylindrical magnet in the section (all soft magnetic material parts were made of pure iron). In terms of magnetic performance, rare earth-iron magnets are superior to these, but in this example, the wall thickness of the cylindrical magnet in the movable part is 1
We used rare earth-cobalt magnets, which are relatively easy to process because they are as thin as a millimeter, and their magnetic performance is less likely to deteriorate due to heat and distortion during processing. If a sufficiently thick structure is to be obtained, a rare earth-iron magnet will provide a higher drive sensitivity for the movable part than a rare-earth-cobalt magnet.

Furthermore, in the present invention, in order to reduce the hysteresis that appears in the relationship between the force acting on the movable part and the displacement, and to reduce changes over time in the sliding part, a bearing made of glassy carbon having a dense uniform structure as shown in FIG. The ruby shown in FIG. 1 and 5 was used for a part of the movable part, and the two formed a sliding surface.

As a result of 30,000 hours of operation at a stroke of 0.5 mm and 60 kHz, the acceleration performance, which was originally 750 [(meter 7 seconds 2) / ampere coil, became 670 [(meter 7 seconds 2) / ampere coil], which is not practical. It is at a good level with no problems.

[Effects of the Invention] As described above, the lens actuator of the present invention has no high-order resonance and is easy to assemble. Furthermore, since the movable part is on the magnet side and the coil side is fixed, there are no problems associated with extremely thin electric wires connecting the coil and the fixed terminal.

In addition, we have adopted a rare earth-cobalt magnet and a combination of ruby and glassy carbon for the sliding surface.
A product with high drive sensitivity and excellent durability was obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens actuator according to an embodiment of the present invention. 1... Ring 1 made of soft magnetic material 2... Cylindrical magnet 3... Ring 2 made of soft magnetic material 4... Fixed yoke 5... Ruby 6... Exciting coil 1 7. ... Excitation coil 2 8 ... Bearing made of glassy carbon 9 ... More than the objective lens. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kizobe Suzuki and 1 other person Article 11

Claims (1)

[Claims] The movable part to which the objective lens is fixed is symmetrical about the rotational axis,
A ring 1 whose main part is made of a soft magnetic material, a part made of a cylindrical ruby and a cylindrical magnet circumscribed to the ruby and magnetized in the axial direction of the cylinder, and a ring 2 made of a soft magnetic material
It is composed of three parts joined in this order,
The fixed bearing inscribed in the cylindrical ruby is made of glass-like carbon having a rotational axis symmetrical shape with an axis of symmetry parallel to the axis of symmetry of the movable part, and has a dense and uniform structure; A yoke made of a soft magnetic material fixed to be inscribed in the bearing in a rotationally symmetrical shape having an axis of symmetry parallel to the axis of symmetry of the part, and a coil installed for the purpose of exciting the soft magnetic material 3. A lens actuator featuring: