JPS60101732A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a small-sized, inexpensive device by making the point of application of an objective lens driving device nearly coincident with the center of gravity of a movable part including an objective lens. CONSTITUTION:The objective lens driving device 13 has two couples of parallel leaf springs 3 fixed each at one terminal to a movable part fixing member 17 and at the other end to a repeating member 16. Two couples of parallel springs 15 for focusing are fixed to the upper and lower flanks of the repeating member 16 each at one end, and also fixed to the objective lens 1 at the other end. Consequently, the objective lens 1 is allowed to move freely in the directions of optical axes Z and Y, and its movement is restrained in other directions by the parallel springs 3 and 15. The objective lens fixing member 14 is wound with a moving coil 2 for tracking so that a magnetic field 21 is applied in the direction of the axis Y, and also wound with a moving coil 5 for focusing so that a magnetic field 51 is received in the direction of the optical axis Z.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an optical pickup device, and in particular, to an optical pickup device, and in particular, to an optical pickup device for picking up information recorded in a chain on an optical recording medium such as a digital audio disk (DAD) or a video disk (VD). There is one C related to an objective lens driving device of an optical pickup device which optically reads images through an objective lens.

[Technical background of the invention and its problems]

Next, a conventional objective lens driving device for an optical pickup device will be explained with reference to FIG. Of the elements constituting the optical pickup device, a light source, other optical systems, a photodetector, and an electrical system including a drive system for the optical pickup device are omitted.

In other words, in order to accurately read recorded information in an optical pickup device, there is a focusing function performed by moving the objective lens (1) in the direction of the optical axis (two axes), and a focusing function that is performed by moving the objective lens (1) in the direction of the optical axis (two axes), and a focusing function that is performed by moving the objective lens (1) in the direction of the optical axis (two axes). It is necessary to have a tracking function for reading the image in the Y-axis direction, and a driving lens driving device is equipped with these functions.

Specifically, the objective lens (1) is fixed to one end of a parallel plate (3) fixed to, for example, a disc-shaped member (4) that can freely move only in the Z-axis direction. ing. Since this parallel plate spring (3) can move only in the Y-axis direction, the objective lens (1) has a structure that can freely move in the Y-axis direction and the Z-axis direction. and the objective lens (
A moving coil (2) for tracking is connected to 1), and a moving coil (5) for focusing is connected to the disc-shaped member (4).

Each moving coil (MC) (2) and (5) is connected to a magnetic field (2,) or (5I) by a permanent magnet (not shown).
), and by energizing each moving coil (MC) (2) or (5), an electromagnetic force is generated, and the objective lens (1) is moved in the Z-axis direction or It will be displaced in the Y-axis direction.

In the optical pickup device, focus control must be performed so that the deviation between the focus of the objective lens (1) and the recording surface of the optical recording medium is always within the range of the focal depth (approximately 2 μm) of the objective lens (1). . Further, tracking control must control the positional deviation of the spot from the bit to within 101 μm.

For this purpose, it is important for stable tracking control that no movement (crosstalk) of the beam spot in the radial direction of the optical recording medium occurs during focus drive control. The problem with the objective lens drive device is that this stable tracking control is extremely difficult.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an optical pickup device equipped with an objective lens drive device capable of performing stable tracking control.

[Summary of the invention]

That is, the present invention includes a light source that generates a light beam, an objective lens that has a function of converging the light beam onto a bit point on an optical recording medium, and a system that moves the objective lens in response to changes in position on the optical recording medium. In an optical pickup device, the optical pickup device includes at least an objective lens drive device that detects the reflected light of a light beam focused on an optical recording medium and converts it into an electrical signal. This optical pickup device is characterized in that the center of gravity of the movable part including the objective lens is substantially aligned with the center of gravity of the movable part, and the image-side principal point of the objective lens or its vicinity is aligned with the center of gravity of the movable part.

[Embodiments of the invention]

The inventors investigated the reason why stable tracking control is extremely difficult with the objective lens drive device shown in Figure 1.
As shown in the figure, the center of gravity of the movable part (I
υ and the image-side principal point (C) of the objective lens are separate, and when the focus driving force (F') is applied to the object, the center of gravity of the action point (Il
It was found that the dynamic balance between the l principal points (C) deteriorated and it was difficult to perform stable tracking control.

Therefore, in the present invention, the point of action (A
) and the center of gravity (13) of the ijJ moving part, and by matching the image-side principal point of the objective lens ((:) and its vicinity with the center of gravity (B) of the moving part, crosstalk can be reduced. By improving the dynamic balance, it is possible to reduce the amplitude of the mechanical sub-resonance, and the phase rotation in high-frequency shipboard applications of several KHz is reduced, making it possible to perform stable follow-up control.

The reason for this is explained with reference to Figure 3. When a parallel ray is incident on the objective lens aperture), the rotation axis is at the node α1) on the image side.
Since both sides of the objective lens are air, the light that passes through the principal point (C) coincides with the principal point (C)), and the light that passes through the image side node (I-η always coincides with the optical axis (Z-axis), so the image (Q) does not move.In other words, if the objective lens (1) is driven around the principal point (C) on the image side, the optical axis of the objective lens (1) will change from (center to (2')
), the image does not move even if it moves by an angle (θ), so there is no movement (crosstalk) of the beam spot in the radial direction on the optical recording medium during focus drive control, and the neck of the lens does not move during focus drive control. Even if swinging motion occurs, it does not lead to undesired movement of the beam spot, so there is no disturbance of reflected light, and stable tracking control is possible.

Next, an embodiment of the optical pickup device of the present invention will be described with reference to FIGS. 4 and 5. However, the same reference numerals as in FIG. 1 indicate the same parts.

That is, the laser beam (6a) emitted from the light source (6) is
, passes through the quarter-wave plate (9), is converged by the objective lens (1), and reaches the recording surface of the optical recording medium (IG) as a minute spot.Next, the light beam reflected by the recording surface (6b)
The light travels backward along the optical path, passes through the objective lens (1), passes through the quarter-wave plate (9), polarizing beam splitter (8), and condenser lens system Ql, and is guided to the photodetector (1). It is photoelectrically converted into an electrical signal.From this electrical signal, a signal indicating the presence or absence of a bit and a positional information signal between the recording surface and the objective lens (1) are obtained.

Among these, the position information signal is amplified and supplied to the objective lens drive device (13) moving coil via the drive circuit.

As shown in FIG. 5, in this objective lens driving device (13), one end of two pairs of parallel plate springs (3) is fixed to a movable part fixing part shrine (17), and the other end is fixed to a relay member θ(i ) I: [i
41 has been added. C), the relay part (Ib) can move freely only in the Y-axis direction. One end of two pairs of parallel plates α9 for focusing is fixed to the downward side surface of the relay section 1 ([e] 1), and an objective lens (1) is fixed to the other end.

This structure allows the objective lens (1) to move freely only in the optical axis (Z-axis) direction and the Y-axis direction, and its movement in other directions is regulated by the parallel plate t3) (Is).

The objective lens fixing member α4 has a tracking moving coil (2,
) is wound, and a focusing moving coil (5) is wound so as to receive force from the magnetic field (58) in the Z-axis direction.
is wrapped.

By aligning the point of action of the drive unit with the center of gravity of the movable unit and aligning the image-side principal point (C) of the objective lens (1) with the center of gravity of the movable unit, the objective lens (1) is
Even if the image is tilted, the image does not move and crosstalk is reduced. Therefore, it is possible to construct an optical pickup having stable tracking control characteristics since the positional information component generated by the reflected light is not affected by the tilt of the objective lens (1).

Figure 6? The drive characteristics of the Ni-Draking actuator are shown. That is, a curve CID indicating gain and a curve 0 indicating phase.
In this example, the sub-resonance around IKHz (which occurs in the conventional structure) shown by the dotted lines (211) and (221) is completely eliminated, and an optical pickup device with stable follow-up control characteristics is obtained.

In addition to the structure of this embodiment, the point of action of the objective lens driving device, which is the main part of the claims, is made to substantially coincide with the center of gravity of the movable part including the objective lens, and the image-side principal point of the objective lens is Of course, it is only necessary to satisfy the condition that the vicinity including the center of gravity of the movable part coincides with the center of gravity of the movable part.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an optical pickup device that has stable follow-up control characteristics, can be easily adjusted and assembled, and is small and inexpensive.

[Brief explanation of drawings]

FIG. 1 is an explanatory perspective view of an objective lens driving device of a conventional optical pickup device, FIG. 2 is an explanatory diagram showing the driving position of the objective lens, FIG. 3 is an explanatory diagram showing the positional relationship of the objective lens, and FIG. The figure shows the configuration of an optical pickup device according to an embodiment of the present invention, and FIG. 5 is an explanatory perspective view of an objective lens driving device of an embodiment of the optical pickup device of the present invention.
The figure is a graph showing the drive characteristics of the tracking actuator. 1... Objective lens 2... Tracking coil 3.
...Parallel leaf spring for tracking 4...Member 5...Focusing coil 6...
Light source 6a...Laser beam 6b-reflected light 7...Collimation lens 8...
Polarized beam slitter 9...1/4 wavelength plate 1o...Optical recording medium 11
...Focal lens 12...Photodetector 13...Objective lens drive device 14...Objective lens fixing member 15...Focus plate spring 16...Relay member 17...Moving part fixing Parts Agent Patent Attorney Mr. Inoue Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] a light source that generates a light beam; an objective lens that has a function of converging the light beam onto a bit point on an optical recording medium; In the optical pickup device, the optical pickup device includes at least an objective lens driving device for moving the optical recording medium, and a photodetector for detecting reflected light of the light beam focused on a front optical recording medium and converting it into an electric signal. The apparatus is characterized in that the point of action of the device is made to substantially coincide with the center of gravity of the movable part including the objective lens, and the vicinity thereof, including the image-side principal point of the objective lens, is made to coincide with the center of gravity of the movable part. Optical pickup device.