JPS59193551A - Controller for light focusing position - Google Patents

Abstract

PURPOSE:To perform both tracking control and focusing control by driving an objective lens with no tilt toward the vertical and horizontal axial directions via a parallel spring, respectively. CONSTITUTION:An objective lens 4 is moved in the thickness direction of a disk 8 to give a fine adjustment to the focusing position of an incident laser beam to the displacement of the disk in the optical axis direction of the incident laser, i.e., to the focusing control carried out by a light focusing position controller 5. While the lens 4 is moved in the radial direction of the disk 8 to give the tracking control, i.e., a fine adjustment of the focusing position of the incident laser to the displacement of the disk in the radial direction. An objective lens barrel 10 can be moved only in the vertical and horizontal axial directions by means of a focusing direction mobile elastic matter 12 which can move vertically and a radial mobile elastic matter 26 which can move horizontally.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to light focusing position control of a so-called optical disk device that optically records, reproduces, erases, etc. information by irradiating a recording medium with a light beam such as a laser beam. Regarding equipment.

<Prior Art> Conventionally, when operating a disk in an optical disk device, an information trunk portion on the disk is displaced in the vertical direction (ie, in the optical axis direction) due to surface wobbling during rotation. Unfortunately, the information l/rank section on the disk was displaced in the left-right direction (that is, in the disk radial direction) due to the eccentricity between the rotation axis of the disk and the motor shaft that rotates the disk. For this reason, in order to adjust the light focus position of the light beam to follow the displacement of the information track on the disk and always be positioned on the information trunk, the light focus east position is controlled in the light 111 direction (). A-Cussing control) and position control (dragging control) in the disk radial direction.

A well-known conventional mechanism for controlling the above-mentioned light focusing position is a mechanism that uses a rotating mirror to perform tracking control and also performs focusing control by moving the objective lens up and down using electromagnetic force. In the above-mentioned tracking control using a rotating mirror, there is a problem in that the light beam incident on the disk is tilted from the vertical direction.

Therefore, in recent years, various mechanical devices have been proposed that perform the above-mentioned tracking control and focusing control by driving the objective lens itself in two axial directions (up, down, left and right) using electromagnetic force.

However, this mechanical device also has various problems. For example, an objective lens barrel is supported by a comb-shaped elastic body whose one end is attached to a fixed support, and the coil that extends to the objective lens barrel is connected to a magnetic circuit attached to the fixed support. In a mechanical device of the type that drives the objective lens barrel using an electromagnetic force, since the objective lens barrel is supported by a rubber-like elastic body, the restraining force against the tilt of the objective lens barrel is weak, and therefore the electromagnetic force When a force-based driving force is not applied to the center of gravity of the objective lens barrel, a force couple occurs, which causes the objective lens barrel to rotate. As a result, the optical axis of the light beam is tilted with respect to the central axis of the objective lens,
Due to the effects of off-axis aberrations and comatic aberrations, the light beam is no longer properly focused on the information trunk on the disk, degrading the quality of the information.

On the other hand, the objective lens barrel is supported by a 2Mi parallel spring so as to be movable in directions perpendicular to each other, and a coil attached to the objective lens barrel side and a magnetic circuit exposed to the fixed support side are connected. In mechanical devices of the type that drive the objective lens barrel by electromagnetic force between the objective lens barrel and The control coil and the focusing control coil move independently in two axial directions within the respective magnetic gear knobs of the magnetic circuit for dragging control and the magnetic circuit for focusing control, which are attached to the fixed support side. In addition, it is necessary to increase the gap distance between the respective magnetic gill knobs in advance, which disadvantageously makes the entire mechanical device stiffer.

<Purpose> The present invention has been made in view of the above points, and is capable of driving an objective lens in two axes (up, down, left and right) without tilting, in a light focusing position control device that performs tracking control and focusing control of an optical disk device. The object of the present invention is to obtain a mechanical device that allows the overall shape to be made more compact.

<Example> Hereinafter, an example of the optical focusing position control device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration explanatory diagram showing the structure of an optical disk device. Reference numeral 1 is a laser light source that emits laser light 2, 36 is a mirror, and 4 is an objective lens that focuses the laser light 2 on the disk recording medium surface. 5 is a light focusing position control device that drives the objective lens 4 vertically and horizontally to control the light focusing position to follow the recording track of the disk recording medium;
6 is an optical head that houses the above optical system. Reference numeral 7 denotes a recording/erasing coil that applies a magnetic field to the surface of the disk recording medium when recording or erasing information. 8 is a disk containing a recording medium 8', and 9 is a motor for rotationally driving the disk. Here, sub-cushing control (by the optical focusing position control device 5), that is, the displacement of the disk in the optical axis direction of the incident laser is controlled. Fine adjustment of the focusing position of the incident laser beam is performed by moving the objective lens 4 in the thickness direction of the disk 8, while tracking control by the optical focusing position control device 5, that is, adjustment of the incident laser beam with respect to disk displacement in the radial direction, is performed by moving the objective lens 4 in the thickness direction of the disk 8. Fine adjustment of the focusing position is performed by moving the objective lens 4 in the radial direction of the disk 8.

FIG. 2 is a side sectional view showing the structure of the light focusing position control device in detail. The non-switching focusing control device will be explained. IO is a lens barrel that supports the objective lens 4, and the lens barrel 10 is movable in the vertical direction with respect to the holder 11 by an elastic body 12 movable in the focusing direction.
will be installed in 13 is a permanent magnet for focusing, 14
is the focusing yoke plate, 15 is the focusing force/
These yokes form a closed magnetic path and are fixedly attached to the holder 11. A focusing magnetic gap 16 is provided between the focusing yoke plate 14 and the focusing yoke 15.

Reference numeral 17 denotes a focusing drive coil, and the focusing drive coil 17 is arranged to cross the focusing magnetic gap 16, and the lens barrel 1o.
is fixed to. When a focusing control mechanism is applied to the focusing drive coil 17, a magnetic field is generated in the coil 17, and due to interaction with the magnetic field generated by the permanent magnet 13 for focusing, the focusing drive coil 1
7, the lens barrel 1o, and the objective lens 4 are displaced in the optical axis direction of the incident laser.

The focusing control device 18 is formed by the above configuration. Next, the tracking control device will be explained.

19 is a permanent magnet for tracking, 20 is a yoke plate for tracking, 21 is a yoke for tracking,
These form a closed magnetic path. Further, these are fixedly installed in a holder (not shown) of the entire optical focusing position control device. A tracking magnetic gap 2 is provided between the tracking yoke plates 1 and 20 and the tracking yoke 21.
2 is provided. Reference numeral 23 denotes a radial drive coil, and the radial drive coil 23 is disposed across the dragging magnetic gap 22 and is fixed to the radial drive coil holder 24. As shown in the figure, the radial drive coil holder 24 is installed to be movable in the horizontal direction by a magnetic body, so when a trunking control current is applied to the radial drive coil 23, a magnetic field is generated in the coil 23, and the tracking The focusing control device 18 is activated by interaction with the magnetic field generated by the permanent magnet I9.
is displaced in the radial direction.

The tracking control device 25 is formed by the above configuration.

FIG. 3 is a plan view of the light focusing position control device shown in FIG. 2. As shown in the figure, the objective lens barrel 10 is moved in two axial directions, vertically and horizontally, by a seven-axis movable elastic body 12 that is movable in the vertical direction and a radially movable elastic body 26 that is movable in the horizontal direction. It is set so that it can only be moved.

This prevents the objective lens 4 from tilting. Further, a sub-cannon drive coil 17 is installed so as to be movable only in the direction across the focusing magnetic gap 16, and a radial drive coil 23 is installed so as to be movable only in the direction across the dragging magnetic gap 22. Therefore, each magnetic gap can be made sufficiently narrow, and therefore electromagnetic force can be used efficiently. Therefore, the permanent magnet can be made smaller, and the overall shape of the light focusing position control device can be made more compact.

Next, a description will be given of the motion characteristics of the objective lens barrel lO based on the force//ing control mechanism and the tracking control mechanism.

(I) Regarding the motion characteristics based on the focusing control mechanism.

As shown in FIGS. 2 and 3, the drive source for focuser/nog control is fixed to the intermediate support 11/between the closed magnetic path for focusing and the focuser drive coil 17 fixed to the objective lens barrel 10. is an electromagnetic interaction. Here, the intermediate support 11 is connected. From the above structure, the weight of the movable part in the focusing direction (consisting of the objective lens 4, objective lens barrel 10, and hook drive coil 17) is M F, and the vertical spring constant of the parallel spring 12 movable in the focusing direction is Let Kr be the displacement XF of the objective lens barrel 10 in the focusing direction when the objective lens barrel 10 is subjected to a force Fr based on the above-mentioned electromagnetic interaction during vertical movement. If the frequency is f (Hz), the motion phase delay is 00 to 90° for O<f<fF, and 9 for fr<f.
00 to 1800, +800 for f F << f
converges to. Therefore, if the focusing target position is YF, by advancing the phase of the signal of the focusing driving force FF during movement to this focusing target position YF by the phase lead compensation circuit, the displacement XF of the movable part in the focusing direction with respect to the focusing target position YF is The motion phase delay of can be made smaller than 1800 degrees. This allows stable focusing control.

(■l) Regarding motion characteristics based on the tracking control mechanism.

As shown in FIGS. 2 and 3, the drive source for tracking control is installed in a closed magnetic path for tracking fixed to the fixed support 27 side and a tracking drive coil holder 24 fixed to the intermediate support 11 side. This is an electromagnetic interaction between the tracking drive coil 23 and the tracking drive coil 23. The fixed support body 27 and the radially movable parallel spring 26 are connected to each other.

From the above structure, if the weight of the focusing control device 18, which is a movable part in the tracking direction, is MT, and the horizontal spring constant of the disk radially movable parallel spring 26 is KT, then the focusing control device resonance frequency is called fT. have. On the other hand, the intermediate support 11 and the objective lens barrel IO are connected by a parallel spring 12 that is movable in the focusing direction, but when the tracking control is driven, the parallel spring 12 that is movable in the focusing direction slightly becomes elastic in the horizontal direction. Move in that direction to have it. For this reason, the objective lens barrel 10 has a spring constant f'r (referred to as a secondary resonance frequency under the horizontal spring constant of the parallel spring 12 movable in the focusing direction).
When moving in the left-right direction, there are a primary resonance frequency and a secondary resonance frequency.

However, the horizontal spring constant fiKr,' of the focus/nog direction movable parallel spring 12 is extremely large, and KF'>>KT
It is. Therefore, the secondary resonance frequency f'T is sufficiently higher than the primary resonance frequency fT by <f'T>1. Here, when the tracking driving force FT based on the electromagnetic interaction is applied, the motion phase delay of the displacement XT of the objective lens barrel 10 in the tracking direction is as follows, where f is the frequency, o<f<
fT is 0° to 90°, and tr < f <f'T
and 900 to 270°, and f'T<f, 270° to 3
It is 60°. Note that when the tracking and driving force FT is applied, it is necessary to make the motion phase delay of the displacement XT of the objective lens barrel 10 toward the Toranokinog target position YT smaller than 180° in the frequency band of the tracking control signal. Even if a phase lead compensation circuit is used to advance the phase of the signal of the trunking driving force FT, since there is a limit to the amount of phase lead, compensation can only be made to an extent that does not exceed the above-mentioned 180°. Therefore, in order to further compensate, it is necessary to set the secondary resonance frequency f'T sufficiently higher than the frequency band of the tracking control signal. In optical disk devices, the frequency band of the tracking control signal varies greatly depending on its use, but is generally in the range of 1 to 4 KHz. From this point, the secondary resonance frequency f
It has been found that it is appropriate to set 'T to approximately 8 kHz or higher.

A mechanism design method to satisfy these setting conditions will be described below.

As mentioned above, the secondary resonance frequency f'T is determined by the horizontal spring constant KF' of the parallel spring 12 movable in the focusing direction and the weight M1 of the movable part in the focusing direction. If the spring constant KF' is increased, the result is a dog, and if the weight M of the movable part in the focusing direction is decreased, the result is a dog. However, the means for reducing the weight MF of the movable part in the focusing direction cannot be expected to do much because there is a limit to reducing the weight of the objective lens 4 and lens barrel 10 (usually 0.5 g to l Og [designed)] . Therefore, the same
Spring constant K in the horizontal direction of the force 7 movable parallel spring 12
I tried increasing F'. If the width of the four force song direction movable parallel spring 12 is XF and the thickness is yF, then KF'/
It turned out to be KF-(xF/yF)2.

Therefore, in order to increase the horizontal spring constant KF' of the parallel spring 12 movable in the focusing direction, the width XF of the parallel spring 12 movable in the focusing direction must be widened, and f'T--i-f
,,is. Based on the above relationship, the thickness YF of the parallel spring 12 movable in the focusing direction is set to 20 to 50 μm, and the width of the spring 12 is set to 50 to 50 μm of yF! It has been found that it is sufficient to design it to about 00 times.

As described above, by using the parallel spring 12 movable in the force/ring direction, it is possible to make the motion phase delay of the displacement XT of the objective lens 4 with respect to the tracking target position smaller than 180° in the frequency band of the tracking control signal. At this time, it is important to also use compensation by a phase lead compensation circuit.

According to experiments, the above focus song direction movable parallel spring 1
When a beryllium copper alloy with a thickness of 30 to 50 μm was used for No. 2, stable focusing control and dragging control became possible.

<Effects> According to the present invention described in detail above, there is no risk that the position of the objective lens will be tilted in a light focusing position control device that correctly tracks a light beam used in an optical disk device to a recording medium. This allows the overall shape of the device to be made more compact.

[Brief explanation of the drawing]

Figure 1 is a configuration explanatory diagram showing the structure of an optical disk device;
This figure is a side sectional view showing the structure of the light focusing position control device in detail, and FIG. 3 is a plan view of the light focusing position control device shown in FIG. 2. In the figure, 4. Objective lens 8' Recording medium 10° Lens barrel I: Holter 12 Elastic body movable in the flaker song direction 13. Permanent magnet for focusing Ill: No.
Yoke plate for focusing I5: Yoke for focusing 16: Magnetic gap for focusing 17: Drive coil for 7-piece song 18: Permanent magnet for focusing 19° Permanent magnet for tracking 20 Yoke plate for tracking 1-21:) Racking yoke 22
Magnetic air gap for tracking 23 Niradial, drive coil 24 Niradial drive coil holder 25 Dragging control device 26 Radial direction'j5JIM elastic body
27: Fixed support agent Patent attorney Aihiko Fukushi (and 2 others) Ku n) Ya 1 faction Ku 4 faction

Claims (1)

[Claims] l A focusing control device and a trunking control device for driving the focusing control device in a tracking control direction are installed in a fixed support, and the focusing control device includes an intermediate support; An objective lens barrel connected to the vaginal intermediate support via a parallel spring movable in a focus knob direction, and an electromagnetic means for driving the objective lens barrel in a focusing direction (focusing direction); electromagnetic means for driving the device in the tracking control direction via the intermediate support, and the focusing control device and the fixed support are coupled by a disk radially movable parallel spring movable in the tracking control direction. Features a light focusing position control device.