JPH0916982A - Objective lens drive - Google Patents

Abstract

(57) [Summary] [Object] To provide an objective lens driving device capable of reading and writing optical discs having different characteristics with a single device. [Structure] This apparatus is equipped with two objective lenses. When the optical disc in use is ejected (201) and a new optical disc is inserted (203), the objective lens used immediately before is kept in the optical path (202).
. Using this objective lens, the control track of the optical disc is accessed (204), and it is determined whether the stored disc attributes can be read (205). If it is determined that the disc attribute cannot be read, the objective lens is switched so that another objective lens is held in the optical path (206), and the control track is accessed again (204). When the disc attribute can be read (207), the process shifts to standby such as changing the setting of the signal processing circuit (208), and the recording / reproducing operation is started by the changed control system ( 209).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device used in a reproducing device or a recording device for an optical information recording medium such as an optical disk or a magneto-optical disk.

[0002]

2. Description of the Related Art In recent years, along with the development of optical information recording media such as optical discs and magneto-optical discs, objective lens driving devices used for reproducing devices of these optical information recording media have been actively developed. The objective lens driving device has already been widely spread as a CD-R0M typified by a compact disc (CD) and a laser disc (LD).

Recently, an objective lens driving device has been developed not only as a reproducing device but also as an optical recording device. In particular, an M0 (Magneto Optical) system or a PC (Phase) system has been developed.
Change) and other recording methods are known.

[0004]

Generally, the recording structure of an optical disc or a magneto-optical disc is defined by a standard. However, it is expected that the recording density will improve with the passage of time. For example, the size of a pit, which is a unit in which information is recorded, is likely to reach submicron from the current 1 micron.

In order to realize this, the wavelength of the laser light used is shortened, or the NA (Numeri) of the objective lens is
The device is devised to increase the cal aperture and reduce the spot diameter of the light beam.

Discs having different substrate thicknesses are also emerging as a new standard, and there is a risk that the new device will not be able to record or reproduce information on the discs of the conventional standard.

Therefore, the present invention provides an objective lens driving device capable of reading and writing not only optical discs and magneto-optical discs currently in general use but also optical discs and magneto-optical discs having different characteristics with one device. With the goal.

[0008]

In order to achieve the above object, in the present invention, a movable body which is driven in a thickness direction of an information storage medium and in a direction orthogonal to the thickness direction, and mounted on the movable body. Determination means for determining the compatibility between the plurality of objective lenses and the objective lens already existing in the optical path of the laser beam when starting recording / reproduction with respect to the information storage medium, and the determination means determines incompatibility If
The objective lens driving device has a switching means for disposing another objective lens in the optical path.

The switching means generates a signal for moving the movable body in a direction orthogonal to the thickness direction of the information storage medium. Further, when a movable body driven in the thickness direction of the information storage medium and a direction orthogonal to the thickness direction, an objective lens having a plurality of focal points and mounted on the movable body, and recording / reproduction with respect to the information storage medium are started. And a determination means for determining compatibility with a focus that is already available,
The objective lens driving device has a switching unit that sets another focus to an available state when the determination unit determines that the focus is unsuitable.

The switching means generates a signal for moving the movable body in the thickness direction of the information storage medium.
Further, a movable body driven in the thickness direction of the information storage medium and a direction orthogonal to the thickness direction, an objective lens mounted on the movable body so as to have a plurality of optical characteristics, and recording / reproduction with respect to the information storage medium are performed. At the time of starting, a judging means for judging compatibility with the optical characteristics already in the usable state, and a switching means for setting other optical characteristics to the usable state when it is judged as unsuitable by the judging means. The objective lens driving device having The determining means determines the suitability of the optical characteristic for the information reproduction of the control track of the information storage medium.

[0011]

According to the present invention having the above construction, a plurality of optical characteristics (for example, optical elements such as an objective lens) can be mounted and switched, so that reading and writing of optical disks and magneto-optical disks having different characteristics can be performed. However, it is possible to record and reproduce with one device.

Further, in the present invention, the optical characteristic which is already in the usable state because it was used for the previous recording / reproducing is first used for the recording / reproducing this time. Therefore, the number of times the optical characteristics are switched can be reduced, and the life of the objective lens switching mechanism and the like can be extended.

It should be noted that the user rarely uses different kinds of disks every time, and in many cases, the same kind of disks are used continuously in many cases. Therefore, the configuration of the present invention is extremely significant in the general usage of the optical disc.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment of the objective lens driving device of the present invention will be described with reference to FIGS. Here, FIG. 1 is a plan view of the objective lens driving device, FIG. 2 is a partial sectional view taken along the line AA in FIG. 1, FIG. 3 is a sectional view taken along the line BB in FIG. 1, and FIG. FIG. 5 is a block diagram showing a signal processing system, and FIG. 5 is a flow chart for explaining an objective lens switching operation.

The disk 1 (optical disk, magneto-optical disk, etc.) used for recording / reproducing information is held by a chucking means such as a magnet chuck with respect to a spindle motor 3 fixed to a base 2 for recording / reproducing. At times, the spindle motor 3 is driven to rotate stably.

A carriage 4 is arranged near the lower portion of the disk 1. A first movable body 5 and a second movable body 6 are mounted on the carriage 4. The first movable body 5 is a flat blade 5a facing the disk 1 surface.
And a cylindrical coil bobbin 5b fixed to the lower part of the blade 5a.
Consists of A sliding bearing 5c is provided at the center of the blade 5a and the coil bobbin 5b.

On the blade 5a, a plurality of, here two, objective lenses 8a and 8b are fixed separately. These objective lenses 8a and 8b have different optical characteristics (for example, the numerical aperture (NA) of the objective lens 8a is 0.45, and the objective lens 8b
The numerical aperture of is selected as 0.6). The mounting positions of these two objective lenses 8a and 8b are adjusted so that the center of gravity of the entire mass of the first movable body 5 substantially coincides with the rotation axis 7. That is, the first movable body 5 has a structure in which the weight is balanced with respect to the rotating shaft 7 by the two objective lenses 8a and 8b.

A focus coil 9 is wound around the side surface of the coil bobbin 5b, and on the focus coil 9,
Two rectangular tracking coils wound in a plane
100a and 100b are attached. The two tracking coils 100a and 100b are attached at positions symmetrical with respect to the rotation axis 7.

Around the focus coil 9 and the tracking coils 100a, 100b, the permanent magnets 10a, 10a,
Magnetic circuits 12a and 12b including 10b and yokes 11a and 11b are provided. As shown in FIG. 3, the focus coil
9 and tracking coils 100a, 100b are permanent magnets 10a,
There is a relationship between 10b and the yokes 11a and 11b,
They are arranged so as to face each other with a magnetic gap of a predetermined length interposed therebetween.
The permanent magnets 10a and 10b give magnetic fields to the focus coil 9 and the tracking coils 100a and 100b, respectively.

When the focus coil 9 is energized and the magnetic flux is received from the permanent magnets 10a and 10b, a Lorentz force is generated, and the first movable body 5 moves to the disk.
A minute translational drive is performed in the thickness direction 1 (axial direction of the rotating shaft 7). Also, Lorentz force is generated by the tracking coils 100a, 100b being energized and the magnetic fluxes from the permanent magnets 10a, 10b being generated, so that the first movable body 5 moves in the radial direction of the disk 1 (around the rotation axis 7). It is driven by minute rotation.

Further, on the surfaces of the tracking coils 100a and 100b at positions separated by 180 ° around the coil bobbin 5b,
Two magnetic bodies 101a and 101b made of iron pieces or the like are provided. The magnetic bodies 101a and 101b are attached at positions symmetrical with respect to the rotating shaft 7. And one objective lens 8
Are in the optical path 41 (discussed below), these magnetic materials 10
1a and 101b are just permanent magnets 10a and 10 of the magnetic circuits 12a and 12b.
There is a relationship between b and the yokes 11a and 11b. Magnetic circuit
By arranging the magnetic bodies 101a and 101b in the 12a and 12b, the first movable body 5 can magnetically maintain its neutral position.

On the other hand, a rotary shaft 7 is erected and fixed on the second movable body 6, and the first movable body 5 is held and mounted via the rotary shaft 7. A pair of radial coils 13a and 13b are attached to both ends of the carriage 4 at exactly the same distance from the center of gravity of the carriage 4. A magnetic field is applied to the radial coils 13a and 13b from the radial magnetic circuits 14a and 14b fixed to the base 2.

The radial magnetic circuits 14a, 14b include back yokes 15a, 15b, center yokes 16a, 16b, permanent magnets 17a,
The radial coils 13a, 13b are movably inserted in a magnetic gap defined by the center yokes 16a, 16b and the permanent magnets 17a, 17b. The two radial magnetic circuits 14a and 14b have the same structure,
The direction of magnetization of the permanent magnets 17a and 17b coincides with the thickness direction of the magnetic gap.

Further, there are 2 before and after both ends of the carriage 4.
A pair of four slide bearings 19a, 19b are provided, and two guide rails 18a, 18b are arranged in parallel in a relationship of being inserted into these slide bearings. Both ends of the guide rails 18a and 18b are fixed to the base 2. The carriage 4 is movably supported along the guide rails 18a and 18b.

Then, when the radial coils 13a and 13b are energized and the magnetic flux is received from the radial magnetic circuits 14a and 14b, Lorentz force is generated and the second movable body is moved.
6 is translationally driven in the radial direction of the disk 1.

The magnetic gap width of the radial magnetic circuits 14a, 14b is such that the second movable body 6 can be moved by a required distance in the longitudinal direction of the guide rails 18a, 18b, in other words, the objective lenses 8a, 8b. The disk 1 is formed to be long enough in the same direction so that it can be moved in the radial direction from the outermost circumference to the innermost circumference.

Next, the optical system and signal processing system of the apparatus will be described with reference to FIG. The laser light for irradiating the disc 1 is fixed to the bottom of the movable body 4 and
It is generated by an optical unit 20 that is movable integrally with the. The laser beam LB emitted from the semiconductor laser 21 in the optical unit 20 is converted into a parallel beam through the collimator lens 22 and bent by 90 ° by the first beam splitter 23a, and the inside of the carriage 4 from the radial direction of the disc 1. Be led to. An optical path (specifically, space) 41 for introducing the laser light LB is provided at the bottom of the carriage 4
The LB passes through the optical path 41 and enters the objective lens 8 (8a or 8b). The laser beam LB incident on the objective lens 8 is given a predetermined focusing property and is focused on the information storage surface of the disc 1.

Here, when the system is in the information reproducing state, the laser beam LB guided to the disc 1 is intensity-modulated according to the information recorded on the information storage surface, that is, the presence or absence of the minute pits. It is returned to the objective lens 8 again. The reflected laser light LB returned to the objective lens 8 passes through the optical path 41 and is again guided to the fixed optical unit 20. Then, the light passes through the first beam splitter 23a and is split into two paths by the second beam splitter 23b.
An image is formed on the first photodetector 25a and the second photodetector 25b via a and 24b.

Reflected laser light guided to the photodetectors 25a and 25b
The LB is converted into an electric signal corresponding to the size of the beam spot, and is supplied to the track control circuit 27 and the focus control circuit 28 provided in the control unit 26. The signals generated by the track control circuit 27 and the focus control circuit 28 are used for the focus direction control and the track direction control as the focus offset signal and the track offset signal of the objective lens 8 (8a, 8b).

By using the focus offset signal and the track offset signal, the positional deviation (focus deviation) of the objective lens 8 in the focusing direction is detected, and the current value given to the focus coil 9 is controlled so as to correct this positional deviation. . Further, by using the track offset signal, the positional deviation of the objective lens 8 in the track direction is detected, and the current value given to the tracking coils 100a, 100b is controlled so as to correct this positional deviation.

The reflected laser light LB guided to the photodetector 25b is also supplied to the information reproducing circuit 29. This information is various information recorded on the disc 1, and is sent to a host system (for example, a personal computer, etc.) not shown and displayed as characters, still images, and moving images on the display.
It is also output as music or voice from the speaker. In this case, the carriage 4 follows the track of the information storage surface of the disc 1 and is controlled to move in the radial direction of the disc 1 by a large drive or a minute drive.

An external host system (not shown) (for example, a personal computer) is provided in the control unit 26.
A recording signal generating circuit 30 for generating a recording signal according to the information input from the first movable body 5 is controlled so that one of the objective lenses 8a and 8b is arranged in the optical path 24 of the laser beam LB described above. It includes an optical characteristic switching circuit 31 that generates a signal for performing the operation.

Next, switching between the two objective lenses 8a and 8b will be described. The disc 1 that can be used in the device of the present invention is not limited to one type of disc as in the conventional case, and the disc recording density, the allowable amount of warp,
It is possible to use a plurality of types of discs having different standards such as a difference in the thickness of the disc substrate. For example, not only CD-ROM discs but also MO discs, PC discs, etc. can be used. And two objective lenses 8a, 8b
Has been adapted to handle the available discs.

For example, in the case of using a disk which requires a small spot diameter of the laser beam LB, the numerical aperture (N
A large objective lens of A) is selected, and when a disk that needs to increase the spot diameter of the laser beam LB is used, an objective lens of small numerical aperture (NA) is selected.

When the user of the apparatus mounts the target disk 1 on the spindle motor 3, this input signal is sent to the optical characteristic switching circuit 31 and the objective lens 8 suitable for the disk 1 is used.
The following control is performed so that the laser beam is positioned on the optical path 41 of the laser beam LB.

First, as shown in FIG. 5, the disk in use is ejected from the apparatus (201), and a new disk is inserted (2).
03) Think of the case. At this time, the objective lens (for example, 8a) used immediately before is held in the optical path as it is (202).

The disc attributes are recorded on a so-called "control track" existing adjacent to the "lead-in area" near the innermost periphery of the disc.
Specifically, various conditions necessary for recording / reproducing on / from the disc, such as disc type, disc manufacturer name, write power, and read power, are recorded. When a new disc is inserted into the device, the objective lens 8a held in the optical path will access this "control track".
(204) Attempt to read the information.

In order to accurately read the recorded information (including the information of the "control track") on the disc, NA is required.
It is necessary to select the correct objective lens which is suitable for the above and to arrange it in the optical path. However, until the attribute information recorded on the "control track" is read, the type of the disc is unknown and the objective lens cannot be selected correctly.

Therefore, as described above, first, the operation of reading the disc attribute is started by using the objective lens 8a used previously. Then, it is judged whether the disc attribute can be read within a fixed time (205). If the disc attributes can be read within a fixed time, the disc recording / reproducing operation continues.

If it is determined that the disc attribute cannot be read after a certain period of time, the objective lens
It is determined that the disc that cannot be accessed by 8a, that is, the disc specifications do not match the objective lens 8a, and the objective lens 8b is held in the optical path by rotating the carriage 4 by 180 °. (20
6). When switching between the objective lenses 8a and 8b,
Rotational drive control of the magnetic circuits 12a and 12b mounted on the second movable body 6 is performed.

Then, the "control track" is accessed again (204), and the operation of reading the attribute of the disk is restarted. In this way, if the objective lens 8b suitable for the disc specifications is selected, the disc attributes can be read (207). Then, on the basis of the information read from the "control track", it shifts to standby such as setting various characteristics of tracking control and focus control and changing the setting of the signal processing circuit (208), after which the setting is changed. The recording / reproducing operation is started by the control system thus set (209).

In this embodiment, the two objective lenses 8a, 8a
Although the device configuration includes only b, the switching operation (206) may be performed twice or more if the device includes three or more objective lenses having different optical characteristics.

If the disc attribute cannot be read even after the objective lens switching operation (206) is repeated a predetermined number of times (for example, the number of objective lenses, or an arbitrarily set numerical value), this apparatus records. A signal indicating that the disc cannot be reproduced, that is, the disc is incompatible, is output to the control system. And read the disk attributes
The startup operation of the device is automatically terminated without passing through (207). The disc incompatibility signal is preferably transmitted to the user by displaying on a display or the like.

By discriminating the disc attribute by the above optical characteristic switching operation, for example, it corresponds to a device structure in which there is no caddy for mounting the disc and the user himself has to insert the disc into the device. it can. Further, it is possible to obtain an effect that it is possible to shorten the time until the apparatus shifts to the recording / reproducing operation.

This can be easily imagined because, for example, a user who listens to music frequently uses the music CD continuously and rarely alternately uses the music CD and the movie CD. That is, the user rarely uses different kinds of disks every time, and in many cases, the same kind of disks are used continuously in many cases. As described above, in the general usage of the optical disc, the control method as described above performed in the optical characteristic switching circuit 31 becomes extremely meaningful.

Further, according to the above-mentioned control method, the number of times the objective lens is switched can be extremely reduced, so that the life of the objective lens switching mechanism, that is, the various mechanisms relating to the rotational drive of the first movable body can be reduced. It will be possible to postpone.

According to the objective lens driving device of the present invention which operates as described above, two objective lenses can be switched and used according to the standard or specification of the disc, and therefore, the standard or specification of the disc is adapted. Dedicated (separate)
It is not necessary to prepare a plurality of objective lens driving devices.
Therefore, an objective lens driving device that can handle various kinds of information satisfactorily with only one device is provided.

Next, a second embodiment of the objective lens driving device of the present invention will be described with reference to FIGS. 6 and 7. In addition,
In the following description, the same parts as those in the above-described embodiment are designated by the same reference numerals, and duplicate description will be omitted.

In the above-described embodiments, a plurality of objective lenses having different NAs are used by switching in order to change the optical characteristics. On the other hand, in this embodiment, one objective lens is formed in a shape having a plurality of optical characteristics.

Specifically, the lens surface of the objective lens is divided into a plurality of areas in a ring shape, and each area has a lens surface shape with different specifications. As the lens surface shape, the invention described in Japanese Patent Application No. 7-5299 can be used as it is. Therefore, it is not necessary to switch and use a plurality of objective lenses, and one objective lens can form two or more focal points. Then, by selecting one of the focal points of the objective lens, it is possible to change the optical characteristics on the recording surface of the disc and realize the function equivalent to that of the first embodiment.

As shown in FIG. 6, the objective lens 24 used in this embodiment is a multifocal type objective lens having a structure in which one convex portion is formed in the center of the lens surface. The focal point of the laser beam that has passed through the convex portion is structured to form an image at a position farther than the focal point of the laser beam that has passed through other portions. In order to switch between these two focal points 24a and 24b, the first movable body 5 to which the objective lens 24 is fixed is linearly moved along the rotation axis 7, and the diameter of the beam spot is focused so as to focus on the recording surface of the disc. The size of can be changed.

For example, the focal point 24a with respect to the recording surface of the disk
In the state where the image is formed at, the focal point 24b forms an image at a position where the recording and reproduction are not affected at all (the disc outer side than the disc recording surface). Also, focus on the recording surface of the disc 24
In the state where the image is formed at a, the focus 24b forms an image at a position where the recording and reproduction are not affected at all (the disc inner side than the disc recording surface). Therefore, the two focal points 42a and 42b do not affect each other, and only one of them always contributes to the recording / reproducing operation.

In this embodiment having such a configuration, the control mode of the optical characteristic switching circuit 31 is as follows. That is, as shown in FIG. 7, when the disc in use is ejected (301) from the device and a new disc is inserted (303), the focus of the objective lens 42 used immediately before (for example, 24
Data (a) such as focal length is stored in the optical characteristic switching circuit 31 (302).

The disc attributes are recorded on a so-called "control track" existing adjacent to the "lead-in area" near the innermost periphery of the disc.
Specifically, various conditions necessary for recording / reproducing on / from the disc, such as disc type, disc manufacturer name, write power, and read power, are recorded. When a new disc is inserted into the device, the focus 24a of the objective lens 24 stored in the optical characteristic switching circuit 31 is used to access this "control track" (304) and try to read the information. .

In order to accurately read the recorded information on the disc (including the information of the "control track"), NA is required.
It is necessary to select the correct focus for which
However, until the attribute information recorded on the "control track" is read, the disc type is unknown and the focus cannot be selected correctly.

Therefore, as described above, first, the operation of reading the disc attribute is started by using the focus 24a used previously. Then, it is judged whether or not the disc attribute can be read within a fixed time range (305). If the disc attributes can be read within a fixed time, the disc recording / reproducing operation continues.

When it is determined that the disc attribute cannot be read after the elapse of a certain time, it is determined that the disc that cannot be accessed by the focus 24a, that is, the disc specifications do not match the focus 24a, and the first The movable body 5 is linearly driven in the axial direction (focusing direction) of the rotating shaft 7 to switch the focus so that the focus 24a of the objective lens 24 is selected (306).

Specifically, by receiving a signal from the optical characteristic switching circuit 31, a control current is applied to the focus coil 9 to linearly drive the first movable body 5 in the thickness direction of the disc 1 (direction of the optical path). To do. In the control system, the currently used focal point 24a has already been recognized (302), so if a control current is applied to perform linear driving in the direction of imaging at a focal point 24b that is different from that focal point 24a. Good.

Then, the "control track" is accessed again (304), and the operation of reading the attribute of the disk is restarted. In this way, if the focus that matches the specifications of the disc is selected, the disc attributes can be read (307). Then, based on the information read from the "control track", it shifts to standby such as setting various characteristics of tracking control and focus control or changing the setting of the signal processing circuit (308), and then changes the setting. The recording / reproducing operation is started by the control system (30
9).

In this embodiment, the apparatus has two focal points. However, if the apparatus has an objective lens having three or more different focal points, the switching operation is performed twice or more.
(306) may be performed.

If the disc attribute cannot be read even after the focus switching operation (306) is repeated a predetermined number of times (for example, the number of focal points or an arbitrarily set numerical value), this apparatus will not record or reproduce data. A signal indicating that the disc is possible, that is, disc incompatibility is output to the control system. Then, the startup operation of the device is automatically terminated without the reading of the disk attribute (307).

According to the present embodiment as described above, since it is necessary to move the first movable body by a short distance when switching the optical characteristics, it is possible to perform the switching operation faster than in the first embodiment. Becomes

Further, in this embodiment, the spot diameter of the focal point 24a is smaller than the spot diameter of the focal point 24b, and the magnetic substance 101
a, 101b and magnetic circuits 12a, 12b make the first movable body 5
Is configured to form a substantially focal point 24a on the disc 1 in the neutral position. Therefore, the following effects can be obtained.

That is, since the spot diameter associated with the focal point 24a is small, the allowable tracking deviation and focus deviation are extremely small, and it is necessary to position the objective lens 24 with high accuracy. However, in this embodiment, the focus 24a
Is set to a state in which a spot is already formed on the disk 1 in the neutral state of the first movable body 5. Therefore, the defocus is small, the DC current for correcting the defocus is small, the substantial controllability determined by the current limitation of the drive amplifier can be increased, and stable recording / reproducing can be performed.

On the other hand, since the spot diameter associated with the focal point 24b is large, the permissible error of focus deviation and tracking deviation is larger than that when the focal point 24b is used. In other words, it is possible to perform sufficiently satisfactory control even in the state in which a slight DC current is passed in order to correct the defocus.

Needless to say, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the second
Instead of the multifocal objective lens shown in the embodiments, it is possible to use an objective lens (an objective lens having a sectional wave shape) in which two or more focal points are arranged in parallel in one optical element.
In this case, the optical characteristics can be switched by driving the first movable body in the tracking direction instead of driving it in the focus direction.

Further, in the above-described embodiments, the configuration in which a plurality of objective lenses or a plurality of focal points are switched has been described. However, a plurality of focal points may be formed by dividing a laser beam using an optical element such as a hologram element. You may comprise. In this case, the optical characteristics can be switched by driving the first movable body in the focus direction.

The present invention is not limited to the application to the objective lens driving device, but is also applied to an information recording / reproducing device having a plurality of heads (for example, a magnetic disk device having a plurality of magnetic heads). It is possible.

[0069]

As described above, according to the present invention, reading and writing of optical disks having different characteristics can be performed by one device.

[Brief description of the drawings]

FIG. 1 is a plan view showing a first embodiment of an objective lens driving device of the present invention.

FIG. 2 is a plan view of an objective lens driving device.

FIG. 3 is a sectional view of an objective lens driving device.

FIG. 4 is a block diagram showing an optical processing system and a signal processing system.

FIG. 5 is a flowchart for explaining an objective lens switching operation.

FIG. 6 is a sectional view showing a second embodiment of the objective lens driving device of the present invention.

FIG. 7 is a flowchart illustrating a focus switching operation.

[Explanation of symbols]

 1 Disk 2 Base 3 Spindle Motor 4 Carriage 5 First Movable Body 6 Second Movable Body 7 Rotation Axis 8a, 8b, 24 Objective Lens 9 Focus Coil 10a, 10b Permanent Magnet 11a, 11b Yoke 12a, 12b Magnetic Circuit 20 Optical Unit 24a, 24b Focus 31 Optical characteristic switching circuit 41 Optical path 100a, 100b Tracking coil 101a, 101b Magnetic material

Claims (6)

[Claims] 1. A movable body driven in a thickness direction of an information storage medium and in a direction orthogonal to the thickness direction, a plurality of objective lenses mounted on the movable body, and when starting recording / reproducing with respect to the information storage medium. A determination means for determining compatibility with an objective lens already existing in the optical path of the laser beam, and a switch for arranging another objective lens in the optical path when the determination means determines that the compatibility is not satisfied. And an objective lens driving device. 2. The objective lens driving device according to claim 1, wherein the switching means generates a signal for moving the movable body in a direction orthogonal to the thickness direction of the information storage medium. 3. A movable body driven in the thickness direction of the information storage medium and in a direction orthogonal to the thickness direction, an objective lens having a plurality of focal points and mounted on the movable body, and recording / reproducing to / from the information storage medium. When starting, a determination means for determining compatibility with a focus that is already in an available state, and a switching means for setting another focus to an available state when the determination means determines that the focus is not available, An objective lens driving device having. 4. The objective lens driving device according to claim 3, wherein the switching means generates a signal for moving the movable body in the thickness direction of the information storage medium. 5. A movable body which is driven in a thickness direction of the information storage medium and a direction orthogonal to the thickness direction, an objective lens which is mounted on the movable body so as to have a plurality of optical characteristics, and an information storage medium. When recording / reproducing is started, a determination unit that determines compatibility with an optical characteristic that is already available, and if the determination unit determines that the optical characteristic is not compatible, sets another optical characteristic to an available state. An objective lens driving device comprising: a switching unit. 6. The objective lens driving device according to claim 5, wherein said judging means judges suitability of optical characteristics for information reproduction of a control track of the information storage medium.