JPH01134733A - System for controlling objective - Google Patents

Abstract

PURPOSE:To obtain a high-speed access by arranging a magnetic sensor in a fixed condition at a position somewhat separated from an objective, and providing a magnetic at a position in the vicinity of the objective in being faced on the magnetic sensor. CONSTITUTION:As a lens system, to an optical system holder 4, a light source 3 to be faced to an optical disk 1, collimating lens 5, a beam splitter 6, a detecting lens 7 and a light detector 8 are provided, and an objective 9 operated corresponding to the lens system, a driving mechanism 10 and an amplifier 11 are provided. An actuator is composed of a fixed part 14 and a movable part 12 where the objective 9, etc., are provided, a magnet 15 is arranged to the movable part 12, magnetic sensors 13 and 13 are arranged to the fixed part 14 corresponding to the magnet 15, and the movable part 12 is engaged to the fixed part 14. As a result, by a signal generated by means of the magnetic sensors 13 and 13 and the magnet 15, a servo loop can be controlled, an automatic oscillation, etc., can be suppressed, and the oscillation of the objective at the time of the access can be suppressed. Thus, the access time can be shortened.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an improvement in an apparatus for reproducing or recording a disc-shaped optical information recording medium (optical disk), and particularly relates to an improvement in an apparatus for reproducing or recording a disc-shaped optical information recording medium (optical disk). The purpose is to reduce the free vibration amplitude, thereby shortening the access time.

(Prior Art) In a filing device that records large amounts of information on an optical disk and can retrieve this information within a short time, short access time is an important performance as well as filing capacity.

This access means searching for a necessary track among the grooves or information tracks written linearly or concentrically on the optical disc.

Information is reproduced from or recorded on the optical disc by irradiating the optical disc with laser light, and an optical pickup device is used for this purpose. This optical pickup device is equipped with an objective lens that focuses a laser beam onto an optical disk, and this objective lens is moved by an actuator in a direction perpendicular to the surface of the optical disk (focusing direction) and in a direction perpendicular to the information track (
(tracking direction).

To explain specifically how to search for the necessary track mentioned above, the servo loop (state in which the optical pickup is correctly controlled) of the focus servo (control means) for the optical pickup is closed, and the search starts from a state in which the optical pickup is stopped. This refers to a series of operations in which the optical pickup is moved while the focus servo's servo loop is closed, and after the optical pickup is stopped, the tracking servo's servo loop is closed and information is read out.This filing device in particular can shorten this time. required.

During access, the optical pickup device is moved in the radial direction (tracking direction) of the optical disc. At this time, the tracking actuator that holds the objective lens movably in the tracking direction causes free vibration. Usually this frequency is determined by the main resonance frequency of the actuator.
It is about 70Hz.

The settling time of this vibration is determined by the damping factor (usually set to about 0.1 to 1) of the actuator.

When an actuator with such a main resonance frequency and damping factor causes free vibration, several cycles of settling time are required to stop the objective lens held by the tracking actuator even after the optical pickup device has stopped moving. Although it depends on the moving speed of the optical pickup, the amplitude in this case is usually much larger than the track pitch of 1.6 μm on the optical disk.

If the actuator causes such vibration during access, the time required to read the contents of the track after the optical pickup device stops moving increases. This settling time is a major problem for filing devices that aim to shorten access time, so a method has been proposed in which a position detection mechanism is installed on the objective lens and a servo is applied to reduce the free vibrations that occur during movement. (Tokuko Sho 62-
15933). An optical sensor is generally used as the position detection mechanism.

In the above-mentioned known example, two photodiodes are placed on the objective lens side which is held in a movable state with respect to the fixed side, and an LED that functions as a light source is placed on the fixed side, and the fluctuation of the relative distance between the two photodiodes is Detected by the signal.

Further, as shown in FIG. 7, a reflective object 51 is mounted on the movable part 50, and an LED 53 and a photodiode 54 are mounted on the fixed part 52.
・There are also some that set up. This is Japanese Patent Application Publication No. 62-4062
This method has already been disclosed in Japanese Patent Publication No. 5 and Japanese Unexamined Patent Publication No. 62-40630.

(Problems to be Solved by the Invention) In the example described in Japanese Patent Publication No. Sho 62-15933 in which a photodiode is disposed on the side of a movable part, a plurality of lead wires leading to the outside obstruct the operation of the actuator. There was a problem.

On the other hand, in the method shown in FIG. 7, there is no problem that the signal line obstructs the operation of the actuator, but since reflection is used, the signal level is small and the sensitivity is poor, and the emitted light from the LED is directly incident on the photodiode. There have been problems such as a decrease in the S/N ratio and the need for a photodiode with a large light-receiving area to increase sensitivity.

Furthermore, since the sensitivity and accuracy of position detection largely depend on the directional characteristics of the light source, for example, if a semiconductor light emitting element with a large divergence angle is used, there is a drawback that the characteristics will vary widely.

The present invention provides a novel objective lens control method that eliminates the above-mentioned difficulties, and particularly aims to enable position control of the objective lens without interfering with the operation of the actuator and to achieve high-speed access. .

[Structure of the invention]

(Means for solving the problem) In order to achieve this object, the present invention detects the position of the objective lens placed opposite to the recording medium, and controls the position based on this result. A method is adopted in which a magnetic sensor is fixedly placed at a position slightly in front of the object, and a magnet is placed facing the magnetic sensor at a position near the objective lens.

(Function) As described above, the present invention provides a small and simple method for detecting the position of the objective lens by using a magnetic field, and furthermore, vibration of the objective lens during access is suppressed, and the detection can be performed in a short time. In addition, by applying the magnet, unnecessary wiring to the actuator movable part can be eliminated, and the S/C ratio can also be improved.

(Example) The present invention will be explained in detail with reference to FIGS. 1 to 5, and although some parts overlap with the conventional technology due to convenience, new numbers will be added and explained.

FIG. 1 is a cross-sectional view schematically showing a filing device according to the present invention, which is roughly divided into an optical disk 1 and an optical pickup device 2 having a lens system converging thereon.

The middle lens system is constructed by installing necessary parts in an optical system holder 4, and in this optical system holder 4, a passage for a necessary optical path is installed facing the optical disc 1, and a direction perpendicular to this optical path is installed. Another optical path is also provided. A light source 3 composed of a semiconductor laser is placed at the end of the optical path, and a collimating lens 5 and a beam splitter 6 are installed, and a detection lens 7 and a photodetector 8 are installed corresponding to the optical path of the optical path, that is, the beam splitter 6. do. An amplifier 11 is provided which operates in accordance with this lens system and is electrically connected to the objective lens 9, the drive mechanism 10, and the photodetector 8 and drive mechanism 10 corresponding to the detection lens 7, which are important parts of the present application.

A perspective view and a sectional view of the actuator equipped with the objective lens 9 are shown in FIGS. 2 and 3. In this device, the movable part I2 and the magnetic sensor 13, 13, etc. necessary for adjusting the objective lens 9 are installed as described above. As shown in the figure, the movable direction of this movable part is the vertical direction a of the focusing direction and the horizontal direction of the tracking direction.

By the way, as will be described in detail later, the magnetic sensor 15 installed on the movable part and the magnetic sensor 13 formed on the fixed part output a signal depending on the strength and direction of the lines of magnetic force generated at their set positions.

By the way, assuming that free vibration occurs in the actuator, the situation in which the magnet moves in this case is schematically shown in Figure 5a.
, b and FIGS. 6a and 6b, in the present invention, the servo loop, which has not been considered at all in the past, can be controlled by the signal generated by the magnetic sensor 13.13 and the magnet 15 installed opposite thereto. This suppresses free vibration, etc.

As the magnetic sensor 13.13, a Hall element, a coil, or a magnetoresistive element can be applied.

As described above, a minute magnet 15 is installed at the end of the actuator movable part 12 that fixes the objective lens 9, but this magnetic force does not affect the actuator operation, and its weight is such that it does not deteriorate its function.

For example, the dimensions are 1 rrxa X 1 + m X 2 m
As can be understood from the fact that if a samarium cobalt (specific gravity 8 g/cJ) magnet is used, the weight will be about 16 mg. As mentioned above, the magnetic lines of force output signals depending on their strength and direction.

For example, if the direction of the magnetic pole 15 is set as shown in FIG. 4, the signal output from the single magnetic sensor 13 will move in accordance with free vibration, as described above. To explain each magnetic sensor, when the magnet is moved to positions 1, 2, and 3 as shown in FIG. 4a, the magnetic sensors change correspondingly as shown in FIG. 4. Furthermore, as shown in FIG. 5a, if the difference between the outputs of the two magnetic sensors 13 is obtained, the position of the magnet 15 can be changed to 1, 2, 3, 4, etc.
5, positive and negative signals are obtained as shown in FIG. 5, which can be used as the objective lens 9 position detection signal.

Next, a method for controlling the objective lens 9 will be explained.

After reproducing, erasing, or writing information on the disc-shaped optical information recording medium, the optical pickup device is moved to a position corresponding to the inner or outer periphery of the disc-shaped optical information recording medium for track selection. do.

During this movement, the tracking servo is open, and when the movement is further stopped, vibrations occur in the tracking direction of the actuator movable portion 12, that is, in the radial direction, due to free vibration or other factors.

Along with this, an objective lens position detection signal is generated as in the conventional example.

Here, a servo loop, which is a vibration control method such as free vibration according to the present invention, will be described.

Now suppose that when the objective lens 9 moves toward the outer circumference of the optical disk 1, it is positive, and when it moves toward the inner circumference, it is assumed that the objective lens 9 is moved inside the optical disk 1 by a positive signal, and conversely, by a negative signal, it is moved outside the optical disk 1. Configure the servo loop to move each

Note that if the positive/negative of the position detection signal is reversed, the servo loop may be reversed.

As described above, in the present invention, the vibration of the objective lens 9 during access is suppressed by the servo loop, and the tracking servo loop can be settled within a shorter time.

The actuator is composed of a fixed part 14 and a movable part 12 in which an objective lens 9 etc. are installed, and this movable part 12 is equipped with a magnet 1.
5, magnetic sensors 13 and 13 are arranged in the fixed part 14 in correspondence with the magnet 15, and the movable part 12 is locked to the fixed part 14 as described later.

The movable part 12 has a forcing direction control necessary for focusing the laser light spot on the signal recording surface of the information recording medium, and a tracking direction control necessary for making the light spot follow the signal track. This control requires a device that drives the objective lens 9 to detect and correct errors in both directions.

As shown in the perspective view of FIG. 2 and the sectional view of FIG. 3, this drive device has a plate-shaped fixing portion 14 made of a magnetic material such as iron, and a support plate 17 as shown at the left end of FIG. Install. A pair of yokes 19.19 made of magnetic material are installed parallel and perpendicularly to each other approximately at the center of the fixed portion 14, and a yoke 20.20 is further installed opposite to this, and further inside this yoke. The magnets 21 and 21 are placed in close contact with each other.

The moving part 12 is made of a non-magnetic material such as synthetic resin, and the objective lens 9 is adhered to it via a mounting part formed at the end thereof.A rectangular cylindrical four-force coil is attached surrounding the pair of yokes 19 and 19. 22.22 is adhesively arranged, and the movable part 15 facing the magnet has a tracking coil 23.2.
3. Glue and arrange.

To enable these to be driven, a pair of metal plate springs 18 and 18 are installed parallel to the support plate 17 made of synthetic resin, and a hinge body 26 made of synthetic resin is placed at the ends of the plate springs tg and is. Furthermore, a thin hinge body 27 is arranged between both ends of this hinge body 26. As a result, the end portion of the hinge body 26 can be driven in the forcing direction with respect to the support plate 17 by the pair of leaf springs 1g and 18. 4 Such a structure is integrated by fitting the end 28 of the hinge body 26 into the notch 29 formed in the movable part 12 and attaching the support column 30 to the support hole formed in the support plate 17.

As a result, the movable portion 12 can be driven not only in the forcing direction but also in the tracking direction. The drive method of this drive device is not limited to this example, and a shaft rotation sliding method is also possible.

〔Effect of the invention〕

As explained above, the present invention provides a small and simple objective lens position detection method that does not interfere with the original movement of the actuator, and also suppresses vibration of the objective lens during access, thereby stably closing the tracking servo loop. This makes it possible to shorten access time.

Furthermore, by using a magnet, wiring to the actuator moving part can be omitted, and the S/N ratio is improved compared to a method where the S/N ratio deteriorates due to noise generated by external light. This has advantages such as eliminating the need for wiring.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a perspective view of the main part thereof, Fig. 3 is a sectional view of Fig. 2, and Fig. 4 is a magnetic sensor according to an embodiment of the present invention. Figures showing the applied circuit configuration, Figures 5a and 6b and Figure 6a and b are diagrams showing the configuration and its output when the relative positions of the magnet and magnetic sensor are changed, and Figure 7 shows the conventional technology. It is a diagram.

Claims (3)

[Claims] (1) When controlling the position of an objective lens of an optical pickup equipped with a lens system that focuses a laser beam on a recording medium based on the detection result of the position of the objective lens, a magnetic sensor is fixedly arranged at a distance from the objective lens, An objective lens control method characterized in that a magnet is set at a position near the objective lens and facing the magnetic sensor. (2) The objective lens control method according to claim 1, wherein a Hall element, a coil, or a magnetoresistive element is applied as the magnetic sensor. (3) The objective lens control method according to claim 1, wherein the displacement of the objective lens is detected by difference signals of a plurality of magnetic sensors.