JPH0454294B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention provides access to a target position on an optical disk by linearly moving an optical head in the radial direction of a rotating optical disk. The present invention relates to an optical disk device for recording information on an optical disk or searching and reproducing information.

(Prior Art) An optical disk is a high-density information recording medium that uses laser light, and optical disk devices using this have recently attracted a lot of attention as an unprecedentedly large-capacity information memory. Application to capacitive image file devices is being considered.

When used as an image file device, a large amount of image information is recorded on an optical disk as a series of pits in the form of a spiral track, and each piece of recorded information is searched and reproduced as needed. In order to perform this quickly and stably, it is necessary for the optical head to have accurate and high-speed random access to the target position of the optical disk.

This is especially important when searching and reproducing recorded information. However, conventionally conceived optical disk devices have not necessarily been able to achieve their initial objectives due to problems with the access mechanism of the optical head and the structure of the optical head.

In other words, in order to achieve high-speed access,
The use of linear motors is essential. This linear motor has the relationship "F=ma=B1i...(1)" where F is force, a is acceleration, B is the magnetic flux density of the linear motor magnetic circuit, and 1 is the effective length of the coil in the magnetic circuit. .

Therefore, once the structure of the linear motor, the materials used (magnet, yoke, etc.), the length of the coil, etc. are determined,
The force "F" of this linear motor is limited to a certain value or less due to size limitations, usable current capacity, current response, etc.

In this way, in order to achieve faster access with a limited force "F", from the above equation (1), by reducing the mass m of the moving part of the linear motor as much as possible, a larger acceleration a can be achieved. obtained,
A linear motor can be moved quickly.

Therefore, it is essential for the mass m of the linear motor movable part to be smaller in order to realize high-speed access.

In an optical disk device, the mass m of the movable part of the linear motor is determined mainly by the weight of the optical head.

Next, in recent years, semiconductor lasers have been developed as light sources for reading and recording in the above-mentioned optical disk devices.

Although this semiconductor laser has an optical output of about 20 mW, its size is about 5 mm square and its weight is about 1 g. Therefore, it is a stable and compact device that integrates the functions necessary for an optical head of an optical disk device, focusing means, tracking means, laser beam focal position deviation detection means, track position deviation detection means, and semiconductor laser light source. We were able to create an optical head that weighs about 100g.

As mentioned above, by equipping the moving part of the linear motor with a small and lightweight optical head using a semiconductor laser, that is, with a small mass m, a large acceleration a can be obtained with the limited force F of the linear motor, resulting in high speed. Access becomes possible.

However, according to equation (1), the acceleration a of the linear motor
is proportional to the drive current i. Therefore, even if a constant current is applied, the linear motor moves at a constant acceleration, making it impossible to properly control the movable part of the linear motor.

Therefore, in order to accurately position the linear motor, that is, the optical head, to the target position at high speed, in addition to a position detector, it is necessary to detect the moving speed of the moving parts of the linear motor, and to There was a demand for something that could perform high-speed and accurate speed control.

As a result, there has been a need for an optical head that can quickly and accurately access a target position on an optical disk and that can quickly record or reproduce information.

(Problems to be Solved by the Invention) As mentioned above, there is a need for an optical head that can quickly and accurately access a target position on an optical disk and that can quickly record or reproduce information. An object of the present invention is to provide an optical disk device that allows an optical head to access a target position on an optical disk at high speed and accurately, and that can quickly record or reproduce information.

[Structure of the Invention] (Means for Solving the Problems) The optical disk device of the present invention includes a linear motor having a movable part that is movable in the radial direction of an optical disk having a track on which information is recorded; A semiconductor laser oscillator that is attached to the movable part of the motor and generates a laser beam; a focusing means that focuses the laser beam from the semiconductor laser oscillator onto the optical disk; and a focusing means that focuses the laser beam from the semiconductor laser oscillator onto the optical disk. an optical head integrally equipped with a detection means for receiving a defocus signal of a laser beam irradiated onto the optical disk and a positional deviation signal with respect to the track; a laser beam irradiated onto the optical disk by the optical head; a position detection means for detecting the irradiation position of the beam light; a position pulse generation means for generating a position pulse corresponding to the irradiation position detected by the position detection means; a counting means for counting the position pulses from the position pulse generation means; A position difference detection means for detecting a difference between a target position specified in advance and the detected irradiation position based on the count value by the counting means; means for generating a reference speed signal for the linear motor according to the difference between the two; means for generating a current speed signal for the linear motor at the detected irradiation position; and determining the difference between the reference speed signal and the current speed signal. , a drive means for moving the movable part of the linear motor at a speed corresponding to the reference speed signal to move the irradiation position of the laser beam irradiated onto the optical disk to the specified target position; and the optical system. A laser beam integrally provided in the head and moved to a target position designated by the drive means is positioned on the track of the optical disk in accordance with a positional deviation signal obtained by the detection means. It consists of tracking control means.

The optical disk device of the present invention includes a transport means having a movable part, an optical head attached to the transport means that generates a laser beam, and an optical head that detects the irradiation position of the laser beam irradiated onto the optical disk. a position detection means for detecting a difference between the irradiation position detected by the position detection means and a pre-specified target position; a position difference detection means for detecting the difference between the irradiation position detected by the position detection means and the irradiation position; means for generating a reference speed signal of the conveyance means according to the difference between the reference speed signal and the current speed signal; means for generating a current speed signal indicating the current speed of the conveyance means at the detected irradiation position; By determining the difference, the movable part of the transport means is moved at a speed corresponding to the reference speed signal, and the irradiation position of the laser beam irradiated onto the optical disk is moved to the specified target position. It consists of a moving means and a means for performing tracking control and focusing control on the optical head moved by the moving means.

(Function) In order to achieve high-speed and reliable access to the target position of the optical head using a linear motor, the present invention accelerates the optical head to the maximum when it is far from the target position. As long as the optical head is accelerated and decelerated as it approaches the target position, and the moving speed of the optical head is zero at the target position, accurate positioning to the target position can be achieved.

There is a target speed curve that allows for quick and reliable positioning to the target position, and if the optical head can be moved along this target speed curve, it will be possible to move the optical head quickly and reliably as described above. Positioning to a desired target position is possible.

For this purpose, a means is provided to detect the moving speed of the linear motor corresponding to the moving speed of the optical head.
By comparing this detected movement speed with the target speed curve and controlling it so that the error is zero, the optical head will eventually move along the target speed curve, allowing for high-speed and reliable positioning. This is how it was done.

(Example) An example of the present invention will be described below with reference to the drawings.

In FIGS. 1 and 2, 1 is an optical disk, 2 is a motor for rotating the optical disk 1, and 3 is an optical head for recording and reproducing. The optical head 3 is fixed to a movable part 4 of a DC linear motor 6 which is composed of a movable part 4 and a fixed part 5, and is thereby linearly moved in the radial direction of the optical disk 1 by the linear motor 6. Reference numeral 7 denotes an optical scale fixed to the movable part 4, and 8 a detector for detecting the position of the optical scale 7. These detect the position of the movable part 4 (that is, the optical head 3) using a so-called overlapped grid detection method. It is designed to detect the location. 9 is a positioning servo circuit for the linear motor 6, which drives the linear motor 6 at high speed according to a target position signal supplied from a main control section (not shown) and an output signal from the detector 8, and controls the movable section 4 (i.e. Accurate positioning of the optical head 3).

To explain the positioning servo circuit 9 in detail, the output signal of the detector 8 is transmitted to the position signal processing circuit 10.
By performing predetermined signal processing, a position pulse a and a speed signal c obtained by differentiating a position signal b for positioning are obtained. This position pulse a is supplied to an up-down counter 11, which outputs a current position signal representing the current position of the movable portion 4 to a subtraction circuit 12. Therefore, when the target position signal is supplied,
The subtraction circuit 12 that receives the signal performs a predetermined subtraction process and outputs the difference between the current position signal and the target position signal to the function generation circuit 13. The function generating circuit 13 is composed of, for example, a ROM and a D/A converter, and generates a speed curve signal according to the difference signal from the subtracting circuit 12. This speed curve signal is supplied to the differential amplifier 14 together with the speed signal c obtained from the position signal processing circuit 10, so that the differential amplifier 14 outputs a signal according to the difference between the two signals. The output of the differential amplifier 14 is supplied to the drive circuit 16 via the analog switch 15 which is closed to the a side at this time, and the drive circuit 16 thereby drives the linear motor 6 to drive the function generation circuit 13. The moving part 4 (that is, the optical head 3) of the linear motor 6 is made to reach the target position by controlling the speed according to the speed curve. When the movable part 4 reaches the target position, the comparator 17 that compares the target position signal and the current position signal outputs a coincidence signal.
5 to side b. Then, the output of the differential amplifier 18, which outputs a difference signal between the position signal b from the position signal processing circuit 10 and the speed curve signal from the function generation circuit 13, is connected to the drive circuit 16 and becomes a position servo loop. 4 positioning (electrical locking to the target position) is performed. By positioning the DC linear motor 6 like this, for example, the diameter is 30 cm.
Access time of about 0.1 seconds can be easily achieved for an optical disk of about 100 kHz.

On the other hand, as shown in detail in FIG. 2, the optical head 3 fixed to the movable part 4 of the linear motor 6 includes a semiconductor laser oscillator 21 that generates a laser beam for recording or reproducing information, and a collimator. a controlling lens 22, a polarizing beam splitter 23, a galvanometer mirror 24 as a tracking mechanism for accurately positioning a beam on a spiral track on the optical disk 1, a quarter wavelength plate 25,
an objective lens 26 as a focusing mechanism that focuses the beam light onto the optical disk 1; a voice coil 27 that drives the objective lens 26;
It integrally includes a cylindrical lens 28, a convex lens 29, and a photodetector 30 that receives reflected light from the optical disk 1 and performs photoelectric conversion. That is, the beam light from the laser oscillator 21 is collimated by the lens 22, passes through the beam splitter 23, is reflected by the galvanometer mirror 24 toward the optical disk 1 side, and passes through the 1/4 wavelength plate 25 to the objective lens 26.
The light beam is focused and positioned as a spot-like beam of light onto a track on the optical disk 1. The reflected light from the optical disk 1 due to this light irradiation passes through the objective lens 26 and the 1/4 wavelength plate 25, is reflected by the galvano mirror 24, is further reflected by the beam splitter 23, passes through the lenses 28 and 29, and becomes light. An image is formed on the light receiving surface of the detector 30 and photoelectrically converted.

Therefore, the detection of the defocus of the beam light on the optical disk 1 and the focusing control based on the detection signal are performed using an astigmatism optical system formed by a combination of a cylindrical lens 28 and a convex lens 29, and a photodetector 30. By using the output of the focusing servo circuit 31 to control the voice coil 27 according to the focus shift signal and driving the objective lens 26, accurate focus shift detection and focusing based on the detection can be performed. In addition, such a focusing means is disclosed in, for example, Japanese Patent Application Laid-Open No.
This means is already well known from the publication No. 104539, and the present invention does not focus on this means, so the above explanation will be omitted. Further, the above-mentioned focusing means is given as an example, and other methods may be used.

Furthermore, the detection of the radial positional deviation of the beam light relative to the track on the optical disk 1 and the tracking control based on the detection signal can be carried out using, for example, the photodetector 30 as a two-split photoreceiver.
The output of 0 is input to the tracking servo circuit 32 to extract a positional deviation signal, and this tracking servo circuit 32 drives the drive coil 24M of the galvanomirror 24 according to the positional deviation signal to rotate the galvanomirror 24. By doing so, accurate positional deviation detection and tracking based on the positional deviation detection can be performed. Incidentally, such a tracking means is already well known, and since the present invention does not focus on this means, further explanation will be omitted.

Further, the above-mentioned tracking means is given as an example, and other methods may be used.

By configuring the optical disk device in this way, the optical head 3 is moved to a predetermined target position by the linear motor 6, and the optical head 3 is positioned at high speed to the target position by the linear motor 6. Since track tracking is performed by the galvanometer mirror 24 provided in the optical head 3, high-speed random access to the target position of the optical head 3 can be performed, and moreover, accurate track tracking can be performed. Therefore, information can be stored on the optical disc 1 or retrieved and reproduced quickly. In addition, a light source (semiconductor laser oscillator 21) necessary for recording or reproduction, a focusing mechanism (objective lens 26, voice coil 27),
A tracking mechanism (galvano mirror 24) and a detection mechanism necessary therefor (lenses 28, 29,
Since the optical head 3, which is equipped with an integrated photodetector 30), is attached to the movable part of the linear motor 6, the optical system can be simplified, the optical path can be made the shortest distance, and misalignment of the optical path can be prevented. This results in the following effects and thus high stability.

For reference, if you sample A4-sized document image information at a rate of 8 lines/mm, it will be about 4 megabits, but if you perform one-dimensional band compression, it will be about 500 kilobits. , this amount of image information occupies only a few tracks on an optical disk. Therefore, as described above, recording or reproduction can be easily performed by high-speed positioning using the linear motor and tracking using the tracking mechanism.

[Effects of the Invention] As detailed above, the optical head can access the target position on the optical disk at high speed and accurately.
It is possible to provide an optical disk device that can quickly record or reproduce information.

[Brief explanation of the drawing]

FIGS. 1 and 2 are configuration diagrams showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Optical disk, 3... Optical head, 4... Movable part, 5... Fixed part, 6... Linear motor, 7... Optical scale, 8... Position detector, 9... Positioning servo circuit, 21... Semiconductor laser oscillator, 24... Galvanometer mirror, 26...Objective lens, 27...Voice coil, 30...Photodetector, 31...Focusing servo circuit, 32...Tracking servo circuit.

Claims (1)

[Claims] 1. A linear motor having a movable part movable in the radial direction of an optical disk having a track on which information is recorded, and a semiconductor attached to the movable part of the linear motor to generate a laser beam. a laser oscillator; a focusing means for focusing a laser beam from the semiconductor laser oscillator onto the optical disk; an optical head integrally equipped with a detection means for obtaining a defocus signal and a positional deviation signal with respect to the track; a position detection means for detecting the irradiation position of the laser beam irradiated onto the optical disk by the optical head; a position pulse generating means for generating a position pulse corresponding to the irradiation position detected by the position detecting means; a counting means for counting the position pulses from the position pulse generating means; position difference detection means for detecting a difference between a specified target position and the detected irradiation position; means for generating a reference speed signal; means for generating a current speed signal of the linear motor at the detected irradiation position; and determining the difference between the reference speed signal and the current speed signal, a drive means for moving the laser beam at a speed corresponding to the reference speed signal to move the irradiation position of the laser beam irradiated onto the optical disk to the specified target position; , tracking control means for controlling the position of the laser beam that is moved by the drive means to the target position specified on the track of the optical disk according to the positional deviation signal obtained by the detection means. An optical disk device characterized by: 2. A transport means having a movable part; an optical head attached to the transport means and generating a laser beam; and a position detection means for detecting the irradiation position of the laser beam irradiated onto the optical disk by the optical head. , a position difference detection means for detecting a difference between the irradiation position detected by the position detection means and a prespecified target position; and a difference between the target position and the irradiation position detected by the position difference detection means. means for generating a reference speed signal of the conveyance means in accordance with the current speed of the conveyance means; means for generating a current speed signal indicating the current speed of the conveyance means at the detected irradiation position; By determining the difference, the movable part of the transport means is moved at a speed corresponding to the reference speed signal, and the irradiation position of the laser beam irradiated onto the optical disk is moved to the specified target position. 1. An optical disk device comprising: means; and means for performing tracking control and focusing control on an optical head moved by the moving means.