JPS61216140A - Detecting system for eccentric degree of optical disk medium - Google Patents

Abstract

PURPOSE:To detect the eccentric degree of a medium in real time and to secure the high positioning accuracy by detecting a shift degree of a variable density degree of the reflected light at a boundary part which is produced by the eccentric movement of an optical disk medium in the form of a change of the quantity of light received by a photodetector. CONSTITUTION:The parallel luminous fluxes reflected from a boundary part 11 straight through a half mirror 14 and is received by a photodetector 15. The change of a variable density image is produced on the photodetecting surface of the detector 15 in response to an information recording area (pregroup processed part) Rg and a non-recording area (pregroup unprocessed part) Rn. For the change of a distribution of the received light quantity and intensity, the position change of the part 11 produced by an eccentric movement can be detected as the change of the received quantity of light having high sensitivity. When the position of the part 11 is moved by the eccentricity, the output of the detector 15 is reduced at the inner side and increased at the outer side to show the relationship between the eccentric degree and the received light quantity. Thus it is possible to obtain the information on eccentricity with high sensitivity.

Description

[Detailed Description of the Invention] [Summary] The amount of eccentricity of an optical disc medium is detected by irradiating light onto the boundary between an information recording area and a non-recording area of an optical disc medium, and photoelectrically converting the brightness of the reflected light. It is used for.

[Industrial application field]

The present invention relates to an optical disk device such as an optical disk device or a magneto-optical disk device, and more particularly to a method for detecting the amount of eccentricity of an optical disk medium.

In recent years, with the increase in speed and capacity of electronic computers, storage devices, which are the main part of computers, are also required to have higher density and larger capacity. Currently, magnetic storage devices such as magnetic disks, which are easy to record and play back, are the mainstream, but optical disk drives or magneto-optical disk drives that optically record and play back information are, in principle, several orders of magnitude better than current magnetic disks. It is attracting attention as a recording medium that can provide high recording density, access time comparable to magnetic disks, and low bit cost comparable to magnetic tape.

[Conventional technology]

In an optical disc device, it is necessary to position a minute light spot formed by a lens at a predetermined position on an optical disc medium (hereinafter referred to as medium in 11). For this purpose, we use a pre-group method in which grooves with a phase structure for positioning are formed in advance on the medium.
A common method is to obtain a track error signal together with a required information signal.

FIG. 5 shows a principle diagram of a conventional trunk error signal. In the figure, 1 is a medium, 2 is a width of about 1 micron and a depth of λ/
8 (λ is the wavelength of the laser beam) and is called a trunk. The trunk 2 is formed in a concentric circle shape on the disc-shaped medium 1, and the concentric circle that is closer to the center is called the inside (innet) and the one that is farther from the center is called the outside (outer).

Reference numeral 3 denotes an objective lens which irradiates the medium 1-A with a minute spot of laser light. Reference numeral 4 denotes a semiconductor laser, and the emitted light from the semiconductor laser 4 is converted into a parallel beam by a collimating lens 5, refracted at a right angle by a polarizing beam splitter 6, and formed into a minute light spot on the trunk 2 via an objective lens 3. The reflected light from the minute light beams 1 through 1-rack 2'2 travels backward through the objective lens 3, straight through the polarizing beam splitter 6, and is received by the two-split photodetector 8 via the light receiving lens 7.

The optical plane intensity of the light receiving surface of the two-split photodetector 8 is projected weakly on the groove bottom and strongly on the groove edge due to optical interference between the groove bottom and the groove edge of the track 2.

When such an optical plane intensity characteristic is divided into two by the two-split photodetector 8 and inputted to the differential amplifier 9, the waveform of the track error signal as shown in the figure is obtained at the output terminal P thereof.

This track error signal waveform is a waveform when a minute light spot moves on the track 2 from 1nner to outer, and a zero cross point without a stepped portion indicates the center position of each track. When the minute light spot moves from 1nner to outer, the waveform appears with the slope including the zero cross point of the stepped portion reversed.

Therefore, if this track error signal is fed back to the minute optical spot moving device, it is possible to always follow the target track despite the eccentricity of the medium. This is the so-called trasoking servo.

[Problem that the invention seeks to solve]

When a medium is mounted on a spindle of an optical disk device and rotated, the medium rotates eccentrically due to mechanical accuracy errors, and the amount of eccentricity can reach several hundred microns. Since the width of the trunk is about 1 micron, it will cross several hundred tracks in one revolution.

Because of the large amount of eccentricity of the trunk, the conventional tracking servo system has the disadvantage that it is difficult to obtain high positioning accuracy in real time in the case of high-speed access.

The present invention was created in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide an eccentricity detection method that can detect the eccentricity of a medium in real time and obtain high positioning accuracy.

[Means to solve the problem]

FIG. 1 shows a diagram explaining the principle of the present invention. Figure smell;
Reference numeral 1 denotes an optical disc medium, and a boundary 1 between an information recording area Rg and a non-recording area Rn on its recording surface.
1 includes an optical system 12 that irradiates a parallel light beam with a diameter slightly larger than the predicted maximum eccentricity of the optical disk medium 1 via a half mirror 14; A photodetector 1 that receives light through
5, and a circuit breaker 16 that cuts off the dark current of the photodetector 15.

The amount of eccentricity is detected by detecting the amount of movement of the grayscale image of the reflected light from the boundary portion 11 that occurs with the eccentric movement of the optical disk medium 1 as a change in the amount of light received by the photodetector 15. can do.

[Effect]

FIG. 2 shows the intensity distribution of the amount of light received by the photodetector 15 in the present invention. When the optical disk medium 1 in FIG. 1 is decentered to 1nner, the intensity distribution of the amount of light received by the photodetector 15 becomes dark as shown at 181 in FIG. When the brightness and darkness are balanced as shown in FIG. 2(b) and the optical disk medium 1 is eccentric to the outer side, the light becomes bright as shown in FIG. 2+c). Therefore, by setting the diameter W of the parallel light beam to be slightly larger than the predicted maximum eccentricity, a change in the position of the boundary portion 11 can be detected as a change in the amount of received light with high sensitivity.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In order to make the explanation of the configuration and operation easier to understand, each figure is shown in detail, the same parts are given the same reference numerals, and repeated explanation thereof will be omitted.

FIG. 1 shows a diagram of the principle of the present invention. In the figure, reference numeral 12 denotes an optical system, which is composed of a light emitting element 13 (not necessarily the semiconductor laser 4) and a collimating lens 5 that produces a parallel beam of light.
” Boundary part 1 between information recording area Rg and non-recording area Rn
1 is irradiated with a parallel beam of light.

The diameter W of the parallel light beam is set to be slightly larger than the predicted maximum eccentricity of the optical disk medium 1.

The reason why the parallel light beam is used here is to reduce the influence of undulation of the optical disk medium 1.

The parallel light beam reflected from the boundary part 11 passes through the half mirror 1
4 and is received by a photodetector 15. Photodetector 15
There is an information recording area (pre-group processing section) on the light receiving surface.
Rg and non-recording area (pre-group non-processed area) Changes in gradation image corresponding to Rn appear.

The change in the intensity distribution of the amount of received light is as explained in FIG. 2, and the change in the position of the boundary portion 11 that occurs due to the eccentric movement can be detected as a change in the amount of received light with high sensitivity.

FIG. 3 shows the output characteristics of the photodetector in the present invention. In the figure, when the position of the boundary portion 11 moves with eccentricity, the output of the photodetector 15 changes weakly at 1nner (strongly changes at outer) as shown, and the relationship between the amount of eccentricity and the amount of received light is expressed.

In the figure, d is a dark current, and in order to extract only eccentricity information, the circuit breaker shown in FIG. I'm going to have a good time.

Therefore, the diameter W of the parallel light beam is determined by the optical disk medium 1
Set slightly larger than the expected maximum eccentricity. In other words, by setting the width W of the light receiving surface of the photodetector 15 to be slightly larger than the predicted maximum eccentricity of the optical disk medium l, highly sensitive eccentricity information can be obtained.

FIG. 4 shows a block diagram illustrating an applied embodiment of the present invention. In the figure, reference numeral 21 denotes a moving distance measuring device for a carriage mounted with an optical head and moving in the radial direction of an optical disk medium.The analog type uses a photoelectric potentiometer, and the digital type uses a slit plate. The method used is known.

22 is an eccentric amount detector of the present invention, and 16 is a high-pass filter. By adding only the eccentricity information of the output of the moving distance measuring device 21 and the output of the eccentricity amount detector 22 in the adder 23,
At its output terminal Q, relative position information between the carriage and the trunk of the optical disk medium can be detected.

〔Effect of the invention〕

As described above in detail, the optical disk medium eccentricity detection method of the present invention has the effect of enabling faster access in an optical disk device.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is the intensity distribution of the amount of light received by the photodetector 15 in the present invention, Fig. 3 is the output characteristic of the photodetector in the present invention, and Fig. 4 is an application of the present invention. FIG. 5 is a block diagram illustrating an embodiment of the present invention. FIG. 5 shows a principle diagram of a conventional track error signal. In the figure, 1 is an optical disc medium, 11 is a boundary part,
12 is an optical system, 14 is a half mirror 115 is a photodetector,
16 indicates a circuit breaker, respectively.

Claims (1)

[Claims] An optical system that irradiates a boundary (11) between an information recording area and a non-recording area of an optical disc medium (1) with a parallel light beam having a diameter larger than the eccentricity of the optical disc medium (1). System (1
2) and a photodetector (15) that receives reflected light from the boundary portion (11), the boundary portion (11) occurring due to eccentricity of the optical disk medium (1). 11) A method for detecting the amount of eccentricity of an optical disk medium, characterized in that the amount of eccentricity is detected by detecting the amount of movement of the photodetector (15) as a change in the amount of light received by the photodetector (15).