JPH0834005B2 - Optical disk device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of an optical disk device, and more particularly to improving the track servo during random access.

2. Description of the Related Art In an optical disk device, there is a need for speeding up random access for moving to a target location at high speed for writing or reading. In this case, when moving to a predetermined track, the tracks from the current track to the target track are counted while moving, and the track is moved to that place.
At this time, the disk is rotating and the disk is generally eccentric. Therefore, an error occurs in the track count amount, the track servo is performed, the address is read from the track, and the correction operation is repeated to search for the target track.

Problems to be Solved by the Invention Due to the above, even if the moving speed is increased, the search time cannot be shortened so much. Further, when the track servo is performed after the movement, there is a drawback that even if the optical head is stopped, it has a relative speed due to the eccentricity of the disk and cannot be pulled into the track servo. Therefore, the track cross signal requires two phases with different phase shifts from the track. This includes a carrier such as a video disk, and in the case of a 1 / 4λ to 1 / 6λ pit, it is possible to detect the relative direction from two phases of the reproduction carrier and the track error signal. However, the once-writable disk (DR
In AW) devices, etc., only pregrooves with a depth of 1 / 8λ are generally used, and before writing, only a single-phase signal of a track error signal, which is a so-called push-pull signal, was obtained. In view of these, it is an object of the present invention to provide an optical disk device capable of two-phase detection even when accessing a disk that does not include a carrier with a track of 1 / 8λ.

Means for Solving the Problems The present invention aims to obtain two phases having the same phase by the conventional track detection by the main beam and the sub-beam, and at least two spots are formed on the track of the optical disk. If one spot is located at the center of the track, the other is placed so as to cover approximately half the track, and the reflected light from each spot is taken out by a detector that is divided into two parts in parallel with the track. This is an optical disk device in which the output is converted into one signal through a differential amplifier, the relative directions of the light beam and the track are detected from the two signals for each spot, and the signal is moved to a predetermined track.

Example The present invention will be described by way of an example. FIG. 1 shows an example of a structural drawing of the optical head of the present invention. The light of the laser 1 passes through the collimator lens 2 and the grating 3 to diffract the light beam. At this time, the 0th-order diffracted beam is used as the main light source as in the case without the grating 3. At this time, in the DRAW head, the first-order diffracted light needs to be a fraction of the main diffracted light. That is, when writing to the disk, only the 0th-order beam obtains the writing power, and the writing power is not written by the first-order diffracted light. As described above, the main and sub beams form spots on the track surface of the optical disk 7 through the beam splitter 4 and the 1/4 wavelength plate 5 and the objective lens 6, and the reflected light is reflected by the beam splitter 4 at the main detector. 8 and auxiliary detector 9. Usually, a means for focusing servo by the cylindrical lens 10 or the like is included here, but it is omitted here. Here, the spot for the disk surface is the main spot P ₁
90 and sub Supotsuto P ₂ whereas Toratsukupitsuchi P ₁ is P ₂ if the center of the track is shifted half track as in Figure 2 a
° Try to shift. Detector 8,9 is taken out by a differential amplifier A _1, A ₂ the output of each divided into two parts in the direction parallel with the track, to obtain an error signal TE _1, TE _2. If there is a spot in the center of the track, the intensity of the reflected light is symmetrical with respect to the center of the light, but if it is shifted by half as shown in Fig. 2, the phase of the reflected wavelength is changed by the track and the intensity of the reflected light is changed. Are asymmetric, which causes a difference in the output of the detector.
Therefore, as shown in FIG. 2C, when the error signal TE ₁ corresponding to the main beam is 0, the signal TE ₂ corresponding to the sub beam becomes maximum, and when the beam and the track are moved relatively,
Two-phase signals are obtained as shown in FIG. Therefore, the relative direction to the track can be extracted from this signal. Therefore, the relative direction detection based on the two-phase signals is conventionally known and omitted. Even if the moving speed of the optical head becomes slower than the moving speed of the track due to the eccentricity, it is possible to reliably count to the predetermined track. Further, it is possible to surely perform the pull-in of the track servo with the target track. Here, although the sub-beam is made by grating, one laser emission source may be used. In this case, the degree of freedom is further increased by operating only during access.

According to the present invention, the reflected light of the spot in the center of the track,
Each detection signal is obtained from the reflected light of the spot that covers almost half of the track. Since these two detection signals have a phase difference of approximately 90 degrees, it is easy to detect the direction in which the track crosses, and high-speed access to a predetermined track is possible. You can

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is a diagram for explaining its operation.

Claims (1)

[Claims] 1. An apparatus for moving a light beam to a predetermined track of an optical disk for recording and reproducing, wherein first and second spots are formed on the optical disk, and the first spot is located at the center of the track of the disk. When the second spot is positioned so as to cover approximately half of the track, the first and second spots respectively correspond to the reflected light of the first and second spots in a direction parallel to the track. First and second to detect with a detector divided into two
Detection means, phase comparison means for comparing the phases of the first and second detection outputs that have passed through the differential amplifier of the detector output divided into two, and the movement of the light beam with respect to the track by the output of the phase comparison means. An optical disk device comprising a detection means for detecting a direction.