JPS645376B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a position detection device, and in particular, is capable of accurately detecting a so-called tracking error in which a light spot deviates from a portion having a diffraction effect on a target object having a portion that diffracts light. The present invention relates to a position detection device.

In general, it can be assumed that the part having the diffraction effect on a target object having a part that diffracts light is provided in a band shape, or is substantially formed in a band shape in the low frequency region to be controlled.
Controlling the light spot so that it lies on this band shape will be referred to as tracking control.

As a means for detecting a tracking error, there is a method of detecting the amount of imbalance in a far-field pattern of light diffracted and reflected from the position of an information track (hereinafter referred to as a track) on a target object. This is called a far-field method, and will be explained using FIGS. 1 and 2.

FIG. 1 is an explanatory diagram of the principle of the far-field system, in which 1 is an objective lens, 2 is a disk as a target object, and 3 is a pit formed on the disk 2. A large number of pits 3 are formed on the disk 2, and information is recorded on the disk 2 in the form of these pits 3. Reference numeral 4 denotes an incident light beam, and it is assumed that the incident light beam 4 is focused onto the disk 2 by the objective lens 1.

If the light spot is placed on the pit 3 without any horizontal deviation, the reflected light from the disk 2 will be symmetrical, as shown by the solid line A in FIG. 1A. Of course, where there is no pit 3, there is left-right symmetry as shown by the solid line B in FIG. 1B. However, when the light spot deviates from pit 3, the first
As shown by the solid line C in FIG.

As described above, the principle of the far-field method is to detect a tracking error based on the left and right unbalanced components of the far-field pattern that occur when the light spot deviates from the pit 3.

FIG. 2 is a block diagram of a typical optical system of the far-field system, in which 5 is a semiconductor laser diode, 6 is a collimating lens, 7 is a beam splitter, and 8 is a two-split photodetector. The light emitted from the semiconductor laser diode 5 (indicated by the broken line in the figure) is collimated by the collimating lens 6, passes through the beam splitter 7 and the objective lens 1, and is focused on the track portion of the disk 2 (in the figure, the pit 3). be done. The reflected light from the disk 2 (indicated by a solid line in the figure) passes through the objective lens 1 and the beam splitter 7 and enters the two-split photodetector 8.

As described above, the far-field method has the advantage of a simple optical system, but it has the problem that erroneous tracking signals are generated due to the inclination of the reflective surface of the disk 2. That is, the third
As shown in the figure, if the reflective surface of the disk 2 is tilted away from the orientation perpendicular to the optical axis of the incident light, the light spot will be located exactly at the pit 3 part on the track as shown in Figure 3a. However, the reflected light (d) will be left and right unbalanced. Also, pit 3 and pit 3 on the track
As shown in FIG. 3b, the reflected light H becomes unbalanced between the left and right sides. For this reason, the tracking servo works to cancel out this tilt error signal, so that the light spot deviates from the track position on the disk 2.

In view of the above points, the present invention takes advantage of the fact that the farfield pattern in the non-pitted area accurately has only information on the inclination of the disk, and makes corrections corresponding to the inclination of the disk from the farfield pattern in the non-pitted area. The present invention provides a position detection device that suppresses the influence of the disk tilt on the tracking error signal to an extremely small level by obtaining a signal and correcting the tracking error signal using the correction signal. The explanation will be based on.

FIG. 4 is an explanatory diagram of the tracking error signal, and as shown in FIG.
It is recorded in the form of Pit 3. When the light spot is exactly on the track and there is no tilt of the disk 2, the tracking error signal is zero as shown in FIG. 4b. If the light spot is exactly on the track, but the disk 2 is tilted, the tracking error signal will be as shown in FIG. 4c. Normally, since the light spot is exactly on the track, the tracking error signal should be zero. On the other hand, the unevenness signal obtained by reproducing the recorded signal is small at the pit 3 portion and large at the portion other than the pit 3, as shown in FIG. 4d.

As is clear from FIG. 3b, the portion of the tracking error signal shown in FIG. 4c that corresponds to the pit-free portion only shows information on the inclination of the disk 2. Therefore, the zero-crossing point of the unevenness signal shown in FIG. 4d is detected to distinguish pitted portions from non-pitted portions, and the amount of the non-pitted portion of the tracking error signal shown in FIG. 4c is extracted. By correcting the tracking error signal accordingly, the influence of the tilt of the disk 2 can be significantly reduced.

FIG. 5 is a circuit block diagram of the tracking servo system. The optical system used is the same as that shown in FIG. 2, and details are omitted. Reference numeral 9 designates an uneven signal reproducing section, 10 a non-pitted portion tracking error signal extraction section, 11 a correction adjustment section, 12 a differential tracking error extraction section, 13 an amplifier section, and 14 a tracking actuator. The concavo-convex signal of the disk 2 enters a two-split photodetector 8, and both outputs from the two-split photodetector 8 are input to a concavo-convex signal reproducing section 9 and a differential tracking error extracting section 12. The concavo-convex signal reproducing section 9 reproduces the concavo-convex signal by the sum of both outputs from the two-split photodetector 8. On the other hand, the differential tracking error extraction section 12 generates a tracking error signal based on the difference between the two outputs from the two-split photodetector 8. This tracking error signal is extracted from the non-pitted portion tracking error signal extractor 10.
and is input to the amplification section 13. The non-pitted portion tracking error signal extraction section 10 consists of a gate circuit, and extracts a tracking error signal from only the non-pitted portion based on the unevenness signal from the unevenness signal reproducing section 9. Non-pitted portion tracking error signal extraction unit 10
The output is converted by the correction adjustment section 11 according to a predetermined relationship, and is added to the output signal of the differential tracking error extraction section 12 at the amplification section 13. A tracking actuator 14 is controlled by the output of the amplifying section 13.

In this way, the influence of the disk tilt component is removed from the tracking error signal in the servo loop by utilizing the fact that the non-pitted portion tracking error signal includes only disk tilt information.

FIG. 6 shows another embodiment, and the same components as those shown in FIG. 5 are given the same reference numerals and their explanations will be omitted. As is clear from Fig. 4c, the effect of the tilt of the disk 2 is extremely large in the non-pitted part, and since this part does not contain a tracking error signal, it is better to discard the tracking error signal in the non-pitted part. Accurate tracking error signals can be obtained. Therefore, in this embodiment, a pit part tracking error signal extracting part 15 is provided which extracts a tracking error signal of only the bit part from the output signal of the differential tracking error extracting part 12 under the control of the output signal of the unevenness signal reproducing part 9. The output signal of the pit tracking error signal extracting section 15 is input to the amplifying section 13.

As explained above, according to the position detection device according to the present invention, a correction signal corresponding to the disk inclination is obtained from the non-pitted portion tracking error signal, and the tracking error signal is corrected with this correction signal. The influence of the tilt of the target object on the tracking error signal can be suppressed to an extremely low level, and its industrial value is extremely high.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the principle of the far-field method.
Figure 2 is a configuration diagram of a general optical system in the far-field method, Figure 3 is an explanatory diagram of the far-field pattern when the disk is tilted, and Figures 4-
6 shows an embodiment of the present invention, FIG. 4 is an explanatory diagram of a tracking error signal, FIG. 5 is a circuit block diagram of a tracking servo system, and FIG. 6 is a diagram of a tracking servo system in another embodiment. FIG. 3 is a circuit block diagram. 1...Objective lens, 2...Disc (target object),
3... Pit, 4... Incident light beam, 5... Semiconductor laser diode, 6... Collimating lens, 7... Beam splitter, 8... 2-split photodetector, 9... Concave/convex signal reproducing unit, 10... Tracking error signal extraction in non-pitted area 11... Correction adjustment section, 12... Differential tracking error extraction section, 13... Amplification section, 14... Tracking actuator, 15... Pit section tracking error signal extraction section.

Claims (1)

[Claims] 1. A light source, a light focusing means for focusing light emitted from the light source onto a target object, a light detection means for detecting reflected light from the target object, and a light detection means for detecting light reflected from the light detection means on the target object. unevenness signal reproducing means for optically reproducing the uneven recording signal; and differentially extracting a tracking error signal indicating that the focused light spot has deviated from the information track on the target object from the output signal of the light detection means. a differential tracking error extraction means for extracting a tracking error signal of only a pitless portion of the information track from the tracking error signal under the control of the unevenness signal; A position detecting device comprising: a correction signal inserting means for inserting a correction signal corresponding to the pitless portion tracking error signal at a predetermined location in a tracking servo loop including the error extracting means.