JPH054734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a disk inclination detection device, and more particularly, to an apparatus for detecting the inclination of the disk, which is installed in an optical disc recording and reproducing device.

BACKGROUND ART Conventionally, there have been optically readable information recording disks (hereinafter referred to as "disks"). It is difficult for this disk to maintain its flatness permanently, and the height between the center and the outer edge often changes and deforms into a bowl shape. Inclination may occur on the disk surface at the inner and outer peripheral edges.

When recording information on a disk that has undergone the above deformation, the light beam is not irradiated perpendicularly to the disk surface, so the beam spot is distorted and distorted pits are formed, or sometimes no pits are formed at all. If the pit is distorted, the frequency characteristics during playback will deteriorate, and the above-mentioned slope at the inner peripheral edge of the disc will be a particular problem in the CAV system. Furthermore, when reproducing a disc, the beam reflected by the disc does not return accurately to the pickup, making it impossible to accurately detect information.

For this reason, there have conventionally been disk reproducing apparatuses that use a device as shown in FIG. 4 to detect the inclination of the disk and control the attitude of the recording/reproducing element in accordance with the inclination of the disk. In FIG. 4, a write-once type disk 10 has a medium 12 on a transparent substrate 11.
It is equipped with a membrane. light emitting diode 1
3 and the light receiving elements 14 and 15 are located along the radial direction of the disk 10. Light receiving element 14,1
5 outputs a signal of a level corresponding to the amount of light beam received from the light emitting diode 13 reflected by the medium 12 of the disk 10, and the light receiving elements 14 and 15
Each output signal is differentially amplified by a differential amplifier 16, and a signal having a level corresponding to the inclination of the disk 10 is outputted from a terminal 17.

Problems to be Solved by the Invention In the above-mentioned write-once type disk 10, pits are formed by irradiating a laser beam during recording to evaporate a part of the medium 12, so there are no pits in the recorded area. The light reflectance is low, and the unrecorded portion has a high light reflectance.

For this reason, for example, if the inner circumferential portion of the disk 10 from the position corresponding to the light emitting diode 13 is a recorded portion and the outer circumferential portion is an unrecorded portion, the differential amplifier can be used even if the disk 10 is not tilted. There was a problem in that the output level of the disc 16 changed and an erroneous signal indicating the tilt of the disk 10 was output.

Further, as shown in FIG. 5, in a disk 19 having an air sandwich structure in which two disks 10 are placed facing each other with a spacer 18 in between, the back surface (top surface)
There was a problem in that the light beam reflected by the disk enters the light-receiving elements 14 and 15 as shown by broken lines in the figure and causes disturbance, making it impossible to accurately detect the inclination of the disk 19.

The present invention has been made in view of these points, and it is an object of the present invention to provide a disk inclination detection device capable of accurate inclination detection.

Means for Solving the Problems In the present invention, a pair of detection elements is irradiated with a portion of the light beam reflected by the disk, and the amount of irradiation of each element changes depending on the inclination of the disk.

The RF signal detection circuit detects whether information is recorded based on the presence or absence of high frequency components of the electrical signal.

The gain switching circuit switches the amplification degree for each output signal of the pair of photodetecting elements according to the detection signal of the RF signal detection circuit.

The differential amplifier differentially amplifies the output signals of the pair of photodetecting elements amplified by the gain switching circuit to generate a signal having a level corresponding to the degree of inclination of the disk.

Function In the present invention, the light beam is focused on the disk, and the light beam reflected by the back surface of the disk does not enter the optical system. The gain of the output signal of the photodetector element is switched, so that the differential output/disk tilt amount characteristics are always kept constant.

Embodiment FIG. 1 shows a block system diagram of an embodiment of the apparatus of the present invention. In the figure, a laser beam emitted from a laser diode 21 passes through a prism 22 constituting an optical system, and is focused onto the medium 12 of the disk 10 by an objective lens 23.

Therefore, when recording and reproducing on the disk 19 with the air sandwich structure as shown in FIG.
The light beam reflected at
It never enters 3. Therefore, the light beam reflected on the back surface does not enter the photodetecting elements 27a, 27b as a disturbance.

The laser beam reflected by the disk 10 passes through the objective lens 23, is reflected by the prism 22, and is guided to the half mirror 25. half mirror 2
The laser beam that has passed through 5 is irradiated onto a photodetector 26, where it is photoelectrically converted. Further, the laser beam reflected by the half mirror 25 is irradiated onto adjacent photodetecting elements 27a and 27b. By the way, if the disk 10 is horizontal as shown by the solid line, the reflected light beam of the half mirror 25 will be irradiated onto the boundary between the photodetecting elements 27a and 27b.
If the disk 10 is tilted as shown by the broken line (or one-dot chain line), the reflected light beam of the half mirror 25 will be irradiated with a bias toward the photodetecting element 27a (or 27b).

The photodetector element 26 photoelectrically converts the light beam and outputs a signal whose level changes depending on the presence or absence of pits in the medium 12 of the disk 10, and this output signal is sent from a terminal 28 to a reproduction circuit (not shown) in the next stage. ) and is also supplied to the RF signal detection circuit 29. The RF signal detection circuit 29 includes a photodetection element 26
Detects the presence or absence of high frequency components in the output signal. As a result, when a high frequency component is detected by scanning the information-recorded part where pits are formed on the disc 10, a high-frequency component is detected by scanning the unrecorded part where pits are not formed, for example at H level. When not, an RF detection signal that is at L level is generated and supplied to the gain switching circuit 30.

Further, the signals photoelectrically converted by the photodetecting elements 27a and 27b are automatically gain-controlled by AGC circuits 31 and 32, respectively, and are made to the same level during recording and playback, which have different amounts of light. The signal is supplied to an amplifier 33. Gain switching circuit 3
0 switches the amplification degree for the output signals of the AGC circuits 31 and 32 when the RF detection signal is at L level and at H level, and sends each signal to the inverting input terminal and non-inverting input terminal of the differential amplifier 33. supply to each.

Here, if there is no gain switching circuit 30,
The output of the differential amplifier 33 and the amount of inclination of the disk have a relationship as shown by the solid line in FIG. The relationship is as shown below. Therefore, the gain switching circuit 30 corrects the characteristic shown by the solid line to become the characteristic shown by the solid line when the recorded portion of the disk 10 is scanned with the RF detection signal at the H level. In this way, the differential amplifier 3
The output of No. 3 is always made to have a solid line characteristic and is supplied to the non-inverting input terminal of the differential amplifier 34.

Further, the tracking error signal coming from the terminal 35 is supplied to the tracking coil 36, whereby the objective lens 23 is displaced and tracking control is performed. At the same time, a low frequency component of the tracking error signal is extracted by a low frequency filter 37 and supplied to an inverting input terminal of a differential amplifier 34. The differential amplifier 34 subtracts the tracking error signal from the low-pass filter 37 from the level of the disk tilt detection signal from the differential amplifier 33 and outputs the result. This signal is supplied from a terminal 38 to a tilt motor (not shown) that displaces the attitude of the optical head (prism 22, objective lens 23, etc.) which is a recording/reproducing element.

In this way, the gain switching circuit 30 makes the differential output/disk tilt amount characteristics constant between the recorded portion and the unrecorded portion of the disk 10, and there is no possibility of erroneously detecting the tilt amount.

Furthermore, since the tilt is detected using a laser beam used for recording and reproducing information, there is no need to provide a light source exclusively for tilt detection.

Effects of the Invention As described above, in the device of the present invention, the reflected light beam from the back surface of the disk does not enter the optical system, the reflected light beam from the back surface does not cause disturbance, and the gain can be switched depending on whether or not information is recorded on the disk. By doing so, the differential output/slope characteristic becomes constant at all times, and has features such as being able to accurately detect the slope.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of an embodiment of the device of the present invention, FIG. 2 is a diagram for explaining the optical path of the laser beam shown in FIG. 1, and FIG. Diagram for explaining the slope amount characteristics, 4th
5 and 5 are diagrams showing the configuration of each example of a conventional device. 21... Laser diode, 23... Objective lens, 25... Half mirror, 26, 27a, 27
b...Photodetection element, 29...RF signal detection circuit,
30... Gain switching circuit, 31, 32... AGC
Circuit, 33, 34...Differential amplifier.

Claims (1)

[Claims] 1. An optical system condenses and irradiates a light beam onto a disk to record information, and converts the light beam reflected by the disk and incident on the optical system into an electrical signal to record information. A disk inclination detection device installed in a playback device and detecting the inclination of the disk is irradiated with a portion of the light beam reflected by the disk, and the amount of irradiation varies depending on the inclination of the disk. an RF signal detection circuit that detects whether or not information is recorded based on the presence or absence of a high frequency component of the electric signal; a gain switching circuit that switches according to the detection signal; and a differential circuit that differentially amplifies the output signals of the pair of photodetecting elements amplified by the gain switching circuit to generate a signal with a level corresponding to the degree of inclination of the disk. A disk inclination detection device characterized by comprising a dynamic amplifier.