JPH03216817A - Optical disk device - Google Patents

Abstract

PURPOSE:To prevent the damage of an optical disk and an objective lens to improve the reliability by providing a focusing control abnormality detecting circuit consisting of an adding circuit which detects the quantity of reflected light and a comparator circuit which detects the level of the quantity of reflected light. CONSTITUTION:All outputs of detectors in a pickup 3 are applied to a reflected light quantity sum detecting circuit 10 to obtain a reflected light quantity sum signal. The output of this circuit 10 is applied to a comparator 11 and is compared with the output of a reference voltage generating circuit 12. The output of the comparator 11 is applied to a focusing control circuit 5, and a focusing control on/off switch in the focusing control circuit 5 is turned off by a focusing abnormality detection signal 22 of the output of the comparator 11 if the focusing control is abnormal. Thus, possibility of contacting between the optical disk and the objective lens is greatly reduced to prevent flaws of the optical disk and the damage of the objective lens, and the reliability of an optical disk device is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application In recent years, write-on optical disc devices such as compact discs (CDs) and laser discs (LDs), as well as document files, data files, and image files, have become widespread.

Such an optical disk device includes an optical disk for recording and reproducing information, a disk motor for rotationally driving the optical disk, a focusing control circuit for focusing a light beam for recording information on the optical disk, and reproducing information from the original disk. A focused light beam spot with a diameter of about 1 μm is placed on the signal recording track on the optical disk by 0.1 μm.
It consists of a tracking control circuit for accurate tracking with μm precision, a pickup circuit for recording and reproducing signals via a light beam, and the like.

The present invention relates to a focusing control circuit for such an optical disc device. If the focusing control circuit malfunctions, there is a possibility that the objective lens and the optical disk will come into contact with each other, causing great damage to the apparatus. The present invention provides a simple and inexpensive device that prevents contact between an objective lens and an optical disk even when a focusing control circuit malfunctions and improves the reliability of an optical disk device.

Conventional technology Conventionally, optical disc devices have a focusing control circuit that has a ninth focusing control circuit to protect the optical disc, objective lens, etc. in the event of a malfunction.
It is equipped with a protection circuit as shown in the figure. In FIG. 9, a disk motor 2 is rotating an optical disk l, and a light beam is irradiated onto the optical disk 1 through a pickup 3 and an objective lens 4 attached to the pickup 3, and the reflected light is reflected inside the pickup 3. The output of the detector is received by the focusing control circuit 5. R
It is applied to the F detection circuit 6 and the address detection circuit 7.

Further, the output of the RF detection circuit is applied to the signal processing circuit 8 and also to the focusing control circuit 5 at the same time. Further, the output of the address detection circuit is applied to the signal processing circuit 8 and simultaneously to the focusing control circuit 5. Here, the focusing control circuit 5 drives the objective lens 4 in the vertical direction so that the focus of the light beam emitted from the inside of the pickup 3 is always on the recording surface of the optical disk 1, and when the focusing control is lost, the RF detection circuit The focusing control circuit 5 immediately stops operating when there is no output from the address detection circuit 6 or when there is no output from the address detection circuit 7. Also, linear motor 9
is for moving the big up 3 in the radial direction. Furthermore, as seen in Japanese Patent Laid-Open No. 62-154235, a method has been proposed in which the shape of the detector inside the pickup 3 for detecting the focus error signal is devised to detect abnormalities in the focusing operation.

Problems to be Solved by the Invention In the case of the above-mentioned conventional example, the circuit configuration is complicated, and it is easily affected by dropouts and scratches on the optical disk, resulting in poor reliability. Furthermore, when devising the shape of the detector as in Japanese Patent Application Laid-Open No. 62-154235, etc., there is a drawback that the detector has special specifications and becomes expensive.

In view of the above-mentioned problems, the present invention provides an inexpensive and highly reliable optical disc and objective lens protection device.

Means for Solving the Problems The structure of the present invention is characterized by having a flashing control abnormality detection circuit consisting of a simple addition circuit for detecting the amount of reflected light and a comparator circuit for detecting the level of the amount of reflected light. A contact prevention means is provided to prevent contact between the optical disc and the objective lens.

Function: By providing the above-mentioned contact prevention means, the present invention drastically reduces the possibility of contact between the optical disk and the objective lens, eliminates damage to the optical disk and damage to the objective lens, and improves the reliability of the optical disk device.

Embodiment FIG. 1 shows a first embodiment of the present invention, in which an optical disk 1 is rotationally driven by a disk motor. All the outputs of the detectors inside the pickup 3 are applied to a reflected light amount sum detection circuit 10, where a reflected light amount sum signal is obtained. Further, the output of the reflected light amount sum detection circuit 10 is applied to a comparator 11 and compared with the output of the reference voltage generation circuit 12. The output of the comparator 11 is applied to the focusing control circuit 5, and when the focusing control is abnormal, a focusing control ON/OFF switch inside the focusing control circuit 5 is turned off by a focusing abnormality detection signal 22 output from the comparator 11. That is, the output of the reference voltage generating circuit l2 is set in advance to about 1/3 to 1/'2 of the maximum value of the sum of reflected light amounts at a focused point, which is predicted based on the reflectance of the optical disc, the power of the light beam, etc. If the sum of the amounts of reflected light becomes less than the reference voltage, it is assumed that the focusing control has failed due to a malfunction of the focusing control circuit, and the focusing control is forcibly stopped. Further, in this embodiment, the total sum of the outputs of the detectors is taken as the sum of reflected light amounts, but this is done to improve detection accuracy, and it is not necessary to take the total sum. For reference, FIG. 2 shows the output waveform of the sum of reflected light amounts when the objective lens approaches the optical disk. FIG. 3 is a second embodiment of the present invention, which shows the detection principle of the skew beam method. An optical axis 16 of a sub-beam for focusing is located a little apart from the optical axis 14 of the main beam, and is irradiated onto the optical disc 1 through the objective lens 4. Furthermore, optical disc 1
The reflected light is incident on the focusing detector 15 via the objective lens l. When the position of the optical disc 1 changes as shown in the optical disc position i13 (a, b, c), the output waveforms of the focusing detectors S1 and S2 become as shown in FIG. 4, and as the objective lens 4 approaches the optical disc 1, The position at which the reflected light enters the focusing detector changes. At the focal point position b, the amounts of light incident on the detectors S1 and 82 are equal. In the case of the focus error detection method using the skew beam method, the output levels of the detector 15, Sl and S2, change depending on the relative positional relationship between the objective lens 4 and the optical disk 1, so focusing can be performed by monitoring the output of the detector 15. The operating state of the control circuit can be known more accurately. That is, when the objective lens 4 moves toward the optical disk at the start of focusing control, the level of the detector S2 never reaches Vl, l2x during normal operation. During normal operation, the outputs of Sl and S2 are approximately at the same level, which is about 1 and 2'' of Vmax.

Therefore, as shown in FIG. 5, the output level of the reference voltage generation circuit 12 of the focusing control abnormality detection means is
By setting the level between Il3x and Vmax/2, it is possible to reliably detect that the objective lens 4 has come too close to the optical disk 1 in the event of a malfunction of the focusing control circuit, and by stopping the focusing control circuit, the objective lens 4 can be detected. Contact between the optical disc 1 and the optical disc 1 can be prevented. FIG. 6 shows another example of the focusing control abnormality detecting means, which indicates that the focusing control is abnormal even if the output of the focusing detector S2 mentioned above reaches a level of 1/'2 or less of VIll2x during the focusing control operation. The output of the reference voltage generating circuit 12 is set to about Vm-x/4', and when the output falls below that level, the focusing control circuit is stopped. Polarity inversion circuit 25
is for matching the polarity of the focusing control abnormality detection signal. Furthermore, FIG. 7 shows still another example of the focusing control abnormality detection means, which not only stops the focusing control circuit when an abnormality is detected in the focusing control circuit, as explained in the previous example, but also stops the focusing control circuit.
At the same time, it attempts to forcibly pull the objective lens 4 away from the optical disc 1.

Focusing control signal 20 is switched to switch 1 in normal state.
9. The voltage is applied to the objective lens driving voice coil 17 via the driving amplifier 18, so that the objective lens 4 is always in focus.
is driving. When an abnormality occurs in the focusing control, the abnormality detection signal 22 is applied to the switch 19 to turn off the focusing control circuit, and at the same time, the objective lens constant direction drive signal 21 is sent to the objective lens driving voice coil 17 via the drive amplifier 18. Applied to objective lens 4
is pulled in the direction away from the optical disc 1. Here, the objective lens constant direction drive signal 21 returns to Ov after a predetermined period of time, and the objective lens 4 also returns to its initial position.

FIG. 8 shows yet another example, which is a further improvement of the embodiments shown in FIGS. 5 and 6. The present embodiment is configured so that an abnormality in the focusing control circuit can be stably detected even when the reflectance of the optical disc 1 or the power of the optical beam changes. Since the focusing detector S1 always outputs Vmax output once at the start of operation, this is input to the peak hold circuit 23 to hold the level, and the attenuator 24 outputs the Vmax output to the comparator 1.
The optimum level for abnormality detection is input to S1 and compared with the output of S2 to obtain a focusing abnormality detection signal 22. The peak hold circuit 23 uses the memory of a microcomputer or the like to always take in the 31 disks at the start of the focusing control operation.

As described above, it is possible to provide a contact prevention means that prevents the objective lens from coming into contact with the optical disk in the event of a focusing control malfunction, etc., with a relatively simple configuration and at low cost. The contact prevention means according to the present invention can be applied to a wide range of optical disc devices in general, and is even more effective when the focus error detection method is the skew beam method, such as in optical disc glass master manufacturing machines. It is enormous.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a detection method for the sum of reflected light amounts in an optical disk device according to an embodiment of the present invention, FIG. 2 is a graph showing changes in the sum of reflected light amounts depending on the position of the objective lens, and FIG. 3 is a skew beam FIG. 4 is a diagram of the output waveform of a focusing detector using the skew beam method. FIG. 5 is a block diagram of a second embodiment of the focusing error detection means of the present invention. 6 is a block diagram of a third embodiment of the focusing control abnormality detection means, FIG. 7 is a block diagram of an embodiment that moves the objective lens away from the optical disk when a focusing control abnormality occurs, and FIG. 9 is a block diagram of an embodiment of the same peak hold circuit, and FIG. 9 is a block diagram of a conventional example. DESCRIPTION OF SYMBOLS 1... Optical disc, 2... Disk motor, 3... Pickup, 4... Objective lens, 5... Focusing control circuit, 6
...RF detection circuit, 7...Address detection circuit, 8...Signal processing circuit, 9...
Linear mode, 10...Reflected light amount sum detection circuit,
11...Comparator, 12...Reference voltage generation circuit, 15...Focusing detector, 17...Voice coil for driving objective lens, 18... ... Drive amplifier, 19 ... Switch, 22 ... Focusing control abnormality detection signal, 23 ... Peak halt circuit, 24 ...
...Atten evening.

Claims (5)

[Claims] (1) A driving means for rotationally driving an optical disk, which is an information recording medium for recording or reproducing information, and recording information on the optical disk by condensing and irradiating a light beam from a semiconductor laser or the like onto the optical disk through an objective lens. a pickup means for detecting reflected light from the optical disk and reading prerecorded information; and a focusing control means for controlling the position of the objective lens so that the light beam is focused on the recording surface of the optical disk. a focusing control abnormality detection means for detecting the amount of reflected light from the optical disc and detecting an abnormal state of the focusing control based on the level of the amount of reflected light; and when the focusing control is abnormal, the focusing control is stopped and the optical disc and the An optical disc device characterized by comprising a contact prevention means for preventing contact with an objective lens. (2) The focus error detection method of the focusing control means is a skew beam method that uses a sub-light beam for focusing separately from the main light beam for recording and reproducing, and the focusing error detection means detects errors from the optical disc. 2. The optical disc apparatus according to claim 1, further comprising contact prevention means for detecting an abnormality and stopping said focusing control means when the amount of reflected light exceeds a predetermined level. (3) The focusing control abnormality detection means includes contact prevention means for detecting an abnormality and stopping the focusing control means when the amount of reflected light from the optical disk becomes less than a predetermined level. Optical disk device. (4) Contact prevention in which the focusing control abnormality detection means detects an abnormality when the amount of light reflected from the optical disk reaches a predetermined level, stops the focusing control means, and forcibly moves the objective lens in a direction away from the optical disk. Claims 1 to 3 characterized by comprising means.
The optical disc device according to any one of the above. (5) At the start of control in which the focusing control means drives the objective lens so that the light beam is focused, the focusing control abnormality detection means holds the amount of reflected light to a peak, and the amount of reflected light reaches a predetermined level with respect to the peak held level. 4. The optical disc device according to claim 2, further comprising contact prevention means for detecting an abnormality and stopping the focusing control means when the focusing control means is stopped.