JPS63214933A - Method for detecting stain of lens for optical pick-up - Google Patents

Abstract

PURPOSE:To stably and securely detect the soil of the lens of an optical pick-up by executing the detecting decision of the stain of the lens of the optical pick-up according to the value of a focusing sum signal in a state in which focusing servo is executed to the surface of the substrate of the optical disk of the optical pick-up by a focusing servo system. CONSTITUTION:The threshold level of a comparator 15 is set so that an output signal from the comparator 15 goes to '0' when the stain of the lens of the optical pick-up 7 is less than an allowable limit in the state focusing on the surface of the substrate of the optical disk 6. If it is less than the allowable limit, the output signal (stain detection signal) from a D flip flop 16 goes to '0' and if it exceeds the allowable limit it goes to '1'. A control part 17 checks the output signal from the D flip flop 16 and decides that '0' does not mean the stain of the lens and '1' means the stain of the lens. At the time of executing the detecting decision, the focusing servo is executed to the surface of the substrate of the optical disk 6 and the optical pick-up 7 is in relatively nearly stopping state, and also the value of the focusing sum signal is kept nearly constant, so that the detection can be stably and securely executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for detecting dirt on a lens of an optical pickup in an optical disc device.

2. Description of the Related Art In a conventional optical disk device, dirt on the lens of an optical pickup is detected during a focus servo pull-in operation immediately after power is turned on. A method for detecting lens dirt will be described below.

When the device power is turned on, the optical pickup is continuously raised from a standby position away from the optical disk toward the optical disk. During this upward movement, the focus servo operation of the focus servo system is inhibited.

When focusing on the surface (lower surface) of the base material of the optical disc is detected by the differential signal of the focus error signal, the detection and determination of dirt on the lens of the optical pickup is performed from the value of the lens sum signal at that time. The optical pickup continues to rise even during this determination.

Note that, if dirt on the lens is not detected as a result of this detection judgment, the operation of the optical disc device is stopped. On the other hand, if no dirt on the lens is detected, the optical pickup is continued to be raised and focus servo is applied to the recording layer of the optical pickup.

FIG. 9 shows a circuit configuration for detecting lens dirt using the conventional method described above, where FE is a focus error signal and FS is a focus sum signal.

As is well known, the focus error signal FE is created by adding and subtracting the output signals of the split photodetector installed in the optical pickup, and the focus error signal FE is generated when the focus of the optical pickup is on the surface of the base material or recording layer of the optical disc. It is a bipolar signal that becomes zero when the focal point moves up and down, and becomes positive or negative as the focal point moves above and below it.

The focus sum signal FS is a sum signal of the output signals of the divided photodetectors, and is proportional to the amount of linearly incident light to the divided photodetectors. In other words, when the optical pink-up is focused on the surface of the base material of the optical disc, the value of the focus sum signal is inversely proportional to the degree of contamination of the lens of the optical pickup.

The focus sum signal FS is input to a binarization circuit 1 and is binarized at a certain threshold level. This binary signal is input to the D flip-flop 2.

The focus error signal FE is differentiated by a differentiating circuit 3,
The differential signal is binarized by a binarization circuit 4 at a certain threshold level. 5 is a D flip-flop for temporarily holding this binary signal.

In such a configuration, when the optical pickup is raised and the focal point of the optical pickup passes through the surface of the base material of the optical disk, a noculus is output from the binarization circuit 4. At the timing of the falling edge (trailing edge) of this pulse, D
A trigger pulse is generated from the flip-flop 5, and the output of the binarization circuit 1 is held in the D flip-flop 2.

Here, the threshold level of the binarization circuit 1 is such that if the dirt on the lens of the optical pickup is below the allowable limit during focusing on the base material surface of the optical disc, the binarization signal is 0'';
If the dirt on the lens exceeds the allowable limit, the binary signal is set to 1". Therefore, if the lens dirt exceeds the allowable limit, the output signal of the D flip-flop 2 will be 11". Therefore, lens dirt is detected.

Problems to be Solved by the Invention However, the above-described lens dirt detection method has a problem in that the reliability of lens dirt detection and determination is low (and detection errors are likely to occur).

This problem arises for the following reasons. Detection and judgment of contamination on the lens of an optical pickup is performed while the optical pickup is moving upward. However, since a damperless slide bearing type actuator is generally used as the actuator for raising the optical pickup, the optical The fluctuation in the pickup rising speed is relatively large.

Due to this speed fluctuation, the waveform of the differential signal of the focus error signal changes, so the binarized pulse of this differential signal fluctuates, and as a result, the pulse width fluctuates, resulting in the timing of the lens dirt detection judgment (the timing of the trigger pulse). timing) becomes unstable.

Since the optical pickup is being raised and the value of the focus sum signal changes with time, detection errors are likely to occur if the timing of lens dirt detection and determination changes as described above.

The present invention has been made in view of the above-mentioned problems, and provides an optical system that can stably and reliably detect dirt on the lens of an optical pickup by eliminating the adverse effects caused by fluctuations in the rising speed of the optical pickup and fluctuations in the timing of detection judgment. The purpose of the present invention is to provide a method for detecting dirt on a pickup lens.

In order to solve the above-mentioned problems, the present invention aims to solve the above-mentioned problems by applying focus servo to the surface of the base material of the optical disk of the optical pickup using the focus servo system. Based on the value, dirt on the lens of the optical pickup is detected and determined.

As described above, according to the lens dirt detection method of the present invention, the focus servo is applied to the base material surface of the optical disc, and the optical pickup is stopped while the optical pickup is substantially stopped relative to the base material surface of the optical disc. Detection and judgment of lens dirt cannot be performed. That is, detection and determination of lens dirt cannot be performed while the value of the focus sum signal is approximately constant.

Therefore, it is possible to not only eliminate the influence of conventional variations in the lifting speed of the optical pickup, but also to stably and reliably detect dirt on the optical pickup lens without being affected by variations in the lens dirt detection/judgment timing. can.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a simplified configuration of the main parts of an optical disc device according to an embodiment of the present invention, where 6 is an optical disc and 7 is an optical pickup.

The optical pickup 7 of this embodiment employs a focusing method called the so-called "double knife method" and has a built-in four-split photodetector 8. This 4-split photodetector 8 is divided into A, B, C, and D surfaces, and the optical pickup 7 is focused on the base material surface of the optical disc 6 (lower surface in the drawing) or the recording layer surface of the optical disc 6. and,
Side A.

The sum of the output signals of surfaces B and D becomes equal to the sum of the output signals of surfaces B and D, and in the defocused state, the difference between each phase becomes positive or negative depending on the direction.

Reference numeral 9 denotes a general focus servo system for focusing the optical pickup 7, which includes a focus error signal detection circuit 1o, a phase compensation drive amplifier (not shown), and the like.

This focus error signal detection circuit 10 detects the sum of output signals of surfaces A and C of the 4-split photodetector 8 and surface B.

This is an addition/subtraction circuit that calculates the difference from the sum of the output signals of D, and outputs the calculation result as a focus error signal FE.

11 is a differentiation circuit that differentiates the focus error signal FE. The differential signal of the focus error signal output from the differentiating circuit 11 is input to the comparing circuit 12. This comparison circuit 12 is for comparing the differential signal of the focus error signal with a certain threshold level and shaping it into a pulse.
This corresponds to the binarization circuit 4 in FIG. Reference numeral 13 denotes a monostable multivibrator, which is triggered by the falling edge of the output pulse of the comparator circuit 12.

14 is a focus sum signal detection circuit, which outputs a sum signal of output signals of surfaces A, B, C, and D of the four-split photodetector 8 as a focus sum signal FS. Reference numeral 15 is for comparing the focus sum signal FS with a certain threshold level and binarizing it, and corresponds to the binarizing circuit 1 in FIG.

16 is a D flip-flop corresponding to the D flip-flop 2 in FIG. The output signal of the comparator circuit 15 is input as a data signal to this D flip-flop 16, and the output signal of the monostable multivibrator 13 is input as a trigger signal.

Reference numeral 17 denotes a control section that controls the entire apparatus. Comparison circuit 1
The output signal of 2 and the output signal of the D flip-flop 16 (lens dirt detection signal) are input to the control section 17.

The operation of detecting dirt on the lens of the optical pickup for the optical disc device configured as described in 5 above will be explained.

Immediately after the power of the optical disk device is turned on, the control unit 17
The focus servo system is controlled by the optical pickup 7.
The actuator (not shown) of the optical pickup 7 is driven to continuously raise the optical pickup 7 from the standby position. Further, the D flip-flop 16 is reset by the control section 17.

When the optical pickup 7 rises and its focal point passes through the surface of the base material of the optical disk 6, a pulse is output from the comparator circuit 12. The falling edge of this pulse triggers the monostable multivibrator 13, causing its state to transition from a stable state to a metastable state.

Further, the control unit 17 operates the focus servo system 9 in response to the output pulse of the comparison circuit 12 so as to focus the optical pickup 7 on the surface of the base material of the optical disc 6.

After a certain period of time has elapsed, when the focus servo system 9 applies focus servo to the surface of the optical disk 9, the state of the monostable multivibrator 13 transitions to a stable state. Monostable multivibrator 13 at this time
The transition of the output signal causes the D flip 70 knob 16 to be triggered, and the output signal of the comparison circuit 15 is latched.

Here, in a state in which the optical disc 60 is focused on the surface (lower surface) of the base material, the comparison circuit 15 is set. Therefore, if the lens dirt is below the permissible limit, the output signal (stain detection signal) of the D flip-flop 16 becomes ``0'', indicating that the lens dirt exceeds the permissible limit. In this case, the output signal of the D flip-flop 16 becomes "l".

The control unit 17 checks the output signal of the D flip-flop 16, and if the signal is "0", it is determined that the lens is not dirty, and if the signal is "1", it is determined that the lens is dirty. .

In this way, at the time when the detection and determination of lens dirt is performed, the focus servo is applied to the base material surface of the optical disc 60, and the optical pickup 7 is in a state of almost stopping relative to the base material surface of the optical disc 6. , the value of the focus sum signal is almost constant. Therefore, it is possible to reliably detect the dirt on the lens without being affected not only by fluctuations in the rising speed of the optical pickup 7 but also by fluctuations in the timing of detection and determination.

In addition, if lens dirt is detected as described above,
The control unit 17 stops the device operation.

On the other hand, if lens dirt is not detected, the control unit 17
starts control for performing a focus pull-in operation to the surface of the recording layer of the optical disc 6, similar to the conventional one.

Note that in this embodiment, the detection and determination of lens dirt is performed based on the value of the signal obtained by converting the focus sum signal into a binary value by the comparator circuit 15. You may go.

Further, in this embodiment, the lens dirt detection operation was performed when the device power was turned on, but it may be performed at other times.

Furthermore, in this example, the "double knife method" was adopted as the focusing method, but the "astigmatism method"
The lens dirt detection method of the present invention can be similarly applied to optical disc devices that employ other focusing methods such as the "Foucault method."

Effects of the Invention As is clear from the above description, the present invention applies focus servo to the surface of the base material of an optical disc, substantially stops the optical pickup relative to the surface of the base material of the optical disc, and improves the focus sum signal. Since the lens dirt detection judgment is performed when the value is almost constant, it is possible to eliminate the influence of fluctuations in the rising speed of the optical pickup as in the conventional method, and it is not affected by fluctuations in the lens dirt detection judgment timing. This has the effect that dirt on the lens of the optical pickup can be detected stably and reliably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of an optical disc device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional lens dirt detection circuit. 6... Optical disc, 7... Optical pickup, 8...
・4-split photodetector, 9...Focus servo system, 10
... Focus error signal detection circuit, 11 ... Differentiation circuit, 12 ... Comparison circuit, 13 ... Monostable multivibrator, 14 ... Focus sum signal detection circuit, 15
...Comparison circuit, 16...D flip-flop, 17
...control section. Name of agent: Patent attorney Toshio Nakao and 1 other person10
--- Focus error signal detection $ circuit 14-7 Orcus Kazunobu

Claims (1)

[Claims] In an optical disc device, detection and determination of dirt on a lens of an optical pickup is performed based on a value of a focus sum signal while a focus servo system is applying focus servo to a surface of a base material of an optical disc of an optical pickup. How to detect dirt on the pickup lens.