JPH02308427A - Optical disk driving device - Google Patents

Abstract

PURPOSE:To execute the focus control of an optical disk whose reflection factor is different by varying the gain of a detecting electric signal at every movement of one stroke of an objective lens until a search point being a prescribed threshold is detected. CONSTITUTION:When data of a current value and an input stage gain GS, etc., is not stored in a memory 12 such as the time when a power source is turned on, a search point is detected by moving an objective lens 3 under the control of a CPU 11, and when it cannot be detected even when the lens 3 moves to the stroke end, an output of a photodetector 4 is varied by a prescribed gain. It is executed until the search point can be detected and data at that time is stored in the memory 12. When this data is stored once, thereafter, an open loop control is executed by its value, therefore, the movement to the search point is executed at a high speed and even an optical disk whose reflection factor is different can be brought to focus servo control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc drive device for driving an optical disc, and particularly relates to improvement of focus servo control during focus servo pull-in.

[Conventional technology]

In an optical disc drive device, it is necessary to maintain a constant distance between the objective lens and the surface of the optical disc so that the light spot irradiated onto the surface of the optical disc is always focused on the recording surface. Optical disc is approximately 180Orpl~2400rp
The optical disc rotates at a rotational speed of approximately 500 m, and surface runout (vertical movement) of several hundred μm occurs depending on the precision of the device and the optical disc. Therefore, in order to keep the distance constant even when surface wobbling occurs, so-called focus control is performed in which the objective lens is moved up and down according to the surface wobbling. Focus control is generally performed by feedback control, and distance detection used for feedback control is usually performed based on the amount of light detected by a split-type optical sensor provided in the optical head.

[Problem to be solved by the invention]

However, the amount of light detected by the optical disc drive device depends on the reflectance or transmittance of the optical disc.

That is, the reflectance varies, and for example, as the reflectance decreases, the amount of detected light decreases. In this case, the amount of light received up to the retractable area of the photodetector cannot be obtained, and focus control may not be possible. On the other hand, if the reflectance increases, the amount of detected light will overflow, making focus control impossible.

This invention was made in view of the above circumstances, and when the amount of light detected from the optical disk does not reach the search point even with one stroke of movement of the objective lens, the amount of light is amplified by a predetermined gain until the search point is detected. To provide an optical disk drive device which can carry out focus servo control at high speed even for optical disks with different reflectances by amplifying the gain, storing the gain determined by the gain, and performing servo pull-in using this from the next time. The purpose is to

[Means to solve the problem]

The optical disc drive device according to the present invention converts the amount of light from the optical disc into an electrical signal, compares it with a predetermined threshold value, and when the objective lens moves to the end of its movement, the electrical signal and the threshold value are combined. The gain of the electrical signal is changed by a predetermined amount in accordance with the difference between the two, and the determined gain is stored in the storage means.

[Effect]

In this invention, when performing focus servo control on optical disks with different reflectances, the gain of the detected electrical signal is changed every time the objective lens moves one stroke until a search point, which is a predetermined threshold value, is detected. Therefore, focus can be controlled even on optical discs with different reflectances. Further, the gain once set is stored in the storage means, and the focus servo control is performed based on the gain from next time onwards, so that the time until servo pull-in is shortened.

〔Example〕

The present invention will be described in detail below based on the drawings showing one embodiment thereof.

FIG. 1 is a block diagram showing the configuration of a focus servo system of an optical disk drive according to the present invention. In the figure, ■ is a disc-shaped optical disc, and a recording layer 1a for recording information is formed inside the disc. The optical disc 1 is rotatable by a disc motor 2, and an objective lens 3 faces the bottom surface thereof. The objective lens 3 is used to focus a laser beam from a light source (not shown) onto an optical spot 7 of a predetermined system on the surface of the recording layer 18 of the optical disc 1. The objective lens 3 is movable in its front axis direction by a lens drive section 8 serving as a drive means, and is also movable in the radial direction of the optical disc l by means not shown.

The lens drive unit 8 uses a linear motor, and its position in the optical axis direction is determined by the amount of current applied to it.

In addition, a photodetector 4 having two light receiving surfaces for detecting the amount of reflected light from a light spot irradiated on the optical disc 1 is provided on an optical head (not shown), and the sum signal SS is sent via an amplifier 5 to determine the amount of light. given to vessel 6. The amplifier 5 amplifies the sum signal from the photodetector 4 with a predetermined gain, and is controlled to amplify the sum signal when the reflectance of the optical disc 1 is low and the amplitude of the sum signal is small; When the amplitude of the sum signal is high, the gain is controlled to be lowered so that the sum signal does not overflow. This control is performed by an input stage gain setter 13 that variably sets the manual stage gain GS. The sum signal given to the light quantity determiner 6 is then compared with a search point which is a predetermined threshold.

This search point is used to determine whether or not the objective lens 3 has entered the area where the focus servo can be retracted, and when the sum signal exceeds this search point, it is a search point that indicates that the focus servo can be retracted. Outputs a detection signal PS. Also, photodetector 4, 2
The difference signal DS of the two light receiving surfaces is given to the light amount determiner 6, and the light amount determiner 6 determines the sum signal SS and the difference signal DS.
Detects the zero cross point of , thereby outputting a pull-in completion signal LS, uses the sum signal SS at that time as a reference signal, and outputs a deviation signal ΔS for performing closed-loop control.

On the other hand, the input stage gain setter 13 is CPt1ll, which will be described later.
At the same time, the set input stage gain GS is stored in the memory 12 via cputi.
is memorized.

The search point detection signal PS from the light amount determiner 6 is CP
given to UII. The CPU II outputs a gradually increasing digital current to drive the lens drive section 8 during open loop control, and when the search point detection signal PS is input, the current value at that time is stored in the data memory 12. Control. . Furthermore, when switching from open-loop control to closed-loop control, control is performed so that data on the input stage gain GS is stored in the memory 12. Note that the memory 12
The stored contents are erased when the power is turned off and the optical disc 1 is replaced.

The digital data of the current value outputted from the CPU II is converted into an analog triangular wave current by the D/A converter 10 and is applied to the lens driving section 8 via the loop switch 9.

Furthermore, when the search point detection signal PS is output to the CPU, the CPU II stores the current value at that time in the memo 2, and also uses a current with a reduced slope of the analog triangular wave, that is, the lens drive unit 8 at a low speed. A driving current is output to the lens driving section 8 via the D/A converter 10 and the loop switch 9.

On the other hand, the pull-in completion signal LS outputted by the zero cross of the difference signal DS from the photodetector 4 is given to the switching terminal of the loop switch 9, whereby the loop switch 9 changes the control loop from the open loop by the CPU II to the lens control. 7 to a closed loop.

During closed loop control, the lens control section 7 drives the lens drive section 8 based on the deviation signal ΔS, and outputs an amount of current that constantly keeps the distance between the objective lens 3 and the optical disc 1 constant through so-called feedback control.

The operation of the optical disc drive device of the present invention configured as described above will be explained below.

Note that the objective lens 3 has moved to the position closest to the optical disk 1, that is, to the upper stroke end of the lens drive section 8, before the control.

FIG. 2 is a flowchart showing the operation when the focus servo is pulled in. First, it is determined whether data such as the current value and input stage gain are stored in the memory 12 (Sl), and when the power is turned on or when the optical disk 1 is replaced, the current value and If the input stage gain GS is not stored, set the input stage gain GS to a switching value (S2), and then the CPU II outputs digital data of a current value for high-speed driving to lower the objective lens at high speed, This is D/A converted and output as a triangular wave analog current to the lens drive section 8 via the loop switch 9 (S3).

Then, it is determined whether the sum signal SS from the photodetector 4 exceeds the search point, that is, whether it is greater than a predetermined level (S4), and if it is greater than the predetermined level, the digital data of the current value at that time is stored in the memory. Remember on 12 S5
), the sum signal SS even if the objective lens moves a full stroke.
If not greater than the predetermined level, the input stage gain GS of the amplifier 5 is increased by the predetermined gain using the manual stage gain setter 13 (S6), and the process returns to step 3. This allows focus servo control even for optical discs 1 with different reflectances. Next, the CPU II generates digital data of the current value for low-speed drive and outputs it to the lens drive unit 8 (S7), and determines whether the difference signal PS crosses zero, that is, whether the focus servo pull-in is completed. (S8), and if it is not completed, the process returns to step 7 to drive the lens drive section 8 until the zero crossing and completion, and the objective lens 3 is lowered. If completed, the input stage gain GS set by the input stage gain setting device 13
Please remember this in January 2 (S9), stop the output of digital data from the CPU 11 (5IO), and light intensity judger 6.
In response to the pull-in completion signal LS from , the loop switch 9 switches the control loop from open loop control by the CPU II to closed loop control by the lens controller 7, and the focus servo pull-in operation is completed.

On the other hand, if data has already been stored in the memory 12 in step 1, the stored digital data of the current value and the input stage gain GS are read out (S12.513), and the manual stage gain setter 13 sets the amplifier 5. The input stage gain GS is set (S14). Then, the lens driving section 8 is driven using the read current value to move the objective lens 3 to the search point (S15). Then, as in step 4, it is determined whether the sum signal SS is greater than a predetermined level (
S16), when the current value exceeds a predetermined level, digital data of the current value for low speed drive is output from CPIJII (51
7) Similarly to step 8, it is determined whether or not retraction is completed (318), and if it is completed, the process moves to step 10.
If not completed, return to step 17. In this way, the search for the search point can be performed at high speed, and
- Once the variable current value and input stage gain are stored, open-loop control is performed based on those values, so movement to the search point becomes faster and the time until servo pull-in is shortened.

Furthermore, in this embodiment, the input stage gain is incremented based on the light amount of the sum signal and is stored, so that focus servo control can be performed even for optical discs with different reflectances.

In this embodiment, the search point is detected based on the level of the sum signal, and when the search point cannot be detected, the input stage gain is incremented. However, the present invention is not limited to this, and the input stage gain can be changed depending on how the search point is taken. may not be incremented, but may be changed by other changing methods such as degreement.

〔Effect of the invention〕

As explained above, according to the present invention, when data is not stored in the memory such as when the power is turned on, a search point is detected by moving the objective lens, and the search point is detected by moving the objective lens to the stroke end. If the search point cannot be detected, the output of the photodetector is changed by a predetermined gain until the search point is detected.Then, the memorized servo gain allows high-speed movement to the search point. Even if there is a focus servo control, an equivalent effect can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a focus servo system of an optical disk drive according to the present invention, and FIG. 2 is a flow chart showing a servo pull-in operation of the focus servo system. 1... Optical disk 3... Objective lens 4... Photodetector 5... Amplifier 6... Light quantity determiner 11.
. . CPU 12 . . . Memory 13 . . . Input stage gain setter In the drawings, the same reference numerals indicate the same or equivalent parts.・ Agent: Masao Oiwa 2 Figure

Claims (1)

[Claims] (1) In an optical disc drive device that performs focus servo control to make a light spot irradiated from a light source onto an optical disc via an objective lens to a predetermined diameter, and moves the objective lens in the direction of its optical axis, from the optical disc. a light amount detecting means for detecting the light amount, converting it into an electric signal, and outputting it; an amplifying means for amplifying the electric signal; a gain setting means for setting the gain of the amplifying means; a signal determining means for comparing a gain with a threshold value; a storage means for storing a set gain; and a signal determination means for comparing a set gain with a threshold value; control means for controlling the gain setting means to change the gain by a predetermined amount according to the gain, and when the gain is stored in the storage means, the electric signal is amplified by the stored gain; An optical disc drive device characterized by: