Apparatus of controlling tracking for a disk

An apparatus includes a controller storing information on dense/sparse state of the tracking error signal in connection with characteristic of the signal generated by a phase encoder while tracking servo of a servo unit is inactivated, and, in data reproduction mode, identifying a current disk phase based on characteristic of the signal generated by the phase encoder, and adjusting tracking characteristic of the servo unit based on the stored information in connection with the signal characteristic in order to compensate an effect rate of eccentricity on the identified disk phase. Through minute adjustment of servo characteristic for each disk phase, error range of TE signal to track in real time is reduced. Therefore, tracking for an eccentric disk becomes easier and more reliable.

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on patent application Ser. No. 2001-0063107 filed in KOREA on Oct. 12, 2001, which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tracking control apparatus for a disk recording medium, more particularly, to an apparatus of measuring how much an eccentricity affects each phase of a disk and controlling disk tracking based on the measured each effect rate.

2. Description of the Related Art

In general, most of the disks become eccentric during rotation because of variation in disk manufacturing or disk clamping condition. If an eccentricity of a disk is too high to conduct an exact tracking, it is difficult to reproduce data from the disk normally.

To overcome such a bad situation, a disk device measures an eccentricity of a disk and adjusts characteristic of a tracking servo to compensate the measured eccentricity at a start-up operation.

A conventional eccentricity measuring method rotates a placed disk with a tracking servo off, counts pulse train produced every track cross of an optical pickup and disk revolutions, and divides the pulse count by the number of disk revolutions. Because the value resulted from the division represents how much a disk is eccentric, gains of a tracking servo are adjusted based on the eccentricity measured as above to compensate eccentricity of the disk overall.

However, even though eccentricity of a disk is high, the high eccentricity has different effects on respective disk phases. Namely, a certain disk phase is affected less by the high eccentricity than other phases.

Nevertheless, if gains of a tracking servo are increased to make more sensitive to compensate an eccentricity overall irrespective of different effect of eccentricity on respective disk phases, a tracking servo may diverge unexpectedly, namely, an objective lens of an optical pickup may be biased to the utmost side when a scratch is encountered on a disk phase an eccentricity has small effect on.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a disk tracking control apparatus that measures how much an eccentricity of a rotating disk affects respective disk phases and that adjusts characteristic of a tracking servo minutely according to the measured individual effect on each disk phase.

A disk device of reproducing data from a disk recording medium in accordance with the present invention is characterized in that it comprises: reading means reading signals written on a rotating recording medium and producing recorded signals and a tracking error signal out of the read signals; a phase encoder generating a signal of which characteristic varies according to phase of the rotating disk; a servo unit controlling tracking of an objective lens equipped in said reading means; and a controller storing information on dense/sparse state of the tracking error signal in connection with characteristic of the signal generated by said phase encoder while tracking servo of said servo unit is inactivated, and, in data reproduction mode, identifying a current disk phase based on characteristic of the signal generated by said phase encoder, and adjusting tracking characteristic of said servo unit based on the stored information in connection with the signal characteristic in order to compensate an effect rate of eccentricity on the identified disk phase.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order that the invention may be fully understood, a preferred embodiment thereof will now be described with reference to the accompanying drawings.

FIG. 1is a simplified block diagram of a disk device in which the first embodiment of a disk tracking control method of the present invention is embedded.

The disk device ofFIG. 1comprises an optical pickup20for reading written signals from the surface of an optical disk10; an R/F unit30for producing binarized signals and a TE (Tracking Error) and a FE (Focusing Error) signal through filtering and combining the signals detected by the pickup20; a driving unit50for driving a sled motor21to move the optical pickup20and a spindle motor22to rotate the disk10; a servo unit40for conducting tracking/focusing operation of an objective lens in the pickup20and controlling the driving unit50to rotate the disk10at a constant speed; a digital signal processing unit60for restoring original data from the binarized signals using a self clock synchronized with the binarized signals in phase; a phase encoder80for generating a pulse train with duty ratio varying cyclically during rotation of the spindle motor22; a memory90for storing data; and a microcomputer100for controlling an overall reproducing operation, especially, for measuring eccentricity effect on each disk phase based on the pulses from the phase encoder80and adjusting tracking servo characteristic of the servo unit40according to measured individual eccentricity effect.

When the disk10is placed on a tray (not shown) equipped in the disk device, the microcomputer100controls the driving unit50through the servo unit40to rotate the placed disk10in CLV (Constant Linear Velocity) manner by the spindle motor22. While the disk10is rotated, the phase encoder80outputs successive pulses that have different duty ratios cyclically, e.g., pulses302with increasing duty ratio as shown inFIG. 3. The pulses are applied to the microcomputer100. The phase encoder80may be implemented with an FG signal generator that is integrated in the spindle motor22in general.

The microcomputer100controls the servo unit40to turn a focusing servo on and a tracking servo off. This state with focusing on and tracking off is called ‘traverse state’.

If the disk10is little eccentric during rotation, an objective lens of the optical pickup20would form an ideal trajectory201on the disk10in traverse state as illustrated inFIG. 2, otherwise, it would form an undesirable trajectory202.

Therefore, TE signal would be produced like as301ofFIG. 3in case of an eccentric disk. For example, if the trajectory202ofFIG. 2is partitioned into four phases, sinusoidal TE signal is dense at phases ‘a-b’ and ‘c-d’ and sparse ‘b-c’ and ‘d-a’.

The waveform301of TE signal drawn, inFIG. 3is produced only when tracking servo is off. Namely, TE signal is not produced like asFIG. 3in case that tracking servo is activated to record/reproduce data from a disk.

The microcomputer100samples the TE signal, and pulses from the phase encoder80simultaneously and stores sampled data in the memory90.

After the disk10rotates at least once, the microcomputer100analyses the sampled data in the memory80. Through the analysis, the microcomputer100identifies dense and sparse section of the TE signal and examines ranges of duty ratio of the pulses for respective dense and sparse sections at the same time. In the analysis, if values of successive sampled data show rapid change it is dense section and if do smooth change it is sparse section. As another way, a section having relatively more peak values is judged dense and the other section is sparse.

In addition, the microcomputer100counts the number of peak values (or vibrations) for respective dense and sparse sections to measure effect rate of eccentricity on each section. Each count is stored in connection with corresponding section. Finally, a desirable information table is constructed in the memory90as illustrated inFIG. 4. Each turning point from dense to sparse and vice verse is determined to a boundary between dense and sparse section.

After construction of the information table like asFIG. 4, if disk reproduction is requested the microcomputer100moves the pickup20to an initial or a target position in order to reproduce data from the disk10. At the same time, the microcomputer100calculates duty  ratio of pulses outputted from the phase encoder80.

And, the microcomputer100identifies which range among the stored variation of duty ratio in the memory90the calculated duty ratio belongs to. For example, if the calculated duty ratio is about 40%, the microcomputer100judges a current disk phase to ‘a-b’ referring to the information table ofFIG. 4.

Because the information table shows that the disk phase ‘a-b’ is badly affected by disk eccentricity, possibility of tracking error is relatively high in this disk phase. Thus, the microcomputer100increases gains of the tracking servo or an amplifying rate of the TE signal in proportion to effect rate at the detected disk phase ‘a-b’. Consequently, the tracking servo becomes so sensitive that it can track better even in a bad disk phase where a track swings severely.

If the calculated duty ration is about 60%, the current phase is determined to ‘b-c’ where effect rate of eccentricity is relatively low. Thus, the microcomputer100makes the tracking servo insensitive. Because of insensitiveness of the tracking servo, the tracking servo is less likely to diverge even though unexpected noise of TE signal arises in the disk phase of low effect-rate of eccentricity.

In addition, because the microcomputer100is able to know how much a next track following current one on the identified disk phase is affected by disk eccentricity, it can adjust characteristic of the tracking servo to meet a next track in advance before the next track arrives. For example, if the calculated duty ratio is about 50%, which means that the current phase is ‘a-b’, it can be known that a next disk phase (phase ‘b-c’) is less affected by disk eccentricity. Therefore, the microcomputer100may make the tracking servo of present high-sensitivity insensitive before the pickup20reaches the phase ‘b-c’. If characteristic of the tracking servo is adjusted beforehand, tracking servo operates with low sensitivity as soon as a track on the phase ‘b-c’ is reproduced.

FIG. 5is another simplified block diagram of a disk device in which the second embodiment of a disk tracking control method of the present invention is embedded. The disk device shown inFIG. 5replaces the phase encoder80encoding rotation angle of the spindle motor22with a phase encoder110encoding phase directly from a placed disk. The other elements are same as the disk device ofFIG. 1.

The phase encoder110ofFIG. 5, as shown inFIG. 6a, includes a light emitting unit (LEU)17radiating a planar beam arranged radially with respect to a placed disk onto the disk; and a light detecting unit (LDU)18that is composed of a series of photo diodes or photo transistors detecting the planar beam individually.

The LEU17may be implemented with a series of laser diodes arranged in a line or with a single light emitting element and an enclosing box of which bottom has parallel slits that transform a light from the light emitting element into parallel individual beams.

Furthermore, a disk11for this embodiment has a phase identifying circle-band11aalong outermost circle102as shown inFIG. 6b. The phase identifying circle-band11aincludes a transparent inner circle-band11cof which width varies linearly from 0 at a certain start line11bto full width of the phase identifying band11aat that line11b.

The phase encoder110is placed to cover above and below the phase identifying circle-band11aof the disk11as shown inFIG. 6a.

A microcomputer120included in the disk device ofFIG. 5has as many input ports as the outputs of the phase encoder110as shown inFIG. 5. Namely, each input port of the microcomputer120is connected to an output pin of each photo diode or photo transistor.

While the disk11structured as above is rotated in the disk device ofFIG. 5, the parallel beams171from the LEU17of the phase encoder110are incident to the LDU18at the opposite side only through the transparent inner circle-band11cformed in the phase identifying circle-band11a. Therefore, the microcomputer120receives n-bit data sequentially in the form ofFIG. 6cthrough its input ports while the disk11rotates.

The microcomputer120identifies a current disk phase based on the ratio of ones (or zeros) to n bits inputted from the phase encoder110.

Afterwards, the microcomputer120measures disk eccentricity based on vibration of TE signal and effect rate of eccentricity on each of partitioned disk phases in the traverse state the same as in the first embodiment. The measured quantities are stored in the memory90.FIG. 6dshows an exemplary information table including the measured quantities.

During data reproduction (or record), a current disk phase is identified from the ratio of ones (or zeros), to n-bit data outputted simultaneously from the phase encoder110, and effect rate of eccentricity on the identified disk phase is known from the information table stored inFIG. 6d. Finally, characteristic of the tracking servo is adjusted accordingly to meet the known effect rate of eccentricity on that phase. This shortly-explained operation is totally same with the first embodiment explained in detail before.

The above-explained disk tracking control method adjusts servo characteristic for each disk phase to match with different effect rate of eccentricity on each disk phase. Thus, an error range of TE signal to track in real time is reduced, whereby, tracking for an eccentric disk becomes easier and more reliable.