JPH0627028Y2 - Servo device for rotating recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a servo device in which a servo mechanism works well even when a rotary recording medium such as an optical disk has a defect.

[Outline of device]

The servo device in the rotary recording medium of the present invention is, for example,
Memory means for periodically storing the control amount of the actuator for reading information from the rotating recording medium, and a defect detecting section for detecting an abnormal value of a servo error signal due to a defect of the rotating recording medium are provided, and the servo is performed by the defect detecting section. When an abnormal value of the error signal is detected, the data stored in the memory means is configured to be output as the control amount from the time when the acceleration of the actuator becomes zero, and the operation of the actuator is changed by the disturbance of the servo circuit. It prevents inaccuracies.

[Prior Art] In a recording / reproducing apparatus for a rotating recording medium such as an optical disc, normally, in order to accurately irradiate a laser beam on a circumferential track of the optical disc, at least a focus servo and a tracking are performed on an optical head. It is necessary to apply a servo.

By the way, as shown in FIG. 3, when there is a defective portion K on the recording surface of the optical disc D in which a large flaw or foreign matter is attached, as a matter of course, when the defective portion is irradiated, Normal information is not reproduced from the laser light, and the tracking error signal and the focus error signal detected from the reflected light also have abnormal values.

Even if such a defective portion is in a short period, the reproduced recording information can be restored to some extent by interpolating the data with the CRCC code. However, a tracking servo error signal or a focus servo error that occurs periodically. The error signal causes a large disturbance in the servo circuit due to the mechanical transfer characteristics of the actuator, causing track jumps and focus servo misalignment.

Therefore, for such a defect of the optical disc, a method of holding the servo error signal at a value immediately before the defect, a method of increasing the response time constant of the servo and passing the defective portion by its flywheel effect, etc. are taken. There is something.

[Problems to be solved by the invention]

However, the state changes quickly with respect to the time axis, and
The servo system as described above is not effective enough for defects such as a wide range, and the stable operation of the servo system is not completely improved.

[Means for solving problems]

The present invention has been made in consideration of such problems,
Memory means for recording the control amount of the actuator with reference to the rotational angle position of the rotary recording medium, a defect detecting section for detecting a defective position of the rotary recording medium, and a control section for controlling reading and writing of the memory means. Is added to the servo device so that the servo circuit operates smoothly even with a defective rotating recording medium.

[Action]

The main component of the servo error signal in the servo device of the rotary recording medium is a periodic function, and for example, in one adjacent track, one cycle of the servo error can be considered to be almost the same. Therefore, at least one of the rotating recording media
The servo error signal of the periodic part is stored in the memory means,
If rewriting is performed for each rotation, the servo error signal of the previous cycle is output when the defective portion is encountered, and the abnormal servo error signal can be removed to avoid the servo disturbance in the defective portion. become able to.

〔Example〕

FIG. 1 is a block diagram of a rotary recording medium servo apparatus according to an embodiment of the present invention.

In this figure, D is an optical disk, and X _reff is a target value for tracking the optical disk.

_{Reference numeral} 10 denotes an arithmetic circuit for calculating an operation amount (tracking error) from a difference between a target value X _reff and a control amount of a controlled object (hereinafter referred to as an actuator) 12 which will be described later. A tracking error signal is _supplied to the actuator via a phase compensator 11. 12 are supplied.

Reference numeral 13 denotes an observer circuit that generates a displacement signal x and an acceleration signal from the control amount of the actuator 12, and the displacement signal x is supplied to the control unit 15 via the A / D converter 14.

The control unit 15 is provided with a rewritable memory (RAM) 16, and the displacement signal x is stored in this memory 16 with the rotational position of the optical disc as an address.

Reference numeral 17 designates a rotation clock output FG outputted from a motor M rotating the optical disc D or a turntable of the optical disc, and an address data generator for outputting an address signal of the memory 16 by a phase reference PG. 18 designates D / A conversion. The reference numeral 19 designates an output amplifier which also serves as a phase compensator.

Reference numeral 20 is a defect detection unit 20 for detecting an abnormal value of the tracking error signal, and detects the defect position of the optical disc by comparing the RF signal reproduced from the optical disc with a reference voltage. Further, the ECC demodulation flag obtained from the data interpolation unit of the reproduction signal processing circuit may be used as the defect position detection signal.

Since the tracking servo device according to the embodiment of the present invention is configured as described above, the displacement signal of the actuator 12 formed by the observer circuit 13 is normally input to the A / D converter 14 for control. At the same time as being stored at a predetermined address of the memory 16 via the unit 15, that is, at an address corresponding to the rotational position of the optical disc, the D / A
It is fed back to the arithmetic circuit 10 via the converter 18 and the phase compensator 19.

Therefore, the actuator 12 is controlled by the tracking error signal output from the arithmetic circuit 10, and is controlled so as to track the track of the rotating optical disc.

However, if there is a defective portion on the recording surface of the optical disc as shown in FIG. 2, the reproduction RF signal is dropped or dropped at time B ₁ , and the displacement x of the actuator forming the tracking error signal is also disturbed.

Such a defect on the recording surface usually occurs cyclically thereafter when the rotation cycle of the optical disk is represented by L ₁ , L ₂ , L ₃ , L ₄ , ... ₃ of point _{B 2}
At the time points B ₃ , B ₄ , of the periods L ₄ , L ₅ ,
This occurs over several tracks.

Therefore, in the embodiment of the present invention, when the defect detection unit 20 outputs the defect signal S _B , the value of the displacement signal x is set to the control unit 15.
In (1), the data is partially interpolated and stored in the memory 16, and in the next cycle L ₃ , the interpolated memory data D _m is output.

That is, when there is a defect between the previous rotation period L ₂ of the T _34, the between T ₅₆ of the next rotation cycle L ₃ displacement signal of the memory 16 where the data is interpolated is read as indicated by a dotted line.

Further, the defect signal S _B in the period L ₃ causes the data in the memory 16 to be read out similarly during the next period T ₇₈ of the period L ₄ .

Periods T ₁₂ , T ₂₃ , T ₃₄ for replacing this data
Is determined on the basis of a time point when the acceleration of the actuator calculated by the observer circuit 13 becomes zero. At this time point, instead of the displacement signal x of the actuator 13, the displacement data ( The output of D _m ) is characterized in that the response characteristics of the servo system are not significantly disturbed. That is, the actuator generally has a transfer characteristic ^{_{+ 2ζω n + ω 2 n x}} = 0 of the secondary system, but when the acceleration is close to zero is approximated as ^{_{2ζω n + ω 2 n x =}} 0, the servo system is non-oscillatory In this state, x is set.

When a defect is output during a certain rotation cycle L of the optical disk, a series of displacement data captured in the previous cycle is stored in the memory 16 when the acceleration before and after the defect occurs becomes zero. By replacing the present displacement data with the current displacement data, the disturbance of the servo error due to the defect can be minimized. (Usually, defects on the recording surface tend to be gradually expanded at the same place over several tracks.) Note that the displacement data taken into the memory 16 when a defect occurs is initially interpolated data, While the defect continues thereafter, the displacement signal may not be stored in the memory 16 and the first interpolated storage data may be output in the same replacement period until the defect disappears.

Although the displacement signal and the acceleration signal are detected by the observer circuit 13, the displacement sensor and the acceleration sensor may be provided directly on the actuator.

Although the tracking servo has been described in the above embodiments, an actuator for performing focus servo may be used as a target. Further, the servo device of the present invention is generally a servo device for rotating recording media in which an error signal is periodically output. It goes without saying that it can be applied to.

Further, although the control amount of the controlled object is configured to respond only to the displacement signal, it is needless to say that it can be applied to a servo system that performs speed control.

[Effect of device]

As described above, the servo device for the rotary recording medium of the present invention stores the control amount of the actuator at least one rotation corresponding to the rotation angle of the rotary recording medium, and the stored data is updated every cycle. Therefore, even if there is a defect in the rotary recording medium, there is an advantage that the stored data can continue the smooth servo function without causing confusion in the servo circuit.

Further, since the replacement of the servo data is based on the time when the acceleration of the actuator becomes zero, there is an effect that the servo circuit is not disturbed.

[Brief description of drawings]

FIG. 1 is a block diagram of a servo device showing an embodiment of the present invention, FIG. 2 is a timing waveform diagram showing the operation of the servo device, and FIG. 3 is a plan view showing a defective portion of an optical disk. In the figure, 10 is an arithmetic circuit, 12 is a controlled object (actuator), 15 is a control unit, 16 is a memory, 17 is an address data generation unit, 20 is a defect detection unit, and D is an optical disk.

Claims (1)

[Scope of utility model registration request] 1. A rotary recording medium, an arithmetic unit for inputting a control target value and a control amount of the rotary recording medium and outputting a servo error signal, an actuator controlled by the servo error signal, and a control amount of the actuator. Is stored in correspondence with the rotational position of the rotary recording medium, and the stored data is updated in a rotation cycle, a defect detecting section for detecting a defect of the rotary recording medium, and a defect from the defect detecting section. When a signal is output, a control unit is provided, which reads the pre-update record information stored in the memory means instead of the control amount from the time when the acceleration of the actuator becomes zero, and supplies it to the arithmetic circuit. A rotary recording medium servo device.