Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-10-26
2004-03-30
Hindi, Nabil (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053140, C369S044110
Reexamination Certificate
active
06714493
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an optical disk apparatus for writing information to an information carrier (a recording medium) or reproducing information recorded on the information carrier by using a light beam from a light source, like a laser, more particularly, the present invention relates to an optical disk apparatus that can detect an abnormal state of an actuator when a focusing control or a tracking control is performed.
Now optical disk apparatuses that can record/reproduce information to/from an optical disk (information carrier or recording medium) having a recording layer formed of a phase-change medium or a magneto-optical medium have come into practical use. Such an optical disk apparatus irradiates a recording surface of the optical disk with a light beam converged by a converging lens (an objective lens) included therein so as to cause a phase change or inversion of magnetic polarization in the recording layer, thereby the information can be recorded onto the optical disk. As for the reproduction, the optical disk apparatus can reproduce the information from the optical disk by detecting reflected light from the optical disk.
In the recording/reproduction operation mentioned above, the light beam is to be subjected to a focusing control in order to accurately place a converging point of the light beam on the recording surface of the optical disk. The focusing control is realized by moving the converging lens in a direction substantially perpendicular to the surface of the optical disk so as to move a focus of the light beam in a thickness direction of the optical disk. In the focusing control, a focusing actuator that is composed of a voice coil motor, for example, is used for moving the converging lens. Once the focus of the light beam is positioned on the recording surface of the optical disk, the focusing actuator controls the movement of the converging lens to keep a distance between the recording surface and the converging lens substantially constant (this corresponds to a state where a focusing servo is performed).
In the focusing control, a relatively large driving current may be applied to the focusing actuator continuously because of a breakdown of a circuit included in a focusing servo system or the like. When such a large driving current continuously flows through the focusing actuator over a time period longer than a predetermined time period, a power supplied to the focusing actuator may exceed the maximum rating power thereof, causing overheating of the focusing actuator. This overheating may cause the focusing actuator to be damaged.
As a method for protecting the actuator from being damaged, there is a known method in which the driving of the focusing actuator is stopped when the driving current for the actuator exceeds a predetermined current value (Japanese Patent Publication No. 6-64745, for example). In accordance with the method, it is possible to determine that the focusing actuator is driven abnormally in a case where the current having the magnitude exceeding a predetermined magnitude is continuously applied to the focusing actuator, as shown in
FIG. 1A
, when the optical disk apparatus begins the operation or the focusing servo is performed. Thus, the damage of the actuator can be prevented.
Moreover, when the focusing servo is performed, a transient disturbance may occur because of a partial waver caused by a local undulation or unevenness of the recording surface of the optical disk generated in a fabrication process of the optical disk, a vibration applied to the optical disk apparatus or the like. In a case where the focusing actuator is driven in order to suppress the aforementioned external disturbance, a driving current shown in
FIG. 1B
, for example, flows through the focusing actuator. By supplying such a driving current to the focusing actuator, it is possible to make the movement of the converging lens follow the waver of the optical disk, thus maintaining the appropriate focusing state.
However, according to the aforementioned conventional method for protecting the actuator, when the driving current shown in
FIG. 1B
is supplied to the focusing actuator, it is determined that the driving of the focusing actuator is in the abnormal state at a time at which the current value exceeds the predetermined current value even if the power does not exceed the maximum rating power expressed as the product of a predetermined time period (rating time) and a predetermined current value (rating current), so that the driving of the focusing actuator is stopped. This prevents the supply of the driving current having a necessary magnitude to the focusing actuator, resulting in a failure of the focusing servo.
On the other hand, as a method of protecting the actuator, there is another known method in which the driving current for the focusing actuator is integrated by using a predetermined time constant and the driving of the focusing actuator is stopped when the integration result (that is, the power) exceeds a predetermined value (Japanese Patent No. 2864799, for example). In accordance with this method, it is not determined that the driving of the focusing actuator is in the abnormal state when the driving current shown in
FIG. 1B
flows through the focusing actuator. Thus, it is possible to continue the focusing servo.
The latter protection method utilizes an integration technique (a signed value integration) in which an output of an integrator is always approximately zero in a case where the driving current goes between a plus side (charging) and a minus side (discharging). This is because this method takes a case of suppressing the disturbance in one direction (a direction in which the converging lens becomes closer to the optical disk or a direction opposite thereto) occurring at a period substantially the. same as the rotation period of the optical disk into consideration. In this case, in order to protect the actuator, it is sufficient that the integration result of the current value when the driving current corresponding to such a flash or transient unidirectional disturbance flows through the actuator is obtained. During a period in which no transient disturbance occurs (when the normal servo is performed), the driving current fluctuates between the positive and the negative while having the smaller amplitude. It is preferable according to this conventional protection method that the driving current when the normal servo is performed is not contained in the current integration value used for determining whether or not the condition for protecting the actuator is satisfied.
In recent years, the rotation speed of the optical disk in the optical disk apparatus has been largely increased. However, this causes a problem of occurrence of an external disturbance having a high frequency. It is known that the waver caused when the optical disk rotates contains not only a waver occurring in synchronization with one rotation of the optical disk (a primary component) but also a component N times the primary component (a higher degree component). In a case of rotating the optical disk at 160 Hz to 180 Hz, for example, the primary waver having the frequency of 160 Hz to 180 Hz and a high frequency component (the high-frequency disturbance) having 2 kHz to 3 kHz may be generated. Such a high-frequency disturbance largely influences the focusing servo.
Herein, the influences of the high-frequency disturbance on the focusing servo are described.
FIG. 2
shows loop characteristics of the focusing servo system in the conventional optical disk apparatus. The waver having a lower frequency and a large amplitude, such as the primary component of the waver, is generated in a lower-frequency region (100 Hz or less, for example). Thus, as shown with Line A in
FIG. 2
, it is necessary to set the loop gain in the lower-frequency region to be a large value so as to improve the ability of following the waver of the optical disk. This enables the focusing actuator to be driven in such a manner that a deviation of t
Fujiune Kenji
Kishimoto Takashi
Watanabe Katsuya
Yamamoto Takeharu
Akin Gump Strauss Hauer & Feld L.L.P.
Hindi Nabil
Matsushita Electric - Industrial Co., Ltd.
LandOfFree
Optical disk apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical disk apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical disk apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3261895