Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
2002-01-14
2004-10-05
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S030160
Reexamination Certificate
active
06801480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an optical disc apparatus which reads and writes data to an optical disc such as a CD, an MD, or a DVD.
Particularly, the invention relates to a control of a track jump in which a pickup head is moved to an objective track formed in a recording surface of an optical disc.
2. Related Art
Conventionally, there is an optical disc apparatus which reads data recorded on an optical disc such as a CD, an MD, or a DVD, and which writes data to such an optical disc. In an optical disc, a plurality of tracks are formed concentrically or spirally on a recording face. An optical disc apparatus detects a reflected light beam of a light beam illuminating the tracks to read out recorded data, and irradiates the tracks with a light beam to write data thereto.
When data recorded on an optical disc are to be read out, or when data are to be recorded to an optical disc, an optical disc apparatus performs a track jump for moving a pickup head to an objective one of many tracks formed in a recording surface of the optical disc. An objective track is a track from which data are to be read out, or into which data are to be written. A track jump is an operation of moving an illumination position of a light beam in a radial direction of the optical disc to place the illumination position of the light beam on the objective track.
Hereinafter, a track jump will be described. In a track jump, used is a tracking error signal indicative of the degree of deviation in a radial direction between the illumination position of the light beam and a track formed in the recording surface. The tracking error signal is obtained from a light beam which is reflected from the optical disc, and which is detected while moving the illumination position of the light beam in a radial direction of the optical disc.
In a usual optical disc apparatus, a pickup head is placed on a thread which is movable in a radial direction of an optical disc. A lens of the pickup head is attached so as to be movable on the thread in a radial direction of the optical disc. A track jump is conducted with moving the thread, or without moving the thread.
A track jump which is conducted with moving the thread will be described.
The optical disc apparatus moves the thread in a radial direction of the optical disc. This causes the main unit of the pickup head placed on the thread to be moved in a radial direction of the optical disc, and hence the center (the illumination position of the light beam) of the lens crosses sequentially tracks formed in the recording surface of the optical disc. At this time, also the movement of the lens of the pickup head with respect to the thread is conducted. A mirror portion which totally reflects a light beam is formed between adjacent tracks. A sinusoidal tracking error signal indicating that the center of the lens crosses a track is obtained from the amount of reflected light from the optical disc. One wavelength of the tracking error signal is produced each time the center of the lens crosses a track. When the wave number of the tracking error signal is counted, therefore, it is possible to obtain the number of tracks which the center of the lens has crossed.
Immediately before the start of a track jump, the optical disc apparatus calculates the number of tracks which are to be crossed before the center of the lens reaches the objective track position. Specifically, the number of tracks which are to be crossed is calculated from the difference between a track address indicative of the current track position of the pickup head, and that indicative of the objective track position. The current track position is obtained by reading data of the track.
When the center of the lens reaches a position which is separated by a certain distance from the objective track, the optical disc apparatus stops the thread. For example, the thread is stopped when the center of the lens reaches a track which is 100 tracks short of the objective track. When the optical disc apparatus moves the thread in this way, the main unit of the pickup head is moved to the vicinity of the objective track.
The movement of the lens with respect to the thread is continued even after the thread is stopped, so that the center of the lens is kept to be moved toward the objective track. When it is judged from the counted wave number of the tracking error signal that the center of the lens reaches the objective track, the optical disc apparatus conducts a tracking servo control to attain a track-on in the objective track.
A tracking servo control is a control of positioning the center of the lens on the center of a track.
In the case where the movement velocity of the lens is not substantially zero, the track pull-in is sometimes failed even when a tracking servo control is conducted, and hence a track-on in the objective track cannot be attained. Therefore, a control is conducted so that, when the center of the lens reaches a position which is separated by a certain distance from the objective track, the movement velocity is gradually reduced, and, when the center of the lens reaches the objective track position, the movement velocity is made substantially zero.
For example, a method is proposed in which, when the center of a lens reaches the objective track position, a braking operation is conducted so as to make the movement velocity of the lens substantially zero, and a tracking servo control is then conducted (the Unexamined Japanese Patent Application Publication No. Hei08-263849).
An optical disc apparatus is proposed in which the movement velocity of a thread is made constant during a track jump, whereby the control of the timing of conducting a braking operation is facilitated (the Unexamined Japanese Patent Application Publication No.Hei10-340459). The publication discloses a technique in which the rotational speed of a thread motor for moving a thread is made constant, thereby making the movement velocity of the thread constant.
3. Problems to Be Solved
However, the amount of braking which is applied when it is detected that the center of the lens reaches the objective track position is constant. When the movement velocity of the lens immediately before a braking operation is conducted is high, therefore, the lens fails to stop in the objective track position, and overshoots the position. When the movement velocity of the lens immediately before a braking operation is conducted is low, the braking is excessively applied, and the center of the lens is sometimes returned with respect to an optical disc. In this context, the return does not mean a movement of the lens in the opposite direction, but means a phenomenon in which the relative movement direction of the lens with respect to the optical disc is oriented in a returning direction (the direction along which the lens is separated from the objective track) because of eccentricity of the optical disc or the like.
Conventionally, immediately after a braking operation is completed, a tracking servo control is conducted so as to attain a track-on in the objective track. However, it is not certain whether, at the timing when a braking operation is completed, the center of the lens is positioned on a track or in a mirror portion formed between tracks. When a tracking servo control is conducted while the center of the lens is positioned in a mirror portion, the drive control cannot be correctly performed, and the lens is sometimes returned or suddenly accelerated, thereby causing track slipping.
In a conventional optical disc apparatus, therefore, it is often that a track-on in the objective track is not attained and a track jump is again conducted. As a result, the time period required for attaining a track-on in the objective track is prolonged, and the reliability of the apparatus main unit is not excellent.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an optical disc apparatus in which, when a movement of a lens is to be stopped, a braking operation of a degree corresponding to the movement
Dinh Tan
Funai Electric Co., Ltd
Morgan & Lewis & Bockius, LLP
LandOfFree
Optical disk drive apparatus capable of braking the optical... 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 drive apparatus capable of braking the optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical disk drive apparatus capable of braking the optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3332364