Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-01-11
2002-01-22
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044250, C369S053370
Reexamination Certificate
active
06341107
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical storing apparatus from/to which information is read and written by a positioning control of a laser beam to a medium track on the basis of a tracking error signal and, more particularly, to an optical storing apparatus for correcting a tracking error signal so that a lead-in and an on-track control of a laser beam to a track center can be properly executed.
2. Description of the Related Arts
Attention is paid to an optical disk as a storing medium serving as a nucleus of multimedia which has rapidly been developing in recent years. For example, as for an MO cartridge of 3.5 inches, MO cartridges of 128 MB, 230 MB, 540 MB, 640 MB, and the like are provided. An optical disk drive using such an MO cartridge is provided as an external storing apparatus of a desktop type personal computer. Further, the use of the optical disk drive is also strongly desired in a notebook sized personal computer having an excellent portability which has rapidly become popular in recent years. In order to equip the optical disk drive as an external storing apparatus as standard equipment, therefore, a miniaturization, a thin size, and further, a low price are requested.
The optical disk drive has a pickup of a linear driving type in the direction which traverses tracks on a medium. The pickup is constructed by a fixed optical system fixed to a casing and a movable optical system which is linearly driven by a VCM. A movable optical unit mounted on a carriage is equipped with a lens actuator and has a relatively complicated mechanism which requires a two-dimensional degree of freedom such that an objective lens is moved in the direction which traverses the tracks by a current supply of a tracking coil and the objective lens is moved in the vertical direction by a current supply of a focusing coil. Such a pickup of the double driving type in which the lens actuator is mounted on the carriage performs a speed control for an acceleration, a constant speed, and a deceleration by the driving of the carriage by the VCM at the time of a seek control (coarse adjustment) for moving a beam toward a target track and executes a lead-in control for leading the beam to the target track by the driving of the lens actuator when the laser beam approaches the target track. After completion of the lead-in to the target track, the beam is allowed to trace the target track by the positioning control of the lens actuator and, simultaneously, to trace a medium eccentricity or the like by the driving of the carriage by the VCM. The structure of the pickup mechanism of the double driving type in which the lens actuator is mounted on the carriage is, however, complicated and the beam positioning control is also complicated since the control of the carriage and that of the lens actuator are combined, so that there are limitations to realize the miniaturization, thin size, and reduction in costs of the pickup. There is, accordingly, a pickup of a single driving type for executing all of the seek control for moving the beam toward the target track, the lead-in control for the target track, and the tracking control for the target track after completion of the lead-in only by the driving of the carriage by the VCM without using the tracking actuator. In the pickup of the single driving type, it is sufficient to mount simple parts such as objective lens, focusing actuator, and the like onto the carriage. Consequently, the carriage can be made small and thin, its mass can be sufficiently reduced, and an inertia occurring by the carriage movement can be reduced as compared with the double driving type in which the lens actuator is mounted, so that a high trace response speed can be obtained. Since it is sufficient to perform only the control by the VCM, there is an advantage such that the seek control, the target track lead-in control, and the tracking control can be also realized by simple control systems and enough reduction in costs can be expected as a result.
On the other hand, in the optical disk drive, arbitrary tracks on the optical disk are accessed at random. In this instance, in order to read information stored on the optical disk or write information to the optical disk, it is necessary to execute a tracking control for accurately positioning the laser beam toward the target track at a high speed. For the purpose of the tracking control, in the optical disk drive, a tracking error signal (hereinbelow, called a “TES”) is optically detected. As a method of obtaining the TES in the optical disk apparatus, a push-pull method (far field method) in which detecting sensitivity is high and a signal is obtained by a single beam and an optical system and a circuit are simple is used. The TES signal which is obtained by the push-pull method is a signal obtained by optically and indirectly detecting a deviation (positional error) between the track center and the laser beam by using an interference of the light. The tracking control based on the TES in the single driving type pickup is executed as follows. In the seek control for moving the laser beam to the target track, the speed of the carriage is controlled by the driving of the VCM. That is, a speed control such that a target speed is set in accordance with the number of remaining tracks to the target track and, after acceleration, the target speed is maintained is executed. During the speed control, a down-count such that the number of tracks is obtained by detecting a zero-crossing point of the TES and the number of remaining tracks to the target track is obtained is performed. When the number of remaining tracks to the target track is reduced to a specified value, the control is switched to the deceleration control. When the laser beam approaches a position just before the target track during the deceleration control, the control is switched to a position servo control based on the TES, the VCM is feedback controlled so that the TES is set to zero, and the beam is led to the target track. When the lead-in to the target track is succeeded, an on-track signal is obtained, and the seeking operation is completed. In a state where the laser beam is allowed to trace the track center by the tracking control (on-track control), the reading operation or writing operation from/to the optical disk is permitted. In the tracking control, since the TES is equal to zero at the track center, the carriage is driven by the VCM by the feedback control for always setting the TES to zero. Even if there is a positional fluctuation of the target track due to a disk rotational eccentricity or the like, the laser beam is always allowed to trace the track center.
A desirable position signal having a proportional relation for a physical positional deviation amount (distance) X of a light spot (laser spot) of the laser beam from the track center is set to an ideal TES Z
desired
. The TES is, so to speak, merely a signal obtained by performing a modulation by the interference of light to the ideal TES Z
desired
. The magnitude of the TES and the actual positional deviation amount X, therefore, do not always have the proportional relation. This is because the positional error is detected as a TES by using the interference of light and is a phenomenon caused by the nature of the TES which is obtained by the push-pull method.
FIG. 1
shows the ideal TES Z
desired
and a TES Y for the actual positional deviation amount X with respect to a case where a track pitch TP=1.1 &mgr;m. The positional deviation amount X of the axis of abscissa is equal to X=0 at the track center and has a width of ±0.55 &mgr;m in the lateral direction. As a normalized signal level of an axis of ordinates, a value obtained by converting the level of the TES Y by the track pitch TP=1.1 &mgr;m is used. Y=0 at the track center and a range of ±0.55 &mgr;m in the vertical direction is shown. The relation between the positional deviation amount X and the TES Y in
FIG. 1
shows an almost sine wave
300
an
Greer Burns & Crain Ltd.
Huber Paul W.
LandOfFree
Optical storing 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 storing apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical storing apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2825970