Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-07-14
2001-06-12
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044250, C369S112010
Reexamination Certificate
active
06246646
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focus control apparatus installed in a reproduction apparatus which reproduces data from a multilayer optical recording medium.
2. Description of Related Art
One way to improve the recording density of a disk is multiplexing of information in a direction perpendicular to the disk's surface. A multilayer optical disk is capable of implementing such perpendicularly multiplexed information recording. With a double-layer optical disk in use, for example, first and second layers are formed with a spacer region in between as shown in
FIG. 1
, and the first layer closer to the light irradiated surface of the disk is made translucent so that light receives the second layer.
In reproduction of such a multilayer optical disk, changing the layer from which recorded information is to be read requires that a focus control apparatus should carry out a focus jump operation to rapidly focus read light on the next reading layer.
Normally, the focus jump operation to shift the focal point of read light from the information recorded surface on one layer to the information recorded surface on another is executed based on zero-crossing detection of a focus error signal which is generated based on the output of a pickup.
Specifically, the pickup is provided with a focus actuator, a read-light emitting optical system, for example, which moves an objective lens for determining the focal point of the optical system along the optical axis to thereby shift the focal point of the read light in a direction perpendicular to the surface of the disk. In the initial stage of the focus jump operation, this focus actuator is supplied with an acceleration signal or a focus jump enable signal to shift the focal point of the read light to a target recording surface. Based on the timing of zero-crossing which is detected one after another from a focus error signal acquired during displacement of the focus actuator that is implemented in response to the acceleration signal, a series of operations of terminating the supply of the acceleration signal, supplying a deceleration signal to the focus actuator to stop the displacement of the focus actuator that has taken place in response to the acceleration signal or stopping supplying the deceleration signal and restarting focus servo on the target recording surface.
In this focus control apparatus for a multilayer optical disk, while the point at which a focus error signal passes a zero-crossing point is detected during a focus jump operation, zero-crossing detection is actually carried out with a level a little apart from the zero level taken as a threshold value in consideration of an influence of a noise component or the like. However, the amount of a change in the level of the focus error signal during a focus jump operation is not always constant due to a difference in reflectance from one layer of the disk to another or some stain or the like on the objective lens. If the threshold value is fixed, therefore, a stable focus jump cannot be expected when the supply of an acceleration signal or deceleration signal is stopped at the zero-crossing timing that has been detected in accordance with the fixed threshold value.
OBJECT AND SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a focus control apparatus for a multilayer optical recording medium, which can adequately perform a focus jump on a multilayer optical recording medium.
According to one aspect of this invention, a focus control apparatus for a multilayer optical recording medium for implementing such focus jump control as to temporarily release a focus servo on one layer of a loaded multilayer optical recording medium, shift a focus position of read light on another target layer and then restart the focus servo on the another target layer, is characterized in that a threshold value corresponding to an amount of a change in a level of a focus error signal of the loaded multilayer optical recording medium is set, and the focus jump control is carried out based on a result of comparison between the level of the focus error signal and the set threshold value.
According to another aspect of this invention, a focus control apparatus for a playback apparatus for playing back a recording medium having information recording surfaces on at least two layers formed perpendicular to a surface of the recording medium, comprises pickup means for irradiating a read light on the recording medium, receiving return light of the read light from the recording medium, and generating a read signal indicative of information recorded on the recording medium and a focus error signal indicative of a focus error of the read light with respect to each of the information recording surfaces; zero-crossing detection means for detecting zero-crossing by comparing a level of the focus error signal with a positive threshold value and a negative threshold value; instruction means for generating a focus jump instruction; drive means for performing a focus servo operation to drive a focus actuator of the pickup means in order to focus the read light on each target information recording surface in accordance with the focus error signal, starting an acceleration operation of the focus actuator in response to the focus jump instruction in order to shift a focus position of the read light from the recording surface of one of the at least two layers to the recording surface of another layer, stopping the acceleration operation in accordance with zero-crossing detection by the zero-crossing detection means, thereafter starting a deceleration operation of the focus actuator and then stopping the deceleration operation and returning to the focus servo operation in accordance with zero-crossing detection by the zero-crossing detection means; and threshold value setting means for setting the positive threshold value and the negative threshold value according to an amount of a change in a level of the focus error signal.
REFERENCES:
patent: 5748597 (1998-05-01), Kim
patent: 6027594 (2000-02-01), Nishiuchi et al.
Abe Hiroyuki
Bradshaw Alex
Kawana Kazushige
Matsuda Norio
Naohara Shinichi
Edun Muhammad
Pioneer Electronic Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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