Focus pull-in method and optical disk device
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorTomoaki Ryu
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Abstract
In a focus control of an optical disk with a fast reproduction velocity and a large face deflection, the present invention can effect a mistakeless and reliable focus pull-in method. The present invention comprises: means for applying a braking signal to a focus actuator before closing a focus control loop; means for detecting a reversal of a relative velocity between an objective lens performing a focus search operation and an optical disk which effects an up-and-down motion due to the face deflection; and means for detecting the relative velocity between the objective lens and the optical disk from a focus error signal which is detected in each layer of a multi-layer disk.
Claims12
A focus pull-in method for pulling-in a light spot irradiated through an objective lens onto a recording layer of an optical disk using a focus actuator which can move a position of said objective lens, comprising the steps of:
- (a) applying a search voltage to said focus actuator to drive said objective lens to a direction for approaching to a focusing plane of said optical disk;
- (b) detecting whether or not a focus error signal which is based on a reflected light from said optical disk attains a first signal level;
- (c) applying a braking signal indicating a stop of operation to said focus actuator, when it is detected in said step (b) that said focus error signal reaches said first signal level during a term for allowing a control start of a predetermined focus control;
- and
- (d) starting said predetermined focus control, when a zero-crossing of said focus error signal is detected in the term for allowing said control start, wherein
- said step (c) includes a step of applying said braking signal, when it is detected that all addition signals based on a reflected light from said optical disk exceed a second signal level and said focus error signal reaches said first signal level in the term for allowing said control start.
The focus pull-in method according to claim 6, wherein
- said optical disk includes a first and second recording layers, and
- said step (e) includes a step of obtaining a first detection time of said focus error signal detected with respect to said first recording layer and a second detection time of said focus error signal detected with respect to said second recording layer, to obtain said relative velocity based on a time difference between said first and second detection times.
An optical disk device having a focus control loop and a focus search loop, comprising:
- an objective lens for forming a light stop on a recording layer of an optical disk;
- an optical detector that receives a reflected light from said optical disk for outputting a focus error signal based on the received reflected light;
- a search waveform generator that generates a search voltage for driving said objective lens to a direction which approaches to a focusing plane of said optical disk in response to a focus search instruction;
- a braking signal generator that generates a braking signal indicating a stop of operation to said focus actuator, when it is detected that said focus error signal reaches said first signal level during a term for allowing a control start of a predetermined focus control;
- a zero-crossing detector that detects that a focus error signal reaches a state of zero-crossing;
- and
- a switching device that reopens said predetermined focus control, when said zero-crossing detector detects zero-crossing during the term for allowing said control start, wherein
- said optical detection means comprises:
- a photoelectric conversion element for providing a photoelectric conversion signal by photoelectric conversion of said reflected light;
- and
- an addition amplifier for totally adding said photoelectric conversion signal obtained from each area of said photoelectric conversion element to obtain all addition signals, wherein
- said braking signal generator generates said braking signal, when said all addition signals exceed a second signal level and said focus error signal reaches said first signal level during the term for allowing said control start.
Dependencies are inferred from the claim text.