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US 4,786,794 AGranted
Focus servo-circuit with ordered reference level setting means
AssigneeOlympus Optical Co., Ltd.
InventorMasanori Doi
Life of this patent
Estimating the term…
Abstract
In order to focus light beams which are projected onto an optical recording medium, the focusing optical system is moved in a vertical direction to the surface of the recording medium. A focus error signal produced by receiving the light returning from the recording medium is compared in turn with a predetermined plurality of reference levels. A focus servo-means is operated when this signal reaches the reference level within the focus pull-in region after passing through a predetermined order of reference levels.
Claims15
A focus servo-means comprising:
- an optical recording medium;
- a light source which generates light;
- a focus servo-loop means including
- an optical system for collecting the light generated by the light source and for projecting said light onto said optical recording medium,
- a focus actuator applies a driving signal to said optical system to move said opticl system varying distances from said recording medium,
- a photodetector detects the light reflected from said recording medium,
- an error signal producing circuit connected to said photodetector, said error signal producing circuit for producing focus error signals corresponding to the light detected by said photodetector, and
- a driving circuit amplifies said focus error signals from said error signal producing circuit and for outputs the amplified focus error signals as driving signals for said focus actuator;
- a switch connected between said driving circuit and said error signal producing circuit, said switch opening and closing said focus servo-loop means;
- a moving signal producing means for outputting a move signal to the driving circuit to move said optical system varying distances from said recording medium, said move signal being applied to said driving circuit when said switch is opened;
- an ordered reference level setting means for setting a plurality of ordered reference levels from the focus error signal characteristics, at least one of said ordered reference levels being set within a focus pull-in region;
- a comparing means for successfully comparing over time said plurality of ordered reference levels with the focus error signal detected from said error signal producing circuit when said move signal is applied to said driving circuit;
- and
- a servo-starting means for closing said switch to set a focus servo-state when the focus error signal, from said error signal producing circuit which has said move signal applied to said driving circuit, is at least equal to said plurality of ordered reference levels as compared by said comparing means, said focus error signal being within said focus pull-in regional when said focus servo-state is set.
11 more elements
Dependencies are inferred from the claim text.