Optical Disc Focus Detection via Signal Level Prediction
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Solution Overview
Problem
Optical disc apparatuses face challenges in accurately detecting the focus of an objective lens on a signal surface due to similarities in reflected signals from the medium surface and signal surface, making it difficult to set detection conditions that distinguish between the two, especially when the difference in output signals is small.
Innovation Solution
Incorporating a drive unit for relative movement of the objective lens, focus detection means, signal level measurement, and prediction means to differentiate between medium surface and signal surface reflections by measuring and predicting signal levels, allowing accurate focus detection on the signal surface even when differences are minimal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the detection condition is set to detect the reflected signal from the signal surface, then the focus detection accuracy is improved, but the medium surface reflection may also satisfy the detection condition causing erroneous detection
Solution Approach 1:
The patent measures the signal level of medium surface reflection in advance before performing focus detection. This preliminary measurement allows the system to predict whether medium surface reflection will interfere with focus detection and adjust the detection strategy accordingly, preventing erroneous detection while maintaining accurate focus detection when possible
Solution Approach 2:
The patent uses the measured medium surface reflection signal level as feedback to determine the focus detection method. When the medium surface reflection signal level is high, the system switches to an alternative detection approach that avoids using the reflected light signal, thereby eliminating the harmful interference while maintaining focus detection capability
2Reliability
If the detection condition is set to avoid medium surface reflection, then false detection is reduced, but it becomes difficult to detect focus on some optical disc media with small signal differences
Solution Approach 1:
The system performs preliminary measurement of the medium surface reflection signal level before focus detection. Based on this preliminary information, it predicts whether medium surface reflection will cause interference and selects the appropriate detection method in advance, ensuring both reliability and accuracy
Solution Approach 2:
The patent dynamically changes the detection parameters based on the measured medium surface reflection signal level. When the medium surface reflection is strong, it adjusts the detection condition to use alternative signals (such as direct light or different wavelength signals) instead of reflected light, thereby maintaining accurate focus detection while avoiding false detection
3Measurement precision
If the objective lens is moved relative to the medium surface for focus detection, then focus state can be detected, but the detection process takes time and may miss the optimal focus point
Solution Approach 1:
The patent measures the medium surface reflection signal level before the focus detection process begins. This preliminary measurement allows the system to predict potential interference and prepare the appropriate detection strategy, enabling faster and more accurate focus detection by avoiding unnecessary lens movements when medium surface reflection will cause false detection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable detection of the focus state on the signal surface by predicting and accounting for medium surface reflections, reducing errors and improving reading accuracy for optical disc media with small signal differences.
Implementation Method 1
an optical pickup for outputting an output signal according to reflected light from the optical disc medium
Data Source
AI summary
An optical disc apparatus includes an optical pickup for outputting an output signal according to reflected light from an optical disc medium, measures a level of a reflected signal corresponding to reflected light from a medium surface prior to reading of information recorded on the medium, predicts, based on the measured level of the reflected signal, whether or not the reflected signal from the medium surface will satisfy a predetermined detection condition when a focus state is to be detected, and uses a result of the predicting to detect a state where the output signal satisfies the predetermined detection condition as a state where a focus of an objective lens included in the optical pickup is on a signal surface of the medium while relatively moving the objective lens with respect to the medium surface when the information recorded on the medium is to be read therefrom.