Optical Disc Focus Control Using Signal Segmentation
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Solution Overview
Problem
Conventional optical disc drives face challenges in accurately focusing on the signal surface due to the presence of fake signals, especially in media with low reflectance, making it difficult to distinguish between genuine and fake focusing error signals, leading to potential misalignment and incorrect focusing.
Innovation Solution
An optical disc apparatus with a focus controlling section that detects reflection signals within a predetermined range of distance between the objective lens and the disc surface, using a biaxial actuator and servo signal processing to differentiate between genuine and fake signals by analyzing the focusing error and pull-in signals, allowing precise focus detection and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional optical pickup is used to read optical disc media, then the device can read multiple disc types using wavelength-selective objective lens, but fake signals from surface reflection cause incorrect focusing especially on low reflectance media
Solution Approach 1:
The patent segments the focus detection process into multiple stages: initial focus detection using surface reflection signals, followed by verification using signal surface reflection signals. This segmentation allows the system to distinguish between fake signals (from surface reflection) and genuine signals (from signal surface reflection), resolving the contradiction between versatility and focusing accuracy.
Solution Approach 2:
The patent introduces an intermediary verification mechanism where the focus control unit uses signal surface reflection signals as a mediator to confirm focus accuracy. The system first detects surface reflection signals for initial focus acquisition, then uses signal surface reflection signals as an intermediary to verify and correct any focusing errors, particularly on low reflectance media.
2Measurement precision
If the objective lens is moved closer to the disc surface to detect signal surface reflection, then focusing accuracy improves, but the system becomes more sensitive to fake signals from surface reflection
Solution Approach 1:
The patent implements feedback by continuously monitoring both surface reflection signals and signal surface reflection signals. The focus control unit uses the signal surface reflection signals as feedback to verify focus accuracy and correct any deviations caused by fake signals from surface reflection, enabling precise focusing even when the objective lens is close to the disc surface.
Solution Approach 2:
The patent replaces reliance on mechanical distance adjustment alone with an optical verification system. Instead of solely depending on the physical position of the objective lens, the system uses optical signals (signal surface reflection) to verify focus, substituting mechanical precision with optical verification to eliminate sensitivity to fake signals.
3Reliability
If dedicated drives are provided for each optical disc medium, then reading reliability is maximized, but device complexity and cost increase significantly
Solution Approach 1:
The patent achieves universality by enabling a single optical pickup to reliably read multiple optical disc types (CD, DVD, Blu-ray) with different wavelengths and reflectance characteristics. The focus control unit is designed to handle various disc types by adapting to different signal characteristics, eliminating the need for dedicated drives for each media type while maintaining reading reliability.
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 accurate focusing on the signal surface even in the presence of fake signals, reducing the likelihood of misalignment and improving the reliability of optical disc reading across various media types.
Implementation Method 1
The objective lens 14L refracts and outputs the laser beam, which is led from the light-emitting element 11 through the beam splitter 12 and the hologram element 14H, so as to be focused on a point at a distance of a predetermined focal length F different for every wavelength.
Implementation Method 2
The hologram element 14H of the objective lens body 14 refracts the laser beam, which is led through the objective lens body 14 and reflected on a medium, so that the laser beam has a numerical aperture (NA) corresponding to the wavelength thereof
Implementation Method 3
The photodetector 13 comprises plural optical detecting elements arranged in an N×N matrix, for example. The photodetector 13 respectively outputs signals for the strength of the light detected by the respective plural light-receiving elements.
Data Source
AI summary
One of the objects of the invention is to provide an optical disc apparatus capable of focusing on a signal surface regardless of appearance of a fake signal. The optical disc apparatus includes: an optical pickup for outputting a signal on the basis of reflection light of the optical disc, the optical pickup including an objective lens; a driving section for moving the objective lens of the optical pickup relative to an optical disc surface; and a focus controlling section for carrying out a focus detecting operation by detecting a reflection signal on a signal surface of the optical disc from the output signal of the optical pickup within a predetermined range of distance between the objective lens and the optical disc surface while the objective lens is being moved relative to the optical disc surface by means of the driving section.