Optical Disk Unit Focus Control via Dynamic Threshold Adjustment
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Solution Overview
Problem
Existing optical disk drives require separate drives for different types of media, such as CD, DVD, and Blu-ray, which is inconvenient and costly, and face challenges in achieving focus control due to variations in signal levels caused by dust, temperature, and axial runout, leading to difficulties in distinguishing between actual and fake signals.
Innovation Solution
An optical disk unit with a single objective lens capable of selectively irradiating light of multiple wavelengths, using a control section to detect peak levels of fake signals and adjust threshold values based on detected peak levels to achieve focus control on the signal surface, regardless of the optical pickup's state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single objective lens is used to handle multiple optical disk media types, then device complexity is reduced and versatility is improved, but measurement precision deteriorates due to signal level variations from dust, temperature, and axial runout
Solution Approach 1:
The patent applies dynamics by making the threshold value dynamic rather than fixed. The control section automatically adjusts the threshold value based on the detected peak level of the fake signal, allowing the system to adapt to varying signal conditions caused by dust, temperature changes, and axial runout while maintaining accurate focus detection across different optical disk media types
Solution Approach 2:
The patent changes the parameter of the threshold value from a fixed constant to a variable that depends on the detected fake signal peak level. By establishing the threshold value as a function of the fake signal characteristics, the system maintains measurement precision despite variations in signal strength caused by environmental factors and media differences
2Device complexity
If fixed threshold values are used for focus detection, then device complexity is reduced, but reliability deteriorates due to inability to adapt to varying signal conditions
Solution Approach 1:
The system performs self-adjustment by automatically determining the threshold value based on the characteristics of the fake signal detected during operation. The control section uses the detected peak level to establish an appropriate threshold without requiring external calibration or manual intervention, enabling the system to adapt to changing conditions while maintaining simplicity
Solution Approach 2:
The patent implements feedback by using the detected fake signal peak level to adjust the threshold value for focus detection. The system continuously monitors the fake signal characteristics and uses this information to optimize the threshold, creating a closed-loop control mechanism that improves reliability while maintaining operational simplicity
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 focus control on various optical disk media types with a single drive, improving focus accuracy by dynamically adjusting threshold values based on detected signal levels, even in conditions with low signal detection due to dust or temperature variations.
Implementation Method 1
outputting signals based on light reflected by the optical disk medium
Implementation Method 2
refracts and outputs light that has been guided from the light emitting elements through the beam splitter 12 and the hologram element 14H so that focal points are focused at positions specified by focal distance F that is different for each wavelength
Implementation Method 3
The hologram element 14H of the objective lens body 14 diffracts laser light that has been guided by means of the objective lens 14L and reflected by the medium so as to become a predetermined numerical aperture (NA) for each wavelength of laser light
Data Source
AI summary
An optical disk unit, for reading signals stored on an optical disk medium, is provided with an optical pickup 23 selectively irradiating light of one wavelength, from several mutually different wavelengths, to an optical disk medium by means of a single objective lens and outputting signals based on light reflected by the optical disk medium, a drive section for causing relative movement of the objective lens of the optical pickup with respect to a surface of the optical disk medium, wherein a peak level of a fake signal generated in the received light signal based on surface reflection at the optical disk surface while the objective lens is being moved relative to the optical disk medium surface by the drive section is detected, and the received light signal is compared with a threshold value that is set based on the detected peak level, to detect reflected light of a data storage layer.