Optical Disk Focal Position Control with Spherical Aberration Correction
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Solution Overview
Problem
Optical disk apparatuses face challenges in reliably detecting the target recording layer on Blu-ray disks due to the influence of spherical aberration and the close proximity of recording layers, which can lead to failure in focus search operations and potential collisions with the optical disk.
Innovation Solution
The apparatus includes an objective lens, spherical aberration correcting means, and a recording layer detecting mechanism that uses sum and focus error signals to reliably identify and maintain focus on the target recording layer, even when layers are closely spaced or have similar reflectivity, by employing a redetection period and overrun mechanism to ensure accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the objective lens is driven to move closer to the optical disk to detect the recording layer, then the focus position approaches the target layer, but spherical aberration increases and detection accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by performing spherical aberration correction before the focus search operation. The correction amount is calculated based on the objective lens position and disc type, and the spherical aberration correcting lens is pre-adjusted to compensate for aberrations that will occur during the subsequent focus search, thereby improving detection accuracy without suffering from excessive aberration effects.
Solution Approach 2:
The patent replaces pure mechanical focus searching with an optical correction mechanism. By introducing a spherical aberration correcting lens that can be optically adjusted based on calculated parameters, the system substitutes mechanical trial-and-error focusing with an optically-assisted precision approach, reducing the harmful effects of spherical aberration during detection.
2Reliability
If the focus search operates without spherical aberration correction, then the control process is simple, but the objective lens may collide with the optical disk due to inaccurate detection
Solution Approach 1:
The patent replaces complex mechanical collision avoidance mechanisms with an optical calculation and correction system. By calculating the spherical aberration based on lens position and disc type, and applying optical correction through the spherical aberration correcting lens, the system achieves reliable collision prevention without requiring complex mechanical safety mechanisms.
Solution Approach 2:
The system performs preliminary spherical aberration correction before the focus search begins, based on pre-calculated parameters from the objective lens position and disc type. This preliminary optical adjustment ensures that subsequent focus searching is performed with minimal aberration, thereby preventing detection errors that could lead to lens-disk collision.
3Measurement precision
If the spherical aberration correction amount is increased to improve detection accuracy, then the focus search precision improves, but the response time increases due to additional calculation and adjustment steps
Solution Approach 1:
The patent performs spherical aberration correction in advance before the focus search operation. The correction amount is calculated based on the current objective lens position and disc type, allowing the focus search to proceed with pre-compensated optical parameters. This preliminary correction improves accuracy without significantly extending the overall search time, as the correction setup is prepared beforehand.
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
This solution enables reliable detection of the target recording layer, preventing collisions and ensuring accurate focus servo operation, even in cases where spherical aberration and close layer spacing complicate the identification process.
Implementation Method 1
an objective lens for converging the light beam emitted from a light source to irradiate the optical disk
Implementation Method 2
a spherical aberration correcting means for correcting the spherical aberration produced by the light beam according to the recording layer to be used
Implementation Method 3
a light receiving means for receiving reflected light of the light beam and generating a sum signal indicating the quantity of light of the reflected light
Implementation Method 4
a focus error signal for outputting the signal level as a function of the distance from the focal position of the light beam to the recording layer
Data Source
AI summary
An optical disk apparatus can reliably detect the target recording layer of an optical disk having two recording layers. The optical disk apparatus is adapted to recording information on and reproducing information from an optical disk formed by sequentially laying a first recording layer, a second recording layer and a cover layer. The focal point of the light beam is moved closer to the optical disk from the side of the cover layer and the focal point of the light beam is determined to be coming close to the recording layer when the signal level of the focus error signal falls below a positive focus error threshold value after rising above the latter or rises above the negative focus error threshold value after falling below the latter. Then, the focal point of the light beam is kept on moving toward the optical disk after the detection of the recording layer and the recording layer that is detected last is determined to be the first recording layer when the recording layer is not re-detected within a re-detection period.