Optical Pickup Driving Apparatus for Multi-Layer Disk Positioning
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Solution Overview
Problem
Conventional beam spot positioning methods for multi-layer optical disks face challenges in quickly and reliably positioning the optical spot on the deepest recording layer, leading to potential collisions and increased wait times due to inaccurate focus error signal detection, especially when the reflective index of the layers is low.
Innovation Solution
An optical pickup driving apparatus and method that control the movement of the objective lens based on focus error signals, using slice level voltages to determine movement limits and focus positioning, ensuring accurate detection and avoidance of collisions by setting specific movement distances and using multiple slice level voltages for approaching and backward movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the objective lens is moved quickly to position the beam spot on the deepest recording layer, then the positioning speed is improved, but the risk of collision with the optical disk increases
Solution Approach 1:
The patent applies preliminary action by performing a focus search sequence that first moves the objective lens to a position above the deepest recording layer (but not too close to avoid collision), then moves it closer while monitoring for focus error signal. This preliminary positioning approach allows rapid movement while maintaining safety margins, resolving the contradiction between speed and collision avoidance reliability.
2Measurement precision
If the focus error signal detection threshold is set to be more sensitive, then the positioning precision is improved, but the detection reliability deteriorates due to false signals from low reflective index layers
Solution Approach 1:
The patent segments the focus search process into multiple stages with different detection thresholds. During the initial search phase, a less sensitive threshold is used to avoid false detection from low reflective index layers. Once the beam spot approaches the target layer, the threshold becomes more sensitive for precise positioning. This segmentation allows the system to achieve both detection reliability and precision at different phases of the positioning process.
Solution Approach 2:
The patent implements dynamic adjustment of the focus error signal detection threshold based on the current position of the objective lens. The threshold sensitivity changes dynamically during the focus search: initially less sensitive to avoid false signals, then becoming more sensitive as the beam spot approaches the recording layer. This dynamic adaptation resolves the contradiction between precision and reliability by optimizing the threshold setting for each phase of the positioning process.
3Reliability
If conventional focus control is applied to multi-layer disks, then the beam spot can be positioned on recording layers, but the operation start-up time is increased due to sequential layer scanning
Solution Approach 1:
The patent applies preliminary action by pre-positioning the objective lens to a calculated position above the deepest recording layer before initiating the focus search. This preliminary positioning, based on known layer depth information, allows the system to skip unnecessary scanning of intermediate layers and directly target the deepest layer, significantly reducing operation start-up time while maintaining positioning accuracy through subsequent focus error signal monitoring.
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 rapid and reliable beam spot positioning to the deepest recording layer, reducing the risk of collisions and shortening operation start-up times by accurately detecting focus error signals and adjusting movement accordingly.
Implementation Method 1
a light beam from an optical pickup is caused to impinge on an optical disk
Data Source
AI summary
In an optical pickup driving apparatus and method, a moving device is controlled when an objective lens is moved toward a recording surface and it is detected that the voltage of the focus error signal has reached a slice level voltage H corresponding to displacement of predetermined magnitude from a reference potential E. The objective lens is moved toward the recording surface by a maximum of an upper limit of a predetermined amount of movement and when the amount of movement of the objective lens reaches the predetermined amount of movement, so as to move the objective lens away from the recording surface. And when it is detected during a period of backward movement of the objective lens, that the voltage of the focus error signal has reached the second slice level voltage H corresponding to displacement of predetermined magnitude from the reference potential E, control of beam spot positioning is performed so as to focus an optical spot.