Optical Disc Tracking Servo Boundary Offset Compensation

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Solution Overview

Problem

Existing recording and playing apparatus face challenges in stabilizing tracking on optical discs due to boundary offsets when converging light on the boundary between recorded and unrecorded tracks, which affects the accuracy and stability of tracking servo operations.

Innovation Solution

The apparatus employs a specific configuration of photosensors in the photo detector, including first to eighth photosensors, strategically positioned to cover regions where 0th-order, +1st-order, and −1st-order diffracted light are incident, allowing for the calculation of tracking error signals that reduce boundary offsets through coefficients k1 and k2, thereby improving tracking stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the Advanced Push-Pull method is used to reduce tracking offset, then tracking stability is improved, but boundary offset occurs when converging light on the boundary between recorded and unrecorded tracks

Engineering Contradiction:

Improvetracking stabilityVSAvoidtracking accuracy at boundary

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The photo detector is divided into multiple photosensors (first to eighth photosensors) arranged in specific regions. This segmentation allows independent detection of different light components (0th-order, +1st-order, -1st-order diffracted light) and enables separate processing of boundary offset and tracking error signals, resolving the contradiction between overall tracking stability and boundary-specific accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different photosensors are positioned to cover specific regions with different detection characteristics. The first and second photosensors detect overlapped light at the boundary, while the third to sixth photosensors detect 0th-order light, and the seventh and eighth photosensors detect diffracted light. This local differentiation enables precise boundary offset compensation without affecting overall tracking stability.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If multiple photosensors are arranged to detect boundary offset, then tracking accuracy is improved, but device complexity increases

Engineering Contradiction:

Improveboundary offset detection accuracyVSAvoidphoto detector structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The photo detector with multiple photosensors serves multiple functions simultaneously: detecting boundary offset, detecting tracking error, and maintaining tracking stability. By integrating these functions into a single multi-sensor structure rather than separate systems, the patent improves measurement precision while controlling overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent combines boundary offset detection and tracking error detection into a unified photo detector structure. The multiple photosensors work together to generate both types of signals through coordinated detection of different light orders, merging what could have been separate detection systems into one integrated component.

Inventive Principle:

Principle #5Merging (Combining)

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 configuration significantly reduces boundary offsets, enhancing the stability and accuracy of tracking servo operations, even with varying groove pitches and diffraction angles, leading to more reliable data reading and writing on optical discs.

Implementation Method 1

a light source; an optical system including a plurality of optical elements, the optical system converging light generated by the light source onto a track of the recording medium

Methodology Applied

Scientific EffectLight: Light

Implementation Method 2

transmitting 0th-order light, +1st-order diffracted light, and −1st-order diffracted light, which are reflected by the recording medium

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

a photo detector including first to eighth photosensors, each of the first to eighth photosensors generating an output signal depending on incident light

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 4

transmitting 0th-order light, +1st-order diffracted light, and −1st-order diffracted light, which are reflected by the recording medium

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS9911449B2Recorder and player apparatus stably keeping track of recording medium

Publication Date: 2018.03.06 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

The first, third, fourth, and seventh photosensors are disposed on one side with respect to the centerline, and the second, fifth, sixth, and eighth photosensors are disposed on another side with respect to the centerline. The first and seventh photosensors are positioned between the third and fourth photosensors in the direction parallel to the centerline. The second and eighth photosensors are positioned between the fifth and sixth photosensors in the direction parallel to the centerline. The first photosensor receives overlapped light of the 0th-order light with the +1st-order diffracted light, the second photosensor receives overlapped light of the 0th-order light with the −1st-order diffracted light, each of the third to sixth photosensors receives the 0th-order light, and does not receive the +1st-order diffracted light and the −1st-order diffracted light, and each of the seventh and eighth photosensors receives at least the 0th-order light.