Optical Disk Defect Detection Using Radial Pixel Array Segmentation
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Solution Overview
Problem
Existing methods for optically checking magnetic disks struggle with accurately detecting minute defects due to the Gaussian distribution of laser beam intensity, leading to errors in defect position determination and type classification.
Innovation Solution
An optical checking apparatus with a detector array of pixels that shifts the magnetic disk radially during rotation, using output signals from adjacent turns to determine defect positions and types by comparing specular reflection signals from current, previous, and subsequent disk areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the laser beam irradiates the magnetic disk surface with Gaussian intensity distribution, then the detection covers a larger area, but the defect position determination accuracy deteriorates due to scattered light from nearby defects
Solution Approach 1:
The patent divides the detection area into multiple radial sections by using a detector array with multiple pixels arranged radially. Each pixel or group of pixels detects specular reflection from a specific radial zone, allowing independent analysis of each section to determine defect positions accurately while maintaining comprehensive coverage of the entire disk surface.
Solution Approach 2:
The patent introduces the radial dimension as a new parameter for defect detection. By arranging detector pixels radially and analyzing the reflected light intensity distribution across different radial positions, the system can distinguish between defects at different radial locations, thereby improving position determination accuracy while maintaining large detection area coverage.
2Area of stationary object
If the laser beam irradiates the magnetic disk surface with Gaussian intensity distribution, then the detection covers a larger area, but the defect type classification accuracy deteriorates due to scattered light influence
Solution Approach 1:
The patent segments the detection area into multiple radial zones detected by different pixels. By analyzing the specular reflection characteristics from each radial zone separately, the system can accurately classify defect types (such as scratches, pits, or discoloration) based on their specific radial position and light reflection pattern, reducing misclassification caused by scattered light from adjacent defects.
Solution Approach 2:
The patent applies local quality analysis by examining the light reflection characteristics at each specific radial position detected by individual pixels. Each pixel's detection signal is analyzed to identify local defect properties, allowing accurate classification of defect types based on their unique optical signatures at their specific radial locations, thereby improving overall classification accuracy.
3Ease of operation
If the irradiated area is kept greater than the coverage of detection by the detector, then the checking process is simplified, but the defect position determination accuracy deteriorates due to overlapping detection areas
Solution Approach 1:
The patent segments the detector into multiple pixels, each responsible for a specific radial zone. This segmentation allows the system to maintain simple checking procedures while achieving precise defect position determination, as each pixel independently detects defects in its designated radial area without overlap confusion.
Solution Approach 2:
The patent resolves the overlapping area problem by utilizing the radial dimension. By assigning different radial zones to different pixels and analyzing the reflected light intensity distribution across the radial direction, the system can accurately determine defect positions even when the irradiated area exceeds the detection coverage, eliminating position determination errors.
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
Enhances the accuracy of defect detection by reducing the influence of scattered light from nearby defects and allows for precise determination of convexity/concaveness, enabling the detection of smaller defects and improving overall defect classification.
Implementation Method 1
a rotating magnetic disk is irradiated with a laser beam in a slanted direction to have a specular reflection from the disk surface form an image on a detector
Implementation Method 2
detects a specular reflection and scattered light from the disk surface
Data Source
AI summary
An apparatus for optically checking magnetic disk defects that makes possible more accurate determination of positions of minute defects by illuminating an area greater than a checkup area with an illuminating beam having a Gaussian distribution is to be provided. The apparatus is configured of a specular reflection detecting device including a detector having a detecting face including an array of multiple pixels, and a processing device that figures out the position of each defect by using, in addition to the output signal from each of the pixels of the detector that detected a specular reflection from the checkup area, also output signals of some pixels out of the multiple pixels having detected the specular reflection from the checkup area of one turn before and the checkup area of one turn after, both adjoining in the radial direction, and determines the type of the defect.