Position Demodulation Using Lissajous Figure Correction
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Solution Overview
Problem
In storage devices, accurately determining the position of a magnetic head based on servo patterns is challenging due to the difficulty in associating signal readings with head position, especially when the head is moving, requiring a correction process to improve positional accuracy.
Innovation Solution
A position demodulation apparatus comprising a demodulator and a correcting module that processes first and second demodulation signals with a 90-degree phase difference, correcting their traces to maintain a constant ratio of intersection lengths on orthogonal axes, allowing for accurate head position determination despite moving velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position determination is based on servo pattern signals, then position information can be obtained, but the accuracy deteriorates when the head is moving due to difficulty in associating signal readings with head position
Solution Approach 1:
The patent introduces Lissajous figures as an intermediary representation that transforms the relationship between demodulation signals and head position. By plotting the first and second demodulation signals against each other to create Lissajous figures, the system creates a visual and mathematical intermediary that clearly indicates head position through the figure's characteristics, resolving the difficulty of directly associating signals with position during movement
Solution Approach 2:
The patent uses changes in the characteristics of Lissajous figures (analogous to color changes in optical detection) to indicate different head positions. The shape, orientation, and other properties of the Lissajous figures change systematically with head position, providing a reliable and accurate indicator that works regardless of head movement velocity
2Measurement precision
If a correction process is applied to improve position accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical correction processes with a signal processing approach using Lissajous figures. Instead of physically adjusting or mechanically correcting position measurements, the system uses mathematical transformation of demodulation signals into Lissajous figure representations, which automatically provide corrected position information through the figures' inherent geometric properties
Solution Approach 2:
The patent changes the parameter representation from raw demodulation signal amplitudes to Lissajous figure characteristics (shape, orientation, etc.). This parameter transformation simplifies the correction process because the Lissajous figure parameters directly encode the corrected head position information, eliminating the need for complex correction algorithms
Data Source
AI summary
According to one embodiment, a position demodulation method includes demodulating a first demodulation signal and a second demodulation signal having a phase difference of 90 degrees to the first demodulation signal based on a read-out signal obtained by reading out a servo pattern recorded on a medium by the head for positioning of a head with respect to the medium; correcting the first and second demodulation signals in which, when a trace of a Lissajous figure is drawn representing the first and second demodulation signals as values on coordinate axes different from each other on a plane, a ratio of respective lengths between intersections of the trace intersecting with two axes orthogonal at an origin of the plane is kept constant; and demodulating a positional signal for determining a position of the head based on the first and second demodulation signals after being corrected at the correcting.