Variable Demodulation Window for High-Speed Magnetic Disk Head Positioning
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Solution Overview
Problem
Existing magnetic disk devices face challenges in maintaining head position demodulation accuracy and stability as seek speed increases, leading to indefinite amplitude of the fundamental wave component during demodulation, which limits the seek speed for maintaining linearity and accuracy.
Innovation Solution
The demodulation window is switched such that the amplitude of the fundamental wave component of the null-type burst pattern transitions from decreasing to increasing with an increase in seek speed, using a magnetic disk device with a voice coil motor and spindle motor, and a read/write channel that includes a DFT demodulator and speed correction unit to adjust the demodulation window based on seek speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a fixed or narrowed demodulation window is used, then the demodulation process is simple, but the seek speed is limited to 0.3 m/sec or 0.5 m/sec while maintaining linearity and accuracy
Solution Approach 1:
The patent applies dynamics by making the demodulation window variable rather than fixed. The window width is dynamically adjusted based on the instantaneous seek speed: when seek speed is high, the window is narrowed to maintain resolution; when seek speed is low, the window is widened to improve signal stability. This dynamic adaptation resolves the contradiction by allowing high seek speeds (improving speed parameter) while maintaining demodulation accuracy (preserving measurement precision parameter).
Solution Approach 2:
The patent changes the parameter of demodulation window width based on seek speed conditions. By monitoring the instantaneous seek speed and adjusting the window width accordingly, the system maintains optimal demodulation performance across varying speed conditions. This parameter change enables the system to operate at higher seek speeds while preserving measurement precision through appropriate window width selection.
2Speed
If the demodulation window is narrowed to improve linearity at high speeds, then the seek speed can increase, but the signal amplitude becomes indefinite during demodulation
Solution Approach 1:
The system dynamically adjusts the demodulation window width based on real-time seek speed measurement. At high seek speeds, the window is narrowed to maintain linearity and prevent signal amplitude indefiniteness. At lower speeds, the window is widened to ensure stable signal capture. This dynamic behavior resolves the contradiction between speed and reliability by adapting the window to current operating conditions.
Solution Approach 2:
The patent implements feedback by continuously monitoring the instantaneous seek speed and using this information to adjust the demodulation window width. This closed-loop control ensures that the window width is always optimal for current conditions, preventing signal amplitude indefiniteness while maximizing seek speed capability. The feedback mechanism maintains reliability across varying speed conditions.
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 approach enhances the linearity and stability of head position demodulation even at higher seek speeds, allowing for improved seek speed up to 3 m/sec while maintaining demodulation accuracy, compared to fixed or narrowed demodulation windows which are limited to 0.3 m/sec and 0.5 m/sec respectively.
Implementation Method 1
a read head HR that reads a null-type burst pattern recorded on a magnetic disk 2
Implementation Method 2
a discrete Fourier transform (DFT) demodulator 8A that extracts a fundamental wave component from a burst pattern signal
Implementation Method 3
a voice coil motor 4 that moves the magnetic head HM to a target track
Implementation Method 4
a spindle motor 3 that rotates the magnetic disk 2
Data Source
AI summary
According to one embodiment, a head position demodulating method and a magnetic disk device switch a demodulation window such that an amplitude of a fundamental wave component of a null-type burst pattern transitions from a decreasing direction to an increasing direction along with an increase in seek speed during demodulation of the null-type burst pattern recorded on a magnetic disk.