Spiral Frame Integration Windows for Non-Coherent Repeatable Runout Reduction
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Solution Overview
Problem
The generation of non-coherent repeatable runout during the spiral-based self-servo writing (SSW) process in hard disk drives is significantly affected by sync marks, which distort the center of weight integration and increase position-error signals, making it challenging to achieve precise servo spiral writing.
Innovation Solution
The method involves positioning spiral frame integration windows such that servo spiral sync marks occur partially or completely outside of the integration windows, thereby excluding the magnetic transitions of sync marks from the amplitude integration, reducing the impact on spiral amplitude integration values and minimizing non-coherent repeatable runout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If sync marks are included in the amplitude integration process, then timing information is provided for SSW, but non-coherent repeatable runout increases due to distortion of center of weight
Solution Approach 1:
The integration window is segmented into multiple sub-integration windows, allowing selective integration of signal portions. By dividing the integration window, the system can exclude sync mark regions from amplitude integration while still capturing timing information, thus resolving the contradiction between preserving timing information and maintaining measurement precision.
Solution Approach 2:
The harmful sync mark portions are extracted and excluded from the amplitude integration process. The integration window is positioned to capture only the servo spiral signal portions while deliberately excluding the sync marks, thereby removing the source of distortion while preserving the necessary timing information for SSW.
2Quantity of substance
If integration windows include sync marks, then complete signal integration is achieved, but position-error signal increases due to sync mark distortion
Solution Approach 1:
The sync marks, which cause harmful distortion when included in integration, are used beneficially to define the boundaries of integration windows. By positioning integration windows to exclude sync marks, the system converts the previously harmful element into a useful reference for determining where to start and stop integration, thereby eliminating position-error while maintaining signal integration.
Solution Approach 2:
Different portions of the spiral signal are treated differently: sync mark regions are excluded from amplitude integration while other regions are included. This local differentiation allows the system to integrate signal portions that contribute to accurate position measurement while excluding portions that introduce error.
3Loss of information
If sync marks are positioned asymmetrically in servo spirals, then timing reference is provided, but center of weight distortion occurs during integration
Solution Approach 1:
The asymmetrically positioned sync marks are extracted from the integration process by positioning integration windows to exclude them. This allows the timing reference function of sync marks to be preserved while their harmful effect on center of weight calculation is eliminated.
Solution Approach 2:
The integration window positioning is made dynamic and adaptive, being adjusted for each servo spiral crossing to optimally exclude sync marks while capturing the servo spiral signal. This dynamic adjustment compensates for the asymmetric positioning of sync marks and maintains manufacturing precision.
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 effectively reduces the non-coherent repeatable runout associated with each servo spiral, leading to improved positioning accuracy and reduced errors during the SSW process, enhancing the precision and efficiency of servo spiral writing in hard disk drives.
Implementation Method 1
a read head. Specifically, the radial head position at a particular servo spiral is computed by finding the center of weight of the integrated magnetic transition amplitudes of the servo spiral
Implementation Method 2
a magnetic head of the HDD is positioned relative to a disk surface based on timing and position information in the servo spirals
Data Source
AI summary
A method for collecting position information in a disk drive having a read head and a disk with a set of spirals formed thereon includes: while the read head crosses a first spiral included in the set of spirals, opening a first frame integration window; while the first frame integration window is open, generating first signals with the read head as the read head crosses over a first set of magnetic transitions; closing the first frame integration window; after closing the first frame integration window, generating second signals with the read head as the read head crosses over a second set of magnetic transitions; and determining a radial position of the read head by integrating amplitudes of the first signals, wherein the first set includes magnetic transitions having a first polarity, and the second set includes two or more magnetic transitions having a second polarity.