Dual Clock Self-Servo Writing for Hard Disk Drive Zone Transitions
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Solution Overview
Problem
Current self-servo writing technologies in hard disk drives face challenges in minimizing error rates and optimizing disk space usage due to limitations in angular and linear data density, particularly at the inner diameter, when writing servo patterns at different frequencies.
Innovation Solution
The implementation of a dual read channel self-servo write system that uses two synchronized clock signals to transition between zones, allowing for parallel frequency synchronization and stepped-up angular frequency from coarse to intermediate and final servo frequencies, thereby reducing error rates and minimizing disk space occupied by servo data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single clock signal is used for self-servo writing, then the system complexity is reduced, but the error rate increases when transitioning between zones with different frequencies
Solution Approach 1:
The clock signal system is segmented into two separate synchronized clocks: a first clock for tracking location data and a second clock for writing new location data. This segmentation allows independent frequency control for reading and writing operations, enabling accurate frequency transitions between zones without compounding errors, thus reducing the error rate during frequency stepping while maintaining manageable system complexity through modular clock management.
Solution Approach 2:
A frequency synchronization mechanism acts as an intermediary between the two clocks, coordinating their frequency transitions. This intermediary synchronizes the clocks during zone transitions, ensuring that frequency changes are coordinated and errors are minimized, while the system maintains the benefit of having separate clock signals for optimized reading and writing operations.
2Quantity of substance
If servo patterns are written at higher frequency to increase angular data density, then disk space usage is optimized, but the error rate during frequency transitions increases
Solution Approach 1:
The system dynamically adjusts the frequency of the second clock based on the zone being written, allowing higher frequencies for increased angular data density in outer zones while maintaining lower frequencies in inner zones. The frequency transitions are dynamically managed through synchronization with the first clock, ensuring accurate transitions without compounding errors, thus achieving high angular data density while maintaining reliability.
3Productivity
If intermediate spirals are written at different frequencies in different portions of the disk, then storage efficiency is optimized, but the complexity of frequency management increases
Solution Approach 1:
The system applies different frequency characteristics to different portions of the disk through zoned frequency management. The first clock operates at a base frequency for tracking, while the second clock is frequency-modulated according to the specific zone being written. This local quality approach optimizes storage efficiency in each zone by using appropriate frequencies while the synchronization mechanism manages the complexity of frequency transitions, preventing error compounding.
Data Source
AI summary
Zone self-servo write (SSW) technology is disclosed that leverages two clock signals synchronized in parallel to transition between zones to write servo patterns at different frequencies while minimizing error rate despite the different frequencies. Two separate clock signals (“clocks”) are used to locate and lock to different reference spirals. By updating both clocks in parallel instead of in series, error rate for writing while stepping up frequency across zones is reduced.