Self-Servo-Write Spiral Sync-Mark Detection for HDD Servo Wedge Positioning
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Solution Overview
Problem
Existing hard disk drive (HDD) servo writing techniques are costly and error-prone, requiring precise placement of servo wedges and often necessitating special hardware or complicated feedforward mechanisms, with limited tolerance for position errors in the spiral waveform.
Innovation Solution
The method involves writing servo wedges using a self-servo write system that utilizes spiral sync-mark detection, allowing for adjustable frequency and phase of the servo write clock to align the wedge-to-wedge time intervals with desired locations, enabling precise positioning without the need for prewritten seed servo wedges and reducing the requirement for precise location of the spiral waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional servo writing techniques are used with special hardware and feedforward mechanisms, then positioning accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system uses self-servo-write where the disk itself provides the reference signal through spiral sync marks that are detected during normal operation. The servo writing process uses feedback from the actual disk rotation to automatically adjust and lock onto the correct positioning, eliminating the need for external special hardware or complex feedforward mechanisms while maintaining high positioning accuracy
Solution Approach 2:
The invention implements a feedback mechanism where the spiral sync mark detection provides continuous position information that is fed back to the servo controller. The system monitors the detected sync mark positions and adjusts the servo write clock frequency and phase accordingly, creating a closed-loop system that achieves precise positioning without requiring complex open-loop feedforward hardware
2Reliability
If traditional servo writing with prewritten seed servo wedges is used, then positioning reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The system performs preliminary action by writing spiral sync marks to the disk during the manufacturing process. These sync marks serve as reference signals that enable the self-servo-write process to automatically establish accurate positioning. The preliminary placement of these reference marks simplifies subsequent manufacturing steps and eliminates the need for complex seed servo wedge pre-writing procedures
Solution Approach 2:
The disk is made self-sufficient by incorporating spiral sync marks that provide all necessary reference information for servo writing. The system uses its own rotation and the embedded sync marks to automatically establish accurate positioning without requiring external pre-written seed patterns or complex manufacturing procedures, thereby improving both reliability and ease of manufacture
3Manufacturing precision
If strict position tolerance is enforced for spiral waveform, then servo wedge accuracy is improved, but process flexibility decreases
Solution Approach 1:
The feedback mechanism continuously monitors the actual position of detected sync marks and dynamically adjusts the servo write clock frequency and phase to compensate for position errors. This closed-loop control allows the system to achieve high servo wedge accuracy even when the spiral waveform has position variations, thereby maintaining manufacturing precision while increasing process flexibility and tolerance
Solution Approach 2:
The system transitions from a static, rigid positioning approach to a dynamic adaptive approach. The servo write clock frequency and phase are continuously adjusted based on real-time sync mark detection results, allowing the system to adapt to variations in spiral waveform positioning. This dynamic adjustment maintains high accuracy while significantly increasing tolerance for manufacturing variations
4Adaptability or versatility
If spiral sync-mark detection with adjustable clock is used, then positioning adaptability is improved, but control complexity increases
Solution Approach 1:
The control mechanism uses simple feedback from sync mark detection positions to automatically adjust the servo write clock frequency and phase. The system compares detected sync mark positions with expected positions and makes proportional adjustments, creating an intuitive and straightforward control loop that achieves high adaptability without requiring complex control algorithms or additional hardware
Data Source
AI summary
Writing servo wedge code to a disk is disclosed. A wedge-to-wedge time interval is determined. At least until it is determined that a lock criterion is met: For each wedge-to-wedge time interval, a wedge frequency error is computed based on an adjustable clock. The clock is adjusted based on one or more of the wedge frequency errors. It is determined whether a lock criterion is met based on one or more of the wedge frequency errors. After the lock criterion is met, servo wedge code is written to the disk.