Self-Servo Write Stitching for Disk Drive Alignment
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Solution Overview
Problem
Self-servo writing techniques in disk drives face challenges with servo wedge misalignment and interruptions, leading to track squeeze and synchronization issues due to radial and circumferential position errors, which affect data storage and retrieval efficiency.
Innovation Solution
A control system that writes a servo test track after a reference servo track, allowing the write head to position and align new servo tracks based on detected radial and circumferential positions, offset values, and repeatable run-out components, ensuring seamless alignment and minimizing repetitive position errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If self-servo writing is used to reduce manufacturing time, then productivity is improved, but servo wedge misalignment and track squeeze occur due to radial and circumferential position errors
Solution Approach 1:
The patent implements a feedback mechanism where the servo controller continuously monitors the radial and circumferential positions of the read/write head using servo information from previously written tracks. This feedback is used to dynamically adjust head positioning and timing parameters during the self-servo writing process, compensating for position errors and preventing servo wedge misalignment while maintaining high productivity
Solution Approach 2:
The patent replaces the traditional mechanical servo writer system with an electronic control-based self-servo writing system. Instead of using external mechanical positioning devices, the system uses electronic servo controllers and software algorithms to position the read/write head and write servo patterns, eliminating the need for expensive mechanical infrastructure while achieving comparable or better precision
2Manufacturing precision
If traditional servo writers are used to ensure precise servo pattern writing, then manufacturing precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent enables the hard disk drive to write its own servo patterns using its internal read/write heads and servo control systems, without requiring external servo writer equipment. The drive uses previously written servo information to position and time the writing of new servo patterns, making the system self-sufficient and eliminating complex external positioning infrastructure
Solution Approach 2:
The patent makes the read/write head serve dual functions: both writing user data and writing servo patterns. The same actuator and head assembly used for data operations are also used for servo writing, eliminating the need for separate specialized servo writing mechanisms and reducing overall system complexity
3Productivity
If sectional spiral servo tracks are written to reduce writing time, then productivity is improved, but interruptions cause gaps or overlapping of servo wedges leading to track misalignment
Solution Approach 1:
The patent writes a test servo track before the actual servo patterns to establish reference timing and position information. This preliminary action creates a foundation that ensures proper alignment and timing for subsequent servo wedge writing, preventing gaps or overlaps even if interruptions occur during the writing process
Solution Approach 2:
The system continuously monitors writing progress and uses feedback from the test track and previously written servo patterns to adjust timing and positioning parameters. This real-time feedback ensures that servo wedges are written with correct spacing and alignment, maintaining track continuity despite interruptions in the writing process
Data Source
AI summary
A control system includes a write head that writes servo data on a rotating medium. A control module signals the write head to write a servo test track on the rotating medium and subsequent to a reference servo track. The reference servo track is written prior to an interrupt event. The control module detects a position of the servo test track relative to the reference servo track and signals the write head to write a new servo track based on the position after the interrupt event.