In-Drive Erase Spirals for Single-Surface HDD Servo Positioning
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Solution Overview
Problem
Single-surface hard disk drives (HDDs) face challenges in erasing recording surfaces due to interference from obsolete spiral tracks, requiring external equipment and partial disassembly, which is time-consuming and costly in high-volume manufacturing.
Innovation Solution
An in-drive erase process is implemented using erase spirals written at a different frequency than data patterns, with a controlled erase window to prevent complete overwrite, allowing the HDD to erase its own surfaces without external equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external equipment is used to erase recording surfaces, then erasure thoroughness is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The HDD performs erasure of its own recording surface using its internal writer and reader components. The writer writes erase patterns while the reader detects spiral track positions, enabling the device to erase itself without external equipment. This eliminates the need for external media bulk erase devices or servo-track writers.
Solution Approach 2:
The writer component performs multiple functions: writing data patterns during normal operation and writing erase patterns during erasure operations. The reader similarly serves both data reading and spiral track detection functions. This multi-functionality eliminates the need for dedicated external erasure equipment.
2Reliability
If external equipment is used for erasure, then erasure completeness is improved, but manufacturing time increases
Solution Approach 1:
The self-erasure capability allows HDDs to be erased in-place during the manufacturing process without requiring removal from clean rooms or setup of external equipment. This significantly reduces manufacturing cycle time and increases throughput while maintaining erasure effectiveness.
3Reliability
If spiral tracks are completely overwritten during erasure, then erasure effectiveness is improved, but the ability to reuse erase spirals for positioning is lost
Solution Approach 1:
The erasure process applies different treatments to different regions: erase patterns are written between spiral tracks to erase data, while the spiral tracks themselves are preserved. This local differentiation allows the system to achieve both erasure effectiveness and positioning capability.
Solution Approach 2:
Spiral tracks are written first as a preliminary step before data erasure. These pre-written spiral tracks serve as positioning references that guide the erasure process, ensuring that erase patterns are written in the correct locations without completely overwriting the positioning structures.
4Device complexity
If a single recording surface is used, then device simplicity is improved, but in-drive erasure capability is lost
Solution Approach 1:
The patent transitions from a multi-surface approach to a single-surface approach by utilizing the temporal dimension (different write frequencies) and spatial positioning (radial locations between spirals) to enable in-drive erasure. Erase spirals are written at a different frequency than data patterns, allowing differentiation and enabling self-erasure on a single surface.
Data Source
AI summary
In an in-drive erase process in a single-surface HDD, erase spirals on the surface being erased can be employed to control writer position. A reader-to-writer timing offset value is determined for a plurality of radial locations on the surface to be erased, and an erase window is determined for a radial location disposed between two erase spirals. The erase window includes an erase start time, which is based on a spiral exit time of a reader and the reader-to-writer timing offset value for the radial location, and an erase stop time, which is based on a spiral encounter time of the reader and the reader-to-writer timing offset value. The erase window prevents complete erasure of erase spirals, so that the servo system of the HDD can continue to servo off of the erase spirals. The erase spirals may be written with a lower slope than conventional spiral tracks.