Calibrating Spiral Servos for Hard Disk Drive Track Spacing
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Solution Overview
Problem
Conventional servo writers for magnetic-medium-based storage devices are large, expensive, and face bottlenecks in manufacturing due to increased servo writing time as track density increases, leading to imprecise radial spacing between servo tracks caused by variations in spiral slope.
Innovation Solution
A method and apparatus for calibrating spiral servos in self-servo-write processes by determining the measured slope of spirals and using it to calibrate radial spacing between servo tracks, involving a processing module that scales target timing and track pitch according to the slope ratio, and includes submodules for noise removal and system gain determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional servo writers are used to write servo information, then servo tracks can be written with high accuracy, but the device size is large and manufacturing cost is high
Solution Approach 1:
The patent implements self-servo-write where the disk drive itself writes the servo information using its own read/write heads and servo control system, eliminating the need for external servo writers. The servo patterns are written during normal disk operation using the drive's inherent capabilities, making the system self-sufficient for servo track creation
Solution Approach 2:
The patent extracts the servo writing function from the external servo writer device and integrates it into the disk drive's normal operation. By using the drive's own heads and control systems to write servo information, the complex external equipment is removed while retaining the essential servo track writing capability
2Quantity of substance
If track density is increased to improve storage capacity, then more data can be stored, but servo writing time increases creating a manufacturing bottleneck
Solution Approach 1:
The patent enables continuous servo writing throughout the entire radial extent of the disk during normal operation. Unlike conventional methods that require sequential writing of each track, the self-servo-write process continuously writes servo information as the disk rotates and the head moves radially, eliminating idle time and making the servo writing process as efficient as data writing
Solution Approach 2:
The patent writes servo information preliminarily during the initial formatting operation before data writing begins. By establishing servo tracks in advance using the self-servo-write method, subsequent data operations can proceed without additional servo writing delays, even as track density increases
3Ease of manufacture
If spiral slope variations occur during self-servo-write, then the process is simpler, but radial spacing between servo tracks becomes imprecise
Solution Approach 1:
The patent implements feedback by reading back the written spiral patterns and measuring the actual slope. The measured slope information is fed back to the control system, which then adjusts the head positioning and timing to compensate for slope variations, ensuring precise radial spacing between servo tracks despite variations in the writing process
Solution Approach 2:
The patent dynamically adjusts writing parameters such as head velocity, radial positioning, and timing based on the measured spiral slope. By changing these parameters in response to actual measurements, the system compensates for slope variations and maintains precise radial spacing between servo tracks
Data Source
AI summary
Methods, systems, and apparatus, including computer program products, are described for calibrating servos, and in some implementations for calibrating spiral servos for use in self servo write processes. In one aspect, a method is provided that includes measuring a slope of a spiral written to a machine readable medium, and adjusting a parameter in accordance with the measured slope to calibrate spacing of servo tracks, with respect to variation between a target slope and the measured slope for the spiral, for writing the servo tracks to the machine readable medium using the spiral as a reference and the adjusted parameter to generate a same radial spacing between servo tracks from spirals with different slopes.