Fly Height Control via Readback Signal Distortion
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Solution Overview
Problem
Current data storage devices using magnetic media face challenges in accurately controlling fly height and crosstrack position over the disk surface, especially when dealing with random data, as existing methods like harmonic ratio testing are insensitive and require multiple servo sectors for accurate clearance detection.
Innovation Solution
The use of Volterra kernels to extract distortion components from readback signals allows for simultaneous estimation and control of fly height and crosstrack position, enabling closed-loop control using measurements derived from linear and second-order Volterra kernels, along with a normalized sum of taps, which can operate with user/random data and provide increased bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If harmonic ratio testing is used to detect clearance, then clearance detection is performed, but the method is insensitive and requires multiple servo sectors for accurate detection
Solution Approach 1:
The patent replaces traditional mechanical/clearance-based sensing methods (harmonic ratio testing) with a signal processing approach using Volterra kernels to extract distortion components from readback signals. This substitution enables more sensitive and accurate clearance detection by analyzing signal distortion characteristics rather than relying on mechanical servo sector patterns.
Solution Approach 2:
The patent changes the detection parameter from harmonic ratio (traditional method) to distortion component magnitude (new method). By monitoring the magnitude of distortion components extracted via Volterra kernels, the system achieves higher sensitivity and accuracy in clearance detection, resolving the contradiction between measurement precision and productivity.
2Measurement precision
If Volterra kernels are used to extract distortion components, then measurement precision and bandwidth are improved, but device complexity increases
Solution Approach 1:
The patent implements self-service by using the readback signal itself as the source of measurement information. The Volterra kernels process the existing readback signal to extract distortion components that contain clearance and position information, eliminating the need for separate sensing mechanisms or additional hardware, thus managing complexity while improving precision.
Solution Approach 2:
The patent makes the readback signal serve multiple functions: data retrieval and clearance/position measurement. By processing the same signal through Volterra kernels to extract distortion components, the system achieves multi-functionality, improving measurement precision without requiring separate dedicated sensing hardware, thereby managing device complexity.
3Manufacturing precision
If closed-loop control is implemented using Volterra kernel measurements, then alignment and spacing control are improved, but control system complexity increases
Solution Approach 1:
The patent implements feedback control by using distortion component magnitudes from Volterra kernel processing as feedback signals. These feedback signals provide real-time information about clearance and crosstrack position, enabling closed-loop control adjustments to maintain optimal alignment and spacing, thereby improving manufacturing precision through intelligent feedback mechanisms.
Data Source
AI summary
A controller extracts a distortion component of a readback signal from a magnetic read head. The distortion component may be found using a finite length Volterra series, for example. The controller estimates a clearance between the read head and a recording medium based on the distortion component. This clearance measurement can be used for closed loop fly-height control of the read head.