HDD Spacing Fluctuation Measurement via HDI Sensor
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Solution Overview
Problem
Current hard disk drives face challenges in accurately measuring and controlling the fluctuating spacing between the magnetic read/write head and the disk surface, especially as recording density increases, leading to potential system failures due to inconsistent flying height and disk distortions.
Innovation Solution
A method utilizing a head-disk interference sensor to analyze signals generated by a heat-producing element in the slider, allowing for sector-by-sector touchdown power determination and providing quantitative data on spacing fluctuations, enabling precise monitoring and compensation of disk distortions and misalignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the flying height is decreased to increase recording density, then the recording area density is improved, but the spacing control precision deteriorates due to increased sensitivity to disk distortions and misalignments
Solution Approach 1:
The patent segments the measurement process into sector-by-sector analysis, dividing the disk rotation into discrete measurement units. This allows identification of spacing variations in different radial zones, enabling targeted compensation for disk distortions and misalignments while maintaining overall high recording density
Solution Approach 2:
The patent implements feedback control by using the head-disk interference sensor to continuously monitor spacing fluctuations and providing real-time measurements of touchdown power variations. This feedback enables dynamic adjustment of spacing control parameters to compensate for disk distortions, maintaining precision even at reduced flying heights
2Ease of operation
If traditional touchdown detection methods are used, then the reference point determination is simplified, but the measurement accuracy deteriorates due to inability to detect sector-by-sector spacing variations
Solution Approach 1:
The patent applies segmentation by analyzing touchdown power measurements for each sector individually rather than as a single averaged value. This sector-by-sector approach reveals spacing variations caused by disk distortions and misalignments that would be masked in traditional overall touchdown detection, significantly improving measurement precision
Solution Approach 2:
The patent uses excessive measurement action by continuously monitoring touchdown power across all sectors and performing detailed statistical analysis (standard deviation, maximum deviations) beyond what traditional single-point touchdown detection provides. This excessive analysis ensures accurate detection of even minor spacing fluctuations
3Reliability
If real-time monitoring of spacing fluctuations is implemented, then the reliability is improved, but the device complexity increases due to additional sensors and signal processing requirements
Solution Approach 1:
The patent achieves multi-functionality by using the head-disk interference sensor for multiple purposes: touchdown detection, spacing fluctuation measurement, and disk condition monitoring. This universal use of existing sensors provides real-time reliability monitoring without adding separate dedicated sensors, thereby limiting the increase in device complexity
Solution Approach 2:
The patent implements self-service by utilizing the existing head-disk interference sensor and its signal processing capabilities to perform spacing monitoring functions. The system uses its own operational signals (touchdown power variations) for self-diagnosis and monitoring, reducing the need for additional external monitoring equipment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate, real-time monitoring and compensation of spacing fluctuations, preventing system failures by providing detailed information on disk conditions and allowing for automated maintenance, thereby ensuring reliable operation and quality control in hard disk drives.
Implementation Method 1
the head element also includes a head-disk interference (HDI) sensor (or, HDIs). This sensor is a resistive temperature sensor used to detect a temperature change in the head that is induced by changes in clearance during head vibrations or by a direct contact caused by contacting with disk asperities
Implementation Method 2
a controllable heater element (35), is located adjacent to the write gap (90) and, by heating the region surrounding the gap, can cause protrusions (not shown) of the ABS (200) of the head portion relative to the undisturbed shape of the ABS when it is not heated
Implementation Method 3
The hydrodynamics of the air layer between the ABS and the rotating disk surface supports the slider at its fly height above the disk
Data Source
AI summary
A method for determining the surface distortions of a disk in a spin-stand or single or multiple disk hard disk drive (HDD) utilizing a DFH type write head. A stepwise power curve is supplied to the DFH head, the head is flown over a chosen track on the disk, and the high frequency signal from a HDI sensor is analyzed in order to determine the step of an initial touchdown power and the step of a complete touchdown power as a function of individual sectors in a sector subdivision along a chosen track. The HDI sensor signal is averaged within each step of the power curve between these two steps and a Ratio variable,Ratio=(Max. amplitude)/(RMS amplitude)is calculated for each step and is averaged over each rotation of the disk during the step.