HDD Head Protrusion Calibration via Dynamic Fly Height Heater Control
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Solution Overview
Problem
Current hard disk drive (HDD) technologies face challenges in maintaining optimal head-disk spacing due to manufacturing variations and environmental changes, leading to inconsistent read and write gap clearances, which affect magnetic performance and reliability.
Innovation Solution
A method using multiple heat-producing elements within the HDD to create adjustable dynamic fly height (DFH) protrusion profiles, controlled by varying the power ratio between heaters, allowing for precise calibration and optimization of read and write gap clearances through a vibration sensor or read-back signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple heater elements are used to create adjustable DFH protrusion profiles, then head-disk spacing control is improved, but device complexity increases
Solution Approach 1:
The heating system is divided into multiple independent heater elements (first heater and second heater) positioned at different locations on the air bearing surface. Each heater can be independently controlled to create different protrusion profiles, enabling precise adjustment of head-disk spacing at various regions of the head.
Solution Approach 2:
Different heater elements are activated with different power levels to create localized thermal expansion effects. By controlling the power ratio between heaters, the protrusion profile can be customized for specific operational conditions, optimizing clearance at critical areas such as the read gap or write gap.
2Manufacturing precision
If DFH protrusion is used to reduce static fly height, then manufacturing precision is improved, but reliability deteriorates due to inconsistent clearance
Solution Approach 1:
The system transitions from a static fly height to a dynamic fly height where the air bearing surface protrusion can be adjusted in real-time. The heater power ratio is dynamically changed based on operational mode (reading vs. writing) and environmental conditions, allowing the head to adapt to varying requirements and maintain reliable clearance.
Solution Approach 2:
The thermal expansion characteristics of the air bearing surface are exploited by changing the temperature parameter through controlled heating. By adjusting the heater power ratio, the degree of protrusion is changed, which directly affects the fly height and clearance between head and disk, enabling compensation for manufacturing variations.
3Manufacturing precision
If heater power ratio is varied to optimize read and write gap clearance, then manufacturing precision is improved, but energy consumption increases
Solution Approach 1:
Instead of uniformly heating the entire air bearing surface, only specific heater elements are activated or partially activated based on the operational requirements. For example, during read operations, only the heater near the read gap is activated, while during write operations, the heater near the write gap is activated, reducing overall energy consumption while achieving the desired clearance optimization.
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 enhances touch-down detection accuracy, reduces clearance variations, and improves HDD performance by optimizing head-disk spacing, addressing issues like the 1st sector write problem and enhancing reliability across various operational conditions.
Implementation Method 1
separately controllable heater elements (35), (95) are located adjacent to the two gaps (30) and (90) and, by heating the region surrounding the gaps, can cause protrusions (not shown) of the ABS (200) of the head portion
Implementation Method 2
When subjected to this increased temperature, the materials forming the head begin to expand in accordance with their respective thermal expansion characteristics. This leads to a thermally deformable ABS and a resulting protrusion profile
Implementation Method 3
The hydrodynamics of the air layer between the ABS and the rotating disk surface supports the slider at a static fly height above the disk
Implementation Method 4
The hydrodynamics of the air layer between the ABS and the rotating disk surface supports the slider at a static fly height above the disk
Implementation Method 5
By further equipping the head (or HDD) with a vibration sensor or equivalent sensing device or by employing an alternative method to measure profiles, such as read-back signals themselves, head/disk clearances can be determined and touch-down events can be detected
Data Source
AI summary
Dynamic fly height (DFH) controlled read/write heads using multiple heaters have their heater powers set within a range of ratios that allows minimum clearances to be set between the read-gap and the write-gap and the surface of a disk, thereby providing improved touch-down detection. Determining the correct range of power ratios requires varying the ratio to create an adjustable protrusion profile for the read and write elements in the head and measuring values of the ratio and corresponding values of read gap and write gap clearances that create points of minimum clearance. By adjusting the ratio of power supplied to the heaters, different protrusion profiles can be produced, clearance control for sigma reduction can be obtained and read/write readiness and operation consistency and reliability can be improved.