Head Floating Height Control via Thermal Expansion
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Solution Overview
Problem
In magnetic disk devices, the floating height of the head relative to the recording medium must be precisely controlled to prevent collisions and maintain high recording density, but initial start-up characteristics deteriorate due to thermal expansion and lubricant sticking, making it difficult to distinguish and adjust for varying head and medium combinations.
Innovation Solution
A method involving a conductive body in the head to thermally expand and adjust the floating height using a write-verify module to check and correct the floating height by adding specific current values to the heater and recording coil, with a correction table managing different temperature conditions to enhance start-up characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the floating amount of the head is reduced to achieve high recording density, then recording density is improved, but collisions between the head and minute protrusions on the magnetic disk surface are likely to occur
Solution Approach 1:
The patent changes the physical parameter of the head by controlling its temperature through a heater. By adjusting the temperature, the head's dimensions change due to thermal expansion, which allows precise control of the floating height. This enables the floating height to be optimized for high recording density while maintaining a safety margin to prevent collisions with surface protrusions.
Solution Approach 2:
The patent makes the floating height dynamically adjustable by incorporating a heater that can change the head's temperature in real-time. This dynamic control allows the system to adapt the head position according to operating conditions, achieving both high recording density and collision prevention by optimizing the floating height during operation rather than relying on fixed mechanical tolerances.
2Manufacturing precision
If the floating amount of the head is reduced below the tolerance range to achieve higher recording density, then recording density is improved, but the clearance between the head and magnetic disk surface varies for different heads within a mechanical tolerance range
Solution Approach 1:
The patent uses temperature as a controllable parameter to compensate for mechanical tolerance variations. By adjusting the heater current, the head's thermal expansion can be controlled to achieve a consistent optimal floating height across different heads, regardless of their initial mechanical variations. This allows the system to adapt to different head characteristics and maintain uniform performance.
Solution Approach 2:
The patent implements a feedback mechanism where the floating height is monitored and the heater current is adjusted accordingly. This closed-loop control compensates for variations in mechanical tolerance by actively adjusting the thermal expansion of the head, ensuring that all heads achieve the same optimal floating height regardless of their initial manufacturing variations.
3Reliability
If the floating position of the head is elevated due to lubricant sticking immediately after start-up, then start-up characteristics deteriorate, but the floating amount becomes higher than in steady state
Solution Approach 1:
The patent applies preliminary action by pre-heating the head or applying a specific heater current pattern during the start-up phase. This preliminary thermal action compensates for the lubricant sticking effect that occurs when the head first contacts the disk surface, preventing excessive floating height increase and maintaining good start-up characteristics. The system proactively addresses the lubricant sticking issue before it significantly degrades performance.
Solution Approach 2:
The patent uses periodic or time-varying heater current patterns during start-up to manage the floating height. By applying thermal energy in a controlled time-dependent manner, the system counteracts the transient lubricant sticking effect and achieves smoother transition to steady-state operation, improving start-up characteristics without causing excessive floating height variation.
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
Effectively maintains optimal floating height and improves write/read characteristics by distinguishing and correcting head deterioration immediately after start-up, preventing errors and enhancing reliability.
Implementation Method 1
utilizing the projection phenomenon of the head floating surface caused by thermal expansion when current is supplied to the heater
Implementation Method 2
when current is supplied to the heater
Data Source
AI summary
According to one embodiment, a storage device includes a recording medium, a driving module, a head, a conductive body, a write-verify module, and a projection amount controller. A conductive body is mounted on the head, and changes a projection amount of the head by thermally expanding the head with heat from a current carried by the conductive body. The write-verify module executes a write-verify check to check whether content written in any location on the recording medium is correct when the driving module starts rotating the recording medium. The projection amount controller controls the projection amount of the head by adding a first value to a current in a steady state carried by the conductive body if the content is correct, and adding a second value with an absolute value greater than that of the first value to the current in the steady state if the content is not correct.