Dual Heater Fly-Height Control via Frequency Dithering
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Solution Overview
Problem
In magnetic recording disk drives with dual independent heaters for thermal fly-height control, it is challenging to determine the combinations of heater power values that result in touchdown at the desired location due to embedded contact sensors being connected in parallel, which provides a single combined output signal, making it impossible to distinguish the signal output of each sensor when both heaters are operating simultaneously.
Innovation Solution
The method involves connecting the dual embedded contact sensors in parallel to minimize electrical contact pads and using a dithering technique where the heater power is oscillated at different frequencies to analyze the combined output signal, allowing for the determination of touchdown for various combinations of heater power values by recording the power values when the sensor signals exceed a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If dual embedded contact sensors are connected in parallel to minimize electrical contact pads, then the number of electrical contact pads is reduced, but it becomes impossible to distinguish the signal output of each sensor when both heaters are operating simultaneously
Solution Approach 1:
The patent applies periodic action by dithering each heater at a different frequency (first frequency for first heater, second frequency for second heater). This causes each embedded contact sensor to produce signals at its respective dither frequency, allowing the controller to distinguish and separate the combined sensor signals through frequency analysis, thus resolving the measurement difficulty while maintaining the parallel connection configuration
2Measurement precision
If heater power is dithered at different frequencies to enable signal separation, then touchdown determination accuracy is improved, but the control system complexity increases
Solution Approach 1:
The patent implements feedback by having the controller monitor the combined output signals from the parallel-connected embedded contact sensors, analyze the signals at the respective dither frequencies to determine touchdown conditions, and adjust the heater power levels accordingly. This feedback mechanism enables accurate touchdown determination through frequency-based signal separation while maintaining manageable control system complexity
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 calibration of the dual heaters, ensuring precise control of slider-disk spacing by identifying the correct combinations of heater power values that result in touchdown, thereby maintaining optimal fly-height even under varying conditions.
Implementation Method 1
When current is applied to the heater, the heater expands and causes the head to expand and thus move closer to the disk surface
Implementation Method 2
The resistance of the ECS changes in response to temperature changes so the voltage across the ECS can be used to determine touchdown
Data Source
AI summary
A method and system for determining slider-disk contact in a hard-disk drive (HDD) that has dual independent heaters for thermal fly-height control, and dual embedded contact sensors, includes dithering power to the two heaters at different frequencies. The HDD has the two contact sensors electrically connected to provide a single combined output signal in response to the dithering. The single combined output signal is analyzed to detect two signals at the two different frequencies. When either detected signal exceeds a predetermined touchdown threshold value, the values of heater power for the two heaters are recorded, indicating that that combination of heater power values corresponds to slider-disk contact.