Head-Medium Contact Detection via Oscillating Electrostatic Force
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Solution Overview
Problem
Conventional contact detection methods in magnetic storage systems, particularly in low-clearance technology (LCT) and non-modulation head-disk interfaces, face limitations such as slow contact detection capabilities and inability to reliably detect head-medium contact events at middle diameter locations due to stiff air bearings and thermal time constraints.
Innovation Solution
Applying an AC signal to cause oscillations in electrostatic force between a slider and a magnetic recording medium, using the resulting thermal sensor signal's phase or amplitude harmonics to detect head-medium spacing changes and contact, allowing for faster and more reliable contact detection without heater-induced fly height modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional contact detection methods are used in low-clearance technology, then head-medium contact can be detected, but the detection speed is slow and reliability is reduced due to thermal time constraints
Solution Approach 1:
The patent applies periodic AC signals at specific frequencies (e.g., 20-100 kHz) to the slider or medium to induce oscillatory electrostatic forces. This periodic excitation creates time-varying thermal coupling that modulates the thermal sensor output, enabling detection of contact events within less than one disk revolution by analyzing harmonic components of the periodic response
Solution Approach 2:
The patent replaces conventional mechanical/heater-based contact detection with an electromagnetic-based method. AC signals generate oscillating electrostatic forces that modulate thermal coupling, and thermal sensors detect these modulations electrically, eliminating the need for heater-induced fly height modulation and achieving faster, more reliable detection
2Measurement precision
If heater-induced fly height modulation is used for contact detection, then contact events can be detected, but wear increases and detection accuracy at middle diameter locations deteriorates
Solution Approach 1:
The patent replaces mechanical heater-induced fly height modulation with electromagnetic oscillating electrostatic forces. The AC signals create oscillatory forces that modulate thermal coupling without requiring physical heater activation or fly height changes, eliminating wear while maintaining detection accuracy
Solution Approach 2:
The patent introduces thermal coupling as an intermediary mechanism. The oscillating electrostatic forces modulate the thermal coupling between slider and medium, which in turn modulates the thermal sensor output. This indirect detection path avoids direct mechanical contact and heater-induced wear while providing accurate contact detection
3Productivity
If AC signals are applied to cause oscillations in electrostatic force, then contact detection speed increases, but the system complexity increases due to signal generation and harmonic analysis
Solution Approach 1:
The patent employs feedback through harmonic analysis of thermal sensor signals. The detected signal is analyzed for specific frequency harmonics (first and second harmonics of the AC signal frequency), and this feedback information is used to determine contact events. The system adjusts detection based on the measured harmonic components, enabling fast detection while managing complexity through targeted frequency analysis
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
Enables faster contact detection with reduced wear and improved reliability, capable of declaring contact in less than one disk revolution, and effectively handles low-modulation interfaces and middle diameter locations, enhancing recording density and system performance.
Implementation Method 1
applying an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the AC signal causing an oscillation in an electrostatic force between the slider and the medium at the frequency of the AC signal
Implementation Method 2
causing, by the oscillating electrostatic force, an oscillation in a signal produced by a thermal sensor at the slider, the thermal sensor signal oscillating at the AC signal frequency
Data Source
AI summary
An apparatus comprises circuitry configured to apply an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium. The applied AC signal causes an oscillation in an electrostatic force and clearance between the slider and the medium at the frequency of the AC signal. A thermal sensor is configured to generate a sensor signal at the AC signal frequency in response to sensing changes in temperature resulting from the oscillating clearance. A detector is coupled to the circuitry and the thermal sensor. The detector is configured to detect one or both of head-medium spacing changes and head-medium contact using a phase of a first harmonic or an amplitude of a second harmonic of the thermal sensor signal.