HDI Sensor DC Signal Touch Down Detection
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Solution Overview
Problem
Existing methods for touch down detection in dynamic flying height hard disk drives are unreliable, especially when the touch down vibration is weak, as they heavily rely on the AC component of the head-disk interference sensor, which can produce faulty results.
Innovation Solution
A method using the DC signal from a head-disk interference sensor to determine touch down by systematically increasing heating power and analyzing the corresponding DC response signal, employing three methods: Minimum Slope Method, Slope's Slope method, and Linear Fit of the Slope, to provide accurate and reliable touch down detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the AC component of the HDI sensor is used for touch down detection, then the detection method is simple, but the reliability is poor especially when touch down vibration is weak
Solution Approach 1:
The patent changes the detection parameter from the AC component to the DC component of the HDI sensor signal. By systematically increasing heater power and analyzing the DC response signal curve, the method achieves reliable touch down detection even when vibrations are weak, resolving the contradiction between simplicity and reliability.
2Measurement precision
If the DC signal curve analysis method is used, then the measurement precision is improved, but the device complexity increases due to systematic power increase and curve analysis
Solution Approach 1:
The patent applies preliminary action by systematically increasing heater power in a controlled sequence before detection. This pre-established power increase pattern creates a predictable DC signal curve that simplifies the subsequent analysis process, allowing precise touch down detection through curve interpretation rather than complex real-time processing.
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
These methods improve the accuracy and reliability of touch down detection, providing robust results even in cases with weak vibrations, by interpreting the DC signal curve and identifying the touch down point with high precision.
Implementation Method 1
By applying power to the heater element and heating the region surrounding the gap, thermal expansions 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 2
the head element typically also includes a head-disk interference (HDI) sensor (or multiple HDI). This sensor is typically 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 disk asperities.
Data Source
AI summary
Methods are provided for determining the heater power level of a dynamic flying height (DFH) type write head at which a touch down (TD) occurs. Each method makes use of the DC component of a head-disk interference (HDI) sensor and the determination of the TD heater energy is deduced from certain characteristics of the function relating heater power to HDI DC signal strength. Characteristics that provide reliable indication of a TD include points of minimum slope, structure of the slope's slope and the properties of a linear fit to the slope if the slope does not converge to a consistent value. It is found that the use of all methods in combination allow a reliable TD determination under virtually all conditions.