Disk Drive Touchdown Sensor Calibration via Multi-Bias Resistance
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Solution Overview
Problem
Existing disk drive systems face challenges in accurately detecting defects on disk surfaces due to variations in touchdown sensor behavior caused by fabrication tolerances, leading to inconsistent defect detection and potential false positives.
Innovation Solution
The implementation of a touchdown sensor with a thermoresistive material and a control circuitry that estimates a reference resistance based on measured resistance values at different bias levels, allowing for the generation of an operating bias value to achieve a target operating temperature, ensuring consistent defect detection across disk drives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If touchdown sensor is used to detect defects on disk surfaces, then defect detection capability is provided, but fabrication tolerances cause variations in sensor behavior leading to inconsistent detection and false positives
Solution Approach 1:
The patent applies preliminary calibration action by measuring the resistance of the touchdown sensor at multiple bias levels before actual defect detection operations. This preliminary characterization establishes a baseline resistance profile that accounts for fabrication variations, enabling subsequent compensation during normal operation to achieve consistent defect detection across all sensors regardless of manufacturing tolerances.
Solution Approach 2:
The patent changes the operating parameters of the touchdown sensor by measuring resistance at multiple different bias levels rather than a single fixed bias. This multi-parameter approach captures the full resistance characteristics of the sensor, allowing for accurate modeling and compensation of fabrication variations, thereby improving detection consistency across sensors with different manufacturing tolerances.
2Measurement precision
If multi-level bias calibration is performed to achieve target operating temperature, then defect detection accuracy is improved, but calibration time and complexity increase
Solution Approach 1:
The multi-level bias calibration is performed as a preliminary action during manufacturing or initialization, establishing accurate sensor characteristics before production use. Although this preliminary step requires multiple measurements, it eliminates the need for continuous calibration during operation, reducing long-term time loss and improving defect detection accuracy from the outset.
Solution Approach 2:
The calibration process is designed to be self-characterizing, where the sensor's own resistance measurements at different bias levels provide the data needed to model its behavior. This self-service approach eliminates the need for external reference standards or complex calibration equipment, reducing calibration complexity and time while maintaining high measurement precision.
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 and consistent detection of defects on disk surfaces, minimizing false detections and ensuring reliable defect scanning across a family of disk drives by calibrating the bias signal to achieve a target operating temperature for each sensor.
Implementation Method 1
The disk drive comprises a head comprising a touchdown sensor (6) comprising a thermoresistive material
Implementation Method 2
a control circuitry (8) operable to heat the touchdown sensor (6) to a target operating temperature
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk, the head comprising a touchdown sensor. A bias signal is applied at a first bias value to the touchdown sensor and a corresponding first resistance of the touchdown sensor is measured. The bias signal is applied at a second bias value to the touchdown sensor and a corresponding second resistance of the touchdown sensor is measured. A reference resistance of the touchdown sensor is estimated based on the first and second bias values and the first and second resistances. An operating bias value is generated for the bias signal based on a predetermined operating temperature of the touchdown sensor, the reference resistance, and a thermal coefficient of resistance (TCR) of the touchdown sensor, wherein the TCR specifies a change in temperature of the touchdown sensor relative to a change in the resistance of the touchdown sensor.