Adaptive Threshold for Disk Drive Touchdown Detection
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Solution Overview
Problem
Conventional touchdown detection methods in disk drives are prone to inaccurately declaring head contact due to contamination or slow ramping conditions, leading to premature detection of touchdown events.
Innovation Solution
An adaptive threshold system is implemented using control circuitry to determine fly height values and adjust the thermal actuator power level, allowing for accurate detection of head touchdown by evaluating a moving window of fly height values and avoiding premature declarations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed threshold is used for fly height detection, then the detection method is simple and fast, but it leads to premature touchdown detection due to contamination or slow ramping conditions
Solution Approach 1:
The patent implements a moving window approach where the threshold is dynamically adjusted based on recent fly height measurements. Instead of using a fixed threshold, the system continuously updates the threshold based on the maximum fly height values observed within a sliding window of recent measurements. This dynamic adaptation allows the system to distinguish between actual touchdown events and temporary variations caused by contamination or slow ramping conditions.
Solution Approach 2:
The system performs preliminary measurements of fly height values before declaring a touchdown event. By collecting and analyzing a sequence of fly height measurements within a moving window, the system prepares sufficient data to confidently determine whether a touchdown has occurred, avoiding premature declarations while maintaining detection responsiveness.
2Reliability
If the thermal actuator power level is increased to ensure head contact, then touchdown detection reliability improves, but it causes premature contact and potential head media collision
Solution Approach 1:
The system continuously monitors fly height values and uses this feedback to adjust the thermal actuator power level. By comparing recent fly height measurements against the dynamically updated threshold, the system can precisely control when to increase actuator power, ensuring reliable touchdown detection while preventing premature head-media contact through continuous monitoring and adaptive control.
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
The system effectively differentiates between actual touchdown events and contamination-induced slow ramping conditions, ensuring precise detection and maintaining optimal head-media spacing.
Implementation Method 1
Heat generated by the thermal actuator causes local thermal expansion of the head, which locally reduces the spacing between the head and magnetic media
Data Source
AI summary
A disk drive is disclosed comprising a disk, a head for writing data to the disk, and control circuitry coupled to the head. The control circuitry is operable to determine a first set of fly height values and determine a threshold based on the first set of fly height values. The control circuitry determines a second set of fly height values, adjusts the threshold based on the second set of fly height values, and detects a head characteristic based on the adjusted threshold. The head characteristic is detected by detecting a head touchdown event and/or detecting contamination related to the head based on the adjusted threshold.