Digital Head Touchdown Detection in Storage Read Channels
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Solution Overview
Problem
Existing data storage systems fail to accurately and timely detect head touchdown events, leading to potential damage during magnetic recording, as they process signals only once per disk revolution in the analog domain, unable to differentiate between intermittent and full touchdown.
Innovation Solution
Processing storage device head contact sensor signals in the digital domain within the read channel, allowing for more frequent monitoring and differentiation between types of touchdown, enabling faster and more precise detection by configuring components like high-pass filters, variable-gain amplifiers, and analog-to-digital converters to analyze signals during idle or write operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If head contact sensor signals are processed in the analog domain once per disk revolution, then the system structure is simple, but the detection timing is slow and cannot differentiate between intermittent and full touchdown
Solution Approach 1:
The patent replaces analog domain signal processing with digital domain signal processing. The head contact sensor signals are converted to digital signals and processed using digital signal processing techniques, including computing the moving sum of squares and comparing to a threshold. This substitution enables more frequent monitoring (multiple times per revolution) and better differentiation between touchdown types, resolving the contradiction between detection precision and system complexity.
2Speed
If head contact sensor signals are monitored continuously, then the detection speed improves, but the false detection during servo read operations increases
Solution Approach 1:
The patent implements preliminary action by squelching (suppressing) the head contact sensor signals during servo read operations before actual touchdown detection begins. This preliminary suppression prevents false detections during servo operations, while allowing continuous monitoring during other operations. The system selectively enables detection based on operation type, maintaining both fast detection speed and high reliability.
3Reliability
If the storage device uses traditional analog processing, then the device complexity is low, but the ability to prevent damage through timely detection is insufficient
Solution Approach 1:
The patent replaces the traditional analog processing architecture with a digital processing architecture. The read channel is configured to process head contact sensor signals in the digital domain, computing the moving sum of squares and comparing against a threshold to detect touchdown events. This digital substitution provides more reliable and timely detection to prevent damage, while the complexity is managed through efficient digital signal processing algorithms.
4Measurement precision
If signal processing occurs only during idle periods, then the detection accuracy is high, but the response time to touchdown events increases
Solution Approach 1:
The patent implements continuous monitoring of head contact sensor signals during all non-servo operations, including idle periods and write operations. By continuously processing signals in the digital domain and comparing the moving sum of squares to a threshold, the system maintains high detection accuracy while responding immediately to touchdown events regardless of the current operation state, eliminating the delay associated with periodic or idle-only processing.
Data Source
AI summary
A method of detecting head touchdown in a storage device includes monitoring storage device head contact sensor signals, and processing the monitored storage device head contact sensor signals in a digital domain. The processing may occur in a data path of the storage device, such as the read channel of the storage device. The processing may monitor for head touchdown only during other than read operations. Further, during servo read operation, the storage device head contact sensor may continue to generate signals, and the storage device head contact sensor signals may be squelched. Storage device head contact sensor signals also may be squelched during intervals before and after the servo read operation. The processing may includes accumulating a moving sum of squares of the storage device head contact sensor signals, and comparing the moving sum of squares of the storage device head contact sensor signals to a threshold.