Magnetic Head Multi-Sensor RRO Reduction
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Solution Overview
Problem
Hard disk drives (HDDs) face challenges in accurately positioning magnetic heads due to significant non-coherent repeatable runout (RRO), which affects the SSW process and read operations, leading to increased manufacturing time and read errors.
Innovation Solution
The use of multiple read sensors in a magnetic head, such as a configuration for two-dimensional magnetic recording (TDMR), allows for the determination of a final radial position based on multiple radial positions, reducing the effect of non-coherent RRO by a factor of 1/√N, thereby improving positioning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If synchronous averaging of PES over multiple revolutions is performed to reduce non-coherent RRO, then positioning accuracy is improved, but manufacturing time is significantly increased
Solution Approach 1:
The patent divides the positioning measurement into multiple independent segments by using N separate read sensors, each providing an independent PES measurement. This allows parallel processing of multiple measurements simultaneously, achieving the same statistical reduction in non-coherent RRO (factor of 1/√N) as sequential averaging over multiple revolutions, but in a single revolution cycle.
Solution Approach 2:
The patent transitions from the time dimension (multiple revolutions) to the spatial dimension (multiple read sensors positioned at different radial locations) to achieve the same goal of reducing non-coherent RRO. By taking measurements across multiple spatial positions simultaneously, the system achieves positioning accuracy equivalent to temporal averaging without the time penalty.
2Measurement precision
If the number of read sensors is increased to reduce non-coherent RRO, then positioning accuracy is improved, but device complexity is increased
Solution Approach 1:
The patent makes each read sensor serve multiple functions: each sensor not only provides positioning information but also contributes to reducing non-coherent RRO through statistical averaging. The same hardware components (read sensors) are used for both tracking servo patterns and measuring radial position, eliminating the need for separate measurement devices and reducing overall system complexity.
Solution Approach 2:
The patent combines the positioning measurement function with the existing read sensors used for data retrieval. By integrating the RRO reduction capability into the existing read sensor array, the system achieves enhanced positioning accuracy without adding separate measurement subsystems, thus minimizing the increase in device complexity.
3Manufacturing precision
If synchronous averaging is performed for each data track during SSW, then servo sector writing accuracy is improved, but the SSW process time is greatly increased
Solution Approach 1:
The patent performs preliminary positioning measurements using multiple read sensors during a single revolution, before the actual servo sector writing begins. By establishing accurate radial position information in advance using the multi-sensor approach, the system eliminates the need for time-consuming synchronous averaging during the SSW process itself, thereby maintaining high writing accuracy while improving overall process speed.
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 reduces non-coherent RRO, enhancing the accuracy of servo sector writing and read operations, thereby improving HDD manufacturing efficiency and performance by minimizing read errors and reducing the time required for the SSW process.
Implementation Method 1
a magnetic head configured to perform two-dimensional magnetic recording (TDMR)... the first magnetic servo information is read by the first read sensor and the second magnetic servo information is read by the second read sensor
Data Source
AI summary
A method for positioning a magnetic head having first and second read sensors and one write head includes: while the magnetic head is at a first position relative to a disk medium, reading first magnetic servo information written on a first surface of the disk medium, with the first read sensor, and reading second magnetic servo information written on the first surface of the disk medium with the second read sensor; determining a position error of the magnetic head based on the first and second magnetic servo information; and repositioning the magnetic head to a second position relative to the disk medium to compensate for the determined position error of the magnetic head.