D-Servo Regions in Patterned-Media Disk Drives
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Solution Overview
Problem
Conventional servo patterns are difficult to precisely write and align in patterned-media magnetic recording disk drives, making it challenging to achieve accurate read/write head positioning.
Innovation Solution
The use of randomly magnetized 'data' dots in angularly spaced sectors as servo sectors, known as D-servo regions, which are identified numerically and used to determine the precise radial and circumferential position of the read/write head through a look-up reference table, allowing for self-servowriting and improved servo control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional servo patterns are used in patterned-media disk drives, then servo control function is provided, but manufacturing precision and alignment accuracy deteriorate due to the complexity of servo patterns and difficulty in precise writing
Solution Approach 1:
The patent applies multi-functionality by using the same data dots for both data storage and servo control functions. The data dots in angularly spaced sectors serve dual purposes: storing data and providing servo information for head positioning. This eliminates the need for separate conventional servo patterns, thereby simplifying the structure and improving manufacturing precision.
Solution Approach 2:
The patent merges the data dots and servo sectors into a unified structure where data dots in angularly spaced sectors function as servo sectors. This consolidation combines two previously separate functions (data storage and servo control) into a single integrated system, reducing complexity and improving alignment precision.
2Manufacturing precision
If conventional servowriter or self-servowriting method is used, then servo sectors are written, but manufacturing precision deteriorates due to inability to achieve required precision in writing desired patterns at specific disk locations
Solution Approach 1:
The patent implements self-service by using the data dots themselves to provide servo information. The system leverages the existing data dot structure to generate readback signals for positioning, eliminating the need for separate servo writing operations. This self-servicing approach inherently achieves high precision since the same dots are used for both data and servo functions.
Solution Approach 2:
The data dots serve multiple functions: they store data and simultaneously provide servo control information through their magnetization patterns. This universal usage of data dots for both purposes eliminates the need for separate servo writing processes, thereby achieving high manufacturing precision without additional complexity.
3Reliability
If D-servo regions with randomly magnetized dots are used, then servo control effectiveness is improved, but measurement precision requirements increase for determining head position within D-servo regions
Solution Approach 1:
The patent employs feedback mechanisms where the readback signals from randomly magnetized dots are compared with reference signal waveforms stored in a lookup table. This feedback process allows the system to determine the precise radial and circumferential position of the read/write head by matching the actual readback signal with stored reference signals, thereby achieving high measurement precision despite the random magnetization.
Solution Approach 2:
The system creates a copy of the expected readback signals by storing reference signal waveforms in a lookup table. These reference copies are generated from the known torque constant of the actuator and elastic modulus of the crash stop, allowing precise comparison with actual readback signals to determine head position accurately.
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 precise positioning of the read/write head, enhancing the servo control system's effectiveness in patterned-media disk drives by utilizing the same dots for data and servo purposes, thereby simplifying the writing process and improving alignment precision.
Implementation Method 1
First the actuator is biased against the ID crash stop by applying direct current (DC) to the actuator coil
Implementation Method 2
The dots in the annular band are randomly magnetized, i.e., either into or out of the disk, so that each track in each D-servo region provides a generally random readback signal at the data frequency
Data Source
AI summary
A patterned-media magnetic recording disk drive has head positioning servo sectors on the disk that do not contain special patterns but merely use the same type of dots that are used for data. The “data” dots in angularly spaced sectors of the data tracks function as the servo sectors and are denoted as D-servo regions. The D-servo regions extend across an annular band of the disk, which may be a bootstrap band for self-servowriting. The dots in the annular band are randomly magnetized so that each track in each D-servo region provides a generally random readback signal at the data frequency. The precise radial and circumferential position of the read/write head within a D-servo region is determined by comparing the readback signal with a set of reference signal waveforms from a look-up reference table and finding the reference signal waveform that matches the readback signal.