Unipolar Servo Burst Patterns for Track Alignment
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Solution Overview
Problem
Patterned-media magnetic recording disks with discrete servo sectors face challenges in aligning concentric data tracks with the center of rotation during servowriting, leading to imperfect magnetization of servo islands, which complicates the demodulation of position error signals.
Innovation Solution
The implementation of a ¼ track offset unipolar servo burst pattern on magnetic media allows for effective demodulation of position error signals even when magnetized in the same direction, enabling precise head positioning without the need for bipolar bit patterns or complex channel functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If discrete servo islands are patterned on patterned-media disks during a separate fabrication process, then data density is increased, but the concentric data tracks cannot be perfectly aligned with the center of rotation during servowriting
Solution Approach 1:
The servo sector is divided into multiple discrete servo islands that are separately patterned during fabrication. These islands are then magnetized in different directions to create burst patterns that provide positioning information even when track alignment is imperfect.
Solution Approach 2:
The servo islands are pre-patterned during the disk fabrication process before servowriting. This preliminary patterning allows the subsequent servowriting step to focus on magnetization rather than pattern formation, enabling the system to tolerate misalignment between the fabricated tracks and the rotational center.
2Ease of operation
If the write head is held at a fixed radial position during servowriting, then the servowriting process is simplified, but the write head traverses multiple tracks as servo sectors pass, making it impossible to magnetize islands according to the desired pattern
Solution Approach 1:
The system transitions from a static write head position to a dynamic positioning system. The write head is moved radially in response to feedback signals from the servo islands, allowing the head to track the correct data track even as the disk rotates and tracks are misaligned with the rotational center.
Solution Approach 2:
The servo islands provide feedback signals that indicate the radial position of the write head relative to the correct track. This feedback is used to adjust the head position dynamically during servowriting, ensuring accurate magnetization of the intended servo islands despite track misalignment.
3Ease of manufacture
If unipolar bit patterns are used for servo bursts, then the demodulation of position error signals becomes complex or impossible, but bipolar bit patterns require more complex magnetization processes
Solution Approach 1:
The system uses asymmetric positioning of servo bursts within the servo sector. By offsetting the bursts from the sector center and using different radial positions for different bursts, the system creates an asymmetric pattern that can be demodulated even with unipolar magnetization. The asymmetry in position compensates for the symmetry in magnetization direction.
Solution Approach 2:
The system transitions from relying on magnetic polarity differences (one dimension) to relying on radial position differences (another dimension) for demodulation. By encoding position information in the radial location of servo bursts rather than in their magnetic polarity, the system enables unipolar magnetization while maintaining demodulation capability.
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 solution enables accurate head alignment and data track maintenance by allowing position error signals to be demodulated from unipolar magnetized burst patterns, simplifying the servowriting process and improving data density in patterned-media disks.
Implementation Method 1
The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume
Implementation Method 2
The servo islands are patterned into a position error signal (PES) field that generates a servo readback signal that is demodulated into a PES for positioning the read/write head
Implementation Method 3
This makes it impossible during the servowriting process for the head to magnetize the islands in the servo sectors according to the desired pattern
Data Source
AI summary
A magnetic data storage system having a magnetic disk having burst patterns for providing a position error signal (PES) wherein each magnetic burst pattern is offset from an adjacent burst pattern by ¼ track pitch. All of the magnetic bits of the burst patterns can be unipolar magnetized, and the bits of each burst pattern can be aligned with one another in radial and circumferential direction. The magnetic media can be a bit patterned media wherein the magnetic bits of the burst patterns are magnetically isolated portions separated by non-magnetic spaces or non-magnetic material.