Magnetic Disk Servo Timing Alignment for CDS Positioning Control
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Solution Overview
Problem
The Constant Density Servo (CDS) scheme in magnetic disk apparatuses has limitations in servo control, particularly in determining servo data writing frequencies and timing, leading to complex calculations and potential errors in positioning control.
Innovation Solution
The magnetic disk apparatus employs a method where servo data is written with aligned temporal positions for preambles, sync marks, and burst patterns across different radial positions, ensuring consistent intervals and frequencies, simplifying the determination of servo gate signal timing and reducing phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If servo data is written at a constant recording frequency regardless of radial position, then the servo control calculation is simple, but the area where user data can be written is reduced
Solution Approach 1:
The patent changes the recording frequency parameter from constant to variable based on radial position. Specifically, the recording frequency is set to be higher on the outer diameter side and lower on the inner diameter side, allowing the servo data to be written more efficiently in different radial regions while maximizing the user data area.
Solution Approach 2:
The patent applies different recording frequencies to different radial positions on the magnetic disk. The outer diameter region uses a higher recording frequency while the inner diameter region uses a lower recording frequency, optimizing servo data writing for each local region's characteristics.
2Area of stationary object
If servo data is written with different recording frequencies at different radial positions (CDS scheme), then the user data writing area increases, but the servo control becomes more complex and prone to positioning errors
Solution Approach 1:
The patent pre-calculates and stores the correspondence between radial positions and recording frequencies in a lookup table before actual servo data writing. This preliminary preparation allows the servo control system to quickly retrieve the appropriate frequency without complex real-time calculations, reducing control complexity while maintaining the CDS scheme's benefits.
Solution Approach 2:
The patent introduces a radial position detection mechanism as an intermediary that provides accurate radial position information to the servo control system. This intermediary component enables precise frequency selection based on radial position without requiring complex direct calculations between frequency and position parameters.
3Area of stationary object
If the recording frequency is increased on the outer diameter side to maximize user data area, then the user data writing area increases, but the positioning precision may deteriorate due to rotational velocity variations
Solution Approach 1:
The patent adjusts the recording frequency parameter according to radial position to compensate for rotational velocity variations. By setting higher frequencies on the outer diameter where linear velocity is higher and lower frequencies on the inner diameter where linear velocity is lower, the patent maintains consistent positioning precision across different radial positions while maximizing user data area.
Solution Approach 2:
The patent replaces mechanical positioning methods with a data-based approach using pre-calculated frequency-position correspondence tables. This substitution allows precise positioning control through digital lookup rather than mechanical adjustments, maintaining accuracy despite varying rotational conditions.
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 facilitates easier calculation of servo gate signal timing, reduces phase errors, and maintains accurate positioning control, even with rotational fluctuations, thereby enhancing the efficiency and reliability of servo data writing.
Implementation Method 1
a magnetic head 22 and a magnetic disk 11. On the magnetic disk 11, servo regions SV are arranged
Implementation Method 2
the magnetic head 22 moves in the radial direction of the magnetic disk 11
Data Source
AI summary
According to an embodiment, a magnetic disk apparatus includes a magnetic head and a magnetic disk. On the magnetic disk, servo regions are arranged in a circumferential direction at even intervals. Each of the servo regions is a region in which servo data including data pieces is written. A recording frequency of the servo data is different between continuous first radial positions on the magnetic disk. A first data piece among the data pieces is written in each of the servo regions at a first circumferential position where movement times of the magnetic head in the circumferential direction are aligned among the first radial positions. The movement times are based on timing when the magnetic head passes over a reference position on a circumference of the magnetic disk.