Disk Drive Servo Timing Adjustment for Zone Boundary Transients
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Solution Overview
Problem
The zoned servo sector format in disk drives can lead to loss of synchronization during seek operations when the head crosses a servo zone boundary due to incorrect adjustments in servo control parameters, resulting from misestimation of the servo zone boundary location.
Innovation Solution
The solution involves adjusting at least one of the disk locked clock and timing window when the head crosses a servo zone boundary to compensate for timing transients, using techniques such as adjusting the center frequency of a phase locked loop, adding transition offsets to the timing window, and overlapping servo sectors to facilitate smooth transitions between zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the data rate of servo sectors is increased in outer diameter zones to improve format efficiency, then disk capacity is improved, but synchronization is lost during seek operations when crossing servo zone boundaries
Solution Approach 1:
The patent applies preliminary action by detecting the approach to a servo zone boundary before the head actually crosses it. The system estimates the boundary location in advance and preemptively adjusts the servo gate and sync window parameters to compensate for the upcoming data rate change, preventing synchronization loss before it occurs.
Solution Approach 2:
The patent implements feedback by continuously monitoring the head position relative to servo zone boundaries and using this information to dynamically adjust timing parameters. The system measures the actual head position, compares it with expected positions, and modifies the servo gate and sync window accordingly to maintain synchronization across zone transitions.
2Reliability
If the servo gate and sync window are adjusted to compensate for timing transients during zone crossing, then synchronization is maintained, but the complexity of the servo control system increases
Solution Approach 1:
The patent applies dynamics by making the servo gate and sync window parameters variable rather than fixed. The system dynamically adjusts these parameters based on the head's radial position and the detected servo zone, allowing the timing windows to adapt to different data rates in inner and outer zones while maintaining a unified control approach.
Solution Approach 2:
The patent implements parameter changes by modifying the timing parameters (servo gate width, sync window position and duration) according to the servo zone being accessed. The system changes these parameters based on the data rate associated with each zone, enabling proper synchronization without requiring completely separate control systems for different zones.
3Reliability
If the location of servo zone boundary is estimated to enable timely parameter adjustment, then synchronization is maintained, but positioning precision is reduced when the estimate is incorrect
Solution Approach 1:
The patent applies beforehand cushioning by creating a buffer zone in the timing estimates. The system uses conservative estimates for boundary locations and incorporates margin into the timing adjustments, ensuring that even if the boundary estimation is slightly off, the adjusted servo gate and sync window still capture the incoming servo sectors properly.
Solution Approach 2:
The patent replaces direct mechanical measurement of boundary locations with an electronic estimation system that uses the known disk geometry, rotational speed, and head position feedback to calculate boundary locations. This substitution allows for more flexible and accurate boundary detection without physical markers.
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 ensures continuous synchronization and accurate head positioning across servo zones, increasing disk capacity by optimizing servo sector placement and reducing errors during seek operations, while also accounting for ambient temperature variations.
Implementation Method 1
adjusting the center frequency of a phase locked loop
Implementation Method 2
a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM)
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of servo sectors defining a plurality of servo tracks, wherein the servo tracks form a plurality of servo zones, and a servo data rate of servo sectors in a first servo zone is different than a servo data rate of servo sectors in a second servo zone. A disk locked clock is synchronized to the data rate of the servo sectors in the first servo zone, wherein the disk locked clock for generating a timing window relative to the servo sectors. When the head crosses from the first servo zone to the second servo zone, at least one of the disk locked clock and the timing window is adjusted to compensate for a timing transient.