Z-height Control via Servo Wedge Timing in Disc Drives
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Solution Overview
Problem
Maintaining the precise Z-height between the actuator arm and the data storage disc surfaces is challenging, especially as data storage density increases, leading to potential read/write errors and surface damage due to unacceptable Z-height variations.
Innovation Solution
A method utilizing a servo wedge on the disc surfaces to measure time differences of a head pair encountering top and bottom servo wedge boundaries, employing a transfer function to adjust the Z-height, ensuring the time difference matches the target certification time difference, thus maintaining optimal read/write performance without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data storage density is increased, then storage capacity is improved, but Z-height control precision deteriorates leading to read/write errors and surface damage
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the time difference between head encounters with top and bottom servo wedge boundaries, compares this measured time difference to a target certification time difference, and adjusts the actuator arm assembly Z-height accordingly to maintain optimal read/write performance
Solution Approach 2:
The patent replaces traditional mechanical Z-height sensing mechanisms with a timing-based measurement system that uses the servo wedge boundaries and measures the time difference of head encounters, converting a mechanical positioning problem into a temporal measurement problem that can be controlled through software algorithms
2Device complexity
If traditional Z-height control methods are used, then device complexity is maintained, but measurement precision of Z-height deteriorates
Solution Approach 1:
The patent introduces the servo wedge boundaries as intermediary reference markers on the disc surface, which the read/write head encounters at specific times during rotation. These boundaries serve as temporal markers that enable precise indirect measurement of Z-height without requiring direct mechanical sensing
Solution Approach 2:
The patent uses the existing servo wedge structure, originally designed for track positioning, to also serve as a reference for Z-height measurement. The same servo wedges that guide radial positioning are copied in functionality to provide vertical positioning information through timing measurements
Data Source
AI summary
A data storage device includes a disc, an actuator arm assembly, a servo clock, and a feedback and control system. The disc includes a top and bottom surfaces and a servo wedge. The servo wedge includes a top surface boundary and a bottom surface boundary. The actuator arm assembly supports a head pair configured for interaction with the top and bottom surfaces. The servo clock is configured to determine a top time at which the head pair encounters the top surface boundary and a bottom time at which the head pair encounters the bottom surface boundary during a disc read/write interaction. The feedback and control system is configured to determine an operation time difference; compare the operation time difference to a certification time difference correlating to a target vertical position of the actuator arm assembly relative to the disc; and move the actuator arm assembly to the target vertical position.