Disk Drive Write Clock Compensation for Vibration
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Solution Overview
Problem
Hard disk drives (HDDs) face challenges in maintaining data accuracy due to external linear vibrations, which cause jitter in the data island frequency and disrupt the synchronization of write clock pulses, especially because conventional feedback-based phase-locked-loop control systems are limited in responding to high-frequency disturbances.
Innovation Solution
A linear vibration sensor is positioned with its sensitivity axis aligned tangentially to selected tracks, generating a feed-forward control signal to synchronize the write clock frequency with the modulated data island frequency, which is added to the control voltage input of the voltage-controlled oscillator in the write clock generator to adjust for tangential vibration-induced frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedback-based phase-locked-loop control system is used to synchronize write clock pulses, then the system can maintain basic timing synchronization, but it cannot effectively respond to high-frequency vibration disturbances
Solution Approach 1:
The patent applies preliminary action by using a feed-forward control approach where the vibration sensor detects tangential vibrations and generates a compensation signal before the vibration affects the write timing. This compensation signal is added to the clock signal in advance, allowing the system to counteract high-frequency vibrations before they cause timing errors, thus resolving the contradiction between synchronization accuracy and response speed.
2Measurement precision
If the write clock frequency is adjusted to compensate for vibration-induced frequency modulation, then timing accuracy under vibration is improved, but the system complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a vibration sensor as a mediator between the mechanical vibration and the clock control system. The sensor converts physical vibrations into electrical compensation signals that can be processed and added to the clock signal, providing a bridge that enables timing correction without requiring complex direct control of the write head mechanics.
Solution Approach 2:
The patent replaces mechanical timing adjustment mechanisms with an electronic signal processing approach. Instead of mechanically adjusting the write head position or speed in response to vibration, the system substitutes this with electronic compensation by adding vibration-derived signals to the clock signal, simplifying the mechanical system while maintaining timing precision.
3Reliability
If the linear vibration sensor is positioned with tangential sensitivity alignment, then the compensation effectiveness for frequency modulation is maximized, but the mounting precision requirements increase
Solution Approach 1:
The patent applies parameter changes by optimizing the sensor's sensitivity orientation parameter. By aligning the sensor's sensitive axis with the tangential direction of disk rotation, the system maximizes the sensor's response to the specific vibration mode that causes frequency modulation. This parameter optimization ensures that even with standard mounting tolerances, the sensor captures the relevant vibration information for effective compensation.
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 effectively compensates for linear vibration disturbances, ensuring precise timing of write pulses and maintaining data island frequency synchronization, even under high-frequency tangential vibrations, thereby enhancing data integrity and accuracy.
Implementation Method 1
A linear vibration sensor is positioned with its sensitivity axis aligned tangentially to selected tracks, generating a feed-forward control signal to synchronize the write clock frequency with the modulated data island frequency
Implementation Method 2
which is added to the control voltage input of the voltage-controlled oscillator in the write clock generator to adjust for tangential vibration-induced frequency modulation
Data Source
AI summary
A disk drive is described that uses a vibration sensor to generate a compensating feed-forward control signal to synchronize the write clock frequency with the modulated data island frequency. A linear vibration sensor is positioned with its sensitivity axis aligned with the tangential direction of a track at the radial position of the write head. The tangential component of the external linear vibration is measured by the sensor. The feed-forward control signal derived from the linear vibration sensor modifies the control voltage input to VCO (voltage controlled oscillator) in the write clock generator to adjust the write clock frequency to compensate for the modulated data island frequency caused by the tangential component of the linear vibration.