Data Storage Head Positioning via Upsampled PES Compensation
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Solution Overview
Problem
Existing data storage devices face challenges in accurately tracking target tracks due to repeatable runout (RRO) disturbances, which can cause misalignment and errors in head positioning, especially when the RRO frequency exceeds the Nyquist frequency, leading to aliased disturbances that complicate precise actuation.
Innovation Solution
The implementation of upsampling the position error signal (PES) to regenerate the RRO disturbance at its original frequency, allowing for the generation of feed-forward compensation values that can be combined with the control signal to cancel out RRO effects, along with the use of notch filters to attenuate mechanical resonances and peak filters to adjust gain and phase responses for optimal compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the sampling frequency is kept at the Nyquist frequency for cost efficiency, then the device complexity is reduced, but the measurement precision deteriorates due to aliased disturbances when RRO frequency exceeds Nyquist frequency
Solution Approach 1:
The system dynamically adjusts the sampling frequency based on the detected RRO frequency. When RRO frequency exceeds the Nyquist frequency, the sampling frequency is increased to prevent aliasing. This dynamic adaptation allows the system to maintain measurement precision only when necessary, rather than continuously operating at high sampling rates, thus resolving the contradiction between device complexity and measurement precision.
Solution Approach 2:
The sampling frequency parameter is changed from a fixed Nyquist rate to a variable rate that adapts to the RRO frequency characteristics. By detecting the RRO frequency and adjusting the sampling frequency accordingly, the system ensures accurate measurement of head positioning errors even when RRO frequency exceeds the original Nyquist frequency, while avoiding unnecessary high sampling rates when not needed.
2Measurement precision
If the sampling frequency is increased to capture high frequency RRO, then the measurement precision is improved, but the use of energy increases due to higher processing requirements
Solution Approach 1:
The sampling frequency is dynamically adjusted based on the detected RRO frequency characteristics. The system operates at the minimum necessary sampling rate to capture the RRO disturbance, increasing frequency only when high frequency RRO is detected. This dynamic approach ensures measurement precision is maintained while minimizing energy consumption by avoiding continuous high-rate sampling and processing.
Solution Approach 2:
The system applies partial upsampling rather than continuous full-rate sampling. By detecting the specific RRO frequency and applying selective upsampling only when and where needed, the system achieves the necessary measurement precision for high frequency RRO compensation without the full energy cost of continuously operating at the highest sampling rate.
3Reliability
If feed-forward compensation is applied to cancel RRO effects, then the reliability of tracking is improved, but the device complexity increases due to additional compensation mechanisms
Solution Approach 1:
The system uses feedback from the position error signal to detect RRO frequency and generate appropriate compensation signals. By continuously monitoring the PES and adapting the compensation based on detected RRO characteristics, the system achieves reliable tracking accuracy while keeping the compensation mechanism relatively simple and adaptive rather than requiring complex predetermined compensation for all possible RRO frequencies.
Solution Approach 2:
The system performs preliminary detection of RRO frequency and generates compensation values in advance before they are needed for tracking correction. By detecting the RRO disturbance and pre-calculating compensation signals, the system improves tracking reliability through proactive correction while maintaining simpler processing requirements compared to reactive compensation methods.
Data Source
AI summary
A data storage device comprising a head actuated over a disk comprising a plurality of tracks. The head is positioned over a target track, and a sampled position error signal (PES) is generated representing a position of the head relative to the target track. The sampled PES is filtered with a servo compensator to generate a sampled control signal, and the sampled control signal is upsampled to generate an upsampled control signal. The sampled PES is upsampled to generate an upsampled PES, and the upsampled PES is processed to generate compensation values. The upsampled control signal is combined with the compensation values to generate a compensated control signal, and the position of the head over the target track is adjusted based on the compensated control signal.