Fly Height Measurement Thermal Decay Compensation
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Solution Overview
Problem
Conventional data storage devices face challenges in maintaining optimal fly height of the head over a disk due to thermal decay of spacing patterns, which affects recording quality and detection accuracy, especially as the frequency of the spacing pattern increases, leading to varying rates of thermal decay.
Innovation Solution
The implementation of a method to estimate changes in fly height by using two different spacing patterns written at different frequencies, with constants A and B derived from measurements at varying intervals to compensate for thermal decay, allowing for accurate adjustment of fly height actuation to maintain target fly height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single spacing pattern is used for fly height measurement, then the measurement process is simple, but thermal decay affects measurement accuracy especially at higher frequencies
Solution Approach 1:
The patent divides the measurement process into segments by using multiple spacing patterns with different frequencies (e.g., first spacing pattern at frequency f1, second spacing pattern at frequency f2). Each pattern experiences different thermal decay rates, allowing the system to segment the measurement into frequency-specific channels that can be independently calibrated and compensated.
Solution Approach 2:
The patent changes the frequency parameter of the spacing patterns used for measurement. By using spacing patterns at different frequencies, the system exploits the frequency-dependent thermal decay characteristics to generate multiple measurements that can be combined to compensate for thermal effects and improve overall measurement accuracy.
2Measurement precision
If spacing pattern frequency is increased to improve measurement resolution, then measurement detail improves, but thermal decay rate increases reducing accuracy
Solution Approach 1:
The patent implements a feedback mechanism where measurements from multiple spacing patterns with different frequencies are continuously monitored. The system uses the differential decay rates observed between patterns to calculate compensation factors that are fed back to correct the fly height measurement, thereby maintaining reliability even at higher frequencies.
Solution Approach 2:
The patent creates a composite measurement approach by combining results from multiple spacing patterns with different frequencies. Rather than relying on a single pattern, the system synthesizes a composite measurement that leverages the strengths of each frequency band while compensating for their individual thermal decay weaknesses.
3Measurement precision
If thermal decay compensation is implemented using multiple spacing patterns, then measurement accuracy improves, but processing complexity increases
Solution Approach 1:
The patent performs preliminary calibration and characterization of the thermal decay characteristics for each spacing pattern frequency during manufacturing or initial setup. This preliminary action creates lookup tables or calibration factors that are stored in memory, allowing the control system to apply simple compensation corrections during operation without performing complex real-time calculations.
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 thermal decay in fly height measurements, ensuring consistent recording quality and detection accuracy by accurately adjusting the fly height actuation, thereby optimizing data storage operations.
Implementation Method 1
a heater which controls fly height through thermal expansion
Implementation Method 2
a piezoelectric (PZT) actuator which controls the fly height through mechanical deflection
Implementation Method 3
An air bearing forms between the head and the disk due to the disk rotating at high speeds
Data Source
AI summary
A data storage device is disclosed comprising a head actuated over a disk. A first spacing pattern is written to the disk and a second spacing pattern is written to the disk different from the first spacing pattern. A first fly height measurement (FHM1_1) is generated by reading the first spacing pattern and a first fly height measurement (FHM2_1) is generated by reading the second spacing pattern. After an interval, a second fly height measurement (FHM1_2) is generated by reading the first spacing pattern and a second fly height measurement (FHM2_2) is generated by reading the second spacing pattern. A change in the fly height of the head is estimated based on:(ΔFHM2−B·ΔFHM1)/(A−B)where ΔFHM1 represents a difference between FHM1_1 and FHM1_2, ΔFHM2 represents a difference between FHM2_1 and FHM2_2, and A and B are constants.