Disk Drive Microactuator Gain Estimation via Sinusoidal Injection
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Solution Overview
Problem
As data track density increases in disk drives, existing servo systems face challenges in maintaining accurate head positioning and tracking performance due to variations in microactuator gain over time, influenced by environmental changes and degradation, which affects the stability and efficiency of the servo loop.
Innovation Solution
A dual-state actuator system combining a voice coil motor (VCM) with a microactuator, where a disturbance sinusoid is injected into the microactuator servo loop to estimate and adjust the microactuator gain, enabling feed-forward compensation to maintain target frequency response and performance, while allowing continuous operation without periodic calibration interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If microactuator gain is adjusted periodically through calibration, then tracking performance is maintained, but operational interruptions occur and productivity is reduced
Solution Approach 1:
The patent implements continuous gain estimation by injecting a sinusoidal disturbance signal into the microactuator control loop during normal operation. This allows the system to continuously monitor and adjust microactuator gain without stopping the disk drive, eliminating periodic calibration interruptions while maintaining tracking performance through real-time adaptation.
Solution Approach 2:
The system performs preliminary gain estimation by analyzing the response to injected sinusoidal disturbances before actual tracking errors occur. By continuously monitoring the microactuator's frequency response characteristics, the system proactively adjusts gain parameters to prevent performance degradation rather than reacting to errors after they occur.
2Adaptability or versatility
If microactuator gain is estimated frequently, then adaptability to environmental changes is improved, but system complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the response to injected sinusoidal disturbances is continuously analyzed to estimate microactuator gain. The estimated gain feeds back into the control algorithm, enabling automatic adaptation to environmental changes and degradation. This closed-loop feedback approach provides high adaptability using standard control system components without requiring complex external measurement equipment.
Solution Approach 2:
The system performs self-diagnosis and self-adjustment by using its own operational signals to estimate microactuator characteristics. The sinusoidal disturbance is injected into the existing control loop, and the system analyzes its own response to determine gain changes, eliminating the need for external calibration equipment or complex additional sensors.
3Measurement precision
If sinusoidal disturbance is injected into the servo loop, then gain estimation accuracy is improved, but tracking performance during injection may be affected
Solution Approach 1:
The patent uses a small-amplitude sinusoidal disturbance signal that is sufficient to elicit a measurable response from the microactuator but small enough to not significantly disrupt normal tracking operations. This partial action approach allows accurate gain estimation while minimizing the impact on tracking performance, as the disturbance amplitude is carefully selected to be just enough for measurement purposes.
Solution Approach 2:
The sinusoidal disturbance signal acts as an intermediary tool to probe microactuator characteristics without directly interfering with the primary tracking function. By using this intermediate signal and analyzing the system's response, the patent indirectly measures gain changes while the main servo loop continues to operate, effectively separating the measurement function from the control function.
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 stabilizes the servo loop, enables frequent gain estimation during normal operations, and maintains tracking performance by adjusting microactuator gain in real-time, reducing the impact of environmental changes and degradation.
Implementation Method 1
a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM)
Implementation Method 2
Any suitable microactuator may be employed, such as a suitable piezoelectric (PZT) actuator
Data Source
AI summary
A disk drive is disclosed comprising a head, a disk surface, and a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface. A microactuator compensator processes a position error signal (PES) to generate a first control signal, and a disturbance sinusoid is injected into the first control signal to generate a second control signal, wherein the microactuator is controlled in response to the second control signal. Feed-forward compensation is generated corresponding to the injected disturbance sinusoid, and a third control signal is generated in response to the PES and the feed-forward compensation, wherein the VCM is controlled in response to the third control signal. A gain of the microactuator is estimated in response to the feed-forward compensation.