Micro Actuator Gain Control via Polynomial Approximation
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Solution Overview
Problem
Existing magnetic disk devices face challenges in accurately controlling micro actuators due to voltage dependency, which leads to distortion in output displacement and errors in calculating the amplitude ratio MA gain, resulting in inaccurate positioning of the magnetic head.
Innovation Solution
A magnetic disk device is designed with a control unit that calculates the gain of the micro actuator using an approximation polynomial with stored coefficients, considering distortion and voltage dependency, allowing for precise control of the micro actuator by calculating the amplitude ratio MA gain through discrete Fourier transform (DFT) and polynomial approximation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polynomial approximation is used to calculate MA gain from voltage-dependent gains, then voltage dependency is considered, but distortion of output displacement cannot be accounted for resulting in inaccurate gain calculation
Solution Approach 1:
The patent applies feedback by measuring the actual output displacement of the micro actuator and using this information to correct the gain calculation. The system measures the relationship between input voltage and actual output displacement, then uses this feedback to determine the amplitude ratio MA gain that accounts for both voltage dependency and distortion, thereby resolving the contradiction between considering voltage dependency and accounting for output distortion accuracy
Solution Approach 2:
The patent changes the parameter used for gain calculation from simple voltage-dependent gain ratios to amplitude ratio MA gain that incorporates actual output displacement measurements. By changing from theoretical polynomial approximation to measurement-based parameter calculation, the system simultaneously accounts for voltage dependency and output distortion, improving both measurement precision and reliability
2Manufacturing precision
If the second actuator is used for fine positioning, then positioning accuracy is improved, but voltage dependency of the gain requires complex control considerations
Solution Approach 1:
The patent simplifies the control of the second actuator by changing from complex polynomial approximation control to a simpler amplitude ratio MA gain calculation based on actual output measurements. This approach maintains high positioning accuracy while reducing control system complexity by using direct measurement-based gain determination instead of complex voltage-dependent polynomial models
Solution Approach 2:
The system enables the micro actuator to self-characterize its gain characteristics through actual operation and measurement. By having the actuator perform test movements and measuring its actual output displacement in response to known inputs, the system automatically determines the amplitude ratio MA gain without requiring external complex modeling, thereby simplifying control while maintaining precision
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 enables accurate positioning of the magnetic head by accounting for voltage-dependent distortion, improving the control of micro actuators and reducing errors in displacement, thus enhancing the overall performance of the magnetic disk device.
Implementation Method 1
the control unit calculates the gain of the second actuator from the approximation polynomial in which the coefficient stored in the storing unit is used and amplitude of a voltage input to the second actuator
Implementation Method 2
A gain at each of the voltage amplitudes is calculated from ratios of amplitudes obtained from DFT (discrete Fourier transform) to input and output waveforms of the sine waves
Implementation Method 3
it is known that a gain of input and output of the second actuator used in this type of the magnetic disk device have voltage dependency
Data Source
AI summary
According to one embodiment, a magnetic disk device includes a magnetic disk, a magnetic head, a first actuator that moves the magnetic head to a predetermined position on the magnetic disk, a second actuator that is provided in the first actuator and adjusts a position of the magnetic head, a control unit that controls operations of the first actuator and the second actuator, and a storing unit that stores a coefficient of an approximation polynomial calculated based on an approximation formula for approximating voltage dependency of a gain of the second actuator. When controlling the operation of the second actuator, the control unit calculates the gain amplitude of the second actuator from the approximation polynomial in which the coefficient is used and amplitude of a voltage input to the second actuator.