Notch Filter Damping Ratio Adjustment for Disk Drive Positioning
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Solution Overview
Problem
In magnetic disk drives, changes in rotation speed alter the sampling period of positional information, leading to unintended changes in the frequency characteristics of the notch filter, which adversely affect the accuracy of magnetic head positioning control.
Innovation Solution
A magnetic disk drive with a notch filter that adjusts its parameters, specifically the damping ratio, based on changes in sampling period, using a computation unit to maintain desired frequency characteristics by recalculating the discrete-time system transfer function from a continuous-time system transfer function via bilinear transform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rotation speed of the magnetic disk is changed, then the sampling period of positional information changes, but the frequency characteristics of the notch filter deviate from desired values, adversely affecting positioning control accuracy
Solution Approach 1:
The notch filter parameters are made dynamic by automatically adjusting them according to the sampling period. The control unit computes new filter parameters based on the current sampling period value, allowing the filter to adapt its frequency characteristics dynamically as the rotation speed changes, thereby maintaining optimal positioning control accuracy across different operating conditions
Solution Approach 2:
The invention changes the parameters of the notch filter (specifically the frequency characteristics) in response to changes in sampling period. By computing new parameter values based on the relationship between sampling period and filter characteristics, the system maintains desired frequency response despite variations in rotation speed-induced sampling period changes
2Reliability
If the sampling period changes due to rotation speed variation, then the frequency characteristics of the notch filter change from desired values, but maintaining fixed filter parameters simplifies the control system
Solution Approach 1:
The control unit performs self-adjustment by automatically computing new notch filter parameters based on the current sampling period. This self-service mechanism eliminates the need for external manual tuning or complex adaptive control systems, as the filter parameters are autonomously updated according to the relationship between sampling period and desired frequency characteristics
Solution Approach 2:
The system uses feedback from the sampling period value to adjust the notch filter parameters. The control unit continuously monitors the sampling period and computes appropriate parameter adjustments, creating a closed-loop system that maintains frequency characteristics stability without requiring additional sensors or complex control architecture
Data Source
AI summary
According to one embodiment, a magnetic disk drive includes a notch filter, a parameter storage unit and a computation unit, when the sampling period changes from a first sampling period to a second sampling period, the computation unit computes a damping ratio parameter related to the damping ratio in a second set of parameters at the second sampling period, based on a first absolute value at a first angular frequency of a first transfer function computed from a first set of parameters at the first sampling period and a second absolute value at the first angular frequency of a second transfer function computed from the first set of parameters at the second sampling period, and the notch filter is set with the second set of parameters at the second sampling period is computed.