Disk Runout Measurement Using Virtual Servo Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for measuring disk runout in disk drives face challenges such as contamination from fine dust particles and instability due to radial head position deviations, making precise measurement and effective control difficult.
Innovation Solution
The implementation of a virtual concentric servo-control method using a disk drive configuration with an actuator, servo controller, calculation module, and adjustment module, which calculates a virtual target orbit value to suppress disturbances and adjust the gain, allowing for precise measurement of disk runout without physical contact and maintaining servo control reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the actuator is pushed to the stopper provided at the inner periphery of the disk to measure runout using the inner-periphery push scheme, then the runout measurement can be performed, but fine dust particles are generated causing contamination that adversely influences the disk drive
Solution Approach 1:
The patent extracts the measurement function from the physical contact method by implementing a virtual concentric servo-control method that calculates a virtual target orbit value without pushing the actuator to the stopper. This separates the measurement capability from the harmful physical contact, allowing runout measurement without generating dust particles.
Solution Approach 2:
The patent replaces the mechanical push method with a computational approach. Instead of physically pushing the actuator to the stopper and reading servo data, the system uses a calculation module to compute a virtual target orbit value that represents the runout, substituting mechanical contact with mathematical calculation.
2Ease of operation
If the servo-free scheme is used to measure runout by supplying current to the voice coil motor with feed-forward control, then the measurement process is simplified, but the head position deviates in the radial direction making stable measurement difficult when disturbance occurs
Solution Approach 1:
The patent introduces feedback control into the measurement process. The servo controller maintains the head position on the target orbit by using feedback from the servo data, allowing the system to compensate for disturbances and maintain stable measurement conditions while keeping the process relatively simple.
Solution Approach 2:
The patent implements dynamic control during the measurement process. The virtual target orbit value is calculated while accounting for the dynamic interaction between the head and disk, allowing the system to adapt to disturbances and maintain measurement stability rather than using a static approach.
3Measurement precision
If the head remains physically stopped to read servo signal and store runout in memory, then the runout correction table can be generated, but the method cannot achieve stable measurement when disturbance occurs causing radial head position deviation
Solution Approach 1:
The patent introduces a virtual target orbit value as an intermediary that mediates between the head position and the runout measurement. This virtual orbit allows the system to measure runout without the head being physically stopped, maintaining measurement stability by using the virtual orbit as a reference that accounts for disturbances.
Data Source
AI summary
According to one embodiment, a disk drive includes an actuator, a servo controller, a calculation module and an adjustment module. The actuator is configured to move the head over a disk, in the radial direction of the disk. The servo controller is configured to make the head move along a target orbit on the disk, in accordance with the distance the actuator has been moved. The calculation module is configured to calculate, as disk runout, a virtual target orbit value supplied to the servo controller to suppress the disturbance at the target orbit. The adjustment module is configured to multiply the virtual target orbit value by a gain that has been preset.