Spinstand Aggressor Track Positioning Accuracy
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Solution Overview
Problem
Conventional spinstand systems face challenges in achieving accurate and repeatable head positioning due to mechanical limitations and variations in servo pattern quality, leading to inaccuracies in writing aggressor tracks at precise locations.
Innovation Solution
The system measures the actual location of aggressor tracks written on a disk, allowing for precise positioning and interpolation of track locations, using a combination of coarse and fine positioners, a processor, and a servo calibration procedure to correct radial positioning errors, enabling accurate measurements beyond the limitations of the piezo actuator's step size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional servo pattern is written on the disk for head positioning, then the head can be positioned at radial locations, but the positioning accuracy degrades due to variations in servo pattern quality and mechanical limitations
Solution Approach 1:
The system performs preliminary actions by writing multiple test tracks at known radial positions before the actual measurement. These test tracks serve as reference markers that are read back to calculate correction factors. By preparing these reference tracks in advance, the system establishes a baseline for accuracy correction without interfering with the final measurement process.
Solution Approach 2:
The system implements feedback by reading back the test tracks written at known positions, comparing the actual read positions against the intended write positions, and using this discrepancy information to calculate correction factors. These correction factors are then applied to subsequent measurements to compensate for positioning errors, creating a closed-loop system that continuously improves accuracy.
2Manufacturing precision
If the piezo actuator is used for radial positioning, then the head can be moved to different radial locations, but the minimum step size limits the precision of aggressor track writing
Solution Approach 1:
The system replaces the mechanical positioning limitation with an electronic/software-based correction approach. Instead of trying to improve the mechanical piezo actuator's step size, the system uses software algorithms to calculate and apply correction factors that compensate for positioning errors. This substitution of mechanical improvement with computational correction avoids the complexity of redesigning the mechanical positioning system.
Solution Approach 2:
The system changes the approach from controlling physical position parameters directly (piezo step size) to controlling correction parameter values. By writing test tracks at multiple known positions and measuring actual vs. intended positions, the system derives correction parameters that can be applied to all subsequent positioning operations, effectively changing the control parameter from mechanical displacement to computational correction.
3Adaptability or versatility
If multiple aggressor tracks are written at off-track locations to assess central track changes, then measurement coverage is improved, but the variability in servo pattern quality introduces measurement scatter
Solution Approach 1:
The system segments the disk into multiple radial zones by writing test tracks at different radial positions (e.g., inner, middle, outer regions). Each zone is independently measured and corrected using its own correction factors derived from local test tracks. This segmentation allows the system to handle variability across different radial locations independently, improving overall measurement coverage while maintaining precision through localized corrections.
Solution Approach 2:
The system changes the measurement approach by introducing correction parameters that adjust for radial position variations. Instead of treating all measurements uniformly, the system applies position-dependent correction factors that compensate for servo pattern quality variations at different radial locations. This parameter adjustment allows the system to maintain measurement precision across the entire disk surface while preserving adaptability to different measurement scenarios.
Data Source
AI summary
Systems and methods for improving the accuracy of test measurements involving aggressor tracks written to the disks are provided. One such method involves erasing a circumferential band of a disk, writing a central track on the circumferential band, measuring and storing a first track profile of the central track, writing an aggressor track on each side of the central track at a preselected aggressor track offset from the central track, measuring and storing a track profile of the aggressor tracks at the preselected aggressor track offset, measuring and storing a second track profile of the central track, performing the prior actions exactly n times where n is greater than or equal to 1, determining an estimated distance between the aggressor tracks based on the respective track profiles, determining a selected measurement using the estimated distance between the aggressor tracks, and the first and second track profiles of the central track.