Triangle Dither Servo Control for Disk Drive Track Squeeze
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Solution Overview
Problem
Existing disk drive systems face performance issues due to 'track squeeze,' where transient decreases in servo track spacing reduce the fidelity of servo information, leading to decreased servo control system performance, especially during head positioning operations.
Innovation Solution
The implementation of a triangle-shape dither signal, generated by summing odd harmonics of a fundamental frequency, is injected into the servo control system to maintain constant servo track crossing velocity and improve head positioning accuracy by compensating for track squeeze effects, allowing the head to cross multiple servo tracks during access operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional servo control is used without dither signal, then the system is simple, but track squeeze causes decreased servo control performance and head positioning accuracy
Solution Approach 1:
A periodic triangle-shaped dither signal is injected into the servo control system to modulate the head positioning. This periodic action causes the head to cross multiple servo tracks during access operations, spreading the impact of track squeeze and maintaining measurement precision without requiring fundamental system redesign
Solution Approach 2:
The invention changes the positioning parameters by introducing a dither signal that varies the head position dynamically. By summing odd harmonics of a fundamental frequency, the system creates a triangle-shaped waveform that optimizes track crossing velocity while compensating for track squeeze effects
2Measurement precision
If sinusoidal dither signal is used, then the head positioning accuracy is improved, but the servo track crossing velocity varies causing low-velocity crossings that reduce performance
Solution Approach 1:
The invention replaces the symmetric sinusoidal waveform with an asymmetric triangle-shaped waveform. This asymmetric shape maintains the beneficial positioning accuracy improvements while ensuring more uniform track crossing velocities, eliminating the low-velocity crossing problem inherent in sinusoidal modulation
Solution Approach 2:
The system dynamically adjusts the dither signal characteristics by using a triangle waveform with controlled rise and fall times. This dynamic approach optimizes the velocity profile during track crossings, maintaining higher velocities compared to sinusoidal modulation while preserving positioning accuracy
Data Source
AI summary
A data storage device is disclosed comprising a head actuated over a disk. The head is used to read servo information from the disk and generate a position error signal (PES) representing a position of the head over the disk. A control signal is generated based on the PES and a triangle-shape dither signal, and the head is positioned over the disk using the control signal.