Dual Stage Actuator Servo Loop Evaluation via Sinusoidal Signals
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Solution Overview
Problem
As data track density increases in disk drives, existing servo systems face challenges in accurately positioning heads over tracks, particularly in high-density environments, where microactuators are employed in conjunction with voice coil motors to enhance tracking performance, but methods to evaluate the performance of dual-stage actuators are limited.
Innovation Solution
A dual-stage actuator servo loop evaluation method is introduced, where sinusoidal signals are added to both voice coil motor and microactuator control signals, and their responses are measured to compute closed loop responses, allowing for the calculation of error rejection curves and open loop responses, thereby assessing the overall performance of the dual-stage actuator system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data track density increases, then storage capacity improves, but positioning accuracy deteriorates
Solution Approach 1:
The actuator system is divided into two independent stages: a voice coil motor (VCM) for coarse positioning and a microactuator for fine positioning. This segmentation allows each stage to specialize in different positioning tasks, with the VCM handling large displacements and the microactuator providing precise adjustments, thereby maintaining positioning accuracy even as track density increases.
Solution Approach 2:
The microactuator is integrated within the existing VCM actuator assembly, forming a nested dual-stage system. The microactuator is positioned to provide additional fine-positioning capability while working in conjunction with the VCM, allowing the system to achieve high positioning precision without requiring a complete redesign of the actuator architecture.
2Reliability
If dual stage actuator is employed, then tracking performance improves, but evaluation difficulty increases
Solution Approach 1:
The evaluation method incorporates feedback mechanisms where the system measures the actual response of the dual-stage actuator to commanded movements and compares it against expected performance. By analyzing the feedback signals from both the VCM and microactuator stages, the system can assess tracking performance and identify areas for improvement without requiring complex external measurement equipment.
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 method enables comprehensive evaluation of dual-stage actuator performance, improving head positioning accuracy and tracking capabilities in high-density data environments by providing detailed metrics on closed loop responses and error rejection curves.
Implementation Method 1
a voice coil motor (VCM) to position the head radially over the disk
Implementation Method 2
a piezoelectric (PZT) actuator
Data Source
AI summary
A method of evaluating a dual stage actuator (DSA) servo loop in a disk drive is disclosed. The disk drive comprises a dual stage actuator (DSA) servo loop operable to actuate a head over a disk surface. A first sinusoidal signal A1 is added to a VCM control signal B1 generated by a VCM servo loop. A response of the VCM control signal B1 to the first sinusoidal signal A1 is measured, and a closed loop response of the VCM servo loop is computed in response to A1 and B1. A second sinusoidal signal A2 is added to a microactuator control signal B2 generated by a microactuator servo loop. A response of the microactuator control signal B2 to the second sinusoidal signal A2 is measured, and a closed loop response of the microactuator servo loop is computed in response to A2 and B2.