Parallel Servo Control for Multi-Surface HDD Head Positioning
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Solution Overview
Problem
Traditional hard disc drives (HDDs) typically operate one head at a time, limiting data throughput and reliability when accessing multiple disc surfaces, as they require switching control between heads to fulfill host requests.
Innovation Solution
The implementation of a servo control system that uses an out-of-phase driving scheme to concurrently position multiple heads over different disc surfaces by coupling micro-actuators to arms and utilizing a coarse actuator for initial positioning, followed by fine positioning through micro-actuator drive circuitry that drives the micro-actuators in opposite directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional hard disc drives operate one head at a time, then control complexity is reduced, but data throughput is limited
Solution Approach 1:
The actuator system is segmented into multiple independent micro-actuators, each capable of independently positioning a separate head. This allows parallel operation of multiple heads without requiring a completely new control architecture, as each micro-actuator can be controlled independently while sharing common resources like the coarse actuator and power device.
Solution Approach 2:
The single power device and coarse actuator serve multiple functions by being shared across all micro-actuators and heads. This universal approach allows the system to maintain relatively simple common infrastructure while achieving parallel head operation through the micro-actuator level differentiation.
2Productivity
If multiple heads are positioned concurrently on different disc surfaces, then data throughput increases, but positioning precision control becomes more difficult
Solution Approach 1:
Positioning control is segmented into two independent stages: coarse positioning handled by the shared coarse actuator for all heads, and fine positioning handled by individual micro-actuators for each head. This segmentation allows each head to be precisely positioned independently without interfering with other heads, maintaining positioning precision while enabling concurrent operation.
Solution Approach 2:
The coarse actuator performs preliminary positioning of all heads to their respective tracks before the micro-actuators engage for fine positioning. This preliminary action establishes a common starting point and rough positioning, making the subsequent fine positioning by individual micro-actuators more straightforward and precise.
3Device complexity
If a single power device drives multiple micro-actuators in opposite directions, then device complexity is reduced, but control precision for each actuator decreases
Solution Approach 1:
Driver circuitry acts as an intermediary between the single power device and the multiple micro-actuators. This intermediary component receives power from the single power device and distributes it to multiple micro-actuators with appropriate polarity control, enabling precise control of each actuator in opposite directions without requiring separate power devices.
Solution Approach 2:
Instead of providing separate power devices for each micro-actuator, the system inverts the approach by using a single power device that can drive multiple actuators in opposite directions through clever circuit configuration. The driver circuitry inverts the polarity of the power signal as needed to drive different micro-actuators in opposite directions.
Data Source
AI summary
A data storage device includes a first data storage surface and a second data storage below the first data storage surface. The data storage device also includes a first micro-actuator coupled to a first arm that supports a first head over the first data storage surface, and a second micro-actuator coupled to a second arm that supports a second head over the second data storage surface. The data storage device further includes a coarse actuator, to which the first and second arms are coupled, that positions the first head and the second head between corresponding first and second tracks on the respective first and second data storage surfaces. Micro-actuator drive circuitry finely positions the first head over the first track and the second head over the second track by concurrently driving the first micro-actuator and the second micro-actuator in opposite directions.