Split Actuator Drive Slew Rate Limiting for Multi-Actuator HDDs
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Solution Overview
Problem
Magnetic hard disk drives (HDDs) with multiple rotary actuators face challenges in maintaining positioning accuracy due to mechanical interactions between actuators, where vibrations from one actuator can adversely affect the operation of another, especially during sensitive operations like writing data or calibration procedures.
Innovation Solution
The solution involves modifying the seek operation of the 'aggressor' actuator by limiting its slew rate to prevent mechanical disturbances, ensuring it does not exceed a threshold value, particularly during acceleration and deceleration phases, to minimize the impact on the 'victim' actuator, thereby maintaining positioning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the aggressor actuator performs high-acceleration seek operations to improve access speed, then productivity increases, but mechanical vibrations are generated that deteriorate positioning accuracy of the victim actuator
Solution Approach 1:
The patent applies dynamics by making the slew rate limit adaptive rather than fixed. The limit is dynamically adjusted based on the victim actuator's current operation state - using stricter limits when the victim is performing sensitive operations (writing, calibration) and more relaxed limits during less sensitive operations. This dynamic adaptation allows the aggressor actuator to maintain high productivity when possible while ensuring positioning accuracy when needed.
Solution Approach 2:
The patent changes the parameter of slew rate limit from a constant value to a variable value that depends on the victim actuator's operation state. By monitoring the victim actuator's state and adjusting the aggressor's slew rate threshold accordingly, the system optimizes the trade-off between access speed and positioning accuracy across different operational scenarios.
2Measurement precision
If the slew rate of the aggressor actuator is limited to reduce mechanical disturbances, then positioning accuracy of the victim actuator is improved, but the access speed of the aggressor actuator is reduced
Solution Approach 1:
The system dynamically adjusts the slew rate limit based on real-time monitoring of the victim actuator's operation state. When the victim is performing sensitive operations, a lower slew rate limit is applied to ensure positioning accuracy. When the victim is idle or performing less sensitive operations, the limit is relaxed to allow faster access. This dynamic approach optimizes the trade-off between positioning accuracy and access speed.
Solution Approach 2:
The system periodically monitors the victim actuator's operation state and adjusts the aggressor's slew rate limit accordingly. This periodic assessment allows the system to adapt to changing operational conditions, applying appropriate slew rate limits at different time intervals based on what the victim actuator is currently doing.
3Productivity
If multiple rotary actuators operate simultaneously to increase throughput, then productivity increases, but mechanical interactions between actuators generate vibrations that worsen positioning accuracy
Solution Approach 1:
The system uses feedback by monitoring the victim actuator's operation state and using this information to control the aggressor actuator's slew rate. This feedback mechanism allows the system to coordinate multiple actuators' operations, reducing mechanical interactions and vibrations when the victim is performing sensitive operations while maintaining high throughput when conditions permit.
Data Source
AI summary
A seek operation of a first actuator in a multi-actuator drive is modified, so that one or more disturbance-generating portions of the seek operation do not adversely affect operation of a second actuator in the drive. Radial motion of the aggressor actuator is controlled by limiting a slew rate of the first actuator during one or more portions of the seek operation to be less than or equal to a threshold value. Because slew rate of the first actuator is the rate of change of radial acceleration of the aggressor actuator with respect to time, limiting the slew rate of the first actuator prevents or reduces mechanical disturbances caused by jerk associated with motion of the first actuator.