Actuator Coupling Re-characterization for HDD Position Accuracy
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Solution Overview
Problem
In hard disk drives with multiple actuators, mechanical disturbances caused by one actuator can interfere with the operation of another, leading to position errors and degraded performance due to changing mechanical coupling characteristics over time, such as aging or environmental changes.
Innovation Solution
A method to re-characterize the mechanical coupling between actuators by monitoring position errors and using the determined mechanical transfer function to modify compensation, ensuring effective inter-actuator compensation and maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple actuators are used to increase productivity, then data access speed and throughput are improved, but mechanical coupling between actuators causes position errors and reliability degradation
Solution Approach 1:
The system continuously monitors position errors of the second head and uses this feedback to update the mechanical transfer function. The servo controllers exchange information about actuator commands and position errors, enabling real-time adjustment of compensation parameters to maintain position accuracy despite mechanical coupling effects.
Solution Approach 2:
The system performs preliminary characterization of the mechanical coupling between actuators by determining the mechanical transfer function before normal operation. This pre-characterization allows the system to prepare compensation parameters in advance, and the transfer function is updated periodically or when position errors exceed thresholds, ensuring compensation is ready before critical errors occur.
2Reliability
If mechanical coupling compensation is applied to maintain position accuracy, then reliability is improved, but system complexity increases due to additional sensing and control mechanisms
Solution Approach 1:
The system uses the existing read heads to detect position errors and the existing actuators to apply compensation. The servo controllers that already exist are enhanced to exchange information and coordinate control, rather than adding entirely new sensing or actuation systems. The mechanical transfer function is determined using normal operational data from the heads and actuators.
3Adaptability or versatility
If the mechanical transfer function is continuously updated to adapt to changing mechanical coupling, then adaptability is improved, but loss of time occurs during re-characterization operations
Solution Approach 1:
The system performs re-characterization of the mechanical transfer function periodically or based on triggers such as when position errors exceed a threshold. This periodic updating balances the need to adapt to mechanical changes (from aging, temperature, etc.) with the cost of time lost during re-characterization operations, avoiding both excessive updates and insufficient adaptation.
Data Source
AI summary
In a device with first and second heads, the second head is held at a radial location over one or more disks via a second actuator that moves the second head. A position error of the second head is read while performing a seek with a first actuator, the first actuator moving the first head over the one or more disks. A mechanical transfer function is determined between the first actuator and the second actuator based on the position error of the second head. The mechanical transfer function is used to provide compensation for the second head via the second actuator in response to subsequent seek of the first actuator.