Split-Actuator HDD Feedforward Compensation for Cross-Coupling
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Solution Overview
Problem
In magnetic hard disk drives (HDDs) with multiple rotary actuators, mechanical interactions between actuators can significantly affect the positioning accuracy of magnetic heads, leading to vibrations that degrade the accuracy of one actuator when another is in motion.
Innovation Solution
A victim feedforward signal is added to the microactuator control signal of a 'victim' actuator based on the voice-coil motor (VCM) control signal of an 'aggressor' actuator, using a transfer function that models the disturbances caused by the aggressor's VCM commands, to compensate for positioning inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple rotary actuators are used to increase data access throughput, then productivity is improved, but mechanical interactions between actuators cause vibrations that worsen positioning accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors the position of the victim actuator and adjusts its control signal in response to disturbances caused by the aggressor actuator. This closed-loop feedback enables the system to maintain positioning accuracy despite mechanical interactions between multiple actuators operating simultaneously.
Solution Approach 2:
The patent introduces a feedforward signal as an intermediary element that mediates the interaction between actuators. This feedforward signal, generated based on the aggressor actuator's control signal and a pre-determined transfer function, compensates for anticipated disturbances before they affect the victim actuator's positioning, thereby resolving the contradiction between high throughput and positioning accuracy.
2Speed
If high acceleration is applied to the aggressor actuator for fast seeking, then speed is improved, but vibrations generated worsen the positioning accuracy of the victim actuator
Solution Approach 1:
The patent applies preliminary action by determining the transfer function in advance through calibration procedures. This pre-characterization of the mechanical interaction allows the controller to generate appropriate feedforward compensation signals before the victim actuator is affected by the aggressor actuator's high-acceleration motion, thereby maintaining positioning accuracy during fast seeking operations.
Solution Approach 2:
The controller uses feedback from the victim actuator's position sensor to detect positioning errors caused by vibrations from the aggressor actuator. This feedback information is used to adjust the victim actuator's control signal in real-time, compensating for the effects of high-acceleration seeking and maintaining positioning accuracy.
3Manufacturing precision
If feedforward compensation is implemented to reduce cross-actuator coupling effects, then positioning accuracy is improved, but device complexity increases due to additional control signals and transfer function determination
Solution Approach 1:
The patent uses feedback from the victim actuator's position sensor to verify the effectiveness of the feedforward compensation and to make real-time adjustments. This feedback mechanism ensures that the increased complexity of the control system directly translates to improved positioning accuracy by continuously optimizing the compensation based on actual system behavior.
Solution Approach 2:
The system performs self-characterization through calibration procedures that automatically determine the transfer function between actuators. This self-service approach reduces the need for manual tuning and complex external measurement equipment, thereby limiting the increase in device complexity while still achieving accurate feedforward compensation.
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 approach effectively reduces the impact of one actuator's motion on another, enhancing the positioning accuracy of the victim actuator by compensating for disturbances, thereby improving the overall performance and accuracy of multi-actuator HDDs.
Implementation Method 1
a first voice coil motor (VCM) and to which the first head and the first microactuator are mounted
Implementation Method 2
a first microactuator configured to move the first head relative to the magnetic disk
Data Source
AI summary
In a multi-actuator drive, the effect of moving a first actuator (the so-called “aggressor actuator”) in on a second actuator (the so-called “victim actuator”) is reduced or compensated for. A victim feedforward signal is added to a microactuator control signal of the victim actuator in response to a voice-coil motor (VCM) control signal that is applied to the aggressor actuator. The feedforward signal is configured to compensate for disturbances to the victim microactuator caused by VCM commands provided to the aggressor actuator. The feedforward signal is based on a transfer function that models commands added to the victim microactuator, which is coupled to the head of the victim actuator, as a function of the aggressor VCM control signal applied to the aggressor actuator.