Voice Coil Motor Control Signal Adjustment for Hard Drive Positioning
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Solution Overview
Problem
Temperature-induced changes in drag forces affect the performance of voice coil motor assemblies in hard drives, leading to positioning errors due to unduly large DC offset components in position error signals, which are not accurately accounted for in existing technologies.
Innovation Solution
A method and apparatus that determine a position error signal and its DC offset component during a seek operation, adjusting the voice coil motor control signal by applying a different drag component value if the DC offset exceeds a threshold, thereby modifying the voice coil motor control signal to compensate for temperature-dependent drag forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed drag component value is used in VCM control signals, then the device complexity is reduced, but positioning accuracy deteriorates due to temperature-induced drag force changes
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed drag component value to a dynamically adjustable drag component value. The control system continuously monitors positioning errors and adjusts the drag component value in real-time to compensate for temperature-induced drag force changes, thereby maintaining positioning accuracy without requiring complex additional hardware
Solution Approach 2:
The patent implements feedback by using positioning error information from seek operations to adjust the drag component value. The system measures positioning errors, determines appropriate drag component adjustments, and applies these adjustments to subsequent control signals, creating a closed-loop control system that improves positioning accuracy while maintaining relatively simple device architecture
2Manufacturing precision
If drag component value is adjusted to compensate for temperature changes, then positioning accuracy is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent applies self-service by enabling the control system to automatically adjust the drag component value using its own positioning error measurements. The system performs seek operations, analyzes positioning errors, determines appropriate drag component adjustments, and applies these adjustments without external intervention or additional complex control mechanisms, thereby improving positioning accuracy while minimizing increases in device complexity
3Measurement precision
If temperature sensor is added to directly measure temperature changes, then drag force compensation accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses positioning error as an intermediary indicator to infer temperature-induced drag force changes. Instead of directly measuring temperature with additional sensors, the system measures positioning errors during seek operations, which serve as indirect indicators of drag force variations. This intermediary approach allows the system to compensate for temperature effects without adding complex temperature sensing hardware
Solution Approach 2:
The patent replaces the mechanical/physical approach of direct temperature sensing with a control-theory-based approach. Instead of using temperature sensors and thermal measurements, the system uses electrical control signal adjustments based on positioning error feedback to compensate for temperature-induced drag changes, thereby avoiding additional sensor hardware and reducing device complexity
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 improves the positioning accuracy and performance of hard drives by dynamically accounting for temperature changes, reducing positioning errors and maintaining optimal seek and settling times across varying temperatures without the need for a temperature sensor.
Implementation Method 1
positioning of the actuator assembly is controlled by the applied current through the voice coil, which generates a magnetic field that interacts with magnetic fields of permanent magnets
Implementation Method 2
Temperature-induced changes in drag forces affect the performance of voice coil motor assemblies in hard drives
Data Source
AI summary
A method includes performing a first seek operation using a first voice coil motor (VCM) control signal by utilizing a first drag component value. The method further includes determining a position error signal (PES) and a DC offset component of the PES measured during the first seek operation, and determining that the DC offset component is above a predetermined threshold. In response to determining that the DC offset component is above the predetermined threshold, the method further includes determining a second drag component value different than the first drag component value. The method further includes generating a second VCM control signal by applying the second drag component value.