Adaptive Back-EMF Rectification for Disk Drive Head Parking
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Solution Overview
Problem
Existing systems fail to effectively adaptively tap and rectify back-EMF voltages from a DC motor during power interruptions in magnetic disk drives to safely park and unload read/write heads, leading to potential damage from unsuppressed motor-generated voltages.
Innovation Solution
A system comprising a H-bridge configuration of power transistors with comparators across each motor winding, a state machine, and a full-wave rectifier, which cyclically turns ON and OFF transistors based on comparator inputs to rectify and supply back-EMF voltages to the VCM, allowing safe parking of the read/write head during power interruptions without relying on timing information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive rectification using Schottky diodes is used, then the system is simple to implement, but it cannot adaptively suppress motor-generated voltages during power interruptions
Solution Approach 1:
The system uses voltage comparators to continuously monitor the back-EMF voltages across motor windings and provides feedback control signals to power transistors. This feedback mechanism enables adaptive suppression of motor-generated voltages by turning on appropriate transistors when voltage thresholds are exceeded, resolving the contradiction between reliability and complexity.
Solution Approach 2:
The system utilizes the motor's own back-EMF voltages during power interruptions to power the VCM and perform head parking operations. The rectification system automatically activates when back-EMF exceeds thresholds, enabling the system to serve itself during power failures without external intervention, improving reliability without proportional complexity increase.
2Measurement precision
If timing-based commutation control is used, then motor control precision is improved, but the system becomes more complex and requires precise timing information
Solution Approach 1:
The system replaces timing-based commutation control with voltage-threshold-based control using comparators. Instead of relying on precise timing information and complex control logic, the system simply monitors voltage levels and activates transistors when back-EMF exceeds predetermined thresholds, achieving accurate voltage detection with reduced complexity.
3Use of energy by moving object
If full-wave rectification with H-bridge configuration is implemented, then energy utilization efficiency is improved, but the device complexity increases
Solution Approach 1:
The H-bridge configuration with power transistors serves multiple functions: it performs full-wave rectification of back-EMF voltages, suppresses motor-generated voltages during power interruptions, and provides controlled energy transfer to the VCM. This multi-functionality justifies the increased device complexity by achieving superior energy utilization efficiency.
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
Enables adaptive full-wave rectification of back-EMF voltages, ensuring safe parking of the read/write head by utilizing the motor's momentum, reducing wear and tear, and eliminating the need for precise timing, thus enhancing the reliability of disk drive operations during power interruptions.
Implementation Method 1
the spindle motor 16 acts as a generator and sinusoidal back electro-motive force (BEMF) is generated across each winding in the spindle motor 16
Implementation Method 2
adaptive full-wave rectification of back-EMF voltages by turning ON and OFF transistors based on voltage crossings
Data Source
AI summary
An embodiment of a disk drive power system is described. The system is operable such that during power interruption, the system taps electric power by rectifying the back-EMF generated across each winding of a DC motor and supplying power to a voice-coil motor to park a read/write head safely away from an associated magnetic disk surface.