Voice Coil Motor Head Parking via Back-EMF Pulsing
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Solution Overview
Problem
Existing disk drive technologies face challenges in quickly parking heads without causing excessive heating and damage to electronics or motors, as large currents used for rapid head retraction can lead to overheating.
Innovation Solution
A pulse width modulation approach is employed, monitoring back EMF between pulses to determine head velocity and selecting current pulses to efficiently park heads, using pulse amplitude modulation to adjust velocity and match a designed velocity profile, thereby minimizing heating and ensuring safe parking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If large current is provided to the voice coil motor for rapid head parking, then the head parking speed is improved, but excessive heating of the electronics occurs leading to potential damage
Solution Approach 1:
The patent applies periodic current pulses to the voice coil motor instead of continuous large current. The controller delivers a sequence of current pulses with specific timing and amplitude characteristics, allowing the motor to achieve rapid head positioning while the periodic nature of the pulses prevents sustained overheating of the electronics.
Solution Approach 2:
The patent dynamically adjusts the current pulse amplitude and timing based on real-time feedback from back-EMF sensing. The controller modifies the pulse characteristics during operation to optimize both speed and thermal management, transitioning from fixed-parameter pulses to adaptive, dynamically controlled pulses.
2Speed
If large current is provided to the voice coil motor for rapid head retraction, then the head retraction speed is improved, but damage to the electronics or motor occurs due to excessive heating
Solution Approach 1:
The patent implements feedback control by sensing the back-EMF voltage generated by the voice coil motor during operation. The controller uses this feedback information to determine the actual motor velocity and position, then adjusts subsequent current pulses accordingly. This closed-loop feedback ensures reliable operation by preventing conditions that would cause damage while maintaining rapid retraction speeds.
Solution Approach 2:
The patent changes the electrical parameters of current delivery from continuous high current to pulsed current with varying amplitude and duration. By modifying these parameters dynamically based on motor response, the system achieves fast retraction while staying within safe thermal and electrical limits, thereby maintaining component reliability.
3Productivity
If pulse width modulation is used to monitor back EMF and select current pulses, then head parking efficiency is improved while minimizing heating, but the system complexity increases
Solution Approach 1:
The patent replaces complex mechanical sensing and control mechanisms with electrical sensing through back-EMF measurement. Instead of using additional mechanical sensors or complex position encoders, the system uses the electrical back-EMF signal naturally generated by the motor to infer velocity and position, thereby achieving efficient control without proportionally increasing hardware 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 method allows for rapid and efficient head parking while minimizing heat generation and potential damage, effectively addressing the need for quick head retraction without overheating the electronics or motor.
Implementation Method 1
a voice coil motor (VCM) 112. The VCM 112 includes a voice coil 134 mounted to the actuator 130 and positioned in an air gap of the VCM 112
Implementation Method 2
The back EMV is measured between current pulses. The back EMF may be directly related to the sum of the actuator velocity and the product of the coil resistance with the VCM current
Implementation Method 3
By measuring the back EMF between pulses when the VCM current is at a substantially reduced value (e.g., close to zero), the back EMF becomes a function of the actuator velocity only
Data Source
AI summary
A method and device for parking heads of a disk drive device involves receiving a command to immediately park the heads. A first pulse is provided to a voice coil motor causing the heads to move toward a parked position. After the first pulse, the VCM current is reduced substantially (e.g., close to zero) and back EMF in the voice coil motor is measured to determine speed of the heads. The voice coil motor is iteratively pulsed, and back EMF is measured between pulses to track a desired velocity profile to park the heads.