Delayed Braking for Voice Coil Motor Unloading
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Solution Overview
Problem
Existing data storage devices face challenges in safely unloading heads during power failures, as the back electromotive force (BEMF) voltage generated by spindle motors may not provide sufficient braking power to prevent heads from contacting ramps at excessive velocities, potentially damaging the heads.
Innovation Solution
The implementation of a control circuitry that assigns priority levels to voice coil motors (VCMs) based on their initial velocity and position, applying differential brake voltages to manage the unloading process, including immediate braking for high-priority VCMs and delayed braking for low-priority VCMs to optimize braking power and prevent head damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If immediate braking is applied to all VCMs during power failure, then head protection is improved, but the limited BEMF voltage current capacity is exceeded, reducing braking effectiveness
Solution Approach 1:
The patent segments the VCM braking control into priority-based groups. The control circuitry determines which VCMs require immediate braking (those at risk of ramp contact) and which can tolerate delayed braking. This segmentation allows the limited BEMF voltage current capacity to be allocated effectively to high-priority VCMs while deferring low-priority ones, resolving the contradiction between protecting all heads and having sufficient braking power for each.
Solution Approach 2:
The control circuitry performs preliminary assessment of VCM positions and velocities before applying braking. By evaluating which VCMs are at risk of contacting ramps and prioritizing them, the system prepares the braking strategy in advance, ensuring that limited BEMF voltage capacity is applied where most needed while delaying braking for VCMs that are not yet at risk.
2Power
If delayed braking is applied to low-priority VCMs, then BEMF voltage current capacity is preserved for high-priority VCMs, but low-priority VCMs may experience excessive velocity
Solution Approach 1:
The control circuitry performs preliminary velocity assessment and applies braking to low-priority VCMs after a controlled delay period. This preliminary evaluation allows the system to determine safe delay durations that preserve BEMF voltage capacity while preventing excessive velocities in low-priority VCMs.
Solution Approach 2:
The braking strategy is dynamically adjusted based on real-time VCM velocity and position feedback. The control circuitry continuously monitors low-priority VCMs during the delay period and applies braking when appropriate, creating a dynamic response that balances current capacity preservation with velocity control.
3Power
If differential priority-based braking is implemented, then braking power distribution is optimized, but control system complexity increases
Solution Approach 1:
The control system segments VCMs into priority groups based on simple position and velocity thresholds. This segmentation approach optimizes braking power distribution without requiring complex control algorithms, as each VCM can be independently classified and controlled based on straightforward criteria.
Solution Approach 2:
Each VCM's priority status is determined by its own position and velocity characteristics rather than complex system-wide optimization. The control circuitry uses simple rules to assess which VCMs need immediate attention, allowing the system to self-organize the braking strategy without elaborate control logic.
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 frequency of head ramp contact at excessive velocities, thereby minimizing damage and ensuring reliable operation during power failures by optimizing the use of BEMF voltage for braking.
Implementation Method 1
the back electromotive force (BEMF) voltage generated by spindle motors may not provide sufficient braking power
Data Source
AI summary
A data storage device is disclosed wherein multiple voice coil motors (VCMs) are unloaded using a back electromotive force (BEMF) voltage generated by a spindle motor. A velocity and position of each VCM is measured, and a priority assigned to each VCM based on the measured velocity and position. During a delay interval, the BEMF voltage is used to apply a first brake voltage to a high priority VCM and to apply a second brake voltage to a low priority VCM, wherein the second brake voltage is lower than the first brake voltage. After the delay interval, the BEMF voltage is used to apply the first brake voltage to the high priority VCM and to apply a third brake voltage to the low priority VCM, wherein the third brake voltage is higher than the second brake voltage.