HDD Spindle Motor Back-EMF Rectification for VCM Retract
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Solution Overview
Problem
In hard disk drives, the discontinuous operation of voice coil motors during power-off retract procedures limits the average current available due to motor voltage drops, particularly when using low-capacitance capacitors, which restricts the torque and efficiency of the VCM current supply.
Innovation Solution
Implementing a spindle current boost through synchronous rectification or synchronous spindle step-up, where the spindle motor outputs are forced into a brake condition during the VCM off-time, pre-charging the spindle current to ensure readiness for the subsequent VCM driving phase, thereby increasing the VCM current and torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If discontinuous VCM driving mode is used during power-off retract, then energy efficiency is improved, but average VCM current is limited due to motor voltage drops
Solution Approach 1:
The patent applies preliminary action by pre-charging the spindle current during the VCM off-time through synchronous rectification or synchronous spindle step-up. This prepares the motor voltage in advance so that when the VCM enters the driving phase, sufficient current is already available, eliminating the limitation caused by voltage drops during the discontinuous mode operation.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring that the spindle current charging process occurs continuously during the VCM off-time, rather than allowing the motor voltage to drop. The synchronous rectification or step-up operation keeps the energy transfer active, ensuring that current is continuously replenished to the spindle motor, which then becomes available for VCM operation.
2Device complexity
If smaller capacitors are used on the motor voltage line, then device complexity is reduced, but motor voltage drops increase limiting VCM current
Solution Approach 1:
The patent applies self-service by making the spindle motor itself the source of charged current for the VCM operation. Through synchronous rectification or synchronous spindle step-up, the spindle motor's own back-EMF is used to charge its current during VCM off-time. This eliminates the need for external capacitors to store energy, as the spindle motor serves its own charging needs, allowing smaller or no capacitors on the motor voltage line.
3Use of energy by moving object
If spindle BEMF rectification is performed continuously, then energy recovery is maximized, but spindle current cannot be pre-charged for VCM operation
Solution Approach 1:
The patent applies segmentation by dividing the VCM operating cycle into distinct phases: during the VCM off-time, BEMF rectification is interrupted and the spindle outputs are forced into brake condition for current pre-charge; during the VCM Ton time, normal BEMF rectification resumes. This temporal segmentation allows the system to alternate between energy recovery and current pre-charge modes, optimizing both functions throughout the cycle.
Solution Approach 2:
The patent implements periodic action by repeatedly interrupting and resuming BEMF rectification in synchronization with the discontinuous VCM driving mode. The rectification is periodically stopped during VCM off-time to allow current pre-charge, then periodically restarted during VCM Ton time for energy recovery. This periodic alternation ensures that current is always available when needed while maximizing energy recovery during VCM operation.
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 allows for a higher VCM current amplitude and reduced motor voltage drops, enhancing the torque generation and responsiveness during emergency retract operations, even with smaller capacitors, thus improving the overall efficiency and reliability of the HDD system.
Implementation Method 1
An approach in performing emergency (e.g., power-off) retract with a VCM energized with the back electromotive force (BEMF) of the spindle motor
Implementation Method 2
spindle BEMF rectification is performed with synchronous rectification or synchronous spindle step-up
Implementation Method 3
voice coil motors (VCMs) to move the heads with respect to the disk(s)
Data Source
AI summary
A back electromotive force (BEMF) of a spindle motor in a hard disk drive is rectified and exploited to drive a voice coil motor (VCM) in the hard disk drive to retract the heads of the hard disk drive to a park position. The VCM is driven in a discontinuous mode comprising an alternation of VCM on-times and VCM off-times. Rectifying the BEMF of the spindle motor is discontinued before the end of the VCM off-times, Toff with the spindle motor brought into a brake condition wherein the spindle motor is short-circuited and the spindle BEMF forces currents through the windings of the spindle motor. The spindle current is thus pre-charged and made ready to cope with a VCM current request at the next VCM on-time.