Hard Disk Drive Head Parking Bias Control to Prevent VCM Saturation
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Solution Overview
Problem
In hard disk drives, the voice coil motor power stage often enters full saturation during the head parking procedure, leading to undesirable acoustic noise due to voltage ripple, especially when the spindle motor voltage is lower than the bias voltage used to hold the heads in position.
Innovation Solution
A control circuit is implemented to automatically adjust the bias voltage V2 based on the voltage Vmotor, preventing power stage saturation by reducing the voltage if saturation is detected, and using rectified back electromotive force from the spindle motor to drive the voice coil motor during the parking process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bias voltage V2 is increased to hold the heads in position, then the heads are prevented from bouncing back, but the power stage enters full saturation causing voltage ripple and acoustic noise
Solution Approach 1:
The control circuit continuously monitors the voltage Vmotor and compares it with the bias voltage V2. When saturation is detected (Vmotor < V2), the circuit automatically adjusts the bias voltage downward to eliminate the saturation condition, thereby removing the source of acoustic noise while maintaining head positioning stability.
Solution Approach 2:
The bias voltage V2 is dynamically adjusted based on the actual voltage Vmotor available from the rectified back electromotive force. By changing the bias voltage parameter in response to saturation conditions, the system prevents full saturation and eliminates voltage ripple-induced acoustic noise while maintaining sufficient holding force.
2Reliability
If the bias voltage V2 is set manually with a large margin, then the heads are securely held in position, but the driving voltage is reduced due to power stage saturation
Solution Approach 1:
The bias voltage V2 transitions from a static manually-set value to a dynamic value that automatically adapts to the available voltage Vmotor. This dynamic adjustment ensures the bias voltage is always optimal - high enough to prevent bouncing but low enough to avoid saturation and preserve driving voltage.
Solution Approach 2:
The control circuit automatically detects saturation conditions and self-adjusts the bias voltage without external intervention. The system monitors its own operating state and corrects the bias voltage setting to prevent both bouncing and saturation, eliminating the need for manual margin adjustment.
3Ease of operation
If constant voltage V1 is applied to move heads to parking position, then the movement is simple to control, but acoustic noise is generated during the holding phase due to power stage saturation
Solution Approach 1:
The parking procedure is divided into two distinct phases: a first phase using constant voltage V1 for head movement (maintaining simplicity), and a second phase using dynamically adjusted bias voltage V2 for holding (eliminating noise). This segmentation allows each phase to use the most appropriate control strategy.
Solution Approach 2:
The control circuit periodically checks for saturation conditions during the holding phase and adjusts the bias voltage accordingly. This periodic monitoring and adjustment ensures acoustic noise is eliminated while maintaining the simplicity of constant voltage control during the movement phase.
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 solution effectively reduces acoustic noise by maintaining a stable voltage supply to the voice coil motor, ensuring the heads are parked without bouncing and minimizing operational noise.
Implementation Method 1
A control circuit is provided for a voice coil motor in a hard disk drive having a spindle motor. The control circuit may be configured to rectify a back electromotive force of a spindle motor in a hard disk drive.
Implementation Method 2
The control circuit may be configured to energize a voice coil motor in the hard disk drive using the rectified back electromotive force of the spindle motor via a voice coil motor power stage to retract a head of the hard disk drive to a park position.
Data Source
AI summary
An embodiment method includes rectifying a back electromotive force of a spindle motor in a hard disk drive and energizing a voice coil motor in the hard disk drive using the rectified back electromotive force of the spindle motor via a voice coil motor power stage to retract a head of the hard disk drive to a park position. The head is retracted by moving the head towards the park position during a first retract phase and retaining the head in the park position during a second retract phase by applying a bias voltage to the voice coil motor power stage during a bias interval of the second retract phase. The method also includes producing a saturation signal indicative of onset of saturation in the voice coil motor power stage and controlling the bias voltage during the second retract phase.