VCM Back-EMF Detection for Disk Drive Parking Control
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Solution Overview
Problem
Existing disk drive technologies face issues with power loss during parking of transducer heads, leading to inefficient power usage and potential damage due to uncontrolled velocity and acoustic noise during emergency retract operations.
Innovation Solution
A method and apparatus that monitor the back electromotive force (bemf) of the voice coil motor to detect the arrival of the transducer head at the parking position, allowing for a controlled drive stop sequence to be initiated, reducing power consumption and preventing head bounce back.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed retract sequence is used for emergency parking, then the transducer head can be moved to the parking ramp, but excessive power is consumed and the actuator continues running after the head is already parked
Solution Approach 1:
The patent implements feedback by monitoring the back EMF signal from the VCM to detect when the transducer head has reached the parking ramp position. The system continuously measures the back EMF and compares it against threshold values to determine arrival at the destination, then provides feedback to stop the retract sequence, preventing unnecessary continued operation and power consumption.
Solution Approach 2:
The patent replaces the mechanical timing-based stop mechanism with an electrical sensing mechanism. Instead of using a pre-determined fixed-time sequence or mechanical switches, the system uses electrical signal detection (back EMF monitoring) to sense the head's position and control the stopping point, achieving more precise and energy-efficient control.
2Reliability
If a blind retract method is used, then the transducer head can be parked, but the velocity is not well controlled causing head bounce back and potential damage
Solution Approach 1:
The patent uses feedback control by continuously monitoring the back EMF signal which reflects the actual velocity of the VCM. The system compares the measured back EMF against expected values and adjusts the drive current accordingly to maintain controlled velocity throughout the retract sequence, preventing excessive speed and subsequent bounce back.
Solution Approach 2:
The patent utilizes the back EMF signal, which is naturally generated by the spinning motor itself, as the sensing mechanism. The motor's own electrical characteristics provide the feedback information needed for velocity control, eliminating the need for separate sensors or external monitoring systems.
3Use of energy by moving object
If PWM method is used to save power during parking, then power consumption is reduced, but acoustic noise is generated in the audible frequency spectrum
Solution Approach 1:
The patent employs periodic PWM actuation to drive the VCM during the retract sequence. By using pulsed width modulation with appropriate frequency selection, the system achieves efficient power delivery while the periodic nature of the control allows for optimized switching that reduces acoustic noise generation compared to continuous or poorly-timed switching.
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 reduces power requirements and minimizes the risk of head damage by accurately detecting the parking position and terminating the drive current promptly, thus enhancing the reliability of the parking process.
Implementation Method 1
the back emf (electromotive force) from the spinning spindle motor for the disk. The back emf is the voltage generated by virtue of the motor spinning.
Implementation Method 2
The parking area may be a ramp, which requires power to exert some force to move the transducer head up the ramp to a stop next to the magnet.
Data Source
AI summary
A method and apparatus for controlling the parking of a transducer head in a disk drive. A drive current is provided to a motor which controls movement of the head in a direction to move the head to a parking position. The arrival of the head at the parking position is detected. Upon this detection, a drive stop sequence is initiated to stop providing the drive current a short time after the head reaches the parking position. In one embodiment, it is determined whether the head has reached the parking position by monitoring the back emf (bemf) of the motor controlling the head, typically a voice coil motor (VCM). The detection of a sharp decline in the bemf indicates the head has stopped.