Motor Control Device for Emergency Head Retraction in Disk Drives
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Solution Overview
Problem
Conventional hard disk drive devices face challenges in maintaining sufficient torque for head retraction due to capacitor voltage depletion during emergency operations, leading to potential head collision risks and the need for large capacitors, which increase circuit size and cost.
Innovation Solution
A motor control device that alternates between short-circuit and rectifying modes to manage back electromotive force, using transistors to connect and disconnect power supply lines effectively, thereby maintaining necessary power to the voice coil motor during emergency operations without enlarging the circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitance of the capacitor is increased to maintain sufficient voltage during head retraction, then the reliability of emergency operation is improved, but the circuit area and component cost increase
Solution Approach 1:
The patent implements periodic switching between capacitor discharge mode and BEMF rectification mode. The control section alternates between using the pre-charged capacitor for power supply and rectifying the back electromotive force from the spindle motor, creating a periodic action that maintains voltage without requiring a large capacitor. This resolves the contradiction by using time-based switching rather than increasing component size.
Solution Approach 2:
The patent enables the spindle motor to serve dual purposes: not only rotating the disk but also generating back electromotive force that is rectified and used to power the voice coil motor during head retraction. This self-service approach allows the system to use its own operational byproduct (BEMF) to maintain reliability, eliminating the need for a larger capacitor.
2Stability of the object's composition
If the capacitance of the capacitor is increased to maintain sufficient voltage during head retraction, then the power supply stability is improved, but the component cost increases
Solution Approach 1:
The control section implements periodic switching between capacitor discharge and BEMF rectification modes, maintaining stable power supply voltage without requiring a large, expensive capacitor. This time-based strategy achieves power supply stability through operational sequencing rather than component scaling.
Solution Approach 2:
The spindle motor is made multi-functional by using it both for disk rotation and as a power generation source through BEMF rectification. This universality allows the system to maintain power supply stability using existing components, reducing component costs while achieving the desired stability.
3Area of stationary object
If the capacitor voltage is allowed to decrease to maintain circuit area, then the circuit size is reduced, but the torque of the voice coil motor decreases temporarily
Solution Approach 1:
The control section uses periodic switching between capacitor discharge mode and BEMF rectification mode to maintain voice coil motor torque. By alternating between these two power sources, the system prevents voltage from dropping to zero and maintains sufficient torque for head retraction while using a smaller capacitor.
Solution Approach 2:
The control section acts as an intermediary that manages power transfer between the capacitor and the BEMF rectification circuit. It switches between these two power sources to maintain stable voltage and torque, preventing the harmful effect of torque decrease while keeping the circuit area small.
4Area of stationary object
If the capacitor voltage decreases to nearly zero volts, then the circuit area is reduced, but the power to draw the arm toward the ramp side is weakened
Solution Approach 1:
The control section implements periodic switching between capacitor discharge mode and BEMF rectification mode to maintain adequate power for drawing the arm to the ramp side. This alternating power supply prevents voltage from dropping to zero, maintaining sufficient power while using a smaller capacitor.
Solution Approach 2:
The system uses the spindle motor's own back electromotive force as a self-service power source during head retraction. This allows the system to maintain adequate power for arm retraction without relying solely on a large capacitor, reducing circuit area while preserving necessary power levels.
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 ensures stable power supply to the voice coil motor during head retraction, reducing the risk of head collision and allowing for smaller capacitors, thus minimizing circuit size and cost while maintaining reliable operation.
Implementation Method 1
power supply for the voice coil motor is provided, for example, from the voltage of a pre-charged capacitor for retraction, and from the rectified voltage of the back electromotive force (BEMF) of the spindle motor from inertial rotation
Data Source
AI summary
The objective of this invention is to provide a motor control device, and a disk drive device using the same, in which during emergency operation it is possible to supply necessary power to the motor while limiting enlargement of the circuit area. During the retraction operation, control is performed to alternate between a short-circuit mode in which each terminal U, V, W of the spindle motor M1 is short-circuited to the terminal ICOM, and a rectifying mode in which the back electromotive force of the spindle motor M1 is rectifies and output to the power supply line ISO3V, VGND while the input of power from the power supply line ISO3V, VGND to the spindle motor M1 is blocked.