VCM Retraction Circuit Using Back-EMF Smoothing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing disk drive technologies experience acoustic noise issues during head retraction due to voltage pulse fluctuations from rectified back electromotive force after power cutoff, which complicates precise speed control and increases the risk of head impact.
Innovation Solution
A disk drive system that utilizes a detection means to control the polarity and timing of the drive voltage applied to a second motor, adjusting it to a constant reference voltage to maintain a prescribed speed, thereby mitigating acoustic noise and ensuring reliable head retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage pulse from rectified back electromotive force is used to drive VCM during head retraction, then head retraction can be achieved without external power source, but acoustic noise occurs due to voltage fluctuations
Solution Approach 1:
A smoothing circuit is introduced as an intermediary component between the rectified voltage source and the VCM. This circuit filters out voltage pulses and fluctuations, providing a smooth drive voltage to the VCM while maintaining the ability to retract the head using back electromotive force from the spindle motor, thereby eliminating acoustic noise without sacrificing retraction reliability
Solution Approach 2:
The system uses the back electromotive force generated by the spindle motor itself during rotation to power the VCM for head retraction. This self-service mechanism eliminates the need for external power sources during retraction operations, while the smoothing circuit ensures this self-generated power does not cause acoustic noise
2Object-generated harmful factors
If constant voltage is applied to VCM during retraction operation, then acoustic noise is reduced, but precise speed control becomes difficult and head may impact crash stop
Solution Approach 1:
A feedback control system is implemented where the actual speed of the head is measured and compared with the target speed. The control unit adjusts the drive voltage to the VCM based on this feedback, maintaining constant speed control during retraction. This prevents the head from impacting the crash stop while working in conjunction with the smoothing circuit to maintain low acoustic noise levels
3Reliability
If speed control is implemented during retraction, then head impact is mitigated, but system complexity increases due to additional control circuits
Solution Approach 1:
The control unit is designed to perform multiple functions: it controls the VCM drive voltage for speed regulation, monitors head position, and coordinates with the smoothing circuit. By consolidating these functions into a single control unit, the system achieves reliable impact protection without proportionally increasing overall system complexity
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
The system effectively inhibits acoustic noise and ensures precise control of the head retraction speed, enhancing the reliability and durability of the disk drive by smoothing the drive voltage and current, reducing the risk of head impact.
Implementation Method 1
The arm is moved by driving an actuator using, for example, a voice coil motor (VCM)
Implementation Method 2
the voltage obtained by rectifying a back electromotive force of the spindle motor that continues to turn even after the power is cut off
Data Source
AI summary
To provide a disk drive capable of inhibiting the occurrence of acoustic noise caused by a voltage pulse when the head is retracted using a speed control method using voltage obtained by rectifying a back electromotive force after the power source has been cut off from the rotation of a spindle motor. Retraction control circuit is used to control the on and off modes of transistors in accordance with the speed of VCM. The voltage across VCM becomes a voltage that can be regulated with VCM voltage control circuit. At this time, voltage is supplied to the terminals based on the voltage of ISO5V that is the rectified voltage of the back electromotive force of the spindle motor and the pulsating voltage is synchronized and produced at both terminals. As a result, the potential difference across VCM is such that the pulsating voltage is negated and acoustic noise is inhibited.