Spread Spectrum Spindle Motor Control for HDD Positioning
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Solution Overview
Problem
The servo control system in data storage devices is adversely affected by repeatable runout (RRO) and non-repeatable runout (NRRO) disturbances caused by the spindle motor, which can lead to inaccuracies in head positioning during data access operations.
Innovation Solution
Implementing a spread spectrum control of the spindle motor by swinging the frequency of the pulse width modulated (PWM) control signal between a minimum and maximum frequency, using a spread spectrum controller to attenuate these disturbances and maintain accurate head positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the spindle motor operates at a fixed frequency, then the motor provides stable rotational speed, but repeatable runout (RRO) and non-repeatable runout (NRRO) disturbances occur causing head positioning inaccuracies
Solution Approach 1:
The patent applies dynamics by making the PWM control signal frequency variable rather than fixed. The spread spectrum controller dynamically adjusts the PWM frequency within a range centered at a nominal frequency, which dynamically changes the motor operating point to avoid resonant frequencies that cause RRO and NRRO, thereby improving head positioning accuracy without sacrificing rotational stability
Solution Approach 2:
The patent changes the frequency parameter of the PWM control signal from a constant value to a variable value that swings between minimum and maximum frequencies. This parameter change allows the system to avoid fixed-frequency resonances and disturbances, reducing RRO and NRRO while maintaining effective motor control
2Object-affected harmful factors
If the PWM control signal frequency is swung between minimum and maximum frequencies, then RRO and NRRO disturbances are attenuated, but the control system complexity increases
Solution Approach 1:
The patent introduces a spread spectrum controller as an intermediary component between the PWM generator and the spindle motor. This intermediary device handles the frequency modulation and swing operations, isolating the complexity from the main control system while achieving disturbance attenuation through frequency variation
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 effectively reduces RRO and NRRO disturbances, improving the accuracy and stability of the head positioning servo control system by dynamically adjusting the PWM frequency to counteract motor-induced imperfections.
Implementation Method 1
a spread spectrum controller configured to swing a frequency of a pulse width modulated (PWM) control signal used to control the spindle motor between a minimum frequency and a maximum frequency
Data Source
AI summary
A data storage device is disclosed comprising a head actuated over a disk, and a spindle motor configured to rotate the disk. A pulse width modulated (PWM) control signal is generated having a frequency based on a PWM clock, the spindle motor is controlled using the PWM control signal, and a frequency of the PWM clock is swung between a minimum frequency and a maximum frequency at a swing rate.