Motor Controller Signal Conditioning for Cogging Noise Reduction
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Solution Overview
Problem
Brushless DC motors experience audible vibrations due to harmonic components in motor coil currents and back electromotive forces (BEMF) voltages, leading to torque ripple and noise, which can affect data recovery in disk drives and annoy users.
Innovation Solution
A motor controller with a signal conditioner that alters the amplitude or phase of harmonic components in motor-coil drive signals to reduce the magnitude of torque ripple and noise, using a harmonic compensator to generate a conditioning signal that compensates for existing torque ripple, thereby minimizing motor vibrations at the cogging frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If motor coils are driven with standard drive signals containing harmonic components, then the motor operates with standard torque production, but audible vibrations and noise are generated due to torque ripple at cogging frequency
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal drive signals with modified harmonic components in lookup tables before motor operation. The signal conditioner retrieves these pre-conditioned signals based on rotor position, eliminating the need for real-time harmonic modification while reducing noise and vibration at cogging frequency.
Solution Approach 2:
The signal conditioner acts as an intermediary device between the motor controller and motor coils. It receives standard drive signals, modifies their harmonic content by adding compensating components, and outputs conditioned signals that reduce torque ripple. This intermediary approach isolates the complexity from both the controller and motor while achieving noise reduction.
2Object-generated harmful factors
If harmonic components in motor-coil drive signals are altered to reduce torque ripple, then noise and vibration are reduced, but the device complexity increases due to additional signal conditioning circuitry
Solution Approach 1:
The patent changes the parameters of drive signals by modifying their harmonic components. Specifically, it adjusts the amplitude and phase of selected harmonic frequencies in the drive signals to compensate for torque ripple at cogging frequency. This parameter modification is achieved through lookup tables containing pre-calculated waveforms with optimized harmonic content.
Solution Approach 2:
The complex harmonic modification process is performed in advance during system design or initialization, with optimal drive waveforms stored in lookup tables. During motor operation, the signal conditioner simply retrieves and outputs these pre-optimized signals based on rotor position, avoiding real-time computation complexity while maintaining noise reduction benefits.
3Reliability
If standard drive signals are used without conditioning, then the motor controller structure remains simple, but data recovery in disk drives is affected due to motor vibrations
Solution Approach 1:
The system uses feedback from rotor position sensing to select and output appropriate conditioned drive signals from lookup tables. The signal conditioner continuously monitors rotor position and retrieves pre-calculated drive waveforms that are optimized for the current operating state, ensuring minimal torque ripple and vibration while maintaining simple real-time control architecture.
Data Source
AI summary
An embodiment of a motor controller includes a motor driver and a signal conditioner. The motor driver is operable to generate a motor-coil drive signal having a first component at a first frequency, and the signal conditioner is coupled to the motor driver and is operable to alter the first component. For example, if the first component of the motor-coil drive signal causes the motor to audibly vibrate (e.g., “whine”), then the signal conditioner may alter the amplitude or phase of the first component to reduce the vibration noise to below a threshold level.