Motor Driver Back-EMF Resonance Detection
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Solution Overview
Problem
Existing motor-driven systems, such as voice coil motors (VCMs), face performance impairments due to mechanical ringing caused by unknown or varying resonant frequencies, leading to imprecise operation and reduced lifespan, especially in consumer electronics where components may differ across manufacturing lots and age over time.
Innovation Solution
A method and apparatus for dynamically determining the resonant frequency of a motor-driven mechanical system by detecting the back electromotive force (BEMF) signal and measuring the time between polarity changes, allowing for real-time adjustment of the drive signal to minimize energy at the resonant frequency, thereby reducing ringing and enhancing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed pre-programmed resonant frequency is used in the motor driver, then the device complexity is reduced and manufacturing cost is lowered, but the measurement precision and reliability deteriorate due to variations in manufacturing processes, different vendors, and aging effects
Solution Approach 1:
The motor driver automatically detects the resonant frequency of the VCM by itself without requiring external measurement equipment or manual configuration. The system uses its own output signals to excite the VCM and measures the resulting back-EMF signal to determine the resonant frequency, enabling self-configuration and eliminating the need for pre-programmed fixed values
Solution Approach 2:
The system measures the back-EMF signal generated by the VCM in response to drive signals and uses this feedback information to automatically determine the resonant frequency. This closed-loop approach allows the motor driver to adapt to actual VCM characteristics rather than relying on predetermined values
2Ease of manufacture
If the resonant frequency is pre-programmed into the motor driver before operation, then the ease of manufacture is improved, but the adaptability deteriorates because the resonant frequency may vary due to different vendors, manufacturing processes, or aging
Solution Approach 1:
The system transitions from a static, fixed resonant frequency value to a dynamic detection process that determines the resonant frequency at runtime. The motor driver automatically measures the resonant frequency when the VCM is first operated and can update this value as needed, allowing the system to adapt to manufacturing variations and aging effects
Solution Approach 2:
The resonant frequency parameter is changed from a fixed pre-programmed value to a dynamically determined value based on actual measurements. The system detects and uses the actual resonant frequency of the specific VCM unit rather than relying on a generic predetermined value
3Stability of the object's composition
If mechanical ringing is reduced by filtering the drive signal through a notch filter, then the stability is improved and mechanical settling time is reduced, but the device complexity increases and requires accurate knowledge of the resonant frequency
Solution Approach 1:
The system performs resonant frequency detection before implementing filtering control. By determining the resonant frequency in advance through automatic detection, the system can then apply appropriate filtering without requiring complex real-time frequency analysis, simplifying the overall control architecture
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 enables accurate and automatic detection of resonant frequencies, allowing for improved autofocus response times, image quality, and extended system lifespan by dynamically filtering out the resonant frequency, accommodating variations in manufacturing and aging effects.
Implementation Method 1
driving a current step into the motor-driven mechanical system and detecting a BEMF (back electromotive force) signal therefrom
Data Source
AI summary
A method and apparatus for automatic resonance detection is disclosed for a motor-driven mechanical system such as a voice coil motor (VCM) in which a resonance detector and driver are provided. The automatic resonance detector is implemented on the same integrated circuit as the driver, and dynamically determines the natural resonant frequency of the VCM driven by the driver. The resonant frequency is determined by measuring the back electromotive force (BEMF) of the VCM, detecting the slope of the BEMF signal, and determining the resonant frequency from the slope of the BEMF signal.