Haptic Transducer Resonance Tracking Using Back-EMF Phase Control
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Solution Overview
Problem
Vibro-haptic transducers, such as linear resonant actuators, face challenges in maintaining resonance frequency due to sample-to-sample variations, aging, and user interaction, leading to inconsistent vibration feedback in devices like mobile phones.
Innovation Solution
A method and apparatus that estimate the back electromotive force (EMF) of a haptic transducer based on current and terminal voltage, compare the phase of the voltage signal with the estimated back EMF, and adjust the driving signal's frequency and phase to converge to the resonant frequency, using a resonant frequency tracker with a back EMF modeling module and a controlling circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the haptic transducer is operated at a fixed resonant frequency, then the vibration feedback is consistent and reliable, but the system cannot adapt to frequency variations caused by manufacturing tolerances, aging, and user interaction
Solution Approach 1:
The system employs a feedback mechanism where the back-EMF signal from the haptic transducer is continuously monitored and used to adjust the driving signal frequency. The phase difference between the driving signal and back-EMF signal is detected, and the frequency is automatically tuned to maintain resonance, thereby adapting to frequency drift while maintaining reliable vibration feedback.
Solution Approach 2:
The system transitions from a static fixed-frequency operation to a dynamic frequency-tracking operation. The resonant frequency is continuously estimated and updated based on real-time back-EMF measurements, allowing the system to adapt to changing conditions while maintaining optimal performance.
2Adaptability or versatility
If the resonant frequency is continuously tracked and adjusted, then the system adapts to frequency variations, but the control system complexity increases
Solution Approach 1:
The system uses the back-EMF signal generated by the haptic transducer itself as the reference for frequency tracking, eliminating the need for external sensors or complex measurement systems. The transducer's own operational characteristics provide the feedback needed for automatic frequency adjustment, simplifying the overall control architecture.
Solution Approach 2:
The back-EMF signal serves multiple functions: it indicates the transducer's velocity, provides frequency information for resonance tracking, and serves as a feedback signal for control adjustment. This multi-functionality reduces the need for separate sensing and control components, thereby reducing system complexity.
3Reliability
If the driving frequency is adjusted to track resonance, then the vibration quality is maintained, but the phase instability and impulsive noise occur during frequency transitions
Solution Approach 1:
The system uses periodic sinusoidal driving signals to excite the haptic transducer during frequency transitions. This periodic excitation allows for smooth frequency sweeping and avoids abrupt changes that would generate impulsive noise, while still enabling accurate resonance tracking through the periodic back-EMF measurements.
Solution Approach 2:
The system prepares for frequency transitions by using smooth frequency sweeping rather than abrupt changes. The frequency is adjusted gradually over time, cushioning the transition to prevent impulsive noise while maintaining vibration quality throughout the transition process.
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 ensures that the driving signal is consistently tuned to the resonant frequency of the haptic transducer, enhancing the accuracy and reliability of tonal vibration notifications and feedback, reducing hardware complexity, and eliminating impulsive noise.
Implementation Method 1
estimating, based on a current through the haptic transducer and a terminal voltage across the haptic transducer, a back electromotive force, EMF, voltage representative of a velocity of a mass in the haptic transducer
Implementation Method 2
Vibro-haptic transducers, for example linear resonant actuators (LRAs), are widely used in portable devices such as mobile phones to generate vibrational feedback to a user
Implementation Method 3
In order to generate tonal vibration notifications efficiently, it may be desirable to operate the haptic actuator at its resonance frequency
Data Source
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AI summary
Embodiments described herein relate to methods and apparatus for driving a haptic transducer with a driving signal. The method comprises estimating, based on a current through the haptic transducer and a terminal voltage across the haptic transducer, a back electromotive force, EMF, voltage representative of a velocity of a mass in the haptic transducer; comparing a phase of a voltage signal derived from the terminal voltage with a phase of the estimated back EMF voltage; and based on the comparison, adjusting a frequency or a phase of an output signal, wherein the driving signal is derived from the output signal, such that a frequency of the driving signal converges to a resonant frequency of the haptic transducer.