LRA Resonance Control Through Continuous Back-EMF Phase Tracking
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Solution Overview
Problem
Linear resonant actuators (LRAs) face efficiency drops and mechanical noise when operating outside a narrow resonant frequency range due to lot-to-lot variations, temperature changes, and aging, and existing methods to track and control resonant frequency often require switching between drive and sense modes, reducing efficiency and introducing noise.
Innovation Solution
A method for continuous resonator drive frequency control using back-emf estimation and phase coherence detection, which iteratively adjusts the resonator drive frequency to maintain phase coherence with estimated back-emf, eliminating the need for separate sense modes and reducing mechanical noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switching between drive and sense modes is used to track resonant frequency, then resonant frequency tracking is achieved, but efficiency and acceleration are reduced and mechanical noise is introduced
Solution Approach 1:
The patent combines the drive and sense modes into a single continuous drive mode, eliminating the need to switch between modes. The back-emf is sensed continuously during normal operation by measuring the voltage across the resonator while it is being driven, thus merging the sensing function into the driving process and avoiding the efficiency losses and mechanical noise associated with mode switching.
Solution Approach 2:
The patent implements continuous resonator drive without interruption for sensing purposes. The resonator is driven continuously at the resonant frequency, and the back-emf is measured continuously during this drive process, ensuring uninterrupted useful action and maintaining high efficiency while avoiding the acceleration drops and mechanical noise that occur during mode switching.
2Reliability
If switching between drive and sense modes is used to track resonant frequency, then resonant frequency tracking is achieved, but mechanical noise is introduced
Solution Approach 1:
The patent combines the drive and sense modes into a single continuous drive mode, eliminating the need to switch between modes. The back-emf is sensed continuously during normal operation by measuring the voltage across the resonator while it is being driven, thus merging the sensing function into the driving process and avoiding the mechanical noise associated with mode switching.
3Loss of energy
If continuous resonator drive with back-emf estimation is used, then efficiency and acceleration are maintained, but complex back-emf estimation circuitry is required
Solution Approach 1:
The patent replaces complex mechanical sensing systems with an electrical estimation approach. Instead of using separate mechanical sensors or complex sensing circuits, the back-emf is estimated electronically by measuring the voltage across the resonator during drive and using this information to determine the resonant frequency, thus maintaining efficiency while reducing device complexity.
4Strength
If operating LRA resonator outside narrow F0 range is avoided, then vibration amplitude is maximized, but frequency adjustment capability is limited
Solution Approach 1:
The patent implements dynamic frequency adjustment by continuously monitoring the back-emf during operation and adjusting the drive frequency in real-time to track the resonant frequency. This dynamic approach allows the system to adapt to changes in resonant frequency due to temperature, aging, or manufacturing variations, maintaining maximum vibration amplitude while providing the necessary frequency adjustment capability.
Solution Approach 2:
The patent uses feedback from the back-emf measurement to adjust the drive frequency. The measured back-emf is used to determine whether the drive frequency is above or below the resonant frequency, and this feedback information is used to iteratively adjust the drive frequency to maintain operation at the resonant peak, thus maintaining maximum vibration amplitude while enabling frequency adaptation.
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 maintains efficient operation and minimizes mechanical noise by continuously driving the resonator at or near the resonant frequency, ensuring consistent vibration amplitude and acceleration without the inefficiencies of mode switching.
Implementation Method 1
In sense mode, back-emf is sensed (measured), and used to iteratively adjust drive frequency
Implementation Method 2
Linear resonant actuators (LRAs) use a resonator to provide haptic feedback. LRA resonators are driven at (or near) a resonant frequency (F0) to optimize efficiency and maximize vibration amplitude/strength (performance)
Data Source
AI summary
For a resonator system such as a (haptic) LRA, a methodology for resonant frequency (F0) tracking/control with continuous resonator drive, based on estimating back-emf, including estimating resonator resistance based at least in part on the sensed resonator drive signals, with back-emf estimated based at least in part on the sensed resonator drive signals and the estimated resonator resistance. A phase difference is detected between the resonator drive signals, and the estimated back-emf signals, generating control for resonator drive frequency, which can be used to iteratively adjust the resonator drive frequency until phase coherent with the estimated back-emf signals (F0 lock), such as for driving the resonator at or near a resonant frequency. An amplitude control loop can be used to iteratively adjust resonator drive amplitude based on a difference between estimated back-emf and a target back-emf derived from a rated back-emf and the resonator frequency resonant frequency.