Linear Resonant Actuator Drive Control Using Phase Difference Feedback
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Solution Overview
Problem
Existing methods for determining the resonance frequency of linear resonant actuators (LRAs) in electronic devices are inaccurate and cannot be performed during haptic events, leading to suboptimal vibration performance and potential user annoyance due to incorrect frequency estimation.
Innovation Solution
A method that adjusts the frequency of the drive signal for LRAs using a feedback control loop based on the phase difference between voltage and current, converging to a predetermined phase difference at resonance, allowing for accurate frequency determination during haptic events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resonance frequency is determined using a separate measurement outside of a haptic event, then the resonance frequency can be estimated, but the measurement cannot be performed during haptic events and may disturb the user
Solution Approach 1:
The patent combines the resonance frequency measurement process with the haptic event execution. The driver chip continuously monitors the phase difference between voltage and current during normal haptic operation, merging the measurement function with the haptic actuation function. This eliminates the need for separate measurement events that would disturb the user while maintaining accurate resonance frequency tracking throughout device usage.
Solution Approach 2:
The patent implements continuous resonance frequency monitoring during haptic events by constantly measuring the phase difference between voltage and current. This continuous measurement approach ensures the resonance frequency is always up-to-date without interrupting haptic events or requiring separate measurement periods, maintaining both measurement accuracy and uninterrupted user experience.
2Reliability
If the resonant frequency varies due to fabrication variations and environmental factors, then the vibration performance degrades, but frequent separate measurements increase device complexity
Solution Approach 1:
The patent implements a feedback mechanism where the driver chip continuously measures the phase difference between voltage and current during haptic events and uses this information to track resonance frequency variations. This real-time feedback allows the system to adapt to fabrication variations and environmental changes without requiring complex external measurement systems, maintaining reliable vibration performance through simple, integrated monitoring.
3Productivity
If the drive frequency deviates from the resonant frequency, then the vibration amplitude decreases and unwanted ringing occurs, but accurate frequency tracking requires continuous measurement
Solution Approach 1:
The patent replaces complex mechanical frequency tracking methods with an electrical measurement approach. By measuring the phase difference between voltage and current in the electrical domain, the system can accurately track resonance frequency and maintain optimal drive frequency without mechanical sensors or complex mechanical feedback mechanisms, improving both vibration effectiveness and measurement precision.
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 provides precise control of the drive signal frequency, enhancing vibration amplitude and reducing unwanted ringing, while avoiding separate measurement events that disturb the user.
Implementation Method 1
determining a phase difference between a voltage and a current over the LRA
Implementation Method 2
adjusting a frequency of the drive signal using a feedback control loop such that the determined phase difference converges to a non-zero pre-determined phase difference at resonance
Implementation Method 3
electrical current running in a stationary coil actuates a moveable magnet back and forth, in a linear manner
Data Source
Figure 1A~2
Figure 3
Figure 4A
AI summary
A method, processing system and control circuit for driving a linear resonance actuator, LRA, in an electronic device, comprising generating a drive signal to drive the LRA, wherein the frequency of the drive signal is initially set to an initial frequency (fi); determining a phase difference (Δφ) between a voltage and a current over the LRA; and adjusting the frequency of the drive signal using a feedback control loop such that the determined phase difference (Δφ) converges to a non-zero pre-determined phase difference at resonance (Δφ0). The invention further relates to an electronic device with a linear resonant actuator driven using such method, processing system or control circuit.