LRA Resonant Frequency Tracking Using Back-EMF Current Sensing
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Solution Overview
Problem
Existing methods for determining the resonant frequency of linear resonant actuators (LRAs) in consumer electronics are inaccurate over time due to manufacturing tolerances and environmental factors, leading to inefficient vibrations and increased power consumption, and require additional components and complexity, such as High-Z measurements, which cause interruptions and distortions.
Innovation Solution
A current-based resonant frequency tracking system that measures the drive current and back electromotive force (EMF) of LRAs using a current resistor and analog-to-digital converter, allowing continuous monitoring without interrupting the driving signal, thus enabling accurate and efficient tracking of the resonant frequency using standard audio amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If High-Z measurement is used to determine resonant frequency, then resonant frequency can be measured, but driving signal must be interrupted causing artifacts and distortions
Solution Approach 1:
The patent enables continuous measurement of resonant frequency by monitoring the back-EMF signal during normal operation without interrupting the driving signal to the LRA. The amplifier continuously receives the back-EMF signal from the LRA output and processes it to determine resonant frequency, allowing the LRA to maintain continuous vibration output without artifacts or distortions.
2Measurement precision
If High-Z measurement is used to determine resonant frequency, then resonant frequency can be measured, but additional components and circuitry are required
Solution Approach 1:
The patent makes the LRA amplifier multi-functional by enabling it to perform both its primary function of driving the LRA and a secondary function of measuring resonant frequency. The amplifier receives and processes the back-EMF signal from the LRA output to determine resonant frequency while simultaneously maintaining the driving signal to the LRA, eliminating the need for separate measurement circuitry or High-Z switching components.
3Ease of manufacture
If factory measurement is used to determine resonant frequency, then initial resonant frequency is known, but frequency drifts over time due to environmental factors
Solution Approach 1:
The patent implements a feedback mechanism where the amplifier continuously monitors the back-EMF signal from the LRA and uses this information to track changes in resonant frequency over time. This real-time feedback allows the system to adapt to environmental changes such as temperature and humidity variations, maintaining accurate resonant frequency determination throughout the product lifecycle rather than relying solely on initial factory measurements.
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
The system provides accurate and efficient resonant frequency determination for LRAs, reducing costs and complexity by eliminating the need for High-Z measurements and specialized amplifiers, while ensuring consistent and powerful vibrations.
Implementation Method 1
measuring a frequency of the back electromotive force current as a resonant frequency of the linear resonant actuator
Data Source
AI summary
A current based resonant frequency tracking system and methods can include: providing a haptic pattern with a processor, the haptic pattern including both a haptic pattern start time and a haptic pattern stop time; driving a linear resonant actuator according to the haptic pattern with an amplifier coupled to the processor, and the amplifier having an output coupled to the linear resonant actuator; detecting a current sense signal having a back electromotive force current after the haptic pattern stop time with a current frequency tracker coupled to the output of the amplifier; measuring a frequency of the back electromotive force current as a resonant frequency of the linear resonant actuator; and detecting cycles in the back electromotive force current after the haptic pattern stop time.