Two-Tone Impedance Identification for Electromagnetic Haptic Loads
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Solution Overview
Problem
Existing methods for determining the mechanical impedance of electromagnetic loads, such as linear resonant actuators, are sensitive to noise and suffer from slow convergence, leading to inefficiencies in driving haptic transducers and generating precise vibrations.
Innovation Solution
A system that generates a waveform signal with two tones to drive the electromagnetic load, allowing for the determination of mechanical impedance parameters by analyzing the amplitude and phase information of current and back electromotive force signals, thereby identifying the mechanical impedance more accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-tone or broadband noise methods are used to determine mechanical impedance, then the measurement process is simpler, but the measurement precision deteriorates due to noise sensitivity and slow convergence
Solution Approach 1:
The patent segments the excitation signal into two distinct frequency tones instead of using broadband noise or single-tone excitation. This segmentation allows the system to probe the mechanical impedance at multiple discrete frequencies, improving measurement precision by capturing frequency-dependent characteristics while maintaining a relatively simple signal generation approach
Solution Approach 2:
The patent introduces an intermediary signal processing stage that separates and analyzes the response at each tone frequency independently. By using intermediate frequency domain analysis (FFT) to isolate the response at f1 and f2, the system achieves higher measurement precision without requiring complex direct time-domain deconvolution, thus balancing accuracy with processing simplicity
2Adaptability or versatility
If adaptive feedback control is implemented to track changing impedance parameters, then the adaptability improves, but the system complexity and computational requirements increase
Solution Approach 1:
The patent implements periodic impedance identification by repeatedly applying the two-tone excitation signal at intervals. This periodic measurement approach allows the system to track changing impedance parameters over time without requiring continuous complex adaptive control, thereby achieving adaptability through simple periodic updates rather than continuous complex feedback processing
Solution Approach 2:
The patent changes the excitation frequency parameters (using two distinct tones f1 and f2) to probe different aspects of the mechanical impedance. By varying the frequency parameters of the excitation signal rather than changing the entire control architecture, the system achieves adaptability to different operating conditions with minimal increase in system complexity
3Measurement precision
If multiple measurement frequencies are used to accurately capture mechanical impedance characteristics, then the measurement precision improves, but the measurement time and productivity decrease
Solution Approach 1:
The patent applies partial action by using only two specific frequency tones (f1 and f2) rather than sweeping through a broad frequency range. This selective excitation at two discrete frequencies provides sufficient information to characterize the mechanical impedance while significantly reducing measurement time compared to full frequency sweeps, thus balancing precision with productivity
Solution Approach 2:
The patent performs preliminary frequency domain analysis (FFT) to quickly identify the response at the two excitation frequencies. By pre-processing the signal to extract only the relevant frequency components rather than performing complete impulse response analysis, the system achieves accurate impedance measurement with reduced computational time, improving productivity without sacrificing 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 reduces noise sensitivity and improves the accuracy of mechanical impedance identification, enabling more efficient optimization and adaptation of haptic signals to maintain consistent vibration resonance across varying conditions.
Implementation Method 1
An LRA may be modelled as a mass-spring electro-mechanical vibration system
Implementation Method 2
Re and Le are the DC resistance and coil inductance of the coil-magnet system, respectively; and Bl is the magnetic force factor of the coil
Data Source
AI summary
A method for identifying a mechanical impedance of an electromagnetic load may include generating a waveform signal for driving an electromagnetic load, the waveform signal comprising a first tone at a first driving frequency and a second tone at a second driving frequency. The method may also include during driving of the electromagnetic load by the waveform signal or a signal derived therefrom, receiving a current signal representative of a current associated with the electromagnetic load and a back electromotive force signal representative of a back electromotive force associated with the electromagnetic load. The method may further include determining amplitude and phase information of the current signal responsive to the first tone and second tone, determining amplitude and phase information of the back electromotive force signal responsive to the first tone and second tone, and identifying parameters of the mechanical impedance of the electromagnetic load based on the amplitude and phase information of the current signal and the amplitude and phase information of the back electromotive force signal.