LRA Drive Amplitude Control Using Back-EMF Gradient Feedback
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Solution Overview
Problem
Current haptic actuators, such as linear resonant actuators (LRAs), require complex calibration and struggle to respond immediately to changes in drive signal amplitude, limiting their versatility and requiring overdriving techniques that are difficult to control effectively.
Innovation Solution
A method and system that monitor the gradient value of the response signal to adjust the amplitude of the drive signal, using a controller to change the amplitude levels based on calculated gradient values, allowing for more precise control of haptic feedback without the need for extensive calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If overdriving is used to accelerate the LRA's oscillations, then the response time is improved, but it becomes difficult to know when to stop the overdriving
Solution Approach 1:
The system monitors the BEMF signal from the LRA to detect when the oscillation amplitude has reached the target level. This feedback mechanism automatically determines when to stop the overdriving phase, solving the problem of not knowing when to cease overdriving while maintaining fast response times.
Solution Approach 2:
The system applies overdriving as a preliminary action to quickly accelerate the LRA oscillations toward the target amplitude. By preparing the system for rapid response and then using feedback to terminate the overdrive at the precise moment the target is reached, the system achieves both speed and precision.
2Measurement precision
If calibration is performed for a specific haptic actuator based on its BEMF response, then the control accuracy is improved, but the system complexity increases and it limits the use to a specific actuator
Solution Approach 1:
The system uses the BEMF signal, which is a universal property of all LRAs, as the basis for control. By monitoring this inherent electrical response rather than requiring actuator-specific calibration data, the system achieves accurate control across different LRA models without increasing complexity or limiting versatility.
Solution Approach 2:
The LRA actuator provides its own measurement signal through its BEMF response. The system leverages this self-generated electrical signal to monitor oscillation amplitude and determine when the target level is reached, eliminating the need for external calibration equipment or actuator-specific reference data.
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 enables faster and more accurate achievement of desired haptic feedback levels, reducing the complexity of system calibration and enhancing the adaptability of haptic actuators to various operating conditions.
Implementation Method 1
When a current is passing in one direction through the coil it creates a magnetic field that repels the magnet. When passing the current in the other direction the magnetic field attracts the magnet.
Implementation Method 2
Following Lenz's law, upon oscillation of the mass, a back electromotive force, BEMF, is generated across the actuator that opposes the voltage of the source that created it.
Data Source
AI summary
An apparatus and method for adjusting an amplitude of a drive signal applied to a device are presented. The method of driving a device includes providing a drive signal to drive the device, monitoring a gradient value of the response signal; and changing an amplitude level of the drive signal based on the gradient value. The monitoring of the gradient value includes sensing an electrical parameter of the response signal and calculating the gradient value based on the electrical parameter.