Linear Resonant Actuator Control via Back-EMF Feedback
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Solution Overview
Problem
Conventional linear resonant actuators face challenges in maintaining consistent vibration frequency due to component variations and environmental changes, leading to inefficiencies in vibration control, particularly in managing damping and resonance frequency drift.
Innovation Solution
A control system for linear resonant actuators incorporating an induction coil to sense vibration speed, which generates an induction voltage used to adjust the vibration signal, allowing for feedback control to maintain optimal vibration levels by applying forces in specific directions based on predefined thresholds, thereby stabilizing vibration speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the linear resonant actuator operates at resonance frequency to achieve high vibration efficiency, then the vibration output is maximized with lower input power, but the narrow bandwidth causes vibration to drop significantly when the driving frequency drifts even slightly from the resonance frequency
Solution Approach 1:
The patent employs feedback control by measuring the back electromotive force (BEMF) of the driving coil and using it to regulate the driver output. The controller intermittently cuts off the driver output to measure the BEMF, then adjusts the driving frequency based on the measured resonance frequency to maintain operation at peak efficiency despite frequency drift caused by temperature changes, component variations, or aging.
2Measurement precision
If the driver output is cut off intermittently to measure the back electromotive force for feedback control, then the resonance frequency can be detected and maintained, but the time utilization of the driving is reduced
Solution Approach 1:
The controller implements periodic measurement by intermittently cutting off the driver output at specific intervals to measure the BEMF. This periodic interruption allows for regular resonance frequency detection and adjustment without requiring continuous stoppage, optimizing both measurement accuracy and driving efficiency.
3Measurement precision
If a Hall element or accelerometer is added to the linear resonant actuator for position or acceleration detection, then the control precision is improved, but the device complexity increases and control system stability becomes more difficult to ensure
Solution Approach 1:
The patent utilizes the existing driving coil to generate the back electromotive force that serves as the feedback signal for resonance frequency detection. This self-service approach eliminates the need for additional sensors like Hall elements or accelerometers, maintaining device simplicity while achieving precise control through the BEMF measurement mechanism.
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 effectively maintains vibration displacement within a specific range, suppressing vibration above a certain speed and ensuring continuous, undamped natural vibration, thus enhancing the control and stability of linear resonant actuators.
Implementation Method 1
an induction coil (303) for sensing speed of the linear resonant actuator (411)... the induction coil (303) being disposed outside the vibrator (301) and being fixed with respect to the vibrator (301)... the induction voltage of the induction coil (303) being amplified into an induction signal
Implementation Method 2
one or more driving coils (302)... to drive the linear resonant actuator (411) according to a driving signal outputted by the processing unit (430)
Implementation Method 3
a displacement restoring force device (304)... wherein the displacement restoring force device (304) further includes at least one elastic member
Data Source
AI summary
The invention discloses a control system and a vibration control method for an LRA. The vibration control method comprises: providing an induction coil, the arrangement and the winding of the induction coil able to obtain an inductive voltage proportional to LRA vibration speed; generating a vibration signal according to inductive voltage and feeding back to a driver connected to the LRA to control the vibration of LRA; wherein the generated vibration signal satisfying the following: when induction voltage is lower than a low-speed threshold, the vibration signal causes the driver to apply a driving force in the same direction; when induction voltage is higher than a high-speed threshold, the vibration signal causes the driver to apply a driving force in the opposite direction; when induction voltage is between the low-speed threshold and the high-speed threshold, the vibration signal does not force the driver to apply force.