Linear Resonant Actuator Drive Control Using Back-EMF Feedback
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Solution Overview
Problem
Linear Resonant Actuators (LRAs) experience efficiency drops when driven away from their resonant frequency due to environmental factors, and conventional driving methods result in inadequate braking and inefficient drive periods.
Innovation Solution
An apparatus and method that adjust the duration of positive and negative drive intervals based on measured back-emf to maintain LRA operation at its resonant frequency, using a class AB or class D driver with a signal generator, ADC, and controller to optimize drive signals and braking performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the LRA is driven during only two quadrants (T1 and T3) with predetermined drive interval, then the control implementation is simplified, but the drive frequency becomes greater than the resonant frequency and braking performance deteriorates
Solution Approach 1:
The patent dynamically adjusts the drive signal parameters including drive interval duration, off interval duration, and gain values based on measured back-emf and detected LRA state (coasting, braking, or acceleration). This dynamic adaptation allows the system to maintain optimal resonant frequency operation and effective braking performance across varying operating conditions, resolving the contradiction between simplified control and reliable braking.
Solution Approach 2:
The system continuously measures back-emf during off intervals and uses this feedback to detect LRA state and adjust subsequent drive signals. The feedback mechanism enables the controller to adapt drive parameters in real-time, ensuring both simplified control implementation and effective braking performance by optimizing the drive waveform based on actual LRA response.
2Force
If a large gain is applied to the back-emf for braking control, then the braking force is improved, but the drive amplitude becomes smaller for the same input signal
Solution Approach 1:
The patent implements dynamic gain adjustment where the gain applied to back-emf varies based on the detected LRA state (coasting, braking, or acceleration) and operating conditions. During braking phases, higher gain is applied to maximize braking force, while during acceleration phases, lower gain preserves drive amplitude. This state-dependent gain modulation resolves the contradiction between braking force and drive amplitude.
3Device complexity
If the drive frequency is kept constant, then the control implementation is simplified, but the efficiency drops sharply when the resonant frequency shifts due to environmental factors
Solution Approach 1:
The system measures back-emf during off intervals to detect resonant frequency shifts caused by environmental factors such as temperature changes and mechanical wear. This feedback information is used to dynamically adjust the drive frequency to track the actual resonant frequency, maintaining high efficiency while adapting to environmental variations without requiring complex predetermined frequency schedules.
Solution Approach 2:
The patent dynamically changes the drive frequency parameter based on measured back-emf characteristics and detected resonant frequency shifts. By adjusting the drive frequency to match the actual resonant frequency under varying environmental conditions, the system maintains optimal efficiency while using relatively simple control logic to track frequency changes.
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
Improves LRA efficiency by maintaining operation at resonant frequency and enhances braking performance by dynamically adjusting drive intervals and gain application.
Implementation Method 1
an LRA has a mass that is secured to a spring, and the mass is moved by use of a coil that is located in proximity to the mass
Implementation Method 2
the driver is shut-off or placed in a high impedance state to allow the back electromotive force (back-emf) to be monitored
Data Source
AI summary
A method for driving a Linear Resonant Actuator (LRA) is provided. During a first off interval, the back-emf of the LRA is measured. During a first off interval, a timer is started when the back-emf reaches a predetermined threshold, and after a predetermined delay has lapsed following the back-emf reaching the predetermined threshold during the first off interval, the LRA is driven over a drive interval having a length and drive strength. A second off interval is entered following the drive interval, and during the second off interval, the back-emf of the LRA is measured. During the second off interval, the timer is stopped when the back-emf reaches the predetermined threshold. The value from the timer that corresponds to the duration between the back-emf reaching the predetermined threshold during the first off interval and the back-emf reaching the predetermined threshold during the second off interval determines the length.