Haptic Engine Mass Displacement Estimation Using Back EMF and Magnetic Reference Crossing
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Solution Overview
Problem
Existing haptic engines face errors in estimating mass displacement due to coil resistance estimation issues and inability to sense low-velocity drift caused by load disturbances, such as a user moving a mobile device, which affects the accuracy of tactile feedback.
Innovation Solution
A haptic engine design incorporating a Hall comparator to detect magnetic field crossings and generate signals for estimating mass displacement, using back electromotive force (EMF) voltage, which is more robust against low-velocity drift and does not require an application-specific integrated circuit (ASIC) or magnetic interference shields, and can be manufactured using existing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back EMF integration method is used to estimate mass displacement, then the displacement estimation can be obtained, but errors occur due to coil resistance estimation issues and inability to sense low-velocity drift
Solution Approach 1:
The patent combines two displacement estimation methods: back EMF integration and magnetic reference crossing detection. The back EMF provides continuous displacement estimation while the magnetic reference crossing events provide periodic correction points, merging the advantages of both methods to achieve accurate and reliable displacement measurement that overcomes the limitations of using either method alone.
Solution Approach 2:
The system uses magnetic reference crossing events as feedback to correct the back EMF integration results. When the magnetic mass crosses a magnetic reference, the comparator generates a signal that provides feedback to reset or correct the integrated displacement value, eliminating drift accumulation and improving long-term measurement reliability.
2Measurement precision
If Hall sensing elements and multi-bit data converter circuits are used to detect magnetic field, then detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts only the essential function needed for displacement estimation: detecting when the magnetic mass crosses magnetic references. Instead of using complex multi-bit Hall sensors to continuously measure magnetic field strength, the system uses a simple comparator to detect crossing events, taking out only the necessary detection capability while eliminating unnecessary complexity.
Solution Approach 2:
The system replaces expensive, complex Hall sensing elements with a simple, inexpensive comparator circuit. The comparator provides sufficient functionality for the application (detecting magnetic reference crossings) at a much lower cost and with significantly reduced circuit complexity, accepting that the solution is simpler and more limited but adequate for the task.
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 solution provides accurate mass displacement estimation, is cost-effective, and resistant to z-axis shifts over system life, with fewer components and routing, effectively correcting low-velocity drift errors and improving the robustness of haptic feedback.
Implementation Method 1
one or more actuators, such as piezoelectric transducers, electromechanical devices, and/or other vibration inducing devices, that are mechanically connected to the input surface. Drive electronics coupled to the one or more actuators cause the actuators to induce a vibratory response into the input surface
Implementation Method 2
A Hall comparator is used to detect crossing of a magnetic reference
Implementation Method 3
driving a mass to move within the frame along a movement axis, the movement of the mass inducing a back electromotive force (EMF)
Data Source
AI summary
In an embodiment, a single-sided or double-sided moving magnet haptic engine comprises: a frame; one or more magnetic field sources mounted to the frame and operable to generate a magnetic field and a back electromotive force (EMF) voltage; a magnetic mass positioned within the frame and operable to move within the frame along a movement axis; a comparator mounted to the frame, the comparator operable to detect the magnetic field and to generate a signal indicating a crossing of one or more magnetic references by the magnetic field; and a processor coupled to the one or more sensors and operable to estimate a displacement of the magnetic mass on the movement axis based on the back EMF voltage and the signal. Other embodiments are directed to a single-sided or double-sided moving coil haptic engine.