Stylus Position Interpolation in Touch Sensors
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Solution Overview
Problem
Existing touch sensor systems face challenges in accurately interpolating the position of a stylus with high resolution, especially when the stylus tip is small compared to the sensor pitch, as determining a closed-form continuous function for complex geometries is difficult, leading to increased cost and measurement time with current methods.
Innovation Solution
The use of empirical interpolation functions determined through curve fitting of measured capacitance data, incorporating angle adjustments and noise reduction penalties, allows for improved accuracy without significant increases in circuitry or measurement time, using a test apparatus to collect data and develop multivariate cubic polynomial functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional methods are used to determine stylus position, then the system is simpler to implement, but the measurement precision is insufficient and the measurement time increases
Solution Approach 1:
The patent performs preliminary curve fitting to determine interpolation functions during an offline calibration phase. These pre-computed functions are then stored and applied during online stylus position measurement, eliminating the need for time-consuming real-time curve fitting and enabling fast, accurate position determination.
Solution Approach 2:
The patent replaces complex real-time computational geometry calculations with pre-computed empirical interpolation functions derived from measured capacitance data. This substitution of mechanical/computational approaches with data-driven models significantly reduces measurement time while maintaining high precision.
2Measurement precision
If more circuitry is added to improve measurement precision, then the stylus position can be determined more accurately, but the device complexity and cost increase
Solution Approach 1:
The patent uses empirical interpolation functions that copy and generalize patterns from measured capacitance data at known positions. These functions capture the relationship between capacitance measurements and stylus position without requiring additional physical sensors or circuitry, achieving high precision through computational modeling rather than hardware expansion.
Solution Approach 2:
The patent changes the approach from direct geometric calculation to empirical parameter fitting. By determining interpolation functions through curve fitting of measured capacitance values, the system achieves high measurement precision using existing sensor data and computational methods rather than adding complex circuitry.
3Measurement precision
If the sensor pitch is reduced to improve resolution, then the stylus position can be measured more accurately, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the measurement approach from relying on fine sensor pitch to using empirical interpolation functions. By fitting functions to measured capacitance data, the system achieves high resolution position measurement regardless of the physical sensor pitch, thereby maintaining ease of manufacture while improving measurement 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 enables accurate stylus position estimation with reduced noise sensitivity and static offset, achieving high-resolution reporting comparable to display pixel pitch without excessive cost or time, enhancing user experience in touch-sensitive systems.
Implementation Method 1
measuring a capacitance from rows and columns in the matrix close to that location to the electrically conductive tip of the stylus
Data Source
AI summary
Systems and methods for determining interpolation functions for a stylus position on a sensor matrix and estimating such a position are provided. In one disclosed embodiment, a test apparatus comprises a stylus configured to be positioned on a sensor matrix at each location of a set of known locations. One or more processors are configured to access the touch sensor data corresponding to the set of known locations, where the data is produced in response to positioning the stylus on the sensor matrix at the set of known locations. Stylus location data reflecting the set of known locations is accessed. A stylus position interpolation function is then determined by curve fitting based on the touch sensor data corresponding to the set of known locations and the stylus location data reflecting the set of known locations.