Laplace-Constrained Touchscreen Calibration for Non-Linear Distortion

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Solution Overview

Problem

Existing touch display systems face challenges in accurately mapping touchscreen coordinates to display coordinates due to non-linear distortions, particularly in graphical user interfaces that require precise cursor control, as conventional calibration methods like 3-point or 25-point calibration are insufficient for handling strong non-linearities and noise in touchscreen hardware.

Innovation Solution

The implementation of a generalized Laplace-constrained fit method that reduces the number of independent fit parameters by constraining polynomial expansions to obey the laws of physics, such as Ohm's Law and Kirchhoff's Junction Rule, allowing for more reliable interpolation and extrapolation beyond the calibration grid and reducing noise effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional calibration methods (3-point or 25-point calibration) are used to map touchscreen coordinates to display coordinates, then the calibration process can be completed with standard procedures, but the accuracy of mapping is insufficient when strong non-linear distortions and noise are present in touchscreen hardware

Engineering Contradiction:

Improvemapping accuracyVSAvoidcalibration reliability under non-linearity

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the mathematical parameters used in calibration by transitioning from conventional polynomial fits to Laplace-constrained polynomial expansions. This constraint based on physical laws (Laplace's equation) reduces the number of independent fit parameters while improving the reliability of calibration under strong non-linear distortions and noise conditions

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional mechanical calibration approach (direct polynomial fitting) with a physics-based approach (Laplace-constrained fitting). This substitution uses physical laws to guide the mathematical model, resulting in more reliable interpolation and extrapolation beyond the calibration grid

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If the number of calibration targets is increased to improve mapping accuracy, then better calibration can be achieved, but the complexity and time required for calibration increases

Engineering Contradiction:

Improvecalibration accuracyVSAvoidcalibration time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent changes the mathematical model to Laplace-constrained polynomial expansions, which reduce the number of independent fit parameters. This parameter reduction allows achieving high calibration accuracy with fewer calibration targets, thereby reducing calibration time while maintaining precision

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If conventional polynomial fits are used without physical constraints, then the calibration can accommodate various distortion patterns, but noise in touchscreen coordinates severely degrades the quality of interpolation and extrapolation

Engineering Contradiction:

Improvedistortion pattern flexibilityVSAvoidinterpolation accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent replaces unconstrained polynomial fitting with Laplace-constrained fitting that incorporates physical laws. This constraint significantly reduces noise effects during interpolation and extrapolation while maintaining the ability to handle various distortion patterns through the generalized Laplace expansion

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent converts the harmful effect of noise in touchscreen coordinates into a beneficial outcome by using Laplace constraints. The constraints act as a filter that reduces noise amplification during interpolation and extrapolation, improving overall calibration reliability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8049740B2Method and apparatus for laplace constrained touchscreen calibration

Publication Date: 2011.11.01 ELO TOUCH SOLUTIONS INC(US)

AI summary

A computer readable medium has instructions to calibrate a touch system by detecting touch points on a touchscreen that are each associated with touchscreen coordinates in a touchscreen coordinate system. The instructions associated each of the touch points with known calibration targets, and each of the calibration targets has display coordinates in a display coordinate system that is associated with at least one of a display screen and an operating system. The instructions fit the display coordinates and the touchscreen coordinates non-linearly with respect to each other based on a generalized Laplace-constrained fit that is used to identify correction parameters used to map a user generated run-time touch point on the touchscreen to a display coordinate location on a display screen. The correction parameters represent non-linear corrections.