Capacitive Touch Detection Using Signal Rise Rate
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive touch sensors face challenges in reliably detecting touches due to small and variable capacitance changes, influenced by finger size, shape, positioning, and the use of gloves, leading to erroneous detections and the need for additional complex and expensive force sensors for active haptic feedback.
Innovation Solution
The method detects touch by evaluating the rate of change and amplitude of the sensor signal over time, using specific thresholds and rise times to differentiate between approaching and touching, ensuring detection independence from influencing parameters, and incorporating a waiting period and tolerance checks to validate contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed amplitude threshold is used for touch detection, then the detection method is simple, but reliable triggering cannot be guaranteed due to variations in finger size, shape, positioning, and glove use
Solution Approach 1:
The patent changes the detection parameter from a fixed amplitude threshold to a dynamic threshold based on the rate of change of sensor amplitude. Instead of comparing amplitude directly to a constant value, the system evaluates how quickly the amplitude is changing, which remains relatively consistent across different finger types and conditions. This parameter transformation resolves the contradiction by maintaining simplicity while improving reliability.
2Measurement precision
If the sensor is made highly sensitive to detect all touches, then detection sensitivity increases, but false detections occur when objects approach without touching
Solution Approach 1:
The patent applies dynamics by evaluating the temporal behavior of the sensor signal through its rate of change. Instead of using a static threshold comparison, the system monitors how the amplitude evolves over time. During approach without touch, the amplitude changes gradually, whereas during actual contact, the rate of change exhibits a distinct pattern. This dynamic evaluation enables the system to distinguish between approach and contact, maintaining high sensitivity while reducing false positives.
3Measurement precision
If additional force sensors are added to detect active contact for haptic feedback, then contact detection accuracy improves, but device complexity and cost increase significantly
Solution Approach 1:
The patent makes the capacitive sensor element multi-functional by enabling it to detect both passive approach and active contact using the same sensor and evaluation method. By analyzing the rate of change of the sensor amplitude, the system can distinguish between different types of interaction without requiring separate force sensors. This universality resolves the contradiction by achieving accurate contact detection while maintaining system simplicity and avoiding additional hardware complexity.
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 provides reliable and sensitive touch detection, independent of finger size, shape, and glove use, reducing false positives and eliminating the need for additional force sensors, while maintaining high sensitivity and accuracy.
Implementation Method 1
When an object touches or comes near the surface of a capacitive touch sensor, the capacitance of the sensor element changes.
Implementation Method 2
small amounts of charge are transferred in several successive cycles from the sensor element, whose capacitance value is relatively small and variable, to an integration capacitor with a known, fixed, and significantly larger capacitance value
Data Source
Figure 1
AI summary
The invention relates to a method for detecting contact on a capacitive sensor element, wherein a capacitance value of the sensor element is measured by means of a continuously applied integration method in which respective voltages applied to an integration capacitor with a known capacitance value are measured by means of an A/D converter and are processed to give a raw sensor value. The method according to the invention is characterized in that the temporal behaviour of the sensor amplitude is evaluated and used to detect contact on a sensor element.