Capacitive Touch Panel Position and Force Detection
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Solution Overview
Problem
Existing touch panel systems using pyroelectric bodies face issues with accurately detecting pointer position and pressing force due to false detections from heat-generating objects and temperature changes, leading to erroneous readings.
Innovation Solution
An electrostatic capacitance type touch panel system with a drive electrode, position detection electrode, and pressing force detection electrode, where a controller provides drive signals and acquires signal values to detect pointer position and pressing force based on signal changes, using rate of change and smoothed values to differentiate between thermal noise and actual pressing force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pyroelectric body is used to detect pointer approach and pressing force, then both position and pressing force can be detected by a single component, but false detections occur when heat-generating objects approach and temperature changes
Solution Approach 1:
The patent divides the detection function into two separate electrode systems: position detection electrodes for detecting pointer position through capacitive coupling changes, and pressing force detection electrodes for detecting pressing force through capacitance changes caused by pressure-sensitive material thinning. This segmentation eliminates the false detection problems of pyroelectric bodies while maintaining the ability to detect both position and pressing force.
Solution Approach 2:
The patent replaces the pyroelectric effect-based detection system with an electrostatic capacitance-based detection system. Instead of using thermal effects (pyroelectric effect) that are sensitive to temperature changes and heat-generating objects, the system uses electrical field-based capacitive coupling to detect both position and pressing force, eliminating thermal interference.
2Reliability
If an electrostatic capacitance type touch panel is used to detect position and pressing force, then false detections from temperature changes are reduced, but pressing force detection accuracy decreases when temperature changes occur due to dielectric constant changes in the pressure-sensitive material
Solution Approach 1:
The patent introduces a temperature detection unit that monitors the temperature of the touch panel, and a correction unit that uses the temperature information to correct the pressing force detection results. When temperature changes cause dielectric constant variations, the correction unit adjusts the pressing force values based on the detected temperature, maintaining detection accuracy across different temperature conditions.
Solution Approach 2:
The patent compensates for temperature-induced dielectric constant changes by dynamically adjusting the pressing force detection parameters based on detected temperature. The correction unit modifies the interpretation of capacitance changes in response to temperature variations, ensuring accurate pressing force measurement despite environmental temperature changes.
3Measurement precision
If pyroelectric effect is used for approach detection, then pointer position can be detected, but approach detection fails when pointer temperature equals pyroelectric body temperature
Solution Approach 1:
The patent replaces the pyroelectric effect-based position detection with an electrostatic capacitance-based position detection system. The position detection electrodes detect changes in capacitive coupling between the pointer and the electrode surface, which occur regardless of temperature differences. This electrical field-based detection method works consistently across all temperature conditions, eliminating the limitation of pyroelectric detection.
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 system accurately detects pressing force and position without pyroelectric bodies, reducing false positives from temperature changes and improving detection accuracy by using electrostatic capacitance changes and smoothing processing.
Implementation Method 1
the pointer is capacitively coupled with the drive electrode and the position detection electrode, electrostatic capacitance between both these electrodes decreases
Implementation Method 2
when the touch panel is pressed by the pointer, a pressure-sensitive material disposed between the drive electrode and the pressing force detection electrode becomes thinner
Data Source
AI summary
A touch panel system includes an electrostatic capacitance type touch panel including a drive electrode, a position detection electrode, and a pressing force detection electrode; and a controller configured to provide a drive signal to the drive electrode and acquire a position signal value from the position detection electrode and a pressing force signal value from the pressing force detection electrode. The controller detects a position of a pointer based on the position signal value, and acquires a pressing force generated by the pointer based on a rate of change of a smoothed value of the pressing force value based on the pressing force signal value.