Piezoelectric Pressure Signal Processing for Touch Panels
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Solution Overview
Problem
Piezoelectric pressure sensors generate transient signals, making it challenging to accurately measure static or slowly varying applied forces, and existing methods struggle with noise and DC offset variations, affecting the reliability and sensitivity of force measurement in touch panels.
Innovation Solution
A method that conditionally integrates processed pressure signals based on a state register value, which transitions depending on signal properties, and includes steps to manage DC offsets and noise, such as resetting residual DC offsets and using thresholds to filter out noise, allowing for accurate force measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piezoelectric sensors are used for pressure sensing, then the touch panel can detect pressure and distinguish different user interactions, but the sensors generate transient signals making accurate measurement of static or slowly varying forces difficult
Solution Approach 1:
The system performs preliminary actions by detecting the start and end of user interactions using capacitance sensors before processing piezoelectric signals. This allows the system to prepare integration windows and thresholds in advance, improving the accuracy of force measurements during static or slowly varying pressure conditions.
Solution Approach 2:
The system uses feedback by continuously monitoring piezoelectric signal properties (mean, standard deviation, gradient) and adjusting integration parameters accordingly. When the signal indicates a static condition, the system switches to integration mode to accumulate force measurements, while dynamic conditions trigger different processing modes, thereby improving measurement reliability.
2Measurement precision
If conditional integration of piezoelectric signals is implemented, then force measurement accuracy improves, but noise and DC offset variations affect reliability
Solution Approach 1:
The system dynamically adjusts integration parameters based on real-time signal analysis. By evaluating signal properties such as mean, standard deviation, and gradient, the system adapts integration thresholds and windows to current conditions, maintaining accuracy while filtering out noise and DC offset variations that would otherwise degrade measurement reliability.
Solution Approach 2:
The system changes parameters by modifying integration windows, thresholds, and signal processing gains based on detected signal characteristics. When static pressure is detected, longer integration windows are used to improve signal-to-noise ratio, while dynamic conditions use shorter windows, thereby managing the trade-off between accuracy and noise rejection.
3Measurement precision
If multiple state register values are used to manage different user interaction behaviors, then measurement accuracy improves, but processing complexity increases
Solution Approach 1:
The system segments user interactions into distinct states (e.g., initial contact, sustained pressure, release) using a state register with multiple values. Each state has optimized processing parameters, allowing accurate differentiation of interaction types while keeping the complexity manageable through systematic state transitions based on simple signal thresholds.
Solution Approach 2:
The system applies partial integration only when and where needed based on signal conditions, rather than continuously integrating all piezoelectric signals. By using state registers to enable integration only during specific conditions (e.g., sustained static pressure), the system improves measurement accuracy for relevant interactions while avoiding unnecessary processing complexity during transient or irrelevant events.
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
Improves the accuracy and reliability of force measurement in touch panels by effectively handling transient signals and noise, maintaining sensitivity and processing speed, and enabling distinction between different types of user interactions.
Implementation Method 1
Piezoelectric pressure sensors generate transient signals
Implementation Method 2
Projected capacitance touch panels operate by detecting changes in electric fields caused by the proximity of a conductive object
Data Source
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AI summary
A method of processing signals from a touch panel for combined capacitive and force sensing includes receiving, from the touch panel, pressure signals from a plurality of piezoelectric sensors and capacitance signals from a plurality of capacitive touch sensors. The method also includes determining, based on the capacitance signals, a user interaction period during which a user interaction with the touch panel occurs. The method also includes generating processed pressure signals based on the received pressure signals. The method also includes measuring a force applied to each of the plurality of piezoelectric sensors by the user interaction during the user interaction period by conditionally integrating the corresponding processed pressure signals according to a state register corresponding to the user interaction. The state register takes one of two or more values. Each user interaction is initialised in a first state value. The user interaction transitions between state register values in dependence upon the current state register value, and one or more pressure signal properties.