Capacitive Sensing Surface Displacement for Pressure Object Identification
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Solution Overview
Problem
Existing capacitive sensing technologies struggle to reliably distinguish between objects resting on a touch-sensitive surface and those applying pressure, as variations in capacitance due to pressure changes are not sufficient to differentiate between fingers applying different levels of pressure or orientation.
Innovation Solution
A sensing apparatus comprising a capacitive sensor and a displacement sensor, with a processing element that identifies which object applied a displacement load by analyzing changes in capacitive coupling characteristics over time, allowing for accurate detection of pressure inputs on a touch-sensitive surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensing is used to detect multiple touches, then spatial position resolution is improved, but the ability to distinguish between resting and pressing objects deteriorates
Solution Approach 1:
The sensing surface is divided into multiple independently movable segments or zones. When an object applies pressure, only the local segment under that object displaces, while other segments remain stationary. This segmentation allows the system to associate displacement events with specific spatial locations, enabling reliable identification of which object is pressing among multiple resting objects.
Solution Approach 2:
The invention adds a temporal dimension to the sensing by monitoring changes in capacitive coupling over time. Instead of relying solely on static capacitance values, the system detects dynamic changes that occur when an object transitions from resting to pressing state, providing an additional discrimination criterion that resolves the ambiguity between resting and pressing objects.
2Measurement precision
If capacitive coupling variations are used to measure pressure, then pressure detection capability is improved, but the ability to differentiate between objects deteriorates
Solution Approach 1:
The system first detects which objects are resting on the sensing surface and establishes their baseline positions. When pressure is applied, the system identifies the pressing object by detecting which pre-identified resting object's location corresponds to the displacement event, rather than relying solely on pressure magnitude measurements.
Solution Approach 2:
The invention introduces displacement of the sensing surface as an intermediary physical phenomenon that mediates between the applied pressure and the capacitive coupling changes. This displacement acts as a clear, unambiguous signal that directly links the pressure event to a specific spatial location, serving as a reliable mediator for object identification.
3Measurement precision
If the sensing surface is made compliant to detect pressure, then pressure sensitivity is improved, but the complexity of the system increases
Solution Approach 1:
The sensing surface itself serves dual functions: it acts as both the capacitive sensing element and the displacement sensing element. The compliant surface naturally displaces under pressure, and this self-generated displacement is detected through changes in capacitive coupling, eliminating the need for separate displacement sensors or complex mechanical structures.
Solution Approach 2:
The capacitive sensing surface is designed to perform multiple functions simultaneously: detecting the presence of objects, measuring their positions, detecting pressure through displacement, and identifying which object is pressing. This multi-functionality reduces overall system complexity by eliminating the need for separate sensor systems for each function.
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
Enables precise identification of which object is applying pressure, improving the accuracy of input selection on touch-sensitive devices by differentiating between resting and actively pressing objects based on capacitive coupling changes.
Implementation Method 1
capacitive sensor comprising a sensing surface moveably mounted relative to the frame and configured to measure, as a function of time, characteristics of capacitive couplings between the sensing surface and a plurality of objects at different locations over the sensing surface
Implementation Method 2
a displacement sensor configured to detect when there is a displacement of the sensing surface relative to the frame due to a displacement load applied to the sensing surface by one of the objects
Data Source
AI summary
A sensing apparatus including a frame; a capacitive sensor comprising a sensing surface moveably mounted relative to the frame and configured to measure, as a function of time, characteristics of capacitive couplings between the sensing surface and a plurality of objects at different locations over the sensing surface; a displacement sensor configured to detect when there is a displacement of the sensing surface relative to the frame due to a displacement load applied to the sensing surface by one of the objects; and a processing element configured to identify which of the objects applied the displacement load based on changes in the measured characteristics of the capacitive couplings for the respective objects during a time period around when the displacement of the sensing surface is detected.