Stretchable Force Sensing Sheet With Diode-Isolated Sensor Array
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Solution Overview
Problem
Existing force sensor arrays face challenges in accurately measuring pressures on human body parts due to non-conformability, especially on complex shapes like the feet, and suffer from cross-talk inaccuracies in matrix addressing, leading to erroneous force measurements.
Innovation Solution
A flexible force sensing array is developed using an elastically stretchable sheet with conductive paths, a layer of piezoresistive material, and a semiconductive layer, allowing for precise measurement of physical forces and minimizing interference with support surfaces, while incorporating a diode-like characteristic to reduce cross-talk between sensor elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a flexible sensor array is used to measure pressures on the human body, then the array can conform to body surfaces, but the array interferes with the support surface function and gives erroneous measurements due to the hammocking effect
Solution Approach 1:
The patent uses a thin film substrate that is both flexible and stretchable, allowing the sensor array to conform to body surfaces while maintaining measurement accuracy. The thin film construction eliminates the hammocking effect by being sufficiently compliant to match the support surface contour without creating measurement errors.
Solution Approach 2:
The patent changes the physical parameters of the substrate by making it elastically stretchable with specific tensile properties. This allows the sensor array to dynamically adapt its tension state to match the support surface, preventing both excessive conformability that causes hammocking and insufficient conformability that prevents accurate measurement.
2Device complexity
If wire core sensing elements are used in the sensor array, then the array structure is simplified, but the array becomes non-stretchable and cannot conform to complex body shapes
Solution Approach 1:
The patent replaces wire core sensing elements with a thin film substrate containing embedded sensing elements. This thin film construction provides both flexibility and stretchability, enabling the array to conform to complex body shapes like feet while maintaining structural simplicity through the integrated film design.
Solution Approach 2:
The patent uses a composite structure combining the thin film substrate with elastic properties and embedded sensing elements. This composite material approach achieves both stretchability for conformability and structural simplicity, eliminating the need for separate wire core components.
3Productivity
If matrix addressing is used to measure sensor element resistances, then the measurement process is efficient, but cross-talk between non-addressed sensor elements causes measurement inaccuracies
Solution Approach 1:
The patent extracts or removes the cross-talk effect from the measurement system by using measurement techniques that isolate individual sensor element resistances. This allows matrix addressing to remain efficient while eliminating the harmful parallel current paths that cause cross-talk inaccuracies.
Solution Approach 2:
The patent introduces an intermediary measurement approach that acts as a mediator between the matrix addressing system and the sensor elements. This intermediary technique enables efficient matrix addressing while preventing cross-talk by using measurement sequences or circuit configurations that isolate individual element measurements.
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 solution enables accurate and non-intrusive measurement of forces on irregularly shaped body parts, reducing tissue damage risks and improving the mapping of support surfaces, with enhanced sensitivity and reduced cross-talk errors.
Implementation Method 1
a layer of sensing material positioned in contact with the first plurality of conductive paths and having an electrical characteristic that varies in response to physical forces exerted thereon
Implementation Method 2
an elastically stretchable sheet
Data Source
AI summary
A force sensing array includes multiple layers of material that are arranged to define an elastically stretchable sensing sheet. The sensing sheet may be placed underneath a patient to detect interface forces or pressures between the patient and the support structure that the patient is positioned on. The force sensing array includes a plurality of force sensors. The force sensors are defined where a row conductor and a column conductor approach each other on opposite sides of a force sensing material, such as a piezoresistive material. In order to reduce electrical cross talk between the plurality of sensors, a semiconductive material is included adjacent the force sensing material to create a PN junction with the force sensing material. This PN junction acts as a diode, limiting current flow to essentially one direction, which, in turn, reduces cross talk between the multiple sensors.