Stretchable Fabric Force Sensor Arrays for Curved Surface Mapping
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Solution Overview
Problem
Existing force sensor arrays are not conformable to complex, compoundly curved shapes such as human body parts, leading to inaccurate measurements and potential tissue damage from pressure sores, especially in areas like the feet of individuals with diabetes.
Innovation Solution
Development of elastically stretchable fabric-like pressure or force sensor arrays using thin, flexible individual sensor elements arranged in a matrix with conductive threads coated with piezoresistive material, allowing for conformability to irregular surfaces and minimization of cross-talk through diode-like circuit elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rigid force sensors are used, then measurement precision is improved, but adaptability to curved surfaces deteriorates
Solution Approach 1:
The force sensors are constructed using flexible printed circuit board (FPCB) substrates with force-sensitive resistors patterned on the flexible substrate. This flexible film structure allows the sensor array to conform to curved surfaces while maintaining force measurement capability through the inherent flexibility of the FPCB and adhesive layers.
Solution Approach 2:
The sensor array employs a composite structure combining rigid force-sensitive resistor elements with flexible bonding materials and substrates. This composite approach integrates the measurement precision of rigid force-sensitive components with the adaptability of flexible bonding layers, enabling the array to maintain structural integrity on curved surfaces.
2Adaptability or versatility
If fabric force sensors are stretched, then adaptability to dynamic surfaces is improved, but measurement precision deteriorates
Solution Approach 1:
The force sensor array is divided into multiple discrete force-sensitive resistor elements arranged in an array pattern on the flexible substrate. This segmentation allows each element to independently respond to local forces while the overall array can be stretched or deformed, maintaining measurement capability across dynamic surfaces through distributed sensing.
Solution Approach 2:
The flexible substrate and bonding structure are designed to dynamically deform with the underlying fabric or surface without compromising sensor functionality. The force-sensitive resistors maintain their electrical and mechanical properties during stretching, allowing the sensor array to adapt to dynamic surface changes while continuing to provide accurate force measurements.
3Ease of operation
If force sensors are made flexible, then ease of operation is improved, but manufacturing precision deteriorates
Solution Approach 1:
The flexible printed circuit board substrate serves multiple functions: it provides the flexible support structure, acts as the mounting platform for force-sensitive resistors, and serves as the electrical interconnection medium. This multi-functionality simplifies the overall structure and reduces the number of separate components that would otherwise require precise alignment during manufacturing.
Solution Approach 2:
The adhesive layers and flexible substrate structure are designed to self-align and self-adjust during the manufacturing process, reducing the need for high-precision external alignment equipment. The flexible nature of the substrate allows for tolerance compensation and automatic positioning of sensor elements during assembly.
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 accurate measurement and mapping of forces on complex shapes, reducing the risk of tissue damage by providing timely feedback for corrective measures, such as adjusting footwear to prevent ulcers.
Implementation Method 1
The sensor arrays include a plurality of force sensitive resistors
Implementation Method 2
elastically stretchable fabric force sensor arrays... flexible substrate... adhesive layers
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Force or pressure transducer arrays (30) have elastically stretchable electrically conductive polymer threads (31), (32) disposed in parallel rows and columns that contact at intersections thereof a piezoresistive material (37) which has an electrical resistivity that varies inversely with pressure or force exerted thereon to form a matrix array of force or pressure sensor elements. The threads are fixed to a single one or pair of flexible elastically stretchable substrate sheets (33), (35) made of thin sheets of an insulating polymer such as PVC, or for greater elasticity and conformability to irregularly- shaped objects such as human body parts, an elastically stretchable fabric such as LYCRA or SPANDEX. Elastic stretchability of the sensor arrays is optionally enhanced by disposing either or both row and column conductive threads (201-1), (201-2) in sinuously curved, serpentine paths rather than straight lines.