Design and fabrication of soft sensors with conductive thermoplastic polyurethane

• Main Author: Cui, Honglin
• Other Authors: Yeong Wai Yee
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; 3D printing; Piezoresistive sensing; Additive manufacturing; Soft sensor; Conductive thermoplastic urethane
• Online Access: https://hdl.handle.net/10356/176053
• Institution: Nanyang Technological University

Flexible Sensors are soft electronic devices that can detect and perceive external signals from physical stimuli like force, strain, and heat to chemical stimuli like organic compounds and ions. They are utilized everywhere in our modern daily lives, from wearable devices and environmental monitoring to industrial applications; and the demand is still rising. A significant trend is also witnessed in the conventional rigid solid-state sensing systems based on silicon PCBs are now replaced by soft, flexible, stretchable, and lightweight systems, especially in the abovementioned fields. However, further investigation of the working mechanisms of some of these soft sensors is required as they can be quite different from that of the conventional solid-state sensors, resulting in distinctive features in their sensing capability, such as the negative piezoresistive effect of FFF-made piezoresistive soft sensors. This report presents the design and development of a novel soft piezoresistive sensor fabricated by the Fused Filament Fabrication (FFF) process with insulating and conductive TPU. The research aims to develop a piezoresistive force sensor with conductive thermoplastic polyurethane which can be fabricated in a single process by multi-material FFF process. These sensor will be applied on an existing type of gripper developed earlier by Goh et al. The sensor is designed to be flexible, lightweight, sensitive to the application of force, and can fit with the structural design of the gripper. A series of controlled variable tests on different periodic patterns, cross-sectional structure designs, and printing parameters are conducted to optimize the sensor’s sensitivity under the application of compressive force. The application of the sensor to be directly fabricated onto the soft gripper’s fingertip will be tested. This project 8 also focuses on investigating the piezoresistive mechanism of the sensor, which is absent in most research in the relevant field. This project contributes to the field of soft robotics and 3D printed electronics by providing a novel sensor design and a set of printing setups to optimize the performance of a piezoresistive sensor available to be fabricated by the most commonly used additive manufacturing technology FFF (fused filament fabrication) with a common, accessible, and cheap material which is cTPU (conductive thermoplastic polyurethane). An optimized sensor design is achieved, which can generate a drastic 42% drop in resistance under an even force of 50N. When it is applied on the gripper’s surface, it is also observed that a similar 42% drop in resistance is present on the directly fabricated sensor. With the integration of the pre-existing soft gripper, this sensor can be deployed in the manufacturing industry for applications such as handling fragile or slippery items or collaborating with human workers.