Signal Conditioning Circuit for 3D Printed Flexible Strain Sensor for Hand Orthosis Application

Flexible soft sensors and actuators are essential elements for the realization of novel smart robotic, orthotic, and prosthetic hands. In this paper, we present a strain sensor that is designed in-house, and 3D printed directly into a polymer-based orthotic finger. This sensor was fabricated using conductive and soft filament materials consisting of a composite of thermoplastic polyurethane (TPU) and carbon nanotubes (CNT). Signal conditioning circuit models were developed for the sensor to enhance and process the data received. Various components including Wheatstone bridge, differential amplifiers, and active low pass filters have been implemented for designing the signal conditioning circuit, and several simulation results were obtained. This approach converts the variable resistance of this strain gauge into a linearized voltage signal which helps in the easier characterization of finger movement.