3-D-Printing and Reliability Evaluation of an Easy-to-Fabricate Position Sensing System for Printed Functional Wearable Assistive Devices

The aging population has increased the demand for advanced medical assistive devices with actuators and sensors to enhance independence in daily activities. However, the integration of sensors into rehabilitation devices in a direct and cost-effective manner remains a challenge. This study proposes a scalable linear encoder, fabricated using 3-D-printing technology. The encoder is a fully printed concept, including the electrical circuitry, and is benchmarked in a sensorized hand orthosis (sHO). It is constructed using two commercially available materials: one electrically conductive and one nonconductive. The encoder utilizes an encoder setup with a fixed scale and a sliding sensing head (SH). Encoder’s resolution and robustness are tested under various conditions, including actuation speeds, temperatures, printing repeatability, and fatigue. The results demonstrate the stable operation of the encoder, providing a resolution of 1.2 mm. The sHO incorporates three encoders with geometric shifts, along with a printed electrical circuit and inserted microcontroller for detecting finger flexion and movement direction. This setup further improves the resolution to 0.4 mm. The proposed linear encoder offers an effective and inexpensive approach for integrating sensors into medical assistive devices.