An intensity-modulated fiber optic pressure sensor for hand-exoskeleton interactive force detection

Accurately monitoring the finger interactive force without affecting the actuation is one of the challenges in hand exoskeleton. In this paper an intensity-modulated fiber optic pressure sensor used in hand rehabilitation exoskeleton is proposed. The sensor was designed by attaching a short section of optical fiber to a rigid structure fabricated by 3D printing, and when the structure received external force, it would cause changes in light intensity. The diameter of the sensor was 13mm and the height was smaller than 4mm. It had the advantages of thin thickness, simple structure, high sensitivity and good repeatability. What's more, it could be easily integrated into the hand exoskeleton without affecting the actuation. We found that one of the key factors affecting the sensor was the length of the force portion of the fiber. In order to argued this influencing factor, prototypes with fiber force lengths of 2.4mm, 3.5mm, 4.7mm, 5.9mm and 7.1mm were designed and fabricated, and calibrated by a Six-Axi Force/Torque Transducer. The results showed that the sensor had better performance when the length was neither too long nor too short (3.5mm and 4.7mm).