Development of a Fiber Optic Grip Force Sensor for fMRI-Based Human Motor Control Studies

Magnetic Resonance (MR)-compatible grip force sensors are increasingly used in human motor control studies, offering fast, high resolution and sensitive behavioral measurements. In neuroscience studies, force and position sensors enable haptic device control and safe human interaction in MR environments. This paper presents a low-cost, lightweight, and accurate fiber optic grip force sensor with a compliant 3Dprinted structure. Capable of measuring grip force (0-500 N) in and out of MRI settings, it utilizes intensity-modulated fiber optics to detect light intensity changes from the compliant structure's elastic deformation, converting force into horizontal displacement. Test results show that both fiber optic grip force sensor prototypes exhibit a highly linear force-to-voltage relationship, with accuracy levels of 2% for PLA and 5.3% for TPU; both exhibit high precision, fast response, and a wide force range. The TPU-based model achieves a sensitivity of 0.001 V/N, and with a 10-bit ADC, it offers a resolution of 0.195 N—making it well-suited for human motor control studies.