Design and evaluation of a compact, integrated fMRI-compatible force sensor printed by additive manufacturing

The past decade has seen an increasing number of motor control studies using functional magnetic resonance imaging to explore the underlying neural mechanisms. To enable advanced experimental paradigms under well-controlled and reproducible conditions, a number of fMRI-compatible haptic interfaces have been developed for such studies. These devices typically rely on actuation principles and transmissions with non-linear behavior and large output impedance. Fiberoptic force sensors are a common and well-established means of measuring interaction forces with subjects or to reduce the inherent dynamics of the haptic interface through force feedback. The elastic probes for such sensors are typically fabricated by expensive methods such as electro-erosion of non-ferromagnetic metals or injection moulding of polymers, or are realized by milling of polymers, resulting in bulky structures. In this paper we propose a compact and integrated elastic probe for fiberoptics-based force sensing, developed using low-cost off-the-shelf 3D printing technology. Characterization of the sensor probe shows high linearity, repeatability and temporal stability, as well as high reproducibility in terms of the manufacturing process. The realized sensor is integrated into a linear grasper to evaluate its performance in force-feedback applications, underlining the potential of this technology for use in fMRI-compatible haptic interfaces.