Design of a new fMRI compatible haptic interface

In this paper, we present the design of a new fMRI compatible haptic interface with 3DOFs, based on electrical DC actuation, for the study of brain mechanisms of human motor control. In order to evaluate the validity of the proposed solution, we performed some preliminary experiments with a single degree of freedom device to test the compatibility with the fMRI environment. The 1DOF design was extended to the implementation of a 3DOFs parallel manipulator with 3UPU kinematics. Due to the dimensional constraints imposed by the fMRI environment, the choice of the dimensions and of the adopted mechanical solution was a result of an optimization process, that is presented in this work. Reachable workspace, kinematic isotropy, end-point stiffness, minimum force and translational clearance were studied in different configurations to select the stroke of the prismatic joint and the radius difference between the moving platform and the base. A further optimization of the mechanical design was then conducted in order to reduce the torque requested to the actuators for gravity compensation and consequently improve the performance of the manipulator. The final design resulted in a system capable of satisfying all the environment and user requirements.