MR Compatible ERF Driven Hand Device for Rehabilitation After Stroke

This paper presents the design, fabrication and testing of a novel, one degree of freedom, magnetic resonance (MR) compatible, computer controlled, variable resistance hand device that will be used in fMRI studies of the brain and motor performance during rehabilitation after stroke. The device consists of four major subsystems: a) the Electro-Rheological Fluid (ERF) resistive element; b) the gearbox; c) the handles and d) the sensors: one optical encoder and one force sensor was implemented into the device design to measure the patient induced motion and force, respectively. A key feature of the device is the use of electro rheological fluids (ERF) to achieve resistive force generation. ERFs are fluids that experience dramatic changes in rheological properties, such as viscosity or yield stress, in the presence of an electric field. Using the electrically controlled rheological properties of ERFs, compact resistive elements with an ability to supply high resistive torques in a controllable and tunable fashion, have been developed. The hand device is designed to resist up to 50% of maximum level of gripping force of a human hand and be controlled in real time. Our study demonstrates that there is neither an effect from MR environment on the ERF properties and performance of the sensors, nor significant degradation on MR images by the introduction of ERF driven hand device in the MR environment. The results are encouraging in combining functional Magnetic Resonance Imaging methods, with MR compatible robotic devices for improved effectiveness of rehabilitation therapy.