MR compatible ERF driven hand rehabilitation device

This paper presents the design, fabrication and preliminary tests of a novel, one degree of freedom, 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 attached to the ERF resistive element's shaft to measure the patient induced motion and force, respectively. A key feature of the device is the use of electro theological 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. Our preliminary tests demonstrate that the device can apply, on a human hand holding the device handles, resistive forces that exceed 150 N. In addition the activated ERF maintain its properties in the magnetic environment without creating degradation of the MR images. The results are encouraging in combining functional magnetic resonance imaging methods, with MR compatible robotic devices for improved effectiveness of rehabilitation therapy.