Granular Jamming Gripper for an Ankle Rehabilitation Robot

Abstract Rehabilitation exercises are a crucial component in the treatment of ankle injuries. With the increasing demand on physiotherapists, many advances have been made in robotassisted ankle rehabilitation, which require an attachment mechanism of the foot or leg on the device. However, securely holding the ankle may cause physical discomfort and for the patient to feel constrained to the mechanism. This paper introduces a gripper of the plantar surface of the foot for ankle rehabilitation employing a universal Granular Jamming Gripper (GJG). It consists of a granule filled membrane that allows the patient’s foot to be immersed in it when it is filled with air and hardens around the foot when vacuum is applied. The paper also investigates the optimal filling percentage of the membrane, membrane thickness and the effect of granule types of different physical properties (ground coffee, table salt, coffee/salt mixture, and granular sugar) on the gripping ability and overall function of the GJG. Tensile and immersion tests demonstrated the suitability of the GJG for gripping a foot model as well as the increased gripping function with a 0.25 mm membrane filled to 60 % with granulated sugar.