Pneumatic Joint Design for Enhancing Spacesuit Flexibility

The flexibility of spacesuits made of soft material is limited by high-pressure differences across the garment, which can induce strong tensile stress and stiffen soft materials. This paper describes a new single-axis pneumatic joint design for the enhancement of spacesuit flexibility. The joint is based on the implementation of an isotensoid shape that can theoretically carry interior pressure without circumferential stress. By introducing excess skin material into the isotensoid along a circumferential direction, local slack regions are generated, which enable expansion and contraction, resulting in a flexion motion with low resistance torque. Joint prototypes were fabricated from silicone rubber–coated Vectran woven fabric (Kuraray, Tokyo, Japan) and were subjected to flexion tests using a custom-made robotic arm. The torque measurement results showed that the increase in torque was low until the flexion angle reached 80° and rose rapidly at higher angles. It was concluded that the presence of excess skin can effectively provide flexibility at low angles and that increased torque at higher angles should be addressed in future design improvements.