Design of a Robotic Arm for Validating an FEA Model of Expected Elbow Torque in an Extravehicular Activity Suit Sleeve

Abstract

Extravehicular Activity (EVA) spacesuits have been developed since the early 1960s to protect astronauts from their environment outside of the spacecraft. EVA suits must protect astronauts in extreme environments while also providing the mobility to support EVA operations such as spacecraft or habitat maintenance and planetary surface exploration. Current testing of spacesuits to ensure sufficient mobility is performed with the crewmember in the suit. An alternative method of evaluating the mobility of EVA suits would be to use robotic systems to measure fit and performance metrics such as joint torque and contact pressure between the suit and the inhabitant. In this research, the Robotic Arm for Evaluating Spacesuit Torque and Contact (RAESTAC) was developed to capture joint torque at the elbow joint of a Size 4 EMU pressure garment and create a framework to measure contact pressure at the anterior forearm, bicep, and olecranon in future work. RAESTAC will be used in the Aerospace Human Systems Lab (AHSL) to validate a Finite Element Analysis (FEA) model of a soft fabric EMU spacesuit sleeve that was developed by Dr. Dillon Hall and Dr. Bonnie J. Dunbar. RAESTAC incorporates a 3D printed arm into an inflated lower arm pressure garment assembly, modeled after the Extravehicular Mobility Unit (EMU). Driven by steel wire cables attached to a servo motor, a gear train assembly and two S-type load cells, the RAESTAC system rotates the 3D printed arm at the elbow through a 120-degree arc at pressure garment pressures of 0-4.3 psid. It was demonstrated that RAESTAC was capable of measuring elbow joint torque as a function of elbow joint angle and pressure garment air pressure (0-4.3 psid). The results presented in this thesis show that the data obtained by RAESTAC are within the range of published literature and could be used to test future EVA suit pressurized soft fabric joint designs.