Modeling and Control Methods for Supporting Scapulohumeral Rhythm with a Robotic Exoskeleton

The shoulder is a highly mobile joint complex that depends on the movements of three component articulations. Biomechanics research has shown an inherent coordination pattern among these joints during various movements, which has been termed scapulohumeral rhythm (SHR). This motion is considered important for proper shoulder function, and alterations in this coordination have been correlated with an increased risk for impingement and other musculoskeletal injuries. A tiger team review found that contemporary space suit (Extravehicular Mobility Unit, or EMU) designs limited the shoulder motion of crewmembers and contributed to shoulder injuries experienced during training. While current NASA efforts are being made to address this issues in upcoming suit designs, other restrictions on suit geometry or operating conditions are difficult to address with these methods. These include additional resistance from suit pressurization and fatigue during extended extravehicular activity (EVA). One possible solution is to use robotic devices, such as powered exoskeletons, in tandem with these suit changes. Providing direct support for proper shoulder motion in the presence of configuration- and time-dependent disruptions could reduce the risk of shoulder injury and improve EVA performance. The goal of this research is to explore robotic exoskeletons as a means to correct and support proper shoulder complex motion in the presence of environmental and physiological disturbances. This will begin with the development a novel kinematic model of the shoulder complex that can be used to estimate the configuration of the scapula. The model will use a reduced set of measurements relative to traditional motion capture methods, which are infeasible in highly occlusive environments. This will be followed by the design and evaluation of a mechanism for directly mobilizing the scapula during various tasks. This system will be compared with an existing upper body exoskeleton in terms of range of motion, joint loads, and other dynamic properties. This work will conclude with the formulation of robot control strategies for supporting and modifying scapular motion. These algorithms will be responsive to pressurized suit resistance, variable loading from tool use, and crewmember fatigue. This research will use Harmony, an existing upper body exoskeleton in the ReNeu Robotics Lab, as a platform for testing these concepts. The project will also utilize NASA resources on astronaut anthropometry and EMU characteristics to ensure applicability to mission objectives. The outcomes of this work will support Technical Areas 7.3 (Human Mobility Systems) and 6.2 (Extravehicular Activity Systems) by furthering knowledge of shoulder biomechanics and exploring new methods to reduce the incidence of EVA injury. In the future, these findings can support the development of assistive exoskeletons for use in both spaceflight and planetary missions. The shoulder is a highly mobile joint complex that depends on the movements of three component articulations. Biomechanics research has shown an inherent coordination pattern among these joints during various movements, which has been termed scapulohumeral rhythm (SHR). This motion is considered important for proper shoulder function, and alterations in this coordination have been correlated with an increased risk for impingement and other musculoskeletal injuries. A tiger team review found that contemporary space suit (Extravehicular Mobility Unit, or EMU) designs limited the shoulder motion of crewmembers and contributed to shoulder injuries experienced during training. While current NASA efforts are being made to address this issues in upcoming suit designs, other restrictions on suit geometry or operating conditions are difficult to address with these methods. These include additional resistance from suit pressurization and fatigue during extended extravehicular activity (EVA). One possible solution is to use robotic devices, such as powered exoskeletons, in tandem with these suit changes. Providing direct support for proper shoulder motion in the presence of configuration- and time-dependent disruptions could reduce the risk of shoulder injury and improve EVA performance. The goal of this research is to explore robotic exoskeletons as a means to correct and support proper shoulder complex motion in the presence of environmental and physiological disturbances. This will begin with the development a novel kinematic model of the shoulder complex that can be used to estimate the configuration of the scapula. The model will use a reduced set of measurements relative to traditional motion capture methods, which are infeasible in highly occlusive environments. This will be followed by the design and evaluation of a mechanism for directly mobilizing the scapula during various tasks. This system will be compared with an existing upper body exoskeleton in terms of range of motion, joint loads, and other dynamic properties. This work will conclude with the formulation of robot control strategies for supporting and modifying scapular motion. These algorithms will be responsive to pressurized suit resistance, variable loading from tool use, and crewmember fatigue. This research will use Harmony, an existing upper body exoskeleton in the ReNeu Robotics Lab, as a platform for testing these concepts. The project will also utilize NASA resources on astronaut anthropometry and EMU characteristics to ensure applicability to mission objectives. The outcomes of this work will support Technical Areas 7.3 (Human Mobility Systems) and 6.2 (Extravehicular Activity Systems) by furthering knowledge of shoulder biomechanics and exploring new methods to reduce the incidence of EVA injury. In the future, these findings can support the development of assistive exoskeletons for use in both spaceflight and planetary missions. More »