Author: Anthony J. NejmanPublisher:
ISBN:
Category :
Languages : en
Pages : 116
Book Description
A mechanical exoskeleton has the capacity to replicate the properties of a pressurized space suit with regards to motion resistance. Using such an exoskeleton for ground based mission training and research provides a lower-cost, less operationally-complex alternative to using a space suit. To that end, NASA is supporting the development of such a device, termed a Space Suit Simulator (S3). The S3 must be designed to allow the wearer the same range of motion allowed in a space suit, and the joints must be actuated to produce the experienced resistive torques. The challenge moving forward is to develop a lower limb (ankle, knee, hip) exoskeleton and then a whole-body exoskeleton that includes multiple interconnected joints with some joints having multiple degree-of-freedom, such as the hip and shoulder. A kinematic design of the lower-body exoskeleton was developed by using Denavit-Hartenberg notation and transformation matrices to derive the Jacobian matrix, which was in turn used to develop a method of testing for singular configurations along a given path of motion. The S3 was tested for singularities while operating through a standard walking gait cycle, and no singularities were uncovered. Translational manipulability of the S3 end effector was analyzed at near-singular configurations along the gait cycle to determine directions of motion which may result in increased joint torques or loss of freedom of motion. A graphical representation of the leg and S3 end effector workspace verified that the S3 allows the human leg to move within the operational envelope anticipated during space suit use. The four degree-of-freedom exoskeleton design eliminates constrictive singularities by aligning human and exoskeleton joint axes. A computational algorithm, based on the Preisach hysteresis model, was used to mimic space suit joint hysteresis behavior in knee flexion and hip abduction/adduction, and it was demonstrated that linear actuators may be used to produce the required joint torque resistance. The kinematic design and computational hysteresis algorithms will support the further development of a physical space suit simulator.
