The exoskeleton is an external structural mechanism with joints and links corresponding to those of the human body. Worn by the human, the exoskeleton transmits torques from proximally located actuators through rigid exoskeletal links to the human joints. This paper presents the development of an anthropometric seven degree-of-freedom powered exoskeleton for the upper limb. The design was based on a database defining the kinematics and dynamics of the upper limb during daily living activities, as well as joint physiological and upper limb anatomical considerations, workspace analyses, and joint ranges of motion. Proximal placement of motors and distal placement of pulley reductions were incorporated into the design of a cable-driven wearable robotic arm. This design led to low inertias, high-stiffness links, and back-drivable transmissions with zero backlash. Potential applications of theexoskeleton as a wearable robot include use as: (1) a therapeutic and diagnostics device for physiotherapy, (2) an assistive (orthotic) device for human power amplifications, (3) a haptic device in virtual reality simulation, and (4) a master device for teleoperation.

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Integrating human and robot into a single system offers remarkable opportunities for creating a new generation of assistive technology. Having obvious applications in rehabilitation medicine and virtual reality simulation, such a device would benefit both the healthy and disabled population. The aim of the research is to study the kinematics and the dynamics of the human arm during daily activities in a free and unconstrained environment as part of an on-going research involved in the design of a 7 degree of freedom (DOF) powered exoskeleton for the upper limb. The kinematics of the upper limb was acquired with a motion capture system while performing a wide verity of daily activities. Utilizing a model of the human as a 7 DOF system, the equations of motion were used to calculate joint torques given the arm kinematics. During positioning tasks, higher angular velocities were observed in the gross manipulation joints (the shoulder and elbow) as compared to the fine manipulation joints (the wrist). An inverted phenomenon was observed during fine manipulation in which the angular velo-cities of the wrist joint exceeded the angular velocities of the shoulder and elbow joints. Analyzing the contribution of individual terms of the arm’s equations of motion indicate that the gravitational term is the most dominant term in these equations. The magnitudes of this term across the joints and the various actions is higher than the inertial, centrifugal, and Coriolis terms combined. Variation in object grasping (e.g.power grasp of a spoon) alters the overall arm kinematics in which other joints, such as the shoulder joint, compensate for lost dexterity of the wrist. The collected database along with the kinematics and dynamic analysis may provide the fundamental understanding for designing powered exoske-leton for the human arm.

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Recent research into the mechanics of walking indica-tes that a quasi passive wearable device could be created which dramatically reduces the metabolic energy used in walking especially when the wearer is carrying additional torso weight. Target population groups include military personnel who must carry heavy battle packs and body armor, hikers, letter carriers, and the quasi disabled. This latter group includes a significant fraction of the elderly who have reduced leg strength and/or higher weight torsos. The device is called PUUMA, an acronym for Personal Unpowered Univer-sal Mobility Assistant. Though walking has been studied extensively, there appears to be a limited under-standing of the interplay between the kinetic and potential energy of the torso when driven by legs that can store and release energy. This thesis introduces a simplified model which enables simulation of the entire walking process including the epoch following heel strike. One simulation goal was to explore the knee spring properties which enable lossless walking. Simulations show that there are two knee spring con-figurations which allow for lossless walking. It is also shown that the percentage of kinetic energy trans-ferred to a knee spring can be a significant fraction of the torso kinetic energy. PUUMA’s basic idea is the incorporation of torsion springs at the knee joints which absorb torso kinetic energy following heel strike and then release that stored energy later in the step. An application of the capstan effect is introduced which enables a practical implementation of two knee spring configurations. In particular, the design allows the thigh and shank to be dynamically coupled to a microprocessor controlled knee spring thereby allowing both unimpeded leg swing and kinetic energy transfer to the knee spring. Another use of the capstan effect is introduced which allows for a microprocessor controlled brake that can freeze the knee at its maximum torsion and then release it later in the walking cycle. A design is shown which embo-dies the architectural ideas created. Several of the key components were designed, prototyped and tested.

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Exoskeletons for human performance augmentation are controlled and wearable devices that can increase the speed, strength, and endurance of the operator. To help those who need to travel long distances by feet with heavy loads such as infantry soldiers, we are developing a lower extremity exoskeleton for human performance enhancement at the Nanyang Technological University (NTU). Together with the exoskeleton linkages, an exoskeleton foot is designed to measure the human and the exoskeleton’s ZMP. By using the measured human ZMP and the human leg position signals, the exoskeleton’s ZMP can be modified by trunk compensation. Simulation results are demonstrated and the prototype being developed is introduced.

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Space-suited activity is critical for human space-flight, and is synonymous with human planetary exploration. Space suits impose kinematic and kinetic boun-dary conditions that affect movement and locomotion, and in doing so modify the metabolic cost of physical activity. Metabolic requirements, found to be significantly elevated in space-suited activity, are a major driver of the allowable duration and intensity of extravehicular activity. To investigate how space suited locomotion impacts the energetics of walking and running, I developed a framework for analyzing energetics data, derived from basic thermodynamics, that clearly differentiates between muscle efficiency and energy recovery. The framework, when applied to unsuited locomotion, revealed that the human run-walk transition in Earth gravity occurs when energy recovery for walking and running are approximately equal. The dependence of muscle efficiency on gravity -during locomotion and under a particular set of assumptions- was derived as part of the framework. Next, I collected and transformed data from prior studies of suited and unsuited locomotion into a common format, and performed regression analysis. This analysis revealed that in reduced gravity environments, running in space suits is likely to be more efficient, per unit mass and per unit distance, than walking in space suits. Second, the results suggested that space suits may behave like springs during running. To investigate the spring-like nature of space suit legs, I built a lower-body exoskeleton to simulate aspects of the current NASA spacesuit, the Extravehicular Mobility Unit (EMU). Evaluation of the exoskeleton legs revealed that they produce knee torques similar to the EMU in both form and magnitude. Therefore, space suit joints such as the EMU knee joint behave like non-linear springs, with the effect of these springs most pronounced when locomotion requires large changes in knee flexion such as during running. To characterize the impact of space suit legs on the energetics of walking and running, I measured the energetic cost of locomotion with and without the lower-body exoskeleton in a variety of simulated gravitational environments at specific and self-selected Froude numbers, non-dimen-sional parameters used to characterize the runwalk transition. Exoskeleton locomotion increased energy re-covery and significantly improved the efficiency of locomotion, per unit mass and per unit distance, in reduced gravity but not in Earth gravity. The framework was used to predict, based on Earthgravity data, the metabolic cost of unsuited locomotion in reduced gravity; there were no statistical differences between the predictions and the observed values. The results suggest that the optimal space-suit knee- oint torque may be non-zero: it may be possible to build a ‘tuned space suit’ that minimizes the energy cost of locomotion. Furthermore, the observed lowering of the self-selected run-walk transition Froude number during exoskeleton locomotion is consistent with the hypothesis that the run-walk transition is mediated by energy recovery.

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