The design and development of a high-performance robotic device is a process with numerous competing factors. The mechanism weight and stiffness exist at opposite ends of the spectrum, the goal being to achieve the highest structural rigidity while maintaining the lowest segmental inertias. Contributing to these underlying requirements are factors such as the operational workspace, desired joint torques, motor placement, link design and cable selection. Since the device will operate in direct contact with humans, additional requirements emerge regarding comfort and safety of operation.

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Biomechanical experiments suggest that it may be possible to build a leg exoskeleton to reduce the metabolic cost of walking while carrying a load. A quasi-passive, leg exoskeleton is presented that is designed to assist the human in carrying a 75 lb payload. The exoskeleton structure runs parallel to the legs, transferring payload forces to the ground. In an attempt to make the exoskeleton more efficient, passive hip and ankle springs are employed to store and release energy throughout the gait cycle. To reduce knee muscular effort, a variable damper is implemented at the knee to support body weight throughout early stance.

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Exoskeleton robots are promising assistive/rehabilitative devices that can help people with force deficits or allow the recovery of patients who have suffered from pathologies such as stroke. The key component that allows the user to control the exoskeleton is the human machine interface (HMI). Setting the HMI at the neuro-muscular level may lead to seamless integration and intuitive control of the exoskeleton arm as a natural extension of the human body. At the core of the exoskeleton HMI there is a model of the human muscle, the “myoprocessor,” running in realtime and in paral-lel to the physiological muscle, that predicts joint torques as a function of the joint kinematics and neural activation levels. This paper presents the development of myoprocessors for the upper limb based on the Hill phenomenological muscle model. Genetic algorithms are used to optimize the internal parameters of the myoprocessors utilizing an experimental database that provides inputs to the model and allows for performance assessment. The results indicate high correlation between joint moment predictions of the model and the measured data. Consequently, the myoprocessor seems an adequate model, sufficiently robust for further integration into the exoskeleton control system.

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Techniques are provided for controlling an exoskeleton actuator at a joint of a human-exoskeleton system by receiving system parameters for the human-exoskeleton system, receiving generalized coordinates for the human-exoskeleton system, and determining an equivalent joint torque for the exoskeleton actuator to compensate for a selected force. While providing partial or complete compensation of selected gravitational and external forces, one embodiment of the present invention mitigates the amount of interference between voluntary control and assist control, thereby allowing humans to quickly humans adapt to an exoskeleton system.

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The purpose of this study was to investigate the metabolic cost of wearing a prototype exoskeleton (EXO) while walking with a range of heavy loads, and to analyze the associated gait biomechanics. Ten Army enlisted men participated in the study. Oxygen consumption (VO2) and gait biomechanics were measured while Soldiers walked at 4.83 km/h and 0% grade under three realistic load weight configurations that were comprised of Army clothing and equipment: fighting load (20 kg), approach march load (40 kg), and emergency approach march load (55 kg). The volunteers were tested under all load configurations with and without wearing the EXO prototype. Mean VO2 significantly increased while wearing the EXO compared to not wearing the EXO across all conditions. Mean VO2 scaled to body mass and scaled to total mass also significantly increased while wearing the EXO. Mean VO2 and mean VO2 scaled to body mass significantly increased with load, however, there were no significant EXO by load interaction effects for both the non-scaled and scaled VO2. The kinematic and kinetic data revealed significant changes when wearing EXO compared to not wearing EXO. In summary, volunteers walked with shorter and faster strides; maintained a more flexed posture with reduced movement at the individual leg joints; braked with higher ground reaction forces at heel strike; and pushed off with lower force at toe off. This study demonstrated that use of an exoskeleton prototype increases users’ metabolic cost while carrying various loads and alters their gait biomechanics compared to conventional load carriage using a backpack.

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