Series Elastic Actuators provide many benefits in force control of robots in unconstrained environments. These benefits include high force fidelity, extremely low impedance, low friction, and good force control bandwidth. Series Elastic Actuators employ a novel mechanical design architecture which goes against the common machine design principal of “stiffer is better”. A compliant element is placed between the gear train and driven load to intentionally reduce the stiffness of the actuator. A position sensor measures the deflection, and the force output is accurately calculated using Hooke’s Law (F=Kx). A control loop then servos the ac-tuator to the desired output force. The resulting actuator has inherent shock tolerance, high force fidelity and extremely low
impedance. These characteristics are desirable in many applications including legged robots, exoskeletons for human performance am-plification, robotic arms, haptic interfaces, and adaptive suspensions. We describe several variations of Series Elastic Actuators that have been developed using both electric and hydraulic components.

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Current State of Powered Gait Devices.

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Many devices are available on the market for the evaluation and rehabilitation of patients suffering from muscular disorders. Most of them are small, low-cost, passive devices based on the use of springs and resistive elements and exhibit very limited (or even not any) evaluation capabilities; extended muscular force evaluation is only possible on stationary, expensive, multi-purpose devices, available only in hospitals, which offer many exercise modes (e.g. isokinetic mode) that are not available on other devices. The objective of this thesis is to make the functionalities currently only implemented on bulky multi-purpose devices available at a lower cost and in a portable fashion, enabling their use by a large number of independent practitioners and patients, even at home (tele-medecine applications). In order to achieve this goal, a portable rehabilitation device, using a magneto-rheological fluid brake as actuator, has been designed. This particular technology was selected for its high level of compactness, simple mechanical design, high controllability, smooth and safe operation. The first part of this thesis is devoted to the design of MR-fluid brakes and their experimental validation. The second part is dedicated to the design of the rehabilitation device and the comparison of its performances with a commercial multi-purpose device (CYBEX).

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Kinematic and dynamic models of a human body are presented. The models intend to represent paraplegics wearing a powered exoskeleton. The proposed exoskeleton fully controls the motion of the hip and knee joints, i.e., each lower extremity contains four actuators, three at the hip joint and one at the knee joint. A spring-loaded ankle-foot orthosis completes the exoskeleton. The kinematic model involves a large number of degrees of freedom, 34-DOF. The dynamic model presents a general formulation that can be implemented for any human task – walking, running, jumping, climbing stairs, etc. Traditional dynamic models simplify the motion of bipeds by considering a limited number of movements contained in the sagittal plane and by focusing on a particular task. A 3D model of a human body has been developed to simulate motion.

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A lower extremity exoskeleton, configurable to be coupled to a person, includes: leg supports configurable to be coupled to the person’s lower limbs and designed to rest on the ground during stance phases, with each leg support having a thigh link and a shank link; two knee joints, each configured to allow flexion and extension between respective shank and thigh links; an exoskeleton trunk configurable to be coupled to the person’s upper body, rotatably connectable to the thigh links of the leg supports, allowing for the flexion and extension between the leg supports and the exoskeleton trunk; two hip actuators configured to create torques between the exoskeleton trunk and the leg supports; and at least one power unit capable of providing power to the hip actuators. In use, power is supplied to the hip actuators in an amount to reduce the energy consumed by a user during a walking cycle.

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