Joints are failure points for deployable systems and moving devices. Their reliability is therefore of great concern for space applications. Efficiency is also critical as the power budgets are limited in space and energy dissipation must therefore be avoided. Weight and dimensions must be reduced as much as possible since they have a direct impact on launch costs and thus on space mission budgets. A new type of joint design that meets the extensive and demanding space requirements would be of great use. This study tries to retrieve interesting mechanisms in the huge pool of clever designs from nature. The number of species of insects is truly awesome, for example there are over 600,000 scientifically described species of beetles with at least twice that number remaining to be disco-vered and described. And beetles are only one type of insect. To put that number in perspective, there are probably around 10,000 species of birds, and maybe 4,000 species of mammals. The total number of interes-ting mechanisms in insect species, birds and mammals is almost beyond imagination. In this work a biomime-tic approach is used in order to assess the possibility of improving robotic joints for space applica-tions. The work concerns the identification of classes of joints in nature which could inspire the design of a feasible system in which the mechanical subsystem and the actuation subsystems are merged. This report presents a study with the overall goal of finding biological articulation concepts which, when tran-slated to a mechanical equivalent, can improve performance of articulated robot systems for space applications.

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Metabolic studies have shown that there is a metabolic cost associated with carrying load [1]. In previous work, a lightweight, underactuated exoskeleton has been described that runs in parallel to the human and supports the weight of a payload [2]. A state-machine control strategy is written based on joint angle and ground-exoskeleton force sensing to control the joint actuation at this exoskeleton hip and knee. The joint components of the exoskeleton in the sagittal plane consist of a force-controllable actuator at the hip, a variable-damper mechanism at the knee and a passive spring at the ankle. The control is motivated by examining human walking data. Positive, non-conservative power is added at the hip during the walking cycle to help propel the mass of the human and payload forward. At the knee, the damper mechanism is turned on at heel strike as the exoskeleton leg is loaded and turned off during terminal stance to allow knee flexion. The passive spring at the ankle engages in controlled dorsiflexion to store energy that is later released to assist in powered plantarflexion. Preliminary stu- dies show that the state machines for the hip and knee work robustly and that the onset of walking can be detected in less than one gait cycle. Further, it is found that an efficient, underactuated leg exoske-leton can effectively transmit payload forces to the ground during the walking cycle.

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