Abstract
The development of powered assistive devices that integrate exoskeletal motors and muscle activation for gait restoration benefits from actuators with low backdrive torque. Such an approach enables motors to assist as needed while maximizing the joint torque muscles, contributing to movement, and facilitating ballistic motions instead of overcoming passive dynamics. Two electromechanical actuators were developed to determine the effect of two candidate transmission implementations for an exoskeletal joint. To differentiate the transmission effects, the devices utilized the same motor and similar gearing. One actuator included a commercially available harmonic drive transmission while the other incorporated a custom designed two-stage planetary transmission. Passive resistance and mechanical efficiency were determined based on isometric torque and passive resistance. The planetary-based actuator outperformed the harmonic-based actuator in all tests and would be more suitable for hybrid exoskeletons.
Highlights
IntroductionCommercial exoskeletons provide interventions for improving mobility after paralysis [5,6,7]
Actuators 2021, 10, 203. https://With an estimated 17,000 new cases of spinal cord injury (SCI) per year [1], restoration of standing and walking are consistently rated as top priorities for people with SCI [2,3,4].Commercial exoskeletons provide interventions for improving mobility after paralysis [5,6,7].These devices have been optimized for functional replacement, with the robotic device providing all of the joint torques required for motion
Future testing of a complete exoskeleton platform will reveal what joint torque is required to facilitate high speed hybrid gait. It is clear the planetary transmission is the superior transmission—isometric torque increased by 38% while passive resistance decreased by approximately 30% across all joint speeds compared to the harmonic transmission
Summary
Commercial exoskeletons provide interventions for improving mobility after paralysis [5,6,7] These devices have been optimized for functional replacement, with the robotic device providing all of the joint torques required for motion. This approach is effective for people without any volitional movement. These robot-enabled gait devices typically follow preprogrammed kinematic trajectories, without any influence from the user. With this control scheme, passive dynamics such as joint friction are not an important consideration in the design process; instead, the focus is on overall device size, weight, and ease of use. The goal is to make a robotic system that is as unintrusive to the wearer as possible
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