Abstract
Adjustable compliant actuators are being designed and implemented in robotic devices because of their ability to minimize large forces due to impacts, to safely interact with the user, and to store and release energy in passive elastic elements. Conceived as a new force-controlled compliant actuator, an adjustable rigidity with embedded sensor and locking mechanism actuator (ARES-XL) is presented in this paper. This compliant system is intended to be implemented in a gait exoskeleton for children with neuro muscular diseases (NMDs) to exploit the intrinsic dynamics during locomotion. This paper describes the mechanics and initial evaluation of the ARES-XL, a novel variable impedance actuator (VIA) that allows the implementation of an add-on locking mechanism to this system, and in combination with its zero stiffness capability and large deflection range, provides this novel joint with improved properties when compared to previous prototypes developed by the authors and other state-of-the-art (SoA) devices. The evaluation of the system proves how this design exceeds the main capabilities of a previous prototype as well as providing versatile actuation that could lead to its implementation in multiple joints.
Highlights
Research focused on rehabilitation and gait assistance has grown rapidly in recent years
New devices try to overcome the bandwidth limitation and improve the performance of Series elastic actuators (SEAs) by incorporating an extra elastic element in the transmission train. These actuators, such as the compact SEA [4], the high-performance SEA [5], and the Compat Rotary SEA [3], improve the force-control performance under a wider range of forces/torques at the device joints when compared to traditional SEAs, the energy storage capability will still depend on the resulting fixed springs constants; a proper selection of the elastic constant based on the application, intended user and control strategy needs to be performed [4]
These devices are incorporated in several powered prosthetics in order to improve their energy efficiency, such as the AMP-Foot 3.0 [22], allowing this ankle prosthetic to change its elastic behavior along gait, while preloading a spring from which energy is released at the push-off at the end of the support phase
Summary
Research focused on rehabilitation and gait assistance has grown rapidly in recent years. New devices try to overcome the bandwidth limitation and improve the performance of SEAs by incorporating an extra (softer) elastic element in the transmission train. These actuators, such as the compact SEA [4], the high-performance SEA [5], and the Compat Rotary SEA (cRSEA) [3], improve the force-control performance under a wider range of forces/torques at the device joints when compared to traditional SEAs, the energy storage capability will still depend on the resulting fixed springs constants; a proper selection of the elastic constant based on the application, intended user and control strategy needs to be performed [4].
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