Design, Modelling, and Experimental Evaluation of a Compact Elastic Actuator for a Gait Assisting Exoskeleton

This paper presents a Transmissive Force Sensing Elastic Actuator (TFSEA) for exoskeleton applications. Exoskeletons can serve as orthotic or rehabilitative devices enabling people with paraplegia to walk. Several exoskeletons have been commercialized, most of which are above 23 kg, making them too heavy and bulky for people with paraplegia to put on and take off by themselves. One of the bottlenecks of achieving lightweight exoskeleton design is actuation. This work focused on developing a compact, lightweight and high-performance actuator. Using the differential property of harmonic drive, a new elastic actuator configuration was created. A dynamic model was developed for the proposed design and a model-based controller was implemented. Various tests were done to evaluate the performance of the actuator. The results showed that the torsional spring exhibits linearity of 99.99%, with no backlash or hysteresis. Thejoint can output 100 Nm peak torque with a large-torque bandwidth of 5 Hz. Moreover, it weighs only 1.56 kg, leading to a torque density of 64 Nm/kg and a power density of 360 W/kg, the highest published to date in the same torque and power rating.