Upslope walking with transfemoral prosthesis using optimization based spline generation

Powered transfemoral prostheses are robotic systems that aim to restore the mobility of transfemoral amputees by mimicking the functionalities of healthy human legs. The advantage of using a powered prosthetic device is the enhanced performance on various terrains. One of the most frequent terrain found during daily locomotion (other than flat ground) is the surface with slope. In this work, we introduce a framework to generate upslope walking gaits automatically utilizing an online algorithmic formulation. This approach is inspired from analyzing human gait characteristics during upslope walking. In particularly, it is found that the ankle and knee trajectories of upslope walking share a similar pattern with flat ground walking during the middle section (from 20% to 80%) of one step. This observation motivates us to propose an approach of blending the first portion of nominal flat ground gaits with a set of cubic splines to achieve upslope gaits. Importantly, parameters of these cubic splines are solved using an online optimization, which gives the users ability to traverse in different terrains without using any intention detection algorithm. For the last portion of a step, an impedance controller with low gains is considered upon the contact of prosthetic legs to the ground, which allows the users to step onto unknown terrains. The proposed framework is validated on a custom transfemoral prosthesis AMPRO II with showing automatic motion switches between flat ground and upslope walking.