Optimal bipedal robot walking on an inclined surface

The role played by the trunk in gait is relatively unexplored in the literature. Considering that the upper body makes up two third of the body weight and to look at its role as being purely passive is a puzzling hypothesis. This paper investigates the postural strategies to adapt to walking on an inclined surface. Results show that after heel strike the upper body tends to rotate slightly backward over the stance leg to absorb the impact following heel strike, followed by mostly forward swaying, causing horizontal accelerations of the trunk. The fluctuation of the leg length is decreasing at the beginning of the step then increases at the end. This can be explained by the contraction of the muscles and the flexion of the knee and the ankle before push off and at heel strike. Further, the stance leg behaves like an inverted pendulum swinging about the stance foot for most of the step period. The upper body has a role during walking on slope. The torso leans down on the slope to help propel the body forward.