How leg/foot compliance and posture affects impact forces during landing

Current legged robots are brittle and fragile when performing a wide range of locomotion tasks. This can be the case during the execution of dynamic locomotion trajectories such as jumping or hopping where impact forces can significantly increase and reach levels of an order of magnitude higher than the gravitational/weight forces of the robot. Legged robots like humanoids with rigid and heavy feet can generate high impact forces during the landing contact with the ground. These can effectively damage the leg/foot, its actuation and structure. This paper study the effect of compliance on a leg/foot system which incorporates intrinsic elasticity both in the joint level and the foot We study how configuration dependent Cartesian inertia and joint level stiffness and damping affect the impact. Based on this a landing motion strategy is proposed to reduce the impact force. To determine landing motion property of multi D.O.F leg we used a non-linear contact model and multi-body dynamics simulation and considered a floating base model. Results demonstrate how the proposed strategies can protect the components of a leg from impacts.