Humanoids’ Feet: State-of-the-Art & Future Directions

Abstract

Robotic feet play a fundamental role in the walking performance of a biped robot. Feet are essential to maintain dynamic stability and to propel the body during walking. They may ensure stability on uneven terrains. Yet, complex feet are seldom used on humanoids. This paper surveys 36 types of robotic feet we found in the literature. We classified them according to strategy, capabilities, structure, number of degrees of freedom, actuation method of ankle and foot, type of actuator, sensorization and type of control. Subsequently, we analyzed the dynamic and static models of flexible feet. We discussed considerations on foot dynamics or kinematics in the robot’s whole body control system. We analyzed both active joints control for feet including actuated joints, and control for feet with elastic elements (for example, a rubber layer in the sole). Finally, we present some limitations of robotic feet and possible future developments.

A study on the benefits of using variable stiffness feet for humanoid walking on rough terrains

“…Choi et al [18] introduced variable compliant humanoid foot design using a leaf spring and rubber balls in series. This promising approach of variable compliance feet is still very rare in the literature for humanoid robots [19]. For now, the studies of variable stiffness structures are almost entirely limited to the field of prostheses.…”