No abstract

The large majority of legged robots currently employ ball-feet or flat-feet. More recently soft feet have been introduced, to improve walking performance on uneven grounds. Nevertheless, their novel adaptability requires sensor systems beyond traditional Force/Torque sensors to estimate the distribution of forces on the contact surface. This paper shows how a perception layer realized with Inertial Measurement Units allows a soft foot to reconstruct not only the shape of the foot -hinting at the shape of the ground beneath -but also, under precise hypotheses, the contact force distribution. The problem is theoretically formalized and analysed with a quasi-static approach in the Sagittal plane. Then, theoretical results are experimentally validated in a simplified foot-ground interaction scenario. The force reconstruction provided by the proposed method allows to correctly identify the sole contact location arising from obstacles with radius down to 1 cm.

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.