The Sensitivity of the Static Center of Pressure as a Criterion to assess Balancing Controllers Performance

Legged locomotion has received increasing attention from the robotics community. Contacts stability plays a critical role in ensuring that robots do not fall and it is a key element of balancing and walking controllers. The Center of Pressure is a contact stability criterion that defines a point which must be kept strictly inside the support polygon in order to ensure postural stability. We introduce the concept of the sensitivity of the static center of pressure, roughly speaking the rate of change of the center of pressure with respect to the system equilibrium configurations, as an additional criterion to assess the robustness of the contact stability. We show how this new concept can be used as a metric to assess balancing controllers performance and we apply it to evaluate the performance of two different balancing controllers. The analytical analysis is performed on a simplified model and validated during balancing tasks on the iCub humanoid robot.