Passive safe falling of humanoid robots

Abstract

This thesis reports the study of the problem of passive safe falling of the humanoid robot TORO (TOrque controlled humanoid RObot) developed by DLR (German Aerospace Center) in Oberpfafenhoffen, Germany. Passive falling refers to all those cases when control of the robot during fall is difficult or even not possible. Since the control is not available, this kind of phenomenon can be made safe only through the implementation of protective gear. Analyzing deeply the characteristics of TORO and studying the state of the art of the problem, airbags are individuated as the technology that best matches the requirements of this kind of application. The idea is to develop an experimental campaign to study the phenomenon and the effectiveness of airbags. Since it is too dangerous to make the experiments directly with TORO, as it was not designed for safe falling, a mockup of the robot is designed and built to match both kinematic and inertial characteristics. Then different airbag solutions are realized and implemented. The mockup is then tested by falling in different poses with and without airbags and accelerations of hip and chest are acquired through accelerometers. Merging the knowledge acquired from experiments with theoretical relations we develop an analytical model to describe the phenomenon. The model is a 3D representation of the robot, replicating its volume and mass distribution. This information is then used to identify direction of fall, contact points and dynamics of the fall and impacts. Using the estimated dynamics, we can estimate the times, decelerations and forces involved in the fall. The model results are then compared with the experimental ones. This kind of model can be used as a framework for improvement of airbag design, inflation/deflation control logics and estimation of forces/decelerations for cases different than the tested ones. The learnings can potentially be used as a basis to design future more robust humanoids.