Why Should Robots in Unstructured Environments Perform a Dynamically Balanced Regular Gait ?

During a day, moving in an unstructured environment, man is realizing different types of walk, requiring from him on-line trajectory planning and permanent changes of gait parameters (turning, stopping, speeding up and slowing down, switching from the walk on a flat ground to the walk on inclined surfaces or staircases, etc.). Besides, apart from realizing the motion, there appears frequently the need to perform some additional tasks, e.g. manipulation. In view of the expectation that the future robots will share with humans their living and working environment, it is expected from them to be endowed with similar capabilities of motion. We think that a necessary prerequisite for fulfilling all these tasks is a permanent maintenance of dynamic balance, which may be achieved by the realization of a regular gait. Therefore, one of the basic characteristics of regular bipedal walk of humanoid robots is the maintenance of their dynamic balance during the walk, whereby a decisive role is played by the unpowered degrees of freedom arising at the foot-ground contact. Hence, the role of Zero-Moment Point (ZMP) as an indicator of dynamic balance is indispensable. On the other hand, we are witnesses of the diverse realizations of locomotion systems, from those with human-like feet, aiming to mimic in full the human gait, passive walkers, which practically roll on specially profiled feet, to the footless locomotion systems. It is quite clear that any of these systems can realize a gait (very often such gait is not dynamically balanced), but our present study shows that the performances of such walking systems are essentially different and inapt to meet the requirements that are put before the humanoids in a human environment. The work points out the indispensability of the regular, fully dynamically balanced gait for the simultaneous realization of locomotion-manipulation activities, as well as for the walk in an unstructured environment.

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