Abstract Summary
Robot locomotion has become increasingly common to transport and assist humans in complex environments. Even though legged locomotion does not correspond to the most efficient transportation system, in some circumstances it is the only reasonable option to overcome obstacles, as stairs, or to move on rough routes, as slippery and uneven surfaces. As nature has provided ad-hoc solutions, results of the optimization process of the evolution, engineering and robotics have often found inspiration in biological behaviors, generating an entire new field, known as bio-inspired engineering. Most existing quadrupedal robots has been developed only with a single rigid trunk and the actuation is limited to legs and associated joints in order to reduce the complexity of the model to process during the simulations. However the optimization process carried out by the natural evolution shows that most legged vertebrates use flexible spines and supporting muscles to provide auxiliary power during the dynamic behaviors, resulting in higher speeds and lower cost of transport (CoT) during locomotion. In this context, this paper presents a non-linear optimization process to identify the highest performance gaits parameters of a quadruped robot, with a flexible trunk. The optimization process is done using different techniques such as the trajectories optimization carried out through direct or indirect methods and the evolutionary algorithms that are based on a heuristic search inspired by Charles Darwin’s theory of natural evolution and reflects the process of natural selection. Since the identification of the optimal gaits requires the complete definition of the ground reaction forces coupled with the optimal trajectories of the body and its vibrational modes, it is possible to determine what is the influence of the main parameters linked to the vibration of the trunk on the optimal gait resulting from the optimization process. In the final part of the paper is presented a comparison between the results obtained using different optimization techniques and is presented the comparison of the optimal gaits obtained in the case of flexible spine with respect to the case of a rigid trunk to demonstrate the benefits of the elastic model in term of efficiency. Through the observation of the different optimal gait from the two models it is shown that the elastic model permit to find the gallop, often observe in nature, as the output of the optimization process under certain hypothesis and this permit to demonstrate the benefits of the new elastic model of the trunk.
