Abstract
The design of bipedal robots is generally fulfilled through considering a sequential design approach, where a synergistic relationship between its structure and control features is not promoted. Hence, a novel integrated structure-control design approach is proposed to simultaneously obtain the optimal structural description, the torque magnitudes, and the on/off time intervals for the control signal input of a semi-passive bipedal robot. The proposed approach takes advantage of the natural dynamics of the system and the control signal activation/deactivation for generating stable gait cycles with minimum energy consumption. Consequently, the passive features of the semi-passive bipedal robot are included in the integrated structure-control design process through evaluating the system behavior along consecutive passive and semi-passive walking stages. Then, the proposed design approach is formulated as a nonlinear discontinuous dynamic optimization problem, where the solution search is carried out using the differential evolution algorithm due to the discontinuities of the semi-passive bipedal robot dynamics. The results of the proposal are compared with those obtained by a sequential design process. The integrated structure-control design achieves a reduction of 63.55% in the value of the performance function related to the synergy between the walking capability and energetic efficiency, with a reduction in the activation of the control and its magnitude of 95.41%.
Highlights
The integrated design problem is solved by the DE algorithm variant DE/rand/1/bin through considering the following algorithm parameters: a population size of NP = 80 individuals and stop criterion Gmax = 6000 are established; the scale factor F and crossover factor CR are randomly assigned at each generation of the optimization process, where the former is taken from the interval 0.3 ≤ F ≤ 0.9 and the latter from 0.8 ≤ CR ≤ 1
A nonlinear discontinuous dynamic optimization problem with mixed design variables is formulated by taking into account the walking capability and energy consumption of the Semi-Passive Bipedal Robot (SPBR)
A comparison between the proposal and a sequential design process indicates that the proposal reduces around 63.55% the value of the performance function related to the synergy between the walking capability and energetic efficiency with respect to the sequential design
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Artificial bipedal walkers are systems that can walk due to the alternated execution of single and double support phases of their legs. The single support or swing phase is defined as the locomotion phase where only one foot is on the ground; the double support phase is described when both feet of the system is in contact with the walking surface [1]. There exist three types of bipedal machines that can develop stable gait cycles [2]. The first type studies the fully actuated bipedal robots that are mechatronic systems where a precise joint-angle control is required to produce bipedal locomotion
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