Energy expenditure of a biped walking robot: instantaneous and degree-of-freedom-based instrumentation with human gait implications

Abstract

SUMMARYEnergy expenditure (EE) is an important criterion for design and control of biped walking robots. However, the cause-effect analyses enabled by total EE, which is lumped over a time duration and all system degrees-of-freedom (DOFs), are limited. In this study, robotic gait energetics is evaluated through a DOF-based instrumentation system designed for instantaneous evaluation of bidirectional current and applied voltage at each joint actuator. The instrumentation system includes a dual-module arrangement of buffers and attenuators, and accommodates and synchronizes the voltage and current measurements from multiple actuators. For illustrative purposes, this system is implemented at each DC servomotor in a biped robot, DARwIn-OP, to analyze the electrical EE rates for walking at various speeds. In addition, a DOF-based model of instantaneous human EE rate is employed to enable quantitative characterization of robotic walking EE relative to that of humans. The robot's instantaneous lower-body EE rates are consistent with its periodic walking cycle, and their relative trends between single and double support phases are analogous to those of humans. The robotic cost of transport (COT) curve as a function of normalized speed is also consistent with the human COT in terms of its convexity. Conversely, the contrasting distributions of EE throughout the robot and human DOFs and the robotic COT curve's considerably larger magnitudes, smaller speed ranges, and higher sensitivity to speed illustrate the energetic consequences of stable but inefficient static walking in the biped robot relative to the more efficient dynamic walking of humans. These energetic characteristics enable the identification of the joints and gait cycle phases associated with inefficiency in biped robotic gait, and reflect the noticeable differences in the system parameters (rigid and flat versus segmented feet) and gait control strategies (bent versus straight knees, instants of peak ankle actuator torques, static versus dynamic balance stability). The proposed general instrumentation provides a quantitative approach to benchmarking human gait as well as general guidelines for the development of energy-efficient walking robots.

An experimental energy consumption comparison between trajectories generated by using the cart-table model and an optimization approach for the Bioloid robot

“…The high energy consumption at low velocities has been reported for both humans and robots. In their study, Roberts et al 35 present experimental results where the energy consumption at 0.025 m/s was nine times higher than that at 0.15 m/s. Another reason explaining the high COT obtained is the compliance margin and slope of the servomotors, which were configured to their maximal values to guarantee a precise tracking of the reference trajectory.…”

“…This is because during the experimentation we could not guarantee that the robot would walk on a perfect straight path, and as a consequence, the distance traveled by the robot was different from 0.75 m. Our COVs are consistent with those reported in similar experiments. In their study, Roberts et al 35 reported COVs ranging from 5.9% to 12.4% for the energy expenditure of the DARwIn-OP humanoid robot. In the study by Ogura et al, 45 the electrical energy expenditure of the WABIAN robot is measured for three walking styles and two different step lengths (a total of six experimental configurations).…”

“…These values are by far greater than those reported for similar robots. For NAO, 18 the COT ranges between 2.4 and 5.8, and for the DARwIn-OP, 35 from 1.5 to 9.0. The high COT we obtain for the Bioloid is caused by the low gait speeds used during the experiments.…”

“…The largest part of these works present simulation results, 27,[32][33][34] whereas the number of experimental studies is still scarce. 25,35 This imbalance is due to the fact that most simulation studies use simplified models, which are very valuable as proof of concept, but which cannot be considered valid mathematical representations of real robots. For example, in the study of Roussel et al, 32 the Coriolis matrix is not considered, and the studies by Huang and Hase 33 and Tlalolini et al 34 consider bidimensional prototypes.…”

A Model for Economic and Environmental Evaluation of Inter-/Intra-Terminal Containers Flows

“…Robotized gantry cranes, for moving containers, or biped robots for manipulation tasks, such as lifting and carrying heavy weights, are being adopted mainly for high volume handling. Within these applications, biped robots are required to satisfy not only the power requirements [4], but also advanced balancing and locomotion capabilities [5,6], which are critical for carrying loads [7] and that are required to physically interact with the human-made environment [8,9,10]. There are many elements that affect the efficiency of containers flow.…”