Multi-objective control in human walking: insight gained through simultaneous degradation of energetic and motor regulation systems

Minimization of metabolic energy is considered a fundamental principle of human locomotion, as demonstrated by an alignment between the preferred walking speed (PWS) and the speed incurring the lowest metabolic cost of transport. We aimed to (i) simultaneously disrupt metabolic cost and an alternate acute task requirement, namely speed error regulation, and (ii) assess whether the PWS could be explained on the basis of either optimality criterion in this new performance and energetic landscape. Healthy adults ( N = 21) walked on an instrumented treadmill under normal conditions and, while negotiating a continuous gait perturbation, imposed leg-length asymmetry. Oxygen consumption, motion capture data and ground reaction forces were continuously recorded for each condition at speeds ranging from 0.6 to 1.8 m s −1 , including the PWS. Both metabolic and speed regulation measures were disrupted by the perturbation ( p < 0.05). Perturbed PWS selection did not exhibit energetic prioritization (although we find some indication of energy minimization after motor adaptation). Similarly, PWS selection did not support prioritization of speed error regulation, which was found to be independent of speed in both conditions. It appears that, during acute exposure to a mechanical gait perturbation of imposed leg-length asymmetry, humans minimize neither energetic cost nor speed regulation errors. Despite the abundance of evidence pointing to energy minimization during normal, steady-state gait, this may not extend acutely to perturbed gait. Understanding how the nervous system acutely controls gait perturbations requires further research that embraces multi-objective control paradigms.

Experimental Evaluation of Different Controllers for Cooperative Adaptive Cruise Control

Cooperative Adaptive Cruise Control (CACC) systems which enable vehicle following with tight inter-vehicle head-way offer unique advantage to promote transportation mobility. CACC systems are a step forward the commercially available Adaptive Cruise Control (ACC) systems as they utilize inter-vehicle wireless communication for more advanced control system design. This work studies different wireless communication topologies, i.e., receiving wireless communication from one or more preceding vehicles, and different error-regulation controllers, i.e., linear vs non-linear, for CACC. Through robot following experiments, we show that appropriately designed CACC systems can all achieve vehicle following. For emergency hard braking, however, a non-linear vehicle-following controller which generates strong braking action at short inter-vehicle distances can reduce the risk of collision.

A Frequency Coordination Control Strategy for Islanded Microgrid

This paper investigates a frequency coordination control strategy for islanded microgrid. The dynamic process is divided into three levels including the dynamic support, droop control and zero error regulation. The control strategy is classified into primary and secondary frequency regulation. Simulation is performed on DIgSILENT and the results verify the effectiveness of the proposed control strategy and improve the performance of system frequency regulation.