The impact of event-triggered control on the energy consumption of a legged robot

Abstract

In event-triggered control (ETC) the control task is only executed when needed to ensure performance or stability. A well known property of ETC is that it can reduce the number of control task executions while retaining similar performance. A large amount of research is focused on how ETC can be used to achieve energy savings in wireless networked control systems. However, the effect of ETC on the actuation energy consumption and whether it could be used as a strategy to achieve actuation energy savings has been unexplored. This thesis presents a study of the impact of ETC on the energy consumption of a legged robot. The focus is on the control task of balancing the robot on top of its legs. To perform this study, a system allowing real-time control and energy monitoring of the robot is developed. This system allowed an experimental comparison between a standard periodic time-triggered controller and a periodic event-triggered controller. Three experiments were performed that enabled time-triggered control and ETC to be compared during transients. The results show that ETC is capable of affecting the energy consumption while reducing the number of control updates. During the first two experiments the system was brought into a transient state by starting the system from nonzero initial conditions. During the third experiment a disturbance was applied on the control input of one leg pair. In the first experiment the energy consumption during ETC increased with 3.0% while in the second and third experiment the energy consumption decreased with 3.2% and 7.8% respectively. These differences occurred while reducing the number of control updates by at least 35.9%. Analysis of the results suggest that the differences in energy consumption are due to the different control input during ETC combined with the effect of unmodeled dynamics.