Hybrid-triggered formation tracking control of mobile robots without velocity measurements

This article focuses on solving the leader-follower formation tracking problem of multiple mobile robots under a hybrid-triggered mechanism without leader's velocity measurements. Two kinds of networks are considered: the detection network, which enables the relative detections by agents' onboard sensors, and the communication network, which is used to implement the transmissions of local information. The followers are divided into two groups based on their detection capacity of leader's information. By merely sensing the relative information from the leader, the first group of followers implement high gain observers to estimate leader's angular and linear velocities. In the rest followers, the transmitted information and relative detections from neighboring agents are used to estimate leader's velocities and position in a distributed way; after that, event-triggered observer-based controllers are proposed to drive the agents toward desirable formation. Periodic event-triggered mechanisms (PETMs) are used to avoid continuous-time checking of event-triggering conditions; and the maximum allowable sampling periods (checking periods and transmission periods) are determined to guarantee the stability of the sampled-data system. Since PETM is only applied in communication networks, the mechanism used in this work is a hybrid-triggered one. Moreover, the inter-sampling (-checking, -transmission) times are allowed to be time-varying and asynchronous. Finally, numerical examples are presented to illustrate the effectiveness and conservativeness of the proposed methods.