# Differentially-Driven Robots Moving in Formation--Leader-Follower Approach
###### Abstract  
The paper is devoted to the leader-follower approach for multiple mobile robots control and its experimental verification. The formation control of mobile robots is motivated by the concept of virtual leader tracking, which is enhanced by the collision avoidance between the robots proposed in our previous work. The effectiveness of this approach was verified through realisation of experiments with use of MTacker mobile robots. The OptiTrack vision system was used for robots localization. Software part with control algorithms and communication was prepared with use of the Robot Operating System. leader-follower control; collision avoidance; experimental verification +
Footnote †: journal: Applied  
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formation. This solution is similar to the one presented in reference [13], but a different definition of trajectory was considered. The Authors of [11] have additionally carried out interesting experiments where the synchronization controller was checked during the disturbance. The research study [12] develops the controller with trajectory tracking task with use of suboptimal model predictive control in two variants. Both solve optimal control problem where cost function involve the dynamics model of robot. The terminal state penalty term utilizes a potential function. Unfortunately in comparison to [11], this paper research results were only supported by simulation studies. A large number of research concerning cooperative control of mobile robots formation uses potential functions. For example [14] where the controller synthesis is based on proposition of potential function that obtains the minimum value in the situation of achieving the desired formation, whereas for collision occurrence, the potential function goes to infinity. Proposed solutions ensure almost global asymptotic convergence of formation shape and orientation with guarantee that no collision appears. Another interesting solution considering the use of potential function is discussed in reference [15]. The Author considers formation control of mobile robots with nonholonomic constraints and utilizes linear feedback technique and collision avoidance appearing between agents. A potential function is used to determine a repulsive vector in the controller. This solution ensures rapid convergence of formation to desired trajectory thanks to a goal exchanged algorithm. Some important aspects in formation control concern practical matters and, for example [16] presents cooperative motion coordination for mobile robots using vision-based control. The Authors consider formation control in obstacle environment under sensing (in terms of visibility) and communication constraints. The solution allows for safe navigation of the formation with use of only the minimal information obtained from vision-based feedback. In the proposed solution, the velocity estimates was not exchanged between robots. This ensures proper behaviour of the controller in case of no communication between robots. Moreover, the on-board cameras used as localization sensors are assumed to deliver limited range of field-of-view. Thanks to these properties the controller has very strong practical features. Other propositions concerning some practical aspects of mobile robots formation control can be found in references [17; 18]. In reference [17], vision-based control with on-board camera and absence of the feature depth information is presented. In the paper [18] formation control with lack of the orientation measurements is described. Instead of attitude measurements, the Authors used designed observer. Another general idea of leader-follower control is discussed in reference [19]. In this paper, control for heterogeneous underactuated vehicles network in planar case is proposed. This concept implies that the vehicles do not have to be identical and may have a different dynamic structure.