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A key problem in cooperative robotics is the maintenance of a geometric configuration during movement. As a solution for this, a multi-layered and distributed control system is proposed for the swarm of drones in the formation of hierarchical levels based on the leader-follower approach. The complexity of developing a large system can be reduced in this way. To ensure the tracking performance and response time of the ensemble system, nonlinear and linear control designs are presented; (a) Sliding Mode Control connected with Proportional-Derivative controller and (b) Linear Quadratic Regular with integral action respectively. The safe travel distance strategy for collision avoidance is introduced and integrated into the control designs for maintaining the hierarchical states in the formation. Both designs provide a rapid adoption with respect to their settling time without introducing oscillations for the dynamic flight movement of vehicles in the cases of (a) nominal, (b) plant-model mismatch, and (c) external disturbance inputs. Also, the nominal settling time of the swarm is improved by 44% on average when using the nonlinear method as compared to the linear method. Furthermore, the proposed methods are fully distributed so that each UAV autonomously performs the feedback laws in order to achieve better modularity and scalability. INDEX TERMS Unmanned aerial vehicles (UAVs), distributed control, hierarchical systems.

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In this paper, we present a HRI study that reports on the potential of NAO as a socially assistive robot in Pakistan. Our findings generated through interviewing 2 parents and 5 teachers on the plausibility of using NAO robot as an interaction partner show that both groups welcomed the use of NAO at schools. They, however, were sceptical due to missing NAO's facial expressions and certain body parts such as nose and lips. They also emphasised the importance of creating natural text to speech interface for the Urdu Language. Our findings taken from 7 autistic children to measure their level of social interaction during HRI revealed that children positively engaged with the NAO robot and showed a significant number of both verbal and non-verbal behaviours.