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Rigid Payload Transport System with Loosely Coupled RobotsAuthor: Pulkit Verma Date: 2019-08-02 Report no: IIIT/TH/2019/105 Advisor:Kamalakar Karlapalem AbstractPayload Transport is one of the newly explored areas, where a robot or a formation of robots are used to transport a payload from one point to another. Multiple approaches to payload transportation have been carried out using either ground robots or aerial vehicles like drones. A single robot or a drone has an advantage in terms of its low cost and less dependency on other robots but has a single point of failure. Hence various coordinated multi-robot systems came to existence to overcome the disadvantage. We focus on building a multi-robot system which moves in a formation carrying a load from one place to another. We support failure resiliency where if any robot fails, there is always a backup robot available to replace the failed robot. In this thesis, we present a mechanism to handle the failures in a multi-robot system by robot replace- ment. In our work, we use multiple non-holonomic differential drive robots which moves in a formation following a known trajectory. A formation here refers to a group of robots carrying a payload on them while maintaining the desired shape. A decentralized leader-follower based formation control law is used to move the robots in a formation. There are recharging stations present along the route taken by the robots. When the robots in formation reach a recharging station, a check is performed based on the remaining robots battery capacity. If any of the robots in the formation has low battery capacity, it therefore, cannot continue the task of transportation and is replaced by a charged robot present at the recharging station. In this work, we focus on building a custom robot that is capable of carrying a payload with a lifting mechanism and an accurate localization. The kinematics and dynamics are developed for a differential drive, non-holonomic robot. We also developed a friction and battery model and derived a relation to between the robot dynamics and the power capacity of the battery. Further, we presented a novel concept which ensures that the multi-robot system lasts much longer than the battery life of an individual robot. Each robot is considered having two operating states: Charg- ing and Discharging. A robot in charging state means that the robot is present at the recharging station or is fully charged, waiting the replacement to happen and does not contribute to payload transport, whereas a robot in discharging state means a robot in formation transporting a payload and therefore is under continuous discharge. A system-level optimization is presented to decide upon these operational state (charging or discharging) of each robot in the system. The optimization provides the ids of the robots that need replacement at a particular recharge hub. We also present an algorithm for robot replacement to increase the running life of the Multi-Robot Payload Transport System. We also introduce the concept of robot battery recharge hubs which are present along the trajectory. Robots in the formation can be replaced at these hub locations with charged robots using a replacement mechanism. The robot ids obtained by the optimization are considered for replacement. The replacement algorithm is used to replace the low battery robot with the charged robot at the nearest recharge hub. We compare the optimization approach with a baseline approach and show that the Multi-robot system carrying a payload lasts longer using the optimization approach than the baseline. In a baseline approach, a certain threshold is considered (30%, 40% of the total battery, in our work), and the robot below this threshold will be considered for replacement. We showcase the efficacy of the proposed approach over the baseline approach through simulations and experiments with real robots. Full thesis: pdf Centre for Data Engineering |
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