| Abstract: | Fault tolerance in a team of cooperative and distributed object-lifting robots is dealt with. It is assumed that one of four object lifting robots misses a portion of its lifting power and the robots must redistribute the load among themselves to perform their task. Two distributed and cooperative methods for load reallocation among the position-controlled robots without requiring them to change their grasp positions are introduced. The first method benefits from the existing redundancy in the number and lifting power of robots. In the second method, the object is tilted in order to move the zero moment point (ZMP) away from the faulty robot and, consequently, redistributing the load. Difficulties in controlling ZMP movements are pointed out. Therefore, the second fault-clearing procedure is designed such that the ZMP position is controlled without resorting to sophisticated or centralized control algorithms. Stability of the proposed methods is mathematically proven and the deadlocks are investigated. It is also noted that the required sensory system and robot behavior in the proposed strategies are exactly the same as those used in the object-lifting task. Consequently, no additional complexity is imposed on the system. The basic idea in ALLIANCE is used for developing a mechanism for each robot to process help requests and select proper actions in a distributed fashion without negotiating with its teammates. Simulation results are given to support the developed methods. |
