Autonomous and electric robots appeared in agriculture to perform activities on the fields. The management systems dedicated to farms thus need to integrate software for the scheduling of a fleet of such robots. As agricultural systems are by nature subject to unpredictable events, it seems necessary to provide a solution for online scheduling. As a first step toward a global solution, we propose a model for a sub-problem that targets to provide the next route of each robot of the fleet in order to satisfy a subset of the demands for activities on fields emitted by the farmers. In this work, we present a mixed integer linear programming formulation for the sub-problem using the prize-collecting concept called here Prize-Collecting Robot Scheduling Problem with Time Window and Precedence Constraints. Specific constraints are introduced to ensure that PC-RSP provides viable solutions for the targeted online process.