Manufacturing systems consist of machines and robots together with a cell controller that coordinates and supervises the flow of parts through the cell. To reduce the amount of data exchanged between the controller and the processing components, a concept based on the theory of hierarchical control is developed. It uses on-line simulation to gain the expected behavior of the working components. Therefore for every robot and machine a corresponding model inside the cell controller exists that runs synchronized with the robot or machine. In addition, these internal models supervise their external counterparts to realize the task of monitoring. Because the internal models run synchronized with the external components, their state can be used by the higher levels of the cell controller to guarantee proper flow of parts through the cell.