9 th International Conference May 18-20, 2010, Tatranské Matliare CONTROL OF POWER SYSTEMS 2010 High Tatras, Slovak Republic SLOSH-FREE POSITIONING OF LIQUID-CONTAINERS USING A MACHINE WITH FLEXIBLE CONVEYOR BELT Peter Hubinský, Thomas Pospiech, Branislav Vranka Slovak University of Technology in Bratislava, Slovakia Faculty of Electrical Engineering and Information Technology Institute of Control and Industrial Informatics peter.hubinsky@stuba.sk, pospiech@hs-heilbronn.de, branislav_vranka@hotmail.com Abstract: The paper presents a feed-forward control method for slosh-free positioning of containers with liquids using a machine with flexible conveyor belt. The dynamic model of the controlled system is described, based on two single-mode oscillatory subsystems and simple techniques of parameter identification. This mathematical model is analogous to the two-mode damped pendulum system. Feed-forward signal shaping algorithms are employed for control of linear horizontal movement of containers. Presented method was tested in an industrial application. A deterministic hard-real-time communication is required between the PLC and servo amplifier (e.g. Ethernet POWERLINK). The principle structure, calculations, time duration and the robustness of the basic types of input shaper for proposed digital feed-forward signal filtration are described. Keywords: liquid container transfer, elimination of residual vibration, two-mode system, input signal shaping 1 INTRODUCTION The state-of-the-art filling systems for liquid food as for example milk or yoghurt are fully automated machines, the complete production process is controlled by numerous sensors and various actuators and is running without any impact of persons. Among the procedural challenges (as for example cleaning the container before the liquid is filled in), two main requirements must be fulfilled for the actual function of these systems: On the one hand, the container must be filled with the corresponding liquid and on the other hand it must be sealed afterwards. In industrial application, two basic concepts for an operation mode are distinguished from each other: continuous and discontinuous operation. During continuous operation, the containers are transported on conveyor belts. The single working stations or production steps (as for example container cleaning, filling and sealing) do not stop the conveyor belt i.e. they are carried along with the containers. The mechanical and electrical efforts of such machines are significant and thus correspondingly cost-intensive. With discontinuous (clocked) machines, the above mentioned operation steps are static. The conveying belt with the containers must be stopped and started for every filling sequence. This modular and economic design is opposed by a critical operational range. After the containers have been filled with liquid, several operation sequences pass by until they are sealed. The critical problem is the movement of the liquid inside the container, initiated by periodic starting and stopping of the conveyor belt. The oscillations excited by individual cycles can superimpose and if this movement becomes too heavy, the liquid spills over the container. As soon as the cup seam is contaminated (in this case by the liquid), the cap cannot be fixed onto the cups anymore, so containers cannot be hermetically sealed. Apart from that, this operational area is sterile (see figure 1) and therefore spilled liquid would imply increased cleaning efforts. In addition, installing any sensors in this area of the machine is undesirable (especially because of sterility, maintainability and price) – this means that the only possibility will be a feed-forward control method. On the other hand, maximal production output is desired, which leads to a minimum movement time. Together with the actual filling procedure (feeding the liquid into the container), this transporting time is the longest process period in this kind of lines. The specified problem can therefore be summarized as follows: Directly after stopping the conveyor belt, the liquid and the conveyor belt must be calm which means they must not perform any movements (resonance!). Furthermore, a maximum deflection of the liquid within the container at a minimum process period must not be exceeded. These tasks should be solved without measuring the liquid surface or the vibration of the conveying belt during the process. 1