Design of a dynamic robot packaging system for the food industry - 2008.TEL.7276 1
S
UMMARY
To decrease the number of personal working in food packaging factories, robots are often used. Robots require a reliable control system to assure full boxes however. Furthermore, products are often delivered in a continuous flow, so it must be assured no products will pass the last robot in line. To optimally use the expensive robots, it is also required that the usage of the robots is close to their maximum capacity. Finally, it is desired that the whole packaging line is as simple and cheap as possible. To fulfill all these requirements, a new concept for a robot packaging line has been developed, and is described in this report. Innovative about the concept is that it uses one box conveyor to transport boxes to all robots in line, where existing lines use multiple box conveyors or box placing systems to store boxes in a separate buffer. There is another company that also uses one box conveyor, but this company needs a real complicated control system to control these lines and still problems are found in fluctuating product flow situations. The concept described in this report uses a much more simple control system. This is possible because of the design of the box conveyor, which moves boxes only stepwise and not continuous as in the existing design with one box conveyor.
The stepwise box conveyor movement means that boxes should be hold at some pre-defined positions. Stopping the boxes can be done by the conveyor itself, but then all boxes should move and stop at the same time. Another way of stopping the boxes is by some kind of a mechanical device, like hydraulic cylinders. All boxes can then be stopped and moved separately. Using these cylinders at certain positions, buffer positions are created. These buffer places are however now on the conveyor itself, and therefore won’t require extra space and expensive buffer placing equipment.
To test and optimize the concept, a simulation is made. This simulation consists of a control part and a simulation elements part. The control part can later on be used as a real world control system. The simulation-elements part replaces the physical parts. This is done to make developing the control system easier.
To optimize the robot packaging line concept, some equations containing the speed of the box conveyor and the product conveyor have been formulated. When satisfying these formulas and therefore choosing the speed of the conveyors appropriately, it is assured that no products will pass the last robot and that all boxes will be completely filled. With these formulas, the optimal buffer size can also be calculated. This optimal buffer size depends mainly on the possible rate of change in product flow. When the product flow is almost constant, so with low fluctuations, no buffer is needed and the concept where boxes move at the same time can be used. When fluctuations are higher, a larger buffer is needed.
The basic functions the design of the box conveyor should comply with are that it should bear the boxes, it should transport the boxes, it should stop the boxes and it should guide the boxes in the correct direction. Using a morphological analysis with these functions, six box conveyor concepts are come up with. Depending on the customer requirements one of these concepts can be chosen.
Design of a dynamic robot packaging system for the food industry - 2008.TEL.7276 2
