Mercedes has upgraded the van assembly lines at its Ludwigsfelde plant with a new, automated systemAccording to my guide around Mercedes-Benz Ludwigsfelde, Peer Braun, the working environment has been greatly improved; it is much quieter and open, the idea being to view the whole assembly process from one side of the hall to the other. But the upgrades to the assembly lines at Ludwigsfelde, Germany, are not just cosmetic. The plant is piloting a new approach to lineside operations using a much higher level of automation. At the first assembly station we visit, we observe the automated guided vehicles (AGVs) in operation and the process seems very simple and effective. The robotic vehicle delivers a fresh set of door kits (enough for three vehicles) to line workers, automatically replenishing the parts then removing the empty containers.
Using in-house expertiseBehind this seemingly simple operation lies a huge amount of planning, scheduling, designing and building. Firstly, the AGVs have been designed and built by an in-house team using outsourced technologies, such as sensors from Sick. Similarly, the trucks carrying the parts have been built in-house, with a large contribution to the design coming from the line workers. These, along with the lineside layout for parts storage, were subject to a consultation process, in which the engineering team responsible for the project collaborated closely with the line workers to optimise the operation and integration of the automated units, and the layouts of the parts trucks and assembly stations.
The AGVs circulate around the assembly hall according to a cycle time relating to the takt time of the assembly operations. This ensures precise delivery of the scheduled parts. The robotic vehicles use a variety of visual sensors to follow a marked track around the hall, pausing only to deliver parts and to recharge their batteries at a floor-mounted, fast-charge point. These robotic units are able to deliver a variety of components ranging from interior trims to heavier parts such as batteries. While the majority of the workstations are serviced by the AGVs, a small number still require a manually operated truck to deliver the parts and it presents an interesting contrast to see both methods in operation.
implementing kittingMany of the parts are supplied to the lineside in kits (another part of the optimisation process) and these kits are put together manually due to the widely differing parts and materials, making it very challenging to automate. The delivery AGVs drop off the empty carts and pick up the next batch of kits. This process requires the AGVs to perform a fairly complex series of manoeuvres to detach the empty cart in the correct position to be refilled and recouple with the next load. Although fully functioning, the automated systems are still being fine-tuned and the space available in certain areas of the hall would appear to compromise the otherwise smooth flow of the operation.
The kitting process highlights the ingenuity of the project, combining both human and machine operations. An AGV guides the empty cart through various storage points. It is programmed with the scheduled parts which are required in the following cycle, with the human operative able to view the part number via a digital display. At the appropriate storage point, the AGV pauses and illuminates the correct part bin, using one of an impressive array of carefully positioned lights on top of the robotic vehicle, indicating which part should be selected for that kit.
"We invested a great deal of time in creating and optimising the car-sets [kitting], the development of which was driven by the assembly workers"– Sebastian Streuff, Mercedes-Benz
Appreciating manual dexterityThe presence of the human operative highlights the limitations of automating this part of the process; the variations in size, shape, texture and other characteristics of the parts would require a number of different robots to complete the picking operation. By contrast, a single human worker can complete the task whatever the variations. Once the part is picked, the operator activates a hand control indicating that the AGV can move to the next part location.
The whole process was performed with quiet efficiency during our visit; the current volumes and takt time have made Ludwigsfelde the perfect pilot plant for Mercedes to develop this technology. Interestingly, it seems that the human element – the line workers’ considerable input into the design and layout of the automated parts trucks and workstations – has made a significant contribution to the success of this automation project.