Enhanced process reliability for internal customers' production


Stöcklin Logistik AG has realized an automated small parts warehouse for Daimler AG in the Dusseldorf “Sprinter” plant where the assembly lines are provided with components on a ‘Just-in-Sequence’ basisThough the stock retrieval strategy required for positioning containers precisely in the channels has certain restrictions, a throughput of about 360 load carriers per hour is currently achieved. A portal robot as well as the integrated conveyor and control system, among other things, play an important part in the performance of the system.

The new automated small parts warehouse (SPW) was installed on the upper floor of an existing building. Extensive conveyor lines, including loops, are connected to the new warehouse, which are connected to the inbound goods area, specific processing places and outbound goods area. The three-lane rack structure of the SPW with basic container dimensions of 400 x 600mm has over 16,000 storage positions. These are served by three fully automatic BOXer aisle stacker cranes from Stöcklin - a series that has proven its value for almost 15 years as the best-seller in the field of automated small parts warehousing. The devices are equipped with box pickers in order to be able to reliably handle plastic containers and special load carriers. The SPW, including periphery, is operated five working days a week on a three-shift rotation basis.

State of the art and competitive warehouse logistics as top priority

The Daimler plant in the capital of North-Rhine Westphalia is subject to constantly growing process requirements. In order to match performance with the increasing requirements in a forward thinking manner, at the beginning of 2017 it was decied to invest in an automated assembly line. Not only has the new system enabled Mercedes to live up to the new requirements, it has also recued time- and resources through the ‘supermarket’ significantly.

"One of the main challenges of the project was to implement an automated solution with limited space available,"

reported Markus Blaß, plant planner at Daimler in Dusseldorf.

"Our system partners were asked to implement a sequence-controlled assembly line supply based on short throughput times and maximum system availability."

At the same time, resource requirement had to be minimized to comply with lean processes and increase throughput capacity as much as possible in order to further boost the economic efficiency of the entire system.

Modularity and flexibility desired

A time window of just nine months was estimated for the first construction level from the order award in mid-September 2017. All functions had to be modular and standardized in design. This also applied to the manual workplaces, which according to the requirement of the automobile manufacturer had to be designed to be as compact as possible and take into account ergonomic requirements. Additionally, to minimize walking distances and enhance process efficiency, it had to be possible to handle several functions at the same individual stations.

Stöcklin installed the SPW, including a preliminary zone, on the upper floor of an existing industrial building. The area available measured 63.5m in length, 33.0m in width and 6.5 m in heigth. Primarily Euro containers of the German Association of the Automotive Industry, boxes but also special load carriers up to a permissible maximum of 25 kg each are transported and stored. The vast majority have basic dimensions of 300x200, 400x300 (15.7x11.8 inces), 600x400 and 800x600 in varying heights. Allowance also had to be made for the fact that various Euro container bases, such as waffle, ribbed and flat bases, had to be transported and precisely gripped via the converyor technology. Minor damage or traces of use to the continually circulating containers should not hinder the martieral flow. As a result, corresponding tolerances already had to be included in the design of the converyor and handling technology.

Automatic identification and depalettizing

The intralogistic solution covers the entire process from inbound to outbound. Daimler's in-house Warehouse Management System (WMS) is subject to central administration and control. The WMS communicates with the StöcklinWCS (warehouse control system), a warehouse place administration system, which also includes material flow control including control center. Since the existing WMS already has an integrated warehouse control computer, Daimler AG only needed the StöcklinWCS main module is a WinCC plant visualization based on the TIA portal is also included in its scope of application.

Since the go-live and final acceptance in late summer 2018, the Euro pallets, already provided with labels by the supplier companies of the inbound goods zone, are guided to different load carriers. These primarily involve Euro and industrial pallets. Depalletization is handled by a line portal robot that is equipped with two freely programmable axes, a maintenance-free rotary current servo drive, incremental path measurement system and a camera, with which the robot identifies the container. At the same time, the pictures provide information on how the Euro pallets have to be provided to the container converyor technology after separation. As a result, they are brought to the right position for storage using a rotary converter. Special containers, for example, from overseas, outsize pallets and grid boxes in comparison are first provided with forklift support at the manual packing places,where they are measured. This information is necessary to determine the subsequent handling in SPW. The current alignment of the load carrier is also recognized to guarantee rapid positioning through the rotary lift converter.

Exact task distribution at IT level

After the check and control barcode registration, each Euro pallet is communicated to the higher system by the WCS. The higher system (WMS) assigns a corresponding storage space, depending on the container type, to enable single, double or four-deep storage accordingly. The compartment depths, on the other hand are administered by the WCS with the WMS ensuring that only the permissible number of containers is in each case assigned for the same storage place. This simultaneously ensures that only the same articles/batches are stored in the same place. In order to be able to store all container types accommodating their different dimensions, the SPW was designed as shelved racking. Moreover, thanks to the option of four-deep storage for the smaller Euro pallets (300x200, 400x300) (11.8x7.9 inches, 15.7x11.8 inches), higher storage density was possible.

"Group formation" is a special feature of this project. Group formation starts, as soon as a container has left the I-point.

"The goal is to assign the maximum number of possible container classes to one load handling device, thus optimizing the free travel of the aisle stackers and decreasing redundancies,"

according to Stöcklin logistics project manager Serkan Zeyrek.

In the process, the WCS ensures that containers with the same material content are distributed as equally as possible across all three lanes of the SPW. During the group formation, the system also ensures that channels are always completely filled. Storage in one channel is dependent on the same material and drawing geometry status numbers, as well as corresponding batches.

Integrated safety and intelligence

The container places are supplied and removed in the automated small parts warehouse by three automatic, 6.50 m high BOXer D1 aisle stackers. These are each fitted with a box-picker and custom-designed according to the principle of "group formation" for carrying up to four load units. The custom design allows the BOXer to safely pick up and transport a total weight of up to 100 kg in one tour. In addition, the devices have two industrial cameras, including spotlights, which are attached to allow the goods on the load handling device to be filmed from above. Transmission to the customer IT network occurs via Ethernet. Integrated energy management is another feature of the BOXer SPW. This allows the aisle stackers to be operated in periods with low throughput with reduced, conservative travel dynamics. When not in use, most of the electrical components can be disconnected from electricity supply and put into sleep mode. Excess braking energy is fed back into the main power grid.

Improved service quality due to sequencing

Most of the containers are intended to transfer components to the sequencers.

"Both of the sequencers serve to retrieve the containers with components needed in assembly corresponding to the predefined construction sequence and supply them to the rack loading,"

explained Stöcklin expert Serkan Zeyrek.

"In addition, they are equipped with a buffer function to compensate for performance fluctuations in the event of any irregular tugger train shutdown times."

The sequencing and filling of the racks for the tugger trains occurs via three conveyor system loops, which are arranged on three conveyor levels: +600, +1,200 and +1,800 mm. The process is triggered by the WMS generating a transport order to the destination space for each tugger train. The information transmitted includes the storage coordinates and a sequence/tour per container. Based on this information, the WCS calculates which Euro pallet is to be assigned to which tugger train rack and initiates the retrieval process as required. After arrival of the container, which was previously aligned to fit the correct rack position through a rotary lift converter, the WCS confirms the order to the higher-level customer system.

The conveyor system can handle 360 Euro pallets an hour. The reason for this comparatively low throughput is that the Daimler system prescribes exactly which load carriers are to be retrieved in what order and to be positioned in a precise position in the channel. Consequently, the containers, which come in five different sizes, must be turned to the correct position after depalletization. They are also turned to ensure that the attached barcode is easier/ convenient to scan for the employee. Moreover, to maintain the sequences, it the Euro pallets may have to be repositioned from the storage bay in order to allow access to those at the back that are immediately required. The effort involved in each case results in restrictions in the retrieval strategy and reduces the throughput capacity, which in the best case scenario would normally be up to 600 containers an hour.

The option for manual rack loading was created consequtively. During the manual rack loading, the relevant containers are supplied to the workplaces from the SPW through outsourcing nodes to the workstations. Provision is also made for sufficient buffer capacity in the conveyor system in this area. Moreover, as a supplement to the full container retrievals, partial retrievals are possible for operators at the picking workstations. In addition, especially urgent materials can be passed through in the cross-docking procedure in the outbound process. The WMS transmits the corresponding telegrams through the Euro pallets to the system control. The cross docking occurs through the preliminary zone of the BOXer SPW in terms of material flow.

Current and future needs secured

If the process requirements continue to increase, the integrated overall system solution for a sequence-controlled line supply can be adjusted in a relatively short time. Allowance for the preconditions required for this was already made during the development of the system layout.

"We are extremely satisfied with the solution we chose, which can be flexibly adjusted at any time to new requirements and tasks as well as expanded,"

stated Markus Blass, plant planner at the Daimler plant in Duesseldorf.