INPUT-OUTPUT MODEL FOR SEQUENCING SYSTEMS

An input-output model for production and logistics processes is a framework for documenting and predicting the flows to and from individual organisational units such as companies, factories, factory units, distribution centres. Figure 1 illustrates an input-output model for a sequencing system on an actual business case from the automotive industry.

Fundamental terms describing the input-output relations are objects, activities, technological aspects and restrictions (Dyckhoff 2003, pp 20).

Figure 1 Input-Output-Model CASE FROM AUTOMOTIVE INDUSTRY

As mentioned above, this simulation model is based on a case that finds application in business practice. Following the process analysis, the collected and aggregated data is used to create a model of the supply chain including pre- supplier, supplier and manufacturer. Figure 2 presents an overview of this automotive supply chain.

The sets of components are produced in job lot production by the pre-supplier. They are packed in boxes (one set per box) and shipped to the supplier. The next process step within the supply chain is the target process: the sequencing system for the sets which are provided for the assembly line producing seating systems. The corresponding first-tier supplier delivers the seating systems just- in-sequence to the manufacturer’s production line. In this respect the sequencing unit represents a push-pull boundary: the upstream supply process is based on forecast oriented production, whereas the downstream process flow planning is pull-driven and impulse-controlled.

Sequencing Storage, Storing Handling, Transfer Provision Input Sequence Output Sequence Sequence Planning

and Scheduling Trigger

(Impulse) Objects Activities Decoupling I/O Technology & Restrictions

Figure 2 Automotive Supply Chain with embedded sequencing system SIMULATION STUDIES

We use an event-controlled simulation environment (plant simulation/UGS) enabling the possibility to adapt and test the whole process without interventions in the running production process. The study of combining simulation methods with optimisation methods in an iterative way is seen as a promising area (Harrison 2003, p 10).

The considered supply chain (see figure 2) modelled with plant simulation is completed by the embedded Cube-Sorter Model (CSM). It constitutes the sequencing transformation process and its control logic is developed by a project partner. This type of simulation can be classified as distributed simulation (Wenzel et al. 2003, Spiekermann 2007).

Distributed simulation offers various opportunities, e.g.

• recovery options concerning existing simulation models or model components, • replacement of simulation components by real systems,

• possibility to keep specific process knowledge by building encapsulated modules within shared projects (Rabe 2003, p 137).

Primarily, within our project distributed simulation offers the possibility to integrate the respective developed modules of the geographically distributed project partners working on different design platforms.

The Process Model - Adaption

Subsequent to the generation of the basic model, the aim of the following project continuation is to create an easy to handle and manageable way to implement the function of the well-formed XML-interface and the to-be process with the logic of the CSM. On its course to becoming the to-be model the as-is model bifurcates into parallel paths. On the one side, it has to be ensured that all significant changes to the to-be model, compared to the as-is state, are implemented along the way and work correctly. On the other side, the new XML- interface has to be defined and realised.

pre-supplier (second-tier) Assembly line vehicles supplier (first-tier) manufacturer Assembly line for seating systems Job lot production of components (set of add-on parts)

Other parts Storage Sequencing process … …

A definition describes the obligatory structure of the XML-files shared between the independent systems of the simulation and the realised CSM as well as the communication structure between these systems. Based on a prototype software of the CSM provided by our project partner, the interface is scrutinised and an iterative process of testing, bug reporting and bug fixing moves the interface toward its completion. Additionally, the implementation of the changes to the as- is model is executed and subjected to testing.

Figure 3 Project process model

Because of the divided complexity this approach achieves an easy to handle and manageable version of the to-be model with an optimised way to define and fix errors arising within the respective models.

The XML-interface - design and structure

The CSM is implemented as an embedded element interconnected with two well- formed interfaces. The communication between the different systems is carried out through Extensible Markup Language (XML) interfaces (W3C 2006). For synchronisation needs it is necessary to make sure that a uniform platform is being used and that the access to the XML files is being regulated. Both requirements are met in cooperation with our partners.

As mentioned, the communication between the logically and geographically divided systems is managed by XML. Besides the slightly higher demand on storage space, compared for example to the Character Separated Values (CSV), XML features two important assets which can be benefited from in the communication process between the interacting servers. The first one is the circumstance of the easily understood nature of the XML files. The hierarchical structure and the option of free nomenclature of the used nodes facilitate comprehension. The second and most important part is the option of defining a binding agreement of the interface structure and the corresponding procedure between the attending project partners. This allows for concerted action of the split team with a common understanding of the communication. To ensure that on both sides of the communication the respective needs are met, a component diagram in Unified Modeling Language (UML) was developed (see figure 4). Its functions being of prime importance.

To-Be model Function-added As-Is Model Stable XML-Interface Offline Scrutiny XML- Interface As-Is Supply Chain

Business Case Distributed Simulation As-Is Model Prototype XML-Interfaces

Figure 4 Component diagram (UML-Notation)

Delivery component: The purpose of this part is to procure the required material for one production cycle of four weeks according to data that is stored in a document and which can be modified to suit custom needs and is loaded at the start-up of the simulation. Furthermore, the task of creating the order sequence and the corresponding handoff of the in XML-converted production need is accomplished with different methods within the administrative part of the model. CSM component: As explained, our partners had to deliver the CSM. Its main task is the process of transformation of the material which was received from the delivery component.

Production component: Constituting the basis of the order sequence, the production receives the sequenced material which it then uses to produce the seating systems.

The Communication – Logic and Structure

The physical structure and the programmed logic of the systems are designed to meet the requirements of an open and geographically divided system.

As figure 5 shows, it is possible to run the simulation connected through any network capable of transferring the XML data.

The HFU server simulates the production of the seating systems including the supplier, manufacturer and the customer. It transfers the material described in the XML files to the GIT server which starts the transformation process of sequencing the material. The material is delivered on demand back to the HFU server and used for the production of the seating systems. Storing the data and visualisation of the simulation results is realised by a web service provider.

CONCLUSION

With this approach, the creation of distributed simulation studies with two different systems is achieved. On this basis, alternate process analyses (what-if scenarios) are designed and evaluated. The goal to gather information in terms of behaviour and performance of the CSM and the integrated supply chain is reached through measuring different key performance indicators. The results of the analyses complete further feasibility studies, forming a ground work for building and testing of a first physical prototype of the CSM.

As has been demonstrated, the applied distributed simulation is a powerful planning approach enabling the employment of different project partners for common supply chain design purposes, adding their specific strengths to the endeavour. In lockstep with these advantages there arise a number of challenges that will need to be resolved, especially issues of standardisation (synchronisation needs, interface specifications) requiring intensive communication and reliable agreements between the involved partners.

REFERENCES

Dyckhoff H (2003) "Grundzüge der Produktionswirtschaft”, Berlin:Springer. Harrison TP (2003) "Principles for the Strategic Design of Supply Chains", in Harrison TP, Lee HL, Neele JJ (Ed.) The Practice of Supply Chain Management: Where Theory and Application Converge, Kluwer Academic Publishers.

Rabe M (2003) "Steuerungskonzeption für ein neues Automobilwerk", in Bayer et. al. (Ed.) Simulation in der Automobilproduktion, Berlin:Springer, pp 129. Schmollinger M, Siestrup G (2006) "Web Services and B2B-Communication for Medium-Sized Business", in ERP Management Journal, Issue 1, pp 36-39.

Simchi-Levi D, Kaminsky P, Simchi-Levi E (2003) "Designing and Managing the Supply Chain. Concepts, Strategies and Case Studies" New York:McGraw Hill. Spieckermann S (2007) "Diskrete, ereignisorientierte Simulation in Produktion und Logistik – Herausforderungen und Trends",

<http//:www.simplan.de/pdf/Spieckermann_SimVis05.pdf>, (2007-04-15). SUCULOG (2007) "Sustainable Net-by-Cube Logistics (SUCULOG)", Research project financed by the Federal Ministry of Education and Research (BMBF), Germany. The project organisation includes two universities and six involved companies and institutes. Our project partner Green IT is working on the CSM- component (www.green-it.de). Project direction: Prof. Dr. H.-D. Haasis.

W3C (2004) "Extensible Markup Language (XML) 1.1", issued by Bray T, Cowan J, Maler E, Paoli J, Sperberg-McQueen CM & Yergeau F,

<http://www.w3.org/TR/2004/REC-xml11-20040204/>, (2007-04-23).

Wenzel S, Bernhard J, Nickel S et al. (2003) "SILVER Simulationsbasierte Systeme zur Integration logistischer und verfahrenstechnischer Entschei- dungsprozesse", Dortmund:Fraunhofer-Institut für Materialfluss und Logistik.

SUPPLY CHAIN DESIGN OF VOLUNTARY SUSTAINABILITY INITIATIVES –