Executable Simulation Lifecycle Management Framework Using ...

8th IEEE International Conference on Automation Science and Engineering August 20-24, 2012, Seoul, Korea

Executable Simulation Lifecycle Management Framework using Extensible and Interoperable Simulation Language Hyunsoo Lee, and Amarnath Banerjee, Member, IEEE systems with CAD/E systems. Currently most of the commercial SLM software such as SIMULIA SLM[2], consist of PLM platform, CAD/CAE software and other simulation functions. However, the software has limitations from the fact that the simulations rely primary on the interactions among physical components, using limited CAD/CAE software’s simulation and analysis functions. As a result, the extent of simulation stays at the product level, and fails to capture the overall processes and cannot link product design and manufacturing processes. The ability to perform detailed investigation and analysis at the overall process level and modeling of manufacturing processes have been recognized as a crucial factor for successfully completing the R&D functions in an organization. A framework integrating the design process and manufacturing process is required.

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Abstract— There has been some recent change in focus in R&D from the concept of managing product lifecycle data to identifying and representing crucial data and using it for simulation to study dynamic process behavior and characteristics. One of the relatively new concepts that has evolved to address this change is Simulation Lifecycle Management (SLM) concept, which can be considered as the next version of PDM/PLM systems currently used in R&D. There are relatively few research studies or related frameworks that can adequately support the SLM concepts. This paper proposes an executable and interoperable SLM framework using an eXtensible Petri Net Markup Language (xPNML). Unlike other proprietary simulation languages, xPNML has advantages in terms of interoperability, flexibility and incorporation of simulation parameters. An executable SLM framework using xPNML is shown here using a conceptual scenario. The use of modular concept of xPNML is discussed to demonstrate concise and consistent simulation model development.

A SLM framework is expected to demonstrate the following characteristics - process coverage, collaboration, generality, support for large-scale processes, and integration. Table 1 summarizes the characteristics and specifications required in an advanced SLM framework.

I. INTRODUCTION There has been considerable amount of emphasis on the concept of Simulation Lifecycle Management (SLM) in the past few years from companies that have Research and Development (R&D) functions. SLM is considered as the next generation in the evolution of Product Lifecycle Management (PLM) System / Product Data Management (PDM) systems. There are several global manufacturing companies that have started to launch projects using the SLM concept even though the concept is in its infancy and continues to evolve.

TABLE I.

Characteristics

Specifications

Process

- Covers the areas from product item to overall processes using extended simulation functions

Coverage

The SLM concept originated as a combination of PLM with reinforced simulation functions. Some of the initial effort in SLM development was led by Dassault Systems. While existing PLM systems have been focusing just on managing product data such as managing version of drawings or design, there was a significant increase in demand for managing intellectual property associated with simulation tools, data, and processes as related to product or process development. One of the alternative solutions is to get more knowledge from the collaboration, integration and decision support among engineering data (e.g. drawings) and to utilize them in a meaningful manner. Using this perspective, several commercial PLM system vendors started to unify their PLM

- Supports multiple designers’ cooperative modeling and integration

Extension-ability

- Supporting the representation and simulation of large scale processes

Generality (Interoperability)

237

(The design decision is determined considering process modeling and its simulations)

Collaboration

Integration

Hyunsoo Lee is an assistant professor in the school of Industrial Engineering, Kumoh National Institute of Technology, Gumi, Korea, PO 730-701 (e-mail : [email protected]). Amarnath Banerjee is an associate professor in the department of Industrial and Systems Engineering, Texas A&M University, College Station, TX 77843-3131, USA (phone: 979-458-2341; fax: 979-458-4229; e-mail: [email protected] ).

978-1-4673-0430-6/12/$31.00 ©2012 IEEE

CHARACTERISTICS OF ADVANCED SLM FRAMEWORK

- Integration with other systems/platforms : PLM systems, CAD/CAE systems, and so on - Independent of vendor-specific system : Use of interoperable formats and standards

For instance, SIMULIA SLM and extended PLM frameworks meet several characteristics, mainly process coverage, collaboration and integration. However, extensionability and generality issues are ignored. While the existing SLM frameworks do not meet these characteristics completely, this paper suggests a new and executable SLM framework. As an interchangeable format in the suggested SLM framework, the eXtensible Petri Net Markup Language (xPNML) is used. The xPNML is an inherited and modified language from Petri Net Markup Language (PNML). xPNML has a data structure that accommodates simulation parameters (e.g. number of steps, replication numbers and total simulation run time) in its meta

effectiveness parameters for each project’s lifecycle. Lee, et al. [5] have applied similar approaches to the design of a health care process. Even though the SLM concept and related systems are still in their early stages, its developments have slowly accelerated with the replacement of PLM systems in different organizations. It is expected that the next development in SLM concept will be to discuss how to construct a general SLM framework with the characteristics shown in Table 1.

model, which makes it a suitable format for implementing SLM. In addition, its other supporting ability for Petri Nets such as modularity can contribute to improving the generality and collaboration aspects in a SLM framework. A more detailed review of SLM and xPNML is provided in section II. Section III shows the proposed SLM architecture satisfying the listed conditions, and Section IV describes the use of the modularity concept of xPNML within the SLM framework. II. BACKGROUND AND LITERATURE REVIEW A. Simulation Lifecycle Management (SLM) As discussed in section I, SLM is an evolving concept. There are only a few research studies [1,3,6] that have looked into the modeling and operational characteristics of SLM. However, several global companies have recognized the importance of SLM and have started using and implementing the concept. For example, in 2009 P&G have introduced a SLM system to reinforce the modeling and simulation abilities. Currently, SLM concepts have been implemented in limited form using several commercial PLM/CAD/CAE/Simulation tools. There are several existing efforts linking product designs and process modeling, some of which are listed here. In [3], Lee, et al., have combined design processes and manufacturing processes with checking shop floor’s capability and uncertainties. A shop floor manufacturing simulation model is used to select the best performing design process among several alternative design processes.

(a) Meta model of xPNML Type Definition

The incorporation of process coverage, extension-ability, and interoperability are three main challenges that exist in the development of a general SLM system. The use of vendor specific tools in existing SLM systems makes it difficult for collaborative process designers to integrate and run their simulation models. One of the requirements of a good and stable SLM system is to provide the ability to interface with the component systems of a contemporary manufacturing environment. In addition, the SLM system should be able to integrate simulation models for different processes that are developed by multiple designers. An interchangeable format for exchanging information between SLM and other systems / among SLM modules is a primary requirement. There are only a few interchangeable formats that exist for simulation models as compared to CAD systems. Among them, xPNML is considered as one of the good interchangeable formats that can be possibly used for supporting SLM. The structure and characteristics of xPNML are discussed below. B. eXtensible Petri Net Markup Language (xPNML)

(b) Nodes for FCPN-std

Figure 1. Meta model of xPNML Type Definition for FCPN-std [1]

The xPNML was developed by Lee, et al. [6] as an alternative interchangeable format based on PNML[7].

This has extended from a manufacturing application to several other areas, such as construction field and supply chain management. Doloi [4] modeled several construction projects into process models and ran them for checking cost and other

Both languages support the representation of Petri Net models. Petri Net is a directed bipartite graph that can represent discrete/continuous event simulation models. Petri Nets, with 238

its many variations, such as Colored Petri Nets, Stochastic Petri Nets, Fuzzy Petri Nets and hybrid models, serve as general purpose simulation models to represent systems displaying stochastic behaviors. Petri Nets are independent modeling framework capable of capturing static behaviors of systems as well as simulating dynamic system behavior in a vendor neutral form. Petri Nets can serve as an executable model, which can be used for monitoring and controlling processes in several devices. Lee and Banerjee [8] compared Petri Nets with IEC 61499, a Function-Block based standard representation methodology, and showed its effectiveness. As a popular representation language for Petri Nets, PNML has several advantages such as use of XML, simple/easy structure from an UML based meta model and extension-ability using PNTD (Petri Net Type Definition). However, it does not have the ability to incorporate information that is required to perform system simulation and analysis. For example, information describing simulation parameters such as number of replications, simulation runs, warm-up period are essential data for running a simulation model and producing statistically reliable outputs. The xPNML meta model, which is an extension based on PNML, has the structure to capture the information required for performing simulation and analysis.

- XML based file format ** : Unique characteristics of xPNML, compared to PNML * : Improved characteristics of xPNML, compared to PNML

The following section provides an executable SLM framework using xPNML and its conceptual model. III. EXECUTABLE SLM FRAMEWORK A. Definition, Functions of SLM and Its Issues While many research studies have used “simulation module/function” for prior tests and checking “Design for Manufacturing (DfM)” feasibility, the objectives of a SLM framework are not limited to the implementation of DfM or “Concurrent Engineering (CE)”. The main objective of SLM is to reinforce R&D functions required for product development. In order to define a (R&D-oriented) SLM framework, there is a need for prior classification of simulation functions. This paper classifies simulation functions into two groups: “BOM analysis” and “process simulation”. The BOM (Bill of Materials) analysis includes CAE analyses of product component(s), manufacturability and assembly tests using BOM. The other simulation function - process simulation - handles selections of devices, layout of manufacturing facilities, process modeling and its discrete/continuous simulation. The most important thing in SLM is that two simulation functions have the ability to interact with each other. For example, manufacturability (e.g. meeting tolerance) in BOM analysis can be controlled by the selection of suitable manufacturing devices in the process simulation. From this perspective, SLM can be defined as a framework that not only manages engineering data but also achieves engineering objectives using “BOM analysis” and “process simulation”.

Fig. 1 shows the xPNML metal model supporting FCPN-std [8], a generalized Petri Net model that can capture variance type uncertainty and ambiguity type uncertainty. As shown in Fig. 1, the use of entities, Settings and Analysis makes it possible to capture the run time parameters of a simulation model as well as the structure of the simulation model. In addition, other Petri Net models such as Stochastic Petri Nets and Fuzzy Petri Nets can be represented using Timeinfo and fuzzy related entities such as Threshold and Fuzzy_Inference_Rule. The detail schema and usages, including the representation for Modular Petri Nets and the xPNML file generation technique using Common Type Definition (CTD) and User Defined Module Definition (UDMD), are explained in [1, 6]. xPNML is a better interchangeable format than PNML, from the point of view of representing SLM. Table 2 shows advantages of using xPNML for representing SLM systems, as compared to PNML. TABLE II. SLM Characteristics

In terms of its functions, the function of managing engineering data is inherited from PLM system and expands the range to analysis data and simulation results. Fig. 2 shows the function and architecture of a SLM framework.

THE ADVANTAGES OF XPNML IN SLM Advantages of xPNML - Represent generalized Petri Net models *

Process coverage

- Incorporated in simulation model as well as information for simulation parameters and analysis **

Collaboration

- Integrate into a large scale simulation model using Modular_Petri_Net and Modular_Object entities *

Extension-ability

- Design of large and general simulation model using CTD and UDMD **

Integration

- Capture the interface using Label, Attributes and General entities *

Generality

- Vendor-independent simulation model using Petri Nets

Figure 2. The Architecture and Functions of SLM Framework

The SLM framework consists of three main modules: PLM module, BOM analysis module and Process simulation module. Each module interfaces with the related tools and databases. When it is implemented, the engineering DB can be 239

integrated with the process DB. In addition, the SLM framework can be installed for CAD tools as a plug-in module. The design considerations of SLM framework are to check the characteristics as shown in Table 1. As the design trends require the collaboration among multiple designers and related tools, there are likely to be design data exchange issues such as using interoperable format in multiple CADs and/or integration between mechanical CAD drawings and electronic CAD drawings. In order to solve these issues, the common interchangeable format such as STEP file format (ISO 10303) can be applied. The research studies in [9, 10] have extensively handled design data exchange. However, there have been fewer research studies in interchangeable format among process modeling and simulation tools. This paper focuses on how xPNML can be effectively used to exchange data between process modeling and simulation tools.

of uncertainties within the target process. The five stage modeling can select the suitable Petri Net types for modeling with respect to the degree of uncertainties: no uncertainties (for describing sequences of processes only), variance type uncertainties, ambiguous type uncertainties and mixed uncertainties. For example, when a process has both types of uncertainties – variability and ambiguity, the process is designed using the FCPN-std framework. In this case, the interchangeable format is to support the related entities such as Fuzzy_inference_rule, Threshold and so on. In order to use the most appropriate Petri Net structure, the consistency and capabilities supporting various Petri Net models are important criteria for selecting suitable interchangeable simulation model format. The proposed SLM framework uses the xPNML format for modeling and simulation as xPNML has inbuilt capabilities to support enforcement of such conditions.

B. Petri Net Based Process Simulation and Data Exchange using xPNML Petri Net is applied as the primary simulation methodology in the proposed executable SLM framework. The advantages and characteristics of Petri Net model have been discussed in section II earlier, and it is summarized here in Table III.

The following section shows a conceptual scenario in a photovoltaic cell manufacturing example.

TABLE III. Characteristics Multi-functional process model

Scalability

Modularity Vendor-independent Model

C. Conceptual Scenario: SLM System for Manufacturing Photovoltaic Panel The design of photovoltaic panel manufacturing process has been studied extensively due to the recent increase in demand and green energy requirements. However, there are few studies in the integration of the design process and manufacturing processes for photovoltaic panels. The primary reason for this lack of integration is due to the large number of processes and subprocesses. Moreover, the existence of a number of material suppliers and alternative manufacturing processes make the processes more complex and much larger. Even though most of the processes consist of several standardized processes, the demand for customized panels and the necessity for more energy efficient cell require a tight integration between design and manufacturing processes and the related supporting system, the SLM system. A similar situation arises in semiconductor, display and automotive industries.

ADVANTAGES OF PETRI NET MODELS Detail features of Petri Net Models - Can be used for process monitoring, simulation and control - Applicable in devices / hardware - The type of Petri Net models can be changed based on the degree of uncertainties in the target processes : Timed Petri Net, Colored Petri Net, Stochastic Petri Net, Fuzzy Petri Net and FCPN-std model [1] - Consistent and easy design using Parametric Petri Net modules [11] - Common process model with interchangeable file format such as PNML and xPNML

IV. MODULARITY OF XPNML AND ITS REPRESENTATIONS In the xPNML data model, the modular concepts are supported by the entities, Modular_Petri_Net and Modular_ Object. As shown in Fig. 1, Modular_Petri_Net consists of Petri_Net, Object and Arc. It means that a part of a Petri Net or the entire Petri Net model itself can be used as a Petri Net module. This coincides with the general modular concept. As an example, two different Petri Nets representing resource sharing processes are illustrated in Fig. 4. These Petri Nets can be represented using one Petri Net module – Resource Sharing Module – one of the several defined Parametric Petri Net modules in [11]. This module is set up with three parameters: processing time, number of processes and number of shared resources.

These characteristics make the proposed SLM model a modeling and simulation framework that is capable of modeling, information exchange and execution. From the point of view of simulation modeling and execution, the “modularity” characteristic is particularly important. This is due to the need for enforcing consistency in modeling that is required for integrating different simulation models. In general, the degree of complexity in process modeling is higher than in CAD modeling. This could result in a situation where multiple process models can be generated for the same process by multiple designers depending on their modeling approach. In order to prevent such a situation, Lee and Banerjee suggested several commonly used Parametric Petri Net modules in [11]. The use of these Petri Net modules can streamline the design of large scale process models as well as enforce consistency in process modeling. In addition, another advantage in using Petri Net models is the use of a five stage modeling paradigm [1, 11] that can account for different types

The photovoltaic cell manufacturing process consists of four main processes: poly-silicon process, wafer/ingot process, cell manufacturing process and module making process. Fig. 3 shows the conceptual SLM framework showing full-scale photovoltaic cell manufacturing processes.

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Figure 3.

Conceptual Scenario for Photovoltaic Cell Manufacturing Process

that the PNML file in Table IV represents the “Resource sharing processes”.

As discussed in sections II and III, the process simulation module uses a Petri Net based simulation and xPNML as the representation file format. Due to the generalized nature of Petri Nets and their variations, some simulation models which are developed using other simulation methods or commercial simulation tools can be converted into Petri Net models. There are research studies [12] that have developed and tested this type of conversion. Each Petri Net model corresponding to the individual processes and subprocesses can be integrated into a single Petri Net model covering the entire manufacturing process. The use of Petri Net module and the xPNML’s modular concept can help the process designers to integrate them concisely and maintain consistency. The following section provides a more detail description of xPNML supporting modularity as an interchangeable simulation file format in the SLM framework.

TABLE IV.

A PNML REPRESENTATION OF THE FIRST PETRI NET MODEL ILLUSTRATED IN FIGURE 4.

PNML File

This leads to significant amount of redundant code while trying to represent the second Petri Net model. As shown in Fig. 4, P5 in the first model has the same functionality (a place tracking the available resources) as P7 in the second model. Similarly, T3 in the first model is equivalent to T4 in the second model. Without using the modular concept, the second model’s PNML code uses redundant code, making the code longer and not readily reusable. This problem can be easily prevented using the xPNML model. The common module is

Figure 4. Two different Petri Nets Representing Resource Sharing Processes

Table IV shows a PNML file representation of the first Petri Net shown in Fig. 4. The main issue in representing the two Petri Nets is the fact that the common features in two processes are ignored. In other words, it is difficult to identify

241

captured using the entity, Modular_Petri_Net. Table V shows a portion of the CTD for representing Modular_Petri_Net. TABLE V.

recognition of Parametric Petri Net modules from a given Petri Nets. This can provide the mechanism to automatically generate modular xPNML files for existing Petri Net models that are in use. A more detailed interface design is required among CAD/CAE tools and simulation modules to ensure a robust SLM framework that can be easily reused.

PORTION OF CTD FOR REPRESENTING MODULAR_PETRI_NET

REFERENCES [1]

[2] [3]

The resource sharing modules in the two Petri Nets are shown in Table VI. The common module in the different Petri Nets is easily represented by changing the attributes and elements in Modular_Petri_Net.

[4] [5]

TABLE VI.

REPRESENTATION OF PARAMETRIC PETRI NET MODULE First Resource Sharing Module [6] Second Resource Sharing Module [7] [8]

The use of modular entities in xPNML can prevent coding redundancy and standardize the modeling process. This becomes particularly significant when the number of Petri Net parts in the SLM framework is large and have complex relationships. In addition, process modeler can specify partial semantics within Petri Nets using the attribute, module. The use of modular concept within xPNML makes it easy to design and develop large scale simulation model in a brief, modular and consistent manner aligning with the similarities that exist between manufacturing processes.

[9] [10] [11]

[12]

V. CONCLUSION The SLM concepts and its framework are slowly replacing existing PLM systems. Even though SLM concept and adoption is still in its infancy, different industries are realizing its importance and advantages. However, current SLM frameworks are primarily based on several PLM/CAD vendor-specific tools. This paper suggests a more generalized and advanced SLM concept and framework that is independent of vendor specific implementation. The suggested SLM framework consists of a process simulation module, a BOM analysis module, a PLM module and an integrated DB. The process simulation module uses Petri Net as a simulation methodology and xPNML as an interchangeable file format. The use of xPNML enables creation and implementation of smaller Petri Net modular entities that can be used to integrate the underlying processes that make up the entire manufacturing process. As part of further studies, we plan to explore automatic 242

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