- Email: [email protected]
Enhanced modelling and DSS tools to support green manufacturing
Copyright @ lFAC Manufacturing, Modeling, Management and Control, Patras. Greece, 2000
ENHANCED MODELLING AND DSS TOOLS TO SUPPORT GREEN MANUFACTURING
F1avio Bonfatti (1), Paola Daniela Monari (1), Sebutiano Sighinolfl (2)
(1) Dept. of Engineering Sciences, University ofModena and Reggio Emilia, via Campi 2131B, 41100. Modena Italy Tel +39059376732 Fax +39059376799 E-mail [email protected] (2) Democenter. viale Virgilio 55,41100 Modena Italy Tel +39 059 848810 Fax +39059848630 E-mail [email protected]
Abstract: the EPSPRIT 25359 EPSYLON project introduced a high semantic level process and product model conceived in order to collect the full life-cycle information of a product, from manufacturing to final recycling or disposal. The process model is the shared kernel of new software applications and integrated legacy systems, providing decision support to different company business areas. Such supporting tools contribute to collecting of data for the model updating, which, in turn makes available information on the actual shop-floor performances and capabilities to any enquiring tool at any time. This is particularly useful for the control of atypical activities competing with the manufacturing mainstream for the employment of the productive resources. Copyright © 2000 IFAC. Keywords: modelling, management, integration, simulation, manufacturing
1.
aimed at creating a specification language to capture the process knowledge that will facilitate the complete and correct exchange of process information among manufacturing applications (Schlenoff, C., Gruninger, M., et al., 1997). In the new economy an enterprise can have also a not conventional meaning. Actually, virtual enterprises and virtual factories are describing business partnerships and supply chains conceived as enterprise networks. Such networks allow small and medium enterprises to join resources and different skills in order to increase their comprehensive competitiveness in the market Indeed the need of process data exchange is an open issue in particular for enterprise networks. A number of standards like EDIFAcr, 1S010303 and ANS1 X12 are providing the basis for increasingly reliable solutions. Nevertheless also emerging standards like XML are supporting the development of new solutions for enterprise networks. This is the case of the EP 28448
INTRODUcnON
The context of this paper is enterprise modelling. where a huge number of other initiatives already exists. Under the umbrella of the ESPRIT research program significant initiatives are the EP 8224 project, RUMS - A rule based manufacturing modelling system; the EP 2165 project, IMPPAcr An approach to integrate product and process modelling for discrete parts manufacturing; the EP 8997 project, COMPLAN Concum:nt manufacturing planning and shop-floor control for small-batch production. Many modelling solutions are based on the building block approach, Petri nets or IDEF (Mayer, R. ]., et al. 1995). Among others, the GRAI Integrated Methodology (Doumeningts, 1989) defined a reference model based on three different formalisms for modelling the main enterprise subsystems. A further relevant initiative is the Process Specification Language project (PSL),
285
GNOSIS-VF project - Toward the virtual factory: delivering configuration, scheduling and monitoring services through a web-based client-server architecture. The GNOSIS-VF project is aimed at developing an integration platform for supporting the exchange of process data within virtual factories. The GNOSIS-VF model of the distributed production process is inspired to that developed during the EP 25359 EPSYLON project, which is based on a rule based approach. Indeed, EPSYLON started from the rule-based modelling approach developed by the RUMS project (Bonfatti, et al.,1997), addressing the formalisation capability for all shop-floor activities, both manufacturing and atypical ones, like returned products recycling and resources maintenance. The formalised factory activities are used to feed the software tools dedicated to decision support, planning and control, providing them with details about the state and capability of the shop-floor, in particular reflecting the effects of concurrent activities liable to detract resources from the mainstream production. It is the aim of this paper to describe the basis of the EPSYLON model and the features of the developed supporting tools that take advantage of the shared model.
2.
THE CONTEXT OF THE ENHANCED MODEL
A key notation affecting the competitiveness of enterprises in the coming times is green manufacturing. Resource consumption and pollution have provided the initial push to the promulgation of environmental laws that have started to impose restrictions on company actIVItIes affecting ecological and health issues. It can not be denied that nowadays green manufacturing represents an increasingly important factor for competitiveness in a conscious market demanding both quality and environmental safeguards. Most successful enterprises, with few exceptions, maintain their competitiveness by fast reactions to market evolution, by innovative products and modification of their production lines. This is an even more complicated task when taking into account the new environmental issues, affecting both the production system and the product structures themselves. Facing new issues like the recycling of products at the end of life-cycle, while maintaining the production line capabilities and effectiveness, and studying new prototypes are all aims that cannot be neglected, but whose achievement has various implications for the manufacturing mainstream. Such a considerations are particularly true of small and medium enterprises, but also in the large ones it may be difficult to gain a comprehensive top management overview of the shop-floor activity, when the information flow between different functional areas may be distracted. This is typical of large enterprises, but the lack of knowledge is also a factor for small enterprises where a flat organisational schema allows key
persons to keep the enterprise know-how.
3.
THE MODEL KERNEL
The EPSYLON approach relies on rule based model. The inspiring objective of and guiding principle for its definition has been the capacity to reduce the acceptance problems for users not skilled in the adoption of commercial IT tools for scheduling, shop-floor monitoring, simulation of interesting scenarios and other, besides the collection of very detailed information about the factory. A number of commercial tools can be customised by the users or they are sufficiently generic to be applied in different areas, but in most cases the final result is that the knowledge must be adapted to such tools. Difficulty in use and doubts over usefulness as well poor data formalisation, are the main problems. The EPSYLON approach aims to gain the confidence of the end users by taking into account that their targets and knowledge address the shop-floor and its processes, dealing with concepts that are strictly related to the working environment. In brief, the EPSYLON approach is a modelling solution for every manufacturing environment, particularly conceived to embrace the whole know-how of shopfloor performance, with an almost unique capacity to formalise the atypical activities brought about by the requirements of green manufacturing.
3.1
1ntensional and extensional model
A main characteristic of the model is that it is a two layer model, based on definition of knowledge at the intensional and the extensional levels. The intensional level is used to defme the concepts useful in describing the shop-floor, i.e. the types of interest, like part types, resource types and so on (see paragraph 2.2). The extensional level facilitates the defmition of the state information concerning the shop-floor, namely the instances of the types defined at the intensional level. A simple example would be the following: every shop-floor has the concept of resource, while the extensional description of the shop-floor needs to assess the existing resource instances of the declared types; it means that if a Lathe resource type is defined at the intensional level, then instances lAthe-A and lAthe-B can be introduced in the extensional shop floor. How can such a knowledge be used? Tools using the model know the behaviour of the lAthe type defined at the intensional level, hence they can determine the precise behaviour of the instances lAthe-A and Lathe-B when a certain activity must be carried out. Note that also the capability of the resource types to perform all the activities concerned can be formalised by means of the basic elements of the model. In this way, a detailed shop-floor behaviour and state consistency is always ensured. Furthermore, to change the shop-floor by adding new resource
286
instances or removing some of the existing ones is very simple since the resource types are already defined Modified scenarios can be built to study the shop-floor reactions to machine failures, starting new processes or benefits of introducing new machines.
3.2
and outputs can characterise the same operation type. Detailed operations have primary and secondary inputs (I) and outputs (0); primary I and 0 belong to the process mainstream, while secondary I and 0 are goods like consumable materials (I) and scrap (0).
Process flow: it represents the process schema describing manufacturing or atypical shop-floor activities. Complex process flows can be described by operations and alternatives, named splits and joins. The alternatives, with branch percentages, are conceived to introduce parallel process paths, different operation results as in the test operations and, in general, every process flow distribution need An operational schema is based on chained nodes linking the proper operations and alternatives. A node is used to build the precedence between two operations (alternatives), identifying the part types produced and consumed by such operations (alternatives). Initial and final nodes of a schema are characterised by a single operation (alternative).
The primitives of the intensional model
The model is based on a set of primitive concepts derived from the practical manufacturing environment. Every tangible entity and activity characterising the shop-floor can be fonnalised through such primitives. As a result, the user can immediately employ his knowledge and experience to construct the model of different entities, having available a set of concepts that is used to and suitable for the required definition. For example, a product structure may be defined on the specifics of the technical office, while the maintenance manager will define the resource structure by taking into account the maintenance requirements of its components. Both of them are based on the same hierarchical composition structure, well known and comprehensible to every user.
@
Manufactured
D Purchased
o o Recycled Retumerl
[>
Order: it represents the request for parts in a given quantity for a given date. Acquisition orders are of two kinds: purchasing orders or take-back orders. The latter concern returned parts coming from customers at the end of their life cycle or for repair. Manufacturing orders concern parts, whose production is guided by a proper operational schema. Resources or their components are subjects of maintenance orders. Different maintenance processes can involve the same resource, hence when issuing a maintenance order it must be decided which schema shall be executed.
Consumable
OScrnp ~ Resoun:e
o
Generic
Part repository: the model detail can classify part types not only on the basis of categories they belong to, but also according to different possible states, asking for a definition of repository being able to identify properly the contained parts (for example waste oil or new oil tanks). In brief, the model defines a location as a physical place where part types can be stored. The concept of buffer is used to describe a part type in a certain state and within a particular location. Every resource, when performing a task, receives the materials to be worked from input buffers and delivers the resulting products and byproducts to output buffers.
Fig. 1. Part categories and icons In brief, the model is based on the following primitive concepts:
Part type: it formalises compounds or components necessary to represent materials, products and resources managed on the shop-floor. Parts can be grouped into families, can have a composition structure and may belong to built-in categories (see Fig. I). Besides, every part type has a state that can be changed as a consequence of the treatment it is subjected to.
Resource: this is an abstract primitive, since the model is based on resource specialisations, namely primary, manpower and auxiliary resources. These are the resource categories used to detail the shopfloor behaviour when activities are carried out. A primary resource is an autonomous resource able to perform one or more operation types, a capability that is formalised by the concept of task. Manpower and auxiliary resources assist primary resources when they are in charge of certain operations and the operative case requirements are stated again by means of the task types. So, a task is the definition of the behaviour of a primary resource when
Operation type: this represents every kind of activity performed on the shop-floor, whose description is resource-free (Bonfatti, et al.,1998). It means that an operation formalises an activity without saying how a certain type of resource can carry out the activity itself, so that an operation can be described just as a black box linking input and output materials. By defining the operations the user can describe the simplest steps of his processes postponing implementation issues than will be solved by other primitives. In the most generic case, multiple inputs
287
perfonning one or more operation types. The behaviour of a primary resource specified by the task is composed of (i) a configuration requirement in tenns of manpower and auxiliary resources needed to succeed in accomplishing the operations concerned; (ii) a time schedule for the configured primary resource, which states the engagement time of both materials and the resources involved (primary, then manpower and auxiliary when needed). It can be argued that, in general, the engagement time for the same task may vary on the basis of the state and availability of the resource before starting the new activity. This is taken into account by means of configuration constraints and temporal frames of the primary resource types. The former are constraints due to the re-configuration needs of a primary resource when passing from the execution of a given task to another. The latter describes at the intensional level the link between features (time variables) of the primary resource engagement and the time variables of the manpower and auxiliary types it requires to work. When planning the activities by scheduling the proper tasks, the primary resource schedule can be finalised on the basis of the formalised constraints and the acquired knowledge of the state of the resource assessed by the tasks already planned.
3.3
The extensional model
The process dynamics can be simulated, controlled or scheduled once the shop-floor is designed in tenns of location and resource instances. Defining the extensional model with existing locations and resources, the intensional model is able to provide the knowledge necessary to know the shop-floor behaviour and potential with the declared instances. Also, the extensional model pennits the introduction into the system of all the constraints that may affect every resource instance behaviour, by defining the relations between the resource instances and the location instances. Consider again the previous example concerning the instances Lathe-A and LatheB corresponding to the same resource type Lathe. Both of them are able to perform a certain operation type according to the definitions provided in the intensional model, for example cutting dies. Nevertheless, only Lathe-B is used to produce dies. Actually, Lathe-B will be allowed to perform the cutting dies operation being linked to the proper location instances, that is the input locations providing the proper input steel bars and the output location devoted to store the dies. This exemplifies how proper links among resources and locations at the extensional level can limit the resource performances according to the actual or desired material flows within the shop-floor. Furthermore, shop-floor reconfigurations at the extensional level can be studied in order to evaluate change in the company strategy or to face unusual situations, trying to reduce the side effects of such events. The potential of the extensional model combined with the intensional model is very high, limiting the amount of further process forrnalisations required when modifying the shop-floor scenario for the definition of the desired configuration.
Operational logic: it defines in a simple way the shop-floor dynamics, by means of process, buffer, resource and task execution logic. The lower precision in operational logic is balanced by greater model usability. Firstly, the process flow logic is linked to the alternatives and concerns the flow distribution among their branches, weighting importance of every branch against a percentage, if needed. Secondly, the resource logic is aimed at determining the values of temporal variables identifying the boundaries of the resource engagement time. Each resource has an associated list of behaviour rules describing the time constraints detennined by a configuration change, a particular task execution or a certain buffer employment. Thirdly, three main constraints on buffer behaviour constitute the buffer logic: (i) Buffer finite capacity can be imposed by physical constraints on the location to which the buffer belongs. (ii) Buffer minimum storage time is used when a certain time must elapse before the next operation start. (iii) Buffer maximum storage time is used when the part requires to be worked by a given deadline. Finally, the task execution logic stipulates how task assignment takes place. Observing that one or more resources can perform an operation type and that every resource generally can perform more operations, the task execution logic can be expressed according to two different points of view: (I) for every resource, it can express the criteria for the selection of the next task to be executed; (2)for every operation, it can express the criteria for the selection of the next task to be executed.
3.4
The graphical interface
The use of tenns that are well understood by the end user is only the first step toward the success of the proposed modelling approach. A further step is the capability of providing the user with an easy to use and intuitive modelling tool. The EPSYLON process model has a graphical interface for the process definition which facilitates the process construction, thus reducing the user training needs. The process manager is simply required to introduce some data concerning its daily experience, that is, part types and operation types, then the graphical constructor can be used to build every process. During the experiment phase of the EPSYLON prototypes the effectiveness and user-friendliness of the graphical tool encouraged confidence among users in the employment of the software. After the first steps resulting in the process framework forrnalisations, the full model versatility can be tested by filling the system with any required timing detail and resource engagement for previously defined activities. In
288
particular, the user can refme the model by filling the system with rules that represent constraints like reconfiguration needs of a resource changing its present activity, buffer links and further constraints provided through the operational logic.
4.
EPSYLON TOOL SUITE
The EPSYLON process modeller is just the core of a software tool suite developed during the project. In fact, it is necessary to make the model potential available to proper enterprise supporting tools in order to get benefits from its content. Hence, the EPSYLON architecture provides also two decision support systems for maintenance and recycling respectively, one simulation and one strategic analysis service, as well as an integration capability for user legacy systems, in particular monitoring and scheduling applications. Furthermore, any need for data exchange can be satisfied with a translation tool providing STEP compliant model data. Being SME the main target of the developed solution, the EPSYLON software has been conceived to satisfy the user needs in terms of both reduced investment and well defined intervention area. In brief, an EPSYLON installation can be based on the process modeller plus the proper supporting tool to meet the main company needs. After that, the user can upgrade its installation by adding other EPSYLON tools or integrating its legacy systems to take advantage of the EPSYLON process model content, all the knowledge already formalised since the initial installation being available.
s.
encapsulation module able to fmalise the integration of package any already used that must be integrated (see Fig. 2).
INTEGRATION OF SCHEDULER AND MONITORING LEGACY SYSTEM
The benefits derived from the employment of the EPSYLON modelling approach are tangible even though the adoption of its management tools has a low impact on the user site. Having in mind people used to working with legacy systems and enterprises with low investment capacity, a typical scenario for SME, the need for integration between the proposed model and the existing user supporting tools is clear with the objective of reducing acceptance problems of new software. Nowadays, whenever an IT solution is capable of ensuring a working integration and interaction between the different tools occupied with the support for different company areas (pDMlERPIMRP), such a solution is generally out of the SME scope (Miller 1999).
ScbeduJina encap.ul.tioo module
GeneraJ Service
Monitoring encapsulation module
Fig. 2. Legacy system integration The core of the EPSYLON integration is the interface module, based on a Database Interface layer and a General Service layer. The former makes the model knowledge accessible to the legacy systems in a transparent way, the latter is a workflow manager engine dealing with the factory information requests issued by any integrated IT supporting tool. The most significant case may be the integration of monitoring and scheduling packages already installed in a user factory before the introduction of EPSYLON. By integrating commercial packages for the control and the scheduling of the shop-floor, such packages can exploit the detailed knowledge stored in the feeding model, contributing also to the continuous refinement and updating of the model itself. In fact, not only is the status of the running processes verified, but also any modification in their used performances is noticed by the managers, which can decide on a model updating on the basis of the observed shopfloor behaviour. The need for model adjustment a short time after the software installation may be caused by a still rough formalisation of the process knowledge. Nevertheless, in the following the model updating would arise from the increased manager skill in keeping the control on the shop-floor trends.
6.
MAINTENANCE AND RECYCLING DSS
A number of modelling tools have already been developed for the creation of IT support systems, so the EPSYLON approach might seem to be a wheel reinvented, since GUI for process defmition and tools integration are not a novelty. On the contrary, considering the EPSYLON modelling capability for both manufacturing and atypical activities which can be represented and managed in a unified way, a number of applications can be developed or integrated for the support to the decision making. EPSYLON provides a model versatility that is missing in the majority of other existing solutions mainly devoted to the manufacturing scope. To prove the EPSYLON model effectiveness and address the question of support in decision making in the atypical activities of end user companies, two decision support systems for resource maintenance and
It must be observed that the EPSYLON interface module is a gateway for the integration of the EPSYLON process model with any other kind of commercial package already existing in a SME that can take advantage of its high level of detail. The result is achieved by an application independent basic integration service, that must be completed with an
289
recycling have been developed. The DSS have been conceived for employment at the operative level and at the management level. In the first case, a tool interface into the shop-floor is provided and addresses the decisional requirements of the workers. In particular, the study of recycling activity highlighted a critical subject, namely uncertainty of the state of returned products, the main side effects of which is in general errors within warehouses, bad resource employment and consequently low process effectiveness. At present, the main efforts of researchers and software producers have addressed the recycling issues in the design phase (Simon 1994; Andreu 1995; Dowie and Simon 1994) and in the disposal phase of products, neglecting the need for user support during the execution of recycling. EPSYLON fills this empty support area by providing checklists and decisional criteria for every intervention in the recycling processes defmed by the process modeller. The best practices become the daily results. Returning to the management level of the DSS, it ensures control over the supported areas on the basis of analysis functions which consider the feedback provided by the operative modules employed in the shop-floor. This feedback is very precious not only for the running process survey and the historical data collection, but also for considering the usefulness of the provided support and the consequent possibility of updating it, when needed. Actually the EPSYLON recycling DSS offers the means of ensuring the effectiveness of the design for recycling by enhancing the feedback from the shopfloor and the adherence of the processes to the desired practice.
maintenance DSS is tested in a company forging parts for the automotive industry; simulation and recycling support systems are tested in a company providing refurbishing services for telecommunication devices and in a company providing refurbishing of railway equipment; fmally, the full simulation services made of discrete and continuous simulation tools fed by the process modeller are used in a second company providing railway equipment refurbishing.
REFERENCES Andreu, J.J., (1995). The Remanufacturing Process. DDR!TR24 Technical report, DFE. Bonfatti, F., Monari, P. D. and Paganelli, P. (1997). A rule-based manufacturing modelling system. International Journal on Computer Applications in Technology UCAT, 10, 1-2. Bonfatti, F., Monari, P. D. and Paganelli P. (1998). Resource-free and resource-dependent aspects of process modelling: a rule-based conceptual approach. International Journal of Computer Integrated Manufacturing, UCIM, 11,1. Doumeingts, G., et al. (1995). GRAI Approach: A Methodology for Re-Engineering the Manufacturing Enterprise. Re-engineering the enterprise, Galway, Chapman & Hall. Dowie, T. and Simon, M. (1994). Guidelines for designing for disassembly and recycling. DDRlTR18 Technical report, DFE. Mayer, R. J., et al. (1995). IDEF3 process description capture method report, Knowledge Based Systems Inc., Texas. Miller, E. (September 1999). Integrating PDM and ERP, CAE and Midrange ERP Magazine. Schlenoff, C., Gruninger, M., et al. (1997). The Process Specification Language (PSL) Overview and Version 1.0 Specification. NIST Internal Report (NISTIR) 6459. Simon, M. (1994). Product design for sustainable development, DFEITR19 Technical report. DFE.
7. CONCLUSIONS The enhanced process modelling system for lean operation management, developed by the EPSYLON project, offers a solution to the wider control and knowledge collection of every manufacturing shopfloor. It also offers the capability to collect the knowledge related to atypical activities, besides the chance of getting support tools in the related areas or integrate any legacy system. that means to provide the modelled knowledge to the cited packages. The basic core model can be viewed and understood also in the shop-floor area, meeting in a short time the requirements of any enterprise user, and this is possible since it has been founded on their common experience and perception. This should reduce the difficulties in the data flow from the factory to the management, with a number of benefits coming from the concentration of increasingly updated process know-how within the information system. At present the EPSYLON software is tested in four experiments. Every test case is targeted to the requirements of the end user, giving reason to a proper software configuration always based on the process modelling tool and proper supporting tools. The integration of monitoring and scheduling legacy systems with the
290
ENHANCED MODELLING AND DSS TOOLS TO SUPPORT GREEN MANUFACTURING
F1avio Bonfatti (1), Paola Daniela Monari (1), Sebutiano Sighinolfl (2)
(1) Dept. of Engineering Sciences, University ofModena and Reggio Emilia, via Campi 2131B, 41100. Modena Italy Tel +39059376732 Fax +39059376799 E-mail [email protected] (2) Democenter. viale Virgilio 55,41100 Modena Italy Tel +39 059 848810 Fax +39059848630 E-mail [email protected]
Abstract: the EPSPRIT 25359 EPSYLON project introduced a high semantic level process and product model conceived in order to collect the full life-cycle information of a product, from manufacturing to final recycling or disposal. The process model is the shared kernel of new software applications and integrated legacy systems, providing decision support to different company business areas. Such supporting tools contribute to collecting of data for the model updating, which, in turn makes available information on the actual shop-floor performances and capabilities to any enquiring tool at any time. This is particularly useful for the control of atypical activities competing with the manufacturing mainstream for the employment of the productive resources. Copyright © 2000 IFAC. Keywords: modelling, management, integration, simulation, manufacturing
1.
aimed at creating a specification language to capture the process knowledge that will facilitate the complete and correct exchange of process information among manufacturing applications (Schlenoff, C., Gruninger, M., et al., 1997). In the new economy an enterprise can have also a not conventional meaning. Actually, virtual enterprises and virtual factories are describing business partnerships and supply chains conceived as enterprise networks. Such networks allow small and medium enterprises to join resources and different skills in order to increase their comprehensive competitiveness in the market Indeed the need of process data exchange is an open issue in particular for enterprise networks. A number of standards like EDIFAcr, 1S010303 and ANS1 X12 are providing the basis for increasingly reliable solutions. Nevertheless also emerging standards like XML are supporting the development of new solutions for enterprise networks. This is the case of the EP 28448
INTRODUcnON
The context of this paper is enterprise modelling. where a huge number of other initiatives already exists. Under the umbrella of the ESPRIT research program significant initiatives are the EP 8224 project, RUMS - A rule based manufacturing modelling system; the EP 2165 project, IMPPAcr An approach to integrate product and process modelling for discrete parts manufacturing; the EP 8997 project, COMPLAN Concum:nt manufacturing planning and shop-floor control for small-batch production. Many modelling solutions are based on the building block approach, Petri nets or IDEF (Mayer, R. ]., et al. 1995). Among others, the GRAI Integrated Methodology (Doumeningts, 1989) defined a reference model based on three different formalisms for modelling the main enterprise subsystems. A further relevant initiative is the Process Specification Language project (PSL),
285
GNOSIS-VF project - Toward the virtual factory: delivering configuration, scheduling and monitoring services through a web-based client-server architecture. The GNOSIS-VF project is aimed at developing an integration platform for supporting the exchange of process data within virtual factories. The GNOSIS-VF model of the distributed production process is inspired to that developed during the EP 25359 EPSYLON project, which is based on a rule based approach. Indeed, EPSYLON started from the rule-based modelling approach developed by the RUMS project (Bonfatti, et al.,1997), addressing the formalisation capability for all shop-floor activities, both manufacturing and atypical ones, like returned products recycling and resources maintenance. The formalised factory activities are used to feed the software tools dedicated to decision support, planning and control, providing them with details about the state and capability of the shop-floor, in particular reflecting the effects of concurrent activities liable to detract resources from the mainstream production. It is the aim of this paper to describe the basis of the EPSYLON model and the features of the developed supporting tools that take advantage of the shared model.
2.
THE CONTEXT OF THE ENHANCED MODEL
A key notation affecting the competitiveness of enterprises in the coming times is green manufacturing. Resource consumption and pollution have provided the initial push to the promulgation of environmental laws that have started to impose restrictions on company actIVItIes affecting ecological and health issues. It can not be denied that nowadays green manufacturing represents an increasingly important factor for competitiveness in a conscious market demanding both quality and environmental safeguards. Most successful enterprises, with few exceptions, maintain their competitiveness by fast reactions to market evolution, by innovative products and modification of their production lines. This is an even more complicated task when taking into account the new environmental issues, affecting both the production system and the product structures themselves. Facing new issues like the recycling of products at the end of life-cycle, while maintaining the production line capabilities and effectiveness, and studying new prototypes are all aims that cannot be neglected, but whose achievement has various implications for the manufacturing mainstream. Such a considerations are particularly true of small and medium enterprises, but also in the large ones it may be difficult to gain a comprehensive top management overview of the shop-floor activity, when the information flow between different functional areas may be distracted. This is typical of large enterprises, but the lack of knowledge is also a factor for small enterprises where a flat organisational schema allows key
persons to keep the enterprise know-how.
3.
THE MODEL KERNEL
The EPSYLON approach relies on rule based model. The inspiring objective of and guiding principle for its definition has been the capacity to reduce the acceptance problems for users not skilled in the adoption of commercial IT tools for scheduling, shop-floor monitoring, simulation of interesting scenarios and other, besides the collection of very detailed information about the factory. A number of commercial tools can be customised by the users or they are sufficiently generic to be applied in different areas, but in most cases the final result is that the knowledge must be adapted to such tools. Difficulty in use and doubts over usefulness as well poor data formalisation, are the main problems. The EPSYLON approach aims to gain the confidence of the end users by taking into account that their targets and knowledge address the shop-floor and its processes, dealing with concepts that are strictly related to the working environment. In brief, the EPSYLON approach is a modelling solution for every manufacturing environment, particularly conceived to embrace the whole know-how of shopfloor performance, with an almost unique capacity to formalise the atypical activities brought about by the requirements of green manufacturing.
3.1
1ntensional and extensional model
A main characteristic of the model is that it is a two layer model, based on definition of knowledge at the intensional and the extensional levels. The intensional level is used to defme the concepts useful in describing the shop-floor, i.e. the types of interest, like part types, resource types and so on (see paragraph 2.2). The extensional level facilitates the defmition of the state information concerning the shop-floor, namely the instances of the types defined at the intensional level. A simple example would be the following: every shop-floor has the concept of resource, while the extensional description of the shop-floor needs to assess the existing resource instances of the declared types; it means that if a Lathe resource type is defined at the intensional level, then instances lAthe-A and lAthe-B can be introduced in the extensional shop floor. How can such a knowledge be used? Tools using the model know the behaviour of the lAthe type defined at the intensional level, hence they can determine the precise behaviour of the instances lAthe-A and Lathe-B when a certain activity must be carried out. Note that also the capability of the resource types to perform all the activities concerned can be formalised by means of the basic elements of the model. In this way, a detailed shop-floor behaviour and state consistency is always ensured. Furthermore, to change the shop-floor by adding new resource
286
instances or removing some of the existing ones is very simple since the resource types are already defined Modified scenarios can be built to study the shop-floor reactions to machine failures, starting new processes or benefits of introducing new machines.
3.2
and outputs can characterise the same operation type. Detailed operations have primary and secondary inputs (I) and outputs (0); primary I and 0 belong to the process mainstream, while secondary I and 0 are goods like consumable materials (I) and scrap (0).
Process flow: it represents the process schema describing manufacturing or atypical shop-floor activities. Complex process flows can be described by operations and alternatives, named splits and joins. The alternatives, with branch percentages, are conceived to introduce parallel process paths, different operation results as in the test operations and, in general, every process flow distribution need An operational schema is based on chained nodes linking the proper operations and alternatives. A node is used to build the precedence between two operations (alternatives), identifying the part types produced and consumed by such operations (alternatives). Initial and final nodes of a schema are characterised by a single operation (alternative).
The primitives of the intensional model
The model is based on a set of primitive concepts derived from the practical manufacturing environment. Every tangible entity and activity characterising the shop-floor can be fonnalised through such primitives. As a result, the user can immediately employ his knowledge and experience to construct the model of different entities, having available a set of concepts that is used to and suitable for the required definition. For example, a product structure may be defined on the specifics of the technical office, while the maintenance manager will define the resource structure by taking into account the maintenance requirements of its components. Both of them are based on the same hierarchical composition structure, well known and comprehensible to every user.
@
Manufactured
D Purchased
o o Recycled Retumerl
[>
Order: it represents the request for parts in a given quantity for a given date. Acquisition orders are of two kinds: purchasing orders or take-back orders. The latter concern returned parts coming from customers at the end of their life cycle or for repair. Manufacturing orders concern parts, whose production is guided by a proper operational schema. Resources or their components are subjects of maintenance orders. Different maintenance processes can involve the same resource, hence when issuing a maintenance order it must be decided which schema shall be executed.
Consumable
OScrnp ~ Resoun:e
o
Generic
Part repository: the model detail can classify part types not only on the basis of categories they belong to, but also according to different possible states, asking for a definition of repository being able to identify properly the contained parts (for example waste oil or new oil tanks). In brief, the model defines a location as a physical place where part types can be stored. The concept of buffer is used to describe a part type in a certain state and within a particular location. Every resource, when performing a task, receives the materials to be worked from input buffers and delivers the resulting products and byproducts to output buffers.
Fig. 1. Part categories and icons In brief, the model is based on the following primitive concepts:
Part type: it formalises compounds or components necessary to represent materials, products and resources managed on the shop-floor. Parts can be grouped into families, can have a composition structure and may belong to built-in categories (see Fig. I). Besides, every part type has a state that can be changed as a consequence of the treatment it is subjected to.
Resource: this is an abstract primitive, since the model is based on resource specialisations, namely primary, manpower and auxiliary resources. These are the resource categories used to detail the shopfloor behaviour when activities are carried out. A primary resource is an autonomous resource able to perform one or more operation types, a capability that is formalised by the concept of task. Manpower and auxiliary resources assist primary resources when they are in charge of certain operations and the operative case requirements are stated again by means of the task types. So, a task is the definition of the behaviour of a primary resource when
Operation type: this represents every kind of activity performed on the shop-floor, whose description is resource-free (Bonfatti, et al.,1998). It means that an operation formalises an activity without saying how a certain type of resource can carry out the activity itself, so that an operation can be described just as a black box linking input and output materials. By defining the operations the user can describe the simplest steps of his processes postponing implementation issues than will be solved by other primitives. In the most generic case, multiple inputs
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perfonning one or more operation types. The behaviour of a primary resource specified by the task is composed of (i) a configuration requirement in tenns of manpower and auxiliary resources needed to succeed in accomplishing the operations concerned; (ii) a time schedule for the configured primary resource, which states the engagement time of both materials and the resources involved (primary, then manpower and auxiliary when needed). It can be argued that, in general, the engagement time for the same task may vary on the basis of the state and availability of the resource before starting the new activity. This is taken into account by means of configuration constraints and temporal frames of the primary resource types. The former are constraints due to the re-configuration needs of a primary resource when passing from the execution of a given task to another. The latter describes at the intensional level the link between features (time variables) of the primary resource engagement and the time variables of the manpower and auxiliary types it requires to work. When planning the activities by scheduling the proper tasks, the primary resource schedule can be finalised on the basis of the formalised constraints and the acquired knowledge of the state of the resource assessed by the tasks already planned.
3.3
The extensional model
The process dynamics can be simulated, controlled or scheduled once the shop-floor is designed in tenns of location and resource instances. Defining the extensional model with existing locations and resources, the intensional model is able to provide the knowledge necessary to know the shop-floor behaviour and potential with the declared instances. Also, the extensional model pennits the introduction into the system of all the constraints that may affect every resource instance behaviour, by defining the relations between the resource instances and the location instances. Consider again the previous example concerning the instances Lathe-A and LatheB corresponding to the same resource type Lathe. Both of them are able to perform a certain operation type according to the definitions provided in the intensional model, for example cutting dies. Nevertheless, only Lathe-B is used to produce dies. Actually, Lathe-B will be allowed to perform the cutting dies operation being linked to the proper location instances, that is the input locations providing the proper input steel bars and the output location devoted to store the dies. This exemplifies how proper links among resources and locations at the extensional level can limit the resource performances according to the actual or desired material flows within the shop-floor. Furthermore, shop-floor reconfigurations at the extensional level can be studied in order to evaluate change in the company strategy or to face unusual situations, trying to reduce the side effects of such events. The potential of the extensional model combined with the intensional model is very high, limiting the amount of further process forrnalisations required when modifying the shop-floor scenario for the definition of the desired configuration.
Operational logic: it defines in a simple way the shop-floor dynamics, by means of process, buffer, resource and task execution logic. The lower precision in operational logic is balanced by greater model usability. Firstly, the process flow logic is linked to the alternatives and concerns the flow distribution among their branches, weighting importance of every branch against a percentage, if needed. Secondly, the resource logic is aimed at determining the values of temporal variables identifying the boundaries of the resource engagement time. Each resource has an associated list of behaviour rules describing the time constraints detennined by a configuration change, a particular task execution or a certain buffer employment. Thirdly, three main constraints on buffer behaviour constitute the buffer logic: (i) Buffer finite capacity can be imposed by physical constraints on the location to which the buffer belongs. (ii) Buffer minimum storage time is used when a certain time must elapse before the next operation start. (iii) Buffer maximum storage time is used when the part requires to be worked by a given deadline. Finally, the task execution logic stipulates how task assignment takes place. Observing that one or more resources can perform an operation type and that every resource generally can perform more operations, the task execution logic can be expressed according to two different points of view: (I) for every resource, it can express the criteria for the selection of the next task to be executed; (2)for every operation, it can express the criteria for the selection of the next task to be executed.
3.4
The graphical interface
The use of tenns that are well understood by the end user is only the first step toward the success of the proposed modelling approach. A further step is the capability of providing the user with an easy to use and intuitive modelling tool. The EPSYLON process model has a graphical interface for the process definition which facilitates the process construction, thus reducing the user training needs. The process manager is simply required to introduce some data concerning its daily experience, that is, part types and operation types, then the graphical constructor can be used to build every process. During the experiment phase of the EPSYLON prototypes the effectiveness and user-friendliness of the graphical tool encouraged confidence among users in the employment of the software. After the first steps resulting in the process framework forrnalisations, the full model versatility can be tested by filling the system with any required timing detail and resource engagement for previously defined activities. In
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particular, the user can refme the model by filling the system with rules that represent constraints like reconfiguration needs of a resource changing its present activity, buffer links and further constraints provided through the operational logic.
4.
EPSYLON TOOL SUITE
The EPSYLON process modeller is just the core of a software tool suite developed during the project. In fact, it is necessary to make the model potential available to proper enterprise supporting tools in order to get benefits from its content. Hence, the EPSYLON architecture provides also two decision support systems for maintenance and recycling respectively, one simulation and one strategic analysis service, as well as an integration capability for user legacy systems, in particular monitoring and scheduling applications. Furthermore, any need for data exchange can be satisfied with a translation tool providing STEP compliant model data. Being SME the main target of the developed solution, the EPSYLON software has been conceived to satisfy the user needs in terms of both reduced investment and well defined intervention area. In brief, an EPSYLON installation can be based on the process modeller plus the proper supporting tool to meet the main company needs. After that, the user can upgrade its installation by adding other EPSYLON tools or integrating its legacy systems to take advantage of the EPSYLON process model content, all the knowledge already formalised since the initial installation being available.
s.
encapsulation module able to fmalise the integration of package any already used that must be integrated (see Fig. 2).
INTEGRATION OF SCHEDULER AND MONITORING LEGACY SYSTEM
The benefits derived from the employment of the EPSYLON modelling approach are tangible even though the adoption of its management tools has a low impact on the user site. Having in mind people used to working with legacy systems and enterprises with low investment capacity, a typical scenario for SME, the need for integration between the proposed model and the existing user supporting tools is clear with the objective of reducing acceptance problems of new software. Nowadays, whenever an IT solution is capable of ensuring a working integration and interaction between the different tools occupied with the support for different company areas (pDMlERPIMRP), such a solution is generally out of the SME scope (Miller 1999).
ScbeduJina encap.ul.tioo module
GeneraJ Service
Monitoring encapsulation module
Fig. 2. Legacy system integration The core of the EPSYLON integration is the interface module, based on a Database Interface layer and a General Service layer. The former makes the model knowledge accessible to the legacy systems in a transparent way, the latter is a workflow manager engine dealing with the factory information requests issued by any integrated IT supporting tool. The most significant case may be the integration of monitoring and scheduling packages already installed in a user factory before the introduction of EPSYLON. By integrating commercial packages for the control and the scheduling of the shop-floor, such packages can exploit the detailed knowledge stored in the feeding model, contributing also to the continuous refinement and updating of the model itself. In fact, not only is the status of the running processes verified, but also any modification in their used performances is noticed by the managers, which can decide on a model updating on the basis of the observed shopfloor behaviour. The need for model adjustment a short time after the software installation may be caused by a still rough formalisation of the process knowledge. Nevertheless, in the following the model updating would arise from the increased manager skill in keeping the control on the shop-floor trends.
6.
MAINTENANCE AND RECYCLING DSS
A number of modelling tools have already been developed for the creation of IT support systems, so the EPSYLON approach might seem to be a wheel reinvented, since GUI for process defmition and tools integration are not a novelty. On the contrary, considering the EPSYLON modelling capability for both manufacturing and atypical activities which can be represented and managed in a unified way, a number of applications can be developed or integrated for the support to the decision making. EPSYLON provides a model versatility that is missing in the majority of other existing solutions mainly devoted to the manufacturing scope. To prove the EPSYLON model effectiveness and address the question of support in decision making in the atypical activities of end user companies, two decision support systems for resource maintenance and
It must be observed that the EPSYLON interface module is a gateway for the integration of the EPSYLON process model with any other kind of commercial package already existing in a SME that can take advantage of its high level of detail. The result is achieved by an application independent basic integration service, that must be completed with an
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recycling have been developed. The DSS have been conceived for employment at the operative level and at the management level. In the first case, a tool interface into the shop-floor is provided and addresses the decisional requirements of the workers. In particular, the study of recycling activity highlighted a critical subject, namely uncertainty of the state of returned products, the main side effects of which is in general errors within warehouses, bad resource employment and consequently low process effectiveness. At present, the main efforts of researchers and software producers have addressed the recycling issues in the design phase (Simon 1994; Andreu 1995; Dowie and Simon 1994) and in the disposal phase of products, neglecting the need for user support during the execution of recycling. EPSYLON fills this empty support area by providing checklists and decisional criteria for every intervention in the recycling processes defmed by the process modeller. The best practices become the daily results. Returning to the management level of the DSS, it ensures control over the supported areas on the basis of analysis functions which consider the feedback provided by the operative modules employed in the shop-floor. This feedback is very precious not only for the running process survey and the historical data collection, but also for considering the usefulness of the provided support and the consequent possibility of updating it, when needed. Actually the EPSYLON recycling DSS offers the means of ensuring the effectiveness of the design for recycling by enhancing the feedback from the shopfloor and the adherence of the processes to the desired practice.
maintenance DSS is tested in a company forging parts for the automotive industry; simulation and recycling support systems are tested in a company providing refurbishing services for telecommunication devices and in a company providing refurbishing of railway equipment; fmally, the full simulation services made of discrete and continuous simulation tools fed by the process modeller are used in a second company providing railway equipment refurbishing.
REFERENCES Andreu, J.J., (1995). The Remanufacturing Process. DDR!TR24 Technical report, DFE. Bonfatti, F., Monari, P. D. and Paganelli, P. (1997). A rule-based manufacturing modelling system. International Journal on Computer Applications in Technology UCAT, 10, 1-2. Bonfatti, F., Monari, P. D. and Paganelli P. (1998). Resource-free and resource-dependent aspects of process modelling: a rule-based conceptual approach. International Journal of Computer Integrated Manufacturing, UCIM, 11,1. Doumeingts, G., et al. (1995). GRAI Approach: A Methodology for Re-Engineering the Manufacturing Enterprise. Re-engineering the enterprise, Galway, Chapman & Hall. Dowie, T. and Simon, M. (1994). Guidelines for designing for disassembly and recycling. DDRlTR18 Technical report, DFE. Mayer, R. J., et al. (1995). IDEF3 process description capture method report, Knowledge Based Systems Inc., Texas. Miller, E. (September 1999). Integrating PDM and ERP, CAE and Midrange ERP Magazine. Schlenoff, C., Gruninger, M., et al. (1997). The Process Specification Language (PSL) Overview and Version 1.0 Specification. NIST Internal Report (NISTIR) 6459. Simon, M. (1994). Product design for sustainable development, DFEITR19 Technical report. DFE.
7. CONCLUSIONS The enhanced process modelling system for lean operation management, developed by the EPSYLON project, offers a solution to the wider control and knowledge collection of every manufacturing shopfloor. It also offers the capability to collect the knowledge related to atypical activities, besides the chance of getting support tools in the related areas or integrate any legacy system. that means to provide the modelled knowledge to the cited packages. The basic core model can be viewed and understood also in the shop-floor area, meeting in a short time the requirements of any enterprise user, and this is possible since it has been founded on their common experience and perception. This should reduce the difficulties in the data flow from the factory to the management, with a number of benefits coming from the concentration of increasingly updated process know-how within the information system. At present the EPSYLON software is tested in four experiments. Every test case is targeted to the requirements of the end user, giving reason to a proper software configuration always based on the process modelling tool and proper supporting tools. The integration of monitoring and scheduling legacy systems with the
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