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Journal of the Chinese Institute of Industrial Engineers,Vol.23,No.1,pp.34-47(2006)DESIGN(规划) FOR LOGISTICS IN SET-BASEDCONCURRENT同时的 ENGINEERING工程 ENVIRONMENT（环境）Hsing-Pei Kao*Institute of Industrial Management工程管理National Central University中央大学Chung-Li,Taoyuan 320,R.O.C.ABSTRACT摘要Design for Logistics(DFL)and Set-based Concurrent Engineering(SBCE)are two conventionally常规 separated methodologies for product design.The former intends to design products by taking into consideration the logistics system that the product needs to fit in,whereas the latter explores a set of design alternatives to converge on a final specification for both product and processes.Within the scheme of integrating DFL and SBCE,we develop a decision support framework to estimate logistics time and cost for a set of design alternatives and determine the best design by making tradeoff between these two perform-ance measures.In the proposed framework,High Level Petri Nets,Activity Based Costing,and TOPSIS are applied for the necessary functions.Keywords:set-based concurrent engineering,design for logistics,high level Petri nets,activity-based costing,TOPSIS.1.INTRODUCTION导言*Product design is the creation of a synthesized solution that satisfies needs.This usually involves consideration of various parameters and alternative configurations of various components.As the prevalent methodology,Concurrent Engineering(CE)simultaneously designs products and related processes by integrating resources into a collaborative course to develop,manufacture,and deliver economicallyquality products.Most CE researches,such as Design for Manufacture and Assembly(DFMA),focus on technical aspects and internal activities concerning product development。Owing to information and communication technology(ICT),the continuum of integration has extended to establish process-based relationships with trading partners that results in better synchroni-zation,responsiveness,and flexibility.Evidently, two evolving trends coexist and intertwine with each other in this networked industry.On the one hand, CE implementation of individual companies has shifted to cross-firm Collaborative Engineering. On the other hand,the emerging Collaborative Sup-ply Chain focuses on integrating business processesbetween trading partners with respect to planning ，sourcing,production,and delivery.Coinciding with the confluence of these two trends,Design for Logistics(DFL)and Design for Supply Chain Man-agement(DFSCM)becomes crucial.Briefly defined,DFL is a design approach seen from a single com-panys viewpoint,considering the capacities of trading partners during product design to increase logis-tics efficiency and service levels.Lately,DFSCM comes to the fore in collaboration and sharing design information between trading partners toachieve significant synergies in the development of new products.In this study,we focus on DFL.As shown in Figure 1, Figure 1.Business processes of product design and duct development,internal operations, and trading partnerships are interrelated in terms of process logic and resource availability.This relationship suggests that the logistics process should adapt to the requirements of new products while certain constraints are imposed on the design by logistical factors.Therefore,during the design phase,ex-amining the full scope of the logistics process and its capacity is important for efficiency of component supply and,finally,finished product delivery.Other-wise,excessive design changes,delays and costswould be likely to occur after the logistics process is set into action.Since Mather,the concept of DFL has been constantly mentioned in CE researches. However,the scope regarding DFL has been defined differently and there are only few operational methods for DFL analysis.Despite the fact that these studies provide sound logic with sophisticated mathematical methods,they do not explicitly relate the logistics process with product structure or they usually evaluate logistics performance merely based on single criterion.Furthermore,they overlookthe practicality that the embodiment design(the preliminary scaled engineering drawing)is essential for selecting suppliers and,later on,detailed design specification for scheduling downstream logisticsactivities and estimating related costs.Aside from the notable advantages of CE,its conventional implementation does have certain weaknesses.Referred as the point-based approach, the design team makes early commitments to a single solution and progressively refines it as the design process evolves.Yet,there is no guarantee that the process will ever converge and produce an optimalsolution.Additionally,since the design solution generated through any upstream function will be reviewed by downstream functions,more feedback loops or iterations will occur and,thus,increase project complexity and development costs. An improved approach is the Set-Based Concurrent Engineering(SBCE)originally implemented by Toyota Motor.This new approach seeks to define regions of the design space,characterize boundaries of current capabilities and discover where these boundaries can be expanded.By generating several design alternatives to select from,SBCE is consistent with the prevailing postponement strategy that decisions which constrain future choices are postponed for as long as possible until there is enough information available.Although it mayrequire more time to define solutions at an early stage and higher project cost by operating parallel design teams,SBCE makes it more likely that the best solution will be found and convergence will occur more rapidly in the later stages.There are two more potential benefits of SBCE.One is the early involvement of a greater number of suppliers will intensifycom-petition between the design teams in quality,project completion time and cost as well as commitment to a stable supply.The other is that the unselected design alternatives can be retained for future service if business conditions change.Although only few SBCE studies have been published,it should become an emerging design practice to develop more robust products and processes.When implementing SBCE,it is often found that the solution is Pareto optimal if none of the design alternatives is superior in every technical and manufacturability criterion.Thus,when the outcome of SBCE is a set of competing solutions,either making tradeoff decisions among the given criteria or adding more criteria for further comparison is encouraged.When evaluating alternative designs,it would be a logical approach to assess later logistics performance with respect to time,cost and balance of divergent objectives. At this point,the relation between SBCE and DFL regarding product design becomes evident due to the two-way relationship between product design and logistics,the postponement of design decision, and logistics performance for the evaluation of design alternatives.In short,regarding the SBCE setting, DFL provides additional criteria for determining which design solution is optimal. With in the scheme of integrating DFL and SBCE,we develop a decision support framework,SBCEDFL,to evaluate design alternatives in terms of multiple logistics criteria.Referring to,we define the logistics system as the total flow of materials,from the acquisition of raw materials to delivery of finished products to the market.To be precise,it covers inbound,production and outbound logistics of a manufacturing company(Figure 2).Assumptionsabout the framework include:(1)the product is designed with and assembled from modules,(2)there are multiple configuration alternatives of the product,(3)there are multiple component suppliers to select from the supplier base;the long-term collaboration has been established with suppliers to develop new products,(4)there are multiple product channels to select from the customer base,and(5)reliable information about logistical factors can only be obtained from the generated design alternatives.Figure 2.Logistics performance evaluation in the SBCE setting.Along with the SBCEDFL framework,we commence by modeling the logistics process with respect to each design alternative.Then,according to each process model,we estimate the logistics time and cost.Finally,we determine the best design alternative which will give us an optimal balance between these two performance measures.To provide needed analytical functions,High-Level Petri Nets(HLPN),Activity-Based Costing(ABC)and Technique for Order Preference by Similarity to Ideal Solution(TOPSIS) are applied respectively.This approach is advantageous since each method measures a given aspect of logistics performance in a flexible framework which may include other criteria of interest.In Section 2,we review literature related to DFL,Postponement of Design Decisions and SBCE to illustrate how they are interrelated.In Section 3, the SBCE deployment process and SBCEDFL architecture are presented.From section 4 to section 6,the logistics temporal simulator,logistics process costing,and logistics time/cost tradeoff decision are describedrespectively.In Section 7,a hypothetical case of designing a notebook computer is presented.Section 8 concludes and offers suggestions for future research.2.LITERATURE REVIEWAs logistics is about the process of moving materials and products into,through,and out of a firm,supply chain covers a broader scope in that it manages both the flow of materials and the relationships among channel intermediaries from the point of origin of raw materials through to the final consumer. While DFL focuses on the interface between logistics engineering,manufacturing logistics,design for packaging and design for transportability, DFSCM draws attention to delayed product differentiation,commonality,standardization,process step matching and postponement.As only few studies use the exact term DFL or DFSCM,a number of others address product design from logistics,design postponement and supplier involvement perspectives.Related issues include:(1)the relationship between DFL and the manufacturing changes,(2)therelationship between logistics systems and productdesign,e.g.,standardization of parts,postponement,modularity and configurations of end item,(3)the relationship between product variety,production process and the supply chain performance,(4)design for customization,localization,distribution,inventory,and delivery,(5)the hierarchical representation of DFL,and(6)critical areas of DFL,including packaging and transportation,concurrent and parallel processing,and postponement and delayed differentiation.Outside the academic research,product development for supply chain is getting serious attention from industry.For instance,in an on-going project, the Supply-Chain Council focuses on integrating product design process into a supply chain which is represented by Supply-Chain Operations Reference-model(SCOR).A subset of the SCOR logisticprocesses is applicable at the product design phase:(1)Plan Source-identify and select supply sources,assess supplier performance,and manage sup-plier network;(2)Enable Source-manage sourcing rules and maintain source data;(3)Plan Deliver-balance delivery resources with requirements and establish delivery plans;(4)Enable Deliver-manage deliver rules and assess delivery performance.The concept of postponement involves delaying activities until the latest possible point in time.The logic behind postponement is that the delay leads to greater availability of information and thus the riskand uncertainty in those activities can be reduced. Recently,the postponement strategy has been adopted to cope with different levels of uncertainty regarding product development,purchasing,production and logistics.According to7,rather than optimal or point solutions,it is important to preserve design freedom by searching and discovering more satisfying solutions in problem areas.Since SBCE has been publicized as an innovative design process where design specifications are given target ranges rather than a specific value,it is asserted to allow for betteroptimization of the product as well as flexibility of process to absorb unexpected design changes.By implementing SBCE,several design teams analyze, develop,and communicate about sets of solutions in parallel and relatively independently. Although SBCE involves delaying decisions about the final design,it has a fundamental difference from other prominent delayed product differentiation strategies.SBCE deliberately explore a broad range of possible solutions simultaneously in the earlierdesign stage and,as the design progresses,they gradually narrow their respective sets of solutions based on additional information from all the sets and thus converge on a final solution.In contrast,the general design postponement starts by making a generic or family product that is later differentiated into a specific end-product.Figure 3.Deployment process of SBCEDFL3.SBCE DEPLOYMENT PROCESS AND SBCEDFL ARCHITECTUREIn the SBCEDFL framework,the design project extends over three stages which include generation,evaluation and prioritization of design alternatives(Figure 3).The first stage focuses on technical requirements such as quality and manufacturability.Whereas the design tasks involve a mapping process from functional requirements of a product to its design parameters and manufacturing process variables, Quality Function Deployment(QFD)is advocated to systematically proceed with this mapping process through product planning,assembly/part deployment,production planning and planning for process control.In the SBCE setting,the front end activities(including product planning,customer requirement specification and functional design)are performed jointly by all design teams which will execute the rest of the process independently to generate their own design alternatives.Regarding products embodiment design and production planning,computer-aided design(CAD)and computer-aided production planning (CAPP)are utilized while manufacturability is the core issue associated with internal operations.Where as design alternatives generated from stage 1 could be comparable in terms of quality and manufacturability,their logistics processes may differ with respect to supplier sourcing,time and cost.According to each logistics process,stage 2 involves the assessment of its time and cost.In stage 3,tradeoffs are made between logistics time and cost to determine the best design alternative.As a decision support framework,SBCEDFL can be perceived as a computer-aided logistics planning(CALP)system used by the product manager who oversees all aspects of the product line.The outcome of the entire process is a design package which consists of the product design specification,production and in-bound-outbound logistics plans.Concerning the supplier involvement along the SBCE process,logistics network evaluation,supplier and channel evaluation, and final logistics plan go well with the procedure of partner selection:pre-qualifying partners,evaluating a product design concerning the capabilities of potential partners,and selecting the optimal set of partners.Furthermore,it should be valuable to refer to the logistic processes of SCOR for implementing SBCE in planning and enabling both supply and delivery activities,which can be seen in Section 2.4.LOGISTICS TEMPORAL SIMULATORLogistics Temporal Simulator is used to estimate lead-time from ordering materials to delivery of finished goods according to each design alternative. To begin with,a generic process model consisting of necessary logistics operations is converted into an HLPN model to estimate logistics time via simulation.As a general theory of discrete parallel systems,Petri nets are effective for modeling and simulating the dynamic behavior of the complex systems in which distributed,concurrent,asynchronous and nondeterministic events are inherent.The unique properties of Petri nets are their power in modeling system behavior,computing steady-state probabilities for performance measures,and analyzing deadlocksand setting conflict resolution priorities.In the last three decades,a great number of Petri nets extensions have been developed to simulate,schedule and control various processes.A basic Petri net model is a directed bipartite graph with two node types called places(denoted by)and transitions()which are connected by directed arcs()indicating whether a place is an input or output place of a transition.Places may contain tokens()which represent certain objects;while the number of tokens may change during the execution ofthe net.A transition is enabled if each of its input places contains enough tokens and it can fire by consuming tokens from the input places and producing tokens for the output places.A marking M,meaning the assignment of tokens to the places,is a function from the set of places P to a non-negative number N。If the marking of a place p is a non-negative integer k,then we say that p is marked with k tokens.An initial state of a Petri net is called the initial marking,M0. Analysis of Petri nets can be performed through matrix operations or by enumerating all possible markings to form reachability trees for checking whether some arbitrary state(s)can be reached from M0.Owing to the complexity of modeling logistics processes,an HLPN extended with various colored tokens,temporal properties of transitions and hierarchical architecture is utilized here.Different colors represent the unique attributes of tokens which stand for actual objects,such as components being assembled.Each token is marked with a timestamp andtransitions are marked with delay which can be expressed as a constant or a probability distribution to model the temporal behavior of the dynamic p