Concurrent Engineering http://cer.sagepub.com
A Multiple Perspective Product Modeling and Simulation Approach to Engineering Design Support Xiu-Tian Yan Concurrent Engineering 2003; 11; 221 DOI: 10.1177/106329303038027 The online version of this article can be found at: http://cer.sagepub.com/cgi/content/abstract/11/3/221
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CONCURRENT ENGINEERING: Research and Applications A Multiple Perspective Product Modeling and Simulation Approach to Engineering Design Support Xiu-Tian Yan* CAD Centre, Department of Design, Manufacture and Engineering Management, Strathclyde University, James Weir Building, 75 Montrose Street, Glasgow G1 1XJ, United Kingdom
Abstract: The competitive market requires better products designed and made in a shorter time with higher quality and lower cost. The speed of launching products onto the market and more importantly the quality of the products become increasingly important factors for a new product to become successful. With rapid advancement in computing power both in terms of hardware capability and software functionalities, product engineering designers are now better equipped to create and make new and novel products than ever before. Engineering designers have so far benefited from computer systems to aid their various design activities. Yet, at the same time, they still feel the inadequacy of these systems in coping with the increasing pressure for them to produce better products in a shorter time. Without committing further expense to develop super-computer design support systems, how the current systems are being best used becomes an important issue and research avenue for investigation. This paper describes an innovative design process model for computer based engineering design through an integrated and coherent use of these CAD systems. The design approach based on the computer multiperspective modeling and evaluation derived from the above design process model can provide comprehensive and integrated design support for various engineering design activities. The pragmatic approach derived in this research promotes the novel use of existing systems in an integrated yet manageable manner. Examples of how these systems have been used are described in the paper to illustrate the benefits. Key Words: multiperspective modeling, design evaluation, knowledge intensive modeling, simulation.
1.
Introduction
The increasing pressure from customers in today’s competitive market requires many manufacturing companies to produce a variety of products to satisfy rapidly changing market conditions. These products have to satisfy a whole spectrum of requirements ranging from basic functional requirements to esthetic requirements for different cultures and times. From a technology capability point of view, rapid advancement in available technologies means that there are now far more options available to a designer to solve a given design problem than any other time in design history. Companies as well as research institutions hence actively seek enabling technologies to facilitate their product development and improve their productivity and effectiveness in generating new design solutions and products. In order to achieve the above, designers want to make more informed design decisions to cut down rework, and more importantly to be more confident about their design solutions and the intended product performance once the design solutions are passed on to manufacture the products.
*E-mail:
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Due to a human being’s limitation in remembering relatively small amounts of information [1], it is infeasible to expect a designer to remember all abstract design descriptions and details – or effectively a comprehensive product model. Instead, a designer should do what a human does best, which is for the person to utilize his/her strength in judging a solution based on multiple criteria evaluation/reasoning and previous experience, making intuitive decisions during design, exploring fully design solution space, and knowing how to perform a number of design studies by investigating alternative solutions. On the contrary, over the last decade, the computational power of computer systems has increased exponentially. These achievements have resulted in the availability of higher performance computers at a relatively lower cost. This consequently presents an unprecedented opportunity for designers to rethink the traditional design methods and practice, especially within small to medium sized companies. With the rapid development of computer technology, computers can be relied on to remember and process a vast amount of information associated with a product being designed. They can perform many iterative design tasks, e.g. data storage and retrieval, computing, rulebased reasoning, and so forth. Computer systems can also handle very well both static and dynamic informa-
Volume 11 Number 3 September 2003 1063-293X/03/03 0221–14 $10.00/0 DOI: 10.1177/106329303038027 Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 16, 2008 ß reserved. 2003 Sage © 2003 SAGE Publications. All rights Not forPublications commercial use or unauthorized distribution.
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tion being generated during design processes. The above observation can lead to a division of the design tasks into the two broad categories: low level design activities such as storing information and retrieving details of partial design solutions, and overall high-level tasks which human beings are good at, e.g. decision makings, evaluating design solutions based on experience etc. Through this task division, design tasks can be clearly distributed among designers and computer systems and consequently the tasks can be effectively executed. This approach naturally leads to the need to identify specifications of computer systems to support design. From a software development point of view, more relevant for product design engineers is the fact that a number of advanced Computer Aided Design (CAD) systems are now available at affordable prices and can be run on PC-based platforms. This has created great opportunities for engineering designers especially working in small to medium sized companies, to think how to make the best use of these available technologies. Whilst these systems have improved design support markedly, due to the complex and individual experience based nature of product design process and modeling, no such computer system has so far been developed, which has sufficient functionality to handle all aspects of complex product modeling and design. This is therefore an interesting and challenging time for engineering designers seeking to use these tools, which provide some support, but not all the support designers hoped for. Therefore identifying appropriate methods and subsequent strategy of how to use these tools become very important for successful product development. The aim of the research is to identify a suitable and practical approach in using current available CAD tools and optimising the use of these tools to provide maximum design support in allowing designers to create sufficiently detailed and comprehensive product models so that they can use these tools to improve design productivity and quality significantly. This paper describes an innovative yet pragmatic approach to product modeling and simulation support in product development – a well-established important area for virtual product development. The work focuses on the real needs of developing a practical approach for product design engineers to use current available advanced CAD tools. This approach is based on the research results of using integrated computer based design approach in product design [2] and experience that the author has had in practising this approach in teaching various classes for both BEng/MEng Product Design Engineering and MSc in Computer Aided Engineering Design. The research results from the author’s other research projects [3,4] have also been used in the development of this multiple perspective
product modeling approach. The design environment and facility available to students involved in practising this approach are very similar to many small to medium sized companies. Using these environments, a product can be defined and represented by using product multiperspective models, each of these perspectives being further represented by models of multilevel complexity. This comprehensive modeling is the proposed pragmatic method used to provide an enhanced support to design solution generation process. This approach allows one to investigate more design alternative solutions (to improve solution quantity) and produce better-considered solutions (to improve quality). Potential difficulties that one might face using this approach are discussed in the paper. Examples of projects will be given to discuss what can be achieved by applying the techniques used in research projects and introduced in student design projects.
2.
Product Design and Modeling
Product design engineering is a subject of true multidisciplinary nature and is a process of solution generation. The focus of the design activities is therefore on solution generation and product development rather than on a specific traditional academic discipline. It is a well-known fact that many products under consideration by designers are often the results of integrated artifacts engineered using knowledge and technology from a number of disciplines. The design research community has been studying and trying to understand the engineering design and its process for the last half century. The common understanding of traditional engineering design so far is that engineering design is a process of generating solutions, which satisfy customer’s requirements [5]. A number of design process models have been created, typically represented by French’s model [5], Pahl & Beitz’ model [6] and Pugh’s model [7]. These models are intended to be general and aim to guide designers to traverse a series of design stages and carry out a number of design activities in order to understand and solve design problems. It is noticeable however that these models are unable to provide sufficient and specific guidelines for product development using computer-based tools. It is therefore not possible to use them directly in a computer support design environment. In an effort to investigate and clarify a design process model for product modeling and simulation using computer support tools, the author has derived a computer support design process model, shown in Figure 1. This model is based on the research work carried out on the deployment of several computer support systems previously. The model has been validated to some extent by systems including
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Multiperspective Product Modeling and Simulation Legends: Existing information flow Activity decomposition
Desi sign In Initia tiali lization and icatio ion task clarif c ific
Evolving information flow
A statement of customers need
Solution information flow
Market Research results
Analysis of need
Product Design Specifications
Co Concepts aand itativ ive Models M ls Qualit A set of concepts and their models
Concept generation & evaluation
A Dictionary of Working Principles
Information n expa ex pa ndi nding
Fully developed Concept models
Fig
Embodi odiment aand titativ tive Models M Quanti Embodiment and their models
Embodiment/ Detail Design
Fully developed solution models
Mult ltii-Pers rspectiv ive Modelsfunction model; Mo Systems
Multi-Perspective Model Construction
Geometry evaluation Model;
Component database for Embodiment Design
Component Matching/ Sizing
Product Assembly model; Finite-element analysis model;
Simulation/ Visualization/ Comparison
Dynamic evaluation model;
A Library of Simulation Blocks/Elements
Kinematic analysis model; Product cost model; Control program model; Aesthetic model;
Analysis is aand S Simula latio tion M Models ls
Fully computer evaluated and defined design solution for final assessment, then prototyping/manufacturing
Figure 1. A proposed computer support design process and its modeling and simulation for product design.
FORESEE [8] and FORESEE2 [9], DeCoSolver [4], and Schemebuilder [2]. The design process can be broadly divided into three stages in the computer supported design environment, namely design problem understanding through an analysis of need, initial solution generation through the conceptual design process, and solution refinement and finalization through computer-based embodiment and detail design. In endeavoring to develop a fully intelligent computer support for engineering design, researchers and CAD system developers have made significant advancements. However, in particular in the area of engineering problems computing, there is little well developed support for the first stage of the above design process model, mainly due to the need to interface with customers in order to capture their requirements, and the complexity and diversification of these design activities during these stages. Intensive research effort has been focused on the understanding of
and providing support for conceptual design [5,10–12], and their associated tools [13–15]. The final stage – computer-based embodiment and detail design is currently the main stage with a reasonable computer support. Engineering designers now have access to more tools to aid them to improve their design. Due to more interactions at this stage, computer design systems can be expected to support designers in component modeling, component matching and sizing, and behavior simulation and alternative solution comparison. This decomposition enables one to investigate even further the constituents of each of these design support activities and their interactions. A further study of product modeling reveals that currently most engineering design practitioners focus their modeling effort primarily on the product’s geometry aspect. This can be attributed to the fact that most CAD systems provide modeling support in the geometric perspective
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modeling of a product. However, it is important to note that a product is a multifaceted artifact. Most engineers will start to investigate other aspects of a product after the geometry model is completed. It is argued in this paper that the conventional component geometry-based modeling should be enriched and broadened to be multiperspective modeling for a product. Based on this enrichment of modeling, it is therefore possible for the subsequent product behavior evaluation and comparison of solution alternatives to be also multiperspective. Only with such a design support approach and associated environment, can a designer make fully informed design decisions based on thorough evaluations of alternative solutions. During any design process, designers also need to use reference information e.g. working principles, component database etc., as shown in Figure 1 to enable them to be more productive, systematic, and effective. In addition, the design information in Figure 1 tends to be qualitatize and abstract at the early design stage and this information become more quantitative at the later design stage as more and more design decisions are committed to concretise a design solution. This design information feature is ideally suited for computer-based support as computer systems support well incremental expansions of design information. The computer-based design process model in Figure 1 also depicts the important idea of computer-based design support at the embodiment design stage. Design tasks at this stage can be further decomposed into: component matching/sizing, product model construction and evaluation through simulation/visualization/comparison. Since current computer support systems have not been fully developed to support multi-aspect modeling and simulation, this paper argues that it is important to develop a pragmatic framework and concept in thinking of using currently available systems. In addition, skills and techniques are required to fully support multiperspective modeling and simulation. The following sections of this paper describe the framework and an advanced way of using modern computer systems in supporting product design and development. The roles of computer based simulation tools, and the benefits and precautions of using these systems are then discussed.
3.
Multiple Perspective Modeling
To be successful in today’s competitive market, manufacturing companies need to produce more innovative products as well as a variety of products to satisfy the consumers’ changing needs. This requires engineering designers know how to use more efficient and effective methods of conceiving more alternative solutions, refining chosen design solutions, and finally
converting them into better products to satisfy everincreasing and rapidly changing market needs. One important approach to address the above need is to encourage engineering designers to maximize the benefits derived from the use of computer support tools. More specifically, an integrated use of existing heterogeneous tools should be coherently adopted and product models adequately created to support designers to make more informed decisions. An artifact or more specifically a product can be considered as a system that can be decomposed into subsystems of different levels of resolutions and complexity [11] based on ‘‘Theory of Technical Systems’’ [16]. A product is like any system, and hence has many properties, which define the composition of the product. The product also has many behavioral properties that are exhibited when the product interacts with its environment. It is therefore ideal if a designer has access to a virtual design and evaluation environment within which a product shows its behaviors when its model interacts with this environment. Based on these evaluations, the designer can then validate or modify the initial product property definitions represented in the model. To support fully the above, an integral and comprehensive product virtual model as well as its evaluation environment are required. This is however impossible with current available technologies. 3.1
Model Partition and Integration
From previous research works [17–19], it is demonstrated that one or more perspective product modeling and simulation can help product design engineers to produce better-considered design solutions with little increase of the product development cost. Building on the above work, Figure 1 describes a nonexhaustive list of important modeling aspects and associated models that one should consider and create for successful product development. These include: geometrical modeling, kinematic modeling, assembly modeling, various analysis modeling including Finite-Element Analysis modeling, product dynamic behavior modeling, product cost modeling, control/control programming modeling, and ergonomic/esthetic modeling. It is obviously difficult if not impossible to find an allround perfect computer support system, which is capable of handling all above perspectives. The key to such a multiperspective modeling approach is the use of what is termed in this research the principles of product model partition and consequent integration. The partition principle states that, by applying the observation and understanding of the product model resolution and complexity phenomena, product modeling can be tackled more effectively by dividing or partitioning the totality of the model into a finite number of distinctive perspective models. Having
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Multiperspective Product Modeling and Simulation
investigated each of these perspective models adequately both in terms of depth and breadth, these aspect models can be integrated to give a totality of a product modeling, the principle of model integration. The process of partitioning and integration may be repeated several times before an adequate understanding of a design problem can be achieved and an optimum solution produced. An appropriate model partition using product perspective views as partition guidelines will allow one to concentrate on a local aspect of product modeling, that a designer is interested in at a particular time. Creating such a perspective modeling focus, a designer can have a full understanding of the design requirements from that perspective. Consequently the designer can explore these models and produce an optimum design solution to satisfy the requirements. In addition, a designer can evaluate all modeling perspectives and determine the important ones for a particular product design based on the overall design requirements and the weighting of each requirement. The identification of these important aspects for a particular design problem concerned helps a designer to concentrate on the key aspects of the design problem. More effort and time spent on these aspects can ensure that better quality design solutions can be produced with consideration of these aspects. Once all perspective models are investigated to a sufficient level of detail or resolution, these models can be integrated to derive the integral product property and behavioral definition. Having studied well the virtual product and its definition, a designer can have full confidence in the final design solution. There are currently no product perspective model integration tools available. However, designers can consult model integration principles or a checklist to make judgment as to whether each perspective design model will interface or fit compatibly with the rest of perspective models. Although each of these perspective models focus on one aspect of a product model, it is inevitable that they will share some of product definition properties, such as one or any number of five basic product definition properties: namely structure, form, material, dimensions, and surface quality [20] which completely describe and define a product collectively. Using the definition of these basic properties, it is possible to identify any potential problems. Automatic or semi-automatic checking systems will be researched in the future. Within each of these important aspects, a concept of multilevel of model complexity has also been introduced to accommodate the requirements of modeling product details with different modeling resolutions. More complex models can be created by including more details of an aspect of the product. These complex models enable a designer to conduct more in-depth investigation of a chosen design aspect. This can lead to a better understanding of the design problem, and the generation of
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better solutions. Using a simple submodel for part of the product can improve the computational efficiency. 3.2
Level of Model Complexity
A product can be decomposed into subsystems, as has been demonstrated by other research work [21,22]. The modeling of the product can be tackled accordingly by creating submodels of these subsystems. The integration of these subsystem models at the abstract level allows one to have an overview of the product. This high-level overall model allows a designer to see the overall behavior of the intended product to be derived from this solution model. It is essential that a computer design support tool be able to assist designers to focus on one aspect of a product in a great depth without losing overall sight of the product. Equally important, designer should also be supported to have a good overall understanding of product models, without losing a grip on detailed aspect models. It is therefore argued here that the multicomplexity level and multiperspective modeling approach to product modeling is essential to future successful product development, as it facilitates designers in investigating a product’s behavior from different perspectives at different levels of the modeling resolution. This approach can also allow designers to trade off between the conflicting requirements of high computational speed and high level of accuracy of the model. By combining different subsystem models with different model levels of complexity, the product model represents a product with sufficient details. At the same time this model will not require undue computational power to solve/visualize it. 3.3
Data Exchange among Models and Model Library
It is clear from the above discussion that the effective support for engineering design requires multiperspective and complexity-level modeling of a product. These partial models from different perspectives at different levels of resolution form an integral product model with sufficient details for product behavior evaluation. The data communication among these partial solution models, possibly through communication links using standard data formats/protocols, is the key to product model integration. To achieve an effective model composition, configuration, and integration, a model library of the commonly used and parameterized product modeling components can be created and some examples are shown in Figure 2. A collection of these models in each aspect forms a comprehensive reusable product-modeling library. Figure 2 shows a library of basic geometric component elements, assembly models, and some functional simulation models for commonly used components. This model can also
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(a)
(b)
(c)
Figure 2. Some example model libraries (a) Geometric component developed in FORESEE2 system; (b) Assembly product design elements developed in FORESEE2 system; (c) Functional simulation model library.
include trained neural network based behavior prediction models, which can predict the performance behavior of a phenomenon such as oil flow-rate through a parameterized oil container system, the feasibility of manufacturing a particular thin walled tubular component with given dimensions and material properties. Such a library provides a designer with a rich source of models to support multicomplexity level modeling and multiperspective modeling. The component design models created in this research can be interfaced with other component models. Figure 3 shows an example how a high level component model is created using the underlying component behavior model based on Bond Graph theory [26], as shown in (a), its high level function encapsulated function block model in (b), and the easy to use interface to the model in (c). The example shows the detailed model can be masked or encapsulated into a higher-level model shown in Figure 3. Through applying this technique, the ability to interface with
other models and the interchangeability of the models at a different complexity level is supported in this approach. Figure 4 shows some example geometric models developed for the library using different CAD systems. Generally speaking, the support for geometry modeling has been more advanced than other aspects of product modeling. The geometric modeling approach is developed using open CAD system structures and the program based geometry creation tools. Examples demonstrate that most of the CAD systems can be used to create geometric models. The lead-screw (Figure 3(a)) was created using IDEAS CAD system. The following two models(Figure 3(b), (c)) were created using the OpenCASCADE system [23,27]. A gear pair (Figure 3(d)) was created by using AutoLISP – a programming method provided by the AutoCAD system. This model derived from the AutoLISP programming method gives a designer/student much more flexibility in
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Multiperspective Product Modeling and Simulation
(b)
(a) (c) Figure 3. (a) A D.C. motor simulation model using the underlying component behavior block diagram model converted from a Bond Graph model; (b) Its high level encapsulated function block model; and (c) The easy to use interface to the model.
Figure 4. Another example model: AutoLISP created gear mesh geometry model and mechanism model for simulation. Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 16, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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manipulating these models. In addition to geometric models created using readily available menu commands from a CAD system, the programming method provides designers with a unique and flexible way of creating other perspective models of the product, e.g. kinematic behavior of the gear-pair, tolerance definition of the pair, and so forth. Most current CAD systems provide the above open programming facility and the approach is applicable in the other systems. Geometric modeling has been standardized through the effort of many researchers and international organizations over the last twenty years. However, other perspective modeling of a product, e.g. function modeling, cost modeling etc. has not achieved the same level of standardization. One of the obvious problems with many current computer modeling methods is that they are very much domain dependent. Product design engineers have to be trained to be able to use them in different application domains in order to be competent in using all these domain dependent technologies. This in itself is a very challenging task for product design engineers. In addition, when different application domains are to be interfaced using corresponding modeling methods, modeling using a computer is becoming a daunting task even for many researchers, let alone the new product design engineers. However, the modeling separation of data and control and function decomposition employed in a method called Modern Structured Analysis in [24] suggests that a high level function block oriented method used to model high energy systems can also be used to model information related systems. This method suggested the integrated modeling approach adopted in the research leads to advancement in modeling and simulation of interdisciplinary and multidisciplinary products such as mechatronic products. Models of different perspectives can also be generated concurrently using the information derived from other models [3]. The next section describes how product models are used to evaluate a design solution using simulation.
4.
Multiple Perspective Product Evaluation
One of the main benefits of having product computational models is that a design solution can be fully evaluated within a virtual design environment without incurring the cost of making physical prototypes and other associated cost, e.g. rework, longer lead-time etc. Computer based product evaluation include: the assessment of material selections, components sizing and their tolerances assignment, product structure, assembly, kinematic and dynamic behavior of mechanical and electrical mechanisms, functional behaviors including static and dynamic behavior, ergonomic behavior and esthetic attractiveness of a
design solution. Some of the above evaluations can be carried out by using one perspective computer model, whereas some others may require more perspective models. The geometrical model of a design solution has mostly been used so far for evaluation and they can provide a good visualization of the solution, and hence are useful for several visually related perspective evaluations, such as component sizing, assembly, mechanisms, ergonomic behavior and esthetic evaluations. These evaluations can be carried out by a designer through visual inspection of a 3-D model on a 2-D screen. Simulation techniques can provide a designer with a step-by-step imitation of the behavior (normally one aspect or perspective) of a physical system in a computer. 4.1
Simulation and its Role in Product Evaluation
A simulation process provides designers with an opportunity to visualize the dynamic and transient behavior of a physical product under a predefined set of conditions. It is argued in this paper that simulation techniques can greatly empower designer’s ability in foreseeing the product behavior in a virtual simulation environment. This section will briefly review the available simulation techniques and their potential applications in product multiperspective evaluations. Simulation technology has been traditionally used for system analysis and control system design. It has also been used for mechanism analysis and validation. Various simulation techniques have been studied and successfully used in different applications to predict the behavior of a physical system. The notation and representation of a physical system can be different depending on the modeling methodology employed for a particular modeling approach. Typical modeling methods for simulation include clock-based mechanism geometric solid modeling [19], block diagram [24], signal flow diagram [25], bond graph approach [26], Yourdon diagram [24] and schematic diagram, and so forth. These simulation methods were generally developed for a specific discipline/aspect of a product and can only cope with the aspect of a product/system within the discipline/ aspect. Whilst simulation technology has advanced rapidly in the last two decades due to significant computer technology advancements, it has only been used in product design particularly in product synthesis in a very limited way. Emerging interdisciplinary subjects, such as mechatronics, on one hand remove many design constraints and a designer can work in a much wider design space, but on the other hand design process becomes more complicated due to much more possible combinational solutions for a given problem. The verification of a product design scheme from a multiperspective point of view can become a quite difficult task without appropriate computer support.
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Multiperspective Product Modeling and Simulation
To overcome these difficulties, the author has developed a pragmatic approach to modeling these interdisciplinary systems based on Yourdon’s concept. This approach enables designers to model product subsystems using encapsulated high-level function blocks. Due to its high-level approach, these blocks also provide an easier way of interfacing with other subsystems in different disciplines. This has greatly enhanced the compatibility and interchangeability of product models with different resolutions and different perspective. With properly defined multiperspective product models, it is possible to simulate each perspective model first and the useful results can then be fed into other perspective models. This has been the approach used in the research. It is envisaged that real-time multiperspective model evaluation via simulation requires much powerful computer resources and close coordination among simulation tasks. Moreover it is difficult to achieve real-time concurrent simulations of several perspective models of a virtual product with current available computer technology, and this remains a challenging and interesting research topic for future work. 4.2
Evaluation through Simulation, Visualization, and Comparison
Figure 1 also illustrates in detail the design stages where computer based modeling and simulation can play an important role for product design. The multiperspective models are composed through MultiPerspective Model Construction activity through which the structure, form, and possibly material are determined. Component Matching/Sizing activity then determines the dimension, material selection, and surface quality and other details of the product. The evolving multiperspective models then can be used for evaluation mainly through Simulation/Visualization/ Comparison activities clearly shown in the figure. Simulation is a general technique, which can be applied alone to assess the step-by-step behavior of a model under a set of given working condition in an environment. A discrete simulation technique is used in this approach. By combining with visualization techniques and tools, the behavior of a model can be visually assessed, e.g. motion of a mechanism displayed to show the type of motion of the model, graphs shown to indicate the energy consumption level or required power in the form of electricity voltage and current and so forth. Each simulation model with a particular set of design parameter values represent a design solution and simulation results can be used to foresee the solution’s behaviors, termed in this research as one solution world. Several simulation models with their associated simulation result sets form several solution worlds and designers can compare these solution worlds to determine the optimum solution. Through such a
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comprehensive evaluation employing techniques in simulation/visualization and comparison, a scheme generated at the conceptual design stage can be fully evaluated and the product embodiment design is hence better supported than any conventional design approach. More specifically dynamic performance of a mechatronic product can be evaluated by using a unified simulation approach [17], in which energy transformation from an energy form to another will be clearly illustrated and the efficiency of each component/ subassembly can be readily available to a designer. The same computer model can be used to match the components, which interface with each other. This allows a designer to determine rapidly the correct parameter values for a given design scheme and subsequently carry out evaluation. The simulation system also provides a highly interactive interface, allowing a designer to change instantly the values of any design parameter and get immediate feedback of the effect caused by the changes. This has proven to be an extremely useful facility offered by an appropriate use of a computer simulation model, especially for new designers who need to repeat many times to evaluate as well as to learn the behavior of a design object. Simulation has also been used to evaluate mechanism kinematics, which includes the velocity, path, and geometries of mechanisms. In this particular application domain, a computer can generate repeatedly the track/ path of a particular point of a mechanism. In assembly modeling, a computer can generate many frames of graphic representations of a product at different positions during its assembly process and these frames of images can then be animated. 4.3
System Implementation
The overall system requirements include the development of an overall system user interface and a central database system, allowing a user to interact with other specialized systems, which provide detailed modeling and simulation functionalities and sharing same information for a product under development. The overall system architecture is designed such that it requires a user to start from a function model. Once the function model is converted into a scheme with specified components and their interconnection, a designer can proceed to any aspect of product modeling, as long as sufficient model data are available for modeling. The normal route to simulation is after the product multiperspective models are generated so that sufficient simulation and evaluation data are available to start a simulation session. The implementation of the approach is based on the integrated novel use and development of available open systems based on the computer design process model depicted in Figure 1. The component
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design module of the system has been developed by using MS Visual Cþþ in conjunction with an Open CAD system entitled Open CASCADE [27] – a 3-D model development platform. The Open CASCADE system consists of reusable Cþþ object libraries, many reusable 3-D models and development tools. The dynamics simulation module was developed on a commercial system Simulink – a simulation system developed by the MathWorks [28]. The intersystem multiperspective model data sharing and communication at the moment is realized at a simple level and data share is controlled by a user interacting with the central database system and a specific commercial system. This provides a designer with a maximum control of the model complexity and data sharing. Further unified user interface will be developed as part of the effort of this on-going project.
5.
Case Examples
The approach described in the paper has been employed in several research and teaching projects, including the design, modeling, and simulation of a wallclimbing robot, a motorized drug delivery system, a washing machine system, an intelligent vacuum cleaner robot and a wheelchair system for disabled users. The following aspects are covered for most of the above systems: modeling of the product geometry as a basis for other perspective modeling, kinematic modeling of the mechanisms used, control of each system and other relevant perspective modeling and associated simulation for evaluation. An example used here is the modeling of an intelligent vacuum cleaner system and its assembly, all of which have been modeled as shown in Figures 5 and 6. The
Figure 5. Some examples of product multiperspective modeling. (a) An intelligent vacuum cleaner product structure model; (b) An esthetic evaluation model; (c) A Bond Graph based functional model of the key component of the system – a D.C. motor; (d) A vacuum cleaner’s assembly model for evaluation. Downloaded from http://cer.sagepub.com at PENNSYLVANIA STATE UNIV on April 16, 2008 © 2003 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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Figure 6. (a) A product simulation model of the vacuum cleaner product function model derived from instantiation of the functional simulation blocks in the model library; (b) Simulation results of the dynamic behavior of one drive wheel of the vacuum cleaner system.
example shows a five-perspective model of the Vacuum cleaner system, namely, the product structure model – assembled model Figure 5(a), product aesthetic model (b), a Bond Graph model describing the energy flow and interaction of the key component – the D.C motor (c), the assembly model of the vacuum cleaner system (d), and the Vacuum cleaner system simulation model shown in Figure 6. These models collectively enable a designer to identify clearly the problem of a design solution by simulating graphically the kinematic and assembly behavior of the virtual product model. Using the evaluation techniques described in Section 4.1, a design solution can be optimized by resimulating the behavior with a modified design and comparing these solutions. The approach has been effective and successful in improving solutions of these research and teaching product development and modeling projects at an advanced level.
Another perspective of product simulation/application domain is the dynamic simulation of an energetic system in which energy flow is of significant importance and interest to designers. In these modeling projects, designers can select the correct power components based on the simulation analysis of power requirements to each component of the system. A customized system with a library of component functional blocks has been implemented for a commercial simulation system – Simulink. Using these library component function blocks, designers are able to simulate energy flow and control requirements. Figure 5(c) shows a basic Bond graph model of a D.C. motor and its use in the form of converted model object is shown as in Figure 6. Using Bond Graph theory based rules, a bond graph representation as shown in Figure 5(c) can be converted into a block diagram based representation, shown in Figure 3(a). This block diagram can be implemented in a
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Figure 7. (a) A physical model of the intelligent vacuum cleaner system built based on the models; (b) Its internal view of the prototype control system.
simulation system such as Simulink, which allows one to model a dynamic system using control blocks. Using object-oriented software design methodology, a low-level complex block diagram can be further simplified into a high level block and Figure 3(b) shows a parameterized high level block representing a D.C. motor. With a library of such parameterized commonly used components as shown in Figure 2(c), the dynamic performance of a mechatronic product can be evaluated by using a unified simulation approach developed by the author [17], in which energy transformation from one energy form to another will be clearly illustrated and the efficiency of each component/ subassembly can be readily available to a designer. A library of commonly used engineering components has been developed and is composed of a number of expandable sublibraries. A user can easily select a component and configure a product model to simulate the behavior of the product as shown in Figure 6(a). The same computer model can be used to match the components interfacing with each other. This allows a designer to determine rapidly the correct parameter values for a given design scheme and carry out evaluation. The simulation system also provides a highly interactive interface, allowing a designer to change instantly the values of any design parameter and get immediate feedback of the effect due to the changes made. This has proven an extremely useful facility offered to students, who need to repeat the evaluation many times to learn the behavior of a design object. Figure 6(b) shows an example plot of simulation results of the dynamic behavior of one drive system for one of the wheels of the vacuum cleaner system. A designer can determine from these simulation results the maximum power requirements and maximum speed the vacuum cleaner can travel and so forth. This information can offer designers great insights to the systems they are dealing with. Similarly an assessment of how the product should be used in its environment
can also be made by employing the virtual product in a virtual environment. Having evaluated all these perspective models of the vacuum cleaner system in such a virtual environment, designers have much more confidence in their design solutions as they have been thoroughly assessed their design solutions from multiple perspectives of the product. Once the final solution is fully evaluated, a prototype system can be built to validate physically the design solution and to realize some aspects, which cannot or has not been evaluated in a virtual environment due to various reasons. Figure 7 shows a physical prototype vacuum cleaner system and its internal control and drive system developed for a project. Using multiperspective CAD models, designers managed to construct the prototype systems with much reduced rework.
6.
Conclusion
This paper has described a new approach to supporting product design by introducing multiperspective modeling and simulation. The approach proposed by the author has been adopted to deal with multidisciplinary product engineering design more effectively and has been used in several design projects successfully. A modeling approach, unifying the representation of mechanical, electrical, hydraulic, and pneumatic systems based on Bond graph and block diagram methods, is used as the underlying modeling methodology. The approach has been developed to empower designers’ ability to design and enhance the confidence of their decisions. A novel function block oriented modeling method to support the modeling and design of a product has been derived and proved effective in handling energetic system design, based on an informal evaluation of the method. In combining the customized commercially available kinematic and assembly modeling and simulation systems through
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loose integration techniques, the pragmatic multiperspective modeling and simulation approach has been developed. Through the introduction to and use of this approach, new designers such as senior student design engineers appreciated the importance of and gained the benefits of using multiperspective modeling and evaluation. This approach has broadened design engineers’ understanding significantly from single geometric modeling to much more comprehensive modeling, and evaluation in an integrated manner. It promotes the practice and thinking of design, modeling and evaluating design solutions in a virtual world using existing design support tools. Adopting this approach can also systematically help design engineers to consider fully important aspects of a product development prescribed in many design textbooks. Although no formal evaluation of the approach has been carried out, it was apparent during the use of the approach by senior student design engineers and researchers that the approach provides much more detailed design support and better evaluations of the design solution, which would be extremely difficult to do using other methods, including paper based design. From this informal evaluation of the approach, however design engineers found it is difficult to understand Bond Graph theory, as student designers have not gained sufficient experience and knowledge about the specific components they need to use. Industrial designers have not been introduced to Bond Graph theory either. This raised the need of developing a large library of higher-level encapsulated component models with an easy interface to facilitate these design engineers to adopt this approach.
7.
Further Work
The work described in this paper is part of an on-going project within which there are areas for further research. The work has largely been tried on mechatronic products. The models generated in the component library are hence very much mechatronic-product specific. This requires further expansion to cope with other domain specific product design. The data communication among different systems is through bespoke data protocols defined within the research approach. It would be beneficial to try use standards, such as STEP to facilitate communications among different systems. Currently, this approach is being used to design a mechanical product and it is hoped through this investigation that the approach will be further evaluated. In addition, it is believed that real-time concurrent model construction and evaluation of these multiperspective models will provide much improved responsiveness and give true multiperspective and real-time simulation of the product. This remains as a challenging research task.
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Biography Xiu-Tian Yan Xiu-Tian Yan is the Postgraduate Coordinator and the Course Director for MSc in Computer Aided Engineering Design and a Lecturer in Product Design Engineering in the Department of Design, Manufacture and Engineering Management of Strathclyde University. Previously, he was a research associate at the Engineering Design Centre, Lancaster University. He received his PhD from Loughborough University of Technology in 1992. He is a Chartered Engineer and a member of Institution of Electrical Engineers. His research interests include computer support product design using AI techniques, knowledge intensive product modelling and simulation, design synthesis for life cycle phases, and mechatronic systems design. He has published nearly 70 technical papers in major international journals and conferences in the fields.
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