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英文原文
FEATURE-BASED COMPONENT MODELS FOR VIRTUAL PROTOTYPING OF HYDRAULIC SYSTERM Abstract: This paper proposes a feature-based approach for the virtual prototyping of hydr

aulic systems. It presents a framework which allows the designer to develop a virtual hydraulic system prototype in a more intuitive manner, i.e. through assembly of virtual components with engineering data. The approach is based on identifying the data required for the development of the virtual prototypes, and separating the information into behaviour, structural, and product attributes. Suitable representations of these attributes are presented, and the framework for the feature-based virtual prototyping approach is established,based on the hierarchical structure of components in a hydraulic system. The proposed framework not only provides a precise model of the hydraulic prototype but also offers the possibility of designing variation classes of prototypes whose members are derived by changing certain virtual components with different features. Key words: Computer-aided engineering; Fluid power systems;Virtual prototyping 1.Introduction Hydraulic system design can be viewed as a function-to-form transformation process that maps an explicit set of requirements into a physical realisable fluid power system. The process involves three main stages: the functional specification stage,the configuration design stage, and the prototyping stage.The format for the description of the design in each stage is different. The functional specification stage constitutes the initial design work. The objective is to map the design requirements. To achieve this, the design problems are specified Correspondence and offprint requests to: Dr S. C. Fok, Schoool of Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798. The designer must identify the performance attributes, which can include pressure, force, speed, and flowrate, with the required properties such as size, cost, safety and operating sequence. performance requirements for each attribute. In this stage, the design is abstracted in terms of the performance attributes with associated values. The objective of the configuration design stage is to synthesise a hydraulic circuit that performs the required functions conforming to the performance standards within defined constraints. A typical hydraulic system is made up of many subsystems. The smallest building block in a subsystem is the standard hydraulic component (such as valves, cylinders,pumps, etc.). Each type of

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standard component serves a specific elemental function. The design effort in the configuration design stage is fundamentally a search for a set of optimal arrangements of standard components (i.e. hydraulic circuit) to fulfil the functional requirements of the system. Based on this framework, the designers would normally decompose the overall system functions in terms of subfunctions. This will partition the search space and confine the search for smaller hydraulic subcircuits to perform the subfunctions. Computers are often used to support the configuration design process. For example, Kota and Lee devised a graph-based strategy to automate the configuration of hydraulic circuits. After the development of the hydraulic circuits, digital simulation tools are often used to study and evaluate these configurations. With these tools, designers can compare the behaviour of different circuits and also analyse the effects when subcircuits are combined. In the configuration design stage, the design is traditionally represented as a circuit drawing using standard icons to symbolise the type of standard component. This is a form of directed graph S(C,E) where the circuit S contains components C in the form of nodes with relations between components denoted by edges E. The prototyping stage is the verification phase of the system design process where the proposed hydraulic circuit from the configuration design stage is developed and evaluated. Physical prototyping aims to build a physical prototype of the hydraulic system 666 S. C. Fok et al. using industrial available components. The process of physical prototyping involves the following: Search for appropriate standard components from different manufacturers. Pre-evaluation and selection of components based on individual component cost, size, and specification, and compatibility factors between components. Procurement and assembly of the selected components.Test and evaluate the physical prototype based on the overall system requirements. Use other components or redesign the circuit (or subcircuits) if necessary.Besides dynamics, the development of the physical prototype must take into consideration other factors including structure,cost, and weight. The dynamics data are used to confirm the fluid power system behaviour whereas the geometric information is used to examine the assembly properties. The development of the physical prototype will provide the actual performance,structure, and cost of the design. The main disadvantage of physical prototyping is that it is very tedious and time consuming to look for a set of suitable combinations of standard components from among so many manufacturers. Although the basic functions of the same types of standard component from different manufacturers do not differ, their dynamics, structural and cost characteristics may not be similar, because of design variation. Hence, for a given hydraulic circuit, different combinations of

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parts from different manufacturers can have implications on the resulting system,in terms of dynamics, structure, and cost. Value engineering can be used at this stage to improve the system design by improving the attributes at the component level. This includes maximizing the performance-to-cost ratio and minimising the size-to-performance ratio. Virtual prototyping can be viewed as a computer-aided design process, which employs modelling and simulating tools to address the broad issues of physical layout, operationalconcept, functional specifications, and dynamics analysis under various operating environments. The main advantage of virtual prototyping is that a hydraulic system prototype can be assembled, analysed, and modified using digital computers without the need for physical components, thus saving lead time and cost. The main requirement of a virtual hydraulic system prototype is to provide the same information as a physical prototype for the designer to make decisions.To achieve this, the virtual prototype must provide suitable and comprehensive representations of different data. Furthermore, transformation from one representation to another should proceed formally. Xiang et al. have reviewed the past and current computer-aided design and prototyping tools for fluid power systems. The work revealed that the current tools could not provide a complete representation of the design abstractions at the prototyping stage for design judgement. Most of the tools concentrate on the dynamics behaviour. Vital geometrical and product information that relates to the system prototype consideration and evaluation is frequently missing.To advance the development of computer-aided virtual prototyping tools for fluid power systems, there is a need to address the formal representations of different abstractions of behaviour,structural, and product data along with their integration. This paper focuses on these issues and proposes the formalism of a unified component model and the taxonomy based on the feature-based approach. In Section 2, we discuss the feature- based approach focusing on the key information and their representations required for hydraulic system prototyping. Section 3 presents a formalism of the feature-based model and structure for the development of virtual hydraulic system prototypes.The structure is illustrated with an example. Future work and conclusions are given in Section 4. 2. Feature-Based Approach Features can be defined as information sets that refer to aspects of attributes that can be used in reasoning about the design, engineering or manufacturing processes. The concept of using features to integrate CAD/CAPP/CAM is not new and there are many papers on the application of this approach in CIM. In all these applications, the feature model is regarded as the basis whereas design by features is the key for the integration. To develop a feature model, the relevant

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information concerning the design must be identified and grouped into sets based on the nature of the information. The relevant information should contain sufficient knowledge for activities such as design, analysis, test, documentation, inspection, and assembly, as well as support various administrative and logistic functions. Design by features is the process of building a model of the design using features as primitive entities. The feature model provides the standardisation of relevant data. Through the design by features approach, vital knowledge of the design will be generated and stored. Together, the feature model and the design by features approach will provide the essential information, which can be used, not only for the simultaneous consideration of many different concerns with the design, but also to interface the many activities in the design realisation process, including the life cycle support operations. The main drawback of the feature-based design approach is that the feature model should be properly defined . This can be difficult, as features are sets of knowledge that are application dependent. The organisation of the features can also be application specific. Non-trivial data-management problems could arise if the feature model is not properly defined. To avoid these problems, the type,representation and structure of the features should be resolved prior to using the feature-based design methodology. The main concern when developing a feature model is that it is application-specific. In the domain of virtual prototyping of hydraulic systems, the details of the constituent standard components must be able to be used to describe the overall system. The component features are bearers of knowledge about that part. To create a suitable feature model for hydraulic system design based on the assembly of standard components, the relevant information associated with various standard components must be identified and classified. This definition Feature-Based Component Models 667 of the component feature set can then be extended to encompass the subsystem feature set based on the hierarchical structure between the components in the subsystem. In the same manner, a hierarchical structure for the hydraulic system feature representation would evolve by considering the system as a hierarchy of subsystems. The necessary information required for a proper description of the virtual prototype must be no less than that derived by the designer from a physical prototype for decision making. These data should generally include the shape, weight, performance properties, cost, dimensions, functionality data, etc. Comparison with the physical prototyping process, the information required for each standard component could be separated into three distinct groups: behaviour attributes, structural attributes, and product attributes. 2.1 Behaviour Attributes The behaviour of a hydraulic component can be defined in terms of the dynamics

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characteristics used to satisfy the functional requirements. Consider a hydraulic cylinder connected to a load. Its function is to transmit a force from the stroke of the piston to the load. The maximum force it can transmit can be used to define the functionality and the behaviour requirements can be specified in terms of the desired load acceleration characteristics. Hence for a hydraulic component, behaviour attributes express functionality and can be reflected in the dynamics characteristics. The designer is responsible for the proper definition of the overall system behaviour characteristics in terms of the desired dynamics. A standard component will have its own behaviour and provide a specific function.Complex functions that cannot be achieved by a single standard component are derived using a combination of components. Hence, the behaviour of the standard component will play an important role as the individual behaviours of components together with their arrangement can alter the overall system function . The behaviour of a standard component can be nonlinear and can be dependent on the operating conditions. When two components are combined, it is possible that their behaviours can interact and produce undesired or unintended characteristics. These unwanted behaviours are assumed to have been resolved during the configuration design stage. The hydraulic circuit used in the prototyping stage is assumed to be realisable and without any undesirable interacting behaviours. This means that the output behaviour of a component will provide the input to the subsequent component. The representation of behaviours for hydraulic systems has been widely investigated. These representations include transfer functions, state-space and bond graphs. Transfer functions (for single-input–single-output systems) and state-space equations (for multiple-input–multiple-output systems) are based on the approximation of the dynamics about a nominal operating condition. The power bond graph model is based on the causal effects that describe the energy transformations in the hydraulic system. This approach is appealing for hydraulic system analysis. The main disadvantage is that the derivation of the dynamics equation in a bond graph of a complicated fluid power system can become very tedious. As a result, recent work has concentrated on the used of artificial intelligence to represent the nonlinear mapping between the input and output data, which can be obtained via experimental work. These nonlinear mappings can be accomplished using artificial neural networks . It is quite natural for a hydraulic system designer to use input–output data to describe the behaviour of a hydraulic component. The configuration design of a hydraulic system is often achieved through steps of function decomposition. To design a hydraulic system, the designer often tries to decompose the functions and their requirements down to the component level.

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中文译文

基于原型液压系统特征的机构模型 摘要:本文为原型液压系统的设计提出了一种基于特征的方法。它提出了
一个框架,允许设计师以更加直觉的方式开发一个真实液压机构原型,例如, 通过真实的工程学数据进行设计。这种方法是在真正原型数据的基础上发展 起来的, 它可以分离信息入行为,结构,和产品属性。这些属性被用适当 的表示法提出, 并且框架为基于特点的真正原型 的方法建立,根据组分等 级结构在一种液压机构。它所提出的框架不只是真实的液压系统的一个精确 模型,而且为设计成员提供了当由于某些零件的一些特性改变导致系统改变 而获得一个新的液压系统精确模型的可能性。 关键词: 计算机辅助工程; 液压动力系统;真实样机 1. 介绍 液压机构设计可能被看作是一个为映射明确套要求入物理可实现的液 压能力系统的作用对形式变革过程。这个过程涉及三个主要阶段: 功能规划 阶段,结构设计阶段, 和样机制造阶段。描述各个设计阶段的所用的格式 是不同的。 功能的规划是所有设计中最初的工作。为了达到这个要求, 设计问题 是以指定的书信和印成单行本发给新加坡南阳大道南阳技术大学机械和制 造工程的Dr S. C. Fok。明确地根据作用和表现。设计师必须确定产品的性 能和属性, 其中包括压力, 强度, 速度和流体速度, 以及一些所必需的 东西如尺寸大小,成本, 安全要求和操作顺序。其次, 设计师必须叙述出 各个特征的精确性能要求。在这个阶段,设计以摘要的形式写出产品的相关 性能要求。 结构设计阶段的目标是完成一个液压系统回路。这个回路能完成系统设 计参数规定的各个功能。一种典型的液压机构由许多子系统组成。组成子系 统的最小模块是标准液压系统元件(譬如阀门, 气缸,液压泵等。). 每种

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液压标准元件都有各自的特殊作用。结构设计阶段的任务就是从根本上找到 一个基本液压元件(例如液压回路)的布置图。这个基本的液压回路能达到 系统的各个功能要求。根据这个结构, 设计师通常把整个系统功能模块分 成一个个最基本的子函数。这样就能隔开搜索空间,通过搜索较小一级的液 压系统基本回路去实现各个子函数的功能要求。 在外观设计过程中计算机往往会发挥很大的作用。例如, Kota 和Lee 想出了一个基于图表的液压系统回路结构的自动设计方法。在液压回路被发 展以后,人们经常被使用数字模拟实验工具来学习和评估这些结构。通过这 些工具, 设计师能比较不同的电路块的功能,并且能够分析出这些功能块 结合后的效果。在结构设计阶段,传统上设计往往用一张回路图来代表标准 元件。这里是被(C ,E)包含结构C 的回路S以结的形式联系组分之间由边E 表示的地方图表的形式。 样机设计阶段是结构设计过程中提出的液压回路的证明阶段。通过这个 阶段能证明结构设计中对回路的提出与评估是否正确。实际样机的目的是建 立液压机构666 S 的一个物理原型。使用工业可利用的零件。 涉及真实样 机的过程以下: 从不同的制造商手中寻找适当的标准零件。零件的选择和评 估是建立在零件之间的成本,尺寸大小,规格和互换性等因素之上的。选择 的零件取得和装配。根据整个系统要求测试和评估物理原型。使用其它零件 或重新设计电路(或支电路) 如果需要。除动力学以外, 物理原型的发展必 须考虑到其它因素包括结构,成本与重量。动力学数据用来确认液压动力系 统的性能,但是几何学信息用来系统的安装性能。 物理样机的研制将提供 设计产品的真实性能,结构和设计成本。 物理样机的主要缺点是, 它必须非常繁琐和费时地从在许多制造商手 中寻找一套标准零件的适当组合。由于设计的变化,从不同的制造商购买的 同样类型的标准零件的作用都不相同, 他们的动力学, 结构和费用特征也 不可能相似。因此, 为同样的一个液压回路,选择不同的制造商的标准零

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件去组装, 所完成的系统, 最后在力学、 结构和产品的成本等方面也会不同。 在这一过程中可以使用评估工程,通过在零件标准特性上的改变来改进在这 个情况下的系统设计。其中就包括最优化的性价比率和对零件大小进行最合 理的设计。 真正样机设计过程可能被观看作为一个计算机辅助设计过程, 它 可以使用模拟制造和模拟仿真工具来验证样机的物理布局, 操作, 功能规格, 以及在在各种各样的操作环境下的力学分析。虚拟样机的主要好处是, 不需 要实际零件,通过使用数字计算机就可以对一个液压机构原型进行装配和分 解,因而大大的节省了时间和费用。 一个真正虚拟液压机构样机的主要要求是,它必须能像真实的产品一 样,为设计者提供信息和帮助他们做出决定。为了达到这个要求, 虚拟样 机必须提供另外不同数据的适当和全面表示法。 此外,从一个表示方法到 另一个表示方法的改进应该进行下去。 Xiang 等。回顾了过去和当前的液 压动力系统的计算机辅助设计和样机制造工具。工作显示, 当前的工具不能 在样机制造阶段为设计评断提供一个完全抽象的设计表示法。 大多工具集 中在动力学行为。 而与系统原型需要考虑和评估关系密切的重要几何信息 和产品信息往往被错过。在液压动力系统的虚拟样机制造方面,为推进虚拟 样机计算机辅助设计工具的发展,有必要找到一种把性能、结构和产品数据 这些独立的抽象信息综合在一起的正式表示法。这篇论文以这些问题中心, 提出一个统一元件模型的标准和以基于特征方法为基础的分类学。 在第二 部分, 我们讨论了基于特征的方法,这些方法主要集中在液压系统模型化 所要求的关键信息和他们的表示方法上。 第三部分主要介绍的是基于特点 的模型标准和为虚拟液压系统模型发展而提出的结构。并通过一个例子来说 明这种结构。论文的第四部分是结论和展望。

2.基于特的方法
那些特征可以定义为信息块,这些信息块是涉及到设计、工程或者制造 过程方面的特性。其中使用的特性集成CAD、CAPP与CAM的概念并不是新出现

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的,在CIM中就有许多有关这种应用的论文。在所有这些应用中,特征模型 被认为是基础,而通过特征进行设计是所有东西综合的钥匙。 为了开发一 个特征模型,必须能够识别与设计有关的信息,并能根据信息的性质进行分 组。有关的信息应该包含诸如设计,分析,测试,文件,检查和收集活动的 足够的知识,还有支持各种各样管理和后勤的功能。基于特征的设计是使用 特征作为原始实体模型过程的设计。 特征模型提供了标准化的有关数据。 通 过特性接近的设计,设计中的至关重要的知识将被产生和存储。为了避免这 些问题,特性的类型,表示和结构问题应该在使用基于特征的设计方法之前 被解决。当开发一个特征模型时,主要关注的是它的具体应用。在液压系统 的虚拟模型制造领域中,标准元件组成部分的细节必须能够用来描述整个系 统。同样的,用于液压的系统特性表示的一种分层结构将通过把系统考虑为 子系统的分层而得以进化。为虚拟模型的一个适当的描述所要求的必要信息 必然不少于设计者为了决策而引出物理的原型中的信息。这些数据应该一般 包括形状,重量,性能特性,成本,尺寸,功能参数等。与物理的原型化过 程所要求的信息相比,对每种标准元件所需要信息能被分成完全不同的三 类: 行为属性,结构属性,和制造属性。依据用于满足功能要求的动力学 特征可以定义一个液压元件的行为。考虑到液压的圆筒连接装载,其功能是 把力从活塞传送到负载。 它能传送的最大力能被用来定义功能和行为。在 期望的根据期望的负载加速度特性可以划分各种要求。因此,对于一个液压 元件,并且为动力学特征所反映的行为属性可以表达功能。 依据期望的动 力学特性,设计者对整个系统的行为特征的适当定义负责。一个标准元件有 其自身的行为并且提供具体功能。不能被一个单一的标准元件完成的复杂功 能使用使用多个元件。 因此,标准元件的行为将起重要的作用,因为与各 个元件的独自功能以及它们的布置同时改变整个系统的功能。 一个标准元件的性能可能是非线性的并且可以依赖于操作的条件。 当 两个组成部分被组合时,它们的行为相互作用并且产生不希望得到或者非故

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意的特性是可能的。这些不需要的行为被假定在配置期间被解决设计阶段。 用于原型阶段的液压的电路被假定实现同时,没有任何不受欢迎的人相互作 用的行为。 这意味着一个组成部分的输出行为将提供输入到后来的组成部 分。表示行为因为液压的系统广泛地已被调查。 这些表示包括转移功能, 状态空间和合同图表。 转移功能(对于单一输入的单一输出系统)和状态空 间方程(对于多重输入的多重输出系统)基于关于一个名义的操作条件的动 力学的逼近。力量合同图表模型基于在液压的系统中描述能量转换的有原因 的结果。 这接近对液压的系统分析有感染力。 主要的不利是一种复杂的流 体力量系统的一张合同图表中的动力学方程的起源能变得十分乏味。 因此, 最近工作已集中于代表在输入和输出数据之间绘制地图的非线性使用人工 智能,这能通过实验的工作被获得。 这些非线性能使用人工的网络被完成。 液压的系统设计者一般会使用输入输出来数据描述一个液压的组成元 件的特性 一个液压的系统的结构设计经常通过功能分解的步骤取得。 为了 设计一个液压系统,设计者常常把它的功能和要求分成一个个最简单的基本 单元。


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