【作者】 李晓红；

【导师】 孙立镌；

【作者基本信息】 哈尔滨理工大学 ， 计算机应用技术， 2004， 硕士

【摘要】 特征造型技术是面向制造全过程的,是CAD发展的一个重要里程碑,它使CAD/CAPP/CAM的真正集成化成为可能,为解决产品从设计到制造的一系列问题奠定了理论和技术基础。 语义特征造型是一种可以声明的造型方法,它不但能提供定义良好的特征语义的详细描述,同时能有效地维护造型过程的整个语义。事实上,语义特征造型系统一个基本思想就是在一个特征模型中把形状信息与功能信息有机地联系在一起,共同构成特征的语义。Bidarra, R.等人研究了特征语义即特征类的详细描述并指出语义特征造型系统的最终目的是维护特征模型的有效性。特征语义的详细描述是由三部分组成的:⑴特征的参数化形状:由特征形状的元素、参数和属性构成;⑵特征的有效性条件:由各种约束,即代数约束、尺寸约束、语义约束、相互作用约束组成;⑶ 用户输入数据的接口:由几何约束、依附约束组成,它们用来确定该特征的方向和位置。在特征类中嵌入有效性标准使得特征具有可调整性,提供形状继承和形状组合机制,使复合特征及自定义特征能正确生成,从而提高了系统设计效率,增强了特征造型能力。特征模型有效性维护是为了保证模型中所有的特征必须符合特征类中描述的特征语义而进行的对每个造型操作的监测过程。有效性维护的两个基本原则是:⑴一个被认为是有效的造型操作应该产生一个满足所有约束的特征模型,这样才能保证模型中的每个特征都体现了那一时刻设计者的设计意图;⑵当一个无效的造型操作后,用户应该收到用于解决约束冲突的帮助。维护特征模型的有效性即特征语义的有效性是借助于使用有效性约束来进行的,这些约束是特征定义的一部分,在创建特征和随后的造型阶段,通过检查这些约束是否满足即约束之间是否发生冲突来说明该特征是否有效,而许多有效性冲突即约束冲突都是由特征相互作用引起的。因此在语义特征造型系统中,特征相互作用起着非常重要的作用,无论是特征类的描述还是特征模型的有效性维护都离不开特征相互作用。针对目前语义特征造型系统中存在的“特征语义不能很好地维护主要是由于特征相互作用的分类不完整造成的”这一问题,本人从研究特征间发生的<WP=5>相互作用机制入手,借助于面向对象的思想,依据特征相互作用的定义极其影响,提出了全新的特征相互作用的分类方法,确定了特征相互作用的范围,描述了特征相互作用管理器在特征模型有效性维护中的作用及工作过程,提出了HUST-CAID系统中语义特征相互作用机制解决方案,并用实例加以说明,进一步指出了下一步的研究重点。方法中引入的面向对象技术最终保证了语义特征造型系统中特征语义的一致性和有效性。更多还原

【Abstract】 Feature modeling is product-oriented and it is an important milestone of CAD development,which really makes integrated CAD/CAPP/CAM possible.It is also the theory and technological foundation of solving products problems.Semantic feature modelling is a declarative feature modelling approach that not only provides a well-defined specification of feature semantics,but also effectively maintains this semantics during the modeling process.In fact ,one of the basic ideas of feature –based modeling is the ability to associate functional information to shape information in a feature model,that form the semantic of the feature together.Bidarra,R.reserches feature semantics,e.g. the detailed description of feature class ,and describes that validity maintenance of semantic feature models is its final aim.Feature class specification is classified into three categories : (1)specification of feature parameterised shape that encapsulates elements,parameters and natures of feature shape;(2)specification of feature validity conditions that involves a varity of constraints such as algebraic constraint,dimension constraint,semantic constraint and interaction constraint;(3)interface of user-supplied data to the feature model that determines the appropriate normal positions and orientations such as attach constraint and geometric constraint.Embedding validity criteria in each feature class makes feature adjustable,provide the mechanism of shape inheritance and shape composition in order to achieve the user-definde and compound feature.So it enhances the efficiency of designing process and improves the ability of modeling.Feature model validity maintenance is the process of monitoring each modeling operation in order to ensure that all features in feature model conform to the semantics specified in their respective classes.The basic principles of validity maintenance can be summarized as follows:(1)A modeling operation,to be <WP=7>considered as valid,should yield a feature model that conforms to all constraints.This ensures that every feature in the model conforms to the designer intent explicitly specified up to that moment.(2)After an invalid modeling operation,the user should be assisted in overcoming the constraint violations in order to recover model validity again.Maintaining feature model validity,e.g.feature semantic validity is by means of validity constraints that is the member in the defination of feature.At the creation of a feature and later modeling step,validity checking ,whether those constraints are valid,indicates feature validity.Many validation violations,e.g.constraint violations are caused by feature interaction.So feature interactions play a major role in semantic feature modeling system,either the specification of featur class or validity maintenance of feature model.Feature-based modeling systems fail to adequately maintain feature semantics, mainly due to an incomplete classe of feature interaction phenomena. Aiming at researching feature interaction mechanism and according to a definition and influence of feature interactions, this paper that based on the technology of oriented-object, presents a new taxonomy for feature interaction, and determines the feature interaction scope of each operation.It describes the role and the excuting process of interaction manager in feature model validity maintenance,proposes a solving method of semantic feature interaction mechenism in HUST-CAID system,and illustrated.This paper point out the next research key. Ultimately oriented-object technology introduced in this method ensures consistency and validity of feature semantics in semantic feature modeling systems.更多还原