Abstract: To solve the problem of geometric tolerance transformation caused by datums'conversion in the process of machining and assembling of parts,a new method of tolerance transformation based on variation of tolerance zone was proposed.According to the types of geometric features,the Degree of Free (DOFs) of functional geometry in different spatial locations constrained by other geometric features were analyzed.By using spatial locations,DOFs of functional geometry constrained by designing datums were obtained.The coordinate system of positioning datums was estabished and checked for its redundancy and completeness.According to the spatial relationship among designing datums,positioning datums and functional geometry,the accumulation equation was used to get the value of geometric tolerance related to the functional geometry after transformation.Based on the proposed method,a software package was developed,and a case study was conducted to prove the feasibility and accuracy of proposed method.

Key words: geometric tolerance, tolerance zone, datum, small displacement vector

摘要： 针对当前零件加工或装配过程中基准转换导致的几何公差转化问题,提出一种基于公差变动域的几何公差转化技术。根据几何公差关联的功能几何特征类型,解析功能几何处于各空间位置时被其他几何特征约束的自由度;利用功能几何的空间位置,获得其被设计基准约束的自由度;构建定位基准体系,并对其冗余性和完备性进行检查;根据设计基准、定位基准和功能几何之间的定位关系,采用公差累积方程实现功能几何相关的几何公差转化求解。基于上述研究开发了几何公差转化软件系统,通过实例分析验证了上述方法的可行性与有效性。

关键词: 几何公差, 公差域, 基准, 小位移矢量