Abstract: To analyze the locating error of fixture design and to estimate the performance of fixture,the locating error model for a workpiece in fixtures was formulated based on kinematics principle.The locating error was described as a function of the contact point's position variation.The contact pairs between the workpiece and the locators were investigated,and the search rules of the directional dimension paths could further be given for each contact pair.The vector linkage project principle was used to obtain the directional dimension path algorithm which could directionally calculate the position variation of contact point with the known parameters and their tolerances in the vector chain.Otherwise,the directional dimension chain must be generated by connecting two directional dimension paths.With the consideration of category and independence of unknown parameters,the directional dimension chain algorithm was formulated for the position variation of contact point under the condition of the unknown parameters and their tolerances in the vector chain.The methods of duplication deletion and zero deletion were proposed to map the locating scheme into the corresponding directional dimension chain,which ensured the rationality of calculated locating error.The flowchart of the locating error was given,and the result showed that the automatic calculation of locating error could be easily realized.The proposed method could supply the technique support for application of computer aided fixture design system.

Key words: locating error, contact point position error, directional dimension path, directional dimension chain, fixture design

摘要： 为了分析与计算夹具设计过程中的定位误差,以评估夹具的性能,根据运动学原理建立工件的定位误差模型,将定位误差描述为工件与夹具定位方案之间接触点位置变化的函数。研究了工件与夹具定位元件的接触类型,给出各类接触的有向尺寸路径搜索规则,利用矢量环投影原则获得有向尺寸路径算法,实现了矢量环不存在未知参数及其公差情况下接触点位置误差的求解。若矢量环存在未知数,则连接两条有向尺寸路径形成一个封闭的有向尺寸链,根据未知参数的类型及独立性的影响,推导出有向尺寸链的求解算法,建立矢量环存在未知参数及其公差情况下接触点位置变化的表达式。提出去重去零与转换方法,建立定位方案与有向尺寸链的映射关系,确保定位误差计算结果的合理性。通过实例给出了定位误差的计算方法与步骤,计算结果表明所提出的定位误差计算模型通用性好,计算过程易于实现自动化,可为促进计算机辅助夹具设计系统的实用性进程提供技术支持。

关键词: 定位误差, 接触点位置误差, 有向尺寸路径, 有向尺寸链, 夹具设计