基于连杆机构模型的公差原则应用与检验方法研究

The application of the tolerance principle by the GD&T specification of the geometric feature will bring about the tolerance compensation, and so as to improve the manufacturing profits. The tolerance compensation is transferred from the precision surplus of a geometric feature, which are the consequence due to the deviation of the virtual condition of the geometric feature from the extreme material condition boundary specified by the tolerance principle. But there not exist the general calculation and inspection method for the tolerance compensation of the target geometric feature, when the tolerance related requirement is applied to more than one datum, and therefore, it fails to apply the tolerance related requirement effectively. In order to calculate and to inspect the tolerance compensation, a linkage mechanism model is proposed in this project. The frame of the representing mechanism denotes the actual virtual condition of the datum feature, the objective links denotes the extreme material condition the datum feature, and the kinematics equation of the representing mechanism can be used to represent the relationship among many factors, such as the geometry, spatial arrangement, tolerance type, of the target feature and its datum features under that various tolerance principles are applied. Based on investigation of the representation and the establishment of the virtual state of the datum features, and based on the datum composition theory, the relative motions between the virtual condition and the extreme material condition are summarized up firstly, then, the relative motion are mapped into the unit of the mechanism members and kinematics joints, and lastly, the equivalent linkage mechanism is established. According to the resulting mechanism of the functional dimension of assembly feature, the relationships between the tolerance compensation and the mechanism structure and moving of the representing mechanism are sum up, then the calculation equations of the tolerance compensation and the inspection rules of geometric feature are built up. The tolerance grade relationship, among the datum features and that between the target feature and datum feature, are investigated based on the kinematics equations of the representing mechanism, and the application principles of tolerance principles are established. This project will provide a complete fundamental theory and methodology for the automation of the tolerance analysis and synthesis.

应用公差原则可获得补偿公差，从而增加制造效益。补偿公差由几何要素的实效状态偏离公差原则设定的极限状态所形成的精度富余转化而成，但多个基准遵循相关要求的补偿公差却无法计算和检测，因而造成相关要求应用困难。提出建立补偿公差计算和检验方法的连杆机构模型，机构的机架和连杆分别对应基准要素的实效状态和极限状态，则机构运动学方程可以表示各种公差原则下的目标要素和基准要素的几何类型、空间布局、公差类型之间的关系。研究基准要素实效状态的表示与建立方法，根据基准组成原理归纳实效状态和极限状态的相对运动关系,建立相应的等价表示机构。以装配作用尺寸形成机理为线索，综合补偿公差和表示机构的结构尺寸和运动参数之间的关系，建立补偿公差的计算公式和几何要素检验方法。根据机构运动学方程，研究基准要素之间、基准要素与目标要素之间的公差等级协调关系，建立各种公差原则的应用规则。为公差分析和综合的自动化方法提供完整的理论支持。

在公差设计中，目标要素和基准要素应用公差相关要求可获得补偿公差，从而扩大目标要素的公差带、增加制造效益。补偿公差包括奖励公差和转移公差，奖励公差由目标几何要素的材料实效状态偏离公差相关要求设定的极限状态所形成的精度富余转化而成，转移公差由基准几何要素的材料实效状态偏离公差相关要求设定的极限状态所形成的精度富余转化而成。由于多个基准要素应用公差相关要求的转移公差无法计算、这种情况下目标要素精度合格与否也无法检测检验，因而造成公差相关要求难以实际应用。本项目针对这一困难局面，研究转移公差计算方法、应用公差相关要求的被测要素检验方法、应用公差相关要求的设计原则。首先提出采用连杆机构模型表示基准要素的材料实效状态和极限状态之间的关系，根据目标要素和基准要素的几何类型、空间布局、公差类型等等信息，建立表示机构的机构组成原理。利用机构运动学方程表示各种公差相关要求情况下基准要素实效状态和设计设定极限状态的关系，利用连杆曲线包络方法计算各种公差相关要求下的转移公差。然后，以装配作用尺寸形成机理为线索，研究目标要素和基准要素应用公差相关要求的应用规则，建立基准要素之间、基准要素与目标要素之间的公差等级协调关系以及尺寸公差和几何公差的协调性设计方法。为公差分析和综合的自动化方法提供完整的理论支持。