# A Tolerance Type Screening Method Based on Similarity Evaluation
## 6 Conclusions  
In this paper, a similarity assessment method for screening tolerance types is proposed. This method evaluates the similarity from four aspects, such as tolerance elements, component elements, the spatial relationship of elements, and use performance, and obtains four sub-similarity evaluation index values, on the basis of which the weights of each sub-similarity are determined by using the hierarchical analysis method for the linear combination, and the similarity evaluation expression for screening tolerance types is obtained. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Legend**} & \multirow{2}{*}{**Tolerance Element Set**} & \multicolumn{3}{c}{**Relative Spatial Relation Set**} \\ \cline{3-6}  & & **Between Tolerance** & **Between the** & & \\  & & **Element and Datum** & **Constituent** & & \\  & & **(Converted to** & **Elements and** & & \\  & & **Tolerance Type)** & **Datum** & & \\ \hline \multirow{3}{*}{Figure 7a} & \{cylindricity, coaxiality, total runout, Medium-long\} & \{coaxiality, runout, total runout, parallelism, position\} & \{Vertical, Overlapping, Vertical, Vertical\} & \{plane, cylinder, plane\} & \{High speed rotation, active contact\} \\ \hline \multirow{3}{*}{Figure 7b} & A collection of all case & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Similar elements of target part tolerance elements and case part tolerance elements. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Resource Cases**} & \multirow{2}{*}{\(\mathbf{S(E_{\text{tc}},E_{\text{to}})}\)} & \multirow{2}{*}{\(\mathbf{S(R_{\text{tc}},R_{\text{to}})}\)} & \multirow{2}{*}{\(\mathbf{S(A_{\text{cc}},A_{\text{co}})}\)} & \multirow{2}{*}{\(\mathbf{S(F_{\text{tc}},F_{\text{to}})}\)} & \multirow{2}{*}{\(\mathbf{S(T_{\text{c}},T_{\text{o}})}\)} & \multirow{2}{*}{**Literature [17]**} \\ \hline
7b & 0.6523 & 1 & 1 & 0.4150 & 0.7678 & 1 \\ \hline
7c & 0.4594 & 1 & 1 & 1 & 0.7841 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: The results of similarity assessment between the target tolerance specification case and the resource case. Finally, through the implementation of the case, a specific implementation step of how to use the similarity assessment method proposed in this paper to screen the tolerance type is described, and the effectiveness of the method is verified. Through comparative analysis, it can be seen that the similarity assessment method proposed in this paper has a relatively strong performance in distinguishing resource cases and can provide reliable resource cases for tolerance designers to screen the types of target tolerance elements and avoid decision-making errors. The method proposed in this paper has distinctive characteristics of use in determining similarity metrics. In determining the similarity comparison meta-set, the professional domain knowledge of tolerance specification design is comprehensively considered: first, the mapping relationship between tolerance type and tolerance element and the directional position mapping relationship between tolerance type and tolerance element and tolerance datum in the process of tolerance specification design is fully utilised to transform the similarity assessment of tolerance element into the similarity assessment of tolerance type; Secondly, the influence of the relative scale between the geometric dimensions of the tolerance element and those of the adjacent elements on the similarity assessment is taken into account, and the calculation method for the relative scale and the application method of its calculation results in the set of similarity elements are constructed.