# A Tolerance Type Screening Method Based on Similarity Evaluation
## 2 Related Work
### Tolerance Type Screening  
In the field of tolerance specification design knowledge, there are multiple alternative tolerance types for the same assembly feature element. However, in engineering practice, only the tolerance types that meet the functional requirements of the product are required to be labeled on the assembly feature elements of a part. For this reason, in computer-aided tolerance specification design, designers are required to optimize the tolerance types obtained from automatic reasoning. This usually boils down to two categories.  
Alternative optimization method. This method is commonly used in tolerance design methods based on technology and topology-related surfaces (RRTSs) [18; 19] and design methods based on assembly positioning constraints [19; 20; 21; 22]. The characteristic of alternative optimization is that the determination of shape tolerances is still based on the empirical rules provided by ASMY14.5-1994 [23] and the standards of ISO 1101:2012 [24]. However, the selection of shape tolerances increases the difficulty of decision-making for designers. The available shape tolerance types for cylindrical surfaces include roundness, cylindricity of the cylindrical surface, straightness of the axis, and straightness of the cylindrical surface in the axial plane. Choosing which tolerance type to use from above will cause confusion for designers, and this process will inevitably increase the difficulty of their decision-making.  
Screening Optimization. This method is commonly used in tolerance specification design methods based on inference rules [11; 25; 26] especially in methods for the automatic generation of tolerance specifications based on ontology [17; 26]. First, tolerance domain knowledge is used to infer all tolerance classes that match assembly feature elements. On this basis, the designer screens the tolerance types based on the type of tolerance zone and the intuitiveness of the tolerance symbols, the working characteristics of the mating parts, and the freedom of the tolerance bands, and, finally, optimizes to obtain the marked tolerances of the parts.  
From the above review, it is clear that the existing tolerance type screening methods still require designers to subjectively screen tolerance types based on their design experience, and it is still a challenge to reduce the subjective involvement of designers in the tolerance design process and screen out tolerance types that match the work scenarios.  
In summary, this paper uses the OWL ontology language [27; 28] based on tolerance domain knowledge to represent past tolerance specification problems and their scenarios as resource cases, and at the same time considers the problems representing each new tolerance specification as target cases. Similar objects for case retrieval are selected by combining the main decision elements of tolerance specification design, and the similarity metric is improved to increase the accuracy of similarity retrieval, which provides methodological support for the final determination of tolerance types to reduce the subjectivity of designers.