# A Tolerance Type Screening Method Based on Similarity Evaluation
## 1 Introduction  
Similarity is a phenomenon widely existing in nature, social economy, and engineering fields [1, 2]. In the field of mechanical engineering, when two objects are similar, the methods and strategies for solving problems can often be borrowed from each other, or even be exactly the same [2]. This similarity brings convenience to decision-makers and can effectively shorten the decision-making time [3, 4]. For example, in the part design process, using the method of similarity comparison can significantly improve the efficiency of part design [5, 6, 7]. In the process research of additive manufacturing, optimizing the experimental design scheme with the help of similarity-based design can accelerate the process of process research and improve the research efficiency [8]. In a mechanical fault diagnosis system, by conducting similarity assessments and developing a fault-type library based on them, the accuracy of fault diagnosis can be greatly improved [9, 10]. In terms of tolerance specification design, the reasonable determination of geometric tolerance type, tolerance principle, and tolerance value of parts is helpful to improve product quality and reduce manufacturing cost, among which the determination of part tolerance type is the basis for determining the tolerance principle and tolerance value. However, there is still an obvious deficiency in the current study of computer-aided generation tolerance type: The computer will reason to obtain all the tolerance types that match the characteristics of the assembly. There are too many indicators, and, in the actual labeling, further manual screening is required [11]. Due to the differences in designer experience and ability, this situation may increase the uncertainty and decision difficulty in product development. Therefore, it is still an important challenge for computer-aided tolerance design. The tolerance specifications for parts are usually closely related to the structural features (shape features of tolerance elements, direction, and position with reference benchmarks, etc.) and the working characteristics of the parts. Parts with the same structural features and working characteristics can usually adopt the same tolerance type. Therefore, a similarity assessment method based on feature measurement can be established to screen the tolerance types of parts. The tolerance type obtained through rule-based automatic reasoning is regarded as the target case, while the existing engineering practice cases and the cases of expert design results are regarded as resource cases. The similarity assessment method is used to evaluate the similarity between the design target case and the resource cases, and the resource case with the highest similarity is selected as the reference or reused for the design target case, thus realizing the screening of tolerance types. In summary, this paper proposes a similarity calculation evaluation method for screening tolerance types. By using resource cases with similar structural and functional characteristics as a basis for designers to select tolerance types, it helps avoid the selection of tolerance types that do not meet the performance requirements of the product, while also reducing the decision-making difficulty for designers. The remainder of this paper is organized as follows. In Section 2, an overview of related work such as the similarity assessment method and tolerance type screening is provided. Section 3 introduces the similarity evaluation strategy for screening tolerance types. By analyzing the formation of tolerance schemes, we define tolerance specification design resource schemes (resource schemes) and tolerance design target schemes (target schemes) and identify them as similarity evaluation objects and similar elements within these evaluation objects. Additionally, we analyze the similar elements, determine the sub-similar elements of each, and form a set of similar elements. Based on this, we establish similarity measurement formulas for each similar element and between evaluation objects.