Research On Intelligent CAD Technology Of Fixture Based On Knowledge Engineering

Fixture design directly affects the product development cycle and production quality,it is one of the key links of product development and design.With the aggravation of the market demand for customized design,the traditional fixture design method has been unable to meet the current production and manufacturing needs of products,especially the complex fixture design of multiple varieties and small batches,which seriously restricts the production efficiency of enterprises.In this thesis,the case retrieval method and reuse method of fixture design are systematically studied,aiming at the problems such as the accuracy rate,reuse rate and low intelligence degree of fixture design.The intelligent CAD system of fixture based on knowledge engineering is developed through the technical integration of many fields,which promotes the development of fixture design towards automation and intelligence.The specific research content of this thesis is shown as follows:1)In order to meet the requirement of automation and intelligence of fixture design,the design scheme of fixture intelligent CAD system based on knowledge engineering was completed.2)Research on preprocessing method of character text data.In order to solve the problem of insufficient preprocessing methods of process model characteristic information,two preprocessing methods of character text data,Label Encoding and one-hot Encoding,are introduced.In other words,ordered character text data is preprocessed by label encoding method,and unordered character text data is preprocessed by hot coding method.Preprocessing different types of text data in different ways is more consistent with the thinking logic and algorithm input requirements.It effectively makes up for the deficiency of incomplete description of feature information in a single way.3)Study on case retrieval technology of similar fixture based on vector Angle cosine.Aiming at the problem of low accuracy of keyword based retrieval,a case retrieval method of similar fixture based on vector Angle cosine is proposed.This method takes the MBD characteristic information of process model as input,introduces the vector Angle cosine algorithm and characteristic weight coefficient,measures the similarity of fixture cases in multi-dimensional space,and retrieves similar fixture cases for reference in fixture structural variation design.4)Case study of similar fixture reuse technology based on configurable BOM structure.Aiming at the low reuse rate of existing fixture cases in enterprises,a fixture case reuse method based on configurable BOM structure is proposed.The method involves configurable BOM structure transformation method,configurable structure extension method and automatic assembly method.Firstly,the retrieved BOM structure of similar fixture assembly was decoupled,and the configurable BOM structure of the fixture was generated by using the skeleton technology.Then the parameterized parts or non-standard self-made parts are extended to configurable BOM structure by human-computer interaction to increase the diversity of configured parts.Finally,BOM structure can be configured through knowledge engineering technology driving fixture,and the configured parts can be assembled into new fixtures by automatic assembly technology.5)Based on the above theory and the actual needs of the enterprise,the intelligent CAD system of fixture based on knowledge engineering was developed on the UG/NX platform,and the overall structure and main functional modules of the system were introduced.The effectiveness of the system is verified by taking the design of connecting rod drilling jig,a key component of Marine diesel engine,as an example.