Research And Implementation Of Constraint-based Sketch Modeling Technology

With the vigorous development of computer technology,computer-aided design technology has grown rapidly,and it is widely used in electronics,mechanical design,aerospace and other fields.Sketch modeling technology is a key technology in computeraided design and the basis of 3D feature modeling.Sketch modeling technology enables designers to draw the 2D outline of the model according to design requirements,then add sketch constraints,and use operations such as extrusion and rotation to generate 3D models.The MTSS software independently developed by the Institute of Computer Simulation Technology of UESTC is capable of modeling and simulating a variety of traveling wave tubes.However,due to the lack of sketch modeling system in its modeling module,complex models cannot be created.However,the structure of TWT is complex and there are many kinds of TWT,so simple modeling methods may not be able to meet the requirements of creating complex TWT models.Therefore,this thesis studies the theoretical characteristics of 2D sketch modeling technology,designs and implements a sketch modeling prototype system that can complete relatively complex model creation,and applies it to MTSS software.The research content of this thesis can be divided into the following parts:(1)Several key algorithms in sketch modeling technology are studied,including sketch constraint algorithm and direction determination algorithm based on constraint.For the sketch constraint algorithm,the sketch constraint space model and the sketch constraint system model are designed,and the constraint system model is decomposed,and finally solved by numerical method.The relatively complicated direction determination algorithm based on constraint is the direction determination of geometric elements with 1 remaining degree of freedom,which mainly derives the current moving direction of elements according to the determined moving direction of geometric elements and constraint relations.(2)Design and implement sketch modeling prototype system.Firstly,the main functions of the sketch system are determined through demand analysis,and the overall structure of the system is designed.Then,the functions of user interaction,twodimensional geometry creation,capture,cutting and extension,sketch constraint,storage and reading of sketch files are designed and implemented respectively.(3)Finally,an example of mechanical irregular non-standard parts and electron gun is used to verify the sketch system designed in this thesis.Firstly,the operation flow of the sketching system is described.Then,taking mechanical non-standard parts and electron gun as examples,the corresponding 2D sketching is created by the sketching system respectively,and then the corresponding 3D model is generated by rotation and stretching operation.The practicability and efficiency of the sketch system are verified by these two examples.