基于Petri网的虚拟装配环境建模及其应用

通过分析虚拟装配环境的结构及性能，针对场景图数据结构在虚拟装配应用中的不足，定义了一种基于知识的层次对象时间Petri网，并用于建立虚拟装配环境的应用层模型。该模型以虚拟手的位姿作为输入，运行后输出具体的操作事件更新场景图，完成装配活动，以满足虚拟装配环境的实时和并发等动态性能要求，实现了虚拟装配大量离散事件的处理及装配意图的响应。给出了基于知识的层次对象时间Petri网的产品装配模型表达，不仅表达了产品结构及装配关系，同时记录零部件在装配过程中的方位及约束状态等动态信息，从而在虚拟装配环境中实现了装配与拆卸并存的实际装配活动。此外，还给出了由产品装配层次图生成的基于知识的层次对象时间Petri网装配模型的算法，说明了基于应用层模型的装配、拆卸操作以及装配过程仿真，开发了原型系统。

Modeling & application of virtual assembly environment based on Petri net

Through analyzing the structure and characteristics of Virtual Assembly Environment(VAE),a Knowledge-based Hierarchical Object-Oriented Timed Petri Net(KHOOTPN) was defined,and the application layer model of VAE based on KHOOTPN was constructed to address the limitations of the scene graph structure in virtual assembly application.With the input of posture and position of virtual hand,the model outputted the event for updated scene graph to realize the activity of virtual assembly.Thus the requirements of real-time and concurrence of VAE were satisfied,and the treatment of large number of discrete events and capture of assembly intention were also realized.Furthermore,the representation of assembly model based on KHOOTPN was proposed,which could not only represent the structure and assembly relationship of a product,but also record dynamic information such as the position and constraint state of each component in the process of assembly.Therefore,both the assembly and disassembly were implemented in VAE.Moreover,the algorithm of generation of KHOOTPN-based assembly model from assembly hierarchical graph was presented.Based on application layer model,the operation of assembly and disassembly,as well as the simulation of assembly process,were also illustrated.Finally,the prototype system was developed.