Research On Digital Twin-Based Task Rescheduling For Robotic Assembly Line

Assembly is the critical step in the manufacturing process.Robotic assembly technology in automatic production line has greatly improved production efficiency and product quality.However,in assembly process,dynamic disturbances such as processing time change and advance delivery may occur,which would cause the scheduling deviation.Traditional scheduling methods are not sufficient to meet the real-time and adaptive requirements in smart manufacturing,which belong to off-line scheduling or predictive-reactive scheduling.Due to digital twin(DT)’s characteristics of virtual reality interaction and real-time mapping,it is an important way to improve the efficiency of product assembly by applying DT to the task scheduling for robotic assembly line(RAL)to realize the timely and dynamic adjustment of scheduling scheme under uncertain interference through virtual-reality control mode.This thesis takes RAL as the research object,introduces DT,and focuses on the online rescheduling model and method for RAL based on DT.The main work is as follows:(1)Modeling of task rescheduling for RAL based on DT.To solve the task rescheduling problem of RAL,a DT model for RAL is proposed.Physical entity(PE)is the foundation of DT model.The PLC and RFID sensing technology is used to realize the perception and access of multi-source data in the production process and promote the integration of “robotics-material-environment”.Based on the equipment parameters and workflow of the physical RAL,the virtual entity(VE)of RAL is constructed by integrating geometric model,physical model,behavior model and rule model.What’s more,the virtual-reality interaction and data processing mechanism of RAL is described,and the mapping mechanism between PE and VE,the virtual-reality control mode,as well as the twin data fusion processing mechanism are described in detail,which promote the self-evolution and self-updating of the DT model and provides model support for task scheduling of RAL.(2)Research on task rescheduling method for RAL driven by DT.A mathematical model of task scheduling for RAL is established by taking the total working time and load balancing as the optimization objectives.By analyzing the adaptive objective thresholds of RAL from the perspectives of event trigger and user demand trigger,a DT driven unit-production line-level mixed rescheduling strategy is proposed.At the same time,to solve the problem of too long computing time in traditional assembly planning methods,taking both the computing time and solution quality into consideration in virtual-reality control mode,an improved elite retention strategy and adaptive sparks number are introduced to propose a rescheduling algorithm for RAL based on an improved discrete fireworks algorithm.The effectiveness of the proposed method is verified by task scheduling experiments of RAL.(3)Design and implementation of a prototype system of DT based task scheduling for RAL.Based on the elements of physical RAL,on the virtual model simulation platform,design and implement the task scheduling prototype system for RAL to verify the feasibility of the proposed model and method.The system consists of the physical RAL module,the virtual RAL module,the DT data management module and the scheduling decision module,to achieve the unified management of manufacturing resources of RAL,real-time monitoring of manufacturing process and rescheduling under uncertain events,so as to make timely response to manufacturing requirements.