Research On Multi-load AGVs Scheduling Methods For Shopfloor Logistics

The multi-load AGVs are widely used in the dispatching of a variety of materials in the workshop.The multi-load AGVs scheduling system,the core component of material transportation for the intelligent workshop,is of great significance to improve logistics efficiency and production stability.Therefore,this paper conducts an in-depth study on the scheduling for multi-load AGVs,classified into four essential sub-problems as the generation and selection of dispatching tasks,the assignment of dispatching tasks,the assignment of recycling tasks,and AGVs integrated path planning.The main work of this paper is as follows:Firstly,the generation and selection of dispatching tasks method is studied.For the generation of tasks,a reorder point method based on forward-looking information such as cutting tool change is proposed.For the selection of dispatching tasks,the new rule based on SSTFP(Smallest Slack Time First Picked)and SDFP(Shortest Distance First Picked)is designed.By constructing a task evaluation function,a preliminary matching between AGVs available and the dispatching tasks to be assigned is achieved.The experimental results demonstrate that the proposed new rule is superior to other classical rules in terms of the performance based on concentration and stability of timely dispatching tasks.Secondly,the method of assignment of dispatching tasks is studied.To solve the assignment,the paper presents the IHS(Improved Harmony Search)algorithm.Based on adoption of segmental coding,task execution range of AGVs corresponding to the harmony segment is assigned,and element sequence is the sequence of tasks.A comprehensive application of HMCR(Harmony Memory Considering Rate),random two-point cross-collaborative search and local search have been proved effective in algorithm optimization.The experimental results demonstrate that IHS algorithm is superior to other classical algorithms in the scheduling for multi-load AGVsThirdly,the dynamic recycling tasks assignment method is studied.Recycling tasks generated are classified in various urgency levels.A recycling alert task pool is established to ensure the timely completion of recycling tasks and avoid the exceptions such as the burst of the cache area.According to AGVs recycling rule designed in this paper,the matching between AGVs available for recycling tasks and the tasks to be allocated is achieved.Different alert time thresholds can be allocated with different schemes.Through scheme evaluation,the optimal distribution scheme can be obtained.The experimental results demonstrate that the proposed new method is more effective in the recycling scheduling for AGVs compared with other classical rules.Fourthly,the integrated path planning method for AGVs is studied.Based on the results of IHS and the dynamic recycling tasks assignment,the sequence of dispatching and recycling tasks for each AGV is deterimined and the specific routes between tasks are sorted according to the length of time.Therefore,the shortest path for each AGV is determined.The status of AGVs is detected in real time and potential conflics between AGVs are judged according to the time window.If there is a collision,the type of conflict is judged and the corresponding resolution strategy is given according to its priority,which can guide AGVs in the workshop to pass through each channel without collision.The experimental results demonstrate that AGVs path planning method based on time window can effectively solve the problem of AGVs conflict.Lastly,based on the above theoretical research,a multi-load AGVs scheduling prototype system for CNC(computer numerical control)workshop is designed and developed to optimize the dispatching and recycling materials for multi-load AGVs in the actual workshop.The experimental results certify the effectiveness of the proposed method.In conclusion,the main work and novel points are summarized.Possible future research directions are prospected.