Research On Integrated Scheduling Base On Essential Path

Previous production scheduling problem generally decomposition products according to the workpiece, the processing and assemble respectively processing , but these algorithms of production scheduling problem mainly suitable for mass production of the same products. When production task is multiple variety and small batch, especially single product, considering processing and assembling separately will dissever the parallel processed interrelationship which is existed between processing and assembling and then influence the production efficiency. Therefore, this paper studies the complex product processing and assembly integrated scheduling optimization has theoretical and practical value.In appearance, the sum of the longest path processing time in Product Processing tree is the lower bound of product completion time. In fact, it forms essential long path which affects the results of scheduling, because the processes on the same equipment are the serial processing. In order to reveal the application for essential path, avoid the problem of delaying product processing which is caused by forming the longer essential path, the paper presents an integrated scheduling algorithm base on dynamic essential short path after the concept of essential path put forward. The algorithm adopts dynamic long-path strategy and selects the planning and scheduling process in the standby operation set which are consisted of the schedulable process; adds the process and process in the standby operation set to the front of the other side to form essential path; calculates and determines the essential short path; schedules the standby process in the essential short path; stops processing standby process till the set is empty.According to the existing flexible integrated scheduling algorithm select the processing machine of the procedure by short-time strategy, which may cause a long serial processing-time of procedures on the same machine and may form essential long path, the paper presents a step-by-step type flexible integrated scheduling algorithm base on static idle period of each machine. The algorithm adopts short-time strategy to select the planned processing machines of procedures firstly. Then calculate all the static idle period of each machine and static overlap period separately. Part of serial procedures which are on same machine and in overlap period will be adjusted to idle time of other machines, and then determine the final process machine. Finally, determine the scheduling sequence by the allied critical path method.Examples show that the integrated scheduling algorithm base on dynamic essential short path algorithm and flexible integrated scheduling algorithm based on shortening essential path can reduce serial processing-time of procedures on the same machine, increase parallel process time among procedures, and reduce product completion time without increasing algorithm complexity.