Event and object oriented simulation to fast evaluate operational objectives of mixed model assembly lines problems

In this paper an event and object oriented simulator for assembly lines is presented. The tool, developed in Java, is capable to simulate mixed model assembly lines, with stochastic task times, parallel stations, fixed scheduling sequences, and buffers within workstations. The simulator is a flexible supporting tool in finding solution of the mixed model assembly line balancing problem (and the optimal sequencing and buffer allocation problems associated to it). It is capable to immediately calculate the throughput of a complex line, by simply receiving as inputs three arrays representing: the task times durations, the line configuration (number of workcentres, of buffers within them, of parallel workstations in each workcentre, of tasks assigned to each workcentre), and the sequence of models entering the line. Its fastness and flexibility allow its utilization in those algorithms and procedures where the evaluation of a fitness function (which includes the throughput as performance indicator) has to be performed several times. It allows overcoming the limit of using others measures of throughput, presented in literature, that are poorly correlated to its real value when the complexity of the line increases. The simulator is an expandable tool; in its current version provides the possibility to simulate both straight and U-shaped lines, and to generate both random and fixed sequences of models entering the line.