LCM cycle based optimal scheduling in robotic cell with parallel workstations

Robot-centered cells play a more and more important role in the fields of incorporate automation and repetitive processing in order to increase productivity and to improve quality. In practice, it is always desired to achieve maximum/near-maximum throughput in a robotic cell. Sometimes, even a small improvement in throughput will be one of the highlighted objectives in robot scheduling, for instance, in the 3C industry of communication, computer and consumer electronics. In this paper, the scheduling problem in an n-workstation (n<;=8) m-stage robotic cell with parallel workstations is discussed by considering the constraints in real engineering practice, including free/non-free pick-up, allowed time window, and free/non-free process. A new method is proposed for optimal scheduling by means of optimally arranging each blocked cycles in every LCM cycle (Least Common Multiple), and assembling them in a proper order. This method is applied to a practical scheduling problem for a 7-workstation robotic cell. It is shown that the throughput is dramatically enhanced after optimization in the engineering scenario. Moreover, by comparing the resultant increase in revenue with the additional equipment costs, the result diagrams also provide managerial insights into links between throughput and cell layout flexibility.