Production Scheduling and Cell Formation for Virtual Cellular Manufacturing Systems

In this paper, an approach using the concept of genetic algorithms is proposed as a powerful but simple means of scheduling the manufacturing operations of a virtual cellular manufacturing system (VCMS). A mathematical model is developed to describe the characteristics of a VCMS, which includes the constraints related to the delivery due dates of the various products and the maximum capacities of the manufacturing resources. The objectives are to set up virtual manufacturing cells and to formulate feasible production schedules for all manufacturing operations, in order to minimise the total material and component travelling distance incurred in manufacturing the products. A new genetic based scheduling algorithm is proposed as an optimisation tool to determine the solution. The proposed algorithm differs from the conventional genetic algorithms in that the populations of the candidate solutions consist of individuals from various age-groups, and each individual is incorporated with an age attribute to enable its birth and survival rates to be governed by predefined ageing patterns. By generating the evolution of the populations with the genetic operators of selection, crossover and mutation, the proposed approach provides excellent results by maintaining a better balance between the exploitation and the exploration of the solution space, and thus improves the computational speed and the solution quality. The condition ensuring stable search performance is also derived. The superiority of the proposed algorithm is illustrated by solving the production-scheduling and cell-formation problems for a virtual cellular manufacturing system, and the results are compared with those obtained by using a conventional optimisation technique.