Line balancing in robotic cells

In this study, an m-machine robotic cell producing a single part type is considered. The loading and unloading of the machines and the material transportation between the machines are carried out by a single robot. It is assumed that a part requires a number of operations to be processed on the machines, which arehighly exible CNC machines. One of the exibilities that these machines possess is the capability of performing dierent operations as long as the required cutting tools are loaded on their tool magazines. Therefore, it is possible to process atask on one of several dierent alternative machines. The processing time of the pat on a machine is the sum of the individual processing times of the operations assigned to that machine. There are precedence relations between the operations. The aim is to determine the assignment of the operations to the machines and the 1-unit robot move cycle that minimize the cycle time, long run average time between the production of two consecutive parts. In this study, 1-unit cycles in which starting with an initial state, the robot loads and unloads each machine exactly once and returns back to the initial state, are considered. A mathematical programming based exact solution procedure as well as a heuristic algorithm is developed for this NP-Hard problem. The effectiveness of the heuristic algorithm is tested through an extensive computational study.