Optimal Scheduling of the Reentrant MultiDegree Cyclic MultiHoist Scheduing Problem The current paper deals with the cyclic multihoist scheduling problem in electroplating lines considering rentrance. Identical parts are produced with processing time windows. Moreover, reentrance is also considered. These together make it more challenged to obtain better schedules improving the productivity. To achieve this, multidegree cycles are considered. To our best knowledge, this is the first research in this generally complicated scenario. In order to maximize the productivity of the production line, i.e. minimize the cycle time for a given degree, operations of hoists are first analyzed in detail to avoid their collision. Then, operations related the reentrance are modeled. Based on these work, a mixed integer linear programming model is proposed. An industrial instances is used to test the proposed model. It is solved using the commercial software ILOG CPLEX. Results illustrate the efficiency of the proposed approach.

An Optimal Control Approach to Scheduling and Production in a Process using Decaying Catalysts Abstract   This article presents a novel approach to optimise scheduling and production planning to meet seasonal demand in an industrial process using decaying catalysts, based on its formulation as a multistage mixedinteger optimal control problem (MSMIOCP). Unlike existing methodologies, the MSMIOCP formulation allows to solve this problem as a standard nonlinear optimisation problem without combinatorial optimisation methods, which can be advantageous in providing reliable, robust and efficient solutions. Using this formulation, four case studies of this problem, differing in reaction or deactivation kinetics, are investigated. Two different solution implementations are used, each having their own relative advantages. The first implementation demonstrates a bangbang behaviour for the linear scheduling controls, consistent with a theoretical analysis, but faces integration problems and does not always produce high quality solutions. The second implementation, while not demonstrating the bangbang property, always produces high quality solutions and shows the advantages of the MSMIOCP formulation over existing methodologies.