Technicians scheduling and routing problem for elevators preventive maintenance

In geographically distributed infrastructures, Preventive Maintenance (PM) plays an important role since it improves the serviceability of components. The purpose of this paper is to investigate the scheduling and routing problems associated with the PM of elevator repair service companies. The article presents two mathematical models and considers the objective function of increasing customer satisfaction with regard to the timely presence of PM teams as one of its significant contributions. The chance-constrained approach was also used to formulate the model in uncertain circumstances. Additionally, random data sets were used to measure the accuracy and performance of the presented models. As a solution approach to the problem in large instances, we developed the Variable Neighborhood Search (VNS) algorithm. As a result of analyzing the sensitivity of the models, we are able to determine the effects of inputs on the objective function and solution time. By increasing the bounds of the time window in the sensitivity analysis, the trial values were compared. Based on the results, increases in the earliest arrival time led to increases in the objective function, whereas increases in the latest arrival time led to reductions of the penalty and objective function. It was also possible to significantly reduce the solution time by adding symmetry-breaking constraints. An analysis of VNS was conducted in comparison with a model based on Mixed Integer Programming (MIP). The developed VNS outperforms the MIP for a variety of scale problems and maintenance team sizes.