DOI: 10.14457/tu.the.2016.1684
title: Multi-workday ergonomic workforce scheduling with personal and task constraint

description: This dissertation deals with the Workforce Scheduling Problem (WSP) with a planning period that covers several workdays which is a multi-workday workforce scheduling problem (MW-WSP). An occupational ergonomic hazard in a workplace or workstation is considered. The safety law of industry states that workers must not be exposed to hazards beyond a daily permissible level. There are three commons approach to prevent or reduce occupational ergonomic hazards (e.g., engineering approach, administrative approach, personal protection equipment). The administrative approach is a popular tool which job rotation can be managed to increase the safety and decrease risk of exposure to excessive hazards. The complex personal and task constraints are considered. Workers are heterogeneous in terms of personal skill, ability, and preference. Workstations might have a multiple task and specific operation schedule in each workday. Multi-objectives are considered, the combination of three objectives; hazard exposure balancing, productivity, and satisfaction of workers; is introduced. Productivity, it is common-that management seeks a workforce scheduling solution with high productivity. When assigning a worker to a job that he/she can perform effectively, it is reasonable to expect high performance from such worker-job assignment. In other words, the productivity directly relates to the person-job fit score. Workers with an unequal person-job fit score prefer a different task/team. When applying job rotation, a work schedule can affect the systems productivity and satisfaction of workers. Moreover, a multi-workday schedule can reduce fluctuation in the amount of hazard exposure among workers. Considering all the objectives, this research aim to provide not only more hazard protection to workers but also keep productivity and satisfaction high.The mathematical models of the problem formulate are in the form of a mixed integer programming (MIP). The multi-objective approach called the LP-metric method is used to navigate to solutions are compatible to the decision maker’s opinion. The optimal values from each aspect are set as target goal values for the LP-metric model. The optimization software IBM ILOG CPLEX V12.4.0 is used to solve the problem optimality. The WSP is a NP-hard problem, thus MW-WSP is more complex. When problem size increases, it is very difficult to find optimal solution with CPLEX. So, a genetic algorithm (GA) is employed to solve this problem. The permutation encoding is presented as the problem solution. The GA operation such as crossover is proposed with revised specific for the problem. The GA tool procedure is coded on the MATLAB script file (m-file).From the numerical example, the LP-metric method return of a solution with respect to pre-set weigh and satisfied problem constraint. From the computation experiment, it is confirm that CPLEX could only guarantee the optimal solution for small size problems. The proposed GA could reach near optimal solution within reasonable computation time.  Moreover, the application of multi-workday workforce scheduling was applied to vehicle routing and workers scheduling problems with manual material handling. An optimization and heuristic methods are proposed for problem solution approach.