A new bi-objective approach for including ergonomic principles into EOQ model

Worldwide, production systems are demanding new procedures and tools towards responsible inventory management, both in theory and in practice. In real industrial environment, manual fmaterial handling activities such as loading/unloading and stocking/picking operations are performed daily when a purchase/production material order is processed into industrial plants, and can be source of work-related musculoskeletal disorders. Only in the last four years, environmental and social aspects of the production systems have been progressively introduced in lot-sizing international theory, mostly in order to address the increasing request of ‘sustainability’ in modern society. Research in the lot-sizing area is fundamentally driven by the first basic model and by a large set of succeeding incremental steps, developed in order to better reflect real industrial problems and constraints. The social impact of economic order quantity policies has not been thoroughly investigated and is often discussed only via a descriptive approach. This work develops a new two-step approach capable of considering the social impact of lot-sizing procedures in terms of ‘ergonomics’ along with traditional annual logistic costs. Such approach divides the lot-sizing decisions in two main types: ‘In-house’, where the most influential decision variable is the size of the packaging units to move within the plant; ‘In-bound’, where the optimal number of ergonomic bins to purchase per order determines the minimum total cost. The outcome is what is defined as the ‘ergonomic lot-size’, which permits companies to reduce the ergonomic risks for their workers, while continuing to be profitable and efficient in assembly line part feeding.