A note on picker blocking models in a parallel-aisle order picking system

This note develops analytical picker blocking models to simply and accurately assess picker blocking in parallel-aisle order picking systems when multiple picks occur at a pick point. The Markov chain-based models characterize the two bounding walking speeds for modeling picker movement: unit walk-time and instantaneous walk-time. The unit-walk time model has a state space transition matrix that is reduced by a factor of 16 for both narrow-aisle and wide-aisle systems. Additionally, the model improves upon the existing literature by providing a closedform expression for the narrow-aisle system with instantaneous walk-time. We provide experimental results to demonstrate how picker blocking is influenced by pick density in a variety of scenarios under varying assumptions regarding the maximum number of picks at a pick point. These results broaden those previously presented in the literature, as well as demonstrate the improved efficiency of our model. 1