The effects of picker-oriented operational factors on hand-off delay in a bucket brigade order picking system

During collaboration between neighboring pickers in a bucket brigade order picking, the downstream picker frequently experiences productivity loss in the form of a hand-off delay while waiting for a new tote from the upstream picker. This paper proposes an analytical model to quantify the hand-off delay of downstream pickers under non-deterministic pick times and non-instantaneous walk times of the upstream pickers. Numerical analyses show the effects of the magnitude of pick time, the variation of pick time, and the forward walk time on the hand-off delay, and simulation models show the effects of the number of pickers and their skill differences. We conclude that stable pick times are especially important to reduce hand-off delays and that slowest-to-fastest picker assignments offset hand-off delays with the blocking delays.