Two Picker Cooperation Strategies for Zone Picking Systems With PTL Technology

Cooperation between pickers occurs when many picking assignments are needed to fill large orders. This study discusses two strategies for use in zone picking systems with pick-to-light (PTL) technology: along-a-line collaboration, i.e., collaboration along a zone line, and across-a-line asynchronization, i.e., relaxation of synchronization across a conveyor line. Queueing models, Continuous-timed Markov chains (CTMC), and simulations were used to determine if the strategies could improve throughput and cycle time. In simulations with industry cases and data, the along-a-line collaboration showed a 26.7~53.2% reduction, the across-a-line asynchronization showed an 8.2~21.0% reduction, and combining the strategies showed a 50.9~66.3% (on average 57.4%) reduction in cycle times compared to regular zone pickings without collaboration. An analytical comparison confirmed that using either strategy, or combining them, for zone picking systems with PTL technology can improve throughput and reduce work-in-process, particularly for large orders.