A Lindley-type equation arising from a carousel problem

TL;DR

This paper models a two-carousel system with a single picker using a Lindley-type equation, deriving explicit solutions for waiting times and showing insensitivity of key performance metrics to pick-time distribution.

Contribution

It introduces a Lindley-type equation for the carousel system's waiting time and provides explicit solutions, highlighting performance insensitivity to pick-time distribution.

Findings

Explicit solution for the waiting time equation.

Mean waiting time and throughput are insensitive to pick-time distribution.

The model extends Lindley's equation to carousel operations.

Abstract

In this paper we consider a system with two carousels operated by one picker. The items to be picked are randomly located on the carousels and the pick times follow a phase-type distribution. The picker alternates between the two carousels, picking one item at a time. Important performance characteristics are the waiting time of the picker and the throughput of the two carousels. The waiting time of the picker satisfies an equation very similar to Lindley's equation for the waiting time in the PH/U/1 queue. Although the latter equation has no simple solution, we show that the one for the waiting time of the picker can be solved explicitly. Furthermore, it is well known that the mean waiting time in the PH/U/1 queue depends on to the complete interarrival time distribution, but numerical results show that, for the carousel system, the mean waiting time and throughput are rather insensitive to the pick-time distribution.