Design of walk -and -pick order fulfillment systems.

Abstract

The objective of this research was to answer two important questions, which relate to the operation and design of walk-and-pick investigated the order hatching problem, both in theory and in practice. This study found that certain special cases or variants of the order hatching problem are solvable, while other cases of the problem are NP-hard. A Mixed Integer Programming (MIP) model was developed and used to obtain near-exact solutions. The MIP provided good lower and upper bounds to the problem, which proved useful in the investigation of the heuristic solution procedures. An additional MIP model was presented to find exact solutions. An order batching heuristic was presented, which shows strong results in a numerical experiment. Although good solutions are obtained with this particular heuristic, the results indicate that it is computationally intensive. Furthermore, solutions obtained through the MIP model suggest there is still room to obtain even better solutions, via heuristic procedures, although the challenge is to do so without further increasing computational burden. The second question investigated the assignment of tours to individual pickers, to ensure that pickers are not overworked, while completing all tours as quickly as possible. This was a new problem and combines research from the fields of Ergonomics, specifically manual material handling, Manufacturing and Production, specifically warehousing, and Scheduling. The complexities of this new problem were discussed from both a theoretical and a practical perspective. A method for determining a good lower bound for this problem was introduced, as well as a heuristic that provides near-optimal solutions to the problem. In order to utilize this particular heuristic, the number of pickers in the system is needed; therefore, two methods for determining the number of pickers needed by the system were developed.