Jose Ildefonso U. Rubrico

Metaheuristic scheduling of multiple picking agents for warehouse management

Purpose – This paper aims to develop a scheduler for multiple picking agents in a warehouse that takes into account distance and loading queue delay minimization within the context of minimizing makespan (i.e. picking time).Design/methodology/approach – The paper uses tabu search to solve the scheduling problem in a more global sense. Each search iteration is enhanced by a custom local search (LS) procedure that hastens convergence by driving a given schedule configuration quickly to a local minimum. In particular, basic operators transfer demand among agents to balance load and minimize makespan. The new load distribution is further improved by considering a vehicle‐routing problem on the picking assignments of the agents with relocated demands. Loading queue delays that may arise from the reassignments are systematically minimized using a fast scheduling heuristic.Findings – The proposed tabu scheduler greatly improves over a widely practiced scheduling procedure for the given problem. Variants of the t...

Scheduling multiple agents for picking products in a warehouse

In this paper, the final stage of a multiphase approach for solving the picking problem in a warehouse is addressed. Given a number of agents, each with its own set of picking sequences (trips or routes) to accomplish, a dispatching problem is described and shown to have a non-polynomial search space with respect to the number of agents and number of routes. A simulation-based scheduling procedure is proposed to solve the problem. The aim is to reduce potential delays induced by agent queues. Extensive statistical simulations on a realistic warehouse operating at varying conditions are conducted to show that the said dispatching procedure is able to make significant improvements with respect to minimizing operating time, on the average, over the case when no dispatching policy is applied to the agents

Route generation for warehouse management using fast heuristics

In this paper, fast heuristics for a centralized multi-agent route planner are presented and computationally evaluated. We solve a sub-problem of warehouse scheduling involving the routing of intelligent agents as a preliminary step in optimizing the total schedule. The problem involves the generation of routes for automated agents tasked with the transfer of items within a warehouse from storage pallets to a common loading shed. The goal is to minimize the total distance of the routes and the number of routes generated. This constitutes a multiple-objective optimization problem which is NP-hard and hence can take a prohibitively long time to solve using existing search-based techniques. The approach adapted here is to model the system as a split delivery vehicle routing problem (SDVRP) with grid distances and to solve it using heuristics based on tested operations research concepts. Twenty-two such heuristics are tested including the well-known greedy nearest-neighbor (NN) heuristic, and the established savings heuristic of Clarke and Wright. The author introduces two SDVRP variations of the NN algorithm, namely the nearest-fill (NF) and nearest-fill farthest-start (NFFS) heuristics. Existing SDVRP improvement procedures are also considered and generalized to produce numerous heuristic variations. This novel approach of applying fast vehicle routing heuristics to multi-agent routing has the advantage of yielding good quality results within a very short period of time. The results of the study show that the greedy NFFS heuristic combined with the improvement procedures, consistently produces superior results with regard to minimization of distance and the number of routes in an the instances tested.

Teaching Multiple Robots by a Human

The main function of robots is to assist humans with tasks. We can find successful examples in factories and hospitals. Yet, service mobile robots, designed to help humans in houses, are still in its early stages. The current state of service mobile robotics inspired me to start my research in this field. First, during my Master thesis I developed a semi-direct teaching method for robots. The method conveys human knowledge on how to grasp objects through the use of a teaching tool. I evaluated the method by teaching mobile robots with a parallel gripper. The system met the proposed targets, yet, the results showed me that small robots with limited capabilities cannot be used for many tasks.

Design of AVS/RS under group constraint

Abstract Distribution centers, which are essential to our society, are becoming increasingly important. Although the efficiency of an AVS/RS (Autonomous vehicle storage and retrieval system) makes it a promising system, there is still much to be studied regarding its effective use and design. This paper proposes a method of designing AVS/RSs through a quantitative consideration of group constraint by utilizing probability theory. The proposed algorithm also deals with the problem of designing the sizes of several buffers, and considers the effect of load fluctuations, which are important for real-world operation, by use of queuing network theory. Effectiveness of the proposed algorithm is shown with simulations of various number of groups, those of various safety factors for fluctuations, and those of various evasion rates for buffer overflow. The design results are shown to be much different from those which do not consider those factors. The results prove that the proposed method provides an accurate quantitative assessment of the AVS/RS’s constraints.