Online Dispatching Rules For Vehicle-Based Internal Transport Systems

On-line vehicles dispatching rules are widely used in many facilities such as warehouses to control vehicles' movements. Single-attribute dispatching rules, which dispatch vehicles based on only one parameter, are used commonly. However, multi-attribute dispatching rules prove to be better in general. In this study, we introduce new dispatching rules and evaluate their performance compared to several good dispatching rules in literature, using the experimental design of a real case study. The performance criteria are minimizing the average load waiting time while keeping the maximum load waiting time as small as possible and better utilize vehicles. The experiments show that newly introduced hybrid dispatching rule yields the best performance overall

Sequencing CONWIP flow-shops: Analysis and heuristics

In this paper, we address the backlog sequencing problem in a flow-shop controlled by a CON\VIP production control system with the objective to minimise the make span We characterise the problem and analyse its similarities and differences with the permutation flow-shop problem A comparison of same well-known flow-shop heuristics is carried out and a simple and fast dispatching rule is proposed. Regarding the more simple and faster heuristics, the proposed dispatching rule outperforms those commonly used for the permutation flow-shop problem. --Scheduling,Sequencing,Flow-Shop,Constant Work in Process (CONWIP),Heuristics,Dispatching Rules

Multi-Attribute Dispatching Rules For Agv Systems With Many Vehicles

Internal transport systems using automated guided vehicles (AGVs) are widely used in many facilities such as warehouses, distribution centers and transshipment terminals. Most AGV systems use online dispatching rules to control vehicle movements. In literature, there are many types of dispatching rules such as single- and multi-attribute dispatching rules. However, a dispatching rule that is good for all cases does not exist. In this research, we study a specific type of AGV environments which has not received much attention from researchers - AGV systems with many vehicles as can be seen in airport baggage handling systems. We propose two new multi-attribute dispatching rules for this type of environment and compare their performance with that of two of the best dispatching rules in literature. Using simulation we show that the new multi-attribute dispatching rules are robust and perform very well

Dynamic Scheduling of Handling Equipment at Automated Container Terminals

In this paper we consider the problem of integrated scheduling of various types of handling equipment at an automated container terminal in a dynamic environment. This means that the handling times are not known exactly beforehand and that the order in which the different pieces of equipment handle the containers need not be specified completely in advance. Instead, (partial) schedules may be updated when new information on realizations of handling times becomes available. We present an optimization based Beam Search heuristic and several dispatching rules. An extensive computational study is carried out to investigate the performance of these solution methods under different scenarios. The main conclusion is that, in our tests, the Beam Search heuristic performs best on average, but that some of the relatively simple dispatching rules perform almost as good. Furthermore, our study indicates that it is effective important to base a planning on a long horizon with inaccurate data, than to update the planning often in order to take newly available information into account.beam search;dynamic scheduling;container terminal;dispatching rules

Solving two production scheduling problems with sequence-dependent set-up times

In today�s competitive markets, the importance of good scheduling strategies in manufacturing companies lead to the need of developing efficient methods to solve complex scheduling problems. In this paper, we studied two production scheduling problems with sequence-dependent setups times. The setup times are one of the most common complications in scheduling problems, and are usually associated with cleaning operations and changing tools and shapes in machines. The first problem considered is a single-machine scheduling with release dates, sequence-dependent setup times and delivery times. The performance measure is the maximum lateness. The second problem is a job-shop scheduling problem with sequence-dependent setup times where the objective is to minimize the makespan. We present several priority dispatching rules for both problems, followed by a study of their performance. Finally, conclusions and directions of future research are presented.Production-scheduling, set-up times, priority dispatching rules

An investigation of the dispatching and expediting rules in buffer management : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Production Technology at Massey University

Buffer Management is a proactive way of controlling the flow of materials on a shop floor. For shops using the Drum-Buffer-Rope (DBR) scheduling system, information on the effectiveness of non-constraint resources can be captured by monitoring the buffer status. Practitioners use this information to initiate improvement efforts and to decide to expedite when some of the inevitable disruptions are likely to undermine shop performance. This study attempts to investigate three areas in Buffer Management: dispatching rules, expediting rules, and variance reduction. The selected dispatching rules are First-Come-First-Served (FCFS), Shortest Processing Time (SPT) and Minimum Slack Time (MINSLK). Both static and dynamic expediting rules are compared. Reduction in the coefficient of variance for processing times from 100% to 50% corresponds to the process of quality improvement. Mean protective capacity of non-constraint resources is varied to represent different levels of loading on the shop. Inventory and due date measures are used to appraise shop performance. Simulation results indicate that the FCFS dispatching rule is the method of choice if due date performance is important. The shop using the SPT dispatching rule produces lower cycle times. The dynamic expediting rule is only preferred in the shop using FCFS and when mean protective capacity is low. The reduction in processing time variability renders a dramatically improved shop performance

Evolving control rules for a dual-constrained job scheduling scenario

Dispatching rules are often used for scheduling in semiconductor manufacturing due to the complexity and stochasticity of the problem. In the past, simulation-based Genetic Programming has been shown to be a powerful tool to automate the time-consuming and expensive process of designing such rules. However, the scheduling problems considered were usually only constrained by the capacity of the machines. In this paper, we extend this idea to dual-constrained flow shop scheduling, with machines and operators for loading and unloading to be scheduled simultaneously. We show empirically on a small test problem with parallel workstations, re-entrant flows and dynamic stochastic job arrival that the approach is able to generate dispatching rules that perform significantly better than benchmark rules from the literature

New dispatching paradigm in power systems including EV charging stations and dispersed generation: A real test case

Electric Vehicles (EVs) are becoming one of the main answers to the decarbonization of the transport sector and Renewable Energy Sources (RES) to the decarbonization of the electricity production sector. Nevertheless, their impact on the electric grids cannot be neglected. New paradigms for the management of the grids where they are connected, which are typically distribution grids in Medium Voltage (MV) and Low Voltage (LV), are necessary. A reform of dispatching rules, including the management of distribution grids and the resources there connected, is in progress in Europe. In this paper, a new paradigm linked to the design of reform is proposed and then tested, in reference to a real distribution grid, operated by the main Italian Distribution System Operator (DSO), e-distribuzione. First, in reference to suitable future scenarios of spread of RES-based power plants and EVs charging stations (EVCS), using Power Flow (PF) models, a check of the operation of the distribution grid, in reference to the usual rules of management, is made. Second, a new dispatching model, involving DSO and the resources connected to its grids, is tested, using an Optimal Power Flow (OPF) algorithm. Results show that the new paradigm of dispatching can effectively be useful for preventing some operation problems of the distribution grids

Dynamic adjustment of dispatching rule parameters in flow shops with sequence dependent setup times

Decentralized scheduling with dispatching rules is applied in many fields of production and logistics, especially in highly complex manufacturing systems. Since dispatching rules are restricted to their local information horizon, there is no rule that outperforms other rules across various objectives, scenarios and system conditions. In this paper, we present an approach to dynamically adjust the parameters of a dispatching rule depending on the current system conditions. The influence of different parameter settings of the chosen rule on system performance is estimated by a machine learning method, whose learning data is generated by preliminary simulation runs. Using a dynamic flow shop scenario with sequence dependent setup times, we demonstrate that our approach is capable of significantly reducing the mean tardiness of jobs