J. M. A. Tanchoco

Characterization of automatic guided vehicle dispatching rules

SUMMARY Hardware failures notwithstanding, the ability of an automated system operating according to promised potential is dependent upon the operational control measures in force. In this paper, some heuristic rules for dispatching Automatic Guided Vehicles (AGVs) in a job shop environment are presented. The rules are useful for assigning priorities to work stations requesting the services of a vehicle for material pickup. The likely effects of these rules on the performance of a job shop are postulated. Simulation results to demonstrate the effects of these rules arc also presented.

Potentials for bi-directional guide-path for automated guided vehicle based systems

Most current applications of automated guided vehicle systems (AGVS) in manufacturing shop environments employ uni-directional guide-paths for vehicle routing despite the fact that bi-directional vehicles exist. In this paper comparisons and issues regarding unidirectional and bi-directional flows are presented. Also presented is a model of a bi-directional traffic flow guide-path. The effect of the traffic flow pattern on the shop throughput is demonstrated and compared to that of a uni-directional flow system of an equivalent facility. The model is implemented using computer simulation.

Virtual flow paths for free-ranging automated guided vehicle systems

Recent technological development in vehicle design allow vehicles to operate without physical guide paths, i.e. free-ranging automated guided vehicles. This paper addresses the problem of defining flow paths for these vehicles. A model is presented whereby the number of allowable flow paths and the flow directions between nodes (representing pickup/delivery stations and aisle intersections) of the layout network are determined. Examples are presented to demonstrate the approach.

Solution methods for the mathematical models of single-loop AGV systems

Guide path simplification can potentially reduce the complexity inherent in conventional, multi-loop automated guided vehicle systems (AGVs). A single-loop configuration is one alternative. A procedure for designing single-loop AGV systems, the OSL method was presented in a previous paper. In this paper, we suggest faster and more efficient methods for solving the two mathematical models in the OSL procedure. The first model called the valid single-loop problem (VSLP) is used to determine an initial single loop for the procedure. The method suggested is a heuristic procedure that starts from a loop around one of the departments and keeps adding departments to the loop until a valid single loop is constructed. The second model called the single-loop station location problem (SLSLP) is used to determine the location of the pick-up and delivery stations along a given loop. The method suggested converts the mixed integer formulation into a linear formulation.

A LISP-based controller for free-ranging automated guided vehicle systems

Abstract This paper describes the development of an intelligent controller for a fleet of free-ranging automated guided vehicles. The vehicle controller will operate in real-time. Once a transportation request is received, the location where the demand is generated and the nature of the demand is sent to the vehicle controller. Based on this information and the current status of the system, the vehicle controller will perform dispatching, routing, and scheduling tasks for the free-ranging vehicles. For the selected vehicle, the vehicle controller finds a route and then it will schedule the vehicle along that route in a non-conflicting manner. The vehicle controller is capable of detecting and preventing collisions before they occur. Once a collision is detected, the vehicle controller will explore different solutions to prevent the collision. The alternative which will result in the least delay time is the solution which will be selected by the vehicle controller. The inputs to the system are the layout t...

Comparison of dynamic routeing techniques for automated guided vehicle system

An automated Guided Vehicle (AGV) System with a limited number of vehicles cannot perform all of the transportation requests on demand. When a capacitated AGV system is used, then it is possible for the material handling system to become the bottleneck. There are many factors that affect the efficiency of an AGV system including how vehicles are routed and schedules. This paper presents a new dynamic approach to AGV routing. Simulation is used to study the effectiveness of this approach.

Concurrent design and economic justification in developing a product

SUMMARY In todays globally competitive world it is essential to design products with maximized functionality and minimized costs. An environment that facilitates the interactions between design and justification would enhance such a decision process. A conceptual framework for such a concurrent design and justification system is presented in this paper. A prototype implementation was developed to explore the usefulness of the design justification concept Actual data from the design of an electromagnetic/radio frequency shield, a component in electrical metering equipment, was used. In this implementation the design justification environment allowed the decision maker to see the potential economic implications of different design alternatives. It also enabled the decision maker to take advantage of their present knowledge and combine it with that of the environment to better analyse the design of the shield throughout the entire product development period.

Impact of empty vehicle flow on performance of single-loop AGV systems

With the increasing trend in the use of automated guided vehicles systems (AGVS) in manufacturing, the need for design tools becomes greater. The problem is that optimized static design models do not ensure expected performance due to the difficulty in capturing the dynamic operational characteristics of the vehicle system. This study shows that by using the single-loop guide path configuration some of the dynamic features of the system, like the impact the empty vehicle flow has on the systems performance, is reduced. Thus, a more reliable prediction of system performance is achieved

Design procedures and implementation of the segmented flow topology (SFT) for discrete material flow systems

In this paper, both the single pick-up and delivery station (SPDS) and the multiple pick-up and delivery station (MPDS) cases of the segmented flow topology (SFT) system configuration are presented. These systems configurations serve as the backbone of a heuristic design procedure for SFT. This design procedure consists of an upper and lower bound calculation and a search procedure that minimizes the total system cost (transportation, setting up pick-up and/or delivery stations, and material handling devices). Two examples of the implementation of the procedure are given.

Estimation of tool requirements in single-stage multimachine systems

As machine tools become more versatile, single-stage multimachine systems (SSMS) have emerged in which all the operations of a part are performed on a single machine. In this system, parts stay on a machine all through their operations while tools are delivered to the machines as requested. The performance of the system is then restricted by the tooling conditions. This paper addresses the problem of how many tools should be maintained in an SSMS under a tool sharing environment. An open queueing network-based approach is proposed which not only determines tool requirement levels but also predicts the tool waiting time given the tooling capacity. The tool life and tool delivery are taken into consideration in determining the tool requirement levels. A simulation study is performed to evaluate the proposed approach.