Pius J. Egbelu

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.

Framework for dynamic positioning of storage/retrieval machines in an automated storage/retrieval system

A methodology is presented based on linear programming formulation and which minimizes the service response time in an automated storage/retrieval system (AS/RS) through the optimal selection of the dwell point of the storage/retrieval (S/R) machine when idle. Two separate models are developed; one model is based on the minimization of expected travel time while the other is based on the minimization of the maximum travel time between points. The procedure is very suitable for dynamic control of an AS/RS. The architecture for the automated implementation of the dwell point selection methodology in an actual industrial setting is also given. An example problem is presented to illustrate the application of the control techniques.

Guide path design and location of load pick-up/drop-off points for an automated guided vehicle system

SUMMARY The guide path layout for an automated guided vehicle system (AGVS) is a critical component in the overall design of a flexible manufacturing system (FMS) that utilizes AGVs for materials handling. Not only does it affect the total distance travelled by the vehicles but it also affects vehicle requirements and space utilization. In this study, the problem of selecting the guide path as well as the location of pick-up and drop-off points for outward and inward bound parts to departments is addressed. The problem is modelled and solved as a linear integer program with the objective of minimizing the total distance travelled.

Pull versus push strategy for automated guided vehicle load movement in a batch manufacturing system

Abstract Most automated guided vehicle (AGV) dispatching rules reported in literature to date are based on the attributes of the vehicles and the workcenters from where the loads originate. These rules can therefore be described as source driven vehicle dispatching rules. In none of these rules is the load pickup priority determined based on the states of the load destinations. Therefore, the priority assignment algorithms used by source driven rules are inflexible for application in some manufacturing systems, especially those based on the just-in-time (JIT) principle. What is required for JIT manufacturing therefore is a demand driven rule. In this paper, an algorithm that assigns load movement priority based on the demand states of the load destinations is presented. When applied to the material flow of an illustrative shop, analysis indicates that the algorithm performs competitively with some of the best source driven rules currently reported. It also provides a material flow and workcenter priority assignment flexibility not matched by any source based rules.

Positioning of automated guided vehicles in a loop layout to improve response time

Abstract One of the control decisions in the operation of an Automated Guided Vehivle (AGV) System is that of determining the home positions for idle vehicles. A home position is a location strategically selected within the AGV System network for holding idle vehicles. Such point selection is based on the system operational objective. In this paper, the problem of selecting the home positions vehicles in a single loop type AGV network is addressed. Several single loop home selection models, along with solution methodologies are presented. The models are constructed based on the objective of minimizing the dead travel time of vehicles.

A heuristic approach to the three-dimensional cargo-loading problem

SUMMARY Since no exact analytical method for solving the three-dimensional cargo-loading problem has been developed, the heuristic approaches with practical assumptions are still useful. A dynamic programming approach to this problem is proposed in this paper. Loading a three-dimensional cargo space is done layer by layer, a special property which is taken advantage of in the proposed algorithm. The computational performance of this heuristic is demonstrated by comparing its results with suggested values published by the General Services Administration, Washington, DC.

A framework for estimating manufacturing cost from geometric design data

In the early stages of a product development process, the estimated manufacturing cost is the primary information needed to determine the profitability of a product. The more reliable is the cost estimating process, the more likely the right decision will be made. In this research, a framework to estimate the lowest product manufacturing cost from its AND/OR tree representation of alternate processes is developed. Although, the manufacturing cost considered is focused on processing and material handling costs, the framework also makes provision for the inclusion of other sources of costs such as fixture and set-up costs. To show the full scope of the system, the aggregate estimates of these other sources of costs have also been modelled and included in the framework. Unlike some earlier research which analyses a single arbitrary process sequence, the cost estimation system developed chooses the best process sequence from among all feasible alternative sequences. The process sequence selection is based on the minimization of the total manufacturing cost from among all the feasible process sequences. Because it is assumed that the process costs are sequence-dependent, a mathematical model combined with a heuristic solution are employed to determine the lowest manufacturing cost estimate and consequently, the minimum cost process sequence. By providing the complete overview of the framework, future development and enhancement is easier and more transparent to undertake.

Scheduling in a manufacturing shop with sequence-dependent setups

Abstract In this paper, the problem of scheduling multiple jobs in a flexible manufacturing cell with multiple machine stations is addressed. Due to the large capital investments that usually characterize flexible manufacturing systems (FMS), an area of control of great interest to system users is that of maximizing the system performance through the minimization of machine idle and setup times. The magnitude of total time spent on machine setups and idle times is influenced by the availability of jobs, job mix, similarities of jobs and job scheduling procedure used. Similar jobs on the same machine require less setup times. Similarly, the use of an adequate scheduling method also reduces total idle and setup times. Such reduction improves the flow times of jobs. In this paper, a heuristic algoritm for scheduling jobs with sequence dependent setup times in a FMS is presented. The measure of performance for evaluating schedule adequacy is the production makespan.

ADVISOR: A computer-aided material handling equipment selection system

This paper develops and describes a systematic computer-assisted methodology for the selection of material handling equipment (MHE). A microcomputer based system called ADVISOR models the material handling equipment selection process and employs information on 77 of the most common equipment types used in material transport, positioning, unit formation, and storage. The system identifies the appropriate equipment type for an application in two stages. At the primary stage, potential equipment types are identified through the use of physical requirements of the material handling activities specified by users. Eligible equipment are ranked according to their normalized accumulated rating and placed in a candidate equipment list. After this, a second stage involving an economic analysis for each eligible equipment is performed. The evaluation criteria provided by ADVISOR include present worth (PW).equivalent uniform annual cost (EUAC), return on investment (ROI), and payback period(PP) methods. Through ADVIS...

Material flow control in AGV/unit load based production lines

The use of automated guided vehicles (AGVs) as transporters and mobile workstations in automated assembly lines is on the increase. This is due in part to the flexibility AGVs introduce in the design of production lines. In this paper, models for the management and control of material flow through AGV based production lines are developed. The use of the models permits the line designer to optimally determine the launch times of successive unit loads of parts into the line to minimize production makespan while balancing between line idleness and the idleness of vehicles employed on the line. The use of the models for AGV based production line design purposes is demonstrated through example problems.