Abdulrahman Al-Ahmari

A joint optimisation model for inventory replenishment, product assortment, shelf space and display area allocation decisions

Abstract In this paper, we propose an optimisation model to determine the product assortment, inventory replenishment, display area and shelf space allocation decisions that jointly maximize the retailer’s profit under shelf space and backroom storage constraints. The variety of products to be displayed in the retail store, their display locations within the store, their ordering quantities, and the allocated shelf space in each display area are considered as decision variables to be determined by the proposed integrated model. In the model formulation, we include the inventory investment costs, which are proportional to the average inventory, and storage and display costs as components of the inventory costs and make a clear distinction between showroom and backroom inventories. We also consider the effect of the display area location on the item demand. The developed model is a mixed integer non-linear program that we solved using LINGO software. Numerical examples are used to illustrate the developed model.

Integration of CAD and a cutting tool selection system

This paper describes a novel concept for the integration of a CAD system and a knowledge based system of the selection of cutting tools and conditions for turning operations (EXCATS). This integrated system (CADEX-CATS) is capable of processing CAD data and automatically generating the component representation file for EXCATS using the IGES neutral format and a feature recognition approach. The workpiece representation model is capable to describe sophisticated turned components using Prolog facts and other operational linked keywords. In addition, CAPP related features are effectively incorporated into the CADEXCATS system. A set of rules is established for the automatic determination of set-up, detection of complex geometries, recognition of grooves and other important features. Illustrative examples are presented to test and validate the developed system.

Deadlock recovery for flexible manufacturing systems modeled with Petri nets

This paper deals with deadlock problems in Petri nets by adding a set of recovery transitions. Different from traditional deadlock control methods by deploying control places for a net model to be controlled, this work adds transitions to a net model to recover all deadlock markings. First, we present an iterative approach. At each iteration step, an integer linear programming problem (ILPP) is formulated to design a recovery transition and the objective function is used to maximize the number of deadlock markings recovered by the obtained transition. The process is carried out until all deadlock markings are recovered. As a result, only a small number of recovery transitions are needed to recover all the deadlock markings, i.e., the resulting net model with recovery transitions is live. Second, we develop another ILPP to find all recovery transitions at a time. The constraints of the ILPP ensure that every deadlock marking is recovered by at least one selected recovery transition and the objective function is used to minimize the number of selected recovery transitions. Then, a minimal number of recovery transitions are obtained by solving one ILPP only. Both approaches can make a net model live with all reachable markings. Finally, serval examples are provided to demonstrate the proposed approach.

Nonpure Petri Net Supervisors for Optimal Deadlock Control of Flexible Manufacturing Systems

This paper illustrates that Petri nets with self-loops are more powerful than pure nets in modeling and control of flexible manufacturing systems. A self-loop in a Petri net cannot be mathematically represented by its incidence matrix. This paper presents a mathematical method to design a maximally permissive Petri net supervisor that is expressed by a set of control places with self-loops. A control place with a self-loop can be represented by a constraint and a self-loop associated with a transition whose firing may lead to an illegal marking. The constraint is designed to ensure that all legal markings are reachable and the self-loop is used to prevent the system from reaching illegal markings by disabling the transition at a specific marking. A marking-reduction approach is developed in order to cut down the considered markings, which can greatly decrease the computational overhead of the proposed method. An integer linear programming model is developed to compress the number of control places, aiming to reduce the structural complexity of the resulting supervisors. Finally, illustrative examples are used to validate the proposed method and to demonstrate that it can obtain an optimal supervisor for some cases that cannot be optimally controlled by pure net supervisors.

Robustness of deadlock control for a class of Petri nets with unreliable resources

A variety of deadlock control policies based on Petri nets have been proposed for automated manufacturing systems (AMSs). Most of them prevent deadlocks by adding monitors for emptiable siphons that, without an appropriate control policy, can cause deadlocks, where the resources in a system under consideration are assumed to be reliable. When resources are unreliable, it is infeasible or impossible to apply the existing control strategies. For systems of simple sequential processes with resources (S^3PR), this paper bridges the gap between a divide-and-conquer deadlock control strategy and its application to real-world systems with unreliable resources. Recovery subnets and monitors are designed for unreliable resources and strict minimal siphons that may be emptied, respectively. Normal and inhibitor arcs are used to connect monitors with recovery subnets in case of necessity. Then reanalysis of the original Petri net is avoided and a robust liveness-enforcing supervisor is derived. Examples are presented to illustrate the proposed methodology.

R-TNCES: A Novel Formalism for Reconfigurable Discrete Event Control Systems

This study deals with the formal modeling and verification of reconfigurable discrete event control systems (RDECSs). The behavior of an RDECS is represented by that of control components (CCs) and the communication among them. A new formalism, called Reconfigurable Timed Net Condition/Event Systems (TNCES) (R-TNCES), is proposed for the optimal functional and temporal specification of RDECS, which is defined by a behavior module and a control module. The former is a union of various superposed TNCESs, where TNCES-based CC modules are basic units. The latter is a set of reconfiguration functions dealing with the automatic transformations of these TNCESs in response to errors or user requirements by enabling or disabling CC modules, changing condition signals and/or event signals among them, and also treating the state feasibility before and after reconfigurations. To control the verification complexity of R-TNCES, a layer-by-layer verification method is developed, where the similarities of different TNCESs in the behavior module are considered. The contribution of this original paper is applied to a benchmark production system.

Rapid prototyping and rapid manufacturing in medicine and dentistry This paper presents an overview of recent developments in the field of rapid prototyping and rapid manufacturing with special emphasis in medicine and dentistry

The fundamentals and latest developments of Rapid Prototyping (RP) and Rapid Manufacturing (RM) technologies and the application of most common biomaterials such as titanium and titanium alloy (Ti6Al4V) are discussed in this paper. The issues while fabricating pre-surgical models, scaffolds for cell growth and tissue engineering and concerning fabrication of medical implants and dental prostheses are addressed. Major resources related to RP/RM technology, biocompatible materials and RP/RM applications in medicine and dentistry are reviewed. A large number of papers published in leading journals are searched. Besides the titanium and titanium alloys which were established as bio-compatible materials over five decades ago, other biocompatible materials such as cobalt-chromium and PEEK have also been increasingly used in medical implants and dental prosthesis fabrication. For over a decade RP technologies such as Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) along with the Fused Depositing Modelling (FDM) are predominantly employed in the fabrication of implants, prostheses and scaffolds. Recently Electron Beam Melting (EBM) has been successfully employed for fabrication of medical implants and dental prostheses with complex features. In dentistry crown restoration, the use of thin copings of Ti6Al4V made by the EBM process is an emerging trend. This review is based upon the findings published in highly cited papers during the last two decades. However the major breakthrough in the field of RP/RM for medical implants and dental prostheses took place in the last decade. The fabrication of medical implants and prostheses and biological models have three distinct characteristics: low volume, complex shapes and they are highly customised. These characteristics make them suitable to be made by RM technologies even on a commercial scale. Finally, current status and methodology and their limitations as well as future directions are discussed.

A methodology for selection and evaluation of advanced manufacturing technologies

The problem of selection and justification of advanced manufacturing technologies (AMT) is a multi-attribute problem which involves both tangible and intangible factors. To select the best manufacturing technology that achieves most of the company requirements, it is necessary to use an appropriate selection approach that takes into consideration the different quantitative and qualitative factors of company objectives and AMT benefits. In this paper, a methodology for the selection of AMT is presented to assist the decision maker in selecting technologies that meet their needs. The suggested methodology combines two databases for the manufacturing company and AMT information, and multi-criteria decision making (MCDM) tools (analytical hierarchy process and fuzzy analytical hierarchy process). The developed methodology is tested and validated using a real application from Saudi Arabian Industry.

Iterative Deadlock Control by Using Petri Nets

Deadlocks should be eliminated in resource allocation systems such as flexible manufacturing systems. An iterative deadlock control policy is usually considered to be a natural solution with reasonable computational cost for a large-scale system where direct methods would be prohibitively expensive (and in some cases impossible) even with the best available computing power. This paper reviews the existing iterative deadlock prevention policies for discrete event systems that are modeled with Petri nets. A number of technical problems in the existing iterative deadlock control approaches are formulated and discussed. Their solutions are illustrated through case studies. We conclude that the suitability, effectiveness, and efficiency of an iterative deadlock control approach are sensitive to specific examples, and no general algorithm is found in the literature, which works well for all cases.

Optimal MRP offsetting for assembly systems with stochastic lead times: POQ policy and service level constraint

This study deals with component supply planning in assembly systems, i.e. where several types of components are needed to produce one finished product. The actual component lead times have random deviations, so they can be considered as random variables. MRP approach with Periodic Order Quantity policy is considered. The aim is to find the optimal MRP offsetting. The proposed model and algorithms minimize the sum of the setup and average holding costs for the components, while satisfying a desired service level.