Jocelyn Drolet

Physically reconfigurable virtual cells: a dynamic model for a highly dynamic environment

Abstract This paper presents a scheduling framework for sustaining a manufacturing environment that is said to be very dynamic and turbulent. The framework proposes five modules: part family formulation, family sequencing, cellular configuration, jobs scheduling and system monitoring. The modules will configure the workstations in virtual, dynamic or hybrid cells. Decision criteria are exclusively economic and aim at minimizing the cost for transfering unit loads and the cost for relocating processors.

Dynamic cellular manufacturing system (DCMS)

Abstract This paper presents a dynamic cellular manufacturing system (DCMS) that sustains the turbulent environment of small make-to-order manufacturers and subcontractors. The DCMS exploits the workstation moveableness to reconfigure the cells. The system is composed of 4 modules; loading and routing module, dynamic cell configurator, scheduling module and system monitoring. The core of the DCMS is the cost based algorythm for dynamic cell configuration, its decision criteria are exclusively economic and aim at minimizing the overall cost for transfering unit loads and relocating workstations.

Simulation-based performance comparison between dynamic cells, classical cells and job shops: a case study

This paper presents the results of a simulation-based performance comparison between dynamic cellular (DC) manufacturing systems and two other well-known systems, namely classical cells (CC) and job shop systems (JS). The performance comparison is made at different levels of turbulence. The experiment contains 13 independent variables, most of them related to demand turbulence, and 17 dependant variables related to performance measure. A stochastic simulation model developed on Microsoft Visual FoxPro 5.0 was used in combination with LINDO (a linear/integer programming software) to obtain the initial results. In view of the large number of variables and the time required to run each experiment, a Taguchi plan was used to optimize the model. The results obtained from the analysis of variance indicate that dynamic cellular manufacturing systems are generally more efficient than classical cellular systems or job shop systems, especially with respect to the average and maximum throughput time, mean and maximum work-in-process, mean and maximum tardiness, and the total marginal cost for a given horizon.

Mixed production, flexibility and SME

In this study, a step by step management approach is developed in order to help SME (Small Manufacturing Enterprise) to reach basic, system, and aggregate flexibility and agility, despite their lack of resources. This research is justified by the fact that some large factories are lowering their fixed cost by moving processing machine towards specialized SME, and creating intelligent network of factories based on innovation, agility and JIT philosophy.

Scheduling factories of the future

Abstract The trend toward factories of the future, indicates that world class manufacturing systems will have no more than 20 highly productive machines with an automated material handling system. These factories will operate in Just-In-Time mode under computer control. The machines, in general, will be more versatile. It is also expected that by the year 2000, cutting speed will be up to 10 times faster than todays standards. Reduced lot sizes will dramatically increase the demand on material handling; cooperative workstations will have to be close to each other. The numerical control code will not be generated until the specific routing for a certain order is known. A typical factory order will require only a few units up to less than a hundred. Every order will be produced in exact quantity Just-In-Time for shipping, hence with no inventory. We strongly believe that the virtual cell concept, extensively documented by McLean, etc., and others, will meet the requirement for the factory of the future. This concept has the potential for making flexible manufacturing systems (FMS) even more efficient, because of its inherent capability for sharing resources. Contrary to the group technology cell configuration, a virtual cell is not identifiable as a fixed physical grouping of workstations, but as data files and processes in a controller. Upon selection of a job order, a virtual cell controller is created. The controller takes over the control of a set of workstations capable of processing the job for which they have been selected. This temporary grouping of workstations is called a virtual cell. Once all resources have been requested and awarded, processing can begin. Parts are moved from workstation to workstation similar to a flow line sequence. We have extended the virtual cell concept proposed by McLean and we have developed a scheduling algorithm that permits the creation of virtual cells and schedule them under workstations and tools availability constraints. Equally important, the algorithm is characterized by its polynomial time complexity. The size of the model grows quickly, but linearly, and remains reasonable for a typical size factory. It is efficient enough to be executed in real time for scheduling any virtual cell based system within hundred of seconds with current computer technology. The scheduling model has many advantages that makes it suitable for scheduling factories of the future. Firstly, it permits consideration of critical tools. Secondly, it provides a quick reaction to unexpected events. Finally, it enables a coherent planning of resource utilization, potentially reducing possibilities of delays and deadlock, which are very common in fast pace manufacturing systems.

Adaptation of JIT phylosophy and Kanban technique to a small-sized manufacturing firm; a project management approach

Abstract In this study, a project management approach is used, in order to implement some elements of the Just-In-time philosophy to a small-sized manufacturing firm. The objective of this applied research was to overcome some of the problems that most of small firms are facing when implementing JIT, such problems are: lack of materials and human resources, high employees turnover, lack of influence over suppliers, etc. In order to overcome those obstacles, a project management approach was used. As a result of this project, productivity and quality went up, and lead time went down from six to less then two months.

Studying the performance of a dynamic cellular manufacturing system

This paper aims at studying and comparing the performance of a Dynamic Cellular Manufacturing System (DCMS) with a Classical Cellular Manufacturing System (CCMS). A case study has been realized through the use of a bench test and several measures of performance were collected. The study indicates that the DCM concept permit gains both in terms of performance and flexibility by capitalizing on the advances in computer science and information technology. Even though the dynamic cellular concept is in its early infancy, research being conducted tends to indicate that this new organization paradigm may be a serious rival to the classical cellular organization.

Object oriented simulation with Smalltalk-80: a case study

The authors relate their experience with object-oriented simulation. They begin with a few historical developments that led to object-oriented programming. The objectives of an object-oriented simulation model developed as a case study are presented. A virtual cellular manufacturing system which has served as the referent system for the experimentation is introduced. The object-oriented modeling methodology which has been followed during the incremental phases of development and the strategic and tactical plan for sustaining the experimental investigation are presented. Finally, the results of the experimental investigation that focus uniquely on the object-oriented experience are presented. It is concluded that Smalltalk provides an excellent set of features, capable of supporting object-oriented discrete-event simulation.<<ETX>>

A Virtual Cell Scheduling Algorithm

In this chapter, we begin by defining a new manufacturing concept termed Virtual Cellular Manufacturing System (VCMS). The VCMS is an expansion of the virtual cell concept proposed by McLean and all at the NIST AMRF in the early 1980’s [4].

Comparison study of scheduling rules and set-up policies for a SMT production line

This paper examines the effects of some independent variables on the performance of an electronic manufacturing Surface Mount Technology (SMT) production line operating in a highly dynamic environment. Variables considered are: scheduling rules and set-up policies. Experimental design, ANOVA and simulation techniques (Awesim, C) are used in order to predict the performance of a SMT line on the work-in-process, the throughput time and set-up time.