A CTPN‐based scheduler for a flexible manufacturing cell

Abstract

This paper first presents hierarchical scheduling and control architecture for a flexible manufacturing cell (FMC) that is currently set up at the Mechanical Industrial Research Laboratories of the Industrial Technology Research Institute at Hsinchu, Taiwan. With this architecture, we focus on the scheduling problem of the FMC and present a scheduling mechanism based on a colored timed Petri net (CTPN) model. The CTPN model has three functions in the proposed mechanism: the first one is to formally describe pallet flows and resource constraints in the FMC by the event‐condition relation; the second one is to analyze conflict points among the pallet flows; the third one is to evaluate the used dispatching rules concerned with the selection of machine routings, the selection of work‐in‐process pallets in inter‐medium buffers and the assignment of the commonly used material‐handling device. Using the CTPN‐based scheduler, an appropriate combination of dispatching rules for each given batch can be selected to fit given criteria, e.g. minimum batch completion time, maximum resource utilization or minimum tardiness, etc. Moreover, real‐time status of the FMC can be represented in the mechanism for obtaining the on‐line scheduling effect.     

Scheduling of machines and automated guided vehicles in FMS using differential evolution

This paper addresses the problem of simultaneous scheduling of machines and two identical automated guided vehicles (AGVs) in a flexible manufacturing system (FMS). For solving this problem, a new meta-heuristic differential evolution (DE) algorithm is proposed. The problem consists of two interrelated problems, scheduling of machines and scheduling of AGVs. A simultaneous scheduling of these, in order to minimise the makespan will result in a FMS being able to complete all the jobs assigned to it at the earliest time possible, thus saving resources. An increase in the performance of the FMS under consideration would be expected as a result of making the scheduling of AGVs as an integral part of the overall scheduling activity. The algorithm is tested by using problems generated by various researchers and the makespan obtained by the algorithm is compared with that obtained by other researchers and analysed.     

Tabu search for the job-shop scheduling problem with multi-purpose machines

In this paper we study the following generalization of the job-shop scheduling problem. Each operation can be performed by one machine out of a set of machines given for this operation. The processing time does not depend on the machine which has been chosen for processing the operation. This problem arises in the area of flexible manufacturing. As a generalization of the jobshop problem it belongs to the hardest problems in combinatorial optimization. We show that an application of tabu search techniques to this problem yields excellent results for benchmark problems.Supported by Deutsche Forschungsgemeinschaft, Project JoP-TAG     

Modelling and simulation of just-in-time flexible systems

The increasing worldwide competition requires economical manufacture, high quality and short delivery time. The Just-In-time (JIT) philosophy of manufacturing is increasingly being considered by manufacturing organizations, as a response to the increased pressure to supply high quality products with short delivery times and at low cost. A very simple shop floor control system that was developed by Toyota in the 1970s specifically for their Just-In-Time assembly plant, has received considerable attention in the Western World, and is known as the ‘kanban’ system (literally translated as ‘card’ system). Japan’s success has prompted many scholars and practitioners, to turn their attention to Japanese management practices. This article is to address the modelling, simulation and implementation issues of Just-In-Time in flexible manufacturing environments. Priority nets are used for modelling and analysis of the kanban system. A large number of simulation runs are conducted/presented to probe the behaviour of the system, with respect to different parameter changes.     

适合柔性生产的调度技术

具有竞争力的生产组织要求精益化和柔性的数据处理方法，用于订单计划的制订以及订单的执行。现代生产调度技术严格遵循企业流程，并有效支持所有生产后勤工作部门的应用者。其结果是低成本、经改善的供货能力和员工更高的积极性。     

Hours-per-vehicle controlling – the renaissance of staff productivity

In the global automobile industry, the Hours-Per-Vehicle factor (HPV) is turning more and more into a key indicator for personnel productivity analysis of a production plant. HPV rankings are compiled and personnel goals are derived from comparison of HPV benchmarks. Besides program units and the budget, HPV is advancing to be one of the dominant controlling indicators. Against this background, there is an increasing demand for effective HPV controlling. The major task of such controlling is to ensure the required transparency for the influencing variables as well as to recommend measures to improve personnel productivity. In this context, HPV controlling is not just to be incorporated in the existing target and controlling landscape, but also into existing personnel productivity improvement processes. This article takes up these requirements and demonstrates approaches to a solution. Moreover, it describes the potential and also the limits of HPV applications.     

Virtual fusion: a hybrid environment for improved commissioning in manufacturing systems

Efficiency and quality are major factors contributing to profits in manufacturing systems. Production downtime occurs during commissioning of a new system, adoption of new processes, system faults, or (un)planned maintenance; all of which result in reduced production and profit loss. Current techniques for evaluating change to a manufacturing system rely on simulation and modeling to verify processes, but ignore the physical interactions of the work parts on the system. Implementation techniques to evaluate commissioning focus on identifying issues with the cyber interfaces, ignoring the physical interfaces. To validate the cyber and physical interfaces simultaneously, physical work are sent through the system, resulting in significant costs from scrapped work parts and loss of production time. This research proposes a virtual fusion environment where the physical interfaces between a virtual work part and a manufacturing system can be investigated in real-time, on the physical system, without the expenses associated with physical work parts. The virtual environment includes a virtual fusion filter to monitor discrepancies between the physical and virtual systems, and generate a hybrid virtual-physical input signal to the system level controller for virtualisation of a work part onto a physical system. Experimental demonstrations validate the feasibility of the proposed approach.     

Making IT fit: the design of integrated manufacturing systems

One of the important implications of information technology (IT) is that it has made possible widespread automation in manufacturing industry. However, the bulk of this has involved discrete automation of single plant items or process elements rather than the total production system. Although the capital cost of such total system automation is a significant factor in slowing the rate of change in this direction, there are also a number of problem issues related to the integration of machines, computers and human systems within manufacture and design. Arguably the types of issue involved are not fully understood and in many cases the technological change is demanding totally new approaches and responses to the design of production systems and the traditional manufacture/design connections.The paper explores some of the issues raised in advanced manufacturing systems, drawing on case study research into the adoption of flexible manufacturing systems as an example of computer-integrated manufacture. It comments on the experience of case study firms and presents some comments on the design problems facing those responsible for integrated manufacturing systems.