Decentralized WIP-oriented manufacturing control (DEWIP)

DEWIP is a manufacturing control system for job shop environments aiming at achieving short and reliable lead times by establishing WIP control loops between the manufacturing work centres. The paper describes the mode of function, the setting of parameters and simulation results of the new manufacturing control system. The setting of parameters is done with the aid of the funnel model and the theory of logistic operating curves, both developed at the Institute of Production Systems at the University of Hanover. The simulation is conducted using industrial data and makes it possible to assess DEWIP with regard to lead times, WIP level, performance and schedule reliability. DEWIP is compared both with an uncontrolled process and with the manufacturing control systems Load oriented order release (LOOR), Conwip and Polca. The results suggest that DEWIP and the models employed for the setting of parameters are suitable for job shop production and therefore offer a valuable alternative to prevailing centralized manufacturing control systems.     

Neural networks in production planning and control

The purpose of this paper is to present a selection of the most significant ANN (artificial neural network) applications used to solve PPC (production planning and control) problems. Therefore, the paper itself is a reasoned classification rather than a simple survey. The PPC domain is divided into various areas, and for each area one or more examples of ANNs are discussed, together with the benefits and drawbacks of their application to that particular area. Finally, two case studies developed by the authors are reported and discussed to analyse the main implementation problems to be considered when using ANNs.     

A comment on: A note on the EOQ-JIT relationship

In a recently published note in this journal the need for independent control of the production rate (R) and production time (L) was established in order to adapt the economic production quantity (EPQ) model in JIT settings. In this comment we aim to improve the relevance of EPQ in a JIT environment. We focus on two issues, namely, modelling the production rate as a decision variable and also deriving an expession for the optimal number of batches (n* ) for the raw materials and/or subcomponents needed.     

FORRIDGE - Principles of good practice in material flow

The post World War II Industrial Revolution has driven production away from the old 'economies of scale' to the new 'economies of scope'. Apparently Japanese led, the associated roots of present good practice on material flow can be traced back in the USA to Jay Forrester and in the UK to Jack Burbidge. Specifically, in the supply chain scenario, Forrester exposed the importance of system structure in relating and integrating information flow with material flow. Similarly Burbidge led the way in exploiting cycle time reduction, synchronization of orders throughout the chain, simplified product structures, and streamlined component flows. This paper unites their contributions to material flow engineering and shows how present day system design methodologies incorporate their ideas on best practice. These principles are particularly relevant to the product delivery process (PDP) which governs material flow in supply chains.     

Shop floor control system for tool rooms

A shop floor control system (SFCS), which is the most important component of any production control system, ff has a direct e ect on the productivity of a tool room. The SFCS presented in this paper aims at streamlining various tool room activities, such as process planning, operations scheduling, loading, progress monitoring, and performance monitoring. The system discussed in this paper is characterized by simplicity and is user friendly. Basic information, consisting of three types of information (order details, process details, and part details), is input through interactive dialogue sessions. On-line updating of the process information is carried out, again through interactive dialogue sessions. The basic input to the system along with the on-line updating enables a number of useful and important reports and documents to be generated ff by the system for e ective control of the shop floor. The reports generated include operations scheduling, process sheet, part list, ffi job card, load pending report, e ciency report, etc. This SFCS is developed for a medium sized tool room in an automotive company and its successful implemention reduced paperwork and improved resource management and has resulted in productivity. It can be said that this system offers a first venture into computer integrated manufacturing (CIM) for a tool room.     

Layered supervisory control architecture for reconfigurable automation

The development of control systems and supporting software remains one of the greatest obstacles to the widespread implementation of highly adaptive reconfigurable automation technology. This paper will present the structure of a modular automation control system designed to support rapid reconfiguration and redeployment of automation components. The paper will first present the concept of a layered system architecture and the use of modular automation components to support the construction of a wide variety of automated systems. This layered system architecture is then applied to the proposed modular supervisory control system responsible for configuring and driving automated production resources. Each of the control components comprising this modular control system will be presented.     

Robustness evaluation of multisite distributed schedule with perturbed virtual jobshops

A method for evaluating the robustness of medium term multisite distributed schedule is presented. The method of robustness evaluation is based on steps and tools associated with the conceptual model of a MultiSite Reactive Production Activity Control (MSR-PAC). The MSR-PAC makes it possible to study the sensitivity of the scheduled plans in presence of perturbations. These must be evaluated before being dispatched to the shop-floors. At present, to the best of the authors' knowledge, there is no means to make this evaluation in the distributed systems such as extended enterprise. The monitoring of errors is based on the discrepancy between the two flow-shape functions that model respectively the dynamics of the scheduled manufacturing orders and the state of the perturbed production. The MSR-PAC is based on a multisite agent system and on the monitoring of the perturbed virtual jobshops. The method can also be used for controlling short term distributed production activities.     

The impact of learning opportunities and decision authority on occupational health

In an investigation of 418 employees in the Norwegian Postal Service, employees with high learning opportunities and high decision authority were found to be better off on psychological functioning, health and organizational outcome variables than employees with low scores on these variables. Decision authority and learning opportunities had specific and independent impact on subjective health, psychological functioning, coping style and organizational outcome variables. There were, however, also interaction effects between demands, learning opportunities, and decision authority on subjective health. Learning opportunities and decision authority were operationalized with a questionnaire, supplemented with questions on the opportunities to learn skills beyond the present job situation. It is suggested that this is a particularly important dimension for coping with the present day rapid changes in working life, where the objective for many workers will be to broaden their repertoire and competence to increase their flexibility in the labour market.     

终极控股股东超额控制与现金持有量价值的实证研究

文章以我国资本市场2002年非金融类A股公司为样本,实证研究了终极控股股东控制权与现金流权分离对公司现金持有量水平及其市场价值的影响.研究结果发现:(1)当终极控股股东为国有股东时,控制权/现金流权系数与现金持有量水平显著正相关;而当终极控股股东为非国有股东时,控制权/现金流权系数与现金持有量水平虽然正相关,但不能通过显著性检验.表明在两权分离的情况下,国有终极控股股东对高现金持有量水平具有较高的偏好;(2)当终极控股股东为国有股东,且其控制权与现金流权存在分离时,现金持有量的价值为0.769元;而当终极控股股东控制权与现金流权不存在分离或虽存在分离但终极控股股东为非国有股东时,现金持有量的价值为1.206元.从而表明在两权分离的情况下,国有终极控股股东对高现金持有量水平的偏好是一种控股股东利益侵占动机.