摘要:

This research investigates the potential of using a neural network approach in real-time control of flexible manufacturing systems. A hierarchical manufacturing controller, consisting of two neural network structures, is proposed. The first neural system participates in the feasibility analysis, and the other, at the lower level, in the process of dispatching and control. At the first level, a Sigma-Pi type of connection is used to translate work-in-process (WIP) move requests into directed arcs. Through a filter scheme, infeasible arcs are identified and eliminated from further consideration. At the second level, a modified Hopfield-Tank model is developed to determine the correct moves. Its goal is to deliver the right WIP to the right workstation, and process it at the right time. An example is used throughout the paper to illustrate the architecture developed. This two-phase control procedure provides adaptability, speed, and good solution quality which are important for real-time control of flexible manufacturing systems.

ISSN:0020-7543    

DOI:10.1080/00207549508904848

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper, a mathematical model is developed for the analysis of optimal replenishment policies for items which experience lumpy demands. In order to avoid disrupting the inventory system, a cutoff transaction size ofwunits is specified such that customer demands with sizes exceedingwunits will be filtered out of the inventory system and treated as special orders to be satisfied by special deliveries. Customer demands with sizes > units will be met From stock. The control discipline is the (s, S) inventory policy with continuous review and the nature of the demands is approximated by a stuttering Poisson distribution. Recursive formulae are developed for the determination of the probabilities of the lead time demand and the available inventory position. The optimal values of the control parameters,sandS, are determined. The theoretical results obtained are illustrated with a numerical example.

ISSN:0020-7543    

DOI:10.1080/00207549508904849

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

he problem of order-release planning for discrete parts manufacturing is addressed. Traditionally, order-release planning in a multi-stage shop is performed with material requirements planning (MRP) logic, which generally assumes that capacity is infinite and that lead times can be estimated using historical data, past experience, and general rules-of-thumb. These assumptions often result in infeasiblc plans. A new approach to order-release planning termed BACKSIM, that is based on discrete simulation, is proposed. With this approach, order-release plans are generated via a backward explosion logic similar to MRP except that a simulation model of the facility is used. Since the simulation model accurately captures real-world capacity constraints and operational rules, the order-release plans are theoretically feasible. Essentially, component lead times are calculated based on the anticipated queueing in the system each time BACKSIM is executed. A technique is developed that allows BACKSIM to be fairly compared with the MRP approach.

ISSN:0020-7543    

DOI:10.1080/00207549508904850

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Our paper studies a two-class-based rectangular-in-time automated storage/ retrieval system (AS/RS). We present explicit formulas for the optima! boundary of the two storage areas as well as for the expected single command cycle time for an optimally designed rack. In the basic model each crane handles a single aisle. These formulas provide the designer with a full picture of the quantitative effects of the various factors (i.e., access frequencies of the two storage areas, and dimensions of the rack) on the optimal boundary of the two storage areas and the achievable cycle lime in the warehouse. We also develop expected travel time formulas for the dual command AS/RS with two-class-based storage policies and obtain the optimal boundary with a one-dimensional search procedure. Similar developments (i.e., expected travel time formulas and optimal boundary search procedures) are discussed for AS/RS with a single command policy but with each crane handling multiple aisles.

ISSN:0020-7543    

DOI:10.1080/00207549508904851

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Servo-pneumatic systems can provide an alternative to the use of conventional binary pneumatic drives and servo-electric systems. However, a migration path needs to be identified for this to become a practical reality in industry. In this paper, methods for employing pneumatic drives in applications with timing and profile control requirements are investigated. This study is based on a high speed food packaging machine used in industry which currently employs on/off pneumatic actuation. The paper illustrates how advanced features of modem motion controllers can be utilized and what control functions are required to exploit the potential of servo-pneumatic actuation. It also serves to illustrate how pneumatic servos may provide an effective alternative to the use of electric servo mechanisms in some applications. The contribution of this paper is significant in the sense that it illustrates the process of applying servo-pneumatic systems which are currently not well established in industry. The paper should be useful for machine designers who wish to gain an insight into the use of pneumatic servo drives.

ISSN:0020-7543    

DOI:10.1080/00207549508904852

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Statistical process control (SPC) is a statistical based approach that monitors long-term process performance. It is used to identify and remove causes of process disturbances. Automatic process control (APC) is an engineering based approach that monitors processes and provides short-term adjustments. It is used to continually compensate for process disturbances. This paper focuses on control systems that combine these two approaches and may provide improved process performance when compared with either approach. The objective is to investigate the conditions at which SPC or APC or both are applicable as well as the control limits that minimize the total quality loss.

ISSN:0020-7543    

DOI:10.1080/00207549508904853

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper studies the flexible deterministic robotic scheduling problem (FDRSP) where one tool changer (robot) is in charge of several machining operations and overlapping tool changes are not allowed. The relationship between the FDRSP and the economic lot scheduling problem (ELSP) is explored. The most promising solution techniques for the ELSP guaranteeing feasibility in advance are modified and applied to the FDRSP. It is concluded that the basic period approach performs the best in small problems, while the rounding to powers of two approach is superior for medium to large problems.

ISSN:0020-7543    

DOI:10.1080/00207549508904854

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor