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In this paper, closed-form travel-time expressions for flow-rack automated storage and retrieval systems are developed. The expressions, which are based on a continuous approach, are compared for accuracy, via simulation, with exact models which are based on a discrete approach.There is no significant difference between the results obtained from the continuous-approach-based closed-form expressions and the ones from the discrete-approach-based exact solutions. The closed-form expressions are easy to calculate due to their simplistic forms, even without a computer, while the exact solutions are extremely complex. On the basis of computation time, the proposed closed-form expressions are extremely practical when compared with the discrete-approach-based expressions, which require extensive computation time.The closed-form travel-time expressions developed in this study can be used to (1) establish performance standards for existing AS/RS, (2) evaluate throughput performance for flow-rack AS/RS alternative design configurations, and (3) compare different storage techniques for improved system performance. Due to their simplistic, yet accurate, definitions, the closed-form expressions, as well as the results of this study, are applicable to industry.Keywords Automated storage and retrieval systems (AS/RS) · Flow-Rack AS/RS · Inventory management Notations b:shape factor T :normalization factor E(SC): single-cycle expected travel time

In this paper, a novel Mahalanobis–Taguchi system (MTS)-based fault detection, isolation, and prognostics scheme is presented. The proposed data-driven scheme utilizes the Mahalanobis distance (MD)-based fault clustering and the progression of MD values over time. MD thresholds derived from the clustering analysis are used for fault detection and isolation. When a fault is detected, the prognostics scheme, which monitors the progression of the MD values, is initiated. Then, using a linear approximation, time to failure is estimated. The performance of the scheme has been validated via experiments performed on rolling element bearings inside the spindle headstock of a microcomputer numerical control (CNC) machine testbed. The bearings have been instrumented with vibration and temperature sensors and experiments involving healthy and various types of faulty operating conditions have been performed. The experiments show that the proposed approach renders satisfactory results for bearing fault detection, isolation, and prognostics. Overall, the proposed solution provides a reliable multivariate analysis and real-time decision making tool that (1) presents a single tool for fault detection, isolation, and prognosis, eliminating the need to develop each separately and (2) offers a systematic way to determine the key features, thus reducing analysis overhead. In addition, the MTS-based scheme is process independent and can easily be implemented on wireless motes and deployed for real-time monitoring, diagnostics, and prognostics in a wide variety of industrial environments.

This study presents the design and development of a Web-based programmable logic controller (PLC) system architecture that supports "hands-on" laboratory exercises in automated manufacturing systems control area for distance education. The system architecture allows remote users to access and control a PLC-based table-top manufacturing system via the Internet. A Web site has been designed and developed that facilitates interactivity and supports PLC programming and control. The architecture has been tested and implemented in the course Emgt 334 Computer Integrated Manufacturing Systems at the Integrated Systems Facility (ISF) in the Engineering Management Department at the University of Missouri-Rolla during Fall 2001. This study shows that software tools available in the market can be integrated to develop a fairly complex, yet effective, learning environment for distance education. The architecture presented in this paper is not dependent on specific PLC hardware or software configuration, it represents a generic infrastructure.

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