1,723,826 research outputs found
Petri net models for message manipulation and event monitoring in an FMS cell
No full textA shop floor control system (SFCS), the central part of a computer integrated manufacturing system, performs the production activities required to fill orders received from the factory level control system. In order to effectively control these activities, a hierarchically decomposed SFCS (equipment, workstation, and shop) can be devised and implemented. The controller at each level is functionally decomposed into planner, scheduler, and executor which perform various tasks such as part dispatching, resource selection and assignment, message passing, event monitoring, communication, machine code downloading, etc. In particular, the executor is responsible for (1) monitoring and interpreting input messages, (2) making execution-based decisions, and (3) broadcasting messages and downloading machine instruction. The purpose of the paper is to present the interpreted Petri net models of the executors embedded in the workstation and equipment level controller. Each event is captured and processed and then some actions associated with the event are taken. These series of activities are modelled using interpreted Petri nets in which a circle node represents the set of actions (e.g. message sending, state variables and database updating, etc.), a bar node represents an event (e.g. message capturing), and an edge represents the transition between two nodes. The execution models have been implemented in an FMS cell with dumb planner and schedulers (meaning that planning and scheduling problems are randomly solved). The form description of the executors presented in this paper will provide the shop floor control engineer with the basis of the rapid generation of shop floor control software. Since the Petri nets detect and process all the events, including even planning and scheduling events, an FMS cell can be intelligently controlled by plugging in a planner and scheduler into the Petri net models.X113sciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A ROBUST ADAPTIVE SCHEDULER FOR AN INTELLIGENT WORKSTATION CONTROLLER
No full textA shop floor control system (SFCS) consisting of three hierarchical control levels (shop, workstation, and equipment) is described. Each controller plans, schedules, and executes the activities necessary to process an order. An intelligent workstation controller (IWC), which is a part of the SFCS, is described in detail. The IWC receives information such as part type and quantity, part routeing specifications, and process plans from the shop level controller and coordinates production activities. The IWC performs three main functions-planning, scheduling, and execution in real-time in order to ensure completion of jobs assigned by the shop controller. The focus of this paper is to develop a robust adaptive scheduler to support the IWC which fits within the functional SFCS architecture. The objectives of this paper are: (1) to develop a neural network model that generates several part dispatching strategies based on workstation status; (2) to develop a multi-pass simulator that evaluates the generated strategies and selects the best strategy to maximize system efficiency; and (3) to compare the efficiency of the scheduling function with other single-pass strategies with respect to several performance criteria.X1163sciescopu
Real-time sonar image enhancement for AUV-based acoustic vision
No full textSonar imaging is considered the only feasible sensing solution for underwater investigations by autonomous underwater vehicles (AUVs) in zero-visibility water conditions. State-of-the-art forward-looking imaging sonars can acquire high resolution images at high frame rates, making the acquired images nearly similar to video images acquired using optical cameras. However, the sonar images are corrupted with speckle noise. In this paper, a speckle noise reduction algorithm is proposed for AUV operation. Unlike the conventional algorithms, the proposed algorithm is adequate for real-time treatment. In order to evaluate the performance of the proposed algorithm, an experiment was conducted by using a forward-looking imaging sonar. Based on the experimental results, it was confirmed that the proposed algorithm can effectively reduce the noise. (C) 2015 Elsevier Ltd. All rights reserved.1166sciescopu
Planning and sequencing heuristics for feature-based control of holonic machining equipment
No full textThe intelligent manufacturing system program was proposed by Japan in 1989. Five participating regions-Australia, Canada, the European Community, Japan, and the United States-currently are involved in developing 21st century manufacturing technology through an investment of US $1.2 billion over 10 years. Korea joined the program and will start work on one of the six ongoing projects, holonic manufacturing systems (HMSs). The objective of the paper is to develop the control architecture of the holonic machining unit (HMU) for construction of the HMSs and to present some planning and sequencing heuristics for feature-based control of the HMU. Further, the paper provides the HMU's functionality using the IDEF0 function modeling method. The basic operation of the decision maker among the HMU's functions is to determine an efficient feature sequence in real time from the nonlinear feature graph used to represent a process plan. To this end, two methodologies are applied sequentially to managing a nonlinear process plan: removal of the OR nodes and then grouping and sequencing the features in the feature graph. Markov chain theory is used to compute the path preference indicator for removing the OR nodes, that is, for selecting the best path among those surrounded by OR nodes. The resulting graph is the AND graph, from which the feature type nodes are formed into sequenced groups. The CNC codes associated with the features in each group are combined and downloaded to the CNC machine. The development of the methodologies can help manufacturers efficiently cope with unexpected failures encountered during computer-automated machining.X119sciescopu
Rapid development of a distributed shop floor control system from an XML model-based control software specification
No full textAs the level of distribution in a shop floor grows, the development of a distributed Shop Floor Control System (SFCS) is of significant interest. Since hand-woven control software is expensive and difficult to reconfigure, a formal methodology that supports generating control software rapidly is in need of exploitation. Although a number of approaches on such purposes have been presented, they lack some of following characteristics: (1) ease of modelling a nature of a distributed SFCS, (2) rapid modelling capability, (3) integrity between specification and development methodologies, and (4) automatic software development capability. The objective of the paper is to propose a rapid development methodology that fulfils given characteristics through a formal model-based control software specification. Specifically, formal models, a resource model and an Monitoring-Decision making-Execution (M-D-E) model are proposed to specify Unit of Control Devices (UCDs) and their control processes performed in a distributed manner. The formal models are represented in the XML format to make them neutral to any model-building or development tools. In addition, the distributed SFCS control engine, a middleware for rapid development, is proposed to develop control software automatically from the XML-compliant formal models. As a result, the proposed set of formal models and control engine organizes the rapid development methodology most appropriate for a distributed SFCS.X114sciescopu
A systematic approach for developing a new business model using morphological analysis and integrated fuzzy approach
No full textDespite the growing importance of developing a novel business model, most previous studies on business model remain conceptual and theoretical. A paucity of empirical studies has hindered the use of the business model concept in practical purposes. Hence, this study proposes a systematic approach to new business model development (NBMD) that helps business practitioners to develop, evaluate and select the best business model to meet the business objectives. The proposed approach comprises two stages: identification of business model alternatives and business model evaluation and selection. During the first stage, a set of business model alternatives are derived by exploring all the possible combinations of a morphological matrix, and in the second stage, we conduct an evaluation and selection of a suitable business model. Morphological analysis (MA) has been employed for the derivation and aggregation of business model alternatives, and decision-making approach that integrates fuzzy extent analytic hierarchy process (FAHP) and fuzzy technique for order of preference by similarity to ideal solution (TOPSIS) methods is used as an evaluation and selection tool. Finally, to illustrate the applicability of proposed approach, a case study on the development of a business model for a Telco has been presented. (C) 2013 Elsevier Ltd. All rights reserved.X111922sciescopu
Efficient sculptured pocket machining using feature extraction and conversion
No full textA methodology is presented for finding a feature that can be used from design to manufacturing for sculptured pockets. A feature is the core concept necessary to realize a fully integrated CAD/CAM system; the information contents embedded in the feature can be easily conveyed from one application to another. However, the feature generated in one application may not be directly suitable for another without being modified with more information. This paper presents a methodology for decomposing a bulky feature of a sculptured pocket into compact features to be efficiently machined. In particular, the paper focuses on two tasks: (1) to horizontally segment a bulky feature into intermediate features and to generate their temporal precedence graph, and (2) to further decompose each intermediate feature vertically into smaller manufacturing features and to apply the variable feed rate to each small feature. The proposed method will provide better efficiency in machining time and cost than the classical method, which uses a long string of NC code.X116sciescopu
Integrated framework of IDEF modelling methods for structured design of shop floor control systems
No full textThe information architecture for a shop floor controller provides the accurate and relevant data in an appropriate format. The information architecture is built by specifying the information requirements and by defining the information handling mechanism. The objective of the paper is to capture and specify the information requirements of workstation and machine controllers for hierarchical shop floor control in a discrete part manufacturing system. The information contents managed by the workstation and machine controllers are identified through IDEF0 function modelling activities. The IDEF0 function modelling method is used in order to guarantee the complete capture of the required information contents. Once being captured through inputs, outputs, controls and mechanisms of the function model, they are classified into two categories: message and stored data. The flow models and specifications of the identified messages are presented using a variant IDEF3 process modelling method. Since the sequence of the messages does not appropriately appear on the function model, a dynamic message flow model is needed which describes message flows among controllers and functional modules. The captured data and their semantic relationships are modelled using the IDEF1X data modelling method. In particular, the evolution of planning and scheduling data is also identified and modelled as part of the information requirements. The specified information requirements show an integrated view of context of a SFCS, increase the understanding of functionality of a SFCS, and provide the stable basis for the SFCS development. The approach suggested in this paper can avoid the fatal errors in terms of information management in operating shop floor control software.X1114sciescopu
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