An Optimal Deadlock Prevention Policy for Flexible Manufacturing Systems Using Petri Net Models with Resources and the Theory of Regions

In this paper, an optimal deadlock prevention policy for flexible manufacturing systems (FMSs) is proposed. In an FMS, dead-locks can arise because of a limited number of shared resources, i.e. machines, robots, buffers, fixtures etc. Deadlock is a highly undesirable situation, where each of a set of two or more jobs keeps waiting indefinitely for the other jobs in the set to release resources. The proposed optimal deadlock prevention policy is based on the use of reachability graph analysis of a Petri net model (PNM) of a given FMS and the synthesis of a set of new net elements, namely places with initial marking and related arcs, to be added to the PNM, using the theory of regions, which is a formal synthesis technique toderive Petri nets from automaton-based models. The policy proposed is optimal in the sense that it allows the maximal use of resources in the system according to the production requirements. Two examples are provided for illustration. RID=" ID=" <E5>Correspondence and offprint requests to</E5>: M. Uzam, Ni&gbreve;de &Uuml;niversitesi, M&uuml;hendislik-Mimarlik Fak&uuml;ltesi, Elektrik-Elektronik M&uuml;hendisli&gbreve;i B&ouml;l&uuml;m&uuml;, Kamp&uuml;s, 51100, Ni&gbreve;de, Turkey. E-mail: murat_uzam&commat;hotmail.com     

A new algorithm for determining production schedules when solving the multi-product economic lot sizing problem in flow shops

In this paper, we study the generation of production schedules in the multi-product economic lot sizing problem in flow shops (i.e., the FS-ELSP) under the power-of-two policy. To investigate this problem, we first review the mathematical model for the FS-ELSP and Ouenniche and Boctor’s (O&B’s) heuristic, and we comment that there exist several problems in O&B’s heuristic if we try to use it to generate feasible production schedules for the FS-ELSP. Therefore, we propose two new heuristics, namely, the modified O&B’s heuristic and Huang and Yao’s (H&Y’s) heuristic to improve O&B’s heuristic. To compare the performance of these three heuristics, we randomly generate 500 instances for each of the seven levels of utilization rate from 0.4 to 0.75. Based on our numerical experiments, we conclude that H&Y’s heuristic significantly outperforms O&B’s heuristic and the modified O&B’s heuristic.     

Assessment of positional error and hole quality during vibration-based drilling of aerospace alloy

Journal of Mechanical Science and Technology - Modulation assisted drilling (MAD) superimposes low frequency (&lt; 1000 Hz) and high amplitude (&lt; 150 µm) vibrations to the cutting...     

Statistical Analysis of Defect Dection in Glass Fiber Reinforced Polymers Using Frequency Modulated Thermal Wave Imaging

Russian Journal of Nondestructive Testing - Active infrared thermography (AIRT) has emerged as an extensively applied non-destructive testing and imaging (NDT&amp;I) methodology for examining...     

Prediction of heat transfer coefficient and compressor power consumption for CO2 with impurities under pipeline transporting condition

Journal of Mechanical Science and Technology - In CCS (carbon capture &amp; storage) process, carbon dioxide is captured with impurities of various componets and different concentration. Under...     

CB&I wins tank work at Oman refinery

Chicago Bridge & Iron (CB&I) has been awarded a US$50 million turnkey contract for all tankage at the grassroots Sohar Refinery in Sohar, Oman. CB&I's contract is with JGC Corp, the main engineering contractor for the entire US$1 billion facility.     

A practical R&D selection model using fuzzy pay-off method

The aim of this paper is to develop a practical R&D portfolio selection model that addresses effective R&D project valuation issue, while it tackles R&D uncertainty in portfolio optimization. Fuzzy sets theory is employed to capture and model the inaccuracy in project information. To avoid the well-known complications of fuzzy real option valuation, the fuzzy pay-off method is used to more effectively value R&D projects. The resulting problem is formulated as a fuzzy zero–one integer programming model which is later transformed into a crisp mathematical formulation to solve the problem for various degrees of risk. A numerical example is used to illustrate the proposed approach.     

Deep and Handcrafted Feature Fusion for Automatic Defect Detection in Quadratic Frequency Modulated Thermal Wave Imaging

Russian Journal of Nondestructive Testing - Recent advancements of nondestructive testing and evaluation (NDT&amp;E) with machine learning, artificial intelligence, and the internet of things...     

FEEDFORWARD CONTROL STRATEGIES FOR TRACKING PERFORMANCE IN MACHINE AXES

Three feedforward (FFD) control techniques for position-servo machine axes are compared. All three FFD controllers are used with two different PID feedback (FBK) controllers. The two different FBK controllers have two different closed-loop bandwidths. They are demonstrated using experimental data from a linear motor test system and from simulations. Laboratory results using the linear motor hardware demonstrate that the velocity &amp; acceleration (V&amp;A) FFD controller improves tracking in all case considered, while the other two FFD controllers actually degrade performance in many cases. Through simulation this degradation is attributed to extreme sensitivity to round off errors. This sensitivity is the result of a complex controller that is implemented outside of the feedback loop.     

离心通风机的优化组合设计方法实例

用５－５６风机及６－４９风机的实例阐述了采成先数系优化组合设计离心风机的方法,并说明了采用该方法设计的风机在系列化生产时可大量减少工装胎具,方便生产管理,阐明了用优先数系方法改变离心风机性能的可靠性。     

重型装备研发型制造企业PLM系统的关键技术

PLM 系统是重型装备研发型制造企业信息化的重要集成平台。根据重型装备研发型制造企业的经营特点及需求,对 PLM 系统关键技术进行综述,为今后企业实施 PLM 系统提供参考。     

An intelligent CAD system for development of controllers of active magnetic bearings

The purpose of this study is to establish a CAD (Computer Aided Design) system for research and development (R&D) of a new product. In the R&D process of a new product, the design objects are frequently redesigned based on the experimental results obtained with prototypes. The CAD/CAE systems (which is based on computer simulation of physical phenomena) are effective in reducing the number of useless prototypes of a new product. These kinds of conventional CAD/CAE systems do not provide a function to reflect the experimental results to the redesign process, however. This paper proposes a methodology to establish the CAD system, which possesses the engineering model of a designed object in the model database, and refines the model on the basis of experimental results of prototype. The blackboard inference model has been applied to infer model refinement and redesign counterplan by using insufficient knowledge of R&D process of new products.     

A dimensioning and tolerancing methodology for concurrent engineering applications II: comprehensive solution strategy

Dimensioning and tolerancing (D&T) is a multidisciplinary problem which requires the fulfillment of a large number of dimensional requirements. However, almost all of the currently available D&T tools are only intended for use by the designer. In addition, they typically provide solutions for the requirements one at time. This paper presents a methodology for determining the dimensional specifications of the component parts and sub-assemblies of a product by satisfying all of its requirements. The comprehensive solution strategy presented here includes: a strategy for separating D&T problems into groups, the determination of an optimum solution order for coupled functional equations, a generic tolerance allocation strategy, and strategies for solving different types of D&T problems. A number of commonly used cost minimization strategies, such as the use of standard parts, preferred sizes, preferred fits, and preferred tolerances, have also been incorporated into the proposed methodology. The methodology is interactive and intended for use in a concurrent engineering environment by members of a product development team.     

精密模具零件的高速加工技术及策略

分析了高速加工的机床功能部件、高速加工刀具刀柄及安装要求,从切削走刀方式及加工顺序的选择等方面,论述了精密模具零件高速加工工艺技术及策略。通过实例,总结了高速加工中应注意的实际问题,对解决精密模具工作零件及复杂零件的高效加工具有一定的实际意义。     

光学相干层析术无损检测血糖的测量效果评价

为改进现有光学相干层析术(OCT)无损检测血糖评价方法的不足,提出将OCT信号斜率相对变化量和相对标准误差相结合来评价测量结果,并同时得到血糖的理论测量精度。首先,分析了OCT系统共焦函数对测量结果的影响及OCT信号斜率相对误差的计算方法,然后,通过对3只新西兰白兔进行活体实验来评价OCT无损检测血糖的测量结果。在测量血糖引起的OCT信号斜率相对变化量的同时,对OCT信号斜率相对误差也进行了计算,从而获得血糖的理论测量精度。新西兰白兔活体实验表明,线性度较好的拟合区间下OCT信号斜率相对变化量和相对误差分别为(3.7%)/mmol和0.068,(3.4%)/mmol和0.026,(0.93%)/mmol和0.019,血糖理论测量精度分别为±3.7 mmol,±1.5 mmol和±4.1 mmol。OCT信号斜率的相对变化量和相对标准误差相结合的评价方法能更有效地提高血糖理论测量精度,而且拟合区间越大,血糖的测量精度越高。     

How Crusader Solid Modelling Uses Simulation to Accelerate Design and Mitigate Development Risk

Crusader is the US Army’s next generation cannon artillery system; it is a two-vehicle system consisting of a tracked self-propelled howitzer and a tracked ammunition resupply vehicle. Currently in demonstration/validation with fielding scheduled for 2008, Crusader is the US Army’s highest-priority combat vehicle development program. The Crusader development approach relies heavily on modelling and simulation (M&S) to accomplish program development objectives. In particular, M&S is being employed to streamline development by accelerating design and integration while simultaneously mitigating technical, cost, and schedule risk. To achieve these goals, Team Crusader is implementing a system simulation development process that provides for early, evolutionary and iterative design and integration. The primary building blocks of this process are: 1. Support models, including static solid modelling, dynamic solid modelling, human factors modelling, object modelling, and M&S metrics. 2. Integration support models, including the dynamic object model and the visual prototype, as well as simulators, emulators, and stimulators (SES). A common simulation framework emplaced across the development team provides the development environment to ensure M&S compatibility and integrability.     

Numerical Study of the Sensitivity of Tilting-Pad Journal Bearing Performance Characteristics to Manufacturing Tolerances: Dynamic Analysis

In engineering practice, the predictions of bearing steady state and the dynamic characteristics are based on the bearing nominal dimensions. However, as the authors showed in a previous study (Fillon, et al. (1) Fillon, M., Dmochowski, W. and Dadouche, A. 2007. Sensitivity of Tilting Pad Journal Bearing Performance Characteristics to Manufacturing Tolerances. Trib. Transactions, 50: 387–400. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), manufacturing tolerances related to the bearing geometry (e.g., bearing clearances or angular pivot position) can significantly affect the steady-state characteristics such as the operating temperature, the minimum film thickness, and the power loss. This paper investigates changes to the bearing dynamic properties due to variations of the design parameters within the manufacturing tolerances. The dynamic properties of the tilting-pad journal bearings are represented by eight linear coefficients of stiffness and damping.

The study presents results obtained for realistic variations of bearing clearance, preload, pivot offset, as well as the pad angular extension. As an example, five-pad tilting-pad journal bearings with a diameter of 76.2 mm (3 in.) and three different L/d ratios have been used.     

Evaluating measurement and process capabilities by GR&R with four quality measures

This paper proposes a procedure for assessing a measurement system and manufacturing process capabilities using Gage Repeatability and Reproducibility (GR&R) designed experiments with four quality measures. In this procedure, a GR&R study is conducted to obtain replicate measurements on units by several different operators. The gage and part variance components are then estimated by conducting analysis of variance (ANOVA) on the GR&R measurement observations. Finally, the acceptance and rejection criteria of the precision-to-tolerance ratio (PTR), signal-to-noise ratio (SNR), discrimination ratio (DR), and process capability index (C_p or C_pk), are employed to assess the measurement and process capabilities. Three previously studied case studies are provided for illustration; in all of which the procedure provided efficient capability assessments at minimal computational and statistical efforts. In conclusion, the procedure proposed in this research using GR&R designed experiments provides valuable procedure and helpful guidelines to quality and production managers in assessing the capabilities of a measurement system and manufacturing process, and deciding the needed actions for improving performance.     

Feature Representation and Database Schema of an Object-Oriented Feature-Based Product Model for Hydraulic Manifold Blocks

The model is developed with C&+: in a Windows environment.     

A Six-sigma approach for benchmarking of RP&M processes

This paper presents a methodology of using six-sigma quality tools for benchmarking of rapid prototyping & manufacturing (RP&M) processes. It involves the fabrication of a geometric benchmark part and a methodology to control and identify the best performance of the process to reduce the variablity in the fabricated parts. The approach is demonstrated with a case study based on the direct laser sintering (DLS) process for prototyping using plastic powder. In the case study an identified set of six-sigma/ statistical process control tools is employed to determine and best tune factors affecting the desired outcomes of the built parts.