Simulation-based optimization of personnel assignment planning in sequenced commercial vehicle assembly: A software tool for iterative improvement

This paper presents a simulation-based planning software for high complexity production settings which currently undergoes first real-data industry application tests in commercial vehicle assembly. The system will also be applicable in other industries with a sufficiently high number of products and variants. The solution enables the forecasting of required personnel and temporary additional workers (“floaters”) for every cycle at the production line. It periodically collects process times, sequence and feature data for the vehicles. The cumulated workload is calculated under consideration of flexibilities. A web-based user interface enables to set and change reference data, define process simulations and to compile diagrams and charts for the analysis of the results of the different simulation runs. Various filters as to time periods, vehicle types or feature variants allow the planner a target-oriented analysis and provide feedback for improving production line tacting. Finally, some qualitative results of a first industry test in commercial vehicle assembly give feedback about the usability of existing analytical features and desirable additional features.     

Simulation-based optimization of multiple-task GRID applications

This paper deals with the performance optimization of multiple-task applications in GRID environments. Typically such applications are launched by a Resource Manager, which only takes into account the application’s resource requirements and current availability on the GRID. Here a novel approach is presented, that performs resource management in user space, making it possible to exploit application modularity and flexibility and to take into account expected performance figures produced by GRID simulation. The objective is to make optimized choices that can lead to reduced application response times. After an introduction to the GRID simulation environment used, the structure of an application launcher able to optimize a number of application tasks and their mapping on the GRID is sketched, presenting the encouraging performance results obtained.     

Simulation-based optimization of Markov reward processes

This paper proposes a simulation-based algorithm for optimizing the average reward in a finite-state Markov reward process that depends on a set of parameters. As a special case, the method applies to Markov decision processes where optimization takes place within a parametrized set of policies. The algorithm relies on the regenerative structure of finite-state Markov processes, involves the simulation of a single sample path, and can be implemented online. A convergence result (with probability 1) is provided     

Simulation-based heuristic method for container supply chain network optimization

With the emerging of free trade zones (FTZs) in the world, the service level of container supply chain plays an important role in the efficiency, quality and cost of the world trade. The performance of container supply chain network directly impacts its service level. Therefore, it is imperative to seek an appropriate method to optimize the container supply chain network architecture. This paper deals with the modeling and optimization problem of multi-echelon container supply chain network (MCSCN). The problem is formulated as a mixed integer programming model (MIP), where the objective is subject to the minimization of the total supply chain service cost. Since the problem is well known to be NP-hard, a novel simulation-based heuristic method is proposed to solving it, where the heuristic is used for searching near-optimal solutions, and the simulation is used for evaluating solutions and repairing unfeasible solutions. The heuristic algorithm integrates genetic algorithm (GA) and particle swarm optimization (PSO) algorithm, where the GA is used for global search and the PSO is used for local search. Finally, computational experiments are conducted to validate the performance of the proposed method and give some managerial implications.     

A scheme for mechanical assembly design and assembly line layout conceptualization

A scheme in this paper makes possible to analyze a complex assembly design at an early design stage and generate assembly sequences efficiently. The designer's knowledge is used to obtain the preference module set. The modulability of the set is tested and used to generate assembly sequences hierarchically. Sequences generated by this scheme reflect the designers' preference for modules and facilitates to figure out an assembly line layout from an assembly design. The applicability of the scheme is verified in an example.     

不确定条件下基于仿真的流程工业调度方案优化

针对流程工业需求和产率不确定性问题,提出了一种基于仿真优化架构的调度问题求解方法,调度方案包括生产装置加工量和加工方案的确定,以及装置间侧线分流点系数的规划。建立了带有不确定性概率分布的调度仿真模型,在此基础上,根据流程工业生产调度的特点,应用多种群遗传算法搜索优化方案。并以某炼厂为例,结果表明此方法具有良好的鲁棒性。     

Swarm-based intelligent optimization approach for layout problem

Layout problem is a kind of NP-Complete problem. It is concerned more and more in recent years and arises in a variety of application fields such as the layout design of spacecraft modules, plant equipment, platforms of marine drilling well, shipping, vehicle and robots. The algorithms based on swarm intelligence are considered powerful tools for solving this kind of problems. While usually swarm intelligence algorithms also have several disadvantages, including premature and slow convergence. Aiming at solving engineering complex layout problems satisfactorily, a new improved swarm-based intelligent optimization algorithm is presented on the basis of parallel genetic algorithms. In proposed approach, chaos initialization and multi-subpopulation evolution strategy based on improved adaptive crossover and mutation are adopted. The proposed interpolating rank-based selection with pressure is adaptive with evolution process. That is to say, it can avoid early premature as well as benefit speeding up convergence of later period effectively. And more importantly, proposed PSO update operators based on different versions PSO are introduced into presented algorithm. It can take full advantage of the outstanding convergence characteristic of particle swarm optimization (PSO) and improve the global performance of the proposed algorithm. An example originated from layout of printed circuit boards (PCB) and plant equipment shows the feasibility and effectiveness of presented algorithm.     

Estimation of digraph costs for keyboard layout optimization

The main aim of this study was to estimate the digraph costs (interkey-stroke times) based on the digraph (two consecutive keys) tapping rates for the optimization of keyboard layouts considering the touch typing principles. The study also investigated the effects of column, row, hand and period on digraph-tapping rate. For the purpose, a laboratory experiment was performed with seven subjects using a conventional keyboard. Digraph-tapping rates of a total of 241 same hand digraphs were recorded for a duration of 2-min. The interkey-stroke times were calculated as the digraph costs for the same hand digraphs using the estimated mean digraph-tapping rates. The different hand digraph costs were calculated based on the same hand digraph costs and the results of a previous study. The results indicated significant column, row, hand and period effect on the digraph-tapping rate. Using the digraph costs and the digraph frequencies of the considered language in a quadratic assignment problem, an optimal touch typing keyboard layout can be developed to satisfy all but one of Dvorak's touch typing criteria. As an application, an optimal keyboard layout, called Turkish I-layout, is developed for Turkish language. The comparison results between I and existing Turkish F and Q layouts showed that the I-layout is superior both according to the results of the optimization and Dvorak's criteria.Relevance to industryOptimal and ergonomic keyboard layouts improve typing performance and reduce the likelihood of upper extremity disorders. The digraph-tapping rates estimated through this study are essential for the development of such layouts.     

Multi-objective layout optimization for an orbital propellant depot

Structural and Multidisciplinary Optimization - The overall layout optimization design of an orbital propellant depot involves the optimization of shape, size, and positions of propellant tanks in...     

Checkerboard patterns in layout optimization

Effective properties of arrangements of strong and weak materials in a checkerboard fashion are computed. Kinematic constraints are imposed so that the displacements are consistent with typical finite element approximations. It is shown that when four-node quatrilateral elements are involved, these constraints result in a numerically induced, artificially high stiffness. This can account for the formation of checkerboard patterns in continuous layout optimization problems of compliance minimization.     

Combinatorial optimization in facility layout

This research provides the means of a realistic or a close to realistic layout development using practical constraints and objectives. An experimental system, FLUKES, is constructed based on the method for testing purpose. FLUKES uses these factors not only for the evaluation of layout, but also for the search to solution. This system develops optimized layouts within the boundary of the practical factors.     

Simulation-based optimization of process control policies for inventory management in supply chains

A simulation-based optimization framework involving simultaneous perturbation stochastic approximation (SPSA) is presented as a means for optimally specifying parameters of internal model control (IMC) and model predictive control (MPC)-based decision policies for inventory management in supply chains under conditions involving supply and demand uncertainty. The effective use of the SPSA technique serves to enhance the performance and functionality of this class of decision algorithms and is illustrated with case studies involving the simultaneous optimization of controller tuning parameters and safety stock levels for supply chain networks inspired from semiconductor manufacturing. The results of the case studies demonstrate that safety stock levels can be significantly reduced and financial benefits achieved while maintaining satisfactory operating performance in the supply chain.     

Smoothness preserving layout for dynamic labels by hybrid optimization

Computational Visual Media - Stable label movement and smooth label trajectory are critical for effective information understanding. Sudden label changes cannot be avoided by whatever forced...     

Truss layout optimization within a continuum

The present work extends truss layout optimization by considering the case when it is embedded in a continuum. Structural models often combine discrete and continuum members and current requirements for efficiency and extreme structures push research in the field of optimization. Examples of varied complexity and dimensional space are analyzed and compared, highlighting the advantages of the proposed method. The goal of this work is to provide a simple formulation for the discrete component of the structure, more specifically the truss, to be optimized in presence of a continuum.     

Designing parallel assembly lines

In this paper, alternative assembly line design strategies for a single product are discussed. The problem occurs when the production volume is substantially high and there are more operators needed than the number of assembly operations. The objective is to determine the number of assembly lines with minimum total manpower. It is allowed to have multiple assembly lines with identical configuration. A 3-phase methodology is proposed; 1) assembly line balancing, 2) determining parallel stations, 3) determining parallel lines. Later, the proposed procedure is illustrated with a numerical example.     

Two-arm kinematic posture optimization for fixtureless assembly

This article focuses on finding optimal kinematic postures for two robot arms performing various assembly tasks without the aid of jigs and fixtures. The goal of the work is to identify the manipulator postures that would result in some optimum kinematic conditions for initiating a typical male-female assembly. Specifically, the article addresses issues related to the following question: In the absence of preset jigs and fixtures, where are the optimum location in the 3-dimensional work space and the optimum orientations of the assembly parts (therefore, the postures of the manipulators holding the parts) to perform a fixtureless assembly? First, using velocity and force ellipsoids a performance criterion is developed for the optimal kinematic posture based on constraints that are imposed by the kinematic coupling of the two robot arms as well as the environment. Next, an algorithm based on a null-space search technique is formulated to “search” for the posture of the two-arm system that maximizes the performance criterion within the set of postures that satisfy given constraints. Finally, the algorithm is demonstrated numerically for two planar robots performing typical fixtureless assembly operations. © 1995 John Wiley & Sons, Inc.     

Tool maintenance optimization for multi-station machining systems with economic consideration of quality loss and obsolescence

Tools used in a machining process are vulnerable to frequent wear-outs and failures during their useful life. Maintenance is thus considered essential under such conditions. Additionally, it is widely recognized that the maintenance of manufacturing equipments and the quality of manufactured product are highly interrelated. However, few detailed study has been found in the literature dealing with the effects of maintenance policies on the operational performance of such a system, especially the long-term average cost. The need for a method to determine the optimal tool maintenance policy has become increasingly important. Since the multiple tools in a multi-station machining system generally have significant interactive impacts on the product quality loss, the optimal multi-component maintenance models for several policies are investigated to address the interdependence among these tools. Three distinctive multi-component maintenance policies, i.e., age replacement, block replacement, and block replacement with minimal repair, are identified and analyzed. The proposed approach focuses on these maintenance policies with consideration of both component catastrophic failures, and the interdependence of component degradations on the product quality loss as well as the obsolescence cost. The effects of various maintenance policies on the system performance are simulated, and they are used to determine the best policy for a given system. An illustrative example is used to demonstrate effectiveness and applicability of the proposed approach. The results presented a comparative analysis of specified maintenance policies with respect to the total maintenance cost with consideration of the product quality loss and the obsolescence cost.     

An evolutionary approach for layout optimization of a three-dimensional truss

Layout optimization is defined as the simultaneous optimization of three aspects, i.e. topology, size and geometry. In this paper, a new approach based on evolutionary genetic search is employed to find the optimal design. The proposed approach departs from standard Genetic Algorithms (GA) in that it does not use binary strings in the representation of the possible solutions. The approach is applied to a 2-D benchmark example and a well-known space truss example. This 25-bar-truss is solved by using the proposed approach, with good results. The effect of removing the restriction of area grouping and the free location of joints and supports in the 25-bar truss are also investigated, with and without symmetry. Major drawbacks in finding the optimal solution by using the ground structure approach are overcome in the proposed method.