A Petri net-based heuristic for simple assembly line balancing problem of type 2

In this paper, a Petri net-based heuristic is presented to solve simple assembly line balancing problem type-II (SALBP-2). Petri net is a mathematical and graphical tool to model and analyze for discrete event systems. SALBP-2 minimizes cycle time for given number of workstations. The presented heuristic determines available tasks and assign task to current workstation by using reachability analysis, one of the main properties of Petri nets, and token movement. Solution of SALBP-2 is implemented by iteratively solving the problem for several trial cycle time. If the cycle time is infeasible for given number of workstations, the heuristic increases the cycle time by a value until finding a feasible solution. To improve the solution, a binary search procedure is implemented between the first feasible solution and the last infeasible solution. Three versions of the heuristic are developed by integrating with forward, backward, and bidirectional procedures. All of them are coded in MATLAB, and their efficiencies are tested on benchmark datasets with 302 instances. Also a comparison study is made with a direct procedure and five heuristics based on differential evolution algorithm. Test and comparison results show that the proposed heuristic obtains good results for SALBP-2. Its performance is superior especially in large assembly lines.     

Assessing the structural complexity of manufacturing systems configurations

Modern manufacturing systems are increasingly required to be flexible and adaptable to changing market demands, which adds to their structural and operational complexity. One of the major challenges at the early design stages is to select a manufacturing system configuration that both satisfies the production functional requirements and is easy to operate and manage. A new metric for assessing the structural complexity of manufacturing system configurations is presented in this paper. The proposed complexity metric incorporates the quantity of information using an entropy approach. It accounts for the complexity inherent in the various modules in the manufacturing system through the use of an index derived from a newly developed manufacturing systems classification code. The code captures the effect of various component types and technologies used in a manufacturing system on the system’s structural complexity. The presented metric would be helpful in selecting the least complex manufacturing system configuration that meets the requirements. An engine cylinder head production system is used to illustrate the application of the proposed methodology in comparing feasible but different manufacturing system configurations capable of producing the cylinder head based on their structurally inherent complexity.     

单臂自动抓料装置的工控组态设计

自动抓料装置用于注塑机器上自动抓取塑料成品或浇口料柄,根据不同塑件的开、出模情况,模具结构及工作现场状况,由PLC控制其工作过程。利用工控组态软件,进行自动抓料装置的工控组态设计,实现了自动抓料装置工作过程的实时动态监控。     

面向绿色制造模式调度的Petri网模型及优化算法

针对绿色制造模式的作业车间调度中,不但要缩短生产周期和降低生产成本,而且要减少资源消耗和对环境的负面影响这一问题,建立包含加工时间、生产成本、资源消耗和环境影响等信息的Petri网模型。通过为机器分配工序来消解因机器库所共享引起的冲突,得到表示调度方案的标识图。提出生成可行调度标识图的三种方 法,并采用多目标遗传算法和多目标模拟退火算法相结合的混合算法对其优化。仿真结果表明算法的可行性和有效性。     

Integrated knowledge-based assembly sequence planning

This paper presents a novel approach and system for the automatic generation, selection and evaluation, optimisation, and simulation of assembly plans. The information and knowledge about a product and its assembly (e.g. assembly constraints, solid model and CAD database, heuristic rules) are described using a hybrid approach and model with numeric and symbolic representation. A new methodology is presented to generate all feasible assembly sequences of the product by reasoning and decomposing the feasible subassemblies, and representing them by the assembly Petri net modelling. Qualitative strategic constraints are then used to evaluate the feasible assembly sequences. In order to obtain a good assembly sequence, some quantitative criteria such as assembly time and cost, workstation number, operator number, and part priority index are applied to select the optimal assembly sequence. Based on DFA analysis, MTM time analysis, and assemblability analysis, estimates are made of the assembly time and cost of the product when each of these sequences is used. A knowledge-based system KAPSS has been developed to achieve the integration of generation, selection evaluation, and visualisation of the assembly sequences.     

特种电极零件曲面的CAD/CAM

简述了对某在研设备中一个关键电极零件的CAD/CAM进行了探讨,即由离散点云构建曲面模型;曲面的加工工艺,包括装夹工艺、走刀路径设计、加工精度控制等.实践表明,此方法和措施切实可行.     

Automated fixture configuration using projective geometry approach

The geometric and topological specification of a workpiece boundary is usually represented in a specific data format in a CAD database. To retrieve a set of workpiece data, to analyse its shape in addition to the machining requirements, and to determine the proper fixture configuration accordingly, are not trivial tasks when a part has a complicated shape. The real challenge is to recognise and synthesise the shape of a workpiece from its data representation. Consequently, the decision for fixturing can be made when the shape of a workpiece and the relationship of the shape and the fixturing configuration can be derived by a systematic methodology. In this paper, a projective spatial occupancy enumeration (PSOE) approach is applied as a representational and manipulating scheme for developing algorithms in automatic fixture configuration. The workpiece is projected onto the working plane of the fixture baseplate. A 2D projection is defined as a matrix of cells which can represent a workpiece with an arbitrary shape. Using a discrete search based upon the matrix of cells, the fixture types and their locations are generated according to a set of heuristic algorithms. This work is a generalisation and extension of previous works for prismatic parts. The same methodology is equally applicable in general robot grasping.     

A rule-based frame system for concurrent assembly machines

The aim of this research is to develop a rule-based frame system for printed circuit board (PCB) assembly to generate the component feeder arrangement and placement sequence for concurrent chip placement machines. A knowledge base of frames, assertions and rules are used in the methodology to solve the PCB assembly process of SMT components. The system has been implemented using an AI programming environment, GOLDWORKS^®. A heuristic approach is used to minimize placement cycle time in PCB assembly. The objective of the solution method is to reduce theX-Y table displacement, movement and component feeder translation movement. Such a system is aimed at obtaining good solutions to the problem as illustrated by an example.     

双臂机器人抓持工件的力分解

针对双臂机器人抓持工件的协调运动 ,研究了抓持力的分解 ,基于最小范数和最小关节广义驱动力得到了力分解的两种方案 ,算例的仿真计算验证了方案的可行性。     

基于粗糙集的零件合并专家知识获取方法

以装拆时间、装拆难度、材料成本、制造成本、再设计和后处理成本,以及产品质量等的变化程度作为零件是否合并的条件属性,零件是否合并作为决策属性,应用粗糙集理论分析设计过程中的专家经验和知识.在经典粗集理论的基础上,以属性重要度作为启发式信息来计算属性核和属性约简,并以此挖掘隐含在经验数据中的专家知识,形成零件是否可以合并的决策规则.最后,以小型塑封机再优化设计为例,验证了该方法的实用性和有效性.     

No-wait flowshop scheduling problem to minimize the number of tardy jobs

This research addresses the m-machine no-wait flowshop scheduling problem with the objective of minimizing the number of tardy jobs. The problem is known to be NP-hard even for the two machines, and literature reveals that no heuristics have been developed for this problem. In this paper, we propose an efficient heuristic based on simulated annealing, where we first adapt the single-machine optimal algorithm to our problem to develop two new heuristics, NOTA and NOTM. An improved simulated annealing heuristic, called SA-GI, is then developed by feeding the best performing heuristic among NOTA, NOTM, and EDD into the simulated annealing algorithm. A second proposed heuristic, called SA-IP, further improves the SA-GI solution by using insertion and pair-wise exchange techniques. Based on the computational experiments, the overall relative percentage errors of the heuristic SA, SA-GI, and SA-IP are 8.848, 8.428, and 0.207, respectively. The computational times of the three heuristics are close to each other, and the largest average time is less than one second, and hence, the computational time is not an issue. Therefore, the heuristic SA-IP is the best one.     

Set-up reduction in PCB automated assembly

An heuristic approach to reduce set-up time in printed circuit board assembly is given. A single insertion/ placement machine is considered, and set-up time is taken as directly proportional to the number of component replacements. The problem is formulated as an IP model, for which a heuristic method is developed. The method includes two algorithms: sequence and mix. The algorithms are implemented in LISP, and an extensive series of experiments is performed and their results are presented.     

Machinability and set-up orientation for five-axis numerically controlled machining of free surfaces

In this paper, we investigate the problems of determining machinability and part set-up orientation for a given surface model. We first develop kinematic models of the five-axis machines, based on the axis configuration, then develop algorithms for determining the feasibility of one-set-up machining (machinability) and the part orientation for types C-A and A-B tool configurations. Machinability is determined by a computationally efficient procedure for finding the intersection of the feasible tool motion on the sphere and a visibility map which we call the binary spherical map (BSM). The part set-up is so chosen as to give the smallest rotational range among all feasible configurations. The algorithms developed have been tested via numerical simulations. The results show that they can be readily implemented in a CAD/CAM system, as an automated process planner selecting the efficient machine type and part set-up for NC machining.     

基于任务适应性的多指手抓取规划

针对多指手抓取过程中手指与物体构成的执行系统，通过在任务空间引入力椭球和速度椭球的概念，构建了反映抓取映射传递特性的力传动比和速度传动比解析公式。在综合考虑传动比和抓取构型偏离奇异位置等要求的基础上，提出了反映抓取构型任务适应性的抓取评价指标，用于对抓取构型进行最优规划。结合实例说明了上述评价指标应用于多指手最优抓取规划的有效性。     

Multi-objective optimization for optimum tolerance synthesis with process and machine selection using a genetic algorithm

This paper presents a new approach to the tolerance synthesis of the component parts of assemblies by simultaneously optimizing three manufacturing parameters: manufacturing cost, including tolerance cost and quality loss cost; machining time; and machine overhead/idle time cost. A methodology has been developed using the genetic algorithm technique to solve this multi-objective optimization problem. The effectiveness of the proposed methodology has been demonstrated by solving a wheel mounting assembly problem consisting of five components, two subassemblies, two critical dimensions, two functional tolerances, and eight operations. Significant cost saving can be achieved by employing this methodology.     

Grasping force controller for parallel grip with fuzzy rules emulated networks

A grasping force regulation for industrial parallel grips is developed without any requirement of mathematic model regarding to the contact mechanism and system dynamic. The physical system including the grasping dynamic and contact mechanism is considered as a class of unknown nonlinear discrete-time systems. An adaptive network called multi-input fuzzy rules emulated network (MiFREN) is implemented as the controller. This control scheme is performed by if-then rules which can be directly defined by human knowledge regarding to the gripper’s specification and objects. The learning algorithm based on gradient search is developed to tune all adjustable parameters inside MiFREN. The system performance and stability can be guaranteed by the time-varying learning rate. An industrial parallel grip SCHUNK-WSG 50 with the proposed controller demonstrates the performance via the experimental setup. Furthermore, the performance can be spontaneously improved within the next iteration of the learning process.     

Multilevel Lot Sizing with a Genetic Algorithm Under Fixed and Rolling Horizons

This paper proposes a genetic algorithm (GA) as a heuristic for multilevel lot sizing, combined with the Bit Mod heuristic developed in this context, and invoking adaptive probabilities for crossover and mutation. The influence of various parameters under fixed and rolling horizons is detailed. Design of experiments methodology is used in this connection. In the rolling horizon, the behaviour of the GA and other rules are compared with and without freezing the plan. The performance of the GA is compared with the cost-modified Wagner Whitin algorithm and cost-modified silver meal methods. The superiority of the proposed method is discussed, and case studies are given.This revised version with a corrected online cover date was published online in April 2004.     

A new methodology for predicting crack initiation life for rolling contact fatigue based on dislocation and crack propagation

A new methodology for predicting crack initiation life is presented and validated experimentally. The methodology considers that the total fatigue life is the summation of crack initiation life and crack propagation life, since fatigue failures are due to crack initiation and crack propagation. It has been established that the crack propagation life can be estimated based on a modified Paris’ law when the size of crack is larger than a certain value. However, there has been no verified method for estimating the crack initiation life with good accuracy. The proposed methodology for predicting the crack initiation life is based on a dislocation model, and the constants for the model are determined by the crack initiation lives obtained by a new approach. This new approach determines the crack initiation life by subtracting the predicted crack propagation life from the experimentally obtained total fatigue life. The developed crack initiation life model is combined with a crack propagation life model for the prediction of fatigue life. It is noted that the standard deviation in the ratios of experimental life to predicted life by the developed fatigue life model is only 14% of that by the International Standard.     

A heuristic threshold policy for fault detection and diagnosis in multivariate statistical quality control environments

In this paper, a heuristic threshold policy is developed to detect and classify the states of a multivariate quality control system. In this approach, a probability measure called belief is first assigned to the quality characteristics and then the posterior belief of out-of-control characteristics is updated by taking new observations and using a Bayesian rule. If the posterior belief is more than a decision threshold, called minimum acceptable belief determined using a heuristic threshold policy, then the corresponding quality characteristic is classified out-of-control. Besides using a different approach, the main difference between the current research and previous works is that the current work develops a novel heuristic threshold policy, in which in order to save sampling cost and time or when these factors are constrained, the number of the data gathering stages is assumed limited. A numerical example along with some simulation experiments is given at the end to demonstrate the application of the proposed methodology and to evaluate its performances in different scenarios of mean shifts.     

冗余度柔性机器人协调操作刚性负载的动力学模型及仿真

冗余度柔性机器人协调操作系统集合了冗余度机器人、柔性机器人和协调操作机器人的优点 ,具有广泛的应用前景。本文研究了冗余度柔性机器人协调操作动力学 ,给出了两 4R冗余度柔性机器人协调操作一刚性负载的动力学模型 ,并进行了仿真分析。仿真结果表明 ,该模型是可行的。