Calculating production rate of a flexible manufacturing module

This paper presents a closed form equation for calculating production rate of a flexible manufacturing module (FMM) which operates under stochastic conditions, including random machining times, random part loading and unloading times, and random pallet transfer times. Random operational conditions may arise due to the randomness in the variety of parts introduced into the system. The FMM consists of two machines, one pallet handling system, and a loading/unloading robot. The model and the resulting closed form equations allow the FMM designers and operation engineers select the most appropriate parameters for the maximum production output rate.     

Part spectrum based methodology for cell sizing in flexible manufacturing systems

This paper describes a part spectrum based methodology which enables the determination of an optimum size for flexible manufacturing cells. The methodology incorporates a systems approach in that it enables the sizing of cells to achieve specified manufacturing objectives while maintaining a realistic level of flexibility and an acceptable level in terms of complexity of control.The proposed methodology for cell sizing is based on two component characteristics: processing time and number of operations. Furthermore, it is generalised in its implementation in that the effects of case specific factors such as processing sequence of components and location of machines in relation to each other are negated.The validation of the proposed methodology for cell sizing using data obtained from manufacturing companies implementing flexible manufacturing systems is also described.     

基于虚拟仪器的双轴柔性辊弯成型机控制系统设计

在介绍变截面辊弯成型原理的基础上,描述了双轴变截面辊弯成型机结构,阐述了基于虚拟仪器思想的成型机控制系统构成,给出了实现变截面成型的软件设计思想,最后通过成型实验分析了成型轨迹控制精度.     

双臂机器人无碰撞运动规划

针对双臂机器人任务操作中的非结构化环境特点 ,本文对双臂机器人无碰撞运动规划问题作了深入的研究 ,将 C空间法成功地应用于双臂机器人的无碰撞运动规划 ,通过建立时变 C空间 ,提出了从臂无碰撞状态数据库(CSDB)概念。在本算法中 ,双臂机器人无碰撞运动路径可以通过对从臂无碰撞状态数据库的搜索获得 ,运用该算法可以在时变 C空间中得到一条最优的无碰撞运动路径 ,本算法已经在双臂 SCARATES型机器人上通过试验论证 ,证明算法可行 ,效率较高     

多托盘柔性加工中心单元的托盘交换技术

设计了一种链式输送交换机构。此机构特点:结构简单、便于扩展工位、节约空间。     

Crops: Implementation of a knowledge-based system to plan and monitor the production of a flexible line

CROPS (Coherent Rules for On-line Production Scheduling) is a general system aimed to plan and to control a flexible manufacturing system. The CROPS system receives production orders on a time-scale of one or two weeks from a medium-range planning (MRP) system. The planning and scheduling of those orders are made using a hierarchical temporal network that allows the easy use of rules which represent expert knowledge and common-sense reasoning. Furthermore, the hierarchical temporal network is flexible enough to take into account unavoidable perturbations occurring during plan execution without the need to replan all operations every time a perturbation occurs. Once the operations are planned, the control system transforms them into orders that are sent to the workshop (or to a simulator). With the help of rules, the control system monitors and diagnoses the execution of the orders using a model that maintains a continuous image of the workshop.     

一种用于柔性单元的双摆杆上下料机构

在开发设计柔性加工中心单元的过程中,为了能更好地实现多托盘柔性加工中心单元的上下料,设计了一种双摆杆上下料机构.此机构特点是结构简单、节约空间及易于生产等.     

A methodology for investigating effects of cell size on operational flexibility in flexible manufacturing systems

There are two aspects to cell formation in flexible manufacturing systems, cell sizing or deciding on the optimum number of machines to be allocated to each cell, and then allocation of specific machines to each cell. Although the latter problem has been investigated extensively there is a paucity of published work on the former. This paper discusses the effects of cell sizing on operational flexibility.Operational flexibility is that aspect of flexibility that enables manufacturing systems to respond with speed and efficiency to changes in the manufacturing environment while maintaining an effective level of control.     

A multiobjective genetic algorithm for scheduling a flexible manufacturing system

Though the designers of Flexible Manufacturing Systems (FMS) strive to ensure the maximum flexibility in the system, in practice, after the implementation of such systems the operational executives often find it hard to accommodate frequent variations in the part designs of incoming jobs. This difficulty can very well be overcome by scheduling the variety of incoming parts into the system efficiently. In this work an appropriate scheduling mechanism is designed to generate a nearer-to-optimum schedule using Genetic Algorithm (GA) with two different GA Coding Schemes. Two contradictory objectives of the system were achieved simultaneously by the scheduling mechanism. The results are compared with those obtained by different scheduling rules and conclusions are presented.     

An activity-based predicate/transition net model of operational control planning for a flexible manufacturing system

An effective flexible manufacturing system (FMS) relies on a hierarchy of decisions, including the control of the FMS operation. The FMS operation usually is dynamically constrained by the limited resources such as pallets, machines, tools, carts, etc. Most analytical models make many assumptions and oversimplify the complicated decision problems. This study proposes the predicate/transition (Pr/Tr) net, a high level petri net, as a model for operational control planning. Firstly, the activities (modes) and their resources usage in FMS were analysed and aggregated into activity sets. Then, the flow of parts among activities was traced to obtain the mode transition diagram, and then the Pr/Tr net model was introduced. We incrementally defined the predicates and transitions into this model. Finally, a comprehensive FMS Pr/Tr net model was derived. By implementing it into a rule-based simulation model, it is well suited for FMS operational control planning because of its inclusiveness and high flexibility.     

The control of a flexible manufacturing system by short-term goal identification

The control of manufacturing systems is characterised by the need to make a compromise between conflicting goals. Traditional research concentrates on steady-state optimisation of single objectives that are not necessarily relevant to decision making in a production environment. The advent of flexible manufacturing systems (FMSs) with automated material handling and limited buffer space highlights the need to provide computationally-efficient solutions to work out scheduling and dispatch problems for real-time applications. The authors have adopted a knowledge-based approach to achieve effective real-time FMS control. In the context of the current system status and planned system activities, short-term goals are identified which lead to appropriate jobdispatch decisions. This approach has been implemented in a prototype control system written in Prolog. To obtain knowledge in this area of scarce expertise, a “define-build-learn” cycle was adopted. First, functional concepts are defined and built into the control system, then the corresponding system characteristics are studied and the results used for further cycles of concept definition and building. This paper describes the development of this operational system.     

Developing a computer control system for a flexible manufacturing cell

This article focuses on the development of a computer control system for a flexible manufacturing cell. The paper outlines the various modules that are required for a computer control system and elaborates on the development of some of these modules. This is part of an ongoing research project at the University of the Witwatersrand. The aim of the project is to demonstrate the viability of flexible manufacturing systems to South African industry. Thus the main constraints of the project were cost, ease of implementation, and ease of maintainability. This necessitated the use of existing machinery and of computer systems and software that were readily available and already familiar to industry.     

Impact of operation flexibility and dispatching rules on the performance of a flexible manufacturing system

Operation flexibility is one of the eight common types of flexibility that exist in flexible manufacturing systems. Dispatching rules are commonly used in loading the machines. This paper studies the effects of different levels of operation flexibility and various dispatching rules on the performance of a flexible manufacturing system. The system performance considered is mean flow time. Simulation results indicate that the mean flow time cannot be always improved by increasing the level of operation flexibility. Altering the dispatching rules seems to have a more significant effect on the mean flow time performance than changing the level of operation flexibility.     

Modeling and analysis for a kind of flexible manufacturing system involving time factors

Time control and management are important in flexible manufacturing systems (FMS). The time to finish the machining unit is uncertain because of the uncertainties of the workpieces, so the whole time to finish the FMS is also variable. In order to reduce the time to finish for the whole FMS to improve efficiency, the modeling and analysis method for this timing kind of FMS based on standard Petri net is proposed. The modeling method is a mapping from the machining units to the component of a Petri net, and the timing factors are represented by a timing function on the place set. With the Petri net model obtained and its reachability graph, the timing factors influencing the implementation of the FMS are analysed and presented. In addition, the method is obtained to find the best state line for the implementation of the FMS.     

Virtual integration with a multi-criteria partner selection model for the multi-echelon manufacturing system

Virtual integration (VI) offers a way to make manufacturing systems more agile and competitive. VI integrates the production resources of many manufacturing systems (partners) efficiently, and that leads to a rapid response to market changes. Based on the VI concept these partners throughout the world will form a virtual enterprise (VE). Thus to select partners is the essential and the most important issue. The main objective of this paper is to develop a partner selection and production-distribution planning with the novel partner selection model, based on the analytic hierarchy process (AHP) methodology, multi-attribute utility theory (MAUT) and integer programming (IP), for the VI with multiple criteria. The AHP and MAUT methods are use to assess and set weights for each partner candidate and the IP model applies these weights to find the optimal partners from the potential ones and provide the suitable production-distribution plan to the elective partners. Finally, a case study has been provided to substantiate a feasible quality solution of the proposed model.     

Modeling the control of a flexible manufacturing cell for automatic verification and control program generation

Shortened product life-cycles decrease the output rate of manufacturing systems. Offline verification of the control systems promises to increase the output. However, to make offline verification possible some major improvements of the current development process of manufacturing systems are needed. Information handling and development of control programs based on information reuse are two of the most important improvement areas. This paper presents the results of the modeling of a real manufacturing cell according to a previously presented method for offline verification and program generation based on information reuse.     

Part input into a flexible flow system: An evaluation of look-ahead simulation and a fuzzy rule base

This article reports an investigation into part-input methods for an implemented flexible flow system (FFS). Two new dynamic methods—look-ahead simulation and a fuzzy heuristic rule base—are compared to three simple myopic static sequencing rules and one dynamic rule. It is shown using simulation that for the existing system, the best sequence generated from the minimum production set performs very well, but the dynamic methods outperform the sequence when the system is modified and the sequence is unaltered. It is concluded that for a stable FFS, the static determination of the best input sequence is appropriate, but that a rapidly changing FFS—due to machine breakdown, changes in production requirements, etc.—may benefit from a dynamic part-input method. The look-ahead simulation outperforms the fuzzy rule base, and appears to be a more promising dynamic method. Suggestions for future research and evaluation are given.     

Generation and Simulation of Robot Trajectories in a Virtual CAD-Based Off-Line Programming Environment

This paper presents a new approach to the generation and optimisation of the position and orientation trajectories in Cartesian task space, and simulation in a virtual CAD-based off-line programming environment. A novel concept of the robot pose ruled surface is proposed, and defined as a motion locus of the robot orientation vector, i.e. the vector of equivalent angular displacement. The planning for trajectories of robot end-effectors can be accomplished by generating the robot pose ruled surface and optimising its area under the constraints with good kinematics and dynamics performances. The established optimisation model is based on functional analysis and dynamics planning, and is simplified by using high-order polynomial space curves as the robotic position and orientation trajectories. The developed system, RoboSim, is a virtual integrated environment which can be used as a testbed for automatic motion planning and simulation for robots. Two examples are given to verify the feasibility of the proposed approach and models, and to demonstrate the capabilities of generation, optimisation, and simulation modules and libraries in the RoboSim package. The simulation results show that the approach and system are feasible and useful for motion planning, performance analysis and evaluation, and CAD-based prototyping and off-line programming in both the virtual and the real design and planning environment.