A genetic algorithm based approach to optimal fixture configuration

In this paper the application of genetic algorithms (GAs) to the fixture configuration optimisation problem is presented. A general purpose fixturing verification system has been developed to check the validity of individual fixture configurations by analysing various contact types in the workpiece-fixture system. Based on the information provided by the verification system, a genetic algorithm based approach carries out the evaluation process to determine the most statically stable fixture configuration among a large number of candidates. The preliminary implementation is introduced to demonstrate the ability of GAs and two different coding schemes are tested to explain their influence on the performance of GAs.     

A review and analysis of current computer-aided fixture design approaches

A key characteristic of the modern market place is the consumer demand for variety. To respond effectively to this demand, manufacturers need to ensure that their manufacturing practices are sufficiently flexible to allow them to achieve rapid product development. Fixturing, which involves using fixtures to secure workpieces during machining so that they can be transformed into parts that meet required design specifications, is a significant contributing factor towards achieving manufacturing flexibility. To enable flexible fixturing, considerable levels of research effort have been devoted to supporting the process of fixture design through the development of computer-aided fixture design (CAFD) tools and approaches. This paper contains a review of these research efforts. Over seventy-five CAFD tools and approaches are reviewed in terms of the fixture design phases they support and the underlying technology upon which they are based. The primary conclusion of the review is that while significant advances have been made in supporting fixture design, there are primarily two research issues that require further effort. The first of these is that current CAFD research is segmented in nature and there remains a need to provide more cohesive fixture design support. Secondly, a greater focus is required on supporting the detailed design of a fixture's physical structure.     

Development of an Internet-enabled interactive fixture design system

Fixture design is a complex and an intuitive process. An efficient fixture design system is essential to cut costs and reduce the product lead-time. In today's manufacturing landscape, various computer-aided systems exist to aid the various stages of manufacturing. A fixture design system should be able to transfer information with the various other systems to bring about a seamless product design and manufacturing environment. A fixture design system should also be portable on different operating platforms. This paper addresses the development of an Internet-enabled interactive fixture design system. The Internet and the use of XML as a file format provide a means for the transfer of information and knowledge between the various computer-aided manufacturing systems. The system has been implemented using Java and is based on a three-tier Thin Client-Fat Server architecture. This ensures the platform independent performance of the system. A locating scheme independent interactive fixture design method has also been developed in this work for detailed fixture design.     

Finite element formulation for dynamics of planar flexible multi-beam system

In some previous geometric nonlinear finite element formulations, due to the use of axial displacement, the contribution of all the elements lying between the reference node of zero axial displacement and the element to the foreshortening effect should be taken into account. In this paper, a finite element formulation is proposed based on geometric nonlinear elastic theory and finite element technique. The coupling deformation terms of an arbitrary point only relate to the nodal coordinates of the element at which the point is located. Based on Hamilton principle, dynamic equations of elastic beams undergoing large overall motions are derived. To investigate the effect of coupling deformation terms on system dynamic characters and reduce the dynamic equations, a complete dynamic model and three reduced models of hub-beam are prospected. When the Cartesian deformation coordinates are adopted, the results indicate that the terms related to the coupling deformation in the inertia forces of dynamic equations have small effect on system dynamic behavior and may be neglected, whereas the terms related to coupling deformation in the elastic forces are important for system dynamic behavior and should be considered in dynamic equation. Numerical examples of the rotating beam and flexible beam system are carried out to demonstrate the accuracy and validity of this dynamic model. Furthermore, it is shown that a small number of finite elements are needed to obtain a stable solution using the present coupling finite element formulation.     

A feature-based fixture design methodology for the manufacturing of aircraft structural parts

In fixture design for the manufacturing of aircraft structural parts, there are various challenges and serious problems in industry, such as difficulty in design knowledge capture and reuse, and the arbitrary or non-standard nature of design, which influence the efficiency and quality of fixture design. This paper proposes a feature-based fixture design methodology in which previous fixture design cases and design rules are described in association with features and thus the design knowledge is integrated with geometric information of aircraft structural parts, which are the main concern of this project. In this methodology, machining features of the structural parts and their associated attributes are identified by feature recognition technique from the 3 dimensional (3D) part models defined based on model-based definition (MBD) technique. The feature-based part information models are then established and are used to retrieve previous fixture design cases and design rules stored in the knowledge base. Fixture designers will choose the appropriate retrieved design cases as the starting point for new fixture design or use previous designs to assess his/her current design. In this way the process of new fixture design can be improved. In the current stage of the research, a prototype feature-based fixture design system based on CATIA for the manufacturing of aircraft structural parts has been developed and used by a large airplane manufacturer.     

Design and construction of a variable-aperture gripper for flexible automated assembly

The growing market demand for a wide variety of product models and small batch production makes flexible robotized production systems an emerging need in industry. Today, in manufacturing applications, general purpose grippers are not very considered, and robot end effectors are properly designed for the specific task with a strongly limited versatility. Flexibility is thus usually obtained by using a different tool for each family of parts: a tool changing system allows the robot to rapidly replace the tool on the end effector; tools are stored in a tool magazine allocated in the workcell. However, such systems are expensive and their use can affect the working cycle-time. This paper presents the design and testing of a variable-aperture, cost-effective gripper, capable of adapting its aperture (grasp width) to different handling demands, without affecting the working-cycle time of the production system. The solution proposed consists of (1) an electrically-actuated mechanism, which allows it to satisfy flexibility requirements, by regulating the aperture in hidden time; (2) a pneumatically-actuated mechanism to achieve high performance in open/close operations. Simulations and preliminary tests showed that this type of design can be a suitable solution to increase flexibility in robotized workcells without increasing the cycle time.     

An efficient parallel algorithm for geometrically characterising drawings of a class of 3-D objects

Labelling the lines of a planar line drawing of a 3-D object in a way that reflects the geometric properties of the object is a much studied problem in computer vision, considered to be an important step towards understanding the object from its 2-D drawing. Combinatorially, the labellability problem is a Constraint Satisfaction Problem and has been shown to be NP-complete even for images of polyhedral scenes. In this paper, we examine scenes that consist of a set of objects each obtained by rotating a polygon around an arbitrary axis. The objects are allowed to arbitrarily intersect or overlay. We show that for these scenes, there is a sequential lineartime labelling algorithm. Moreover, we show that the algorithm has a fast parallel version that executes inO(log³ n) time on an Exclusive-Read-Exclusive-Write Parallel Random Access Machine withO(n ³/log³ n) processors. The algorithm not only answers the decision problem of labellability, but also produces a legal labelling, if there is one. This parallel algorithm should be contrasted with the techniques of dealing with special cases of the constraint satisfaction problem. These techniques employ an effective, but inherently sequential, relaxation procedure in order to restrict the domains of the variables.This research was partially supported by the European Community ESPRIT Basic Research Program under contracts 7141 (project ALCOM II) and 6019 (project Insight II).     

Miniaturized planar filters exhibiting flexible placement of three transmission zeros suitable for duplexer design

In this work, we show that a stub‐loaded open‐loop double resonator filter can produce three transmission zeros at finite frequencies close to the passband when designed using our proposed asymmetric feed point topology. We demonstrate that by selecting the length of the stub, the placement of double transmission zeros on either the high side of the passband or the low side of the passband can be selected. This selection can be achieved by using a single design parameter: the stub length. The flexibility in the double zero placement makes these filters particularly advantageous for duplexer designs. Two duplexers are fabricated using the proposed filter topology in a microstrip on a duroid substrate and substrate‐embedded stripline via Low‐Temperature Cofired Ceramic technology (LTCC). The measurements show steep attenuation of approximately 30 dB, close to the filters' passband as well as a compact size down to 0.075λ × 0.17λ.     

对象族拓扑约束求解的研究

针对当前对象族模型在求解拓扑约束时存在的缺陷,提出一种求解拓扑约束的新方法,这种方法在求解拓扑约束时,把拓扑约束映射为布尔约束满足问题,通过用SAT求解器求解布尔约束来求解拓扑约束。实践证明,该方法不仅直接关联与拓扑约束指定的特征的语义,而且当模型中存在大量相交的特征时也是可行的,提高了拓扑约束求解的效率。     

Parametric active membrane for segmentation of multiple objects in an image

We propose a topology adaptive active membrane that can segment images of multiple objects present in a scene. The parametric active membrane evolves in image space and splits into multiple membranes. The shape of the membrane can be constrained according to the shape of the objects present in a scene. We have shown that this active membrane model is also suitable for segmenting images of touching objects. The proposed segmentation technique unifies the membrane evolution and membrane splitting process. The methodology is tested for a number of real images from biomedical and machine vision domains that demonstrate the efficacy of the proposed scheme.     

A heuristic triangulation algorithm for multiple planar contours using an extended double branching procedure

This paper presents a heuristic triangulation algorithm for reconstructing surfaces over a set of cross-sectional contours. The multiple branching problem, an important problem of conventional triangulation methods, is reated as a set of double branchings, and an algorithm based on countour merging is developed. Several imaginary contours are generated to handle the multiple branching problem with many branch contours. A double branching algorithm based on the partitioning of the root contour is also proposed. The results show that our method works well even for objects with many complicated branches.     

平面点集Delaunay三角剖分的分治算法

为发展图形网格化技术,研究了平面点集的三角剖分算法.根据经典算法中在实际应用中遇到的共性问题,提炼了3个工具算法;为了更好地表示平面区域划分的拓扑信息,引入了双链接边表(DCEL)的数据结构.在此基础上,设计并实现了平面集Delaunay三角剖分分治算法,并对特殊退化情况进行了处理,通过计算表明了该算法时间复杂度为0(N* logN).实验数据结果验证了该算法的正确性、健壮性.     

Solving topological constraints for declarative families of objects

Parametric and feature-based CAD models can be considered to represent families of similar objects. In current modelling systems, however, the semantics of such families are unclear and ambiguous.We present the Declarative Family of Objects Model (DFOM), which enables us to adequately specify and maintain family semantics. In this model, not only geometry, but also topology is specified declaratively, by means of constraints. A family of objects is modelled by a DFOM with multiple realizations. A member of the family is modelled by adding constraints, e.g. to set dimension variables, until a single realization remains. The declarative approach guarantees that the realization of a family member is also a realization of the family.The realization of a family member is found by solving first the geometric constraints, and then the topological constraints. From the geometric solution, a cellular model is constructed. Topological constraints indirectly specify which combinations of cellular model entities are allowed in the realization. The system of topological constraints is mapped to a Boolean constraint satisfaction problem. The realization is found by solving this problem using a SAT solver.     

Intelligent fault-tolerant system of vibration control for flexible structures

This paper describes an intelligent fault-tolerant control method for vibration control of flexible structures. We consider a case where the fault phenomena of the control system for flexible structures can be treated as a change of system parameters. Therefore, the adaptive control method can be applied to a vibration control system for flexible structures with a fault. In this paper, a neural network (NN) adaptive control system is used to compensate for the change in the parameters of a plant with a fault. When the characteristics of the plant and of a nominal model have been agreed by a NN adaptive control system, the control method designed for the nominal model, such as decoupling feedback control or linearizing feedback control, can be used even if the change in the system parameters has been caused by a fault. To confirm the effectiveness of the proposed fault-tolerant control method, the simulational results from a 5-link robotic arm are shown at the end of the paper. This work was presented, in part, at the Fourth International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–22, 1999     

基于PMAC的航空结构件柔性工装分布式控制系统设计

航空结构件是航空飞行器中的重要组成部分，航空结构件的自动化柔性工装质量直接影响航空飞行器的飞行安全水平。为降低系统位置和姿态控制误差，减小航空结构件的磨损面积，设计了基于PMAC的航空结构件柔性工装分布式控制系统。采用PMAC运动控制器，接收电子部件的反馈信号，控制步进电机、直流电机和交流电机。结合工控机、定位器、伺服电机和分布式通信网络，完成硬件系统的设计。根据航空结构件柔性工装操作设备的组成结构和工作原理，构建相应模型。确定航空结构件在目标曲面上的柔性工装位置，从移动位置和装配力两个方面，计算柔性工装控制量。在PMAC控制器的作用下，通过位姿的调整实现系统的航空结构件柔性工装分布式控制功能。系统测试结果表明，设计分布式控制系统的位置和姿态控制误差分别降低了13cm和0.32°，且设计系统控制下航空结构件的磨损面积较小。     

面向并行工程的组合夹具辅助设计系统设计与开发

提出了一种基于Web的计算机辅助夹具设计系统原型,并采用基于UML的ICONIX开发过程实现,通过用例图、对象类图、Robustness图和顺序图明确了系统对象类的功能、关联以及协同关系．     

A modular flexible scalable and reconfigurable system for manufacturing of Microsystems based on additive manufacturing and e-printing

Digital manufacturing technologies [1] are gaining more and more importance as key enabling technologies in future manufacturing, especially when a flexible scalable manufacturing of small medium series of customized parts is required. The paper describes a new approach for design manufacturing of complex three dimensional components building on a combination of digital manufacturing technologies such as laminated objects manufacturing, laser and e-printing technologies. The micro component is made up of stacks of functionalized layers of polymer films. The concept is currently developed further in the project SMARTLAM [2], [3], funded by the European Commission. The manufacturing system is based on a flexible, scalable and modular equipment and application features approach which enables the manufacturing of different small size batches without tool or mask making in short time. Different modules can be combined by defined hardware and software interfaces. Avoiding time consumable and difficult programming caused by manufacturing a new conceptual approach a Function-Block Runtime (FORTE) executes generated control application platform-independently and coordinates component module functionalities. The control system is designed to integrate all processes as well as the base platform with features far beyond ordinary PLC systems. One aspect is the use of process data out of the data acquisition system to simulate and optimize the processes. These results are incorporated into the main machine control system. Another aspect is the vision system for flexible quality control and closed-loop positioning control with visual servoing.The paper shows the overall concept of SMARTLAM and exemplarily demonstrates the control system as well as the modular equipment approach by the example of the control system for alignment of different stacks and inspection system.     

Connecto ergo sum! an exploratory study of the motivations behind the usage of connected objects

The Internet of Things seems about to revolutionize individuals' attitudinal and behavioral patterns and their habits. Increasingly, everyday objects will come with connected features and functions. In this context, it is crucial for companies to study motivations to use connected products and to understand the specific role played by user’s connectedness. On the basis of individual interviews with 43 users of various connected objects, this research explores such motivations and proposes a theoretical framework in which desirable attributes, perceived value, and psychological traits play a key role. The results are then discussed from both theoretical and managerial perspectives.