Experimental investigation of the performance of a reconfigurable fixturing system

A reconfigurable fixturing system has been developed for computer-integrated assembly environments. The fixturing system employs a number of fixture modules that are set-up, adjusted and changed automatically by the assembly robot without human intervention. A commercially available computer-aided design (CAD) package with the help of a dedicated software program is used for the design, analysis, and verification of the fixture layout. The robot program for setting-up, adjusting, and dismantling the designed fixture is generated automatically. This paper presents and discusses the accuracy of such a reconfigurable fixturing system in view of the off-line programming techniques. The experimental techniques to measure the accuracy and repeatability for setting-up the fixture are presented. The measured results of the robot positioning various types of locating fixture modules are presented and compared with the intended position settings. From the comparison, the accuracy that is to be expected from such an approach to fixturing and measures for improvement are discussed. The cycle times involved in setting-up the fixture modules are also presented and analysed. These results provide an initial guide for manufacturing industries interested in employing such systems in their computer-integrated assembly environment.     

FIX-DES: A computer-aided modular fixture configuration design system

This paper presents a computer-aided modular fixture configuration design system: FIX-DES. When fixturing requirements are specified as locating/clamping surfaces and points, a fixture configuration will be automatically generated by

1. Selecting fixture elements from a fixture element database to form fixture units based on fixture element assembly relationships.
2. Placing the fixture units and elements into position on a baseplate while the fixturing requirements and assembly relationships (e.g. hole alignments) are maintained.

The fixture element assembly relationships can be established automatically when the geometric models and fixturing functions of the fixture elements are specified so that the FIX-DES system can be applied easily to different fixture systems. The system also provides the interactive design and design modification functions for human expert involvement. The system was developed with core programs in C and C++ and interface programs in a specific CAD environment. The system has been successfully applied in industry and can be transferred easily to other CAD systems. The overall structure of the FIX-DES system is introduced in the paper. The development of the automated fixture configuration design (AFCD) functions are presented in detail. Finally a fixture configuration design example is given to illustrate the application of the system.     

基于网络的夹具设计信息模型与应用研究

根据夹具设计特点论述了集成工艺设计中夹具设计信息数据结构，应用面向对象的方法描述了夹具设计的制造工艺信息类和制造资源信息类体系结构，建立了数据结构中夹具设计的装夹工艺模型和夹具资源模型，根据建立的信息模型开发了装夹工艺信息子系统和夹具资源信息子系统，并在网络环境下得到了应用。     

Quality design of fixture planning for sheet metal assembly

Fixturing plays an important role in enhancing weld quality of the sheet metal assembly process. However, traditional experience-based fixturing schemes and purely optimal fixturing schemes are often sensitive to location fluctuation of the designed locators. In this paper a mathematical representation of deterministic locating and total fixturing for a flexible workpiece is developed first, then a virtual beam model is proposed to evaluate the degree of flexibility of the locating points. A quality design model of fixture planning for sheet metal assembly with resistance spot welding is then developed; both the performance expectation and the variance are considered in the formulation of the objective function; a prescribed factor is used to weight the two objectives. The finite element model based on ANSYS software is set up with a spot weld feature employed and genetic algorithm is used in the optimization process. A simple example and an industrial case illustrate the feasibility of the developed model. This work provides a basis for improving the quality of sheet metal assembly in the design phase.     

A Fast Interference Checking Algorithm for Automated Fixture Design Verification

Fixtures are tooling devices used to locate, support and hold workpieces during a manufacturing process. The major purpose of a computer-aided fixture design (CAFD) system is to provide a fixture design based on fixturing principles and workpiece information. Interference checking between the machining tool and fixture units, as well as between fixture units, is one of the important functions of automated fixture design. This paper presents a fast interference checking algorithm for automated modular fixture design validation. It is based on the study of the geometric characteristics of modular fixture components and the machining tool. The fixture component model is simplified into a 2D contour model with height information. The tool-path model is represented by a moving dot for 3-axis operations, or a moving line segment in 5-axis operations, as the fixture component model is different from the popular collision detection procedure using swept volume and is more efficient for fixturing verification. Application of this method will greatly reduce the computation complexity for fixturing interference checking. The method is implemented with a CAFD system. An example is given at the end of the paper.     

基于表面网格离散化与遗传算法的复杂工件装夹布局规划方法

装夹是工件加工过程中首先面临的问题,而稳定装夹则是保证工件加工质量与生产安全的必要条件。为此系统地提出了基于稳定性指标与稳定量度的工件装夹布局优化模型及其遗传算法求解技术。根据静力平衡条件与线性规划技术,提出装夹稳定性的判断依据及其解算方法,实现装夹时工件"稳不稳"的定量描述;依据力的超椭球方程,将超椭球体积定义为装夹稳定量度,用以描述工件装夹稳定时"有多稳"的问题;引入离散化思想,构建了以使装夹稳定量度达到最大为目标的复杂工件装夹布局规划模型,根据每一代的装夹稳定性,定义个体的适应度评价函数,提出装夹布局规划模型的遗传算法求解技术。提出的基于稳定性指标与稳定量度的装夹布局规划方法,由于只涉及接触点的坐标及其法矢量信息,不仅适用于具有复杂表面的工件,而且能够避免工件处于非稳定状态下优化模型的求解过程,提高了计算效率,为复杂工件装夹布局方案的合理设计提供了基础理论。     

A systematic conceptual design of modular fixtures

The replacement of dedicated fixtures by modular fixturing systems seems to be a trend in the manufacturing field, especially in meeting the desire for greater flexibility but the selection of appropriate modules from a modular fixturing system and subsequent assembly is itself not an easy task. This research provides a systematic design method to help dedicated fixture users to convert to modular fixturing system users. This method classifies modules into five functional groups and then selects proper modules from each group in accordance with the functional request of the fixture assembly. This systematic design of modular fixtures helps a dedicated fixture user to build an economical and efficient modular fixturing system.     

An experimental evaluation of the capabilities of a fluidised-bed fixturing system

A phase-change fixture is a single adaptive device which can hold parts of various shapes and sizes while they are subjected to a wide variety of manufacturing operations. In this paper, a fundamental experimental investigation of adaptable fluidised-bed phase-change fixturing systems is presented. The results of this experimental investigation, which focuses on evaluating the ability of these fixtures to resist complex combinations of axial, bending and torsional loads, have provided estimates of the fixturing capability of this class of fixtures. This work has precipitated the development of a semi-automated hydraulically-operated prototype fixturing system, which is currently being employed to fixture parts of various shapes and sizes for several diverse manufacturing tasks, including metal-cutting operations, on a horizontal-axis LeBlond-Makino MC65-A60 machining centre.     

An integrated fixture planning system for minimum tolerances

Fixture planning is an important aspect of process planning. The steps involved in automatic fixture planning are manufacturing feature recognition, setup planning and fixture configuration planning. In the present work, an integrated setup and fixture planning system is developed for minimum tolerances at critical regions using a data exchanged part model as an input. A platform-independent STEP-based automatic feature recognition system that can recognize both design and manufacturing features, including intersecting features is implemented. An automatic setup planning module is developed for generating setup plans for complete machining of a given component. A fixture planning module is developed applying the criteria of uniqueness, stability, accessibility and tolerance minimization. A case study is presented to demonstrate the capabilities and integration between the various modules of the system.     

Automated setup and fixture planning system for box-shaped parts

The topic of the research is related to the domain of computer-aided manufacturing process planning. This paper deals with the problem of setup and fixture planning for the machining of box-shaped parts on the horizontal machining centres. The setup and fixture planning involves the definition of setups, the setup sequence and conceptual design of fixtures for each setup. The central topic of this research is the automation of the conceptual design of fixtures. This topic is interconnected with the setup planning, and accordingly, the aim of the author has been the integrated handling of tasks of setup and fixture planning and the finding of solution in an integrated system. Based on the workpiece model, the developed system automatically determines the setup sequence, the content of setups and the conceptual solution of fixture for each setup. The paper presents the problems of fixture solutions and the partial tasks of workpiece holding, the typical solution of partial tasks and the conditions of their application and finally offers a new method, which makes the integrated handling of tasks of setup and fixture planning and finding solution in an integrated system possible.     

Computer-Aided Fixture Design Verification. Part 1. The Framework and Modelling

Computer-aided fixture design (CAFD) techniques have been advanced rapidly so that fixture configurations can be generated automatically, for both modular fixtures and dedicated fixtures. Computer-aided fixture design verification (CAFDV) is the technique for verifying and improving existing fixture designs. In this paper, the framework of CAFDV is introduced based on two models, i.e., geometric and kinematic models. The fixturing tolerance and stability verification will be presented in separate papers.     

The computer-aided design of modular fixturing systems

The flexibility of modular fixturing systems can be exploited to significantly enhance the productivity of computer integrated manufacturing facilities. A major impediment to the implementation of this philosophy is the absence of viable methodologies for the automated design and assembly of these fixturing systems. This paper addresses this technological void by proposing a CAD/CAM tool for the automated design and robotic assembly of modular fixturing systems which can form the basis for a fully automated design system. The development of automated flexible fixturing technologies that transcend the traditional time-consuming and expensive practice of manual assembly would significantly contribute to the evolution to the factory-of-the-future.     

基于特征的夹具设计方法研究

将特征技术引入夹具设计 ,提出基于加工特征的、面向夹具设计的工艺模型和基于装夹特征的装夹模型 ,介绍了基于实例与基于规则推理相混合的装夹模型提取方法和装夹元件的选择方法     

Fixture layout optimization for flexible aerospace parts based on self-reconfigurable swarm intelligent fixture system

Based on the development demand of a novel intelligent fixture system, a self-reconfigurable intelligent swarm fixture system is presented. This paper deals with the fixturing layout optimization of a flexible aerospace workpiece. A new fixturing principle, “N-2-1-1,” is put forward. The optimization procedure for fixture layout combined with genetic algorithm and finite element analysis is developed and verified by case study simulation.     

A literature survey of fixturedesign automation

This paper gives a review of fixture-design research, most of it done in the 1980s. The major topics of the review are the fixturing principles (supporting, locating and clamping), automated fixture design (configuration, assembly and verification), and fixture hardware design (dedicated, modular and electric/magnetic types).     

Automatic design of machining fixtures: Conceptual design

Fixtures are used in many manufacturing operations. Owing to the great variety of parts and manufacturing operations, parts may have different sets of fixturing requirements and call for different design strategies. Although there are numerous possibilities for fixture designs, a few basic configurations are clearly identifiable. Based on the belief that it would be more promising to develop one design strategy for each type of fixture than to attempt to develop a general strategy for all types of fixtures, a three-stage design process has been proposed for automatic design of fixtures: conceptual, configuration, and detail design. This paper focuses on the conceptual design stage. A methodology is presented by which the part shape, part features, and cutting force field are analysed to generate conceptual designs of fixtures.     

基于线性不等式方程组解的存在性及其通解的工件可达/可离性分析算法

工件的可达/可离性反映了将工件安装到/脱离出夹具装夹布局的可能性,分析可达/可离性有助于在工件上正确选择装夹表面和装夹点。为此依据工件与装夹元件的实际接触或装配情况,利用泰勒定理提出了工件可达/可离性模型。通过将工件安装到/脱离出装夹布局的可能性等价于可达/可离性模型的解的存在性,借助任意数可表达为两个非负数之差这一数学技巧作为桥梁,将工件可达/可离性模型的解的存在性问题转化为线性规划问题,提出了工件可达/可离性的判断方法。尤其是在判断可达/可离性模型有解的情况下,继而考虑了工件安装到/脱离出装夹布局的方向性。在此基础上,进一步将可达/可离的方向性转化为可达/可离性模型的通解,由此构建了求解线性不等式方程组的Γ-算法。这个“先有解-再求解”的算法仅涉及到装夹元件在工件表面处的位置与单位法矢量信息,不仅适用于形状复杂的工件,而且避免了可达/可离性模型无解情况下依旧求解的局限性,同时也拓展和丰富了自动化夹具设计的理论基础。     

Computer-Aided Fixture Design Verification. Part 3. Stability Analysis

In fixture design, a workpiece is required to remain stable throughout the fixturing and machining processes in order to achieve safety and machining accuracy. This requirement is verified by a function of the computer-aided fixture design verification (CAFDV) system. This paper presents the methodologies of fixturing stability analysis in CAFDV. A kinetic fixture model is created to formulate the stability problem, and a fixture stiffness matrix (FSM) is derived to solve the problem. This approach not only verifies fixturing stability, but also finds the minimum clamping forces, fixture deformation, and fixture reaction forces. The clamping sequence can also be verified with this approach.     

表面形状为自由曲面零件的装夹设计研究

表面形状为自由曲面零件的夹具设计是机械制造领域中的一个难点问题。但是,该类夹具的设计尚未引起广大夹具设计人员的充分注意,成功的设计范例也为数不多,这一现实已不能满足日益增长的自由曲面零件加工制造的要求。本文结合８６３／ＣＩＭＳ关键技术攻关项目“面向并行工程的计算机辅助夹具设计”的实践并加以扩展,重点讨论了该类夹具设计领域的零件装夹这一难点问题,并根据确定性定位理论与曲面理论给出了自由曲面零件上定位点的选取算法与夹紧点选取策略。     

A systems approach to fixture planning and design

Within the last decade, the manufacturing research community has addressed many of the micro issues of automating the fixture design process using computers. Most of this research has concentrated on the geometric and kinematic factors that determine the configuration of a computer-aided fixture design (CAFXD) system. However, before the implementation of any of the researched micro issues can be accomplished, a systematic approach to fixture planning and design must be recognised that considers the macro issues (process planning and fixture design) of the complete design to manufacturing process. In order to improve the effectiveness and implementation of researched micro issues in fixture design, a generic model of the functional activities can provide an understanding of the process and information exchanged between process planning and fixture design. This paper presents such a generic IDEF working model that promotes the functional integration of these two functions — developed from a systems perspective.