Computer-aided design of mechanisms: 1984 and beyond

This special issue on computer-aided design of mechanisms has the objective of representing the state-of-the-art in computer-assisted mechanism analysis and synthesis. The events of the past 25 years are reviewed in this article. The brief look at today and the potential future of this fast-growing area are meant to set the stage for this special issue of Mechanism and Machine Theory.     

Computer-aided automatic design

After a survey of the design process to underline the different stages in which the use of a computer can be utilized with profit, some programs developed to assist the mechanical designers in their job are discussed. These are organized into an integrated system made up of a supervisor (MLINK), two basic languages (MEDES and TEADI), and several post-processors which are briefly described. Further improvements of the system are also discussed concerning new programs to be developed and new types of hardware to be adopted.     

平面连杆机构计算机辅助设计

本文利用平面连杆机构的设计原理及利用杆法进行运动分析和误差分析的参数化设计,借助于软件VB6.0辅助设计得到进行可视化编程实现可视化,平面四杆机构并对机构进行平面动画仿真演示,非常实用,快捷方便,给设计人员提供了很大的方便,且利用它进行教学可以生动、直观地展现平面四杆机构的运动特点,取得良好的教学效果.     

Computer-aided kinematic analysis of basic spatial mechanisms

Using the spherical coordinate system in conjunction with the principle of algebraic correspondence between the displacement equations of the plane, spherical and spatial four-bar mechanisms and the plane and spatial slider-crank mechanisms, an efficacious procedure has been developed to carry out kinematic analysis for the coupler and output link of the mechanisms. The iteration-free nature of the procedure precludes any non-convergence problem and the inherent complexity of the 3-dimensional analysis is mitigated substantially.     

汽车车身造型的计算机辅助设计

利用计算机辅助设计方法代替传统的风洞实验进行车身造型建模和CFD数值模拟具有开发周期短,费用低,有良好的复现性,可进行可视化处理等优点.研究表明根据流经车身的速度大小适当地改变车身的曲线形状将有效地减少气动阻力系数,从而提高汽车的性能.     

集成TRIZ的计算机辅助公理化设计系统

为融合先进技术,快速有效地进行创新设计,将计算机辅助创新与公理设计及发明问题解决理论集成,提出集成发明问题解决理论方法的计算机辅助公理化设计系统模型.扩展了发明问题解决理论方法与公理设计的集成点,旨在使设计过程更加简洁有效、设计结果更具创新性;提出了基于信息公理的模糊方案评价方法,应用模糊理论量化定性的评价指标,推进了公理设计在方案评价中的应用,为产品设计提供科学的决策依据;开发了基于集成模型的原型系统,并以停车档机构的改进设计为例,验证了系统的有效性与实用性.     

碟形弹簧计算机辅助设计

采用内点惩罚函数法寻求最优值,以离合器摩擦片磨损后碟形弹簧工作压力变化最小为目标函数对其进行优化设计.     

电液位置伺服系统的计算机辅助设计

利用面向对象编程的思想对电液位置伺服系统CAD软件进行开发.该软件以中文WindowsXP为操作平台,用MicrosoftAccess建立的数据库为基础,以Autodesk公司的AutoCAD2005和MathWorks公司的Matlab7.0为支撑软件,利用VisualBasic6.0开发语言,将系统原理图绘制、参数计算、元件选取、动态仿真集成于一体.使用该软件进行电液位置伺服系统的设计,可获得工程上直接可用的系统原理图.     

Computer-aided feature-based design for net shape manufacturing

Contemporary computer-based design tools are not suitable for concurrent engineering oriented product design due to (a) their particular and stand-alone functionality, (b) the lack of a capability to support interactive decision-making, and (c) the heavy involvement of designer expertise and experience. This paper presents a feature-based design for a manufacturing framework which is able to support the practice of concurrent engineering by providing functions designed specifically for net shape product design and on-line design guidance. Knowledge-based and object-oriented modeling technologies are employed to develop design evaluation facilities. An object-oriented product model, embedded with product design and process knowledge, is constructed and used for design evaluation. Geometric reasoning is performed on features, feature interactions, and overall shape to identify areas that may conflict with design principles. This paper concentrates on design for net shape manufacturing with an emphasis on die casting and injection molding processes. However, the proposed framework is general enough for other net shape processes by customizing process specific features and encoding process design rules.     

Computer-aided methods in bespoke breast prosthesis design and fabrication

This case study presents a method of utilizing computer-aided design technologies to provide bespoke, external breast prostheses. The technique is illustrated through a case study of a mastectomy patient. Photogrammetry methods were used to capture the breast form when supported by a brassiere and the unsupported breast and defect side. Computer-aided design techniques were used to generate a digital prosthesis based upon the supported breast shape and with a fitting surface that matched the defect side. Furthermore, a two-part mould was designed and fabricated using rapid prototyping methods. A colour-matched prosthesis was then fabricated in a gel-based, platinum-cured silicone.     

基于实例的计算机辅助装配过程设计

为了简化装配过程设计,使过于依赖人类经验的装配过程设计自动化,提出了基于实例推理技术的计算机辅助装配过程设计方法.提出装配线设计系统体系结构,研究如何确定装配过程设计系统的输入信息,利用基于实例的推理技术将装配功能树映射为装配过程机制树,以实现装配过程设计.将装配实例分解为装配过程功能需求、装配过程行为和装配过程机制三个层次,根据输入零件类型和装配过程类型计算装配实例的相似性系数,并基于模糊评价方法从多个可行相似实例中选择最优的装配过程实例,通过机床修改、单元操作修改和工艺编程修改三步对实例进行修改,以满足给定的装配功能需求.运用具体实例验证了所提方法的正确性.     

冷弯中梁轧辊孔型的计算机辅助设计

介绍了铁道货车用冷弯中梁成型与普通冷弯型钢成型的不同之处,分析了冷弯中梁的设计难点及解决方案.给出了冷弯中梁的成型原理、成型道次分配及孔型尺寸的确定方法.建立了数学模型;并应用计算机辅助孔型设计计算了冷弯中梁各架次孔型尺寸;进行了孔型优化.对冷弯中梁辊式成型的轧辊结构进行了设计.     

KIDYAN: Computer-aided kinematic and dynamic analysis of planar mechanisms

The paper deals with a method of kinematic and dynamic analyses of planar linkages and describes a general program based on it. Both make use of a theorem saying that every planar mechanism consists of several Assur groups and of one or more driving links. Likewise, the corresponding program is composed of subprograms for the analysis of these groups.Two examples are presented.     

Computer-aided design of manipulation robots via multi-parameter optimization

In the paper are presented the basic ideas of computer-aided design of manipulation robots based on adopted optimizational criteria and on set constraints of strengths, as well as on actuator capabilities. Using complete models of manipulator dynamics, a simulation programme was derived, giving at its output the optimal design parameters of manipulator. An algorithm was formed, optimizing simultaneously two of the several significant manipulator parameters. In one case these are two diameters of circular cross-section segments, in another, one is a diameter and the other the reducing ratio of the DC motor type actuator.     

Computer-aided design helps design what may be world's smallest scanning tunneling microscope

Computer-aided design (CAD) played a crucial role in designing what is believed to be the world's smallest scanning tunneling microscope. Conventional scanning tunneling microscopes (STMs) are 2) to 6) in diameter. NEC researchers needed an STM only 1) in diameter to study objects in a high magnetic field at very low temperature within a tank of liquid helium. NEC engineers built the microscope in-house and at a local machine shop using a combination of commercial components and others that they built themselves. Computer-aided design was crucial in the fitting of all the required components within the very tight envelope requirement. An inexpensive Macintosh and PC-based CAD program, Vellumfrom Ashlar, Inc., San Jose, California, was used to evaluate a wide range of possible configurations in minimal time.     

Computer-aided geometric design of legs for a walking vehicle

A legged vehicle is potentially more energy efficient and mobile than conventional vehicles in rough terrain. The performance of such a legged vehicle is strongly dependent on the leg geometry. In general, a leg linkage which possesses three-degree-of-freedom foot motion is adequate. A preliminary design of the leg with a view to good energy efficiency resulted in a four-bar leg. This was described by S. M. Song et al. [Mech. Mach. Theory 19, 17–24 (1984)]. In the present paper, the mobility of the legged vehicle is brought into consideration in the leg design. A study of the mobility of a six-legged vehicle shows that a large walking envelope is required for each leg linkage. In order to satisfy this requirement, the original four-bar leg was modified into a seven-bar leg by mounting another four-bar linkage on the coupler of the original four-bar linkage. Also, a different type of leg linkage based on pantograph mechanism was designed. A comparison of the leg performance of both types of leg is made in this paper and the pantograph leg is found to be more effective.     

基于ASP模式的计算机辅助工业设计系统研究

为了解决计算机辅助工业设计在区域网络化制造环境下的应用问题 ,提出了一种基于应用服务提供商模式的应用方案 ,给出了基于应用服务提供商模式的计算机辅助工业设计体系结构。所开发的系统由形态、色彩、人机和评价四个工具集构成 ,工具集中的每个独立工具按照可重用组件技术开发 ,以COM组件形式动态加载到CAD平台中。研究了工具集开发中的风格形态布局模板、色彩方案库、人机操作部件库和外观评价等关键技术。在具体实施中采用框架技术开发了原型系统 ,初步实现了面向区域内机床企业的计算机辅助工业设计应用服务。该系统可提高企业的设计能力 ,是区域网络化制造的重要组成部分     

Computer-aided design on a perforated single-layer absorber under space constraints

As investigated by the Occupational Safety and Health Act (OSHA) in 1970, noise is highly responsible for the psychological and physiological illnesses of workers. Therefore, noise control for an enclosed manufacturing system using sound absorbers becomes indispensable. Considering the minimal acoustic wool used in the high-performance sound absorber during design optimization, the ratio of the sound absorption coefficient to the thickness of acoustic wool, a cost- and performance-oriented design index, is then applied and served as a researched objective accordingly; what’s more, the thickness of the absorber is fixed in advance for the sake of maintenance and access. In this paper, not only is the graphic analysis studied, but also, the computer-aided numerical assessments are presented. In the computer-graphic analysis on sensitivity, one set of design data is developed first. Additionally, the successive algorithm of iteration techniques and the original design data are carried out independently. Moreover, the results are then confirmed by the Kuhn-Tucker condition for accuracy purposes. It is shown that the theoretical and simulated results are in good agreement. The economical design of the sound absorber proposed in this study definitely provides a quick and optimal approach to minimize the amount of acoustic wool used and retain the higher acoustic performance of perforated single-layer absorbers under space restrictions.     

Computer-aided design of work dependent cams for single spindle automats

A design methodology for designing the work dependent cams for single spindle automatic machines is presented in the form of interactive graphic package in ANSI FORTRAN-77 language. The package displays the cam profile, the input and output variations, cutter path and other useful graphic outputs. The cam profile synthesis and radius of curvature evaluations are made using screw theoretic approach and differential geometry respectively. As examples of software development some photographs of graphic outputs are shown.     

Computer-aided design of hydrostatic journal bearings including shaft bending effect

Most analyses of hydrostatic journal bearings assume that there is no deflection of the shaft. This paper shows that prediction of bearing performance from ‘no bending’ theory would underestimate the eccentricity ratio, power ratio, and lubricant flow rate. The computerised iteration technique developed gives full performance data for multi-pocket hydrostatic bearings once the dimensions and operating conditions are known.