基于三坐标测量机的曲面数字化研究与实践

曲面数字化是逆向工程关键技术,针对三坐标测量机原有曲面扫描方式的不足,探讨曲面测量中面片的划分方式和扫描路径的规划技术。     

Investigation on sampling size optimisation in gear tooth surface measurement using a CMM

Coordinate measuring machines (CMMs) are widely used in the gear manufacturing industry. One of the main issues for contact inspection using a CMM is the sampling technique. In this paper the gear tooth surfaces are expressed by series of parameters and inspection error compensation and initial value optimisation method are presented. The minimum number of measurement points for 3D tooth surfaces are derived. If high precision is required, more points need to be inspected. The sampling size optimisation is obtained from the criterion equation. The surface form deviation and initial values are optimised using the minimum zone method and genetic algorithms. A feature-based inspection system for spur/helical gears is developed and trials and simulations demonstrate that the method developed is suitable and very effective. This revised version was published online in October 2004 with a correction to the issue number.     

三坐标测量机在高速测量过程中的动态误差研究

本文研究了三坐标测量机在高速测量过程中的动态误差。以一台移动桥式三坐标测量机为例,分析了其动态误差的产生原因,建立了其动态误差的数学模型,并对动态误差进行了全面的测量和补偿。实验证明,三坐标测量机的动态误差具有一定的重复性,可用软件补偿,从而提高三坐标测量机快速测量的精度。     

NURBS曲面结构与分面策略

复杂的曲面需要将面拆分成多块,然后再将曲面搭接成需要的连续性级别即可.基于NURBS标准4边结构与特殊状态的3边曲面结构、周期曲面、封闭曲面、修剪面等非4边结构,提出复杂造型NURBS曲面拆分为基础曲面与混合曲面的分面策略及分面时应注意的问题.并结合实际案例,分析同一造型的曲面的2种不同分面思路.     

复杂曲面加工干涉避免及轨迹的规划

对复杂曲面进行分析,通过调节后跟角和摆动角来避免刀具与被加工曲面发生干涉,并提出了复杂曲面五坐标数控加工刀具轨迹的规划算法,以改善曲面加工精度和加工效率。     

Tool path strategy and cutting process monitoring in intelligent machining

Intelligent machining is a current focus in advanced manufacturing technology, and is characterized by high accuracy and efficiency. A central technology of intelligent machining—the cutting process online monitoring and optimization—is urgently needed for mass production. In this research, the cutting process online monitoring and optimization in jet engine impeller machining, cranio-maxillofacial surgery, and hydraulic servo valve deburring are introduced as examples of intelligent machining. Results show that intelligent tool path optimization and cutting process online monitoring are efficient techniques for improving the efficiency, quality, and reliability of machining.     

工艺设计过程中的切削体分解组合策略

为实现工艺设计过程中对产品设计数据的有效重用,提出了一种切削体分解组合策略.该策略利用对切削体的分解组合,向工艺设计提供所需的基本工艺路线、工艺模型、尺寸公差等工艺数据.为生成符合工艺要求的切削特征,阐述了切削体分解算法和分割面的生成方法;研究了几何约束、工艺约束下的分割面分解优先级确定规则;探讨了单元切削体组合条件和优先组合策略.通过实例阐述了该策略下的工艺设计过程,验证了该策略的可行性和有效性.     

基于人体热释电特征多策略融合的识别方法

针对现实复杂环境中,利用单个或多个热释电传感器对人体目标识别时所表现出的不稳定性和抗干扰性较差问题,提出了一种基于人体热释电特征的多策略融合识别方法。该方法以不确定性理论为基础,首先利用不同空域的传感器,获取人体不同部位的置信度,其次结合不同的融合策略实现对人体目标的识别。融合策略分为两种,第一种策略首先使用同空域融合,然后使用同时域融合,这种策略充分利用了分布式传感网络的特性,融合了最优置信度以实现对人体目标的高精度识别,第二种策略则首先使用同时域融合,然后使用同空域融合。该策略能实现对人体目标的实时识别,但不能保证较高的识别精度。实验结果表明多策略融合既能克服单传感器或多传感器在对人体目标进行识别时,所表现出的不稳定性和不可靠性,又能增强系统识别时的鲁棒性和有效性。与其他融合方法相比突出体现了本文方法的优势。     

The relationship between surface roughness and burnishing factor in the burnishing process

This investigation examines burnishing using a microscopic perspective and elucidates the mechanism of surface roughness improvement by asperity deformation. This study uses tribology theory to propose a burnishing factor L _b to explain why the same burnishing result can be obtained in different burnishing conditions. The burnishing factor was determined by appropriate experiments, and the results demonstrated that a quadric curve relationship exists between surface roughness and burnishing factor and is analogous to the Stribeck curve in lubrication regimes.     

模块化设计中的模块创建策略

这里针对模块化设计中方案设计讨论了模块的特性,并在此基础上提出了模块创建的策略,及其实现方法。构建了模块创建子系统。     

The significance of near surface microstructure in the wear process

The wear process in which flake-like debris is developed and removed from the surface of metals in sliding contact is the direct result of heavy plastic deformation of a thin surface layer. The repeated ploughing of asperity contacts over a mating surface can produce high dislocation densities and eventual change in the microstructure to a cell-type structure found in heavily deformed metals. Cell sizes depend on material characteristics such as stacking fault energy, the applied stress and the temperature. It is shown that a cell structure can present many suitable pathways for subsurface crack generation and the release of thin wear flakes without the benefit of asperity cold welding and shear. Depth of crack formation and severity of wear can be associated with stacking fault energy. Changes in the microstructure caused by frictional heating or change in strain rate can cause abrupt changes in wear mode.     

气相色谱-质谱联用仪器国产化中的数据处理系统设计

数据处理系统是气相色谱-质谱联用仪器(GC-MS)的国产化进程中关键部分之一。而国内对于GC-MS的研究重点往往放在仪器硬件,而忽视数据处理系统的重要性。本文首先论述数据处理系统在GC-MS国产化中的重要性,之后提出一种数据处理系统的整体方案设计。最后,对设计中两大组件进行深入研究。并进行实验,实验结果显示,本文提出的数据处理系统获得的结果与国外商用仪器获得的结果完全一致。     

基于图像处理的机器人目标识别与定位系统

为实现移动机器人对目标的导引,提出了一种简单有效的方法。机器人视觉系统的关键技术是对目标实时、准确的提取,而目标提取的实质是图像分割。该文介绍了一种基于色彩空间参照表的适用于机器人视觉系统目标提取的图像分割算法,通过图像处理计算出主动目标图像特征的质点来实现对目标的定位,利用神经网络建立了目标从图像空间到摄像机空间的坐标对应关系,从而对空间运动目标进行了定位。仿真结果也验证了该方法的有效性和可行性。     

Strip shape modeling and its setup strategy in hot strip mill process

Shape setup model (SSM) plays a critical role to achieve satisfactory precision of strip shape in hot strip mill process (HSMP). However, for the design of shape model, the lack of systematic shape theory restricts the high accuracy of strip shape. In this paper, the procedure of SSM will be generally introduced and practically demonstrated with a real HSMP producing system. The mechanism of shape modeling and design strategy of SSM is introduced. Special concentration is placed on modeling and calculating the thermal extension and wear of the roll, and mathematical model of roll gap profile is set up on this basis. Then the mechanism of strip profile and flatness is introduced by revealing the shape forming process. Furthermore, the setup strategy of SSM is proposed, whose target is to calculate reference values for shape control actuators. The other focus of this paper concerns on the applicable issue of SSM integrated with the presented design approach. An Ansteel 1,700-mm HSMP line will be employed for the experimental background.     

An adaptive control strategy for the abrasive waterjet cutting process with the integration of vision-based monitoring and a neuro-genetic control strategy

This paper presents an integrated approach for the monitoring and control of abrasive waterjet (AWJ) cutting process. A machine-vision-based monitoring approach was proposed to obtain the bore diameter of the focusing nozzle from time to time. A neuro-genetic approach, proposed by Srinivasu and Ramesh Babu (Appl Soft Comput 8(1):809–819, 2008) was employed as a control strategy to modify the process parameters, such as water pressure, abrasive flow rate, and jet traverse rate, so as to maintain the desired depth of cut, with changes in the diameter of the focusing nozzle monitored with a machine vision system. By combining the monitoring and control strategies, an integrated approach for adaptive control of AWJ cutting process is realized. The effectiveness of the proposed integrated approach for adaptive control of AWJ cutting process was shown by comparing the results obtained from the experiments with the process parameters suggested by the control strategy to achieve the desired depth of cut. From the results of the study, it is seen that the proposed monitoring system is capable of monitoring the focusing nozzle diameter with a mean absolute deviation of 0.05 mm and that the neuro-genetic strategy is capable of modifying the controllable process parameters to maintain the desired depth of cut with a mean absolute deviation of 0.87 mm.     

A model to simulate surface roughness in the pad dressing process

Pad dressing, which is one of the most important planarization processes, is widely used in CMP. The estimation of surface roughness under various machining parameters (such as dressing force, diamond density of the dresser, rotational speed of the dresser, different machining paths, etc.) is essential to the pad dressing process. In this study, elastic-plastic theory and the wear model are used to construct the expression for the magnitude of material removal as a function of the indentation depth. The deformation of the pad is obtained by using elastic-plastic theory, and the material removal caused by individual micro-contacts is calculated with the help of wear theory. Finally, the macroscopic wear volume is found by summing the volumetric wear of each individual micro-contact. A parametric study is conducted to explore the influence on the surface roughness results and the pad dressing interfacial phenomena of operational parameters. The results reveal that a rapid initial improvement followed by a leveling off, manifesting a saturation effect. Moreover, the model shows that a higher dressing force with a dresser speed close to the pad speed and a moderate translation speed increase the material removal rate corresponding with a lower surface roughness dressing.     

Molecular dynamics simulation of the contact process in AFM surface observations

In the present work, several molecular dynamics simulations have been performed to clarify dynamically the contact mechanism between the specimen surface and probe tip in surface observations by an atomic force microscope (SFM) or friction force microscope (FFM). In the simulation, a three‐dimensional model is proposed where the specimen and the probe are assumed to consist of monocrystalline copper and rigid diamond or a carbon atom, respectively. The effect of the cantilever stiffness of the AFM/FFM is also taken into consideration. The surface observation process is simulated on a well‐defined Cu{100} surface. From the simulation results it has been verified that the surface images and the two‐dimensional atomic‐scale stick‐slip phenomenon, just as is the case for real AFM/FFM surface observations, can be detected from the spring force acting on the cantilever. From the evaluation of the behaviour of specimen surface atoms, the importance of the specimen stiffness in deciding the cantilever properties can also be understood. The influence of the probe tip shape on the force images is also evaluated. From the results it can be verified that the behaviour of the specimen surface atoms as well as the solid surface images in AFM/FFM surface observations can be understood using the molecular dynamics simulation of the model presented.     

Small sample parts recognition and localization from unfocused images in precision assembly systems using relative entropy

Recognition and localization of mechanical parts using machine vision is a common approach in precision assembly systems. However, positional inaccuracy in assembly systems often produces unfocused images. Hence, existing methods of part recognition and localization are vulnerable to failure. In this paper, we present a part recognition and localization method, based on relative entropy, which can be applied to small samples. First, a template image is generated based on the contour of the parts and divided into several regions. The intensity distribution of the regions was sampled to generate template features. Then, the captured image is segmented using the Gaussian mixture model and the expectation maximum algorithm to extract the target part in the image. Part features are also generated by sampling the target part image using the template features. Furthermore, an optimization model is established in which the objective function is the sum of the relative entropy between the image features, the template features, and the region matching error correction term. By solving the optimization model, the location of the part can be obtained. The proposed method is compared with the edge and invariant feature-based methods through experiments. The results show that the proposed method has higher robustness and is suitable for the recognition and localization of parts with unfocused images. By using this method, the flexibility and reliability of precision assembly systems can be improved.