Digital manufacture of titanium prosthesis for cranioplasty

Based on multi-point forming (MPF) technology, a novel digital manufacturing method of cranial titanium plates for the repair of skull defects is developed in this paper. First, a 3D triangular mesh model of the skull is constructed from a CT data set. Then, a non-uniform rational B-splines-format (NURBS-format) patch surface is obtained by surface interpolation based on the skull polygon model. Finally, the patch surface model is input to MPF CAD/CAM software and the cranial titanium prosthesis is deformed by an MPF press. The method has many new features compared with other means. Implementing medical image processing and MPF technology, the method can remarkably shorten the production cycle of titanium cranioplasty, as well as offer improved fitting precision. About 20 practical applications have been finished, which prove the feasibility and efficiency of the method.     

颅骨点云模型的优化配准

由于颅骨的三维点云数据模型复杂且不同人的颅骨差异较小,对其配准精度要求较高。为了提高颅骨点云模型的配准精度和收敛速度,提出了一种先粗配准再细配准的配准方法。首先,对颅骨点云数据模型进行去噪、简化和归一化等预处理;然后,通过区域划分、区域配准和求解组合系数以及求解刚体变换等步骤实现区域层次上的颅骨粗配准;最后,通过引入动态迭代系数来改进基于旋转角约束的迭代最近点算法,并采用该改进的ICP算法实现颅骨的细配准,从而达到精确配准的目的。实验结果表明:与ICP算法相比,改进的ICP算法的配准精度和收敛速度分别提高了约30%和50%。证明该种先粗配准再细配准的颅骨点云模型配准方法是一种精度高、速度快的有效颅骨配准算法。     

Contribution towards modelling of two-stage reciprocating compressors

The paper presents the results of simulation of a two-stage two-cylinder reciprocating compressor system with inter- and after-cooling. The equations representing the unsteady gas flow in the piping system, with inclusion of friction and heat transfer effects, were solved in the characteristic form by means of the modified Benson numerical mesh-method. The predicted results were compared with the experimental data showing good agreement.     

基于IPFIX的数据传输

本文详细说明了ipfix协议,它为网络管理者提供了访问IP流信息的途径。为了将IP流信息从发送进程传输到接收进程。必须要有一个描述流数据的通用方法和一个传输流数据的标准方式。本文详细介绍了ipfix flow record和templates数据是如何从ipfix发送进程传输到接收进程的,传输所依赖的协议是一个可以发现网络阻塞的传输协议。     

Atlas of spherical four-bar mechanisms

An atlas or catalogue of mechanisms provides a useful aid in the synthesis of mechanisms for new applications. The atlas stores mechanisms together with their coupler paths. Fourier techniques can be used as a convenient means for representing, in normalized form, curves for planar mechanisms. This paper looks at the extension to spherical four-bar mechanisms. In particular, a means for projecting a spherical curve onto a plane is discussed which depends only on the geometry of the curve and not on the choice of world coordinate system.     

Accurate multi-robot targeting for keyhole neurosurgery based on external sensor monitoring

Robotics has recently been introduced in surgery to improve intervention accuracy, to reduce invasiveness and to allow new surgical procedures. In this framework, the ROBOCAST system is an optically surveyed multi-robot chain aimed at enhancing the accuracy of surgical probe insertion during keyhole neurosurgery procedures. The system encompasses three robots, connected as a multiple kinematic chain (serial and parallel), totalling 13 degrees of freedom, and it is used to automatically align the probe onto a desired planned trajectory. The probe is then inserted in the brain, towards the planned target, by means of a haptic interface. This paper presents a new iterative targeting approach to be used in surgical robotic navigation, where the multi-robot chain is used to align the surgical probe to the planned pose, and an external sensor is used to decrease the alignment errors. The iterative targeting was tested in an operating room environment using a skull phantom, and the targets were selected on magnetic resonance images. The proposed targeting procedure allows about 0.3 mm to be obtained as the residual median Euclidean distance between the planned and the desired targets, thus satisfying the surgical accuracy requirements (1 mm), due to the resolution of the diffused medical images. The performances proved to be independent of the robot optical sensor calibration accuracy.     

Systematic evaluation of FRAP experiments performed in a confocal laser scanning microscope

The diffusion coefficient as well as the dimensionality of the diffusion process can be determined by straightforward and facile data analysis, when fluorescence recovery after photobleaching (FRAP) is measured as a function of time and space by means of confocal laser scanning microscopy. Experiments representing one-dimensional diffusion from a plane source or two-dimensional diffusion from a line source are readily realized. In the data analysis, the deviations of the actual initial conditions from ideal models are consistently taken into account, so that no calibration measurements are needed. The method is applied to FRAP experiments on solutions of Rhodamine B in glycerol and aqueous suspensions of polymethyl methacrylate microspheres.     

Special configurations of spatial mechanisms and robot armsSpezielle konfiguration räumlicher mechanismen und roboterarme

A novel general method is developed for determining special configurations of all single-loop mechanisms. The results are illustrated by means of numerical examples. In addition special configurations of robot arms are investigated, and a simple result which has important practical application is deduced; “when all the screws representing the instantaneous motion of the joints of a robot arm are reciprocal to a common screw or screw then the end effector cannot have free instantaneous movement parallel to the axis or axes of the reciprocal screws”.     

A theory of smeared continuum damage mechanics

This paper considers smeared continuum damage mechanics based on the equivalent elliptical crack representation of a local damage. This approach provides a means of utilizing the crack energies derived in fracture mechanics, and of identifying the local damage state from local stress and strain information. The strain energy equivalence principle is used to derive the effective continuum elastic properties of a damaged solid in terms of the undamaged elastic properties and a scalar damage variable. The scalar damage variable is used to develop a consistent damage evolution equation. The combination of representing local damage as an equivalent elliptical crack, the determination of effective elastic properties using a strain energy equivalence principle, and a consistent damage evolution equation yields a simple, yet powerful local approach for continuum damage analysis     

Topographical analysis in the SEM using an automatic focusing technique

A novel technique for automated topographical analysis in the SEM has been investigated. It utilizes a 16-bit minicomputer arranged to act as an automatic focusing unit. The computer is coupled to the objective lens of the microscope, by means of a digital to analogue converter, and may regulate the excitation of the lens under program control. Further digital-to-analogue converters allow the computer to act as a programmable scan generator by applying ramp waveforms to the scan amplifiers, permitting the beam to be swept over a small sub-region of the field of interest. The video signal is sampled and applied to an analogue-to-digital converter; the resultant binary numbers are stored in computer memory as an array of values representing relative image intensities within a subregion. A differencing algorithm applied to the collected data allows the level of objective lens excitation to be found at which the sharpness of the image is optimized, and the excitation may be related to the working distance for that subregion through a previous calibration experiment. The sensitivity of the method for detecting small height changes is theoretically of the order of 1 μm.     

Algorithms of background suppression in the problem of detection of point targets in images

Various approaches to estimation and suppression of a motionless background with the use of texture correlations in the problem of detection of small-size dynamic targets are considered. Algorithms of suppression of a locally flat background, background suppression by means of bilateral filtration, and an algorithm of background estimation and suppression with the use of an autocorrelation function are implemented. For anisotropic textures with boundary transitions, an algorithm of background estimation and suppression along the boundary and an algorithm of three-channel filtration are proposed and implemented. Operation of these algorithms on textures representing different classes of images is compared. It is demonstrated that the algorithm with background estimation along the boundaries yields good results for model data with a large number of linear boundaries, but its operation on mixed-type textures is less efficient than that of other available approaches. Among the considered algorithms, the approach based on three-channel filtration ensures the greatest increase in the signal/noise ratio for various textures modeling real images.     

具有区间参数的不确定结构静力区间分析的一种算法

将结构系统中的不确定性参数用区间数来表示,用有限元法建立静力区间线性方程组。对该方程组的求解提出了一种区间逐步离散的方法。此方法通过令独立的不确定性参数取区间内的离散值,将区间线性方程组的求解转化为相应的确定性问题,再搜索各方程解中的最大最小值得到每个区间分量的边界。先用数学算例对该算法的正确性和有效性进行了验证,然后应用于静力区间分析的工程算例,并与其它算法进行了比较。计算结果表明该算法的计算效率和准确性较高。     

基于 CATIA的自由曲面重构以及应用

利用CATIA强大的自由曲面设计的功能特点，结合颅骨修复实例探讨了CATIA在曲面重构方面的新应用。     

TYRE DYNAMICS MODELLING OF VEHICLE BASED ON SUPPORT VECTOR MACHINES

Various methods of tyre modelling are implemented from pure theoretical to empirical or semi-empirical models based on experimental results. A new way of representing tyre data obtained from measurements is presented via support vector machines (SVMs). The feasibility of applying SVMs to steady-state tyre modelling is investigated by comparison with three-layer backpropagation (BP) neural network at pure slip and combined slip. The results indicate SVMs outperform the BP neural network in modelling the tyre characteristics with better generalization performance. The SVMs-tyre is implemented in 8-DOF vehicle model for vehicle dynamics simulation by means of the PAC 2002 Magic Formula as reference. The SVMs-tyre can be a competitive and accurate method to model a tyre for vehicle dynamics simulation.     

Rigorous Application of Tolerance Analysis in Setup Planning

Decades of computer-aided process planning research has resulted in techniques that automate portions of the process planning task such as operation sequencing and cutter path optimisation. Nonetheless, solutions to other areas such as setup planning and fixturing remain elusive. Setup planning research has received increased attention in recent years. The importance of tolerance analysis in setup planning has been recognised. However, due to the lack of a common measure for different types of tolerances, the analysis is carried out in an ad hoc fashion and often results in suboptimal setup plans. In this paper, a tolerance normalisation approach is presented to provide an accurate means for direct comparison of different types of geometric tolerances and dimensional tolerances. A normalised tolerance is an angle representing the maximum permissible rotation error when locating a component. It is calculated based on rigorous analysis of manufacturing errors involved in component setups. The formulae for tolerance normalisation are derived and the use of normalised tolerance in setup planning is illustrated.     

Lattice fringe studies of (100) defects in enamel crystallites

Lattice imperfections in the structure of shark (Nataprion brevirostrais) enamel crystallites have been studied by means of lattice-imaging in a high-resolution transmission electron microscope. Line defects exhibiting various lengths (100–2500 Å) and widths (10–30 Å) and demonstrating phase behaviour different from that of the host crystal were observed along the fringes representing (100) lattice planes. When defect sites were subjected to an electron beam, an annealing process was observed in which the difference in phase contrast eventually disappeared and the defect itself became an intricate part of the (100)-type lattice planes. A through-focal series of the defects show a reversal in phase contrast. By examining the contrast behaviour under certain focal conditions and by adopting the Fresnel diffraction mode, the refractive index of the defect regions was determined to be lower than that of the apatite crystal. Present findings suggest that the interlayering structure along the (100) planes is responsible for the line defects observed in enamel apatites.     

Study on the tolerance allocation optimization by fuzzy-set weight-center evaluation method

The tolerance allocation optimization method by fuzzy-set weight-center evaluation is used to derive the manufacturing difficulty coefficient, through quantifying the manufacturing condition factors which all affect the manufacturing cost, including the forming means of the blank, element size, machining surface features, operator’s skills, and material’s machinability. The coefficient is then converted into a weight factor used in the inversed square model representing the relationship between the cost and tolerance, a cost-objective function model based on optimal tolerance allocation according to the manufacturing conditions is thus established for optimizing and allocating the tolerances. Integrating this model into computer-aided-tolerance-allocation makes it more convenient, accurate, and feasible.     

面向机电产品全生命周期的虚拟维修系统

以全生命周期理论为基础，以虚拟现实软件为表现手段，按照组件的思想提出面向机电产品设计的虚拟训练与维修系统框架，该系统由核心组件和应用组件组成，用系统总线构建各组件之间的通讯机制和关联关系。介绍了虚拟维修应用组件的组成、功能和在进行故障诊断时采用的可以快速定位的伪故障树法。开发了震雄集团有限公司注塑机虚拟训练与维修系统。     

不确定结构区间分析的仿射算法

将结构系统中的不确定性参数用区间数表示,建立系统的区间有限元控制方程.对该方程组的求解提出一种基于导数信息的仿射算法.此方法通过令独立的不确定性参数转换成仿射型,将区间线性方程组的求解转化为相应的确定性问题,再搜索各方程解中的最大最小值,得到每个区间分量的边界.先用数学算例对该算法的正确性和有效性进行验证,然后应用于静力区间分析的工程算例,并与其他算法进行比较; 计算结果表明该算法的可行性和有效性.     

基于威布尔与模糊C均值的滚动轴承故障识别

提出一种基于威布尔分布与模糊C均值(fuzzy C-means,FCM)聚类算法相结合的滚动轴承故障识别方法。针对不同故障类型的威布尔分布模型的尺度参数、形态参数和威布尔负对数能够较好地刻画轴承运行的状态特性,提取其尺度、形态和威布尔负对数似然函数等3个参数构建表征轴承运行状态的特征向量。模糊C均值根据样本相对于聚类中心的隶属度确定样本的亲疏程度而实现分类。实验中,首先采用组合形态滤波器对滚动轴承原始信号进行降噪,然后建立威布尔分布模型,将提取的特征向量输入模糊C均值分类器进行故障诊断和识别。结果表明,该方法对机械故障诊断识别准确率高,可以作为滚动轴承故障识别的重要手段。