三维图像扫描技术在髋骨测量中的应用研究

基于结构光扫描测量原理,研究髋骨空间几何形貌的测量方法和技术,经过光条扫描、数据采集、数字建模等过程,建立髋骨的精密数学模型,利用数学模型,不仅能精确测量髋骨标志点距离等几何参数,还能获得髋骨的表面积、体积、曲率等传统方法难以得到的其它重要几何参数.通过在髋骨标志点处嵌入标准钢球,实现用关节臂测量机对髋骨标志点坐标的精密测量.利用关节臂测量机与髋骨数字模型进行比对测量,证明标志点距离测量精度小于0.05 mm.     

六关节机械臂逆运动学的快速求解算法

对最常用的六关节机械臂,给出一种直接获取逆运动学最优解,并且运算速度更快的方法,以提高机械臂快速响应能力。这种方法不需要先从机械臂正向运动学方程中求逆运动学方程的全部解,然后再从中选择最优解,而是根据对末端的姿态和位置的要求,直接求出最优解,即先求出第5个坐标系的坐标原点和第4、5、6个关节角的旋转角度,再根据第5个坐标系原点的坐标以及第4、5、6个关节角的旋转角度求出第1、2、3个关节角的旋转角度。仿真结果证明了6个关节角计算的正确性和可行性。     

多关节测量臂在轮毂曲面创建中的应用

介绍了多关节测量臂的工作原理,阐述了用多关节测量臂获取轮毂点云的过程,并利用逆向工程软件Imageware对轮毂点云进行曲面创建.实践表明,多关节测量臂在逆向工程技术中具有显著的特点和广泛的应用价值.     

摄影测量中编码标志点设计方案概述

大尺寸三维测量中,通常在被测物体表面设置一些具有唯一特征的编码标志点,通过解码可实现不同图像中同名点的匹配。本文首先介绍了摄影测量技术中编码标志点的作用和分类,分析了点状编码标志点和环状编码标志点的编码原理及存在的问题,总结了各种改进方案的特点,然后根据编码标志点的设计要求讨论了两类编码标志点的特点,最后对编码标志点的设计提出了一些改进思路。     

基于标志点的多视角三维测量数据配准技术的研究

本文通过引入标志点 ,提出了一种在三维测量系统中对三维测量数据进行配准的方法。该方法通过对标志点的提取 ,首先得到一组匹配点对 ,然后运用SVD奇异值矩阵分解算法求出转换参数R和T ,进而以此作为所有三维测量数据的旋转矩阵R和平移向量T从而实现配准。本文论述了该方法的基本原理 ,并通过实例证明了该方法的有效性     

关节臂式坐标测量系统的数学模型和参数简化

关节臂式柔性三坐标测量系统,是一种新颖坐标系测量系统,它具有量程大、体积小、重量轻、使用灵活等优点.论文首先基于Denavit-Hartenberg方法建立了关节臂式柔性三坐标测量系统的理想数学模型和误差模型,然后建立复合球坐标系,简化了误差模型,为进一步研究关节臂式坐标测量机的标定和误差奠定了理论基础.     

基于编码技术的测量标志点研究

在近景测量中,为了通过图像处理、数据处理的方法获取运动物体的轨迹与姿态,就需要在运动物体上增加标志点。在后期的图像处理和数据处理过程中需要对标志点先进行判读,而标志点一般都是人工识别,或人工辅助识别。不能完全智能化的原因是计算机对图像中的标志点不能完全区分。本文设计了一种基于编码点测量标志点,解决了以上的问题。     

关节臂测量机的校准方案与选择

使用常见的通用测量标准器具,就关节臂测量机的校准,制订经济有效、切实可行的校准方案,从而达到满足关节臂测量机性能的校准要求.     

CMAC在三关节机械臂逆运动学求解中的应用研究

传统的方法用于解决机械臂逆运动学问题不仅计算量大,而且还有不唯一解问题,很难用于机械臂的实时控制.系统地研究了CMAC神经网络在三关节机械臂逆运动学求解中的应用.简单介绍了CMAC网络,形象描述了三关节机械臂在二维平面的运动;接着,详细解释提出的三关节机械臂逆运动学问题解决方案,并且分析了基于2个CMAC网络的正、逆模型;最后,通过仿真得到验证：在求解逆运动学方面,CMAC网络学习算法比较简单,收敛速度快,且不存在局部极小问题.     

印品质量控制中的密度测量与色度测量

在印刷品质量控制中为了得到更多的可靠数值,越来越多地选择用仪器测量法来代替主观评价法.这就是密度测量法和色度测量法.     

Three-Dimensional Finite Element Analysis of Prosthetic Finger Joint Implants

The purpose of this study was to develop high resolution three-dimensional (3D) finite element (FE) models of the Swanson^® (No. 2) and NeuFlex^® (No. 10) joint implants to: simulate implant function; evaluate stress distributions and bending stiffness of these implants; and assess their comparative potential for fracture and range of motion (ROM) in flexion and extension. Geometric representations of the implants accurate to within 20 μm were achieved using digital laser imaging technology. Images were transferred to ANSYS 5.7 using appropriate interfacing software and 3D FE models of the implants were constructed. Hyperelastic material properties of the silicone elastomers were derived experimentally from uniaxial tensile tests on implant sections. Both implants experienced maximum von Mises stresses at 90° of flexion and minimum stresses at the neutral position of flexion (Swanson: 0°, NeuFlex: 30°). Within the reported functional ROM (33°–73°), the NeuFlex implant exhibited lower maximum von Mises stress and bending stiffness than the Swanson. The Swanson implant, which has a straight hinge, exhibited lower peak stresses and bending stiffness than the NeuFlex for flexion less than 20°. Areas of high von Mises stress for the Swanson implant included the stem–hinge junction and the peripheral zone of the body of the hinge, corresponding to clinical reports of fractures. In the NeuFlex implant, the maximum stress occurred on the dorsal surface of the hinge. Bending stiffness of the NeuFlex implant was modelled to be substantially less than that of the Swanson throughout the functional ROM (33°–73° of flexion). The resting position of the Swanson implant is at 0° of flexion. A moment was required to extend the NeuFlex implant from 30° to 0° of flexion. These results suggest that the NeuFlex may potentially facilitate flexion of the metacarpophalangeal (MP) joint, whereas the Swanson may promote a more extended position of the joint.     

Differences between the wear couples metal-on-polyethylene and ceramic-on-ceramic in the stability against dislocation of total hip replacement

After total hip replacement an insufficient range of motion (ROM) can lead to contact between femoral neck and rim of the cup (= impingement) causing dislocation and consecutive material failure. The purpose of this study was to analyse the influence of different wear couples on the ROM and stability against dislocation. By means of a special testing device the ROM until impingement, the ROM until dislocation as well as the resisting moment against levering the head out of the cup were experimentally determined. Various total hip systems with cup inserts made of ceramic and polyethylene were comparatively examined in different implant positions. Maximum resisting moment as well as the ROM until impingement and dislocation were clearly influenced by the implant position. Furthermore, the stability against dislocation was affected by design parameters, whereas in the case of appropriate implant position differing wear couples (metal-on-polyethylene vs. ceramic-on-ceramic) had a minor impact. However, as shown by tests under lubricant conditions, ceramic-on-ceramic couples provided less dislocation stability in unfavourable implant position in comparison to metal-on-polyethylene. Therefore, ceramic-on-ceramic couples should only be applied in the case of optimised implant orientation preventing impingement and dislocation with subsequent material failure like chipping off or breakage.     

等分多读数头位置偏差对测角误差的影响研究

提出了一种针对等分多读数头系统中读数头位置偏差对抑制测角误差作用机理的分析方法。介绍了读数头在非理想位置引入测角误差的理论分析和仿真实验方法,利用频谱分析法分离谐波误差,获得各阶误差幅值的衰减率用以计算测角误差。将该方法应用于等分双读数头编码器误差分析,结果表明读数头在0.5°位置偏差时,引入的测角误差在±0.09″范围内。     

Regional variation in the mechanical properties of the vertebral column during lateral bending in Morone saxatilis

Unlike mammalian, disc-shaped intervertebral joints (IVJs), the IVJs in fishes are biconid structures, filled with fluid and thought to act as hydrostatic hinge joints during swimming. However, it remains unclear which IVJ structures are dominant in mechanical resistance to forces in fishes, and whether variation in these tissues might impact the function of the vertebral column along its length. Here, we measured the dynamic mechanical behaviour of IVJs from striped bass, Morone saxatilis. During lateral bending, angular stiffness was significantly lower in the caudal and cervical regions, relative to the abdominal region. The neutral zone, defined as the range of motion (ROM) at bending moments less than 0.001 Nm, was longer in the caudal relative to the abdominal IVJs. Hysteresis was 30–40% in all regions, suggesting that IVJs may play a role in energy dissipation during swimming. Cutting the vertical septum had no statistically significant effect, but cutting the encapsulating tissues caused a sharp decline in angular stiffness and a substantial increase in ROM and hysteresis. We conclude that stiffness decreases and ROM increases from cranial to caudal in striped bass, and that the encapsulating tissues play a prominent role in mechanical variation along the length of the vertebral column.     

Extreme reaches and maximal reachable workspace for rotary tools mounted on a Stewart platform manipulator

Abstract

A new type of problem associated with the extreme reaches of the Stewart platform manipulator is dealt with in this paper. Given a specified orientation of the tool axis, the problem involves finding the extreme distance that the tool bit mounted on the mobile platform can reach from its home position along any specified direction. During the motion, the mobile platform is allowed to be rotated about the tool axis to adjust the configuration of the driving mechanism to prevent premature activation of the kinematic constraints. A numerical optimization algorithm based on the concept of the cyclic coordinate descent method is developed for solving this problem, in which all three types of kinematic constraints, namely the actuator stroke constraint, the passive joint limitations, and the link interference conditions, have been taken into account. In addition, a numerical example is presented to demonstrate the ability of the proposed method to find the optimal reachable workspace of the robot.     

Topological derivatives for fundamental frequencies of elastic bodies

In this article a new method for topological optimization of fundamental frequencies of elastic bodies, which could be considered as an improvement on the bubble method, is introduced. The method is based on generalized topological derivatives. For a body with different types of inclusion the vector genus is introduced. The dimension of the genus is the number of different elastic properties of the inclusions being introduced. The disturbances of stress and strain fields in an elastic matrix due to a newly inserted elastic inhomogeneity are given explicitly in terms of the stresses and strains in the initial body. The iterative positioning of inclusions is carried out by determination of the preferable position of the new inhomogeneity at the extreme points of the characteristic function. The characteristic function was derived using Eshelby's method. The expressions for optimal ratios of the semi-axes of the ellipse and angular orientation of newly inserted infinitesimally small inclusions of elliptical form are derived in closed analytical form.     

Photographic evidence for the third-order rainbow

The first likely photographic observation of the tertiary rainbow caused by sunlight in the open air is reported and analyzed. Whereas primary and secondary rainbows are rather common and easily seen phenomena in atmospheric optics, the tertiary rainbow appears in the sunward side of the sky and is thus largely masked by forward scattered light. Up to now, only a few visual reports and no reliable photographs of the tertiary rainbow are known. Evidence of a third-order rainbow has been obtained by using image processing techniques on a digital photograph that contains no obvious indication of such a rainbow. To rule out any misinterpretation of artifacts, we carefully calibrated the image in order to compare the observed bow's angular position and dispersion with those predicted by theory.     

标定飞机方向舵角位移的视觉测量法

飞机飞行性能试验前需标定其方向舵的角位移传感器.基于单目视觉,以三个圆心为靶面的基本标志,圆周为辅助标志;用两直线段的交点标明圆心位置.取平行于像面的直径为特征直径,借助它容易从像面椭圆图像提取靶面深度信息,并建立简单、精确的逆透视变换公式.设计了亚像素法处理照片,能精确测出圆心像点位置和特征直径的像长,用来求圆心的世界坐标,得到靶面的平面方程.舵的角位移可用靶面角位移表示.计算机仿真结果,圆心像点位置测量误差小于0.02 pixel,角位移测量误差小于0.005°.靶面与舵轴不平行导致的测量误差能及时修正,可降低对靶面安装的要求,使操作简单.能在现场标定飞机副翼、襟翼,升降舵、方向舵的角位移.     

人造板上下料机械手的动力学分析及仿真

目的 实现包装生产线上的自动化搬运作业,全面系统地了解人造板上下料机械手的动态特性,探究该机械手各关节所需驱动力大小及变化规律。方法 建立人造板上下料的三维结构模型,制定机械手一周期内的运动流程,通过拉格朗日方程法对机械手进行建模,通过系统动力学仿真软件(Adams)仿真出机械手的动态特性并验证动力学模型的准确性。结果 得到了机械手各关节(角)速度、(角)加速度、力与力矩变化曲线,(角)速度变化平缓无突变,(角)加速度、力与力矩曲线在6～9 s时变化剧烈,仿真曲线与动力学模型数据基本拟合。结论 动力学模型建立正确,后续应优化驱动或通过结构优化方式使整个运动过程更加平稳。     

Theory and simulation for the identification of the link geometric errors for a five-axis machine tool using a telescoping magnetic ball-bar

The position invariant geometric inaccuracies of a machine tool are the first to influence the quality of machined parts. A systematic approach is presented to identify some of these errors on a five-axis machine tool. The methodology is applied to the link error parameters such as joint misalignments, angular offset and rotary axis separation distance. A method based on the mathematical analysis of singularities of linear systems is used to assist in selecting a minimal but sufficient set of link error parameters for the calibration of a machine tool. A number of criteria are proposed in order to verify that the identified parameters accurately predict the positioning errors of the true machine. Finally, the numerical effectiveness of this method is shown through simulations.