Mesh smoothing method based on local wave analysis

As the mesh models usually contain noise data,it is necessary to eliminate the noises and smooth the mesh.But existed methods always lose geometric features during the smoothing process.Hence,the noise is considered as a kind of random signal with high frequency,and then the mesh model smoothing is operated with signal processing theory.Local wave analysis is used to deal with geometric signal,and then a novel mesh smoothing method based on the local wave is proposed.The proposed method includes following steps:Firstly,analyze the principle of local wave decomposition for 1D signal,and expand it to 2D signal and 3D spherical surface signal processing;Secondly,map the mesh to the spherical surface with parameterization,resample the spherical mesh and decompose the spherical signals by local wave analysis;Thirdly,propose the coordinate smoothing and radical radius smoothing methods,the former filters the mesh points’ coordinates by local wave,and the latter filters the radical radius from their geometric center to mesh points by local wave;Finally,remove the high-frequency component of spherical signal,and obtain the smooth mesh model with inversely mapping from the spherical signal.Several mesh models with Gaussian noise are processed by local wave based method and other compared methods.The results show that local wave based method can obtain better smoothing performance,and reserve more original geometric features at the same time.     

Automated kinematic feasibility evaluation and analysis of mechanical systems

Kinematic analysis, as a first step in design of a mechanical system, should consider feasibility of the design and any pathological properties of the kinematic model selected. Automated numerical methods are presented in this paper to assemble the mechanism in a feasible configuration, if one exists, and to identify and eliminate any redundant constraints that may have been defined. An efficient and reliable numerical method is developed to detect singularities in a kinematic system and to solve the system if solutions exist beyond the singular point. The method developed is shown to be effective for kinematic analysis of systems with both holonomic and nonholonomic constraints. Two examples are discussed to demonstrate the solution method for kinematically driven mechanical systems.     

Matlab优化工具箱在齿轮传动设计中的应用

Matlab优化工具箱具有强大的科学计算能力,在工程设计领域得到了广泛的应用。以齿轮传动可靠性为基础,合理设置目标函数和约束条件,以齿轮中心距最小和齿宽最小双目标函数建立了数学模型,利用Matlab优化工具箱进行编程计算。实例证明,使用Matlab优化工具箱进行优化设计,不仅可以提高计算精度,而且可以减少计算时间,此方法简单实用,易于设计人员掌握,因此在工程设计领域有较强的实际应用价值。     

滚削大质数螺旋齿轮机床挂轮的优化选择

滚削大质数螺旋齿轮必须使用分齿、进给、差动三组挂轮。由于实际挂轮的传动比与理论值之差异,会造成被加工齿轮的误差。笔者推荐一种改进的方法,可消除分齿挂轮及进给挂轮带来的误差,最终造成齿轮误差的仅有差动挂轮,这样可大幅提高被加工齿轮的精度。     

电容式Lamb波器件的信号接收方法

提出了激励和接收均使用电容式叉指换能器(Capacitive Interdigital Transducers,CIDT)的集成化的电容式Lamb波器件。利用电容式叉指换能器直接激励和接收Lamb波非对称模式的方式,解决了机电耦合效率的问题。在分析各种电容检测电路的基础上,针对Lamb波电容式检测的特殊性,选择了直流电路法来进行接收电容变化规律的测量。为说明直流电路法的适用性,设计了波动检测验证实验。实验结果表明:用直流电路法测量得到的声波信号与其理论计算值之间误差仅为2.4%,证明了直流电路法的适用性,解决了目前Lamb波器件的功能材料层的制作工艺均与传统集成电路工艺不兼容的问题。     

弧齿锥齿轮参数调节状态下行波共振特性及其影响规律研究

针对某型航空发动机中央传动锥齿轮在实际使用中因行波共振造成的从动轮断裂失效问题,采用仿真分析与试验验证相结合的方法,研究弧齿锥齿轮参数调节状态下的行波共振特性及其影响规律。基于有限元方法对齿轮进行模态分析,讨论辐板厚度和工作温度对齿轮行波共振特性的影响;基于Hertz接触理论对啮合齿轮进行瞬态动力学分析,重点讨论行波共振状态下负载功率、工作温度及阻尼系数对齿轮应力分布的影响。仿真与试验对比结果表明：模态计算和动力学分析的仿真结果误差均在合理范围内。在满足齿轮设计有关要求前提下,调整辐板厚度可避开共振转速或共振频率。在振动应力分布的共振参数敏感性方面：当齿轮在三四节径行波共振状态下工作时,齿根处应力值最大,辐板正面应力值最小;随着齿轮负载功率、工作温度和阻尼系数变化,从动轮辐板正面应力变化较小,辐板背面和齿根处变化较大。在该齿轮改进和优化设计中,需重点针对三四节径行波共振进行处理。     

冗余驱动消除并联机构位形奇异原理

一般并联机构的雅可比矩阵都是方阵，而冗余驱动并联机构由于输入构件数大于输出构件自由度数，其雅可比矩阵具有非方阵的特殊性。传统的观点认为冗余驱动能够消除奇异，但是没有给出严格的数学意义上的证明和构造冗余驱动的具体方法。从可操作度的角度研究了冗余驱动并联机构的奇异性，最终给出了判别方法。用数学方法证明了冗余驱动可以消除奇异位形，并通过实例给出了具体的构造方法。     

弧齿锥齿轮精加工工艺方法综述

分析弧齿锥齿轮热处理后精加工原理,归纳出各种加工方法的特点和应用范围。为了消除弧齿锥齿轮热处理后的变形,采用珩齿、硬齿面刮削、磨齿、研齿加工工艺。根据以上加工方法特性,介绍了UMC/UMG磨削技术的应用和弧齿锥齿轮的新型加工方法。     

基于非瞬时支链位形设计的并联机构内部奇异消除方法

引入新支链的冗余驱动方法是目前减少或消除并联机构奇异的有效方法,如何确定所引入支链的结构形式、布置方式和最少支链个数是该冗余驱动方法的核心问题,然而关于这些问题至今尚没有系统的理论和方法。依据螺旋理论系统分析并联机构的约束奇异、驱动奇异和支链奇异三种奇异位形,强调位于工作空间内部的约束奇异和驱动奇异位形是对机构性能影响最为严重的位形,提出一种基于非瞬时支链位形设计的并联机构内部奇异消除方法,以3-RPR型、3-RRR型、4-RPTR型、3-RRRT型和3-RPS型等五种典型的并联机构为例,系统阐述该方法的设计过程。结果表明除了动平台和基平面重合的位形以外,该方法能够消除并联机构的其所有内部奇异位形。该成果为解决冗余驱动方法的关键理论问题提供了参考。     

2D 激光雷达和摄像机最小解标定的 多解筛选及参数优化

多解问题是2D激光雷达和摄像机最小解标定方法的热点难题,本文针对多解问题,在最小解标定过程中提出3个改进措施。首先,利用传感器的可视空间约束剔除棋盘格不能被传感器观测的假解。然后,利用边界激光点到边界线段的约束,改进了真解选择的误差评价函数。最后,利用棋盘格边界约束求解平移向量的最小二乘解。实验中进行仿真数据和真实数据测试,结果表明本文方法对比Francisco方法能提高真解命中率和标定精度。当激光点的噪声方差小于20 mm时,本文方法的真解命中率在98%左右,满足实际应用的需求。相对与传统最小解标定方法,本文利用棋盘格边界约束和可视空间约束对多解集合进行筛选,并优化了平移向量,因此有效提高最小解标定方法的性能。     

Design of drives with double-reduction wave gears for servosystems

The design technique of kinematic diagrams of reducers with double-reduction wave gears as the output stage of electromechanical drive. The application of double-reduction wave gear in the electromechanical drive can significantly reduce its dimension specifications and mass while decreasing the load capacity and efficiency.     

Precision balance method for cupped wave gyro based on cup-bottom trimming

The mechanical balance process is the key process to eliminate the quadrature error and improve the performance of the cupped wave gyro.The conventional mechanical balance method for cupped wave gyro based on cup-wall trimming requires high control accuracy of trimming quantity,which increases the production cost and decreases the fabrication efficiency in large extent.However,it is hard to reach the high balance accuracy with the natural frequency split of mHz grade by using the conventional method.In this paper,the lumped mass dynamic model of the cupped wave gyro is built by discretization method,and the effects of different position trimming on the natural frequency are analyzed.It is pointed out that trimming off a tiny quantity of material from cup-wall causes large variation of the natural frequency is the main reason for the low accuracy of the conventional mechanical balance method.Then,a precision balance method for cupped wave gyro based on cup-bottom trimming is presented and the entire procedures of this method are given.The static balance process and dynamic balance process of the precision balance method are simulated by the finite element software.The simulation result shows that the precision balance method based on cup-bottom trimming brings less additional natural frequency split in the static balance process,minimizes the natural frequency split to mHz grade and rectify the angle of mode offset to 0.1° grade in the dynamic balance process,furthermore,the method decreases the requirement for control accuracy of trimming quantity evidently.The research work provides references for structure optimization design and balance process plan of the cupped wave gyro.     

An angular constraints solving approach for assembly modeling based on spherical geometry

In this paper, a novel approach for solving angular constraints based on spherical geometry is presented. This method can determine the orientation of a set of parts given the mating constraints between them with the decoupled property of the angular and distance constraints. The combination of angular constraints can be categorized into two cases: operable and un-operable. The former can be solved efficiently by introducing simple spherical surface reasoning. The latter is solved by employing spherical surface four-linkage mechanism. In this way, the rotation transformation matrix of the dependent rigid body is worked out. This new method has the advantages over numerical approach and symbolic approach of clear geometric solubility, geometric operability, and avoiding simultaneously solving all the constraint equations in the model. Moreover, it is an easy and efficient way to determine whether there exist redundant constraints. The presented algorithm has been successfully implemented in our assembly prototype system, InteVue.     

Nonlinear wave interaction of three Stokes’ waves in deep water: Banach fixed point method

Based on Banach fixed point theorem, a method to calculate nonlinear superposition for three interacting Stokes’ waves is proposed in this paper. A mathematical formulation for the nonlinear superposition in deep water and some numerical solutions were investigated. The authors carried out the numerical study with three progressive linear potentials of different wave numbers and succeeded in solving the nonlinear wave profiles of their three wave-interaction, that is, using only linear wave potentials, it was possible to realize the corresponding nonlinear interacting wave profiles through iteration of the method. The stability of the method for the three interacting Stokes’ waves was analyzed. The calculation results, together with Fourier transform, revealed that the iteration made it possible to predict higher-order nonlinear frequencies for three Stokes’ waves’ interaction. The proposed method has a very fast convergence rate.     

Photothermoplastic recording of contour holograms by means of inverted wave in brillouin scattering

Thermoplastic recording of contour holograms is based on the use of dual-frequency radiation comprising the pump-wave radiation (λ-0.694 μm) and radiation of the wave inverted relative to the pump wave in Brillouin scattering. Two possible arrangements for contour holograms recording are studied: an arrangement with additional amplification of the inverted wave radiation in the laser active medium, and an arrangement with isolation of the optical circuit of the laser from the inverted laser radiation. It is found that the reduced duration of the inverted wave pulse relative to the pump-pulse width, typical of Brillouin scattering, does not cause any loss of sensitivity of the photothermoplastic material. The proposed method of recording contour holograms ensures power stability of the output dual-frequency radiation with a changing frequency interval and makes it possible to study nonstationary objects.     

一种可调式二轴铣刀头架的设计与实现

为降低手术刀柄专用机床的改造成本,设计了一种新型可调式二轴铣刀头架。由于采用了斜齿轮消除间隙机构,有效补偿了调节过程中产生的齿侧间隙。介绍了该装置的结构和工作原理及实现方法,并推导了薄片斜齿轮间加工垫片厚度的计算公式。经实践表明:该装置结构简单、运行平稳,很好地满足了生产要求。     

渐开线齿廓非圆齿轮的变啮合角特性

指出非圆齿轮传动具有变啮合角的特性,并且推导出啮合角的表达式。以椭圆（含高阶椭圆）齿轮及偏心圆齿轮为例,给出啮合角变化的规律及啮合角约束条件。对于椭圆齿轮副,啮合角随着椭圆偏心增大而增大。当偏心率达到相当大的数值时,啮合角成为直角,两齿轮的齿廓脱离接触而推动啮合。这就从理论上解释了非圆齿轮传动中失去啮合现象的原因,同时为传动的设计提供了基础条件。     

Measurement range expansion of continuous wave ultrasonic anemometer

This study was conducted to expand the measurement range of a continuous wave ultrasonic anemometer (CWUA) that uses phase difference measurement. A CWUA has a narrower measurement range than conventional ultrasonic anemometers because it can measure the phase difference up to the half-cycle of the used ultrasonic signals. In this study, a method of expanding the measurable range of the phase difference using a phase delay circuit and a frequency divider was developed. Through experiments, it was found that this method doubled or quadrupled the measurement range when the method was used. Furthermore, an algorithm for determining the validity of the measurement data by comparing them with the previous data was implemented with a wind velocity measurement error of less than ±1 μs to solve the problem caused by the use of the frequency divider and to produce a stable measurement system.     

A study on using deviation function method to reshape a rack cutter

In this paper a method for the modified profile of a rack cutter is presented. The deviation function method is used to reshape a rack cutter. The author proposes a modified geometry of a rack cutter to generate the driving gear of internal gear pairs. Based on the double envelope concept, the driven gear of a set of internal gear pairs can be determined. In this study, the Von-Mises stress analysis of the reshaped internal gear pairs was carried out and the specific phenomena was also investigated. The results show that it is possible to compensate elastic deformation and reduce contact stress between conjugate gear pairs. In addition, according to the tooth contact analysis on the gear pairs, reshaped gears and conventional gears have also been investigated. Computerized design of internal gears using the proposed method and simulation of their meshing and contact stress analysis of asymmetric internal gears has been developed. The developed method is illustrated with numerical examples.     

On the optimal design of multi-speed gear trainsConception optimale des trains d'engrenages aux vitesses multiples

An efficient method for analyzing multi-speed gear trains is presented and used in this paper. This new technique obtains equations for the diameters of all the gears used in the transmission based on information contained in the speed diagram. The form of the equations is such that they can be generated by the computer automatically. Further, the equations are applicable to the general arrangement, the single composite arrangements, and the double composite arrangements. As a result, all of the promising kinematic arrangements possible for a given number of speeds can be easily studied. By promoting different constraints and objective functions, trace-offs between different parameters can easily be examined. The technique is illustrated using a case study of a 9 speed gear train. A multi-parameter optimization technique is used to solve 19 different arrangements for a weighted objective function minimizing volume and maximizing stiffness.