Error Analysis and Accuracy Assessment of GPS Absolute Velocity Determination without SA

Error sources which decrease the accuracy of GPS in absolute velocity determination have been changed since SA was turned off. Firstly, quantities of all kinds of error sources that influence velocity deter-mination are analyzed. The potential accuracy of GPS absolute velocity determination is derived from both theory and field GPS data simulation. After that, two tests were carried out to evaluate the performance of GPS absolute velocity determination in the case of a static and an airborne GPS receiver and INS (Inertial Navigation System) instrument in kinematic mode. In static mode, the receiver velocity has been estimated to be several mm/s with the carrier-phase derived Doppler measurements, and several cm/s with the receiver generated Doppler measurements. In kinematic mode, GPS absolute velocity estimates are compared with the synchronized measurements from the high accuracy INS. The root mean square statistics of the velocity discrepancies between GPS and INS come up to dm/s. Moreover, it has a strong correlation with the accel-eration or jerk of the aircraft.

A novel method to predict static transmission error for spur gear pair based on accuracy grade

This paper proposes a novel method to predict the spur gear pair’s static transmission error based on the accuracy grade,in which manufacturing errors(MEs),assembly errors(AEs),tooth deflections(TDs)and profile modifications(PMs)are considered.For the prediction,a discrete gear model for generating the error tooth profile based on the ISO accuracy grade is presented.Then,the gear model and a tooth deflection model for calculating the tooth compliance on gear meshing are coupled with the transmission error model to make the prediction by checking the interference status between gear and pinion.The prediction method is validated by comparison with the experimental results from the literature,and a set of cases are simulated to study the effects of MEs,AEs,TDs and PMs on the static transmission error.In addition,the time-varying backlash caused by both MEs and AEs,and the contact ratio under load conditions are also investigated.The results show that the novel method can effectively predict the range of the static transmission error under different accuracy grades.The prediction results can provide references for the selection of gear design parameters and the optimization of transmission performance in the design stage of gear systems.

Research on Transmission Accuracy Characteristic Analysis of RV Reducer

The accuracy of RV reducer transmission is mainly affected by the transmission accuracy. Taking the high precision RV-80E reducer as the research object, aiming at its structural characteristics, the rigid-flexible coupling model of RV reducer is established by using ADAMS multi-body dynamics simulation software, and the correctness of the model is verified. At the same time, the rigid-flexible coupling model is used to design several groups of simulation prototypes with different errors, and the influence of different error factors on the transmission accuracy of the whole machine is analyzed by simulation. Finally, through different error factors, it is concluded that the error combination of positive equidistance+negative offset or negative equidistance+positive offset can effectively reduce the influence of transmission error on the transmission accuracy of the whole machine.

Design of Pinion Machine Tool-settings for Spiral Bevel Gears by Controlling Contact Path and Transmission Errors

This paper proposes a new approach to design pinion machine tool-settings for spiral bevel gears by controlling contact path and transmission errors. It is based on the satisfaction of contact condition of three given control points on the tooth surface. The three meshing points are controlled to be on a predesigned straight contact path that meets the pre-designed parabolic function of transmission errors. Designed separately, the magnitude of transmission errors and the orientation of the contact path are subjected to precise control. In addition, in order to meet the manufacturing requirements, we suggest to modify the values of blank offset, one of the pinion machine tool-settings, and redesign pinion ma- chine tool-settings to ensure that the magnitude and the geometry of transmission errors should not be influenced apart from minor effects on the predesigned straight contact path. The proposed approach together with its ideas has been proven by a numerical example and the manufacturing practice of a pair of spiral bevel gears.

Separation of Comprehensive Geometrical Errors of a 3-DOF Parallel Manipulator Based on Jacobian Matrix and Its Sensitivity Analysis with Monte-Carlo Method

Parallel kinematic machines （PKMs） have the advantages of a compact structure,high stiffness,a low moving inertia,and a high load/weight ratio.PKMs have been intensively studied since the 1980s,and are still attracting much attention.Compared with extensive researches focus on their type/dimensional synthesis,kinematic/dynamic analyses,the error modeling and separation issues in PKMs are not studied adequately,which is one of the most important obstacles in its commercial applications widely.Taking a 3-PRS parallel manipulator as an example,this paper presents a separation method of source errors for 3-DOF parallel manipulator into the compensable and non-compensable errors effectively.The kinematic analysis of 3-PRS parallel manipulator leads to its six-dimension Jacobian matrix,which can be mapped into the Jacobian matrix of actuations and constraints,and then the compensable and non-compensable errors can be separated accordingly.The compensable errors can be compensated by the kinematic calibration,while the non-compensable errors may be adjusted by the manufacturing and assembling process.Followed by the influence of the latter,i.e.,the non-compensable errors,on the pose error of the moving platform through the sensitivity analysis with the aid of the Monte-Carlo method,meanwhile,the configurations of the manipulator are sought as the pose errors of the moving platform approaching their maximum.The compensable and non-compensable errors in limited-DOF parallel manipulators can be separated effectively by means of the Jacobian matrix of actuations and constraints,providing designers with an informative guideline to taking proper measures for enhancing the pose accuracy via component tolerancing and/or kinematic calibration,which can lay the foundation for the error distinguishment and compensation.

Design and Accuracy Analysis of a Metamorphic CNC Flame Cutting Machine for Ship Manufacturing

The current research of processing large size fabrication holes on complex spatial curved surface mainly focuses on the CNC flame cutting machines design for ship hull of ship manufacturing. However, the existing machines cannot meet the continuous cutting requirements with variable pass conditions through their fixed configuration, and cannot realize high-precision processing as the accuracy theory is not studied adequately. This paper deals with structure design and accuracy prediction technology of novel machine tools for solving the problem of continuous and high-precision cutting. The needed variable trajectory and variable pose kinematic characteristics of non-contact cutting tool are figured out and a metamorphic CNC flame cutting machine designed through metamorphic principle is presented. To analyze kinematic accuracy of the machine, models of joint clearances, manufacturing tolerances and errors in the input variables and error models considering the combined effects are derived based on screw theory after establishing ideal kinematic models. Numerical simulations, processing experiment and trajectory tracking experiment are conducted relative to an eccentric hole with bevels on cylindrical surface respectively. The results of cutting pass contour and kinematic error interval which the position error is from -0.975 mm to ＋0.628 mm and orientation error is from -0.01 rad to ＋0.01 rad indicate that the developed machine can complete cutting process continuously and effectively, and the established kinematic error models are effective although the interval is within a ＇large＇ range. It also shows the matching property between metamorphic principle and variable working tasks, and the mapping correlation between original designing parameters and kinematic errors of machines. This research develops a metamorphic CNC flame cutting machine and establishes kinematic error models for accuracy analysis of machine tools.

Development of analysis model for geometric error in turning processes

A finite element model was established for analyzing the geometric errors in turning operations and a two-step analyzing process was proposed. In the first analyzing step, the cutting force and the cutting heat for the cutting conditions were obtained using the AdvantEdge. Also, the deformation of a workpiece was estimated in the second step using the ANSYS. The deformation was analyzed for a 150 mm-long workpiece at three different measuring points, such as 10, 70 and 130 mm from a reference point, and the amounts of the deformation were compared through experiments. /n the results of the comparison and analysis, the values obtained from these comparison and analysis represent similar tendencies. Also, it is verified that their geometric errors increase with the increase in temperature. In addition, regarding the factors that affect the deformation of a workpiecc, it can be seen that the geometric error in the lathe is about 15%, the error caused by the cutting force is about 10%, and the deformation caused by the heat is about 75%.

Study on Wheel and Workpiece Position Error Influence on Surface Shape Accuracy during Ceramic Ball Grinding

The reasons for bringing surface accuracy error in ultra-precision grinding ceramic ball joint were analyzed,and the influences wheel position error and shaft run-out error on the ball joint surface accuracy were discussed.Through establishing three-dimensional grinding model,the mathematical relationship between the position error and surface accuracy was derived,and the distance from any point on spherical surface to the ideal center was calculated when position error existed,and a precise surface shape was got,and theoretical support was provided to improve the surface accuracy during the grinding process.Using self-developed ultraprecision grinding machine to do the ceramic ball grinding experiment,the surface accuracy PV value of ceramic spherical joint is 4.8μm.

Research on Influence Mechanism of Transmission Accuracy for Harmonic Drive Mechanism Considering Multi-factor Coupling

The influence mechanism of transmission accuracy for harmonic drive mechanism considering multi-factor coupling was studied. According to analysis of influence factors of transmission accuracy for harmonic drive mechanism, it was obtained that the transmission errors of harmonic drive mechanism include processing errors and installation errors. The transmission error is produced by eccentric vector, it directly affects the rotation angle of output shaft and it makes harmonic drive mechanism produce backlash. Then analyze the movement error caused by the rigid wheel machining error, the flexible wheel machining error, the assembly error of the rigid wheel and the flexible wheel, the wave generator component, and the comprehensive expression method of motion error generated by each error source was obtained. The performance test device of space drive mechanism was used to test, and the law of the transmission accuracy of harmonic drive mechanism with temperature, speed and assembly clearance was obtained. The test results show that the transmission accuracy of harmonic drive mechanism decreases with increasing temperature, and the speed has little effect on the transmission accuracy of harmonic drive mechanism;the assembly quality has a significant impact on harmonic drive accuracy.

General design principle of artillery for firing accuracy

In this paper,based on the topological description method,the kinematic and dynamic equations of the projectile flight and projectile-artillery coupling system during the whole process of firing are constructed.The factors that can affect the projectile burst points,namely the state parameters of the projectile on the muzzle and state parameters of the barrel muzzle,as well as the factors that affect the barrel muzzle state parameters,are analyzed.On this basis,the design principle of artillery firing accuracy is proposed.The error analysis and the corresponding inverse problem,the extraction method of key parameters affecting artillery implicated motion,the conformal and control method of rotating band are analyzed and presented.Finally,the presented method is verified through a vehicle mounted howitzer case,and the muzzle state parameter interval is obtained meeting the given firing accuracy.In addition,the sensitivity analysis of artillery parameters shows that the less the correlation between the parameters and the barrel,the less the influence on the projectile implicated motion.The analysis of the coupling effect between rifling and the rotating band shows that the uniform rifling is the optimal form for the conformal of the rotating band during firing.

考虑多源误差影响的谐波减速器传动误差建模与分析

为解决现有谐波减速器传动误差建模方法的不足,提出一种考虑装配误差、齿面误差的综合误差建模方法。该方法首先建立装配误差和齿面误差数学模型,并进行误差影响参数分析。其次,测量实验样机装配偏心量和歪斜角度,基于模型得到对应偏心误差、歪斜误差模型理论值,齿面加工误差幅值按一般加工工况大小代入模型,得到对应加工误差模型理论值;然后,分别进行500 h、1500 h、3000 h时长的磨损实验,磨损后进行齿面形貌扫描和数据分析,得到对应的齿面形貌参数,基于模型得到对应的磨损误差模型理论值。最后,综合考虑多源误差影响,设置3组同型号样机,进行传动误差实验。实验结果表明:考虑装配偏心、歪斜和齿面加工等影响因素,传动误差的实验测量值与模型理论值误差在1.7~3.3%之间;综合考虑装配偏心、歪斜、齿面加工、齿面磨损等影响因素,在磨损500 h、1500 h、3000 h后传动误差的实验测量值与模型理论值误差分别在-3.45~2.07%、-5.88~-2.94%、1.33~5.33%之间。

计算全息检测技术的精度溯源研究现状分析(内封面文章)

随着光学系统性能的要求越来越高,非球面、自由曲面等复杂光学曲面能够提升系统的成像性能,因此提升复杂光学曲面的检测精度极为重要。干涉检测是测量复杂光学曲面的重要手段,其中计算全息检测法(Computer Generated Hologram,CGH)作为干涉检测中的一种,因其精度高和设计自由度大等优点得到了广泛的应用。但是在CGH检测复杂曲面的过程中存在的各类误差会影响波前检测的精度。文中首先介绍了计算全息法的检测精度现状,其次归纳总结了造成计算全息法误差的主要因素。分别介绍了不同误差的产生原理、影响效果、相对应标定补偿方法及适用情景和优缺点;并介绍了基于CGH占空比与线条位置误差的调研现状分析以及现有的研究方法;最后对计算全息法检测的精度溯源和精度提升研究趋势进行了展望。

一种基于光电自准直法的装甲战车原位校炮系统

为了解决当前装甲战车校炮时空受限、精度低、过程复杂、无法现场原位校炮等问题,提出了一种基于光电自准直法的装甲战车原位校炮系统。基于镜炮一致性原理,设计校炮装置的机械结构;构建平行光管及其内部光路结构,利用光学自准直原理实现模拟无穷远处虚拟靶标;建立校炮装置的误差模型,通过对误差模型进行分析与合成以评定校炮装置参数的精确性,确定装置允许的最大误差值;通过实验对系统性能进行了实际测试与验证。结果表明:利用所设计的误差模型,其校准误差最大不超过传统校炮方式的60%,且时间缩短了一半以上,符合设计要求,具有较强的稳定性。装甲战车原位校炮系统可应用于装甲战车校炮工作,提高校炮的效率及精度、实现现场原位校准,为装甲战车校炮提供了一种新方法、新思路。

基于新一代几何技术规范的装配误差建模

针对由于公差设计不合理而导致的服役于复杂工况的机械装备性能下降等问题,提出一种综合考虑制造与装配误差的机械产品装配精度分析方法。该方法首先利用有限元分析机械装备零部件装配误差导致的变形,并提取发生形变的关键特征面;然后基于新一代几何技术规范(GPS)将特征面的变形转化为尺寸与形位公差数据,并与设计公差进行叠加,实现变形—误差—公差的转换;随后基于雅可比旋量理论,构建综合考虑制造与装配误差的公差分析模型支撑机械装备的公差精量化设计;最后以某型机载作动筒为工程应用对象,对比分析了是否考虑受力变形条件下装配精度分析的结果差异,结果显示该方法相较于原有方法具有更高的计算准确性,能为精密机械产品精度设计提供更加准确的指导。

发动机舱软管系检测系统精度分析与仿真

针对发动机舱软管系振动干涉检测系统中工业机器人基坐标系和发动机坐标系不统一的问题,基于空间坐标转换原理提出了多目标归一化算法。在模拟振动时,该系统由于试验操作误差,不能准确运动到设定位置的精度,基于蒙特卡罗模拟的数值仿真方法分析检测系统的精度。以多目标归一化算法为基础构建精度模型,使用计算机进行蒙特卡罗模拟试验分析各操作环节对系统精度的影响,并从操作方面提出提高系统精度的补偿措施。仿真结果表明:车身标定环节误差放大倍数为78,测量块标定环节误差放大倍数为22,末端执行器(TCP)标定环节误差放大倍数为20,采取对同一点多次测量的方法可以提高试验成功率。

机械加工中有限元技术的计算精度优化研究

有限元模型技术被广泛应用于机械加工领域,其也是实现数字控制与现代加工的核心理论技术,得到了各领域研究者的广泛关注与深入探讨。基于有限元模型的计算仿真模拟技术能够大幅提升机械加工制造的精度,大量的机械加工零件实验也为有限元模型提供详细的数据参考。文中通过总结有限元分析技术的研究历史,分析归纳了当前有限元分析技术中精度优化的核心策略及其不足之处,展望了在机械加工过程中有限元分析技术的未来发展方向。

无人机倾斜测量在大比例尺地形图绘制中的应用及精度分析

无人机倾斜测量技术应用于大比例尺地形图绘制中不仅可以提高工作效率、节约人力物力成本,更能克服人工测量受地形限制的不足。为了探究无人机倾斜摄影测量多个维度精度,在无人机航测系统基本原理分析基础上,研究了航测系统误差来源和误差评定标准,通过以某村庄航空摄影测量进行试验,对无人机倾斜测量的点位精度、高程精度、长度精度和面积精度进行了系统分析。结果表明:无人机倾斜测量的多个维度精度均满足要求,该技术方法适用于大比例尺地形图绘制。

一种提高多基地天波雷达目标定位精度的方法

分析了引起多基地天波雷达目标定位误差的原因,对测距误差和定位模型误差两种影响定位精度的主要因素进行了仿真计算。比较发现,定位误差主要来源于多站定位模型,由定位模型中电离层虚高的假定条件与实际不符所引起。给出了减小模型误差,提高定位精度的方法。以某多基地天波雷达系统为对象,对修正后的定位模型进行了不同误差条件下的模拟测试,并利用系统对目标船的跟踪数据进行了验证。结果表明,模型改进后目标定位的精度得到了较大程度的提高。

北斗系统GEO卫星伪距多路径误差改正

北斗系统地球静止轨道(GEO)卫星因相对于地面近似静止,其多路径误差相对于其他类型较为严重,且表现出系统波动现象。为提升定位精度,本文在GEO卫星伪距多路径误差特征研究的基础上,采用奇异谱分析方法对其进行修正,并通过伪距单点定位(SPP)验证伪距多路径误差修正效果。选取测站CUT0连续10d的静态观测数据进行修正试验。研究发现,GEO卫星伪距多路径误差序列表现出较强的天重复性,且多路径误差中的系统误差项越大,重复性也越强;在运用奇异谱分析方法修正GEO卫星伪距多路径误差各系统误差项后,多路径组合(MP)观测值和SPP的定位精度均有一定程度提升。

样品尺寸对脉冲穿透法声速测量误差的影响

岩心的声速测量能够提供关键的储层地质信息,对储层评价和地质模型构建具有实际应用价值。脉冲穿透法是一种常用的声速测量方法,但它要求样品尺寸远大于波长(约10倍)。当特殊场景如需在测井信号主频8~20 kHz下测量样品声速时,被测样品长达数米,不仅制备困难,还存在声波信号衰减大的问题。关于试样尺寸能否缩小或能缩小到什么程度的定量研究很少见到公开报道。该文将数值模拟和实验测量相结合,系统定量地研究了圆柱状样品长度及直径与波长之间的比值对脉冲穿透法声速测量精度的影响。研究表明:为确保脉冲穿透法声速测量的准确性,建议样品沿传播方向上的长度不低于4倍声波波长,横向尺寸不低于2倍波长。研究结果突破了传统脉冲穿透法要求样品尺寸远大于波长的限制,为优化声速测量方法和提高测量精度提供了理论支持。