Geometric error analysis of an over-constrained parallel tracking mechanism using the screw theory

This paper deals with geometric error modeling and sensitivity analysis of an overconstrained parallel tracking mechanism. The main contribution is the consideration of overconstrained features that are usually ignored in previous research. The reciprocal property between a motion and a force is applied to tackle this problem in the framework of the screw theory. First of all, a nominal kinematic model of the parallel tracking mechanism is formulated. On this basis, the actual twist of the moving platform is computed through the superposition of the joint twist and geometric errors. The actuation and constrained wrenches of each limb are applied to exclude the joint displacement. After eliminating repeated errors brought by the multiplication of wrenches, a geometric error model of the parallel tracking mechanism is built. Furthermore,two sensitivity indices are defined to select essential geometric errors for future kinematic calibration. Finally, the geometric error model with minimum geometric errors is verified by simulation with SolidWorks software. Two typical poses of the parallel tracking mechanism are selected, and the differences between simulation and calculation results are very small. The results confirm the correctness and accuracy of the geometric error modeling method for over-constrained parallel mechanisms.     

伺服加工平台的综合误差建模与补偿

伺服加工平台的几何误差是影响工件加工形貌精度的重要因素。在多体系统理论的基础上,首先,运用低序体阵列描述伺服平台多体系统的拓扑结构,建立各相邻体间的齐次变换矩阵,构建其综合误差模型;其次,利用雷尼绍测量系统对平台的定位误差、直线度误差、俯仰误差、偏摆误差以及两轴之间的垂直度误差进行辨识,将辨识得到的误差值代入构建的模型得出平台几何综合误差;最后,选择凸锥面、平面、球面3种面型工件补偿试验,对误差模型进行原理性验证。研究表明,经补偿后加工所得3种面型工件表面精度均提高了25%左右,证实了提出的补偿方法可用于伺服加工平台几何误差控制。     

A fault-tolerant triple-redundant voice coil motor for direct drive valves: Design, optimization, and experiment

A direct drive actuator (DDA) with direct drive valves (DDVs) as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor (TRVCM) used for redundant DDVs. The TRVCM features electrical/mechanical hybrid triple-redundancy by securing three stators along with three moving coils in the same frame. A permanent magnet (PM) Halbach array is employed in each redundant VCM to simplify the system structure. A back-to-back design between neighborly redundancies is adopted to decouple the magnetic flux linkage. The particle swarm optimization (PSO) method is implemented to optimize design parameters based on the analytical magnetic circuit model. The optimization objective function is defined as the acceleration capacity of the motor to achieve high dynamic performance. The optimal geometric parameters are verified with 3D magnetic field finite element analysis (FEA). A research prototype has been developed for experimental purpose. The experimental results of magnetic field density and force output show that the proposed TRVCM has great potential of applications in DDA systems.     

基于双捷联算法的POS误差在线标定方法

为了提升位置和姿态测量系统(POS)的精度,结合POS工作过程中典型的匀速直线运动,提出了一种准实时的POS误差在线标定方法。首先设计了基于双捷联算法的在线标定方案,对系统误差方程进行简化处理,求出中时期导航条件下的系统误差状态转移阵。然后根据POS的两段相邻匀速直线运动导航误差,对系统误差参数进行在线标定,并通过可观测性分析得出POS运动与系统误差在线标定效果之间的对应关系。车载试验和飞行试验结果表明,在POS正常遥感作业过程中,本文提出的在线标定方法能够有效提升系统精度。     

压电式微型合成射流多域耦合数值模拟

合成射流器的设计与仿真是优化其性能参数的关键。针对目前合成射流器的计算模型在建立物理模型时存在简化误差而导致仿真精度降低的问题,提出了一种基于多域耦合分析的全流场计算模型。该模型采用通用有限元分析软件ANSYS中的压电耦合单元实现电场 结构场的直接耦合分析,并通过ANSYS与流体仿真软件CFX间的耦合接口完成流场 结构场的同步双向耦合,最终实现了压电式合成射流器真实物理过程的数值模拟。基于此模型对合成射流器的工作过程进行了模拟,并研究了驱动电压和腔体结构参数对喷口速度的影响。结果表明：多域耦合模型能准确模拟合成射流的形成过程,数值模拟与实验结果的变化趋势一致,且相对误差不超过8%,为合成射流器的优化设计及控制提供了理论依据。     

On-line diagnostics of a self-contained flight actuator

A mathematical model describing the dynamics of a self-contained flight control actuator is established. Typical failures of the actuator are defined in the space of the model parameters in the form of a failure pattern library. A diagnostic model of the actuator, intentionally sensitive to particular failures, is defined. A diagnostic procedure, featuring on-line parameter estimation of the diagnostic model, failure detection, and isolation, is proposed. A failure prediction procedure, utilizing trends exhibited by parameter estimates, is formulated. The results are verified by computer simulation     

机器视觉导引系统中摄像机的标定方法

针对无人机(UAV)自主起飞与着陆机器视觉导引系统中摄像机的标定问题,讨论了标定摄像机内参数的重要意义,选定了包含畸变因素的摄像机透视投影模型。采用改进两步法进行摄像机内参数标定,结果中主要参数相对误差均小于1%,位置误差小于0.2像素,证明了所选择模型和标定方法的合理性。分析并验证了影响标定精度的因素,包括模型选择、图像拍摄质量和标定靶精度。针对机器视觉导引的应用条件,基本解决了准确、快速标定摄像机内参数的实际问题。     

高分影像辅助下的航空高光谱严密几何检校方法

 惯性测量单元(IMU)与传感器视准轴的偏心角和偏心矢量是造成航空线阵列高光谱数据几何校正误差的主要原因之一。在分析偏心角与偏心矢量误差来源之后提出该误差由IMU主轴与传感器主轴的角度偏差、测区固定偏差、GPS中心与传感器投影中心相对偏差组成,在此基础上建立了较为严密的检校模型。针对模型解算时需要大量高精度控制点的问题,提出了一种高分影像辅助下的亚像元精度控制点自动提取方法。通过多地区、多传感器高光谱航测实验表明,亚像元精度控制点能有效提高模型解算精度。新检校模型可获得亚像元校正精度,推扫式传感器——应用型机载成像光谱仪(AISA)建模中误差约为0.39个像元,摆扫式传感器——实用型模块化成像光谱仪(OMIS)建模中误差约为0.23个像元,校正后的影像可直接进行拼接。     

基于MEMS陀螺仪辅助的粒子群优化磁力计校正

目前磁力计校正中存在需要采集大量数据、获取良好的初值和已知准确的传感器噪声分布等问题,传统的粒子群优化磁力计校正算法能够解决以上问题,但是该算法只能用于磁力计简化模型,校正其中9个误差参数,造成补偿不准确的问题。该算法借助MEMS陀螺仪建立矢量目标函数,采用随机漂移粒子群优化算法估计磁力计12个误差参数,具有较强的全局搜索能力和动态适应性。经过仿真与实测实验表明,该算法在磁力计绕其任意2个单轴不完整旋转1周即可实现校正,并且能够在磁场变化情况下保持精度,相比于传统算法补偿精度高、操作简单。     

Extrinsic calibration of a laser displacement sensor in a non-contact coordinate measuring machine

In order to implement 3D scanning of those complicated parts such as blades in the aviation field,a non-contact optical measuring system is established in the paper,which integrates a laser displacement sensor,a probe head,the frame of a coordinate measuring machine (CMM),etc.As the output of the laser sensor directly obtained possesses the 1D length of the laser beam,it needs to determine the unit direction vector of the laser beam denoted as (l,m,n) by calibration so as to convert the 1D values into 3D coordinates of target points.Therefore,an extrinsic calibration method based on a standard sphere is proposed to accomplish this task in the paper.During the calibration procedure,the laser sensor moves along with the motion of the CMM and gathers the required data on the spherical surface.Then,both the output of the laser sensor and the grating readings of the CMM are substituted into the constraint equation of the spherical surface,in which an over-determined nonlinear equation group containing unknown parameters is established.For the purpose of solving the equation group,a method based on non-linear least squares optimization is put forward.Finally,the system after calibration is utilized to measure the diameter of a metallic sphere 10 times from different orientations to verify the calibration accuracy.In the experiment,the errors between the measured results and the true values are all smaller than 0.03 mm,which manifests the validity and practicality of the extrinsic calibration method presented in the paper.     

面向飞机装配的机器人定位误差和残差补偿

工业机器人由于其高柔性和低成本而被越来越多地应用到飞机自动钻铆系统中,使用精度补偿有效地提高机器人的绝对定位精度是保证产品质量的关键,为进一步提高机器人末端定位精度,提出了基于误差相似度的残差补偿方法。首先使用基于运动学参数标定的方法辨识出机器人的几何参数误差,再利用基于误差相似度的方法对残余误差进行估计,实现对机器人的误差和残差的补偿。以工业机器人KUKA KR-30 HA为对象所进行的试验验证表明,机器人的绝对定位精度平均值由补偿前的0.879mm经过定位误差补偿后提高到0.194mm,经过残差补偿后进一步提高到0.141mm,经过定位误差和残差补偿后的机器人最大误差由1.492mm降低为0.296mm,最大绝对定位精度误差降低了80.16%。该方法能有效地补偿参数辨识后遗留的残差,进一步提高机器人的定位精度。     

Calibration method of quartz accelerometer on dynamic centrifuge

This paper proposes a novel method for calibrating error coefficients of the quartz accelerometer faster on the dynamic centrifuge, which can generate a continuous dynamic acceleration excitation. Firstly, working principle and structure of the dynamic centrifuge are analyzed, the error sources and the uncertainty of the dynamic centrifuge are expounded, and relevant coordinate systems are established. Then, according to the characteristics of the input specific forces and the propagating method...     

Energy-saving and accurate motion control of a hydraulic actuator with uncertain negative loads

Pump controlled hydraulic actuators are wildly used in the aerospace industry owing to the advantages of energy-saving and integrated configurations. Negative loads may occur to actuators due to external force loads or the inertial force when the actuator decelerates significantly. Uncertain negative load working conditions may cause cavitation, actuator vibration, and even instability to the motion control if the actuator is without sufficient meter-out damping. Various types of hydraulic configuration schemes have been proposed to deal with negative loads of hydraulic actuators. However, few of them can simultaneously achieve energy saving and high control accuracy. This study proposes an energy-saving and accurate motion tracking strategy for a hydraulic actuator with uncertain negative loads. The actuator’s motion is driven by a servomotor pump, which gives full play to the advantage of energy-saving. The meter-out pressure is controlled by proportional valves to provide the optimized meter-out damping. The nonlinear adaptive robust control law is designed, which guarantees the control stability and achieve high tracking accuracy. An integrated direct/indirect adaptation law obtains satisfactory parameter estimations and model compensation for asymptotic motion tracking. Comparative experiments under different working conditions were performed to validate the advantages of the proposed control strategy.     

Systematic Geometric Error Modeling for Workspace Volumetric Calibration of a 5-axis Turbine Blade Grinding Machine

A systematic geometric model has been presented for calibration of a newly designed 5-axis turbine blade grinding machine. This machine is designed to serve a specific purpose to attain high accuracy and high efficiency grinding of turbine blades by eliminating the hand grinding process. Although its topology is RPPPR (P: prismatic; R: rotary), its design is quite distinct from the competitive machine tools. As error quantification is the only way to investigate, maintain and improve its accuracy, calibration is recommended for its performance assessment and acceptance testing. Systematic geometric error modeling technique is implemented and 52 position dependent and position independent errors are identified while considering the machine as five rigid bodies by eliminating the set-up errors of workpiece and cutting tool. 39 of them are found to have influential errors and are accommodated for finding the resultant effect between the cutting tool and the workpiece in workspace volume. Rigid body kinematics techniques and homogenous transformation matrices are used for error synthesis.     

基于干扰观测器的四旋翼无人机离散时间容错控制

为了飞行控制方案便于在计算机上实现，针对具有外部干扰和执行器加性故障的四旋翼无人机（UAV）角度运动方程，给出一种基于干扰观测器的离散时间跟踪控制方案。通过设计离散时间干扰观测器抑制外部干扰和执行器故障的不利影响，并结合干扰观测器设计离散时间控制器。通过数值仿真验证了基于干扰观测器的离散时间容错控制方案的有效性。仿真结果表明，设计的离散控制器能够保证外部干扰和执行器故障综合作用下的四旋翼UAV系统跟踪控制性能。     

基于速度误差的系统级标定方法

为降低捷联惯导系统误差参数标定过程对高精度转台的要求,提出一种基于速度误差的系统级标定方法。在惯性器件误差参数模型和捷联惯导系统误差方程的基础上,以惯导系统转动前后的导航速度误差为观测量,编排设计旋转方案,对加速度计和陀螺的误差参数进行拟合标定。仿真结果表明,与传统的分立式标定方法相比,在保证标定精度的同时,对高精度转台的要求更低,可应用于外场标定。     

IABC: An iteratively automatic machine learning boosted hand-eye calibration method for laser displacement sensor

An on-machine measuring (OMM) system with a laser displacement sensor (LDS) is designed for measuring free-form surfaces of hypersonic aircraft’s radomes. To improve the measurement accuracy of the OMM system, a novel Iteratively Automatic machine learning Boosted hand-eye Calibration (IABC) method is proposed. Both the hand-eye relationship and LDS measurement errors can be calibrated in one calibration process without any hardware changes via IABC. Firstly, a new objective function is derived, containing analytical parameters of the hand-eye relationship and LDS errors. Then, a hybrid calibration model composed of two kernels is proposed to solve the objective function. One kernel is the analytical kernel designed for solving analytical parameters. Another kernel is the automatic machine learning (AutoML) kernel designed to model LDS errors. The two kernels are connected with stepwise iterations to find the best calibration results. Compared with traditional methods, hand-eye experiments show that IABC reduces the calibration RMSE by about 50%. Verification experiments show that IABC reduces the measurement deviations by about 25%-50% and RMSEs within 40%. Even when the training data are obviously less than the test data, IABC performs well. Experiments demonstrate that IABC is more accurate than traditional hand-eye methods.     

MEMS加速度计组合在分度头上的标定方法

提出了一种在分度头上标定MEMS加速度计组合的测试方法,该方法可以标定出加速度计组合的刻度系数误差、加速度计零偏、三轴不正交度误差、安装误差角,同时可以分离出分度头转位机构角位置误差.首先通过建立一系列坐标系,推导了重力加速度在加速度计敏感轴的分量表达式.然后采用谐波分析法给出了误差标定方程,利用最小二乘法和Kalman滤波器进行误差参数的估计,并对估计结果进行了对比分析.最后通过三次独立实验标定结果的重复性和残差验证了该方法的正确性.     

一种双轴旋转惯性导航系统的重要参数快速自标定方法

为了提高双轴旋转惯导重要参数标定的快速性和精度,提出一种快速自标定方法。通过设置不同的标定路径可以在10 min内完成陀螺和加速度计的零偏以及标度因数误差的标定。该方法利用基于姿态误差观测的卡尔曼滤波完成陀螺零偏的估计。通过六位置翻滚并以速度误差作为观测量进行卡尔曼滤波,完成加速度计的零偏及标度因数误差的标定。使天向陀螺绕方位轴旋转4周,使水平陀螺绕水平轴转动4周,通过计算旋转前后的姿态误差完成陀螺标度因数误差的估计。仿真和试验结果表明,该方法可以实现双轴旋转惯导重要参数10 min内完成自标定,且具有较高的精度。     

Positioning error compensation for parallel mechanism with two kinematic calibration methods

Compared with serial mechanisms, the parallel mechanism (PM) theoretically exhibited higher positioning accuracy, dynamic performance, strength-to-weight ratio, and lower manufacturing cost, but they had not been widely used in the practical application. One key issue, positioning accuracy, which directly affected their performance and was greatly influenced by the errors of kinematic structure parameters was analyzed. To effectively enhance the positioning precision of PMs, a novel modeless kinematic calibration method, namely the split calibration, was presented and its compensation effect of the positioning error was comprehensively compared with that of an integrated method on two different types of PMs. A strange phenomenon-correct and incorrect identified results were derived from two different PMs by the same integrated method, respectively-which had not been reported yet was discovered, and the origin of it was revealed utilizing numerical simulations. Finally, respective merits and drawbacks of these two methods obtained in this paper provided underlying insights to guide the practical application of the kinematic calibration for PMs.