A multilevel calibration technique for an industrial robot with parallelogram mechanism

This paper presents a multilevel calibration technique for improving the absolute accuracy of an industrial robot with a parallelogram mechanism (ABB IRB2400). The parallelogram structural error is firstly modeled based on the partial differential of the position function of a general four-bar linkage and the linearization of the position constraints of the parallelogram mechanism, the model coefficients are fitted from experimental data. Secondly, an absolute kinematic calibration model is established and resolved as a linear function of all the kinematic parameters, as well as the base frame parameters and tool parameters. Finally, contrary to most other similar works, the robot joint space (rather than Cartesian space) is divided into a sequence of fan-shaped cells in order to compensate the non-geometric errors, the positioning errors on the grid points are measured and stored for the error compensation on the target points. After the multilevel calibration, the maximum/mean point positioning errors on 284 tested configurations (evenly distributed in the robot common workspace) are reduced from 1.583/0.420 mm to 0.172/0.066 mm respectively, which is almost the same level as the robot bidirectional repeatability.     

A two-step calibration methodology of multi-actuated mechanical servo press with parallel topology

We present a two-step calibration methodology of multi-actuated mechanical press with parallel topology and illustrate the method with a case study of a dual-actuated servo press with parallel topology. The kinematic model of the servo press is established firstly. From the total differentials of the kinematic equations, the error sensitivity matrix is obtained to find out linear dependent parameters and the effects of kinematic parameters on the press accuracy are studied. It is found that the press mechanism has the advantage that the press accuracy at the working area is less sensitive to the kinematic parameter errors. The experiment is carried out to measure the motions of the moving platform and slider. By the kinematic error model, the kinematic parameters of the active and passive chains are identified, respectively. Experimental results show that the accuracy of the servo press improves by 82% after kinematic calibration.     

基于病态参数分离的机器人运动学标定测量构型优化

针对一种高灵巧性机器人及其连杆参数高敏感性与高定位精度需求,为解决机器人运动学标定随机测量构型存在绝对 定位精度低、参数辨识效果及标定结果鲁棒性较差的问题,提出一种病态参数分离与 DETMAX-改进差分进化(DETMAX-IDE) 算法的机器人运动学标定测量构型分步优化方法。 首先,建立机器人位置误差模型。 其次,建立一种可观性综合指标,评价不 同机器人标定测量构型的总体可观测性和灵敏度。 最后,分离机器人运动学位置误差模型的病态参数,建立测量构型优化目标 函数和约束条件,提出一种基于 DETMAX 算法与改进差分进化算法结合的分步迭代优化算法(简称为 DETMAX-改进差分进化 算法,简写为 DETMAX-IDE 算法),开展机器人运动学标定测量构型分步迭代优化。 通过机器人运动学标定仿真与实验,验证 了所提方法的有效性。 实验结果表明,与随机测量构型相比,所提方法对应的机器人绝对定位精度的平均值和均方差分别降低 了 62. 09% 和 62. 45% 。     

基于球杆仪检测信息的并联机构运动学标定

由于并联构型装备难于实现全闭环反馈控制,使运动学标定成为一项具有显著经济价值并能非常有效提高并联构型装备精度的手段,运动学标定通常包括误差建模、测量、辨识和补偿4个环节。基于以上因素,以5自由度混联机械手TriVariant为对象,研究一种基于球杆仪检测信息的运动学标定方法。首先建立球杆仪测量值与影响末端可补偿位姿误差的几何误差源的映射关系,并给出可辨识条件。在此基础上,以误差参数辨识矩阵条件数为评价指标,探讨合理设置球杆仪安装位置和数目的方法。最后,计算机仿真和试验验证了所提出方法的可行性和有效性,并指出仍然需要解决的若干问题。     

基于视觉的三自由度微动平台输入耦合研究

为了提高精密微动平台的定位精度,提出了一种计算微动平台输入耦合位移系数的实验方法.构建显微视觉测量系统,以柔顺铰链式平面三自由度微动平台为研究对象,实时跟踪测量微动平台输入位移；对平台与图像之间的坐标系进行标定,有效提高了平台的输入位移和耦合位移的测量精度.实验表明,基于显微视觉的测量结果与Ansys模拟仿真结果相符,对微动平台的分析与设计具有一定的参考意义.     

Study on optimal calibration configurations of a parallel type machining center under a single planar constraint

This paper examines the parameter observability of a calibration system that consrains a mobile platform to a planar table to take the calibration data. To improve the parameter observability, we find the optimal configurations providing the calibration with maximum contribution. The QR-decomposition is used to compute the optimal configurations that maximize the linear independence of rows of an observation matrix. The calibration system is applied to the parallel type manipulator constructed for a machining center. The calibration results show that all the necessary kinematic parameters assigned in a Stewart-Gough platform are identifiable and convergent to desirable accuracy.     

Kinematic calibration of gantry hybrid machine tool based on estimation error and local measurement information

This paper presents the kinematic calibration of a four degrees-of-freedom (DOF) hybrid machine tool based on a novel planar 3-DOFs parallel mechanism and a long movement of the worktable. Closed-form solutions are developed for both the inverse and direct kinematics about the parallel mechanism. The error model is built and the mechanism accuracy is investigated. Two types of kinematic calibration method are proposed by a simple measurement device. The first type of calibration method is based on estimation error, and can easy improve the machine tool accuracy quickly by estimating the error trends. The second type of kinematic calibration method is based on local measurement information, which includes the position errors and does not include the pose errors of the machine tool. The calibration tests showed the effectiveness of the calibration methods, which can be useful for the similar types of parallel machine tool.     

Kinematic calibration analysis of 3SPS + 1PS bionic parallel test platform for hip joint simulator

As the key component of the parallel hip joint simulator, 3SPS + 1PS bionic parallel test platform owns four degrees of freedom including three rotations and one translation. When the moving platform stays at a given translation position, the parallel manipulator can represent three-dimensional rotating gait motions of the hip joint for the purpose of evaluating the friction characteristics of biological materials. Because of the manufacturing and assembling errors, the actual structure parameters of the parallel manipulator are not more accurate than the theoretical values and its reduced simulation accuracy will bring the uncertain evaluation. So in order to improve the precisions in the design, manufacture and assembly of the parallel manipulator, it is necessary to calibrate the kinematic parameters. Considering the structural characteristics of the parallel manipulator, its error model and the corresponding compensation method are established based on the complete differential-coefficient theory. According to the constant values of two orientation angles, the orientation residual matrix is constructed by adopting the incomplete measurement method and the forward kinematics functions, so its cost function can be defined. The iterative algorithm based on the least square method is applied to identify the structure parameters and obtain their optimal solutions, and then the actual kinematic calibration process is simulated by numerical method. The simulation results show that the comprehensive orientation error after calibration is greatly decreased, and the effectiveness of the calibration method is validated.     

基于CPA方法的串联工业机器人运动学标定精度试验研究

几何参数误差是影响工业机器人定位精度的主要误差源,约占总误差的80％以上.基于圆点分析法(circle points analysis,CPA)所标定的几何参数与机器人的实际结构相关,并且能够将几何参数误差与其他误差源解耦.研究表明CPA方法的测量策略对其标定精度具有较大影响.针对基于CPA方法的串联工业机器人运动学标...     

低成本柔顺板式精密定位平台的理论与试验

基于柔顺薄板的弹性变形原理,提出一种低成本、整体式柔顺精密定位平台的设计方法。设计一种平板弹簧机构,使平台能够在较低精度驱动器的驱动下获得高精度的位移输出,从而大幅度降低精密定位平台的成本。建立平台的刚度模型,分析驱动器的精度与平台的定位精度之间的相互关系。最后,分析加工误差对平台定位精度的影响,得出影响定位精度的关键结构参数。通过试验测试,得出驱动器的输入位移和精度分别为4 mm和10m,平台的输出位移和精度分别为9 m和40 nm,线性度为0.33,从而验证了该设计方法的正确性。该平台结构紧凑,成本低,具有很好的性价比,应用前景广阔。     

Research on surface normal measurement and adjustment in aircraft assembly

Drilling and riveting are commonly used in aircraft panel assembly process. Due to the fixture positioning error and the deformation of workpiece, the real position and orientation of the workpiece as well as its 3D geometry at the drilling position varies from the nominal CAD model, which would cause an unfavorable impact on assembly quality. Therefore, surface normal measurement and adjustment at the drilling position is of great importance. In this paper, a fast and effective non-contact measurement method for normal vector and height of moderately curved surfaces is accomplished by four laser displacement sensors, and a dedicated NC machine tool is also developed for normal adjustment. Firstly, a novel sensor calibration method based on laser tracker is introduced, which can acquire the sensors’ position and orientation in Tool Coordinate System (TCS) at the same time. The normal vector at hole position is calculated by cross product of any two non-parallel vectors constructed by the four laser projection points on the panel surface. Secondly, the kinematic model of the machine tool is established to calculate the adjustment of each axis of the machine tool with the Homogeneous Transformation Matrix (HTM). Besides, an innovative method to identify the distance of two rotary centers based on two laser interferometers is proposed. Finally, a series of experiments are conducted to validate the feasibility of the proposed method. The results show that the angle deviation can be reduced to less than 0.5° after adjustment, while the accuracy of the surface height is ±0.04 mm.     

悬臂式掘进机视觉位姿检测系统外参标定方法

当前巷道掘进过程中高粉尘、低照度等因素严重影响外参标定精度。针对以平行激光线为特征的悬臂式掘进机位姿检测系统外参标定难题,提出一种基于数字全站仪的系统外参标定方法,详细分析系统外参标定误差对测量系统的影响。通过建立视觉位姿测量系统中各模块之间的坐标转换关系,对系统外参标定原理进行数学建模,利用全站仪位姿检测方法得到全站仪系统外参标定结果下机身相对于巷道的位姿,对普通外参标定结果得到的机身相对于巷道位姿进行精度评价。实验结果表明:悬臂式掘进机全站仪系统外参标定方法位置测量误差在 ± 3 mm内,姿态角角度测量误差在0.08°内;利用全站仪系统外参标定方法得到精度结果: x、y和z方向的位置平均误差分别提高了13.073 mm、21.511 mm和18.159 mm,偏航角、俯仰角和姿态角的角度平均误差分别提高了0.225°、0.246°和0.246°。     

Control of an equipment for fabricating periodic nanostructure

This study presents the control for an equipment that is designed for fabricating periodic nanostructures. This equipment can generate the patterns required for nanostructure production using direct writing laser lithography. The equipment incorporates a direct writing laser lithography instrument, a linear motor-driven long-stroke stage (X, Y), a piezoelectric-driven two degrees of freedom (2-DOF) nano-stage (Y, θ_z), a 3-DOF laser interferometer measurement system, and a system control unit. The working stage of this equipment is combined by a long-stroke stage and a nano-stage; therefore, it can provide long-stroke and high-precision positioning. The feedback signal for this stage is obtained using a 3-DOF laser interferometer measurement system. Integral sliding-mode controllers are used to control the linear motor-driven stage and PID controllers are used to control the piezo-stage for precision positioning. This paper presents the design of the controllers and the control results. Experimental results show that satisfactory writing results can be obtained at a 100 mm/s scan speed.     

采用间接测量法对VAMT1Y型虚拟轴机床运动学标定的仿真研究

在对虚拟轴机床进行运动学标定的仿真计算过程中 ,采用间接测量法对虚拟轴机床的运动进行间接测量 ,然后通过矩阵重构的方法来解决测量噪声的干扰问题。仿真结果表明 ,虽然在虚轴机床的工作空间里无法将其可能存在的结构误差全部求出来 ,但计算结果完全可以满足机床在工作空间里的运动精度要求。因此采用此方法对虚拟轴机床进行标定是可行的     

Uncertainty propagation in calibration of parallel kinematic machines

This paper outlines in detail a method for determining the uncertainty present in the kinematic parameters (joint locations, initial strut lengths, and spindle location and orientation) for parallel kinematic devices after calibration. The uncertainty estimation method using Monte Carlo simulations was applied to a sequential method for determining the kinematic parameters of fully assembled Hexel Tornado 2000 (a 6–3 Stewart platform) milling machine. Results for the uncertainty present in the kinematic parameters of a Hexel Tornado 2000 milling machine after calibration using a SMX 4,000 laser tracker are shown.     

Analysis and evaluation of objective functions in kinematic calibration of parallel mechanisms

This paper analyses different objective functions for the parameter identification of parallel mechanisms and studies the influence in the position and orientation errors to improve their accuracy. A new objective function considering deviation terms is presented. This function is compared with other widely used functions and the advantages and disadvantages of each function are presented. The geometric parameter identification is performed by external calibration by means of the direct kinematic model. First, the objective functions are defined considering error position, error orientation and deviations in measurement. These functions compare the measured and calculated moving platform coordinates in order to obtain the identified model parameters that minimize this difference. The measured coordinates are obtained by measuring three sphere centres, fixed to the moving platform of a parallel mechanism, and the computed coordinates are given by the kinematic model. Second, the model is solved by the Levenberg–Marquardt algorithm for a number of identification positions. Finally, the calibration is verified in test positions. The results obtained show that the consideration of the deviations in measurement in the objective function with respect to classical approaches allows us to better identify those kinematic parameters corresponding with passive joints that cannot be measured. These findings confirm that a suitable objective function can improve the mechanism accuracy by more than one order of magnitude in both position and orientation errors.     

一种宏微双重驱动精密定位机构的建模与控制

提出一种宏微双重驱动精密定位机构,采用高性能直线电机直接驱动宏动平台,实现系统大行程微米级精度定位;安装在宏动平台上的压电陶瓷驱动微动平台,实现纳米级的分辨率和定位精度,以高频响动态补偿系统的定位误差;采用精密光栅尺反馈微动平台输出端的位置信号,实现定位机构的全闭环反馈控制。在分别建立宏动、微动、宏微机构模型的基础上,提出复合型宏动控制和模糊自校正PID微动控制的宏微控制策略。实验研究表明:系统的动态和稳态性能良好,该定位机构的最大工作行程100 mm,稳定时间小于40 ms,重复定位精度10 nm。     

Development of 2-axis hybrid positioning system for precision contouring on micro-milling operation

A 2-axis hybrid positioning system was developed for precision contouring on micro-milling operation. The system was developed to overcome the micro-positioning limitations of conventional linear stage positioning system on machine tools. A 2-axis flexure hinge type piezoelectric stage was added on a standard milling machine to obtain better machining results. The control method used for the hybrid system was active error compensation type, where errors from linear stages are cancelled by the piezoelectric stage motion. Positioning experiments showed an improvement of machine accuracy which was confirmed by the machining results. A micro-pillar was fabricated for the validation of long-range and high-precision contouring capability. The system was successfully implemented on micro-milling machining to achieve high-precision machining results.     

采用线结构光的电动汽车电池包箱体孔组位置在线测量

三坐标测量机和位置度量规测量新能源汽车电池包箱体孔组效率低,投入大,且无法满足在线检测的要求。为此构建由大理石平台、直线电动机、3D线扫相机等组成的在线电池包箱体孔组位置度检测系统。该系统作为电池包生产线的一部分,在机械手将电池包放入检测平台后,直线电动机带动3D线扫相机获取电池包箱体孔组的3D点云数据。将3D点云投影到标定平面,采用中值滤波降噪预处理,膨胀、腐蚀逼出被检测孔轮廓,提取ROI;Canny边缘检测提取轮廓线,最小二乘法提取特征获取圆心坐标与装配孔半径,并采用柔性定位的方法校正所获得的数据。结果表明,在线电池包箱体孔组位置度检测系统满足电池包装配孔位置度0.2 mm的测量需求。     

6-PSS型并联机床的仿真研究

在对６－ＰＳＳ构型虚拟轴机床进行运动学标定的仿真计算过程中,采用光栅球杆仪对虚拟轴机床的运动姿态进行间接测量,然后通过矩阵重构的方法来解决测量噪声的干扰问题。仿真结果表明,计算出的结果完全可以满足机床在工作空间里的运动精度要求。因此采用此方法对虚拟轴机床进行标定是可行的。