Apply fuzzy interpolation method to calibrate parallel machine tools

A novel and efficient fuzzy interpolation method is proposed to simplify the calibration process for parallel machine tools (PMTs). Either inverse or forward kinematic models must be used in the traditional PMT calibration methods to perform the identification and compensation of the pose errors for PMTs, which made the calibration process time consuming and inefficient in real applications. Instead of using a model, the proposed method presents a modeless technique combined with the fuzzy interpolation method to obtain high calibration accuracies when a small workspace is adopted. This new approach can significantly reduce the complex in traditional PMT calibration processes and greatly simplify the calibration procedures.     

基于标定和关节空间插值的工业机器人轨迹误差补偿

轨迹精度是工业机器人重要的动态性能,目前工业机器人的轨迹精度远低于定位精度,提出一种基于机器人运动学标定和关节空间插值误差补偿的方法来提高机器人轨迹精度。基于MD-H方法建立机器人的运动学模型,在此基础上运用机器人微分运动学理论建立末端位置误差模型和轨迹误差模型。为克服最小二乘法等传统方法在数据噪声较大且不符合高斯分布时收敛慢甚至发散的问题,提出一种基于扩展卡尔曼滤波算法的机器人运动学参数辨识方法,实现运动学参数辨识的快速收敛。经过分析发现机器人误差在关节空间具有连续性的特点,为此提出一种关节空间插值误差补偿方法,建立网格形式的误差补偿数据库,并利用关节空间距离权重函数和已知的网格顶点误差计算各控制点的关节转角误差。通过试验对所提出的参数辨识和关节空间误差补偿方法进行了验证,试验结果表明：经过运动学参数辨识和补偿后机器人的绝对定位精度由1.039 mm提高到0.226 mm,轨迹精度由2.532 mm提高到1.873 mm,应用关节空间插值误差补偿后机器人的轨迹精度进一步提高到1.464 mm。     

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。     

Non-kinematic calibration of a six-axis serial robot using planar constraints

This paper describes a non-kinematic calibration method developed to improve the accuracy of a six-axis serial robot, in a specific target workspace, using planar constraints. Simulation confirms that the stiffness of the robot, as well as its kinematic parameters, can be identified. An experimental validation shows that the robot's accuracy inside the target workspace is significantly enhanced by reducing the maximum distance errors from 1.321 mm to 0.274 mm. The experimental data are collected using a precision touch probe, which is mounted on the flange of a FANUC LR Mate 200iC industrial robot, and a high precision 9-in. granite cube. The calibration method makes use of a linear optimization model based on the closed-loop calibration approach using multi-planar constraints. A practical validation approach designed to reliably evaluate the robot's accuracy after calibration is also proposed.     

工作空间分区的机器人非概率可靠性标定方法研究

全工作空间域的高精度定位是超大工作空间机器人实现全范围精密作业的关键。本文以提高机器人全工作空间域内参数标定的可靠性和空间适应性为目标,研究机器人自身诸多不确定性的非概率量化方法,分析不确定性参数在不同工作空间域对机器人末端定位精度的影响差异,依据定位精度非概率可靠度指标对全工作空间域分区,提出一种在工作空间分区框架下对机器人进行非概率可靠性标定的方法。实例表明,分区标定补偿后,x、y、z三个方向的误差区间的下界和上界平均值分别下降了40.16%、59.36%和59.08%、40.87%以及54.24%、33.98%,且补偿后的机器人响应速度快,运动过程中波动小,证明了本文方法在缩小全工作域内末端误差范围,提升机器人的绝对定位精度及标定的空间适应性方面的有效性。     

近似度加权平均插值的机器人精度补偿方法研究

为实现物流包装的身份和受潮信息双重检测,设计了一种新型的低成本无芯片RFID湿度传感器,使用电耦合LC谐振器(ELC谐振器)作为湿度传感器监测目标环境相对湿度、U型环谐振器作为无芯片编码结构识别目标身份。通过射频仿真软件HFSS研究谐振器结构参数与谐振频率的关系,获得相应拟合公式,为结构参数设计提供理论依据,并在此基础上设计了8位编码结构;系统研究不同质量分数的聚乙烯醇(PVA)溶液对湿度传感器感湿灵敏度和感湿范围的影响,研制出8位无芯片RFID湿度传感器。根据散射参量提取法获得了U型环谐振器的有效电磁参数,表明其具有超材料属性。所研究的湿度传感器具有感湿灵敏度高、编码容量大、结构简单等优点,有望在智能包装领域得到应用。     

CALIBRATION OF A 6-DOF SPACE ROBOT USING GENETIC ALGORITHM

The kinematic error model of a 6-DOF space robot is deduced, and the cost function of kinematic parameter identification is built. With the aid of the genetic algorithm （GA） that has the powerful global adaptive probabilistic search ability, 24 parameters of the robot are identified through simulation, which makes the pose （position and orientation） accuracy of the robot a great improvement. In the process of the calibration, stochastic measurement noises are considered. Lastly, generalization of the identified kinematic parameters in the whole workspace of the robot is discussed. The simulation results show that calibrating the robot with GA is very stable and not sensitive to measurement noise. Moreover, even if the robot＇s kinematic parameters are relative, GA still has strong search ability to find the optimum solution.     

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.     

精密视觉印刷设备的自标定

为了提高全自动视觉印刷设备的精度,提出了一种简易、有效标定基于三自由度平面并联调整台的视觉丝网印刷设备的算法。首先,分析和标定了视觉测量系统,并通过激光干涉仪验证了结果的准确性。然后,分析了三自由度平面并联调整台的几何参数误差;基于印刷设备自身的视觉测量系统,分步标定了并联平台的动平台坐标系、传动比误差和仅需的部分几何误差源。提出了一种满足全姿态且适应不同制程的三角形面姿态插值方法和纠偏调整算法,从而避免了较为复杂的几何全参数辨识,降低了对调试人员的技术要求。实验结果表明：在并联调整台工作空间内,标定后的最大位置误差从标定前的161.6 μm下降为12.3 μm,最大姿态误差从标定前的2.232″下降为0.720″,基本满足印刷设备对精度的要求。     

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% 。     

APPROACH TO IMPROVEMENT OF ROBOT TRAJECTORY ACCURACY BY DYNAMIC COMPENSATION

Some dynamic factors, such as inertial forces and friction, may affect the robot trajectory accuracy. But these effects are not taken into account in robot motion control schemes. Dynamic control methods, on the other hand, require the dynamic model of robot and the implementation of new type controller. A method to improve robot trajectory accuracy by dynamic compensation in robot motion control system is proposed. The dynamic compensation is applied as an additional velocity feedforward and a multilayer neural network is employed to realize the robot inverse dynamics. The complicated dynamic parameter identification problem becomes a learning process of neural network connecting weights under supervision. The finite Fourier series is used to activate each actuator of robot joints for obtaining training samples. Robot control system, consisting of an industrial computer and a digital motion controller, is implemented. The system is of open architecture with velocity feedforward function. The proposed m     

Assessment of non-rigid body,direction- andvelocity-dependent error motions and their cross-talk by two-dimensional digital scale measurements at multiple positions

The conventional volumetric error compensation for a machine tool is based on the machine's kinematic model, which formulates the tool center point (TCP) position based on the assumption of rigid-body motion of each axis. Particularly in large-sized machine tools, error motions that do not satisfy this assumption may have a significant impact on the machine's overall volumetric accuracy. In addition to position-dependent quasi-static error motions included in the conventional kinematic model, this paper proposes a scheme to assess quasi-static cross-talk between axes and direction- and velocity-dependent error motions. This paper proposes test procedures to measure two dimensional (2D) contour error trajectories by using a 2D digital scale (cross grid encoder). Unlike many previous works, this paper proposes to perform the tests at multiple positions over the machine tool's entire workspace, and the error motions are assessed by comparing contour error profiles. An experimental case study on a large-sized bridge-type vertical machine tool shows that such influences can be significant error contributors. The proposed tests can assess error motions only at discrete points where a 2D digital scale is installed. It can be applied as accuracy inspection to ‘‘roughly’’ assess the machine's volumetric accuracy by using a 2D digital scale only, but it is generally not for the compensation.     

Motion error compensation of multi-legged walking robots

Existing errors in the structure and kinematic parameters of multi-legged walking robots,the motion trajectory of robot will diverge from the ideal sports requirements in movement.Since the existing error compensation is usually used for control compensation of manipulator arm,the error compensation of multi-legged robots has seldom been explored.In order to reduce the kinematic error of robots,a motion error compensation method based on the feedforward for multi-legged mobile robots is proposed to improve motion precision of a mobile robot.The locus error of a robot body is measured,when robot moves along a given track.Error of driven joint variables is obtained by error calculation model in terms of the locus error of robot body.Error value is used to compensate driven joint variables and modify control model of robot,which can drive the robots following control model modified.The model of the relation between robot’s locus errors and kinematic variables errors is set up to achieve the kinematic error compensation.On the basis of the inverse kinematics of a multi-legged walking robot,the relation between error of the motion trajectory and driven joint variables of robots is discussed.Moreover,the equation set is obtained,which expresses relation among error of driven joint variables,structure parameters and error of robot’s locus.Take MiniQuad as an example,when the robot MiniQuad moves following beeline tread,motion error compensation is studied.The actual locus errors of the robot body are measured before and after compensation in the test.According to the test,variations of the actual coordinate value of the robot centroid in x-direction and z-direction are reduced more than one time.The kinematic errors of robot body are reduced effectively by the use of the motion error compensation method based on the feedforward.     

Conceptual design and kinematic analysis of a novel parallel robot for high-speed pick-and-place operations

This paper deals with the conceptual design, kinematic analysis and workspace identification of a novel four degrees-of-freedom (DOFs) high-speed spatial parallel robot for pick-and-place operations. The proposed spatial parallel robot consists of a base, four arms and a 1½ mobile platform. The mobile platform is a major innovation that avoids output singularity and offers the advantages of both single and double platforms. To investigate the characteristics of the robot’s DOFs, a line graph method based on Grassmann line geometry is adopted in mobility analysis. In addition, the inverse kinematics is derived, and the constraint conditions to identify the correct solution are also provided. On the basis of the proposed concept, the workspace of the robot is identified using a set of presupposed parameters by taking input and output transmission index as the performance evaluation criteria.     

工业机器人定位误差在线自适应补偿

受工业机器人本体结构几何及非几何误差因素的影响,机器人执行末端的实际运动轨迹与其理论规划轨迹往往不一致,这严重限制了机器人在加工领域的拓展应用。另外,通过研究发现机器人除在工作空间上定位误差等级存在差异分布外,在服役时间上随着机器人工作性能的退化也会显著恶化其定位精度。为解决该问题,提出了一种基于定长记忆窗增量学习的机器人定位误差在线自适应补偿方法。在该方法中,首先定量分析机器人定位误差与位姿的相关关系,将工作空间划分为多个位姿区块并创建校准样本库,建立了位姿映射模型的自适应优化机制以克服空间中误差等级差异分布的问题;然后设计了定长记忆窗增量学习算法,克服神经网络模型的灾难性遗忘缺陷,并平衡了在线模式下建立机器人新、旧位姿数据映射关系的精度和效率,解决了机器人性能退化加剧定位误差影响位姿映射模型适用性的问题,从而确保算法的补偿精度稳定在目标精度水平线以上;最后,利用St?ubli机器人和UR机器人对所提方法进行了精度在线补偿实验验证。实验结果表明该方法可将St?ubli机器人的定位误差从0.85 mm降至0.13 mm,将UR机器人的定位误差从2.11 mm降至0.17 mm,明显提高...     

六自由度工业机器人末端定位误差参数辨识与实验研究

为了提高六自由度工业机器人绝对定位精度,对工业机器人进行了运动学建模,并建立了基于MD-H参数误差的机器人末端定位误差辨识模型,应用激光跟踪仪测量系统采集样本点数据,应用基于奇异值分解的最小二乘法求解辨识模型,以获得几何参数误差,并根据辨识出的误差对机器人末端定位精度进行补偿,实验结果表明,经过辨识和补偿后,工业机器人...     

Full-pose calibration of a robot manipulator using a coordinate-measuring machine

The work reported in this article addresses the kinematic calibration of a robot manipulator using a coordinate measuring machine (CMM) which is able to obtain the full pose of the end-effector. A kinematic model is developed for the manipulator, its relationship to the world coordinate frame and the tool. The derivation of the tool pose from experimental measurements is discussed, as is the identification methodology. A complete simulation of the experiment is performed, allowing the observation strategy to be defined. The experimental work is described together with the parameter identification and accuracy verification. The principal conclusion is that the method is able to calibrate the robot successfully, with a resulting accuracy approaching that of its repeatability.     

Error Modeling and Sensitivity Analysis of a Parallel Robot with SCARA（Selective Compliance Assembly Robot Arm） Motions

Parallel robots with SCARA（selective compliance assembly robot arm） motions are utilized widely in the field of high speed pick-and-place manipulation. Error modeling for these robots generally simplifies the parallelogram structures included by the robots as a link. As the established error model fails to reflect the error feature of the parallelogram structures, the effect of accuracy design and kinematic calibration based on the error model come to be undermined. An error modeling methodology is proposed to establish an error model of parallel robots with parallelogram structures. The error model can embody the geometric errors of all joints, including the joints of parallelogram structures. Thus it can contain more exhaustively the factors that reduce the accuracy of the robot. Based on the error model and some sensitivity indices defined in the sense of statistics, sensitivity analysis is carried out. Accordingly, some atlases are depicted to express each geometric error’s influence on the moving platform’s pose errors. From these atlases, the geometric errors that have greater impact on the accuracy of the moving platform are identified, and some sensitive areas where the pose errors of the moving platform are extremely sensitive to the geometric errors are also figured out. By taking into account the error factors which are generally neglected in all existing modeling methods, the proposed modeling method can thoroughly disclose the process of error transmission and enhance the efficacy of accuracy design and calibration.     

Kinematic modeling and parameter identification of a new circumferential drilling machine for aircraft assembly

Automated fastener hole drilling is a key technology for low-cost and high-quality assembly of aircrafts. In this paper, a new circumferential drilling machine for fuselage assembly of large aircrafts is introduced. In order to meet the required position accuracy of drilled holes, this paper focuses on the kinematic calibration of the machine in order to improve its positioning accuracy. A modeling strategy, which combines the Denavit-Hartenberg (D-H) method and a modified version of the Hayati-Mirmirani (H-M) method, is proposed to deal with the special kinematic structure of the arc-base drilling unit of the machine. Main issues in kinematic parameter identification such as definition of objective function, calibration data selection, acquisition of initial values, and setting of convergence criteria are also discussed. Experiments of repeatability testing and kinematic calibration have been performed, and the results show that the positioning accuracy of the arc-base drilling unit is comparable to its repeatability after calibration. This suggests that the proposed kinematic calibration method is effective. Actual drilling tests have been performed on a simulated aircraft fuselage after implementing the identified kinematic model in the machine’s control software. Position errors of drilled holes are within ±0.5 mm, which meets the requirement for fastener hole drilling in the fuselage assembly of large aircrafts.