Kinematics of 3-RPS parallel manipulators by means of screw theory

In this work the forward position analysis of parallel manipulators with identical limbs, type revolute-prismatic-spherical (RPS), is carried out applying recursively the Sylvester dialytic elimination method. Afterwards, the velocity and acceleration analyses of the mechanisms at hand are addressed using the theory of screws. A numerical example is provided to prove the efficacy of the chosen methodology for the kinematic analyses of the mechanisms under study.     

用连续接触模型进行含间隙转动副的空间机构动力学分析

本文建立了间隙Ｒ副的连续接触模型，并对含间隙Ｒ副的空间机构进行了动力学研究。采用希林（ｓｃｈｉｅｎｌｅｎ）方法建立了机构的动力学方程，通过数值解研究了运动副元素的分离特性和Ｒ副的运动特性。数值计算结果表明：Ｒ副元素的分离时间很短，这说明在研究含间隙Ｒ副机构的动力学问题时，采用连续接触模型是可行的。     

A methodology for actuator failure recovery in parallel manipulators

In this paper, the failure of parallel manipulators is examined considering the failure modes of manipulators. A methodology for investigating the effect of actuator/joint failures on the force/moment capabilities of manipulators is presented, and the criteria for full and partial recovery from these failures are established. The proposed methodology is valid for both planar and spatial parallel manipulators; in the case study and simulation, the planar manipulators are used as an example.     

A new method to study the degree of freedom of spatial parallel mechanisms

The traditional formulae for degree of freedom are not valid in solving the platform for certain complex spatial parallel mechanisms. Therefore, by uniformly depicting the kinematic and geometric constraints of a mechanism with a screw theory, we put forward a new method to study the degree of freedom for the platform of spatial parallel mechanisms. This method should solve the analysis and calculation problems of the degree of freedom in many complex spatial parallel mechanisms, which may not always be solved correctly with traditional formulae.     

A simple method of accuracy enhancement for industrial manipulators

A robot calibration method which includes identification of kinematic parameters and error compensation is presented. The parameter identification process features an easy-to-perform measurement procedure using a low-cost, instrumented, articulated linkage, and with proper planning of the data collection process, the measurement of actual end effector positions can be performed automatically. The basis of the parameter identification approach is akin to that of closed-loop mechanism synthesis. For error compensation, a computation scheme based on the nominal model as opposed to the calibrated one is presented. The resulting algorithm, allowing the exploitation of the closed-form inverse kinematics solutions available for most industrial robots, is computationally efficient and therefore suited for on-line applications. Examples based on simulation studies, devised to include realistic operating conditions, are presented to demonstrate the feasibility of this method. The effects are also investigated of the number of measurements and of the sensor resolution on the overall quality of the identification.     

空间机构位置分析的矢量回归法

本语文给出了一适中矢量回归公式,用来解决空间机构位置分析问题。该方法不需要引入坐标系,计算量小,具有通用性,易于写电算程序,是一种易于掌握的简便方法。     

Re-analysis of the degree-of-freedom configuration of the platforms in spatial parallel mechanisms with constraints spaces

The degree-of-freedom (DoF) configuration of a mechanism, which is an important concept in the field of mechanisms and is the key problem to be solved before mechanisms are designed, has been discussed in our previous article [1]. In this paper, we will further analyze the DoF configuration of the platforms of spatial parallel mechanisms with constraints spaces. According to the physical meaning of reciprocal screws, we can solve the constraints spaces spanned by reciprocal screws, and then solve the free mobility spaces of the platform and its DoF configuration. With this methodology, not only can we differentiate the system from its members, but we also extend the concept of DoF configuration, which should have the attributes of number, type, and direction.     

Principle, theory and software for a new method of screw thread measurement by optical coordinate measuring systems

A new method is explained for optical thread measurement by means of two or three coordinate measuring instruments with a rigid microscope aligned perpendicular to the measuring plane. Measuring points of the flanks are taken in an extra-axial plane above or below of the axial plane respectively. Computer controlled measurement and evaluation of measuring points are carried out by a special evaluation program.     

Computation of the configuration degree of freedom of a spatial parallel mechanism by using reciprocal screw theory

In this paper, we propose a programmable algorithm to investigate the configuration degree of freedom (CDOF) of a spatial parallel mechanism in one Cartesian coordinate system with reciprocal screw theory. According to the physical meaning of reciprocal screws, we first obtain the terminal constraints of every kinematic chain which connects the end-effector with the fixed base, and then gain the free motion(s) of the end-effector and its degree of freedom (DOF). Through analyzing the controllability of the end-effector, we investigate the instantaneous screw expressions for the free motions of the end-effector of a spatial parallel mechanism and the CDOF of the mechanism. The whole mathematical analysis process can be directly embedded in a kind of CAD software, in which the imperfect Kutzbach Grübler formulas or its amendments are mostly utilized to analyze the DOF.     

A new method for determining geometric accuracy in the axis of movement of machine tools

Measurements of geometric accuracy in machine tools, especially of errors in moving machine parts against their theoretical axes, are taken by means of displacement pick-ups moving along a reference standard^1,2, such as a cylindrical test specimen. This procedure is impeded by physical form errors in the standards, especially for heavy machines, as well as by adjustment errors in the standards against the machine part to be measured. These disadvantages can be avoided by using a non-material standard like a laser beam with a four quadrant photodiode as sensor and a special analysis of the measurement data.     

埋地管道泄漏三维坐标-波速联合估计方法

为实现埋地输气管道泄漏精确定位,使用加速度传感器在土表检测泄漏振动声波,并提出基于非均匀L形阵列的泄漏源三维坐标和波速联合估计方法。大孔径非均匀L形阵列内嵌小孔径L子阵,由小孔径子阵结合Root-MUSIC算法求解远场信源DOA与波速的约束关系,再利用大孔径L阵进行波速和近场信源距离的二维空间谱估计,最后根据估计结果计算三维坐标从而降低计算量。定位实验结果验证了L形阵列性能的优越性,基于L形阵列的联合估计法能够估计不同土壤条件下的泄漏振动声波传播速度,并得出泄漏源的三维坐标。相较于使用理论波速的定位方法,联合估计法定位误差降低了90.9%,避免了理论波速误差对定位的不利影响。联合估计法的计算耗时比直接三维空间谱估计降低了88%,且定位精度保持不变。根据远/近场判据计算出信源范围r_min～r_max,实验验证该范围内可实现精确定位。     

数控机床误差的圆轨迹运动激光非接触测量新方法

对数控机床圆运动轨迹的测量是评价机床轮廓加工精度的有效方法之一。传统的测试设备如球杆仪很难实现在高进给速度下对小半径圆轨迹进行测量。本文介绍的利用激光多普勒位移测量仪可以在比较高的速度状态下、在半径从1mm到150mm范围内对数控机床的圆轨迹实现非接触测量，可获得数控机床的几何误差、反向间隙、伺服系统误差等，并能测得相应的圆半径、进给速度及加速度。本文主要论述采用这种新方法对数控机床伺服系统控制性能的优劣进行评价。     

广义P-S-N曲线参数估计的实现方法

针对三参数应力一寿命模型，提出了广义P-S-N曲线参数估计的实现方法。该方法基于广义极大似然法原理，应用相关系数法和数学规划法分别求解均值曲线和均方差曲线参量，然后应用相关系数法求解概率曲线参量。通过对45铜成组法疲劳试验获得的洲数据的分析，验证了该实现方法的有效性。     

A new method for directly measuring the position errors of a three-axis machine. Part 1: theory

This paper presents a measurement method and instrument to measure position changes in a three-axis machine workspace. The proposed instrument, named 3D step gauge, includes two parts. One is composed of three LVDTs and installed in the main spindle. The other is a plate that is fixed on the worktable. Many triangular pyramids are distributed on the plate. Each pyramid profile plane is the basic measurement plane for the LVDTs. When the spindle moves relative to the plate, the LVDTs’ tip ends slide on the pyramid profile planes. From the datum measured by the LVDTs, the differential position changes of the spindle can be obtained by the pyramid’s constructional parameters. In addition, the error effect analysis is used to investigate the accuracy of the method with respect to the factor of the device constructional parameters. Part 1 of this paper gives the basic theory of measuring the differential position changes in the multi-axis machine workspace. Part 2 gives the application of this theory and so the position error in the multi-axis machine workspace can be directly measured. This proposed method and the instrument have been tested using an actual machine tool. The measurement results show good repeatability and high accuracy.     

A novel method of determination of wire lag for enhanced profile accuracy in WEDM

Wire bending due to gap force is a major cause of imprecision in WEDM applications. To achieve higher precision and accuracy the knowledge of gap force and wire lag is extremely essential. In the present research, an in depth study on wire lag phenomenon has been carried out. A novel method to measure gap force intensity and wire lag under any given machining condition has been proposed by developing an analytical model. Experiments were carried out to verify the proposed model. Beside this, the impact of wire deflection on profile accuracy during cutting cylindrical job has been investigated. Based upon the developed analytical model an effective method has been proposed to eliminate this inaccuracy using wire lag compensation technique. The research finding will lead to better understanding of the gap force phenomena and will promote significant development in the domain of high precision WEDM.     

箱体平行孔系加工的坐标法原理及保证加工精度的方法

论述箱体平行孔系加工中坐标法的计算原理，阐明将孔系中心距平面尺寸链转化为线性尺寸链，并确定其坐标尺寸及公差的基本方法，为保证箱体孔系加工精度提供一种有效可靠的计算法。尤其适用于加工中心及数控镗、铣床等机床上孔系加工中的编程计算。     

非整周期采样信号频率估计的相频匹配方法

为提高非整周期采样信号的频率估计精度,提出一种非整周期采样信号频率估计的相频匹配方法。首先,为抑制信号非整周期采样对自相关的影响,对采样信号进行加窗自相关;其次,根据加窗自相关信号初相位为零的特点生成参考信号,实现参考信号与加窗自相关信号的相位匹配;最后,根据柯西不等式,利用参考信号和加窗自相关信号构造反映参考信号和加窗自相关信号频率匹配程度的误差函数,误差函数最小值对应的频率即为信号频率估计值。计算验证和LFMCW雷达测距实验表明该方法不受信号非整周期采样的影响,有效地提高了非整周期采样信号的频率估计精度,改善了LFMCW雷达的测距精度。     

确定6自由度6-3-3并联机构位置正解的数值方法

首先,基于机构学理论和6自由度6—3—3并联机构的基本几何关系。利用MATLAB符号数学计算工具箱得到了求该机构正向位移解的非线性方程组。接着将谊方程组的求解问题转化为非线性最小二乘问题,使用MATLAB优化工具箱库函数lsqnonlin求出了具有明确工程意义的正向位移解。最后,给出了一个算侧。     

A hybrid deep learning model for robust prediction of the dimensional accuracy in precision milling of thin-walled structural components

The use of artificial intelligence to process sensor data and predict the dimensional accuracy of machined parts is of great interest to the manufacturing community and can facilitate the intelligent production of many key engineering components. In this study, we develop a predictive model of the dimensional accuracy for precision milling of thin-walled structural components. The aim is to classify three typical features of a structural component—squares, slots, and holes—into various categories based on their dimensional errors (i.e., “high precision,” “pass,” and “unqualified”). Two different types of classification schemes have been considered in this study: those that perform feature extraction by using the convolutional neural networks and those based on an explicit feature extraction procedure. The classification accuracy of the popular machine learning methods has been evaluated in comparison with the proposed deep learning model. Based on the experimental data collected during the milling experiments, the proposed model proved to be capable of predicting dimensional accuracy using cutting parameters (i.e., “static features”) and cutting-force data (i.e., “dynamic features”). The average classification accuracy obtained using the proposed deep learning model was 9.55% higher than the best machine learning algorithm considered in this paper. Moreover, the robustness of the hybrid model has been studied by considering the white Gaussian and coherent noises. Hence, the proposed hybrid model provides an efficient way of fusing different sources of process data and can be adopted for prediction of the machining quality in noisy environments.