Adaptive two-degree-of-freedom control of feed drive systems

Feed drive systems are widely used in industrial applications, and many efforts for improving their precision control have been made thus far. One of the basic approaches for improving the control accuracy of feed drive systems is to design a controller based on the internal model principle, which states that for a control system to track a reference signal without a steady state error, it needs to include a generator of the reference signal. Feed-forward controllers, such as the zero phase error tracking controller (ZPETC) proposed by Tomizuka, are also employed for improving control performance. However, prior knowledge of plant dynamics and/or reference signal properties is required for both the internal model principle and the feed-forward controller based designs. For precision control, plant dynamics should be identified in real time because feed drive dynamics are affected by varying conditions, such as frictional and thermal effects. This paper presents a new type of adaptive control for arbitrary reference tracking, which requires neither plant dynamics nor reference signal properties for controller design. This type of controller can also reduce the effect of unknown disturbances. The control system is designed using a discrete-time plant model and consists of adaptive feed-forward and feedback controllers. This design is then applied to a feed drive system with a ball screw drive. The effectiveness of the proposed design is demonstrated by simulation and experimental results, which was obtained by applying the proposed control system to an unknown reference signal whose property is varied during control.     

Robust contouring control for biaxial feed drive systems

Contouring control is an effective method of providing precision machine tool control, and various such methods have been proposed to date. However, most existing methods require prior exact knowledge of feed drive dynamics. This paper presents a robust contouring control system design that takes into account dynamics modelling errors and disturbances such as friction. We first present a controller design for biaxial feed drive systems that enables assignment of controller gains, for reducing the error component orthogonal to the desired contour curve, independent of the tangential error component. Although this design provides better control performance with small control input variance, an inherent contour error exists because of the difficulty in calculating the exact contour error for any contour curve in real time. To address this problem, a reference adjustment method is used to estimate the actual contour error. A robust contouring controller is proposed based on the variable structure control. The effectiveness of the robust controller is demonstrated by experimental results using circular and non-circular contour curves.     

Performance of single Si3N4 and mixed Si3N4+PCBN wiper cutting tools applied to high speed face milling of cast iron

In this work two face milling cutter systems were used in high speed cutting of gray cast iron under cutting condition encountered in the shop floor. The first system, called ‘A’, has 24 Si₃N₄ ceramic inserts all with square wiper edges. The second system, called ‘B’, is a mixed tool material system, having 24 wiper inserts, 20 of them are Si₃N₄ intercalated by four PCBN inserts. Cutting speed (v_c), depth of cut (doc) and feed rate per tooth (f_z) were kept constant. Surface roughness (R_a and R_t) and waviness (W_t), tool life (based on flank wear, VB_Bmax) and burr formation (length of the burr, h) were the parameters considered to compare the two systems. System ‘B’ presented better performance according to all parameters, although only end of life criterion based on R_t parameter has been reached.     

Identification of acceleration deceleration profile of feed drive systems in CNC machines

In process planning, trajectory planning has generally disregarded the limitations of the feed drive systems in terms of acceleration, jerk, and motion blending. It results in poor prediction of the feed rate mainly in the transient phases and affects, consequently, the machining integrity and safety. Therefore, identifying and integrating the feed drive system limitations with the trajectory planning of the tool path are crucial in order to achieve the desired feed rate at the appropriate tool position. In this paper, a methodology based on time series modeling is proposed to identify the acceleration/deceleration (Acc/Dec) profile of a feed drive system. This profile provides the relationship between the actual feed rate, assumed proportional to the tachometer signal, and the commanded feed rate specified in the G-Code file. A particular shape of the input has been addressed to allow the application of the time series modeling. The different characteristics of this input are carefully considered to avoid both nonlinear response due to saturation and excitation of the high frequency components of the feed drive. The resulting model is transformed into a Finite Impulse Response (FIR) filter and applied as an (Acc/Dec) processor to determine the actual feed rate from the commanded feed rate. The good agreement between the model output and the experimental results demonstrates the effectiveness of the proposed identification method. It is demonstrated that integrating these limitations with the trajectory planing results in a feasible trajectory.     

CNC齿轮测量中心驱动控制与传动系统设计

描述了CNC齿轮测量中心的工作特点，着重介绍了测量中心驱动控制系统及机械进给系统的设计，并对机械传动系统的性能进行了分析，验算了主要设计参数。该测量机测量精度高，性能稳定，已开始小规模生产。     

Discrete-time robust adaptive multi-axis control for feed drive systems

This paper presents a robust adaptive controller design for multi-axis feed drives systems. The proposed method is designed to compensate for the coupling effects among multiple axes that are neglected in most feed drive controllers. Because inertial force from one axial motion affects the contact force between mechanical parts in other axes, the magnitude of friction at the contact surface varies. Considering this coupling effect in controller designs can improve control performance. Because the coupling effect cannot be known in advance, and it varies with respect to environmental conditions such as temperature, this paper first presents an adaptive controller design. Next, the design is extended to have robust stability for unanticipated plant modelling errors disturbances, because the robustness of adaptive controllers is known to be low due to the complex mechanism of controllers and estimators of plant model parameters. The design problem of the robust controller is formulated as a minimization problem under the linear matrix inequality constraints. The effectiveness of the adaptive multi-axis controller is demonstrated by comparative experiments with an adaptive controller that neglects the coupling effect. In addition, the robust adaptive controller is confirmed to be effective by comparison with a non-robust adaptive controller.     

Multiperformance Optimization in Turning of Free-Machining Steel Using Taguchi Method and Utility Concept

This article presents the application of Taguchi method and the utility concept for optimizing the machining parameters in turning of free-machining steel using a cemented carbide tool. A set of optimal process parameters, such as feed rate, cutting speed, and depth of cut on two multiple performance characteristics, namely, surface roughness and metal removal rate (MRR) is developed. The experiments were planned as per L ₉ orthogonal array. The optimal level of the process parameters was determined through the analysis of means (ANOM). The relative importance among the process parameters was identified through the analysis of variance (ANOVA). The ANOVA results indicated that the most significant process parameter is cutting speed followed by depth of cut that affect the optimization of multiple performance characteristics. The confirmation tests with optimal levels of machining parameters were carried out to illustrate the effectiveness of Taguchi optimization method. The optimization results revealed that a combination of higher levels of cutting speed and depth of cut along with feed rate in the medium level is essential in order to simultaneously minimize the surface roughness and to maximize the MRR.     

FCAW process optimization using the multivariate mean square error

Optimization of welding processes is not a trivial task, mainly due to the great number of required and desirable characteristics that must be analysed. Moreover, the optimization of a welding process with multiple characteristics without considering the variance–covariance structure may lead to inadequate optimum. To help with this task, a method of multi-objective optimization based on the multivariate mean square error applied in the study of multiple correlated characteristics of a flux-cored arc welding process is presented. This method characterized by a combined approach based on the response surface methodology, design of experiments, and principal components analysis consisted of an attempt to achieve the nearest values to specific targets, for each characteristic (penetration, deposition rate, deposition efficiency, convexity index of the weld bead, and dilution), considering the welding variables expressed as a result of welding voltage (V), wire feed speed (Va), and contact tip to workpiece distance (d). The results point, to a good adequacy of the proposed method.     

A decoupled path-following control algorithm based upon the decomposed trajectory error

This paper proposes a new path-following control algorithm for the machine tool servo systems. The control system first decomposes the contouring error into the normal tracking error and the advancing tangential error. A dynamic decoupling procedure is then applied to the system dynamics. Finally, a dynamic decoupled controller is proposed to compensate the decomposed tangential and the normal tracking errors. The normal control minimizes the perpendicular tracking error while the tangential control maintains a desired feed rate. The proposed method is applied to the control of an experimental x–y table. Experimental results show that the proposed control can achieve good tracking and trajectory following characteristics. The new algorithm also enables the design of a non-overshooting controller along the path. This will result in a no-overcutting process for the machine tool operation.     

线性液动压抛光波纹度加工特性研究

目的 探究线性液动压抛光波纹度特性,建立抛光波纹度预测模型,获取最佳加工工艺参数组合。方法结合线性液动压抛光原理,分析抛光波纹度产生机理,探究流场力分布特性,并获得影响波纹度的相关工艺参数。设计单因素试验,探究各工艺参数对波纹度的影响规律,并进行显著性分析,选取显著参数为试验因子,设计正交试验,以试验结果作为训练集,建立基于支持向量回归机（Support Vector Regression,SVR）的波纹度预测模型。以该预测模型为适应度函数,进行遗传算法寻优,以获取最佳工艺参数。结果 线性液动压抛光波纹度由流场力分布特性及工件进给运动共同作用产生,其大小受抛光间隙、抛光速度、进给速度和抛光液黏度影响。单因素试验分析结果显示,抛光波纹度Wa随进给速度和抛光间隙的增大而增大,随抛光速度的增大而减小,随抛光液黏度的增大而先减小、再增大。其中进给速度的影响最显著,抛光间隙和抛光速度次之,而抛光液黏度的影响具有分段差异性,显著性最弱。以正交试验数据所建立的抛光波纹度预测模型的回归相关系数R2为0.992 0。随机验证实验结果显示,各组预测值与真实值的误差均在10%以内,遗传算法寻优得到最佳工艺参...     

A new evaluation to friction analysis for the ring test

A non-constant shear friction approach is proposed to evaluate the friction in ring test. The distribution of shear friction is derived and found to be dependent on the ratio (called F-coefficient) of the second derivative and first derivative of velocity at the z-direction. An upper bound method combined with the F-coefficient is used to simulate the processes of ring test. The calibration curves are reconstructed according to the F-coefficient and show good agreement compared with the literature. A relation between the F-coefficient, neutral line and constant friction factor m are also shown for discussion.     

Indirect cutting force measurement in multi-axis simultaneous NC milling processes

There have been many research works for the indirect cutting force measurement in machining process, which deal with the case of one-axis cutting process. In multi-axis cutting process, the main difficulties to estimate the cutting forces occur when the feed direction is reversed. This paper presents the indirect cutting force measurement method in contour NC milling processes by using current signals of servo motors. A Kalman filter disturbance observer and an artificial neural network (ANN) system are suggested. A Kalman filter disturbance observer is implemented by using the dynamic model of the feed drive servo system, and each of the external load torques to the x and y-axis servo motors of a horizontal machining center is estimated. An ANN system is also implemented with a training set of experimental cutting data to measure cutting force indirectly. The input variables of the ANN system are the motor currents and the feedrates of x and y-axis servo motors, and output variable is the cutting force of each axis. A series of experimental works on the circular interpolated contour milling process with the path of a complete circle has been performed. It is concluded that by comparing the Kalman filter disturbance observer and the ANN system with a dynamometer measuring cutting force directly, the ANN system has a better performance.     

Sliding mode contouring control design using nonlinear sliding surface for three-dimensional machining

Machining accuracy as well as consumed energy saving are important issues in machining by multi-axis feed drive systems. The contour error, which is defined as the error component orthogonal to the desired contour curve, is a good indicator of machining precision. This paper presents a novel sliding mode contouring controller with nonlinear sliding surface to improve the machining accuracy for three-dimensional machining. Unlike the conventional sliding mode control design, the proposed nonlinear sliding surface depends on the output so that the damping ratio of the system changes from its initial low value to its final high value as the output changes from its initial value to the set point. Hence, the proposed algorithm allows a closed-loop system to simultaneously achieve low overshoot and settling time, resulting in a smaller error. Because the contour error is more important than the tracking error with respect to each feed drive, the contour error component is included in the proposed sliding surface. By using the proposed method, simulation and experimental results for a desktop three-axis machine show a significant performance improvement in terms of the contour error.     

Improving tribological properties and machining performance of a-C coatings by doping with titanium

In this study, a-C:Ti _x% coatings with various levels of Ti addition are deposited on cemented tungsten carbide (WC-Co) substrates using a medium-frequency twin magnetron sputtering and unbalanced magnetron sputtering system. This study investigates the tribological properties of the coatings by conducting wear tests against an AISI 1045 steel counterbody under a cylinder-on-disk line contact wear mode using an oscillating friction and wear tester. Additionally, turning tests and high-speed through-hole drilling tests are performed on AISI 1045 steel counterbodies and PCB workpieces, respectively, to investigate the machining performance of coated turning cutters and microdrills. The a-C:Ti _x% coatings not only have improved tribological properties but also demonstrate enhanced machining performance. For sliding against the AISI 1045 steel counterbody under loads of 10 and 100 N, the results show that the optimal friction and wear resistance properties are provided by the a-C:Ti_13% and a-C:Ti_3% coatings, respectively. Meanwhile, the a-C:Ti_20% and a-C:Ti_51% coatings yield the optimal turning and drilling performance, respectively.     

高频响一维直线电机运动平台的研究与开发

高频响、高精度直线电机运动平台直接驱动精密运动系统是近年来发展起来的一种新型进给传动方式。研制一种以直线电机直接驱动的运动平台,阐述该平台的设计与开发过程,并进行调试与测试。实验结果证明:该平台消除了机械传动所带来的不良影响,极大地提高了进给系统的快速反应能力和控制精度。     

Design, analysis, fabrication and testing of a parallel-kinematic micropositioning XY stage

This paper reports on a novel piezo-driven, parallel-kinematic, micropositioning XY stage. This monolithic design is comprised of parallelogram four-bar linkages, flexure hinges, and piezoelectric actuators. Kinematic and dynamic analysis shows that the mechanical structure of the stage has a large work space, high bandwidth and good linearity. The stage system was run in open-loop mode to measure the step response and frequency response. The results show that the resonation frequencies of the two vibration modes are 563 and 536 Hz and the damping ratios are 0.049 and 0.0228. Two fiber optic sensors were added to the system to build a closed-loop positioning system. Linear and circular contouring performance in closed-loop mode suggests high scanning performance for such parallel-kinematic stages. The positioning resolution of the stage, limited only by the feedback sensors used, is about 20 nm.     

基于孔隙率的Cr2O3涂层工艺优化及回归分析

孔隙率是评价Cr2O3涂层质量的重要指标之一。根据Box-Behnken二阶响应曲面法设计了3因素3水平的回归分析试验,采用大气等离子喷涂技术在TC4钛合金表面制备了Cr2O3涂层,以不同工艺条件下的涂层孔隙率作为响应值,建立了喷涂电流、等离子气体和喷距影响因子与响应输出之间的数学模型,讨论了3种影响因子的显著性及交互作用影响,得到涂层孔隙率的连续变量响应曲面和等高曲线。模型可以用于大气等离子喷涂Cr2O3涂层的工艺优化和性能预测,最小孔隙率的预测参数是电流I=500A,氩气流量QAr=40L/min和喷距d=80mm,能获得的最小孔隙率为1.5%。     

Development and Performance of New Gadolinium and Boron Containing Radiation-Absorbing Composite Systems

The theoretical design and the experimental design and development of multifunctional radiation-absorbing composite material systems based on gadolinium, boron, and tungsten has been carried out. Based on theoretical calculations, the effective compositions of these composite subsystems were established for the enhanced absorption of neutron and γ irradiation in various energy spectra. In addition, the systems and systems compositions were designed and processed for enhanced multifunctional performance. Selected and optimized compositions of Gd-B-W system were densified by shock wave consolidation technology. The technological parameters for the explosive consolidation processes and the structure-properties relationships are presented and discussed. The radiation-absorbing properties of the bulk samples were investigated and measured under neutron and gamma irradiation. The theoretical design and the optimization of these composite systems were carried out by the Monte Carlo method with a GEANT 3 program, which contained a special GCALOR package for the simulation of the interaction of thermal and fast neutrons with the composite material systems. During the neutron passage through the samples, the main processes of the interaction of neutrons with matter were considered including elastic and inelastic scattering, neutron fission of nuclei, and radiation capture. The attenuation factor of the irradiation flux is determined as a criterion of efficiency of radiation absorption. For the energy of 0.025 eV (thermal neutrons), gadolinium-containing composites have the maximum absorption capability. In the range of energy spectrum from 1 eV to 10 eV, the boron-containing composites have better absorption performance. For the capture of neutrons in wide energy spectrum, the (n, γ) reaction takes place and tungsten provides enhanced absorption of radiation. In the presence of mixed radiation sources (neutron and γ quanta), the boron- and gadolinium-containing composite materials prepared on the tungsten basis have the best performance. In addition to enhanced radiation absorption properties, these composite systems show also enhancement on other properties such as corrosion resistance in aggressive media.     

Thermal error analysis for a CNC lathe feed drive system

The development of high-speed feed drive systems has been a major issue in the machine tool industry for the past few decades. The resulting reduction in the time needed for tool changes and the rapid travel time can enhance productivity. However, a high-speed feed drive system naturally generates more heat and resultant thermal expansion, which adversely affects the accuracy of machined parts. This paper divides the feed drive system into two parts: the ball screw and the guide way. The thermal behavior model for each part is developed separately, in order to estimate the position errors of the feed drive system caused by thermal expansion. The modified lumped capacitance method (MLCM) and genius education algorithm (GEA) are used to analyse the linear positioning error of the ball screw. Thermal deformation of the guide way affects straightness and introduces angular errors, as well as affecting linear positioning. The finite element method is used to estimate the thermal behavior of the guide way. The effectiveness of the proposed models is verified through experiments using a laser interferometer.     

钨极氩弧焊熔池表面高度测量系统纵向标定

研究基于傅里叶变换轮廓术的钨极氩弧焊熔池表面高度测量系统的纵向标定方法,将一正弦光栅投向置于熔池位置的标定板,用一维精密移动装置带动平板纵向移动,构造不同的已知高度分布.4f系统把标定板上的光栅条纹转移到输出面,在输出面放置白屏接收输出图像,CCD拍摄屏上的光栅条纹,通过数字图像处理求出像素平面每点的位相值,确定系统的位相高度映射关系,对测量系统进行纵向标定并进行焊接实验,初步获得了熔池的表面高度分布.