Design methodology for fully dynamic-controlled polynomial profiles and reduced tracking error in CNC machines

High speed and high precision on computer numerically controlled (CNC) machines are major issues for most industrial automation processes. Among the most important factors for precise motion control are the control law, the controller implementation, and the profile reference. The effects of the control law and controller implementation on the tracking error in CNC machines have been widely studied, while the issue of profile reference has not received the required attention. To improve the dynamics provided by the conventional profile reference, several techniques have been proposed, focusing on peak jerk limitation. The novelty of this work is to develop a generalized methodology designed for producing dynamically constrained higher degree piecewise polynomial profiles, without limits in maximum polynomial degrees. They lead to define in an arbitrary way the dynamics shape, while the peak dynamics values constrained are maintained in order to improve the tracking error on CNC systems and giving the possibility to design fully dynamic-controlled trajectories. For experimentation purposes, a two-axis proportional–integral–derivative controller and profile reference generator are implemented in a low-cost field programmable gate array. The experimentation demonstrates the efficiency of the proposed methodology, showing the peak jerk and tracking error reduction, compared against recent reports from literature.     

Temperature and thickness effects on thermal and mechanical stresses of rotating FG-disks

In the present paper, radial and hoop thermal and mechanical stress analysis of a rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using finite element method (FEM). To model the disk by FEM, one-dimensional two-degree elements with three nodes are used. It is assumed that the material properties, such as elastic modulus, Poisson’s ratio and thermal expansion coefficient, are considered to vary using a power law function in the radial direction. The geometrical and boundary conditions are in the shape of two models including thermal stress (model-A) and mechanical stress (model-B). In model-A there exists no pressure in both external and internal layers, and there is a temperature distribution considered as a second order function in the radial direction of the rotating disk. In this case, the temperature dependency of the material properties is considered and a hyperbolic type is assumed for the geometry of the disk. In model-B, there is a constant pressure only on the internal layer and a pressure on the internal layer of the disk without temperature distribution but with different types of surface profiles. Furthermore, the displacements and stresses for various power law indices (N) and angular velocities are calculated and compared to other results in the literature. The effect of varying thicknesses and dependency of material properties on temperature distribution is investigated.     

基于离散傅里叶变换的分形粗糙表面轮廓合成与研究

针对使用离散傅里叶变换合成的分形粗糙表面轮廓,分别研究轮廓的分形参数(分形维数D、尺度系数C)与传统表征参数的联系,分形参数对轮廓空域几何形貌的影响以及分形参数对轮廓滤波的影响。结果表明,若假设分形轮廓的功率谱密度函数严格满足幂律关系,则可由Parseval定理获得轮廓分形参数与其方均根偏差Rq的定量关系但此时,轮廓的其余传统表征参数为随机值,且相互之间线性无关;分形维数D影响轮廓高低频成分的能量比随着D的增加,轮廓高频成分的能量增加,轮廓空域几何形貌显得凹凸不平;分形维数D相同时,尺度系数C越大,轮廓的方均根偏差越大;在为获得光滑分形轮廓进行滤波时,分形维数D较小的轮廓,可以保留更多的能量。     

Short-term observation of wind energy potentiality in the Wol-Ryong wind site

Accurate analysis of the atmospheric wind profiles and climate characteristics in a certain area is a prerequisite for providing reliable information on a wind energy site. Two 2-D ultrasonic anemometers and one cup anemometer, arranged perpendicularly to the prevailing wind direction, were used to measure the atmospheric wind environment at a height of 4.5 m in the coastal region of Wol-Ryong, Jeju, South Korea. This study aims to estimate future wind resources with various estimation methods. The wind energy is theoretically estimated at 75 m, the hub height of 800 kW and 1500-kW-class wind turbines, at the Wol-Ryong site. Methods using three equations, a logarithmic profile, a modified logarithmic profile, and a power law, are applied for accurate prediction of the atmospheric wind profile. In addition, yearly wind power can be calculated by using the probability distribution from Weibull and Rayleigh profiles. It is found that the predicted wind speed is strongly affected by surface atmospheric conditions such as the friction velocity, atmospheric stability, and averaged roughness length. The Rayleigh profile gives more power generation than the Weibull distribution, especially under low-windspeed conditions. The logarithmic profile method seems to be the proper method for estimating the energy production at the Wol-Ryong site for neutral atmospheric conditions. On the other hand, the other two methods — the modified logarithmic profile method and the power law method — seem to be improper for neutral conditions.     

Monitoring of fat crystallization process using UVP–PD technique

The dynamic response of the cocoa butter shear crystallization process to a step reduction in temperature of a two stage shear crystallizer is investigated by measuring the pulsed ultrasound Doppler based velocity profile (UVP) and pressure drop (PD) in a pipe section. In addition, the velocity of sound, attenuated amplitude of the transmitted signal and temperature are continuously recorded. The temporal variation in rheological properties such as the apparent viscosity at different shear rates and the corresponding radial position in the pipe are determined by fitting the velocity profile and pressure drop to the power law rheological model. The linear dependence of sound velocity on the solid fat content (SFC) in the cocoa butter crystal suspension previously determined using the nuclear magnetic resonance technique is used to characterize crystallization. The cocoa butter crystal suspension is found to be shear thinning, the value of the power law exponent decreasing with increase in SFC. Newly developed software is used to integrate on-line measurement of flow profiles, pressure difference, temperature, velocity of sound and the attenuated amplitude of the transmitted signal. The software also calculates velocity profiles using spectral signal analysis, determines the rheological properties, and provides a graphical user interface and tools for data visualization. It is demonstrated that the cocoa butter shear crystallization process can be monitored using the UVP–PD technique.     

机车发动机用凸轮轴非圆磨削凹弧段轮廓重构方法研究

在分析带有凹弧段的机车发动机用凸轮轴的加工难点的基础上提出了一种凸轮轴磨削新工艺,即采用大小砂轮配合磨削凸轮轴轮廓。为了避免大砂轮磨削时对凹弧段产生干涉, 对比研究三次多项式、五次多项式曲线重构方法,仿真实验分析了两种重构曲线轮廓磨削运动规律,结果表明,五次多项式重构曲线轮廓磨削对机床头架、砂轮架的伺服跟踪性能要求较低,且磨削运动规律曲线较平滑。磨削试验验证了仿真分析的正确性,表明采用基于五次多项式凸轮轴轮廓重构的凹弧段磨削新工艺具有一定的可行性,在保证凸轮轴磨削轮廓精度的同时提高了磨削加工效率。     

Fundamental understanding of the interaction of continuous wave laser with aluminium

In welding, the depth of penetration, weld profile and the corresponding thermal cycle are the three basic outcomes that a user wishes to control flexibly. In laser welding applications, controlled application of power and energy density is the key to achieve predictable control of these characteristics. Creation of an analytical model is an important step towards understanding the underpinning science of laser metal interaction in controlling the depth, bead geometry and thereby temperature profile of a weld. The “power factor model”, which correlates the power applied per unit length to the laser metal interaction time, has been originally developed and validated for mild steel, guides a user on the selection laser system parameters, to achieve specific weld profile. This study is performed to extend the power factor–interaction time model to aluminium alloys by understanding the underpinning laser aluminium interaction parameters in terms of power density, interaction time, specific point energy and their correlation with the weld bead profiles. Although the power factor and interaction time showed a rectangular hyperbolic relationship, as observed in low carbon steel, for a specific weld depth and profile, the absolute magnitude and the characteristic profile of the curve is different due to the intrinsic differences in physical and thermal properties of aluminium as compared to steel. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of power and travel speed by keeping the energy input per unit length constant.     

高速列车轮对磨耗统计规律及预测模型

为研究我国高速列车轮对踏面磨耗规律,对某线路服役高速动车组进行跟踪测试,记录其镟轮周期内的踏面磨耗量,并基于对磨耗统计特征的两次拟合提出轮对型面磨耗预测函数模型。对某高速线路实测型面磨耗量进行拟合,分别得到各走行里程下磨耗量关于型面位置的拟合函数;并进一步对各走行里程下的拟合函数系数进行二次拟合,得到磨耗量关于型面位置及走行里程的二元预测函数。在模型的预测精度与适用性验证时,对比相同走行里程下预测型面和实测型面在轮轨接触几何关系与车辆各关键部件加速度响应两方面结果。对比结果显示,提出的磨耗预测模型在轮轨接触点、等效锥度、轮轨作用力及车辆安全性等各方面均与线路实测结果具有很好的一致性。     

Propagation behavior of SH waves in layered piezoelectric plates

In this study, the propagation of SH waves in a coupled plate consisting of a piezoelectric layer and an elastic layer is analytically investigated. The piezoelectric material is polarized in the z-axis direction and perfectly bonded to an elastic layer. The mathematical model of the SH wave propagation in this plate is based on the type of surface wave solution. Dispersion relations with respect to phase velocity are obtained for electrically open and mechanically free. Numerical examples are provided to illustrate graphically and compare the variations of the phase and group velocities versus the wave number for the different layers. The thickness ratio and the properties of the two layers have a significant effect on the propagation of SH waves. The conclusions are meaningful both theoretically and practically for the design of high-performance surface acoustic wave (SAW) devices.     

Analytical,numerical and experimental approach for design and development of optimal die profile for the cold extrusion of B4C DRMM Al 6061 composite billet into hexagonal section

Aluminium based matrix composites with boron carbide as particle reinforcement called Discontinuous reinforced metal matrix composites (DRMMs) possess high specific strength, high elastic modulus, good wear resistance, damping capacity and thermal stability. But during the development of DRMM composites, compression process like extrusion is an advisable secondary process for homogenous structure. This research work investigates the metal flow behavior of Al-B₄C based DRMM composite through six different die profiles namely third order polynomial, fourth order polynomial, cosine, elliptical, hyperbolic and conical geometry. Extrusion load, stress and strain distribution, and metal flow for above said die profiles are predicted by using analytical approach upper bound technique and compared with finite element method. Cosine and third order polynomial profiles are found to be most optimal in terms of homogenous and minimal extrusion load requirement. To validate the results, specially made Al-B₄C composite through stir casting route was extruded from round to hexagon through an exclusively fabricated cosine die. Results observed from the experiment have good agreement with both analytical and numerical.

     

Monitoring polynomial profiles in quality control applications

In some statistical process control applications, quality of a process or product is characterized by a relationship between two or more variables which is referred to as profile. Sometimes, this relationship can be characterized by a polynomial profile. There are some methods in the literature which can be easily extended and used for monitoring polynomial profiles. In this paper, a new method is proposed for monitoring kth order polynomial profiles in phase II. In the proposed method, the polynomial profiles are transformed to orthogonal polynomial profiles, and the parameters of the transformed model are monitored by separate exponentially weighted moving average control charts. Based on the relationship between the parameters of the main and transformed model, the step shifts in the parameters of main model lead to larger step shifts in the parameters of the transformed model. Hence, this transformation leads to quicker detection in phase II. The performance of the proposed method is compared with the existing methods using numerical simulation runs in terms of average run length criterion.     

基于SH模态导波杆的电站高温结构壁厚测量方法

提出了一种基于SH模态导波杆的电站高温结构壁厚测量方法,该方法使用导波杆将压电传感器与高温被测结构隔开。通过研究发现非频散SH模态导波能通过矩形横截面导波杆将导波信号由传感器导入到高温被测结构中。实验验证了通过特定夹具以干耦合方式将导波杆固定在被测结构表面可以获得较好的信号。使用2MHz中心频率下的汉宁窗调制正弦波信号实现了对处于不同温度被测结构壁厚的监测,室温（25℃）时,壁厚测量值与实际厚度相差0.016mm,高温被测结构实验信号也非常好,波速测量值与拟合曲线所得速度值误差范围为0.1%～2.5%。     

基于倒置声学黑洞的弹性波汇聚检测研究

传统的嵌入式声学黑洞(ABH)以材料的幂律裁剪方式达到阻抗的变化,实现弹性波的汇聚或控制,但同时也破坏了材料本身结构、减小了材料的刚度,限制了其在检测领域作为增敏结构的应用。本文提出一种倒置粘贴式的ABH结构,在一定范围内其厚度变化符合幂律衰减规律,尺寸小巧,易于粘附于被测物体表面而不破坏被测物。有限元仿真结果显示,倒置ABH在中高频激励下在圆心附近有着7倍左右的弹性波汇聚效果。激光多普勒测振仪扫描测试表明,倒置ABH结构具备良好的弹性波汇聚效果,可将弹性波放大2～4倍。将光纤布拉格光栅(FBG)粘贴在该倒置ABH表面,采用强度解调,构成具有汇聚放大作用的弹性波传感器,在无损检测等方面具备重要的应用价值。     

Thermal performance of functionally graded parabolic annular fins having constant weight

The proposed work reports the performance of parabolic annular fins of constant weight made of functionally graded materials. The work involves computation of temperature gradient, efficiency and effectiveness of such fins and compares the performances for different functionally graded parabolic fin profiles obtained by varying grading parameters and profile parameters respectively keeping the weight of the fins constant. The functional grading of thermal conductivity is based on a power function of radial co-ordinate which consists of parameters, namely grading parameters, varying which different grading combinations are studied. A general second order ordinary differential equation has been derived for all the profiles and material grading. The efficiency and effectiveness of the annular fins of different profile and grading combinations have been calculated and plotted and the results reveal the dependence of fin performance on profile and grading parameter.     

3-D Surface roughness profile of 316-stainless steel using vertical scanning interferometry with a superluminescent diode

Surface roughness is one of many parameters that influences on mass stability of standard weight, commonly used as a transfer standard of mass SI unit. One of the most famous non-invasive methods for determining surface roughness from a surface profile of material is a vertical scanning interferometry (VSI) with a white light source. In this research, 3-D surface profiles of 316-stainless steel, usually used as a material for standard weights, are constructed by using VSI, based on Michelson interferometer (MI). Because of its low-coherent properties, low cost, and compact light source, a superluminescent diode (SLD) is chosen as a low-coherence light source in our interferometry system. Since a continuous wavelet transform (CWT) algorithm provides accuracy results, it is also used as a numerical analyzing method for the interferogram signals, taking from our VSI. The surface roughness and measurement uncertainty, calculated from the constructed 3-D surface roughness profiles of 316-stainless steel samples, are discussed.     

Influences of tool pin profile and axial force on the formation of friction stir processing zone in AA6061 aluminium alloy

AA6061 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance. Compared to the fusion welding processes that are routinely used for joining structural aluminium alloys, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile plays a major role in deciding the weld quality. In this investigation an attempt has been made to understand the effect of axial force and tool pin profiles on FSP zone formation in AA6061 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different axial force levels. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the FSP zone formation. From this investigation it is found that the square tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.     

适合于液相检测的乐甫波传感器

乐甫波（Ｌove wave)是声表面波的一种，它是在沉淀于压电基片表面的薄层声波导中传播的表面剪切横波。论述了基片为ＳＴ切压电石英晶体、声波导层分别为聚甲基丙烯酸甲酯（PMMA）和熔融石英（SiO2)的乐甫波器件的制作。通过测量器件的传输参数S21和插损，比较了瑞利波器件和不同声波导层构成的乐甫波器件在气相和液相的特性，证明了乐甫波传感器适合于液相检测而瑞利波传感器不适合，而且，SiO2是构成乐甫波器件声波导层的更合适的材料。     

重载下非牛顿流体线接触弹性流体动力润滑的数值解

对重载下线接触流体润滑时 ,润滑剂的流变学作用和表面变形进行了理论分析 ,从而导出了非牛顿流体的模型 ,指数模型就是其中之一。当指数 n增大时 ,油膜厚度随之上升 ,并且油膜破裂点向接触区中心移动 ,同时润滑油的等效粘度也随之上升 ,当 n=1时计算结果与牛顿流体基本一致。     

Effect of transverse surface roughness and additives in TEHD contacts

Surface roughness effects in mixed rheological thermal EHL of rolling/sliding line contacts are investigated numerically. The surface roughness is assumed to be transverse and its profile is generated by a sinusoidal function defined in terms of its amplitude and wavelength. A homogeneous mixture of Newtonian base oil and power law fluid additive with varying volume fraction, viscosity ratio and power law index is used to represent polymer-modified oils. The velocity profile for the mixed rheological fluid model is obtained using perturbation method to derive Reynolds and mean temperature equations. It is found that the surface roughness effects on EHL characteristics are significantly modified due to the presence of polymeric fluid additives.     

Novel approach to harmonic control for Class F power amplifier with high power added efficiency

This paper presents a new topology to implement Class F power amplifier for eliminating the on -resistance （ RON ） effect. The time-domain and frequency-domain voltage and current waveforms for Class F amplifier are analyzed using Fourier series analysis method. Considering the on-resistance effect, the formulas of the efficiency, output power, dc power dissipation, and fundamental load impedance are given from ideal current and voltage waveforms. For experimental verification, we designed and implemented a Class F power amplifier, which operates at 850 MHz using AlGaAs/GaAs Heterostructure FET （HFET） device, and analyzed the measurement results. Test results show that the maximum PAE of 67% can be achieved at 28 dBm output power level.