Surface quality control of nonmetallic workpieces in diamond abrasive finishing

The paper presents a procedure for measuring laser radiation reflection and scattering coefficients of polished nonmetallic workpieces. A relation between the scattered light intensity and the polished surface roughness is studied. It is demonstrated that colorimetric characteristics of nonmetallic materials can be determined from the light scattering and reflection coefficients.     

高性能零件的性能与几何参数一体化 精密加工方法与技术

随着高端装备和产品的不断发展,对装备和产品制造的性能要求也越来越多和越来越高,涌现出一大批高性能指标要求的关键零部件,其加工已由以往的单纯几何形状和尺寸精度要求,跃升为以性能要求为主、性能与几何参数一体化的精密加工要求。这些高性能零件多呈精密复杂曲面、超高精度,以及材料超硬、超脆、超黏等难加工特征,其性能受几何、材料等多因素耦合作用,采用传统工艺进行精密加工制造十分困难,存在废品率高、加工效率低,特别是性能指标难以保证等难题。从高端制造装备业的需求出发,提出并阐明了高性能零件的特点、分类以及数字化可控去除加工方式的内涵,在此基础上指出了四类高性能零件精密加工所涉及的关键问题,并着重介绍了这些问题的研究现状、存在的难点和可行的解决方案,为面向高性能要求的性能与几何参数一体化的加工理论、方法和工艺技术体系的建立提供参考,以解决高性能零件的精密制造难题。     

一种挠性航天器的自适应姿态控制与振动控制

挠性航天器三轴姿态控制与振动控制需要处理复杂的姿态运动学耦合、动力学力矩耦合、挠性模态与刚体的动力学耦合,以及在轨航天器挠性附件的参数不确定等问题。基于频带分离方法分别设计了姿态控制器和振动控制器,其中的挠性附件振动对姿态的影响以时变干扰模型进行考虑。利用奇异摄动理论,设计了姿态控制器。该控制器由快速角速度环和慢速角度环两回路组成,采用具有较强抗干扰能力的积分型SDRE（State-Dependent Riccati Equation）控制器进行姿态指令跟踪。对于挠性振动,设计了独立模态控制的正位置反馈（PPF）控制器,通过对一阶控制器参数进行调节,使系统当存在结构不确定或参数变化的情况时仍能较好地收敛,保证了系统的鲁棒性。最后仿真表明了在干扰力矩下姿态的稳定性和振动的快速抑制。     

一类具有非线性参数不确定性的系统的自适应控制

针对非线性函数关于未知参数是凹/凸函数的一类非线性系统,设计了基于极大极小策略的自适应控制器.与过去的具有非线性参数不确定性的系统的自适应控制器相比,该控制器能保证闭环系统输出跟踪误差渐近趋于零.最后通过对一个单摆模型的仿真验证了算法的有效性.     

高阶不确定系统的自适应跟踪控制

针对一类未知控制增益的不确定非线性系统,提出了一种自适应跟踪控制方法.文中的不确定性包括时变和时不变参数.基于反步设计法,提出了一种新的自适应控制方法.该方法不采用饱和控制,能保证跟踪误差收敛于零.提出了一个仿真例子,仿真结果说明了该方法的有效性.     

Dynamic quality control in assembly systems

We study an assembly system, in which each end product consists of two different components. The components are produced in batches, with possible defective units. The proportion of defective units in each batch is itself a random variable, known only in terms of its distribution. Defective units can be identified and corrected through an inspection-repair procedure, before final assembly taking place. We are concerned with developing an optimal inspection policy that minimizes the total expected cost due to inspection, repair, and warranty. Particularly, we focus on policies that have simple threshold structures and a near-optimal performance.     

Adaptive trochoidal toolpath for complex pockets machining

This work proposes a novel adaptive trochoidal (TR) toolpath model for complex pocket machining. The proposed model is able to adjust its TR radius, while simultaneously offers an adaptive trochoidal step for generation of each toolpath cycle. With the varying radius, complex regions can be machined by a single strip of TR toolpath. Moreover, the step of each TR cycle can be adjusted with reference to the varied radius so as to maintain a constant radial depth of cut, and hence more stable material removal rate among all TR cycles can be achieved. For the pocket machining cases with complex inner and outer boundaries, experimental study has shown that the proposed TR toolpath can effectively minimise the fluctuation of cutting forces, and achieve better toolpath efficiency.     

Adaptive resonance theory-based neural algorithms for manufacturing process quality control

The demand for quality products in industry is continuously increasing. To produce products with consistent quality, manufacturing systems need to be closely monitored for any unnatural deviation in the state of the process. Neural networks are potential tools that can be used to improve the analysis of manufacturing processes. Indeed, neural networks have been applied successfully for detecting groups of predictable unnatural patterns in the quality measurements of manufacturing processes. The feasibility of using Adaptive Resonance Theory (ART) to implement an automatic on-line quality control method is investigated. The aim is to analyse the performance of the ART neural network as a means for recognizing any structural change in the state of the process when predictable unnatural patterns are not available for training. To reach such a goal, a simplified ART neural algorithm is discussed then studied by means of extensive Monte Carlo simulation. Comparisons between the performances of the proposed neural approach and those of well-known SPC charts are also presented. Results prove that the proposed neural network is a useful alternative to the existing control schemes.     

Adaptive nonlinear tool path optimization for five-axis machining

Current tool path computation in the CAM algorithms approximates the surface by piecewise linear interpolation. In the case of three-axis machining on a CNC machine the tool will exactly reproduce this computed tool path. However in the case of five-axis simultaneous machining the real tool path on the CNC machine will not follow the linear approximation computed by the conventional CAM algorithm. A new CAM algorithm is proposed which approximates the surface to be machined by a piecewise curved approximation. This curve represents the real tool path followed on the five-axis machine. This piecewise curved approximation is further optimized by formulating the tool path computation as the generation of a grid based on a variational smoothness penalty function. This new algorithm considerably improves the accuracy and reduces the number of blocks and machining time.     

柴油机间歇性排气噪声自适应有源前馈控制的DSP仿真

分析了柴油机排气噪声的特征，利用自适应有源前馈系统对噪声进行控制；对间歇性噪声的控制进行了建模分析；对柴油机的排气噪声进行了有源消声的初步设计；参考柴油机实际工况，利用高速信号处理芯片TMS320F2812进行了编程及调试；通过实测数据和DSP仿真实验验证了所采用方法的有效性。     

Review of image quality standards to control digital X-ray systems

A literature review was carried out on quality criteria for the evaluation of image quality for interventional radiology, digital subtraction angiography, computed radiography and direct digital radiography systems. Existing national and international standards were also reviewed. Recommendations for image quality standards for digital X-ray systems are proposed.     

具有类反斜线回滞系统的自适应控制

考虑一类具有类反斜线回滞的不确定非线性系统自适应控制问题.利用神经网络提出了变结构自适应控制方法和近似自适应控制方法,变结构自适应控制方法能保证跟踪误差趋于零,近似自适应控制方法的控制律是光滑的,能保证跟踪误差最终小于任意给定的正数.文中举例说明了结果的有效性.     

Adaptive output feedback sliding mode control for time-delay systems with extended disturbance

This study proposes a new adaptive output feedback sliding mode control (SMC) for mismatched uncertain time-delay systems. First, sufficient conditions in terms of linear matrix inequalities are derived such that the equivalent reduced-order system in the sliding mode is asymptotically stable. Second, based on a new lemma and a novel adaptive law, an adaptive sliding mode controller is designed to guarantee the finite-time reachability of the system states using output feedback only. The proposed method is not limited by the following conditions: (1) the exogenous disturbances must be bounded by a known function of the outputs or by a known function of the state and delayed state variables, and (2) the norm of unmeasured states must be bounded by a constant value. As these conditions are required for the application of most existing SMC approaches for time-delay systems, the proposed approach can be applied to a more generalized system, making it a valuable contribution to the field.     

一类非线性不确定结构系统的鲁棒饱和主动控制

对一类非线性不确定结构系统研究了在外部干扰下的鲁棒饱和主动控制策略.将质量、阻尼、刚度矩阵都存在不确定的结构系统描述为一种不确定中立系统,采用鲁棒饱和主动控制策略,提出基于线性矩阵不等式的代数解.通过提出的控制方法同时保证了结构系统在模型和参数摄动下以及在控制变量和扰动存在非线性不确定性时的鲁棒稳定.最后通过对一个4层建筑大楼在地震波作用下的主动振动控制仿真证明了该方法的有效性.     

The influence of cutting force on surface machining quality

Appropriately controlled cutting forces can contribute not only to the safety and efficiency of machining but also to the quality of machined surfaces. It is even more important when hardened material is cut. The correlation between the cutting force and the surface quality in ball-end milling operations has been investigated by machining P20 steel (HRC 30) work-pieces using solid carbide ball-end cutters. Plane surfaces with different depth of cut were machined using two different cutting strategies. The first strategy cut the test-piece using a cutting force model, whereas the other machined with a feed rate optimization product, which uses the removal rate as an analogue of cutting force to control the feed rate. The test results show that constant surface quality is possible when the cutting forces are controlled through feed rate adjustment. Conversely, a desired surface quality can also be maintained by controlling the cutting force in a predetermined manner.     

改善低频线振动台加速度失真度的自适应重复学习控制

为了抑制低频线振动台系统中存在的摩擦力、推力波动及死区特性,提出了一种新的自适应重复学习控制方法。利用函数逼近技术将死区不确定性表示成正交基函数的线性组合。所设计的控制律由自适应构件、等效PID构件、重复学习构件组成。自适应构件用于在线估计线性组合中的未知参数及摩擦力数学模型的参数;PID构件用来镇定低频线振动台系统,抑制非周期性扰动;重复学习构件在未知对象模型的情况下抑制周期性推力扰动,并提高对周期性输入信号的跟踪能力。采用Lyapunov理论设计的自适应重复学习控制律保证了闭环系统的渐近稳定性和跟踪性能。仿真结果表明该控制方法提高了低频线振动台的跟踪性能,并改善了加速度失真度。     

Adaptive systems in speckle-pattern interferometry

The concept of adaptivity in television holography is discussed, and various realizations of adaptivity are presented. In one possible variation, functions of the components of the optical arrangement may be changed to adapt them to measurement conditions. An additional peculiarity of the technique is that reference waves are produced by holographically reconstructed virtual images. A method, believed to be new, is introduced for synthesizing the phase front of the master object beam that is produced by a simple holographic optical element and is used as a smooth or a speckled reference beam in the electronic speckle-pattern interferometer. An adaptive interferometer is presented as a measuring device for various measuring tasks. Selected applications are shown, demonstrating different aspects of adaptivity.