液晶自适应光学系统中倾斜镜的建模与控制

为了提高液晶自适应光学系统的波前探测精度,研究了该系统中倾斜镜的校正方法。分析了液晶自适应光学系统中各环节的物理特性,利用拉格朗日方程给出了倾斜镜系统模型的基本结构;采用子空间辨识方法确定了模型参数,同时利用非线性最小二乘算法对子空间模型的频域特性进行了修正。修正后模型幅频特性均方根误差为0.024 5dB,相频特性均方根误差为1.9008°。引入Smith控制策略来解决倾斜镜校正波前整体倾斜过程中的时滞问题;利用子空间辨识出的模型分别进行Smith和PID的仿真和实验验证,得到的结果与仿真计算相吻合,即在相同稳定裕度的情况下,采用Smith补偿PID算法的误差抑制带宽比传统PID算法提高了23.97%。最后,用提出的方法对一组湍流整体倾斜信号进行了校正。结果显示:采用Smith补偿PID算法的控制精度比传统PID算法提高了21.03%,证实提出的方法优化了倾斜镜的校正精度,保证了开环液晶自适应光学系统的波前探测精度。     

自适应光学系统中倾斜镜的自适应逆控制

为了克服自适应光学系统中倾斜镜的迟滞响应,提高响应的线性度,改善倾斜镜的控制精度,研究了倾斜镜的迟滞非线性效应。提出了一个基于频率相关的Mutified-Prandtl-Ishlinskii(MPI)模型的补偿方法来在线自适应逆补偿倾斜镜的迟滞非线性。结合反馈PID控制构成了自适应逆前馈复合控制方案,其中自适应逆前馈克服了由于频率等因素引起的迟滞曲线变化,反馈PID则改善了整体的控制性能。建立了倾斜镜二阶系统模型来估计倾斜镜系统的输出,解决了MPI模型参考信号的问题,避免了增加额外前馈传感器,保证了光能量的利用率。实验结果表明,倾斜镜系统15 Hz非线性迟滞率由原来的24.28%降为1.17%,线性度提高了约95%,控制精度较传统PID方法提高了约60%。该方法能够有效补偿倾斜镜的迟滞非线性,提高了自适应光学系统中倾斜镜的校正精度。     

1200mm望远镜开环液晶自适应光学系统设计

为验证液晶自适应光学成像技术校正大气湍流所引起的波前像差的有效性,提高光学系统的能量利用率,应用Ze-max软件设计出了与1200mm望远镜匹配的开环液晶自适应光学系统。针对开环自适应光学系统探测光路和校正光路自身的特殊要求,制定了具体的公差原则,并应用Zemax软件进行了公差分析。分析表明,设计的自适应光学系统具备较宽松的公差条件,容易加工和装调。评价了该光学系统的成像性能,结果表明,设计的自适应光学系统的MTF曲线接近衍射极限,光学传递函数的模在50lp/mm时可达到0.4,而成像CCD的极限分辨率为31lp/mm,充分地利用了CCD相机的分辨资源。该自适应光学系统与1200mm望远镜对接匹配后的组合焦距为19.9m,F数为16,PV值为0.0314λ。     

用自适应预报控制方法提高数控机床加工精度

在ＤＮＣ环境下,以数控铣床曲面加工为对象,运用序后控测、自适应预报控制方法,提高了数控铣床的曲面加工精度,这种方法特别为那些实现实时有困难的加工机床。提供了一种有效的加工质量控制方法。     

自适应光学系统中非共轭问题对波前校正的影响

在常规的自适应光学系统中,变形镜与波前传感器满足共轭位置关系以保证最好的校正效果。现基于角谱理论,通过对光场线性传输过程的仿真,分析了波前传感器偏离与变形镜共轭的位置的情况下波前校正效果所受到的影响。结果表明,波前传感器偏离共轭位置的距离增大和共轭位置波前的增大,均会导致校正效果变差。     

优化的精度控制自适应调节方案

针对非线性不确定系统,研究并优化了基于输入信号参考自适应PID控制方法——在模型参考自适应PID控制的基础上以输入信号为参考代替模型参考对系统进行控制。控制方法是基于李雅普诺夫平衡点稳定定理控制方法的系统稳定性推演的,由于控制方法中引入稳定项后使控制过程带来微分项,控制方法中加入滤波器,通过系统的自适应调节最终使系统趋于稳定状态。同时,在控制中加入PID因子使系统的控制性能趋佳。该方法是基于输入信号为参考的自适应控制,减少了模型参考带来的误差。仿真推演结果显示,被控对象可以有较强的适应能力,趋于实现更优的过程控制效果。文中给出了运用于海洋钻井设备运动补偿装置实例的分析。     

ABCD矩阵与高斯光束光学系统的讨论

本文用ABCD矩阵讨论高斯光束经光学系统传输的理论问題;给出简单和多元件光学系统的总传递矩阵元素、因式分解、光路运算、光束变换,以及系统合成的实用计算方法。     

Implementation of an adaptive fuzzy compensator for coupled tank liquid level control system

In this paper, an adaptive fuzzy control (AFC) system is proposed to realize level position control of two coupled water tanks, often encountered in practical process control. The fuzzy control system includes an adaptive model identifier and controller. The gains of AFC are obtained by using the fuzzy identifier model which is defined by real system outputs and control inputs. The parameters of fuzzy identifier model are adjusted online by using recursive least square algorithm. Because the controller has a recursive form it treats model uncertainties and external disturbances in an implicit way. Thus there is no need to specify uncertainty and disturbances for this controller design in advance. A well-tuned conventional proportional integral (PI) controller is also applied to the two coupled tank system for comparison with the AFC system. Experimentation of the coupled tank system is realized in two different configurations, namely configuration #1 and configuration #2 respectively. In configuration #1, the water level in the top tank is controlled by a pump. In configuration #2, the water level in the bottom tank is controlled by the water flow coming out of the top tank. Experimental results prove that the AFC shows better trajectory tracking performance than PI controller in that the plant transient responses to the desired output changes have shorter settling time and smaller magnitude overshot/undershoot. Robustness of the AFC with respect to water level variation and capability to eliminate external disturbances are also achieved. Experimental results show that AFC is a strong and a practical choice for liquid level control.     

Experimental evaluation of adaptive three-tank level control

Liquid level control through regulation of mass flow rates is an important application in various areas of the power industry. Very often a PID controller is used for these applications. This paper compares a nonconventional PID controller and three different types of adaptive controller, a direct model reference adaptive controller (MRAC), an indirect MRAC with Lyapunov estimation, and an indirect MRAC with recursive least-squares (RLS) updating estimation, for liquid level control. By implementing all four controllers on a three-tank system, the performances of each are compared. All controllers track a sinusoidal input very well and overall exhibit somewhat varying performance. The direct MRAC and the indirect MRAC with RLS estimation give the best performance. With Lyapunov estimation and RLS estimation, all the system parameter estimates converge to the reference model values. However, RLS estimation has a much faster convergence. It is concluded that adaptive liquid level control is an improvement over traditional liquid level control when precise level control in three coupled tanks is desired.     

液晶空间光调制器对真实人眼畸变波前的校正

基于液晶空间光调制器波前调制量大,像素密度高,驱动电压低等优点,用液晶空间光调制器作为校正眼像差的关键元件,研制了用于人眼畸变波前探测和校正的自适应光学系统.介绍了液晶空间光调制器的波前调制原理,利用ZYGO干涉仪测定了位相调制和灰度级的关系曲线.分别用Hartman-Shack波前探测器和高分辨率液晶空间光调制器探测和校正人眼的波前畸变,对近视5 m~(-1) (500度)的人眼进行了自适应校正实验.校正后,系统的波前误差为0.086λ PV和0.013λ RMS, 达到了系统的衍射极限,并可清晰地分辨眼底原来模糊的细胞.实验结果表明,液晶空间光调制器可以有效校正畸变波前,达到提高成像质量的目的.     

Tracking control of cascade systems based on passivity: the nonadaptive and adaptive cases

A new cascade passivity-based control scheme for tracking purposes is proposed in this paper. The proposed scheme is valid for a certain class of nonlinear systems even with unstable zero dynamic, and it is also useful for regulation and stabilization purposes. The cases where all system parameters are assumed to be known (nonadaptive case) and also the case when they are unknown (adaptive case) are considered. Some simulation examples are studied to analyze the behavior of the proposed scheme.     

光学系统MTF测量中的自动背景校正方法

为避免光学系统传递函数(MTF)测量中手动背景校正方法的诸多弊端,提出了自动背景校正方法,这种方法能够准确去除线扩散函数中的背景,并且不受周围环境光照不稳定的影响。将这种方法应用在数字傅里叶法MTF测试中,完成了对镜头MTF的测试。试验结果表明,测试平均误差小于5％。     

Comparative measurement of the breakup length of liquid jets in airblast atomisers using optical connectivity,electrical connectivity and shadowgraphy

A comparative examination of the optical connectivity, electrical connectivity and shadowgraphy techniques for the measurement of the break-up length of atomising liquid jets from a co-axial airblast atomiser is presented. The atomiser was operated over air-to-liquid Momentum Ratios between 27 and 335 and Momentum Flux Ratios between 0.67 and 8.27. Shadowgraphy records instantaneous images of the shadow of the atomising liquid jet when it is back-illuminated by a light source. The electrical connectivity uses the continuity of an electrically conducting atomising liquid jet to measure the potential during the presence of an electrical connection between the spray nozzle and a probe further downstream. The optical connectivity visualises the atomising liquid jet, doped with a fluorescing dye, as it is illuminated from within the nozzle using a laser beam. Comparison of the measured breakup lengths with time resolved shadowgraphy, optical connectivity and electrical connectivity, following the proposed novel processing of the time-dependent potential, showed that the mean values are all within ±15% of each other. The advantages and limitations of each technique are discussed.     

汽车道路模拟系统的模糊自适应控制及仿真

以汽车道路模拟系统为研究对象,根据模糊控制理论,将模糊控制与常规的增量式PID控制相结合,设计出一套模糊自适应控制系统.并对C级路面谱进行仿真再现,仿真结果表明,该控制器比常规PID控制器具有更高的控制精度和更好的动态性能,在道路模拟仿真试验中可以达到非常满意的效果.     

Real-time tracking control of electro-hydraulic force servo systems using offline feedback control and adaptive control

This paper focuses on an application of an electro-hydraulic force tracking controller combined with an offline designed feedback controller (ODFC) and an online adaptive compensator in order to improve force tracking performance of an electro-hydraulic force servo system (EHFS). A proportional-integral controller has been employed and a parameter-based force closed-loop transfer function of the EHFS is identified by a continuous system identification algorithm. By taking the identified system model as a nominal plant model, an H_∞ offline design method is employed to establish an optimized feedback controller with consideration of the performance, control efforts, and robustness of the EHFS. In order to overcome the disadvantage of the offline designed controller and cope with the varying dynamics of the EHFS, an online adaptive compensator with a normalized least-mean-square algorithm is cascaded to the force closed-loop system of the EHFS compensated by the ODFC. Some comparative experiments are carried out on a real-time EHFS using an xPC rapid prototype technology, and the proposed controller yields a better force tracking performance improvement.