Electro-hydraulic proportional servo valve (EHPSV) is a typical precision hydraulic component, widely used in construction machinery, aircraft, ships and other important equipment. When the electro-hydraulic proportional servo valve is working, the pollution particles in the hydraulic oil will cause erosion and wear of the valve element and seriously affect the control precision of the valve. In addition, the hydraulic system is a typical nonlinear system, if the traditional PID controller is used for control, the control precision of the system can not be guaranteed. In this paper, the typical valve controlling cylinder system in hydraulic system is taken as the research object. An ARC controller is designed to control the system, and an erosion wear prediction model is established by finite element simulation to control the valve-controlled cylinder system with high-quality flow compensation under the ARC control architecture. In this paper, the modeling and simulation of valve controlling cylinder system are carried out by MATLB/Simulink. The results show that the adaptive robust controller with erosion wear prediction model can effectively improve the control precision of proportional servo valve.

Bimodal atomic force microscopy (AFM) is an important branch of multi-frequency AFM, which can simultaneously obtain the surface morphology and properties of samples. However, the atomic-scale phenomena in the vibration process of bimodal AFM have not been observed due to the absence of atomic-scale model. In this paper, the molecular dynamics (MD) simulations are used to model bimodal AFM. A double springs oscillator model is used to describe the first two vibration mode of the AFM cantilever. By applying dual-frequencies excitation, the dynamics of the model tip and the tip-substrate interactions are observed. The amplitude, phase shift and the average force change of the tip obtained in the simulation were found to be consistent with the continuum simulation results. The effect of different amplitude ratios on the vibration response of the tip is analyzed and validated by experiments. This novel model makes it possible to simulate two vibration modes of cantilever at atomic scale in bimodal AFM.

Compressed sensing (CS) can be used to obtain a signal through undersampling and reconstruction, which enables the atomic force microscope (AFM) to spatially under-sample the topography information to increase the imaging rate and reduce the amount of probe-sample interaction. However, the imaging mode of the AFM, which would result in the huge occupation of computing resources including computing time and memory space, makes it inefficient and time-consuming to apply the normal image reconstruction method directly to recover the sample topography from undersampled data. And it is unrealistic to recover a high-solution image by the normal compressed sensing. Here, a novel image reconstruction method based on Bayesian compressing sensing for the undersampled AFM data with noise is proposed to significantly reduce the occupation of computing resources while guaranteeing a high-quality image reconstruction. In the proposed method, the AFM image is regarded as a collection of independent vectors and each vector (a subset of the pixels) is recovered separately. The Bayesian compressed sensing is introduced to provide a better reconstruction performance. The reconstruction experiments demonstrate that the proposed method can significantly reduce the occupation of computing resources while achieving high-quality AFM image reconstruction from the undersampled data with noise. The reconstruction time has been shortened from tens of minutes to less than one minute and the RAM used is reduced to only 1/n2 of the normal algorithms, which allows the AFM image reconstruction from undersampled data to be easily and conveniently achieved in any personal computer.

AbstractAtomic force microscope (AFM) is an idealized tool to measure the physical and chemical properties of the sample surfaces by reconstructing the force curve, which is of great significance to materials science, biology, and medicine science. Frequency modulation atomic force microscope (FM-AFM) collects the frequency shift as feedback thus having high force sensitivity and it accomplishes a true noncontact mode, which means great potential in biological sample detection field. However, it is a challenge to establish the relationship between the cantilever properties observed in practice and the tip–sample interaction theoretically. Moreover, there is no existing method to reconstruct the force curve in FM-AFM combining the higher harmonics and the higher flexural modes. This paper proposes a novel method that a full force curve can be reconstructed by any order higher harmonics of the first two flexural modes under any vibration amplitude in FM-AFM. Moreover, in the small amplitude regime, short range forces are reconstructed more accurately by higher harmonics analysis compared with fundamental harmonics using the Sader–Jarvis formula.

Higher harmonics have been widely used to characterize nanomechanical properties of the sample surface in tapping mode atomic force microscopy. They are usually analyzed by the Fourier transform method which provides time-averaged amplitude and phase information. In this paper, we apply the analytic wavelet transform to analyze higher harmonics. The intuitive descriptions of higher harmonics are obtained by the time-frequency analysis of the tip motion signal. The temporal evolutions of the higher harmonics are analyzed. The higher harmonics extracted by the analytic wavelet transform are closely related to the wavelet parameters. Different time and frequency features of higher harmonics can be analyzed through adjusting the wavelet parameters. Moreover, the root-mean-square amplitude and the peak amplitude obtained by the analytic wavelet transform can provide better characterization of sample properties than the amplitude obtained by the Fourier transform method.

This paper presents a new structure of a novel horizontal atomic force microscope probe utilizing a quartz tuning fork. The horizontal structure exhibits high resistance to environmental noise, and thus the probe can maintain good stability throughout the imaging work. The quartz tuning fork, which is utilized as a force sensor due to its simple mechanical structure and self-actuating and self-sensing characteristics, can significantly simplify the mechanical structure of the probe. The probe is divided into three parts: an approximation device, a force sensor, and a three-dimensional scanner. Each part is carefully designed to guarantee the imaging performance. It is verified that the proposed horizontal AFM probe is stable by conducting finite-element analysis, including modal analysis and noise analysis. Furthermore, the probe is fabricated and the experiments are performed to verify its stability. The proposed horizontal AFM probe combined with the existing control system in the frequency modulation succeeds in imaging within 25 μm × 25 μm and 20 μm × 20 μm ranges stably.

The tip motion of the dynamic atomic force microscope in liquids shows complex transient behaviors when using a low stiffness cantilever. The second flexural mode of the cantilever is momentarily excited. Multiple impacts between the tip and the sample might occur in one oscillation cycle. However, the commonly used Fourier transform method cannot provide time-related information about these transient features. To overcome this limitation, we apply the wavelet transform to perform the time-frequency analysis of the tip motion in liquids. The momentary excitation of the second mode and the phenomenon of multiple impacts are clearly shown in the time-frequency plane of the wavelet scalogram. The instantaneous frequencies and magnitudes of the second mode are extracted by the wavelet ridge analysis, which can provide quantitative estimations of the tip motion in the second mode. Moreover, the relations of the maximum instantaneous magnitude (MIM) to the amplitude setpoint and the Young's modulus of the sample surface are investigated. The results suggest that the MIM can be used to characterize the nanomechanical property of the sample surface at high amplitude setpoints.

Here, a novel method, real-time scan speed control for raster scan amplitude modulation atomic force microscopes (AM-AFMs), is proposed. In general, the imaging rate is set to a fixed value before the experiment, which is determined by the feedback control calculations on each imaging point. Many efforts have been made to increase the AFM imaging rate, including using the cantilever with high eigenfrequency, employing new scan methods, and optimizing other mechanical components. The proposed real-time control method adjusts the scan speed linearly according to the error of every imaging point, which is mainly determined by the sample topography. Through setting residence time on each imaging point reasonably, the performance of AM-AFMs can be fully exploited while the scanner vibration is avoided when scan speed changes. Experiments and simulations are performed to demonstrate this control algorithm. This method would increase the imaging rate for samples with strongly fluctuant topography up to about 3 times without sacrificing any image quality, especially in large-scale and high-resolution imaging, in the meanwhile, it reduces the professional requirements for AM-AFM operators. Since the control strategy employs a linear algorithm to calculate the scanning speed based on the error signal, the proposed method avoids the frequent switching of the scanning speed between the high speed and the low speed. And it is easier to implement because there is no need to modify the original hardware of the AFM for its application.

Proportional-integral-derivative (PID) parameters play a vital role in the imaging process of an atomic force microscope (AFM). Traditional parameter tuning methods require a lot of manpower and it is difficult to set PID parameters in unattended working environments. In this manuscript, an intelligent tuning method of PID parameters based on iterative learning control is proposed to self-adjust PID parameters of the AFM according to the sample topography. This method gets enough information about the output signals of PID controller and tracking error, which will be used to calculate the proper PID parameters, by repeated line scanning until convergence before normal scanning to learn the topography. Subsequently, the appropriate PID parameters are obtained by fitting method and then applied to the normal scanning process. The feasibility of the method is demonstrated by the convergence analysis. Simulations and experimental results indicate that the proposed method can intelligently tune PID parameters of the AFM for imaging different topographies and thus achieve good tracking performance.

针对车辆悬架状态无法准确估计的问题,设计了自适应交互式多模型卡尔曼滤波(IMMKF)状态观测器.首先,建立了标准路面激励模型与四分之一线性化悬架模型;然后,利用递归最小二乘方法与IMMKF理论,设计了不同工况下广义悬架模型自适应IMMKF状态观测器;最后,分析了在标准C级路面激励工况下簧载质量变化对悬架系统状态估计的影响.仿真与台架试验结果表明,在簧载质量变化工况下,所设计的自适应IMMKF状态观测器与传统卡尔曼滤波状态观测器相比其估计精度至少可以提高20％.

设计了基于双A RM的频率调制原子力显微镜,以石英音叉探针作为力传感器,由自激励电路驱动探针振动在实时的共振频率处,并保持振幅恒定;采用两块ARM Cortex-M4内核的高性能微控制器进行频率解调和系统控制,频率解调采用软件锁相环设计,控制系统采用嵌入式实时操作系统CMSIS-RTOS RTX进行任务管理和调度,保证了系统的实时性.对标准样品进行扫描表明,该系统可以稳定工作.该频率调制原子力显微镜具有小型化、低成本的优势,可以被应用于教学实验.

We report on the generation of dual-wavelength mode-locked laser pulse in an Er-doped ring-shaped fiber cavity with WS2 nanosheets based saturable absorber (SA), emitting at wavelength of 1531.8 nm and 1556.7 nm. The WS2 nanosheets were precipitated on the head face of fiber patch cord via light precipitation method. By adjusting the polarization of lasing mode, the gain of the Er-doped fiber laser was effectively controlled and the stable dual-wavelength mode-locking operation was achieved. Our investigation revealed WS2's extraordinary nonlinear properties, which make it an excellent material for saturable absorber for passively mode-locked fiber lasers.

In view of the problems of corrosion and bonding of tungsten that have been restricting conducting AFM experiments,a method for the manufacture of AFM probe which is made of tungsten and quartz tuning fork is proposed.Improving the original etching device can enhance rates of finished tungsten corrosion and a new bonding device has been used to increase efficiency of the bonding,which greatly avoids the interference of human factors.Finally,some experiments to test the performance of the probe are conducted.

Recent interest in high-precision positioning stages with large travel ranges has sparked renewed attention to the development of voice coil motors (VCMs). Due to their large output force, VCMs can actuate more complicated flexure structures, eliminate rail friction, and improve positioning speed. The VCM structure is both compact and flexible; hence, it is convenient to design VCMs for a variety of stage structures. Furthermore, VCMs combined with other actuators are able to achieve large travel ranges with high precision. In this paper, we summarize the principles and control methods of a typical VCM, and we analyze its properties, including thrust force, acceleration, and response time. We then present recent research on high-precision VCM positioning stages with large travel ranges.

Higher harmonics of tapping-mode atomic force microscope carries information about the mechanical properties of the sample on a nanometer scale. Unfortunately, the vibration amplitudes of traditional atomic force microscope (AFM) cantilever at higher harmonics are too small for practical AFM imaging. Ritz method demonstrates that specific cutout on the cantilever can realize internal resonance to enhance higher harmonics. In this paper, by COMSOL finite element simulation, the laws for fundamental frequency, second resonance frequency and their ratio each as a function of the size of the cutout and the position of the cutout on the cantilever are achieved. Using focused ion beam to hole the cantilever makes the second resonance frequency close to 6 times that of the fundamental frequency and also the 6th harmonic enhanced. Moreover, we obtain the image of the 6th harmonic on our home-made higher harmonic system.