Vibration reduction control of a voice coil motor (VCM) nano scanner

This paper presents vibration reduction control of a voice coil motor (VCM) nano scanner. We had developed a VCM scanner. The scanner has flexure hinges structure. However, the VCM nano scanner has some problems of thermal drift and small damping compared to the PZT driven nano scanner. Especially, the small damping coefficient of the VCM scanner causes mechanical vibration when the control input signal is near to the resonance frequencies. Additionally, disturbance to the VCM scanner and electronic noise in the sensor also cause the mechanical vibration when they are near to the resonant frequencies. The mechanical vibration reduces the servo bandwidth as well as the accuracy, which deteriorates the AFM image of the samples. We design a pre-filter to reduce the signal applied to the VCM nano scanner and electronic noise in the sensor whose frequency is closed the resonant frequency of the VCM nano scanner. We measure the time and frequency response of the VCM scanner without using the pre-filter and with using the pre-filter. Finally, the topology images of a bare wafer are measured and compared using the AFM.     

Control of voice coil motor nanoscanners for an atomic force microscopy system using a loop shaping technique

The voice coil motor nanoscanner has the advantages of large working range, easy control, and low cost compared to the conventional lead zirconate titanate driven nanoscanner. However, it has a small damping problem which causes mechanical vibration. The mechanical vibration reduces the accuracy as well as servobandwidth, which deteoriates the atomic force microscopy (AFM) image of the samples. In order to solve the vibration problem, the loop shaping technique [for vertical (z)] and input prefilter [for lateral (xy)] are applied. Experimental results of the proposed techniques are presented for vertical (z) and lateral (xy) scanner. Finally, the AFM images are provided to investigate its effect.     

Advances in hybrid laser joining

This paper presents vibration reduction control of a voice coil motor (VCM)-driven actuator for SPM applications. We had developed a VCM nanoscanner. The scanner has flexure hinges structure. However, the VCM nanoscanner has some problems of thermal drift and small damping compared to the PZT driven nanoscanner. Especially, the small damping coefficient of the VCM nanoscanner causes mechanical vibration when the control input signal is near to the resonance frequencies of the scanner. Additionally, disturbance to the VCM scanner and electronic noise in the sensor also causes the mechanical vibration when they are near to the resonant frequencies. The mechanical vibration reduces the servo bandwidth as well as the accuracy, which deteriorates the AFM image of the samples. We design input shaping prefilter to reduce the signal applied to the VCM nanoscanner and electronic noise in the sensor whose frequency is close to the resonant frequency of the VCM nanoscanner. We measure the time and frequency response of the VCM scanner without using the prefilter and with using the prefilter. Finally, the topology images of a bare wafer are measured and compared using the AFM.     

汽轮机旋转部件振动可靠性设计的研究

本文介绍了汽轮机旋转部件的振动可靠性设计方法。该方法以机械概率设计法为基础,把汽轮机旋转部件的固有频率和激振力频率按照实际情况处理为随机变量,在设计阶段确定汽轮机旋转部件避开共振的可靠度。给出了汽轮机叶轮、叶片和转子振动可靠性设计方法以及某些部件振动可靠性设计的实例。     

Influence of the tip mass and position on the AFM cantilever dynamics: Coupling between bending,torsion and flexural modes

The effects of the geometrical asymmetric related to tip position as a concentrated mass, on the sensitivity of all three vibration modes, lateral excitation (LE), torsional resonance (TR) and vertical excitation (VE), of an atomic force microscopy (AFM) microcantilever have been analyzed. The effects of the tip mass and its position are studied to report the novel results to estimating the vibration behavior of AFM such as resonance frequency and amplitude of the microcantilever. In this way, to achieve more accurate results, the coupled motion in all three modes is considered. In particular, it is investigated that performing the coupled motion in analysis of AFM microcantilever is almost necessary. It is shown that the tip mass and its position have significant effects on vibrational responses. The results show that considering the tip mass decreases the resonance frequencies particularly on high-order modes. However, dislocating of tip position has an inverse effect that causes an increase in the resonance frequencies. In addition, it has been shown that the amplitude of the AFM microcantilever is affected by the influences of tip and its position. These effects are caused by the interaction between flexural and torsional motion due to the moment of inertia of the tip mass.     

MEMS-based fast scanning probe microscopes

Scanning probe microscopy is a frequently used nanometer-scale surface investigation technique. Unfortunately, its applicability is limited by the relatively low image acquisition speed, typically seconds to minutes per image. Higher imaging speeds are desirable for rapid inspection of samples and for the study of a range of dynamic surface processes, such as catalysis and crystal growth. We have designed a new high-speed scanning probe microscope (SPM) based on micro-electro mechanical systems (MEMS). MEMS are small, typically micrometer size devices that can be designed to perform the scanning motion required in an SPM system. These devices can be optimized to have high resonance frequencies (up to the MHz range) and have very low mass (10⁻¹¹ kg). Therefore, MEMS can perform fast scanning motion without exciting resonances in the mechanical loop of the SPM, and hence scan the surface without causing the image distortion from which conventional piezo scanners suffer. We have designed a MEMS z-scanner which we have integrated in commercial AFM (atomic force microscope) and STM (scanning tunneling microscope) setups. We show the first successful AFM experiments.     

Frequency Loss and Recovery in Rolling Bearing Fault Detection

Rolling element bearings are key components of mechanical equipment. The bearing fault characteristics are a ected by the interaction in the vibration signals. The low harmonics of the bearing characteristic frequencies cannot be usually observed in the Fourier spectrum. The frequency loss in the bearing vibration signal is presented through two independent experiments in this paper. The existence of frequency loss phenomenon in the low frequencies, side band frequencies and resonant frequencies and revealed. It is demonstrated that the lost frequencies are actually suppressed by the internal action in the bearing fault signal rather than the external interference. The amplitude and distribution of the spectrum are changed due to the interaction of the bearing fault signal. The interaction mechanism of bearing fault signal is revealed through theoretical and practical analysis. Based on mathematical morphology, a new method is provided to recover the lost frequencies. The multi-resonant response signal of the defective bearing are decomposed into low frequency and high frequency response, and the lost frequencies are recovered by the combination morphological filter(CMF). The e ectiveness of the proposed method is validated on simulated and experimental data.     

Robust adaptive vibration control of a flexible structure

Different types of L1 adaptive control systems show that using robust theories with adaptive control approaches has produced high performance controllers. In this study, a model reference adaptive control scheme considering robust theories is used to propose a practical control system for vibration suppression of a flexible launch vehicle (FLV). In this method, control input of the system is shaped from the dynamic model of the vehicle and components of the control input are adaptively constructed by estimating the undesirable vibration frequencies. Robust stability of the adaptive vibration control system is guaranteed by using the L1 small gain theorem. Simulation results of the robust adaptive vibration control strategy confirm that the effects of vibration on the vehicle performance considerably decrease without the loss of the phase margin of the system.     

支座松动转子系统的振动特性分析

针对一端轴承支座与基础之间出现松动的情况，建立了转子-轴承系统的数学模型，利用数值积分等方法对该系统进行了数值模拟。模拟结果表明，系统运动具有多种形式1支座发生松动振动时很容易引起系统的1／3厦其倍数次的振动频谱分量，且频谱成分多以低频为主，伴随幅值较小的高频成分。     

基于Hypermesh和Ansys的卧螺过滤离心机转鼓系的模态分析

卧式螺旋过滤离心机的转鼓系作为整机振动的振源,是研究离心机动载荷与机械振动的重点对象。结构共振与物料分布不均是转鼓系振动的主要原因。对转鼓系进行有限元模态分析,可以避免结构共振的发生。通过UG建立了转鼓系的几何模型,并利用Hypermesh对几何模型进行了六面体网格划分。采用接触对与MPC算法,实现了零部件之间不连续网格的连接。基于BlockLanczos算法,在Ansys中对转鼓系有限元模型进行了特征值提取,得到了转鼓系在有、无离心预应力下的前8阶固有频率与振型。研究表明,转鼓系在给定工作转速下,不会发生结构共振。离心预应力对固有频率的低频成分影响较大,而对中高频成分影响较小。研究结论为整机瞬态动力学分析与转鼓系结构优化研究与设计提供了依据。     

航空机轮刹车振动力学建模与试验分析

为探究飞机刹车系统的振动规律,以航空机轮刹车装置为研究对象,通过对刹车装置的受力分析建立了刹车扭转振动和轴向振动的力学模型,建立刹车振动系统的频率方程,计算出扭转和轴向固有频率,采用m+p动态测试软件对力学模型和固有频率进行验证,理论与试验结果基本一致。在惯性试验台上进行刹车振动测试,通过理论计算和试验结果初步得出了刹车振动规律,为航空机轮刹车装置的设计和改进提供了依据。     

Monitoring gear vibrations through motor current signature analysis and wavelet transform

In gearboxes, load fluctuations on the gearbox and gear defects are two major sources of vibration. Further, at times, measurement of vibration in the gearbox is not easy because of the inaccessibility in mounting the vibration transducers. An efficient and new but non-intrusive method to detect the fluctuation in gear load may be the motor current signature analysis (MCSA). In this paper, a multi-stage transmission gearbox (with and without defects) has been studied in order to replace the conventional vibration monitoring by MCSA. It has been observed through FFT analysis that low frequencies of the vibration signatures have sidebands across line frequency of the motor current whereas high frequencies of vibration signature are difficult to be detected. Hence, discrete wavelet transform (DWT) is suggested to decompose the current signal, and FFT analysis is carried out with the decomposed current signal to trace the sidebands of the high frequencies of vibration. The advantage of DWT technique to study the transients in MCSA has also been cited. The inability of CWT in detecting either defects or load fluctuation has been shown. The results indicate that MCSA along with DWT can be a good replacement for conventional vibration monitoring.     

“Multimode vibration cutting” – A new vibration cutting for highly-efficient and highly-flexible surface texturing

This paper proposes a new vibration cutting method named “multimode vibration cutting” for precision surface texturing. The proposed cutting method utilizes multiple unidirectional vibration modes mainly in the depth-of-cut direction. The vibrations at multiple frequencies induced to the tool tip can generate not only sinusoidal but also highly-flexible trajectories such as trapezoidal, triangular, and distorted triangular waves. Notably, only a sinusoidal vibration can be induced when a single resonant vibration is applied to the tool tip. Compared to conventional highly-flexible cutting methods for surface texturing, such as the utilization of fast tool servo and amplitude control of ultrasonic elliptical vibration cutting, the proposed method is highly-efficient because of its direct usage of high resonant frequencies. Compared to conventional highly-efficient cutting methods for surface texturing, such as linear and elliptical vibration cutting which mainly utilizes the vibration component in the depth-of-cut direction, the proposed method can generate highly-flexible trajectories for various micro texture profiles. In this study, an ultrasonic multimode vibration device is developed, and the mechanics of generating multimode vibrations are demonstrated. Turning experiments with several texture profiles are performed to confirm the validity of the proposed method for highly-efficient and highly-flexible micro/nano surface texturing.     

Components for high speed atomic force microscopy

Many applications in materials science, life science and process control would benefit from atomic force microscopes (AFM) with higher scan speeds. To achieve this, the performance of many of the AFM components has to be increased. In this work, we focus on the cantilever sensor, the scanning unit and the data acquisition. We manufactured 10 microm wide cantilevers which combine high resonance frequencies with low spring constants (160-360 kHz with spring constants of 1-5 pN/nm). For the scanning unit, we developed a new scanner principle, based on stack piezos, which allows the construction of a scanner with 15 microm scan range while retaining high resonance frequencies (>10 kHz). To drive the AFM at high scan speeds and record the height and error signal, we implemented a fast Data Acquisition (DAQ) system based on a commercial DAQ card and a LabView user interface capable of recording 30 frames per second at 150 x 150 pixels.     

Coupled lateral bending-torsional vibration sensitivity of atomic force microscope cantilever

We study the influence of the contact stiffness and the ration between cantilever and tip lengths on the resonance frequencies and sensitivities of lateral cantilever modes. We derive expressions to determine both the effective resonance frequency and the mode sensitivity of an atomic force microscope (AFM) rectangular cantilever. Once the contact stiffness is given, the resonance frequency and the sensitivity of the vibration modes can be obtained from the expression. The results show that each mode has a different resonant frequency to variations in contact stiffness and each frequency increased until it eventually reached a constant value at very high contact stiffness. The low-order vibration modes are more sensitive to vibration than the high-order mode when the contact stiffness is low. However, the situation is reversed when the lateral contact stiffness became higher. Furthermore, increasing the ratio of tip length to cantilever length increases the vibration frequency and the sensitivity of AFM cantilever.     

基于内置传感器的大型数控机床状态监测

随着计算机技术的不断发展,数控机床的发展趋势越来越呈现出大型化和高速化,并且其加工精度也越来越高.在这种情况下,机床如果受到外力的振动或冲击,会直接影响机床的进给系统,从而造成与其相关的各机械部件出现故障,影响到机床的加工精度.因此,机械设备的状态监测及故障诊断非常重要.本文主要讨论基于内置传感器大型数控机床的状态监测问题.     

Finite-element vibration analysis of tapping-mode atomic force microscopy in liquid

Investigation of morphology and mechanical properties of biological specimens using atomic force microscopy (AFM) often requires its operation in liquid environment. Due to the hydrodynamic force, the vibration of AFM cantilevers in liquid shows dramatically different dynamic characteristics from that in air. A good understanding of the dynamics of AFM cantilevers vibrating in liquid is needed for the interpretation of scanning images, selection of AFM operating conditions, and evaluation of sample's mechanical properties. In this study, a finite element (FE) model is used for frequency and transient response analysis of AFM cantilevers in tapping mode (TM) operated in air or liquid. Hydrodynamic force exerted by the fluid on AFM cantilevers is approximated by additional mass and hydrodynamic damping. The additional mass and hydrodynamic damping matrices corresponding to beam elements are derived. With this model, numerical simulations are performed for an AFM cantilever to obtain the frequency and transient responses of the cantilever in air and liquid. The comparison between our simulated results and the experimentally obtained ones shows good agreement. Based on the simulations, different characteristics of cantilever dynamics in air and liquid are discussed.     

振动模态固有频率和阻尼比的EMD识别方法

针对机械系统固有频率和阻尼比的识别问题,提出了基于经验模式分解(EMD)的模态参数识别方法.该方法首先对脉冲激励下机械系统的位移响应进行了EMD分解,确定与该系统的各阶模态对应的固有模式函数(IMF),分别对各阶IMF进行希尔伯特变换以得到各自的瞬时幅值和瞬时相位曲线,并对所得曲线进行线性拟合,最后根据拟合曲线的参数来...     

Six degrees of freedom vibration transmissibility measurement of flexural opto-mechanical structures with 3-axis acceleration sensors

At an early stage of a high-resolution flexural opto-mechanical system design, it is essential to analyze its dynamic characteristics for assessing image quality due to environmental vibration, an experimental method to measure six degrees of freedom (6-DoFs) vibration transmissibility of flexural opto-mechanical structures is proposed in this article. A typical flexural opto-mechanical structure consists of an optical component, a mechanical component and several flexural modules. Using the developed method, optical and mechanical components are considered as rigid bodies. Two feature points which are uncoupled in motion are set in the components separately, and they can express 6-DoFs vibration of each component moderately. Several key points are set in each component too, and their vibrational accelerations are measured with 3-axis acceleration sensors firstly. Then, motion relations between the feature points and key points are established, 6-DoFs vibrational acceleration spectrums of the two feature points are analyzed, and 6-DoFs vibration transmissibility between them is calculated. Thirdly, the experiment is carried out for twenty times, and average 6-DoFs vibration transmissibility is calculated. Uncertainties of this method are discussed with numerical analysis and experiments.     

Linking rigid multibody systems via controllable thin fluid films

This work deals with the mathematical modelling of multibody systems interconnected via thin fluid films. The dynamics of the fluid films can be actively controlled by means of different types of actuators, allowing significant vibration reduction of the system components. In this framework, this paper gives a theoretical contribution to the combined fields of fluid–structure interaction and vibration control. The methodology is applied to a reciprocating linear compressor, where the dynamics of the mechanical components are described with help of multibody dynamics. The crank is linked to the rotor via a thin fluid film, where the hydrodynamic pressure is described by the Reynolds equation, which is modified to accommodate the controllable lubrication conditions. The fluid film forces are coupled to the set of nonlinear equations that describes the dynamics of the reciprocating linear compressor. The system of equations is numerically solved for the case when the system operates with conventional hydrodynamic lubrication and for several cases of the bearing operating under controlled hybrid lubrication conditions. The analysis of the results is carried out with focus on the behaviour of the journal orbits, maximum fluid film pressure and minimum fluid film thickness.