Present Status and Prospect of High-Frequency Electro-hydraulic Vibration Control Technology

Electro-hydraulic vibration equipment(EHVE)is widely used in vibration environment simulation tests,such as vehicles,weapons,ships,aerospace,nuclear industries and seismic waves replication,etc.,due to its large output power,displacement and thrust,as well as good workload adaptation and multi-controllable parameters.Based on the domestic and overseas development of high-frequency EHVE,dividing them into servo-valve controlled vibration equipment and rotary-valve controlled vibration equipment.The research status and progress of high-frequency electro-hydraulic vibration control technology(EHVCT)are discussed,from the perspective of vibration waveform control and vibration controller.The problems of current electro-hydraulic vibration system bandwidth and waveform distortion control,stability control,offset control and complex vibration waveform generation in high-frequency vibration conditions are pointed out.Combining the existing rotary-valve controlled high-frequency electro-hydraulic vibration method,a new twin-valve independently controlled high-frequency electro-hydraulic vibration method is proposed to break through the limitations of current electro-hydraulic vibration technology in terms of system frequency bandwidth and waveform distortion.The new method can realize independent adjustment and control of vibration waveform frequency,amplitude and offset under high-frequency vibration conditions,and provide a new idea for accurate simulation of high-frequency vibration waveform.

Separate Control of High Frequency Electro-hydraulic Vibration Exciter

The working frequency of the conventional electro-hydraulic vibration exciters,which consist of a servo valve and a hydraulic cylinder,is generally restricted within a narrow range due to limited frequency response capability of the servo valve itself.To counteract such restriction,a novel scheme for an electro-hydraulic vibrator,controlled by a two-dimensional valve（2D valve） and a bias valve in parallel,is therefore proposed.The frequency,amplitude and offset are independently controlled by rotary speed,axial sliding of the spool of the 2D valve and axial sliding of the spool of the bias valve.The principle of separate control was presented and the regulation approach of frequency,amplitude and offset was discussed.A mathematical model of the hydraulic power mechanism for the proposed vibration exciter was established to investigate the relationship between the amplitude and the axial sliding of the 2D valve＇ spool,as well as that between the offset and the axial sliding of the bias valve＇s spool at various frequencies.An experimental system was built to validate the theoretical analysis.It is verified that the 2D exciter is capable of working smoothly in a frequency range of 5- 200 Hz.And its frequency,amplitude and offset can be controlled respectively by either closed loop or open loop method.There is a linear relationship between the output amplitude and the spool axial opening of the 2D valve until a point when the flow rate becomes saturate and the amplitude remains constant.The offset displacement of the cylinder＇s piston is linearly proportional to the axial displacement of the spool of the bias valve,when the valve opening is less than 25%.Thereafter,the slop of the offset curve decreases and tends to saturate.The proposed electro-hydraulic vibration controlled by the 2D valve not only facilitates the realization of high-frequency electro-hydraulic vibration,the high-accuracy of vibration can also be achieved by means of independent controls to the frequency,amplitude and offset.

Parameter-dependent vibration-attenuation controller design for electro-hydraulic actuated linear structural systems

The problem of robust active vibration control for a class of electro-hydraulic actuated structural systems with time-delay in the control input channel and parameter uncertainties appearing in all the mass, damping and stiffness matrices is investigated in this paper. First, by introducing a linear varying parameter, the nonlinear system is described as a linear parameter varying （LPV） model. Second, based on this LPV model, an LMI-based condition for the system to be asymptotically stabilized is deduced. By solving these LMIs, a parameter-dependent controller is established for the closed- loop system to be stable with a prescribed level of disturbance attenuation. The condition is also extended to the uncertain case. Finally, some numerical simulations demonstrate the satisfying performance of the proposed controller.

Vibration Analysis and Direct Control of XY Table Automated Assembly Machines

XY table automated assembly machines ensure time saving and quality improving in the electronics industry. Recently, due to the need of higher operation speeds and lighter machines in PCB （Printed Circuit Board） assembly, a challenging problem has arisen which is the table positioning vibration. The high speed with the machine flexibility, make the positioning vibration inevitable although the inner control. The positioning vibration is to be reduced otherwise the machine becomes useless. Firstly, the machine is modeled, the positioning vibration is formulated, and then analyzed. Secondly, using the analysis, three direct control methods are identified to decrease the positioning vibration, they are based on the kinematics, dynamics, and operation of the machine. Thirdly, the methods are examined numerically to evaluate their efficiency. Lastly, the identified methods are discussed to conclude on their application. The results are a real contribution in the vibration control of XY table automated assembly machines, which is classified as industrial knowhow.

Output Waveform Analysis of an Electro-hydraulic Vibrator Controlled by the Multiple Valves

The existing research of the electro-hydraulic vibrator mainly focuses on system stability, working frequency width and output waveform distortion. However, this high frequency performance of the electro-hydraulic vibrator is difficult to be improved greatly due to fast insufficiently frequency response of the servo valve itself and limited compensation capability of the control structure in the vibrator system. In this paper, to realize high frequency vibration, an improved two-dimensional valve （here within defined as a 2D valve） as a main control component is adopted to the parallel connection with a servo valve to control the electro-hydraulic vibrator, Because the output waveforms of this electro-hydraulic vibrator are incapable to be verified through timely feedback as in the conventional electro-hydraulic servo system, the analysis to the output waveform becomes crucial to the design and control of the electro-hydraulic vibrator. The mathematical models of hydraulic actuation mechanism and the orifice area of the parallel valves connection are established first. And then the vibration process is divided into two sections in terms of the direction of the flow, the analytical expression of the excited waveform is solved. Based on relationships exist between working states and the control parameters the analytical results, the vibration boundary positions and the are derived. Finally an experimental system was built to validate the theoretical analysis. It is verified that this electro-hydraulic vibration system could achieve high working frequency, up to 2 000 Hz. The excited waveform is similar to the sinnsoidal waveform. And the ascent and decent slopes of the waveforms are somewhat asymmetrical. This asymmetry is not only caused by the change of the direction of the elastic force but also dependent on the bias position of the vibration. Consequentky the distortion of effective working waveform is less tha~ 10%. This electro-hydraulic vibrator controlled by the multiple valves could not only greatly enhance the working frequency but also precisely control the vibration characteristic variables such as waveform shape.

PI-type Iterative Learning Control for Nonlinear Electro-hydraulic Servo Vibrating System

For the electro-hydraulic servo vibrating system（ESVS） with the characteristics of non-linearity and repeating motion, a novel method, PI-type iterative learning control（ILC）, is proposed on the basis of traditional PID control. By using memory ability of computer, the method keeps last time＇s tracking error of the system and then applies the error information to the next time＇s control process. At the same time, a forgetting factor and a D-type learning law of feedforward fuzzy-inferring referenced displacement error under the optimal objective are employed to enhance the systemic robustness and tracking accuracy. The results of simulation and test reveal that the algorithm has a trait of high repeating precision, and could restrain the influence of nonlinear factors like leaking, external disturbance, aerated oil, etc. Compared with traditional PID control, it could better meet the requirement of nonlinear electro -hydraulic servo vibrating system.

Integral precession calibration method of PIGA on linear vibration table

Linear vibration table can provide harmonic accelerations to excite the nonlinear error terms of Pendulous Integrating Gyro Accelerometer(PIGA).Integral precession calibration method is proposed to calibrate PIGA on a linear vibration table in this paper.Based on the precise expressions of PIGA’s inputs,the error calibration model of PIGA is established.Precession angular velocity errors of PIGA are suppressed by integer periodic precession and the errors caused by non-integer periods vibrating are compensated.The complete calibration process,including planning,preparation,PIGA testing,and coefficient identification,is designed to optimize the test operations and evaluate the calibration results.The effect of the main errors on calibration uncertainty is analyzed and the relative sensitivity function is proposed to further optimize the test positions.Experimental and simulation results verify that the proposed 10-position calibration method can improve calibration uncertainties after compensating for the related errors.The order of calibration uncertainties of the second-and third-order coefficients are decreased to 10^(-8)(rad.s^(-1))/g^(2)and 10^(-8)(rad.s^(-1))/g3,respectively.Compared with the other two classical calibration methods,the calibration uncertainties of PIGA’s nonlinear error coefficients can be effectively reduced and the proportional residual errors are decreased less than 3×10-6(rad.s^(-1))/g by using the proposed calibration method.

Design and Analysis of Axial Thrust Roller-Exciting Vibrating Table and Its Motor-Control System Based on Co-simulation

Aiming at improving the mechanical vibrating equipment,the axial thrust roller-exciting vibrating tables and its motor-control system based on co-simulation were put forward. First, the structures of vibrating table and its surface equations and boundary conditions were established through reversal process. Second,waveform distortion influenced by random and harmonic waves was analyzed by equivalent parametric transition. These two steps were both technological challenge and contribution for the vibrating table.Finally, based on research above, a proportion integration differentiation( PID) motor-control system was built to show its rapid operation and convenient control. All the results show that not only does vibrating table have lower waveform distortion than traditional ones,but its control system narrows down the fluctuation and improves anti-interference performance. Hence,it provides a more extensive selection for efficient and practical mechanical vibrating table.

Shaking table test and numerical analysis of offshore wind turbine tower systems controlled by TLCD

A wind turbine system equipped with a tuned liquid column damper （TLCD） is comprehensively studied via shaking table tests using a 1/13-scaled model. The effects of wind and wave actions are considered by inputting response- equivalent accelerations on the shaking table. The test results show that the control effect of the TLCD system is significant in reducing the responses under both wind-wave equivalent loads and ground motions, but obviously varies for different inputs, Further, a blade-hub-tower integrated numerical model for the wind turbine system is established. The model is capable of considering the rotational effect of blades by combining Kane＇s equation with the finite element method. The responses of the wind tower equipped with TLCD devices are numerically obtained and compared to the test results, showing that under both controlled and uncontrolled conditions with and without blades＇ rotation, the corresponding responses exhibit good agreement. This demonstrates that the proposed numerical model performs well in capturing the wind-wave coupled response of the offshore wind turbine systems under control. Both numerical and experimental results show that the TLCD system can significantly reduce the structural response and thus improve the safety and serviceability of the offshore wind turbine tower systems. Additional issues that require further study are discussed.

Control strategies and experimental verifications of the electromagnetic mass damper system for structural vibration control

The electromagnetic mass damper （EMD） control system, as an innovative active control system to reduce structural vibration, offers many advantages over traditional active mass driver/damper （AMD） control systems. In this paper, studies of several EMD control strategies and bench-scale shaking table tests of a two-story model structure are described. First, two structural models corresponding to uncontrolled and Zeroed cases are developed, and parameters of these models are validated through sinusoidal sweep tests to provide a basis for establishing an accurate mathematical model for further studies. Then, a simplified control strategy for the EMD system based on the pole assignment control algorithm is proposed. Moreover, ideal pole locations are derived and validated through a series of shaking table tests. Finally, three benchmark earthquake ground motions and sinusoidal sweep waves are imposed onto the structure to investigate the effectiveness and feasibility of using this type of innovative active control system for structural vibration control. In addition, the robustness of the EMD system is examined. The test results show that the EMD system is an effective and robust system for the control of structural vibrations.

Experimental Study on Vibration Control of Offshore Wind Turbines Using a Ball Vibration Absorber

To minimize the excessive vibration and prolong the fatigue life of the offshore wind turbine systems, it is of value to control the vibration that is induced within the structure by implementing certain kinds of dampers. In this paper, a ball vibration absorber (BVA) is experimentally investigated through a series of shake table tests on a 1/13 scaled wind turbine model. The reductions in top displacement, top acceleration, bottom stress and platform stress of the wind turbine tower system subjected to earthquakes and equivalent wind-wave loads, respectively, with a ball absorber are examined. Cases of the tower with rotating blades are also investigated to validate the efficacy of this damper in mitigating the vibration of an operating wind turbine. The experimental results indicate that the dynamic performance of the tested wind turbine model with a ball absorber is significantly improved compared with that of the uncontrolled structure in terms of the peak response reduction.

Damage evolution mechanism of rock-soil mass of bedrock and overburden layer slopes based on shaking table test

This paper aims to investigate the seismic motion characteristics of bedrock and overburden layer slope with the prototype model taken from slopes in the Zheduo Mountain in Northwest Plateau of Sichuan Province,China.Based on dimensional analysis and similarity principle,two model tests with different slope angles were carried out.A transfer function analysis method was proposed to interpret the results from shaking table tests.After eliminating trend terms and signal filtering,the time-domain acceleration was transformed into frequency domain.Then the transfer function was calculated by an average periodic chart.The variation of transfer function from different positions was analyzed by Pearson correlation coefficient,and the least square iteration method was used for modal analysis.The effect of seismic intensity on the dynamic response was highlighted.It is found that the transfer function obviously changes when the slopes are destroyed.Results from modal analysis show that the natural frequency decreases with the increase of the excitation intensity,and the damping ratio increases due to slope damage.

Nonlinear Modeling and Identification of Structural Joint by Response Control Vibration Test

Components of mechanical product are assembled by structural joints,such as bolting,riveting,welding,etc.Structural joints introduce nonlinearity to some engineering structures,and the nonlinearity need to be modeled precisely.To meet serious quality requirements,it is necessary to detect and identify nonlinearity of mechanical products for structural optimization.Modal test to acquire a dynamic response has been applied for decades,which provides reliable results for finite element(FE)model updating.Here response control vibration test for identification of nonlinearity is presented.A nonlinear system can be regarded as linearity for particular steady state response,and classical linear analysis tool is applicable to extract modal data for particular response.First,its applicability is illustrated by some numerical simulations.Subsequently,it is implemented on experimental setup with structural joints by shaking table.The stiffness and damping function dependent of relative displacement are fitted to describe its inherent nonlinearity.The spring and damping forces are identified by harmonic balance method(HBM)to predict output response.Based on the identified results,the procedure is recommended that it allows a reliable measurement of nonlinearity with a certain accuracy.

APPLICATION OF FRF ESTIMATOR BASED ON ERRORS-IN-VARIABLES MODEL IN MULTI-INPUT MULTI-OUTPUT VIBRATION CONTROL SYSTEM

The FRF estimator based on the errors-in-variables （EV） model of multi-input multi-output （MIMO） system is presented to reduce the bias error of FRF HI estimator. The FRF HI estimator is influenced by the noises in the inputs of the system and generates an under-estimation of the true FRF. The FRF estimator based on the EV model takes into account the errors in both the inputs and outputs of the system and would lead to more accurate FRF estimation. The FRF estimator based on the EV model is applied to the waveform replication on the 6-DOF （degree-of-freedom） hydraulic vibration table. The result shows that it is favorable to improve the control precision of the MIMO vibration control system.

航空发动机振动环境谱统计归纳方法及振动试验台复现

为满足航空发动机及机载产品研制过程贴近使用环境的振动考核试验需求,需根据发动机实测振动数据给出振动考核试验所需的输入谱图。依据GJB/Z 126-99中给出的环境测量数据归纳方法,建立了发动机实测振动环境谱统计归纳方法并通过程序实现。利用发动机多架次实测试飞振动数据统计归纳得到发动机测点位置的振动实测谱。基于能量等效及信号频域特征分布一致原则,将归纳得到的实测谱转化为可用于振动台输入的振动环境谱,并在振动台上进行了振动信号的复现试验。结果表明:振动台输出信号与发动机实测振动信号频域分布特征一致,在统计频率带宽范围内振动总量最大相差5.7%,证明了转化方法是合理的,为航空发动机机载设备贴近使用环境的振动考核试验方法提供了真实的输入谱图。

悬挂结构模拟振动台试验研究

为研究设置黏滞阻尼器的悬挂结构在地震作用下的抗震性能,对采用刚性连接杆连接和采用黏滞阻尼器连接的悬挂结构进行了1/20比例缩尺模型振动台试验,主要研究了模型结构的动力特性、阻尼比、结构响应及其减振效果。研究结果表明:与普通悬挂模型结构相比,悬挂减振模型结构自振频率有所降低,结构的阻尼比得到提高,特别是第一阶频率和对应阻尼比;悬挂减振模型结构的主体结构顶部和第五层悬挂楼层的加速度峰值响应均小于普通悬挂模型结构,其中悬挂楼层的加速度峰值响应最佳减振幅度可达94.34%。悬挂减振结构主体结构顶部位移峰值响应较普通悬挂结构有明显地降低,且不同的地震波输入有着不同的减振效果,其中Taft波的减振效果最好,El Centro波次之,最后是人工波;主体结构与悬挂楼面的最大相对位移却大于普通悬挂结构,说明主次结构之间的连接越强,其相对位移就越小。同时也说明悬挂减振结构正是利用悬挂楼层的摆动和黏滞阻尼器来耗散能量,从而有着较好的耗能减振效果。

自复位浮置物隔震系统的动力试验与数值分析

提出了一种自复位浮置物隔震系统,该系统采用双层正交导轨隔离水平地震,并通过预拉弹簧绳实现自复位。考虑系统摩擦与弹簧绳刚度,建立了自复位浮置物隔震系统的理论模型,完成了不同工况下的隔震系统振动台试验,结果表明输入地震波的加速度峰值越高,隔震系统的隔震率也会相应提升。在输入地震波加速度峰值为0.15、0.2、0.4、0.62 g时,隔震系统平均隔震率分别为50%、58%、75%、82%。在相同峰值的地震波及楼面波地震动输入下,隔震系统均具有良好的隔震效果且能够实现系统自复位。最后建立了浮置物隔震支座-浮置物体系的有限元模型,验证了隔震系统理论模型的有效性。

爆破振动作用下桥梁桩孔稳定性振动台试验研究

为了解爆破振动对邻近桥梁桩基成孔后桩孔稳定性的影响,以与山体爆破工程计划同时施工的某主跨280 m的斜拉桥为背景,设计、制作土箱和缩尺比1∶40桩孔模型开展振动台试验,研究桩孔孔壁的破坏特征、土体振动速度和动土压力的变化规律。结果表明:土体的振动速度峰值和动土压力峰值均随着爆破强度的增大而增大,在土体产生破坏后,土体的振动速度峰值和动土压力峰值均呈现出非线性增大趋势;爆破强度较小时土体的动土压力峰值曲线为U形,爆破强度较大时桩孔区域土体的动土压力峰值曲线为W形,桩孔中上部区域的动土压力峰值较大;山体爆破振动会使钢护筒底部与土体交界面以下桩孔的中上部区域出现破坏,应对山体爆破施工加强现场监测,桩孔附近的振动速度峰值不宜超过2 cm/s,以保障桩孔的稳定性。

支架固定馆藏人物俑文物的抗震优化设计研究

为优化支架固定馆藏人物俑文物的抗震效果,选取不同尺寸和体态的典型地震易损人物俑文物复制品(武士俑和唐三彩人物俑),开展文物复制品-优化组合措施(支架和卡固件)抗震系统振动台试验,获得影响文物复制品运动状态的关键优化参数、文物复制品与支架相互作用规律,并检验组合措施对较大体积人物俑文物的抗震固定效果。建立文物复制品-组合措施相互作用系统数值分析模型,通过参数分析,获得支架与文物间安装缝隙、在安装缝隙内填充不同种类隔震垫对文物动力响应的影响、文物复制品与固定措施相互作用规律及采用独立支架/组合措施有效固定人物俑的最小支架尺寸,为兼顾安全性及最小干预原则的固定措施优化设计提供必要依据。结果表明:相比独立支架,组合措施能够有效降低人物俑文物动力响应,有效提高固定效果;为保证人物俑文物安全,建议支架与文物间安装缝隙不大于5 mm;在缝隙中填充橡胶垫及硅胶垫可使文物与支架间相互作用力降低50%~75%,有效防止文物局部损伤;当人物俑文物体型超过一定限值,独立支架不再适用,建议选择支架和随形卡固件组合措施。

基于主动激励的掘进机回转台振动抑制研究

悬臂式掘进机截割过程由于煤岩形状、硬度分布的随机性,当截割到硬岩时截割头会产生无规则的剧烈振动,瞬时高强度的冲击对掘进机关键受力部件回转台影响最大,其动态可靠性和寿命影响着截割效率和截割稳定性,为减弱截割过程回转台的振动,首先,基于截割现场回转台易失效损坏现象,建立截割过程回转台力学模型,推导回转台力学方程,研究回转台受力随截割参数变化规律;通过搭建截割试验台,测试截割过程回转台振动响应,结合有限元进行回转台振动模态分析,求解回转台前6阶固有频率及振型,分析回转台剧烈振动的原因。其次,基于工况路径分析理论,建立截割过程回转台工况传递路径分析模型,模拟回转台合成振动,分析各激励点对回转台振动贡献量及贡献程度,准确找到回转台主要激振源。最后,通过施加外部主动激励的方式,分析不同激励频率加载下回转台振动情况,探寻能够降低截割过程回转台振动的激励频段。试验结果表明:外部激振频率处于20~60 Hz,回转台振动幅值降低明显,此频段激励频率对回转台振动控制效果良好,有益于提高回转台寿命,且激振频率为40 Hz时回转台振动最小,回转台振动抑制效果最佳。研究结果有益于丰富回转台振动相关研究理论,实现在不改变机械结构基础上,降低回转台受力与结构变形,可为掘进机回转台的振动问题提供理论参考。