涡流发生器涡激振动抑制研究

通过风洞实验对涡流发生器的涡激振动抑制效果进行了分析研究,确定了涡流发生器的最佳几何参数,并探讨了涡流发生器涡激振动抑制机理.结果表明:从阻力系数的角度,涡流发生器比螺旋条纹圆管有更大的涡激振动抑制优势.热线风速仪的测量结果表明:光滑圆管及涡流发生器圆管尾流展向尾流速度相关系数不受雷诺数及涡流发生器的影响.涡流发生器主要是通过影响边界层的分离进而影响涡街脱落点来抑制涡激振动,对涡街脱落的沿展向三维扩展没有影响.     

Adaptive vibration control of micro-cantilever beam with piezoelectric actuator in MEMS

This paper proposes a dynamical model and the governing equations of motion of the micro-cantilever beams based MEMS with piezoelectric actuator (PZT). The Rayleigh–Ritz method is used to reduce the order of the system and the state equations are presented in modal space. The first ten mode frequencies and mode shapes of the micro-cantilever beam with and without PZT are studied. The effects of PZT on the modal frequencies and shapes of the beam system can be ignored for the reason that the beam holds larger nature frequencies and Q values in micro-scale. A rational linearizing feedback controller with a high gain observer is designed to eliminate the unwanted deflection of the micro-cantilever beam system. The open-loop step response and the effects of situated places of PZT on the frequency responses of the system are discussed. Various frequency responses of the beam system, subject to different applied control voltages and feedback gains, are illustrated. The four resonances are well controlled, while the anti-resonance has little change. Computer simulations are provided to demonstrate the performance of the designed control scheme.     

Comparison of collocation strategies of sensor and actuator for vibration control

Some possible collocation strategies of sensor and actuator pairs for the application to active vibration control systems are analyzed, compared and discussed in this paper. This is becausea well-designed sensor — actuator collocation configuration can provide a simpler control algorithm with excellent performance and stability, especially when velocity feedback is adopted. As an ideal point collocation pair of a sensor and actuator shows high possibility in actual vibration control problems, the advantage of a collocated accelerometer — shaker pair is proven experimentally and discussed first. Then as a similar approach, a collocated piezosensor — piezoactuator pair is analyzed in depth with the in-plane motion coupling. Finally, two configurations of a practically collocated configuration with an accelerometer — piezoactuator pair and a non-overlapped collocated pair of a bimorph piezosensor — two bimorph piezoactuators are described in detail in terms of performance and stability with experimental results. Those two configurations are expected for the applications to more practical active control of vibration systems with the velocity feedback control scheme.     

基于压电执行器的切削振动主动控制实验研究

利用压电执行器,构造了切削振动主动控制实验系统并分析了该系统的控制机理;该系统根据以振抑振的思想,采用位移反馈策略对切削过程的振动行为进行干预,进而实施对振动的主动控制.从实验结果看,达到了明显的减振效果,该系统为将来制作更具商业前景的智能刀杆奠定了良好的基础.     

Thermally induced vibration control of cylindrical shell using piezoelectric sensor and actuator

Shell type components and structures are very common in many mechanical and structural systems. Modeling and analysis of adaptive piezothermoelastic shell laminates represent a high level of sophistication and complexity. In this paper a finite element model is developed for the active control of thermally induced vibration of laminated composite shells with piezoelectric sensors and actuators. The present model takes into account the mass, stiffness and thermal expansion of the piezoelectric patches. A C_o continuous nine-node degenerated shell element is implemented to model the structure. The piezoelectric sensing layer senses the structural vibration and a suitable voltage applied in the piezoelectric actuator layer suppresses the oscillation. Actuator and sensor are coupled together with a control algorithm so as to actively control the dynamic response of the structure in a close loop. Numerical results are generated for a cylindrical shell and it is observed that thermally induced vibration of a laminated cylindrical shell can be suppressed through the application of piezoelectric sensor and actuator. Effects of variation in control gain and piezoelectric layer area coverage (PAC) have been studied. Higher control gain is more effective in damping out the vibration. Although the damping is enhanced by increase in PAC, increase beyond a certain level may not be useful in view of smaller efficacy and increased weight.     

采用双晶片驱动的棒板结合式压电驱动器设计

设计制作了一种采用双晶片压电陶瓷结构的棒板结合式压电驱动器.和瓷片分别粘接在青铜定子的上下两侧.定子上的金属圆柱体被用来放大振动的横向位移,并对金属棒状的转子进行激振,使其旋转.利用有限元分析(FEA)对定子进行了分析,发现在同样的驱动模式下,与传统的单片陶瓷片驱动器相比,该驱动器可以提供更多的横向和纵向的振动位移,大约提高25%左右.这种新结构也可避免不同振动模式之间的模态耦合现象,并产生理想的振动模态,以提高驱动器的运行稳定性.实验表明,驱动器在25 Vo-p低电压下可以提供512r/rain的转速,而单片陶瓷驱动器在该电压下不能工作.这种压电驱动器可以经过优化和调整来满足不同的实际应用,如精确定位仪器,生物工程和光聚焦系统等.     

Manufacture of micro sized threads for micro actuator of laser grating mount

This work presents the fabrication of micro threads of pitch less than 100?μm for micro components. The micro sized threading tool having a tool nose radius less than 40?μm is manufactured by micro wire electric discharge machining (μWEDM) process. This μWEDM process overcomes the difficulties in conventional machining process for production of threading tools and helps in achieving a corner radius as small as 15?μm with specialized wire tool path strategies. This method also helps in fabrication of special micro tools from commercially available or worn-out tungsten carbide tool inserts.     

Shape control in micro borehole generation by EMM with the assistance of vibration of tool

Electrochemical micromachining (EMM) is gaining importance day by day due its advantages that include no tool wear, absence of stress/burr, high MRR, bright surface finish and ability to machine complex shapes regardless of hardness. Overcut and taper formation is the main problem during micro borehole machining. In this paper, an electrical circuit model of EMM is presented for better understanding of the process and experimental MRR is found to be in good agreement with theoretical MRR. In the present set up variation of overcut with voltage, pulsed frequency, vibration amplitude of tool and vibration frequency of tool are investigated. To reduce overcut and taper angle of micro borehole, machining zone is simulated with a reversed taper tool and verified by practical experiments for proper shape control during micro borehole generation. Variation of micro nozzle angle with different feed rates and different times of machining are also investigated for the shape control during micromachining with conical tool. Finally, it has been shown that both reversed taper and forward taper tool can be used for generation of taper less micro features i.e. boreholes.     

Active vibration control of flexible cantilever beam using piezo actuator and Filtered-X LMS algorithm

This paper presents the active vibration control of a flexible cantilever beam. The cantilever beam was excited by steady-state sinusoidal and white noise point forces. The vibrational control system was implemented using one piezo ceramic actuator bonded on the beam and the adaptive controller based on the Filtered-X LMS algorithm. Control results indicated that a considerable vibrational reduction could be achieved in a few seconds. Experimental results, demonstrate the feasibility of active vibration control of the flexible cantilever beam based on piezo ceramic actuator and the Filtered-X LMS algorithm.     

Modelling and testing of a dielectic electro-active polymer (DEAP) actuator for active vibration control

Passive vibration absorbers are really effective only at the tuned frequency. This limit is overcome by adaptive absorbers which offer the possibility to adjust their behaviour according to needs. The paper focuses on a smart actuator for vibration control made up by a dielectric electro-active polymer (DEAP). The DEAP is obtained constraining a silicone corrugated sheet between two silver layers and it is manufactured by Danfoss Polypower A/S. The actuator is fabricated by rolling the DEAP sheet in a cylindrical and core-free shape. The paper describes the static and dynamic characterizations of the actuator. A theoretical model is developed by considering the actuator as a multi-elements model. Moreover, a modal test of the actuator is performed driving it with an electro-dynamic shaker in a frequency range up to 1 kHz. A good agreement between theoretical and experimental data is obtained at lower frequencies. Stiffness and damping laws of the actuator are determined by fitting theoretical expectations and test results. The actuator is proved useful for controlling vibrations at low frequencies because it shows internal resonances at frequencies above 75 Hz. Finally, first results about the use of the DEAP actuator for vibration control of harmonic excitations in a band-limited frequency range below 10 Hz are reported.     

Novel micro deep drilling using micro long flat drill with ultrasonic vibration

This paper highlights the development of micro long flat drills with nominal diameter and flute length of 20 μm and 200 μm, respectively, by precision grinding. Furthermore, it also covers the evaluation of the developed micro long flat drill in micro deep drilling. Micro long flat drills were made of ultra-fine grained cemented carbide containing WC particles with an average particle diameter of 90 nm. First, the study focused on establishing the optimal web thickness of micro long flat drill showing the best performance in micro deep drilling. In drilling experiment, observation was conducted with the aim of finding the best conditions and method of micro deep drilling into both duralumin and stainless steel workpieces. This observation included the applications of ultrasonic vibration (USV) and step feeding method. The study proved that there was an optimum web thickness resulting in the best drilling performance. Furthermore, the application of USV during drilling could lead to a longer tool life significantly. However, there was no improvement of drilling performance in drilling with step feeding.     

Dynamical research on spherical micro actuator with piezoelectric ceramic stacks drivers

This paper develops a 30 mm × 30 mm × 50 mm spherical micro actuator driven by piezoelectric ceramic stacks (PZT), and analyzes its dynamic performances. First, the space coordinate relationship of the spherical micro actuator and a dynamic model are set up. Second, The Runge-Kutta arithmetic is used to calculate the dynamical parameters of the micro actuator; the SIMULINK module of MATLAB is used to build the dynamical simulating model and then simulate it. Third, an experimental sample of the spherical micro actuator is developed, a micromanipulator is integrated with a micro-gripper based on the sample spherical micro actuator, and the experimental research on the micro assembly is conducted between a micro shaft of Φ180 μm and a micro spindle sleeve of Φ200 μm. Finally, the characteristics of the spherical micro actuator influenced by the mass of the metal sphere of the micro actuator, driving signal frequency, friction coefficient of the contact surface between the metal sphere and the friction block of the micro driving unit are analyzed. The experimental results indicate that the rotation resolution of the micro actuator reaches 0.000 1°, the rotation positioning precision reaches 0.000 5°, and the maximum working frequency is about 1200 Hz. The experimental results validate the back rotation vibration model of the spherical micro actuator. The micromanipulator integrated by the spherical micro actuator can meet the requirements of precise micro operation and assembly for micro electro mechanical systems (MEMS) or other microelements in micro degree fields. __________ Translated from Optics and Precision Engineering, 2007, 15(2): 248–253 [译自: 光学精密工程]     

一种用于微谐振器频率调节的静电梳齿结构设计

针对微梳齿谐振器频率偏移的问题,提出了一种用于微谐振器频率调节的曲线形状静电梳齿结构。通过对梳齿简单模型的静电力分析,得出其静电力-位移特性,其斜率就是静电弹性系数;然后从谐振频率出发,分析了影响谐振频率的因素。研究结果表明,对于梳齿式微谐振器,当调谐电压从0 V变化到80 V左右时,器件的有效弹性系数从2.64 N/m减小到1.23 N/m左右,且谐振频率从自然谐振频率18.9 kHz减小到13 kHz,降幅分别为53%和31%。实验结果表明,这种曲线梳齿"软化"了静电微谐振器或者微驱动器的系统弹性,能够有效地调节谐振频率。     

基于FPGA的磁悬浮微驱动器控制系统研究

针对磁悬浮微驱动器的实时精确控制问题,对新型绕组式磁悬浮微驱动器的结构与工作原理进行了研究,对磁悬浮微驱动器中的磁场分布进行了理论分析,提出了一种基于FPGA的磁悬浮微驱动器悬浮系统的运动模型以及PID控制系统,并通过Matlab仿真实验验证了该数学模型。完成了系统的硬件控制电路及相应的软件设计,搭建了基于FPGA的磁悬浮微驱动器悬浮控制实验系统。该系统可利用位置环对磁悬浮微驱动器进行PID控制,并在上位机Delphi界面中显示悬浮状态,通过对所设计的PID控制器的控制精度、大范围精确控制性能、动态性能和跟踪性能进行了实验验证。实验结果表明,该系统响应速度快、可靠性高,可实现2 mm范围的精度为1μm的控制。     

BUEVA: a bi-directional ultrasonic elliptical vibration actuator for micromachining

This paper presents a novel actuator design for vibration-induced micromachining. The bi-directional ultrasonic elliptical vibration actuator (BUEVA) possesses a combination of features that renders it suitable for the machining a wide range of materials over a variety of cutting parameters. The cutting motion is an elliptical tool motion that resembles “spoon feeding”. This cutting action is in contrast to in-plane, horizontal motion utilized by most existing setups. The motion is arrived at through a combination of motions along the tool's axial and transverse directions and by vibrating out of phase and is generated by two stacked ceramic multilayer actuator ring piezo elements. Another distinguishing feature of BUEVA is the use of piezo stacks which ensure high blocking force compared to low force of piezo benders as used in many existing actuators. Furthermore, the amplitude and frequency of vibration of the tool are controlled on-line in order to vary the cutting depth and cutting speed according to the desired cutting parameters. This is a desirable characteristic which allows one to “dial-in” a desirable cutting speed for different workpiece materials. Another attractive BUEVA feature is that the design is very compact and can fit easily into the working space of most milling machining centers without the need for custom motion setups. An off the shelf TiALN-coated carbide turning tool is utilized as the cutting tool. Furthermore, refined versions of previously reported models by other workers in the micromachining field have been developed. Experimental force and surface roughness measurements are compared versus these ideal calculations from the improved models. Compared with these reference models, our refined calculations show improvements in describing chip geometry based on corrected tool motion and which, consequently, resulted in improved estimates of both surface roughness and cutting forces. Verification cutting tests in two different materials (Al2024 and Plexiglas) show good surface integrity and dimensional definition with roughness measurements in reasonable correlation to the refined model calculations.     

Effectiveness of a passive-active vibration isolation system with actuator constraints

In the prediction of active vibration isolation performance, control force requirements were ignored in previous work. This may limit the realization of theoretically predicted isolation performance if control force of large magnitude cannot be supplied by actuators.The behavior of a feed-forward active isolation system subjected to actuator output constraints is investigated. Distributed parameter models are developed to analyze the system response, and to produce a transfer matrix for the design of an integrated passive-active isolation system. Cost functions comprising a combination of the vibration transmission energy and the sum of the squared control forces are proposed. The example system considered is a rigid body connected to a simply supported plate via two passive-active isolation mounts. Vertical and transverse forces as well as a rotational moment are applied at the rigid body, and resonances excited in elastic mounts and the supporting plate are analyzed. The overall isolation performance is evaluated by numerical simulation. The simulation results are then compared with those obtained using unconstrained control strategies. In addition, the effects of waves in elastic mounts are analyzed. It is shown that the control strategies which rely on tmconstrained actuator outputs may give substantial power transmission reductions over a wide frequency range, but also require large control force amplitudes to control excited vibration modes of the system. Expected power transmission reductions for modified control strategies that incorporate constrained actuator outputs are considerably less than typical reductions with unconstrained actuator outputs. In the frequency range in which rigid body modes are present, the control strategies can only achieve 5-10 dB power transmission reduction, when control forces are constrained to be the same order of the magnitude as the primary vertical force. The resonances of the elastic mounts result in a notable increase of power transmission in high frequency range and cannot be attenuated by active control. The investigation provides a guideline for design and evaluation of active vibration isolation systems.     

全柔性并联微动激振台主体机构微位移分析

设计了一种新型全柔性2-RRRP+RRPR三平移微动并联激振台机构.在普通并联机构的位置正解分析的基础上,利用矩阵法——一阶影响系数法,推导出该并联微动激振台机构的微位移输出方程,为后续控制打下基础.最后,举例进行了理论计算,并用ADAMS工程软件对理论计算结果进行模拟,模拟结果显示,二者结果十分相近,进一步说明了用普通并联机构的速度分析方法——一阶影响系数法可以比较容易地对全柔性机构主体机构的微位移进行分析,结果具有一定的准确性.     

微型电磁振动发电装置研究新进展

随着微机电产品的广泛应用,微型电磁振动发电装置因其诸多优点而受到了广泛的重视。为给微型电磁振动发电装置的深入研究及实用化提供参考,介绍了微型电磁振动发电的基本原理和主要特点,重点阐述了国内外微型电磁振动发电装置的研究现状和最新成果,并分析了各种不同类型微型电磁振动发电装置的发电特点。结合目前微型电磁振动发电装置存在的技术问题,展望了微型电磁振动发电装置未来的研究方向和发展趋势。     

微细立铣削切削振动试验研究

基于45钢微细立铣削试验,分析了微细立铣削切削振动的基本特征,研究了直槽立铣加工时铣削参数对振动加速度和振动位移量影响的基本规律.研究结果表明:在同样的切削工况下,微细立铣削的切削振动远大于大直径立铣刀铣削的情况;铣削参数是振动加速度的主要影响因素,振动加速度随铣削参数的增加都呈上升趋势,但轴向切深H和转速n对振动加速度的影响比进给量f更显著;在一定的参数范围内,减小主轴转速n和增大轴向切深H能够减小振动位移量的大小.