失重环境下可控柔性臂的模态特性

在非重力场中,考虑控制器动态反馈的影响,对存在控制器定位约束的柔性臂系统进行动力分析,研 究其在相对平衡位置的模态特性．以具有柔性关节和弹性臂杆的可控柔性臂为研究对象,分析了控制器作用下的反 馈约束特性,将控制器位置和速度增益引入力边界条件,得到了耦合控制器参量的模态特征方程,证明了反馈约束 的存在使得系统特征频率为复频率,且模态主振型是复变函数．通过数值仿真,明确了可控柔性臂的模态特性与控 制器增益之间的关系,得到了不同于经典振动理论的结论．设计了可控柔性臂的仿失重实验平台,试验模态结果证 明了理论分析的有效性．     

Effect of Dual-rate Sampling on the Stability of a Haptic Interface

Conventional controllers in impedance-based haptic interfaces are sampled data systems that utilize position and velocity information for the necessary force feedback. In a canonical virtual wall simulation, this feedback force is generated based on interaction with the wall simulating certain stiffness and damping. Increasing the sampling rate of the controller increases the stable range of virtual wall stiffness. However, an increased sampling rate exacerbates the velocity information, decreasing the stable range of virtual wall damping. In this work, the authors propose a dual-rate sampling scheme in which the position and velocity loops of a haptics controller are decoupled and sampled at different rates. The scheme enables independent sampling of the position data at higher rates, while simultaneously sampling the velocity data at appropriate rates. In this paper, the authors provide experimental and theoretical implications of the effect of dual-rate sampling on the stability of a haptic interface. Experiments with a single degree-of-freedom (DOF) haptic interface reveals an enhanced region of stable virtual wall stiffness for a particular range of virtual wall damping, compared to the values with conventional uniform-rate scheme. Virtual wall stiffness ranging from 150 - 360 Nm/rad was stably implemented over a range of 0 - 1 Nms/rad of virtual wall damping using the proposed scheme at position loop sampling rate of 20kHz and velocity loop sampling rate of 2kHz. Whereas in the conventional scheme, the stable range of virtual stiffness dropped considerably (～ 0 Nm/rad) for the virtual wall damping above 0.1 Nms/rad when the uniform rate sampling of 20kHz was used for both the position and velocity sampling loops. Theoretical stability analyzes using classical control tools and simulations justified the effectiveness of the proposed scheme. The scheme is easy to implement and extensible to multi-DOF haptic interfaces as well.     

An experimental analysis of electrostatically vibrated array of polysilicon cantilevers

Micromechanical cantilevers are one of the most fundamental and widely studied structures in micro-electromechanical systems. Dynamic response of such cantilevers has long been an interesting subject to researchers and different analytical and experimental approaches have been reported to determine it. Theoretical estimation of different damping mechanisms have been reported over years which are relevant particularly in studying the dynamics of the micro-mechanical structures. Most properties and functionalities of the MEMS devices are invariably dependant on the dynamic response of the devices, which in turn depends on the quality factor of the devices or in other words the overall damping present in the system. This paper presents a thorough experimental analysis of vibration characteristics of micro-mechanical cantilevers of different dimensions. Arrays of polysilicon micro-cantilevers of different dimensions have been designed and fabricated using surface micromachining process. The beams are resonated by electrostatic actuation and their vibration characteristics have been observed using Laser Doppler Vibrometer. Also a thorough analysis of modal behaviour of the beams is presented using analytical approach and finite element method based simulation. Different damping mechanisms have been critically reviewed and a semi-analytical estimation of the overall damping is presented. The results are compared with experimental values.     

A cohesive modeling technique for theoretical and experimental estimation of damping in serial robots with rigid and flexible links

Dynamic model incorporating damping characteristics, namely joint damping and structural damping in flexible links, of the serial robots with rigid and flexible links is presented. A novel procedure, based on the unified approach of theoretical formulation and analysis of experimental data, is proposed for the estimation of damping coefficients. First, the dynamic model of a robotic system with rigid and flexible links is presented. Next, the modifications in the dynamic model due to the considerations of damping characteristics of joints and structural damping characteristics of the flexible links are presented. A systematic methodology based on analysis of data obtained from experiments is presented for estimation and determination of damping coefficients of rigid-flexible links. The determination of joint damping coefficients, is based on the logarithmic decay of the amplitude of the oscillations of robotic links, while the structural damping coefficients are estimated mainly using the modal analysis and the method of evolving spectra. The method of evolving spectra, based on the Fast Fourier Transform of the decay of the amplitude in structural vibrations of the robot links in progressive windows is used to estimate the structural damping ratios while the critical structural coefficients are determined using the modal analysis. The methodology is illustrated through a series of simple experiments on simple robotic systems. The experimental results are then compared with the simulation results incorporating the damping coefficients determined using the proposed procedure. The comparisons leads to the validation of the proposed dynamic modeling technique, modeling of the damping characteristics, and the method proposed for estimation of damping coefficients for rigid-flexible link robotic systems.     

Numerical and experimental validation of out-of-plane resonance closed formulas for MEMS suspended plates with square holes

A compact analytical model for out-of-plane resonance evaluation is proposed for large diffuse MEMS vibrating plates with squared holes. A closed form expression was developed from a structural reduced order model with equivalent concentrated mass and stiffness parameters. Results were validated through FEM models and experimental modal analysis. Numerical FEM simulations were performed by 1D, 2D and 3D FEM models; experiments on polysilicon test structures were conducted using an interferometric microscope. Specimens were designed ad hoc to highlight the sensitivity of proposed formulas to main structural dimensional parameters of vibrating plates. Experiments and models helped investigate the sensitivity of the proposed reduced linearized model when exposed to electrostatic non-linear coupling effects and fluidic damping coupling. Both numerical results and experiments are in good agreement with analytical results predicted by closed formulas.     

Design of laminated composite plates for optimal dynamic characteristics using a constrained global optimization technique

The lamination arrangements of moderately thick laminated composite plates for optimal dynamic characteristics are studied via a constrained multi-start global optimization technique. In the optimization process, the dynamical analysis of laminated composite plates is accomplished by utilizing a shear deformable laminated composite finite element, in which the exact expressions for determining shear correction factors were adopted and the modal damping model constructed based on an energy concept. The optimal layups of laminated composite plates with maximum fundamental frequency or modal damping are then designed by maximizing the frequency or modal damping capacity of the plate via the multi-start global optimization technique. The effects of length-to-thickness ratio, aspect ratio and number of layer groups upon the optimum fiber orientations or layer group thicknesses are investigated by means of a number of examples of the design of symmetrically laminated composite plates.     

计入空气阻尼的MEMS微谐振器非线性动力学研究

针对横向振动MEMS微谐振器,计入非线性空气阻尼力,对微谐振器非线性动力学特性进行研究.建立微谐振器非线性动力学模型,计入滑移边界条件和稀薄气体效应,利用FLUENT和MATLAB对Navier-Stokes方程和动力学方程进行求解.经过与国外实验对比,可得出考虑非线性阻尼力的平板振幅值非常接近实验值,振幅峰-峰值误差仅为6%,且优于线性动力学的分析结果.为MEMS器件非线性动力学特性分析提供理论依据.     

Decoupling and tracking control for elastic joint robots with coupled joint structure

The paper deals with the modeling, identification, and control of a flexible joint robot developed for medical applications at the German Aerospace Center (DLR). In order to design anthropomorphic kinematics, the robot uses a coupled joint structure realized by a differential gearbox, which however leads to strong mechanical couplings inside the coupled joints and must be taken into account. Therefore, a regulation MIMO state feedback controller based on modal analysis is developed for each coupled joint pair, which consists of full state feedback (motor position, link side torque, as well as their derivatives). Furthermore, in order to improve position accuracy and simultaneously keep good dynamic behavior of the MIMO state feedback controller, a cascaded tracking control scheme is proposed, based on the MIMO state feedback controller with additional feedforward terms (desired motor velocity, desired motor acceleration, derivative of the desired torque), which are computed in a computed torque controller and take the whole rigid body dynamics into account. Stability analysis is shown for the complete controlled robot. Finally, experimental results with the DLR medical robot are presented to validate the practical efficiency of the approaches.     

On the use of velocity feedback for robot impact control

Most of the existing impact control strategies have relied on integral action and robot joint velocity feedback to achieve the desired damping effect. The limitations of such approaches are discussed in this paper. Based on a robot tip velocity reconstruction scheme, a positive tip velocity feedback method was introduced. This helped overcome the non-colocation problem due to the higher order arm dynamics and enhanced the impact suppression. A control strategy which includes the velocity feedback and an integral control was then developed and implemented on an industrial robot.     

Method for determining a dynamical state-space model for control of thermal MEMS devices

A method is presented for determining lumped dynamical models of thermal microelectromechanical systems (MEMS) devices for purposes of feedback control. As a case study, an electrothermal actuator is used. The physical properties and a set of assumptions are used to determine the basic structure of the dynamical model, which requires the development of the electrical, thermal, and mechanical dynamics. The importance of temperature-dependent parameters is emphasized for dynamical modeling for purposes of feedback control. To confront temperature dependence in a practical yet effective manner, an average temperature is introduced to preserve the energy balance inside the structure. This allows the development of a practical method that combines structure of the model, through the average body temperature, with finite element analysis (FEA) in novel way to perform system identification and identify the unknown parameters. The result is a lumped dynamical model of a MEMS device that can be used for the design of feedback control systems. We compare computer simulated results using the dynamical model with experimental behavior of the actual device to show that our procedure indeed generates an accurate model. This dynamical model is intended for further synthesis of driving signal and control system but also gives a qualitative insight into the relationship between device's geometry and its behavior. The method enables fast development of the model by conducting relatively few static FEA and is verifiable with dynamic experimental results even when temperature measurements are not available.     

基于受力分析的MEMS薄膜系统级模拟方法的研究

介绍一种MEMS系统级模拟方法.该方法直接分析运动物体的受力情况,并结合能量原理,利用受控源的反馈实现耦合作用,建立机电耦合MEMS薄膜的等效电路模型.利用该等效电路实现对薄膜动态行为的系统级模拟,并将Spice和有限元法,Saber的模拟结果进行对比,验证了该模拟方法应用于二维情况分析的有效性.     

矿用LCL型三电平静止无功发生器控制策略

为适应煤矿井下特殊环境,减小矿用静止无功发生器(SVG)的体积和质量,采用LCL滤波器和三电平逆变器作为矿用SVG的主电路拓扑,并针对LCL滤波器电流谐振问题和三电平逆变器中点电位不平衡问题,提出了一种基于串联双电流环有源阻尼控制和动态比例空间矢量调制的矿用LCL型三电平SVG控制策略。串联双电流环有源阻尼控制在网侧电流外环PI控制的基础上,通过增加滤波电容电流内环反馈控制使LCL滤波器具有阻尼特性,有效抑制了电流谐振;动态比例空间矢量调制在基本空间矢量中引入动态比例调整因子,对单位开关周期内平均中点电流进行实时控制,从而实现对中点电位平衡的控制。仿真和实验结果验证了该控制策略在LCL滤波器无阻尼电阻和直流母线电容较小情况下的可行性和良好效果。     

Design, damping estimation and experimental characterization of decoupled 3-DoF robust MEMS gyroscope

This paper reports the design implementation of three degree-of-freedom (3-DoF) non-resonant MEMS gyroscope having 2-DoF drive-mode oscillator. The proposed architecture utilizes structurally decoupled active-passive mass configuration to achieve dynamic amplification of oscillation in 2-DoF drive-mode. This results in higher sensitivity and eliminates the need of mode matching for resonance. A low cost standard Metal-Multi User MEMS Processes (MetalMUMPs) is used to fabricate 20 μm thick nickel based gyroscope with an overall reduced size of 2.2 mm × 2.6 mm. The experimental characterization demonstrated that the frequency response of the 2-DoF drive-mode oscillator has two resonant peaks at 754 Hz and 2.170 kHz with a flat operational region of 1.4 kHz between the peaks. The sense-mode resonant frequency lies at 1.868 kHz within this flat operational region where gain is less sensitive to structural parameters and environmental variations. This results in improved robustness to fabrication imperfections and environmental variations and long term stability without utilizing tuning and feedback control. Gyroscope dynamics and system level simulations using behavioral modeling are carried out to predict the performance of the device. Experimental results show close agreement with the behavioral simulation results due to incorporation of improved damping models in behavioral model developed in CoventorWare.     

某舵机伺服阀衔铁反馈杆组件谐响应分析

对某舵机上射流管电液伺服阀的衔铁及反馈杆组件的工作原理及固有频率进行理论分析,并采用有限元流体仿真软件Workbench中的流体模块Fluent (CFX)分析油液在工作中对反馈杆的阻尼作用,以获得较为真实的阻尼系数,并采用模态分析及谐响应分析模块对衔铁及反馈杆组件进行模态分析得到相关点的固有频率和相应振型,并进行谐响应分析,获得关键点的谐响应曲线.仿真结果表明,该电液伺服阀反馈杆末端在1050 Hz时出现最大振幅,衔铁在1950 Hz处出现最大振幅,为了防止共振对伺服阀工作性能的影响,应在工作中尽量避免这两个频率附近的压力脉冲信号.     

轨道车辆车轮辐板阻尼层对其降噪效果的影响分析*

采用模态叠加法求得阻尼车轮导纳特性,利用已建立的轮轨滚动噪声预测模型,以轮轨表面粗糙度为激励,分析了辐板阻尼层与其厚度对阻尼车轮振动与声辐射特性的影响规律.首先,建立了阻尼车轮三维实体有限元模型,采用Block Lanczos方法计算车轮模态特征;其次,利用模态叠加法求得车轮在单位荷载激励下的频响函数;然后,利用虚拟激励法求得车轮在粗糙度谱激励下的频域振动特性;最后,依据车轮动态响应通过解析的方法求得车轮声辐射频域特性.计算结果表明:(1)车轮辐板敷设阻尼层对车轮1000Hz以下频率的振动与噪声的抑制作用不明显,而对车轮1600Hz以上的高频振动具有良好的抑制作用;(2)车轮辐板双侧敷设阻尼的降噪效果优于单侧阻尼;(3)阻尼层可以有效抑制车轮振动,且车轮辐板敷设阻尼层厚度越厚效果越明显.     

A parameter identification method of horizontal robot arms

In order to develop an advanced control system and a simulation system for a robot arm, it is necessary to establish an accurate identification method for a dynamical model. The parameters of the dynamical model of a robot arm consist of the link length, the position of the centre of mass, the mass of the link, viscous damping, and Coulomb friction. However, it is not necessary to estimate these parameters independently because if several combined constants appearing in the equation of motion are obtained, then the control and simulation can be done using only these combined constants. In this paper, first we show that viscous damping and Coulomb friction are obtained by measuring the relation between the current and angular velocity. Then we propose an effective identification method of inertial terms using the mechanical resonance occurring due to the stiffness of the joints.     

Robust stabilization of large space structures via displacementfeedback

It has been known that static velocity and displacement feedback with collocated sensors and actuators can stabilize large space structures robustly against "any" uncertainty in mass, damping, and stiffness, independently of the number of flexible modes. The authors present dynamic displacement feedback which can achieve such robust stabilization. The proposed control law can be implemented in a decentralized scheme straightforwardly     

二阶系统模糊自适应PID变阻尼控制仿真研究

为了改善二阶系统的动态性能,通常用速度反馈增大等效阻尼比的方法减小输出响应振荡和超调量,但阻尼比增大,系统响应迟钝,快速性变差.当无阻尼自然振荡角频率一定时,阻尼比是影响二阶系统性能的主要因素.在线调整速度反馈通道增益以改变阻尼比从而改善系统性能.由于很难准确建立系统跟踪偏差和偏差变化率与速度反馈通道增益之间的数学模型,所以,模糊自适应PID变阻尼控制结合PID控制和模糊控制的优点,运用模糊推理方法根据系统输出响应的不同阶段在线实时调整系统的阻尼比,从而提高系统快速性和稳定性.仿真结果表明该方法可行,系统动态性能得到明显改善,无超调现象,并具有良好的抗干扰性.     

Design and mechanism analysis of a novel type compact single mirror laser scanner

A novel type of laser scanner employing a permanent magnetic suspension and spherical hinges has been developed. It consists of a single mirror based on linear electromagnetic actuators. This system has design features of playing the role of a two-dimensional tilt actuator by means of driving the electromagnetic actuators, and it provides good mechanical characteristics such as low distortion and damping, high optical angular deflection, and high dynamical performance (more than 1 kHz). This paper describes the configuration of the device and presents experimental results to demonstrate its performance and effectiveness.     

Dynamic analysis of a vertical axis wind turbine using a new windload estimation technique

A new aerodynamic model for obtaining the performance characteristics of a vertical axis wind turbine (VAWT) developed by the authors has been used to obtain estimates of aerodynamic loading, which are subsequently used for the dynamic analysis of a VAWT. The model incorporates gyroscopic effects, structural damping and also power generation through an induction or synchronoustype generator. A computer code written in MS-DOS FORTRAN has been developed for the dynamic analysis of a vertical axis wind turbine, and has been implemented on an IBM compatible 386 AT, for studying the dynamic characteristics of a VAWT. The results obtained from this analysis compare fairly well with other published theoretical and experimental data, and demonstrate that the incorporation of the new wind loading estimation model leads to a definite qualitative improvement in the theoretical predictions of the dynamic characteristics of vertical axis wind turbines.