气体挤压膜轴承的性能分析及其控制器的研究

为了有效克服传统气体轴承的缺点,基于超声激励的气体挤压膜机理,研制了一种新型的气体挤压膜轴承。为了获得关键结构尺寸及相关的控制参数,采用有限元法对压电换能器进行了模态分析和谐响应分析;应用数值解法从理论上证明了轴承的悬浮能力;通过压电换能器的模态实验,确定了其工作频率;同时采用有限元法对所设计的轴承产生的超声波声压进行了分析。在此基础上,设计制作了基于STC单片机的数字控制器硬件电路,编写了不完全微分PID控制程序并在实验台上进行了验证。研究结果表明,该类轴承在超声激励下能够实现悬浮支承。     

Tribological property investigation on a novel pneumatic actuator with integrated piezo actuators

Pneumatic piston–cylinder actuators are commonly used in industry for a variety of automation and robotics applications. In order to suppress leakage, these actuators comprise seal rings which unfortunately introduce friction and affect the positioning accuracy and output force. This article investigates vibrations of the seal generated by integrated piezo actuators to reduce friction force. For this, two piezoelectric stacks are integrated in the cylinder and used to excite vibration modes. This concept was studied in a compact cylinder pneumatic actuator with a bore diameter of 5 mm and a stroke of 10 mm. Dry friction measurement shows a 52% reduction from the original friction force at a driving frequency of 18.29 kHz and vibration amplitude of 0.05 μm. In the wet friction experiments, the friction force can be reduced by 54% from the original wet friction with vibrations at amplitude of 0.04 μm.     

轴/径向耦合式非接触型压电作动器的研究

提出了一种基于近场声悬浮机理的球转子压电作动器,特别设计了可分别沿轴向和径向辐射超声近场的作动器,其目的是为了实现球转子的稳定、可控悬浮和高速旋转,可将其应用到航空航天的高速电机、球轴承传动或姿态传感领域。该新型压电作动器通过轴向与径向悬浮装置的不同耦合形式来提供超声悬浮力并以非接触的方式驱动球转子,实现对球转子的灵活控制。介绍了轴/径向耦合式非接触型压电作动器的结构和工作原理,通过仿真得到了悬浮装置的声场分布形式,深入分析和阐释了球转子的悬浮和驱动机制,加工了样机,搭建了轴/径向耦合式超声悬浮型压电作动器的特性测试系统,通过非接触式激光位移传感器得到了球转子的悬浮特性,并获得了691.5r/min的转速。     

超声波轴承用挤压式压电换能器的共振频率

设计了一种超声悬浮轴承用新型径向挤压式压电换能器,用于验证超声波轴承径向共振频率理论计算的正确性。基于弹性理论、压电方程和机电类比原理,建立压电换能器机电等效电路图,理论推导出了压电换能器径向振动的共振频率方程;然后,应用Matlab软件计算出了压电换能器的共振频率。采用有限元软件对已知结构尺寸的换能器进行模态分析,计算出压电换能器所需振型及该振型下的共振频率,数值仿真分析了换能器结构尺寸对换能器共振频率和径向振幅的影响。最后,设计了 一台样机,从理论、仿真及实验三方面对其共振频率进行验证。实验结果显示：换能器径向振动共振频率的理论值与实验结果相对误差为5.89%,仿真值与实验结果误差为3.53%。实验结果证明了理论计算方法的正确性,为压电挤压换能器的设计提供了理论依据。     

Operation of a model of a normal ultrasonic transducer for immersion and conventional inspection techniques

An experimental and theoretical study of the operation of a model of a normal ultrasonic transducer for various acoustic loads has been performed. It has been established that, in the design of the transducer under study, a relatively thick adhesive layer between the piezoelectric plate and the wear plate abruptly reduces the operating (effective) signal frequency in the case of an immersion load. An equation for estimating the effective frequency for a transducer model has been obtained with allowance for the characteristics of such a layer.     

受控静压挤压油膜阻尼方案及其动态特性分析

提出了在转子主动减振系统中采用静压挤压油膜阻尼器作为控制执行机构的新方案，并对阻尼器的结构形式及适应主动控制研究需要的动力特性分析方法作了介绍。同时分析了这种阻尼器作为控制元件时的一些特性，最后给出了受控静压挤压油膜阻尼器在转子主动减振研究中的应用示例。     

基于高阶板理论的有限单元及其在压电智能结构中的应用研究

带有分布式压电驱动器 /传感器的自适应智能材料结构在振动控制、形状控制、精确定位等方面具有很大潜力而受到广泛的关注。本文把x ,y方向的位移定义为厚度坐标的三次多项式 ,利用板上下自由表面的力边界条件及正交异性复合材料的特性 ,导出了改进的高阶板理论。依据该理论建立了 4节点 2 0自由度矩形板高阶有限单元 ,并对一些算例进行了分析。通过与文献结果的对比 ,验证了改进的高阶板理论和所建立单元的正确性。最后利用所建立的单元 ,分析了压电悬臂梁中压电层在不同脱胶长度情况下板的频率变化 ,计算结果与试验结果相吻合     

An ultrasonic stage for controlled spin of micro particles

In this work, we proposed and developed an ultrasonic stage which can make different kinds of micro particles spin at its center. The stage consists of a circular copper plate and two piezoelectric half-rings bonded onto the bottom surface of the copper plate. The two piezoelectric half-rings have the same size and property, but opposite polarization in the thickness direction. They form a ring concentric with the copper plate. The spin direction of micro particles can be reversed by changing the operating frequency of stage. The spin speed can be controlled by operating frequency and voltage of the stage, and it reaches 955 rpm for a single glass ball with 0.51 mm diameter. The spin of micro particles is caused by travelling waves around the center of the stage, and the travelling waves are generated by anti-symmetric flexible vibration of the stage, excited by the two piezoelectric half-rings.     

超声振动减摩性能的实验研究及理论分析

以超声减摩的核心构件压电振子为研究对象，在测量压电振子参数的基础上通过改变压电振子的工作电压，测量压电振子振动时辐射端面与特定的工作表面间的摩擦系数的变化规律，通过有限元法计算压电振子的振动模态，分析超声振动的减摩机理，以便进行适当的结构设计，利用超声振动的减摩性能制造出超声波悬浮轴承。研究证明，超声振动具有良好的减摩性能，压电振子处于纵向振动模态时减摩效果最好。     

基于特征模型的压电悬臂板振动控制

航天器上悬臂板型挠性附件在扰动作用下将引起包括弯曲和扭转模态的振动,这将影响系统的稳定性和控制精度,尤其是在平衡点附近低频模态频率上的小幅值残余振动很难快速抑制。为了快速抑制压电智能挠性悬臂板系统,包括弯曲和扭转模态的振动,提出采用基于特征模型的非线性黄金分割自适应控制,组合非线性切换逻辑积分阻尼器算法。首先,优化配置压电传感器和驱动器实现了悬臂板的弯曲和扭转模态在检测和驱动上的解耦;其次,设计并建立压电挠性悬臂板试验平台,进行试验模态辨识并获得了悬臂板系统弯曲和扭转振动的模态频率和频响特性;最后,进行压电智能悬臂板的弯曲和扭转振动模态主动振动几种方法试验的比较研究。试验结果表明,采用的控制方法能够快速地抑制压电智能挠性悬臂板的振动。     

Frequency characteristics of non-contact ultrasonic motor with motion error correction

The purpose of this research is to achieve real time motion error correction of the rotor in a non-contact ultrasonic motor (non-contact USM). The rotor is installed in a cylindrical stator with a small gap and designed so that it has a resonant frequency of 22.2 kHz, the 8th flexural mode of vibration. The multi-layered piezoelectric actuators excite the flexural wave traveling in the circumference direction. The ultrasonic vibration produces a sound field that levitates the rotor, and the traveling wave induces a near-boundary streaming to rotate the rotor by viscous force. In this paper, we describe an experimental test of the performance of a non-contact USM. When the flexural vibration amplitude was 0.3 μm, the rotational speed was 4 rpm. The rotational speed and starting torque was proportional to the vibration amplitude. The starting performance to attain rotational speed had a time constant of 2 s for several different amplitudes hence the rotational torque is independent of the rotational speed and the resistance force on the rotor is governed by viscosity. In addition, the non-contact USM has the capability of contact-free micro positioning of the rotor by controlling the deformation of the piezoelectric actuators. The PI controller was constructed to correct the detected motion error of the rotor in the radial direction. As a consequence, a motion error of 0.8 μm for one rotor revolution was reduced to 0.1 μm.     

A linear air bearing stage with active magnetic preloads for ultraprecise straight motion

In this paper, we propose a linear motion stage designed with magnetically preloaded air bearings. The magnetic actuators for preloading air bearings were combined with permanent magnets and coils to adjust the air bearing clearance by actively controlling the magnetic force. The system was designed to achieve a simplified configuration of air bearing stage while providing ultraprecise straight motion by actively compensating for the motion errors. The porous aerostatic bearings and magnetic preload actuators were designed and analyzed numerically for a single-axis prototype linear stage driven by a coreless linear motor. A magnetic circuit model was derived for the magnetic actuators. The static stiffness and load capacity of the air bearing stage in the vertical (magnetically preloaded) direction were experimentally measured and compared with the results from the numerical analysis. Motion control laws for three degrees of freedom (i.e., vertical, pitch, and roll motions) were obtained with a high linearity and independence for each axis. The active compensation of three motion errors, the vertical, pitch and roll motion errors were performed through curve-fitting the three errors measured with combination of capacitive gap sensors and a laser interferometer. The errors were reduced from 1.09 to 0.11 μm for the vertical straightness error, from 9.42 to 0.18 arcsec for the pitch motion, and from 2.42 to 0.18 arcsec for the roll motion as level of measured repeatability.     

Performance investigation on ultrasonic levitation axial bearing for flywheel storage system

The bearing is an important basic mechanical part for supporting a shaft. A flywheel storage system needs a type of noncontact support bearing to enhance the speed of the axis. A magnetic suspension bearing is one type of noncontact bearing but has electromagnetic interference to other electric equipment. Based on the performance research of ultrasonic levitation technology, a novel noncontact bearing called ultrasonic bearing is presented, which consists of a special piezoelectric vibrator supporting the load. Experiments are carried out to study the relationships among the amplitude of the vibrator and levitation clearance, the highest speed of the axis, and the frictional moment of the axis. Results show that the levitation clearance becomes smaller gradually with increasing load; the rotation speed is up to 8946 r/min, and the friction moment is only 2.095×10⁻⁵ N·m when the levitation clearance is 8.53 μm. The ultrasonic bearing is highlighted because of its simple structure, strong levitation ability, and low friction moment.     

微细深孔超声轴向振动钻削装置的设计

基于高频振动切削原理 ,设计了一种振频 2 0± 1KHz、振幅 2 5 μm的新型超声轴向振动钻削装置 ,该装置由数字锁相环频率自动跟踪式晶体管型超声波发生器、轴向半波长圆柱型压电陶瓷换能器、半波谐振圆锥型变幅杆以及工具系统组成 ,可在软质材料上实现微细深孔的精密、超精密加工     

Design of an offset hydrostatic thrust bearing under dynamic loading conditions

An offset hydrostatic thrust bearing is analysed to determine the effect of vibration of the rotating plate on the performance characteristics. The flow developed is asymmetric because the surface rotation axis is offset from the bearing axis. The governing Reynolds equation is solved using semianalytical methods. The average load capacity, frictional force and lubricant flow rate are strong functions of the bearing offset L, bearing number λ, film thickness profile H, film thickness variation ? and the ratio between the frequency of vibration of the rotating plate and the angular speed of rotation.     

基于机敏材料的冗余度柔性机器人弹性动力响应最优控制

为了改善冗余度柔性机器人的动力学品质,采用了振动主动控制方法。设计了具有压电作动器与应变传感器的机敏连杆,构造了冗余度柔性机器人振动主动控制系统的状态空间表达式。利用独立模态空间控制理论设计状态反馈控制器,获得了压电作动器的实际控制电压,并根据连杆中点的应变信号对系统状态进行了近似估计。最后,以平面3R冗余度柔性机器人为例进行了计算机仿真,其结果证明了这种振动主动控制方法的有效性。     

The deflection of a simply supported plate induced by piezoelectric actuators

The coupling effects between the mechanical and electric properties of piezoelectric materials have drawn significant attention for their potential applications as sensors and actuators. In this investigation, two piezoelectric actuators are symmetrically embedded in a simply supported plate. Electric voltages with the same amplitude and opposite sign are applied to the two symmetric piezoelectric actuators, resulting in the bending effect on the plate. The bending moment is derived by using the theories of elasticity and piezoelectricity. The analytical solution of the flexural displacement of a simply supported plate subjected to the bending moment is solved by using the plate theory. The analytical solution is compared with the finite element solution to show the validation of present approach. The effects of the size and location of the piezoelectric actuators on the response of a plate are presented through a parametric study.     

Hybrid controller of a linear piezoelectric walking stage relying on stack/shear piezoelectric actuators

This paper proposes a hybrid control strategy of a novel linear piezoelectric walking stage based on two sorts of piezoelectric actuators, which takes the load variation into account. The proposed stage consists of two parallel 4-bar lever amplification mechanisms with flexure hinges actuated by piezoelectric stacks to heighten the vertical distance (that is more tolerable to the assembly discrepancy), two compression springs (that is able to maintain a fixed linear position without powering), and two shear piezoelectric actuators (that can achieve longer and equivalent to walking motion) in a small form factor. The proposed stage has two operating modes, namely a coarse positioning mode with a more extensive travel range and a fine positioning mode with a nanometer-level resolution, to possess excellent performance for the linear piezoelectric walking stage of load variations. One multimodal switching controller and one feedforward-feedback controller conduct the coarse mode and fine mode, respectively. The optimal frequency for a specific load is obtained through a backpropagation neural network in the multimodal switching control. In the feedforward-feedback control, the inverse mathematical model based on the Bouc-Wen hysteresis model is used to mitigate the hysteresis effect in the feedforward part while the proportional–integral–derivative controller in the feedback part handles the external system disturbances. Experimental results show the proposed hybrid coarse/fine mode control strategy's effectiveness to satisfy an efficient and accurate positioning task.     

Static characteristics of a water-lubricated hydrostatic thrust bearing with a porous land region and a capillary restrictor

In this paper, a water-lubricated hydrostatic thrust bearing with a porous land region and capillary restrictor is proposed, and the results of theoretical and experimental investigations of its static characteristics are presented. The results showed that the water-lubricated hydrostatic thrust bearing with a porous land region had good operating characteristics; in particular, it had a high load capacity and static stiffness close to that of a porous bearing when operating with a clearance of less than 15 μm, and a high load capacity and static stiffness equivalent to that of a pocket bearing when running with a clearance larger than 15 μm.     

Investigating the thermal environment effects on geometrically nonlinear vibration of smart functionally graded plates

An analytical solution for a sandwich circular FGM plate coupled with piezoelectric layers under one-dimensional heat conduction is presented. All materials of the device may be of any functional gradients in the direction of thickness. The solution exactly satisfies all the equilibrium conditions and continuity conditions for the stress, displacement and electric displacement as well as electric potential on the interfaces between adjacency layers. A nonlinear static problem is solved first to determine the initial stress state and pre-vibration deformations of the FG plate that is subjected to in-plane forces and applied actuator voltage in thermal environment in the case of simply supported boundary conditions. By adding an incremental dynamic state to the pre-vibration state, the differential equations that govern the nonlinear vibration behavior of pre-stressed piezoelectric coupled FGM plates are derived. The role of thermal environment as well as control effects on nonlinear static deflections and natural frequencies imposed by the piezoelectric actuators using high input voltages are investigated. Numerical examples are provided and simulation results are discussed. Numerical results for FGM plates with a mixture of metal and ceramic are presented in dimensionless forms. The good agreement between the results of this paper and those of the finite element (FE) analyses validated the presented approach. In a parametric study the emphasis is placed on investigating the effect of varying the applied actuator voltage and thermal environment as well as gradient index of FG plate on the dynamics and control characteristics of the structure.