A self-running standing wave-type bidirectional slider for the ultrasonically levitated thin linear stage

A slider for a self-running standing wave-type, ultrasonically levitated, thin linear stage is discussed. The slider can be levitated and moved using acoustic radiation force and acoustic streaming. The slider has a simple configuration and consists of an aluminum vibrating plate and a piezoelectric zirconate titanate (PZT) element. The large asymmetric vibration distribution for the high thrust and levitation performance was obtained by adjusting the configuration determined by finite elemental analysis (FEA). As a preliminary step, the computed results of the sound pressure distribution in the 1-mm air gap by FEA was com pared with experimental results obtained using a fiber optic probe. The direction of the total driving force for the acoustic streaming in the small air gap was estimated by the sound pressure distribution calculated by FEA, and it was found that the direction of the acoustic streaming could be altered by controlling the vibration mode of the slider. The flexural standing wave could be generated along the vibrating plate near the frequencies predicted based on the FEA results. The slider could be levitated by the acoustic radiation force radiated from its own vibrating plate at several frequencies. The slider could be moved in the negative and positive directions at 68 kHz and 69 kHz, which correspond to the results computed by FEA, with the asymmetric vibration distribution of the slider's vibrating plate. Larger thrust could be obtained with the smaller levitation distance, and the maximum thrust was 19 mN.     

A finite element formulation for sliding beams,Part I

We use the updated Lagrangian and the co-rotational finite element methods to obtain solutions for geometrically non-linear flexible sliding beams. Finite element formulations are normally carried out for fixed domains. Since the sliding beam is a system of changing mass, first we discretize the system by introducing a variable-domain beam element and model the sliding beam by a fixed number of elements with changing length. Second, we transform the system governing equations of motion to a fixed domain and use conventional finite elements (fixed size and number) to discretize the system. Then our investigation is followed by a comparison between two formulations. Finally, we use the co-rotational method in conjunction with a variable domain beam element to obtain the discretized system equations. To do so, we consider the beam to slide with respect to a fixed channel and later we consider a formulation in which the beam remains at rest and the channel slides with a prescribed velocity. We show that both formulations end up with identical discretized equations of motion. © 1998 John Wiley & Sons, Ltd.     

Finite element simulation for a new disc-type ultrasonic stator

This paper is concerned with the development of a new disc-type piezoelectric ultrasonic stator. Linear piezoelectric, mechanical, and piezoelectro-mechanic behaviors of a metal disc structure embedded with piezoelectric actuator are considered. Using a finite element method, a dynamic formulary is modeled for the new disc-type piezoelectric ultrasonic stator. In this model, a 3-dimensional (D) mechanical element with an extra electrical degree of freedom is used to simulate dynamic vibration modes and analyze characteristic responses such as electrical impedance response, phase response, and mechanical frequency response for a new disc-type piezoelectric ultrasonic stator. An adaptive boundary condition, simple support condition with three nonequal-triangular fixed points near the edge for the mechanism design of a new disc-type piezoelectric ultrasonic stator is defined so that a lateral elliptical motion of the contact point between stator and rotor can be realized for driving the rotor. The finite element results have been compared with the experimental measurements. As a result, the analysis model seems to be similar to the real condition.     

恒压式径向柱塞泵定子的位移振动特性分析

恒压式径向柱塞泵的工作状态可分为恒流状态和恒压状态,而定子在这两个工作状态下表现出不同的振动频率特性.首先建立了径向柱塞泵定子的动力学模型,然后对其在两个状态下的位移振动频率特性进行分析,并设计振动测试装置对JB32H型径向柱塞泵定子的进行振动试验研究.分析及试验结果表明:无论在恒流状态还是在恒压状态,定子振动具有周期性;由于恒压控制系统的作用,恒压状态下的位移振动频带要比恒流状态下的位移振动频带窄;在恒压状态的频带范围内,恒流状态下的幅值要小于恒压状态下的幅值.研究的结果有助于柱塞泵的振动噪声控制.     

带柔性静子结构高速转子支承刚度修正方法

针对某涡轴发动机带柔性过渡段悬臂动力涡轮转子支承刚度的修正方法开展研究。以动力涡轮模拟转子为研究对象,建立了转子的有限元分析模型,基于SAMCEF分析软件计算得到了转子的前三阶临界转速和振型,在高速旋转试验器上完成了全转速范围内的动力特性试验,分析确认了柔性过渡段是导致模拟转子前两阶临界转速存在较大计算误差的主要原因,基于临界转速试验结果,提出了一种转子支承刚度的修正方法并对模拟转子的支承刚度进行了修正,推算得到了柔性过渡段的横向刚度。其次,以真实动力涡轮转子为研究对象,按修正方法对真实动力涡轮转子的支承刚度进行了修正,支承刚度修正后其前两阶临界转速的计算误差大幅减小,验证了该修正方法的正确性,修正后的计算模型很好地反映了真实转子的实际情况。研究工作对类似高速转子支承刚度的修正有重要的指导意义,可有效提高航空发动机带柔性静子结构高速柔性转子的建模精度。     

A sliding superconducting contact

We have found that solder coated spring wire brushes can make a sliding superconducting contact with a rotating superconducting commutator. With a relative velocity of 0.5 cm s^?1 between brushes and rotor, we observe critical currents of up to 0.1 A. Below the critical current we detect no resistance above 10^?7 Ω.     

基于滑动峰态算法的信号弱冲击特征提取及应用

机械故障振动信号中往往含有故障引起的弱冲击成分,冲击信号具有显著的非高斯特性,而零时滞四阶累积量即峰态能够描述信号偏离高斯分布的程度;基于峰态这一特性,本文提取一种基于滑动峰态算法的弱冲击特征提取方法,首先对原信号进行滑动峰态计算,获得一个新的峰态时间序列,然后对该峰态时间序列进行傅立叶变换,提取出信号中冲击成分的频率特征。通过强背景信号及噪声环境下弱冲击特征提取的仿真研究,证明了该方法具有很好的冲击特征提取能力。以实测齿轮断齿信号分析结果证明了该方法的有效性。     

A simplified calculation model for the sliding contact boundaries in a hydrostatic piston mechanism

The objective of this study was to discuss simplified calculation models for the piston/cylinder sliding mechanism in which boundary contact partly occurs invariably. An efficient prediction of the boundary leakage and friction is often needed, such as in a swash-plate axial piston machine whose lubrication test is hard to perform due to the mechanism complexity. In order to model this physically uncertain lubrication regime, two calculation models were compared to compute the lubrication behaviors: “rigid boundary model”, whose theoretical concept was previously reported in the literature, and “elastic boundary model”, newly proposed in this study. Developed numerical algorithms commonly facilitated the simultaneous calculation of body motion and fluid film pressure to observe piston motion, reaction forces, and power loss. The results showed that simulations using the elastic boundary model should be more helpful for the prediction in the earlier development stage than the previous model since the methodology provides much less simulation time than full-order calculation, higher accuracy than the rigid model, and useful engineering parameters such as surface stress. The proposed calculation model can be extended to various asymmetrically loaded reciprocating piston mechanisms for efficiently predicting the lubrication behavior.     

Investigation of a new stator interior permanent magnet machine

A new stator interior permanent magnet (PM) machine which is developed from the doubly salient PM machine is proposed. The novelty of this machine lies in the split stator pole and full-pitched windings, where tooth-shoe is adopted and the PM is inserted into the stator pole. This configuration can offer higher power density and lower cogging torque ripple than the doubly salient machine. In order to achieve high power density, the smaller thickness of PM may be more favourable. In this case, an analytical method is used to examine the demagnetisation of PM under short-circuit current. A prototype machine for wind power application is designed, built and tested. The experimental results validate the theoretical analysis and the effectiveness of the proposed stator interior PM machine.     

Simultaneous grain boundary motion,grain rotation,and sliding in a tricrystal

Grain rotation and grain boundary (GB) sliding are two important mechanisms for grain coarsening and plastic deformation in nanocrystalline materials. They are in general coupled with GB migration and the resulting dynamics, driven by capillary and external stress, is significantly affected by the presence of junctions. Our aim is to develop and apply a novel continuum theory of incoherent interfaces with junctions to derive the kinetic relations for the coupled motion in a tricrystalline arrangement. The considered tricrystal consists of a columnar grain embedded at the center of a non-planar GB of a much larger bicrystal made of two rectangular grains. We examine the shape evolution of the embedded grain numerically using a finite difference scheme while emphasizing the role of coupled motion as well as junction mobility and external stress. The shape accommodation at the GB, necessary to maintain coherency, is achieved by allowing for GB diffusion along the boundary.     

A thermoelectric stage for ftiros thermochromic films

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 39–41, October, 1989.     

A bend-testing stage for the scanning electron-microscope

The design of a stage to bend materials in a scanning electron-microscope (Stereoscan, Cambridge Scientific Instruments Ltd) is described together with examples of its use in the fracture of composite materials. The bend module, when fitted to a large modular stage, can be used with existing scanning electron microscopes and is capable of bending, under increasing load or cyclic loading conditions, rectangular specimens of a maximum size 44×4×1.5 mm, to a maximum strain of 1.5%. Using the module with a standard display system the non-catastrophic stages of deformation and failure can be followed at higher magnification than has previously been possible. When the module is used in conjunction with a fast scanning and display system, deformation and fracture processes may be recorded at high magnifications while the specimen is being strained.At present on leave of absence at Cavendish Laboratory, Cambridge.Patent applied for.