A standing wave-type noncontact linear ultrasonic motor

In this study, a novel standing wave-type noncontact linear ultrasonic motor is proposed and analyzed. This linear ultrasonic motor uses a properly controlled ultrasonic standing wave to levitate and drive a slider. A prototype of the motor was constructed by using a wedge-shaped aluminum stator, which was placed horizontally and driven by a multilayer PZT vibrator. The levitation and motion of the slider were observed. Assuming that the driving force was generated by the turbulent acoustic streaming in the boundary air layer next to the bottom surface of the slider, a theoretical model was developed. The calculated characteristics of this motor were found to agree quite well with the experimental results. Based on the experimental and theoretical results, guidelines for increasing the displacement and speed of the slider were obtained. It was found that increasing the stator vibration displacement, or decreasing the gradient of the stator vibration velocity and the weight per unit area of the slider, led to an increase of the slider displacement. It was also found that increasing the amplitude and gradient of the stator vibration velocity, or decreasing the weight per unit area of the slider and the driving frequency, gave rise to an increase of the slider speed. There exists an optimum roughness of the bottom surface of the slider at which the slider speed has a maximum     

A stator for a self-running, ultrasonically-levitated sliding stage

Here we propose a self-running, ultrasonically-levitated sliding stage and investigate the levitation and propulsion characteristics of its stator. The stator consists of two aluminum beams and four PZT plates, which have two-paired bimorph configurations. A flexural standing wave was generated along the beam by applying an input voltage to the PZTs, and the stator could be levitated from a flat substrate by the acoustic radiation force generated by its own vibrating beam. The size of the stator was optimized using finite-element analysis (FEA) to maximize the vibration displacement amplitude of the beam. The flexural vibration modes at 24.3 and 102 kHz were the most prominent vibration modes having large displacement amplitudes. The stator was levitated at 23.2 and 96.1 kHz, which are close to the frequencies predicted by the FEA results. A standing wave was observed along the beam. The experimental and the simulated results showed good agreement. The levitation distance h was measured by varying the vibration displacement amplitude of the beam u, and was found to be proportional to u. When a traveling wave was excited along the beam by controlling the temporal phase difference of the two transducers, the stator could be made to hover and to move in the opposite direction to the traveling wave. The stator moved in the positive direction when the phase difference was in the ranges 0 degrees to 200 degrees and 310 degrees to 360 degrees, and in the negative direction when the phase difference was between 220 degrees and 260 degrees.     

An ultrasonically levitated noncontact stage using traveling vibrations on precision ceramic guide rails

This paper presents a noncontact sliding table design and measurements of its performance via ultrasonic levitation. A slider placed atop two vibrating guide rails is levitated by an acoustic radiation force emitted from the rails. A flexural traveling wave propagating along the guide rails allows noncontact transportation of the slider. Permitting a transport mechanism that reduces abrasion and dust generation with an inexpensive and simple structure. The profile of the sliding table was designed using the finite-element analysis (FEA) for high levitation and transportation efficiency. The prototype sliding table was made of alumina ceramic (Al2O3) to increase machining accuracy and rigidity using a structure composed of a pair of guide rails with a triangular cross section and piezoelectric transducers. Two types of transducers were used: bolt-clamped Langevin transducers and bimorph transducers. A 40-mm long slider was designed to fit atop the two rail guides. Flexural standing waves and torsional standing waves were observed along the guide rails at resonance, and the levitation of the slider was obtained using the flexural mode even while the levitation distance was less than 10 microm. The levitation distance of the slider was measured while increasing the slider's weight. The levitation pressure, rigidity, and vertical displacement amplitude of the levitating slider thus were measured to be 6.7 kN/m2, 3.0 kN/microm/m2, and less than 1 microm, respectively. Noncontact transport of the slider was achieved using phased drive of the two transducers at either end of the vibrating guide rail. By controlling the phase difference, the slider transportation direction could be switched, and a maximum thrust of 13 mN was obtained.     

Novel bidirectional linear actuator for electrohydraulic valves

This paper presents a permanent-magnet actuator with bidirectional and high levels of linear force over short strokes. The actuator can be used in electrohydraulic valves. Its static and dynamic performances were analyzed by using two-dimensional finite-element magnetic field solutions that take into account the nonlinearity of the material. The measured and simulated results are highly consistent. Experimental results show that the prototype actuator can produce a force of /spl plusmn/60 N, its nonlinearity is less than 0.5%, and the hysteresis is less than 2% within a stroke of /spl plusmn/1 mm. The actuator's frequency response (-3 dB) can reach 150 Hz.     

A cut-tree-based approach for clustering machine cells in the bidirectional linear flow layout

This paper considers the joint cell clustering-layout problem where machine cells are to be located along the popular bidirectional linear material flow layout. The joint problem seeks to minimize the actual intercell flow cost instead of the typical measure that minimizes the number of intercell movements when the layout problem is excluded from the clustering process. Owing to the computational difficulty, a three-phase approach is proposed using the cut-tree-network model to solve this joint problem. The cell clustering and layout problem is transformed into a multi-terminal network flow model. A cut tree is constructed and partitioned into a number of subgraphs via the selected primary path. Each subgraph is a clustered cell and their locations are assigned to the layout sequence by comparing the cut capacities. Thus, the proposed approach concurrently determines the machine cells and their relative sequences in the bidirectional linear flow layout. Computational procedures are illustrated and additional experiments, with data adapted from the literature, are performed to demonstrate the viability of the approach.     

A simple bidirectional linear microactuator for nanopositioning--the "Baltan" microactuator

A new linear microactuator, using bulk PZT and electro-discharge-machined components, generates a sliding velocity and force of 100 mm/s and 12 mN, respectively, in either direction, and a peak velocity and force of 212 mm/s and 44 mN, respectively. Using a simple combination of two slightly different beams placed in contact with a slider, and vibrated at two different resonance frequencies, 508 and 522 kHz, by a specially designed, axially vibrating piezoelectric element, bidirectional linear motion was obtained. By simply reducing the length of the applied signal, the sliding distance was reduced to 90 nm +/- 2 nm, which could be improved with a variety of control methods. The design offers not only silent operation, slider clamping upon removal of power, and all of the other advantages of piezoelectric actuators, but also the potential to be further reduced in size to sub-mm3 for microrobotics and other applications.     

A method for the fabrication of sculptured thin films of periodic arrays of standing nanorods

A simple method for the fabrication of sculptured thin films (STFs) of periodic arrays of high-aspect-ratio (20:1) standing nanorods on silicon substrates is described. It is based on oblique evaporation onto periodically arranged arrays of "mini-rod" topography using a rotating sample stage. Recently, it has been shown that these nanostructures can be prepared on relatively large areas and at low cost, making the method suitable for technological applications.     

A finite element,linear programming methods for the limit analysis of thin plates

Finite elements having linear moment distributions and use of linearized yield criteria allow one to determine lower bounds to the collapse load of thin plates as solutions of linear programs. The method is quite general and rigorously meets the requirement of the lower bound theorem of limit analysis for concentrated or line load distributions. Ways of treating distributed surface loads are also discussed and tested. Actual bounds are computed for a variety of plate problems governed by Tresca yield criterion and compared with previous solution obtained from higher order stress elements and non-linear optimization techniques. The comparison shows that the present method can yield accurate bounds with considerably shorter computer times and relatively small number of elements. Additional tests show that numerical convergence to the limit loads is assured by suitable refinement of the mesh pattern.     

A novel mixing method for levitated particles using electrostatic fields

A continuous particle mixing system using electrostatic forces and vibrations was developed. The system consists of two symmetrically arranged devices. The same or different types of charged particles were continuously fed from each device in a dispersed state and mixed instantaneously in the space between devices. When charged particles with opposite polarities were fed from each device by changing the direction of the electric field, the particles were homogeneously mixed. The electric field and particle trajectories were numerically calculated to elucidate the particle-mixing mechanism. Furthermore, the mixing state of the particles was evaluated quantitatively using Shannon entropy.     

Advanced precision linear stage for industrial automation applications

In the area of factory automation, accurate positioning systems are increasingly required in various industries to improve the productivity and to lower the manufacturing cost. In this paper, we present a prototype precision linear stage. It has a positioning accuracy of 1 /spl mu/m and a peak speed above 1 m/s. A permanent magnet DC linear motor has been used in the system as the actuator to eliminate the need for mechanical transmission from the rotary to linear motion. To achieve a fast and accurate closed loop response, we develop a state space predictive controller and a dynamic friction compensation system for the precision stage. The system has been optimally tuned using the genetic algorithm. Some experimental results are presented.     

A new method for the numerical solution of the Reynolds equation for gas-lubricated slider bearings

Summary The steady-state Reynolds equation for gas lubricating leads to a quasilinear boundary-value problem in two dimensions. This equation contains a first-order derivative term whose coefficient is nonlinear and also large for most of the practical cases. Thus, this becomes a quasilinear singular perturbation problem. Existing numerical schemes are faced with the failure of convergence as well as numerical instability which often results in overshooting the answers. Asymptotic approximations also give poor results if the film-thickness ratios are not small. In this paper an accurate and reliable numerical scheme is presented. Convergence is proved independent of the bearing numbers and film-thickness ratios. A weighted upwind-difference form is used to discretize the differential equation. Theory of M-matrices and associated inequalities are employed to prove the ensuing monotonicity. The analysis presented in this paper can be extended to a more general class of singular-perturbation quasilinear boundary-value problems. Numerical results and graphs for pressure distributions and bearing loads are provided for the parabolic slider. Comparisons are made with other existing results concerning numerical as well as asymptotic analysis.     

A robust control chart for simple linear profiles in two‐stage processes

In many manufacturing systems, the final product is the result of several dependent stages. In particular, in multistage processes, the quality characteristics of downstream stages are influenced by those in the earlier stages (upstream). This property is referred to as the cascade property, which, if disregarded in process monitoring, may bring about misleading results for the subsequent fault diagnosis. Considering the relationships among consecutive stages of the process, the U statistic is the most widely used method for monitoring multistage processes. Using this method, our paper deals with monitoring a two‐stage process where quality characteristics are represented as simple linear profiles. To guard against the detrimental effect of contaminated data in the phase I of statistical process control, two well‐known robust M‐estimators, including Huber's and bi‐square, are employed for estimation of the process parameters. Under different degrees of autocorrelation across stages of the process and also for different contamination rates, the performances of the proposed methods are compared with that of the conventional least‐square method. From the viewpoint of estimation performance measures, including unbiasedness and efficiency, along with the capability of the control chart in identifying the true source of variation, extensive simulation results reveal that robust estimators outperform the traditional method in a two‐stage process. Meanwhile, it should be noted when there is contamination only in the first stage of the process, the least‐square method performs slightly better.     

计算机求定CoFeB薄膜动力学参数研究

根据化学镀CoFeB薄膜试验得到镀液中反应物浓度、pH值、温度以及对应沉积速率。利用回归分析的研究方法,建立了沉积速率的多元线性回归分析的数学模型：y=b0＋^r∑i=1biχi沉积量与反应物浓度、pH值等实验数据的相关性用剩余方差S来表征,借助于计算机编程运算,求出回归系数与回归系数的估计值b0-6、估计值的置信区间、残差r、残差的置信区间rint。研究上述诸因素所对应的反应动力学参数,求出了镀液沉积速率的方程式：v=k[Co^2＋]^0.82[Fe]^0.38[BH^-4]^1.62[OH^-]^0.83[L1]^-1.02[L2]^-0.95exp（-Ea/RT）以及通过上述的线形回归分析和实验验证可以得到化学镀CoFeB最佳配方。     

An incremental formulation for the linear analysis of thin viscoelastic structures using generalized variables

This paper is concerned with the development of an incremental formulation in the time domain for the displacement and stress analysis of quasistatic, linear, thin viscoelastic structures undergoing mechanical deformation. By representing the viscoelastic behaviour of a material by a discrete creep spectrum and by an incremental constitutive equations, the difficulty of retaining the stress history in computer solutions is avoided. A complete general formulation of linear viscoelastic stress analysis is developed in terms of increments of midsurface strains and curvatures and corresponding stress resultants.     

A coupled boundary/finite element method for the computation of magnetically and electrostatically levitated droplet shapes

A coupled finite element and boundary element method is developed to predict the magnetic vector and scalar potential distributions in the droplets levitated in an alternating magnetic or electrostatic field. The computational algorithm entails the application of boundary elements in the region of free space and finite elements in the droplet region, the two being coupled along the droplet–air interface. The coupled boundary and finite element scheme is further integrated with a WRM‐based algorithm to predict the free surface deformation of magnetically and electrostatically levitated droplets. Several corner treatments for the boundary and finite element coupling and their implications to free surface calculations are discussed. Detailed formulation and numerical implementation are given. Numerical results are compared with available analytical solutions whenever available. A selection of computed results is presented for mag‐ netically or electrostatically levitated droplets under both terrestrial and microgravity conditions. Copyright © 1999 John Wiley & Sons, Ltd.     

A change in the structure of an ultrasonically processed MMA-MAA based photoresist

The structure of a photoresist based on a MMA-MAA copolymer was modified by exposure to an ultrasound with a frequency of 21 kHz and a power density of 300 W/m². The results of the UV and IR spectroscopic measurements show that the ultrasonic processing leads to the formation of C=O double bonds and to the growth of absorption in the 260–360 nm wavelength range.     

A channel-cut crystal monochromator for x-ray standing wave measurements

In many X-ray diffraction experiments (e.g., small angle scattering and perfect crystal experiments) it is necessary to use a monochromator with high angular resolution, often much better than the intrinsic Darwin width of a perfect crystal Bragg reflection. A monolithic silicon crystal monochromator with a variable angular resolution function has been designed and fabricated. It is tunable over a wide range of X-ray energies, and is particularly well suited for X-ray standing wave experiments using synchrotron sources. Although independently conceived, this monochromator is similar is design to one developed by Bonse et al. [1] for a different purpose. It is functionally equivalent to an asymmetric crystal monochromator in providing a narrow angular transmission, yet has several advantages over the latter for standing wave experiments, especially at a synchrotron source. Rocking curves and standing wave measurements are presented.     

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.