压电陶瓷驱动球基微驱动器的动力学研究

研制出了尺寸为30 mm×30 mm×50 mm的压电陶瓷驱动的球基微驱动器样机,并对该微驱动器进行动力学分析以及微型轴孔装配的实验研究。建立了微驱动器金属球空间坐标关系,分析了球基微驱动器的动力学特征,并建立了其动力学模型。采用龙格-库塔法计算出了微驱动器的动力学参数,并利用MATLAB的SIMULINK模块搭建了微驱动器的仿真模型,并对其进行了动力学仿真分析。研制出了球基微驱动器样机,并在此基础上,集成微夹持器形成微操作器,对微驱动器性能进行了实验测试,并开展了Φ180 μm微型轴与Φ200 μm微型孔之间的精密微装配实验研究。最后,分析了微驱动器金属球质量、驱动信号频率、以及金属球与微驱动单元摩擦块接触表面摩擦系数对其性能的影响。实验结果表明:该球基微驱动器的转动分辨率为0.000 1°,转动定位精度为0.000 5°,微驱动器最大工作频率为1 200 Hz。实验结果验证了逆转振动模型的正确性,由该微驱动器所集成的微操作器,完全可以满足对微小元器件的微米级操作与装配等精密作业的要求。     

基于粘滑驱动的球基微操作器动力学建模与分析

球基微操作器是一种广泛应用于微纳米精密作业的微机器人系统,由基座、微操作球和顶端嵌有红宝石球的3根四分压电陶瓷管组成.基于此,通过驱动压电陶瓷管弯曲或摆动,依靠红宝石球与微操作球间惯性摩擦形成的相对位移实现微操作球3自由度的运动.这种摩擦运动中存在粘滑现象,粘滑驱动带来的非线性导致球基微操作器动力学性能复杂.在简化球面高副连接的条件下,建立具有粘滑特性的微操作器系统动力学模型.基于动态摩擦模型,运用数值方法分析多个参数对微操作器运动性能的影响,通过仿真手段完成模型验证.进行微操作器运动测试试验,进一步验证所建立的动力学模型的正确性和有效性.     

Impact drive rotary precision actuator with piezoelectric bimorphs

An impact drive rotary precision actuator with end-loaded piezoelectric cantilever bimorphs is proposed. According to finite element analysis and experiments of the dynamic characteristics of end-loaded piezoelectric cantilever bimorphs, a specific fixed-frequency and adjustable-amplitude is confirmed to control the actuator. The results show that an actuator excited by fixed-frequency and the adjustable-amplitude ramp voltage waveform works with a large travel range (180°), high resolution (1 μrad), speed (0.2 rad/min) and heavy-load ability (0.02 Nm). With advantages of high-precision positioning ability, simple structure and only one percent the cost of traditional impact drive mechanisms, the actuator is expected to be widely used in precision industries. __________ Translated from Optics and Precision Engineering, 2005, 13(3): 298–304 [译自: 光学精密工程]     

Novel precision piezoelectric step rotary actuator

A novel piezoelectric (PZT) precision step rotary actuator was developed on the basis of PZT technology. It adopts the principle of bionics and works with an inside anchoring/loosening of the stator and a distortion structure of the uniformly distributed thin flexible hinge to solve problems such as ineffective anchoring/loosening, low step rotary frequency, small travel, poor resolution, low speed and unsteady output. The developed actuator is characterized by high frequency (30 Hz), high speed (380 μrad/s), large travel (>270°), high resolution (1 μrad/step), and work stability. It greatly improves the ability to drive the existing PZT step rotary actuator. The new actuator can be applied in the field of micromanipulation and precision engineering, including precision driving and positioning and optics engineering. __________ Translated From Journal of Jilin University (Engineering and Technology Edition), 2006, 36(5): 673–677 [译自: 吉林大学学报 (工学版)]     

Friction and Wear Properties of Silicon Carbide in Water from Different Sources

Low friction and low wear of SiC sliding against itself in water at room temperature have been well reported in the past 20 years, and some practical applications have been developed. However, the properties of friction and wear in pure, deionized or distilled water have been mainly observed and not in water from sources in nature. In this article, the fundamental properties of friction and wear between SiC ball and disk are observed in water from ground, river, and sea, and the results are compared with those in deionized water in the viewpoints of modes of lubrication and wear and the resultant values of friction coefficient and wear rate. The smallest friction coefficient (μ_ℓ = 0.005) in steady state is observed in deionized water and the largest (μ_ℓ = 0.013) in sea water. The smallest wear rate (w _s = 2.2 × 10⁻⁷ mm³/Nm) is observed in sea water and the largest (w _s = 3.1 × 10⁻⁷ mm³/Nm) in deionized water. The intermediate values of μ_ℓ and w _s between the smallest and the largest ones are observed in ground and river water. The modes of lubrication and wear, which generated observed values of μ_ℓ and w _s, are considered as mixed lubrication and tribochemical wear. The chemical elements of Na, Cl, Mg, and K in sea water observed on wear particles and pits are thought effective to generate the largest value of μ_ℓ and the smallest value of w _s.     

Experimental discrimination of plowing friction and shear friction

The friction of a diamond spherical indenter sliding on CrN coated nitrided steel was investigated. A friction model was proposed that takes into account plowing and shear friction. With the model the separate contributions of substrate properties and surface condition to the friction were successfully extracted: the shear friction coefficient μ _sh was found to depend exclusively on the surface condition, i.e., not on load on the indenter, hardness of the substrate, and thickness of the coating. On the other hand, the plowing component of friction was independent on surface condition.     

Epoxy, ZnO, and PTFE nanocomposite: friction and wear optimization

To lower the friction coefficient and increase the wear resistance of epoxy, nanoparticles of zinc oxide and polytetrafluoroethylene (PTFE) were added in small volume percents to an epoxy matrix. Tribological testing of the samples in this study was completed on a linear reciprocating tribometer with a 250 N normal load and a 50.8 mm/s sliding speed. Several samples were made and tested following a modified Simplex Method optimization procedure in order to find a volume percent for optimized wear resistance and friction coefficient. The sample with the optimum wear rate consisted of 1 volume percent of zinc oxide nanoparticles and 14.5 volume percent of PTFE nanoparticles. It had a wear rate of k = 1.79 × 10⁻⁷ mm³/Nm; 400× more wear resistant than neat epoxy. The sample with the optimum friction coefficient consisted of 3.5 volume percent of zinc oxide nanoparticles and 14.5 volume percent of PTFE nanoparticles and had a friction coefficient of μ = 0.113, which is almost a 7× decrease in friction coefficient from neat epoxy.     

The effect of copper concentration on the wear resistance of composites based on recycled ShKh15 steel during friction with current collection

The current-voltage characteristic, wear resistance, and friction surface roughness of baked model copper-graphite-ShKh15 steel composites are determined. It is shown that the composites containing under 10% and above 50% Cu produce a friction zone with low conductivity and wear resistance. The composites containing 15–20% Cu produce a friction zone with relatively high conductivity and wear resistance. The maximum parameters of the roughness (R _a = 2.98 μm and R _z = 24.5 μm) appear on the friction surface of the material containing 50% Cu.     

In Situ Studies of Cartilage Microtribology: Roles of Speed and Contact Area

The progression of local cartilage surface damage toward early stage osteoarthritis (OA) likely depends on the severity of the damage and its impact on the local lubrication and stress distribution in the surrounding tissue. It is difficult to study the local responses using traditional methods; in situ microtribological methods are being pursued here as a means to elucidate the mechanical aspects of OA progression. While decades of research have been dedicated to the macrotribological properties of articular cartilage, the microscale response is unclear. An experimental study of healthy cartilage microtribology was undertaken to assess the physiological relevance of a microscale friction probe. Normal forces were on the order of 50 mN. Sliding speed varied from 0 to 5 mm/s, and two probes radii, 0.8 and 3.2 mm, were used in the study. In situ measurements of the indentation depth into the cartilage enabled calculations of contact area, effective elastic modulus, elastic and fluid normal force contributions, and the interfacial friction coefficient. This work resulted in the following findings: (1) at high sliding speed (V = 1–5 mm/s), the friction coefficient was low (μ = 0.025) and insensitive to probe radius (0.8–3.2 mm) despite the fourfold difference in the resulting contact areas; (2) the contact area was a strong function of the probe radius and sliding speed; (3) the friction coefficient was proportional to contact area when sliding speed varied from 0.05 to 5 mm/s; (4) the fluid load support was greater than 85% for all sliding conditions (0% fluid support when V = 0) and was insensitive to both probe radius and sliding speed. The findings were consistent with the adhesive theory of friction; as speed increased, increased effective hardness reduced the area of solid–solid contact which subsequently reduced the friction force. Where the severity of the sliding conditions dominates the wear and degradation of typical engineering tribomaterials, the results suggest that joint motion is actually beneficial for maintaining low matrix stresses, low contact areas, and effective lubrication for the fluid-saturated porous cartilage tissue. Further, the results demonstrated effective pressurization and lubrication beneath single asperity microscale contacts. With carefully designed experimental conditions, local friction probes can facilitate more fundamental studies of cartilage lubrication, friction and wear, and potentially add important insights into the mechanical mechanisms of OA.     

Strain and Stress Fields During Scratch Tests on Amorphous Polymers: Influence of the Local Friction

In this paper, we present results deduced from three-dimensional finite element simulations of scratching, with spherical indenter geometry at different imposed ratios, a/R in the range of 0.1–0.9. For each simulated ratio a/R, the local friction has been increased from 0 to 1. The paper aims at studying the tangential scratch behaviour of homogeneous polymeric substrates, considered in first approximation as elastic linear-hardening plastic material. For only elastic–plastic contacts, without any strain rate or temperature effects, it focuses on studying some characteristic response due to spherical scratching process as a function of scratching conditions (a/R, μ _loc ) such as the stress and plastic strain fields, including the plastic zone dimension and the definition of an volume average plastic strain.     

Interfacial potential barrier theory of friction and wear

An interfacial potential barrier theory to calculate friction and wear is proposed by considering the micro interaction of frictional surfaces. The theory suggests that the performance of friction and wear depends on the magnitude and distribution of the interfacial potential barrier on contact surfaces. The calculation methods of the interfacial potential barrier and standard interfacial potential barrier are then studied and the formulas to calculate the friction force, friction coefficient, and quantity of adhesion wear are derived based on the theory. With its independence and stability, the standard interfacial potential barrier can be used as an index to describe the frictional performance of materials. The calculation results of the friction force with some existing experimental data are consistent with the experimental results performed with an ultra high vacuum atomic-force microscope, which proves that the theory and method are feasible. __________ Translated from Tribology, 2007, 27(1): 54–59 [译自: 摩擦学学报]     

Laminar flow past a sphere rotating in the transverse direction

Laminar flow past a sphere rotating in the transverse direction is numerically investigated in order to understand the effect of the rotation on the characteristics of flow over the sphere. Numerical simulations are performed at Re = 100, 250 and 300, where the Reynolds number is based on the free-stream velocity and the sphere diameter. The rotational speeds considered are in the range of 0 ≤ ω* ≤ 1.2, where ω* is the maximum velocity on the sphere surface normalized by the free-stream velocity. Without rotation, the flow past a sphere experiences steady axisymmetry, steady planar-symmetry, and unsteady planar-symmetry, respectively, at Re = 100, 250 and 300. With rotation, however, the flow becomes planar-symmetric for all the cases investigated, and the symmetry plane of flow is orthogonal to the rotational direction. Also, the rotation affects the flow unsteadiness, and its effect depends on the rotational speed and the Reynolds number. The flow is steady irrespective of the rotational speed at Re = 100, whereas at Re = 250 and 300 it undergoes a sequence of transitions between steady and unsteady flows with increasing ω*. As a result, the characteristics of vortex shedding and vortical structures in the wake are significantly modified by the rotation at Re = 250 and 300. For example, at Re = 300, vortex shedding occurs at low values of ω*, but it is completely suppressed at ω* = 0.04 and 0.6. Interestingly, at ω* = 1 and 1.2, unsteady vortices are newly generated in the wake due to the shear layer instability. The critical rotational speed, at which the shear layer instability begins to occur, is shown to be higher at Re = 250 than at Re = 300. This paper was recommended for publication in revised form by Associate Editor Dongshin Shin Dongjoo Kim is an associate professor in the School of Mechanical Engineering at Kumoh National Institute of Technology. His research interests include computational fluid dynamics, bluff-body wakes, and control of turbulent flows. He has a PhD in mechanical engineering from Seoul National University. He is a member of the American Physical Society and the American Institute of Aeronautics and Astronautics.     

Friction coefficient of soft contact lenses: measurements and modeling

Tribological conditions for contact lenses have very low contact pressures in the range 3–5 kPa and sliding speeds around 12 cm/s. Using a microtribometer a series of experiments was run on commercially available contact lenses made from Etafilcon-A. These tests were run using 10–50 mN of normal load at speeds from 63 to 6280 m/s using a 1-mm radius glass sphere as a pin. The resulting contact pressures are believed to be nearly an order of magnitude larger than the targeted 3–5 kPa. It is hypothesized that the viscoelastic nature of the hydrogel, viscous shearing of the packaging solution, and interfacial shear between the glass sphere and the contact lens all contribute to the friction forces. A model that includes all three of these contributors is developed and compared to the experimental data. The experimental friction coefficients vary from = 0.025 to 0.075. The calculated fluid filmthicknesses were between 1 and 30 nm. The average surface roughness of the lens and the glass sphere are R_a=15 nm and R_a=8 nm, respectively, suggesting that the contact is not in full elastohydrodynamic lubrication. Finally, the largest contributors to the friction force in these experiments were found to be viscous dissipation within the hydrogel and interfacial shear within the contact zone.     

Experimental Evaluation of Friction and Wear Properties of Solid Lubricant Coatings on SUS440C Steel in Liquid Nitrogen

The friction and wear properties of the prevailing different solid lubricant coatings (Ion-plated Au, Ion-plated Ag and RF-sputtered PTFE on SUS440C stainless steel) used in the bearings of high-speed cryogenic-turbo-pumps of liquid rocket engines were experimentally evaluated in liquid nitrogen immersed conditions. Also the above experiments were carried out with two newly proposed solid lubricant coatings of sputter-ion-plated MoSTi and a new ion-plated Pb on SUS440C stainless steel. The friction coefficient and wear rates of the coatings of ion-plated Au, ion-plated Ag, RF-sputtered PTFE, the new ion-plated Pb and MoS₂Ti-SIP (with coating thickness of 0.7±0.1 μm) on SUS440C steel against SUS440C stainless steel ball in liquid nitrogen were compared. Worn surfaces were examined microscopically with a microscope and a profilometer for understanding the mechanisms of friction and wear and transfer film lubrication in liquid nitrogen. It is found that the newly proposed solid lubricant coatings are showing promising results for their use in liquid nitrogen immersed conditions. The sputter-ion-plated MoSTi coating on SUS 440C steel shows a minimum value of friction coefficient (μ=0.015) and wear rate (w_c=0.56 × 10⁻⁶ mm³/N m ) in liquid nitrogen.     

Frictional Voltammetry with Copper

This paper presents an experimental study correlating frictional behavior with in situ voltammetry for a unidirectional sliding contact between a hemispherical tipped alumina probe and a flat rotating copper counterface (maximum Hertzian contact pressure of 68 MPa and sliding speed of 10 mm/s). The contact was immersed in an aqueous 0.1 M Na₂CO₃ solution (pH ∼11) where the copper counterface acted as the working electrode in a potentiostat controlled three-electrode cell; a coiled Pt wire was used as the counter electrode and a saturated calomel electrode (SCE) as the reference. Clear and reproducible trends were found between friction coefficient and published data suggesting the onset of particular redox reactions, graphically presented in a frictional voltammetry plot. At anodic potentials primarily associated with the formation of copper(I) oxide (Cu₂O) (V vs SCE ∼−0.25), the measured friction coefficient was in the range μ ∼0.4–0.5. At cathodic potentials primarily associated with the formation of CuO, Cu(OH)₂, and CuCO₃ (V vs SCE ∼−0.10), the friction coefficient transitions to the range μ ∼0.7–1.0. At sustained cathodic potentials associated with reduction of the native copper oxide, Cu₂O, (V vs SCE ∼−0.65), the friction coefficient is observed to fluctuate between μ ∼0.2 and 0.5, arguably a result of exposure of bare copper due to non-uniform reduction (fractional coverage) of Cu₂O.     

On the DMT theory

The frequent claim that the Tabor parameter μ governs the transition from the DMT theory to the JKR theory is investigated. The change from the simple surface force law σ ∼ A/h ³ of the DMT theory to the Lennard–Jones law σ ∼ A/h ³–B/h ⁹ of the MDT theory and the numerical solutions is noted, and the ‘adhesive force’ is evaluated for both laws. Except in the limit of zero Tabor parameter, when the Derjaguin theories reduce to the rigid-sphere model, the predictions are consistently worse than assuming the sphere to be rigid. A ‘semi-rigid’ sphere model is proposed, which correctly describes the asymptotic behaviour as μ → 0, but leaves a considerable gap before the JKR theory can be applied.     

Development of compact auto focus actuator for camera phone by applying new electromagnetic configuration

In this paper, auto focus actuator, which is used to move a lens module in the mobile phone having a camera module, is developed. Camera module containing auto focus actuator requires to minimize total size because of characteristics of the application area such as mobile phone, digital camera, and personal digital assistant. There are stepping motor, voice coil motor, and piezoelectric motor as auto focus actuator. In this paper, voice coil motor having new electromagnetic configuration is proposed. And actuator using proposed voice coil motor is developed by optimal design method using magnetic circuit analysis. The sectional area of the developed actuator is reduced to 32.4% compared with actuator using general electromagnetic configuration. From the performance test, the developed actuator has moving stroke of 0.64 mm for 2.1 volt, hysteresis of 40 μm, full stroke current of 54 mA, and unit step motion of 3 μm.     

Temperature-Dependent Atomic Scale Friction and Wear on PbS(100)

Friction and wear on PbS(100) surfaces have been investigated on the atomic scale as a function of temperature with atomic force microscopy. At room temperature and above, the PbS(100) surface exhibited low friction (μ < 0.05) in contact with a silicon nitride probe tip, provided that interfacial wear was not encountered. In the absence of wear, friction increased exponentially with decreasing temperature, transitioning to an athermal behavior near 200 K. An Arrhenius analysis of the temperature dependence of friction yielded an activation energy ∆E = 0.32 ± 0.02 eV for the sliding contact of a silicon nitride tip on PbS(100).     

The Effect of Grain Size on Stribeck Curve and Microstructure of Copper Under Friction in the Steady Friction State

In the present work, the effect of grain size on the friction and wear behavior of a copper (Cu) samples under different lubricant conditions was studied. The structural evolution of Cu subsurface layers under friction in different lubricant conditions was considered. All friction tests were conducted under laboratory conditions using a block-on-ring rig. The effects of sliding velocity and load on the friction coefficient and wear rate of Cu with different grain size (1, 30, and 60 μm) were analyzed. The Cu samples with the average grain size of 1 μm were obtained due to severe plastic deformation (SPD) by equal channel angular pressing (ECAP). The Stribeck curves for Cu samples with different virgin grain sizes were considered. Elasto-hydrodynamic lubrication (EHL) and boundary lubrication (BL) regions were mainly studied in the present work. Similar Stribeck curves were found out for Cu samples with different virgin grain size. A load of the transition from the EHL to BL region was increased with a decrease of the grain size. While the friction coefficients were similar in the EHL and BL regions for the samples with different grain sizes, the wear rate was increased remarkably with an increase the virgin grain size. Flow localization during friction in the BL region led to formation of the vortex structure in subsurface layers. Based on the dependence of the microhardness upon the depth, the degree of hardening (H) was evaluated. A correlation between the coefficient of wear and the deformation hardening of Cu samples with different virgin grain sizes was revealed. In order to take into account the effect of the grain size and to predict the Stribeck curve, a parameter, K, as the ratio between hardness of tested and annealed samples, was incorporated into the lubricant number. The theoretical values of the Stribeck curve calculated for preliminary deformed Cu samples (d = 1 μm) and annealed samples (d = 60 μm) were well coincided with the experimental results.     

High-Temperature Vapor Phase Lubrication Using Carbonaceous Gases

Following the pioneering work of Prof. James Lauer, the ability to provide continuous solid lubrication through vapor phase delivery of carbonaceous gases has been successfully demonstrated on a pin-on-disk contact at the temperatures of 650 °C. Results from tribological experiments under 2 N normal load and 50 mm/s sliding speed showed an over 20× reduction in friction coefficient. The samples were silicon nitride (pin) versus CMSX-4 (disk) and the experiments when run in a nitrogen environment with acetylene admixtures. Two repeat experiments gave average friction coefficients of μ = 0.03 and μ = 0.02. The process was robust and provided low friction for the entire 500 m of sliding. Using focused ion-beam milling, high-resolution transmission electron microscopy, and confocal Raman spectroscopy, the resulting solid lubricant was found to be oriented microcrystalline graphite.