Effect of a pulsed electromagnetic field on the surface roughness in superfinishing EDM

It is shown and confirmed that the behaviour of a pulsed electromagnetic field influences the surface roughness especially in superfinishing electrodischarge machining (EDM). In accordance with technological experiments, instrumental measuring and theoretical analysis, some principles of the microenergy EDM process are discovered. An effective method concerning the generator and conducts is proposed to ensure that all discharges occur with desired pulse parameters. A best surface roughness of 0.04 μm R_a is achieved.     

Image distortions in SEM and their influences on EBSD measurements

The high sample tilt angle commonly necessary for an orientation determination by EBSD (electron back-scatter diffraction) is responsible for some simple geometrically caused, but nevertheless essential, image distortions. First of all, the influence of the tilt correction and also the trapezium distortion which appears at low magnifications will be discussed. In the second part, an additional rhomboidal distortion will be introduced which is independent of the magnification used. This distortion appears if the scanned sample surface is out of plane to the tilted stage. Even a small deviation from the parallelity produces an approximately three times bigger error of the Euler angle phi(1) when the sample alignment is based on the image captured from the highly tilted sample. This effect especially concerns small samples (e.g. FIB-lamellae) since they cannot be exactly aligned, but the measurements of bigger samples can also be influenced. As an example a correction procedure is described in detail, based on a repetition of the measurement after a 180 degrees sample rotation.     

Experimental investigation on camera calibration for 3D photogrammetric scanning of micro-features for micrometric resolution

Recently, it has been demonstrated that photogrammetry can be used for the measurement of small objects with micro-features, with good results and lower cost, compared to other established techniques such as interferometry, conoscopic holography, and 3D microscopy.Calibration is a critical step in photogrammetry and the classical pinhole camera model has been tested for magnifications lower than 2×. At higher magnification levels, because of the reduction of the depth of field (DOF), images can lead to calibration data with low reprojection errors. However, this could lead to bad results in the 3D reconstruction.With the aim of verifying the possibility of applying the camera model to magnifications higher than 2×, experiments have been conducted using reflex cameras with 60 mm macro lens, equipped with the combination of three extension tubes, corresponding to 2.06, 2.23, and 2.4 magnification levels, respectively.Experiments consisted of repeating calibration five times for each configuration and testing each calibration model, measuring two artifacts with different geometrical complexity. The calibration results have shown good repeatability of a subset of the internal calibration parameters. Despite the differences in the calibration reprojection error (RE), the quality of the photogrammetric 3D models retrieved was stable and satisfying.The experiment demonstrated the possibilities of the photogrammetric system presented, equipped to very high magnification levels, to retrieve accurate 3D reconstruction of micro-features with uncertainties of few micrometers, comparable with industry’s expensive state-of-the-art technologies.     

基于误差传播理论的PnP问题姿态精度分析

提出了一种在辨识一组典型特征点误差关系的基础上,建立间接测量值与直接测量值之间的最有利函数关系,并根据误差传播理论综合其他特征点的误差影响,最终获得完整的方位、俯仰和倾斜角误差数学模型的PnP问题误差分步分析新方法。以P4P问题研究为例,推导得到了单目视觉测量中相关参数和变量的误差函数解析式,揭示了影响姿态测量精度的误差规律。经P4P姿态解算仿真,验证了误差数学模型的正确性,以及基于误差传播理论的误差分步方法的有效性。分析误差数学模型可以看出:在单目视觉测量参数确定的条件下,方位角测量误差与方位角值无关,与相机高度和合作标志尺寸的比值成正比,在较大范围内俯仰和倾斜角变化对方位角测量误差影响小;俯仰/倾斜角的测量误差与俯仰/倾斜角值有关,与相机高度和合作标志尺寸比值的平方成正比;方位角测量误差小于俯仰/倾斜角测量误差。给出的分析方法和误差解析数学模型对单目视觉测量系统设计有指导作用。     

Uncertainty contribution of tip-sample angle to AFM lateral measurements

AFM measurements are very important for quality control in the photovoltaic, microfluidic, electronic or micro-optic industries. This work proposes an algorithm to complete the uncertainty evaluation of AFM systems along the XY-axis under conditions where tolerance of curved surfaces must be controlled. This algorithm is also tested for tilt angles between tip and sample from 0° to 9° using an experimental arrangement which consists of an AFM instrumented with an inclinometer and four step height standards.Results show good agreement between the theoretical model and experimental results for samples with larger steps TGZ03 (465 nm) and TGZ11 (1416 nm), but with poor results for the smaller samples TGZ01 (17.6 nm) and TGZ02 (73.1 nm). An angle of 9° shows an error of about 3% in the horizontal determination of the step dimension, but it could increase to 47% for a tilt angle of 30° according to the theoretical model.The angle error between tip and sample is included in the uncertainty budget using a uniform distribution. An evaluation is performed in a theoretical rolling machine for imprint lithography where a step must be measured with nominal dimensions of 3 μm—X-axis and 1 μm—Z-axis. An assumed tip-sample angle is assumed that changes from 0° to 22.5° (curved form) and produces an uncertainty contribution to the X measurement of 55.7 nm. This uncertainty is important and must be considered to guarantee tolerances in quality control of curved form products.     

The roughness effect on the frequency of frictional sound

Dry sliding of two bodies in contact generates a wide range of effects like friction, wear, heat and sound among others. The main interest of this study is in the frequency characteristics of the generated sound.In the past, frequency spectrum and sound pressure level with relation to surface topography (surface roughness in particular), have been studied mainly for concentrated contacts like stylus or hemispherical tip pin on a rough surface. Studies on flat–flat contacts were mainly focused on the topography of contacting surfaces and its relation to occurrence or non-occurrence of squeal (high pitch, high sound pressure level sound) in brake systems.The present study aims to clarify the effect of surface roughness on the frequency of non-squealing frictional sound generated in dry flat–flat sliding contact.Sound was generated by the dry contact in rubbing by hand of two rectangular cross-section stainless-steel plates having similar surface roughness. The roughness of the contacting surfaces varied in the range R_z=0.8–12.4 μm. The sound spectra had 5 peaks (P₁, P₂, P₃, P₄ and P₅) in order of increasing frequency and it was found that the peak frequency was shifted when the roughness of the rubbed surfaces changed. The first peak P₁ was most sensitive to change of surface roughness and it shifted from 3.0 to 4.5 kHz when the maximum surface roughness changed from R_z=10.9 to . When the surface was relatively rough, this peak was close to the first bending natural frequency of the plate at 2.377 kHz.     

Investigations on the leaf surface ultrastructure in grapevine (Vitis vinifera L.) by scanning microscopy

Several Scanning microscopy techniques were used to investigate the leaf surface ultrastructure in the local “Razegui” grapevine cultivar (Vitis vinifera L.). Conventional scanning electron microscopy performed on glutaraldehyde‐fixed samples allowed observation of well‐preserved epidermal cells with an overlaying waxy layer. At a high magnification, the waxy layer exhibited crystalline projections in the form of horizontal and vertical platelets. Also, to avoid eventual ultrastructural alterations inherent in the use of solvents during sample preparation, fresh leaf blade samples were directly observed by environmental scanning electron microscopy. A classical image of convex living epidermal cells was observed. At 2400× magnification, epicuticular waxes exhibited a granular structure. However, high‐magnification images were not obtained with this device. The atomic force microscopy (AFM) performed on fresh leaf blade samples allowed observation of a textured surface and heterogeneous profiles attributed to epicuticular wax deposits. AFM topography images confirmed further, the presence of irregular crystalloid wax projections as multishaped platelets on the adaxial surface of grapevine leaf. SCANNING 31: 127–131, 2009. © 2009 Wiley Periodicals, Inc.     

Calibration of step heights and roughness measurements with atomic force microscopes

In this paper we present a method for the vertical calibration of a metrological atomic force microscope (AFM), which can be applied to most AFM systems with distance sensors. A thorough analysis describes the physical z-coordinate of an imaged surface as a function of the observed and uncorrected z-coordinate and the horizontal position. The three most important correction terms in a Taylor expansion of this function are identified and estimated based on series of measurements on a calibrated step height and a flat reference surface. Based on this calibration a number of step heights are calibrated by the AFM with measured values consistent with reference values, where available. Relative standard uncertainty of about 0.5% is achieved for step heights above 200 nm. For step heights below 50 nm, the standard uncertainty is about 0.5 nm. While a calibration of step heights done by AFM and interference microscopy can be compared directly as demonstrated here, this is not straightforward for roughness measurement. To asses this, the exact same area on an important applied surface (a hip joint prosthesis) was measured by both AFM and interference microscopy. Similarities in the images were seen; however, the calculated roughness was significantly different (R_q=3 and 1.5 nm). Applying a low-pass filter with a cut-off wavelength of λ_c=1.5 μm, the appearance of the images and the calculated roughness become almost identical. This strongly suggests that the two methods are consistent, and that the observed differences in shape and roughness in the nanometer range can be explained by the limited lateral resolution of the interference microscope.     

飞秒激光跟踪仪光轴与竖轴同轴度的标定

考虑飞秒激光跟踪仪仪器轴系的几何误差会影响仪器的指向精度并最终影响坐标测量精度,本文研究了激光光轴与竖轴的几何误差对仪器测量精度的影响。提出了激光光轴与竖轴的同轴度标定方法,以降低其不重合带来的跟踪测量误差。首先,基于几何光学原理建立了光轴与竖轴的几何误差模型,分别分析了光轴与竖轴的倾斜与平移误差对仪器测角精度的影响。然后,针对设计的仪器提出了基于旋转成像原理的光轴与竖轴同轴度的检测方法,并设计了一套同轴度检测装置。最后,基于该检测装置,通过调节两组双光楔完成了激光光轴与竖轴的倾斜与平移误差的标定。结果显示,经标定校准后激光光轴与竖轴的角度误差为3.4″;平移误差为26.1μm,得到的结果为仪器后续建立误差补偿模型奠定了基础。     

Evaluation of electron tomography reconstruction methods for interface roughness measurement

We evaluate the suitability of simultaneous iterative reconstruction technique (SIRT), filtered back projection, and simultaneous algebraic reconstruction technique methods for buried interface roughness measurements. We also investigate the effect of total electron dose distributed over the entire tilt series on measured roughness values. We investigate the applicability of the dose fractionation theorem by evaluating the effect of an increasing number of images, i.e., decreasing tilt increment size at fixed total electron irradiation dose on the quantitative measurement of buried interface roughness. The results indicate that SIRT is the most suitable method for reconstruction and a 3° to 5° angle is optimal for the roughness measurement.     

The effect of counterface surface roughness on the wear of UHMWPE in water and oil-in-water emulsion

The South African gold mining industry is at present involved in a programme whereby the hydraulic stoping machinery currently operating on a water-based fluid will be modified to run on mine service water. The wear of the UHMWPE seals is an area of particular concern. This paper examines the effect of type of lubricant and counterface surface roughness on the wear of UHMWPE. A reciprocating sliding wear rig was used with UHMWPE sliding against AISI 431 at an average speed of 0.25 m/s. The contact pressure was 10 N/mm². Tests were conducted in water and in a 5% oil-in water emulsion (5:95). The surface roughness of the steel was varied in the range 0.1–1.0 μm (centreline average). The results of the tests in water showed that the logarithm of the specific wear rate is proportional to the surface roughness. The results of the tests in 5:95 showed that there is a significant transition in specific wear rate at a surface roughness of approximately 0.35 μm. At surface roughness less than 0.35 μm the specific wear rate in 5:95 is considerably lower than the specific wear rate in water, while at surface roughness greater than 0.35 μm the specific wear rate in 5:95 approaches that in water. However, SEM examination of the surfaces from both series of tests showed that, irrespective of lubricant, there was a change in the mode of material removal at a surface roughness of approximately 0.35 μm. The wear mechanisms are discussed as a function of type of lubricant and surface roughness. It is believed that the topography of the counterface is responsible for the change in the mode of material removal.     

A 6-degree-of-freedom measurement system for the accuracy of X-Y stages

A precision 6-degree-of-freedom measurement system has been developed for simultaneous on-line measurements of six motion errors of an X-Y stage. The system employs four laser Doppler scales and two quadrant photo detectors to detect the positions and the rotations of an optical reflection device mounted on the top of the X-Y stage. Compared to the HP5528A system, the linear positioning accuracy of the developed measurement system is better than ±0.1 μm to the range of 200 mm and the vertical straightness error is within ±1.5 μm for the measuring range of ±0.1 mm. The yaw and pitch errors are about ±1 arcsec, and the roll error is about ±3 arcsec within the range of ±50 arcsec.     

Stylus-laser surface calibration system

A stylus-laser surface calibration system was developed to calibrate the NIST sinusoidal roughness Standard Reference Materials (SRM) 2071-2075. Step height standards are used to calibrate the stylus instrument in the vertical direction, and a laser interferometer is mounted on the traversing unit of the stylus instrument to calibrate the instrument in the horizontal direction. The calibration uncertainty (±2δ) for SRM 2075 is ±1.2% for roughness calibrations ((R_a = 1 μm), and ±0.06% for spatial wavelength calibrations (S_m = 800 μm).     

Effects of inclination angles on geometrical features of machined surface in five-axis milling

With the development of manufacturing technology, five-axis milling has been one of the most important solution strategies in machining field. To deepen the understanding of multi-axis processing and improve the application level of the technology, the current work was carried out. This paper investigated the effects of tilt and lead angle on the scallop height, surface roughness, surface topography, and surface damages in five-axis ball-end milling process. Both geometrical analysis and experiment research are conducted to investigate the scallop height after five-axis milling, and variation of the surface roughness and surface topography with tool inclination angle obtained from the experiments was analyzed. Surface damages under the different inclination angles were also observed and analyzed with optical profiler. Several conclusions are made as follows. The inclination angles of the ball-end mill have no effect on the scallop height when only the spherical part of the cutter participates in the cutting process according to the geometrical analysis. Surface roughness with regard to tilt angles presents symmetrical characteristic around 0°. Surface texture feature, especially the texture direction, is closely related with the tool posture. The surface concave pits, convex marks, microscopic cracks, and spot corrosions are mainly the damage forms of the machined surface. More surface blemishes appeared when small inclination angles are adopted in cutting. As a result, the recommendatory inclination angle values for inclination angle are proposed. A better understanding of the five-axis machining process would be given by the detailed analysis of generation reason of the machined surface features, and the results could provide support for process parameter optimization.     

Scanning differential interference contrast microscope

An optical microscope has been developed based on the differential interference contrast method to evaluate the roughness of supersmooth surfaces. The instrument uses a Bragg cell and a translation stage driven by a DC motor to produce an image of an area of a sample. Its lateral resolution is 2 μm and its vertical resolution is subangstrom. It takes only 7 seconds to scan an area of 1 mm². Three different curve fits can be used to remove the tilt, the curvature, and the low spatial frequency features of the sample. A figure for surface roughness is produced that is repeatable to 0.01 Å. The instrument is described and the noise sources and repeatability are discussed. The results of measurements of ring laser gyroscope mirror substrates are shown.     

The distortion elimination of an optical microscope based on optimized windowed Fourier transform

An image distortion elimination method based on optimized windowed Fourier transform processing is proposed in this paper. Simulation testing was performed beforehand to find the optimal window size and grating pitch (in pixels), which are crucial for the distortion calibration accuracy. With the optimized parameters, gratings with different frequencies were fabricated by photolithography as standard plates to calibrate the aberration of the optical microscope. The influence induced by the misalignment of the grating lines and the viewing field axis on the distortion calibration was addressed and eliminated by the proposed method in this paper. With the proposed method, the image distortion of the optical microscope under various magnifications was calibrated successfully.     

Compensation for five DOF motion errors of hydrostatic feed table by utilizing actively controlled capillaries

Five DOF motion errors of a hydrostatic bearing table driven by a coreless type linear motor were compensated by utilizing actively controlled capillaries in the present research. The motion errors of horizontal translation and yaw were compensated simultaneously with the two actively controlled capillaries, and those of vertical translation, pitch and roll were compensated simultaneously with the three actively controlled capillaries. The actively controlled capillaries were designed and their gains were adjusted by conducting micro step response tests. The five DOF motion errors were measured ultra-precisely by combining three measuring methods as follows. The yaw and pitch errors were measured with a laser interferometer, and the roll error was measured by the reversal method. Then, the translational motion errors in the horizontal and vertical directions were measured by the sequential two-point method, where influence of the angular motion errors on the translational measurement was compensated by utilizing the measured angular motion errors. By utilizing the developed capillaries and the combined measuring methods and by applying the iterative control, the motion errors of the horizontal translation, the vertical translation, the yaw, the pitch and the roll were compensated simultaneously and reduced significantly from 0.16 μm, 0.18 μm, 1.96 arcsec, 2.26 arcsec and 0.14 arcsec to 0.02 μm, 0.03 μm, 0.03 arcsec, 0.07 arcsec and 0.02 arcsec, respectively. The remaining motion errors were less than the measuring repeatabilities which were ±0.02 μm for the translational motion errors and ±0.05 arcsec for the angular motion errors. The results show that the present method is not only practical but also effective to realize the ultra-precision feed motion whose accuracy is equal to the currently reachable measuring accuracy.     

Soft-tribology: Lubrication in a compliant PDMS–PDMS contact

We investigate the influence of surface roughness and hydrophobicity on the lubrication of a soft contact, consisting of a poly(dimethylsiloxane) (PDMS) sphere and a flat PDMS disk. The full Stribeck curves, showing boundary, mixed and elasto-hydrodynamic (EHL) lubrication, are presented for varying surface roughness and hydrophobicity. It is found that neither surface roughness nor hydrophobicity influence the friction coefficient (μ) within the EHL regime. However, increasing surface roughness decreases μ in the boundary regime, while extending the limits of the boundary and mixed lubrication regimes to larger values of the product of velocity and lubricant viscosity (Uη). The transition from the mixed lubrication to EHL regime is found to take place at lower values of the film thickness parameter Λ for increasingly rough surfaces. We found Λ=0.7 in the case of a root mean square (r.m.s.) surface roughness of 3.6 μm, suggesting that the effective surface roughness in a compliant compressed tribological contact is lower than that at ambient pressures. Rendering the PDMS surface hydrophilic promotes full-film lubrication and dramatically lowers μ in the boundary regime by more than an order of magnitude. This influence of surface wetting is also displayed when examining a range of lubricants using hydrophobic tribopairs, where the boundary μ decreases with decreasing lubricant–substrate contact angle. Implications of these measurements are discussed in terms of the creation of model surfaces for biotribological applications.     

Reynolds number effects on the non-nulling calibration of a cone-type five-hole probe for turbomachinery applications

The effects of Reynolds number on the non-nulling calibration of a typical cone-type fivehole probe have been investigated for the representative Reynolds numbers in turbomachinery. The pitch and yaw angles are changed from −35 degrees to 35 degrees with an angle interval of 5 degrees at six probe Reynolds numbers in range between 6.60 × 10³ and 3.17× 10⁴. The result shows that not only each calibration coefficient itself but also its Reynolds number dependency is affected significantly by the pitch and yaw angles. The Reynolds-number effects on the pitchand yaw-angle coefficients are noticeable when the absolute values of the pitch and yaw angles are smaller than 20 degrees. The static-pressure coefficient is sensitive to the Reynolds number nearly all over the pitch- and yaw-angle range. The Reynolds-number effect on the totalpressure coefficient is found remarkable when the absolute values of the pitch and yaw angles are larger than 20 degrees. Through a typical non-nulling reduction procedure, actual reduced values of the pitch and yaw angles, static and total pressures, and velocity magnitude at each Reynolds number are obtained by employing the calibration coefficients at the highest Reynolds number (Re=3.17×10⁴) as input reference calibration data. As a result, it is found that each reduced value has its own unique trend depending on the pitch and yaw angles. Its general tendency is related closely to the variation of the corresponding calibration coefficient with the Reynolds number. Among the reduced values, the reduced total pressure suffers the most considerable deviation from the measured one and its dependency upon the pitch and yaw angles is most noticeable. In this study, the root-mean-square data as well as the upper and lower bounds of the reduced values are reported as a function of the Reynolds number. These data would be very useful in the estimation of the Reynolds-number effects on the non-nulling calibration.     

A high precision straight-motion system

In this system, a steel block is completely floated by air pads mounted on a mechanical sliding table. When the table moves, the vertical and horizontal positions and the pitch, roll and yaw angles of the block change because of the misalignment of the sliding table. These changes are detected against references by optical and electronic devices and the positions and angels of the block controlled by changing the supply pressure to each pad. Straight-edge masters and a laser straightness interferometer are used as the references for vertical and horizontal straightnesses, and autocollimators are used to detect the change in pitch and yaw angle attitudes. As a reference to the roll angle attitude, the two straight-edge masters are used. The working length of the system is 1 m. The positional errors of the block motion with respect to the references are less than 0.1 and 0.4 μm and the angular changes are less than 0.2 s of arc.