Cylindrical Lenses Based Spectral Domain Low-Coherence Interferometry for On-line Surface Inspection

This paper presents a spectral domain low-coherence interferometry (SD-LCI) method that is effective for applications in on-line surface inspection because it can obtain a surface profile in a single shot. It has an advantage over existing spectral interferometry techniques because it uses cylindrical lenses as the objective lens in a Michelson interferometric configuration to enable the measurement of long profiles. The adjustable profile length in our experimental setup, determined by the NA of the illuminating system and the aperture of cylindrical lenses, is up to 10 mm. To simulate real-time surface inspection, large-scale 3D surface measurement was carried out by translating the tested sample during the measurement procedure. Two step height surfaces were measured and the captured interferograms were analysed using a fast Fourier transform algorithm. Both 2D profile results and 3D surface maps closely align with the calibrated specifications given by the manufacturer

Application of the morphological alpha shape method to the extraction of topographical features from engineering surfaces

In contrast to the mean-line based filters, morphological filters are function oriented and more suitable for the functional prediction of component performance. This paper presents a novel morphological method based on the alpha shape for the extraction of topographical features from engineering surfaces. Compared to the traditional implementation of morphological filters, the alpha shape method is more efficient in performance for large structuring element. The resulting envelope follows the form of the surface all over such that the distortions caused the end effects are avoided. A series of measured surfaces from the automotive cylinder liner and the bioengineering femoral heads are analyzed using the morphological alpha shape method. The topographical features are successfully extracted, enabling further analysis to the components

Burg algorithm for enhancing measurement performance in wavelength scanning interferometry

Wavelength scanning interferometry (WSI) is a technique for measuring surface topography that is capable of resolving step discontinuities and does not require any mechanical movement of the apparatus or measurand, allowing measurement times to be reduced substantially in comparison to related techniques. The axial (height) resolution and measurement range in WSI depends in part on the algorithm used to evaluate the spectral interferograms. Previously reported Fourier transform based methods have a number of limitations which is in part due to the short data lengths obtained. This paper compares the performance auto-regressive model based techniques for frequency estimation in WSI. Specifically, the Burg method is compared with established Fourier transform based approaches using both simulation and experimental data taken from a WSI measurement of a step-height sample

Absolute height measurement of specular surfaces with modified active fringe reflection photogrammetry

Deflectometric methods have existed for more than a decade for slope measurement of specular freeform surfaces through utilization of the deformation of a sample pattern after reflection from a test surface. Usually, these approaches require two-directional fringe patterns to be projected on a LCD screen or ground glass and require slope integration, which leads to some complexity for the whole measuring process. This paper proposes a new mathematical measurement model for measuring topography information of freeform specular surfaces, which integrates a virtual reference specular surface into the method of active fringe reflection delfectometry and presents a straight-forward relation between height and phase. This method only requires one direction of horizontal or vertical sinusoidal fringe patterns to be projected on a LCD screen, resulting in a significant reduction in capture time over established method. Assuming the whole system has been pre-calibrated, during the measurement process, the fringe patterns are captured separately via the virtual reference and detected freeform surfaces by a CCD camera. The reference phase can be solved according to spatial geometrical relation between LCD screen and CCD camera. The captured phases can be unwrapped with a heterodyne technique and optimum frequency selection method. Based on this calculated unwrapped-phase and that proposed mathematical model, absolute height of the inspected surface can be computed. Simulated and experimental results show that this methodology can conveniently calculate topography information for freeform and structured specular surfaces without integration and reconstruction processes

Investigation of a scale-up manufacturing approach for nanostructures by using a nanoscale multi-tip diamond tool

Increasing interest in commercializing functional nanostructured devices heightens the need for cost-effective manufacturing approaches for nanostructures. This paper presents an investigation of a scale-up manufacturing approach for nanostructures through diamond turning using a nanoscale multi-tip diamond tool (four tip tool with tip width of 150 nm) fabricated by focused ion beam (FIB). The manufacturing capacity of this new technique is evaluated through a series of cutting trials on copper substrates under different cutting conditions (depth of cut 100–500 nm, spindle speed 12–120 rpm). The machined surface roughness and nanostructure patterns are measured by using a white light interferometer and a scanning electron microscope, respectively. Results show that the form accuracy and integrity of the machined nanostructures were degraded with the increase of the depth of cut and the cutting speed. The burr and the structure damage are two major machining defects. High precision nano-grooves (form error of bottom width < 6.7 %) was achieved when a small depth of cut of 100 nm was used (spindle speed = 12 rpm). Initial tool wear was found at both the clearance cutting edge and the side edges of tool tips after a cutting distance of 2.5 km. Moreover, the nanometric cutting process was emulated by molecular dynamic (MD) simulations. The research findings obtained from MD simulation reveal the underlying mechanism for machining defects and the initialization of tool wear observed in experiments

Tars: Timeliness-aware Adaptive Replica Selection for Key-Value Stores

In current large-scale distributed key-value stores, a single end-user request may lead to key-value access across tens or hundreds of servers. The tail latency of these key-value accesses is crucial to the user experience and greatly impacts the revenue. To cut the tail latency, it is crucial for clients to choose the fastest replica server as much as possible for the service of each key-value access. Aware of the challenges on the time varying performance across servers and the herd behaviors, an adaptive replica selection scheme C3 is proposed recently. In C3, feedback from individual servers is brought into replica ranking to reflect the time-varying performance of servers, and the distributed rate control and backpressure mechanism is invented. Despite of C3's good performance, we reveal the timeliness issue of C3, which has large impacts on both the replica ranking and the rate control, and propose the Tars (timeliness-aware adaptive replica selection) scheme. Following the same framework as C3, Tars improves the replica ranking by taking the timeliness of the feedback information into consideration, as well as revises the rate control of C3. Simulation results confirm that Tars outperforms C3.Comment: 10pages,submitted to ICDCS 201

Significant changes in subseries means and variances in an 8000-year precipitation reconstruction from tree rings in the southwestern USA

Both algorithms were applied to an 8000-year long time series of annual precipitation that was reconstructed from tree rings in the southwestern USA. One of the algorithms is the scanning &lt;I&gt;t&lt;/I&gt;-test, which detects significant changes in subseries means (the first center moments) on various time scales. Another is the scanning &lt;I&gt;F&lt;/I&gt;-test, which detects significant changes in subseries variances (the second center moments) on multi-time scales. Firstly, the scanning &lt;I&gt;t&lt;/I&gt;-test identified 22 change points in subseries means and partitioned the series into 23 relatively wet, normal or dry episodes. Secondly, the scanning &lt;I&gt;F&lt;/I&gt;-test detected 15 change points in subseries variances and divided 16 phases in comparatively steady (with smaller variance) or unsteady (with larger variance) features. Thirdly, the 23 wetness-episodes were characterized as the steady or unsteady situations by jointing the results from the scanning &lt;I&gt;F&lt;/I&gt;-test into those from the &lt;I&gt;t&lt;/I&gt;-test. Fourthly, the 23 episodes were compared to those in the TIC and δ&lt;sup&gt;18&lt;/sup&gt;O records from cored sediments in the deep basin of the Pyramid Lake in Nevada by using a coherency analysis of the &lt;I&gt;t&lt;/I&gt;-test between the precipitation reconstruction and the TIC or δ&lt;sup&gt;18&lt;/sup&gt;O series. Fifthly, the 23 episodes were collaborated with some published papers in related studies. In addition, the 23 episodes were also compared with studies of the global climate change and with documents of climate changes in China during the same periods. As the TIC and δ&lt;sup&gt;18&lt;/sup&gt;O record series are high resolution with unequal sampling intervals between 3 and 14 years, an algorithm in the scanning &lt;I&gt;t&lt;/I&gt;-test for dealing with the unequal time intervals was developed in this study

Implementation of line-scan dispersive interferometry for defect detection

Surface assurance is one of the main concerns for advanced manufacturing technologies such as Roll-to-Roll (R2R) technique. The undesired defects present on the barrier films make R2R products suffer from a low efficiency and short life span. In order to enhance the performance and the yield of the products, an inspection system enabling in-line metrology of functional surfaces in production lines is desirable to optimise the manufacturing processes. This paper reports an instantaneous line-scan dispersive interferometry which has sufficient resolutions and nano-scale measurement repeatability to detect defects on flexible PV films. Free from any mechanical scanning and obtaining a surface profile in a single shot allows this setup to minimise environmental effects and to be used on the shop floor. The captured spectral interferogram is analysed using a FFT based algorithm, and the process time can be accelerated through data parallelism using a graphics processing unit (GPU). The performance of the developed system was evaluated experimentally by measuring the polyethylene naphthalate (PEN) films provided by the Centre for Process Innovation (CPI). The experimental details and results are presented in this paper